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.