Palavras-chave: complexos de rutênio, polipiridinas de rutênio, oxidação de água, eletrocatálise, PCET, processos multieletrônicos. Abstract Matias, T. A., Synergic Effects in Dinuclear Ruthenium Polypyridyl for Water Oxidation Reaction and Electrocatalysis, 2015. 147 p. PhD Thesis -Graduate Program in Chemistry. Chemistry Institute of the University of São Paulo, São Paulo. Mononuclear ruthenium polypyridyl complexes have been studied as catalysts of oxygen evolution in water oxidation

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... , but the activated complex of most efficient catalysts assume the formation of dimers indicating the importance of the binuclear structure for their activation. Thereby, in this thesis we propose the study of possible synergistic effects in binuclear ruthenium polypyridyl complexes in order to activate species with high valence as Ru V =O and Ru IV =O for multi-electronic catalytic oxidation reactions. For this purpose, it was prepared a series of ruthenium polyppyridyl complexes using tridentate ligands based in terpyridine and bidentate bipyridine generating binuclear chloride complexes and aqua complexes which are able to act as precursors of the respective high valence active species generated by proton coupled electron transfer (PCET) reactions. The [RuCl(bpy)(phtpy)](PF6) and [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 complexes (phtpy= 4'phenyl-2,2':6',2"-terpyridine, bpy= 2,2´-bipyridine and tpy2ph= 1,3-bis(4'-2,2':6',2"terpyridin-4-yl)benzene) and their respective aqua complexes were synthetized and characterized by spectroscopic and electrochemical techniques. The chloro complexes [RuCl(bpy)(phtpy)](PF6), [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 and [Ru2Cl2(Clphen)2(tpy2ph)](PF6)2 (Clphen= 5-Chloro-1,10-phenanthroline) show only electron transfer reactions where the maximum oxidation state of the ruthenium ion is 3+. However, the respective aqua complexes [Ru(H2O)(bpy)(phtpy)](PF6)2, [Ru2(H2O)2(bpy)2(tpy2ph)](PF6)4 and [Ru2(H2O)2(Clphen)2(tpy2ph)](PF6)4 can be oxidized further by proton coupled electron transfer (PCET), generating high valence complexes where the ruthenium oxidation state can be 4+ and 5+. Complexes of Ru IV =O are generated in relatively low potentials and do not presented significant electrocatalytic activity for oxidation of water to dioxygen, whereas the Ru V =O species ([Ru V (O)(bpy)(phtpy)] 3+ and [Ru2 V (O)2(bpy)2(tpy2ph)] 6+ ) showed to be efficient catalysts for the reaction of water oxidation. The values of TOF for the binuclear complexes (0,97 s -1 ) were about three times larger than for the mononuclear complex (0,32 s -1 ), confirming the presence of synergistic effects accelerating the formation and release of oxygen by the binuclear complex. The electrocatalytic properties of high valence ruthenium polypyridyl complexes were transferred to electrodes surface by reductive electropolymerization of the [Ru2(H2O)2(Clphen)2(tpy2ph)](TfO)4 complex. In this case the electrochemical generation of ruthenium 2+, 4+ and 5+ species were observed whereas the 3+ species was not stable and disproportionated. The modified electrodes preserved the high electrocatalytic activity of the binuclear aqua complexes for water oxidation reaction (TOF de 0,80 s -1 ), and also for oxidation of benzyl alcohol to benzaldehyde with kRuIV= 14,70 L mol -1 s -1 demonstrating the high catalytic efficiency for oxidation of organic substrates.