Synthesis and Characterization of an Osmapentalene Derivative Containing a β‑Agostic Os···H–C(sp3) Interaction

Treatment of cyclopropaosmapentalene (1) with EtCCEt in the presence of AgBF4 gave a new type of polycyclic metallaaromatic complex with a structure containing an sp3 carbon and a β-agostic Os···H–C­(sp3) interaction. This result strongly supported our proposed intermediate in the reaction of cyclopropaosmapentalene 1 with alkynes that produced photothermal osmium carbolong complexes. When EtCCCOMe was used, the reaction gave a more thermally stable ketone-coordinated complex as the major product. The DFT study indicated that the difference in the two reactions is of thermodynamic origin.