Advances in bis(N-heterocyclic carbene) chemistry: new classes of structurally dynamic materials

Abstract

A major challenge in the pursuit of dynamic materials is the dichotomy between reversible structure and electronic conjugation. Guided by the precedence for N-heterocyclic carbenes (NHCs) to dimerize, couple with electrophiles and bind to transition metals, we proposed that linearly opposed bis(NHC)s could, in a similar manner, afford unsaturated homopolymers, alternating copolymers, and metallopolymers. To realize these goals, we developed synthetic methods for accessing ditopic NHCs and investigated their propensities to undergo homopolymerization via dimerization and copolymerization via coupling with ditopic electrophiles or divalent transition metals. The materials obtained from these reactions were of relatively high molecular weight, exhibited electronic properties that were consistent with extensively delocalized systems, and in many cases, were found to be thermally reversible. In addition to expanding the scope of carbene chemistry, these polymers represent significant advancements towards the realization of reversible, conjugated polymers.