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(η² -CO₂ )]⁺ structure involving a side-on bonded CO₂ ligand. The CO-tagged complex and the [Fe(CO)₄ ]^2- [Sc(η² -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.