Morphology dependant oxidation of aromatic alcohols by new symmetrical copper(II) metallatriangles formed by self-assembly of a shared bis-benzimidazolyl diamide ligand

A new bis-benzimidazole-based diamide ligand N2,N2′-bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,1′-biphenyl]-2,2′-dicarboxamide, L and its three Cu(II) metallatriangles of general formula [Cu3(L)3X3]·3X·nH2O (where X = Cl, Br, NO3) have been synthesized and one of them is structurally characterized. X-ray diffraction work reveals that the metallatriangle [Cu3(L)3Cl3]·3Cl·15H2O crystallizes in trigonal R 3 ¯ space group with two independent molecules in the asymmetric unit. The asymmetric unit contains only one-third of the molecules and the rest are generated by the crystallographic 3 ¯ axis. Each copper(II) ion adopts a highly distorted square pyramidal geometry. The copper(II) metallatriangles are used as catalyst to carry out the oxidation of substituted benzyl alcohols heterogeneously, in the presence of tert-butyl hydroperoxide. Interestingly, the ratio of product profile and the percentage conversion of the products changes with the surface morphology of the metallatriangle employed as a catalyst. A kite type morphology is found to be highly selective to the formation of acid product over the aldehyde, while a hexagonal type morphology results in a mixed acid + aldehyde product. The initial rate of formation of the aldehyde is found to be almost independent of the amount of catalyst employed.