Copper arylnitrene intermediates: formation, structure and reactivity

Abstract

The mechanism of oxidation of arylamines by copper enzymes is not clarified yet. Here, we explored a reaction between a possible high-valent copper(II)-oxyl intermediate and arylamine. We have employed a TPA ligand (TPA = tris(2-pyridylmethyl)amine) with the NH₂ group in position 2 of one of the pyridine rings (TPA^NH2). This model system allows generation of [(TPA^NH2)Cu(O)]⁺ in the gas phase, which immediately undergoes a reaction between the arylamino group and the copper oxyl moiety. The reaction leads to elimination of H₂O and formation of a copper–nitrene complex. The structure of the resulting copper–nitrene complex was confirmed by infrared spectroscopy in the gas phase. We show that the copper–nitrene complex reacts by hydrogen atom transfer with 1,4-cyclohexadiene and by an order of magnitude faster by a double hydrogen atom transfer with ethanethiol and methanol. DFT calculations explain the formation of the copper nitrene as well as its reactivity in agreement with the experimental findings.