Silyl olefins

By contrast, the isomerization of silyl olefins and addition of silylacetylenes =C—H bond into imines catalyzed by iridium complexes appears to serve as a suitable route for the synthesis of silylfunctionahzed organic compounds. Hence, the acquisition of experimental data on catalysis by iridium complexes in silicon chemistry may be regarded as an initial stage in the quest for catalytic processes leading to the synthesis of other p-block (e.g. B, Ge, Sn, P)-carbon bond-containing compounds. 

A less orthodox formation of a silylated olefin complex was observed in the reaction of (bipy)Ni(SiCl3)2 with acetylenes (90, 91) ... 

The formation of some silylated i73-allylic complexes has been, however, achieved by reacting substituted silyl olefins with bis(benzonitrile)palladium dichloride. The mechanism is rather complex and two olefin molecules are incorporated in the final i -allylic ligand 169) ... 

Ruthenium complexes including carbonyl derivatives used in the hydrosilylation of alkenes exceptionally give regular saturated products, but predominantly lead to unsaturated silyl olefins, which are the products of dehydro-genative silylation [1-4]. 

A mechanistic scheme of this new type of silyl olefin conversion involves the migratory insertion of the olefin into the Ru-Si bond and vinylsilane into the M-H bond followed by /3-hydrogen and /3-silicon elimination to give l,2-bis(silyl)ethenes, l,l-bis(silyl)ethenes and ethylene (Scheme 1) [46,47]. 

Normally stable sulfonyl ylide 46 reacts with benzaldehyde derivatives under the influence of microwave irradiation to produce a,fl-unsaturated sulfones. P-Silylated olefins are obtained from the corresponding aldehydes or ketones and [Ph3PCH3]I."... 

Terminal acetylenes 268 (R = Bu, /-Bu or Ph) react with the lithium silylcuprate 269 by cw-addition to afford, after work-up with aqueous ammonium chloride, the silylated olefins 270 A similar reaction of 1-dodecyne with the reagent prepared from methylmagnesium iodide and lithium (dimethyl)phenylsilane and a trace of tris(tributylphosphine)platinum(II) chloride gave solely the ( )-alkene 271. In contrast, in the presence of bis(tri-o-tolylphosphine)palladium(II) chloride the regioisomer 272 was the main product. ... 

Study of anions of differentially substituted silyl olefins seems very much worthwhile. 

Hydrosilylation of Cyclopropanes. /S-Silylated olefins are prepared via the hydrosilylation of methylenecyclopropanes in the presence of catalytic amounts of Rh(I) complexes (eq 20). The methylenecyclopropanes used in the process are versatile substrates that have become readily available and have various applications in organic synthesis as building blocks. ... 

The hydrosilylation of methylenecyclopropanes is proposed to proceed via oxidative addition to the olefin, followed by rhodium migration across the strained cyclopropane ring, and eventual reductive elimination to give the silyl-substituted olefins. The process is compatible with aromatic and aliphatic substitution on the olefin and often requires heating. Additionally, cyclopropyl-substituted methylenecyclopropanes may be selectively silylated to give alkenes containing one, two, or three /3-silylated olefin chains. 

Unsaturated ethers, nitriles, amines and silylated olefins can also be metathesized but the activity of these reactions is low compared to that observed with normal, a- and )8-olefins. 

Hydroformylations of (Z)-silyl olefins such as 422 furnish the P-silyl aldehydes 423 with high regioselectivity if the silyl group is bulky enough (TBDPS) (Scheme 3.81). Unfortunately, no diastereoselection was observed when a stere-ogenic carbinol center was present (entries 5-8 in Table 3.3) [132]. 

Exocyclic bis-silylated olefins have been constructed through the Pd(OAc)2-catalyzed reaction of alkynes with a tethered disi-lanyl group. The reactions are carried out in the presence of a tert-alkyl isocyanide, although the precise role of this ligand is unclear. Diimide reduction of the disilylated alkene so-formed followed by Fleming-Tamao-type oxidation of the two C-Si bonds in the saturated product then affords 1,2,4-triols in a stereoselective manner (eq 83).l ... 

The reaction of vinyl epoxide 19 with triphenylsilanoi in the presence of a palladium catalyst affords, after de-silylation, olefin 20. ... 

---