Photoredox catalysis has been a flourishing field in synthetic organic chemistry. Organic chemists have been inspired by Nature and the conversion of photons into potential energy by light-harvesting biomolecules. Recent developments in photoredox catalysis have led to a rapid increase in development of new methodologies in synthetic organic chemistry. The use of transition metal photocatalysts and organic dyes in photo-mediated processes has been proven to be an effective alternative to the harsh and toxic reaction conditions that area needed in classical radical formation. Photoredox catalysis eliminates the need of initiators, stoichiometric additives, and strong oxidants, and allows for the highly efficient formation of new C-C bonds under mild conditions. Photochemistry and radical chemistry work in unison in their ability to undergo photoinduced single electron transfers (SET) or photoinduced electron transfers (PET) and enable one electron reaction pathways.
A plethora of photocatalysts have been developed, mainly using Ir- and Ru-based polypyridyl complexes. Polynuclear gold complexes have come to light in the last decade as another class of photocatalysts. This bench stable complex is marked by its unique photophysical and electrochemical properties, most notable the relatively long-lived excited state. This triplet excited state can be used as a powerful reductant or oxidant when irradiated with UVA light. A class of organic substrates that can be used when working with this gold photocatalyst, is nonactivated bromoalkanes, which could not be used if working with other photocatalysts.
First, the alkylative semi-pinacol using gold photoredox chemistry and nonactivated bromoalkanes was described. A new mode of reactivity of the gold binuclear photocatalyst was found where it was shown to work as a photocatalyst and a Lewis acid. Next, a follow-up to that report was the halogen atom transfer radical addition (ATRA) using gold photoredox catalysis. A mild ATRA reaction was presented where the dual reactivity of the gold photocatalyst was exploited. Mild bromine and iodine transfer reactions, without the use of strong oxidants or toxic additives, are largely unknown, and a metal-based mechanistic pathway was proposed to explain this transformation.
Minisci-type alkylation is of high-interest in the field of medicinal chemistry and drug discovery. With this is mind, a photoredox catalysed Minisci reaction was presented, where the alkylation of an activated heteroarenes was achieved by HAT via chlorine atom generation. Knowing this, the alkylation using primary alcohols was presented, were a the 𝛼-alkoxy radical is formed after a HAT by chlorine atom. When secondary alcohols were used, a reduction of the heteroarene occurred and was described.
Finally, a photo-mediated [3 + 2] cycloaddition using N-aryl cyclopropylamines and α, β- unsaturated carbonyl systems was described. This simple method that was presented does not require the use of photocatalysts or added additives, as it is self-catalyzed. The reaction is proceeding through a single electron transfer (SET) and offers a wide scope for the synthesis of N-arylaminocycloalkyl compounds.
Overall, the collection of work described in this thesis represents the growth of photoredox catalysis in organic synthetic chemistry and the ability to form highly reactive radical without the need of harsh conditions, toxic reagents, or strong oxidants. The use of binuclear gold(I) complexes as a photocatalyst with unique photophysical and electrochemical properties was shown. Compared to Ir- and Ru-based polypyridyl complexes, which cannot react with nonactivated bromoalkanes, the binuclear gold(I) complexes offer broader redox potentials and a newfound dual mode of reactivity. Furthermore, photo-mediated synthetical useful reactions were shown. The application of photoredox catalysis in synthetic chemistry will continue to flourish, and this work is sample of all the possibilities that a simple photon can bring.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/44145 |
| Date | 11 October 2022 |
| Creators | Zidan, Montserrat |
| Contributors | Barriault, Louis |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | CC0 1.0 Universal, http://creativecommons.org/publicdomain/zero/1.0/ |
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