Redox non-innocent ligand controls water oxidation overpotential in a new family of mononuclear cu-based efficient catalysts

Pablo Garrido-Barros, Ignacio Funes-Ardoiz, Samuel Drouet, Jordi Benet-Buchholz, Feliu Maseras, Antoni Llobet

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151 Citations (Scopus)

Abstract

© 2015 American Chemical Society. A new family of tetra-anionic tetradentate amidate ligands, N<inf>1</inf>,N<inf>1</inf>′-(1,2-phenylene)bis(N<inf>2</inf>-methyloxalamide) (H<inf>4</inf>L1), and its derivatives containing electron-donating groups at the aromatic ring have been prepared and characterized, together with their corresponding anionic Cu(II) complexes, [(LY)Cu]<sup>2-</sup>. At pH 11.5, the latter undergoes a reversible metal-based III/II oxidation process at 0.56 V and a ligand-based pH-dependent electron-transfer process at 1.25 V, associated with a large electrocatalytic water oxidation wave (overpotential of 700 mV). Foot-of-the-wave analysis gives a catalytic rate constant of 3.6 s<sup>-1</sup> at pH 11.5 and 12 s<sup>-1</sup> at pH 12.5. As the electron-donating capacity at the aromatic ring increases, the overpotential is drastically reduced down to a record low of 170 mV. In addition, DFT calculations allow us to propose a complete catalytic cycle that uncovers an unprecedented pathway in which crucial O-O bond formation occurs in a two-step, one-electron process where the peroxo intermediate generated has no formal M-O bond but is strongly hydrogen bonded to the auxiliary ligand.
Original languageEnglish
Pages (from-to)6758-6761
JournalJournal of the American Chemical Society
Volume137
Issue number21
DOIs
Publication statusPublished - 3 Jun 2015

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