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-Me3C6H2) or Na(ArA/C(Ph)CHC(Ph)O) (Ar = 3,5-(Bu2C6H3)-Bu-t) with 0.5 equiv of UO2Cl2(THF)(3) results in the formation of UO2((Ar)acnac)(2) (Ar = 2,4,6-Me3C6H2, 1; 3,5-(Bu2C6H3)-Bu-t, 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 I 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*Co-2 to generate [CP*2Co][UO2((Ar)acnac)(2)] (Ar = 2,4,6-Me3C6H2, 3; 3,5-(Bu2C6H3)-Bu-t, 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(C6F5)(3) in CH2Cl2 leads to the isolation of UO(OB{C6F5}(3)) ((Ar)acnac)(2) (Ar = 3,5-(Bu2C6H3)-Bu-t) (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(C6F5)(3).