We report herein the synthetic routes to and spectroscopic and structural characterization of a variety of copper complexes bearing small alkyl-substituted N-heterocyclic carbene (NHC) ligands. Complexes of the type [Cu(NHC)(X)] and [Cu(NHC)2(X)] (X = Cl) were readily synthesized by reaction of Cu(I)Cl with a variety of the carbenes. The molecular structures of the [Cu(NHC)(X)] complexes all show two-coordinate Cu(I) atoms in nearly linear arrangements with C(NHC) Cu Cl angles very close to 180°. Utilizing the smallest alkyl carbene, Me2Im (= 1,3-di-methyl-imidazolin-2-ylidene), the compound adopts an ionic structure featuring a [Cu(Me2Im)2]+ cation and a [CuCl2]− anion. The reaction of copper(I) chloride with two equivalents of some NHCs (NHC = Me2Im, iPr2Im, iPr2ImMe2 [ = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene]) afforded complexes of the type [Cu(NHC)2(X)], which show a trigonal planar geometry with a propeller-like arrangement of the NHC ligands. Furthermore, complexes of the type [Cu(NHC)(OR)] (OR = OAc, OtBu, acac [ = acetylacetonato], DBM [ = dibenzoylmethanato]), were synthesized starting from [Cu(iPr2Im)(X)] (iPr2Im = 1,3-di-iso-propylimidazolin-2-ylidene), and characterized. The molecular structure of [Cu(NHC)(DBM)] clearly reveals the typical bidentate binding mode of the DBM ligand. The compounds reported represent very useful starting points for the investigation of NHC copper(I) chemistry.
