Preparation and properties of triosmium propyl and propylidene complexes

Abstract

Treatment of HOs 3(CO) 10(CHCHCH 3) in THF with LiBHEt 3 gave [HOs 3(CO) 10(CHCH 2CH 3)] −, isolated as the NEt 4 + or NMe 4 + salt. Protonation at −70 °C with HBF 4 formed HOs 3(CO) 10(CH 2CH 2CH 3), which was isolated as a yellow solid stable only at low temperatures. The kinetics of both its equilibration with H 2Os 3(CO) 10(CHCH 2CH 3) at −25 °C and of its decomposition to H 2Os 3(CO) 10 and propene at 19 °C have been determined. Treatment of HOs 3(CO) 10(CHCH 2) with CH 2PPh 3 in THF gave the zwitterionic complex HOs 3(CO) 10(CHCH 2CH 2PPh 3), isolated in 60% yield as a yellow solid. Protonation with HX (X=BF 4 − , CF 3SO 3 − , CF 3CO 2 − ) at −78 °C in dichloromethane occurred at an osmiumcarbon bond to yield [HOs 3(CO) 10(CH 2CH 2CH 2PPh 3)] +, containing a bridging alkyl with one C⋯H⋯Os agostic interaction. At approximately −50 °C partial (X=CF 3SO 3 − ) or complete (CF 3CO 2 − ) isomerization to a terminal alkyl form with coordination of the anion was observed. When the bridging alkyl was the major form, β-elimination occurred readily above −25 °C with formation of [PPh 3CH 2CHCH 2] + and H 2Os 3(CO) 10. The terminal alkyl complex was found to be more stable thermally, and in the case of HOs 3(CO) 10(O 2CCF 3)(CH 2CH 2CH 2PPh 3), the primary path of decomposition at 10 °C was reductive elimination to form [PPh 3CH 2CH 2CH 3] + and HOs 3(CO) 10(O 2CCF 3).