Altering the Balance between Ligand-Based Radical Anion Formation and Dechelation in Electrochemically Reduced
Simon E. Page1, Keith C. Gordon, Anthony K. Burrell
1Department of Chemistry, Massey University, Private Bag 11122, Palmerston North, New Zealand.
Abstract:
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.
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