Synthesis of 4:5-benzo-1-cobalta-2-silacyclopentenes and their reactions with alkynes and alkenes:: An expedient route to silicon-containing polycyclic frameworks

A convenient route to polycyclic compounds incorporating a silicon atom at a ring junction has been developed. Benzosilacyclobutenes tethered to alkynes or alkenes undergo intramolecular cycloadditions in the presence of CpCo(CO)(2). The incorporation of the CpCo(CO) moiety into the benzosilacyclobutene framework occurs regioselectively at the Ar-Si bond of the silacycle to give 1-cobalta-2-silacyclopentenes. On the basis of DFT/B3LYP calculations, a nonadiabatic mechanism involving changes in the spin state is proposed.