Complexed Silylene Derivatives

When the salt 152 was treated with [(COE)2IrCl]2, the product of C-Fl activation of the cyclooctene (COE) ligand 162 was obtained in 65% yield (Scheme 62) if -binding mode of the cyclooctene ligand in 162 was confirmed by X-ray crystallography and NMR spectroscopy. Complex 162 under the action of Fl2SiMes2 was converted into silylene derivative 163 observed by NMR spectroscopy <1999JA9871>. 

Disubstituted silole derivatives are synthesized by the palladium-catalyzed reaction of (trialkylstannyl)di-methylsilane with terminal alkynes (Equation (107)).266 The mechanism is supposed to involve a palladium silylene complex, which is generated via /3-hydride elimination from LJ3d(SiMe2H)(SnBu3) (Scheme 62). Successive incorporation of two alkyne molecules into the complex followed by reductive elimination gives rise to the silole products. 

If doubly-bonded compounds >M = X (M = Si, Ge, Sn) are now well known, this is not yet the case for the heavy allenic derivatives >M = C = X. Transient silaallenes >Si = C = C 160-167 or silaazaallene >Si = C = N—168 were postulated some years ago, but the first stable derivative of this type, a formal 3-stanna-l-azaallene >Sn = C = N —, was isolated only in 1992 by Griitzmacher et al169 The compound Tbt(Mes)Si = C = NR170 has also been obtained, but according to the authors it is closer to a silylene Lewis base complex than to a silacumulene. The first stable silaallene was only reported in 1993 by West et al.111 and the first metastable >Si = C = P— was characterized still more recently.172... 

Conlin and coworkers photolyzed vinyltris(trimethylsilyl)silane 188 in the presence of a variety of trapping reagents such as butadiene, substituted butadienes or silanes and observed products derived from intermediate silenes 189 (formed by rearrangement) or from silylenes 190 resulting from elimination of hexamethyldisilane93. In some cases complex mixtures of products which could have been derived from intermediate silyl radicals were also observed. The reaction products formed from the silene and the silylene in the presence of butadiene, 191 and 192 respectively, are shown in Scheme 32. 

---