Theoretical Study of Divalent Bis(Pentaisopropylcyclopentadienyl) Actinocenes

The existence of divalent bis(pentaisopropylcyclopentadienyl) actinocene compounds, An(CpiPr5)2 for An = (Th, U, Pu, Am, Bk, No, 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(CpiPr5)2 and Am(CpiPr5)2, which are found to be bent by 11 and 12 degrees , 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 [M. E. Fieser et al., J. Am. Chem. Soc. 2015, 137, 369-382] as well as recently synthesized divalent lanthanide analogs Dy(CpiPr5)2 and Tb(CpiPr5)2 [C. Gould et al., J. Am. Chem. Soc. 2019, accepted]. Thermodynamic stability is assessed by calculation of adiabatic reduction potentials of the trivalent precursors [An(CpiPr5 )2] +, and the feasibility of further reduction to obtain as yet unknown monovalent molecular actinide complexes is discussed.