Solution behavior and structural properties of Cu(I) complexes featuring m-terphenyl isocyanides

The synthesis of the m-terphenyl isocyanide ligand CNArMes2 (Mes = 2,4,6-Me3C6H2) is described. Isocyanide CNArMes2 readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNArMes2 and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (mu-X)(2)[Cu(THF)(CNArMes2)](2). Addition of CNArMes2 to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNArMes2)(2) in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNArMes2)(2) to exist as a three-coordinate monomer in the solid state. As determined by solution H-1 NMR and FTIR spectroscopic studies, monomer ClCu(CNArMes2)(2) resists tight binding of a third CNArMes2 unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNArMes2 to cuprous iodide readily affords the tris-isocyanide species, ICu(CNArMes2)(3), as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNArMes2)(3)]OTf (OTf = O3SCF3), which is generated upon treatment of (C6H6)[Cu(OTf)](2) with 6 equiv of CNArMes2 in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [Cul] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNArMes2)(3)]OTf itself serves as a good Lewis acid and is found to weakly bind C6H6 in an eta(1)-C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the eta(1)-C Cu-C6H6 interaction.