There is long-standing interest in nonaqueous uranium
chemistry
because of fundamental questions about uranium’s variable chemical
bonding and the similarities of this pseudo-Group 6 element to its
congener d-block elements molybdenum and tungsten. To provide historical
context, with reference to a conference presentation slide presented
around 1988 that advanced a defining collection of top targets, and
the challenge, for synthetic actinide chemistry to realize in isolable
complexes under normal experimental conditions, this Viewpoint surveys
progress against those targets, including (i) CO and related π-acid
ligand complexes, (ii) alkylidenes, carbynes, and carbidos, (iii)
imidos and terminal nitrides, (iv) homoleptic polyalkyls, -alkoxides,
and -aryloxides, (v) uranium–uranium bonds, and (vi) examples
of topics that can be regarded as branching out in parallel from the
leading targets. Having summarized advances from the past four decades,
opportunities to build on that progress, and hence possible future
directions for the field, are highlighted. The wealth and diversity
of uranium chemistry that is described emphasizes the importance of
ligand–metal complementarity in developing exciting new chemistry
that builds our knowledge and understanding of elements in a relativistic
regime.