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 CuII complexes bearing iminodiacetato (ida) and N-heterocyclic ligands, namely, [Cu2(ida)2(bbbm)(H2O)2] · H2O (1), [Cu2(ida)2(btx)(H2O)2] · 2H2O (2) and [Cu2(ida)2(pbbm)(H2O)2] · H2O · 3CH3OH (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 CuII complexes, namely, {[Cu(fcz)2(H2O)2] · 2NO3}n (4), {[Cu(fcz)2(H2O)] · SO4 · DMF · 2CH3OH · 2H2O}n (5) and {[Cu(fcz)2Cl2] · 2CH3OH}n (6) (fcz = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-l-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.

Graphical abstractA series of copper(II) complexes have been prepared according to appropriate synthetic strategies with the aim of exploiting new catalysts. A green aqueous-medium catalysis process of the oxidative coupling of DMP has been explored by using these complexes as catalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide