Theoretical Study of Divalent Bis(Pentaisopropylcyclopentadienyl) Actinocenes

The existence of divalent bis(pentaisopropylcyclopentadienyl) actinocene compounds, An(Cp^iPr)₂ (An = Th, U, Pu, Am, Bk, No, and Lr), is assessed by density functional theory (DFT) calculations with scalar-relativistic small-core pseudopotentials. The calculations predict ground states with significant 6d occupation for Th, U, and Lr, whereas Am, Bk, and No exhibit 5f ground states. A mixed ground state with predominant 5f character is found for Pu. The complexes exhibit a linear coordination geometry and high S₁₀ symmetry except for Pu(Cp^iPr)₂ and Am(Cp^iPr)₂, which are found to be bent by 11 and 12°, respectively. Absorption spectra are simulated with time-dependent density functional theory (TD-DFT) and compared to experimental spectra of known tris(C₄H₄SiMe₃) and tris(C₅H₃(SiMe₃)₂) compounds [ J. Am. Chem. Soc. 2015 , 137 , 369 - 382 . DOI: 10.1021/ja510831n ] as well as recently synthesized divalent lanthanide analogs Dy(Cp^iPr)₂ and Tb(Cp^iPr)₂ [ J. Am. Chem. Soc. , 2019 , 141 , 12967 - 12973 . DOI: 10.1021/jacs.9b05816 ]. Thermodynamic stability is assessed by calculation of adiabatic reduction potentials of the trivalent precursors [An(Cp^iPr)₂]⁺, and the feasibility of further reduction to obtain as yet unknown monovalent molecular actinide complexes is discussed.