We report mechanistic studies on the insertion reactions of [(NHC)Cu(μ-H)]2 complexes with carbonyl substrates by UV-vis and 1 H 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.
Keywords: Cu hydride; Cu-H hydride transfer; Cu-H monomerization; Cu-hemiaminalate; carbonyls.
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.