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

Abstract

Reaction of the terphenyl bis(anilide) ligand [{K(DME) ₂} ₂L ^Ar] (L ^Ar = {C ₆H ₄[(2,6- ⁱ Pr ²C ₆H ₃)NC ₆H ₄] ₂} ²⁻) with trivalent chloride “MCl ₃” salts (M = Ce, U, Np) yields two distinct products; neutral L ^ArM(Cl)(THF) (1 ^M) (M = Np, Ce), and the “-ate” complexes [K(DME) ₂][(L ^Ar)Np(Cl) ₂] (2 ^Np) or ([L ^ArM(Cl) ₂(μ-K(X) ₂)]) _∞ (2 ^Ce, 2 ^U) (M = Ce, U) (X = DME or Et ₂O) (2 ^M). Alternatively, analogous reactions with the iodide [MI ₃(THF) ₄] salts provide access to the neutral compounds L ^ArM(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.

Abstract

Reaction of a terphenyl bis(anilide) ligand with trivalent halide precursors of Ce and early actinides yield both neutral and “-ate” complexes. These molecules afford comparative insight into f-block metal–arene bonding.