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

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journal contribution
posted on 06.04.2009, 00:00 by Trevor W. Hayton, Guang Wu
Reaction of Li(ArNC(Ph)CHC(Ph)O) (Aracnac; Ar = 2,4,6-Me3C6H2) or Na(ArNC(Ph)CHC(Ph)O) (Ar = 3,5-tBu2C6H3) with 0.5 equiv of UO2Cl2(THF)3 results in the formation of UO2(Aracnac)2 (Ar = 2,4,6-Me3C6H2, 1; 3,5-tBu2C6H3, 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 E1/2 = −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*2Co to generate [Cp*2Co][UO2(Aracnac)2] (Ar = 2,4,6-Me3C6H2, 3; 3,5-tBu2C6H3, 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)(Aracnac)2 (Ar = 3,5-tBu2C6H3) (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.