A review on the consequence of 3D-orienation of Cu/TEMPO/imidazole sequence on selective alcohol oxidation

Abstract

The fascinating properties of the naturally occurring biopolymers and enzymes are benchmark natural materials abetting us to optimize the performance of multifunctional catalytic system based on 3D orientation, propinquity amongst all the active sites and apposite stoichiometry. In the copper/TEMPO/imidazole catalytic triad the formation of (bpy)CuI(NMI) (bpy: bipyridine) (NMI: N-methyl imidazole) facilitated facile oxidation to (bpy)CuII(NMI)-O2·− in the presence of molecular oxygen. In the multicomponent catalytic system TEMPO moiety boost the fixation copper-oxygen radical intermediate. These multifunctional heterogeneous and recyclable catalytic systems (1-6) were prepared by grafting silica surface by orthogonal post-functionalization or single molecule post-functionalization of azide silanes grafted silica with functionalized alkynes (7-12) by CuAAC “click chemistry”. The above said mechanistic studies were pivotal in contriving multifarious copper/TEMPO/imidazole triads involving reaction of the discrete and sequence defined catalytic triads (1-6) to expedite aerobic alcohol oxidation. The catalyst 3a having TEMPO/pyridyl triazole (pyta) dimer grafted in 1:2 stoichiometric ratio outperformed other catalytic systems for the benzyl alcohol oxidation, with high initial TOF value of 63.1. Moreover, the catalyst was recyclable for five consecutive cycles for benzyl alcohol oxidation. This minireview, highlights recent work based on multifunctional CuI/TEMPO/pyta containing triad based heterogeneous catalysts for aerobic alcohol oxidation.