COLIGAND-DEPENDENT SHIFTS IN CHARGE-DISTRIBUTION FOR COPPER-COMPLEXES CONTAINING 3,5-DI-TERT-BUTYLCATECHOLATE AND 3,5-DI-TERT-BUTYLSEMIQUINONATE LIGANDS

Cu(py)2(3,5-DBCat) has been prepared by reacting copper metal with 3,5-di-tert-butyl-1,2-benzoquinone (3,5-DBBQ) in pyridine solution. Crystallographic characterization of the complex obtained as the pyridine solvate (triclinic, P1BAR, a = 13.909(2) angstrom, b = 14.187(2) angstrom, c = 14.570(3) A, a = 75.26(1)degrees, beta = 72.37(1)degrees, gamma = 80.57(1)degrees, V = 2637.9(9) angstrom3, Z = 2) has shown that the molecule is dimeric with square pyramidal metal ions bridged at basal positions by oxygen atoms of the catecholate ligands. Pyridine ligands occupy basal and apical sites of the centrosymmetric dimer. The magnetic moment for the dimer decreases from 2.84 mu(B) at room temperature to 0.52 mu(B) at 5.0 K; exchange coupling is antiferromagnetic and has been theoretically fit with a J value of -95.3 cm-1. Cu(PPh3)2(3,5-DBSQ) has been prepared by reacting stoichiometric proportions of 3,5-DBBQ, PPh3, and copper metal in acetonitrile solution. When the reaction was carried out with twice the stoichiometric quantity of copper metal, the product obtained was [CuI(NCCH3)(PPh3)]2[CuII(3,5-DBCat)2]. Crystallographic characterization (monoclinic, P2(1)/n, a = 16.163(2) angstrom, b = 9.245(1) angstrom, c = 21.312(3) angstrom, beta = 99.78(2)degrees, V = 3138.3(7) angstrom3, Z = 2) has shown that the centrosymmetric complex molecule consists of a central [Cu(3,5-DBCat)2]2- anion with cationic [Cu(NCCH3)(PPh3)]+ units bonded to bridging oxygen atoms of the catecholate ligands. The EPR spectrum of the complex in the solid state is typical of Cu(II). The EPR spectrum of [CuI(NCCH3)(PPh3)]2[CuII(3,5-DBCat)2] in toluene solution was characteristically the radical spectrum of (PPh3)2Cu(3,5-DBSQ). This observation is explained in terms of a Cat-to-Cu(II) electron-transfer reaction.