Four bis(silyl)platinum complexes cis-Pt(SiR 3 ) 2 (PMe 2 Ph) 2 (SiR 3 ) SiMe 2 Ph (1a), SiMePh 2 (1b), SiPh 3 (1c), SiFPh 2 (1d)) have been prepared and their reactions with alkynes and alkenes examined. The X-ray structures of 1a-c exhibit significant distortion from the square planar geometry in the order 1b > 1c > 1a. Complexes 1a-d react with phenylacetylene in solution to give the corresponding insertion complexes cis-Pt{C(Ph)dCH(SiR 3 )}(SiR 3 )(PMe 2 -Ph) 2 (2a-d). Complex 1c reacts also with acetylene to afford the insertion complex cis-Pt-(CHdCHSiPh 3 )(SiPh 3 )(PMe 2 Ph) 2 (2e), whose structure has been determined by X-ray diffraction study. Kinetic studies indicate the insertion process involving prior dissociation of PMe 2 Ph ligand from 1, followed by insertion of phenylacetylene into the Pt-SiR 3 bond. The reactivity toward insertion decreases in the order 1c > 1a > 1b . 1d. Factors responsible for the reactivity order are discussed on the basis of kinetic data and X-ray structures.
A series of trans-and cis-PtR(SiPh 3 )(PMe 2 Ph) 2 complexes have been prepared and their thermolysis reactions in solution examined. The trans isomers (R ) Me, Et) are robust, and only the methyl complex affords MeSiPh 3 as the reductive elimination product in 72-82% yields. In contrast, the cis isomers (R ) Me, Et, Pr, Bu) form the corresponding alkylsilanes in almost quantitative yields (>97%). Despite the selective formation of the reductive elimination products, the cis-alkyl-silyl complexes bearing -hydrogens undergo a rapid repetition of the -hydrogen elimination and insertion processes, as confirmed by a deuteriumlabeling experiment using cis-Pt(CH 2 CD 3 )(SiPh 3 )(PMe 2 Ph) 2 . The alkylsilane formation from the cis isomers proceeds via two reaction paths. One is the direct C-Si reductive elimination. On the other path, the cis-PtR(SiPh 3 )(PMe 2 Ph) 2 complexes are initially isomerized to the corresponding cis-PtPh(SiRPh 2 )(PMe 2 Ph) 2 complexes by the exchange of the Pt-R group with the Si-Ph group, and the resulting phenyl-silyl complexes reductively eliminate alkylsilanes. The methyl-silyl complex decomposes exclusively by the former path, while the other alkyl-silyl complexes (R ) Et, Pr, Bu) follow mainly the latter path. Preparation and thermolysis reaction of the related cis-PtEt(GePh 3 )(PMe 2 Ph) 2 are also reported.
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