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 language | English |
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Pages (from-to) | 6758-6761 |
Journal | Journal of the American Chemical Society |
Volume | 137 |
Issue number | 21 |
DOIs | |
Publication status | Published - 3 Jun 2015 |