Si-C bonds

The view has also existed in the past that the carbon-silicon bond should be similar in behaviour to the carbon-carbon bond and would have a similar average bond energy. There is some measure of truth in the assumption about average bond energy but because silicon is more electropositive than carbon the C—Si bond will be polar and its properties will be very dependent on the nature of groups attached to the carbon and silicon groups. For example, the CH3—Si group is particularly resistant to oxidation but H13—Si is not. 

These reactions proceed by alkoxide or fluoride attack at silicon which results in C—Si bond cleavage and elimination of the leaving group from the fi carbon. These reactions are stereospecific anti eliminations. 

Examples of linear addition reactions that form C-O, C-S, C-N, C-P, C-C, and C-Si bonds are reviewed. Only a few of the growing number of linear additions that form a carbon-transition metal bond are included... 

It has been reported that an allylic C-Si bond can be cleaved by tetrabutylammonium fluoride to give an anionic allylic species, which chemoselectively adds to carbonyl compounds (nitriles, esters, and epoxides failed) to form homoallylsilyloxy compounds13. 

The mechanism of the reaction has been interpreted in terms of a 4- or 6-centre transition state (LV) or (LVI) in which nucleophilic assistance of C-Si bond cleavage occurs this would not be possible for nitration by nitronium tetrafluoroborate. 

The Z-selectivity is understood in terms of the geminal bond participation. The C-Si bond, which is more electron-donating than the C-H bond, occupies the Z-position. 

Volume 2, Catalytic Reactions. An account of palladium-catalyzed reactions involving formation of C—C, C—O, C—H, C-halogen, C—N, C—S, or C—Si bonds, and heterogeneous reactions. 

The C-C bond forming reaction of an organic halide with an organosilane, catalysed by nickel or palladium, is known as the Hiyama cross-coupling. Typically the C-Si bond needs to be activated by either electronegative substituents or by external fluoride anions. 

Usui, Y, Noma, J., Hirano, M. and Komiya, S. (2000) C—Si bond cleavage of trihalomethyltrimethylsilane by alkoxo-and aryloxogold or -copper complexes. Inorganica Chimica Acta, 309, 151. 

The crucial influence on the reactivity pattern in both cases is the very high stabilization that silicon provides for carbocationic character at the p-carbon atom. This stabilization is attributed primarily to hyperconjugation with the C-Si bond (see Part A, Section 3.4.1).85... 

Other types of hyperconjugative interactions are also thought to exist. A recent example involves the compound R2A1A1R2 (R = —CH(SiMe3)2) whose planar structure has been accounted for in terms of a hyperconjugative interaction involving the orbitals of the C—Si bond.1618... 

These alkoxo complexes are also capable of cleavage of the C—Si bond of TMSCF3. The gold(III) fluoroalkoxides m-[AuMe2(OR)(PPh3)] (R = CH2CF3, CF1(CF3)2) can act as catalysts for the Knoevenagel condensation reaction.1775... 

In the case of a C=C bond containing organosilicon compounds, the presence of a Si atom does not exert any appreciable influence on addition in an apolar solvent. In a polar solvent, however, the rupture of the C—Si bond also occurs... 

Thermolysis of 12 with frans-cinnamaldehyde afforded the insertion compound 19, formed through the di-insertion of two carbonyl ligands into the C—Si bond of 12. The reaction of 12 with fumaronitrile yielded the cyclization product 20. X-ray study revealed 20 to be a cyclization product which contains two types of disilyl moieties, imino and N,N-bis(silyl)amino, which are connected by a five-membered ring. 

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