EXAMINATION OF METAL-SILICON BONDING THROUGH STRUCTURAL AND THEORETICAL-STUDIES OF AN ISOSTRUCTURAL SET OF 5-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 s ingle-crystal solid-state structure of each derivative. Carbonyl stret ching frequencies decrease and Os-Si bond lengths increase as R change s in the order from F to Cl to OH to Me. Ab initio calculations were p erformed 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 t he importance of the pi-acceptor capacities of the silyl groups are di scussed.