Uranium carbene compounds

This article gives an overview of the development of uranium carbene complexes. The first example of these compounds was reported in 1981 with the phosphoylide complex Cp3U=CHPMe2Ph but nearly three decades passed before the area witnessed spectacular advances. During this time, actinide methylidene compounds were detected in solid argon, carbenoid uranium species were evidenced in McMurry type reactions, and a series of uranium complexes with N-heterocyclic carbene ligands was isolated. The recent developments in uranium carbene chemistry have to be related to the use of bis-phosphorus stabilized geminal carbon dianions as ligands. Homoleptic complexes and a series of mixed chloro-, tetrahydroborato-, amido-, cyclopentadienyl- and cyclooctatetraenyl-carbene complexes of thorium(IV) and uranium in the +4, +5 and +6 oxidation states have been isolated and characterized. DFT calculations led to a good description of the U=C double bond that demonstrates a double sigma and pi donation toward the metal atom with the involvement of the 5f orbitals. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.