We report herein the synthesis of the first structurally characterized homoleptic actinide aryl complexes, [Li(DME)3]2[Th(C6H5)6] (1) and [Li(THF)(12-crown-4)]2[Th(C6H5)6] (2), which feature an anion possessing a regular octahedral (1) or a severely distorted octahedral (2) geometry. The solid-state structure of 2 suggests the presence of pseudo-agostic ortho C-H···Th interactions, which arise from σ(C-H) → Th(5f) donation. The non-octahedral structure is also favoured in solution at low temperatures.

Reaction of [Ce(NO₃)₃(THF)₄] with 6 equiv of Li(N═C^tBuPh), followed by addition of 0.5 equiv of I₂, affords the homoleptic Ce(IV) ketimide [Li]₂[Ce(N═C^tBuPh)₆] (1), which can be isolated in 44% yield after workup. Similarly, reaction of [ThCl₄(DME)₂] (DME = 1,2-dimethoxyethane) with 6 equiv of Li(N═C^tBuPh) in tetrahydrofuran affords the isostructural Th(IV) ketimide [Li]₂[Th(N═C^tBuPh)₆] (2), which can be isolated in 53% yield after workup. Both 1 and 2 were fully characterized, including analysis by X-ray crystallography, allowing for a detailed structural and spectroscopic comparison. The electronic structures of 1 and 2 were also explored with density functional theory and multiconfigurational wave function calculations. Additionally, the redox chemistry of 1 was probed by cyclic voltammetry, which revealed a highly cathodic Ce(IV)/Ce(III) reduction potential, providing evidence for the ability of the ketimide ligand to stabilize high oxidation states of the lanthanides.

While preparing a follow-up manuscript, we found an error in one of the orbital reduction factors used in our crystal field models, given in Scheme 2. The third equation in that scheme was published as ka2t2 = 1 - 12 N2 2 a'p ; however, the correct formula is k a2t2 = 1 - 12 N'a'p2. (Table Presented).