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ChemCatChem. 2018 Oct 9;10(19):4280-4291. doi: 10.1002/cctc.201800916. Epub 2018 Sep 30.

Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine-alkoxide) Complexes.

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Centre for Sustainable Chemical Technologies University of Bath Claverton DownBath BA2 7AY United Kingdom.
Department of Chemistry University of Bath Claverton Down Bath BA2 7AY United Kingdom.


We report the solution-phase electrochemistry of seven half-sandwich iridium(III) complexes with varying pyridine-alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciation determines the electrochemical response: cationic complexes show over 1 V higher redox potentials that their neutral forms in a distinct demonstration of charge accumulation effects relevant to water oxidation. Building on previous work that analysed the activation behaviour of our pyalk-ligated Cp*Ir complexes 1-7, we assess their catalytic oxygen evolution activity with sodium periodate (NaIO4) and ceric ammonium nitrate (CAN) in water and aqueous tBuOH solution. Mechanistic studies including H/D kinetic isotope effects and reaction progress kinetic analysis (RPKA) of oxygen evolution point to a dimer-monomer equilibrium of the IrIV resting state preceding a proton-coupled electron transfer (PCET) in the turnover-limiting step (TLS). Finally, true electrochemically driven water oxidation is demonstrated for all catalysts, revealing surprising trends in activity that do not correlate with those obtained using chemical oxidants.


Iridium complexes; electrochemistry; homogeneous catalysis; pyridine-alkoxide ligands; water oxidation

Conflict of interest statement

U.S. Patent 9/790/605 by UH et al. contains intellectual property described in this article.

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