The reactivity of the silicon-hydrogen bond in (ethynylhydrosilane)cobalt carbonyl complexes has been studied. Halogenation of the Si‒H bond was achieved under ionic or radical reaction conditions. A spontaneous dehydrogenative coupling reaction was observed with proton donors (methanol, water, benzoic acid, aniline). Hydrosilylation reactions of benzaldehyde, furfural, and phenylacetylene was found to take place without added catalyst. Whereas catalysis by cobalt cannot be excluded in the reaction with proton donors, it seems that the Si‒H bond exhibits higher reactivity in the complex than in the parent silane. Di- and tricomplexed propynylsilanes have been formed upon selective complexation of two or three triple bonds. Although of lower thermal stability, complexes with a reactive Si‒H bond were obtained. © 1990, American Chemical Society. All rights reserved.