Treatment of U(BH(4))(4) with 1 or 3 equiv of Li(2)(SCS) x 1.5 Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH(4))(3)](2) (4) and U(mu-SCS)(3)[Li(Et(2)O)](2) (6), respectively [SCS = (Ph(2)P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH(4))(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.