Mechanistic Studies on the Insertion of Carbonyl Substrates into Cu‐H: Different Rate‐Limiting Steps as a Function of Electrophilicity

Abstract

AbstractWe report mechanistic studies on the insertion reactions of [(NHC)Cu(μ‐H)]2 complexes with carbonyl substrates by UV‐vis and 1H NMR spectroscopic kinetic studies, H/D isotopic labelling, and X‐ray crystallography. The results of these comprehensive studies show that the insertion of Cu‐H with an aldehyde, ketone, activated ester/amide, and unactivated amide consist of two different rate limiting steps: the formation of Cu‐H monomer from Cu‐H dimer for more electrophilic substrates, and hydride transfer from a transient Cu‐H monomer for less electrophilic substrates. We also report spectroscopic and crystallographic characterization of rare Cu‐hemiacetalate and Cu‐hemiaminalate moieties from the insertion of an ester or amide into the Cu−H bond.