Oxidation of electron deficient olefins using a copper(II) complex based on a bis-benzimidazole diamide ligand

Abstract

New bis-benzimidazole based diamide ligands N, N′-bis(2-methyl benzimidazolyl)-benzene-1,3-dicarboxamide [GBBA] and N-Octyl-N, N′-bis(2-methyl benzimidazolyl)-benzene- 1,3-dicarboxamide [O-GBBA] have been synthesized and utilized to prepare Cu(II) complexes of general composition [Cu(GBBA)X2] · nH2O and [Cu(O-GBBA)X2] · n H2O, where X is an exogenous anionic ligand (X = Cl−, NO3−, SCN−). The oxidation of electron deficient olefins has been investigated using [Cu(O-GBBA)X2] · nH2O as catalyst and TBHP as an alternate source of oxygen. The respective ketonic products have been isolated and characterized by 1H-NMR. The complex [Cu(GBBA)(NO3)2] · 4H2O has been characterized structurally. It crystallizes in a monoclinic space group C2/c. Low temperature EPR spectra have been obtained for the complexes that shows gII > gI > 2.0024, indicating a tetragonal geometry in the solution state. The complexes display a quasi reversible redox wave due to the Cu(II)/Cu(I) reduction process. The E1/2 values shift anodically as NO3− < SCN− < Cl−.