Chiral molecular fluoridosilicates and their twin polymerization for the preparation of fluorine-doped mesoporous silica and microporous carbon

The syntheses of chiral pentacoordinated fluoridosilicates and their conversion into fluorine-doped silica and mesoporous carbon are reported. Starting from 4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxasiline] (1) and 8,8′-di-tert-butyl-4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxasiline] (2), the corresponding fluorido complexes 3 and 4 were obtained by the addition of potassium fluoride to the spirocyclic silicon salicylic alcoholates 1 and 2 in the presence of 18-crown-6. The pentacoordinated geometry around the silicon atom of the SiO4F type in 3 and 4 was proved using single-crystal X-ray diffraction analysis. DSC measurements were used to study the thermal behavior of the compounds with regard to their usability in the twin polymerization process. Hence, polymerization of 3 and 4 and the simultaneous twin polymerization of the fluoridosilicate 3 with spirocyclic 1 gave fluorine-doped phenolic resin/silica composites as confirmed by solid state NMR spectroscopic studies (1H, 13C{1H}, 19F, and 29Si{1H}). Carbonization of the as-obtained hybrid materials and subsequent treatment with hydrofluoric acid resulted in microporous carbon with surface areas up to 1060 m2 g−1. Calcination of the hybrid materials produced fluorine-doped silica with BET surface areas up to 239 m2 g−1. Additionally, the synthesis of hybrid materials using the additive assisted twin polymerization of 1 with either tetra-n-butylammonium fluoride or KF gave either microporous carbon (1219 m2 g−1) or mesoporous silica (687 m2 g−1).