Treatment of U(BH4)(4) with 1 or 3 equiv of Li-2(SCS)center dot 1.5Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH4)(3)](2) (4) and U(mu-SCS)(3)[Li(Et2O)](2) (6), respectively [SCS = (Ph2P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH4)2(THF)2 (5). The multiple bond character of the uranium-carbon bond was first revealed by the X-ray crystal structures of the three complexes. The U=C bond in these complexes present a nucleophilic character, as shown by their reaction with a carbonyl derivative. Finally, DFT calculations prove the involvement of both 5f and 6d orbitals in both the sigma and the pi U-C bonds.