Some Recent Studies of the Cleavage of Carbon-silicon and Related Bonds

This brief review will be concerned with heterolytic cleavages of carbon— silicon and related bonds, and will concentrate on some more recent investigations by the author and his co-workers. The C—Si bond is fairly stable towards homolytic fission, and under free radical conditions the C—H bonds of organosilicon compounds are usually more readily attacked than the C—Si bonds1. The C—Si bond is moderately polar, however, (Pauling electronegativities indicate that there is 12% ionic character in the direction CSi+), and is relatively easily attacked by ionic reagents. Since C—H bonds break heterolytically in the same direction, C-Hf, a good indication of the behaviour of an R—Si bond can be obtained by considering the reactions of the corresponding R—H bond2. For example, just as the C—H bond of chloroform, HCC13, is readily broken by attack of hydroxide ion on the hydrogen atom, so the Si—C bond of the compound Me3SiCC13 is broken, even more readily, in alkali, by nucleophilic attack at silicon. Again, just as aryl—H bonds are broken readily by electrophilic reagents such as bromine or sulphur trioxide, so aryl—SiMe3 bonds are also broken readily by these reagents. It is usually but not always true that an R—SiMe3 bond is more reactive than the corresponding R—H bond towards ionic reagents.