University of Tasmania

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Expanding the scope of phenanthroline-based copper(I) complexes in photoredox catalysis

posted on 2023-05-28, 11:08 authored by Nicholls, TP
Recently, research concerning photoredox catalysis has enjoyed renewed interest. Photoredox catalysis provides a mode of small molecule activation that takes advantage of the ability of several transition metal complexes to absorb visible light which facilitates single electron transfer (SET) processes with organic substrates. This mild approach has broad applicability across a vast range of chemical transformations. While ruthenium- and iridium-based photoredox-catalysed transformations have received considerable attention, copper-based complexes remain underexplored in this area. This thesis reports on the development of new synthetic methodology with the broad objective of exploring the scope, limitations, and reactivity of copper-based complexes in photoredox catalysis. In particular, the preparation and study of a library of novel and previously reported copper complexes was conducted. This involved an investigation into the synthesis of homoleptic bis(phenanthroline)copper(I) complexes and heteroleptic phenanthroline-containing copper(I) complexes. Extensive characterisation of their structural, photophysical and electrochemical properties was conducted. Both direct and indirect methods were utilised to characterise the fundamental properties of these complexes including an examination of their reactivity in distinctive atom-transfer radical addition (ATRA) processes. The development of new synthetic methodology began with a proof of concept study in which the weak oxidising power of the prototypical copper-based photoredox catalyst, [Cu(dap)\\(_2\\)]Cl, was utilised to catalyse Povarov-type reactions of N,N dialkylanilines/ N-aryltetrahydroisoquinolines with electron deficient olefins to produce a range of annulated products. This transformation represents the first example of the weak oxidising power of a copper-based photoredox catalyst being exploited to facilitate the oxidation of amines that are ultimately incorporated into synthetic targets. Intriguingly, the presence of trifluoroacetic acid (TFA) in the reaction was found to be essential to facilitate an efficient reaction. An investigation into the role of TFA suggested that the aerobic quenching of putative photoexcited copper(I) species is mediated by TFA. A copper photoredox catalysed dual ˜í¬±-amino C‚Äö-H/ C‚Äö-F bond functionalisation reaction was subsequently developed to enable the synthesis of a library of perfluorinated aromatic compounds. During the development of this protocol it was found that a pulsed irradiation strategy provided enhanced yields and significant rate increases when compared to continuous irradiation. This methodology allows for the rapid synthesis of a broad range of fluorinated arenes under mild conditions. This is the first study identifying the potential of pulsed irradiation in photoredox-catalysis.


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