Complex and process

Abstract

The present invention relates to the field of organic chemistry, specifically to pre-catalysts for producing boronic esters from organic molecules. The invention provides iridium complexes comprising N-N bidentate ligands. The iridium complexes of the invention find use in the production of boronic esters from organic molecules, said boronic esters may be used in cross-coupling reactions to produce more complex organic molecules. The invention further relates to a process for using the iridium complexes of the invention and to a process for preparing the iridium complexes of the invention.

Description

[0001] Complex and Process

[0002] Field of the Invention

[0003] The present invention relates to transition metal complexes. More specifically, the present invention relates to iridium complexes which find use in preparing boronic esters of organic compounds. The invention further relates to a process for the borylation of organic compounds to form boronic esters using the iridium complexes. The invention further relates to a process for preparing the iridium complexes.

[0004] Background of the Invention

[0005] Cross-coupling reactions are routinely used in the synthesis of organic compounds such as natural products and active pharmaceutical ingredients. Cross-coupling reactions represent a powerful set of chemistries for the formation of new carbon-carbon and carbon-heteroatom bonds.

[0006] The formation of boronic esters from organic compounds (a borylation reaction) is an important process in preparing reagents for a number of cross-coupling chemistries, for example for Suzuki-Miyaura cross-coupling reactions.

[0007] As is known in the art, boronic esters may be prepared by C-H bond activation of aromatic and heteroaromatic complexes in the presence of an iridium catalyst, followed by insertion of a boron group from a suitable borylation agent, such as B2Pin2.

[0008] Typically, iridium catalysts used in borylation reactions are prepared in-situ by reaction of [lr(OCHs)(COD)]2 (where COD = 1,5-cyclooctadiene) with a suitable ligand. Most commonly, bidentate heteroaromatic nitrogen containing ligands, such as 2 ,2’-bipyridi ne or 3, 4,7,8, - tetramethyl-1 ,10-phenanthroline, are used. These ligands coordinate to iridium through at least the two sp2-hybridised nitrogen atoms. Herein, such ligands may be referred to as N-N ligands or simply “N-N”. It is believed that in order to form the active borylation catalyst the 1,5-cyclooctadiene ligand must undergo reduction by the OCH3 ligand.

[0009] The formation of boronic esters and catalysts used in borylation reactions are described in Chem. Rev. 2023, 123, 19, 11619-11663.

[0010] However, known pre-catalysts and catalysts for borylation reactions have several deficiencies which complicate their use. The most commonly employed iridium precursor complex, [lr(OCHs)(COD)]2, is moisture sensitive and its synthesis is problematic. Consequently, it is difficult to isolate in a pure form. Moreover, complicated mixtures of metal complexes may be formed when using [lr(OCHs)(COD)]2 to form a borylation catalyst, resulting in inconsistent and unpredictable outcomes in borylation reactions; as noted in J. Am. Chem. Soc. 2013, 135, 20, 7572-7582

[0011] Efforts to isolate borylation pre-catalysts, for instance [lr(OCHs)(N-N)(COD)] where N-N is a 1 ,10-phenanthroline type ligand, have been unsuccessful; such complexes spontaneously decomposing when exposed to air and / or moisture.

[0012] A particular drawback of current borylation catalyst systems is the borylation of the N-N ligand from internal reaction with the active borylation catalyst. This results in the borylated N-N ligand being consumed in the borylation reaction and the formation of unwanted organic by-products which require additional purification steps to remove. Moreover, the borylation of the ligand serves to deactivate the catalyst. Such deactivation is described in J. Am. Chem. Soc. 2019, 141, 41 , 16479-16485.

[0013] Accordingly, there is a need for improved borylation catalysts and pre-catalysts with improved stability.

[0014] Summary of the Invention

[0015] The present invention provides a new class of iridium borylation pre-catalysts which have improved air stability, and which provide active catalysts with increased reactivity compared to catalyst systems of the prior art.

[0016] In a first aspect there is provided an iridium complex of formula (I): comprising an N-N ligand of formula (II):

[0017] wherein:

[0018] Ri and R2 are each independently an organic group having 1-20 carbon atoms; and R3-R6 are each independently a hydrogen atom or an organic group having 1-20 carbon atoms;

[0019] R? and Rs are each independently a hydrogen atom or an organic group having 1-20 carbon atoms, or are linked to form a ring structure;

[0020] X is an anionic ligand; and

[0021] Y1 and Y2 are each independently an alkenyl ligand bonded to the Ir atom through a single alkenyl group.

[0022] It has surprisingly been found that the iridium complexes of formula (I), where R1 and R2 are independently an organic group having 1-20 carbon atoms, are air stable and do not undergo deactivation from borylation of the N-N ligand. The air stability of iridium complexes of formula(l) is particularly surprising because complexes with two alkenyl ligands, Y1 and Y2 according to the present invention, would be expected to be less air stable than those with a single COD ligand.

[0023] Moreover, the inclusion of the alkenyl ligands, Y1 and Y2 according to the present invention, in the complex of formula (I) has surprisingly been found to provide a more active catalyst with higher conversion than when a pre-catalyst or a precursor complex comprising a dialkenyl COD ligand is used (e.g. [lr(OCH3)COD]2).

[0024] It has further surprisingly been found that iridium complexes comprising the N-N ligands of formula (II) do not form under the in-situ conditions known in the prior art, or are formed in such small quantities as to not be useful as borylation catalysts. For instance, In-situ methods combining [lr(OCH3)COD]2 and more highly substituted N-N ligands, such as 6,6’- dimethyl-2,2’-bipyridine, do not yield competent catalysts. It is believed that this failure to catalyse borylation reactions is as a result of the N-N ligand failing to coordinate to the iridium metal (Chem. Rev., 2010, 110, 2, 890-931). Accordingly, the iridium(l) complexes of formula(l) provide an as of yet inaccessible class of borylation catalysts.

[0025] Accordingly, iridium complexes of formula (I) provide air-stable, “off the shelf”, pre-catalysts which can be used to produce highly active borylation catalysts that do not suffer from the undesirable side reactions associated with catalyst systems of the state of the art. Consequentially, the iridium complexes of formula (I) provide predictable, repeatable and high conversion results in borylation reactions whilst reducing by-product formation and catalyst deactivation.

[0026] In a second aspect there is provided a process for preparing a boronic ester using the iridium complexes of formula (I).

[0027] In a third aspect there is provided a process for preparing the iridium complexes of formula (I).

[0028] Definitions

[0029] The point of attachment of a moiety or substituent is represented by For example, -OH is attached through the oxygen atom.

[0030] “Alkenyl” refers to a straight-chain or branched unsaturated hydrocarbon group comprising at least one carbon-carbon double bond.

[0031] “Alkyl” refers to a straight-chain or branched saturated hydrocarbon group. The alkyl group may be unsubstituted. Alternatively, the alkyl group may be substituted. Unless otherwise specified, 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 to methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl and the like.

[0032] The term “cycloalkyl” is used to denote a saturated carbocyclic hydrocarbon radical. The cycloalkyl group may have a single ring or multiple condensed rings. The cycloalkyl group may be unsubstituted. Alternatively, the cycloalkyl group may be substituted. Unless other specified, the cycloalkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Typical cycloalkyl groups include but are not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl and the like. “Alkoxy” refers to an optionally substituted group of the formula alkyl-O- or cycloalkyl-O-, wherein alkyl and cycloalkyl are as defined above.

[0033] “Aryl” refers to an aromatic carbocyclic group. The aryl group may have a single ring or multiple condensed rings. The aryl group may be unsubstituted. Alternatively, the aryl group may be substituted. Unless otherwise specified, the aryl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl and the like.

[0034] “B2pin2” refers to the compound 4,4,4',4',5,5,5',5'-octamethyl-2,2'-bi-1 ,3,2-dioxaborolane, also known as bis(pinacolato)diboron.

[0035] “Beat” refers to (catecholato)boron.

[0036] “Bpin” refers to 4,4,5,5-tetramethyl-1 ,3,2-dioxaboron, also known as (pinacolato)boron.

[0037] “COD” refers to 1 ,5-cyclooctadiene.

[0038] “COE” refers to cyclooctene.

[0039] “Coupling” refers to a chemical reaction in which two molecules or parts of two molecules join together (Oxford Dictionary of Chemistry, Sixth Edition, 2008).

[0040] “HBpin” refers to pinacolborane.

[0041] “HBcat” refers to catechol borane.

[0042] “Halo” or “hal” refers to F, Cl, Br and I atoms or ions.

[0043] “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 be unsubstituted. Alternatively, the heteroalkyl group may be substituted. Unless otherwise specified, the heteroalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heteroalkyl groups include but are not limited to 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, phosphorus and / or sulfur atoms). The heteroaryl group may be unsubstituted. Alternatively, the heteroaryl group may be substituted. Unless otherwise specified, the heteroaryl group may be attached at 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.

[0044] “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, the heterocycloalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heterocycloalkyl groups include but are not limited to epoxide, morpholinyl, piperadinyl, piperazinyl, thirranyl, pyrrolidinyl, pyrazolidinyl, imidazolidinyl, thiazolidinyl, thiomorpholinyl and the like.

[0045] “sp2”, or “sp2-hybridized”, refers to the mixing of an s atomic orbital and two p atomic orbitals to produce a hybrid orbital having both s and p character. For example, the carbon atoms in a benzene ring are all considered to be sp2hybridised carbon atoms.

[0046] “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, -Ra, =0, =S, -O-Ra, - S-Ra, -NRaRb, -CN, -N02, -C(O)-Ra, -COORa, -C(S)-Ra, -C(S)ORa, -S(O)2OH, -S(O)2-Ra, - S(O)2NRaRb, -O-S(O)-Raand -CONRaRb, such as -halo, -C(halo)3(e.g. -CF3), -Ra, -O-Ra, - NRaRb, -CN, or -N02. Raand Rbare independently selected from the groups consisting of H, alkyl, aryl, arylalkyl, heteroalkyl, heteroaryl, or Raand Rbmay be linked to form a heterocycloalkyl group. Raand Rbmay be unsubstituted or further substituted as defined herein. Detailed Description

[0047] Preferred and / or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and / or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise.

[0048] According to a first aspect, the present invention provides an iridium complex of formula (I): comprising an N-N ligand of formula (II): wherein:

[0049] Ri and R2 are each independently an organic group having 1-20 carbon atoms; and

[0050] R3-R6 are each independently a hydrogen atom or an organic group having 1-20 carbon atoms;

[0051] R? and Rs are each independently a hydrogen atom or an organic group having 1-20 carbon atoms, or are linked to form a ring structure;

[0052] X is an anionic ligand; and

[0053] Y1 and Y2 are each independently an alkenyl ligand bonded to the Ir atom through a single alkenyl group.

[0054] In the iridium complex of formula (I), the Ir atom may have an oxidation state of +1 or +3.

[0055] Preferably, the Ir atom has an oxidation state of +1. Accordingly, the iridium complex of formula (I) may be an iridium(l) complex of formula (I).

[0056] The iridium complex of formula (I) comprises an N-N ligand of formula (II):

[0057] It will be understood that the nomenclature of the N-N ligand of formula (II) and that of the iridium complex of formula (I) are the same and are used interchangeably herein.

[0058] Ri and R2 are each independently an organic group having 1-20 carbon atoms.

[0059] R1 and R2 may be the same or different. Preferably, R1 and R2 are the same.

[0060] R1 and R2 may be independently selected from the group consisting of substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chain alkyl, substituted and unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, substituted and unsubstituted C3-C20 (e.g. C3-C10, or Cs-Cs) cycloalkyl, substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) alkoxy, substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6) aryl, and substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6) heteroaryl wherein the heteroatoms are independently selected from sulfur, nitrogen and oxygen.

[0061] Preferably, R1 and R2 are each independently selected from the group consisting of substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chain alkyl, substituted and unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, and substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) alkoxy.

[0062] More preferably, R1 and R2 are each independently selected from the group consisting of methyl, trifluoromethyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, terf-butyl, pentyl (e.g. n-pentyl or neopentyl), hexyl, heptyl, octyl, nonyl, decyl, dodecyl, stearyl, methoxy, ethoxy, / so-propoxy, and terf-butoxy.

[0063] More preferably still, R1 and R2 are each independently selected from the group consisting of methyl, trifluoromethyl, / so-propyl, methoxy, and / so-propoxy. Most preferably, R1and R2are the same and are methyl.Alternatively, R1 and R3, and / or R2 and R4 may be linked to form a ring structure. R1 and R3,and / or R2 and R4 may be linked to form a substituted or unsubstituted cycloalkyl ring, asubstituted or unsubstituted cycloalkenyl ring, a substituted or unsubstituted aryl ring, or asubstituted or unsubstituted heteroaryl ring wherein the heteroatoms are independentlyselected from sulfur, nitrogen and oxygen. R1 and R3, and / or R2 and R4 may be linked toform a substituted or unsubstituted 5-membered aryl ring or a substituted or unsubstituted 6-membered aryl ring. For example, R1 and R3, and / or R2 and R4 may be linked to form asubstituted or unsubstituted 6-membered aryl ring, for example a phenyl ring.Where R1and / or R2are substituted C1-C20straight-chain alkyl, substituted branched-chainC1-C20 alkyl, substituted C1-C20 cycloalkyl, substituted C1-C20 alkoxy, substituted C4-C20 aryl,or substituted C4-C20 heteroaryl groups, each may independently be substituted as definedhereinabove. Where R1 and R3, and / or R2 and R4 are linked to form a ring structure, eachring structure may be further substituted as defined hereinabove.R3, R4, R5, and R6 are each independently a hydrogen atom or an organic group having 1-20carbon atoms. R3, R4, R5, and R6 may each be the same or different.R3, R4, R5, and R6 may be independently selected from the group consisting of hydrogenatom, substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chain alkyl,substituted and unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, substitutedand unsubstituted C3-C20 (e.g. C3-C10, or C3-C8) cycloalkyl, substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) alkoxy, substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6)aryl, and substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6) heteroaryl wherein theheteroatoms are independently selected from sulfur, nitrogen and oxygen. Preferably, R3, R4, R5, and R6 are each independently selected from the group consisting of hydrogen atom, substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chainalkyl, substituted and unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, andsubstituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) alkoxy. More preferably, R3, R4, R5, and R6 are each independently selected from the group consisting of hydrogen atom, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl (e.g. n-pentyl or neopentyl), hexyl, heptyl, octyl, nonyl, decyl, dodecyl, stearyl, methoxy, ethoxy, iso-propoxy, and tert-butoxy.Most preferably, R3, R4, R5, and R6 are each independently hydrogen atoms or methyl.Alternatively, R3 and R1, and / or R4 and R2 may be linked to form a ring structure asdescribed hereinabove. Where R3, R4, R5, and / or R6are substituted C1-C20straight-chain alkyl, substituted branched-chain C1-C20 alkyl, substituted C1-C20 cycloalkyl, substituted C1-C20 alkoxy, substituted C4-C20aryl, and / or substituted C4-C20 heteroaryl groups, R3, R4, R5, and / or R6 may eachindependently be substituted as defined hereinabove.R7 and R8 are each independently a hydrogen atom or an organic group having 1-20 carbonatoms, or are linked to form a ring structure.R7and R8may each be the same or different.R7 and R8 may be independently selected from the group consisting of hydrogen atom,substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chain alkyl, substitutedand unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, substituted andunsubstituted C3-C20 (e.g. C3-C10, or C3-C8) cycloalkyl, substituted and unsubstituted C1-C20(e.g. C1-C10, or C1-C5) alkoxy, substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6)aryl, and substituted and unsubstituted C4-C20 (e.g. C4-C8, or C4-C6) heteroaryl wherein theheteroatoms are independently selected from sulfur, nitrogen and oxygen. Preferably, R7 and R8 are each independently selected from the group consisting of hydrogen atom, substituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) straight-chainalkyl, substituted and unsubstituted C3-C20 (e.g. C3-C10, or C3-C4) branched-chain alkyl, andsubstituted and unsubstituted C1-C20 (e.g. C1-C10, or C1-C5) alkoxy. More preferably, R7 and R8 are each independently selected from the group consisting of hydrogen atom, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl,pentyl (e.g. n-pentyl or neopentyl), hexyl, heptyl, octyl, nonyl, decyl, dodecyl, stearyl,methoxy, ethoxy, iso-propoxy, and tert-butoxy.Most preferably, R7 and R8 are each independently hydrogen atom or methyl.Alternatively, R7 and R8 are linked to form a ring structure. For example, R7 and R8 togetherwith the atoms to which they are attached are linked to form a ring structure. R7 and R8 maybe linked to form a substituted or unsubstituted cycloalkyl ring, a substituted or unsubstitutedcycloalkenyl ring, a substituted or unsubstituted aryl ring, or a substituted or unsubstituted heteroaryl ring wherein the heteroatoms are independently selected from sulfur, nitrogen andoxygen. R7 and R8 may be linked to form a substituted or unsubstituted 6-membered aryl ring.It has surprisingly been found that, unlike pre-catalysts of the prior art, complexes of formula(I) where R7 and R8 are not linked to form a ring structure (i.e. where the N-N ligand offormula (II) is a bipyridyl type ligand) spontaneously form an active borylation catalyst and donot require the addition or inclusion of any form of additive to activate the pre-catalyst.Accordingly, it may be preferred that R7 and R8 are not linked to form a ring structure.Where R7and / or R8are substituted C1-C20straight-chain alkyl, substituted branched-chainC1-C20 alkyl, substituted C1-C20 cycloalkyl, substituted C1-C20 alkoxy, substituted C4-C20 aryl,or substituted C4-C20 heteroaryl groups, each may independently be substituted as definedhereinabove. Where R7 and R8 are linked to form a ring structure, the ring structure may befurther substituted as described hereinabove. For example, the ring structure may be furthersubstituted by one or more methyl groups. It may be preferred that the N-N ligand of formula (II) be one or more selected from:

[0064]

[0065] It may be more preferred that the N-N ligand of formula (II) be one or more selected from:

[0066] In the iridium complex of formula (I), X is an anionic ligand.

[0067] X may be a coordinated anionic ligand, i.e. the anionic ligand is bonded to the Ir atom within the coordination sphere. Alternatively, X may be a non-coordinated anionic. By “non- coordinated anionic ligand”, we mean the anionic ligand is forced to the outer sphere of the metal centre. A non-coordinated anionic ligand, therefore, is dissociated from the Ir atom.The anionic ligand can be generally identified as coordinating or non-coordinating byanalysing the X-ray crystal structure of the complex.Where X is a coordinated anionic ligand, X may be a halo group, an acetate group, an alkoxygroup, a carboxylate group, or an acetoxy group. Where X is a non-coordinated anionic ligand,X may be PF6-, SbF6-, AsF6-, BF4-, OTf-, OMs- (mesylate), OTs- (tosylate), or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. In the iridium complex of formula (I), X is depicted as being bonded to the Ir atom by adashed bond. It will be understood that the dashed bond represents X bonding to the Ir atomeither as a coordinated anionic ligand or a non-coordinated anionic ligand. However, where X is a non-coordinating anionic ligand, the iridium complex of formula (I) may also be represented as an iridium complex of formula (Ia): wherein, R1, R2, R3, R4, R5, R6, R7, R8, Y1, and Y2 are as defined for the iridium complex offormula (I), and wherein X is a non-coordinating anionic ligand as defined hereinabove.Accordingly, the iridium complex of formula (I) may be the iridium complex of formula (Ia),wherein, R1, R2, R3, R4, R5, R6, R7, R8, Y1, and Y2 are as defined for the iridium complex offormula (I), and wherein X is a non-coordinating anionic ligand as defined hereinabove.Preferably, X is a coordinating anionic ligand. More preferably, X may be a halo group (i.e. F-Cl-, Br-, or I-). Most preferably, X may be Cl-.It may be preferred that X is not an alkoxy ligand, for instance it may be preferred that X is not methoxy (OCH3-). It has surprisingly been found that when X is not an alkoxy ligand, for example not methoxy,that the iridium complexes of formula (I) are still able to form an active borylation catalyst. Thisis despite it being believed in the prior art that, as described hereinabove, an alkoxy ligand(e.g. OCH3-) may be involved in the formation of active borylation catalysts. More surprisingstill, and as described hereinabove, when the N-N ligand of formula (II) is a bipyridyl typeligand the iridium complex of formula (I) does not require the addition or inclusion of any formof additive to form the active borylation catalyst. Y1and Y2are each independently an alkenyl ligand. Y1and Y2comprise one or more alkenyl groups. Y1and Y2may each independently be a compound of formula (III): wherein,Rx and Ry may each independently be a hydrogen atom or a C1-C10 carbon containing group.Rx and Ry may be the same or different. Rx and Ry may independently be selected from a hydrogen atom, substituted and unsubstituted C1-C10 (e.g. C1-C8, or C1-C5) straight-chain alkyl, substituted and unsubstitutedC3-C10 (e.g. C3-C8, or C3-C4) branched-chain alkyl, substituted and unsubstituted C3-C10 (e.g.C3-C8, or C3-C5) cycloalkyl, substituted and unsubstituted C1-C10 (e.g. C1-8, or C1-C5) alkoxy,substituted and unsubstituted C4-C10 (e.g. C4-C8, or C4-C6) aryl, and substituted andunsubstituted C4-C10 (e.g. C4-C8, or C4-C6) heteroaryl wherein the heteroatoms areindependently selected from sulfur, nitrogen and oxygen, or Rx and Ry may be linked to form a ring structure. Preferably, Rx and Ry are each independently selected from the group consisting of hydrogen atom, substituted and unsubstituted C1-C10 (e.g. C1-C8, or C1-C5) straight-chainalkyl, and substituted and unsubstituted C3-C10 (e.g. C3-C8, or C3-C4) branched-chain alkyl,or Rx and Ry may be linked to form a ring structure.More preferably, Rx and Ry are linked to form a ring structure.Most preferably, Rx and Ry are linked to form a ring structure which is cyclooctene (i.e.COE). Accordingly, it may be preferred that Y1 and Y2 are the same and are each cyclooctene (i.e. COE). Y1 and Y2 are each bonded to the Ir atom through a single alkenyl group.

[0068] Where either of Yi or Y2 have more than one alkenyl group, it will be understood that Y1 and Y2 are each bonded to the Ir atom through a single alkenyl group.

[0069] It may be preferred that Y1 and / or Y2 have only one alkenyl group, for example both Y1 and Y2 each have only one alkenyl group. It may be preferred that Y1 and / or Y2 are not 1 ,5-cyclooctadiene (COD).

[0070] It may be preferred that the iridium complex of formula (I) be one or more complexes selected from: The iridium complex of formula(I) may further comprise a solvent molecule. For instance, theiridium complex of formula (I) may comprise a solvent molecule (e.g. THF) coordinated tothe Ir atom. For instance, the iridium complex of formula(I) may be present as a solvate. By“solvate” we mean that the complex of formula(I) comprises one or more solvent molecules outside of the coordination sphere of the iridium. The iridium complex of formula (I) may be present as a dimeric species having formula (Ib): wherein, R1, R2, R3, R4, R5, R6, R7, R8, Y1, and Y2 are as already defined, and wherein X is acoordinating anionic ligand as already defined. For the avoidance of doubt, any iridium complex of formula (I) described hereinabove is also contemplated as being present as a dimeric iridium complex of formula (Ib). In a second aspect of the invention there is provided a process for preparing a boronic esterusing an iridium complex of formula (I) as defined in the first aspect of the invention.The process of the invention may comprise the steps of:contacting an organic substrate and a borylation agent to form a reaction mixture;and reacting the organic substrate and the borylation agent in the presence of an activeborylation catalyst to form a boronic ester of the organic substrate, wherein the active borylation catalyst is prepared from an iridium complex of formula (I) of the first aspect of the invention. The active borylation catalyst may be prepared “ex-situ” or “in-situ” from the iridium complex of formula (I). The active borylation catalyst may be prepared by reacting the iridium complex of formula (I) with a borylation agent in a solvent at an elevated temperature. The active borylation catalyst may be prepared “ex-situ" and be added to the reaction mixture. For example, the active borylation catalyst may be prepared by reacting the iridium complex of formula (I) with B2Pin2 in THF at 75 °C for 1 hour to generate the active borylation catalyst. Alternatively, the active borylation catalyst may be prepared "in-situ” by converting the iridium complex of formula (I) into the active borylation catalyst in the presence of the borylation agent of the reaction mixture during the step of reacting the organic substrate and the borylation agent.

[0071] The organic substrate may be an aromatic compound or a heteroaromatic compound comprising a C-H bond. The organic substrate may comprise a 5-membered or 6-membered aryl or heteroaryl ring.

[0072] It has surprisingly been found that the active borylation catalyst formed from the iridium complexes of formula (I) are selective for the borylation of 5-membered aryl and heteroaryl rings.

[0073] Suitably, the iridium complex of formula (I) may be used in the process of the invention to provide the active borylation catalyst in the reaction mixture in an amount of 0.15 mol% or more relative to the organic substrate. For example, the iridium complex of formula (I) may suitably be used to provide the active borylation catalyst in the reaction mixture in an amount of 0.2 mol%, 0.25 mol%, 0.3 mol%, or 0.35 mol% or more relative to the organic substrate. Suitably, the iridium complex of formula (I) may be used in the process of the invention to provide the active borylation catalyst in the reaction mixture in an amount of 2 mol% or less relative to the organic substrate, such as 1.5 mol%, 1 mol%, or 0.75 mol% or less relative to the organic substrate.

[0074] The reaction mixture may comprise a solvent. The solvent may suitably be an ether (e.g. tetrahydrofuran, methyltetrahydrofuran), an aromatic solvent (e.g. toluene), an alkyl solvent (e.g. heptane), or a mixture thereof. Preferably, the solvent is an ether. More preferably, the solvent is THF. Suitably, the solvent does not comprise an alcohol. Alternatively, the organic substrate may act as a solvent. For example, the organic substrate may be the only solvent in the reaction mixture. Where the organic substrate is the only solvent, the process of the invention may be referred to as “solvent free”.

[0075] Typically, the organic substrate and the borylation agent may be reacted in the presence of the active borylation catalyst for a duration of 0.5 to 24 hours, such as from 1 to 16 hours.

[0076] Typically, the step of reacting the organic substrate and the borylation agent may be carried out at a temperature in the range 5 to 100 °C, such as from 10 to 90 °C, from 20 to 80 °C, or from 50 to 70 °C. For example, the reaction mixture may be heated at reflux in an appropriate solvent.

[0077] The borylation agent of the process of the second aspect is not particularly limited and may be suitably selected by a person skilled in the art. Preferably, the borylation agent may be selected from B2pin2, HBpin, (dihydroxyboranyl)boronic acid, HBcat, and bis(catecholato)diboron. More preferably, the borylation agent may be selected from HBpin and B2pin2. Most preferably, the borylation agent may be B2pin2.

[0078] The borylation agent may be added to the reaction mixture in an amount of 1 molar equivalent or more relative to the organic substrate. For example, the borylation agent may be added to the reaction mixture in an amount of 1 .5 molar equivalents, 2 molar equivalents or 2.5 molar equivalents or more relative to the organic substrate.

[0079] In preferred processes of the invention no activator may be added to the process for preparing a boronic ester. For example, in preferred processes of the invention no water, no primary alcohol, or no secondary alcohol may be added to the process for preparing a boronic ester. Accordingly, the process of the second aspect of the invention may be an activator free process for preparing a boronic ester using an iridium complex of formula (I) as defined in the first aspect of the invention.

[0080] It is an advantage of using the iridium complex of formula (I) in the process of the present invention that an activator is not required in order to provide the active borylation catalyst and affect the borylation of the organic substrate. As will be understood, where an activator is used it must be present in a high enough concentration to activate the pre-catalyst.

[0081] However, their concentration must remain low enough so as to not deactivate the active borylation catalyst. The reaction mixture may comprise a non-nucleophilic base. Preferably, the non-nucleophilic base may be selected from a group I or group II metal alkoxide. More preferably, the non- nucleophilic base may be selected from a group I or group II / so-propoxide or terf-butoxide. Most preferably, the non-nucleophilic base may be selected from sodium or potassium / so- propoxide, or terf-butoxide.

[0082] The non-nucleophilic base may be added to the reaction mixture in an amount of 0.1 mol% of more, 0.2 mol% or more, or 0.3 mol% or more relative to the organic substrate. The non- nucleophilic base may be added to the reaction mixture in an amount or 1 mol% or less, 0.7 mol% of less, or 0.5 mol% of less relative to the organic substrate. For example, the non- nucleophilic base may be added to the reaction mixture in an amount of from 0.1 mol% to 1 mol%, from 0.2 mol% to 0.7 mol%, or from 0.3 mol% to 0.5 mol% relative to the organic substrate.

[0083] It has surprisingly been found that the presence of a non-nucleophilic base in the reaction mixture may increase the activity of the active borylation catalyst prepared from the iridium complexes of formula(l) and provide higher conversion of the organic substrate to the boronic ester.

[0084] Typically, the step of reacting the organic substrate and the borylation agent is carried out under inert conditions, such as under an atmosphere of nitrogen or argon, and in the absence of atmospheric moisture.

[0085] In a third aspect of the invention there is provided a process for preparing the iridium complex of formula (I) of the first aspect of the invention.

[0086] The iridium complex of formula (I) may be prepared in a process comprising the steps of: reacting an N-N ligand of formula (II) with an iridium pre-cursor to produce the iridium complex of formula (I), wherein R1-R8 are as defined in relation to the iridium complex of formula(I) of the firstaspect of the invention.It has surprisingly been found that active borylation catalysts comprising the N-N ligand offormula(II) do not form under conditions known from the prior art, or are formed in such smallquantities as to not be useful as borylation catalysts. It is believed that the reaction betweenthe commonly used [Ir(OCH3)COD]2 pre-cursor complex and N-N ligands of formula (II) areinhibited or do not occur due to the increased steric bulk of the R1and R2substituents(Chem. Rev., 2010, 110, 2, 890–931). Accordingly, the iridium complexes of formula(I)provide an as of yet inaccessible class of borylation catalysts via the process according to the third aspect of the invention. The iridium pre-cursor may be a complex of general formula [IrX(Y1or Y2)]2, wherein X, Y1and Y2are as defined in relation to the first aspect of the invention. The iridium pre-cursor is preferably an iridium cyclooctene complex. For example, the iridium pre-cursor may be [IrCl(COE)2]2. The N-N ligand of formula (II) may be prepared by any suitable synthetic methods which are known to the person skilled in the art. The reaction between the N-N ligand of formula (II) and the iridium pre-cursor may becarried out in a suitable solvent. Suitable solvents include polar organic solvents such asTHF, tetramethyltetrahydrofuran, and 1,4-dioxane. The reaction between the N-N ligand of formula (II) and the iridium pre-cursor may be carried out under inert conditions. For example, the reaction between the N-N ligand of formula (II) and the iridium pre-cursor may be carried out in the absence of moisture under an atmosphere of nitrogen or argon. The reaction between the N-N ligand of formula (II) and the iridium pre-cursor may be carried out at room temperature or elevated temperature. For example, the reaction between the N-N ligand of formula (II) and the iridium pre-cursor may be carried out at a temperatureof 30 °C to 50 °C, such as 45 °C.In some process of the third aspect, the anionic ligand X may be provided by substitution. For instance, [IrCl(N-N)(COE)2] may be first prepared and then treated with a silver salt of X, such as AgPF6, to provide the desired anionic ligand, X. In some processes of the third aspect, the alkenyl ligands Y1and / or Y2of one complex offormula (I) may be provided by substitution (e.g. by ligand exchange) with another alkenylligand. For instance, [IrCl(N-N)(COE)2] may be first prepared and then treated with Y1and / or Y2to provide [IrCl(N-N)(Y1)(Y2)].Accordingly, the iridium complex of formula (I) may be prepared in a process comprising thesteps of: reacting an N-N ligand of formula (II), with [IrCl(COE)2] to produce optionally, exchanging the COE ligand(s) with a ligand Y1 and / or Y2 to produce the iridiumcomplex of formula (I), wherein R1-R8and Y1and Y2are as defined in relation to the iridium complex of formula(I) of the first aspect of the invention. ExamplesReagents used were commercially available and were purchased from Sigma Aldrich or TCIAmerica unless otherwise specified.The iridium complexes [Ir(COE)2Cl]2 and [Ir(COD)Cl]2, were commercially available and wereobtained from Johnson Matthey PLC. Catalysts and pre-catalysts were prepared according to the methods described herein. Abbreviations:

[0087] In this Examples section the following abbreviations are used to refer to pre-catalysts and catalysts:

[0088] Preparation of nrCI(6,6’-dimethyl-2,2’-bipyridene)(COE)2l (Me2bpy) (according to the invention) In a nitrogen atmosphere glovebox, a vial was charged with [lr(COE)2CI]2 (1.0 g, 1.12 mmol) and 6,6’-dimethyl-2,2’-bipyridene (0.411 g, 2.06 mmol). Dry THF (3 mL) was added producing a dark solution. The solution was removed from the glovebox and stirred at 45°C for 16 hours. A suspension containing a red precipitate was formed.

[0089] The suspension was treated with 17 mL of hexane and sonicated to remove any remaining material from the walls of the vial. The solid was recovered by filtration through a disposable fritted filter. The filter was dried in an oven for three hours and the product obtained as a red air stable solid. Yield 1.26 g, 1.99 mmol, 88.7 %. CHN: found: 48.90 % C, 5.57 % H, 4.58 % N, Predicted: 48.51 % C, 5.77 % H, and 4.71% N.

[0090] Preparation of nrCI(2,9-dimethyl-1 ,10-phenanthroline)(COE)2l (Me2Phen), nrCI(6,6’-dimethyl- 4,4’-dimethyl-2,2’-bipyridine)(COE)2l (Me4bpy), and nrCI(6,6’-dimethyl-4,4’-ditrifluoromethyl- 2,2’-bipyridine)(COE)2l (Me2CF32bpy) (according to the invention)

[0091] The method used to prepareMe2bpy, above, was followed, except that 2,9-dimethyl-1 ,10- phenanthroline, 6,6’-dimethyl-4,4’-dimethyl-2,2’-bipyridine, and 6,6’-dimethyl-4,4’- ditrifluoromethyl-2,2’-bipyridine ere used in place of 6,6’-dimethyl-2.2’-dipyridene.

[0092] In-situ preparation of catalysts comprising 3,4,7,8-tetramethyl-1 ,10-phenanthroline (Me4Phen) (comparative):

[0093] Comparative catalysts were prepared in-situ according to the method described in J. Am. Chem. Soc. 2014, 136, 11, 4287-4299 and were transferred to the reaction mixture comprising the organic substrate immediately.

[0094] General procedure for the preparation of a boronic esters using complexes of the invention: Inside a nitrogen glovebox, an 8 mL vial was charged with either an iridium complex of formula (I) according to the invention or a solution containingMe4Phen (ca. 0.0075 mmol, 0.5 mol%) and the borylation agent B2Pin2 (ca. 1.5 mmol, 1.0 molar eguiv). The iridium complex and the borylation agent were dissolved in THF (3 mL) and were optionally treated with potassium terf-butoxide solution (KO‘Bu). The solutions were heated at 75 °C for one hour to generate the active catalyst. The vials were cooled to room temperature. The organic substrate (ca. 0.125 mL, 1.50 mmol, 1.0 molar eguiv.) was added to the vial and the resulting reaction mixture stirred for 16 hours and 75 °C. After 16 hours the solution was treated with 1 ,3,5-trimethoxybenzene and analyzed by NMR to determine the overall conversion. Example 1

[0095] Example 1 investigate the performance ofMe2bpy, a complex according to the invention, in the borylation of a number of organic substrates in the presence and absence of an activator. The general procedure for preparing boronic esters was followed for each of experiments 1-7. Where potassium tert-butoxide (KO‘Bu) was added this is shown as an amount in mol% relative to the organic substrate. These results are shown in Table 1 , below.

[0096] Table 1

[0097] Experiments 1-7 demonstrate the ability of complexes of the present invention to form boronic esters from a variety of organic substrates either with or without non-nucleophilic base. Moreover, yields are substantially unaffected by the absence of the non-nucleophilic base. In some instances, yields are improved in the absence of a non-nucleophilic base.

[0098] Example 2

[0099] Example 2 investigates the performance ofMe2bpy andMe2Phen of the invention in the borylation of a number of organic substrates compared to an in-situ generatedMe4Phen, a comparative complex. Potassium tert-butoxide solution (0.5 mol% relative to the organic substrate) was added to each reaction mixture. These results are shown in Table 2, below.

[0100] Table 2

[0101] Experiments 8-15 show that complexes according to the invention give superior conversion of a wide variety of organic substrates to boronic esters as compared toMe4Phen under the same experimental conditions.

[0102] Example 3

[0103] Example 3 investigates the performance ofMe2bpy at various catalyst loadings in the presence and absence of potassium terf-butoxide (a non-nucleophilic based). Where potassium terf-butoxide (KO‘Bu) was added this is shown as an amount in mol% relative to the organic substrate. The general procedure for preparing boronic esters was used. Each experiment of Example 3 may be represented by the following reaction scheme:

[0104] The results from Example 3 are given in Table 3 below.

[0105] Table 3

[0106] Experiments 16-23 show that complexes of the invention achieve high yields for the borylation of lutidine at a variety of catalyst loadings, either in the presence or absence of a non-nucleophilic base.

[0107] Example 4

[0108] Experiment 24 shows the ability of complexes of the invention to achieve borylation of carboxylic acid containing organic compounds. To the best of the present inventor’s knowledge there have been no previous examples of such borylation reactions using iridium borylation catalysts.

[0109] Following the general procedure for the preparation of a boronic esters, the catalystMe4bpy was employed to borylate m-toluic acid using b2pin2 without any protection of the carboxylic acid group. The borylated m-toluic acid compounds were obtained in 100% conversion. The reaction is summarised in the following scheme:

[0110] In comparison to complexes of the present invention, catalysts formed by in-situ reaction of [lrCI(COE)2]2, [lrCI(COD)]2, and [lrOMe(COD)]2 with an N-N ligand not of formula (II) (such a bipyridine) showed no catalytic activity for the same borylation reaction.

[0111] It is therefore a surprising advantage of complexes of the present invention that direct borylation of carboxylic acid bearing organic compounds is possible, and it is further advantageous that no special protection of the carboxylic acid group is required.

[0112] Example 5

[0113] Experiment 25 shows the ability of complexes of the invention to achieve borylation of aniline containing organic compounds. To the best of the present inventor’s knowledge there have been no previous examples of such borylation reactions using iridium borylation catalysts.

[0114] Following the general procedure for the preparation of a boronic esters, the catalystsMe4bpy andMe2CF32bipy were employed to borylate 4-fluoroaniline using b2pin2 without any protection of the aniline group. The borylation of 4-fluoroaniline was achieved in 100% conversion. The reaction is summarised in the following scheme:

[0115] In comparison to complexes of the present invention, catalysts formed by in-situ reaction of [lrCI(COE)2]2, [lrCI(COD)]2, and [lrOMe(COD)]2 with an N-N ligand not of formula (II) (such a bipyridine) showed no catalytic activity for the same borylation reaction. It is therefore a surprising advantage of complexes of the present invention that direct borylation of anilines is possible, and it is further advantageous that no special protection of the aniline group is required.

Claims

Claims1 . An iridium complex of formula (I):comprising an N-N ligand of formula (II):wherein:Ri and R2 are each independently an organic group having 1-20 carbon atoms; and R3-R6 are each independently a hydrogen atom or an organic group having 1-20 carbon atoms;R? and Rs are each independently a hydrogen atom or an organic group having 1-20 carbon atoms, or R? and Rs are linked to form a ring structure;X is an anionic ligand; andY1 and Y2 are each independently an alkenyl ligand bonded to the Ir atom through a single alkenyl group.

2. An iridium complex of formula (I) according to claim 1 , wherein R1 and R2 are independently selected from the group consisting of substituted and unsubstituted C1-C20 straight-chain alkyl, substituted and unsubstituted C3-C20 branched-chain alkyl, substituted and unsubstituted C3-C20 cycloalkyl, substituted and unsubstituted C1-C20 alkoxy, substituted and unsubstituted C4-C20 aryl, and substituted and unsubstituted C4- C20 heteroaryl wherein the heteroatoms are independently selected from sulfur, nitrogen and oxygen.

3. An iridium complex of formula (I) according to claim 1 or claim 2, wherein Ri and R2 are each independently selected from the group consisting of methyl, trifluoromethyl, isopropyl, methoxy, and iso-propoxy.

4. An iridium complex of formula (I) according to any one of the preceding claims, wherein R1 and R2 are the same.

5. An iridium complex of formula (I) according to any one of the preceding claims, wherein R1 and R2 are the same and are methyl.

6. An iridium complex of formula (I) according to claim 1 , wherein R1 and R3, and / or R2 and R4 are linked to form a ring structure.

7. An iridium complex of formula (I) according to any one of the preceding claims, wherein R3, R4, Rs, and Re are independently selected from the group consisting of hydrogen atom, substituted and unsubstituted C1-C20 straight-chain alkyl, substituted and unsubstituted C3-C20 branched-chain alkyl, substituted and unsubstituted C3- cycloalkyl, substituted and unsubstituted C1-C20 alkoxy, substituted and unsubstituted C4-C20 aryl, and substituted and unsubstituted C4-C20 heteroaryl wherein the heteroatoms are independently selected from sulfur, nitrogen and oxygen.

8. An iridium complex of formula (I) according to any one of the preceding claims, wherein R3, R4, Rs, and Re are each independently selected from the group consisting of hydrogen atom, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl (e.g. n-pentyl or neopentyl), hexyl, heptyl, octyl, nonyl, decyl, dodecyl, stearyl, methoxy, ethoxy, iso-propoxy, and tert-butoxy, preferably hydrogen atom and / or methyl.

9. An iridium complex of formula (I) according to any one of the preceding claims, wherein R3, R4, Rs, and Re are each the same.

10. An iridium complex of formula (I) according to any one of the preceding claims, wherein R? and Rs are independently selected from the group consisting of hydrogen atom, substituted and unsubstituted C1-C20 straight-chain alkyl, substituted and unsubstituted C3-C20 branched-chain alkyl, substituted and unsubstituted C3-C20 cycloalkyl, substituted and unsubstituted C1-C20 alkoxy, substituted and unsubstituted C4-C20 aryl, and substituted and unsubstituted C4-C20 heteroaryl wherein the heteroatoms are independently selected from sulfur, nitrogen and oxygen.11 . An iridium complex of formula (I) according to any one of the preceding claims, wherein R? and Rs are each independently selected from the group consisting of hydrogen atom, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl (e.g. n- pentyl or neopentyl), hexyl, heptyl, octyl, nonyl, decyl, dodecyl, stearyl, methoxy, ethoxy, iso-propoxy, and tert-butoxy, preferably hydrogen atom and methyl.

12. An iridium complex of formula (I) according to any one of the preceding claims, wherein R? and Rs are the same.

13. An iridium complex of formula (I) according to any one of the preceding claims, whereinR? and Rs are linked to form a ring structure.

14. An iridium complex of formula (I) according to claim 1 , wherein the N-N ligand of formula(II) is selected from the group consisting of:

15. An iridium complex of formula (I) according to any one of the preceding claims, wherein X is a coordinated anionic ligand or a non-coordinated ligand.

16. An iridium complex of formula (I) according to any one of the preceding claims, wherein X is a halo group, an acetate group, an alkoxy group, a carboxylate group, or an acetoxy group.

17. An iridium complex of formula (I) according to any one of the preceding claims, wherein X is F Cl, Br, or I, preferably Cl.

18. An iridium complex of formula (I) according to any one of the preceding claims, Yi and Y2 may each independently be a compound of formula (III):wherein,Rxand Ryare each independently a hydrogen atom or a C1-C10 carbon containing group.

19. An iridium complex of formula (I) according to any one of the preceding claims, wherein Y1 and Y2 are each cyclooctene.

20. An iridium complex of formula (I) according to any one of the preceding claims, which is one or more selected from the group consisting of:21 . An iridium complex of formula (I) according to any one of the preceding claims, wherein the iridium complex of formula (I) is present as a dimeric species having formula (lb):wherein, Ri, R2, R3, R4, Rs, Re, R7, Rs, Y1, and Y2 are as defined in any one of claims 1 to 20, and wherein X is a coordinating anionic ligand as defined in any one of claims 15 to 17.

22. A process for preparing a boronic ester using an iridium complex of formula (I) as defined in any one of claims 1 to 21 .

23. A process for preparing a boronic ester the process comprising the steps of: contacting an organic substrate and a borylation agent to form a reaction mixture; and reacting the organic substrate and the borylation agent in the presence of an active borylation catalyst to form a boronic ester of the organic substrate, wherein the active borylation catalyst is prepared from an iridium complex of formula (I) as defined in any one of claims 1 to 21 .

24. A process according to claim 22 or claim 23, wherein the reaction mixture further comprises a non-nucleophilic base.

25. A process for preparing the iridium complex of formula (I) according to any one of claims 1 to 21 , the process comprising the steps of:reacting an N-N ligand of formula (II) with an iridium pre-cursor to produce the iridium complex of formula (I),wherein Ri-Rs are as defined in relation to the iridium complex of formula(l) of any one of claims 1 to 21.

26. A process according to claim 25, wherein the iridium pre-cursor is [lrCI(COE)2]2.

27. A process according to claims 26, wherein the process further comprises the step of: exchanging the COE ligands with a ligand Yi and / or Y2 to produce the iridium complex of formula (I), wherein Y1 and Y2 are each independently a compound of formula (III) as defined in claim 18.

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