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Abstract

Fluorine, though abundant on Earth, is not readily available in a form suitable for organic synthesis. While fluoride salts like fluorite exist, they have limited reactivity due to solubility properties. Converting fluorite to hydrofluoric acid (HF) or fluorine gas (F2) increases reactivity but introduces significant safety concerns due to the corrosive and toxic natures of their products.
A more practical approach to fluorination is to use pre-fluorinated starting materials. However, these are often limited in availability and scale. Late-stage fluorination methods offer an alternative but can suffer from low atom economy and functional group compatibility issues. Therefore, developing new, efficient, and selective fluorination methods remains a crucial goal in organic synthesis.
This dissertation aims to expand the knowledge of nucleophilic fluorination reagents, especially those based on masked fluoride compounds such as organofluorosilicates and organofluorogermanates. While organofluorosilicates have been extensively studied, organofluorogermanates are still relatively unexplored as only a few structurally characterised compounds are known. In addition, most known organofluorogermanates contain strongly electron-withdrawing groups, which limits their potential as fluorinating agents. This research aims to fill this gap by synthesising new organofluorosilicate and organofluorogermanate species with different structural features.
In the first part of this study, we prepared new discrete organofluorosilicate and organofluorogermanate species with an imidazolium countercation. The target compounds were synthesised from commercially available organochlorosilanes and organochlorogermanes with a focus on compounds containing more electron-donating substituent groups to increase fluoride-donating potential. Using alkali metals and imidazolium fluoride reagents, five new organofluorosilicates and two new organofluorogermanate salts were successfully synthesised and structurally characterised.
In the study of imidazolium-based organofluorosilicates and organofluorogermanates, we observed unexpectedly low yields in reactions of organochlorosilanes and organochlorogermanes with alkali metal fluorides. Further investigations, including NMR spectroscopy and single-crystal X-ray diffraction, revealed the formation of polymeric alkali metal-based organofluorosilicates and organofluorogermanates as by-products.
The second part of this study focussed on the investigation of the conditions for this reaction and the synthesis of new such species, which had previously been reported only once for an organofluorosilicate compound. Detailed NMR studies showed that alkali metal fluorides are differently reactive, with heavier metal fluorides generally exhibiting higher reactivity. In addition, we have successfully isolated new polymeric organofluorosilicate and organofluorogermanate compounds and structurally characterised them using X-ray diffraction.