Stereodivergent Formation of Alkenylsilanes: syn or anti Hydrosilylation of Alkynes Catalyzed by a Cyclopentadienylcobalt(I) Chelate Bearing a Pendant Phosphane Tether

Abstract The hydrosilylation of alkynes is catalyzed by the di‐ tert ‐butylphosphanylethylcyclopentadienylcobalt chelate 1 . While the reaction of internal alkynes exclusively affords syn hydrosilylation products with triethylsilane, the reaction with triethoxysilane shows predominant anti stereoselectivity. Reactions of terminal alkynes are less selective with triethylsilane and result in cyclotrimerization when triethoxysilane is used.