Complexes for use as catalysts for hydrosilylation reactions

Abstract

The invention relates to platinum complexes which find use as pre-catalysts or catalysts in hydrosilylation reactions, and which may be activated using thermal or UV methods. The invention further relates to a method of producing the platinum complexes of the invention and methods for using the platinum complexes of the invention in hydrosilylation reactions.

Description

[0001] COMPLEXES FOR USE AS CATALYSTS FOR HYDROSILYLATION REACTIONS

[0002] Field of the Invention

[0003] The present invention relates to transition metal complexes and a process fortheir use. More specifically, the present invention relates to transition metal complexes which function as pre-catalysts or catalysts for hydrosilylation reactions, a method for their production, and to hydrosilylation reactions using the complexes.

[0004] Background of the Invention

[0005] Hydrosilylation reactions are used to produce a wide range of organosilicon compounds such as adhesive, sealants, antifoaming agents, and coatings.

[0006] Hydrosilylation reactions comprise the addition of a Si-H moiety into an unsaturated double or triple bond of an organic compound (e.g. C=C, C=C, C=O etc) to produce a silane compound. This reaction may also be referred to as “curing”. An example of a hydrosilylation reaction involving an alkene may be represented by the general equation:

[0007]

[0008] Hydrosilylation reactions are commonly achieved using a homogenous platinum catalyst. An example of a catalytic cycle for the hydrosilylation of an alkene is shown in Scheme 1. A key step in this catalytic cycle is the coordination of the alkene to the platinum atom with loss of a ligand, L.

[0009]

[0010] Scheme 1

[0011] Known platinum catalysts for hydrosilylation reactions may comprise a platinum atom bonded to a cyclopentadienyl ligand substituted with one or more short chain alkyl groups, such as methyl or ethyl. Such catalysts may be activated by application of thermal and / or UV energy.

[0012] (Me-Cp)Pt(Me)3, available as Pt-99 from Johnson Matthey PLC, is widely regarded as being the industry standard hydrosilylation catalyst and may be activated using heat and / or UV light. The structure of (Me-Cp)Pt(Me)3is shown in Scheme 2.

[0013]

[0014] Pt-99 may be used to cure synthetic rubbers by UV and thermal activation at a temperature of greater than 140 °C. J. Appl. Polym. Sci., 136, 48251 describes UV activation of (Me-Cp)Pt(Me)3(Pt-99) in hydrosilylation reactions. The high activation temperatures of commercially available hydrosilylation catalysts result in the use of a large amount of energy in industrial application. Furthermore, the required use of high temperatures limits the range of organic substrates which may be subjected to hydrosilylation due to thermal degradation of more sensitive substrates. However, if a catalyst is provided with too low of an activation temperature, accidental activation may occur. To overcome this problem, catalysts which may be activated at low temperatures, such as Kardstedt catalysts, may be used and be provided with a chemical activation inhibitor. However, the inhibitor may represent an impurity in the resulting silicone.

[0015] For at least the above reasons, there is a need for hydrosilylation catalysts which can be activated at preferred temperatures, and which have tuneable properties.

[0016] Summary of the Invention

[0017] Accordingly, the present invention provides a new class of platinum complexes which find use as pre-catalysts and catalysts in hydrosilylation reactions, and which have tuneable properties, such as being activatable at low temperatures and under mild conditions. Due to the milder activation conditions, the platinum complexes of the present invention allow a greater range of organic substrates to be subjected to hydrosilylation without the addition of photosensitisers.

[0018] In a first aspect of the invention there is provided a platinum complex of formula (I) for use as a catalyst in hydrosilylation reactions:

[0019]

[0020] wherein R1-R3are each independently a substituted or unsubstituted alkyl group comprising from 1 to 8 carbon atoms or a substituted or unsubstituted aryl group comprising 6 to 20 carbon atoms;

[0021] R4is an organic group comprising from 1 to 20 carbon atoms; and

[0022] R5-R8are each independently a hydrogen atom, or an organic group comprising from 1 to 8 carbon atoms, or R5 / R6, R6 / R7, or R7 / R8are linked to form a substituted or unsubstituted aromatic ring structure. The platinum complex of formula (I) comprises a cyclopentadienyl ligand, L:

[0023]

[0024] It has surprisingly been found that inclusion of a carbonyl group (-C(=O) R4) bonded to the cyclopentadienyl ring, L, of the complex of formula (I) allows the conditions under which the catalyst may be activated (thermally and / or photochemically) to be tuned and controlled. The effect of the R4group, as discussed in more detail below, is particularly surprising given its spatial distance from the cyclopentadienyl ring.

[0025] It has been found that a correlation exists between the electron donating nature of the residue, R4, and the activation temperature and photosensitivity of the platinum complex for the hydrosilylation reaction. More specifically, more electron donating R4groups give rise to a lower activation temperature and a higher visible light-stability. Conversely, less electron donating R4groups give risk to a higher activation temperature but a greater susceptibility to photo-activation.

[0026] Further, it has been found that the nature of the residue, R4, can be used to control the frequency of light which may be used to activate the platinum complexes of formula (I). Without being bound by any sort of theory it is believed that the residue, R4, may function as a chromophore in the hydrosilylation reaction and provide a low energy transition state, accessible upon UV irradiation, which facilitates loss of the substituted cyclopentadienyl ligand; a step in the proposed hydrosilylation shown in Scheme 1. It is therefore possible to choose a chromophore which adsorbs a specific frequency of light to activate the platinum complex of formula (I). A particular advantage of this is the ability to choose R4groups which may adsorb light in a frequency range emitted by commercially available UV LEDs (e.g. 310 nm to 365 nm) which have significantly lower energy consumption compared to traditionally used mercury and xenon discharge lamps. Platinum complexes of formula (I) therefore provide catalysts for use in hydrosilylation reactions having lower energy consumption. Furthermore, it has been found that the platinum complexes of formula (I) may be activated by UV irradiation but which are stable to exposure to visible light. Consequently, platinum complexes of formula (I) may be used without the risk of accidental activation.

[0027] In a second aspect of the invention there is provided a method for preparing the platinum complex of formula (I) of the first aspect of the invention, the method comprising the steps of:

[0028] a) reacting a cyclopentadiene salt with a compound of formula R4-C(=O)ORXto produce a cyclopentadienyl ligand, L,

[0029]

[0030] b) reacting a platinum containing starting material of general formula [Pt(R1R2R3)Y] with a silver salt of formula AgQ to form a platinum containing intermediate of general formula [Pt(R1R2R3)Q]; and

[0031] c) reacting the platinum containing intermediate with the cyclopentadienyl ligand, L, to produce the platinum complex of formula (I),

[0032] wherein each of R1-R8are as defined in relation to the platinum complex of formula (I) of the first aspect of the invention, Rxis an alkyl group, Q is selected from 'OTf, 'OMs, 'BF^ ’PFe, ’ SbFe, -CIO4, and p-toluenesulfonate, and Y is a halide.

[0033] The method of the invention has surprisingly been found to produce the platinum complexes of formula (I) with little or no byproduct formation.

[0034] In a third aspect of the invention, there is provided a process for carrying out a hydrosilylation reaction using the platinum complex of formula (I) as defined in relation to the first aspect of the invention as a pre-catalyst or catalyst.

[0035] Brief Description of the Drawings

[0036] Figure 1 shows a series of UV / vis spectra of platinum complexes of formula (I).

[0037] Figure 2 shows a series of UV / vis spectra of platinum complexes of formula (I) predicted using density function theory (DFT) calculations. Figure 3 shows a plot of R4groups their predicted electron donating abilities, the frequency of light which they adsorb, and their thermal stability.

[0038] Figure 4 shows the relationship between the resonance of the C2 carbon on the cyclopentadienyl ligand, L, in the13C NMR spectrum versus activation temperature of the platinum complex of formula (I) for the hydrosilylation reaction.

[0039] Definitions

[0040] The point of attachment of a moiety or substituent is represented by For example, -OH is attached through the oxygen atom.

[0041] “Alkenyl” refers to a straight-chain or branched unsaturated hydrocarbon group comprising at least one carbon-carbon double bond.

[0042] “Alkoxy” refers to an optionally substituted group of the formula alkyl-O- or cycloalkyl-O-, wherein alkyl and cycloalkyl are as defined below.

[0043] “Alkoxycarbonyl” refer to an optionally substituted group of formula alkyl-O-C(=O)- or cycloalkyl-O-C(=O)-, wherein alkyl and cycloalkyl are as defined hereinbelow.

[0044] “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.

[0045] “Alkynyl” refers to a straight-chain or branched unsaturated hydrocarbon group comprising at least one carbon-carbon triple bond.

[0046] “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. “Cycloalkenyl” refers to an unsaturated, non-aromatic carbocyclic ring. The cycloalkenyl group therefore has at least one carbon-carbon double bond, but may have more. In certain embodiments, the cycloalkenyl group may have from 3-15 carbon atoms, in certain embodiments, from 3-10 carbon atoms, in certain embodiments, from 3-8 carbon atoms. The cycloalkenyl group may be unsubstituted. Alternatively, the cycloalkenyl group may be substituted. Unless other specified, the cycloalkenyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Typical cycloalkenyl groups include but are not limited to cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, and the like.

[0047] “Cycloalkyl” refers to 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.

[0048] “Halo”, “halide”, or “hal” refers to F, Cl, Br and I atoms or ions.

[0049] “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.

[0050] “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. Heterocycle” encompasses both heterocycloalkyl groups and heteroaryl groups.

[0051] “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.

[0052] “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, -R9, =0, =S, -O-R9, -S-R9, -NR9Rh, -CN, -NO2, -C(O)-R9, -COOR9, -C(S)-R9, -C(S)OR9, -S(O)2OH, -S(O)2-R9, -S(O)2NR9Rh, -O-S(O)-R9and -CONR9Rh, such as -halo, -C(halo)3(e.g. -CF3), -R9, -O-R9, -NR9Rh, -CN, or -NO2. R9and Rhare independently selected from the groups consisting of H, alkyl, aryl, arylalkyl, heteroalkyl, heteroaryl, or R9and Rhmay be linked to form a heterocycloalkyl group. R9and Rhmay be unsubstituted or further substituted as defined herein.

[0053] As used herein, the term “hydrosilylation” refers to the addition of a Si-H bond across an unsaturated bond, such as a C=C, C=C, or C=O bond. The hydrosilylation reaction may be equally be referred to as curing.

[0054] Detailed Description

[0055] 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. Lower and / or upper limits of any ranges disclosed herein are envisaged to be combinable with one another to provide new ranges, whether explicitly stated or not. For example, the ranges C1-C20and C2-C10are envisaged to be combinable to create the ranges C1-C10, C10-C20, C1-C2, and / or C2-C20. The present invention comprises a platinum complex of formula (I) for use as a catalyst in hydrosilylation reactions.

[0056]

[0057] In the platinum complex of the invention the platinum atom may be present in an oxidation state of +4. The platinum complex of formula (I) may therefore be a platinum(IV) complex of formula (I).

[0058] In the platinum complex of formula (I), R1-R3are each independently a substituted or unsubstituted alkyl group comprising from 1 to 8 carbon atoms or a substituted or unsubstituted aryl group comprising 6 to 20 carbon atoms. In the platinum complex of formula (I), R1-R3may each independently be a substituted or unsubstituted alkyl group comprising from 1 to 8 carbon atoms. For example, R1-R3may each independently be a substituted or unsubstituted alkyl group comprising from 2 to 7 carbon atoms, from 3 to 6 carbon atoms, or from 4 to 5 carbon atoms, and / or R1-R3may each independently be a substituted or unsubstituted aryl group comprising from 6 to 14 carbon atoms, or from 6 to 10 carbon atoms. R1-R3may be the same or different. R1-R3may be a branched or an unbranched substituted or unsubstituted alkyl group. R1-R3may each independently be an alkyl or aryl group selected from trifluoromethyl, methyl, ethyl, n-propyl, / so-propyl, n-butyl, sec-butyl, terf-butyl, pentyl, hexyl, phenyl, naphthyl, and anthracenyl. R1-R3may each independently be an alkyl group selected from methyl, ethyl, n-propyl, and / so-propyl.

[0059] Preferably, R1-R3are the same and are each methyl.

[0060] The platinum complex of formula (I) comprises a cyclopentadienyl ligand, L:

[0061]

[0062] As will be understood the identity of the groups R4-R8defined in relation to the platinum complex of formula (I) are the same as those defined in relation to the cyclopentadienyl ligand, L, and vice-versa, and may be used and referred to equally and interchangeably.

[0063] In the platinum complexes of formula (I) the cyclopentadienyl ligand, L, is substituted with at least a group having formula -C(=O)R4. R4is an organic group comprising from 1 to 20 carbon atoms. R4may be selected from a substituted or unsubstituted Ci-20-alkyl, substituted or unsubstituted C2-2o-alkenyl, substituted or unsubstituted C2-2o-alkynyl, substituted or unsubstituted Ci-20-heteroalkyl, substituted or unsubstituted Ci-2o-alkoxy, substituted or unsubstituted Cs-20-cycloalkyl, substituted or unsubstituted Cs-20-cycloalkenyl, substituted or unsubstituted C2-io-heterocycloalkyl, substituted or unsubstituted C6-2o-aryl, and substituted or unsubstituted C4-2o-heteroaryl. R4may be selected from a substituted or unsubstituted C2-10-alkyl, substituted or unsubstituted C2-io-heteroalkyl, substituted or unsubstituted C2-10-alkoxy, substituted or unsubstituted Cs-w-cycloalkyl, substituted or unsubstituted C4-10-heterocycloalkyl, substituted or unsubstituted Ce-io-aryl, and substituted or unsubstituted C4-10-heteroaryl. R4may be selected from a substituted or unsubstituted C2-C10 (e.g. C3, C4, C5, Cs, C7, Cs, and / or Cg) alkyl, substituted or unsubstituted Cs-w-cycloalkyl (e.g. Cs, C7, Cs, and / or Cg), and substituted or unsubstituted Cs-Cw (e.g. C7, Cs, and / or Cg) aryl.

[0064] In preferred platinum complexes of formula (I), R4may be a substituted or unsubstituted C1-C20, C2-C12, Cs-Cs, orC4-Cs alkyl group. In preferred platinum complexes of formula (I), R4may be an unsubstituted branched or unsubstituted unbranched C1-C20, C2-C12, Cs-Cs, orC4-Cs alkyl group. In preferred platinum complexes of formula (I), R4may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, terf-butyl, pentyl, hexyl, heptyl, octyl, nonyl, or decyl.

[0065] In preferred platinum complexes of formula (I), R4may be an aryl group of formula (II):

[0066]

[0067] wherein Ra, Rb, Rc, Rd, and Reare each independently selected from a hydrogen atom, an organic group comprising from 1 to 10 carbon atoms, a group -X, and / or Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure, wherein -X is selected from -F, -Cl, -Br, -I, -NO2, -S(O)2OH.

[0068] It has surprisingly been found that the nature, in particular the electron donating nature, of the substituents Ra, Rb, Rc, Rd, and Reof the aryl group of formula (II) can be used to tune the activation temperature of the platinum complex of formula (I). This is true despite these substituents being spatially distant from the Pt atom. For example, where Rcis CF3 in the aryl group of formula (II) a platinum complex with a higher activation temperature is obtained as compared to the case where Rcis CH3; CH3 being believed to have a higher electron donating character than CF3.

[0069] Platinum complexes of formula (I) may have low activation temperature. However, it has been surprisingly found that where R4is an aryl group of formula (II) that platinum complexes which form hydrosilylation catalysts having especially low activation temperatures may be obtained.

[0070] Ra, Rb, Rc, Rd, and Remay each independently be selected from hydrogen, nitrile, substituted or unsubstituted Ci-10-alkyl, substituted or unsubstituted Ci-io-heteroalkyl, substituted or unsubstituted C2-C10 alkoxycarbonyl, and substituted or unsubstituted CMO-alkoxy. Ra, Rb, Rc, Rd, and Remay each independently be selected from hydrogen, nitrile, substituted or unsubstituted Ci-s-alkyl, substituted or unsubstituted Ci-s-heteroalkyl, substituted or unsubstituted C2-C5 alkoxycarbonyl, and substituted or unsubstituted C1.5-alkoxy. Ra, Rb, Rc, Rd, and Remay each independently be selected from hydrogen, methyl, ethyl, / so-propyl, methoxy, ethoxy, / so-propoxy, and trifluoromethyl.

[0071] In preferred platinum complexes of formula (I), Ra, Rb, Rd, and Remay be hydrogen and Rcmay be selected from hydrogen, nitrile, substituted or unsubstituted Ci-10-alkyl, substituted or unsubstituted Ci-io-heteroalkyl, substituted or unsubstituted Ci- -alkoxy, substituted or unsubstituted Ci-s-alkyl, substituted or unsubstituted Ci-s-heteroalkyl, and substituted or unsubstituted Ci-s-alkoxy. In preferred platinum complexes of formula (I), Ra, Rb, Rd, and Remay be hydrogen and Rcmay be selected from hydrogen, methyl, ethyl, / so-propyl, methoxy, ethoxy, / so-propoxy, and trifluoromethyl.

[0072] Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure. Where Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure the ring structure may be unsubstituted or further substituted, such as described hereinabove. It may be preferred that Ra / Rband / or Rb / Rcmay be linked to form a ring structure. It may be preferred that Raand Rbmay be linked to form a ring structure. Where Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure, the ring structure may be a substituted or unsubstituted naphthalene, a substituted or unsubstituted 9-fluoreone, a substituted or unsubstituted benzofuran, and / or a substituted or unsubstituted quinoxaline. Where any one or more of Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure, the remaining residues, Ra-Re, may be as defined hereinabove for the case where Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay not be linked to form a ring structure.

[0073] In preferred platinum complexes of formula (I), R4may be a substituted or unsubstituted Ci-020, C2-C12, Cs-Cs or C4-C6 alkyl group, or an aryl group of formula (II) as described hereinabove.

[0074] It may be preferred that R4is one or more group selected from the following:

[0075]

[0076] _ _p4

[0077] It will be understood that5represents R4bonded to the carbonyl carbon of the -C(=O)R4group of the cyclopentadienyl ligand, L, of the platinum complex of formula (I).

[0078] In platinum complexes of formula (I), R5-R8are each independently a hydrogen atom, or an organic group comprising from 1 to 8 carbon atoms. R5-R8may be the same or different, preferably the same. R5-R8may each independently be selected from a hydrogen atom, a substituted or unsubstituted Ci-s-alkyl, substituted or unsubstituted C2-8-alkenyl, substituted or unsubstituted C2-C8 alkoxycarbonyl, substituted or unsubstituted C2-8-alkynyl, substituted or unsubstituted Ci-8-heteroalkyl, substituted or unsubstituted Ci-8-alkoxy, substituted or unsubstituted Cs-s-cycloalkyl, substituted or unsubstituted Cs-s-cycloalkenyl, substituted or unsubstituted C2-8-heterocycloalkyl, substituted or unsubstituted Ce-is-aryl, substituted or unsubstituted C4-8-heteroaryl, and substituted or unsubstituted C1-C10 alkylsilyl. R5-R8may be selected from a hydrogen atom, a substituted or unsubstituted C2-6-alkyl, substituted or unsubstituted C2-6-heteroalkyl, substituted or unsubstituted C2-C6 alkoxycarbonyl, substituted or unsubstituted C2-6-alkoxy, substituted or unsubstituted Cs-6-cycloalkyl, substituted or unsubstituted C4-6-heterocycloalkyl, substituted or unsubstituted Ce-8-aryl, substituted or unsubstituted C4-6-heteroaryl, and substituted or unsubstituted C3-C9 alkylsilyl. R5-R8may each independently be selected from a hydrogen atom, methyl, ethyl, n-propyl, phenyl, methoxycarbonyl, ethoxycarbonyl, phenoxycarbonyl, or trimethylsilyl. Preferably, R5-R8may each by hydrogen.

[0079] Alternatively, R5 / R6, R6 / R7, or R7 / R8are linked to form a substituted or unsubstituted aromatic ring structure. R5 / R6, R6 / R7, or R7 / R8may be linked to form a substituted or unsubstituted aromatic ring structure which is a C5-C7 aromatic ring. R5 / R6, R6 / R7, or R7 / R8may be linked to form a substituted or unsubstituted aromatic ring structure having a substituted or unsubstituted dicyclopentadienyl structure or a substituted or unsubstituted indenyl structure. Where any one or more of R5 / R6, R6 / R7, or R7 / R8may be linked to form a ring structure, the remaining residues, R5-R8, may be as defined hereinabove for the case where R5 / R6, R6 / R7, or R7 / R8may not be linked to form a ring structure.

[0080] Where R5 / R6, R6 / R7, or R7 / R8may be linked to form a substituted or unsubstituted aromatic ring structure, the platinum complex of formula (I) may be a complex of formula (la), (lb), (Ic), or (Ic):

[0081]

[0082] wherein R1-R8are each as defined hereinabove in relation to the platinum complex of formula (I). Preferably, R4may be the aryl group of formula (II) and Ra-Reare as defined hereinabove.

[0083] It may be preferred that the platinum complex of formula (I) is a platinum complex of formula (le):

[0084]

[0085] wherein R1, R2, R3, R5, R6, R7, R8, Ra, Rb, Rc, Rd, and Reare each as defined hereinabove in relation to the platinum complex of formula (I) and the aryl group of formula (II).

[0086] It may be preferred that the platinum complex of formula (I) is one or more selected from:

[0087]

[0088] Rc= H, methyl, trifluoromethyl, methoxy, R4= methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl

[0089] The platinum complex of formula (le) may have a resonance in the13C NMR spectrum corresponding to the C2 carbon of greater than or equal to 96.0 ppm, greater than or equal to 96.5 ppm, greater than or equal to 96.8 ppm, or greater than or equal to 97.0 ppm. The platinum complex of formula (I) may have a resonance in the13C NMR spectrum corresponding to the C2 carbon of less than or equal to 101.0 ppm, less than or equal to 100.5 ppm, less than or equal to 100.0 ppm, or greater than or equal to 99.0 ppm. For example, the platinum complex of formula (I) may have a resonance in the13C NMR spectrum corresponding to the C2 carbon of from 96.0 ppm to 101.0 ppm, from 96.5 ppm to 100.5 ppm, from 96.8 ppm to 100.0 ppm, or from 97.0 ppm to 99.0 ppm, such as 97.5 ppm, 98.0 ppm or 98.5 ppm.

[0090] It has surprisingly been found that the activation temperature of platinum complexes of formula (1e) may be predicted depending upon the resonance of the C2 carbon in the13C NMR spectrum. The C2 carbon is the carbon atom of the cyclopentadienyl ring adjacent to the carbon to which the -C(=O)R4group is attached (i.e. the carbon atom of the cyclopentadienyl ring to which R5or R8is attached), and is shown schematically in Scheme 3. C2carbon

[0091]

[0092] Where platinum complexes of formula (le) have a13C NMR resonance in the range described hereinabove they exhibit an activation temperature which is particularly advantageous for use in hydrosilylation reactions.

[0093] The activation temperature (in °C) of the platinum complexes of formula (le) may be calculated from the13C NMR resonance (in ppm) of the C2 carbon according to the below formula:

[0094] Activation Temperature = [8.785 x C2resonance] - 795

[0095] The platinum complexes of formula (I) may be prepared by reacting a platinum containing starting material, such as [Pt(CH3)3I] with a sodium salt of a cyclopentadienyl ligand. An example of this reaction is shown in Scheme 4.

[0096]

[0097] Scheme 4

[0098] However, the method of Scheme 4 suffers from an unexpected formation of a platinum containing byproduct, as illustrated in Scheme 5.

[0099]

[0100] Scheme 5

[0101] The process of the second aspect of the invention allows for formation of the platinum complexes of formula (I) in high yields and with no or minimal byproduct formation.

[0102] Accordingly, in a second aspect of the invention there is provided a method for preparing the platinum complex of formula (I) of the first aspect of the invention the method comprising the steps of:

[0103] a) reacting a cyclopentadiene salt with a compound of formula R4-C(=O)ORXto produce a cyclopentadienyl ligand, L,

[0104]

[0105] b) reacting a platinum containing starting material of general formula [Pt(R1R2R3)Y] with a silver salt of formula AgQ to form a platinum containing intermediate of general formula [Pt(R1R2R3)Q]; and

[0106] c) reacting the platinum containing intermediate with the cyclopentadienyl ligand, L, to produce the platinum complex of formula (I),

[0107] wherein each of R1-R8are as defined in relation to the platinum complex of formula (I) of the first aspect of the invention, Rxis an alkyl group, Q is selected from 'OTf, 'OMs, 'BF^ ’PFe, ’ SbFe, -CIO4, and p-toluenesulfonate, and Y is a halide.

[0108] It has surprisingly been found that by preparing a platinum containing intermediate of formula [Pt(R1R2R3)Q] that formation of the byproduct [Pt(R1R2R3)Y2]' can be reduced or eliminated. The process of the second aspect of the invention therefore provides a simple ‘one-pot’ process which cleanly produces the platinum complexes of formula (I).

[0109] The cyclopentadiene salt may be any suitable salt of cyclopentadiene. For example, it may be a sodium, a potassium, or a caesium salt of a substituted or unsubstituted

[0110] cyclopentadiene. Rxmay be methyl, ethyl, n-propyl, / so-propyl, or terf-butyl. Preferably, Rxmay be methyl.

[0111] Optionally, the method of the second aspect of the invention may be carried out in the presence of a solvent. For example, the method of the second aspect of the invention may be carried out in the presence of an etherial solvent such as tetra hydrofuran.

[0112] Y is a halide. Preferably Y is iodide.

[0113] In a third aspect of the invention, there is provided a process for carrying out a hydrosilylation reaction using the platinum complex of formula (I) as defined in relation to the first aspect of the invention as a pre-catalyst or catalyst.

[0114] Examples

[0115] Regents and Starting Materials

[0116] lodotrimethylplatinum(IV) may be prepared according to the method described in WO2023 / 099863A1. Sodium cyclopentadienylide, silver trifluoromethane sulfonate, and organic compounds and substrates were obtained commercially from Merck / Sigma-Aldrich or other commercial sources.

[0117] Solvents were dried and degassed according to standard laboratory procedures. All reactions were carried out under a dry nitrogen atmosphere in oven or flame dried glassware, unless otherwise stated.

[0118] General procedure for synthesis of cyclopentadienyl ligands for preparation of platinum complexes of formula (I):

[0119] Cyclopentadienyl ligands found in the platinum complexes of formula (I) may be synthesized according to the general procedure listed below.

[0120] Under a dry nitrogen atmosphere, a solution of sodium cyclopentadienylide in tetrahydrofuran was added to a vigorously stirred solution of methyl 4-trifluoromethylbenzoate (slight excess) in toluene. Once the addition was completed, the reaction was heated to 100 °C, and volatiles (tetrahydrofuran and methanol) were removed by distillation as the reaction progressed.

[0121] After two hours of heating, the reaction was cooled to ambient temperature, becoming a heavy slurry. Tetrahydrofuran was added to dissolve the solids, and the product precipitated by the addition of n-pentane. Lustrous yellow crystals of sodium (4-trifluoromethylbenzoyl)cyclopentadienylide were isolated by filtration and washed twice with pentane. 97 % Yield.

[0122] 1H NMR (400 MHz, THF): δ 8.271 (2 H, d,3JH,H= 8.0 Hz), 8.008 (2 H, d,3JH,H= 8.0 Hz), 6.718 (2 H, v. br), 6.368 (2 H, br).13C NMR (100 MHz, THF): δ 181.05, 149.31, 129.69, 129.56 (q,2JC,F= 32.0 Hz), 126.32, 123.90 (q,3JC,F= 3.7 Hz), 122.91, 116.28 (br).19F NMR (376 MHz, THF): δ -63.6.

[0123] General procedure for synthesis of platinum complexes of formula (I):

[0124] Platinum complexes of formula (I) may be synthesized in a one pot synthesis according to the general procedure outlined below. This procedure has the advantage of forming the cyclopentadienyl ligand in-situ.

[0125] Sodium (4-trifluoromethylbenzoyl)cyclopentadienylide, iodotrimethylplatinum(IV), and silver trifluoromethane sulfonate were combined in equimolar quantities in tetrahydrofuran, and stirred for two hours at ambient temperature. Volatiles were removed under reduced pressure, and the remaining solids were triturated with n-pentane to extract the extremely soluble product complex. The resulting slurry was filtered, and the solids were washed with additional pentane. The combined pentane fractions were concentrated to dryness, affording the final (4-trifluoromethylbenzoyl)cyclopentadienyl)trimethylplatinum(IV) complex as a pale yellow solid, in 68% yield.

[0126] 1H NMR (400 MHz, THF): δ 8.220 (2 H, d,3JH,H= 8.1 Hz), 8.131 (2 H, d,3JH,H= 8.1 Hz), 6.731 (2 H, m), 6.272 (2 H, m), 1.286 (9 H,2JH,Pt= 82.6 Hz).13C NMR (100 MHz, THF): δ 185.70, 143.21, 132.66 (q,2JC,F= 32.3 Hz), 128.71, 125.59 (q,3JC,F= 3.9 Hz), 123.02, 104.61 (1JC,Pt= 14.4 Hz), 104.35, 99.20 (1JC,Pt= 10.7 Hz), -16.37 (1JC,Pt= 707 Hz).19F NMR (376 MHz, THF): δ -64.3.

[0127] Four complexes were prepared according to the general procedure, the identities of which are summarized in Table 1 below:

[0128]

[0129]

[0130] Table 1

[0131] The UV / vis spectra of Complex Numbers 1-4, dissolved in inhibitor-free tetrahydrofuran, are shown in Error! Reference source not found..

[0132] General procedure for hydrosilylation reactions, catalyst activity and thermal stability determination

[0133] Stock solutions of catalyst candidates were prepared in dichloromethane at a concentration of 1.00 mg Pt per 1.00 mL dichloromethane (required mass of catalyst complex is determined by wt% Pt in each catalyst complex). A 2.00 g sample of liquid synthetic rubber (LSR) mixture was prepared by combining Gelest DMS-V21 (1.8727 g) and Gelest HMS-501 (133 pL) which were well-mixed immediately prior to experimentation.

[0134] Catalyst activity and thermal stability in hydrosilylation reactions was determined using a DSC instrument comprising a dark chamber and mercury discharge lamp. Samples were analysed relative to a Pt-99 and a blank, and the onset of reaction determined from the observed exotherm. Selection of suitable R4groups by density functional theory (DFT)

[0135] The present inventors have found that density functional theory (DFT) computer modelling can be used to select suitable R4groups which may act as chromophores for use with specific frequencies of light.

[0136] The lowest energy conformer for each compound was obtained by generating conformational ensembles using CREST1with the GFN2-xTB2semi-empirical method in the iMTD-GC workflow1. Refinement of each ensemble was carried out using CENSO3with the B97-D34’5functional and def2-SV(P)6basis set for the cheap pre-screening step, and the r2SCAN-3c composite method7for the screening and optimisation steps. TURBOMOLE (V7-89was used as the backend DFT code for CENSO. The lowest energy CENSO generated conformer was then further geometry optimized using TURBOMOLE with the r2SCAN-3c method and the DCOSMO-RS implicit solvation model10for CH2CI2. UV-vis spectra in implicit CH2CI2 solvent were then simulated by performing time-dependent density-functional theory (TDDFT) single-point calculations on the geometries obtained above, using the range-separated wB97X-V hybrid functional11and the def2-TZVPP basis set. For each compound, the 16 lowest excitations in the A1 irreducible representation were calculated, which was sufficient to cover the spectral range of ca. 150 to 350 nm. Seminumerical exchange12,13was used in combination with the wB97X-V functional for calculation efficiency.

[0137] The results from this work are summarised in Error! Reference source not found.. Error! Reference source not found, shows that adsorption in the UV region can be influenced by varying the nature of substituents on an aryl group of formula (II) as compared to commercially available Pt-99. For example, where R4is an aryl group of formula (II), substitution in the Rcposition with a more electron withdrawing group (e.g. NO2) have been shown to provide platinum complexes with improved thermal stability and improved activation by UV light. For example, where R4is an aryl group of formula (II), substitution in the Rcposition with a more electron donating group (e.g. N(CH3)2) have been shown to provide platinum complexes which may be more easily activated using heat and improved resistance to activation by UV light.

[0138] DFT calculation also allows the UV / vis spectra of complexes of the invention to be predicted, allowing the frequency of light required to activate the complex to be obtained. An example of spectra of platinum complexes of formula (I) predicted by DFT is shown in Error! Reference source not found..

[0139] 13C NMR Spectrometry The present inventors have found that using13C NMR spectrometry it is possible to measure the degree of electron density imparted by the R4, and therefore predict the activation temperature of the platinum complex of formula (le). Error! Reference source not found, shows the direct correlation between the chemical shift of the C2carbon (Scheme 3) of the cyclopentadienyl ligand, L, of the platinum complex of formula (le) (Complexes 1-3) and the measured activation temperature of the same complex in hydrosilylation reaction.

[0140] 13C NMR spectra of the platinum complexes of formula (I) were collected in d8-tetrahydrofuran using a 400 MHz Bruker spectrometer, with an Avance III console. Because the solvent is non-deuterated, spectra were collected in without locking, and shimming was performed using the proton signal. No solvent suppression was used. Spectra were calibrated by referencing the solvent signals.

[0141] References

[0142] 1. Pracht, P.; Bohle, F.; Grimme, S.; Automated exploration of the low-energy chemical space with fast quantum chemical methods, Phys. Chem. Chem. Phys., 2020, 22, 7169-7192. https: / / doi.org / 10.1039 / C9CP06869D

[0143] 2. Bannwarth, C.; Ehlert, S.; Grimme, S.; GFN2-xTB — An Accurate and Broadly Parametrized Self-Consistent Tight-Binding Quantum Chemical Method with Multipole Electrostatics and Density-Dependent Dispersion Contributions J. Chem. Theory Comput. 2019, 15 (3), 1652-1671. https: / / doi.org / 10.1021 / acs.jctc.8b01176 3. S. Grimme, F. Bohle, A. Hansen, P. Pracht, S. Spicher, and M. Stahn; Efficient Quantum Chemical Calculation of Structure Ensembles and Free Energies for Nonrigid Molecules; J. Phys. Chem. A 2021, 125, 19, 4039-4054.

[0144] https: / / doi.org / 10.1021 / acs.jpca.1c00971

[0145] 4. Grimme, S. (2006), Semiempirical GGA-type density functional constructed with a long-range dispersion correction. J. Comput. Chem., 27: 1787-1799.

[0146] https: / / doi.org / 10.1002 / jcc.20495

[0147] 5. Grimme, S., Ehrlich, S. and Goerigk, L. (2011), Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem., 32: 1456-1465. https: / / doi.org / 10.1002 / jcc.21759

[0148] 6. Weigend, Florian, Ahlrichs, Reinhart. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 7, 3297 (2005).

[0149] https: / / doi.org / 10.1039 / B508541A

[0150] 7. Stefan Grimme, Andreas Hansen, Sebastian Ehlert, Jan-Michael Mewes; r2SCAN-3c:

[0151] A “Swiss army knife” composite electronic-structure method. J. Chem. Phys. 14 February 2021; 154 (6): 064103. https: / / doi.org / 10.1063 / 5.0040021.

[0152] 8. R. Ahlrichs, M. Baer, M. Haeser, H. Horn, and C. Koelmel Electronic structure calculations on workstation computers: the program system TURBOMOLE Chem. Phys. Lett. 162 (3): 165-169 (1989). https: / / doi.org / 10.1016 / 0009-2614(89)85118-8 9. Sree Ganesh Balasubramani, Guo P. Chen, Sonia Coriani, Michael Diedenhofen, Marius S. Frank, Yannick J. Franzke, Filipp Furche, Robin Grotjahn, Michael E. Harding, Christof Hattig, Arnim Hellweg, Benjamin Helmich- Paris, Christof Holzer, Uwe Huniar, Martin Kaupp, Alireza Marefat Khah, Sarah Karbalaei Khani, Thomas Muller, Fabian Mack, Brian D. Nguyen, Shane M.

[0153] Parker, Eva Perlt, Dmitrij Rappoport, Kevin Reiter, Saswata Roy, Matthias Ruckert, Gunnar Schmitz, Marek Sierka, Enrico Tapavicza, David P. Tew, Christoph van Wullen, Vamsee K. Voora, Florian Weigend, Artur Wodyhski, Jason M. Yu;

[0154] TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations. J. Chem. Phys. 14 May 2020; 152 (18): 184107. https: / / doi.org / 10.1063 / 5.0004635

[0155] 10. Sinnecker S, Rajendran A, Klamt A, Diedenhofen M, Neese F. Calculation of solvent shifts on electronic g-tensors with the conductor-like screening model (COSMO) and its self-consistent generalization to real solvents (direct COSMO-RS). J Phys Chem A. 2006 Feb 16;110(6):2235-45. https: / / doi.org / 10.1021 / jp056016z.

[0156] 11. Mardirossian, Narbe and Head-Gordon, Martin; wB97X-V: A 10-parameter, range- separated hybrid, generalized gradient approximation density functional with nonlocal correlation, designed by a survival-of-the-fittest strategy. Phys. Chem. Chem. Phys.

[0157] 16, 9904-9924 (2014) https: / / doi.org / 10.1039 / C3CP54374A

[0158] 12. Plessow, P. and Weigend, F. (2012), Seminumerical calculation of the Hartree-Fock exchange matrix: Application to two-component procedures and efficient evaluation of local hybrid density functionals. J. Comput. Chem., 33: 810-816.

[0159] https: / / doi.org / 10.1002 / jcc.22901

[0160] 13. Christof Holzer; An improved seminumerical Coulomb and exchange algorithm for properties and excited states in modern density functional theory. J. Chem. Phys. 14 November 2020; 153 (18): 184115. https: / / doi.org / 10.1063 / 5.0022755

Claims

Claims1. A platinum complex of formula (I) for use as a catalyst in hydrosilylation reactions:wherein R1-R3are each independently a substituted or unsubstituted alkyl group comprising from 1 to 8 carbon atoms or a substituted or unsubstituted aryl group comprising 6 to 20 carbon atoms;R4is an organic group comprising from 1 to 20 carbon atoms; andR5-R8are each independently a hydrogen atom, or an organic group comprising from 1 to 8 carbon atoms, or R5 / R6, R6 / R7, or R7 / R8are linked to form a substituted or unsubstituted aromatic ring structure.

2. A platinum complex of formula (I) according to claim 1, wherein R1-R3each independently an alkyl or aryl group selected from trifluoromethyl, methyl, ethyl, n- propyl, / so-propyl, n-butyl, sec-butyl, terf-butyl, pentyl, hexyl, phenyl, naphthyl, and anthracenyl, preferably methyl, ethyl, n-propyl, and / so-propyl.

3. A platinum complex of formula (I) according to claim 1 or claim 2, wherein R1-R3are the same and are each methyl.

4. A platinum complex of formula (I) according to any one of the preceding claims, wherein R5-R8are each independently selected from a hydrogen atom, a substituted or unsubstituted Ci-s-alkyl, substituted or unsubstituted C2-8-alkenyl, substituted or unsubstituted C2-C8 alkoxycarbonyl, substituted or unsubstituted C2-8-alkynyl, substituted or unsubstituted Ci-8-heteroalkyl, substituted or unsubstituted Ci-8-alkoxy, substituted or unsubstituted Cs-s-cycloalkyl, substituted or unsubstituted C3-8- cycloalkenyl, substituted or unsubstituted C2-8-heterocycloalkyl, substituted or unsubstituted Ce-is-aryl, substituted or unsubstituted C4-8-heteroaryl, and substituted or unsubstituted C1-C10 alkylsilyl.

5. A platinum complex of formula (I) according to any one of the preceding claims, wherein R5 / R6, R6 / R7, or R7 / R8are linked to form a substituted or unsubstituted aromatic ring structure.

6. A platinum complex of formula (I) according to claim 5, wherein the platinum complex of formula (I) is a complex of formula (la), (lb), (Ic), or (Ic):wherein R1-R8are each as defined in any one of claims 1 to 5.

7. A platinum complex of formula (I) according to any one of the preceding claims, wherein R4is selected from a substituted or unsubstituted Ci-20-alkyl, substituted or unsubstituted C2-2o-alkenyl, substituted or unsubstituted C2-2o-alkynyl, substituted or unsubstituted Ci-20-heteroalkyl, substituted or unsubstituted Ci-2o-alkoxy, substituted or unsubstituted C3-2o-cycloalkyl, substituted or unsubstituted C3-2o-cycloalkenyl, substituted or unsubstituted C2-io-heterocycloalkyl, substituted or unsubstituted Ce-20- aryl, and substituted or unsubstituted C4-2o-heteroaryl.

8. A platinum complex of formula (I) according to any one of the preceding claims, wherein R4is an aryl group of formula (II):wherein Ra, Rb, Rc, Rd, and Reare each independently selected from a hydrogen atom; an organic group comprising from 1 to 10 carbon atoms, a group -X, and / or Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Remay be linked to form a ring structure, wherein -X is selected from -F, -Cl, -Br, -I, -NO2, -S(O)2OH.

9. A platinum complex of formula (I) according to claim 8, wherein Ra, Rb, Rc, Rd, and Reare each independently selected from hydrogen, nitrile, substituted or unsubstituted Ci-10-alkyl, substituted or unsubstituted Ci-io-heteroalkyl, substituted or unsubstituted C2-C10alkoxycarbonyl, and substituted or unsubstituted C1-10-alkoxy.

10. A platinum complex of formula (I) according to claim 8 or claim 9, wherein Ra, Rb, Rc, Rd, and Reare each independently selected from hydrogen, methyl, ethyl, / so-propyl, methoxy, ethoxy, / so-propoxy, and trifluoromethyl.

11. A platinum complex of formula (I) according to claim 8, wherein Ra / Rb, Rb / Rc, Rc / Rd, and / or Rd / Reare linked to form a ring structure, such as a substituted or unsubstituted ring structure.

12. A platinum complex of formula (I) according to any one of the preceding claims, wherein R4is a substituted or unsubstituted Ci-C2o, C2-Ci2, Cs-Cs or C4-C6 alkyl group, or an aryl group of formula (II) as defined in any one of claims 8 to 11.

13. A platinum complex of formula (I) according to any one of claims 1 to 6, wherein R4is one or more groups selected from:

14. A platinum complex of formula (I), wherein the platinum complex is one or more selected from:Rc= H, methyl, trifluoromethyl, methoxy, R4= methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl15. A platinum complex of formula (I) according to any one of claims 8 to 11, wherein the platinum complex of formula (I) has a resonance in the13C NMR spectrum corresponding to the C2 carbon of from 96.0 ppm to 101.0 ppm, from 96.5 ppm to 100.5 ppm, from 96.8 ppm to 100.0 ppm, or from 97.0 ppm to 99.0 ppm, such as97.5 ppm, 98.0 ppm or 98.5 ppm, wherein the C2 carbon is the carbon atom of the cyclopentadienyl ring adjacent to the carbon to which the -C(=O)R4group is attached.

16. A method for preparing the platinum complex of formula (I) according to any one of claims 1 to 15, the method comprising the steps of:a) reacting a cyclopentadiene salt with a compound of formula R4-C(=O)ORxto produce a cyclopentadienyl ligand, L,b) reacting a platinum containing starting material of general formula [Pt(R1R2R3)Y] with a silver salt of formula AgQ to form a platinum containing intermediate of general formula [Pt(R1R2R3)Q]; andc) reacting the platinum containing intermediate with the cyclopentadienyl ligand, L, to produce the platinum complex of formula (I),wherein each of R1-R8are as defined in relation to the platinum complex of formula (I) of any one of claims 1 to 15, Rxis an alkyl group, Q is selected from 'OTf, 'OMs, BF4, ’PFe, 'SbFe, CIO4, and p-toluenesulfonate, and Y is a halide.

17. A process for carrying out a hydrosilylation reaction using the platinum complex of formula (I) of any one of claims 1 to 15 as a pre-catalyst or catalyst.

Images