Isolation of a C3-metalated indolizine complex and a phosphonium ring-fused bicyclic metallafuran from the osmium-induced transformation of pyridine-tethered alkynes

Abstract

The first C3-metalated indolizine complex was prepared from the reaction between cis-[Os(dppm)₂Cl₂] (dppm = 1,1-bis(diphenylphosphino)methane) and propargylic pyridine, HCCC(OH)(2-py)₂. A phosphonium ring-fused bicyclic osmafuran complex was also prepared from the reaction between cis-[Os(dppm)₂Cl₂] and pyridyl ynone, HCC(CO)(2-py). The formation of these two products revealed the intermediacy of metal–vinylidene species regarding [Os(dppm)₂Cl]⁺-mediated alkyne transformations. Comparison of the d⁶ transition-metal precursors employed to activate HCCC(OH)(2-py)₂ suggests that precursors with higher π-basicity favor the vinylidene-involving pathway.