Pentamethylcyclopentadiene dimers[(Cp*MCl)2Cl]+ (M = Ir, Rh) are stable species in the gas phase, and this project seeks to understand the ion chemistry of these species toward O2 via ion-molecule reactions carried out in the trap of an FT-ICR mass spectrometer. Though isolatable O2 complexes are rare,[1] an O2-binding step is predicted to be key to the mechanism of many reactions. For example, O2 binding is computed to be the rate limiting step in oxygen-reduction reactions catalyzed by iridium [2] and also the rate limiting step in O2 insertion into organometallic complexes, which results in bridging oxo-intermediates .[3] Peroxo intermediates are also invoked in water splitting reactions with iridium. The bridging and chelating ligands are key in tuning reactivity, for example, di-μ-oxo iridium species are valuable H2O oxidation catalysts, but require suitable chelation to prevent the formation of iridium oxide nanoparticles[4]. Species with the di-μ-oxo iridium motif can also be tethered to metal oxide surfaces,[5] thereby also avoiding such decomposition. Thus, as the bottle neck in many of the processes is O2 activation or peroxo intermediacy, this project aims to systematically investigate in the gas phase the effect of parameters such as metal and nuclearity (Ir versus Rh, dimer versus monomeric), anionic ligand(s) (Cl versus I, or OH), and functionalized chelating ligands on the reactions with O2.
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