DFT investigation of the ring contraction reaction of (η4-1,2-disilacyclohexadiene)iron tricarbonyls: a crucial intramolecular Si–Si bond activation

The mechanism of the ring contraction reaction of (η4-1,2-disilacyclohexadiene)iron tricarbonyls was studied at the M06/LACVP* level. The Si–Si bond of (η4-1,2-disilacyclohexadiene)iron tricarbonyls 1 was initially broken to form an η4-intermediate 3 by an intramolecular activation reaction with iron via the transition state 2TS. The Si–C bond of intermediate 3 was then activated by an intramolecular cheletropic reaction with iron, which generated a high energy state 5 through the transition state 4TS. Because of the dissociation of the silacarbenoid from 5, the π electrons of one CC bond coordinated to iron produced an intermediate 6 and [:SiMe2]. In particular, the silacarbenoids rapidly formed aggregations by oligomerizations. Finally, intermediate 6 achieved the six membered ring product 8 with the intramolecular nucleophilic reaction to accomplish the ring contraction reaction using the transition state 7TS. The rate-determining step was the intramolecular activation reaction of the Si–Si bond using iron.