Syntheses, crystal structures of a series of copper(II) complexes and their catalytic activities in the green oxidative coupling of 2,6-dimethylphenol

Three mixed-ligand Cu(II) complexes bearing iminodiacetato (ida) and N-heterocyclic ligands, namely, [Cu(2)(ida)(2)(bbbm)(H(2)O)(2)] center dot H(2)O (1), [Cu(2)(ida)(2)(btx)(H(2)O)(2)] center dot 2H(2)O (2) and [Cu(2)(ida)(2)(pbbm)(H(2)O)(2)] center dot H(2)O center dot 3CH(3)OH (3) (bbbm = 1,1'-(1,4-butanediyl)bis-1H-benzimidazole, btx = 1,4-bis(1,2,4-triazol-1-ylmethyl) benzene, pbbm = 1,1'-(1,3-propanediyl) bis-1H-benzimidazole), in addition to three fcz-based Cu(II) complexes, namely, {[Cu(fcz)(2)(H(2)O)(2)] center dot 2NO(3)}(n) (4), {[Cu(fcz)(2)(H(2)O)] center dot SO(4) center dot DMF center dot 2CH(3)OH center dot 2H(2)O}(n) (5) and {[Cu(fcz)(2)Cl(2)] center dot 2CH(3)OH}(n) (6) (fcz = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl) methyl] ethanol) have been prepared according to appropriate synthetic strategies with the aim of exploiting new and potent catalysts. Single crystal X-ray diffraction shows that 1 and 2 possess similar binuclear structures, 3 features a 2D pleated network, and 4 exhibits a 1D polymeric double-chain structure. Complexes 1-6 are tested as catalysts in the green catalysis process of the oxidative coupling of 2,6-dimethylphenol (DMP). Under the optimized reaction conditions, these complexes are catalytically active by showing high conversion of DMP and high selectivity of PPE. The preliminary study of the catalytic-structural correlations suggests that the coordination environment of the copper center have important influences on their catalytic activities. (C) 2008 Published by Elsevier B. V.