Synthesis and comparison of iso-structural f-block metal complexes (Ce, U, Np, Pu) featuring η⁶-arene interactions

Reaction of the terphenyl bis(anilide) ligand [{K(DME)₂}₂L^Ar] (L^Ar = {C₆H₄[(2,6-ⁱPr²C₆H₃)NC₆H₄]₂}²⁻) with trivalent chloride “MCl₃” salts (M = Ce, U, Np) yields two distinct products; neutral L^ArM(Cl)(THF) (1M) (M = Np, Ce), and the “-ate” complexes [K(DME)₂][(L^Ar)Np(Cl)₂] (2Np) or ([L^ArM(Cl)₂(μ-K(X)₂)])_∞ (2Ce, 2U) (M = Ce, U) (X = DME or Et₂O) (2M). Alternatively, analogous reactions with the iodide [MI₃(THF)₄] salts provide access to the neutral compounds L^ArM(I)(THF) (3M) (M = Ce, U, Np, Pu). All complexes exhibit close arene contacts suggestive of η⁶-interactions with the central arene ring of the terphenyl backbone, with 3M comprising the first structurally characterized Pu η⁶-arene moiety. Notably, the metal-arene bond metrics diverge from the predicted trends of metal-carbon interactions based on ionic radii, with the uranium complexes exhibiting the shortest M-C_centroid distance in all cases. Overall, the data presents a systematic study of f-element M-η⁶-arene complexes across the early actinides U, Np, Pu, and comparison to cerium congeners.