Morgan, Patrick
(2022)
Exploring sustainability in fluorine methodologies.
PhD thesis, University of Nottingham.
Abstract
The fluorination of organic compounds is extremely important to the modern world, especially within the chemical sciences, however as we transition to a more sustainable future, current industrial fluorination methodologies grow increasingly unsuitable towards the preparation of these fluorinated molecules, especially from an energy and materials perspective. To address this new fluorination, defluorination and fluorine transfer methodologies have been developed with a focus on improved sustainability over traditional fluorination techniques.
This thesis explores new methodologies to control the reactivity of fluorine: from the enhancement of reactivity of metal fluoride salts, one of the more sustainable sources of fluorine available, through the treatment with organometallic complexes; to the activation of fluorine within perfluorinated organic moieties, enabling the selective transfer of fluorine between two organic substrates, providing the potential of utilising waste sources of fluorine as feedstocks in the future.
A series of group 9 organometallic complexes were targeted and synthesised, to investigate their catalytic fluorination potential upon treatment with metal fluoride salts. Treatment of these complexes bearing fluorinated ligands with silver oxide resulted in the formation of a new class of cyclometallated and orthometallated rhodium and iridium complexes, providing new catalytic targets for the fluorination of organic electrophiles.
The fluorination potential of transition metal fluoride complexes upon treatment with acyl chlorides was examined, providing first evidence of nucleophilic fluorination from [RhF(CO)(PPh3)2]. The catalytic fluorination of acyl chlorides with [(η5,κ2C-C5Me4CH2C6F5CH2NC3H2NMe)- RhCl] was investigated, utilising metal fluoride salts as the fluorine source, affording the quantitative fluorination of a range of electron deficient and electron rich acyl chlorides under mild conditions. A procedure for catalyst recovery, regeneration and reuse was established. In-situ FTIR analysis and variable time normalised analysis of this catalytic fluorination procedure gave further insights into this catalytic reaction enabling a plausible mechanism to be proposed.
A transfer fluorination reaction was developed through the treatment of [(η5,κ2C-C5Me4CH2C6F5CH2NC3H2NMe)-RhCl] 22, and organic electrophiles in the absence of an external fluorine source, resulting in the formation of a bimetallic rhodacycle and a new fluorinated product. Multi-spectral analysis provided an understanding of the environment required to generate nucleophilic fluorine within the perfluorinated ligand, enabling the transfer of fluorine to occur between the perfluorinated group and an organic electrophile via C−F bond activation. The transfer of fluorine was tracked in real time using in-situ IR analysis
The synthesis of functionalised partially fluorinated heteroarenes was investigated through the defluorination of pentafluoropyridine. A catalytic transfer fluorination protocol was adapted enabling fluorine transfer from pentafluoropyridine to benzoic anhydride. Additionally, the catalytic selective mono-defluorination and hydrodefluorination of pentafluoro-pyridine was achieved using commercially available group 8 and 9 catalysts.
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