Exploring the Effects of Reduction or Lewis Acid Coordination on the U═O Bond of the Uranyl Moiety

Reaction of Li(ArNC(Ph)CHC(Ph)O) ((Ar)acnac; Ar = 2,4,6-Me(3)C(6)H(2)) or Na(ArNC(Ph)CHC(Ph)O) (Ar = 3,5-(t)Bu(2)C(6)H(3)) with 0.5 equiv of UO(2)Cl(2)(THF)(3) results in the formation of UO(2)((Ar)acnac)(2) (Ar = 2,4,6-Me(3)C(6)H(2), 1; 3,5-(t)Bu(2)C(6)H(3), 2), which were isolated as orange crystalline solids in good yields. The structure of 2 has been confirmed by X-ray crystallography, while the solution redox properties of 1 and 2 have been measured by cyclic voltammetry. Complex 1 exhibits a reversible reduction feature at E(1/2) = -1.52 V (vs Fc/Fc(+)), while complex 2 exhibits a reduction feature at -1.35 V (vs Fc/Fc(+)). Complexes 1 and 2 react with Cp*(2)Co to generate [Cp*(2)Co][UO(2)((Ar)acnac)(2)] (Ar = 2,4,6-Me(3)C(6)H(2), 3; 3,5-(t)Bu(2)C(6)H(3), 4), in moderate to good yields. Both 3 and 4 have been fully characterized, while the structure of 4 has also been determined by X-ray crystallography. Reaction of 2 with 2 equiv of B(C(6)F(5))(3) in CH(2)Cl(2) leads to the isolation of UO(OB{C(6)F(5)}(3))((Ar)acnac)(2) (Ar = 3,5-(t)Bu(2)C(6)H(3)) (5). Complex 5, generated in situ, exhibits an irreversible reduction at -0.78 V (vs Fc/Fc(+), 100 mV/s scan rate) which is considerably lower than the reduction potential observed for 2, consistent with the removal of electron density from the uranyl moiety by coordination of B(C(6)F(5))(3).