Synthesis and comparison of iso-structural f-block metal complexes (Ce, U, Np, Pu) featuring η(6)-arene interactions

Reaction of the terphenyl bis(anilide) ligand [{K(DME)(2)}(2)L(Ar)] (L(Ar) = {C(6)H(4)[(2,6-(i)Pr(2)C(6)H(3))NC(6)H(4)](2)}(2−)) with trivalent chloride “MCl(3)” salts (M = Ce, U, Np) yields two distinct products; neutral L(Ar)M(Cl)(THF) (1(M)) (M = Np, Ce), and the “-ate” complexes [K(DME)(2)][(L(Ar))Np(Cl)(2)] (2(Np)) or ([L(Ar)M(Cl)(2)(μ-K(X)(2))])(∞) (2(Ce), 2(U)) (M = Ce, U) (X = DME or Et(2)O) (2(M)). Alternatively, analogous reactions with the iodide [MI(3)(THF)(4)] salts provide access to the neutral compounds L(Ar)M(I)(THF) (3(M)) (M = Ce, U, Np, Pu). All complexes exhibit close arene contacts suggestive of η(6)-interactions with the central arene ring of the terphenyl backbone, with 3(M) comprising the first structurally characterized Pu η(6)-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-η(6)-arene complexes across the early actinides U, Np, Pu, and comparison to cerium congeners.