A series of Rh- and Ir-hybrid catalysts with varying tether lengths has been prepared by immobilization of RhI, RhIII and IrIII 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 RhIII- and IrIII hybrids afforded the β(Z)-vinylsilanes, as observed for the analogous homogeneous RhIII catalyst. No distinct product selectivity was observed when using the homogeneous RhI precursors as catalysts. However, on using the RhIII hybrid catalysts derived from the RhI 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.