New chromium, molybdenum, and cobalt complexes of the chelating esp ligand

Abstract

Bimetallic carboxylates of Rh(II) are widely recognized for their ability to catalyze carbene transfer reactions such as the cyclopropanation of olefins using organic diazo compounds as carbene precursors. A major goal in catalysis is to find cheaper, more Earth-abundant alternatives to precious metal catalysts. There is therefore currently great interest in the bimetallic paddlewheel chemistry of elements that have lower costs and greater terrestrial abundance than Rh. M2(esp)2(L)2 structures were synthesized and structurally characterized with M = Cr, Co, and Mo, where esp2− = α,α,α′,α′-tetramethyl-1,3-benzenedipropionate, a chelating di-carboxylate ligand that helps stabilize the bimetallic core. Cr2(esp)2(THF)2, Mo2(esp)2, and Co2(esp)2(EtOH)2 were tested as catalysts for decomposition of the diazo compound (4-bromophenyl)diazoacetate methyl ester in the presence of styrene; while the Cr2 and Mo2 complexes showed no difference from a background control, the Co2 complex was found to enhance the rate of dinitrogen extrusion and promote carbene addition to styrene to form the cyclopropane product.