The reaction of bromomethylidynetricobalt nonacarbonyl or, more effectively, of methylidynetricobalt nonacarbonyl with diverse silicon hydrides (R 3SiH, Ph 3SiH, Me 2(EtO)SiH, R n Cl 3 -n SiH ( n = 02), etc. results in formation of silylmethylidynetricobalt nonacarbonyl complexes. Silicon-functional interconversions such as SiCl → SiOH, SiCl → SiOMe, SiOH → SiF, and SiOH → SiOSiMe 3, have provided still other substituted silylmethylidynetricobalt nonacarbonyl complexes, generally in high yield. The compounds Me(HO) 2SiCCO 3(CO) 9 and (HO) 3SiCCo 3(CO) 9 have been incorporated into methylsilicone polymers by H 2SO 4-induced reactions with cyclo-(Me 2SiO) 3.