Half-sandwich iridium complexes for homogeneous water-oxidation catalysis

James D. Blakemore, Nathan D. Schley, David Balcells, Jonathan F. Hull, Gerard W. Olack, Christopher D. Incarvito, Odile Eisenstein, Gary W. Brudvig, Robert H. Crabtree

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Abstract

Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H2O) 3]SO4 and [(Cp*Ir)2(μ-OH) 3]OH can show even higher turnover frequencies (up to 20 min -1 at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H218O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.

Original languageEnglish
Pages (from-to)16017-16029
Number of pages13
JournalJournal of the American Chemical Society
Volume132
Issue number45
DOIs
Publication statusPublished - Nov 17 2010

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Blakemore, J. D., Schley, N. D., Balcells, D., Hull, J. F., Olack, G. W., Incarvito, C. D., Eisenstein, O., Brudvig, G. W., & Crabtree, R. H. (2010). Half-sandwich iridium complexes for homogeneous water-oxidation catalysis. Journal of the American Chemical Society, 132(45), 16017-16029. https://doi.org/10.1021/ja104775j