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The work carried out under the auspices of the present PRF grant has been centered in the field of oxidation catalysis. This is an important topic nowadays due to their importance both form a basic research point of view and also from an industrial perspective. The easy access to efficient and selective catalysts for the oxidation of organic substrates is of great significance for the chemical industry involved, since at the moment most of the oxidative organic transformations both in the lab and at industrial scale are being carried out in an stoichiometric manner with expensive oxidants such as MnO₄^-, CrO₃ etc., and in general are not selective. On the other hand it is generally accepted that one of the bottlenecks for the development of efficient fuel cells for the photo-production of H₂, is the catalytic oxidation of water to molecular dioxygen through a 4H⁺, 4e^- pathway. Most oxidation catalysts contain the M-O motif and our research has been focused on the development of the chemistry associated with the Ru=O. The work has been divided in two main parts, one of them involving Ru mononuclear complexes and second one involving dinuclear Ru complexes bridged by a rigid N4 chelating organic ligand Hbpp [3,5-(bis(2-pyridyl)pyrazole].

 With regard tot mononuclear complexes we have described the synthesis and characterization of a family of enantiomerically pure Ru complexes containing tridentate facial chiral ligands based on the pinene group. The electronic and steric effects associated with the generation of different isomers has been discussed with the involvement of theoretical analysis based on DFT calculations. Preliminary reactivity tests with regard to their catalytic oxidation capacity have already been carried out.

The majority of the work done under the present sponsorship has been spent with dinuclear Ru complexes. We carried out a comprehensive study of the Ru-Hbpp complex employing electrochemical, spectroscopic, kinetic, and theoretical techniques. The complexity of the system requires the application of all of these techniques in order to characterize the reaction mechanism responsible for oxygen-oxygen bond formation. The catalytic process shows a complex and delicate balance of reactions and manifests the need to master critical factors including, oxidation states available to the transition metal, the nuclearity of the complex, electronic couplings between multiple metal centers, the stability of supporting ligands, the nucleating ability of ligands, the geometrical disposition of the ligand(s), and the active versus auxiliary role of the ligands. The work constitutes the first successful water oxidation study were the mechanism has been unambiguously determined and is no doubt a landmark in the field.

 Heterogeneous catalysis has two main advantages with regard to homogeneous catalysis that are: the easiness to separate the catalyst from the products just by filtration and the dramatically reduced translational mobility of the catalyst that avoids destructive intermolecular catalyst-catalyst interactions. In order to benefit from these intrinsic advantages we have anchored our Ru-Hbpp catalyst to solid supports (TiO₂) by modifying the Hbpp ligand without modifying its intrinsic coordination properties. For that purpose two organic ligands based on bis-(2-pyridyl)pyrazole (Hbpp) functionalized with a p-methylenebenzoic acid or its ester derivative were prepared and characterized. The ester-functionalized ligand was then used to prepare a series of related dinuclear ruthenium complexes that were later on anchored in rutile TiO₂ and treated with 0.1M triflic acid solution to generate the homologous water-oxidation catalysts. These new hybrid materials were used to catalytically oxidize water to molecular oxygen in a heterogeneous manner using Ce(IV) as chemical oxidant.

The impact of those works in my carrier, and thus due to the sponsorship of the ACS-PRF grant, has been important up to the point that we were invited to write a specialized review in Angewandte Chemie that is presented also as a contribution. This invitation actually constitutes a tacit recognition that our group has become a reference in the water oxidation catalysis field. Thus it places my group in a privileged situation to further develop this chemistry and continue to be a leader in this scientific area.

For the two post-docts that have been involved in the project their impact has been enormous. First they have had a chance not only to learn this chemistry but also to get familiar with a variety of techniques including: Electrochemistry (cyclic voltammetry, square wave voltammetry, Coulometry etc.), Chromatography (TLC, GC, HPLC, etc) NMR spectroscopy (1 and 2D), Mass Spectroscopy (ESI, MALDI, Atmospheric pressure MS, etc.), Kinetic techniques (UV-vis, Stopped Flow, Specfit, etc.) and finally the manipulation of labeled compounds. This blend of techniques in this highly multidisciplinary project has strongly widened their knowledge and thus they have acquired an excellent scientific formation. As a result of their efforts they have published the work in the best journals in the field (J. Am. Chem. Soc., Angew. Chem., etc.). The combination of all this has allowed to generate first quality scientist ready to get incorporated in first class scientific institutions.