Direct Synthesis of a Copper(II) N-Heterocyclic Carbene Complex in Air

Abstract

Copper N-heterocyclic carbene complexes (Cu-NHCs) are prevalent in the literature, and their stability and catalytic activity have been well characterized and established. In an overwhelming majority of the reported examples, copper is present as Cu(I), owing to the favorable soft–soft interaction. In contrast, there are very few reports of Cu-NHCs containing Cu(II). This can be explained by the unfavorable intermediate/hard–soft interaction between carbon and Cu(II). The syntheses of examples reported thus far require the exclusion of air and moisture and involve the use of NHC transfer reagents or the use of free NHCs. This results in tedious, multistep procedures, making their preparation more time consuming and costly. Herein we report the synthesis and characterization of two air- and moisture-stable Cu(II)-NHC complexes by direct combination of 1,3-bis(pyridin-2-ylmethyl)-1H-imidazolium chloride with copper(II) hexafluorosilicate. Analysis by single-crystal X-ray diffraction revealed that the specie...