ALTERING THE BALANCE BETWEEN LIGAND-BASED RADICAL-ANION FORMATION ANDDECHELATION IN ELECTROCHEMICALLY REDUCED BINUCLEAR COPPER(I) COMPLEXES - A RESONANCE RAMAN SPECTROELECTROCHEMICAL STUDY

The electrochemistry and spectral properties of a series of mono- and binuclear complexes: with bridging ligands based on 2,3-di(2-quinolyl) quinoxaline are reported. The ligands are 2,3-di(2-quinolyl)quinoxalin e (dqq), 6,7-dimethyl-2,3-di(2-quinolyl)quinoxaline (dqqMe(2)), and 6, 7-dichloro-2,3-di(2-quinolyl)quinoxaline (dqqCl(2)). The complexes are [Cu(dqq)(PPh3)(2)]BF4, 1. [BF4]; [Cu(dqqMe(2))(PPh3)(2)]BF4, 2.[BF4]; [Cu(dqqCl(2))(PPh3)(2)]BF4, 3.[BF4]; [(PPh3)(2)Cu(dqq)Cu(PPh3)(2)](BF 4)(2), 4.[BF4](2); [(PPh3)(2)Cu(dqqMe(2))Cu(PPh3)(2)](BF4)(2), 5.[BF4] (2); [(PPh3)(2)Cu(dqqCl(2))Cu(PPh3)(2)](BF4)(2), 6.[BF4](2). The monon uclear complexes reduce at the metal and dechelate, as evidenced by UV /vis spectroelectrochemistry. Reduction of the binuclear complexes res ults in ligand-based radical anion formation for 4 and 6 but decomposi tion of 5 to 2. The reduction species are identified using resonance R aman spectroscopy. The structures of [Cu(PPh3)(2)(C26H14C12N4)][BF4] ( 3.[BF4]) and [(Cu(PPh3)(2))(2)(C26H14Cl2N4)][BF4](2). 2CH(2)Cl(2) (6.[ BF4](2)) were determined by single-crystal X-ray diffraction. 3.[BF4] crystallized in the monoclinic space group <P(1)over bar> with cell di mensions a = 10.956(2) Angstrom, b = 15.278(3) Angstrom, c = 16.032(3) Angstrom, alpha = 100.342(8)degrees, beta = 95.291(13)degrees, gamma = 93.968(12)degrees, Z = 2, rho(calcd) = 1.431 g/cm(3), and R(F-o) = 0 .0589. 6.[BF4](2) crystallized in the monoclinic space group C2/c with cell dimensions a = 21.295(4) Angstrom, b = 24.322(5) Angstrom, c = 2 0.034(4) Angstrom, beta = 112.64(3)degrees, Z = 8, rho(calcd) = 1.486 g/cm(3), and R(F-o) = 0.0422.