Silicon ozone complex

A second possibility is that the ozone forms some kind of complex with the silane before attack on the hydrogen. From this complex, all hydrogens are equally accessible, and the decomposition is first order in complex. In the hope of observing such a complexation, the ultraviolet spectra of ozone/silane mixtures in carbon tetrachloride were examined (33). Although no spectral bands attributable to a silicon-ozone complex were found, it was observed that any silicon-containing species catalyzed the decomposition of ozone. That is, not only triethylsilane, but tri-ethylsilanol and tetramethylsilane as well, destroy ozone in carbon tetrachloride. This result indicates an association of the ozone with the silicon atom, regardless of the functionality of the silicon species (within the types examined) and completely independent of the silicon substrate s... 

These data suggest that the initial step in the reaction of ozone with the Si-H bond is the reversible formation of a silicon-ozone complex. This cannot be the rate step since p would have to be positive (nucleophilic attack) and no primary isotope effect would be predicted. To eliminate the statistical factor for the di- and trihydrosilanes, attack by ozone on the hydridic proton from within the complex must be much more favorable than direct encounter and reaction with uncomplexed ozone and Si-H. 

The reaction of a hydrosilane with ozone results in the rapid, quantitative conversion of the Si-H bond to the Si-OH moiety. The mechanism of this conversion has now been elucidated. It involves a fast, reversible complexation of ozone (acting as a nucleophile) with the silicon atom, followed by rate-determining electrophilic attack by the bound ozone upon the hydridic hydrogen, and decomposition into a RsSi OH radical pair which recombine to produce the silanol. Extensive data concerning the relative rates and other structure-dependent properties in the ozonation of a number of mono-, di-, and trihydrosilanes are presented. 

Step(s) Bi and B2—Hydrogen Abstraction. How the ozonation proceeds from the complex is now considered. If direct o-bond insertion (1) is eliminated on the basis of isotope effects as discussed above, then 5 and 6 are the viable alternatives. The transition state 5 could collapse to form the silicon hydroperoxide 7, while transition state 6 could collapse to form the silicon hydrotrioxide 8 (path Bi) alternatively, 6 could collapse directly to ion or radical pairs (path B2). The transformation 5 -> 7 is not meant to suggest that atomic oxygen is the other product. Since the reaction order in ozone has not been determined, the fate of the other oxygen atom(s) is moot. 

---