Synthesis and characterization of isostructural annulated actinocenes

An isostructural series of four annulated actinocene complexes, M(hdcCOT)₂ (M = Th, U, Np, Pu), is reported. The syntheses proceed through a trivalent starting material when M = U, Np, Pu with subsequent oxidation or, in the case of M = Th, directly from ThCl₄(DME)₂. X-ray crystallography shows that each actinocene has C_2h molecular point symmetry in the solid state, with the metal atoms symmetrically bonded to two 10p-aromatic [8]annulene dianion rings. UV-Vis spectroscopy shows bands that were assigned as ligand-to-metal charge transfer (LMCT) transitions with the aid of time-dependent density functional theory (TDDFT) calculations. Compared to the M(COT)₂ analogs, the LMCT transitions for M(hdcCOT)₂ are red-shifted by B0.1 eV for all four metals. These actinocenes may be readily synthesized and crystallized even on the milligram scale (r1 mg of metal ion content), which will enable future studies of the organometallic chemistry of transplutonium elements.