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The reaction of [AnCl(NR2)3] (An = U, Th, R = SiMe3) with in situ generated lithium-3,3-diphenylcyclopropene results in the formation of [{(NR2)3}An(CH[double bond, length as m-dash]C[double bond, length as m-dash]CPh2)] (An = U, 1; Th, 2) in good yields after work-up. Deprotonation of 1 or 2 with LDA/2.2.2-cryptand results in formation of the anionic allenylidenes, [Li(2.2.2-cryptand)][{(NR2)3}An(CCCPh2)] (An = U, 3; Th, 4). The calculated 13C NMR chemical shifts of the Cα, Cβ, and Cγ nuclei in 2 and 4 nicely reproduce the experimentally assigned order, and exhibit a characteristic spin-orbit induced downfield shift at Cα due to involvement of the 5f orbitals in the Th-C bonds. Additionally, the bonding analyses for 3 and 4 show a delocalized multi-center character of the ligand π orbitals involving the actinide. While a single-triple-single-bond resonance structure (e.g., An-C[triple bond, length as m-dash]C-CPh2) predominates, the An[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CPh2 resonance form contributes, as well, more so for 3 than for 4.

The reaction of UCl4 or ThCl4(DME)2 (DME = dimethoxyethane) with 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetic acid (H4DOTA), and 6 equiv of triethylamine, in dimethyl sulfoxide (DMSO) results in the formation of [AnIV(κ8-DOTA)(DMSO)] (1, An = U; 2, An = Th), which can be isolated in moderate yields after workup. Complexes 1 and 2 are the first structurally characterized actinide-DOTA complexes to feature the κ8 binding mode for the DOTA ligand. In addition, we isolated a few crystals of [U(κ4-H2DOTA)(DMSO)4][Cl]2 (3). Crystallographic characterization of this material reveals that the [H2DOTA]2- ligand in 3 is only coordinated to U4+ by its four carboxylate arms, generating an overall κ4 binding mode. Similar complexes have been previously proposed as intermediates along the H4DOTA complexation pathway, but this intermediate had not been structurally characterized until now.

The reaction of UCl4 or ThCl4(DME)2 (DME = dimethoxyethane) with 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetic acid (H4DOTA), and 6 equiv of triethylamine, in dimethyl sulfoxide (DMSO) results in the formation of [AnIV(κ8-DOTA)(DMSO)] (1, An = U; 2, An = Th), which can be isolated in moderate yields after workup. Complexes 1 and 2 are the first structurally characterized actinide-DOTA complexes to feature the κ8 binding mode for the DOTA ligand. In addition, we isolated a few crystals of [U(κ4-H2DOTA)(DMSO)4][Cl]2 (3). Crystallographic characterization of this material reveals that the [H2DOTA]2- ligand in 3 is only coordinated to U4+ by its four carboxylate arms, generating an overall κ4 binding mode. Similar complexes have been previously proposed as intermediates along the H4DOTA complexation pathway, but this intermediate had not been structurally characterized until now.