Recent advances in CoSalen-catalyzed radical reactions

Abstract

Studies on the radical reactions involving planar N/O four-coordinated cobalt complexes have recently made significant progress. Cobalt salen (N,N′-bis(salicylidene)ethylenediamine) complexes, being one of the most important members of this family, have demonstrated outstanding versatility in the synthesis of small molecules as well as polymers. Herein we summarize important new advances in this field over the past 10 years, including: (1) Co(II/III) catalysis via hydrogen atom transfer; (2) oxidative hydrofunctionalization reactions involving Co(IV); (3) cyclopropanation via Co(III) carbene radicals; (4) reductive couplings via Co(I); (5) cobalt-mediated radical polymerizations. Emphasis is placed on the mechanistic interconnections among various reactions, development of new catalysis modes, and synthetic applications.