Oxidative dimerisation of 2-aminophenol by a copper(II) complex: Synthesis, non-covalent interactions and bio-mimics of phenoxazinone synthase activity

Abstract

This research study aims to overview the synthesis, structural characterization, long range crystalline architectures and bio-inspired oxidative catalysis of a mononuclear copper(II) complex, [Cu(Phen)2(H2O)](NO3)2 (1);[phen = 1,10-phenanthroline]. Single crystal X-ray diffraction study reveals that copper complex crystallizes in C2/c space group and Cu(II) centre exists in a highly distorted trigonalbipyramidal geometry. A close look at supramolecular architecture for this copper(II) complex indicates that oxygen atoms of nitrate ions and H atoms from phenanthroline ligand lead to intermolecular H-bonded 3D crystalline architecture in solid state. Noteworthy O ⋯ π interactions are also operative in between nitrate-O and centroids of ligands to provide additional stability in 3D architecture. Hirshfeld surface analysis further corresponds to the active participation of intermolecular H⋯O bonding and anion ⋯ π interactions. This copper complex has been tested as a bio-inspired catalyst towards oxidative coupling of 2-AP in methanol medium and the catalytic efficiency, kcat/KM(h−1) is found excellent, 1.007 × 107, towards the aerobic oxidation of 2-aminophenol (2-AP). The copper(II) complex in presence of 2-AP exhibits two new additional peaks at −0.13 and 0.49 V which correspond to AP−/AP•− and AP•−/IQ redox couple and suggests the generation of radical as a driving force for the oxidative coupling of 2-AP. Electrospray ionization mass spectrometry of the reaction mixture suggests that the course of oxidative cyclisation proceeds through enzyme-substrate adduct formation during this course of catalysis.