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

Abstract

The Pd(0) complexes NHCPdLn (NHC = N-heterocyclic carbene ligand; L = styrene for n = 2 or PR3 for n = 1) efficiently catalyze the olefin cyclopropanation using ethyl diazoacetate (EDA) as the carbene source with activities that improve any other previous described catalytic system based on this metal. Mechanistic studies have shown that all those catalyst precursors deliver in solution the same catalytic species (IPr)Pd(sty), a 14e, unsaturated intermediate that further reacts with EDA to afford (IPr)Pd(=CHCO2Et)(sty), from which cyclopropane is formed.