Other Functionalized Organosilanes

Nucleophilic substitution of a,/3-epoxysilanes followed by the Peterson elimination is valuable for the stereoselective synthesis of alkenes.3 The reactions with lithium phenylsulfide and diphenylphosphide form alkenyl sulfides and alkenylphosphines, respectively, in a stereospecific manner. 7-Metallo-a,/ -epoxysilanes are isomerized to a-siloxyallylmetals by anionic ring opening and subsequent Brook rearrangement (Equation 

---

The selective organosilane reduction of ketone functions can be effected in the presence of a number of other functional groups including epoxides,320,366 ketals,86,367 thioketals,368 other ketones,369,370 /1-lactams,371 alkynes,372 esters,79,80,83,84,87,320,373,374 a-bromides,76,80,83 amides80,83,84,86,276,320,375... 

A common method to prepare bonded-phase materials is to use silica gel as the solid support and to react functionalized organosilanes onto the surface hydroxyl groups of the silica gel. Of course, other solid support materials can be used provided that they present surface functional groups (e.g., OH, COOH, and NH2) that can participate in modification reactions. The flexibility offered by this approach leads to stationary phase materials with myriad functionalities. Fig. 3 illustrates commonly used organosilane reactants and two example reaction paths that lead to bonded-phase silica. For more discussion on bonded-phase materials, see Ref.. ... 

The reactions are radical chain processes (Scheme 3) and, therefore, the initial silyl radicals are generated by some initiation. The most popular thermal initiator is azobisisobutyronitrile (AIBN), with a half-life of 1 h at 81 °C. Other azocompounds are used from time to time depending on the reaction conditions. EtsB in the presence of very small amounts of oxygen is an excellent initiator for lower temperature reactions (down to —78°C). The procedures and examples for reductive removal of functional groups by (TMSlsSiH are numerous and have recently been summarized in the book Organosilanes in Radical Chemistry. ... 

It is possible to use mixtures of organosilanes carrying different head-groups for tailoring of surface properties. By doing so, issues like nonspecific adsorption or crowding of the active surface functionalities can be addressed. In order to find the best surface composition for the immobilization of the ONDs it is necessary to perform systematic studies varying the silane concentrations and other reaction parameters. Examples of this kind of study with mixtures of epoxy- and amine-silanes has been reported recently [33,34]. 

Various other surface chemistries have been used to attach chemical species to electrode surfaces. For example, Watkins et al. activated the carboxylic acid functionalities on carbon electrodes with thionyl chloride and then reacted this surface with amines [17]. Sagiv and his coworkers have recently invented a clever approach for monolayer-by-monolayer deposition of multilayer films based on organosilane chemistry [18]. Finally, Mallouk et al. have also developed a monolayer-by-monolayer approach for synthesizing well-ordered multilayer films [19]. Because of these interesting new synthetic strategies, covalent attachment of functional groups remains an attractive approach for modifying electrode surfaces. 

In this part, we wish to focus on the study of two types of silanes. Aminoorganosilanes are special members of the alkoxysilanes group. They carry the catalyzing amine function, required for chemical bonding with the silica surface, inside the molecule. This makes them more reactive than other organosilanes and reduces the complexity of the liquid phase reaction system to be studied. Only three components, silica, silane and solvent, are present. Furthermore there is a large interest in the reaction mechanism of silica gel with APTS, since this aminosilane is the most widely used compound of the organosilane family. 

On the other hand, the functionalization of various silicas with covalently bonded organosilanes by different procedures has been studied in the past for various applications.1162"1651 The synthesis of organically modified mesoporous... 

---