Terthienyl carbene complexes

Abstract

Terthienyl (HTTTH) forms part of the family of conjugated 5-membered heterocycles and although many novel conversions of thiophenes and their derivatives have been recorded, the coordination chemistry of terthienyl has been neglected. Dinuclear biscarbene complexes [(CO)5MC(OEt)TTTC(OEt)M(CO) 5l, and monocarbene complexes [M(CO) 5{C(OEt)TTTH}] of the transition metals Cr, Mo and W with terthienyl spacer units were prepared. The reactivity of these complexes with ammonia, their relative stability and their structural features were investigated. The study focuses on electron delocalization of the conjugated TTT moiety and the role of the TIT substituent in stabilizing the electrophilic carbene carbon. Terthienyl substrates are readily mono and dimetallated and the classical Fischer method for the synthesis of carbene complexes was used. Complexes were fully characterized and molecular structures were determined. A single crystal structure determination of the tungsten biscarbene complex indicated a planar configuration of the thienyl rings and partial de localization through the conjugated ring system.