Carbon supported hybrid catalysts for controlled product selectivity in the hydrosilylation of alkynes

A series of Rh- and Ir-hybrid catalysts with varying tether lengths has been prepared by immobilization of Rh^I, Rh^III and Ir^III complexes on carbon black via radical grafting. The performance of the different catalysts was assessed for the hydrosilylation of phenylacetylene with Et₃SiH. The efficiency of the catalysts was dependent on the length of the tethers to the surface. The Rh^III- and Ir^III hybrids afforded the β(Z)-vinylsilanes, as observed for the analogous homogeneous Rh^III catalyst. No distinct product selectivity was observed when using the homogeneous Rh^I precursors as catalysts. However, on using the Rh^III hybrid catalysts derived from the Rh^I precursors to promote hydrosilylation, the major products were the α-vinylsilanes and the origin of the difference in reactivity was found to be a chemical modification of the catalysts during immobilization. Substrate scope is demonstrated for a number of alkynes, and feasible mechanisms supported by DFT calculations are proposed. [graphical abstract]