Ruthenium complexes and their applications

Abstract

The invention relates to ruthenium complexes which may find use in the field of organic chemistry. Specifically, the ruthenium complexes of the invention may be used in the reduction or hydrogenation of carbonyl compounds, such as esters, to alcohols. The invention further relates to a process for reducing or hydrogenating a carbonyl compound, such as an ester, to form alcohols using the ruthenium complexes of the invention.

Description

[0001] Complex and ProcessField of the InventionThe present invention relates to transition metal complexes and their use. More specifically,the present invention relates to ruthenium complexes which find use in the reduction ofcarbonyl containing substrates, such as esters, to form alcohols. The invention furtherrelates to a process for reducing carbonyl containing substrates, such as esters, to formalcohols using the ruthenium complexes.Background of the Invention The reduction of esters is an essential transformation in the chemical industry as a route to primary alcohols. The reduction of esters has conventionally been carried out using reagents (in stoichiometric or excess quantities) such as sodium metal in ethanol (the Bouveault-Blanc reduction) or more recently with a metal hydride reagent, such as LiAlH4or NaBH4. These reduction reactions are, however, difficult to carry out effectively on a large scale, not least due to safety concerns associated with an extremely exothermic quenching step. As such,large scale catalytic reduction reactions use hydrogen gas. Cu- or Zn-based heterogeneouscatalysts are used for ester reduction, primarily in the Natural Detergent Alcohol (NDA) market on very large scale. However, these methods require very high pressures and / or temperatures, in large scale, dedicated production facilities. The chemoselectivity for ester reduction compared to other sensitive functional groups can also be problematic in some cases using these methods. The use of homogeneous catalysts for the reduction of esters has presented itself as anattractive alternative to harsh heterogeneous conditions. In particular, homogeneousruthenium complexes comprising certain tridentate ligands (such as those disclosed inWO2013 / 023307A1) have been applied with great success.Fatty acid methyl esters (FAMEs) are ubiquitous substrates in industry and can be obtained from natural sources. For example, FAMEs can be made from vegetable oils and biomass feedstocks and therefore represent an attractive renewable source of fatty acid esters. However, the hydrogenation of FAMEs to produce alcohols by homogeneous catalysts is more difficult than the hydrogenation of the corresponding ethyl esters. Accordingly, commercially unattractive high temperature and pressure heterogeneous hydrogenation routes are often employed for FAMEs.Consequently, there is a need for more active homogeneous catalysts which can be used atlower loadings in ester hydrogenation reactions, in particular in the hydrogenation reactionscomprising FAME feedstocks. Moreover, the presence of residual catalyst in the resultingproduct of the hydrogenation reaction is undesirable, in particular where the products aresupplied into the food or cosmetics industries. Furthermore, there is a need for catalystshaving a wide applicability to an array of different substrates and which may be capable ofhydrogenating different functional groups. Summary of the InventionThe present invention provides ruthenium complexes which may be used to providehydrogenation catalysts for carbonyl containing substrates, such as esters, which haveimproved activity and which can be used at high substrate to catalyst (S / C) ratios.Accordingly, in a first aspect of the present invention there is provided a ruthenium complex of formula (I) or formula (II): [Ru(L)AZ]W (I)[Ru(L)AZW] (II)wherein L is a tridentate ligand having formula (III): wherein:X is a nitrogen atom and when taken together with R1 it forms an optionally substitutedheteroaryl group when Rx is absent, orX is –SRa, and R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;Y is selected from –SRb, –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or when Y is –PRaRb, –OPRaRb, or –NHPRaRb,Ra and Rb together with the heteroatom to which they are attached form a heterocycle;Z is a carboxylate ligand;W is an anionic ligand selected from the group consisting of carboxylates, hydride, and halide;and A is a neutral ligand selected from the group consisting of phosphines, carbonyl, and sulfoxides, or A is absent. It has surprisingly been found that the ruthenium complexes of the present invention, where Z is a carboxylate ligand, exhibit high activity for the hydrogenation of challenging fatty acid methyl esters (FAME). In particular, it has surprisingly been found that the rutheniumcomplexes of the present invention are able to hydrogenate fatty acid methyl esters at ultra-high S / C ratios at near ambient (e.g.40 °C) temperatures.It has surprisingly been found that the ruthenium complexes of the present invention may beused to provide active catalysts in the hydrogenation of ester containing substrates at ultra-high S / C ratios. Moreover, the ruthenium complexes of the present invention exhibit little to no induction period and rapidly form an active catalyst in the ester hydrogenation catalyticcycle under catalytic conditions.Without being bound by any sort of theory, the present inventors believe that when at least Zis a carboxylate ligand, the ruthenium complexes of the invention rapidly and preferentiallyform an active catalytic species. Consequently, the relative concentration of active catalyticspecies in the reaction is increased and the amount of pre-catalyst needed in the reactionmay be decreased. It has further surprisingly been found that the ruthenium complexes of the invention are capable of providing active catalysts for the hydrogenation of a number of different carbonyl containing substrates. For example, it has surprisingly been found that the ruthenium complexes of the invention may be used to provide hydrogenation catalysts which reducealdehyde containing substrates under especially mild conditions.In a second aspect of the present invention there is provided a process for reducing a carbonyl containing substrate to an alcohol containing substrate in the presence of ahydrogen source and optionally a base using the ruthenium complex of formula (I) and / or theruthenium complex of formula (II) of the first aspect of the invention. Brief Description of the DrawingsFigure 1 shows a tridentate ligand having formula (III).Figure 2 shows the hydrogen uptake of shows the hydrogen uptake of [Ru(η1-OAc)2(SNS)(PPh3)] (Complex C according to the invention) and [Ru(SNS)Cl2(PPh3)](Complex X not according to the invention) in the hydrogenation of methyl decanoate at anS / C ratio of 10,000 / 1, a temperature of 40 °C, using 50 mol% NaOMe versus substrate as a base.Figure 3 shows the hydrogen uptake of [Ru(η1-OAc)2(PNN)(PPh3)] (Complex A according tothe invention) and [Ru(PNN)Cl2(PPh3)] (Complex Y not according to the invention) in thehydrogenation of methyl decanoate at an S / C ratio of 10,000 / 1, a temperature of 40 °C, using 50 mol% NaOMe versus substrate as a base.Figure 4 shows the hydrogen uptake of [Ru(η1-OAc)2(SNS)(PPh3)] (Complex C according tothe invention) and [Ru(SNS)Cl2(PPh3)] (Complex X not according to the invention) in thehydrogenation of ethyl decanoate at an S / C ratio of 100,000 / 1, a temperature of 40 °C, using50 mol% NaOEt versus substrate as a base.DefinitionsThe point of attachment of a moiety or substituent is represented by “-”. For example, -OH isattached through the oxygen atom.“Alkenyl” refers to a straight-chain or branched unsaturated hydrocarbon group comprising atleast one carbon-carbon double bond.“Alkoxy” refers to an optionally substituted group of the formula alkyl-O- or cycloalkyl-O-,wherein alkyl and cycloalkyl are as defined below.“Alkyl” refers to a straight-chain or branched saturated hydrocarbon group. The alkyl groupmay be unsubstituted. Alternatively, the alkyl group may be substituted. Unless otherwisespecified, the alkyl group may be attached at any suitable carbon atom and, if substituted,may be substituted at any suitable atom. Typical alkyl groups include but are not limited tomethyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl and the like.“Alkynyl” refers to a straight-chain or branched unsaturated hydrocarbon group comprising atleast one carbon-carbon triple bond.“Aryl” refers to an aromatic carbocyclic group. The aryl group may have a single ring or multiplecondensed rings. The aryl group may be unsubstituted. Alternatively, the aryl group may besubstituted. Unless otherwise specified, the aryl group may be attached at any suitable carbonatom and, if substituted, may be substituted at any suitable atom. Examples of aryl groupsinclude, but are not limited to, phenyl, naphthyl, anthracenyl and the like.“Cycloalkenyl” refers to an unsaturated, non-aromatic carbocyclic ring. The cycloalkenyl grouptherefore has at least one carbon-carbon double bond, but may have more. In certain embodiments, the cycloalkenyl group may have from 3-15 carbon atoms, in certainembodiments, from 3-10 carbon atoms, in certain embodiments, from 3-8 carbon atoms. Thecycloalkenyl group may be unsubstituted. Alternatively, the cycloalkenyl group may besubstituted. Unless other specified, the cycloalkenyl group may be attached at any suitablecarbon atom and, if substituted, may be substituted at any suitable atom. Typical cycloalkenyl groups include but are not limited to cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, and the like.“Cycloalkyl” refers to a saturated carbocyclic hydrocarbon radical. The cycloalkyl group mayhave a single ring or multiple condensed rings. The cycloalkyl group may be unsubstituted.Alternatively, the cycloalkyl group may be substituted. Unless other specified, the cycloalkylgroup may be attached at any suitable carbon atom and, if substituted, may be substituted atany suitable atom. Typical cycloalkyl groups include but are not limited to cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, adamantyl and the like. "FAME” refers to “Fatty Acid Methyl Ester”. A Fatty Acid Methyl Ester is a methyl ester of a fatty acid. “Fatty acid” refers to a carboxylic acid with a long aliphatic chain (e.g. >6 carbon atoms), which can be either saturated or unsaturated. The aliphatic chain of the fatty acid may be branched or unbranched. In certain embodiments, the aliphatic chain of the fatty acid comprises 12 to 24 carbon atoms. In certain embodiments, the aliphatic chain of the fatty acid comprises 0 to 5 carbon-carbon double bonds. “Fatty alcohol” refers to an alcohol with a long aliphatic chain (e.g. >6 carbon atoms), which can be either saturated or unsaturated. The aliphatic chain of the fatty alcohol may be branched or unbranched. In certain embodiments, the aliphatic chain of the fatty alcoholcomprises 12 to 24 carbon atoms. In certain embodiments, the aliphatic chain of the fattyalcohol comprises 0 to 5 carbon-carbon double bonds.“Halo”, “halide”, or “hal” refers to F, Cl, Br and I atoms or ions.“Heteroalkyl” refers to a straight-chain or branched saturated hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g.nitrogen, oxygen, phosphorus and / or sulfur atoms). The heteroalkyl group may beunsubstituted. Alternatively, the heteroalkyl group may be substituted. Unless otherwisespecified, the heteroalkyl group may be attached at any suitable atom and, if substituted, maybe substituted at any suitable atom. Examples of heteroalkyl groups include but are not limitedto ethers, thioethers, primary amines, secondary amines, tertiary amines and the like. “Heteroaryl” refers to an aromatic carbocyclic group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorusand / or sulfur atoms). The heteroaryl group may be unsubstituted. Alternatively, the heteroarylgroup may be substituted. Unless otherwise specified, the heteroaryl group may be attachedat any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heteroaryl groups include but are not limited to thienyl, furanyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, thiadiazolyl, thiophenyl, oxadiazolyl, pyridinyl, pyrimidyl, benzoxazolyl, benzthiazolyl, benzimidazolyl, indolyl, quinolinyl and the like.“Heterocycle” encompasses both heterocycloalkyl groups and heteroaryl groups.“Heterocycloalkyl” refers to a saturated cyclic hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen,phosphorus and / or sulfur atoms). The heterocycloalkyl group may be unsubstituted.Alternatively, the heterocycloalkyl group may be substituted. Unless otherwise specified, theheterocycloalkyl group may be attached at any suitable atom and, if substituted, may besubstituted at any suitable atom. Examples of heterocycloalkyl groups include but are notlimited to epoxide, morpholinyl, piperadinyl, piperazinyl, thirranyl, pyrrolidinyl, pyrazolidinyl, imidazolidinyl, thiazolidinyl, thiomorpholinyl and the like. “Substituted” refers to a group in which one or more hydrogen atoms are each independently replaced with substituents (e.g. 1, 2, 3, 4, 5 or more) which may be the same or different. Examples of substituents include but are not limited to -halo, -C(halo)3, -Rg, =O, =S, -O-Rg, - S-Rg, -NRgRh, -CN, -NO2, -C(O)-Rg, -COORg, -C(S)-Rg, -C(S)ORg, -S(O)2OH, -S(O)2-Rg, - S(O)2NRgRh, -O-S(O)-Rgand -CONRgRh, such as -halo, -C(halo)3 (e.g. –CF3), -Rg, -O-Rg, -NRgRh, -CN, or -NO2. Rg and Rh are independently selected from the groups consisting of H,alkyl, aryl, arylalkyl, heteroalkyl, heteroaryl, or Rg and Rh may be linked to form aheterocycloalkyl group. Rg and Rh may be unsubstituted or further substituted as definedherein. As used herein, the term “wax ester” refers to an ester of a fatty acid and a fatty alcohol, wherein fatty acid and fatty alcohol are as defined above. As used herein, the term “S / C” is an abbreviation for “substrate / catalyst” and is used to describe the catalyst loading employed in a reaction, i.e. it describes the molar ratio ofcarbonyl-containing substrate (e.g ester containing substrate) and catalyst present in thereaction mixture. In the instance an ester-containing substrate contains more than one estermoiety, the S / C value is adjusted accordingly. As used herein, the term “turnover number” (TON) refers to the number of moles of substrate that a mole of catalyst can convert before becoming deactivated. As used herein, unless otherwise specified, “mol%” describes the amount of moles of thespecified material (e.g. a base) relative to the amount of moles of the ester containingsubstrate, as a percentage.As used herein, the term “hydrogenation” refers to hydrogenation or reduction of a substrate(e.g. of an ester containing substrate) using molecular hydrogen.Detailed DescriptionPreferred and / or optional features of the invention will now be set out. Any aspect of theinvention may be combined with any other aspect of the invention unless the contextdemands otherwise. Any of the preferred and / or optional features of any aspect may becombined, either singly or in combination, with any aspect of the invention unless the context demands otherwise.According to a first aspect, the present invention provides a ruthenium complex of formula (I)or formula (II): [Ru(L)AZ]W (I)[Ru(L)AZW] (II). In the ruthenium complex of formula (I) or formula (II) the Ru atom may have oxidation state of +2. The ruthenium complex of the invention may be a ruthenium complex of formula (I). The ruthenium complex of the invention may be a ruthenium complex of formula (II). The ruthenium complex of formula (I) or formula (II) comprises a tridentate ligand, L. As will be readily understood the tridentate ligand, L, is bonded to the Ru atom through three bonds. The three bonds are formed between the Ru atom and three coordinating atoms of the tridentate ligand, L, within the coordination sphere of the Ru atom.In the ruthenium complex of formula (I) or formula (II), L is a tridentate ligand having formula(III)

[0002] wherein:X is a nitrogen atom and when taken together with R1 it forms an optionally substitutedheteroaryl group when Rx is absent, orX is –SRa, and R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;Y is selected from –SRb, –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or when Y is –PRaRb, –OPRaRb, or –NHPRaRb,Ra and Rb together with the heteroatom to which they are attached form a heterocycle.In the tridentate ligand having formula (III), where X is a nitrogen atom, X and R1together with the atoms to which they attach form an optionally substituted heteroaryl group.Preferably, the heteroaryl group may be a substituted or unsubstituted 5-membered or asubstituted or unsubstituted 6-membered heterocyclic ring. More preferably, the heteroarylgroup is a substituted or unsubstituted 6-membered ring. Even more preferably, theheteroaryl group is selected from substituted or unsubstituted pyridinyl, pyrrolyl, imidazolyl,pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, tetrazolyl, thiadiazolyl, oxadiazolyl, pyrimidyl, benzoxazolyl, benzthiazolyl, benzimidazolyl, indolyl, and quinolinyl.Even more preferably still, the heteroaryl group is a substituted or unsubstituted pyridinylring. Most preferably, the heteroaryl group is an unsubstituted pyridinyl ring.Alternatively, X is –SRa.In the tridentate ligand having formula (III), where X is -SRa, R1 and Rx are each independentlypreferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted orunsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably,R1 and Rx are each independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy. More preferably still, R1 and Rx are each independently selected from hydrogen,methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R1 and Rx are each hydrogen.In the tridentate ligand having formula (III), R1and Rxmay be the same or different.In the tridentate ligand having formula (III), Y is preferably selected from –SRb, –PRaRb, and –NHPRaRb. Most preferably, Y is selected from –SRb and –PRaRb.In the tridentate ligand having formula (III), where X is a nitrogen atom and when takentogether with R1it forms an optionally substituted heterocycle when Rxis absent, Y ispreferably -PRaRb, -OPRaRb, or –NHPRaRb, for example -PRaRb, or –NHPRaRb. In thetridentate ligand having formula (III), where X is -SRa, Y is preferably -SRb.In the tridentate ligand having formula (III), where Y is -OPRaRb or –NHPRaRb it will beunderstood that the phosphorus atom of Y is bonded to the Ru atom in the ruthenium complexof formula (I) or ruthenium complex of formula (II). In the tridentate ligand having formula (III), R2and Ryare each independently preferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstitutedC1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably, R2 and Ry areeach independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl,substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy. More preferably still, R2and Ryare each independently selected from hydrogen, methyl, ethyl,iso-propyl, and tert-butyl. Most preferably, R2 and Ry are each hydrogen.In the tridentate ligand having formula (III), R3a, R3b, R4a, and R4b are each independentlypreferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted orunsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably,R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted orunsubstituted C1-5-alkoxy. More preferably still, R3a, R3b, R4a, and R4b are each independentlyselected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R3a, R3b, R4a,and R4bare each hydrogen.As will be understood, in the tridentate ligand, L, neither of R3a nor R3b are linked with eitherof R4aor R4bto form a ring structure.In the tridentate ligand having formula (III), R5 is preferably selected from hydrogen andmethyl. Most preferably, R5 is hydrogen.In the tridentate ligand having formula (III), Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10- heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10- cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10- heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably, Ra and Rb are each independently selected from substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted orunsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. Most preferably, Raand Rbare each independently selected from methyl, ethyl, iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl. For example, Raand Rbmay each independently be selected from ethyl, iso-propyl, tert-butyl, and phenyl. Raand Rbmay be the same or different. In preferred tridentate ligands having formula (III), Raand Rb are the same. For example, Ra and Rb may be the same and be selected from iso-propyl, tert-butyl, and phenyl. In the tridentate ligand having formula (III), where Y is -PRaRb, -OPRaRb, and / or -NHPRaRbit may be preferred that Raand Rbare each independently selected from iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl. For example, Raand Rbmay each independently beselected from the group consisting of iso-propyl, tert-butyl, and phenyl. In the tridentate ligandhaving formula (III), where X is -SRaand Y is -SRbit may be preferred that Raand Rbare eachindependently selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, pentyl,iso-propyl, and tert-butyl, preferably ethyl.In preferred ruthenium complexes of formula (I) or formula (II), L may be a tridentate ligandhaving formula (IIIa) , wherein:Y is selected from –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or Ra and Rb together with the heteroatom towhich they are attached form a heterocycle; and each Rwis independently selected from the group consisting of hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, and substituted orunsubstituted C1-10-alkoxy.In the tridentate ligand having formula (IIIa), Y is preferably selected from –PRaRb, and –NHPRaRb. More preferably, Y is –PRaRb. In the tridentate ligand having formula (IIIa), R2and Ryare each independently preferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstitutedC1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably, R2 and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl,substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy. Even more preferably, R2and Ryare each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R2and Ryare each hydrogen.In the tridentate ligand having formula (IIIa), R3a, R3b, R4a, and R4b are each independentlypreferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted orunsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably,R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted orunsubstituted C1-5-alkoxy. More preferably still, R3a, R3b, R4a, and R4b are each independentlyselected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R3a, R3b, R4a, and R4bare each hydrogen. As will be understood, in the tridentate ligand having formula (IIIa), neither of R3anor R3bare linked with either of R4aor R4bto form a ring structure. In the tridentate ligand having formula (IIIa), R5is selected from hydrogen, or substituted orunsubstituted C1-5-alkyl. Preferably, R5 is selected from hydrogen and methyl. Most preferably,R5is hydrogen. In the tridentate ligand having formula (IIIa), Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10- heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10- cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10- heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably, Ra and Rb are each independently selected from substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably still, Raand Rbeach independently selected from iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl. For example, Raand Rbmay each independently be selected from iso-propyl, tert- butyl, and phenyl. In the tridentate ligand having formula (IIIa), Raand Rbmay be the same or different.Preferably, Ra and Rb are the same. For example, Ra and Rb may be the same and be selectedfrom iso-propyl, tert-butyl, and phenyl. In the tridentate ligand having formula (IIIa), each Rwis independently preferably selectedfrom hydrogen, and substituted or unsubstituted C1-10 alkyl. More preferably, each Rw isindependently selected from hydrogen, and substituted or unsubstituted C1-5 alkyl. Mostpreferably, each Rwis hydrogen.In alternative preferred ruthenium complexes of formula (I) or formula (II), L may be atridentate ligand having formula (IIIb) , wherein: R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. In the tridentate ligand having formula (IIIb), R1and Rxare each independently preferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstitutedC1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably, R1 and Rx areeach independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl,substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy. More preferably still, R1and Rxare each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R1and Rxare each hydrogen. In the tridentate ligand having formula (IIIb), R2and Ryare each independently preferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstitutedC1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably, R2 and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl,substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy. Even more preferably, R2and Ryare each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R2and Ryare each hydrogen.In the tridentate ligand having formula (IIIb), R3a, R3b, R4a, and R4b are each independentlypreferably selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted orunsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy. More preferably,R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted orunsubstituted C1-5-alkoxy. More preferably still, R3a, R3b, R4a, and R4b are each independentlyselected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl. Most preferably, R3a, R3b, R4a,and R4bare each hydrogen. As will be understood, in the tridentate ligand having formula (IIIb), neither of R3anor R3bare linked with either of R4aor R4bto form a ring structure. In the tridentate ligand having formula (IIIb), R5is selected from hydrogen, or substituted orunsubstituted C1-5-alkyl. Preferably, R5 is selected from hydrogen and methyl. Most preferably,R5is hydrogen. In the tridentate ligand having formula (IIIb), Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10- heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10- cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10- heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4- 10-heteroaryl. More preferably, Raand Rbare each independently selected from substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably still, Raand Rbeach independently substituted or unsubstituted C1-5 alkyl. For example, Raand Rbmay each independently be selected from methyl, ethyl, n-propyl, n-butyl, pentyl, iso-propyl,and tert-butyl. In the tridentate ligand having formula (IIIb), Raand Rbmay be the same or different.Preferably, Ra and Rb are the same. For example, Ra and Rb may be the same and be selectedfrom ethyl, iso-propyl, and tert-butyl.It may be preferred that in the ruthenium complex of formula (I) or formula (II), L is atridentate ligand having formula (IIIa) and / or formula (IIIb).It may be preferred that in the ruthenium complex of formula (I) or formula (II), L is one ormore tridentate ligands of formulae (IIIc), (IIId), and / or (IIIe), , wherein Raand Rbare each independently selected from substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or where the tridentate ligand is a tridentateligand having formula (IIIc) or (IIIe) Ra and Rb together with the heteroatom to which they areattached form a heterocycle. In the tridentate ligand having formula (IIIc) or formula (IIIe), Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10- cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10- heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4- 10-heteroaryl. More preferably, Raand Rbare each independently selected from substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably still, Raand Rbeach independently selected from iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl. For example, Raand Rbmay each independently be selected from iso-propyl, tert- butyl, and phenyl. In the tridentate ligand having formula (IIIc) or formula (IIIe), Raand Rbmay be the same ordifferent. Preferably, Ra and Rb are the same. For example, Ra and Rb may be the same andbe selected from iso-propyl, tert-butyl, and phenyl. In the tridentate ligand having formula (IIId), Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10- heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10- cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10- heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4- 10-heteroaryl. More preferably, Raand Rbare each independently selected from substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl. More preferably still, Raand Rbeach independently substituted or unsubstituted C1-5 alkyl. For example, Raand Rbmay each independently be selected from methyl, ethyl, n-propyl, n-butyl, pentyl, iso-propyl, and tert-butyl. In the tridentate ligand having formula (IIId), Raand Rbmay be the same or different.Preferably, Ra and Rb are the same. For example, Ra and Rb may be the same and beselected from ethyl, iso-propyl, and tert-butyl.It may be preferred that in the ruthenium complex of formula (I) or formula (II), L is atridentate ligand having formula (IIIc). It may be preferred that in the ruthenium complex offormula (I) or formula (II), L is a tridentate ligand having formula (IIId). It may be preferredthat in the ruthenium complex of formula (I) or formula (II), L is a tridentate ligand havingformula (IIIe). It may be preferred that in the ruthenium complex of formula (I) or formula (II),L is a tridentate ligand having formula (IIIc) or (IIIe), formula (IIIc) or (IIId), or formula (IIId) or(IIIe).In the ruthenium complex of formula (I) or formula (II), it may be more preferred that L is oneor more tridentate ligands selected from the group consisting of: In the ruthenium complex of formula (I) or formula (II), it may be most preferred that L is oneor more tridentate ligands selected from the group consisting of: .Alternatively, in the ruthenium complex of formula (I) or formula (II), it may be most preferredthat L is one or more tridentate ligands selected from the group consisting of: . For the avoidance of doubt the abbreviations Ph,iPr,tBu, and Et as used herein will beunderstood to refer to phenyl, iso-propyl, tert-butyl, and ethyl, respectively.In the ruthenium complex of formula (I) or formula (II), Z is a carboxylate ligand. In theruthenium complex of formula (I) or formula (II), Z is a coordinated anionic ligand. Preferably, Z may be a carboxylate ligand having formula (IV) ,where R6 may be selected from substituted or unsubstituted C1-20-alkyl, substituted orunsubstituted C2-20-alkenyl, substituted or unsubstituted C2-20-alkynyl, substituted or unsubstituted C1-20-heteroalkyl, substituted or unsubstituted C1-20-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroary.In the carboxylate ligand having formula (IV), R6 may be preferably selected from substitutedor unsubstituted C1-20-alkyl, substituted or unsubstituted C1-20-heteroalkyl, substituted or unsubstituted C1-20-alkoxy, substituted or unsubstituted C6-10-aryl, and substituted orunsubstituted C4-10-heteroaryl. More preferably, R6 may be selected from substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5-alkoxy, substituted or unsubstituted C6-10-aryl, and substituted orunsubstituted C4-10-heteroaryl. More preferably still, R6 may be selected from methyl,trifluoromethyl, ethyl, propyl, butyl, tert-butyl, pentyl, or phenyl. Most preferably, R6 may bemethyl.Where R6 is methyl it will be understood that the carboxylate ligand having formula (IV), orcarboxylate ligand having formula (IVb) as described below, may be referred to as anacetate (OAc-) ligand. Where R6 is tert-butyl it will be understood that the carboxylate ligandhaving formula (IV), or carboxylate ligand having formula (IVb) as described below, may be referred to as a pivalate (OPiv-) ligand. Z may be coordinated to the Ru atom either as a monodentate or a bidentate ligand. In other words, Z may be coordinated either in an ^1or an ^2coordination mode. Where Z is coordinated to the Ru atom as a monodentate ligand it will be understood that it occupies one coordination sites on the Ru atom and may be regarded as being bonded to the Ru atom by a single oxygen atom. Where Z is coordinated to the Ru atom as a bidentate ligand it will be understood that it occupies two coordination sites on the Ru atom and may be regarded as being bonded to theRu atom by the two oxygen atoms of the carboxylate group or by a delocalised ^-system.Where Z is coordinated to the Ru atom as a bidentate ligand, in an ^2coordination mode, Z may be a carboxylate ligand having formula (IVb) ,wherein R6 is as hereinbefore defined in relation to the carboxylate ligand having formula(IV). As will be understood, where Z is coordinated to the Ru atom as a bidentate ligand, in an ^2coordination mode, the ruthenium complex of the invention is a ruthenium complex of formula (I). As will be further understood, where Z is coordinated to the Ru atom as a monodentate ligand, in an ^1coordination mode, the ruthenium complex of the invention is a ruthenium complex of formula (II).In the ruthenium complex of formula (I) and / or the ruthenium complex of formula (II), W is ananionic ligand selected from the group consisting of carboxylates, hydride, and halide. W may be a coordinated anionic ligand, i.e. the anionic ligand is bonded to the Ru atomwithin the coordination sphere (e.g. where the ruthenium complex is a ruthenium complex offormula (II)). Alternatively, W may be a non-coordinated anionic. By “non-coordinated anionicligand”, we mean the anionic ligand is forced to the outer sphere of the Ru atom (e.g. wherethe ruthenium complex is a ruthenium complex of formula (I)). A non-coordinated anionicligand, therefore, is dissociated from the Ru atom. The anionic ligand can be generallyidentified as coordinating or non-coordinating by analysing the X-ray crystal structure of thecomplex. As will be apparent to the skilled person, where W is a carboxylate ligand and coordinated to the Ru atom, W is coordinated in a monodentate fashion, and may be regarded as carboxylateligand having formula (IV). Where W is a carboxylate ligand and present as a non-coordinatedligand, it may be regarded as either a carboxylate ligand having formula (IV) or formula (IVb). W may be a halide. For example, W may be F-, Cl-, Br-, or I-. Preferably, W may be Cl-, Br-, or I-. More preferably, W may be Cl-. A is a neutral ligand selected from the group consisting of phosphines, carbonyl, andsulfoxides, or A is absent. Preferably, A is a neutral ligand selected from the group consistingof phosphines, carbonyls, and sulfoxides.Preferred phosphines include -PPh3, -PiPr3, -PtBu3, -P(o-tolyl)3, -PAr3, -PPh2Me, and -PCy3,where Ar is a substituted aryl group, for example a substituted phenyl group. Preferably, Armay be a phenyl group substituted with an alkyl group, an alkoxy group, a fluoro group, or a trifluoro methyl group.Preferred sulfoxides include dimethylsulfoxide (DMSO), diethylsulfoxide, dibutylsulfoxide,dihexylsulfoxide, dioctylsulfoxide, and diphenyl sulfoxide. More preferred sulfoxides includedimethylsulfoxide (DMSO) and diphenylsulfoxide. A most preferred sulfoxide is dimethylsulfoxide (DMSO). Accordingly, it may be preferred that A is a neutral ligand selected from the group consistingof -CO, -PPh3, -PiPr3, -PtBu3, -PAr3, -PCy3, -PPh2Me, and DMSO. As will be understood where A is a sulfoxide ligand, the sulfoxide ligand may coordinate to the Ru atom by a bond from either the oxygen atom or the sulfur atom of the sulfoxide ligand.For the avoidance of doubt, any complex depicted in a diagram or figure herein is intendedto include all confirmations and isomers thereof (e.g. fac- / mer- isomers and cis- / trans-isomers) unless explicitly stated otherwise.In a preferred aspect of the present invention the ruthenium complex of formula (I) or formula(II) may be one or more selected from:

[0003] In another preferred aspect of the present invention, the ruthenium complex of formula (I) orformula (II) may be one or more selected from: In a second aspect of the invention there is provided a process for reducing a carbonylcontaining substrate to an alcohol containing substrate in the presence of a hydrogensource, and optionally a base, using the ruthenium complex of formula (I) and / or theruthenium complex of formula (II) as defined in the first aspect of the invention.The process of the invention may comprise the steps of:contacting a carbonyl containing substrate, a hydrogen source, optionally a base,and the ruthenium complex of formula (I) and / or the ruthenium complex of formula (II)to form a reaction mixture; and reacting the carbonyl containing substrate with the hydrogen source to produce analcohol containing substrate.The process of the invention may be referred to as a hydrogenation process or a reductionprocess. The ruthenium complex of formula (I) and the ruthenium complex of formula (II) are as defined in the first aspect of the invention. The carbonyl containing substrate may be an ester containing substrate, an aldehyde containing substrate, a ketone containing substrate, or a carboxylic acid containing substrate. Preferably, the carbonyl containing substrate may be an ester containing substrate, an aldehyde containing substrate, or a ketone containing substrate. Morepreferably, the carbonyl containing substrate may be an ester containing substrate, or analdehyde containing substrate. Most preferably, the carbonyl containing substrate may be an ester containing substrate. Where the carbonyl containing substrate is an ester containing substrate, the ester containing substrate may be any organic molecule comprising one or more ester moieties. For example, the ester containing substrate may be a methyl ester (e.g. methyl acetate), an ethyl ester (e.g. ethyl acetate), or a wax ester. When the ester containing substrate is a monoester, the products of the process are alcohols. When the ester containing substrate is a lactone, the product of the process is a diol. When the ester containing substrate contains multiple ester moieties, the products of the process are a polyol and alcohols. In preferred processes, the process does not produce a hemiacetal by-product. Typically, the hydrogen source may be molecular hydrogen (H2 gas). Typically, the molecular hydrogen is provided to the reaction mixture at elevated pressure. For instance,molecular hydrogen may be provided at a pressure of from 5 barg to 50 barg, such as from10 barg to 40 barg. The ruthenium complex of formula (I) or ruthenium complex of formula (II) may be present inthe reaction mixture in an amount of from 0.001 mol% or more, from 0.002 mol% or more,from 0.003 mol% or more, or from 0.005 mol% or more relative to the ester containingsubstrate. The ruthenium complex of formula (I) or ruthenium complex of formula (II) may be present in the reaction mixture in an amount of from 0.5 mol% or less, from 0.1 mol% orless, from 0.05 mol% or less, or from 0.02 mol% or less relative to the ester containingsubstrate. For example, the ruthenium complex of formula (I) or ruthenium complex offormula (II) may be present in the reaction mixture in an amount of from 0.001 to 0.5 mol%,from 0.002 to 0.1 mol%, from 0.003 to 0.05 mol%, or from 0.005 mol% to 0.02 mol% relativeto the ester containing substrate. As will be understood by the person skilled in the art, the molar percentages expressed above may also be expressed as a ratio of organic substrate to catalyst (S / C) ratio. For instance, 0.001 mol% of the ruthenium complex of formula (I) or ruthenium complex of formula (II) relative to the ester containing substrate corresponds to an S / C ratio of 100,000:1. It is a surprising advantage of the process of the present invention that low loadings of the ruthenium complex of formula (I) or the ruthenium complex of formula (II) can be used whilst maintaining high catalytic activity, in particular in the hydrogenation of ester containing substrates. The reaction mixture may comprise a solvent or may be carried out under so-called “solventfree” conditions. It will be understood that where solvent free conditions are used the estercontaining substrate may act as a liquid medium for the reaction mixture. Where a solvent isused the solvent may suitably selected from one or more of an alcohol, toluene, THF and Me-THF. The reaction mixture may further comprise a base. Suitable bases include metal alkoxides such as sodium methoxide (NaOMe), sodium ethoxide (NaOEt) and potassium tert-butoxide (KOtBu), or bases such as potassium phosphate (K3PO4). The base may be present in an amount of from 20 to 200 mol% relative to the ester containing substrate. For example, the base may be present in an amount of about 40 mol% or more, 50 mol% or more, 80 mol% ormore, or 100 mol% or more relative to the ester containing substrate. Where the carbonylcontaining substrate is an ester containing substrate a base may be required. Where the carbonyl containing substrate is an aldehyde a base may not be required.The step of reacting the carbonyl containing substate (e.g. an ester containing substrate)with the hydrogen source may be carried out at elevated temperature. Typically, atemperature of from 20 to 140 °C may be chosen, such as from 30 °C to 100 °C, or from 30°C to 70 °C.The step of reacting the carbonyl containing substrate (e.g. an ester containing substrate)with the hydrogen source may be carried out over any suitable time period. Typically, the reaction takes place over a time period of from 1 to 16 hours, such as from 2 to 10 hours. Ruthenium complex of formula (I) or formula (II) of the first aspect of the invention may be prepared by a process comprising the step of reacting a ruthenium precursor complex with a tridentate ligand, L, as defined in relation to the first aspect of the invention.Suitable ruthenium precursor complexes include [Ru(η2-OAc)2(PPh3)2],1 [Ru(η2-OPiv)2(PPh3) [Ru Where [Ru(sulfoxide)4Cl2] is used as a ruthenium precursor complex, one or more chloride ligands of the resulting complex of formula [Ru(L)(sulfoxide)Cl2], formed from the reaction of[Ru(sulfoxide)4Cl2] with the tridentate ligand (L), may be replaced using methods known inthe art. For example, chloride ligands may be substituted by one or more carboxylate ligands by treating [Ru(L)(sulfoxide)Cl2] with a silver compound (e.g. silver carbonate or silver oxide) and a carboxylic acid (e.g. acetic acid). Alternatively, a silver carboxylate compound may be used such as silver acetate. The tridentate ligands, L, of the ruthenium complexes of formula (I) or formula (II) may be prepared according to the methods disclosed in WO2013023307A1, WO2014036650A1, and WO2014139030A1. Examples Materials NaOEt, NaOMe, and K3PO4, the ester-containing substrate methyl decanoate, ethyl decanoate, and ethyl benzoate, and solvents are all commercially available, e.g. from Sigma Aldrich, Fisher Scientific, Alfa Aesar, Acros Organics etc. RuCl3.nH2O and RuCl2(PPh3)3is available from Johnson Matthey. Preparation of ruthenium precursor complexes All reactions were carried out under an argon atmosphere using standard Schlenk techniques. Solvents were dried by standard methods and distilled under argon before use. The ruthenium complexes [Ru(η2-OAc)2(PPh3)2],1[Ru(η2-OPiv)2(PPh3)2],2[RuH(η2- OAc)(PPh3)3],3and [Ru(η1-OAc)(η2-OAc)(CO)(PPh3)2],4were prepared according to literature procedures. Preparation of tridentate ligandsAs used herein the terms “SNS ligand” and “PNN ligand” refer to the following tridentateligands: . SNS and PNN ligands were synthesised according to the methods disclosed in WO2013023307A1, and WO2014036650A1.

[0004] Synthesis of [Ru(η1-OAc)2(PNN)(PPh3)] (Complex A) [Ru(η2-OAc)2(PPh3)2] (200 mg, 0.269 mmol) was suspended in acetone (5 mL) and PNN ligand (90.5 mg, 0.282 mmol, 1.05 equiv) was added. The mixture was stirred for 3 h at room temperature. The obtained yellow precipitate was filtered, washed with diethyl ether (2x2mL), n-heptane (4x3 mL), n-pentane (2x3 mL) and dried under reduced pressure. Yield174.7 mg (81%). Anal. Calcd for C42H42N2O4P2Ru (801.83): C, 62.91; H, 5.28; N, 3.49. Found: C, 62.86; H,5.25; N, 3.52. 1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 11.41 (d, 3J(H,H) = 11.4 Hz, 1H;NH), 8.53 (d, 3J(H,H) = 4.8 Hz, 1H; ortho-CH of C5H4N), 7.62 (t, 3J(H,H) = 8.4 Hz, 1H;aromatic proton), 7.17-6.83 (m, 25H; aromatic protons), 6.61 (d, 3J(H,H) = 7.6 Hz, 1H; para-CH of C5H4N), 6.36 (t, 3J(H,H) = 6.4 Hz, 1H; meta-CH of C5H4N), 4.92 (t, 2J(H,H) = 12.5 Hz,1H; NCH2Py), 3.76 (ddd, 2J(H,H) = 13.1 Hz, 3J(H,H) = 5.4, 3J(H,H) = 3.3 Hz, 1H; NCH2Py),3.38-3.24 (m, 1H; NCH2CH2P), 3.15-3.02 (m, 1H; NCH2CH2P), 3.01-2.82 (m, 1H;NCH2CH2P), 2.52 (td, 2J(H,H) = 12.7 Hz, 3J(H,H) = 3.6 Hz, 1H; NCH2CH2P), 1.88 (s, 3H;OCOCH3), 1.44 ppm (s, 3H; OCOCH3).13C{1H} NMR (100.6 MHz, toluene-d8, 25 °C): δ182.2 (d, 3J(C,P) = 2.2 Hz; OCOCH3), 178.0 (s; OCOCH3), 166.0 (s; NCCH2), 155.2 (d,3J(C,P) = 2.2 Hz; NCH of C5H4N), 140.2 (d, 1J(C,P) = 30.1 Hz; ipso-Ph), 137.1-124.5 (m;aromatic carbon atoms), 121.2 (d, 4J(C,P) = 1.7 Hz; meta-CH of C5H4N), 119.3 (s; para-CHof C5H4N), 58.2 (br s; NCH2Py), 48.3 (br s; NCH2CH2P), 38.9 (d, 1J(C,P) = 24.2 Hz;NCH2CH2P), 25.1 (s; OCOCH3), 24.8 ppm (s; OCOCH3).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 53.8 (d, 2J(P,P) = 29.3 Hz), 47.6 (d. 2J(P,P) = 29.3 Hz). Synthesis of [RuH(η1-OAc)(PNN)(PPh3)] (Complex B) [RuH(η2-OAc)(PPh3)3] (100 mg, 0.106 mmol) and PNN ligand (35.6 mg, 0.111 mmol, 1.05 equiv) were suspended in n-heptane (10 mL), and the slurry was refluxed for 2 h. The yellow solid was filtered, washed with diethyl ether (2x3 mL), n-pentane (3x5 mL), and dried under reduced pressure. Yield: 56.0 mg (71%). Anal. Calcd for C40H40N2O2P2Ru (743.79): C, 64.59; H, 5.42; N, 3.77. Found: C, 64.63; H,5.44; N, 3.76. 1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 10.63 (t, 3J(H,H) = 8.7 Hz, 1H; NH),8.26 (br d, 3J(H,H) = 4.9 Hz, 1H; ortho-CH of C5H4N), 7.91-7.65 (m, 10H; aromatic protons),7.23-6.87 (m, 15H; aromatic protons), 6.72 (td, 3J(H,H) = 7,5 Hz, 4J(H,H) = 1.2 Hz,1H; para-CH of C5H4N), 6.48 (d, 3J(H,H) = 7.8 Hz, 1H; meta-CH of C5H4N), 6.09 (t, 3J(H,H) = 6.4 Hz,1H; meta-CH of C5H4N), 3.97-3.77 (m, 2H; NCH2Py), 3.17-2.92 (m, 2H; NCH2CH2P), 2.44-2.32 (m, 1H; NCH2CH2P), 2.27 (td, 3J(H,H) = 11.8 Hz, 4J(H,H) = 2.6 Hz,1H; NCH2CH2P),1.89 (s, 3H; OCOCH3), -18.40 ppm (dd, 2J(H,P) = 26.8 Hz, 2J(H,P) = 24.3 Hz, 1H; Ru-H).13C{1H} NMR (100.6 MHz, toluene-d8, 25 °C): δ 180.1 (br d,2J(C,P) = 3.9 Hz; OCOCH3), 163.1 (s; NCCH2), 154.9 (d,3J(C,P) = 2.4 Hz; NCH of C5H4N), 140.1 (d,1J(C,P) = 34.5 Hz;ipso-Ph), 137.1-124.5 (m; aromatic carbon atoms), 121.8 (s; meta-CH of C5H4N), 119.1 (s;para-CH of C5H4N), 60.5 (br s; NCH2Py), 51.3 (d, 3J(C,P) = 2.7 Hz; NCH2CH2P), 40.0 (d;1J(C,P) = 24.9 Hz; NCH2CH2P), 25.8 ppm (s; OCOCH3).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 78.0 (d, 2J(P,P) = 29.3 Hz), 64.5 ppm (d, 2J(P,P) = 29.3 Hz). Synthesis of [Ru(η1-OAc)2(SNS)(PPh3)] (Complex C) Complex C was prepared following the procedure used for the synthesis of Complex A,using the SNS ligand (54.6 mg, 0.282 mmol, 1.05 equiv) in place of PNN, leading to theproduct as a light-yellow solid. The compound was isolated as a mixture of a major isomer (95%) and two minor species (5%) differing by the relative orientation of the SEt groups withrespect to the SNS ligand plane. Yield: 159.7 mg (88%).Anal. Calcd for C30H40NO4PRuS2 (674.82): C, 53.40; H, 5.97; N, 2.08; S, 9.50. Found: C, 53.33; H, 5.95; N, 2.10; S, 9.45.1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 10.74 (br s, 0.95H; NH major isomer), 10.58 (br s, 0.03H; NH minor species), 9.78 (br s, 0.02H; NHminor species), 8.12 (t, 3J(H,H) = 9.4 Hz; Ph minor species), 7.92 (t, 3J(H,H) = 8.5 Hz, 5H;Ph major isomer), 7.71 (t, 3J(H,H) = 8.1 Hz; Ph minor species), 7.43-7.30 (br m; Ph minorspecies), 7.20 (br t, 3J(H,H) = 6.9 Hz, 5H; Ph major isomer), 7.16-6.99 (m, 5H; Ph majorisomer), 6.95-6.80 (br m; Ph minor species), 2.96-2.87 (m, 2H; NCH2 major isomer), 2.86- 2.71 (m, 2H; NCH2 major isomer), 2.68-2.60 (m, 2H; CH2 major isomer), 2.50 (pseudo t,3J(H,H) = 10.5 Hz, 2H; CH2 major isomer), 2.38-2.25 (m; CH2 minor species), 2.18-2.01 (m, 2H; CH2CH3 major isomer (superimposed with the solvent signal)), 1.88 (s, 3H; OCOCH3 major isomer), 1.70 (br s, 3H; OCOCH3 major isomer), 1.47-1.25 (m, 2H; CH2CH3 major isomer), 1.27 (br s; OCOCH3 minor species), 0.94 (t,3J(H,H) = 7.0 Hz; CH2CH3 minor species), 0.87 ppm (t,3J(H,H) = 7.4 Hz, 6H; CH2CH3 major isomer).13C{1H} NMR of the major isomer (100.6 MHz, toluene-d8, 25 °C): δ 182.4 (br s; OCOCH3), 177.8 (s; OCOCH3), 137.2-124.6 (m; aromatic carbon atoms), 48.9 (s; NCH2), 40.3 (s; SCH2), 30.5 (s; SCH2CH3), 24.7 (s; OCOCH3), 24.6 (s; OCOCH3), 12.8 ppm (s; CH2CH3).31P{1H} NMR (162.0 MHz,toluene-d8, 25 °C): δ 48.8 (s; major isomer, 95%), 47.5 (br s; minor species, 2.5%), 47.3 ppm(br s; minor species, 2.5%). Synthesis of [RuH(η1-OAc)(SNS)(PPh3)] (Complex D) Complex C (200 mg, 0.296 mmol) was dissolved in degassed toluene (5 mL), and a 0.1 Msolution of NaOiPr (4.45 mL, 0.445 mmol, 1.5 equiv) in 2-propanol was added. The mixture was heated 1 h at 60 °C, and the final solution was concentrated under reduced pressure atalmost 3 mL, stirred at room temperature for 30 min., and, after addition of toluene (5 mL),filtered on Celite (fine frit). The filtrate was concentrated under reduced pressure (~ 1 mL), and addition of n-heptane (10 mL) leads to the precipitation of a pale yellow product. The solid was washed with n-heptane (2x2 mL), and n-pentane (2x2 mL), filtered and dried underreduced pressure. The compound was isolated as a mixture of three isomers differing by therelative orientation of the SEt groups with respect to the SNS ligand plane. Yield: 173.6 mg (95%). Anal. Calcd for C28H38NO2PRuS2 (616.78): C, 54.53; H, 6.21; N, 2.27; S, 10.40. Found: C, 54.60; H, 6.15; N, 2.26; S, 10.45.1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 10.70 (br s, 1H; NH minor isomer), 10.18 (br s, 1H; NH major isomer), 10.06 (br s, 1H; NH minor species), 8.12-7.79 (m, 5H; Ph), 7.41-6.80 (m, 10H; Ph), 3.33-3.08 (m; CH2 minor species), 2.89-2.80 (m, 2H; NCH2 major isomer), 2.79-2.71 (m, 2H; NCH2 major isomer), 2.70-2.54 (m; CH2 minor species), 2.53-2.39 (m, 4H; NCH2 and CH2CH3 major isomer), 2.29 (br s, 3H; OCOCH3 minor species), 2.24 (br s, 3H; OCOCH3 minor species), 2.22 (br s, 3H; OCOCH3 major isomer), 2.18-2.05 (m; NCH2 minor and major isomers), 2.04-1.92 (m; CH2 minor species), 1.85-1.72 (m; CH2 minor species), 1.61-1.48 (m, 2H; CH2CH3 major isomer), 1.11- 0.97 (m; CH2CH3 minor species), 0.95 (t,3J(H,H) = 7.0 Hz; CH2CH3 minor species), 0.76 (t,3J(H,H) = 7.3 Hz, 6H; CH2CH3 major isomer), 0.71-0.62 ppm (m; CH2CH3 minor species), -21.54 (d, 2J(H,P) = 23.2 Hz, 1H; Ru-H minor species), -21.82 (d, 2J(H,P) = 26.2 Hz, 1H; Ru-H major isomer), -21.94 ppm (br d, 2J(H,P) = 25.9 Hz, 1H; Ru-H minor species). 13C{1H}NMR (100.6 MHz, toluene-d8, 25 °C): δ 180.7 (s; OCOCH3minor species), 180.6 (s; OCOCH3minor species), 180.3 (s; OCOCH3major isomer), 140.6-124.6 (m; aromatic carbon atoms), 52.8 (s; NCH2minor species), 52.3 (s; NCH2major isomer), 49.9 (s; NCH2minor species), 39.8 (d,3J(C,P) = 3.1 Hz; SCH2major isomer), 35.9 (s; SCH2minor species), 35.3 (s; SCH2minor species), 33.2 (s; SCH2CH3minor species), 31.6 (s; SCH2CH3major isomer), 25.7 (s; OCOCH3minor species), 25.3 (s; OCOCH3major isomer), 13.8 (s; CH2CH3minor species), 13.6 (s; CH2CH3minor species), 13.0 ppm (s; CH2CH3major isomer).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 65.7 (s; 11%), 62.5 (s; 33%), 60.6 ppm (s; 67%). Synthesis of [Ru(η1-OAc)2(PNN)(PPh2Me)] (Complex E) and [Ru(η2- OAc)(PNN)(PPh2Me)]OAc (Complex F) Complex A (200 mg, 0.249 mmol) was dissolved in degassed toluene (5 mL) and PPh2Me(50.8 μL, 55 mg, 0.274 mmol, 1.1 equiv) was added. The mixture was heated at 50 °C for 2h. Addition of n-heptane (10 mL) afforded the precipitation of the product as a dark-yellowsolid which was recovered by filtration. The solid was washed with diethyl ether (2 x 2 mL), n-heptane (4 x 3 mL), and n-pentane (4 x 2 mL) and dried under reduced pressure. Theproduct was obtained as a mixture of Complex E and F in a 1:1 molar ratio. Yield: 155.0 mg(84%). Anal. Calcd for C37H40N2O4P2Ru (739.75): C, 60.07; H, 5.45; N, 3.79. Found: C, 60.15; H, 5.38; N, 3.71.1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 11.14 (br s, 1H; NH compound E), 10.00 (br s, 1H; NH compound F), 8.50-8.40 (m, 1H; ortho-CH of C5H4N Complex F), 8.15-6.69 (m, 19H; aromatic protons), 6.57 (d, 3J(H,H) = 7.8 Hz, 1H; para-CH of C5H4N ComplexE), 6.51 (td, 3J(H,H) = 7.6 Hz, 4J(H,H) = 1.2 Hz, 1H; meta-CH of C5H4N Complex E), 6.42-6.32 (m, 2H; aromatic protons), 6.28 (d, 3J(H,H) = 7.3 Hz, 1H; para-CH of C5H4N ComplexF), 5.65 (t, 3J(H,H) = 6.5 Hz, 1H; meta-CH of C5H4N Complex F), 5.37 (dd, 3J(H,H) = 16.3Hz, 4J(H,H) = 6.6 Hz, 1H; NCH2Py Complex F), 4.72 (t, 2J(H,H) = 12.5 Hz, 1H; NCH2PyComplex E), 3.82-3.72 (ddd, 2J(H,H) = 13.8 Hz, 3J(H,H) = 5.4, 3J(H,H) = 4.0 Hz, 1H; NCH2PyComplex E), 3.51-3.32 (m, 1H; NCH2CH2P Complex F), 3.36-3.28 (m, 1H; NCH2Py ComplexF), 3.28-3.17 (m, 1H; NCH2CH2P Complexes E and F), 3.06-2.96 (m, 1H; NCH2CH2PComplex E), 2.96-2.87 (m, 1H; NCH2CH2P Complex E), 2.79-2.66 (m, 1H; NCH2CH2PComplex F), 2.62-2.50 (m, 1H; NCH2CH2P Complexes E and F), 2.22 (br s, 3H; OCOCH3Complex F), 2.17 (s, 3H; OCOCH3 Complex F), 2.04 (d, 2J(H,P) = 8.3 Hz, 3H; PCH3Complex E), 1.88 (s, 3H; OCOCH3Complex E), 1.67 (s, 3H; OCOCH3Complex E), 1.58ppm (d, 2J(H,P) = 8.1 Hz, 3H; PCH3 Complex F).13C{1H} NMR (100.6 MHz, toluene-d8, 25°C): δ 182.1 (s; OCOCH3 Complex F), 180.5 (d, 3J(C,P) = 2.9 Hz; OCOCH3 Complex E),177.7 (s; OCOCH3Complex F), 177.4 (s; OCOCH3Complex E), 165.9 (s; NCCH2Complex E), 165.3 (s; NCCH2Complex F), 158.2 (s; NCH of C5H4N Complex F), 154.4 (s; NCH ofC5H4N Complex E), 137.3-124.7 (m; aromatic carbon atoms), 121.4 (s; meta-CH of C5H4NComplex E), 120.1 (s; meta-CH of C5H4N Complex F), 119.6 (s; para-CH of C5H4N ComplexF), 119.4 (s; para-CH of C5H4N Complex E), 59.0 (br s; NCH2Py Complex E), 57.3 (br s;NCH2Py Complex F), 50.4 (br s; NCH2CH2P Complex F), 48.1 (br s; NCH2CH2P Complex E), 38.7 (d,1J(C,P) = 24.2 Hz; NCH2CH2P Complex E), 35.5 (d,1J(C,P) = 24.9 Hz; NCH2CH2P Complex F), 25.6 (s; OCOCH3 Complex F), 25.3 (s; OCOCH3 Complex E), 25.0 (s; OCOCH3 Complex F), 24.8 (s; OCOCH3 Complex E), 16.9 (d,1J(C,P) = 26.4 Hz; PCH3 Complex E), 14.8 ppm (d,1J(C,P) = 28.6 Hz; PCH3 Complex F).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 67.0 (d,2J(P,P) = 29.3 Hz; Complex E), 62.0 (d,2J(P,P) = 31.3 Hz; Complex F), 30.9 (d,2J(P,P) = 29.3 Hz; Complex E), 29.9 ppm (d,2J(P,P) = 31.3 Hz; Complex F). Synthesis of [Ru(η1-OAc)2(SNS)(PPh2Me)] (Complex G) Complex C (200 mg, 0.296 mmol) was dissolved in degassed toluene (5 mL), to whichPPh2Me (82.8 μL, 89 mg, 0.445 mmol, 1.5 equiv), and the mixture stirred at 105 °C for 18 h. The resulting light orange solution was concentrated to about 1 mL removing the solvent under reduced pressure. Addition of n-heptane (10 mL) afforded the precipitation of the product as a pale-yellow solid that was filtered, washed with a mixture of diethyl ether / n- heptane (5 / 1 (v / v); 2x2 mL), n-heptane (4x3 mL) and n-pentane (4x2 mL) and dried underreduced pressure. The compound was isolated as a mixture of three isomers differing by therelative orientation of the SEt groups with respect to the SNS ligand plane. Yield: 165.0 mg (91%). Anal. Calcd for C25H38NO4PRuS2(612.75): C, 49.00; H, 6.25; N, 2.29; S, 10.46. Found: C, 48.92; H, 6.27; N, 2.23; S, 10.50.1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 10.51 (br s, 1H; NH minor isomer), 10.34 (br s, 1H; NH major species), 8.07-6.78 (m, 10H; Ph protons), 3.15- 2.80 (m, 3H; NCH2), 2.80-2.58 (m, 2H; CH2), 2.58-2.35 (m, 2H; CH2), 2.34-2.00 (m, 3H;NCH2), 2.07 (br d, 2J(H,P) = 6.1 Hz, 3H; PCH3), 1.92 (s, 3H; OCOCH3), 1.90 (s, 3H;OCOCH3), 1.72-1.54 (s, 1H; CH2CH3), 1.42-1.21 (m, 1H; CH2CH3), 0.86 (t,3J(H,H) = 6.5 Hz, 3H; CH2CH3), 0.77 ppm (br t,3J(H,H) = 6.7 Hz, 3H; CH2CH3).13C{1H} NMR (100.6 MHz, toluene-d8, 25 °C): δ 182.6 (s; OCOCH3), 177.7 (br s; OCOCH3), 138.5-123.2 (m; aromatic carbon atoms), 48.8 (s; NCH2), 47.2 (s; NCH2), 40.9 (s; SCH2), 40.5 (s; SCH2 minor species), 37.2 (s; SCH2), 31.7 (s; SCH2CH3), 30.8 (s; SCH2 minor species), 24.9 (s; SCH2CH3), 24.7 (s; OCOCH3), 24.3 (s; OCOCH3), 13.1 (d,1J(C,P) = 31.2 Hz; PCH3), 12.9 (s; CH2CH3), 12.3 ppm (s; CH2CH3).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 33.5 (s; 4%), 33.0 (s; 13%), 32.4 (s; 83%). Synthesis of [Ru(η1-OPiv)2(SNS)(PPh3)] (Complex H) Complex H was prepared by following the procedure used for the synthesis of C, with[Ru(η2-OPiv)2(PPh3)2] (200 mg, 0.242 mmol) in place of [Ru(η2-OAc)2(PPh3)2] and the SNS ligand (49.0 mg, 0.254 mmol, 1.05 equiv), leading to the product as a light-yellow solid. The compound was isolated as a mixture of a major isomer (93%) and a minor species (7%) differing by the relative orientation of the SEt groups with respect to the SNS ligand plane. Yield: 161.3 mg (88%). Anal. Calcd for C36H52NO4PRuS2(758.98): C, 56.97; H, 6.91; N, 1.85; S, 8.45. Found: C,56.92; H, 6.96; N, 1.80; S, 8.46.1H NMR (400.1 MHz, toluene-d8, 25 °C): δ 11.50 (br s, 1H;NH major isomer), 11.16 (br s, 1H; NH minor species), 7.94 (t,3J(H,H) = 2.1 Hz, 5H; Ph major isomer), 7.43-7.26 (br m; Ph protons minor species), 7.20 (br t,3J(H,H) = 1.7 Hz, 5H;Ph major isomer), 7.16-6.96 (m, 5H; Ph major isomer), 6.94-6.80 (br m; Ph minor species),3.05-2.85 (m, 2H; NCH2 major isomer), 2.84-2.70 (m, 2H; NCH2 major isomer), 2.69-2.45 (m,4H; CH2major isomer), 2.34-2.00 (m, 2H; CH2CH3major isomer (superimposed with the solvent signal)), 1.68-1.43 (m, 2H; CH2CH3major isomer), 1.20 (br s, 9H; OCOC(CH3)3), 0.95 (br s, 9H; OCOC(CH3)3), 0.89 (t,3J(H,H) = 1.9 Hz, 6H; CH2CH3 major isomer).13C{1H} NMR of the major isomer (100.6 MHz, toluene-d8, 25 °C): δ 184.3 (br s; OCOC(CH3)3), 138.1-124.3 (m; aromatic carbon atoms), 48.6 (s; NCH2), 40.2 (s; SCH2), 30.5 (s; SCH2CH3), 37.5 (br s; OCOC(CH3)3), 28.5 (br s; OCOC(CH3)3), 12.6 ppm (s; CH2CH3).31P{1H} NMR (162.0 MHz, toluene-d8, 25 °C): δ 49.8 (br s; minor species, 7%), 47.3 (s; major isomer, 93%).Synthesis of [Ru(SNS)Cl2(PPh3)] (Complex X) (Comparative) The comparative Complex X was prepared according to the method described inWO2014036650A1. Synthesis of [Ru(PNN)Cl2(PPh3)] (Complex Y) (Comparative) The comparative Complex Y was prepared according to the method described inWO2013023307A1. Measurement methodsGas chromatography (GC) measurements were conducted using a Varian GC 648 gaschromatograph system equipped with an Agilent HP-88, 60 m x 0.25 mm x 0.2 µm column.Unless otherwise indicated, reaction conversions were determined by GC analysis using anFID detector. General Procedure for Ester Hydrogenation To an 8 mL vial, a ruthenium complex of the invention was added, followed by base and 2- 20 mmol of ester-containing substrate, and optionally a solvent. The vial was added to aBiotage Endeavor screening system, the stirring head sealed, and the reaction mixturepurged with nitrogen. A purge sequence involved pressurizing to approximately 45 psi nitrogen and releasing the pressure (repeated 5 times). The reactor was pressurised with400 psi hydrogen and heated to the desired temperature. Once the reaction time wascomplete, typically 16 hrs, the reaction was allowed to cool to room temperature. Nitrogen purge cycles (5 repeats) were then carried out to remove hydrogen. The reaction mixture was analysed via GC. Example 1 The general procedure for ester hydrogenation was used to investigate the hydrogenation ofmethyl decanoate at a variety of S / C ratios using [Ru(η1-OAc)2(SNS)(PPh3)]; Complex C.The reactions were carried out in the absence and presence of a solvent. The results fromthese experiments are given in Table 1 Experiment Base S / C Solvent TempConversion (%) (oC) 1K3PO4 1,000 / 1 MeOH 90 35.52 K3PO4 1,000 / 1 Me-THF 90 100.03 NaOMe 1,000 / 1 MeOH 90 27.94 NaOMe 1,000 / 1 Me-THF 90 100.05 K3PO4 1,000 / 1 MeOH 40 3.36 K3PO4 1,000 / 1 Me-THF 40 48.67 NaOMe 1,000 / 1 MeOH 40 1.58 NaOMe 1,000 / 1 Me-THF 40 100.09 NaOMe 10,000 / 1 - 90 33.610 NaOMe 10,000 / 1 - 40 100.011 NaOMe 10,000 / 1 - 40 100.012 NaOMe 10,000 / 1 - 40 100.013 NaOMe 50,000 / 1 - 40 100.014 NaOMe 50,000 / 1 - 40 98.715 NaOMe 50,000 / 1 - 40 98.516 NaOMe 50,000 / 1 - 40 98.417 NaOMe 50,000 / 1 - 40 98.618 NaOMe 50,000 / 1 - 90 19.419 NaOMe 50,000 / 1 - 90 20.320 NaOMe 100,000 / 1 - 40 63.821 NaOMe 100,000 / 1 - 40 62.4Table 1Experiment numbers 1-21 show that Complex C provides an excellent ester hydrogenationcatalyst for the conversion of problematic fatty acid methyl esters to alcohol, such as methyldecanoate to 1-decanol. High conversions were observed at ultra high S / C ratios of up to 100,000 / 1. Surprisingly, high conversions were achieved at the near ambient temperature of40 °C. Moreover, in most instances, Complex C provided higher conversions at 40 °Ccompared to 90 °C. Example 2 The general procedure for ester hydrogenation was used to investigate the hydrogenation ofethyl dodecanoate, ethyl decanoate, and ethyl benzoate at a variety of S / C ratios usingComplex C. The reactions were carried out in the absence and presence of a solvent. Theresults from these experiments are given in Table 2. Experiment Substrate Base S / C Solvent ToempConversion ( C) (%) 22 Ethyl NaOEt 44,000 / 1 - 40 100.0dodecanoate23 Ethyl decanoate NaOEt 100,000 / 1 - 40 40.624 Ethyl decanoate NaOEt 50,000 / 1 Toluene 40 97.025 Ethyl decanoate NaOEt 50,000 / 1 Toluene 40 97.126 Ethyl benzoate NaOEt 50,000 / 1 - 40 97.527 Ethyl benzoate NaOEt 100,000 / 1 - 40 89.228 Ethyl benzoate NaOEt 100,000 / 1 - 40 89.129 Ethyl benzoate NaOEt 100,000 / 1 - 40 88.330 Ethyl NaOEt 10,000 / 1 - 30 96.1undecanoate 31 Methyl oleate NaOMe 25,000 / 1 - 60 100.032 Methyl oleate NaOMe 50,000 / 1 - 50 98.533 Methyl oleate NaOMe 100,000 / 1 - 50 73.634 Ethyl oleate NaOEt 50,000 / 1 - 40 97.135 Ethyl oleate NaOEt 100,000 / 1 - 40 95.7Table 2Experiments 22-35 show that Complex C provides active ester hydrogenation catalysts forthe conversion of a number of ester containing substrates. These experiments further show that high conversions can be obtained at ultra high S / C ratios. Surprisingly, it has been foundthat Complex C shows as good if not better conversion of more problematic methyldecanoate versus ethyl decanoate (e.g. Experiment 20 versus Experiment 23).Moreover, where the substrate comprised a double bond and an ester moiety (e.g. methyl oleate, and ethyl oleate), complexes of the invention were surprisingly found to be selective for the reduction of the ester group over the double bond. Example 3 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate, ethyl decanoate, and ethyl benzoate at a variety of S / C ratios using[Ru(η1-OPiv)2(SNS)(PPh3)]; Complex H. The reactions were carried out in the absence andpresence of a solvent. The results from these experiments are given in Table 3.Experiment Substrate Base S / C Solvent TempConversion (oC) (%) 36 Methyl NaOMe 10,000 / 1 - 40 100.0decanoate 37 Methyl NaOMe 10,000 / 1 - 40 100.0decanoate 38 Methyl NaOMe 10,000 / 1 - 90 16.5decanoate 39 Methyl NaOMe 10,000 / 1 - 90 13.5decanoate 40 Methyl NaOMe 50,000 / 1 - 40 86.6decanoate 41 Methyl NaOMe 50,000 / 1 - 40 90.4decanoate42 Methyl NaOMe 50,000 / 1 - 90 20.5decanoate 43 Methyl NaOMe 50,000 / 1 - 90 15.5decanoate 44 Methyl NaOMe 50,000 / 1 Toluene 40 56.3decanoate 45 Methyl NaOMe 50,000 / 1 Toluene 40 60.2decanoate 46 Ethyl NaOEt 50,000 / 1 Toluene 40 95.0decanoate 47 Ethyl NaOEt 100,000 - 40 94.1benzoate Table 3Experiments 36-47 show the effect of varying the nature of the carboxylate ligand of thecomplexes of the invention. These experiments demonstrate Complex H shows excellentconversion of a variety of ester substrates, including the FAME methyl decanoate, to the corresponding alcohols at near ambient temperatures. Example 4 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate at a variety of S / C ratios using [RuH(η1-OAc)(SNS)(PPh3)]; Complex D.The reactions were carried out in the absence and presence of a solvent. The results fromthese experiments are given in Table 4. Experiment Base S / C Solvent TempConversion (%) (oC) 48 K3PO4 1,000 / 1 MeOH 90 7.549 K3PO4 1,000 / 1 Me-THF 90 60.450 NaOMe 1,000 / 1 MeOH 90 10.151 NaOMe 1,000 / 1 Me-THF 90 95.152 K3PO4 1,000 / 1 MeOH 40 0.053 K3PO4 1,000 / 1 Me-THF 40 4.654 NaOMe 1,000 / 1 MeOH 40 0.055 NaOMe 1,000 / 1 Me-THF 40 100.056 NaOMe 10,000 / 1 - 40 100.057 NaOMe 50,000 / 1 - 90 6.658 NaOMe 50,000 / 1 - 40 33.359 NaOMe 50,000 / 1 - 40 24.0Table 4Experiments 48-59 show the effect of varying the anionic ligand, W, of the complexes of theinvention. These experiments demonstrate that Complex D, where W is hydride, are competent in providing ester hydrogenation catalysts which can convert methyl decanoate to 1-decanol. Example 5 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate at a variety of S / C ratios using [Ru(η1-OAc)2(SNS)(PPh2Me)]; Complex G.The reactions were carried out in the absence and presence of a solvent. The results fromthese experiments are given in Table 5. Experiment Base S / C Solvent TempConversion (%) (oC) 60 NaOMe 1,000 / 1 MeOH 90 6.061 NaOMe 1,000 / 1 Me-THF 90 100.062 NaOMe 1,000 / 1 MeOH 40 0.963 NaOMe 1,000 / 1 Me-THF 40 100.064 NaOMe 10,000 / 1 - 40 74.765 NaOMe 10,000 / 1 - 40 71.366 NaOMe 10,000 / 1 - 90 18.167 NaOMe 50,000 / 1 - 40 30.968 NaOMe 50,000 / 1 - 40 27.369 NaOMe 50,000 / 1 - 40 31.270 NaOMe 50,000 / 1 - 90 16.4Table 5Experiments 60-70 show the effect of varying the neutral ligand, A. Whilst rutheniumcomplexes of the invention comprising the more electron donating PPh2Me ligand do not show as high conversion of methyl decanoate as ruthenium complexes comprising PPh3, competent ester hydrogenation catalysts were provided in each case. Example 6 (Comparative) The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate, ethyl decanoate, and ethyl benzoate at a variety of S / C ratios using[Ru(SNS)Cl2(PPh3)]; Complex X not according to the invention. The reactions were carriedout in the absence and presence of a solvent. The results from these experiments are givenin Table 6. Experiment Substrate Base Solvent S / C ToempConversion ( C) (%) 71 Methyl K3PO4 MeOH 1,000 / 1 90 39.5decanoateMethyl K3PO4 Me-THF 1,000 / 1 90 100.0decanoateMethyl NaOMe MeOH 1,000 / 1 90 28.5decanoateMethyl NaOMe Me-THF 1,000 / 1 90 29.7decanoateMethyl K3PO4 MeOH 1,000 / 1 40 3.0decanoateMethyl K3PO4 Me-THF 1,000 / 1 40 62.7decanoateMethyl NaOMe MeOH 1,000 / 1 40 2.2decanoateMethyl NaOMe Me-THF 1,000 / 1 40 100.0decanoateMethyl NaOMe - 10,000 / 1 90 34.2decanoateMethyl NaOMe - 10,000 / 1 40 100.0decanoateMethyl NaOMe - 10,000 / 1 40 100.0decanoateMethyl NaOMe - 10,000 / 1 40 100.0decanoateMethyl NaOMe - 10,000 / 1 40 100.0decanoateMethyl NaOMe - 50,000 / 1 90 21.5decanoateMethyl NaOMe - 50,000 / 1 40 72.2decanoateMethyl NaOMe - 50,000 / 1 40 78.7decanoateMethyl NaOEt Toluene 50,000 / 1 40 20.8decanoateMethyl NaOEt - 50,000 / 1 40 21.5decanoateMethyl NaOEt - 50,000 / 1 40 3.5decanoateMethyl NaOEt Toluene 50,000 / 1 90 15.6decanoateMethyl NaOEt Toluene 50,000 / 1 90 19.5decanoateMethyl NaOMe - 100,000 / 1 40 1.8decanoateMethyl NaOEt - 100,000 / 1 40 1.7decanoateMethyl NaOEt - 100,000 / 1 40 1.5decanoateEthyl NaOEt - 44,000 / 1 40 98.3dodecanoateEthyl NaOEt - 100,000 / 1 40 9.3decanoateEthyl NaOEt Toluene 50,000 / 1 40 91.2decanoateEthyl NaOEt Toluene 50,000 / 1 40 96.1decanoate99 Ethyl NaOEt Toluene 50,000 / 1 40 93.8decanoate 100 Ethyl NaOEt - 100,000 / 1 40 100.0decanoate 101 Ethyl NaOEt - 10,000 / 1 30 96.1undecanoate 102 Ethyl NaOEt - 50,000 / 1 40 100.0undecanoate 103 Ethyl NaOEt - 100,000 / 1 40 95.6undecanoate 104 Methyl NaOMe - 25,000 / 1 60 84.9oleate 105 Methyl NaOMe - 50,000 / 1 50 100.0oleate 106 Methyl NaOMe - 100,000 / 1 50 49.0oleate 107 Ethyl oleate NaOEt - 50,000 / 1 40 97.1108 Ethyl oleate NaOEt - 100,000 / 1 40 95.9109 Ethyl NaOEt - 50,000 / 1 40 97.3benzoate 110 Ethyl NaOEt - 100,000 / 1 40 100.0benzoate Table 6Comparative Example 6 demonstrates the performance of Complex X in providing an activecatalyst for the ester hydrogenation of various substrates. These data may be compared to those of Examples 1 to 5 where ruthenium complexes of the invention have been used. These data show that ruthenium complexes of the invention, which comprise a carboxylate ligand, provide superior conversion of problematic methyl esters as compared to comparative complexes, which do not comprise a carboxylate ligand, under the sameconditions. For instance, comparing Experiments 13-17 to 84-86, and Experiments 20-21with 92, it can be seen that complexes of the invention are able to achieve excellent conversion of methyl decanoate at ultra high S / C ratios of 50,000 / 1 and 100,000 / 1 attemperatures of only 40 °C. The difference in conversion between ruthenium complexes ofthe invention and those of the comparative example become more marked as the S / C ratio increases. To try to improve the conversion using comparative ruthenium complexes, sodium ethoxide was used as the base. It may be expected that sodium ethoxide may trans-esterify the ester substrate to the ethyl ester making reduction more labile. However, even where sodium ethoxide was used as a base, low conversion to the desired 1-decanol product was observed for comparative ruthenium complexes. Example 7 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate at a variety of S / C ratios using [Ru(η1-OAc)2(PNN)(PPh3)]; Complex A.The reactions were carried out in the absence and presence of a solvent. The results fromthese experiments are given in Table 7. Experiment Base S / C Solvent TempConversion (%) (oC) 111 K3PO4 MeOH 1,000 / 1 90 22.3112 K3PO4 Me-THF 1,000 / 1 90 63.4113 NaOMe MeOH 1,000 / 1 90 25.8114 NaOMe Me-THF 1,000 / 1 90 100.0115 K3PO4 MeOH 1,000 / 1 40 0.0116 K3PO4 Me-THF 1,000 / 1 40 6.8117 NaOMe MeOH 1,000 / 1 40 0.0118 NaOMe Me-THF 1,000 / 1 40 97.9119 NaOMe - 10,000 / 1 40 100.0120 NaOMe - 10,000 / 1 40 98.5121 NaOMe - 10,000 / 1 40 100.0122 NaOMe - 10,000 / 1 90 84.8123 NaOMe - 10,000 / 1 90 84.0124 NaOMe - 50,000 / 1 90 18.5125 NaOMe - 50,000 / 1 40 98.4126 NaOMe - 50,000 / 1 40 95.4127 NaOMe - 50,000 / 1 40 98.4128 NaOMe - 50,000 / 1 40 97.4129 NaOMe - 50,000 / 1 40 95.7130 NaOMe - 50,000 / 1 40 95.9131 NaOMe Toluene 50,000 / 1 40 41.8132 NaOMe - 100,000 / 1 40 25.9Table 7Experiment numbers 111-132 show that Complex A provides an excellent esterhydrogenation catalyst for the conversion of problematic fatty acid methyl esters to alcohol, such as methyl decanoate to 1-decanol. High conversions were observed at ultra high S / Cratios. As with complexes comprising the SNS tridentate ligand, high conversions wereachieved at the near ambient temperature of 40 °C. Moreover, in most instances, ComplexA could provide high conversions at temperatures as low as 40 °C.Example 8 The general procedure for ester hydrogenation was used to investigate the hydrogenation of ethyl dodecanoate, ethyl decanoate, ethyl benzoate, ethyl undecenoate, methyl oleate, andethyl oleate at a variety of S / C ratios using Complex A. The reactions were carried out in theabsence and presence of a solvent. The results from these experiments are given in Table8. Experiment Substrate Base S / C Solvent TempConversion (oC) (%) 133 Ethyl NaOEt 44,000 / 1 - 40 99.0dodecanoate 134 Ethyl NaOEt 100,000 / 1 - 40 62.4decanoate 135 Ethyl NaOEt 50,000 / 1 Toluene 40 79.4decanoate 136 Ethyl benzoate NaOEt 50,000 / 1 - 40 82.8137 Ethyl benzoate NaOEt 100,000 / 1 - 40 72.2138 Ethyl 10- NaOEt 10,000 / 1 - 30 91.3undecenoate 139 Methyl oleate NaOMe 25,000 / 1 - 60 100.0140 Methyl oleate NaOMe 50,000 / 1 - 50 79.6141 Methyl oleate NaOMe 100,000 / 1 - 50 9.9142 Ethyl oleate NaOEt 50,000 / 1 - 40 96.9143 Ethyl oleate NaOEt 100,000 / 1 - 40 96.8Table 8Experiments 133-143 show that Complex A provides active ester hydrogenation catalysts forthe conversion of a number of ester containing substrates. These experiments further showthat high conversions can be obtained at ultra high S / C ratios for ethyl esters at ambient temperatures. Moreover, where the substrate comprised a double bond and an ester moiety (e.g. ethyl 10- decenoate, methyl oleate, and ethyl oleate), complexes of the invention were surprisingly found to be selective for the reduction of the ester group over the double bond. Example 9 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate at a variety of S / C ratios using [Ru(η1-OAc)2(PNN)(PPh2Me)] and [Ru(η2-OAc)(PNN)(PPh2Me)]OAc; Complexes E and F. The reactions were carried out in theabsence and presence of a solvent. The results from these experiments are given in Table9. Experiment Base Solvent S / C TempConversion (%) (oC) 144 NaOMe MeOH 1,000 / 1 90 12.6145 NaOMe Me-THF 1,000 / 1 90 100.0146 NaOMe MeOH 1,000 / 1 40 0.0147 NaOMe Me-THF 1,000 / 1 40 88.7148 NaOMe - 10,000 / 1 40 100.0149 NaOMe - 10,000 / 1 90 39.0150 NaOMe - 50,000 / 1 40 2.8151 NaOMe - 50,000 / 1 40 3.7152 NaOMe - 50,000 / 1 90 11.9153 NaOMe - 50,000 / 1 90 14.9Table 9Experiments 144-153 show the effect of varying the neutral ligand, A. As is observed withcomplexes of the invention comprising the SNS ligand, complexes of the invention comprising the PNN ligand which have a more electron donating PPh2Me ligand do not show as high conversion of methyl decanoate as ruthenium complexes comprising PPh3. However, competent ester hydrogenation catalysts were provided in each case. Example 10 The general procedure for ester hydrogenation was used to investigate the hydrogenation of methyl decanoate at a variety of S / C ratios using [RuH(η1-OAc)(PNN)(PPh3)]; Complex B.The reactions were carried out in the absence and presence of a solvent. The results fromthese experiments are given in Table 10. Experiment Base Solvent S / C Temp (oC) Conversion (%)154 K3PO4 MeOH 1,000 / 1 90 7.2155 K3PO4 Me-THF 1,000 / 1 90 6.8156 NaOMe MeOH 1,000 / 1 90 6.0157 NaOMe Me-THF 1,000 / 1 90 80.1158 K3PO4 MeOH 1,000 / 1 40 0.0159 K3PO4 Me-THF 1,000 / 1 40 0.0160 NaOMe MeOH 1,000 / 1 40 0.0161 NaOMe Me-THF 1,000 / 1 40 37.0162 NaOMe - 10,000 / 1 90 66.8163 NaOMe - 10,000 / 1 40 93.5164 NaOMe - 10,000 / 1 40 88.8165 NaOMe - 10,000 / 1 40 93.5166 NaOMe - 10,000 / 1 90 69.5167 NaOMe - 50,000 / 1 90 4.5168 NaOMe - 50,000 / 1 40 19.3169 NaOMe - 50,000 / 1 90 3.7170 NaOMe - 50,000 / 1 90 4.0Table 10Experiments 154-170 show the effect of varying the anionic ligand, W, of the complexes ofthe invention. These experiments demonstrate that Complex B, where W is hydride, are competent in providing ester hydrogenation catalysts which can convert methyl decanoate to1-decanol. Surprisingly, the performance of Complex B at an S / C ratio of 10,000 / 1 wasbetter at a temperature of 40 °C versus 90 °C.Example 11 (Comparative) The general procedure for ester hydrogenation was used to investigate the hydrogenation ofmethyl decanoate ethyl undecanoate, methyl benzoate, ethyl benzoate, methyl oleate, andethyl oleate at a variety of S / C ratios using [Ru(PNN)Cl2(PPh3)]; Complex Y not according tothe invention. The reactions were carried out in the absence and presence of a solvent. Theresults from these experiments are given in Error! Reference source not found.. Experiment Substrate Base Solvent S / C TempConversion (oC) (%) 170 Methyl K3PO4 MeOH 1,000 / 1 90 28.8decanoate 171 MethylK3PO4Me-1,000 / 1 90 100.0decanoate THF 172 Methyl NaOMe MeOH 1,000 / 1 90 25.2decanoate 173 Methyl NaOMe Me- 1,000 / 1 90 100.0decanoate THF 174 Methyl K3PO4 MeOH 1,000 / 1 40 2.1decanoate 175 MethylK3PO4Me-1,000 / 1 40 78.9decanoate THF 176 Methyl NaOMe MeOH 1,000 / 1 40 0.0decanoate 177 Methyl NaOMe Me- 1,000 / 1 40 100.0decanoate THF 178 Methyl NaOMe - 10,000 / 1 90 91.9decanoate 179 Methyl NaOMe - 10,000 / 1 90 92.5decanoate 180 Methyl NaOMe - 10,000 / 1 40 98.3decanoate 181 Methyl NaOMe - 10,000 / 1 40 98.6decanoate 182 Methyl NaOMe - 10,000 / 1 40 96.0decanoate 183 Methyl NaOMe - 10,000 / 1 40 96.9decanoate 184 Methyl NaOMe - 50,000 / 1 90 24.8decanoate 185 Methyl NaOMe - 50,000 / 1 40 91.4decanoate 186 Methyl NaOMe - 50,000 / 1 40 91.7decanoate 187 Methyl NaOMe - 50,000 / 1 40 91.9decanoate188 Methyl NaOMe - 50,000 / 1 90 20.6decanoate 189 Methyl NaOMe - 50,000 / 1 90 23.0decanoate 190 Methyl NaOMe - 100,000 / 1 40 62.1decanoate 191 Ethyl NaOEt - 10,000 / 1 30 80.1undecanoate 192 Methyl NaOEt - 10,000 / 1 40 96.6benzoate 193 Methyl NaOEt - 25,000 / 1 40 83.9benzoate 194 Methyl NaOEt - 50,000 / 1 40 76.2benzoate 195 Methyl NaOEt - 80,000 / 1 40 68.6benzoate 196 Methyl NaOEt - 100,000 / 1 40 67.4benzoate 197 Methyl NaOMe - 100,000 / 1 40 49.4benzoate 198 Ethyl NaOEt - 100,000 / 1 40 100.0benzoate 199 Methyl NaOMe - 25,000 / 1 60 100.0oleate 200 Methyl NaOMe - 50,000 / 1 50 89.8oleate 201 Methyl NaOMe - 100,000 / 1 50 30.6oleate 202 Ethyl oleate NaOEt - 50,000 / 1 40 96.8203 Ethyl oleate NaOEt - 100,000 / 1 40 96.7Table 11Comparative Example 11 demonstrates the performance of Complex Y in providing anactive catalyst for the ester hydrogenation of various substrates. These data may becompared to those of Examples 7 to 10 where ruthenium complexes of the invention havebeen used. These data show that ruthenium complexes of the invention, which comprise a carboxylate ligand, provide competent ester hydrogenation catalyst with good activity at high S / C ratios and which are active at ambient temperatures (e.g.40 °C). Moreover, under certain conditions Complexes of the invention provide more active catalysts than comparative Complex Y.Example 12 - Hydrogen UptakeFigure 2 and Figure 3 show the hydrogen uptake of Complexes C and X and Complexes Aand Y, respectively, for the hydrogenation of methyl decanoate at 40 °C using 50 mol%NaOMe versus methyl decanoate.As can be seen from these plots, complexes of the invention (i.e. Complexes A and C) donot exhibit any significant induction period and quickly consume hydrogen. Moreover, these plots show that ruthenium complexes of the invention reach higherconversions and proceed to completion more quickly that comparative complexes.Figure 4 shows the hydrogen uptake of Complexes C and X for the hydrogenation of ethylbenzoate at 40 °C using 50 mol% NaOEt versus ethyl benzoate.Here, it is strikingly apparent that complexes of the invention do not exhibit any significantinduction period. In comparison, an induction period of 1-2 hours is observed forcomparative Complex X. From these data it may be concluded that ruthenium complexes of the invention providehighly active ester hydrogenation catalysts when compared to comparative Complexes Xand Y, which do not comprise a carboxylate ligand. Without being bound by any sort oftheory it is believed that this result may be explained by the ruthenium complexes of the invention rapidly forming the active catalyst in the ester hydrogenation catalytic cycle under catalytic conditions.Example 13 – Hydrogenation of other carbonyl containing substratesOn the basis of the performance of ruthenium complexes of the invention in the hydrogenation of ester substrates, a series of experiments were carried out to probe the performance of the performance of the complexes in the hydrogenation of aldehyde substrates; decanal and benzaldehyde. The experimental procedure used for the hydrogenation of ester containing substrates was used with the exception that no base was used. The results from these experiments is given in Table 12. Exp. Substrate Complex Solvent S / C Temp. (°C) Conversion (%)204 decanal A IPA 1,000 / 1 90 100.0205 decanal B IPA 1,000 / 1 90 100.0206 decanal B EtOH 1,000 / 1 90 99.3207 decanal B MeOH 1,000 / 1 90 97.2208 decanal A EtOH 1,000 / 1 90 95.7209 decanal A Me- 1,000 / 1 90 95.1THF 210 decanal D EtOH 1,000 / 1 90 94.1211 benzaldehyde C MeOH 1,000 / 1 90 88.2212 benzaldehyde B MeOH 1,000 / 1 90 82.3213 benzaldehyde A MeOH 1,000 / 1 90 80.3214 decanal A MeOH 1,000 / 1 90 72.2215 decanal C EtOH 1,000 / 1 90 64.6216 decanal X MeOH 1,000 / 1 90 62.7217 decanal C MeOH 1,000 / 1 90 62.4218 benzaldehyde D MeOH 1,000 / 1 90 59.8219 decanal H 1,000 / 1 90 56.6220 decanal Y IPA 1,000 / 1 90 51.2Table 12 These results show that complexes of the invention provide competent aldehyde hydrogenation catalysts, which are capable of operating under a multitude of conditions. Complexes according to the invention comprising either SNS or PNN tridentate ligands provide excellent conversion of decanal and benzaldehyde as compared to comparativeComplexes X and Y.Example 14 – Scaled up hydrogenation reactionsThe hydrogenation of ethyl decanoate was investigated on a larger scale using a 50 mL Parr autoclave reactor.Ethyl decanoate (107.6 mmol, 21.55 g, 25 mL) was added to the autoclave reactor followedby sodium ethoxide (NaOEt) (53.79 mmol, 3.66 g), and Complex C (1.45 mg, 0.0216 µmol)from a 5.84 mg / mL solution in EtOH (250 µL, 1 vol%). The S / C molar ratio was 50,000 / 1, whereas the base concentration was 50 mol% with respect to ethyl decanoate.The gas line was purged three times with nitrogen, three times with hydrogen, and the Parrautoclave reactor pressurised to 28 bar with H2.The reaction mixture was stirred at 1300 rpm, and the reactor slowly heated to 45 °C using amodel 4838 Parr Temperature Controller. The reaction mixture was stirred for 16 hours.At the end of the reaction, the heating was switched off, the reactor was cooled to roomtemperature and the excess hydrogen was vented. The reactor was purged with nitrogenfive times.The final waxy compound was treated with 1.0 M aqueous hydrochloric acid (50 mL),extracted with methyl tert-butyl ether (40 mL) and dried with anhydrous sodium sulfate.The 1-decanol product was isolated and separated from the remaining catalyst by filteringover a plug of silica gel and evaporation of the volatiles in-vacuo.1-decanol was recoveredin a 95% yield (16.16 g) that was analysed by NMR and GC (99% purity).Experiment 13 shows that excellent conversions can be achieved using Complexes of the invention at larger scale. Experimental ConclusionsIt is clear from the Examples that ruthenium complexes of the invention may be used toprovide active catalysts for the effective homogeneous hydrogenation of carbonyl containing substrates, an in particular fatty acid methyl esters. Under many conditions, rutheniumcomplexes of the invention provide superior catalysts to comparative Complexes X and Y,which do not comprise a carboxylate ligand. Moreover, ruthenium complexes of theinvention, comprising carboxylate ligands and tridentate ligands of formula (IIIb) have been shown to be particularly effective in the hydrogenation of FAMEs. Accordingly, ruthenium complexes of the invention offer an attractive suite of pre-catalystsfor use in the hydrogenation of a variety of carbonyl containing substrates.

[0005] The invention may further be defined in relation to the following numbered clauses.1. A ruthenium complex of formula (I) or formula (II):[Ru(L)AZ]W (I)[Ru(L)AZW] (II)wherein L is a tridentate ligand having formula (III): wherein:X is a nitrogen atom and when taken together with R1 it forms an optionally substitutedheteroaryl group when Rx is absent, orX is –SRa, and R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;Y is selected from –SRb, –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or when Y is –PRaRb, –OPRaRb, or –NHPRaRb,Ra and Rb together with the heteroatom to which they are attached form a heterocycle;Z is a carboxylate ligand; W is an anionic ligand selected from the group consisting of carboxylates, hydride, and halide; and A is a neutral ligand selected from the group consisting of phosphines, carbonyl, andsulfoxides, or A is absent.2. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy.3. A ruthenium complex of formula (I) or formula (II) according to clause 1 or clause 2,wherein R2 and Ry are each independently selected from hydrogen, substituted orunsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy.4. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R2and Ryare each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl.5. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R2and Ryare each hydrogen.6. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R3a, R3b, R4a, and R4b are each independently preferably selected fromhydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10- heteroalkyl, and substituted or unsubstituted C1-10-alkoxy.7. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R3a, R3b, R4a, and R4b are each independently selected from hydrogen,substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy.8. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R3a, R3b, R4a, and R4b are each independently selected from hydrogen,methyl, ethyl, iso-propyl, and tert-butyl.9. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R3a, R3b, R4a, and R4b are each hydrogen.10. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein X is a nitrogen atom and when taken together with R1 it forms an optionallysubstituted heterocycle when Rxis absent.11. A ruthenium complex of formula (I) or formula (II) according to clause 10, wherein theheterocycle is a substituted or unsubstituted 6-membered heterocyclic ring, for example substituted or unsubstituted pyridinyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, tetrazolyl, thiadiazolyl, oxadiazolyl, pyrimidyl, benzoxazolyl, benzthiazolyl, benzimidazolyl, indolyl, or quinolinyl.12. A ruthenium complex of formula (I) or formula (II) according to any one of clauses 1 to9, wherein X is -SRaand R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.13. A ruthenium complex of formula (I) or formula (II) according to clause 12, wherein R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, and substituted or unsubstituted C1-10-alkoxy.14. A ruthenium complex of formula (I) or formula (II) according to clause 12 or clause 13,wherein R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, and substituted or unsubstituted C1-5-alkoxy.15. A ruthenium complex of formula (I) or formula (II) according to any one of clauses 12to 14, wherein R1 and Rx are each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl, preferably hydrogen.16. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein Y is selected from –SRb, –PRaRb, and –NHPRaRb, preferably –SRband – PRaRb.17. A ruthenium complex of formula (I) or formula (II) according to clause 10 or 11, whereinY is -PRaRb, -OPRaRb, or –NHPRaRb.18. A ruthenium complex of formula (I) or formula (II) according to any one of clauses 12to 15, wherein Y is -SRb.19. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein R5 is selected from hydrogen and methyl, preferably hydrogen.20. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.21. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein Raand Rbare each independently selected from substituted or unsubstituted C1-5-alkyl, substituted or unsubstituted C1-5-heteroalkyl, substituted or unsubstituted C1-5- alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl, preferably, from methyl, ethyl, iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl.22. A ruthenium complex of formula (I) or formula (II) according to clause 10 or 11, whereinRaand Rbare each independently selected from the group consisting of iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl.23. A ruthenium complex of formula (I) or formula (II) according to any one of clauses 12to 15, wherein Raand Rbare each independently selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, pentyl, iso-propyl, and tert-butyl, preferably ethyl.24. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein L isa tridentate ligand having formula (IIIa) , wherein:Y is selected from –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or Ra and Rb together with the heteroatom towhich they are attached form a heterocycle; and each Rwis independently selected from the group consisting of hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, and substituted orunsubstituted C1-10-alkoxy.25. A ruthenium complex of formula (I) or formula (II) according to clause 24, wherein Rwis independently selected from hydrogen, and substituted or unsubstituted C1-10alkyl.26. A ruthenium complex of formula (I) or formula (II) according to clause 24 or clause 25,wherein each Rwis independently selected from hydrogen, and substituted or unsubstituted C1-5alkyl.27. A ruthenium complex of formula (I) or formula (II) according to any one of clauses 24to 26, wherein each Rwis hydrogen.28. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein L isa tridentate ligand having formula (IIIb) , wherein: R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.29. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein L isone or more tridentate ligands of formulae (IIIc), (IIId), and / or (IIIe), , wherein Raand Rbare each independently selected from substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or where the tridentate ligand is a tridentateligand having formula (IIIc) or (IIIe) Ra and Rb together with the heteroatom to which they areattached form a heterocycle.30. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein Ra and Rb are the same or different, preferably the same.31. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein thetridentate ligand having formula (III) is one or more tridentate ligands selected from the group consisting of: 32. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein thetridentate ligand having formula (III) is one or more tridentate ligands selected from the .33. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein thetridentate ligand having formula (III) is one or more tridentate ligands selected from the group consisting of: 34. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein Z is a carboxylate ligand having formula (IV) or a carboxylate ligand havingformula (IVb) ,,where R6 is selected from substituted or unsubstituted C1-20-alkyl, substituted orunsubstituted C2-20-alkenyl, substituted or unsubstituted C2-20-alkynyl, substituted or unsubstituted C1-20-heteroalkyl, substituted or unsubstituted C1-20-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroary.35. A ruthenium complex of formula (I) or formula (II) according to clause 34, wherein R6is selected from methyl, trifluoromethyl, ethyl, propyl, butyl, tert-butyl, pentyl, or phenyl,preferably methyl.36. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein W is a carboxylate ligand, preferably a carboxylate ligand according to clause34 or clause 35.37. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein A is a neutral ligand selected from the group consisting of phosphines, carbonyls, and sulfoxides.38. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclauses, wherein A is a neutral ligand selected from the group consisting of -CO, -PPh3, -PiPr3, -PtBu3, -PAr3, -PCy3, -PPh2Me, and DMSO.39. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein theruthenium complex of formula (I) or formula (II) is one or more selected from:

[0006] 40. A ruthenium complex of formula (I) or formula (II) according to clause 1, wherein theruthenium complex of formula (I) or formula (II) is one or more selected from: 41. A process for reducing a carbonyl containing substrate to an alcohol containingsubstrate in the presence of a hydrogen source and optionally a base using the rutheniumcomplex of formula (I) and / or the ruthenium complex of formula (II) as defined in any one of the preceding clauses.42. A process according to clause 41, wherein the carbonyl containing substrate is anester containing substrate, or an aldehyde containing substrate, preferably an ester containing substrate.

[0007] References(1) Mitchell, R. W.; Spencer, A.; Wilkinson, G., Carboxylato-triphenylphosphine complexesof ruthenium, cationic triphenylphosphine complexes derived from them, and their behaviour as homogeneous hydrogenation catalysts for alkenes. Journal of the Chemical Society, Dalton Transactions 1973, 846-854.(2) Baldino, S.; Giboulot, S.; Lovison, D.; Nedden, H. G.; Pöthig, A.; Zanotti-Gerosa, A.;Zuccaccia, D.; Ballico, M.; Baratta, W., Preparation of Neutral trans - cis[Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2= diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction. Organometallics 2021, 40, 1086-1103.(3) Young, R.; Wilkinson, G., (Acetato)hydridotris(triphenylphosphine)ruthenium(II).Inorganic Syntheses, 1977, 17, 79-81.(4) Spencer, A.; Wilkinson, G., Reactions of μ3-oxo-Triruthenium Carboxylates with π-acidLigands. Journal of the Chemical Society, Dalton Transactions 1974, 786-792.(5) James, B. R.; Ochiai, E; Rampel, G. L., Ruthenium (II) halide dimethylsulphoxidecomplexes from hydrogenation reactions. Inorganic and Nuclear Chemistry Letters 1971, 7, 781-784

Claims

Claims1. A ruthenium complex of formula (I) or formula (II):[Ru(L)AZ]W (I)[Ru(L)AZW] (II)wherein L is a tridentate ligand having formula (III):wherein:X is a nitrogen atom and when taken together with R1 it forms an optionally substitutedheteroaryl group when Rx is absent, orX is –SRa, and R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;Y is selected from –SRb, –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or when Y is –PRaRb, –OPRaRb, or –NHPRaRb,Ra and Rb together with the heteroatom to which they are attached form a heterocycle;Z is a carboxylate ligand; W is an anionic ligand selected from the group consisting of carboxylates, hydride, and halide; and A is a neutral ligand selected from the group consisting of phosphines, carbonyl, and sulfoxides, or A is absent.

2. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein R2 andRyare each hydrogen.

3. A ruthenium complex of formula (I) or formula (II) according to claim 1 or claim 2,wherein R3a, R3b, R4a, and R4b are each hydrogen.

4. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein X is a nitrogen atom and when taken together with R1 it forms an optionallysubstituted heterocycle when Rxis absent.

5. A ruthenium complex of formula (I) or formula (II) according to claim 4, wherein theheterocycle is a substituted or unsubstituted 6-membered heterocyclic ring, for example substituted or unsubstituted pyridinyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, tetrazolyl, thiadiazolyl, oxadiazolyl, pyrimidyl, benzoxazolyl, benzthiazolyl, benzimidazolyl, indolyl, or quinolinyl.

6. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein X is -SRaand R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.

7. A ruthenium complex of formula (I) or formula (II) according to claim 6, wherein R1 andRxare each independently selected from hydrogen, methyl, ethyl, iso-propyl, and tert-butyl,preferably hydrogen.

8. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein Y is selected from –SRb, –PRaRb, and –NHPRaRb, preferably –SRband – PRaRb.

9. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein Raand Rbare each independently preferably selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.

10. A ruthenium complex of formula (I) or formula (II) according to claim 4 or 5, wherein Raand Rbare each independently selected from the group consisting of iso-propyl, tert-butyl, cyclohexyl, adamantyl, and phenyl.

11. A ruthenium complex of formula (I) or formula (II) according to claim 6 or claim 7,wherein Raand Rbare each independently selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, pentyl, iso-propyl, and tert-butyl, preferably ethyl.

12. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein L is atridentate ligand having formula (IIIa), wherein:Y is selected from –PRaRb, –OPRaRb, and –NHPRaRb;R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or Ra and Rb together with the heteroatom towhich they are attached form a heterocycle; and each Rwis independently selected from the group consisting of hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C1-10-heteroalkyl, and substituted orunsubstituted C1-10-alkoxy.

13. A ruthenium complex of formula (I) or formula (II) according to claim 12, wherein eachRwis hydrogen.

14. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein L is atridentate ligand having formula (IIIb), wherein:R1and Rxare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R2and Ryare each independently selected from hydrogen, substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl;R3a, R3b, R4a, and R4b are each independently selected from hydrogen, substituted orunsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl; R5is selected from hydrogen, or substituted or unsubstituted C1-5-alkyl; Raand Rbare each independently selected from substituted or unsubstituted C1-10-alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroaryl.

15. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein R5is selected from hydrogen and methyl, preferably hydrogen.

16. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein L isone or more tridentate ligands of formulae (IIIc), (IIId), and / or (IIIe),, wherein Raand Rbare each independently selected from substituted or unsubstituted C1-10- alkyl, substituted or unsubstituted C2-10-alkenyl, substituted or unsubstituted C2-10-alkynyl, substituted or unsubstituted C1-10-heteroalkyl, substituted or unsubstituted C1-10-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, andsubstituted or unsubstituted C4-10-heteroaryl, or where the tridentate ligand is a tridentateligand having formula (IIIc) or (IIIe) Ra and Rb together with the heteroatom to which they areattached form a heterocycle.

17. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein Raand Rbare the same.

18. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein thetridentate ligand having formula (III) is one or more tridentate ligands selected from the group consisting of:.

19. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein Z is a carboxylate ligand having formula (IV) or a carboxylate ligand havingformula (IVb),,where R6is selected from substituted or unsubstituted C1-20-alkyl, substituted or unsubstituted C2-20-alkenyl, substituted or unsubstituted C2-20-alkynyl, substituted or unsubstituted C1-20-heteroalkyl, substituted or unsubstituted C1-20-alkoxy, substituted or unsubstituted C3-10-cycloalkyl, substituted or unsubstituted C3-10-cycloalkenyl, substituted or unsubstituted C2-10-heterocycloalkyl, substituted or unsubstituted C6-10-aryl, and substituted or unsubstituted C4-10-heteroary.

20. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein W is a carboxylate ligand, preferably a carboxylate ligand having formula (IV) or formula (IVb) according to claim 19.

21. A ruthenium complex of formula (I) or formula (II) according to any one of the precedingclaims, wherein A is a neutral ligand selected from the group consisting of phosphines, carbonyls, and sulfoxides.

22. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein theruthenium complex of formula (I) or formula (II) is one or more selected from:

23. A ruthenium complex of formula (I) or formula (II) according to claim 1, wherein the5 ruthenium complex of formula (I) or formula (II) is one or more selected from:.

24. A process for reducing a carbonyl containing substrate to an alcohol containingsubstrate in the presence of a hydrogen source and optionally a base using the rutheniumcomplex of formula (I) and / or the ruthenium complex of formula (II) as defined in any one of the preceding claims.

25. A process according to claim 24, wherein the carbonyl containing substrate is anester containing substrate, or an aldehyde containing substrate, preferably an ester containing substrate.

Images