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Ru(II) Water Oxidation Catalysts with 2,3-bis(2-Pyridyl)Pyrazine and tris(Pyrazolyl)Methane Ligands: Assembly of Photo- and Catalytic-Active Subunits in a Dinuclear Structure

Abstract

Two mononuclear Ru(II) complexes, i.e. [RuCl(κ3N-terpy)(κ2N-dpp)]PF6 ([1]PF6; terpy = 2,2':6',2"-terpyridine; dpp = 2,3-bis(2'-pyridyl-pyrazine) and [RuCl(κ3N-tpm)(κ2N-dpp)]Cl ([2]Cl; tpm = tris(1-pyrazolyl)methane), and one dinuclear complex, i.e. [Ru2Cl(κ3N-tpm)(κ2N:κ2N-dpp)Ru(κ2N-bpy)2][PF6]3 ([3][PF6]3; bpy = 2,2'-bipyridine), have been synthesized and their water oxidation catalytic properties have been investigated. A combined DFT and experimental (35Cl NMR, conductivity measurements) study aimed to elucidate the nature of [1]+ and [2]+ in aqueous solution has also been performed, indicating that one water molecule is allowed to enter the first coordination sphere of [2]+ at the ground state, replacing one tpm nitrogen. Conversely, in the case of [1]+, water coordination, assumed to be needed for the water oxidation process, presumably occurs following oxidation of the metal. For all the complexes, a catalytic wave has been detected in acetonitrile/water 1:1 (v/v) solution in the range 1.4-1.7 V vs SCE. In all cases, water oxidation (investigated at pH < 8) takes place initially via a proton-coupled two-electron, two-proton process with formation of a Ru(IV)=O moiety, followed by one electron oxidation and water nucleophilic attack. The TON and TOF values (within the range 16-33 and 1.3-2.2 h-1, respectively) of the complexes are higher than those of the benchmark for [Ru(LLL)(LL)(OH2)]2+-type species (LLL and LL are tridentate and bidentate polypyridine ligands, respectively), that is [Ru(terpy)(bpm)(OH2)]2+.

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Supplementary files

Article information


Submitted
19 Dec 2019
Accepted
13 Feb 2020
First published
13 Feb 2020

Dalton Trans., 2020, Accepted Manuscript
Article type
Paper

Ru(II) Water Oxidation Catalysts with 2,3-bis(2-Pyridyl)Pyrazine and tris(Pyrazolyl)Methane Ligands: Assembly of Photo- and Catalytic-Active Subunits in a Dinuclear Structure

A. De Palo, G. LaGanga, F. Nastasi, M. Guelfi, M. Bortoluzzi, G. Pampaloni, F. Puntoriero, S. Campagna and F. Marchetti, Dalton Trans., 2020, Accepted Manuscript , DOI: 10.1039/C9DT04815D

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