Uranyl Coordination by the 14-Membered Macrocycle Dibenzotetramethyltetraaza[14]annulene.

Reaction of [UO2 (N(SiMe3 )2 )2 (THF)2 ] with 1 equiv of dibenzotetramethyltetraaza[14]annulene (tmtaaH2 ) affords the uranyl complex [UO2 (tmtaaH)(N(SiMe3 )2 ) (THF)] (1) (THF = tetrahydrofuran) as red blocks in 83% yield. Similarly, thermolysis of a mixture of [UO2 (N(SiMe3 )2 )2 (THF)2 ] and 2 equiv of tmtaaH2 affords [UO2 (tmtaaH)2 ] (2), which can be isolated as red-orange crystals in 67% yield after workup. Both 1 and 2 were fully characterized, including analysis by X-ray crystallography. The tmtaaH ligands in 1 and 2 are only coordinated to the uranium center via one β-diketiminate fragment, while the protonated β-diketimine portion of the ligand remains uncoordinated. Reaction of [UO2 (N(SiMe3 )2 )2 (THF)2 ] with 1 equiv of Li2 (tmtaa) in C6 H6 results in the formation of [Li(THF)]2 [UO2 (N(SiMe3 )2 )2 (tmtaa)] (3), which can be isolated in 55% yield as a red-brown crystalline solid. The tmtaa ligand in complex 3 supports a dative interaction between an oxo ligand in the uranyl fragment and a lithium cation, suggesting that tmtaa could be a useful ligand for developing the oxo ligand functionalization chemistry of the uranyl ion.