Enhancement of the Water Oxidation Reactivity of a Ruthenium(IV)Oxo Group by the Oxidation of a Strongly Coupled Redox Center.

VIRGINIA JUAREZ; SOFIA E. DOMINQUEZ; GERMAN E. PIESLINGER; BARALDO VICTORICA, LUIS MARIO

Londres, Reino Unido.

Conferencia; International solar fuels conference 2021; 2021

RSC

Enhancement of the Water Oxidation Reactivity of a Ruthenium(IV)Oxo Group by the Oxidation of a Strongly Coupled Redox Center.The synthesis and redox properties of a new strongly coupled bimetallic ruthenium complex, trans-[Ru(tpy)(bpy)(m-CN)Ru(py)4(OH2)]3+ (1, where tpy = 2,2?:6?,2??-terpyridine, bpy = 2,2′-bipyridine and py = pyridine) are presented. The reported complex combines a visible light absorber and an Ru-aquo complex able to reach a Ru(IV)O redox states. They are linked by a cyanide bridge that promotes a strong coupling between the metallic centres. The Pourbaix diagram and the spectroelectrochemistry at different pHs reveal that the first two oxidation reactions are centred at the aquo complex and result in the Ru(II)-Ru(III)OH and Ru(II)-Ru(IV)O redox states as confirmed by DFT calculations. The electrochemistry reveals that the oxidation by an additional electron triggers the water oxidation reaction. Spectroscopic monitoring of the reaction with an excess of Ce(IV) at pH = 1 indicates that the third oxidation is centred at the chromophore unit and the resulting Ru(III)-Ru(IV)O species is responsible for the water oxidation. The loss of Ce(IV) monitored at 370 nm is first order for both Ce(IV) and catalyst. These results are consistent with a rate equation, −d[CeIV]= kox,[CeIV][1ox] with a kox = 125 M-1 s-1 at T = 298 K. For this system, the oxidation of the strongly coupled chromophore turns on the reactivity of the, otherwise inert, Ru(IV)O group.