Mild and selective transformations of amines and alcohols through bioinspired oxidation with nitrous oxide or oxygen

Abstract

Herein we report on the catalytic oxidation of amines to nitriles with either pure oxygen or nitrous oxide, using the air- and water-stable organometallic complex {[(p-cymene)Ru](μ-H)(μ-Cl)(μ-HCO₂)[Ru(p-cymene)]}BF₄ which has been previously reported to be active for a series of biomimetic transformations, including formaldehyde dehydrogenase and dismutase, and transfer-hydrogenation reactions like deamination of nitriles to alcohols. Inline with these previous studies we now report on other biomimetic properties of this binuclear ruthenium complex which is able to act as well as nitrous oxide reductase (N2OR) and decompose nitrous oxide in the presence of hydrogen donating molecules like amines and alcohols. This complex can be synthesised from the inexpensive and commercially available precursor [Ru(p-cymene)Cl₂]₂ or from ruthenium chloride and renewable α-phellandrene which naturally occurs in eucalyptus oil for example. The selectivities and yields can be controlled by solvents, oxidants and temperature. Albeit oxygen is known as a potent oxidant, the observation that the catalyst can both oxidise alcohols or amines and simultaneously decompose the greenhouse gas nitrous oxide is very interesting. In addition, under similar conditions this catalyst is able to convert aromatic alcohols to benzaldehydes. These reactions with an air stable and robust catalyst were easy to carry out and affordable, making them highly practical. Note, in here we report on the oxidation of benzylamines and benzylic alcohols as model substrates for the initial evaluation of these catalytic set-ups.