Acid base reactions between imidazolin-2-imines (Im(R)NH) and [U(NMeEt)(4)] selectively afforded uranium(IV) imidazolin-2-iminato complexes of the type [U(NIm(tBu))(4)] (1), [U(NIm(Mes))(3)(NMeEt)] (2), and [U(NIm(Dipp))(2)(NMeEt)(2)] (3) depending on the steric demand of the substituents in the 1 and 3 positions of the imidazole heterocycle (R = tBu, Mes, Dipp). This new class of actinide complexes displays short UN bonds and nearly linear U-N-C bond angles, suggesting a U-N bond order higher than 1, as well as extraordinarily high catalytic activity in the polymerization of e-caprolactone.