Stable N-Heterocyclic Carbene (NHC)–Palladium(0) Complexes as Active Catalysts for Olefin Cyclopropanation Reactions with Ethyl Diazoacetate

摘要

The Pd0 complexes [(NHC)PdL_n] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR₃ 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(CHCO₂Et)(sty)], from which the cyclopropane is formed.