Stable N-heterocyclic carbene (NHC)-palladium(0) complexes as active catalysts for olefin cyclopropanation reactions with ethyl diazoacetate

Abstract

The Pd 0 complexes [(NHC)PdL n] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR 3 for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e - unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO 2Et)(sty)], from which the cyclopropane is formed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.