Altering the Balance between Ligand-Based Radical Anion Formation and Dechelation 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)quinoxaline (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)(PPh(3))(2)]BF(4), 1.[BF(4)]; [Cu(dqqMe(2))(PPh(3))(2)]BF(4), 2.[BF(4)]; [Cu(dqqCl(2))(PPh(3))(2)]BF(4), 3.[BF(4)]; [(PPh(3))(2)Cu(dqq)Cu(PPh(3))(2)](BF(4))(2), 4.[BF(4)](2); [(PPh(3))(2)Cu(dqqMe(2))Cu(PPh(3))(2)](BF(4))(2), 5.[BF(4)](2); [(PPh(3))(2)Cu(dqqCl(2))Cu(PPh(3))(2)](BF(4))(2), 6.[BF(4)](2). The mononuclear complexes reduce at the metal and dechelate, as evidenced by UV/vis spectroelectrochemistry. Reduction of the binuclear complexes results in ligand-based radical anion formation for 4 and 6 but decomposition of 5 to 2. The reduction species are identified using resonance Raman spectroscopy. The structures of [Cu(PPh(3))(2)(C(26)H(14)Cl(2)N(4))][BF(4)] (3.[BF(4)]) and [(Cu(PPh(3))(2))(2)(C(26)H(14)Cl(2)N(4))][BF(4)](2).2CH(2)Cl(2) (6.[BF(4)](2)) were determined by single-crystal X-ray diffraction. 3.[BF(4)] crystallized in the monoclinic space group P&onemacr; with cell dimensions a = 10.956(2) Å, b = 15.278(3) Å, c = 16.032(3) Å, 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.[BF(4)](2) crystallized in the monoclinic space group C2/c with cell dimensions a = 21.295(4) Å, b = 24.322(5) Å, c = 20.034(4) Å, beta = 112.64(3) degrees, Z = 8, rho(calcd) = 1.486 g/cm(3), and R(F(o)) = 0.0422.