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

Abstract

Reaction of the terphenyl bis(anilide) ligand [{K(DME)2}2LAr] (LAr = {C6H4[(2,6-iPr2C6H3)NC6H4]2}2−) with trivalent chloride “MCl3” salts (M = Ce, U, Np) yields two distinct products; neutral LArM(Cl)(THF) (1M) (M = Np, Ce), and the “-ate” complexes [K(DME)2][(LAr)Np(Cl)2] (2Np) or ([LArM(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 LArM(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-Ccentroid 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.