Hydrogen atom with silicon hydride

The use of free-radical reactions in organic synthesis started with the reduction of functional groups. The purpose of this chapter is to give an overview of the relevance of silanes as efficient and effective sources for facile hydrogen atom transfer by radical chain processes. A number of reviews [1-7] have described some specific areas in detail. Reaction (4.1) represents the reduction of a functional group by silicon hydride which, in order to be a radical chain process, has to be associated with initiation, propagation and termination steps of the radical species. Scheme 4.1 illustrates the insertion of Reaction (4.1) in a radical chain process. 

Hydride surface termination has the capability for ideal surface passivation, with each hydrogen atom bonding to a single surface-dangling bond. On silicon, hydride termination has been well researched and shown to provide many advantages, including aqueous stability and limited air stability [13]. The hydride-terminated surface is also of interest as it can be used as a precursor for wet chemical reactions. 

Polymethylphenylsiloxanes with active hydrogen atoms and vinyl groups at the silicon atom are industrially manufactured without solvents and are of great practical interest, since they do not release volatile substances when processed into goods. The process occurs in the presence of a catalyst (H2PtCl6 or dimethylformamide) according to the mechanism of hydride attachment. 

Step A—Association of Ozone with the Silicon Atoms. The linear Hammett-type relationship of Figure 1 and Equation 1 indicates a slope, /o, of —1.25. This negative value denotes electrophilic attack by the ozone and/or the development of a partial positive charge on silicon in the transition state. Since the silicon is relatively electropositive, an electrophilic attack by ozone on silicon seems unlikely. The hydrogen bound to silicon, however, is hydridic in character and is the likely site of attack... 

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