Photocatalytic Deoxygenation of N–O Bonds with Rhenium Complexes: From the Reduction of Nitrous Oxide to Pyridine N-Oxides

Abstract

The accumulation of nitrogen oxides in the environment calls for new pathways to interconvert the various oxidation states of nitrogen, and especially their reduction. The large spectrum of reduction potentials covered by nitrogen oxides makes it however difficult to find general systems capable of efficiently reducing various N-oxides. Here photocatalysis unlocks high energy species able to both circumvent the inherent low reactivity of the greenhouse gas and oxidant N<sub>2</sub>O (E°(N<sub>2</sub>O/N<sub>2</sub>) = +1.77 V vs. SHE), and reduce pyridine N-oxides (E<sub>1/2</sub>(pyridine N-oxide/pyridine) = –1.04 V vs. SHE). The rhenium complex [Re(4,4’-tBu-bpy)(CO)<sub>3</sub>Cl] proved to be efficient to perform both reactions under ambient conditions, enabling the deoxygenation of N<sub>2</sub>O as well as synthetically relevant and functionalized pyridine N-oxides.<br>

Deoxygenation of N-heterocyclic N-oxides using isopropanol as a recyclable reductant

“…In recent developments, 30 the research groups led by Xu and Malkov independently reported electrochemical deoxygenation protocols. 31 In our continued effort to develop synthetic methods based on visible-light-induced photocatalysis, 32 we were drawn to the potential of photoredox catalysis to promote oxygen removal from heterocyclic N-oxides under mild conditions via single electron transfer pathways (Fig.…”