Ring-Opening Mechanism of Lithium Bromosilacyclopropylidenoids to Silaallenes

Density functional theory and ab initio quantum mechanical calculations elucidated the ring opening reactions of 1 bromo 1 lithiosilirane (3) and 2 bromo 2 lithiosilirane (4) to 2 silallene (6) and 1 silaallene (7) respectively The ring opening of 3 to 6 can proceed in a stepwise fashion with the intermediacy of a free silacyclopropylidene (9) Here a high energy barrier needs to be overcome in order to open the silacyclopropylidene ring and to generate 6 On the contrary the ring opening of 4 to 7 can occur in a concerted fashion