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 C₆H₆ 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.