Dinuclear Copper(II) Complexes with N,O Donor Ligands: Partial Ligand Hydrolysis and Alcohol Oxidation Catalysis

Abstract

AbstractTwo copper(II) complexes [Cu2(L1)2] (1) and [Cu2(L2)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.