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(SiCl 3 )Cl(CO)(PPh 3 ) 2 is prepared by treatment of OsPhCl(CO)(PPh 3 ) 2 with excess HSiCl 3 and serves in turn as the starting material for the syntheses of three more five-coordinate silyl complexes Os(SiR 3 )Cl(CO)(PPh 3 ) 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(SiR 3 )Cl(CO)(PH 3 ) 2 (R = F, Cl, OH, Me) to explain the trends observed in the IR and X-ray studies, and the importance of the π-acceptor capacities of the silyl groups are discussed.