A comparative study of oxo-ligand effects in the gas-phase chemistry of atomic lanthanide and actinide cations

Abstract

The effects of oxo ligands on lanthanide and actinide cations have been examined for the mono- and dioxocations MO+ and MO2/+ of cerium, neodymium, thorium, and uranium by probing C-H and C-C bond activation of hydrocarbons in an FT-ICR mass spectrometer. The metal monoxide cations are readily available by reaction of the 'bare' metal cations with O2, CO2, N2O, or H2O. In the ensuing oxidation of MO+, UO2/4 is obtained by each of these oxidants, while CeO+ could only be oxidized by N2O. NO2 was necessary for the generation of ThO2/+, and NdO2/+ could not be prepared at all. The monoxides are rather unreactire and only dehydrogenate reactive substrates such as 1-butene and 1,4-cyclohexadiene to generate the corresponding butadiene or benzene complexes. In contrast, CeO2/+ and ThO2/+ react efficiently with different substrates by abstraction of a hydrogen atom and formation of the closed-shell species OMOH+, or by oxygen atom transfer to unsaturated hydrocarbons. In marked contrast, UO2/+ only undergoes very slow adduct formation with unsaturated hydrocarbons. The results are compared with the reactions of the 'bare' metals with respect to the influence of the oxo ligand as well as to the underlying electronic features of the investigated complexes.