Mixed-Ligand Uranyl(V) β-Diketiminate/β-Diketonate Complexes: Synthesis and Characterization

The reaction of [UO2(Ar2nacnac)Cl]2 [Ar2nacnac = (2,6-iPr2C6H3)NC(Me)CHC(Me)N(2,6-iPr2C6H3)] with Na(RC(O)CHC(O)R) (R = Me, Ph, CF3) in tetrahydrofuran results in the formation of UO2(Ar2nacnac)(RC(O)CHC(O)R) (R = Me, 1; Ph, 2; CF3, 3), which can be isolated in moderate yields. The structures of 1 and 2 have been confirmed by X-ray crystallography, while the solution redox properties of 1−3 have been measured by cyclic voltammetry. Complexes 1−3 exhibit reduction features at −1.82, −1.59, and −1.39 V (vs Fc/Fc+), respectively, at a scan rate of 100 mV·s−1. The decrease in the reduction potential follows the electron-withdrawing ability of each β-diketonate ligand. Chemical reduction of 1 and 2 with Cp*2Co in toluene yields [Cp*2Co][UO2(Ar2nacnac)(RC(O)CHC(O)R)] (R = Me, 4; Ph, 5), while reduction of 3 with Cp2Co provides [Cp2Co][UO2(Ar2nacnac)(CF3C(O)CHC(O)CF3)] (6). Complexes 4−6 have been fully characterized, while the solid-state molecular structure of 5 has also been determined. In contrast to the clean reduction that occurs with Cp*2Co, reduction of 1 with sodium ribbon, followed by cation exchange with [NEt4]Cl, produces [NEt4][UO2(Ar2nacnac)(H2CC(O)CH(O)CMe)] (7) in modest yield. This product results from the formal loss of H• from a methyl group of the acetylacetonate ligand. Alternately, complex 7 can be synthesized by deprotonation of 1 with NaNTMS2 in good yield.