Chiral NHC-metal-based asymmetric catalysis

The strong sigma-donor but poor pi-acceptor abilities of N-heterocyclic carbenes (NHCs) result in chemical stability and coordination versatility, thus allowing them to coordinate with many metals ranging from alkaline-earth metals to rare-earth metals. Moreover, the easy introduction of chiral elements into NHCs and the facile preparation of their precursors have made chiral NHCs promising chiral ligands in metal-based asymmetric catalysis. Therefore, strategies for the design of efficient NHC-metal catalysts and novel asymmetric synthetic methodologies have dramatically increased over the past 10 years. Herein, the growing field of chiral NHC-metal-based asymmetric catalysis is comprehensively described. (C) 2011 Elsevier B.V. All rights reserved.