Isolation of Neutral Mononuclear Copper Complexes Stabilized by Two Cyclic (Alkyl)(amino)carbenes

Two (cAAC)2Cu complexes, featuring a two-coordinate
copper atom in the formal oxidation state zero, were prepared by reducing
(Et2-cAAC)2Cu+I− with metallic sodium in THF, and by a one-pot synthesis using Me2-cAAC, Cu­(II)­Cl2, and KC8 in toluene
in a molar ratio of 2:1:2, respectively. Both complexes are highly
air and moisture sensitive but can be stored in the solid state for
a month at room temperature. DFT calculations showed that in these
complexes the copper center has a d10 electronic configuration
and the unpaired electron is delocalized over two carbene carbon atoms.
This was further confirmed by the EPR spectra, which exhibit multiple
hyperfine lines due to the coupling of the unpaired electron with 63,65Cu isotopes, 14N, and 1H nuclei.