Organometallic iridium catalysts based on pyridinecarboxylate ligands for the oxidative splitting of water

Alberto Bucci, Ariana Savini, Luca Rocchigiani, Cristiano Zuccaccia, Silvia Rizzato, Alberto Albinati, Antoni Llobet, Alceo Macchioni

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Abstract

Organometallic compounds [Cp*Ir(κ2-N,O)X] (κ2-N,O = 2-pyridinecarboxylic acid, ion(−1) (1), 2,4-pyridinedicarboxylic acid, ion(−1) (2), 2,6-pyridinedicarboxylic acid, ion(−1) (3); X = Cl (a), NO3– (b)) and [Ir(κ3-N,O,O)(1-κ-4,5-η2-C8H13)(MeOH)] (κ3-N,O,O = 2,6-pyridinedicarboxylic acid, ion(−2) (4)) are effective catalysts for the oxidative splitting of water to O2 driven by Ce4+. They show similar TOFLT values (long-term TOF, 2.6–7.4 min–1) while TOFIN values (initial TOF) strongly depend on the catalyst (1 ≫ 2 > 3 > 4), reaching a maximum value of 287 min–1 (4.8 s–1) for 1a, which is the highest TOF value ever reported for an iridium catalyst. Voltammetric measurements indicate that the oxidative processes of compounds 1–4 are located at values substantially less positive than that of [Cp*Ir(bzpy)NO3] (bzpy = 2-benzoylpyridine; ΔE ≈ 0.2–0.3 V), taken as reference catalyst for water oxidation. In particular, compound 3, having a pendant −COOH moiety in close proximity to an iridium coordination site, as shown by the structure determined by single-crystal X-ray diffraction, exhibits several low-potential oxidation processes.
Original languageEnglish
Pages (from-to)8071-8074
JournalOrganometallics
Volume31
Issue number23
Early online date28 Nov 2012
DOIs
Publication statusPublished - 10 Dec 2012

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