Unique σ-Bond Metathesis of Silylalkynes Promoted by an <i>a</i><i>nsa</i>-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⋮CBut and CH3C⋮CH. A plausible mechanism for the catalytic process is presented.