The uranyl ion, [UVIO2]2+, possesses
rigorously trans, strongly covalent, and chemically
robust U-oxo groups. However, through the use of anaerobic reaction
techniques, both one- and two-electron reductive functionalization
of the uranyl oxo groups has been discovered and developed. Prior
to 2010, this unusual reactivity centered around the reductive silylation
of the uranyl ion which entailed conversion of the oxo ligands into
siloxy ligands and reductive metalation of the uranyl oxo with Group
1 and f-block metals. This review surveys the large
number of new examples of reductive functionalization of the uranyl
ion that have been reported since 2010, including reductive borylation
and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples
of oxo-group functionalization of [UVIO2]2+ that do not involve reduction, mainly with Group 1 cations,
are also covered, along with new advances in the photochemistry of
the uranyl(VI) ion that involve the transient formation of formally
uranyl(V) [UVO2]+ ion.