The chemistry of organo(silyl)platinum(II) complexes relevant to catalysis

Abstract

A variety of silylplatinum complexes cis- and trans-PtR(SiYPh 2)L 2 (R=Me, Et, Pr, Bu, vinyl, phenyl, phenylethynyl; Y=Ph, Me, H, F, OMe; L=PMePh 2, PMe 2Ph), cis-Pt(SiR 3)(SnMe 3)(PMe 2Ph) 2 (SiR 3=SiMe 3, SiMe 2Ph, SiMePh 2, SiPh 3), and cis-Pt(SiR 3) 2(PMe 2Ph) 2 (SiR 3=SiMe 2Ph, SiMePh 2, SiPh 3) have been prepared, and their structures and reactivities toward CSi bond formation and phenylacetylene insertion have been examined by X-ray diffraction analysis, NMR spectroscopy, and kinetic experiments. Three types of processes are operative for CSi bond formation from cis-PtR(SiYPh 2)L 2 complexes giving RSiYPh 2. One is the direct CSi reductive elimination; most of the complexes follow this process. The second type involves isomerization of cis-PtR(SiYPh 2)L 2 to cis-PtY(SiRPh 2)L 2, followed by YSi reductive elimination; this process has been observed for cis-PtR(SiPh 3)L 2 (R=Et, Pr, Bu) and cis-PtR(SiHPh 2)L 2 (R=Me, Et, Pr, Bu). Reactions of alkyl–silyl complexes with hydrosilanes also afford the corresponding alkylsilanes quantitatively, constituting the third type of process. Insertion of phenylacetylene into the PtSi bond of PtR(SiPh 3)L 2 complexes takes place only for the cis isomers. Silyl–stannyl complexes undergo competitive insertion of phenylacetylene into the PtSi and PtSn bonds under kinetic conditions, whereas the insertion into the PtSi bond predominates under thermodynamic conditions. Reactivities of four PtSiR 3 bonds toward insertion relative to the PtSnMe 3 bond have been evaluated: SiMe 3 (>49)>SiMe 2Ph (1.9)>SiMePh 2 (0.69)>SiPh 3 (0.075). Bis-silyl complexes exhibit a rather intricate dependence of the insertion reactivity upon the sorts of silyl ligands, not simply correlated with the reactivity of PtSiR 3 bonds, owing to the insertion process involving prior dissociation of a phosphine ligand. The bis-silyl complexes have a twisted square planar structure significantly distorted from planarity, and the rate of phosphine dissociation is highly sensitive to this distortion.