Silylation bonds

The alkene inserts either in the metal hydride bond or in the metal silyl bond. The latter reaction leads to alkenylsilyl side products and also alkane formation may occur. Similar reactions have been observed for hydroboration, the addition of R2BH to alkenes. (R2 may be the catechol dianion). 

The X-ray structure of 83 was in accord with the prediction of Scheme 4 in that the Si-Cl bond lies in the niobocene bisecting plane trans to the hydride and is elongated compared with classical complexes of the type [M(SiR2Cl)L ]. There was, however, no good reference system that would allow for the comparison of the Nb-Si bond lengths. The metal-silyl bond lengths are strongly affected by Bent s... 

An important area of organocatalysis that was also initiated in the early 1990s has been the realm of Lewis base catalysis. ° On the basis of the noninmitive activation principle of silyl bonding rehybridization, Denmark and Iseki introduced chiral and DMF variants as effective catalysts for enantioselec-... 

Insertion of unsaturated molecules into a transition metal-silyl bond has been suggested for the catalytic reactions related to hydrosilylation and silylcarbonylation. However, there is little direct evidence supporting such a process for unsaturated molecules to insert into a metal-silyl bond in organometallic complexes. " Thus, the fact that 108 is readily derived from 11 and 13 demonstrates the participation of this process in the catalytic cycle of silylformylation. 

The reaction mechanism commonly accepted to account for the double silylation of unsaturated substrates involves three key steps. First, the disli-lane undergoes oxidative addition to the metal center, forming a transition metal-bis(silyl) complex. The unsaturated moiety inserts into the metal-silyl bond, followed by Si-C reductive elimination to give the double sily-... 

A mechanistic rationale for the apparent trans -addition in some of these processes is shown in Scheme 6. Initial insertion of the alkyne into the metal-silyl bond yields an intermediate with an unfavorable interaction between the metal and the silyl group. Coordination of the vinyl part to the metal gives formally a metaUacyclopropene. 

Itami, K., Mitsudo, K., Yoshida, J.-i. Oxidation of 2-Pyridyldimethylsilyl Group to Hydroxyl Group by H202/KF. Implication of Fluoride Ion Accelerated 2-Pyridyl-Silyl Bond Cleavage. J. Org. Chem. 1999, 64, 8709-8714. 

Reaction of silanol groups to give an alkyl silyl bonded phase using an alkyltrichlorosilane)... 

Trimethylsilyl-l,3-oxazine-2,4(3 0 dione (287) is formed by reacting maleic anhydride with trimethylsilyl azide at 55-60°C. On treatment with ethanol, the A-silyl bond is cleaved to give 1,3-... 

The insertion of CO into metal-alkoxide, -amide, and -silyl bonds is much less common than the insertion of CO into metal-alkyl and metal-aryl bonds. Selected insertions... 

The mechanistic scheme presents the conventional oxidative addition— reductive elimination steps to explain the hydrosilylation. The oxidative addition of trisubstituted silanes HSiRs to a metal alkene complex (usually with d and d ° configuration) is followed by migratory insertion of alkene into the M—H bond, and the resulting metal(silyl)-(alkyl) complex undergoes reductive elimination by the Si—C bond formation and regeneration of metal alkene complex in excess of alkene. As the facile reductive elimination of silylalkane from [alkenyl-M]-SiRs species has not been well established in stoichiometric reaction, a modified Chalk-Harrod mechanism has been proposed to explain the formation of unsaturated (vinylsilane) organosilicon product, involving the alkene insertion into the metal-silyl bond followed by C—H reductive elimination (Scheme 2) (38). 

Synthetic Transformations of 2-Pyridyl-substituted Vinyl-silane. 2-Pyridyl-substituted vinylsilanes can be converted into other vinylsilanes. Subjection of 2-pyridyl-substituted vinylsi-lanes to potassium fluoride/methanol leads to the formation of methoxy(vinyl)silanes by pyridyl-silyl bond cleavage (eq 4). The resultant methoxysilanes can be further allowed to react with Grig-nard reagents such as phenylmagnesium bromide to give the corresponding vinylsilanes that are commonly used for various transformations (eq 4). ... 

There are many metal-silyl complexes because of the robustness of the metal-silyl bond. - Several reasons explain this stability ... 

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