Modes of activation of organometallic iridium complexes for catalytic water and C–H oxidation

Andrew J. Ingram, Arron B. Wolk, Cornelia Flender, Jialing Zhang, Christopher J. Johnson, Ulrich Hintermair, Robert H. Crabtree, Mark A. Johnson, Richard N. Zare

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Abstract

Sodium periodate (NaIO4) is added to Cp*IrIII (Cp* = C5Me5–) or (cod)IrI (cod = cyclooctadiene) complexes, which are water and C–H oxidation catalyst precursors, and the resulting aqueous reaction is investigated from milliseconds to seconds using desorption electrospray ionization, electrosonic spray ionization, and cryogenic ion vibrational predissociation spectroscopy. Extensive oxidation of the Cp* ligand is observed, likely beginning with electrophilic C–H hydroxylation of a Cp* methyl group followed by nonselective pathways of further oxidative degradation. Evidence is presented that the supporting chelate ligand in Cp*Ir(chelate) precursors influences the course of oxidation and is neither eliminated from the coordination sphere nor oxidatively transformed. Isomeric products of initial Cp* oxidation are identified and structurally characterized by vibrational spectroscopy in conjunction with density functional theory (DFT) modeling. Less extensive but more rapid oxidation of the cod ligand is also observed in the (cod)IrI complexes. The observations are consistent with the proposed role of Cp* and cod as sacrificial placeholder ligands that are oxidatively removed from the precursor complexes under catalytic conditions.
Original languageEnglish
Pages (from-to)423-433
Number of pages12
JournalInorganic Chemistry
Volume53
Issue number1
Early online date14 Nov 2013
DOIs
Publication statusPublished - 6 Jan 2014

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