Biomimicking Activity Resembling Phenoxazinone Synthase of Heterogenized Oxidovanadium(V) and Its Analogous Homogeneous Complex

Abstract

Oxidovanadium(V) complex [V^VO{Hen(3,5-dcp)₄}] (where H₄en(3,5-dcp)₄, is a Mannich base synthesized from ethylenediamine, paraformaldehyde and 2,4-dichlorophenol) has been anchored onto chloromethylated polystyrene (PS–Cl) cross-linked with divinylbenzene to obtain [V^VO{en(3,5-dcp)₄}]@PS (@ refers to anchoring of complex onto polymer), a heterogeneous compound. Both of the synthesized (homogeneous as well as heterogeneous) vanadium compounds, after characterization, have been explored as biomimicking model catalysts for the type II copper site in phenoxazinone synthase. These compounds catalyze the oxidative condensation of o-aminophenol (OAP) into 2-aminophenoxazine-3-one (APX) by utilizing aqueous hydrogen peroxide in acetonitrile. Various reaction conditions like amounts of catalyst and oxidant, and temperature have been optimized to obtain maximum yield of APX. The polymer-immobilized complex demonstrates excellent catalytic activity, giving 96% yield of 2-aminophenoxazine-3-one under the optimized reaction conditions selectively. Its homogeneous analogue i.e. [V^VO{Hen(3,5-dcp)₄}], is also active and exhibits 83% yield. The heterogeneous catalyst i.e. [V^VO{en(3,5-dcp)₄}]@PS is stable, recyclable and reusable.

Graphical Abstract