Composition with a platinum(IV) pre-catalyst

Abstract

The present invention is a composition comprising a) a compound functionalized with at least one Si-H group; b) a compound functionalized with at least one olefin group; and c) compound of Formula 1: where x, R1, R2, and R3 are as defined herein. The composition provides a pre-catalyst that decomposes quickly to a platinum state that promotes hydrosilylation upon irradiation with light of the appropriate wavelength.

Description

[0001] Composition with a Platinum(IV) Pre-catalyst Background of the Invention The present invention relates to a composition comprising a photoactivated platinum(IV) (Pt(IV)) pre-catalyst, particularly useful in hydrosilylation reactions. Hydrosilylation is commonly used in the silicones industry for the synthesis of silicone polymers and cross-linked materials. UV-initiated hydrosilylation using a photoactive pre-catalyst is becoming more popular as the energy input needed to trigger the reaction is low relative to thermally activated approaches. Pt(IV) species such as cyclopentadienyltrimethylplatinum and its analogs are known as photoactive pre-catalysts (see US 4,510,094; US 8,088,878; and US 10,392,479) for hydrosilylation; Pt(IV) species decompose under UV irradiation to form the catalytically active Pt(0) species. Nevertheless, these known pre-catalysts are often undesirably volatile, and reactions using these pre-catalysts tend to be sluggish. There is a need, therefore, to discover pre-catalysts that enhance reactivity and that exhibit favorable volatility profiles. Summary of the Invention The present invention is a composition comprising a) a compound functionalized with at least one Si-H group; b) a compound functionalized with at least one olefin group; and c) a compound of Formula 1: where each R1is independently C1-C6-alkyl or phenyl; each R2is independently H, methyl, ethyl, or phenyl; Y is Ar(R3)y, a radical, or a C1-C12 hydrocarbyl di-, tri-, or tetraradical; where Ar is a substituted or unsubstituted aromatic di-, tri-, or tetraradical; each R3is independently C1-C6-alkyl, C1-C6-alkoxy, phenyl, NO2, acetyl, trifluoromethyl, or halo; x is from 0 to 5; y is from 0 to 4; and z is 2, 3, or 4, with the proviso that when Y is a radical, z is 2. The present invention addresses a need in the art by providing a composition containing a nonvolatile Pt(IV) pre-catalyst that decomposes rapidly to the catalytically active Pt(0) state under light irradiation. Detailed Description of the Invention The present invention is a composition comprising a) a compound functionalized with at least one Si-H group; b) a compound functionalized with at least one olefin group; and c) a compound of Formula 1: where each R1is independently C1-C6-alkyl or phenyl; each R2is independently H, methyl, ethyl, or phenyl; Y is Ar(R3)y, a radical, or a C1-C12 hydrocarbyl di-, tri-, or tetraradical; where Ar is a substituted or unsubstituted aromatic di-, tri-, or tetraradical; each R3is independently C1-C6-alkyl, C1-C6-alkoxy, phenyl, NO2, acetyl, trifluoromethyl, or halo; x is from 0 to 5; y is from 0 to 4; and z is 2, 3, or 4, with the proviso that when Y is a radical, z is 2. The compound with at least one Si-H group preferably has at least three Si-H groups. The polyorganosiloxane of Formula 2 is an example of such a compound: Formula 2 where each R°is independently H or C1-C6-alkyl; each R′ is independently C1-C6-alkyl or phenyl; the sum of m + n is in the range of from 0, or from 1, or from 2 or from 3, to 1000 or to 400 or to 200 or to 100 or to 50, and wherein n is from 0, or from 1 or from 2 or from 3 to preferably 100 or to 50 or to 20; with the proviso that when n is less than 2, at least one R° is H. Preferably, when n is 0, each of the R° groups is H. The compound functionalized with at least one olefin group preferably is functionalized with at least two terminal olefin groups. Examples of such compounds include 1,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene. The compound functionalized with at least one olefin group may also be a Q-branched or T-branched polyorganosiloxane, as illustrated in Formula 3: R′′ is represented by Fragment 1: where the dashed lines represent the point of attachment to the oxygen atoms; each q is in the range of from 0 to 2000 or to 1000 or to 500 or to 250; each Rais independently C1-C6-alkyl or phenyl; and each Rbis Raor a C2-C8-alkenyl group; with the proviso that at least one of the Rbgroups is a C1-C6-alkenyl group; and R′′′ is C1-C6-alkyl, phenyl or OR′′. Preferably, each Rais methyl and at least one of the Rbgroups is a vinyl group. Accordingly, each R′′ is preferably represented by Fragment 2: An example of a Q-branched polyorganosiloxane is tetrakis(vinyldimethylsiloxy)silane (Fragment 2b, where q = 0), available commercially from Gelest Inc. Q-branched polysiloxanes with q > 0 may be prepared by an acid catalyzed equilibration reaction of tetrakis(vinyldimethylsiloxy)silane with octamethylcyclotetrasiloxane at advanced temperatures, followed by a neutralization step. Chain length (q) can be controlled by adjusting the relative amount of octamethylcyclotetrasiloxane. The compound functionalized with at least one olefin group may also be a linear polyorganosiloxane with two terminal olefin groups, as illustrated in Formula 4: where p is in the range of from 0 or from 2 or from 10, or from 40 or from 50, to 3000 or to 1000 or to 500 or to 250 or to 150; and R′ is preferably CH3. The compound with at least one olefin group may also be a combination of polyorganosiloxanes of Formulas 3 and 4, where the weight-to-weight ratio of the polyorganosiloxane of Formula 3 to the polyorganosiloxane of Formula 4 is preferably in the range of from 10:90 or from 30:70 or from 50:50 or from 60:40, to 95:5. The compound functionalized with at least one olefin group may further comprise structural units of a polyorganosiloxane resin, as illustrated in Fragments 3 and 4: where Rais preferably methyl, ethyl, or phenyl; and the dashed lines represent the points of attachment to other groups. In one embodiment of the invention, the mole:mole ratio of Si-H groups to olefin group groups is in the range of from 0.1:1 or from 0.5:1, to 20:1 or to 10:1 or to 5:1 or to 1.5:1. Each R1of the compound of Formula is preferably independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, or phenyl. Each R3is preferably independently methyl, trifluoromethyl, nitro, or methoxy. Suitable Ar radicals include di-, tri-, or tetraradicals of benzene, naphthalene, anthracene, phenanthrene, pyridine, furan, thiophene, 1,3,5-triazine, pyrazine, and pyrimidine. Diradicals of benzene are preferred Ar radicals. An example of a compound of Formula 1 where Y is a radical, each R2is H, x is 0, and z is 2 is a CpPtMe2 dimer bridged by an ethylene diradical, as illustrated: An example of a compound of 0, z is 2, Ar is a 1,4 phenyl diradical, and each R2is H, is a CpPtMe2dimer bridged with a CH2PhCH2diradical, as illustrated.

[0002] Hydrocarbyl di-, tri-, and tetraradicals include linear, branched, cyclic, and partially unsaturated fragments including ·CH2(CH2)n CH2·, ·CH2CH(CH3)CH2·, cyclopropyl-(CH2·)z; cyclobutyl-(CH2·)z, CH(CH2·)3, and C(CH2·)4; where n = 1 to 10; and z = 2 or 3; or 2, 3, or 4 when the fragment is cyclobutyl-(CH2·)z. The compound of Formula 1 is advantageously prepared using the following steps. In a first step, a cyclopentadienyl alkali metal salt such as sodium cyclopentadiene (Na-Cp) is contacted with R1-Br to form an alkyl or phenyl substituted cyclopentadiene (R1)x-Cp. Examples of preferred R1groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and t-butyl groups. (R1)x-Cp is then contacted with a bis(tetramethylsilyl)amide alkali metal salt such as potassium or sodium bis(tetramethylsilyl)amide or with an alkyl lithium such as n-butyl lithium to form the alkali metal salt of (R1)x-Cp (Intermediate A): Intermediate A can then be contacted with another equivalent of R1-Br to form a further substituted cyclopentadiene, and the reaction can be repeated up to a (R1)5-substituted Cp-alkali metal salt. Norbornadiene dimethyl platinum (II) ((NBD)PtMe2) is dissolved in a suitable donor solvent such as pyridine, then contacted with Y-(X)z, and then Intermediate A to form the compound of Formula 1: where X is CH2Cl, CH2Br, CH2I, CH2triflate, or CH2tosylate. Examples of Y-(X)z starting materials for Y = Ar and y = 0 are illustrated: Br w Where Y = C1-C12-hydrocarbyl, examples of starting materials include: where n = 0 to 10, and z is preferably 2 or 3.

[0003] Examples of specific compounds of the present invention include: R1R1xxR1x Pt Pt R1x ; R1 x ;;where R1is methyl, ethyl, n-propyl, or t-butyl; and x is 0 or 1. Examples Intermediate Example 1 – Preparation of (NBD)PtMe2 (NBD)PtMe2 was prepared using an adapted procedure from Eur. J. Inorg. Chem.2015, 2015, 226–239, wherein deionized water was used to quench the reaction rather than concentrated HCl. NMR spectroscopy of the obtained product matched that previously reported. Intermediate Example 2 – Preparation of p-[HCpPtMe2]2-benzyl-bridged dimer In a nitrogen filled glovebox, (NBD)PtMe2(0.102 g, 0.32 mmol, 1 equiv) was combined with pyridine (4 mL) and a magnetic stir bar in a 20-mL glass vial. The resulting golden yellow solution was stirred at ambient temperature for 30 min, after which time a suspension of 1,4-dibromomethylbenzene (0.042 g, 0.16 mmol, 0.5 equiv) in pyridine (1 mL) was added dropwise. Stirring was continued for 18 h, whereupon the resultant pale-yellow supernatant was separated from the colorless solids and filtered. The solids were discarded without further analysis. The filtrate was concentrated in vacuo and triturated with hexanes (2 x 2 mL) to afford a sticky yellow solid. The solid was then combined with THF (4 mL), followed by addition of NaCp (0.034 g, 0.39 mmol, 1.2 equiv). The reaction mixture was stirred at ambient temperature for 2 h, and the mixture was then passed through a layer of celite atop a plug of Florisil and sequentially filtered through two 0.45-µm PTFE syringe filters. The resulting pale-yellow orange filtrate was then concentrated to dryness and triturated with hexanes (2 x 2 mL). The residue was then taken up in hexanes (12 mL) and passed through a pad of Florisil and two 0.45-µm PTFE syringe filters sequentially, affording a nearly colorless solution. Additional toluene (5 mL) was passed through the filter as well. The combined filtrates were concentrated to dryness and triturated one more time with hexanes (2 mL), affording a pale-yellow solid. Yield: 0.065 g, 59.1 %.1H NMR (400 MHz, C6D6) δ 7.11 (s, 4H), 5.09 (s, 9H), 3.15 (2JPt-H= 97.6 Hz, 4H), 1.24 (2JPt-H = 82.6 Hz, 12H).13C NMR (101 MHz, C6D6) δ 148.06, 97.65, 12.05 (1JPt-C= 660.6 Hz), -18.06 (1JPt-C= 740.9 Hz).195Pt NMR (85 MHz, C6D6) δ -4948.01. Intermediate Example 3 – Synthesis of p-[MeCpPtMe2]2-benzyl-bridged dimer In a nitrogen filled glovebox, (NBD)PtMe2(0.175 g, 0.55 mmol, 1 equiv) was combined with pyridine (2 mL) and a magnetic stir bar in a 20-mL glass vial. The resulting golden yellow solution was allowed to stir at ambient temperature for 20 min, after which time a suspension of 1,4-dibromomethylbenzene (0.073 g, 0.28 mmol, 0.5 equiv) in pyridine (1 mL) was added dropwise. Stirring was continued for 18 h, whereupon the pale-yellow supernatant was separated from the colorless solids and filtered. The solids were discarded without further analysis. The filtrate was concentrated in vacuo and triturated with hexanes (3 x 2 mL) to afford a sticky yellow solid. The material was then combined with THF (4 mL) followed by the addition of solid LiMeCp (0.057 g, 0.66 mmol, 1.2 equiv). The reaction mixture was stirred at ambient temperature for 2 h, and the mixture was then passed through a layer of celite atop a plug of Florisil and sequentially filtered through two 0.45-µm PTFE syringe filters. The resulting yellow-orange filtrate was then concentrated to dryness and triturated with hexanes (2 x 2 mL). The residue was then taken up in hexanes (12 mL) and passed through a Florisil pad and two 0.45-µm PTFE syringe filters sequentially, affording a nearly colorless solution. The filtrate was concentrated to dryness and triturated one more time with hexanes (2 mL), affording a pale-yellow solid. Yield: 0.110 g, 56.0 %.1H NMR (400 MHz, C6D6) δ 7.12 (s, 4H), 5.03 (t, J = 2.1 Hz, 4H), 4.72 (t, J = 2.3 Hz, 4H), 3.18 (2JPt-H= 97.6 Hz, 4H), 1.59 (s, 6H), 1.18 (2JPt-H= 81.9 Hz, 12H).13C NMR (101 MHz, C6D6) δ 147.82, 114.55, 98.60, 93.57, 11.75 (1JPt-C = 658.4 Hz), 11.59, -14.59 (1JPt-C= 743.5 Hz).195Pt NMR (86 MHz, C6D6) δ -4970.37.

[0004] Intermediate Example 4 – Synthesis of meta-[MeCpPtMe2]2-benzyl-bridged dimer In a nitrogen filled glovebox, (NBD)PtMe2 (0.100 g, 0.32 mmol, 1 equiv) was combined with pyridine (2 mL) and a magnetic stir bar in a 20-mL glass vial. The resulting golden yellow solution was allowed to stir at ambient temperature for 10 min, after which time a mixture of 1,3-dibromomethylbenzene (0.043 g, 0.16 mmol, 0.5 equiv) in pyridine (1 mL) was added dropwise. Stirring was continued for 6 h, whereupon solid LiMeCp (0.033 g, 0.38 mmol, 1.2 equiv) and additional pyridine (1 mL) were added. The reaction mixture was stirred for 1 h, and the mixture was then passed through a layer of Celite and two 0.45 µm-PTFE syringe filters. The resulting pale-yellow orange filtrate was then concentrated to dryness and triturated with hexanes (2 x 2 mL). The residue was extracted with hexanes (2 x 10 mL) and passed through a Florisil pad and two 0.45-µm PTFE syringe filters sequentially, affording a pale-yellow solution. The filter pad was further washed with toluene (4 mL) and the combined filtrates were concentrated to dryness and triturated one more time with hexanes (2 mL), affording a pale-yellow sticky solid. Yield: 0.065 g, 57.9 %.1H NMR (400 MHz, C6D6) δ 7.27 – 7.21 (m, 1H), 7.09 – 7.03 (m, 1H), 7.03 – 6.94 (m, 2H), 5.04 (t, J = 1.4 Hz, 4H), 4.75 (t, J = 2.3 Hz, 4H), 3.19 (2JPt-H = 97.9 Hz, 4H), 1.59 (3JPt-H = 3.0 Hz, 6H), 1.20 (2JPt-H = 81.8 Hz, 12H).13C NMR (101 MHz, C6D6) δ 151.28, 124.90, 114.89, 98.89, 93.24, 11.87 (1JPt-C= 663.2 Hz), 11.60, -14.44 (1JPt-C = 740.2 Hz).195Pt NMR (86 MHz, C6D6) δ -4995.56.

[0005] Intermediate Example 5 – Synthesis of o-[MeCpPtMe2]2-benzyl-bridged dimer In a nitrogen filled glovebox, (NBD)PtMe2 (0.145 g, 0.46 mmol, 1 equiv) was combined with pyridine (2 mL) and a magnetic stir bar in a 20-mL glass vial. The resulting golden yellow solution was allowed to stir at ambient temperature for 20 min, after which time a mixture of 1,2-bis(bromomethyl)benzene (0.060 g, 0.23 mmol, 1 equiv) in pyridine (1 mL) was added dropwise. Stirring was continued for 6 h, whereupon solid LiMeCp (0.047 g, 0.55, 1.2 equiv) and additional pyridine (1 mL) were added. After stirring for 1h, a portion of hexanes (6 mL) was added to the reaction mixture. The reaction mixture was then passed through a layer of Celite, a 0.45 µm-PTFE syringe filter, and a 0.20 µm-PTFE syringe filter sequentially. The resulting orange filtrate was then concentrated to dryness and triturated with hexanes (2 x 1 mL). The residue was extracted into hexanes (2 x 8 mL) and passed through aFlorisil pad and two 0.20-µm PTFE syringe filters sequentially. The filtrate was then concentrated to dryness, affording a pale-yellow solid. Yield: 0.095 g, 58.3 %.1H NMR (400 MHz, C6D6) δ 7.24 – 7.17 (m, 1H), 6.97 – 6.89 (m, 1H), 4.95 (t, J = 1.5 Hz, 2H), 4.70 (t, J = 2.4 Hz, 2H), 3.13 (2JPt-H = 96.9 Hz, 1H), 1.57 (JPt-H= 6.0 Hz, 1H), 1.30 (2JPt-H= 81.3 Hz, 2H).13C NMR (101 MHz, C6D6) δ 148.45, 129.45 (JPt-C = 21.3 Hz), 124.93 (JPt-C = 14.7 Hz), 113.87, 98.90, 93.96, 11.49, 11.24 (1JPt-C = 667.4 Hz), -14.92 (1JPt-C= 737.4 Hz).195Pt NMR (85 MHz, C6D6) δ -4965.08.

[0006] Intermediate Example 6 – Synthesis of o-[tBuCpPtMe2]2-benzyl-bridged dimer In a nitrogen filled glovebox, (NBD)PtMe2(0.125 g, 0.39 mmol, 1 equiv) was combined with pyridine (2 mL) and a magnetic stir bar in a 20-mL glass vial. The resulting golden yellow solution was allowed to stir at ambient temperature for 20 min, after which time a pyridine solution (1 mL) of 1,2-bis(bromomethyl)benzene (0.052 g, 0.20 mmol, 0.5 equiv) was added dropwise. Stirring was continued for 1 h, whereupon solid KtBuCp (0.076 g, 0.47, 1.2 equiv) was added. After stirring for 1 h, a portion of hexanes was added to the mixture. The reaction mixture was then passed through a layer of Celite and a 0.45 µm-PTFE syringe filter. The filtrate was then concentrated to dryness and triturated with hexanes (2 x 2 mL). The residue was extracted with hexanes (3 x 5 mL) and passed through a Florisil pad and two 0.20-µm PTFE syringe filters sequentially. The filtrate was then concentrated to dryness, affording a pale-yellow solid. Yield: 0.060 g, 38.2 %.1H NMR (400 MHz, C6D6) δ 7.32 – 7.19 (m, 2H), 7.00 – 6.88 (m, 2H), 5.07 (t, J = 2.3 Hz, 4H), 4.87 (t, J = 2.3 Hz, 4H), 3.19 (2JPt-H = 97.2 Hz, 4H), 1.39 (2JPt-H= 80.9 Hz, 12H), 1.06 (s, 18H).13C NMR (101 MHz, C6D6) δ 148.23, 129.64, 125.05, 97.30, 93.61, 31.63, 31.05, 12.00 (JPt-C = 664.6 Hz), -16.16 (JPt-C = 732.5 Hz).195Pt NMR (85 MHz, C6D6) δ -4936.12 (m).

[0007] Intermediate Example 7 – Preparation of CpPtMe2(CH2CH2CH2)Me2PtCp In a nitrogen filled glovebox, (NBD)PtMe2 (0.055 g, 0.173 mmol, 1 equiv.) and pyridine (5 mL) were charged into a 20-mL glass vial. The contents were stirred for 10 min at room temperature, after which time 1,3-diiodopropane (9.9 µL, 0.0867 mmol, 0.5 equiv.) in pyridine (1 mL) was added to the vial. The mixture was stirred overnight, then removed from the glovebox and dried in vacuo to give an orangish residue. The residue was triturated with pentane and dried further. The orange solid was then taken up in CH2Cl2and pushed through a Florisil pad, giving a yellow filtrate. The filtrate was dried in vacuo to give a yellowish solid (0.014 g, 26%).1H NMR (400 MHz, C6D6) δ 5.31 (m, J = 2.9 Hz, 10H), 1.91 (s, 6H), 1.16 (m, 1H,2JPt-H= 83 Hz);13C NMR (101 MHz, C6D6) δ 96.45, 46.41 (m), 12.84 (m,2JPt-C = 99Hz), -19.44 (m,1JPt-C = 750Hz);195Pt NMR (85 MHz, C6D6) δ -5115.67. The compounds of Intermediate Examples 2-7 (Pre-catalysts) were combined separately with methyl trimethoxy silane (XIAMETER™ OFS-6070 Silane (MTM)). Each pre-catalyst + MTM mixture was added to a pre-mixed blend of a vinyl-terminated polydimethylsiloxane (XIAMETER™ RBL-9119 Polymer (Polymer 1)) and a trimethylsilyl-terminated methylhydrosiloxane-dimethylsiloxane copolymer (DOWSIL™ 6-3570 Polymer (Polymer 2). Each composition was mixed at 2000 rpm for 30 s. (XIAMETER and DOWSIL are Trademarks of The Dow Chemical Company or its Affiliates.) Table 1 illustrates polyorganosiloxane formulations with the catalysts of the present invention. Polymer 1 refers to Xiameter RBL-9119 Vinyl-terminated PDMS; Polymer 2 refers to DOWSIL™ 6-3570 Copolymer; and Catalyst / MTM blend refers to a 1% catalyst (Intermediate Examples 2-6) or 2% catalyst (Intermediate Example 7) in methyl trimethoxysilane (MTM). The concentration of elemental Pt was 18 ppm, and the ratio of Si-H groups to vinyl groups was 0.45:1 for each sample. Table 1 – Polyorganosiloxane Formulations Pt Catalyst Intermediate Ex. No. 2 3 4 5 6 7 Polymer 1 (pbw) 98.78 98.77 98.77 98.77 98.73 98.95 The gel point times for each sample was measured using the following UV-rheology test: UV-activated hydrosilylation cure tests were carried out using an MCR-302 Rheometer equipped with a UV irradiation accessory. Broadband UV of a wavelength between 250 and 450 nm was irradiated, and 4 J / cm2of UV dose was applied (100 mW / cm2x 40 sec). Sample thickness was initially set at 0.3 mm. To generate cure profiles, viscoelastic properties were monitored applying oscillatory shearing within linear viscoelastic regions at 10 rad / sec. Then, the gel times were determined from the G’-G” crossover points. Table 2 illustrates the gel point times for each formulation. Table 2 – Cure Times for Formulations Intermediate Example No. Gel Point Time (min) The formulations o p y, evidenced by gel point times of < 30 min.

Claims

Claims:

1. A composition comprising a) a compound functionalized with at least one Si-H group; b) a compound functionalized with at least one olefin group; and c) compound of Formula 1:where each R1is independently C1-C6-alkyl or phenyl; each R2is independently H, methyl, ethyl, or phenyl; Y is Ar(R3)y, a radical, or a C1-C12 hydrocarbyl di-, tri-, or tetraradical; where Ar is a substituted or unsubstituted aromatic di-, tri-, or tetraradical; each R3is independently C1-C6-alkyl, C1-C6-alkoxy, phenyl, NO2, acetyl, trifluoromethyl, or halo; x is from 0 to 5; y is from 0 to 4; and z is 2, 3, or 4, with the proviso that when Y is a radical, z is 2.

2. The composition of Claim 1 wherein the compound functionalized with at least one Si-H group is a polyorganosiloxane functionalized with at least two Si-H groups and having a degree of polymerization in the range of from 2 to 400; and the compound functionalized with at least one olefin group is a polyorganosiloxane functionalized with at least two vinyl groups and having a degree of polymerization up to 1000.

3. The composition of Claim 2 wherein the compound functionalized with at least two Si-H group is a polyorganosiloxane of Formula 2: ;wherein each R° is independently H or C1-C6-alkyl; each R′ is independently C1-C6-alkyl or phenyl; the sum of m + n is in the range of from 0 to 400, and wherein n is from 0 to 100; with the proviso that when n is 0, each of the R° groups is H.

4. The composition of Claim 3 wherein each R2is H; Y is Ar(R3), wherein Ar is a substituted or unsubstituted di-, tri-, or tetraradical of benzene, naphthalene, anthracene, phenanthrene, pyridine, furan, thiophene, 1,3,5-triazine, pyrazine, or pyrimidine.

5. The composition of Claim 4 where each R1is independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, or phenyl; Y is a substituted or unsubstituted di- or triradical of benzene; y is 0; and z is 2 or 3.

6. The composition of Claim 3 where each R1is independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, or phenyl; each R2is H; Y is a C1-C12 hydrocarbyl di-, tri-, or tetraradical; and y is 0.

7. The composition of Claim 6 where Y is ·CH2(CH2)nCH2·, ·CH2CH(CH3)CH2·, cyclopropyl-(CH2·)z; cyclobutyl-(CH2·)z, CH(CH2·)3, and C(CH2·)4; where n is 1 to 10; z is 2 or 3.

8. The composition of Claim 3 where Y is a radical; each R1is independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, or phenyl; each R2is H.

9. The composition of Claim 1 which is: R1x R1xR1x Pt Pt 1 x ; 1 x ;;where R1is methyl, ethyl, n-propyl, or t-butyl; and x is 0 or 1.

10. The composition of Claim 1 which is: .

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