Examination of metal-silicon bonding through structural and theoretical studies of an isostructural set of five-coordinate silyl complexes, Os(SiR3)Cl(CO)(PPh3)(2) (R=F, Cl, OH, ME)

Os(SiCl3)Cl(CO)(PPh3)(2) is prepared by treatment of OsPhCl(CO)(PPh3)(2) with excess HSiCl3 and serves in turn as the starting material for the syntheses of three more five-coordinate silyl complexes Os(SiR3)Cl(CO)(PPh3)(2) (R = F, OH, Me) via substitution of the chloride groups on silicon. All four compounds were fully characterized, including a single-crystal solid-state structure of each derivative. Carbonyl stretching frequencies decrease and Os-Si bond lengths increase as R changes in the order from F to Cl to OH to Me. Ab initio calculations were performed on the model complexes Os(SiR3)Cl(CO)(PH3)(2) (R = F, Cl, OH, Me) to explain the trends observed in the IR and X-ray studies, and the importance of the pi-acceptor capacities of the silyl groups are discussed.