Synthesis, Characterization, and Electrochemistry of the Homoleptic f Element Ketimide Complexes [Li]₂[M(Nâ• C^tBuPh)₆] (M = Ce, Th)

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.