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

Two (cAAC)(2)Cu complexes, featuring a two-coordinate copper atom in the formal oxidation state zero, were prepared by reducing (Et-2-cAAC)(2)Cu+I- with metallic sodium in THF, and by a one-pot synthesis using Me-2-cAAC, Cu(II)Cl-2, 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 d(10) 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 Cu-63,Cu-65 isotopes, N-14, and H-1 nuclei.