Oxidation of dihydrogen by iridium complexes of redox-active ligands

Mark R. Ringenberg, Mark J. Nilges, Thomas Rauchfuss, Scott R. Wilson

Research output: Contribution to journalArticle


Unsaturated organoiridium complexes were prepared with amidophenolate ligands derived from 2-(2-trifluoromethyl)amino-4,6-di-tert-butylphenol (H 2tBAF) and 2-tert-butylamino-4,6-di-tert- butylphenol (H2tBAtBu). The following 16e complexes were characterized: Cp*M(tBAR) with M = Ir (1F and 1t-Bu), Rh (2F), and (cymene)Ru( tBAF) (3F). These complexes undergo two 1e oxidations at potentials of about 0 and -0.25 V vs Cp2Fe 0/+. The magnitude of δE1/2 is sensitive to the counteranions, and the reversibility is strongly affected by the presence of Lewis bases, which stabilize the oxidized derivatives. Crystallographic measurements indicate that upon oxidation the amidophenolate ligands adopt quinoid character, as indicated by increased alternation of the C-C bond lengths in the phenylene ring backbone and shortened C-N and C-O bonds. Unlike the charge-neutral precursors, the cationic [Cp*M(tBA R)]+ are Lewis acidic and form well-characterized adducts with PR3 (R = Me, Ph), CN-, MeCN (reversibly), and CO. In the absence of competing ligands, the cations oxidize H2. Coulommetry measurements indicate that H2 is oxidized by the monocations [Cp*M(tBAR)]+, not the corresponding dications. Oxidation of H2 is catalytic in the presence of a noncoordinating base at potentials required for the generation of [Cp*M(tBAR)]+. The rate decreases in the order [Cp*M(tBAF)]BArF4 > [Cp*M(tBAF)]PF6 > [Cp*M( tBAt-Bu)]PF6. The reduction of ferrocenium by H2 is catalyzed by Cp*M(tBAR).

Original languageEnglish (US)
Pages (from-to)1956-1965
Number of pages10
Issue number8
StatePublished - Apr 26 2010

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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