Unique σ-Bond Metathesis of Silylalkynes Promoted by an ansa-Dimethylsilyl and Oxo-Bridged Uranium Metallocene

The tetrachloride salt of uranium reacts with 1 equiv of the lithium ligand Li₂[(C₅Me₄)₂SiMe₂] in DME to form the complex [η⁵-(C₅Me₄)₂SiMe₂]UCl₂·2LiCl·2DME (1), which undergoes a rapid hydrolysis in toluene to yield the dimeric bridged monochloride, monooxide complex [{[η⁵-(C₅Me₄)₂SiMe₂]UCl}₂(μ-O)(μ-Cl)•Li•1/2DME]₂ (2). Metathesis of 2 with BuLi in DME gives the mono-bridged dibutyl complex {[η⁵-(C₅Me₄)₂SiMe₂]UBu}₂(μ-O) (3). Complex 2 was characterized by solid-state X-ray analysis. Complex 3 was found to be an active catalyst for the disproportionation metathesis of TMSC⋮CH (TMS = SiMe₃) and the cross-metathesis of TMSC⋮CH or TMSC⋮CTMS with various terminal alkynes. The metathesis of TMSC⋮CH gives TMSC⋮CTMS and HC⋮CH, whereas the cross-metathesis of TMSC⋮CH or TMSC⋮CTMS with terminal alkynes (RC⋮CH) yields TMSC⋮CTMS, TMSC⋮CR, and HC⋮CH. In addition, TMSC⋮CCH₃ also was found to react with ^tBuC⋮CH, yielding TMSC⋮CBu^t and CH₃C⋮CH. A plausible mechanism for the catalytic process is presented.