AbstractThe preparation of 1‐(3‐triisopropoxysilylpropyl)‐3‐(2‐methoxyethyl)‐imidazolium bromide or chloride salts and their reaction with [Rh(COD)(μ‐OMe)]2 (COD=1,5‐cyclooctadiene) to afford the corresponding [Rh(COD)(NHC)X] (X=Br, Cl; NHC=1‐(3‐triisopropoxysilylpropyl)‐3‐(2‐methoxyethyl)‐2‐ilydene‐imidazol) species is described. These new compounds were used as catalyst precursors for acetophenone hydrosilylation. The higher activity of the rhodium‐chlorido complex evidences a clear halide effect in the activation of the catalyst. Immobilization of the catalytic precursor [Rh(COD)(NHC)Cl] on mobile crystalline material 41 (MCM‐41) allows for the preparation of the corresponding heterogeneous catalyst. Reduction of acetophenone to PhMeCH‐O‐SiMe(OSiMe3)2 by hydrosilylation with 1,1,1,3,5,5,5‐heptamethyltrisiloxane is effectively catalyzed by both the homogeneous and the heterogeneous catalysts, in which the homogeneous system is the more active. Interestingly, the heterogeneous catalyst is reusable. Both homo‐ and heterogeneous catalysts are also effective for the copolymerization of terephthalaldehyde and 1,1,3,3,5,5‐hexamethyltrisiloxane, which affords the corresponding poly(silyl ether). The catalyst yields the heterogeneous system polymers with higher molecular weights (Mw=94 000 g mol−1) and a narrow molecular weight distribution (PDI=1.5–1.7).