Uranium(IV) imidazolin-2-iminato complexes: a new class of actinide complexes.

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 U-N 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 ε-caprolactone.