Structural and theoretical insights into the perturbation of uranium-rhenium bonds by dative Lewis base ancillary ligands

Amine-elimination gave the two uranium-rhenium complexes [(Ts(Xy))(THF)(n)URe(eta(5)-C(5)H(5))(2)] [Ts(Xy) = HC(SiMe(2)N-3,5-Me(2)C(6)H(3))(3); n = 0 or 1]; structural and theoretical analyses, and comparison to [(Tren(TMS)) URe(eta(5)-C(5)H(5))(2)] [Tren(TMS) = N(CH(2)CH(2)NSiMe(3))(3)], reveal an increasing sigma-component to the U-Re bond upon removal of dative ancillary ligands from uranium with the pi-component remaining essentially invariant.