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 C6 and C8 cyclic
hydrocarbons. The reactivities of
Ln+ with
c-C8H8+2
m
(m = 0, 2, or 4) were consistent with previous results for
Ln+ +
c-C6H6+2
m
,
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 C6 and C8 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 An+ 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.