Regio-
and Stereoselective Hydrosilylation of Alkynes
Catalyzed by Three-Coordinate Cobalt(I) Alkyl and Silyl Complexes
- Publication date
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Abstract
A three-coordinate cobalt(I) complex
exhibits high catalytic efficiency
and selectivity as well as good functional group compatibility in
alkyne hydrosilylation. [Co(IAd)(PPh<sub>3</sub>)(CH<sub>2</sub>TMS)] (<b>1</b>) (IAd = 1,3-diadamantylimidazol-2-ylidene)
facilitates regio- and stereoselective hydrosilylation
of terminal, symmetrical internal, and trimethylsilyl-substituted
unsymmetrical internal alkynes to produce single hydrosilylation
products in the forms of β-(<i>E</i>)-silylalkenes,
(<i>E</i>)-silylalkenes, and (<i>Z</i>)-α,α-disilylalkenes,
respectively, in high yields. The comparable catalytic efficiency
and selectivity of the Co(I) silyl complex [Co(IAd)(PPh<sub>3</sub>)(SiHPh<sub>2</sub>)] that was prepared from the reaction
of <b>1</b> with H<sub>2</sub>SiPh<sub>2</sub>, and the isolation
of an alkyne Co(I) complex [Co(IAd)(η<sup>2</sup>-PhCCPh)(CH<sub>2</sub>TMS)] from the reaction of <b>1</b> with the acetylene,
point out a modified Chalk–Harrod catalytic cycle for these
hydrosilylation reactions. The high selectivity is thought
to be governed by steric factors
