Copper Diamidocarbene Complexes: Characterization of Monomeric to Tetrameric Species

Treatment of CuCl with 1 equiv of the in situ prepared <i>N</i>-mesityl-substituted diamidocarbene 6-MesDAC produced a mixture of the dimeric and trimeric copper complexes [(6-MesDAC)­CuCl]₂ (<b>1</b>) and [(6-MesDAC)₂(CuCl)₃] (<b>2</b>). Combining CuCl with isolated, free 6-MesDAC in 1:1 and 3:2 ratios gave just <b>1</b> and <b>2</b>, respectively, while increasing the ratio to >5:1 allowed the isolation of small amounts of the tetrameric copper complex [(6-MesDAC)₂(CuCl)₄] (<b>3</b>). Efforts to bring about metathesis reactions of <b>1</b> with MO^tBu (M = Li, Na, K) proved successful only for M = Li to afford the spectroscopically characterized ate product [(6-MesDAC)­CuCl·LiO^tBu·2THF] (<b>5</b>). Attempts to crystallize this species instead gave a 1:1 mixture of <b>1</b> and the monomer [(6-MesDAC)­CuCl] (<b>6</b>). The X-ray structures of <b>1</b>–<b>3</b> and <b>1</b> + <b>6</b>, along with the cation [Cu­(6-MesDAC)₂]⁺ (<b>4</b>), have been determined