COLIGAND-DEPENDENT SHIFTS IN CHARGE-DISTRIBUTION FOR COPPER-COMPLEXESCONTAINING 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. Cryst allographic characterization of the complex obtained as the pyridine s olvate (triclinic, P1BAR, a = 13.909(2) angstrom, b = 14.187(2) angstr om, c = 14.570(3) A, a = 75.26(1)degrees, beta = 72.37(1)degrees, gamm a = 80.57(1)degrees, V = 2637.9(9) angstrom3, Z = 2) has shown that th e molecule is dimeric with square pyramidal metal ions bridged at basa l positions by oxygen atoms of the catecholate ligands. Pyridine ligan ds occupy basal and apical sites of the centrosymmetric dimer. The mag netic moment for the dimer decreases from 2.84 mu(B) at room temperatu re 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 react ion was carried out with twice the stoichiometric quantity of copper m etal, 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 centrosy mmetric complex molecule consists of a central [Cu(3,5-DBCat)2]2- anio n with cationic [Cu(NCCH3)(PPh3)]+ units bonded to bridging oxygen ato ms 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 r adical spectrum of (PPh3)2Cu(3,5-DBSQ). This observation is explained in terms of a Cat-to-Cu(II) electron-transfer reaction.