Oxidation of hydrocarbons with hydrogen peroxide catalysed by nonheme manganese complexes represents one of the most promising approach for selective and sustainable functionalization of non-activated C-H bonds. The catalytic cycle has been proposed to be the same operating in iron catalytic systems, but very few Mn-OOH and Mn=O intermediates have been isolated and characterized up to date due to the intrinsic difficulty to detect and investigate Mn intermediates by the conventional experimental techniques. In this research project we plan to follow the reactions of the manganese catalysts with oxidants, by means of the combined ultrafast time-resolved energy dispersive X-ray absorption spectroscopy (EDXAS) at the Mn K-edge and UV-Vis spectroscopy technique, with the aim of detecting and characterizing the missing intermediates. A wide series of nonheme Mn-complexes containing both tetradentate and pentadentate aminopyridine ligands will be synthetized and the combined EDXAS/UV-Vis technique will be used to detect the formation of high valent manganese(IV)-oxo or manganese(V)-oxo intermediates.
Once characterized the Mn-oxo species the XAS/UV-Vis combined procedure will be used to analyze oxidation reactions of organic substrates such as aryl methyl sulfides by the non-heme manganese-oxo complexes. This will allow us to determine the oxidation mechanism and to determine the kinetic constants of the reactions by following the relative Mn K edge energy shift in the time-resolved XAS spectra.
On the collection of XAS and UV-Vis time-resolved spectra we will to apply a multivariate data analysis to extract the principal components and we will carry out theoretical simulations of the X-ray absorption near edge structure (XANES) to extract accurate structural information on the geometry of the short-living intermediates that are formed during the chemical reactions.
