Early actinide alkoxide chemistry. Synthesis, characterization, and molecular structures of Th(IV) and U(IV) aryloxide complexes

Several synthetic procedures have been developed for the preparation of early actinide aryloxide complexes. Simple alcoholysis of the actinide metallacycle [l brace][(Me[sub 3]Si)[sub 2]N][sub 2][ovr An(CH[sub 2]SiMe[sub 2]N]SiMe[sub 3])[r brace] [An = Th (1), U (2)] using 1 equiv of 2,6-disubstituted phenol results in the protonation of the An-C bond to form mono(aryloxide) complexes An(O-2,6-R[sub 2]C[sub 6]H[sub 3])[N(SiMe[sub 3])[sub 2]][sub 3] [An = U; R = t-Bu (3), i-Pr (4). An = Th; R = t-Bu (5), Me (6)] in essentially quantitative yield. For An = Th, further stepwise substitution products, the bis(aryloxide) or tris(aryloxide) complexes Th(O-2,6-t-Bu[sub 2]C[sub 6]H[sub 3])[sub 2][N(SiMe[sub 3])[sub 2]][sub 2] (7) and Th(O-2,6-t-Bu[sub 2]C[sub 6]H[sub 3])[sub 3][N(SiMe[sub 3])[sub 2]] (8), are readily isolated depending on the stoichiometry of added phenol. Prolonged (36 h) reflux with excess 2,6-di-tert-butylphenol fails to provide the homoleptic Th(O-2,6-t-Bu[sub 2]C[sub 6]H[sub 3])[sub 4] via this simple protonolysis reaction. Thorium metallacycle 1 reacts with 4 equiv of HO-4-t-BuC[sub 6]H[sub 4] to produce polymeric [Th(O-4-t-BuC[sub 6]H[sub 4])[sub 4]][sub x], addition of pyridine to which yields the monomeric adduct Th(O-4-t-BuC[sub 6]H[sub 4])[sub 4](py)[sub 3] (10). For alcoholysis reactions employing the uranium metallacycle (2), addition of slightly greater than 4 equiv of HO-2,6-t-Bu[sub 2]C[sub 6]H[sub 3]more » in refluxing toluene for 6 h provides U(O-2,6-R[sub 2]C[sub 6]H[sub 3])[sub 4] [R = t-Bu (11), i-Pr (12)]. While alcoholysis fails to provide the homoleptic Th(O-2,6-t-Bu[sub 2]C[sub 6]H[sub 3])[sub 4] (9), the authors can prepare this complex via a metathetical procedure. Reaction of ThI[sub 4](THF)[sub 4] with 4 equiv of KO-2,6-t-Bu[sub 2]C[sub 6]H[sub 3] in THF provides 9 in high yield.« less