This thesis describes studies of a "kinetic template effect" which assists the formation of arylphosphonium salts from aryl halides and tertiary phosphines in the presence of a transition metal halide catalyst in refluxing ethanol. The "kinetic template effect" arises from the presence in the aryl halide of a limited range of orthosubstituents capable of intramolecular coordination with the metal at a critical stage of the reaction. In Chapter One, the "kinetic template effect" is compared with the better known "thermodynamic template effect". Earlier work on related "kinetic template effects" in the formation of aryl-phosphorus bonds is reviewed. The evidence for the possible involvement of aryl-metal intermediates in such reactions is also discussed. Chapter Two is concerned with the design and synthesis of potential template molecules. A model is proposed for the features necessary in the template substituent in terms of the nature and position of the donor atom or group essential for the replacement of the ortho-halogen under mild conditions. Chapter Three describes a kinetic study of the nickel (II) catalysed reactions of ortho-haloaryl Schiff's base and ortho-haloarylazo-dyestuff templates with tertiary phosphines. A rate law is deduced which indicates a first order dependence in each reactant, i.e. rate a [template] [phosphine] [catalyst], an overall third order expression. Rate studies also indicate that the nature of the orthohalogen is important, the order of replacement being I > Br > Cl. The effects of substituents remote from the ortho-haloaryl template are also considered. A mechanistic scheme consistent with the rate data is proposed. The X-ray crystal structures of two arylphosphonium salts derived from template aryl halides are discussed in Chapter Four, providing unequivocal proof that the position of replacement of halogen in substrates bearing more than one replaceable halogen, in different positions, is ortho with respect to the template donor group.

No description available.

Hybrid materials synthesized by grafting of organic molecules onto silica surface have found numerous applications in chemistry, biochemistry, and chemical engineering. In particular, the functionalization of silica gel can be accomplished by various surface reactions of immobilized boronic acids. Suzuki coupling has been chosen due to several advantages, such as mild reaction conditions, tolerance to the aqueous environment, and high yields of the products. The objective of this work was to determine the most effective reaction conditions for modifying porous hybrid materials with large specific surface areas and high density of surface organoboron reactive sites by various functional groups. Prior to modification by Suzuki coupling, the surface of silica gel was functionalized by phenylboronic acid. Two methods were tested for immobilization of phenylboronic acid: hydrosilylation and thiol-ene coupling. The later radical reaction between surface alkylthiol groups and 4-vinylphenylboronic acid was found more effective. Obtained boronated silica gel was used for further functionalization by various aryl halides. Surface Suzuki coupling reaction was catalyzed by palladium acetate in the presence of cesium carbonate as a base, while dimethylformamide was chosen as a solvent. The coupling reactions proceeded at mild heating under constant sonication. Such ultrasonic irradiation was reported earlier to have an activating effect on Suzuki coupling. The analysis of the obtained products indicated formation of surface biaryl compounds, the highest yields have been obtained in reactions with iodobenzene and bromobenzene. Thus, novel functionalized organic/inorganic hybrid materials were successfully synthesized by surface modification of mesoporous silica gel.

Mesoporous silica gel was functionalized by various organic functional groups using thiol-ene coupling of surface thiol groups with 4-vinylphenylboronic acid followed by Suzuki coupling with aromatic halides. For better performance, the synthesis was conducted under sonication. The presence of surface functional groups was confirmed by thermoanalysis, FT-IR spectroscopy and characteristic reactions of these groups. Solid-phase conditions of the synthesis eliminate the risk of side reactions of boronic acids.

Indiana University-Purdue University Indianapolis (IUPUI) / Aromatic rings are universal motifs in natural products, pharmaceuticals, agrochemicals, and wide variety of organic materials. Aromatic halides are widely used as synthetic precursors in all these applications. Therefore, tremendous effort has been devoted to activate aryl halides in the past decades. The common methods to activate aryl halides require the use of transition- metals either in the form of Grignard reagents or through the use of transition-metal catalysis. Over the past decade, photoredox catalysis has attracted significant attention as a cogent tool to develop greener synthetic processes and enable new molecular activation pathways under mild conditions. The most common of these approaches uses a photoredox/nickel dual catalytic cycle. While this technology has greatly expanded the toolbox of organic chemists, this method still requires expensive rare-metal-based catalyts. Herein, we present a series of visible light-induced methods that are transition-metal-free. These new base-promoted transformations and their mechanistic work will be discussed in the following order: We will first present our discovery that the dimsyl anion enables visible-light-promoted charge transfer in cross-coupling reactions of aryl halides. This work was applied to the synthesis of unsymmetrical diaryl chalcogenides. This method has a broad scope and functional group tolerance. An electron-donor-acceptor (EDA) complex between a dimsyl anion and the aryl halide is formed during the reaction and explains the observed aryl radical reactivity observed. Then, a visible-light-induced borylation and phosphorylation of aryl halides under mild conditions was developed. Inspired by the mechanistic breakthroughs observed in the previous work. The mechanism of this reaction also involves an aryl radical that is presumed to be formed also via an EDA complex. In other work, a photo-induced phosphonation of ArI using N,N- diisopropylethylamine (DIPEA) and trialkyl phosphites was developed. This method uses very mild conditions, which allowed the preparation a wide variety of functionalized aromatic phosphonates derivatives, including natural products and medicinal compounds. Finally, a photochemical amination of amides was developed via a C(sp 3 )–H bond functionalization process under visible light irradiation. This reaction showed good functional group compatibility without the use of external radical initiators, strong oxidants, or heat source. An EDA complex between N-bromophthalimide and LiOtBu is formed during the reaction.

Au cours de cette thèse, plusieurs nouvelles méthodes d'arylation de nucléophile (oxygéné, azoté et carboné) ont été mises au point ainsi qu'une étude mécanistique. Dans le cadre du projet ANR, nous avons réalisé des travaux dans ce domaine dans le laboratoire du Dr Anny Jutand à L'ENS Paris. D'un point de vue général, nous pouvons donc dire que nos méthodes se situent bien en phase avec les critères de la réglementation européenne visant à diminuer l'impact des produits chimiques sur l'environnement (REACH) par la recherche de nouvelles voies de synthèse moins toxiques et moins polluantes. Travaux en cours et perspectives : Par rapport aux réactions faisant intervenir des catalyseurs au palladium, celles impliquant le cuivre ont très peu été étudiées du point de vue de leur mécanisme. Les premiers travaux concernant le mécanisme de l'arylation de nucléophiles catalysé au cuivre ont débuté depuis seulement quelques années et ont conduit à environ une dizaine de publications. Malgré quelques avancées significatives, beaucoup reste à faire. / In this thesis, several new methods of nucleophilic arylation (oxygen, nitrogen and carbon) were developed and a mechanistic study. As part of the ANR project, we have carried out work in this field in the laboratory of Dr. Anny Jutand at ENS Paris. From a general point of view we can say that our methods are well in line with the requirements of European regulations to reduce the impact of environmental chemicals (REACH) by the search for new synthetic routes less toxic and less polluting. Work in Progress and prospects : Compared to reactions involving palladium catalysts, those involving copper have been studied very little in terms of their mechanism. Early work on the mechanism of arylation of nucleophiles catalyzed copper began last few years and led to about a dozen publications. Despite some significant advances, much remains to be done.

Aromatic rings are universal motifs in natural products, pharmaceuticals, agrochemicals, and wide variety of organic materials. Aromatic halides are widely used as synthetic precursors in all these applications. Therefore, tremendous effort has been devoted to activate aryl halides in the past decades. The common methods to activate aryl halides require the use of transition-metals either in the form of Grignard reagents or through the use of transition-metal catalysis. <br>Over the past decade, photoredox catalysis has attracted significant attention as a cogent tool to develop greener synthetic processes and enable new molecular activation pathways under mild conditions. The most common of these approaches uses a photoredox/nickel dual catalytic cycle.<br>While this technology has greatly expanded the toolbox of organic chemists, this method still requires expensive rare-metal-based catalyts. Herein, we present a series of visible light-induced methods that are transition-metal-free. These new base-promoted transformations and their mechanistic work will be discussed in the following order:<br>We will first present our discovery that the dimsyl anion enables visible-light-promoted charge transfer in cross-coupling reactions of aryl halides. This work was applied to the synthesis of unsymmetrical diaryl chalcogenides. This method has a broad scope and functional group tolerance. An electron-donor-acceptor (EDA) complex between a dimsyl anion and the aryl halide is formed during the reaction and explains the observed aryl radical reactivity observed.<br>Then, a visible-light-induced borylation and phosphorylation of aryl halides under mild conditions was developed. Inspired by the mechanistic breakthroughs observed in the previous work. The mechanism of this reaction also involves an aryl radical that is presumed to be formed also via an EDA complex. In other work, a photo-induced phosphonation of ArI using N,N-diisopropylethylamine (DIPEA) and trialkyl phosphites was developed. This method uses very mild conditions, which allowed the preparation a wide variety of functionalized aromatic phosphonates derivatives, including natural products and medicinal compounds. Finally, a photochemical amination of amides was developed via a C(sp 3 )–H bond functionalization<br>process under visible light irradiation. This reaction showed good functional group compatibility without the use of external radical initiators, strong oxidants, or heat source. An EDA complex between N-bromophthalimide and LiOtBu is formed during the reaction.

<p dir="ltr">Aromatic phosphonates and phosphine oxides are highly desirable synthetic targets used in pharmaceuticals, natural products, agrichemicals, catalysis, and materials science. While a variety of aromatic precursors have been used to access these motifs, aryl halides remain one of the most desirable coupling partners owing to their low cost, commercial availability, and regioselective reactivity. Traditional phosphonation often requires the use of harsh reductants in the presence of liquid ammonia, which are caustic and pose incredible environmental concerns. Milder, transition metal-catalyzed approaches have been developed, but can be limited by air sensitivity, cost, low reaction selectivity, and low functional group compatibility. Photoredox catalysis has been significantly advanced in the past decade in the pursuit of greener, more sustainable avenues to facilitate desirable reaction transformations under mild conditions. These methods most commonly use a dual catalytic strategy in which a metal is paired with an organocatalyst. While these approaches enable facile phosphonation of a variety of aromatic precursors, the metals and organocatalysts used are often expensive and toxic. Indeed, there remains unexplored chemical space for transition metal-free photoredox-catalyzed aryl C-P bond formations. Herein, we present a series of transition metal-free, photoredox-catalyzed approaches to the phosphonation of aryl halides. The approaches and mechanistic works will be discussed in the following order: </p><p dir="ltr">First, the discovery that 10<i>H</i>-phenothiazine (PTZ) enables the transition metal-free phosphonation of aryl halides using trialkyl phosphites will be presented. PTZ serves as a photocatalyst capable of reducing the aryl halide to access aryl radicals, which readily couple with phosphite esters. This transformation exhibits broad functional group tolerance in good to excellent yields. Then, photoredox catalysis by PTZ enables the formation of unsymmetrical aromatic phosphine oxides using triphenylphosphine (PPh₃) and aryl halides. This is the first work in which PPh₃ has been used as the starting material, and the reaction proceeds via the alkaline hydrolysis of quaternary phosphonium salts. The final work exhibits novel photocatalytic activity of <i>N</i>-heterocyclic carbenes (NHC) to activate aryl halides, form aryl radicals, and enable phosphonation. This method displays broad functional group tolerance under mild conditions and highlights its untapped synthetic utility as a photocatalyst.</p>

<p>The main focus of this thesis is the investigation of the dissociation dynamics of aryl halides using femtosecond pump-probe spectroscopy. In the monohalogenated aryl halides, iodo-, bromo- and chlorobenzene, the rate of dissociation following excitation at 266 nm in the gas phase increased with increasing mass of the halogen atom. This process was assigned to predissociation of the initially excited singlet (π, π*) state via a repulsive triplet (n, σ*) state due to spin-orbit interaction. In addition to the predissociative mechanism, a direct dissociation channel was observed in iodobenzene. The rate of the predissociation in bromobenzene was found to be faster in the condensed phase than in the gas phase, which can be explained by solvent-induced symmetry perturbations. <i>Ab initio</i> calculations of the potential energy surfaces of the ground state and several low lying excited states in bromobenzene have been performed in order to verify the suggested mechanism. Substituting one of the hydrogen atoms in bromobenzene affected the predissociation rate significantly. In o-, m- and p-dibromobenzene the predissociation rate increased with decreasing distance between the bromine atoms in accordance with an increased spin-orbit interaction introduced by the bromine substituent. The fastest predissociation rate was observed in 1,3,5-tribromobenzene. With chlorine and fluorine substitution, inductive and conjugative effects were found to be of importance. In the o- and m-isomers of the dihalogenated aryl halides, an additional faster dissociation channel was observed. Guided by <i>ab initio</i> calculations of the potential energy surfaces in the dibromobenzene isomers, we ascribed the fast dissociation pathway to predissociation of an initially excited triplet state. Upon methyl group substitution in bromobenzene, the decreased lifetime of the initially excited state was attributed to an incresaed density of coupled states.</p><p>Another system which has been studied in the condensed phase is diiodomethane. Using Car-Parrinello molecular dynamics simulations we observed a prompt dissociation and subsequent recombination to the isomer, iso-diiodomethane, in acetonitrile solution.</p><p>Vibrational wavepacket dynamics in the C (¹Σ⁺) state of NaK were studied using a direct ionization probing scheme. A simple analytical expression for the pump-probe signal was developed in order to see what factors that govern direct ionization of the vibrational wavepacket. Our experimental data was consistent with a photoionization transition dipole moment that varies with internuclear distance.</p>

The main focus of this thesis is the investigation of the dissociation dynamics of aryl halides using femtosecond pump-probe spectroscopy. In the monohalogenated aryl halides, iodo-, bromo- and chlorobenzene, the rate of dissociation following excitation at 266 nm in the gas phase increased with increasing mass of the halogen atom. This process was assigned to predissociation of the initially excited singlet (π, π*) state via a repulsive triplet (n, σ*) state due to spin-orbit interaction. In addition to the predissociative mechanism, a direct dissociation channel was observed in iodobenzene. The rate of the predissociation in bromobenzene was found to be faster in the condensed phase than in the gas phase, which can be explained by solvent-induced symmetry perturbations. Ab initio calculations of the potential energy surfaces of the ground state and several low lying excited states in bromobenzene have been performed in order to verify the suggested mechanism. Substituting one of the hydrogen atoms in bromobenzene affected the predissociation rate significantly. In o-, m- and p-dibromobenzene the predissociation rate increased with decreasing distance between the bromine atoms in accordance with an increased spin-orbit interaction introduced by the bromine substituent. The fastest predissociation rate was observed in 1,3,5-tribromobenzene. With chlorine and fluorine substitution, inductive and conjugative effects were found to be of importance. In the o- and m-isomers of the dihalogenated aryl halides, an additional faster dissociation channel was observed. Guided by ab initio calculations of the potential energy surfaces in the dibromobenzene isomers, we ascribed the fast dissociation pathway to predissociation of an initially excited triplet state. Upon methyl group substitution in bromobenzene, the decreased lifetime of the initially excited state was attributed to an incresaed density of coupled states. Another system which has been studied in the condensed phase is diiodomethane. Using Car-Parrinello molecular dynamics simulations we observed a prompt dissociation and subsequent recombination to the isomer, iso-diiodomethane, in acetonitrile solution. Vibrational wavepacket dynamics in the C (1Σ+) state of NaK were studied using a direct ionization probing scheme. A simple analytical expression for the pump-probe signal was developed in order to see what factors that govern direct ionization of the vibrational wavepacket. Our experimental data was consistent with a photoionization transition dipole moment that varies with internuclear distance.