Gas-phase, f-element organometallic chemistry: Reactions of cyclic hydrocarbons with Th+, U+, ThO+, UO+, and lanthanide ions, Ln(+)

The extent of reaction of metal ions, M+, with organic molecules depends upon the electronic structure of the metal ion; in particular, the degree to which laser-ablated lanthanide ions, Ln(+) dehydrogenate hydrocarbons is known to reflect the energy needed to excite ground state Ln(+) to a divalent configuration. Reported here are gas-phase reactions of Ln(+) and AnO(n)(+) (An = Th, or U; n = 0 or 1) with C-6 and C-8 cyclic hydrocarbons, The reactivities of Ln(+) with c-C8H8+2m (m = 0, 2, or 4) were consistent with previous results for Ln(+) + c-C6H6+2m, in that the relative dehydrogenation efficiencies reflected the metal ion electronic structure and excitation energy. Additionally, the relatively strong bonding between Ln(+) and cyclooctatetraene (COT) was manifested as abundant condensation adduct, Ln(+)-COT. , The dehydrogenation reactivities of Th+ and U+ with both C-6 and C-8 cyclic hydrocarbons were found to be comparable to that of Ce+, the most reactive Ln(+), consistent with divalent An(+) electronic configurations and a dehydrogenation mechanism initiated by oxidative insertion of Anf into a C-H bond, The most conspicuous discrepancy between the actinide and lanthanide results was the significant dehydrogenation reactivities of the AnO(+), this in sharp contrast to essentially inert behavior of all LnO(+) studied. In view of the similarity between Ce and Th, the substantial reactivity of ThO+ in light of the inert behavior of CeO+ is particularly intriguing and suggests a central role of the metal center in the dehydrogenation process. The activity of the AnO(+) may reflect the distinctive nature of the 5f valence orbitals and could be partly attributable to relativistic effects. An ancillary result of the present investigation was the identification of several metal oxide clusters comprising uranium in multiple valence states.