Dinuclear copper(I) complexes of tris(3,5-dimethylpyrazol-1-yl)methane: Synthesis, structure, and reactivity

The reaction of [Cu(NCMe)4](BF4) with equimolar amounts of the tris(substituted-pyrazolyl)methane ligand HCPz3 or HC(3,5-Me2Pz)3 yields the respective salts [Cu(HCPz3)(NCMe)](BF4) (1a) or [Cu(HC(3,5-Me2Pz)3)(NCMe)](BF4) (1). The acetonitrile ligand of 1 can be replaced by prazine, 4,4′-dipyridine or 1,4-diisocyanobenzene to yield related mononuclear complexes [Cu(HC(3,5-Me2Pz)3)(pyrazine)](BF4) (2), [Cu(HC(3,5-Me2Pz)3)(4,4′-bipyridine)] (BF4) (3) or [Cu(HC(3,5-Me2Pz)3)(1,4- CNC6H4NC)](BF4) (7), respectively. A series of binuclear copper(I) complexes {[Cu(HC(3,5-Me2Pz)3)]2(μ -BL)}(BF4)2 (4, BL = pyrazine; 5, BL = 4,4′-dipyridine; 8, BL = 1,4-diisocyanobenzene) were prepared by treating equal molar ratio of 1 with related mononuclear complexes 2, 3 and 7. In addition, binuclear copper(I) complexes were also prepared from treatment of 2 equiv of 1 with the related bridge ligand. Both of 4 and 5 reformed mononuclear starting complex 1 in acetonitrile solution. However, the more robust complex 8 was stable in acetonitrile solutions. The structure of complexes 1a, 4, 5, and 7 were confirmed by X-ray crystallography. The redox properties of 4 and 8 were examined by cyclic voltammetry and exhibited two quasi-reversible waves suggesting that no significant structural reorganization occurs during the redox process on the electrochemical time scale.