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Abstract

Copper hydrides were first reported in 1844; their value as catalysts for organic reactions has significantly expanded in the last two decades. Copper hydrides with NHC (NHC = N-heterocyclic carbene) ligands typically exist as dimers, [(NHC)Cu(m-H)]₂. The kinetics of insertion of organic substrates into the Cu-H bond are determined by the electronic properties of the substrates. Conversion of the dimer to a monomeric species or insertion into the Cu-H bond can be rate-determining. Remote ligand modification can have a large effect on the dimer-monomer equilibrium, even when substituents are several bonds away from the copper. Destabilization of the [(NHC)Cu(m-H)]₂ dimer relative to the (NHC)Cu-H monomer enables the isolation of rarely observed Cu-H monomers. These highly reactive monomeric complexes insert tri-substituted alkenes into the Cu-H bond.