A laser flash photolysis resonance fluorescence (LFP-RF) technique has been employed to study the kinetics of the reactions of methylvinyl ketone (MVK) with atomic bromine (Br) and atomic chlorine (Cl) as a function of temperature (203 755 K) and pressure (12 600 Torr) in nitrogen bath gas. The results of this study are also compared to published kinetics studies for similar reactions. Over the temperature range 200 K < T < 250 K for the reaction of Br with MVK, measured rate coefficients were pressure dependent suggesting the formation of an adduct. The adduct undergoes dissociation on the time scale of the experiments (< 0.1 s) and establishes an equilibrium between Br, MVK, and MVK Br. At temperatures above 298 K no reaction of Br with MVK was observed. Similarly, over the temperature range 405 K < T < 510 K, the reaction of Cl with MVK shows similar kinetics to that of Br and MVK suggesting an equilibrium is established. Equilibrium constants for adduct dissociation and formation are determined for the forward and reverse rate coefficients in both reactions. Second and third-law analyses are carried out to obtain information about the thermochemistry of the equilibrium reactions for Br with MVK and Cl with MVK. Adduct bond strengths of Br and Cl reactions with MVK are reported and compared to reactions with other unsaturated species. Ab initio calculations for these reactions are also presented in this study. Excellent agreement is observed between theory and experiment. Additionally, a reaction of Cl with MVK was observed over the temperature ranges 600 K < T < 760 K and 210 K < T < 365 K. At the lower temperatures, measured rate coefficients are also pressure dependent, however, the adduct remained stable. At the highest temperatures, the measured rate coefficients were pressure independent, suggesting hydrogen abstraction as the dominant reaction pathway. Energetics obtained from ab initio calculations suggest that only abstraction of the methyl hydrogen is likely to occur at a measurable rate in the temperature range investigated.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2117" Guodong Du. 12/19/2004. Report is also available in paper and microfiche from NTIS.

The thesis entitled “Design and Development of Metal-Free Cross Dehydrogenative Coupling Reactions for the construction of C-S, C-O and C-C bonds” is divided into three Chapters. Chapter 1 is presented in five parts, which reveals the cross dehydrogenative coupling (CDC) strategies for the C–S bond forming reactions through C–H functionalization strategy using heterocyclic thiols and thiones. Chapter 2 presents tetrabutyl ammonium iodide (TBAI) catalyzed chemoselective α-aminoxylation of ketones with N-hydroxyimidates using TBHP as oxidant under cross dehydrogenative coupling (CDC) strategy. Chapter 3 describes a transition metal-free Minisci reaction for the acylation of isoquinolines, quinolines, and quinoxaline. Chapter 1 Iodine Promoted C-S Bond Forming Reactions using Dimethyl Sulfoxide as an Oxidant Chapter 1 reveals the utility of cross dehydrogenative coupling (CDC) reactions for the formation of C–S bonds by employing C–H functionalization strategies.1 The direct functionalization of C–H bonds to form C–C and C–X (N, O, S and P) bonds using metal-free reaction conditions is an interesting research topic in recent years.2 Use of dimethyl sulfoxide as an oxidant is emerging as one of the research topics of great interest and utility.3 Heterocyclic thiols and thiones are important precursors for synthesizing a variety of pharmaceuticals and biologically active compounds.4 Therefore it is useful to develop CDC reactions using heterocyclic thiols and thiones as precursors. In this chapter, we describe CDC reactions of heterocyclic thiols and thiones for the sulfenylation of ketones, aldehydes, α, β unsaturated methyl ketone derivatives, pyrazolones, enaminones and imidazoheterocycles using DMSO as an oxidant Chapter 1: Part 1 Iodine Promoted Regioselective α-Sulfenylation of Carbonyl Compounds using Dimethyl Sulfoxide as an Oxidant: In this chapter, a rare regioselective C–H sulfenylation of carbonyl compounds with heterocyclic thiones and thiols have been described using iodine and dimethyl sulfoxide as reagents. Thus, dimethyl sulfoxide (as an oxidant) and stoichiometric amount of iodine have been used for the sulfenylation of ketones using heterocyclic thiones. Whereas the sulfenylation of ketones with heterocyclic thiols required catalytic amount of iodine. This protocol offers a rare regioselective sulfenylation of (i) methyl ketones in the presence of more reactive α-CH2 or α-CH groups, and (ii) aldehydes under CDC method. A few representative examples are highlighted in Scheme 1.5 The application of this methodology has been demonstrated by synthesizing a few precursors for Julia-Kocienski olefination intermediates. Scheme 1. Iodine promoted rare regioselective α-sulfenylation of ketones and aldehydes Siddaraj , Y.; Prabhu, K. R. Org. Lett. 2016, 18, 6090 Chapter 1: Part 2 Regioselective Sulfenylation of α’-CH3 or α’-CH2 Groups of α, β Unsaturated Ketones using Dimethyl Sulfoxide as an Oxidant: In this chapter, an interesting regioselective sulfenylation of α’-CH3 or α’-CH2 groups of α, β unsaturated ketones using dimethyl sulfoxide as an oxidant and catalytic amount of aq. HI (20 mol %) as an additive has been described. This eco-friendly method uses readily available, inexpensive I2 or HI and DMSO. This methodology exhibits a high regioselectivity without forming Michael addition product in the presence of strong acid such as aq. HI or iodine, which is difficult to achieve under cross dehydrogenative coupling (CDC) conditions. Current methodology exhibits a broad substrate scope. A few examples are shown in Scheme 2.6 Scheme 2. HI and DMSO promoted α’-sulfenylation of α, β unsaturated ketones Siddaraju, Y.; Prabhu, K. R. (Manuscript submitted) Chapter 1: Part 3 Iodine Catalyzed Sulfenylation of Pyrazolones using Dimethyl Sulfoxide as an Oxidant: In this chapter, a sustainable and efficient strategy for the sulfenylation of pyrazolones has been described using metal-free conditions by employing DMSO as an oxidant and iodine as a catalyst. A variety of heterocyclic thiols, heterocyclic thiones and disulfides undergo C–H functionalization reaction with pyrazolone derivatives furnishing the corresponding sulfenylated products in short time. Most of the products are isolated in pure form without column purification. A few examples are presented in Scheme 3.7 Scheme 3. Iodine promoted sulfenylation of pyrazolones Siddaraju, Y.; Prabhu, K. R. Org. Biomol. Chem. 2017, 15, 5191 Chapter 1: Part 4 Iodine-Catalyzed Cross Dehydrogenative Coupling Reaction: Sulfenylation of Enaminones using Dimethyl Sulfoxide as an Oxidant: In this chapter, synthesis of poly functionalized aminothioalkenes has been described using substoichiometric amount of iodine and DMSO as an oxidant. This metal-free methodology enables a facile sulfenylation of enaminones with heterocyclic thiols and thiones. This methodology is one of the simple approaches for the sulfenylation of enaminones under cross dehydrogenative coupling method. A few examples are highlighted in Scheme 4.8 Scheme 4. Cross-dehydrogenative coupling approach for sulfenylation of enaminones Siddaraju, Y.; Prabhu, K. R. J. Org. Chem. 2017, 82, 3084 Chapter 1: Part 5 Iodine-Catalyzed Cross Dehydrogenative Coupling Reaction: A Regioselective Sulfenylation of Imidazoheterocycles using DMSO as an Oxidant: In this chapter, a simple synthetic approach for the regioselective sulfenylation of imidazoheterocycles using iodine as a catalyst and DMSO as an oxidant under cross dehydrogenative coupling (CDC) reaction conditions has been demonstrated. This protocol provides an efficient, mild and inexpensive method for coupling heterocyclic thiols and heterocyclic thiones with imidazoheterocycles. This is the first report on sulfenylation of imidazoheterocycles with heterocyclic thiols and heterocyclic thiones under metal-free conditions. A few examples are shown in Scheme 5.9 Scheme 5. Cross-dehydrogenative coupling approach for sulfenylation of imidazoheterocycles Siddaraju, Y.; Prabhu, K. R. J. Org. Chem. 2016, 81, 7838 Chapter 2 Chemoselective α-Aminoxylation of Aryl Ketones: Cross Dehydrogenative Coupling Reactions Catalyzed by Tetrabutyl Ammonium Iodide: In this chapter, chemoselective α-aminoxylation of ketones with N-hydroxyimidates catalyzed by tetrabutyl ammonium iodide (TBAI) has been presented. The coupling reaction of a variety of ketones with N-hydroxysuccinimide (NHSI), N-hydroxyphthalimide (NHPI), N-hydroxybenzotriazole (HOBt) or 1-hydroxy-7-azabenzotriazole (HOAt) using TBHP as oxidant has been investigated. This α-aminoxylation of ketones is chemoselective as aryl methyl ketones, aliphatic ketones as well as benzylic position are inactive under the reaction condition. A few examples are highlighted in Scheme 6.10 The application of this method has been demonstrated by transforming a few coupled products into synthetically useful vinyl phosphates. Scheme 6. Chemoselective α-aminoxylation of ketones with N-hydroxyimidates Siddaraju, Y.; Prabhu, K. R. Org. Biomol. Chem. 2015, 13, 11651 Chapter 3 A Transition Metal-Free Minisci Reaction: Acylation of Isoquinolines, Quinolines, and Quinoxaline: In this chapter, transition metal-free acylation of isoquinoline, quinoline and quinoxaline derivatives with aldehydes has been described by employing TBAB (tetrabutyl ammonium bromide, 30 mol %) and K2S2O8 as an oxidant under cross dehydrogenative coupling (CDC) reaction. This intermolecular acylation of electron-deficient heteroarenes provides an easy access and a novel acylation method of heterocyclic compounds. The application of this CDC strategy has been illustrated by synthesizing isoquinoline-derived natural products. A few representative examples are shown in Scheme 7.11 Scheme 7. CDC reactions of heteroarenes with aldehydes Siddaraju, Y.; Lamani, M.; Prabhu, K. R. J. Org. Chem. 2014, 79, 3856

Les carburants synthétisés à partir de la biomasse représentent une alternative crédible aux carburants conventionnels. La biomasse lignocellulosique présente en effet une importante disponibilité et son traitement physico-chimique permet d’obtenir une grande variété de composés aux propriétés intéressantes. La structure de ces biocarburants fait cependant intervenir des fonctions oxygénées, qui rendent la compréhension des phénomènes d’oxydation complexes. Le projet 2G-CSAFE, dans lequel s’inscrit le travail présenté ici, a pour objectif d’explorer la cinétique d’oxydation de certains de ces carburants. Les fonctions chimiques étudiées lors de ce travail sont les fonctions cétone, éther et ester. La combinaison de deux de ces fonctions (comme dans le cas des lévulinates) est également étudiée. Après une étude bibliographique qui vise à identifier les informations apportées par les études passées sur les composés les plus simples de chaque famille (acétone, diméthyl-éther et formiate de méthyle), l’accent est mis sur les rares travaux disponibles liés à la butanone, la cyclopentanone, la cyclohexanone, le dibutyl-éther, le formiate de butyle et le lévulinate de méthyle. La cinétique d’oxydation de ces composés est ensuite étudiée par des approches numériques et expérimentales. Des calculs de chimie théorique sont menés dans un premier temps pour étudier l’impact des fonctions oxygénées sur la structure du carburant et pour obtenir les constantes de vitesse relatives aux principales réactions mises en jeu. Des expériences en réacteur auto-agité par jets gazeux sont ensuite réalisées sur une gamme de température pouvant aller de 450 à 1250 K, à des pressions de 1 ou 10 atm et pour des richesses allant de 0,5 à 2. Les données ainsi collectées sont enfin utilisées pour développer des mécanismes cinétiques. L’accord entre les simulations et les données expérimentales est globalement satisfaisant pour des composés aussi complexes et les résultats présentés ici pourront être source d’analogies pour la modélisation d’autres carburants oxygénés. / Fuels produced from biomass are an interesting alternative to conventional fuels. Lignocellulosic biomass is indeed highly available and a wide variety of compounds can be obtained through its physico-chemical conversion. However, the structure of the fuels obtained from such processes involves oxygenated groups that make complicated the understanding of the oxidation chemistry. The work presented here is part of the 2G-CSAFE project, which aims at exploring the oxidation kinetics of these fuels. Chemical functions studied in this work include ketones, ethers and esters. The combination of two functions (as for levulinates) is also investigated. After a literature review aiming at collecting the information reported on the simplest compound of each group (acetone, dimethylether and methylformate), available studies on butanone, cyclopentanone, cyclohexanone, dibutyl-ether, butyl-formate and methyl levulinate are considered. The oxidation of these compounds is thereafter studied by numerical and experimental approaches. Ab initio calculations are performed to study the impact of the oxygenated groups on the structure and to derive rate constants for the major chemical pathways. Experiments are then carried out in a jet-stirred reactor for temperatures ranging from 450 to 1250 K, pressures of 1 or 10 atm and equivalence ratios from 0.5 to 2. The data obtained through these two approaches are finally used to develop and validate kinetic mechanisms. The overall agreement between experiments and simulations is satisfactory and results presented here can be used as a source of analogy for the future modeling of other similar oxygenated fuels.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work describes firstly an efficient and regioselective method for the synthesis of a new series of 2,2,2-trifluoro-1-[4-methoxy-spiro(2H-chromen-2,1 -cycloalkan)-3-yl]ethanones from the Kabbe adducts (spiro[chroman-2,1 -cycloalkan]-4-ones). Yields of 38 % to 61 % were obtained when trifluoroacetylation reactions of mixtures of enolethers and/or acetals derived from four spiro ketones (Kabbe adducts) were performed at a temperature of 45 oC and employing anhydrous chloroform as the solvent. Subsequently, when the respective trifluoroacetylated Kabbe adducts reacted with phenylhydrazine and methylhydrazine at a 1:1 molar ratio in refluxing ethanol for 24 hours, a new series of seven examples of a novel spiro-condensed heterocyclic system, namely 1(2)-methyl(phenyl)-3-(trifluoromethyl)-1,4(2,4)-dihydro-spiro(chromen[4,3-c]pyrazole-4,n -cycloalkanes) where cycloalkanes are cyclopentane, cyclohexane and cycloheptane (n = 1) and tetrahydro-2H-pyran (n = 2) were isolated at yields of between 35 % and 51 %. NMR and X-ray diffraction techniques demonstrated clearly that reactions from methylhydrazine and phenylhydrazine were regioselective and allowed to isolate separately the 1,3- and 2,3-trifluoromethylated isomers, respectively. Subsequently, two examples of new 3-hydroxy-3-(trifluoromethyl)-3,3a-dihydro-4H-spiro(chromen[4,3-c]isoxazole-4,1 -cycloalkanes), derivated from cyclopentanone and cyclopentanone, were obtained from the reaction of 2,2,2-trifluoro-1-[4-methoxy-spiro(2H-chromen-2,1 -cycloalkan)-3-yl]ethanones with hydroxylamine hydrochloride in yields of 42% and 58%, respectively. Finally, the structures of new spiro heterocycles were determined with the aid and simultaneous application of 1H-, 13C{1H}- and 19F-NMR, X-ray monocrystal diffraction, Mass Spectrometry and DFT calculation techniques and their purity were proved by elemental analysis or High Resolution Mass Spectrometry (HRMS). / O presente trabalho descreve inicialmente um método eficiente e regiosseletivo para a síntese de uma nova série de 2,2,2-triflúor-1-[4-metóxi-espiro(2H-cromen-2,1 -cicloalcan)-3-il]etanonas a partir de adutos de Kabbe (espiro[croman-2,1 -cicloalcan]-4-onas). Rendimentos de 38% a 61% foram obtidos quando reações de trifluoracetilação de misturas de enoléteres e/ou acetais derivados de quatro espiro cetonas (adutos de Kabbe) foram realizadas a 45 ºC usando clorofórmio anidro como solvente. Subsequentemente, quando os respectivos adutos de Kabbe trifluoracetilados foram reagidos com fenilhidrazina ou metilhidrazina, em relação molar de 1:1, sob refluxo de etanol por 24 horas, uma série de sete exemplares de um novo sistema heterocíclico espiro-condensado, denominado 1(2)-metil(fenil)-3-(trifluormetil)-1,4(2,4)-diidro-espiro(chromen[4,3-c]pirazol-4,n -cicloalcanos) onde os cicloalcanos são ciclopentano, ciclohexano e cicloheptano (n = 1) e tetraidro-2H-pirano (n = 2), foi isolada em rendimentos entre 35 % e 51 %. Técnicas de RMN e de difração de raios-X demonstraram claramente que as reações a partir da metilhidrazina e da fenilhidrazina foram regiosseletivas e permitiram isolar separadamente os isômeros trifluormetilados 1,3 e 2,3, respectivamente. Em sequência, dois exemplares de novas 3-hidróxi-3-(trifluormetil)-3,3a-diidro-4H-espiro(cromen[4,3-c]isoxazol-4,1 -cicloalcanos), derivados da ciclopentanona e ciclohexanona, foram obtidos a partir da reação de 2,2,2-triflúor-1-[4-metóxi-espiro(2H-cromen-2,1 -cicloalcan)-3-il]etanonas com cloridrato de hidroxilamina em rendimentos de 42% e 58%, respectivamente. Finalmente, as estruturas dos novos espiro heterociclos foram determinadas com o auxílio e aplicação simultânea de experimentos de RMN de 1H, 13C{1H}, 19F, difração de raios-X em monocristais, Espectrometria de Massas e cálculos DFT e, a sua pureza comprovada por Análise Elementar ou por Espectrometria de Massas de Alta Resolução (HRMS).

DICLORO-&#945;-(ALQUILTELURO)CETONAS Estudou-se a reação entre quantidades equimolares de cetonas ou éteres enólicos de silício de cetonas e tricloretos de alquil telúrio, obtendo-se dicloro-&#945;-(organil) cetonas. Em todos os exemplos efetuados obtiveram-se bons resultados apenas nas reações com éteres enólicos de silício. TELURETOS VINíLICOS TRISSUBSTITUíDOS Neste trabalho desenvolvemos um método de preparação de teluretos vinílicos trissubstituídos, obtidos através da reação de adição de tricloreto de aril telúrio e tetracloreto de telúrio a acetilenos aromáticos e alifáticos, levando aos dicloretos de aril-2-clorovinila de configuração Z. A redução da ligação Te-Cl dos dicloroteluro compostos obtidos, levando aos teluretos correspondentes pode ser efetuada em alto rendimento pela reação com um equivalente de NaBH4. A halogenodeteluração destes teluretos vinílicos trissubstituídos foi possível reagindo-os com N-bromosuccinimida/cloreto de alumínio, obtendo-se bromocloroalquenos em rendimentos moderados. 1,1-DIHALO-2-(FENILSELENO)CICLOPROPANOS Outro tópico abordado foi a preparação de 1,l-dihalo(fenilseleno)ciclopropanos, por meio da adição de dihalocarbenos, gerados sob condições de transferência de fase, a selenetos vinílicos de configuração Z ou E. A adição ocorreu com retenção de configuração da ligação olefínica. Também foram preparados, empregando-se a mesma metodologia acima mencionada, selenociclopropanos tri- e tetrassubstituídos. / &#945;- DICHLORO-(ORGANYLTELLURO)KETONES The reaction of equimolar amounts of ketones or ketone trimethylsilylenol ethers with aryltellurium trichlorides in boiling benzene produces &#945; - dichloro-(aryltelluro) ketones in good yields. The reaction with aliphatic tellurium trichlorides give good results only with ketone silyl enol ethers; reaction with ketones gives low yields of the &#945;-dichloro-(organyltelluro)ketones. VINYLIC TELLURIDES (p-Methoxyphenyl)tellurium trichlorides and tellurium tetrachloride react with terminal acetylenes to give 1-chloro-1-organyl-2-[dichloro(p-methoxyphenyl)telluro] ethenes of Z configuration in good yields. The diorganyl tellurium dichlorides are reduced to the corresponding tellurides with sodium borohydride. Halogenodetelluration of these trisubstituted vinylic tellurides was possible by reaction with N-bromosuccinimide/aluminium(III) chloride, producing the correspondent bromochloroalkenes in good yields. 1,1-DIHALO-SELENOCYCLOPROPANES Selenocyclopropanes were prepared by the addition of dihalocarbenes, generated under phase transfer conditions to Z and E disubstituted vinylic selenides. The addition occurs with retention of configuration of the olefinic bond. By employing the above mentioned methodology it was possible to prepare tri- and tetrasubstituted selenocyclopropanes.

Na primeira parte deste trabalho, desenvolvemos duas metodologias para a preparação de &#945;-dicloroteluro cetonas. A primeira utiliza a reação direta de tricloretos de ariltelúrio com cetonas e a segunda envolve a reação do mesmo reagente com éteres enólicos de silício de cetonas. As dicloroteluro cetonas preparadas foram transformadas em &#945;-halo cetonas pela reação com cloro ou bromo, ou utilizando condições de termólise sob pressão reduzida. Dados de ressonância magnética nuclear de 1H e de 13C, de difração de raios-X e de espectros no infra-vermelho foram utilizados na determinação estrutural dos compostos preparados. Numa segunda arte foram preparados &#945;-halo-&#945;-seleno alcanos através da adição de HBr a selenetos vinílicos obtidos por reação de acetilenos aromáticos com selenofenol. Os &#945;-halo-&#945;-seleno alcanos foram transformados em &#945;-selenofenil acetaldeídos por reação de solvólise em DMSO. / In the first parto of this work two methodologies for the synthesis of &#945;-dichlorotelluroketones were developed. The first one employs the reaction of aryltellurium tricholorides with ketones and the second one involves the reaction of the same reagent with silylenol ethers of ketones. The &#945;-dichlorotelluroketones prepared were transformed into &#945;-halo ketones by means of the reaction with chlorine or bromine or by pyrolysis at reduced pressure. 1H and 13C nuclear magnetic ressonance, x-ray difraction and infrared data were used in the structure elucidations of the compounds prepared. In the second part of the work &#945;-halo- &#945;-seleno-alkanes were prepared by addition of hydrogen bromide to vinylic selenides which were prepared by reacting aromatic acetylenes with selenophenol. The &#945;-halo-&#945;-seleno-alkanes were transformed into &#945;-selenophenyl acetaldehydes by solvolysis in DMSO.

The biological activity of the pharmaceutical drugs often depends on how it fits with a receptor making stereochemistry a key component. Selective reactions can limit or avoid the mixture of enantiomers obtained. One such reaction is the selective reduction of a carbon-carbon double bond in the presence of a carbonyl. Although efficient, current asymmetric synthesis methods have limitations such as harsh reaction conditions, the high costs of chiral catalysts and the toxicity of the metal-based catalysts. Catalysts derived from small organic molecules have become an attractive alternative which have been explored more rigorously in recent years. Using a BINOL-derived boro-phosphate catalyst, we have developed a methodology that selectively reduces the carbon-carbon double bond of linear α, β-unsaturated ketones, exclusively giving the corresponding saturated ketone. To the best of our knowledge, this reaction is the first of its kind to accomplish this transformation and results give high yields of >93% and enantioselectivities >90% at room temperature. Furthermore, the products of this novel reaction can be subjected to a choice electrophile, in example benzaldehyde, to afford diastereoselective tertiary alcohol products with enantioselectivities of >88% and diastereoselectivities of up to 99:1.

Ces travaux de thèse portent sur le développement de catalyseurs à base de ligands carbène N-hétérocycliques dérivés de fer et de nickel, deux métaux de transition abondants, pour les réactions de hydrosilylation et de borylation. Le premier chapitre porte sur les travaux réalisés à l’aide de complexes de fer du type [Cp(NHC)Fe(CO)₂][X] (X = I, PF₆) possédant des ligands de type benzimidazole ou imidazole et leur évaluation en hydrosilylation de dérivés carbonylés. Le deuxième chapitre traite de l’utilisation de complexes demi-sandwichs de nickel du type CpNi(NHC) en hydrosilylation d’aldéhydes, de cétones, d’aldimines et de cétimines. Enfin le troisième chapitre est consacré à la réaction de borylation catalysée par des complexes de nickel demi-sandwich CpNi(triazole)X et des complexes de nickel possédant deux ligands chélatants anioniques de type carbene N-hétérocyclique fonctionnalisé par un bras amido. / The research work described in this manuscript has for main objective the development of new homogeneous catalytic systems based on N-heterocyclic carbene (NHC) iron and nickel complexes for hydrosilyation and borylation reactions. The first chapter describes the use of [Cp(NHC)Fe(CO)₂][X] (X = I, PF₆) complexes bearing benzimidazole or imidazole NHC type ligands for hydrosilylation of benzaldehyde and acetophenone. In a second chapter, we have shown that half-sandwich NHC-nickel complexes in the presence of a catalytic amount of NaHBEt3 can be efficient catalysts for the reduction of aldehydes, ketones, aldimines and ketimines in the presence of diphenylsilane. In the last chapter, two new series of non-classical NHC-nickel triazole complexes had been developed: (i) one series with half sandwich NHC-nickel triazole complexes and (ii) another one based on chelating anionic amido-functionalized N-heterocyclic carbene nickel complexes. The two series of complexes were then evaluated in catalytic borylation cross coupling reaction.

Solvent effects play diverse roles in myriads of chemical, physical and biological processes. The solvent interacts with the solute by: i) non-specific (Coulombic, van der Waals interactions) and ii) specific interactions (hydrogen bonding, etc.). These interactions are responsible for solvation of the solute and are collectively termed as “solvent polarity”. Differential solvation of ground and excited electronic states is manifested in the absorption spectrum as a change in the band position, intensity or shape, which is termed as “solvatochromism”. Intermolecular hydrogen bonding (IHB) is a kind of specific solute-solvent interaction, which plays a key role in molecular or supramolecular photochemistry, as well as in photobiology. Solvation and its influence on various physico-chemical and biological processes can be understood by i) top-down; and ii) bottom-up approaches. In the top-down approach, the macroscopic properties like dielectric constant, refractive index are used to understand the microscopic solvation. This approach fails when specific interactions like hydrogen bonding interactions come into play, and furthermore it can reproduce only the macroscopic polarization of the solvent but fails miserably at the cybotactic region of solvation. With the recent advancements in the computational field, the molecular level description of solvation has been within reach for chemical physicists and experimentalists to corroborate their experimental results and in turn to visualize processes of fundamental or technologically relevant problems. The energy levels of the nπ* and ππ* singlet and triplet excited states of aromatic ketones are close-lying and therefore their energy levels can be altered by the substituents. The solvent polarity can be used as a surrogate to tune their energy levels. In certain cases, the lowest triplet or singlet excited states can switch their electronic character with increasing solvent polarity known as “electronic state switching” and thus modulate their photochemical or photophysical properties. Therefore, aromatic ketones were used as solvatochromic probes in this work. Comprehensive analyses of the solvent effects on xanthone (XT), 9,10-phenanthrenequinone (PQ) and benzophenone (Bzp) were carried out using steady-state and nanosecond time-resolved absorption, and resonance Raman spectroscopy in conjunction with ad hoc and classical-molecular dynamics and simulations generated supermolecule-continuum solvent model quantum mechanical calculations to corroborate the experimental outcomes and in turn to visualize the solvation process at the molecular level. The present thesis is divided into eight chapters and the summary of each chapter is described below: Chapter 1 provides a brief literature review of solvation effects and their influence on various physico-chemical and biological processes. Furthermore, the importance of understanding solvation at the molecular level and key concepts are discussed, which forms the heart of this thesis. Chapter 2 discusses the experimental and computational approaches used to study the solvation processes at the molecular level. A detailed explanation of spectroscopic techniques like resonance Raman (RR) and nanosecond-time resolved resonance Raman (ns-TR3) spectroscopy and their experimental and theoretical aspects are discussed, followed by a discussion on the fundamental concepts of computational methods like ab initio calculations density functional theory (DFT), and classical molecular dynamics and simulations (c-MDS) utilized in this study. Chapter 3 focuses on microscopic understanding of solvatochromic shifts observed for 9,10-phenanthrenequinone in protic solvents using UV-Vis and RR spectroscopy in conjunction with an ad hoc explicit solvation model and time-dependent density functional theory (TDDFT) calculations. The hypsochromic shift and bathochromic shift of the singlet nπ* and ππ* electronic transitions in protic solvents are due to hydrogen bond weakening and strengthening in the excited state for the corresponding electronic transitions, respectively as indicated by TD-DFT calculations and Kamlet-Taft linear solvation energy relationships. The hydrogen bond strengthening in the singlet ππ* excited state is further confirmed by Raman excitation profile (REP) analysis of PQ in different solvents. Furthermore, with increasing solvent polarity the two lowest singlet excited states undergo different hydrogen bonding mechanisms, leading to a decreasing energy gap between them. Therefore, hyperchromism of the nπ* transition has been hypothesized to be due to an increasing vibronic coupling between the lowest singlet nπ* and ππ* excited states. In Chapter 4, a real time observation of the thermal equilibrium between the lowest triplet excited states of PQ in acetonitrile solvent was carried out using ns-TR3 spectroscopy and this can explain its high reactivity towards H-atom abstraction, despite the fact that the lowest triplet excited state has ππ* character. Furthermore, extending the concept of hydrogen bonding mechanisms of the lowest singlet to the triplet excited states, the different hydrogen bonding mechanisms exhibited by them can lead to alteration of the intersystem crossing mechanisms in PQ. Chapter 5 highlights the very different role of intermolecular hydrogen bonding in the reduced reactivity of the xanthone (XT) triplet towards H-atom abstraction in protic solvents. The different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states in protic solvents are derived from an ad hoc explicit solvation model, TD-DFT calculations and ns-time resolved absorption (ns-TRA): they separate them further in energy and thereby the nearest T2(nπ*) triplet state to the T1(ππ*) excited state plays an insignificant role in the reactivity towards H-atom abstraction, in contrast to the PQ triplet discussed in Chapter 4. Chapter 6 discusses the structure of XT triplet states using TR3 spectroscopy in combination with TD-DFT studies. The TR3 spectrum of the XT in acetonitrile identified a vibronic coupling mode responsible for the reactivity of XT towards H-atom abstraction, despite the fact that the lowest triplet excited state (T1) has ππ* character. This vibronic active mode is absent in the TR3 spectra of XT in protic solvents (methanol and ethanol). Furthermore, the REP analysis suggests that the nanosecond triplet-triplet absorption spectrum of XT in acetonitrile involves two different species, while in methanol it involves only one species. This observation is in agreement with the previous chapter (Chapter 5) which proposes a different hydrogen bonding mechanisms for the two lowest triplet excited states and their influence on the reduced reactivity towards H-atom abstraction. Chapters 3-6 emphasize the need for a proper solvation model at the molecular level to describe the various photophysical and photochemical processes of aromatic ketones. Therefore, Chapter 7 includes discussions on the bottom-up solvation methodology applied to benzophenone (Bzp) to understand its vibrational and electronic solvatochromic behaviour at the molecular level. Raman and UV-Vis spectroscopic techniques were used in conjunction with a c-MDS-generated supermolecule continuum solvation model DFT calculation to corroborate and to visualize the experimental outcome. The carbonyl stretching frequency of Bzp in protic solvents has two bands, corresponding to free carbonyl and hydrogen bonded carbonyl. Despite the fact that the macroscopic polarity of acetonitrile and methanol solvents are similar, the free carbonyl stretching of Bzp in methanol solvent was blue-shifted by 4 cm-1 with respect to the carbonyl stretching in acetonitrile solvent. The Gutmann’s acceptor number plot for carbonyl stretching frequencies indicates that the free carbonyl group is neighboured by a hydrophobic environment. The c-MDS-generated supermolecule-continuum solvation model DFT calculations suggest that the extended hydrogen bonding network of methanol solvent is responsible for the hydrophobic solvation around the free carbonyl. Furthermore, a linear correlation was obtained for the vibrational and electronic solvatochromism of the carbonyl frequency and energy of the singlet nπ* transition, respectively, which indicates that a variation in excitation wavelength for the singlet nπ* transition can arise from different solvation states. This can have implications for ultrafast processes associated with electron transfer, charge-transfer and also the photophysical aspects of excited states.Finally, Chapter 8 contains overall conclusions of the thesis and future directions for the present research area.