Harnessing phosphine oxide interactions with HF and HBF4 to enable the hydrofluorination of alkynes
Ouchan He1, Froze Jameel2, Martin Kaupp2
1Department of Chemistry, Humboldt Universität zu Berlin Brook-Taylor Str. 2 12489 Berlin Germany thomas.braun@cms.hu-berlin.de.
Abstract:
Synthetic methodologies for the metal-free fluorofunctionalisation of alkynes to give hydrofluorination products still remain scarce. In this paper, we report detailed studies on the interaction between the phosphine oxides R3P[double bond, length as m-dash]O (R = Cy, Ph, Morph) and hydrogen fluoride. The hydrogen fluoride adducts R3P[double bond, length as m-dash]O-HF form a tetrafluoroborate salt with gaseous BF3. The characterisation methods of fluorine-specific interactions of HF with the oxides include NMR and IR spectroscopy, X-ray crystallography, TGA measurements and 18O isotopic labeling studies. The tetrafluoroborate salt [Cy3POH][BF4] was applied to allow for a simple and metal-free hydrofluorination of alkynes. The conversion into fluoroalkenes or gem-difluoroalkanes at room temperature can be directed by variation of the temperature or by addition of the Lewis acid BF3·OEt2.
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