CO Oxidation by Group 3 Metal Monoxide Cations Supported on [Fe(CO)4 ](2).

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5(-) (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4 ](2-) building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5(-) anion is determined to be a CO-tagged complex involving a [Fe(CO)4 ](2-) [LaO](+) anion core. In contrast, the OYFe(CO)5(-) anion is characterized to have a [Fe(CO)4 ](2-) [Y(η(2) -CO2 )](+) structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4 ](2-) [Sc(η(2) -CO2 )](+) isomer co-exist for the OScFe(CO)5(-) anion. These observations indicate that both the ScO(+) and YO(+) cations supported on [Fe(CO)4 ](2-) are able to oxidize CO to CO2 . Theoretical analyses show that [Fe(CO)4 ](2-) coordination significantly weakens the MO(+) bond and decreases the energy gap of the interacting valence orbitals between MO(+) and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile.