Silicon carbon halides

Another application of [Bu4N][Ph3SiF2] 826 involves the silicon-carbon bond cleavage of allyl-, benzyl-, and alkynylsilane derivatives 827-829.826 Subsequent reactions of the generated carbanions with electrophiles (Scheme 112) and alkyl halides (Scheme 113) provide high yields of carbon-carbon coupled products. 

In contrast to the inertness of carbon halides, the halides of silicon and phosphorus are extremely reactive with water, to the extent that they must be protected from atmospheric moisture. A clue to the reactivity of these halides is provided hy the somewhat Similar reactivity of acid halides which readily react with water... 

Carbon halides resist hydrolysis because only s and p orbitals are available for bond formation. This ensures a maximum covalency of four and precludes the donation of electrons by the oxygen atom in a water molecule to a carbon atom. But silicon compounds do hydrolyse, since the unoccupied silicon 3d orbitals lie not far above the 3s and 3p. 

Anderson and Webster (10) showed the pyridyl-silicon bond of 2-(trimethylsilyl)pyridine to be susceptible to cleavage by alcohol and water to form unsubstituted pyridine. Thames and coworkers (11) showed that neutral reagents, including aldehydes, acid halides, chloroformates, and anhydrides, have the ability to cleave several silicon-carbon bonds on select heterocycles (Schemes VI-VIII). However, the silicon-carbon bond of nonheterocycles is not susceptible to neutral reagent cleavage, and too, the full extent of heterocyclic cleavage reactions is not known. 

---