Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents

0582402 - ÚOCHB 2025 RIV GB eng J - Journal Article
Trojan, M. - Kučnirová, K. - Bouzková, Š. - Cvačka, Josef - Čejka, J. - Tavčar, G. - Rybáčková, M. - Kvíčala, J.
Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents.
Organic & Biomolecular Chemistry. Roč. 22, č. 5 (2024), s. 1047-1056. ISSN 1477-0520. E-ISSN 1477-0539
Institutional support: RVO:61388963
Keywords : basis-sets * efficient * design
Impact factor: 3.2, year: 2022
Method of publishing: Open access
https://doi.org/10.1039/D3OB01875J

TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions. To eliminate the possibility of hydrogen fluoride elimination in the above reagents, we prepared four quaternary ammonium fluorides lacking beta-elimination possibility in the hydrocarbon chain, transformed them to the corresponding difluorotriphenylsilicates, and compared their reactivity with that of the commercial reagents. Furthermore, attempts to isolate analogous tetrabutylammonium difluoromethyldiphenylsilicate or difluorodimethylphenylsilicate failed, as was confirmed by comparison of the published experimental data with computed 19F NMR spectra. Finally, we studied the transition states of decomposition of various tetramethylammonium methylphenyldifluorosilicates by DFT methods and found that their relative energies increase with an increasing number of phenyl groups. The formation of difluorosilicates is a nearly barrierless process.
Permanent Link: https://hdl.handle.net/11104/0350784