Silicon hydrotrioxide

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. 

If the reaction is five-centered (6 - 8), a silicon hydrotrioxide may be formed. Since there has been no previous report of a silicon hydro-trioxide, the stability of a species such as 8 under these conditions can only be estimated. Among carbon analogs, the reported dialkyltrioxides have only marginal stability at low temperatures (36, 37), and alkyl hydrotrioxides, proposed as intermediates in the ozonation of alcohols and ethers (38), decompose at ca. —10 °C. Admittedly, speculative extrapolation based on the comparative stabilities of other types of silicon and carbon analogs suggests that a silicon hydrotrioxide 8, should have been observable if it had been present, but this requirement is debatable. 

Although reports of mechanistic studies are scarce for these reactions, Ouellette and Marks did propose a 1,3-dipolar attack by ozone (10). The corresponding intermediate was predicted to be a hydrotrioxide of silicon. 

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