Synthesis and Intermediates in the Formation of a Terphenyl-Substituted Silanetriol: Activation through Hypervalency

According to previous work, 2,6-dimesitylphenyl trifluorosilane does not hydrolyze to the
corresponding silanetriol. However, the formation of this product can be achieved by first
converting the trifluorosilane into the corresponding hypervalent fluorosilicate. Conversion
into the corresponding lithium and rubidium terphenyl tetrafluorosilicates prior to hydrolysis
leads to an increased reactivity of the Si−F bonds compared to 2,6-dimesitylphenyl
trifluorosilane, which allows controlled stepwise fluorine displacement depending on the
nature of the countercation and eventual formation of the silanetriol. The intermediates in
this process, i.e., the corresponding difluorosilanol and fluorosilanediol, can be identified
and isolated depending on the reaction conditions. For the terphenylfluorosilicates the
observed reactivity is more closely related to the corresponding trichlorosilane than to the
trifluorosilane. As its crystal structure shows, 2,6-Mes2C6H3Si(OH)3 forms unique hydrogen-bridged dimers in the solid state that also persist in solution.