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. However, the large spectrum of reduction potentials covered by nitrogen oxides makes it difficult to find general systems capable of efficiently reducing various N-oxides. Here, photocatalysis unlocks high energy species able both to circumvent the inherent low reactivity of the greenhouse gas and oxidant N2O (E 0(N2O/N2) = +1.77 V vs. SHE), and to 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)3Cl] proved to be efficient in performing both reactions under ambient conditions, enabling the deoxygenation of N2O as well as synthetically relevant and functionalized pyridine N-oxides.

Mixing divalent ionic liquids: effects of charge and side-chains.

We have prepared novel divalent ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide anion where two charged imidazolium groups in the cations are either directly bound to each other or linked by a single atom. We assessed the influence of the side-chain functionality and divalency on their physical properties and on the thermodynamics of mixing. The results indicate that shortening the spacer of a divalent IL reduces its thermal stability and increases its viscosity. Mixtures of divalent and monovalent ILs show small but significant deviations from ideality upon mixing. These deviations appear to depend primarily on the (mis)match of the nature and length of the cation side-chain. The non-ideality imposed by mixing ILs with different side-chains appears to be enhanced by the increase in formal charge of the cations in the mixture.

Bifunctional coatings: coupling an organic adhesion promoter with an anticorrosion inorganic layer.

In this work, a multifunctional non-toxic chromium free treatment is proposed. Hexavalent chromium, largely used for anticorrosion surface treatments of aluminum alloys in aeronautics, will soon be completely banned due to its high toxicity (European REACH regulation) and new solutions are required. Here, in a first step, a polymeric film was grafted at the aluminum surface by the surface induced reduction of a diazonium salt. In a second step, the grafted surface was submitted to an anodization treatment, forming a thick aluminum oxide layer protecting the underlying metal against corrosion. No change in the organic coating was detected after the second step of the process. This leads to a multilayer coating, which provides competitive results regarding both the adhesion of paint and corrosion protection.