Conversion of Pd(i) off-cycle species into highly efficient cross-coupling catalysts

Abstract

We report on the facile conversion of [Pd₂(μ-Cl)(μ-η³-R-allyl)(NHC)₂] complexes, which are commonly considered undesirable off-cycle species in cross-coupling reactions, into active [PdCl(μ-Cl)(NHC)]₂ pre-catalysts. All reactions proceed under mild conditions (40 °C, 1–2 hours in acetone) using inexpensive HCl as both an oxidant and chloride source. DFT calculations were performed to explore the possible mechanism of this transformation, which appears to involve a combination of two different pathways. Moreover this study provides insights into factors favoring and hindering Pd(I) dimer formation undesirable in catalysis.