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 R3¯ 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.

A new bis-benzimidazole based diamide ligand and its Cu(II) metallatriangles have been synthesized and structurally characterized. Cu(II) metallatriangles carry out the catalytic oxidation of aromatic alcohols heterogeneously. The ratio and percentage conversion of the product profile undergoes a dramatic change with the surface morphology of the metallatriangle employed.Figure optionsDownload as PowerPoint slideHighlights
► New bis-benzimidazole diamide ligand is synthesized.
► A ligand bridged Cu(II) metallatriangle is synthesized and characterized structurally.
► Metallatriangles are used for the oxidation of aromatic alcohols.
► Morphology changes are associated with altered product profile.