Coating composition comprising an autoxidizable resin and drier comprising a transition metal and ligand

Abstract

The invention relates to a coated substrate and to a coating composition comprising an autoxidizable binder; a transition metal M selected from iron, cerium, manganese and vanadium; and a ligand A, wherein ligand A is of general formula (I) wherein X is a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; n and m are each independently 0, 1 or 2; R1 and R2 are each independently a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S; and R3 and R4 are each independently hydrogen, alkyl, hydroxyl, alkoxyl, aryl or a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S; R5 and R6 are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

Description

[0001] COATING COMPOSITION COMPRISING AN AUTOXIDIZABLE RESIN AND DRIER COMPRISING A TRANSITION METAL AND LIGAND

[0002] Field of the Invention

[0003] The present invention relates to driers for autoxidisable resins, such as alkyds. In particular, the present invention concerns a coating composition comprising an autoxidizable resin, a transition metal and a ligand.

[0004] Background of the Invention

[0005] Autoxidizable resins are well-known in the coatings industry. Alkyd resins are an example of autoxidizable resins. Other examples of autoxidizable resins are resins comprising unsaturated ether groups, for example resins comprising allyl ethers, cyclopentenylethers and vinyl dioxolanes, and polymers or copolymers of butadiene.

[0006] Alkyd resins are widely used in coating compositions such as paint. An alkyd is a fatty acid functionalized polyester resin that comprises unsaturated fatty acids, such as for example oleic acid, linoleic acid, or linolenic acid. Drying of paints comprising autoxidizable resins comprises evaporation of the liquid carrier (organic solvent and / or water) and, subsequently, hardening of the resin via radical autoxidation reactions. The latter is known as chemical or oxidative drying. The fatty acid moieties of the alkyd resin react with oxygen from the atmosphere to form hydroperoxides which subsequently decompose to form free radicals. Recombination of these free radicals causes covalent bonds to be formed between the alkyd polymer chains, thus forming cross-links between polymer chains. In this way, a liquid coating composition that comprises alkyd resin hardens to form a solid cured coating. This process is also referred to as autoxidation or oxidative drying.

[0007] Paints comprising alkyd resins typically form a hard, glossy surface that is easy to clean and resists scratching, water, and chemicals. They are primarily used for trim, doors, cabinets, furniture, floors, and other high-use areas, and are popular with professional painters because they adhere well to most surfaces and “level out” to hide brush marks and small surface irregularities, and cure to a smooth surface that latex paints cannot match.

[0008] The time required for alkyd resin-based coating to dry depends on the concentration and type of unsaturated oil or fatty acids used to prepare the resin. Autoxidation and crosslinking of the unsaturated fatty acid component can proceed unaided, but the time for drying is generally found to be unacceptably long for many practical purposes. The reactions are significantly accelerated by the presence of a metal-based drying catalyst, commonly referred to as a "drier" or “siccative”. Whereas an alkyd resin-based coating may take months to dry in the absence of a drying catalyst, in the presence of such catalyst, drying can be accomplished within a much shorter time.

[0009] Well-known driers include salts containing cobalt (Co), cerium (Ce), iron (Fe), manganese (Mn) and vanadium (V) as the cation; and halides, nitrates, sulphates, and carboxylates such as acetates, ethylhexanoates, octanoates, neodecanoates, and naphthenates, or acetoacetonates, as the anion. The catalytic activity of the polyvalent metal during decomposition of the (hydro)peroxide relies on the repeated transition of the metal ion from the lower to the higher oxidation state and back again, leading to reduction and oxidation of the hydroperoxides to catalyze and accelerate oxidation of the unsaturated oil component of the composition. For this reason, transition metals are commonly employed in such driers, since transition metals are capable of switching from a lower valence state to a higher valence state in a redox reaction with fatty acid peroxides present in the alkyd.

[0010] Three different types of driers have been identified (WO2012079624; Soucek et al Prog. Org Chem. 73, (2012) pp 435-454). Primary driers, also referred to as top driers, surface driers or oxidation driers, promote the top-down hardening of a liquid alkyd resin. The mode of action of primary driers in the autoxidative curing process is deactivation of naturally occurring anti-oxidants, oxygen uptake, peroxide formation and peroxide decomposition. Primary driers are characterized by having at least two accessible valence states which allow catalytic hydroperoxide decomposition and regeneration of the active species. Examples of primary driers are cobalt (Co), cerium (Ce), iron (Fe), manganese (Mn) and vanadium (V) salts and / or complexes. To enhance homogeneous through drying of a coating film, and to improve appearance and quality of the resulting coating film, primary driers are frequently used in combination with auxiliary and coordination driers.

[0011] Coordination driers, also referred to as through driers, promote the film-forming process by interaction with the carboxyl and hydroxyl groups in the polymeric binder. Thus, coordination driers can bridge two or more polymer chains. These carboxyl and hydroxyl groups may be initially present in the binder molecule or formed during the autoxidation process. This group comprises the metal driers based on zirconium (Zr), strontium (Sr), aluminum (Al), bismuth (Bi), lanthanum (La), neodymium (Nd), lead (Pb), and barium (Ba).

[0012] Auxiliary driers, also known as promoters or sacrificial driers, are metal driers that exist in a single oxidation state and are not catalytically active by themselves. Auxiliary driers affect the drying rate by interacting with the primary driers. They include calcium (Ca), zinc (Zn), potassium (K) and lithium (Li) metal soaps.

[0013] The most widely used primary driers are cobalt carboxylates because of their good drying performance at ambient temperature and coloristic properties. However, their use is commonly restricted by health regulations and their presence can require labelling as a suspected carcinogen. Primary driers based on non-cobalt metals, in particular primary driers comprising complexes of iron or manganese and nitrogen-donor ligands are known. In J.W de Boer et al., The quest for Cobalt-Free Alkyd Paint Driers, Eur. J. Inorg. Chem, 2013, 3581-3591, an overview of such driers is given.

[0014] W008003652 describes an alkyd paint with a drier comprising an iron or manganese complex of a tetra-, penta- or hexadentate nitrogen-donor ligand, wherein at least one nitrogen-donor is part of a tertiary amine. Ligands are described as bispidon, tertiary amines with substituents selected from aminoalkyl or heteroaryl, 1,4,7-triazacyclononane with one or more pendent nitrogen groups; cyclam (cyclic amine) cross-bridged ligands; and trispicen.

[0015] WO1 7103620 describes an alkyd resin formulation comprising a chelant capable of binding to a transition metal such as iron or manganese through either three or four nitrogen atoms. A recurring feature of the ligands is that a nitrogen-donor is part of a tertiary amine group. US20220073701 describes an oxidatively curable coating composition comprising an alkyd resin and bispidon ligand or chelant.

[0016] Honzicek et al. have described the catalytic properties of benzoylferrocene, as a representative of cobalt-free drier, with soybean oil (Honzicek et al J. Applied Polymer Science, 2018, Volume135, Issue16, 46184 https: / / doi.org / 10.1002 / app.46184).

[0017] Erben et al. discuss several acyl-substituted ferrocenes as driers for solvent-borne alkyd paints. They describe the drying behavior of acyl-substituted ferrocenes [Fe(Cp)(q5- C5H4COCH3)], [Fe(Cp)(n5-C5H4COCF3)], [Fe(Cp)(n5-C5H4COPh)], [Fe(n5-C5H4COCH3)2], [Fe(o5-CsH4COCF3)2], and [Fe(o5-CsH4COPh)2] and compare these with a commercial cobalt(ll) paint drier (Co Nuodex®) and unsubstituted ferrocene in a solvent-borne phthalic type alkyd resin modified with tall oil. Final relative hardness and drying time were recorded for each system. Substituted ferrocenes were more effective than the commercial cobalt Nuodex® drier. Unsubstituted ferrocene showed a negligible activity toward alkyd resin autoxidation (M. Erben et al. Journal of Molecular Catalysis A: Chemical 353- 354 (2012) 13- 21).

[0018] W02021001410 describes a drier composition comprising an iron-ligand complex with a first ligand which is a cyclopentadienyl group and a second ligand which is other than cyclopentadienyl, wherein the molar ratio of iron cation to cyclopentadienyl group is 1 :1. Example ligands are r^-CeH? and dicarbonyl compounds.

[0019] The issues with respect to drying of alkyd-based paints, as described above, equally apply to other autoxidizable coatings.

[0020] There is a need for autoxidizable coating compositions with a cobalt-free drier that result in a cured coating having sufficient hardness and drying time.

[0021] Summary of the Invention

[0022] It has now been found that a drier composition comprising a ligand A and a transition metal M can be used with an autoxidizable binder to prepare a coating composition having a sufficiently short drying time and sufficient hardness. Accordingly, in one embodiment, the present invention provides a coating composition comprising an autoxidizable binder; a transition metal M, selected from iron, cerium, manganese and vanadium; and a ligand A, wherein ligand A is of general formula (I): wherein

[0023] X is a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; n and m are each independently 0, 1 or 2;

[0024] R1and R2are each independently a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; and R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl, aryl or a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; and

[0025] R5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

[0026] A particularly well-performing drier composition is one wherein the transition metal M is part of a metal-ligand complex [M-Ly]zwherein M is iron; a first ligand L is a substituted or unsubstituted cyclopentadienyl group; and z is 0. In a second embodiment, the present invention provides a coating composition comprising an autoxidizable binder; a metalligand complex [M-Ly]zwherein M is iron; a first ligand L is a substituted or unsubstituted cyclopentadienyl group; and z is 0; and a multidentate nitrogen-donor ligand.

[0027] In a third embodiment, the present invention provides a coated substrate comprising a substrate and a coating, which coated substrate is obtainable by applying a coating composition as defined herein to the substrate and allowing the coating composition to dry. Detailed Description

[0028] A ligand is an ion or molecule that binds to a central metal ion to form a coordination complex. The bonding with the metal ion generally involves formal donation of one or more of the ligand's electron pairs.

[0029] As used herein, an alkyl radical may be branched, unbranched, linear or cyclic. The alkyl radical may be saturated or unsaturated. It may be unsubstituted or substituted. An alkyl radical typically contains from 1 to 40 carbon atoms, in particular 1 to 20 carbon atoms, 1 to 12 carbon atoms, 1 to 6 carbon atoms or 1 to 4 carbon atoms. An alkyl radical may contain from 1 to 3 carbon atoms, for example 1, 2 or 3 carbon atoms. Examples of alkyl radials are methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, isobutyl, hexyl, lauryl, oleyl and cyclohexyl.

[0030] An alkoxyl radical is a group -OR, wherein R is an alkyl radical as defined above.

[0031] An aryl group is an aromatic group having a single ring or multiple rings and comprising only carbon and hydrogen atoms. Typically, it is phenyl, naphthalenyl, biphenyl, fluorenyl, anthracenyl or phenanthrenyl. Preferably it is phenyl or naphthalenyl. It may be substituted or unsubstituted. Substituents may comprise atoms other than carbon and hydrogen. Preferably it is unsubstituted.

[0032] An arylalkyl group is an alkyl group as defined herein, wherein at least one hydrogen atom is replaced with an aryl group as defined above. Examples include benzyl, phenethyl and dibenzylmethyl.

[0033] A heterocyclic group may be aromatic, i.e. a heteroaryl, or non-aromatic, i.e. aliphatic. Typical heteroatoms are N, O and S. A heterocyclic group may be substituted or unsubstituted. A heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S may be aromatic or aliphatic. It may be substituted or unsubstituted. Preferably it is unsubstituted. Suitable groups include furanyl, tetrahydrofuranyl, thiophenyl, pyrrolyl, pyrazolyl, pyrrolidinyl, pyranyl, pyridinyl, piperidinyl, imidazolyl, thiazolyl, pyrazinyl, benzimidazolyl, pyrimidinyl, triazolyl, thiazolyl, dioxanyl, morpholinyl, 1,2-oxathiolanyl, isoxazolyl, oxazolyl, thiadiazinyl, dithiaazinyl, tetrahydro-azepinyl, thiazepinyl, azocinyl, quinolinyl, isoquinolinyl and purinyl. Typically a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S is a heterocyclic group containing one or two heterotoms selected from N, O and S. Examples include pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, pyrazinyl, benzimidazolyl, pyrimidinyl, thiazolyl and pyridinyl. Preferably, it contains one or two nitrogen atoms. Most preferably, a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S is pyridinyl.

[0034] A heterocyclic group that is capable of coordinating to a transition metal through at least one of the heteroatoms means the heteroatom formally donates one or more electron pairs to the transition metal. A group containing a heteroatom that is capable of coordinating to a transition metal through at least one of the heteroatoms means that the heteroatom formally donates one or more electron pairs to the transition metal.

[0035] As used herein, the term substituted means that one or more hydrogen atoms on a group is replaced with an alternative atom or group. Common groups replacing a hydrogen atom in substitution include hydroxyl, alkyl, alkoxyl, carboxyl, aryl, heteroaryl, amino, halogen; in particular hydroxyl, Ci-Ce alkyl, Ci-Ce alkoxyl or halogen.

[0036] In general formula (I), n and m are each independently 0, 1 or 2. Typically they are each 0 or 1 . Both n and m may be 0 or 1. Preferably they are both 0.

[0037] In one embodiment, X is pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl. Typically, X is a pyridinyl group. Preferably, X is a 2-6-pyridinyl group.

[0038] In one embodiment, each of R1and R2are independently pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl. Typically, each of R1and R2are a pyridinyl group, more preferably a 2-pyridinyl group. Preferably, R1and R2are identical. R1and R2are each independently optionally substituted with alkyl, aryl, arylalkyl.

[0039] In one embodiment R3and R4are each hydrogen, C1-6 alkyl, hydroxyl, C1-6 alkoxyl, pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl. Typically, each of R3and R4are a pyridinyl group, more preferably a 2-pyridinyl group. Preferably, R3and R4are identical. R3and R4are each independently optionally substituted with alkyl, aryl, arylalkyl. Typically, R1, R2, R3and R4are each identical. Typically, each of R1, R2, R3and R4are pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl. Preferably, each of R1, R2, R3and R4are a pyridinyl group, more preferably a 2- pyridinyl group.

[0040] Typically, R5and R6are each independently hydrogen, C1-6 alkyl, hydroxyl or C1-6 alkoxyl. More preferably, R5and R6are each independently hydroxyl or C1-4 alkoxyl, preferably hydroxyl. R5and R6may be the same or different. Most preferably both R5and R6are hydroxyl.

[0041] In one embodiment, ligand A is of general formula (II): wherein R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl or a heterocyclic group containing one, two or three heteroatoms selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; and

[0042] R5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

[0043] Accordingly, in one embodiment, the present invention provides a coating composition comprising an autoxidizable binder; a transition metal M selected from iron, cerium, manganese and vanadium; and a ligand A, wherein ligand A is of general formula (II),

[0044] wherein R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl or a heterocyclic group containing one, two or three heteroatoms selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; and

[0045] R5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

[0046] In one embodiment, ligand A is of formula (III):

[0047] The compound of formula (III) has the name pyridine-2,6-diylbis [di(pyridin-2- yl)methanol].

[0048] Transition metal M is selected from iron, cerium, manganese and vanadium. In one embodiment, the transition metal M is iron or manganese. Typically, the transition metal M is iron. Transition metal M may be part of a complex with ligand A, or it may be part of a salt or part of a complex with ligand(s) other than A. In one embodiment, the transition metal M is part of a transition metal-ligand complex, [M-Ly]z, wherein each ligand L is independently a mono, bi- or multi-dentate ligand; y is an integer of from 1 to 6; and z is a charge of -3, -2, -1 , 0, 1 , 2 or 3. Z is typically 1 , 0 or -1 ; preferably 0. Depending on the identity of the transition metal, transition metal M may have an oxidation state of 0, 1 , 2, 3 or 4. Typically, transition metal M has an oxidation state of 2, 3 or 4. For example, if transition metal M is iron it may have an oxidation state of 2 or 3. If transition metal M is manganese it may have an oxidation state of 2, 3 or 4.

[0049] Typically in the transition metal-ligand complex [M-Ly]z, M is iron; and a first ligand L is a substituted or unsubstituted cyclopentadienyl group. Typically z is 0 or +1. Preferably only one ligand L is cyclopentadienyl. Further ligands L may be the same or different and may be any suitable ligand as described herein. Further ligand(s) L are each typically independently aryl, e.g. benzene; cyclic alkadiene, e.g. 1,3-cyclohexadiene; carbon monoxide or a halide ion. [M-Ly]zmay therefore be [CpFe-Ly.i]z.

[0050] In one embodiment the present invention provides a coating composition comprising an autoxidizable binder; a transition metal M selected from iron, cerium, manganese and vanadium; and a ligand A, wherein ligand A is of general formula (I): wherein

[0051] X is a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; n and m are each independently 0, 1 or 2;

[0052] R1and R2are each independently a heterocyclic group containing one, two or three heteroatoms are each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl, aryl or a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; and

[0053] R5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl; and wherein the transition metal M is part of a transition metal-ligand complex, [M-Ly]z, wherein M is iron; each ligand L is independently a mono, bi- or multi-dentate ligand, of which a first ligand L is a substituted or unsubstituted cyclopentadienyl group; y is an integer of from 1 to 6; and z is a charge of -3, -2, -1 , 0, 1 , 2 or 3.

[0054] As used herein, Cp means cyclopentadienyl or r^-CsHs.

[0055] In one embodiment, the transition metal-ligand complex [M-Ly]zis a complex of general formula (IV): or a complex of general formula (V): wherein: p is an integer with a value of 1 , 2 or 3; q is an integer with a value of 0, 1 or 2;

[0056] R9is, independently, hydrogen, alkyl or aryl; and L is a mono-, bi- or multi-dentate ligand. Typically q is 0 or 1. Preferably q is 1.

[0057] Typically each L in general formulae (IV) or (V) is other than a cyclopentadienyl group. Preferably, each L is independently, carbon monoxide (CO), a halide ion, alkyl, aryl, sulfide, thiocyanate, nitrate, azide, hydroxide, oxalate, water, nitrite, isothiocyanate, acetonitrile, pyridine, an alkyl-substituted pyridine, ammonia, ethylenediamine, 2,2’- bipyridine, 1 ,10-phenanthroline, a phosphine (e.g. triphenylphosphine, trimethylphosphine, triethylphosphine benzene, 1 ,2-Bis(diphenylphosphino)ethane (dppe), 1 ,1-bis(diphenylphosphino)methane (dppm)), cyanide, isocyanide, persistent carbene, N-heterocyclic carbene, acetylacetonate, or hydride. More preferably, each L is, independently, selected from carbon monoxide (CO), halide, alkyl, aryl, sulfide, thiocyanate, nitrate, azide, hydroxide, oxalate, water, nitrite, isothiocyanate, acetonitrile, pyridine, ammonia, ethylenediamine, 2,2’-bipyridine, 1 ,10-phenanthroline, triphenylphosphine, trimethylphosphine, triethylphosphine, cyanide, and hydride. Most preferably, each L is independently aryl, e.g. benzene; cyclic alkadiene, e.g. 1 ,3- cyclohexadiene; carbon monoxide or a halide.

[0058] Typically each R9is independently hydrogen, C1-12 alkyl or aryl. The aryl radical may be a polycyclic radical, such as an indenyl radical. The radicals may comprise a heteroatom, such as an oxygen atom. Preferably, the substituent radicals are free of hereoatoms and only comprise carbon and hydrogen atoms. More preferably, the cyclopentadienyl group is unsubstituted cyclopentadienyl; in other words more preferably, each R9is hydrogen. Preferably, the transition metal-ligand complex [M-Ly]zis cyclopentadienyliron(ll) dicarbonyl dimer, cyclopentadienyliron dicarbonyl halide wherein the halide is iodide, bromide or chloride, or r -CsHs Fe(ll) n5-C6H7.

[0059] The iron cation in the iron-ligand complex of general formula (IV) or general formula (V) may have any oxidation state. For example it may be iron(l), iron(ll) or iron(lll). Typically the iron cation is iron(ll) or iron(lll); preferably it is iron(ll).

[0060] In the coating composition, the amount of iron cation comprised in the iron-ligand complex is preferably in the range of from T 10'4wt.% to 1 .0 wt.%, based on the weight of autoxidizable binder. More preferably the amount of iron cation comprised in the iron- ligand complex is in the range of from T 10'3wt.% to 0.1 wt.%, even more preferably of from 0.005 wt.% to 0.05 wt.%. Reference herein to the weight of autoxidizable binder is to the non-volatile weight (often referred to as solid weight) of the autoxidizable binder. Solid weight of autoxidizable binders can suitably be determined according to ISO 3251 :2008 wherein a sample is dried at 105 °C for 60 minutes.

[0061] The iron-ligand complex may be a double sandwich structure such as a TT-arene bis((TT- cyclopentadienyl)iron) ion such as described in structures I - XV by Morrison et al (Morrison et al, 1974, Journal of the American Chemical Society 96:11 pp 3603 - 3608). Combinations of different iron-ligand complexes may be used.

[0062] In case the iron-ligand complex is positively charged, i.e. q is 1 or 2 in Formula (IV), a counter ion is present. The counter ion is in principle not critical. It may be a mono-anion or a di-anion. The type of counter ion may be used to tune the solubility of the iron ligand complex in different solvents. Preferably, the counter ion is a mono-anion selected from PFe’, SbFe', BF4; E^CeFs)', Cl B', I NOa', and carboxylates R'COO' wherein R' is a C1-20 alkyl optionally substituted with heteroatoms; or SC>42'. Preferably the anion is a carboxylate selected from acetate, ethylhexanoate, octanoate, neodecanoate, naphthenate, and acetoacetonate.

[0063] A particularly suitable iron-ligand complex according to general Formula (IV) is cyclopentadienyliron dicarbonyl halide, i.e. a complex of Formula (IV) wherein the cyclopentadienyl group is unsubstituted (all R9groups are hydrogen) with three (m is 3) further ligands L of which two are CO ligands and one is a halide ligand selected from chloride, bromide and iodide. In this complex n is 0. Dicarbonyl cyclopentadienyliron dicarbonyl iodide is especially preferred.

[0064] The iron-ligand complex according to general formula (IV) may be of the following general formula (VI): wherein each R8is, independently, hydrogen, alkyl or aryl; and each R9is independently hydrogen, alkyl or aryl.

[0065] Typically each R8is a hydrogen, C1-12 alkyl or aryl. The aryl radical may be a polycyclic radical, such as an indenyl radical. The radicals may comprise a heteroatom, such as an oxygen atom. Preferably, the substituent radicals are free of hereoatoms and only comprise carbon and hydrogen atoms. More preferably, each R8is hydrogen.

[0066] Typically each R9is a hydrogen, C1-12 alkyl or aryl. The aryl radical may be a polycyclic radical, such as an indenyl radical. The radicals may comprise a heteroatom, such as an oxygen atom. Preferably, the substituent radicals are free of hereoatoms and only comprise carbon and hydrogen atoms. More preferably, the cyclopentadienyl group is unsubstituted cyclopentadienyl; in other words more preferably, each R9is hydrogen.

[0067] A particularly suitable iron-ligand complex according to general Formula (VI) is r^-CsHs Fe(ll) n5-C6H7, i.e. each R8and each R9groups are an H atom.

[0068] A particularly suitable iron ligand complex of general Formula (V) is cyclopentadienyliron dicarbonyl dimer, i.e. a complex of Formula (V) wherein the cyclopentadienyl group is unsubstituted (all R9groups are hydrogen) and all four further ligands L are CO.

[0069] A multidentate nitrogen-donor ligand is an organic structure which will support coordination to a metal through more than one atom, at least one of which must be a nitrogen atom. Typically it is a bidentate, tridentate, tetradentate, pentadentate or hexadentate nitrogen-donor ligand. Preferably, all coordination to the metal atom is through a nitrogen atom.

[0070] Typically, the multidentate nitrogen donor ligand is a bispidon-type ligand, a TACN-type ligand, an N4Py-type ligand, a cyclam ligand or a trispicen-type ligand.

[0071] A bispidon-type ligand is a ligand of general formula (VII) wherein

[0072] R10and R11are each independently alkyl, aryl, alkylaryl or a group containing one or two heteroatoms capable of coordinating to a transition metal;

[0073] R12and R13are each independently hydrogen, alkyl, alkyl-O-alkyl, alkyl-O-aryl, aryl, hydroxyalkyl, -(CH2)rC(O)OR16, wherein R16is hydrogen, alkyl, aryl, halogen, alkoxyl, haloalkyl and haloalkoxyl, hydroxyalkyl, alkyl-O-alkyl, alkyl-O-alkyl-O-alkyl, alkyl-O-aryl or alkylaryl and r is from 0 to 4;

[0074] R14and R15are each independently hydrogen, halogen, hydroxyl, alkoxyl, -NH-C(O)-H, - NH-C(O)-alkyl, -NH2, -NH-alkyl and alkyl;

[0075] Y is -C(O)-, a ketal derivative of -0(0)-, a hemiketal derivative of -0(0)-, a thioketal derivative of -0(0)-, or -(C(R17)2)t-; wherein each R17is independently hydrogen, hydroxyl, alkoxyl, -O-benzyl, -O-(C=O)-alkyl and alkyl; and each t is independently selected from 0, 1 , 2 or 3.

[0076] In one embodiment, R10and R11are each independently Ci-24-alkyl, Ce- -aryl or a group containing a heteroatom capable of coordinating to a transition metal. Preferably the group contains one or two heteroatoms, for example selected from N, O and S.

[0077] Preferably, R10and R11are each independently methyl, ethyl, propyl, benzyl, butyl, hexyl, octyl, dodecyl and pyridine-2-yl; more preferably, at least one of R10and R11is pyridine- 2-ylmethyl or benzyl, preferably pyridine-2-yl methyl.

[0078] In one embodiment, R12and R13are each independently hydrogen, Ci-s-alkyl, Ci-s-alkyl- O-Ci-8-alkyl, Ci-s-alkyl-O-Ce- -aryl, Ce- -aryl, Ci-8-hydroxyalkyl, or -(CH2)rC(O)ORi6, wherein Rie is hydrogen, Ci-4-alkyl. Preferably, R12and R13are each independently - C(O)-OCH3-C(O)-O-CH2CH3 or -CFWH. More preferably, R12and R13are identical.

[0079] In one embodiment, Y is -C(O)- or -(C(R17)2)t-; wherein each R17is independently hydrogen, hydroxyl, Ci-4-alkoxyl and Ci-4-alkyl. Preferably, Y is -C(O)- or -C(OH)2-.

[0080] Preferably R12is identical to R13.

[0081] Preferably t is 0 or 1 ; more preferably t is 0.

[0082] Example bispidon ligands include dimethyl 2,4-di-(2-pyridyl)-3-methyl-7-(pyridin-2- ylmethyl)-3,7-diaza-bicyclo[3.3.1]nonan-9-one-l,5-dicarboxylate; 2,4-di-(2-pyridyl)-3- methyl-7-(pyridin-2-ylmethyl)-3,7-diaza-bicyclo[3.3.1]nonan-9-one-1 ,5-dicarboxylate (N2Py3o-C1) and dimethyl 2,4-di-(2-pyridyl)-3-methyl-7-(N,N-dimethyl-amino-ethyl)-3,7- diaza-bicyclo[3.3.1]nonan-9-one-1.

[0083] In one embodiment, the bispidon-type ligand is a compound of formula (VIII) or (IX):

[0084] Preferably, the bispidon-type ligand is present in the form of [Fe-ligand-Ch], [Fe-ligand- CIJCI, [Fe-ligand-(H2O)](PF6)2, [Fe-ligand]CI2, [Fe-ligand-CI]PF6or [Fe-ligand- (H2O)](BF4)2. Preferably, the bispidon-type ligand is present in the form [Fe-ligand-CI2], [Fe-ligand-CI]CI, [Fe-ligand]CI2or [Fe-ligand-(H2O)](BF4)2. Preferably, the bispidon-type ligand is a compound of formula (VIII) present in the form of [Fe-ligand-CI]CI.H2O, also the active component in Borchi®Oxy Coat, also defined as CAS no. 478945-46-9. A TACN-type ligand is a ligand comprising a 1 ,4,7-triazacyclononanyl group in which at least one nitrogen atom is capable of donating to a transition metal M. In one embodiment a TACN-type ligand is a compound of general formula (X): wherein each R18is independently alkyl, cycloalkyl, heterocycloalkyl, heteroaryl, aryl, arylalkyl or alkylaryl optionally substituted with one or more substituents selected from hydroxyl, alkoxyl, phenoxyl, carboxylate, carboxamide, carboxylic ester, sulfonate, amine, alkylamino and -N+(R19)3; wherein each R19is independently hydrogen, alkyl, alkenyl, arylalkyl, arylalkenyl, alkoxy, alkenyloxy, aminoalkyl, aminoalkenyl, alkylether, alkenylether or -CR20R21; wherein each R20is independently hydrogen or alkyl; each R21is independently an optionally substituted heteroaryl group and wherein at least one of R19is a - CR20R21.

[0085] Typically each R21is independently optionally substituted pyridinyl, pyrimidinyl, pyrazinyl, triazolyl, pyridazinyl, 1 ,3,5-triazinyl, quinolinyl, isoquinolinyl, quinoxalinyl, imidazolyl, pyrazolyl, benzimidazolyl, thiazolyl, oxazolidinyl, pyrrolyl, carbazolyl, indolyl or isoindolyl. Preferably R21is optionally substituted pyridine-2-yl, imidazole-4-yl, pyrazol-l-yl, quinoline-2-yl groups. Most preferably R20is either a pyridine-2-yl or a quinoline-2-yl. Preferably it is unsubstituted or is substituted by alkyl.

[0086] Preferably a TACN-type ligand is 1 ,4,7-trimethyl-1 ,4,7-triazacyclononane.

[0087] A N4Py-type ligand is typically of general formula (XI): wherein each R22and each R23is independently a group -R25-R26;

[0088] R24is hydrogen, alkyl, aryl, arylalkyl, or a group -R25-R26; each R25is independently a single bond or an alkyl-substituted alkylene, alkenylene, oxyalkylene, aminoalkylene, alkenylether, carboxylic ester or carboxylic amide; and each R26is independently an optionally N-alkyl-substituted aminoalkyl group or an optionally alkyl-substituted heteroaryl group, selected from pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl; thiazolyl; pyridazinyl; 1 ,3,5- triazinyl; quinolinyl; isoquinolinyl; quinoxalinyl; oxazolidinyl; carbazolyl; indolyl; and isoindolyl.

[0089] Preferably R23represents pyridin-2-yl or R22represents pyridin-2-yl-methyl. Preferably R22or R23represents 2-amino-ethyl, 2-(N-(m)ethyl)amino-ethyl or 2-(N,N- di(m)ethyl)amino-ethyl. R24is preferably hydrogen, benzyl or methyl. If substituted, R26preferably represents 3-methyl pyridine-2-yl.

[0090] The preferred N4Py ligands are N,N-bis(pyridin-2-yl-methyl)-bis(pyridine-2- yl)methylamine) which is disclosed in WO95 / 34628; MeN4Py (i.e. N,N-bis(pyridine-2-yl- methyl-l,l-bis(pyridine-2-yl)-l-aminoethane and BzN4Py (N,N-bis(pyridin-2-y|-methyl-1 , 1- bis(pyridin-2-y|)-2-pheny|-1 -aminoethane), as disclosed in EP0909809.

[0091] A cyclam ligand is typically of general formula (XII): wherein: each Z is independently -N(R27)-[C(R28)2-C(R28)2]- or -N(R27)-[C(R28)2-C(R29)2-C(R30)2]-; u is 4; each R27is independently hydrogen, alkyl, -CH2CH2OH, pyridin-2-ylmethyl and - CH2COOH or one of R27is linked to the N of another Z via an ethylene bridge; and R28, R29and R30are each independently hydrogen, alkyl or alkylhydroxyl.

[0092] A cyclam ligand may be non-cross-bridged or cross-bridged. Examples of non-cross- bridged ligands are 1 ,4, 8,11-tetraazacyclotetradecane (cyclam), 1 ,4,8,11-tetramethyl- 1 ,4,8,11-tetraazacyclotetradecane (Me^yclam), 1 ,4,7,10-tetraazacyclododecane (cyclen), 1 ,4,7,10-tetramethyl-1 ,4,7,10-tetraazacyclododecane (Me4cyclen), and 1 ,4,7,10-tetrakis(pyridine-2-ylmethyl)-1 ,4,7,10-tetraazacyclododecane (Py4cyclen).

[0093] A cross-bridged cyclam ligand is typically of general formula (XIII): wherein each R31is independently hydrogen, alkyl, arylalkyl, alkenyl, alkynyl. Typically, all nitrogen atoms in the macropolycyclic rings are coordinated with the transition metal. Examples include, when each R31is methyl, 5,12-dimethyl-1 ,5,8,12-tetraaza- bicyclo[6.6.2]hexadecane and, when each R31is benzyl, 5,12-dibenzyl-1 ,5,8,12-tetraaza- bicyclo[6.6.2]hexadecane.

[0094] A trispicen-type ligand is typically of formula (XIV):

[0095] R32R32N-W-NR32R32(XIV) wherein:

[0096] W is -CH2CH2-, -CH2CH2CH2- or CH2C(OH)HCH2-; each R32is independently alkyl, cycloalkyl, heterocyclic, aryl, arylalkyl optionally substituted with hydroxyl, alkoxyl, alkoxyl, phenoxyl, carboxylate, caboxamide, carboxylic ester, sulfonate, amine, alkylamine and -N+(R33)3, wherein each R33is independently hydrogen, alkyl, alkenyl, arylalkyl, arylalkenyl, oxyalkyl, oxyalkenyl, aminoalkyl, aminoalkenyl, alkylether, alkenylether or -CR342 R35; each R34is independently hydrogen or methyl, ethyl or propyl; each R35is independently an optionally substituted heteroaryl group selected from pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl, thiazolyl, pyridazinyl, 1 ,3,5-triazinyl, quinolinyl, isoquinolinyl, quinoxalinyl, benzimidazolyl, oxazolidinyl, carbazolyl, indolyl and isoindolyl, and wherein at least two of R32are -CR342 R35. Preferably three of R32are -CR342 R35. The heteroaryl may be connected to the compound via any atom in the ring of the selected heteroaryl.

[0097] Typically, when R32is heterocycloalkyl, it is selected from pyrrolinyl; pyrrolidinyl; morpholinyl; piperidinyl; piperazinyl; hexamethylene imine; 1 ,4-piperazinyl; tetrahydrothiophenyl; tetrahydrofuranyl; 1 ,4,7-triazacyclononanyl; 1 ,4,8,11- tetraazacyclotetradecanyl; 1 ,4,7,10,13-pentaazacyclopentadecanyl; 1 ,4-diaza-7-thia- cyclononanyl; 1 ,4-diaza-7-oxa-cyclononanyl; 1 ,4,7,10-tetraazacyclododecanyl; 1 ,4- dioxanyl; 1 ,4,7-trithia-cyclononanyl; tetrahydropyranyl; and oxazolidinyl.

[0098] The ligand Tpen (i.e. N,N,N’,N’-tetra(pyridin-2-yl-methyl)ethylenediamine) is disclosed in WO97 / 48787. Other suitable trispicens are described in W002 / 077145 and EP1001009. Other multidentate nitrogen-donor ligands known to those in the art may also be used, and these are discussed below. Typically these ligands may be used in pre-formed transition metal complexes, which comprise the multidentate nitrogen-donor ligand.

[0099] A multidentate nitrogen-donor ligand may be a bidentate nitrogen-donor ligand, such as 2,2'-bipyridine or 1 ,10-phenanthroline, both of which are used known in the art as polydentate accelerant ligands in siccative metal driers. Often 2,2’-bipyridine or 1 ,10- phenanthroline are provided as ligands in manganese- or iron-containing complexes. Other bidentate nitrogen-donor ligands include bidentate amine-containing ligands. 2- aminomethylpyridine, ethylenediamine, tetramethylethylene-diamine, diaminopropane, and 1 ,2-diaminocyclohexane.

[0100] A variety of bi- to hexadentate oxygen donor-containing ligands, including mixed oxygen- and nitrogen-containing donor ligands, are also known. A multidentate nitrogen-donor ligand may be a tetradentate diimine of the general formula (XV): R37-C(A1-O)=N-R36-N=C(A2-O)-R37(XV) wherein:

[0101] A1and A2are aromatic groups;

[0102] R36is a divalent organic radical; and each R37is independently a covalently bonded group.

[0103] Such compounds are described in WO 03 / 029371 A1. Further, EP 1382648 describes the use of complexes comprising 1 ,3-diketones (or 1 ,3-diimines) and bidentate diamines, including bipyridine and phenanthroline.

[0104] A variety of metal driers are described in US 2005 / 0245639, including vanadium, manganese, iron, cobalt, cerium and lead complexes, including those containing imidazoles and pyrazoles such as those described in WO 00 / 11090, and aromatic and aliphatic amines.

[0105] Examples of multidentate nitrogen-donor ligands are dimethyl 2,4-di-(2-pyridy|)-3-methyl- 7-(pyridin-2-y|methyl)-3,7-diaza-bicyclo[3.3.1]nonan-9-one-1 ,5-dicarboxylate; dimethyl 2,4-di-(2-pyridyl)-3-methyl-7-(N,N-dimethyl-amino-ethyl)-3,7-diaza-bicyclo[3.3.1]nonan-9- one-1 , 5-dicarboxylate; 5,12-dimethyl-1 ,5,8,12-tetraaza-bicyclo[6.6.2]hexadecane, 5,12- dibenzyl-1 ,5,8,12-tetraaza-bicyclo[6.6.2]hexadecane, N, N-bis(pyridin-2-yl-methyl-1 , 1 - bis(pyridin-2-yl)-1 -aminoethane, and N, N-bis(pyridin-2-yl-methyl-1 , 1 -bis(pyn'din-2-yl)-2- phenyl-1 -aminoethane; N-methyl-tris(pyridin-2-ylmethyl)ethylene-l,2-diamine; N-octyl- tris(pyridine-2-ylmethyl)ethylene-1 ,2-diamine; N-octadecyl-tris(pyridin-2- ylmethyl)ethylene-l,2-diamine; N-methyl-N,N',N'-tris(3-methyl-pyridin-2- ylmethyl)ethylene-1 ,2-diamine; N-ethyl-N,N',N'-tris(3-methyl-pyridin-2-ylmethyl)ethylene-

[0106] 1.2-diamine; N-methyl-N,N',N'-tris(5-methyl-pyridin-2-ylmethyl)ethyl ene-1 ,2-diamine;N- ethyl- N,N',N'-tris(5-methyl-pyridin-2-ylmethyl)ethylene-1 ,2-diamine; N-benzyl-N,N',N'- tris(3-methyl-pyridin-2-ylmethyl)ethylene-1 ,2-diamine; N-benzyl-N,N',N'-tris(5-methyl- pyridin-2-ylmethyl)ethylene-1 ,2-diamine; N-butyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylene-

[0107] 1.2-diamine; N-octyl-N,N',N'-tris(pyridin-2-ylmethyl)ethyl ene-1 ,2-diamine; N-dodecyl- N,N',N'-tris(pyridine-2-ylmethyl)ethylene-1 ,2-diamine; N-octadecyl-N,N',N'-tris(pyridine-2- ylmethyl)ethyl ene-1 ,2-diamine; N-methyl-N,N’,N’-tris(imidazole-2-ylmethyl)- ethylenediamine; N-ethyl-N,N’,N’-tris(imidazole-2-ylmethyl)-ethylenediamine; N,N’- dimethyl-N,N’-bis(imidazole-2-ylmethyl)-ethylenediamine; N-(l-propan-2-ol)-N,N’,N’- tris(imidazole-2-ylmethyl)-ethylenediamine; N-(1 -propan-2-ol)-N , N’, N’-tris(1 -methyl- imidazol-2ylmethyl)-ethylenediamine; N,N-diethyl-N’,N”,N”-tris(5-methyl-imidazol-4- ylmethyl)-diethylenetriamine; N-(3-propan-l-ol)-N,N’,N’-tris(1-methyl-imidazol-2-ylmethyl)- ethylenediamine; N-hexyl-N,N’,N’-tris(imidazole-2-ylmethyl)-ethylenediamine; N-methyl- N,N’,N’-tris(benzimidazol-2-ylmethyl)-ethylenediamine; N-(3-propan-l-ol)methyl-N,N’,N’- tris(benzimidazole-2-ylmethyl)-ethylenediamine; 1,4,8,11-tetraazacyclotetradecane;

[0108] 1 ,4,8,11 -tetramethyl- 1 ,4,8,11-tetraazacyclotetradecane; 1 ,4,7,10- tetraazacyclododecane; 1 ,4,7, 10-tetramethyl-1 ,4,7, 10-tetraazacyclododecane; 1 ,4,7, 10- tetrakis(pyridine-2-ylmethyl)-1 ,4,7,10-tetraazacyclododecane; N,N-bis(pyridin-2-yl- methyl)-bis(pyridine-2-yl)methylamine; N, N-bis(pyridin-2-yl-methyl-1 , 1 -bis(pyridin-2-yl)-l- aminoethane; N,N,N’,N’-tetra(pyridin-2-yl-methyl)ethylenediamine; N-methyl-tris(pyridin- 2-ylmethyl)ethylene-1,2-diamine; N-butyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylene-1,2- diamine; N-octyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylene-1 ,2-diamine; N-dodecyl-N,N',N'- tris(pyridin-2-ylmethyl)ethylene-1,2-diamine; N-octadecyl-N,N',N'-tris(pyridine-2- ylmethyl)ethylene-1 ,2-diamine; N-methyl-N,N',N'-tris(3-methyl-pyridin-2- ylmethyl)ethylene-1 ,2-diamine; N-ethyl-N,N',N'-tris(3-methyl-pyridin-2-ylmethyl)ethylene- 1 ,2-diamine; N-methyl-N,N',N'-tris(5-methyl-pyridin-2-ylmethyl)ethylene-1 ,2-diamine; N- ethyl-N,N',N'-tris(5-methyl-pyridin-2-ylmethyl)ethylene-1,2-diamine; N-methyl-N,N’,N’- tris(imidazol-2-ylmethyl)-ethylenediamine; N,N’-dimethyl-N,N’-bis(imidazol-2-yl-methyl)- ethylenediamine; N-(1-propan-2-ol)-N,N’,N’-tris(imidazole-2-ylmethyl)-ethylenediamine; N-(1-propan-2-ol)- N,N’,N’-tris(1-methyl-imidazol-2-ylmethyl)-ethylenediamine; N-(3- propan-1 -ol)-N , N’, N’-tris(1 -methyl-imidazol-2-yl-methyl)-ethylenediamine; N-hexyl- N,N’,N’-tris(imidazol-2-ylmethyl)-ethylenediamine; N-methyl-N,N’,N’-tris(benzimidazol-2- ylmethyl)-ethylenediamine; N-(3-propan-1-ol)methyl-N,N’,N’-tris(benzimidazol-2- ylmethyl)-ethylenediamine; 1,4-bis(quinoline-Z-ylmethyl)-7-octyl-l,4,7-triazacyclononane;

[0109] 1.4-bis(quinoline-2-ylmethyl)-7-ethyl-1 ,4,7-triazacyclononane; 1 ,4-bis(quinoline-2- ylmethyl)-7-methyl-l,4,7-triazacyclononane; 1,4-bis(pyridyl-Z-methyl)-7-octyl-l,4,7- triazacyclononane; 1 ,4-bis(pyridyl-2-methyl)-7-ethyl-l,4,7-triazacyclononane; 1 ,4- bis(pyridyl-2-methyl)-7-methyl-1 ,4,7-triazacyclononane; 1 ,4-bis(pyrazol-l-ylmethyl)-7- octyl-l,4,7-triazacyclononane; 1,4-bis(pyrazol-1-ylmethyl)-7-ethyl-l,4,7-triazacyclononane;

[0110] 1.4-bis(pyrazol-1-ylmethyl)-7-methyl-l,4,7-triazacyclononane, 3,5-dimethylpyrazol-l- ylmethyl)-7-octyl-1 ,4,7-triazacyclononane; 3,5-dimethylpyrazol-l-ylmethyl)-7-ethyl-l,4,7- triazacyclononane; 3,5-dimethylpyrazol-l-ylmethyl)-7-methyl-1,4,7-triazacyclononane;

[0111] 1.4-bis(1-methylimidazol-2-ylmethyl)-7-octyl-1 ,4,7-triazacyclononane; 1 ,4-bis(1 - methylimidazol-2-ylmethyl)-7-ethyl-1 ,4,7-triazacyclononane; 1 ,4-bis(1-methylimidazol-2- ylmethyl)-7-methyl-1 ,4,7-triazacyclononane; and 1 ,4,7-tris(quinoline-2-ylmethyl)-1 ,4,7- triazacyclononane or 1 ,4,7-tris(pyridine-2-ylmethyl)-1 ,4,7-triazacyclononane.

[0112] The following multidentate nitrogen-donor ligands are preferred: 5,12-dimethyl-1 ,5,8,12- tetraaza-bicyclo[6.6.2]hexadecane; 5,12-dibenzyl-1 ,5,8,12-tetraaza- bicyclo[6.6.2]hexadecane; 1 ,4,8,11 -tetraazacyclotetradecane; 1 ,4,8,11 -tetramethyl- 1 ,4,8,11 -tetraazacyclotetradecane; 1 ,4,7,10-tetraazacyclododecane; 1 ,4,7,10- tetramethyl-1 ,4,7,10-tetraazacyclododecane; 1 ,4,7,10-tetrakis(pyridine-2-ylmethyl)- 1 ,4,7,10-tetraazacyclododecane; N,N-bis(pyridine-2-yl-methy|)-bis(pyridine-2- y|)methylamine; N,N-bis(pyridine-2-yl-methyl-1 ,1-bis(pyridine-2-y|)-1 -aminoethane; N,N- bis(pyridine-2-yl-methyl-1 ,1-bis(pyridine-2-y|)-2-phenyl-1 aminoethane and 1 ,4,7- trimethyl-1 ,4,7-triazacyclononane.

[0113] The multidentate nitrogen-donor ligand may be of general formula (XVI) or (XVII):

[0114] T((CR38)wR39)v (XVI)

[0115] (R39(CR382)W)2T(CR382)WR40-Q-R40(CR382)WT((CR382)WR39)2 (XVI I) wherein: the or each T is N or CR41, wherein R41is selected from hydrogen, optionally alkylsubstituted alkyl, optionally alkyl-substituted alkyl-oxy-alkyl, optionally alkyl-substituted alkyl-oxy-aryl, optionally alkyl-substituted alkyl-O-arylalkyl, optionally alkyl-substituted hydroxyalkyl, optionally alkyl-substituted aryl and optionally alkyl-substituted arylalkyl; w is 0 if T is CR41and w is 1 if T is N; each R38is independently selected from hydrogen, methyl, ethyl and propyl; each R39is independently selected from -CR382N(alkyl)2; -CR382NR42, in which R42and the nitrogen atom N to which it is attached represent a heterocycloalkyl group optionally substituted with one or more alkyl groups, which is connected to the adjacent CR382 moiety through the nitrogen atom N; or represents an optionally alkyl- substituted heteroaryl group selected from pyridin-2-yl, pyrazin-2-yl, quinolin-2-yl, pyrazol-1-yl, pyrazol-3-yl, pyrrol-2-yl, imidazol-2-yl, imidazol-4-yl, benzimidazol-2-yl, pyrimidin-2-yl, 1 ,2,3-triazol-1-yl, 1 ,2,3-triazol-2-yl, 1 ,2,3-triazol-4-yl, 1 ,2,4-triazol-1-yl, 1 ,2,4-triazol-3-yl and thiazol-2-yl; both R40moieties, if present, are independently selected from an optionally alkyl- substituted heteroarylene group selected from pyridin-2,6-diyl, pyrazin-2,6-diyl, quinolin- 2,8-diyl, pyrazol-1 ,3-diyl, pyrrol-2,5-diyl, imidazol-1 ,4-diyl, imidazol-2,5-diyl, pyrimidin-2,6- diyl, 1 ,2,3-triazol-2,5-diyl, 1 ,2,4-triazol-1 ,3-diyl, 1 ,2,4-triazol-3,5-diyl and thiazol-2,4-diyl;

[0116] Q represents a bridge selected from an alkylene moiety, an arylene moiety or a moiety comprising one or two alkylene units and one arylene unit, which bridge is optionally substituted one or more times with independently selected alkyl groups and hydroxyl groups); or the multidentate nitrogen donor ligand may be of formula (XVIII), (XIX) or (XX): wherein: each R44independently is -H2N(alkyl)2, -CH2NR47or an optionally alkyl-substituted heteroaryl group selected from pyridin-2-yl, pyrazin-2-yl, quinolin-2-yl, pyrazol-1 -yl, pyrazol-3-yl, pyrrol-2-yl, imidazol-2-yl, imidazol-4-yl, benzimidazol-2-yl, pyrimidin-2-yl, 1 ,2,3-triazol-1-yl, 1 ,2,3-triazol-2-yl, 1 ,2,3-triazol-4-yl, 1 ,2,4-triazol-1 -yl, 1 ,2,4-triazol-3-yl and thiazol-2-yl); each R43independently represents -R48-R49; each R45and each R46independently is hydrogen, alkyl, aryl, heteroaryl, arylalkyl and heteroarylalkyl, each of which groups may be optionally alkyl-substituted, with the proviso that no R45or R46may be one of the possibilities permitted for R44; each R48independently is optionally alkyl-substituted alkylene; each R49independently is hydrogen, alkyl, optionally alkyl-substituted aryl, optionally alkyl-substituted heteroaryl, optionally alkyl-substituted heteroarylalkyl, CR382N(alkyl)2 group or CR382NR47; each NR47independently represents a moiety in which R47and the nitrogen atom N to which it is attached represent a heterocycloalkyl group optionally substituted with one or more alkyl groups, which is connected to the remainder of the chelant through the nitrogen atom N; and

[0117] Q is a bridge selected from an alkylene moiety, arylene moiety or a moiety comprising one or two alkylene units and one arylene unit, which bridge is optionally substituted one or more times with independently selected alkyl groups and hydroxyl groups).

[0118] The coating composition may comprise a further primary drier comprising a metal selected from vanadium, manganese, iron, and cerium. Preferably, the coating composition does not comprise cobalt and is thus free of a drier comprising cobalt. The coating composition may further comprise coordination driers and / or auxiliary driers. The autoxidizable binder preferably is an alkyd resin. Any autoxidizable alkyd resin may be used. Such alkyd resins are known in the art. The alkyd resin may have any suitable molecular weight, oil length, or unsaturation of its fatty acid chains. The alkyd resin may be present in any suitable amount, depending on the intended use of the coating composition. Typically, the amount of alkyd resin in the coating composition is in the range of from 20 wt% to 95 wt% based on the total weight of the composition, preferably of from 30 to 90 wt%, more preferably of from 35 to 70 wt%.

[0119] The coating composition of the invention may be a solvent-based composition wherein the autoxidizable binder is dissolved in a suitable organic solvent, or an aqueous coating composition wherein the autoxidizable binder is emulsified or dispersed in an aqueous phase. In case the autoxidizable binder is sufficiently liquid at ambient temperature, the coating composition may be a non-aqueous solvent-free coating composition. Preferably, the coating composition is a solvent-based composition comprising an autoxidizable resin, preferably an alkyd, dissolved in an organic solvent. The components of the drier may be added to the coating composition in any suitable form, for example dissolved in an organic solvent, in solid form, or dissolved, dispersed or emulsified in water.

[0120] The coating composition may comprise one or more additives. Any additive known to be suitable for coating compositions with autoxidizable binders, may be used. Examples of suitable additives include UV stabilizers, dispersants, surfactants, anti-static agents, flame-retardant agents, lubricants, anti-foaming agents, anti-oxidants, plasticizers, antifreezing agents, waxes, and thickeners. The amount of any additive will usually be less than 5 wt%, based on the total weight of the coating composition, preferably less than 3 wt%.

[0121] The coating composition may comprise a hindered amine light stabilizer (HALS). A hindered amine light stabilizer is a derivate of 2,2,6, 6-tetramethylpiperidine. Typically a HALS is present in an amount of from 0.05 to 3.0 wt%, preferably of from 0.1 to 2.0 wt.%, based on the weight of the coating composition.

[0122] The coating composition according to the invention may comprise an anti-skinning agent. Anti-skinning agents are known in the art and include phenols, hydroquinones, hydroxylamines, in particular N,N-dialkylhydroxylamines, and oximes. In a coating composition wherein in the transition metal-ligand complex [M-Ly]z, M is iron; a first ligand L is a substituted or unsubstituted cyclopentadienyl group; and z is 0, it is an advantage of the coating composition according to the invention that it shows no or little skin formation in the paint can and thus can be formulated with only a small amount or even without anti-skinning agent. The coating composition according to the invention preferably comprises less than 0.01 wt.%, more preferably less than 0.001 wt.% antiskinning agent; even more preferably is free of an anti-skinning agent.

[0123] The coating composition according to the invention may for example be used as an adhesive, a primer, a topcoat, a high-gloss or a matt coating, a wood coating, a wall paint or a flooring paint. The coating composition may suitably be used to coat any suitable substrate, such as for example wood, wood-based substrates (e.g. fibreboard, chipboard), metal, mineral substrates (e.g. stone, plaster, concrete, masonry, cement, gypsum), plastic substrates, fibre-based substrates, ceramic substrates such as glass, asphalt, leather, paper. The invention is further illustrated by the following non-limiting examples.

[0124] Raw materials

[0125] Components used in the Examples are listed below with the code used in Table 1 in quotation marks.

[0126] “Setal® 270” is an air-drying long oil alkyd resin based on soya bean oil with 70 wt.% alkyd solids, supplied under the name Setal® 270 SM-70 by Allnex.

[0127] “CoNeo” is Cobalt neodecanoate supplied under the name Durham Nuodex® Cobalt 10 Neo by Venator as 10 wt.% Co in solvent.

[0128] “DryCoat” is a Complex of Mn and 1 ,4,7-trimethyl-1 ,4,7-triazacyclononane, supplied under the name Nuodex® DryCoat by Venator as 1 wt.% Mn in solvent.

[0129] “BOC” is a complex of Fe and bispidon ligand, supplied under the name Borchi® OXY- Coat by Borchers as 0.09 wt.% Fe in solvent.

[0130] “MEKO” is methylethylketoxime (an anti-skinning agent), supplied under the name Exkin® 2 from Venator.

[0131] “Fe(acac)3-4” and “Fe(acac)3-1” are respectively 4 wt.% and 1 wt.% solutions in toluene / ethanol 95:5 (v / v) of tris(acetylacetonato)iron(lll), which complex was supplied by Sigma Aldrich.

[0132] “CpFeCh-4” and “CpFeCh-1” are respectively 4 wt% and 1 wt% solution in heptane of q5- C5H5 Fe(ll) n5-C6H7which complexes were prepared according to the method described in Bootsma, J.; Browne, W. R.; Flapper, J.; de Bruin, B. JACS Au 2022, 2, 531-540. “Py5OH" is pyridine-2,6-diylbis [di(pyridine-2-yl)methanol]), 0.5 wt% solution in toluene / ethanol 95:5 (v / v) which compound was prepared according to the method of Goldsmith, C. R.; Stack, T. D. P. Inorg. Chem. 2006, 45, 6048-6055.

[0133] “TPA” is tris(2-pyridinylmethyl)amine, 1 wt% solution in ethyl acetate which compound was prepared following a modified method of Tyeklar, Z.; Jacobson, R. R.; Wei, N.; Murphy, N. N.; Zubieta, J.; Karlin, K. D. J. Am. Chem. Soc. 1993, 115, 2677-2689. A mixture of 2-picolylamine (3 mmol) (98% Fluorochem), 2-(chloromethyl)amine (6 mmol),

[0134] 1-2 mL dichloromethane (DCM) and 12 mL 1M NaOH was stirred vigorously at room temperature for three days. The reaction mixture was extracted using DCM (3x 5mL). The combined organic layers were dried over sodium sulphate, filtered and the solvent evaporated on the rotary evaporator. The product was purified using column chromatography (neutral alumina, 1% NEta in ethylacetate / heptane 1 :1).

[0135] 2-(chloromethyl)amine was obtained by neutralisation of 2-(chloromethyl)pyridine hydrochloride (97%, Fluorochem) using aqueous sodium hydroxide, e.g., 5 mmol 2- (chloromethyl)pyridine hydrochloride was mixed with 6 mL of 1M NaOH (aq) and 15 mL DCM; after shaking the mixture and separating the layers, the organic layer was dried over sodium sulphate, filtered and the solvent evaporated on the rotary evaporator.

[0136] “N4Py” is 1,1-di(pyridine-2-yl)-N,N-bis(pyridine-2-ylmethyl)methanamine, 1 wt.% solution in ethyl acetate and was prepared following a modified method described in Lubben, M.; Meetsma, A.; Wilkinson, E. C.; Feringa, B.; Que Jr., L. Angew. Chem. Int. Ed. 1995, 34, 1512-1514. A mixture of di(pyridine-2-yl)methanamine, 2-(chloromethyl)amine (6 mmol), 1-2 mL DCM and 12 mL 1M NaOH were stirred vigorously at room temperature for three days. The reaction mixture was extracted using DCM (3x 5mL). The combined organic layers were dried over sodium sulphate, filtered and the solvent evaporated on the rotary evaporator. The product was purified using column chromatography (neutral alumina, 1% NEta in ethylacetate / heptane 1 :1).

[0137] Di(pyridine-2-yl)methanamine was obtained according to Unjaroen, D.; Swart, M.;

[0138] Browne, W. R. Inorg. Chem. 2017, 56, 470-479. Preparation of Compositions

[0139] A composition was prepared by adding to 79 weight parts of Setal® 270 SM-70: the amounts of the components listed in Table 1 ; and heptane to make up the balance to 100 weight parts.

[0140] In Table 1 are listed the primary drier and where present anti-skinning agent of the Examples and Comparative Examples, and the amounts of each based on 100 weight parts of the total composition.

[0141] Table 1 :

[0142] Test methods

[0143] The following test methods were used. Drying time

[0144] Drying times were determined according to ASTM D5895-13 using a BK recorder (wet film thickness 90 pm). After the application of the film on a glass panel (300 x 25 mm), a vertical blunt needle, pressed upon by a 5 g load, was placed into the freshly applied film and then dragged in a straight line through the drying paint in longitudinal direction of the panel. The so-called ‘dry-hard time’, i.e. when drying has proceeded sufficiently that the paint film is not displaced anymore (Stage III of drying in ASTM D5895-13) was determined for the paints within 1 day after preparation. Drying time was determined at 10 °C and 85 % relative humidity and at 23 °C and 50% relative humidity. The drying at 10 °C was determined by applying the paint at 23 °C. Immediately after application the painted glass strip was moved into a room with a temperature of 10 °C. The results are shown in Table 3.

[0145] Kbnig hardness

[0146] The Kbnig hardness of paint films was assessed using the pendulum damping test according to DIN53157. A glass panel was coated with a 90 pm wet film, held at 23 °C and 50% relative humidity and the hardness development in time was monitored with a Kbnig pendulum. The number of oscillations needed to reduce from an initial deflection of 6° to a deflection of 3° was measured. The average of duplicate measurements was recorded. The Kbnig hardness was measured after 1 day and 14 days of storage at 23 °C and 50% relative humidity. The results are shown in Table 3.

[0147] Table 3:

[0148] The results in Table 3 show that in general compositions of the Examples have at least comparable drying times to those of the Comparative Examples. In particular Ex. 2, 3 and 4 have shorter drying times at 10°C and 23°C than any of the Comparative Examples, including C.Ex.1, 2 and 3 which relate to commercially available cobalt, manganese and iron-based primary driers. Ex.1 has a shorter drying time at 23°C than do C.Ex.4 and 5, all of which comprise an Fe(acac)3 drier. Similarly, Ex.2 has a shorter drying time at 23°C than do C.Ex.6 and 7, all of which comprise a CpFeCh drier. The Kdnig hardness of Ex.1, 2, 3 and 4 is comparable or better than that of C.Ex.2 and 3. C.Ex.1 has particularly high hardness. The hardness of C.Ex.6 is higher than Ex.2. However the hardness of Ex.2 is acceptable. Further an order of magnitude more iron is used in C.Ex.6 than in Ex.2 and accordingly, the disadvantages associated with the presence of iron are an order of magnitude higher in C. Ex. 6 than in Ex. 2.

Claims

CLAIMS1. A coating composition comprising an autoxidizable binder; a transition metal M selected from iron, cerium, manganese and vanadium; and a ligand A, wherein ligand A is of general formula (I):whereinX is a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; n and m are each independently 0, 1 or 2;R1and R2are each independently a heterocyclic group containing one, two or three heteroatoms are each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms;R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl, aryl or a heterocyclic group containing one, two or three heteroatoms each independently selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; andR5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

2. A coating composition according to claim 1 , wherein X is pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl.

3. A coating composition according to claim 1 or claim 2, wherein R1and R2are each independently pyridinyl, pyrazinyl, pyrazolyl, pyrrolyl, imidazolyl, benzimidazolyl, pyrimidinyl, triazolyl or thiazolyl.

4. A coating composition according to any one of claims 1 to 3, wherein R1and R2are both identical.

5. A coating composition according to any one of claims 1 to 4, wherein R1, R2, R3and R4are all identical.

6. A coating composition according to any one of claims 1 to 5, wherein ligand A is of general formula (II),wherein R3and R4are each independently hydrogen, alkyl, hydroxyl, alkoxyl or a heterocyclic group containing one, two or three heteroatoms selected from N, O and S, which heterocyclic group is capable of coordinating to a transition metal through at least one of the heteroatoms; andR5and R6are each independently hydrogen, alkyl, hydroxyl, or alkoxyl.

7. A coating composition according to any one of claims 1 to 6, wherein the ligandA is of formula (III):

8. A coating composition according to any one of claims 1 to 7, wherein the transition metal M is iron or manganese.

9. A coating composition according to any one of claims 1 to 8, wherein the transition metal M is part of a transition metal-ligand complex, [M-Ly]z, wherein each ligand L is independently a mono, bi- or multi-dentate ligand; y is an integer of from 1 to 6; and z is a charge of -3, -2, -1 , 0, 1 , 2 or 3.

10. A coating composition according to claim 9, wherein in the transition metal-ligand complex [M-Ly]z, M is iron; and a first ligand L is a substituted or unsubstituted cyclopentadienyl group.

11. A coating composition according to claim 10, wherein the transition metal-ligand complex [M-Ly]zis a complex of general formula (IV):or a complex of general formula (V):(V); wherein: p is an integer with a value of 1 , 2 or 3;q is an integer with a value of 0, 1 , or 2;R9is, independently, hydrogen, alkyl or aryl; and L is a mono-, bi- or multi-dentate ligand.

12. A coating composition according to claim 11 , wherein the transition metal-ligand complex [M-Ly]zis cyclopentadienyliron(ll) dicarbonyl dimer, cyclopentadienyliron dicarbonyl halide wherein the halide is iodide, bromide or chloride, or r^-CsHs Fe(ll) n5-C6H7.

13. A coating composition comprising an autoxidizable binder; a metal-ligand complex [M-Ly]zas defined in any one of claims 10 to 12 and a multidentate nitrogen-donor ligand.

14. A coating composition according to claim 13 wherein the multidentate nitrogendonor ligand is a bispidon-type ligand, a TACN-type ligand, an N4Py-type ligand, a cyclam ligand or a trispicen-type ligand.

15. A coated substrate comprising a substrate and a coating, which coated substrate is obtainable by applying a coating composition as defined in any one of claims 1 to 14 to the substrate and allowing the coating composition to dry.

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