Synthesis of two air and moisture-stable copper(II)-N-heterocyclic carbene complexes

Abstract

N-heterocyclic carbenes (NHCs) are a versatile class of ligands that have been widely applied in transition metal catalysis. However, NHCs are soft bases, and as such, complexes of NHCs with hard acids – such as many first-row transition metals – are typically sensitive to air and moisture, hence requiring multistep preparations. In this work, two examples of rare copper(II)-NHC complexes were prepared directly from 1,3-bis(pyridylmethyl)imidazolium chloride and 1,3-bis(2-pyridylmethyl)benzimidazolium chloride in protic conditions with no effort to exclude air or moisture. X-ray crystallographic analysis showed that both species display distorted square pyramidal geometry. A probe reaction demonstrated both complexes displayed poor catalytic activity for Chan-Evans-Lam coupling reactions.