MECHANISM OF FORMATION OF PLATINUM(O) COMPLEXES CONTAINING SILICON-VINYL LIGANDS

Reactions are described in detail between H2PtCl6 and vinyl-silicon-containing compounds such as 1,3-divinyltetramethyldisiloxane (M(vi)M(vi)) and divinyldimethylsilane ((CH3)(2)Si-(CH=CH2)(2)). The structures of the platinum and silicon products were examined from these reactions with M(vi)M(vi) and 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane (D-4(vi)). The platinum products were all Pt(0)-olefin complexes. The reaction of chloroplatinic acid with M(vi)M(vi) gave a mixture of platinum complexes containing M(vi)D(x)M(vi) ligands (1; x = 0-11). Some complexes are polynuclear with bridging ligands and no metal-metal bonds, such as Pt-2-(M(vi)M(vi))(3) (2). The conversion of Pt(IV) complexes to Pt(0) species resulted in the net conversion of a silicon-vinyl group to a silicon-oxygen group. The reaction of H2PtCl6 with (CH3)(2)Si(CH=CH2)(2) gave both a Pt(0) (4) and a Pt(II) (5) product. A three-dimensional, X-ray crystal structure of 5 was solved, which showed a doubly chloro bridged platinum dimer with no metal-metal bond of stoichiometry C18H38Cl2Pt2Si3. The dimer contained a bridging (CH3)(2)Si(CH=CH2)(2) ligand. Additionally each Pt atom had a chelating (CH3)(2)Si-(eta(2)-CH=CH2)(eta(1)-CH2CH2) ligand, resulting from formal protonation of one of the vinyl groups. Crystallographic data: a = 6.799(3) Angstrom, b = 19.830(8) Angstrom, c = 18.847(10) Angstrom, beta = 95.43(4)degrees; space group P2(1)/c; Z = 4. The structure of 4 was determined by spectroscopic analysis to be a Pt(0)-olefin complex. The structures of 4 and 5 were further confirmed by preparation of chemical derivatives with P(C6H5)(3), which formed known platinum phosphine compounds. Compound 4 converted to compound 5 by reaction with HCl. A mechanism for the reaction of Pt(IV) with silicon-vinyl is presented based on the analysis of platinum, silicon, and gaseous products. Mechanistic experiments included reactions with D2PtCl6 and reactions in the presence of added C2H4 or C2D4.