Selective Formation of Functionalized Disiloxanes from Terphenylfluorosilanes

The reactivity of the sterically hindered organofluorosilane 2,6-Mes2C6H3-SiF3 (1) (Mes =
2,4,6-trimethylphenyl) under hydrolytic conditions differs substantially from that of the
corresponding organo chlorosilane. During the hydrolysis of 1 the combination of thermodynamic (increased Si−F bond strengths compared to Si−Cl) and kinetic aspects (steric
hindrance) favors condensation of intermediately formed silanol over the hydrolysis to give
a silanetriol. In the course of the reaction no evidence for a silanetriol could be found, while
the corresponding difluorosilanol seems to be a key intermediate. The condensation of this
difluorosilanol leads to a tetrafluorodisiloxane, which can be isolated. Further displacement
of the remaining fluorine atoms in this siloxane is possible with organolithium reagents or
base. In the latter case the deprotonated disiloxanetetrol is formed, which due to its fourfold
silanol functionality is a suitable precursor for metallasiloxanes. The deprotonated disiloxanetetrol forms a dimeric structure in the solid state, which is stabilized by hydrogen bonding
and potassium aryl interactions

空间位阻型有机氟硅烷（sterically hindered organofluorosilane）2,6-Mes₂C₆H₃-SiF₃（1，其中Mes代表2,4,6-三甲基苯基（2,4,6-trimethylphenyl)）在水解条件下的反应活性，与对应有机氯硅烷（organochlorosilane）存在显著差异。在化合物1的水解过程中，热力学因素（相较于Si-Cl键，Si-F键键能更高）与动力学因素（空间位阻）的协同作用，使得中间体硅醇（silanol）的缩合反应路径，相较于直接水解生成硅三醇（silanetriol）的路径更具优势。整个反应过程中未检测到硅三醇的生成迹象，而对应的二氟硅醇（difluorosilanol）则是关键反应中间体。该二氟硅醇经缩合反应可生成四氟二硅氧烷（tetrafluorodisiloxane），且该产物可被分离提纯。后续可通过有机锂试剂（organolithium reagents）或碱性试剂，取代该二硅氧烷中剩余的氟原子；若采用碱性试剂路径，则会生成去质子化二硅氧烷四醇（deprotonated disiloxanetetrol），由于其带有四个硅醇官能团，该产物可作为制备金属硅氧烷（metallasiloxanes）的合适前驱体。去质子化二硅氧烷四醇在固态下会形成二聚体结构（dimeric structure），该结构可通过氢键（hydrogen bonding）与芳基钾相互作用（potassium aryl interactions）得以稳定。