The present thesis constitutes an investigation of the synthesis of novel long wavelength ultra-violet, and visible light absorbing diaryliodonium salts and an exploration of their visible light-initiated reactivity. Firstly, a library of novel and known diaryliodonium salts was prepared so that the influence of the location and type of substituent upon the absorption properties of the substituted diaryliodonium salt could be assessed. The target diaryliodonium salts were synthesised using iodoarenes and arenes by one of three approaches: TfOH mediated one-pot synthesis, the use of milder TsOH.H2O and Koser’s reagent, or the application of BF3.OEt2 and arylboronic acids for regiospecific synthesis. Iodonium salts possessing Polycyclic arenes were found to have the most appreciable bathochromic shift of absorption maxima when compared to simple diaryliodonium salts. The absorption spectra of several cyclic vinyl(aryl)iodonium triflates and cyclic diaryliodonium triflates were also recorded to enable further comparison of the absorption maxima of a wider range of hypervalent iodine(III) species. Pyrene and perylene were selected as potential aryl moieties due to their relatively long wavelength absorption maxima, though transformation into iodonium salts could not be accomplished by all routes attempted. Additionally, attempts to transform a short series of established photosensitisers into iodonium salts were also unsuccessful due to their structural complexity. Anthraquinone and fluorenone were successfully converted into hypervalent iodine species, wherein it was found that (9-oxo-9H-fluoren-2-yl)(phenyl)iodonium triflate had good absorption in the visible region. Several substituted fluorenone based diaryliodonium triflates were then synthesised using substituted iodoarenes, and their absorption properties assessed. The photochemical reactivity of the prepared (9H-fluoren-2-yl)(aryl) iodonium salts was then assessed. When irradiated with 430 nm light using a bespoke, self-built, photochemical reactor, photolysis of the C-I bond occurred which in turn could be used to initiate novel C-C cross-coupling reactions without requiring prefunctionalisation of the substrates or addition of transition metal catalysts. The selectivity of the coupling was substrate controlled, with either the phenyl (aryl) or fluorenone moiety of the diaryliodonium salt transferred. EPR studies confirmed that radical species are generated upon photolysis of the diaryliodonium salts, which in turn initiate what is likely to be a radical C-C coupling pathway.
| Date of Award | 6 Jun 2025 |
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| Original language | English |
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| Sponsors | Engineering and Physical Sciences Research Council |
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| Supervisor | Mark Heron (Main Supervisor), Karl Hemming (Co-Supervisor) & Craig Rice (Co-Supervisor) |
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