Cu-H monomers have been commonly invoked in the mechanism of hydrocupration, a key elementary step for substrate activation in Cu-H catalysis. The isolation, kinetic studies and reactivity profile of such species are rare. Using N-heterocyclic carbenes (NHC) containing peripheral bulky groups enabled the isolation of Cu-H monomers and the insertion of internal alkenes. Minor steric changes to these peripheral substituents significantly impact the relative concentration of Cu-H monomer, rate of alkene insertion and reaction of trisubstituted internal alkene. Quantitative 1H NMR kinetic studies on the insertion of cyclopentene to form the corresponding Cu-cyclopentyl complexes demonstrated a strong dependence on the rate of insertion and the concentration of Cu-H monomer. Additionally, a high concentration of Cu-H monomer was crucial for inserting difficult trisubstituted internal alkene, in which the product has been verified by 1H, 13C NMR spectroscopy and X-ray crystallography.

NHC ligands with peripheral bulky groups enable the isolation of Cu-H monomers and insertion of internal alkenes

ACS Spring 2022

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