π-Bonded quinonoid transition-metal complexes

Abstract

Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)₃⁺ and Rh(COD)⁺ produces stable π-bonded η⁶-complexes that are activated to facile reversible deprotonation of the –OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting η⁵-semiquinone and η⁴-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal–organometallic coordination networks. With rhodium as the metal, the π-quinonoid complexes have been demonstrated to play a unique role in multifunctional C–C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of π-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials.