1 research outputs found
Modes of Activation of Organometallic Iridium Complexes for Catalytic Water and C–H Oxidation
Sodium
periodate (NaIO<sub>4</sub>) is added to Cp*Ir<sup>III</sup> (Cp*
= C<sub>5</sub>Me<sub>5</sub><sup>–</sup>) or (cod)ÂIr<sup>I</sup> (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*IrÂ(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)ÂIr<sup>I</sup> 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