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

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 2 O (E°(N 2 O/N 2 ) = +1.77 V vs. SHE), and reduce pyridine N-oxides (E 1/2 (pyridine N-oxide/pyridine) = –1.04 V vs. SHE). The rhenium complex [Re(4,4’-tBu-bpy)(CO) 3 Cl] proved to be efficient to perform both reactions under ambient conditions, enabling the deoxygenation of N 2 O as well as synthetically relevant and functionalized pyridine N-oxides.