A new family of uranium(IV) imido complexes of the form Tp*U-2(NR) (Tp* = hydrotris(3,5-dimethylp-yrazolyeborate; R = benzyl (Bn), para-tolyl (p-Tol), 2,6-diethylphenyl (detp), and 2,6-diisopropylphenyl (dipp)) have been generated by bibenzyl extrusion from Tp*2UBn. Tp*U-2(NBn), Tp*U-2(Np-Tol), and Tp*U-2(Ndetp), along with previously reported Tp*U-2(NPh) and Tp*U-2(NAd) (Ad = 1-adamantyl), readily undergo [2 pi+2 pi] cycloaddition with isocyanates and isothiocyanates to generate kappa(2)-ureato and kappa(2-)thioureato derivatives, respectively. These new uranium(IV) complexes were characterized via multinuclear NMR, vibrational and electronic absorption spectroscopies, and, where possible, X-ray crystallography. The steric demands of the ligands were quantitatively assessed using computational modeling, and it was shown that cycloaddition only occurs for imido species where ligands occupy 90% or less of the coordination sphere.