Mixed-ligand uranyl(V) β-diketiminate/β-diketonate complexes:: Synthesis and characterization

The reaction of [UO2(Ar(2)nacnac)Cl](2) [Ar(2)nacnac = (2,6-(Pr2C6H3)-Pr-i)NC(Me)CHC(Me)N(2,6-(Pr2C6H3)-Pr-i)] with Na(RC(O)CHC(O)R) (R = Me, Ph, CF3) in tetrahydrofuran results in the formation of UO2(Ar(2)nacnac)(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 beta-diketonate ligand. Chemical reduction of 1 and 2 with Cp*2CO in toluene yields [Cp*Co-2][UO2(Ar(2)nacnac)(RC(O)CHC(O)R)] (R = Me, 4; Ph, 5), while reduction of 3 with Cp2CO provides [Cp2Co][UO2(Ar(2)nacnac)(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*Co-2, reduction of 1 with sodium ribbon, followed by cation exchange with (NEt4]Cl, produces [NEt4][UO2(Ar(2)nacnac)(H2C=C(O)CH(O)CMe)] (7), in modest yield. This product results from the formal loss of H-center dot from a methyl group of the acetylacetonate ligand. Alternately, complex 7 can be synthesized by deprotonation of 1 with NaNTMS2 in good yield.