Dinuclear Copper(Ii) Complexes With N,O Donor Ligands: Partial Ligand Hydrolysis And Alcohol Oxidation Catalysis

Two copper(II) complexes [Cu-2(L-1)(2)] (1) and [Cu-2(L-2)(2)] (2) where H2L1=2-hydroxy-3-((3-hydroxy-2,2-dimethylpropylimino)methyl)-5-methylbenzaldehyde and H2L2=2-hydroxy-3-(((1-hydroxypropan-2-yl)imino)methyl)-5-methylbenzaldehyde have been synthesized and used as catalysts in alcohol oxidation. 2,6-Diformyl-4-methylphenol (DFP) based Schiff-base ligands, 3,3 '-(2-hydroxy-5-methyl-1,3-phenylene)bis(methan-1-yl-1-ylidene)bis(azan-1-yl-1-ylidene)bis(2,2-dimethylpropan-1-ol) (H3L ') and 2,2 '-(((2-hydroxy-5-methyl-1,3-phenylene)bis(methanylylidene))bis(azanylylidene))bis(propan-1-ol) (H3L ''), undergo partial hydrolysis to convert one of the azomethine groups to aldehyde group to give H2L1 and H2L2, and then react with copper(II) acetate to yield complex 1 and 2, respectively. These complexes have been characterized by standard methods such as elemental analysis, room temperature magnetic studies, FT-IR, UV-vis, ESI-mass spectral analyses, cyclic voltammogram, etc. The structures of dinuclear complexes with modified ligands have been confirmed by single crystal X-ray diffraction analysis. Complex 1 and 2 have been used as catalysts for the oxidation of benzyl alcohol, 4-methyl benzyl alcohol, 4-methoxy benzyl alcohol, 4-nitro benzyl alcohol and 4-bromo benzyl alcohol to the corresponding aldehyde as the sole product. Efficiency of the catalyst depends on the chain length and substitution on the chain of the ligand.