title: Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex.
abstract: We introduce a new family of complexes with the general formula [Ru(n)(tda)(py)2](m+) (n = 2, m = 0, 1; n = 3, m = 1, 2(+); n = 4, m = 2, 3(2+)), with tda(2-) being [2,2':6',2″-terpyridine]-6,6″-dicarboxylate, including complex [Ru(IV)(OH)(tda-κ-N(3)O)(py)2](+), 4H(+), which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 3(2+) under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV-vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H(+) can be generated potentiometrically, or voltammetrically, from 3(2+), and both coexist in solution. While complex 3(2+) is not catalytically active, the catalytic performance of complex 4H(+) is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s(-1) at pH 7.0 and 50 000 s(-1) at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H(+), manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O-O bond formation.
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ) , Avinguda Països Catalans 16, 43007 Tarragona, Spain.
authors.forename: Roc
authors.initials: R
authors.lastname: Matheu
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Mehmed Z
authors.initials: MZ
authors.lastname: Ertem
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ) , Avinguda Països Catalans 16, 43007 Tarragona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Benet-Buchholz
authors.affiliation: Instituto de Ciencia Molecular (ICMol), Universidad de Valencia , 46980 Paterna, Spain.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Coronado
authors.affiliation: Department of Chemistry, Yale University , P.O. Box 208107, New Haven, Connecticut 06520-8107, United States.
authors.forename: Victor S
authors.initials: VS
authors.lastname: Batista
authors.affiliation: Departament de Química, Universitat Autònoma de Barcelona , Cerdanyola del Vallès, 08193 Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Sala
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ) , Avinguda Països Catalans 16, 43007 Tarragona, Spain.|Departament de Química, Universitat Autònoma de Barcelona , Cerdanyola del Vallès, 08193 Barcelona, Spain.
authors.forename: Antoni
authors.initials: A
authors.lastname: Llobet