Synthesis and Structure of Uranium-Silylene Complexes.

While carbene complexes of uranium have been known for over a decade, there are no reported examples of complexes between an actinide and a "heavy carbene." Herein, we report the syntheses and structures of the first uranium-heavy tetrylene complexes: (CpSiMe ) U-Si[PhC(NR) ]R' (R=tBu, R'=NMe 1; R=iPr, R'=PhC(NiPr) 2). Complex 1 features a kinetically robust uranium-silicon bonding interaction, while the uranium-silicon bond in 2 is easily disrupted thermally or by competing ligands in solution. Calculations reveal polarized σ bonds, but depending on the substituents at silicon a substantial π-bonding interaction is also present. The complexes possess relatively high bond orders which suggests primarily covalent bonding between uranium and silicon. These results comprise a new frontier in actinide-heavy main-group bonding.