Cyclohydrosilylation dimer formation: evidence for Pt0 PtII PtIV catalysis

Article abstract of DOI:10.1016/0022-328X(93)80051-C

An eight-membered cyclic compound, 2,2,3,4,4,6,6,7,8,8-decamethyl-1,5-dioxa-2,4-disilacyclooctane (VIII), along with the expected five-membered 2,2,5,5-tetramethyl-1-oxa-2-silacyclopentane (V) were found to be the major products when vinyldimethylcarbinoxydimethylsilane (I) (i.e. 2-methyl-3-buten-2-oxydimethylsilane) was subjected to cyclohydrosilylation using platinum catalysis.The eight-membered product (VIII) readily undergoes β-elimination during gas chromatography (GC) analysis to extrude 2-methyl-2-butene giving the six-membered 2,2,4,4,5,6,6-heptamethyl-1,3-dioxa-2,4-disilacyclohexane (VI).Contrary to an earlier report (T.H.Lane and C.I.Frye, J.Organomet.Chem.,172 (1979) 213), no siloxetane or silanone intermediates are needed to rationalize the formation of the six-membered cyclic compound.When (Wilkinson's) rhodium catalyst was used for the hydrosilylation, only V was formed.The formation of VIII with platinum catalysis is rationalized by a mechanism utilizing successive oxidative additions to both Pt⁰ and Pt^II catalytic species; i.e. the absence of a second catalytically active level of rhodium is believed responsible for its inability to yield the eight-membered cyclic.Similarly, dimerization of either 1,1-dimethyl-1-silacyclobutane or 1,1,3,3-tetramethyl-1,3-disilacyclobutane to form the cyclooctanes can be readily achieved by platinum catalysis but not by rhodium catalysis.These results constitute the first examples of processes believed to require the presence of not only one but two catalytically active oxidation levels.