Synthesis and structure of a bis-N-heterocyclic carbene complex of uranium tetrachloride exhibiting short Cl center dot center dot center dot C-carbene contacts

Treatment of UCl4 with one or two equivalents of IPr [IPr = {C(NArCH)(2)}, Ar = 2,6-diisopropylphenyl] gives [UCl4(IPr)(2)] as the sole isolable uranium-containing containing product; an X-ray diffraction study showed close Cl center dot center dot center dot C-carbene contacts, but DFT analysis suggests the contacts are the result of aryl chloride steric repulsions as the Cl center dot center dot center dot C orbital interaction is negligible.