Diarylamines (Ar2NH) and phenols (ArOH) comprise the bulk of radical-trapping antioxidant (RTA) additives to petroleum-derived products, owing to their ability to slow hydrocarbon autoxidation through rate-controlling inhibition reactions. While much work has been done to optimize and understand structure-activity relationships of phenolic antioxidants, optimization of highly-reactive diarylamine antioxidants has been comparatively difficult due to their propensity to undergo one-electron oxidation with molecular oxygen. Recently, it was demonstrated that incorporation of nitrogen atoms into the aromatic ring of phenolic antioxidants greatly improves their stability to one-electron oxidation without compromising their antioxidant efficacy. Given these results, it was our supposition that this approach could be extended to the development of highly reactive diarylamine RTAs. Herein we describe the synthesis of a small library of pyridine- and pyrimidine-containing diarylamines and characterize their thermodynamic properties (standard potentials (E°) and N-H bond dissociation enthalpies) as well as their kinetic properties (rate constants for reactions with peroxyl and alkyl radicals) – demonstrating that the approach of N-atom incorporation is also very effective at increasing diarylamines’ stability to one-electron oxidation without compromising their antioxidant efficacy. In fact, the diarylamines described herein are among the best peroxyl-radical trapping antioxidants known, having inhibition rate constants ca. 200-fold greater than the current industry standard. Through a series of mechanistic studies (measuring Arrhenius parameters, kinetic solvent effects, deuterium kinetic isotope effects and transition state calculations) we have provided strong evidence that reactions between electron-rich diarylamines and peroxyl radicals occur by a proton-coupled electron transfer (PCET) mechanism. The reaction of diarylamines with peroxyl radicals at elevated temperatures (>160 °C) is highly relevant industrially, as this reflects the operating environment of lubricants in engine applications. At these temperatures, diarylamines are known to react catalytically as peroxyl trapping RTAs, although the mechanism has yet to be fully elucidated for this important chemistry. Current methods of studying high temperature oxidations suffer from time-consuming and/or air-sensitive analytical methods (e.g. iodometry, GC analysis). To enable rapid, accurate mechanistic studies at high temperature, we have improved the analytical component by developing a fluorescent dye that can be applied in an assay to determine hydroperoxide concentrations in solution in real-time. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-05-22 18:30:09.601

La N-arylation d'amines primaires et secondaires par couplages C-N palladocatalysés de Buchwald- Hartwig est une méthode efficace de synthèse d'arylamines. Jusqu'à présent, la synthèse d'arylamines en série thiophénique n'avait été que peu décrite. Nous nous sommes ainsi intéressés à la réactivité de dérivés substitués des 2- et 3-bromothiophènes dans les couplages C-N palladocatalysés. Par la suite, nous avons également étudié la réactivité d'aminothiophènes dans ces mêmes réactions de couplage. Un grand nombre d'arylamines a ainsi pu être synthétisé. La synthèse de thiénopyrimidinones a aussi été effectuée via la réalisation en "one-pot" d'une réaction de couplage C-N suivie d'une cyclisation intramoléculaire / N-Arylation of primary and secondary amines by Buchwald-Hartwig C-N cross-coupling reactions is a very convenient pathway for the synthesis of arylamines. Up to now, only few examples of arylamines synthesis were described in the thiophene series, although arylaminothiophenes generally show very interesting biological and electronic properties. Thus, we investigated the reactivity of 2- and 3- bromothiophene derivatives in palladium-catalyzed cross-coupling. Then we also studied the reactivity of aminothiophenes in those same cross-coupling reactions. Using this way, the expected diarylamines were successfully synthesized. An easy access to thienopyrimidinone derivatives was also described via a one-pot C-N coupling and intramolecular cyclization

Autoxidation, a radical chain reaction, is largely responsible for the degradation of most man-made and biological materials. These include chemical products such as lubricants, plastics and rubber; as well as biological molecules and membranes within our bodies. The development of means to hinder this process has been a major focus of the petroleum, chemical, pharmaceutical and biotechnology industry over the past century. The two most common strategies to emerge from these efforts have been the use of compounds that either prevent the initiation of autoxidation or trap the propagating radicals, so-called radical-trapping antioxidants (RTAs). Herein, we describe our efforts towards the design and development of extremely potent heterocyclic diarylamine RTAs, and their activity in a variety of applications ranging from isotropic organic solution to mammalian cells. We have elucidated the important structural motifs and mechanistic considerations necessary for the development of next-generation arylamine RTAs. Some of the substituted heterocyclic diarylamines analogs we disclose are among the best inhibitors of high temperature autoxidations described to date. Alongside, we developed novel analytical tools to facilitate the studies and acquisition of results for characterizing RTA activity in organic solutions and lipid bilayers. These fluorescent probes are highly relevant and allow for the determination of hydroperoxide and acid concentrations rapidly, as well as screen (or counter-screen) RTAs in liposomal membranes. Our methodologies address numerous drawbacks from frequently used ‘plug-and-play’ assays and we anticipate they will fill a current unmet need in both industrial and academic laboratories worldwide. Moreover, the recent characterization of ferroptosis – a novel regulated necrotic-like cell-death pathway associated with the accumulation of lipid hydroperoxides – has paved a way forward for studying oxidation induced damage in a biological context. Utilizing our expertise in lipid peroxidation and inhibition, we elucidated the prominent role of autoxidation in the execution of ferroptotic cell death. Alongside, our analytical tools and RTAs have also enabled the identification and characterization of novel ferroptosis inhibitors. Furthermore, this has prompted the development of a correlation to predict anti-ferroptosis activity of small-molecules using simple spectrophotometric assays.

Les ligands multidentes montrent généralement de très bonnes activités dans la catalyse organométallique au palladium à faibles charges. Parmi ces ligands, l'utilisation des ligands polyphosphines ferrocéniques mènent à des résultats intéressants. Des systèmes catalytiques palladium/triphosphine ferrocénique robustes ont permis d'obtenir d'une part des diarylamines et d'autre part des éthers d'aryle et d'hétéroaryle avec de faibles charges catalytiques. Des calculs théoriques de DFT sur le cycle catalytique lors de la formation d'éthers d'aryle et d'hétéroaryle ont été réalisés. La présence d'un troisième groupement phosphino permettrait de stabiliser les états de transition et accélèrerait l'élimination réductrice. Les triarylamines ont pu être obtenues à l'aide d'une diphosphine ferrocénique avec une charge de 2 mol% de palladium. Des résultats modérés à excellents ont été obtenus. Enfin, les thioéthers d'aryle et d'hétéroaryle ont été obtenus avec d'excellents résultats à l'aide d'une tétraphosphine ferrocénique en présence de 0,2 mol% de palladium

Les ligands multidentes montrent généralement de très bonnes activités dans la catalyse organométallique au palladium à faibles charges. Parmi ces ligands, l'utilisation des ligands polyphosphines ferrocéniques mènent à des résultats intéressants. Des systèmes catalytiques palladium/triphosphine ferrocénique robustes ont permis d'obtenir d'une part des diarylamines et d'autre part des éthers d'aryle et d'hétéroaryle avec de faibles charges catalytiques. Des calculs théoriques de DFT sur le cycle catalytique lors de la formation d'éthers d'aryle et d'hétéroaryle ont été réalisés. La présence d’un troisième groupement phosphino permettrait de stabiliser les états de transition et accélèrerait l’élimination réductrice. Les triarylamines ont pu être obtenues à l'aide d'une diphosphine ferrocénique avec une charge de 2 mol% de palladium. Des résultats modérés à excellents ont été obtenus. Enfin, les thioéthers d'aryle et d'hétéroaryle ont été obtenus avec d'excellents résultats à l'aide d'une tétraphosphine ferrocénique en présence de 0,2 mol% de palladium / Multidentate ligands usually show great activities in low loading organometallic catalysis in palladium. Among these ligands, the use of ferrocenyl polyphosphane ligands give interesting results. Robust palladium-ferrocenyl triphosphane catalytic systems have permitted to obtain biarylamines and aryl-heteroaryl ethers in the presence of low catalytic loadings. DFT studies on catalytic cycle during formation of aryl-heteroaryl ethers were carried out. The presence of third phosphino group stabilizes a transition state which enhances the rate of the reductive elimination. Triarylamines were obtained with ferrocenyl diphosphane in the presence of 2 mol% of palladium loading. Moderate to excellent results were obtained. Finally, aryl-heteroaryl sulfides were obtained with excellent results with ferrocenyl tetraphosphane ligand in the presence of 0.2 mol% of palladium.