The understanding of chemical reactivity relies on the development of innovative tools for its comprehension.
The present project will regard the investigation of chemical reactions by means of an innovative method that combines spectroscopic, statistical and theoretical approaches. Specifically, coupled time-resolved UV-Vis/Energy Dispersive X-ray Absorption Spectroscopy (EDXAS) data relative to bimolecular redox reactions occurring in solution, at room temperature, on the second to millisecond time scales will be analyzed using the combination of multivariate statistical and multiple scattering theoretical simulations.
The reactions under study will regard the reactivity of nonheme iron coordination complexes, an emerging class of environmentally friendly catalysts for the oxidation of organic compounds whose mechanism of action and key intermediates involved along the reactive path have not been yet fully characterized.
Firstly, the number (N) of significant species contributing to the UV-Vis/EDXAS data is established by means of statistical tests. Next, the experimental spectra will be decomposed, using a method associated to the Multivariate Curve Resolution (MCR) family, into the N spectral and N concentration profiles belonging to the reaction "pure" species. The decomposition will allow one to gain insights into the life times of all intermediates present in the reaction mixture. Further, each isolated EDXAS spectrum, associated to one of the reaction key species, will be analyzed by multiple scattering (MS) calculations. As a result, it will be possible to optimize the geometrical structure of each reaction intermediate and gain a comprehensive structural and mechanistic picture for the investigated transformations.
The main result of this project would be the possibility of assessing an innovative methodology for the determination of the molecular structure of labile intermediates, as well as for the comprehension of the overall mechanistic picture of the reactions under study. This project has the potential to benchmark a new method to study bimolecular reactive pathways in solution on the second to millisecond time scales, and to interpret the rather complex chemistry going on in the systems we have chosen to investigate. The above objectives and the expected results are appealing both from the point of view of purely ''academic'' research, as well as to the important potential it possesses in applied science.
In fact, in the search for environmentally friendly catalysts for the oxidation of organic substrates, nonheme complexes have surged to the top of the candidates' list. However, an improved understanding of the structures and of the identity of the intermediates key to their catalytic activity is required in order to optimize their rational design.
To this end, the combined application of MCR and advanced MS calculations will allow us to obtain a crucial molecular level understanding of these complex systems, by using an in situ approach that minimizes the perturbation of the system under investigation. Moreover, the use of MCR for the analysis of both the UV-Vis and EDXAS datasets will allow one to drastically diminish the ambiguity of the extracted solutions, by accepting uniquely solutions to the decomposition problem that are common for both sets of spectroscopic data.
Specifically, it is envisioned that the presented approach will enable to add to the comprehension of the reactivity of nonheme iron complexes by:
- determining the nature of the previously unidentified X ligand in the oxo-complex [Fe(IV)(TPA)(O)(X)]+/2+, and to definitely assess whether a Fe(III) or a Fe(V) complex arises as an intermediate immediately after the reaction of [Fe(II)(TPA)(CH3CN)2]2+ with AcOOH;
-understanding whether a DOT or an ET mechanism is active in the sulfoxidation of para-cianothioanisole, para-methoxythioanisole and thioanisole by [N4Py·Fe(IV)(O)]2+, possibly isolating the EDXAS spectrum relative to the Fe(III) oxo-complex [N4Py·Fe(III)(O)]+ and characterizing its structure in solution for the first time.
-Testing if the species [N4Py·Fe(III)(OH)] is formed as an intermediate and/or as a product during the oxidation of 9,10-dihydroanthracene and diphenylmethane by [N4Py·Fe(IV)(O)]2+ and, if so, determining its structure in solution for the first time.
It is strongly believed that the combined experimental-theoretical proposed approach is essential to reliably describe complex systems like those under study.
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