Dissertations / Theses on the topic 'NHC carbene'

N-heterocyclic carbenes (NHCs) can be used as ligands for organometallics complexes, which can then facilitate numerous catalytic applications, such as, C-H activation, small molecule activation and numerous materials applications. The use of anionically-tethered NHCs for usage with electropositive metals has been pioneered by the Arnold group within the last decade. This thesis describes the synthesis of both aryloxide- and amide-tethered NHC organometallic complexes of s-, p-, d- and f-block metals to provide a platform for small molecule activation. Once synthesised, the reactivity of some of these complexes were tested by reaction with CO2 with the aim of turning a molecule considered a harmful (environmentally), waste product into value added products, potentially providing an alternative fuel source. Chapter One introduces the use of anionically-tethered NHCs for use in a number of organometallic complexes as well as their current potential as catalysts for a number of important small molecules. This chapter focuses upon the differences between complexes tethered with anionic O, N, P, S elements, f-element NHC complexes and the use of d-block NHC complexes for catalysis. Chapter Two contains the synthesis and characterisation of a number of aryloxy-tethered NHC p-, d- and f-block organometallic complexes using the ligand H2(LArO R)2. The synthesis of SnII complexes including the synthesis of new ‘normal’ ‘abnormal’ complexes given enough steric bulk around the Sn centre due to the lone pair present in Sn complexes, preventing one of the ligands binding through the classical carbene position and therefore binding through the backbone C4 carbon. The synthesis of MII (Zn, Co and Fe) complexes to compare the solid-state structure and binding mode of the carbenes. The synthesis and characterisation of MIII (Ce and Eu) complexes to assess the solid-state structure and binding modes within f-bock complexes. Chapter Three investigates the reactivity of the MII complexes (Sn, Zn, and Fe) with CO2. Successful reactions were characterised using NMR and further treated with alkynes to target catalytic reactions. Chapter Four contains reactions to target a number of amide-tethered bis (NHC) s-, p-, d- and f-block organometallic complexes using the proligand, H4(LN Mes)Cl3. Deprotonation studies undertaken with a number of bases to give the MI (Li and K) salts and MII (Mg) salts and proved to be unsuccessful upon isolation. Reactions to synthesise the p-, d- and f-block complexes were then undertaken using in situ free carbene production as well as the attempted isolation of the free carbene, both of which also proved unsuccessful. Chapter Five provides an overall conclusion to the work presented in Chapters Two, Three and Four within this thesis. Chapter Six gives the experimental and characterising data for the complexes and reactions.

Les carbènes N-hétérocycliques (NHC) sont très utilisés pour complexer les métaux de transition. Ils quittent rarement ce rôle de ligand ancillaire et trouvent, depuis une vingtaine d’années, des applications en catalyse ou, plus récemment, en chimie médicinale. Dans ce travail, nous discuterons d’une méthode de synthèse douce conduisant à la formation de complexes AgI – NHC via une source d’argent soluble. Cette méthode nous a permis d’obtenir des complexes bien connus mais également d’accéder à une nouvelle série de complexes NHC-Ag-phosphine. Nous présenterons également une nouvelle réaction où des NHC portant une fonction azoture à proximité du carbone du carbène quittent leur rôle de ligand ancillaire et conduisent à la formation d’hétérocycles azotés par cyclisation carbène-nitrène. Cette réaction sera présentée en détail, ainsi que la caractérisation spectroscopique concernant une sous-série de composés fluorescents obtenus par cette méthode. Enfin, nous présenterons une stratégie de post-fonctionnalisation de complexes développée dans notre équipe. Des complexes argent(I)-NHC portant un azoture proches du centre carbénique catalysent leur propre fonctionnalisation. De plus, des complexes de cuivre(I) portant des azotures en position éloignée du centre métallique seront greffés sur des nanoparticules magnétiques pour servir de catalyseur recyclables
N-heterocyclic carbenes (NHC) are widely used to complex transition metals. They rarely leave their role as ancillary ligand and find, since 20 years, applications in catalysis or, more recently, in medicinal chemistry. In this work, we will discuss a mild synthetic method leading to the formation of AgI – NHC complexes via a soluble silver species. This method allowed us to obtain well known complexes but also to access a new series of NHC-Ag-phosphine complexes. We will also present a new reaction where NHC ligands bearing an azide function close to the carbenic center leave their role as ancillary ligand and lead to the formation of nitrogen rich heterocycles by a carbene-nitrene cyclization. This reaction will be presented in detail, along with the spectroscopic characterization regarding a sub-series of fluorescent compounds obtained by this method. Finally, we will present a post-functionalization strategy of complexes developed in our team. Silver(I)-NHC complexes tagged by an azide close to the carbenic center catalysed their own functionalization. Moreover, copper(I) complexes tagged by an azide function in a distant position from the metallic centre will be grafted on magnetic nanoparticles to act as recyclable catalysts

2016 - 2017
Olefin metathesis is one of the most important chemical transformations for the formation of carbon-carbon double bonds. The possibility to build up highly funtionalised alkenes starting from simple olefins makes this reaction indispensable in modern organic synthesis, giving access to a wide range of molecules that would be barely obtained through other synthetic routes. The success of metathesis is due to the development of new and efficient catalysts which can be used in a wide variety of research fields, both in industry and in academia. In this context, the research of the ‘perfect’ metathesis complex still impassions scientists all over the word, and several research papers regarding the development of new catalytic systems are published every year. The group I am part of focuses its attention on the development of new ruthenium metathesis catalysts. Our interest lies in the influence that nature and configuration of substituents on the N-heterocyclic carbene (NHC) ligand could have on the performances of the corresponding metal complexes. In this doctoral thesis, the field of unsymmetrical N-heterocyclic carbene (u-NHC) ruthenium catalysts will be explored. Synthesis and characterisation of several novel complexes will be discussed. Catalytic performances will be evaluated in model metathesis reactions as well as in more attractive metathesis transformations. The relationship between NHC structure and complexes’ behaviours will be investigated using NMR, X-Ray, IR, cyclic voltammetry and DFT calculations. ..[edited by Author]
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N-Heterocyclic Carbenes (NHC) present a viable alternative to traditional phosphine ligands in a variety of organometallic mediated catalytic reactions. Singlet ground-state carbenes are stabilized by the push-pull presence of two adjacent nitrogen atoms in an imidizolium 5-membered ring, allowing neutral electron donor properties. The ability to synthesize a variety of NHC ligands with differing steric and electronic properties is possible by changing the sustiuents on the nitrogen atoms of the imidizolium. Tunable characteristics and enhanced chemical and thermal stability give NHC’s an advantage over phosphines in many catalytic systems. This dissertation focuses on the use N-Hetercyclic Carbenes in a variety of organometallic complexes. The synthesis of NHC complexes with a variety of transition metals is described. The transition metals complexed with NHC’s include palladium, iridium, nickel and ruthenium. The catalytic activity of the metal-NHC complexes is investigated as well.

The syntheses, structures, photophysical properties and applications of three types of photoluminescent organoplatinum(II) complexes containing N-heterocyclic carbene (NHC) ligands are described. The tetradentate dianionic bis(phenolate-NHC) type ligands provide a superior scaffold for constructing thermally stable and efficient deep-blue phosphorescent Pt(II) complexes with λmax of ~440-460 nm and solid-state emission quantum yields of ~30%. Highly efficient blue OLEDs with CIEx, y of (0.19, 0.21) were fabricated based on these emitters with maximum brightness, peak current efficiency and power efficiency of ~9500 cd m^(-2), 24 cd A^(-1) and 17 lm W^(-1), respectively. Structural modification by extending the π-conjugation of the tetradentate bis(phenolate-NHC) ligand leads to strongly phosphorescent platinum(II) complexes with long-lived emissive electronic states that can be used as a luminescent sensor for oxygen. DFT/TDDFT calculations and time-resolved spectroscopic characterizations were performed to gain insight into the structure-photophysics correlation. The N-heterocyclic carbene (NHC) ligand was incorporated into Pt(II) complexes containing tridentate deprotonated 1,3-bis(2-pyridyl)benzene (N^C^N) type ligand. In addition to the [(N^C^N)Pt(NHC)]PF6 type complexes with (N^C^N) in η3-tridentate coordination mode, Pt(II) complexes with η2-bidentate (N^CN) ligands, namely [(N^CN)Pt(NHC)2]PF6, have been isolated and structurally characterized. The highly phosphorescent [(N^C^N)Pt(NHC)]PF6 complexes were used for solution-processed green OLEDs fabrication. The peak current efficiency of 12.5 cd A^(-1) and maximum brightness higher than 2000 cd m^(-2) were achieved. The presence of the pendent pyridyl motif causes quenching of emission of the [(N^CN)Pt(NHC)2]PF6 complexes in solution at room temperature. Turning on solid-state emission of [(N^CN)Pt(nBu2Im)2]PF6 in the presence of an acidic vapor revealed its potential as a luminescent chemosensor. A class of dicationic platinum(II) terpyridyl complexes containing NHC ligand, namely [Pt(tpy)(NHC)](PF6)2, has been synthesized and structurally characterized. Even in the presence of the strong σ-donating NHC ligand, these complexes are non- or weakly emissive in solution at room temperature. However, this class of complexes displays intense emissions in solid state (298 K and 77 K), in glassy solution (77 K butyronitrile) and in PMMA (2 wt.%, 298 K). The ligand (terpyridine) displacement reaction arising from CN attack onto the Pt(II) center has been observed for [Pt(tpy)(nBu2Im)](PF6)2 leading to its application as a chemodosimeter for selective cyanide sensing in aqueous solution.
published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy

The goal of this PhD was to elaborate supported Ru-NHC catalytic materials based on hybrid organic-inorganic materials having imidazolium units perfectly distributed within a silica matrix. Passivation of these imidazolium materials followed by formation of NHC-carbene and reaction with [RuCl2(p-cymene)]2 provided these well-defined surface sites of general structures RuCl2(NHC)(L), where L was para-cymene (p-cymene) or THF depending on the reaction conditions, which could be further replaced by PMe3. These systems were then tested in the hydrogenation of CO2 in presence of amine to give formamides. The mono-NHC systems were highly active only in the presence of PMe3 ligands, but suffered from Ru leaching, evidencing the low stability of the NHC-Ru bond under the reaction conditions. On the other hand, dinuclear bis-NHC Ru systems were also developed, and they displayed much improved activity and stability in the hydrogenation of CO2 in the presence of PMe3 compared to the mono-NHC systems. This allowed the use of much higher reaction temperatures (200 °C) and provided heterogeneous catalysts with performances close to those obtained with the best homogeneous catalysts, Cl2Ru(dppe)2.

Chapter one introduces N-heterocyclic carbenes (NHCs) and discusses their use as ligands for rare earth metal complexes, with particular emphasis upon compounds synthesised from 2009 until the present day. Chapter two details the synthesis and characterisation of the homoleptic scandium-NHC complex [Sc(L)3] (L = [OCMe2CH2(1-C{NCHCHNiPr})]). Reactions of [Sc(L)3] with boranes, CO2 and CS2 are described which exploit the relative lability of the Sc–Ccarbene bond and allow formation of [Sc(L)2(OCMe2CH2(1-B'C{NCHCHNiPr}))] (B' = 9-BBN, BPh3, B(C6F5)3, BH3), [Sc(OCMe2CH2(1-O2CC{NCHCHNiPr})3]n, [Sc(L)2(OCMe2CH2 (1-S2CC{NCHCHNiPr})] and [Sc(L)(OCMe2CH2(1-S2CC{NCHCHNiPr})2]2. The chapter also discusses the reactivity of [Sc(L)3] towards substrates containing acidic C–H and N–H bonds and substrates containing polar E–X bonds (where E = C, Si, B, P and X = Cl, I). Chapter three describes the synthesis and characterisation of the NHC substituted scandium benzyl complexes [Sc(Bn)2(L)]2 and [Sc(Bn)(L)2], and the attempted synthesis of NHC substituted scandium aminobenzyl complexes. The reactivity of [Sc(Bn)2(L)]2 with RX substrates (R = alkyl) is discussed in detail; depending on the nature of the alkyl group, these reactions can allow formation of R–Bn , the result of carbon-carbon coupling. The complex [Sc(Bn)(L)Cl]2 has been isolated from these reactions and is structurally characterised. The reactivity of [Sc(Bn)2(L)]2 towards C–H bonds is explored and attempts to prepare NHC substituted scandium hydrides are described. Comparisons of the relative stability and reactivity of [Sc(Bn)2(L)]2 and [Sc(Bn)3(thf)3] are drawn. Chapter four documents the synthesis and characterisation of [Sc(Odtbp)2(L)] (Odtbp = 2,6-di-tert-butylphenoxide), [Sc(Odtbp)(L)2], and the samarium analogue [Sm(Odtbp)(L)2]. The reactivity of these complexes towards various small molecules is described. The chapter also details attempts to prepare the cationic scandium complexes [Sc(L)2][Bort] (Bort = bis[3,3',5,5'-tetra-(tert-butyl)-2,2-diphenolato]borate) and [Sc(L)2][B(Ph)4]. Chapter five provides overall conclusions to the work presented in this thesis. Chapter six contains all experimental and characterising data for the complexes and reactions detailed in this work.

Ce travail de thèse est consacré à l’étude de la réactivité du spirosilane de Martin, une molécule présentant des propriétés intéressantes notamment en présence de bases de Lewis, qui a trouvé des applications diverses comme la détection d’ions fluorures. En ce qui nous concerne, nous avons choisi d’étudier l’interaction de ce dérivé du silicium avec des bases de Lewis neutres fortes tels que les Carbènes N-Hétérocycliques (NHC) qui ont été beaucoup utilisés pour stabiliser les espèces de basse valence des éléments du bloc p. Alors que les NHC sont connus pour former avec les chlorosilanes des adduits pentacoordinés stables, aucun exemple avec des silanes non halogénés n’avaient été décrits avant notre étude. Nous avons montré qu’en fonction de l’encombrement stérique des NHC étudiés, ils forment avec le spirosilane de Martin des adduits de Lewis normaux et anormaux stables. Les propriétés « Paires de Lewis Frustrées » (FLP) du spirosilane avec des NHC encombrés ont été examinées ainsi que l’accès à des nouveaux ligands NHC anioniques portant un motif siliconate
This thesis work is focused on the reactivity of Martin’s Spirosilane, a molecule that displays some interesting properties in particular with different Lewis base, founding some interesting application such us fluoride sensor. In our study, we have chosen N-Heterocyclic Carbene (NHC) because they are well known for stabilising low-valence states of p-block elements or for disclosing new reactivities. Besides, NHC are known to form relatively stable adducts with tetravalent halosilanes and also to stabilise silicon(0) species through potassium graphite reductions, but, to the best of our knowledge, no pentacoordinated NHC-adducts with a non-halogenated silane partner has been synthesised to date.The first part of my PhD was focused on the update of Martin’s spirosilane synthesis due to some problem of reproducibility with the known procedure. Once obtained the product, it was begun the investigation of the interaction with different NHC carbene that afforded the corresponding adducts that were fully characterised. The different adducts were then studied as potential Frustrated Lewis Pair and as precursors of anionic-type ligands for the metal's coordination

This thesis describes the preparation of a various NHC ligands with five and six-membered rings, different fused aromatic cores and the subsequent synthetic development of their complexation of with Ag, Ru and Pd. The investigation and preparation of these compunds was with the intention of exploring their chemical and physical properties. The synthesis of the NHC ligands proved to be difficult, but analysis and characterisation of the side products from the reactions helped to establish successful synthetic methodologies. In both the five and six-membered research conducted a common attribute was established of a pyrid-2-yl substituent at the 1 position or both the 1 and 3 positions, thus providing new NHC ligands to investigate. The organic syntheis of the research focused on two NHC ligand functionalites, five and six membered rings. The six memerbered rings focused on 1H-perimidine as the core unit and the design of both bidentate and tridentate NHC ligands to mimic the structural binding relationship of 2,2’- bipyridine (bpy) and 2,2’:6’2”-terpyridine (tpy) with various metal salts. The synthesis of the bpy analogues was achieved in good overall yields with minimal synthetic challenges. However, the tpy analogue was unable to be realised due to time constraints and problems associated with its synthesis. The five membered NHC ligands synthesised were to investigate the physical effects of systematically increasing the size of its aromatic core. The main focus of the research was on the phenanthrene imidazole NHC ligands. This was investigated due to the minimal research that has been conducted on this core unit and NHC-complexes. Synthesis of the two-bidentate NHC ligands with an imidazole head group and fused phenanthrene backbone were completed, but this was with a picolyl substituent at the 1 position rather than the pyrid-2-yl substituent. This failure to isolate this product was attributed to steric influences. Pyrene-fused-imidazole NHC ligands were also investigated and pyrene offers a NHC core that hasn’t been investigated previously. However, synthesis and isolation of the NHC ligands proved to be difficult and was associated with the poor solubility of the NHC ligands. The organometallic NHC synthesis was studied extensively with the main focus on establishing appropriate conditions to give a NHC complex. The main metal investigated was ruthenium as subsequent NHC complexes were expected to have potentially interesting properties such as luminescence. The synthesis of a perimidine and phenanthrene NHC ruthenium complexes have not been isolated before, thus giving new NHC complexes. Many different synthetic routes were attempted to synthesise a perimidine NHC ruthenium complex. However, this proved difficult due to associated higher reactivity of the carbene carbon of perimidine with a new side product as a result of this research. The phenanthrene NHC complex synthesis suffered due to time constraints but potential methodology for their synthesis is stated.

N-heterocyclic carbenes (NHCs) have emerged as appropriate replacements for phosphines to synthesized highly active metal complexes in homogeneous catalysis. The advantages of NHCs over phosphines include ease of handling, minimal toxicity and powerful electron donating properties. They bind transition metals with no need of back-donation and yield complexes with enhanced stability. The ability of NHCs to bind all metals from the periodic table, in low and high oxidation states, creates an unprecedented opportunity for the design of new complexes. This dissertation is dedicated to the synthesis of well-defined organosilver and organogold complexes bearing NHC ligands. In addition, two short chapters describe briefly the synthesis of NHC acetylacetonate palladium(II) complexes, and the use of NHC ruthenium(II) indenylidene complexes in ring opening metathesis polymerization reactions. New silver(I) and gold(I) halide mono-NHC complexes are synthesized, structurally characterized, and compared to other existing silver(I) and gold(I) complexes. The silver cation trends to form thermodynamically favored bis-NHC complexes and the success for the synthesis of kinetically favored silver(I) mono-NHC complexes is strongly dependant of the carbene, the solvent, and the silver salts used. In contrast, the synthesis of gold(I) mono-NHC complexes appears easier specially by transmetalation starting from silver(I) NHC complexes. The reactivity of both metals NHC complexes is directly related to the strength of the metal-carbene bond. The gold(I) cation firmly bound to the carbene, undergoes oxidative addition with halogens to afford gold(III) NHC complexes, or dehalogenation in presence of inorganic silver salts to afford cationic gold(I) mono-NHC complexes in coordinating solvent. The coordinating solvent can be replaced by a neutral or anionic group to yield gold(I) NHC complexes with unusual ligands such as olefins, pyridines, sugars. In contrast, the silver(I) cation is weakly bound to the carbene, and silver(I) NHCs decompose in presence of halogens or inorganic silver salts. In conclusion the synthesis of the NHC complexes emphasizes deeply the similarities and the differences between silver and gold chemistries. While NHCs ideally stabilize gold(I) and(III) complexes, phosphines appears to be a more promising alternative than NHCs for the chemistry of silver.

Cette dissertation est dédiée à la synthèse de complexes organométalliques d’argent et d’or portant des ligands NHC et ayant une structure bien définie. Par ailleurs, deux courts chapitres traitent brièvement de la synthèse de complexes NHC d’acétylacétonate de palladium(II), et de l’utilisation de complexes NHC d’indénylidène de ruthénium(II) pour catalyser des réactions de polymérisation par métathèse par ouverture de cycle (ROMP). L’or(I) qui est fortement complexé au carbène subit une réaction d’addition oxydante en présence d’halogènes pour donner des complexes NHC d’or(III), ou encore une déshalogénation en présence de sels d’argent inorganiques pour donner des complexes mono-NHC cationiques d’or(I) dans des solvants coordinants. Ce solvant coordinant peut être remplacé par un ligand neutre ou anionique et générer des complexes NHC d’or(I) avec des ligands peu courants tels que des oléfines, des pyridines, ou même des sucres. En revanche, le cation argent(I) est faiblement complexé au carbène, et les complexes NHC d’argent(I) se décomposent en présence d’halogènes ou de sels d’argent inorganiques
This dissertation is dedicated to the synthesis of well-defined organosilver and organogold complexes bearing NHC ligands. In addition, two short chapters describe briefly the synthesis of NHC acetylacetonate palladium(II) complexes, and the use of NHC ruthenium(II) indenylidene complexes in ring opening metathesis polymerization reactions. New silver(I) and gold(I) halide mono-NHC complexes are synthesized, structurally characterized, and compared to other existing silver(I) and gold(I) complexes. The gold(I) cation firmly bound to the carbene, undergoes oxidative addition with halogens to afford gold(III) NHC complexes, or dehalogenation in presence of inorganic silver salts to afford cationic gold(I) mono-NHC complexes in coordinating solvent. The coordinating solvent can be replaced by a neutral or anionic group to yield gold(I) NHC complexes with unusual ligands such as olefins, pyridines, sugars. In contrast, the silver(I) cation is weakly bound to the carbene, and silver(I) NHCs decompose in presence of halogens or inorganic silver salts

Reproduction de : Thèse de doctorat : chimie et physico-chimie des polymères : Le Mans : 2007. Reproduction de : Thèse de doctorat : chimie : La Nouvelle-Orléans : 2007.
Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre.

L'objectif de cette thèse a été de mettre au point l'introduction d'azoles en meso d'une porphyrine par couplage d'Ullmann; Divers azoles ont pu être introduit par cette méthode avec de bons rendements, par formation d'une liaison carbone-azote. il a même été possible avec certains azotes de réaliser des doubles couplages d'Ullmann, conduisant ainsi à des 5.15-diazolyle-porphyrines. De plus, ces même conditions réactionnelles ont été utilisées pour introduire un ou deux dérivés donneurs d'électrons (carbazole, phénoxazine, phénothiazine). L'introduction d'imidazole, de triazole et de benzimidazole en meso a permis, après alkylation, d'obtenir des précurseurs de carbènes N-hétérocycles (NHC). La coordination de deux équivalents de NHC sur un sel de palladium conduit à un dimère de porphyrines via coordination exocyclique. La géométrie de coordination trans-anti autour du palladium a été confirmée par l'obtention de la structure radiocristallographique de deux complexes. Les études par électrochimie de ces complexes ont révélé une communication interporphyrinique à l'état fondamental, mise en évidence par une succession de quatre vagues monoélectroniques en oxydation.

Lo scopo del seguente lavoro di tesi è la sintesi e lo studio di nuovi leganti chirali N-eterociclici ad anello espanso derivanti dal diacido canforico. Lo sviluppo di nuovi leganti chirali nasce dalla possibilità di utilizzo in catalisi enantioselettiva. Questa tipologia di leganti sono facilmente sintetizzati dal diacido canforico utilizzando diverse vie di sintesi. La via di sintesi utilizzata permette di ottenere facilmente una funzionalizzazione asimmetrica. Il legante è stato studiato nella sintesi di un nuovo complesso chirale di Pd(II) utilizzando diverse condizioni di reazione. Inoltre, sono state studiate numerose vie di sintesi per nuovi leganti utilizzando i precursori dei leganti e due diversi epossidi. The aim of my training period has been the synthesis of new chiral N-heterocyclic carbene precursors starting from camphoric acid. The development of new chiral ligands starts from their possible use in new catalytic systems for enantioselective transformations. These kinds of ligands are easily synthetized from camphoric acid following different strategies. The synthetic pathway used makes simple the asymmetric functionalization. The ligand was employed in the synthesis of a new complex of Pd(II) in different conditions. In addition, numerous synthetic pathways have been investigated for new ligands using their precursors and two different epoxides.

Les carbènes N-hétérocycliques (NHC) sont connus pour être de bons ligands des métaux de transition (TM). Dans ce manuscrit, le premier chapitre est consacré une présentation non exhaustive des différentes approches qui ont été utilisées dans la littérature pour le design de NHCs chiraux efficaces en catalyse enantiosélective. Au début du deuxième chapitre, le nouveau concept est présenté. Celui-ci repose sur la formation d’un axe de chiralité qui est créé lors de la coordination du ligand NHC à un métal de transition. Ce chapitre est consacré à la synthèse de complexes possédant une symétrie C1. Différents sels d’imidazolium, précurseurs des NHCs, ont été synthétisés et utilisé pour former des complexes palladium. Ils ont été sous forme énantiopure par HPLC chirale à l’échelle préparative. Ces complexes ont fait l’objet d’études concernant leurs propriétés chiroptiques et leurs barrières de rotation avant d’être testé en catalyse. Le concept a été ensuite étendu pour la synthèse de complexes d’or et de cuivre. Ces derniers se sont avérés être intéressants car non seulement ils ont permis d’obtenir de bons excès énantiomériques en catalyse mais leurs utilisations comme agent de transfert de ligands NHC a permis de proposer un mécanisme pour le procédé de transmétallation. Le troisième chapitre fait état des travaux qui ont été réalisés sur la préparation de complexes chiraux NHC-TM possédant une symétrie C2. Différents sels d’imidazolium symétriques ont été synthétisés et utilisés pour former des complexes de palladium. Les versions homochirales de ces complexes se sont avérées être d’excellents catalyseurs chiraux pour la réaction l’α-arylation d’amides (jusqu’à 98% ee)
N-heterocyclic carbenes (NHC) are recognized to be excellent ligands towards transition metals ™. In this manuscript, the first chapter is dedicated to a non-exhaustive presentation of the various approaches of the literature which have been used to design chiral NHCs efficient in enantioselective catalysis. As a prelude of the second chapter, the new concept lies on the formation of an axis of chirality during the coordination between the NHC ligand and the transition metal. This chapter is dedicated to the synthesis of complexes with a C1 symmetry. Various imidazolium salts, have been synthesized and then used to generate palladium complexes. These complexes have been obtained in a enantiopurically form thanks to a chiral HLPC resolution at a preparative scale. These homochiral complexes were firstly subjected to studies aiming the investigation of their chiroptic properties and the determination of their rotation barriers values. The concept was then successfully extended to the synthesis of gold- and copper-based complexes. Homochiral copper-NHC complexes were found of particular importance since their applications in catalysis allowed to reach good enantioinductions and as NHC transfer reagents brought some experimental proofs on the transmetalation process. The third chapter disclosed the works that have been done on the preparation of heterochiral NHC-TM complexes possessing a C2 symmetry. Various symmetric imidazolium salts have been synthesized and then used to form the corresponding palladium-based complexes. Homochiral complexes were found displaying good activities for α-arylation of amides and excellent enantioselectivities (up to 98% ee)

Des poly(liquides ioniques) (PILs) arrangés sous la forme de copolymères aléatoires ont été développés avec des architectures telle que ce des nanoparticules à chaine unique ou bien sous la forme de (macro)gels. Ces différentes systèmes ont été employés comme précurseurs de carbènes N-heterocycliques (NHC)s à des fins de catalyses organiques. L’introduction d’anions relativement basiques dans des unités PIL dérives d’imidazolium permet la génération in situ des NHCs actifs pour la catalyse. D’abord, le développement de (macro)gel base sur des unités PIL réactives représente l’étude préliminaire pour la compréhension et analyse de performance catalytique a l’échelé macroscopique. Cette étude a permit cibler des réaction model ainsi comme des conditions et des standards pour établir un système de référence tout au long de cette thèse. Ensuite, ce gel a servi comme base pour développer des nanogels connues comme nanoparticules composées d‘une chaine unique polymère repliée sur elle-même (SCNP en anglais). Ces SCNPs ont été spécialement conçues base sur la mouillabilité des PILs et ont été obtenues par polymérisation contrôlée (méthode RAFT). Dans le premier cas, la nature ionique des precatalyseur NHC a été exploite en promouvant l’interaction entre les dérives d’imidazolium avec des anions basiques supportes dans les polymère en formant un SCNP ioniquement réticulée. Deuxièmement, les propriétés termolatentes des précurseurs de NHC a été mis en valeur en compatibilisant des substrats et precatalyseurs sur la même chaine des polymère en promouvant le repliement des chaines en condensant les substrats sous l’application de chaleur. Finalement, la capabilité intrinsèque des poly(NHC)s pour actuer comme poly-ligands a été démontre de manière novatrice en formant des SCNPs par une réaction de complexation organométallique a l’aide d’un sel d’argent. Dans tout les différentes support polymériques, des aspectes relie aux performances catalytiques ont été mis en avance comme le recyclage du catalyseur, des effet de confinement, la facilite pour augmenter l’echele de synthese des nanoreacteurs, la versatilite des NHC catalyseurs et l’adaptation de different systems pour manipuler ces especes polycarbeniques de une manière simple et efficace
Random copolymers based on poly(ionic liquids) have been developed under different architectures such as single chain nanoparticles (SCNPs) or as (macro)gels. Those different systems have been employed as N-heterocyclic carbenes (NHCs) precurors to be used as organocatalysts. The incorporation of relatively basic counteranions in PIL units derived from imidazolium moieties allows the in situ generation of active NHC species for catalysis. Firstly, a reactive PIL based (macro)gel represents the preliminary study to better understand and analyse the catalytic performance in the macroscale. This study has permitted the identification of suitable model reactions as well as conditions and standards, becoming a reference system all along this thesis. Moreover, this (macro)gel has served as a base for the further development of more sophisticated nanogels known as single chain nanoparticles (aka SCNPs). These SCNPs have specially been designed based on their PIL tunability and synthesised by reversible additions fragmentation chain transfer (RAFT) polymerisation. In first place, the ionic nature of the NHC precatalyst was exploited by triggering the interaction between imidazolium derivatives and basic anions supported in the polymer leading to a ionically cross-linked SCNP. Secondly, the thermolatent properties of NHC precursors was harnessed by proving the compatibility of both substrates and precatalyst supported on the same polymer chain and triggering the folding by condensing the substrates by the simple application of heat. Finally, the intrinsic capacity of poly(NHC)s to act as poly-ligands was innovatively demonstrated by forming SCNPs after organometallic complexation using a silver salt. Overall, the different polymeric supports have served to highlight different aspects related to the catalytic performance of supported catalysts such as recycling, confinement effect, nanoreactor scaling up processes, NHC catalysts versatility as well as the adaptability of these systems for enabling and easy and efficient handling and storage

Chapter one is an introduction, outlining the structure and bonding of N-heterocyclic carbenes (NHCs). It then goes on to give examples of f -metal NHC complexes and describes any reactivity or catalytic activity. Chapter two describes the synthesis of the transition metal NHC complexes [Fe (LMes)2] 3 and [Co(LMes)2] 4 (LMes = OCMe2 CH2(1-C{NCH2CH2NMes})). The heterobimetallic complexes [(LMes)Fe(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(Si Me3)2)2] 5 and [(LMes)Co(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(SiMe3)2)2] 6 were prepared from the reaction between [({Me3Si}2N)2U(NSiMe3SiMe2CH2)] and 3 or 4, respectively. Complex 5 was also synthesised by the reaction between 3 and [U(N{SiMe3}2)2]. The diamagnetic analogue [(LMes)Zn(μ-LMes)Th(μ-{N(SiMe3)Si (Me)2CH2})(N(SiMe3)2)2] 9 was prepared from the reaction between [Zn(LMes)2] and [({SiMe3}2N)2Th(NSiMe3SiMe2CH2)]. The reactivity of 5 is discussed. When 5 was reacted with 2,6-dimethylphenyl isocyanide, [({SiMe3}2N)2U{N(SiMe3)Si(Me2)C(CH2)N(2,6−Me−C6H3)}] 8 was isolated. The reaction with CO resulted in the formation of [({Me3Si}2N)2U{N(SiMe3) Si(Me2)C(CH2)CO}]. 5 showed no reactivity with azides, boranes or m-chloroperbenzoic acid and decomposed when exposed to H2, CO2 or KC8. The reaction between 6 and 2,6-di-tert-butylphenol formed the previously reported monometallic complex [({SiMe3}2N)2U(OC6H3tBu2)]. The serendipitous synthesis of the iron ate complex [Na(Fe{LMes}2)2]+ [Fe(ArO)3]– 10 (Ar = 2,6-tBu-C6H3) is also described. Chapter three describes the synthesis of the aryloxide complexes [HC(3-tBu-5-Me- C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Co(THF)]2 11 and [HC(3- tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Zn(THF)n] 13. Treatment of 11 with pyridine N-oxide resulted in the formation of the pyridine-Noxide adduct [HC(3-tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2 O)Co(C5H5NO)]2 12. When 11 was treated with [({Me3Si}2N)2U(NSiMe3SiMe2C H2)], no reaction occured at room temperature but at 80◦C decomposition occured. When 11 was treated with [(NH4)2Ce(NO3)6] the protonated proligand HC(3-tBu- 5-Me-C6H2OH)3 reformed. The reactivity of 11 with [({Me3Si}2N)Ce(LiPr)2] is also discussed. Chapter three also discusses the preparation of the heterobimetallic complex [HC(3- tBu-5-Me-C6H2O)2-μ-(3-tBu-5-Me-C6H2O)KCo]2 14 and the salt-elimination chemistry of the complex. The preparation of [HC(3-tBu-5-Me-C6H2O)2-μ-(3-tBu-5- Me-C6H2O)KZn]2 15 is also outlined. Chapter four discusses the reactivity of [Ce(LiPr)3] (Li Pr =OCMe2CH2(1-C{NCHC HNiPr})) in C-H and N-H activation and as a catalyst for organic reactions. [Ce(LiPr)3] displayed no C-H activation chemistry with RC−−−CH (R = SiMe3, Ph, tBu), diphenyl acetone, indene or fluorene. [Ce(LiPr)3] also showed no N-H activation chemistry with pyrrole or indole, nor did it react with the lignin model compound PhOCH2Ph. When treated with an excess of benzyl chloride, [Ce(LiPr)3] underwent ligand decomposition to form the acylazolium chloride [(C6H5C(O))OCMe2CH2(1-C(C6H5C (O)){NCHCHNiPr})]Cl 18 and CeCl3. When [Ce(LiPr)3] was added to a mixture of benzaldehyde and benzyl chloride, as a coupling catalyst, the complex decomposed. [Ce(LiPr)4] was tested as a catalyst from the benzoin condensation and for the coupling of benzalehyde and benzyl chloride, however, it resulted in the decomposition of [Ce(LiPr)4]. Chapter four also outlines the catalytic activity of 3. The complex showed no reactivity as a hydrogenation catalyst towards alkenes, aldehydes or ketones but did display reactivity as a hydroboration catalyst for alkenes, aldehydes or ketones. Chapter five presents the conclusions for chapters two to four. The final chapter contains the experimental details from the previous chapters.

Thesis (M.S.)--University of New Orleans, 2004.
Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Chemistry."--Thesis t.p. Vita. Includes bibliographical references.

The work described herein focuses on the synthesis and characterisation of copper(I) complexes bearing N-heterocyclic carbene (NHC) ligands, their use in catalysis as well as organometallic synthesis and related reaction mechanisms. Two classes of complexes were considered: neutral NHC-Cu(I) species and their cationic analogues. Concerning the former, initial efforts were focused on the development of a general and straightforward synthetic methodology towards complexes of the type [Cu(X)(NHC)] (X = Cl, Br, I). More than 10 NHC-Cu(I) species were synthesised in high yields under mild conditions, in air and using technical grade solvents. These complexes exhibited interesting activity in the catalytic dehydrogenation of formic acid/amine adducts proving in three times more efficiency than the copper salts previously employed in such a reaction. Hydroxide- and tert-butoxide analogues showed to be efficient catalysts in the N-methylation of amines with CO₂ as carbon source, and in the dehydrogenative coupling of silanes and carboxylic acids. Experimental and computational work were carried out in order to elucidate the mechanism of these transformations. Regarding the use of these species in organometallic synthesis, homo- and heteroleptic bis-NHC-Cu(I) complexes were employed as carbene transfer reagents to other transition metals. Aside from well-known cationic gold(I) species, two novel palladium(II) analogues were isolated and fully characterised.

Chapter one is an introduction to the less common coordination and oxidation chemistry of palladium; complexes containing Pd-OR, Pd-NR2 and those in the oxidation states of +IV. An outline of PdII/IV catalysed ligand-directed oxidative functionalisation is also included. Chapter two covers the design and synthesis of a range of tethered N-heterocyclic carbene (NHC) complexes of Pd. In addition, the syntheses of a number of new tethered NHC ligands are described. The use of Density Functional Theory (DFT) to model the complexes in this thesis was explored. Chapter three describes the synthesis and characterisation of PdIV halide complexes. The relevance of these compounds to PdII/IV catalysed ligand-directed oxidative functionalisation is explored. DFT was used to probe the reaction pathway for N-bromosuccinimide and iodobenzene dichloride. Chapter four examines reactions with oxidants used to form C-O and C-C bonds. The reaction pathway for iodobenzene diacetate was investigated using DFT. Chapter five contains experimental details and characterising data for the compounds reported.

The use of Au-NHC complexes in homogenous gold catalysis has become very popular during the last 10 years. The work described in this thesis represents a modest contribution towards a better understanding of the reactivity of these fascinating complexes and the intermediate species involved during gold-catalysed transformations. There are two main themes that permeate the following chapters: a) synthesis and reactivity studies of monoaurated species and b) synthesis and reactivity studies of diaurated species. The main motivation for the work presented herein was to develop more efficient synthetic routes towards a series of gold complexes, such as [Au(NHC)Cl], [Au(NHC)(OH)] and [{Au(IPr)}₂(μ-OH)][X], in order to be able to further explore their reactivity. Chapter 2 constitutes the first approach that I had with the chemistry of Au-NHC complexes, and describes our efforts to evaluate how the use of a highly sterically demanding NHC ligand affects gold-catalysed transformations. Chapters 3 and 4 explore alternative, more efficient synthetic routes towards known Au- NHC complexes. For example, a new, highly robust protocol has been developed for the synthesis of [Au(NHC)X] (X = Cl, Br, I) complexes, which are the starting materials to prepare a wide range of Au-NHC based species. Moreover, as a result of our investigations it has been possible to isolate a series of [Au(NHC)(OH)] species and to gain some insight into the stability of these complexes. Chapters 5 and 6 describe the synthesis and applications of digold hydroxide species [{Au(IPr)}₂(μ-OH)][X] in a series of catalytic and stoichiometric transformations. For example, they have been used as silver-free catalysts for water-inclusive gold-catalysed transformations or to access key intermediates in gold catalysis, such as gem-diaurated and σ,π-digold-acetylide species. Finally, Chapter 7 combines what we learned about the reactivity of [{Au(IPr)}₂(μ- OH)][X] in order to develop for the first time a gold-catalysed transformation where two gold centres independently react with two substrate molecules to catalyse the hydrophenoxylation of alkynes.

Scopo del presente lavoro di tesi è la sintesi di un complesso di manganese contenente un legante bis N-eterociclico e la sua applicazione come catalizzatore nelle reazioni di idrosililazione e idroborazione di doppi e tripli legami. I composti organici sililati e borilati sono importanti prodotti intermedi in diversi settori della chimica fine grazie alla loro stabilità e alla loro capacità di essere ampiamente funzionalizzati. Idroborazione e idrosililazione, grazie allo sviluppo di catalizzatori appositi, permettono di ottenere questi composti riducendo coprodotti, sottoprodotti e condizioni operative estreme. Generalmente i catalizzatori impiegati industrialmente contengono metalli di transizione costosi, rari e non biocompatibili. Per questo motivo negli ultimi anni la ricerca si è concentrata sullo sviluppo di nuovi catalizzatori a base di metalli della prima serie di transizione tra cui il manganese, noto per essere abbondante sulla crosta terrestre, economico e biocompatibile. I composti N-eterociclici (NHC) sono una classe di leganti tra le più utilizzate poiché oltre a una grossa variabilità di caratteristiche steriche ed elettroniche, consentono di stabilizzare la specie metallica. I complessi N-eterociclici di manganese sono stati scarsamente applicati nelle reazioni di idroborazione e idrosililazione. Per questo motivo, il gruppo dove ho svolto il mio tirocinio si è dedicato a questo tipo di ricerca, sintetizzando e testando un complesso bis-NHC di manganese nell’idrosililazione di carbonili e solfossidi. Il mio lavoro si inserisce all’interno di questo ampio progetto, applicando nuovamente lo stesso complesso su una serie di substrati e reazioni differenti. In particolare, l’idrosililazione è stata applicata su alchini, alcheni e su carbonili (in questo caso attivando il complesso con la luce visibile). Inoltre, si è testata l’attività catalitica del complesso nell’idroborazione di alchini.

Die metallfreie Aktivierung des Treibhasgases SF6 unter Verwendung von elektronenreichen N-heterocyclischen Carbenen (NHCs) resultierte in der Bildung des jeweiligen 2,2- Difluorimidazolins und Imidazolin-2-thions bzw. 2,2-Difluorimidazolidins und Imidazolidin-2-thions. Die Reduktion der NHCs mit SF4 liefert dieselben Produkte. Im Abbau von SF5CF3 mit NHCs werden ebenfalls die zuvor genannten Produkte erhalten, wobei zusätzlich das entsprechende 2-Fluor-2-trifluormethylderivat gebildet wird. Exemplarisch wurde 1,3-Dimesityl-2,2-difluorimidazolidin [SIMes(F)2] als Fluorierungsreagenz von Aldehyden unter Bildung von Acylfluoriden sowie als Deoxyfluorierungsreagenz eingesetzt. In einem one-pot-Prozess kann zudem die Aktivierung von SF6 mit der Deoxyfluorierung von 1-Oktanol zu 1-Fluoroktan kombiniert werden. Des Weiteren konnte 1,3-Dimesityl-2-fluor-2-trifluormethylimidazolidin [SIMes(F)(CF3)] zur Trifluormethylierung von Me3SiCl und Arenen eingesetzt werden. Der Einsatz von SIMes(F)2 ermöglicht die Darstellung von des NHC-stabilisierten Al(III)- Fluorids [(SIMes)Al(F)(Me)2] durch Monofluorierung von [(SIMes)AlMe3]. Durch Variation des Fluorierungsmittels (SF4, SF6, Me3SnF) kann ein höherer Fluorierungsgrad erreicht und [(SIMes)Al(F)3] synthetisiert werden. Dieser Al-Komplex konnte durch Halogenaustausch mit Me3SiCl in [(SIMes)Al(Cl)3] überführt werden.
The metal-free activation of the greenhouse gas SF6 using electron-rich N-heterocyclic carbenes (NHCs) furnished 2,2-difluoroimidazolines or 2,2-difluoroimidazolidines and 2- thio derivatives of the NHC precursors. The NHCs can reduce SF4 as well to give same products. A complete degradation of an another greenhouse gas SF5CF3 also gave 2,2- difluoro- and 2-thio- derivatives along with the 2-fluoro-2-trifluoromethyl- derivative of the NHC precursors. The 1,3-dimesityl-2,2-difluoroimidazolidine [SIMes(F)2] was taken as an exemplary substrate to be applied in deoxyfluorination reactions and acyl fluorination of aldehydes via aldehydic C(sp2)–H bond activation. Additionally, the activation of SF6 and the fluorination of 1-octanol into 1-fluorooctane can be coupled in a one-pot process. Furthermore, trifluoromethylation of Me3SiCl and arenes was observed with the 1,3-dimesityl-2-fluoro-2- trifluoromethylimidazolidine [SIMes(F)(CF3)]. SIMes(F)2 was also used for the fluorination of complex [(SIMes)AlMe3] to synthesize the NHC stabilized Al(III) fluoride [(SIMes)Al(F)(Me)2]. Various alternative reaction routes have been developed to synthesize the NHC stabilized Al(III) fluorides [(SIMes)Al(F)(Me)2] and [(SIMes)Al(F)3] through the fluorination of [(SIMes)AlMe3] with SF4, SF6 and Me3SnF. The complex [(SIMes)Al(F)3] was successfully employed for a F/Cl exchange reaction by treating it with Me3SiCl to yield [(SIMes)Al(Cl)3] and Me3SiF.

La réaction d'hydrogénation des alcènes est une réaction clé dans de nombreux procédés industriels permettant la production de produits de commodité et de spécialité. D’importants efforts de recherche ont donc été réalisés pour développer des systèmes catalytiques de plus en plus productifs et sélectifs. Parmi les nombreux catalyseurs homogènes et hétérogènes développés à ce jour, les complexes organométalliques d’Iridium(I), très prometteurs, ont été préparés depuis la découverte du catalyseur de Crabtree, [Ir(COD)(py)(PCy3)]BF4, pour répondre à des problèmes de sélectivité dans l'hydrogénation asymétrique ou celle d’oléfines tétrasubstituées fortement encombrées en conditions homogènes. Cependant, l'utilisation industrielle de ce complexe organométallique d’Ir (I) est limité par sa décomposition rapide en solution, qui conduit à la formation de complexes polynucléaires (hydrures pontés d'Iridium) très stables et inactifs en catalyse. Le but de ce travail de thèse a été de développer des matériaux catalytiques contenant des complexes Ir(NHC) isolés à la surface d’une silice contenant des fonctionnalités imidazolium parfaitement distribuées le long de ses canaux poreux. L'isolement des unités Ir(I) sur le support de silice devrait permettre d’empêcher les processus bimoléculaires de désactivation et faciliter la récupération du catalyseur. La préparation des matériaux catalytiques cible se fait grâce a la transformation des unités imidazolium contenues dans le matériau de départ en carbenes d’argent N-hétérocycliques, qui sont ensuite transmétallés en carbènes d’iridium avec le complexe [Ir(COD)Cl]2. Les matériaux obtenus ont été caractérisés par diverses techniques, notamment une technique de RMN très avancée : la RMN de l’état solide utilisant la polarisation nucléaire dynamique. Ceci a permis de mieux comprendre la structure moléculaire des sites de surface iridiés. Les performances catalytiques des complexes Ir-NHC supportés ont été testées dans réaction d’hydrogénation des alcènes et comparées à celles de leurs homologues homogènes. Divers substrats oléfiniques et différentes conditions de réaction ont été testées. Les résultats montrent que le catalyseur supporté est beaucoup plus stable et 50 fois plus actif en terme de vitesse et de productivité. Cette approche a été étendue au développement de catalyseurs d’iridium supportés sur polymère. Le support choisi a été un polyéthylene téléchélique contenant des fonctionnalités iodées terminales. Le solide obtenu après incorporation de l’iridium a été caractérisé par RMN et spectrométrie de masse (MALDITOF). Les performances catalytique de ce nouveau système ont été elles aussi comparées a celles de complexes homologues en solution
Alkene hydrogenation is a key in many bulk and fine chemicals production processes. Major efforts were therefore directed towards the preparation of ever more productive and selective catalysts. Among the large number of homogeneous and heterogeneous catalysts, promising Iridium (I) organometallic complexes were prepared since the discovery of the well-known Crabtree’s catalyst, [Ir(COD)(py)(PCy3)]BF4, to address selectivity issues in homogeneous asymmetric hydrogenation or hydrogenation of highly hindered tetrasubstituted olefins. However, the industrial use of Ir organometallic complexes as catalysts is limited by their fast decomposition leading to the formation of highly stable and inactive polynuclear iridium hydridebridged complexes. The goal of this PhD project was to elaborate supported Ir(I)-NHC catalytic material to prevent such bimolecular deactivation processes. The targeted supported Ir complexes were based on hybrid organic-inorganic material containing regularly distributed imidazolium units along the pore-channels of the silica framework. Beside the Ir-site isolation on the silica support, this catalytic system was also expected to ease catalyst recovery at the end of the hydrogenation. The preparation of the final systems relies on the preparation of supported silver carbenes first, and further transmetallation with an Ir-precursor, namely [Ir(COD)Cl]2. The materials were characterized by several techniques as for example advanced solid state NMR using Dynamic Nuclear Polarization to gain insight into the molecular structure of the Ir surface sites. Catalytic performances of the supported Ir-NHC complexes were tested in alkene hydrogenation and compared to those of homogeneous homologues. Several different substrates and reaction conditions were tested. The results showed that the supported catalyst was much more stable and 50 times more active in term of rate and productivity. A polymer supported Ir-complex was also elaborated using a telechelic polyethylene iodide as support. The polymeric materials were fully characterized by NMR and MALDI-TOF experiments and their catalytic performances were compared to those of molecular analogues and those of silica supported systems

Thesis advisor: Marc L. Snapper
Chapter 1. A Practical Synthesis of 3-Acyl Cyclobutanones by [2 + 2] Annulation. Mechanism and Utility of the Zn(II)-Catalyzed Condensation of alpha-Chloroenamines with Electron-Deficient Alkenes. We have developed a catalytic method for the synthesis of highly functionalized 3-acyl cyclobutanones which are useful building blocks for a variety of natural products. Methods for cyclobutanone synthesis have traditionally been limited to Lewis-acid promoted rearrangement of oxaspiropentanes or cyclizations of ketene and syntheses involving keteneiminium salts have required stoichiometric quantities of a Lewis acid. Furthermore, the mechanism for these types of cyclizations remains unknown. This portion of my research focused on an efficient, catalytic method for the synthesis of 3- acyl cyclobutanones and providing insight into the mechanism for cycloaddition. Chapter 2. Enantioselective Synthesis of Boron-Substituted Quaternary Carbons by NHC-Cu-Catalyzed Boronate Conjugate Additions to Unsaturated Carboxylic Esters, Ketones, or Thioesters. We have developed an enantioselective NHC-Cu-catalyzed conjugate addition of boronate esters to acyclic, trisubstituted alpha, beta-unsaturated carbonyl compounds. Enantioselective conjugate addition of a boronic acid pinacol ester through the use of bis(pinacolato)diboron [B2(pin)2,] to alpha, beta-unsaturated aliphatic and aryl esters promoted by 5 mol % of an NHC-Cu catalyst afforded tertiary beta-boryl carbonyls in high efficiency and enantioselectivity. Trisubstituted alpha, beta-unsaturated esters and thioesters were found to be reactive substrates in the presence of a stoichiometric quantity of methanol. Chapter 3. Metal-Free Catalytic C-Si Bond Formation in an Aqueous Medium and C-B Bond Formation in a Protic Medium. Enantioselective NHC-Catalyzed Silyl and Boryl Conjugate Additions to Cyclic and Acyclic alpha, beta-Unsaturated carbonyls. We have developed a method for enantioselective metal-free silyl conjugate additions through the use of dimethylphenylsilyl) boronic acid pinacol ester [PhMe2SiB(pin)] catalyzed by chiral N-heterocyclic carbenes (NHCs) in basic aqueous thf. Optimization of metal-free conditions demonstrated that the presence of water was required for high efficiency. alpha, beta-Unsaturated cyclic ketones and lactones were examined as substrates, and acyclic ketones, esters and aldehydes were also competent substrates for silyl conjugate addition. beta-Silyl carbonyls were isolated in up to >98% yield and >98:2 er. Chapter 4. Elucidation of Mechanism for Enantioselective NHC-Catalyzed Silyl Conjugate Addition. We propose a catalytic cycle for NHC-catalyzed enantioselective silyl conjugate addition. Mechanistic studies of NHC-catalyzed enantioselective silyl conjugate additions are presented. Optimization of conditions for an inefficient alpha, beta-unsaturated electron-deficient ketone provided insight into the roles for dbu and water. Kinetic data indicate that conjugate addition is first order in PhMe2SiB(pin) and carbene, and DFT calculations support the formation of an NHC-silyl anion as a reactive intermediate in the catalytic cycle
Thesis (PhD) — Boston College, 2012
Discipline: Chemistry

With the blend of addressing issues of sustainable energy with the environmental worries regarding emission of greenhouse gases, there is a motivation to target the efficient chemical reduction of CO2. Re(I) integrated photosensitizers and catalysts, synthesized from commercially available ligands, are introduced with the selective CO2 reduction of formic acid, making for a unique class of Re(I) catalysts typically selective for CO as a reduction product. Furthermore, synthesized Zn(II) phosphino aminopyridine complexes are structurally and computationally characterized as well as observed to function as unprecedented electrocatalysts for the reduction of CO2 to formic acid and CO. Lastly, with the importance and popularity of N-heterocyclic carbenes (NHCs) as a class of ligands in the field of organometallic catalysis, six-membered perimidine based carbenes are further explored. Synthesis of a chelating pyridyl-perimidine NHC in addition to potential transition metal catalysts are also attempted.

Afin de développer des méthodes alternatives à l'activation de systèmes Pi en catalyse homogène par des métaux nobles coûteux et toxiques, nous nous sommes focalisés sur des complexes métalliques et plus particulièrement ceux de la colonne du group XIII. Cette thèse approche une contribution à ce champ d'études, et nous nous sommes particulièrement concentrés sur la chimie de gallium.Trois principaux aspects ont été étudiés dans ce manuscrit: la réactivité des halogénures de gallium(III), des complexes bien définis de gallium (III) portant carbènes N- hétérocycliques (NHCs), et leur activation de systèmes en catalyse.La thèse est divisée en trois chapitres. Le premier chapitre donne un aperçu des travaux effectués dans le domaine de la synthèse organique faisant intervenir des composés de gallium (III) , en se concentrant sur ​​leur utilisation en tant qu’ acides de Lewis et .Dans le deuxième chapitre, nous avons tenté d'exploiter le potentiel catalytique de GaCl3 dans une nouvelle réaction de cycloisomérisation/Friedel-Crafts en tandem. Une section dédiée à l'étude sur l’hydratation d’alcyne catalysée par GaCl3 est également fournie.Le troisième chapitre commence par une description de la synthèse d'une série de complexes de gallium (III) portant diverses NHCs comme ligands pour surmonter les limites des halogénures de gallium(III) en catalyse. Ensuite, des études de méthodologie sur le processus de tandem impliquant arenynes-1,6 avec les gallium(III) complexes neutres et cationiques ont été décrits. Une évaluation cinétique pour des catalyseurs, des divers substrats et l'influence de contreanions sont discutés. En outre, les efforts dans la version asymétrique de cette tandem transformation et des autres cyclisations sont également présentés.Le dernier chapitre reprend les résultats les plus importants obtenus dans la thèse. Et les orientations futures de la recherche sur l'utilisation des complexes NHC- gallium (III) sont discutées
Recently, in order to develop alternative activation methods for Pi-systems in homogeneous catalysis instead of employing expensive and toxic noble metal catalysts, first row transition metals and main group metal complexes have attracted great attention. This thesis is a contribution to it, and we focus on gallium chemistry. There are three main aspects dominating this thesis: gallium(III) halides, well-defined gallium(III) complexes bearing N-heterocyclic carbenes (NHCs), and -systems activation in catalysis.The thesis is divided into three chapters. Chapter I provides an overview of the field of organic synthesis involving gallium(III) compounds, focusing on their use as - or -Lewis acids.In Chapter II, we expose our attempts to exploit the catalytic potential of gallium(III) chloride in a novel tandem cycloisomerization/Friedel-Crafts reaction. A section dedicated to the study on GaCl3-catalyzed alkyne hydration is also provided.Chapter III begins with a description of the synthesis of a series of gallium(III) complexes bearing various NHCs as ligands in order to overcome the limitations of gallium(III) halides in catalysis. Next, methodology studies on the tandem process involving 1,6-arenynes with the neutral and cationic gallium(III) complexes are described. The evaluation of scission kinetics for catalysts, substrates variation and influence of counteranions are discussed. In addition, efforts towards the asymmetric version of this tandem transformation and some other cyclizations are also presented.The concluding chapter reiterates the most important results obtained in the body chapters of the thesis. To conclude, the future directions for the research on the use of the NHC-gallium(III) complexes are discussed

Le sujet de cette thèse porte sur l’étude de ligands hybrides incorporant un donneur carbène N-hétérocyclique (NHC). Les ligands phosphine-NHC construits sur le motif m-phénylène ont conduit à des complexes di- ou tétranucléaires d’Ag, Cu, Au et Ir, et à des complexes bimétalliques Ag/Cu et Ag/Ir par transmétallation sélective du site NHC. Dans le cas des ligands phosphino-picoline-NHC (PNC), la transmétallation des sels de Li ou K correspondants a permis d’isoler des complexes « pinceurs » dé-aromatisés du Cr, Fe et Co. La déprotonation du ligand bis(phosphinométhyl)pyridine (PNP) a été examinée, et les ligands dé-aromatisés mono- et bis-anioniques correspondants ont été utilisés dans des réactions de transmétallation vers le Cr(II) et Zr(IV). Différents modes de coordination des ligands dé-aromatisés, notamment une métallation de la position alpha-CHP, ont été observés. La substitution de la phosphine dans PNC par une fonction imine conduit à un ligand hybride « rédox non-innocent »
The purpose of this work is the synthesis and study of hybrid and potentially “pincer” ligands featuring an N-heterocyclic carbene (NHC) donor. The phosphine-NHC ligands based on the m-phenylene framework led to di- or tetranuclear Ag, Cu, Au and Ir complexes, and to bimetallic Ag/Cu and Ag/Ir complexes by selective transmetallation of the NHC. With the phosphino-picoline-NHC (PNC) ligands, transmetallation from the corresponding Li or K salts led to dearomatised Cr, Fe and Co “pincer” complexes. Deprotonation of the bis(phosphinomethyl)pyridine (PNP) ligand was also examined. The corresponding dearomatised mono- and bis-anionic ligands were isolated as Li or K salts and further used in transmetallation reactions towards Cr(II) and Zr(IV). Different coordination modes of the dearomatised ligands, including side-arm metallation, were observed. Substitution of the phosphine group in PNC by an imine donor led to a hybrid and “redox non-innocent” ligand

Initially, N-heterocyclic carbene ligands (NHCs) were considered ancillary ligands alternative to more classical two-electron donor ligands, phosphorous- (phosphines, phosphites, etc) and nitrogen-based (amines, imines, etc). Nowadays their role in organometallic chemistry is pivotal, and they found application in many different fields. The Cp*Ir(III)-based complexes gained interest during the past years because they may be employed as catalysts in many organic transformations, and the inclusion of a NHC ligand in the coordination sphere of the complex generally enhanced both its robustness and catalytic activity. An appealing catalytic application of Cp*Ir(III)-NHC complexes is the water oxidation reaction, that is the oxidative half-reaction of an overall process called “artificial photosynthesis”. This is a promising route to provide, in the future, the production of green and sustainable energy alternative to the consumption of fossil fuels, and to convert solar energy into chemical one. This PhD thesis is aimed to the study of iridium(III) complexes bearing di-(N-heterocyclic carbene) ligands (di-NHC), focusing either on the synthetic aspects and on the catalytic activity. Furthermore, the evaluation of the final steric and electronic properties of the complexes deriving by changes in the structure of the di-NHC ligand, will be addressed; the final aim is to find a relationship between the structure of the ligand and the properties and catalytic behavior of the complexes. In this regard, the catalytic activity will be evaluated mainly in water oxidation reaction, but also other organic transformations will be considered (transfer hydrogenation of ketones). The obtained results will be divided in four main chapters: i] Synthesis and characterization of a series of mononuclear Ir(III) di-NHC complexes (Chapter 2); ii] Water oxidation reaction catalyzed by the mononuclear Ir(III) di-NHC complexes synthesized in the frame of the present PhD project (Chapter 3); iii] Synthesis, characterization and catalytic activity of novel dinuclear di-NHC Ir(III) complexes (Chapter 4); iv] Reactivity and coordination properties of mono- and di-NHC ligands deriving from non-classical carbene units (Chapter 5). i] Synthesis and characterization of a series of mononuclear Ir(III) di-NHC complexes. A series of novel di-NHC iridium(III) complexes, having general formula [IrClCp*(di-NHC)](PF6), have been synthesized through the transmetalation of the di-NHC moiety from pre-formed, isolated and characterized dinuclear di-NHC silver(I) complexes. In the obtained Ir(III) complexes, the di-NHC ligand is coordinated to the metal centre in chelating fashion; this has been confirmed by the determination of the X-ray crystal structure of some complexes. The optimized synthetic protocol has been extended to several di-NHC ligands having different substituents at the nitrogen atoms and length of the alkyl bridging group. The effect of the substituents on the electron density, both on the metal and the carbene carbon, has been evaluated. ii] Water oxidation reaction catalyzed by the mononuclear Ir(III) di-NHC complexes. Some of the synthesized mononuclear di-NHC complexes have been successfully employed as catalysts for the water oxidation reaction in presence of Ce(IV) (as (NH4)2[Ce(NO3)6], referred also as CAN) as sacrificial oxidant. One of the most active complexes (complex 2) has been tested also in presence of NaIO4, showing activity comparable to that reported in literature for other Ir(III)-NHC complexes. The catalyst fate under turnover conditions has been investigated by detecting the evolving gas via GC-MS measurements, and a small amount of CO2 was observed concomitantly to the O2 evolution. The amount of CO2 derives probably from the oxidative degradation of the ligand set. Complex 2 has been also employed in a photo-induced process, coupled with a photosensitizer ([Ru(bpy)3]2+) and a sacrificial acceptor of electrons (S2O82-), exhibiting activity remarkably different than that observed employing IrCl3 under the same experimental conditions. IrCl3 is a well-known precursor of IrOx nanoparticles, so the observed difference may be considered a proof of the molecular nature of the catalyst. Further investigations allowed to detect, through EPR measurements, the formation of an Ir(IV) species, which is a plausible intermediate in the catalytic cycle, confirming the molecular nature of the employed catalyst. iii] Synthesis, characterization and catalytic activity of novel dinuclear di-NHC Ir(III) complexes. Novel dinuclear di-NHC Ir(III) complexes have been synthesized employing ligand precursors having a flexible and long bridging group between the carbene units or wingtip substituents with donor functionalities. Such complexes have been fully characterized, and in the case of complex 15 the crystal structure was also obtained. Such complexes have been successfully employed as catalysts in transfer hydrogenation of ketones: a scope of substrates has been spanned, and the tested complexes, especially complex 16, showed moderate to good activity. iv] Reactivity and coordination properties of mono- and di-NHC ligands derived from non-classical carbene units. In the frame of a collaboration with the group of Prof. C. J. (Kees) Elsevier (University of Amsterdam), the possibility to obtain Ir(III) complexes with six-membered saturated NHCs was investigated. Unfortunately, the results obtained in this regard are not satisfactory, probably for the intrinsic instability of the ligand precursors and/or of the corresponding free carbenes. Furthermore, the synthesis and the reactivity of mixed NHC-MIC ligands has been successfully carried out. The synthesis of the corresponding silver(I) complexes was performed and a preliminary optimization of the transmetalation reaction conditions has been accomplished, leading to the obtainment of a novel Ir(III) complex bearing a NHC-MIC ligand.
Inizialmente, i leganti carbenici N-eterociclici erano considerati leganti ancillari alternativi ai più classici leganti donatori bielettronici al fosforo (fosfine, fosfiti, etc) e all’azoto (ammine, immine, etc). Al giorno d’oggi il loro ruolo nella chimica organometallica è invece più centrale, e complessi con leganti carbenici trovano applicazione in diversi campi. Negli ultimi anni è aumentato l’interesse verso complessi basati sul frammento Cp*Ir(III), perché possono essere utilizzati come catalizzatori in numerose trasformazioni organiche; inoltre, l’introduzione di un legante NHC nella sfera di coordinazione del complesso dovrebbe aumentare sia la sua stabilità che la sua attività catalitica. Un’interessante applicazione catalitica dei complessi Cp*Ir(III)-NHC è la reazione di ossidazione dell’acqua, che è la semi-reazione di un processo più complesso chiamato “fotosintesi artificiale”. Nell’ambito del problema globale legato alla produzione e al consumo di energia, questo processo rappresenta una possibile alternativa all’utilizzo dei combustibili fossili e in futuro potrebbe permettere la produzione di energia in modo green e sostenibile per conversione dell’energia solare in energia chimica. Questa Tesi di Dottorato ha come scopo lo studio di complessi di iridio(III) aventi nella sfera di coordinazione leganti dicarbenici N-eterociclici (di-NHC) e sarà focalizzata sia sugli aspetti sintetici che sull’attività catalitica dei complessi ottenuti. Inoltre, verranno discusse le proprietà steriche ed elettroniche dei complessi in funzione dei cambiamenti apportati alla struttura dei leganti di-NHC utilizzati; lo scopo ultimo sarà quello di trovare una relazione tra la struttura del legante, le proprietà stereo-elettroniche del complesso e la sua attività catalitica. A questo proposito, l’attività catalitica sarà principalmente valutata nella reazione di ossidazione dell’acqua, ma verranno prese in esame anche altre trasformazioni organiche (transfer hydrogenation di chetoni) I risultati ottenuti verranno divisi in quattro capitoli principali: i] Sintesi e caratterizzazione di una serie di complessi mononucleari di Ir(III) aventi un legante di-NHC nella sfera di coordinazione (Capitolo 2); ii] Reazione di ossidazione di acqua catalizzata dai complessi mononucleari di-NHC di Ir(III) sintetizzati nell’ambito di questo progetto di Dottorato (Capitolo 3); iii] Sintesi, caratterizzazione e attività catalitica di nuovi complessi dinucleari di Ir(III) con leganti di-NHC (Capitolo 4); iv] Reattività e proprietà coordinanti di leganti mono- e dicarbenici derivanti da unità carbeniche non-classiche (Capitolo 5). i] Sintesi e caratterizzazione di una serie di complessi mononucleari di Ir(III) aventi un legante di-NHC nella sfera di coordinazione. Una serie di nuovi complessi mononucleari di iridio(III), aventi un legante di-NHC coordinato è stata sintetizzata mediante reazione di transmetallazione del legante di-NHC dai corrispondenti complessi di argento(I) pre-formati, isolati e caratterizzati. Nei complessi di Ir(III) ottenuti, il legante di-NHC è coordinato al centro metallico in modo chelato; ciò è stato confermato da tecniche di caratterizzazione in soluzione e, per alcuni complessi, dalla risoluzione ai raggi X della struttura. Il protocollo sintetico ottimizzato è stato esteso a leganti di-NHC caratterizzati da diversi sostituenti agli atomi di azoto e da gruppi alchilici a ponte tra le unità carbeniche di diversa lunghezza. E’ stato valutato inoltre l’effetto dei sostituenti sulla densità elettronica presente sul metallo e sul carbonio carbenico. ii] Reazione di ossidazione di acqua catalizzata dai complessi mononucleari di-NHC di Ir(III) sintetizzati nell’ambito di questo progetto di Dottorato Alcuni dei complessi mononucleari di Ir(III) sintetizzati sono stato impiegati con successo come catalizzatori nella reazione di ossidazione di acqua in presenza di Ce(IV) (come (NH4)2[Ce(NO3)6], abbreviato con CAN) come ossidante sacrificale. Uno dei complessi più attivi (complesso 2) è stato testato anche in presenza di NaIO4, esibendo un’attività catalitica comparabile con quella riportata in letteratura per complessi Ir(III)-NHC. L’evoluzione del catalizzatore durante la catalisi è stata valutata determinando i gas prodotti utilizzando un GC-MS ed è stata osservata la formazione di una piccola quantità di CO2, il cui sviluppo è concomitante all’evoluzione di O2. La quantità di CO2 osservata deriva probabilmente dalla degradazione ossidativa dei leganti nella sfera di coordinazione del complesso. Il complesso 2 è stato inoltre utilizzato in un processo foto-indotto, accoppiato a un fotosensibilizzatore ([Ru(bpy)3]2+) ed a un accettore sacrificale di elettroni (S2O82-), mostrando una buona attività catalitica. Il comportamento del complesso 2 (in termini ad esempio di curva di evoluzione dell’ossigeno, tempo di vita del catalizzatore, resa quantica,…) è inoltre diverso da quanto osservato utilizzando IrCl3 nelle stesse condizioni sperimentali. E’ ben noto che IrCl3 è un precursore di IrOx nanoparticellare, perciò la differenza osservata può essere considerata una prova circa la natura molecolare del catalizzatore. Ulteriori investigazioni hanno permesso di identificare, attraverso misure EPR, la formazione di specie di Ir(IV), che è un intermedio probabile del ciclo catalitico; l’insieme di questi dati sembra confermare la natura molecolare del catalizzatore utilizzato. iii] Sintesi, caratterizzazione e attività catalitica di nuovi complessi dinucleari di Ir(III) con leganti di-NHC Utilizzando precursori dei leganti con gruppi lunghi e flessibili a ponte tra le unità carbeniche o aventi sostituenti con una funzionalità donatrice, sono stati sintetizzati nuovi complessi dinucleari di-NHC di iridio(III). Tali complessi sono stati completamente caratterizzati e, nel caso del complesso 15, è stata inoltre risolta la struttura ai raggi X. Questi complessi sono stati impiegati con successo come catalizzatori nella reazione di transfer hydrogenation di chetoni: è stato eseguito uno screening di substrati e i complessi, soprattutto 16, hanno mostrato una buona attività catalitica. iv] Reattività e proprietà coordinanti di leganti mono- e di-NHC derivanti da unità carbeniche non-classiche Nell’ambito di una collaborazione con il gruppo del Prof. C. J. (Kees) Elsevier (Università di Amsterdam), è stata valutata la possibilità di ottenere complessi di Ir(III) con leganti NHC saturi a sei membri. Sfortunatamente, i risultati ottenuti non sono stati soddisfacenti, probabilmente a causa della instabilità intrinseca dei precursori del leganti e/o dei corrispondenti carbeni liberi. Invece, risultati migliori sono stati ottenuti nella sintesi e nello studio della reattività di leganti misti NHC-MIC, infatti sono stati sintetizzati i corrispondenti complessi di argento(I) ed è stata eseguita una preliminare ottimizzazione delle condizioni di reazione per la transmetallazione Ag(I)/Ir(III) del legante; in questo modo è stato ottenuto un nuovo complesso di Ir(III) avente un legante NHC-MIC nella sfera di coordinazione.

Despite the appearance in the market of platinum compounds with minor side effects than cisplatin (i.e. carboplatin and oxaliplatin), they did not solve the ineffectiveness on some types of tumors, having the same mechanism of action proposed for cisplatin (DNA platination). For this reason, many research groups have focused their attention on the synthesis and determination of the anticancer properties of compounds with metals different from platinum. Among the most investigated metals there are certainly ruthenium and gold and, only recently, palladium. The latter, despite belonging to the same group of platinum, has some rather different features: •Better water solubility of its complexes. •Structure-activity relationships and mechanisms of action generally different from platinum compounds. However, the fast dissociation pattern of palladium complexes compared to platinum represents a problem since the speciation, which heavily affects the biological activity and the pharmacokinetic properties, could be increased. To remedy this contraindication the most direct option is the introduction of ligands firmly anchored to the metal such as N-Heterocylic Carbenes (NHCs), which are known to give strong s-bonds with most of the transition metals. Moreover, several NHC-palladium complexes have already exhibited an interesting cytotoxic activity in vitro and tumour growth suppression even in vivo. In this PhD thesis, the synthesis and characterization of new palladium compounds stabilized by different types of N-Heterocyclic Carbenes and important organometallic fragments such as h3-allyl-Pd(II), palladacyclopentadienyl and h2-olefin-Pd(0) will be exposed. The reactivity and the importance in many catalytic processes of the fragments reported in Fig. A1 are well known, on the contrary, their biological activity is almost unexplored. Starting from these premises, it was decided to test the synthesized compounds toward different tumor lines, particularly on ovarian carcinoma, and human fibroblasts (healthy cells). From the antiproliferative activity data collected for about one hundred compounds, emerges that, regardless of the nature of the selected carbene ligand, the most active compounds bear the allyl fragment. For these species the evaluation of their activity in vivo and experiments aimed at identify the primary biological target, in order to propose the possible mechanism of action, are planned. A class of compounds generally slightly less active than that containing the allyl residue is represented by the palladacyclopentadienyl complexes and their derivatives. Nevertheless, for some of the synthesized compounds, an excellent antiproliferative and proapoptotic activity has been shown on ovarian cancer cell lines (CisPt sensitive and CisPt resistance), accompanied by a poor activity against normal cells. For the compound 40a a thorough investigation on the main biological target, which was found to be DNA, and on the degree of uptake in tumor cells was also carried out. Due to the high stability imparted by the palladaciclopentadienyl fragment and the chelatig biscarbene ligand, this compound does not undergo substitution reactions when reacted with reduced glutathione (GSH), which is a potential coordinating species present in abundance in the biological environment. It is therefore reasonable to suppose that the interaction with the DNA occurs through non-covalent interactions with the polynucleotide chain. Finally, the class of compounds decidedly less active than those described so far is represented by the Pd (0) derivatives stabilized by olefinic ligands. For these complexes the antiproliferative and proapoptotic activity was evaluated only in ovarian carcinoma lines, observing only in very few cases IC50 values comparable to those of cisplatin.

In the last twenty years, N-heterocyclic carbenes (NHC) have gained general attention as a class of ligands alternative or complementary to the classical ones, based on phosphorous (phosphines, phosphites, etc.) or nitrogen (amines, imines, etc.) donor atoms. In particular, a growing number of new technological applications based on Au(I)- or Au(III)-NHC complexes has appeared. Noteworthy, up to now the majority of these examples deals with N-heterocyclic monocarbene gold complexes. This PhD thesis is focused on the chemistry of gold complexes with di(NHC) ligands (di(NHC) = di(N-heterocylic carbene)) with particular reference to their synthesis and to the determination of a possible relation between their structure, properties and reactivity. In particular the obtained results are divided in three main chapters: i) Synthesis and characterization of the gold(I) di(NHC) complexes; ii) Oxidation of the gold(I) di(NHC) complexes; iii) Synthesis and reactivity of silver and gold complexes with novel di(NHC) ligands obtained via click reaction. i) Synthesis and characterization of the gold(I) di(NHC) complexes. Gold(I) complexes with different functionalized N-heterocyclic di(NHC) ligands have been prepared by direct deprotonation of the diimidazolium salts, that are the di(NHC) ligand precursors, in the presence of AuCl(SMe2) and of a mild base (NaOAc). In the adopted synthetic conditions, dinuclear dicationic gold(I) complexes presenting a metallamacrocyclic structure with two bridging di(NHC) ligands have been obtained in good yields. The photoluminescence and electrochemical properties of the synthesized complexes are strongly influenced by the structure of the di(NHC) ligand employed, in particular by the bridge present between the two imidazole-2-ylidene rings. Remarkably we identified complex 3 (Y = (CH2)3) as a very strong solid state emitter with an almost unitary quantum yield of emission (Фem = 96 %). The ligands of complex 3 were functionalized with different wingtip substituents, bearing long aliphatic chains of different length, with the aim of obtaining luminescent liquid crystals. The new complexes of this type behave as thermotropic materials, differing from the parent compound 3. ii) Oxidation of the gold(I) di(NHC) complexes. The reactivity of the gold(I) complexes toward oxidative addition of halogen is strongly influenced by the employed halogen and by the structure of the di(NHC) ligand. In general stable Au(III)/Au(III) complexes were obtained; however with the bulkier iodine a mixed valence Au(I)/Au(III) complex is isolated. Moreover the presence of the propylene bridge in the di(NHCs) favors the formation rather novel Au(II)/Au(II) complexes. The nature and the geometry of the obtained products have been fully elucidated in several cases by X-ray analysis. iii) Synthesis and reactivity of silver and gold complexes with novel di(NHC) ligands obtained via click reaction. The copper(I) catalyzed azide alkyne cycloaddition was used to introduce new functionalities (benzyl or polyethyleneglycole chain substituted triazole) on the peripheral positions of the bis(1-methylimidazole)propane core. Using the optimized reaction condition it was possible to prepare the corresponding gold(I) and gold(III) complexes. The in vitro cytotoxic activity of the functionalized gold(III) di(NHC) complexes was evaluated on a series of different neoplastic cell lines and on two healthy cell lines; The functionalized complexes are more active than the parent unfunctionalized ones and they express cytotoxicity preferentially towards the neoplastic cells.
Negli ultimi vent’anni i leganti carbenici N-eterociclici (NHC) sono stati una delle classi di leganti più studiate in chimica organometallica. Questi leganti si sono infatti imposti come valida alternativa ai classici leganti σ-donatori basati su atomi donatori quali fosforo (fosfine, fosfiti, ecc.) e azoto (ammine, immine, ecc.). In particolare in letteratura si riscontra un numero sempre crescente di lavori riguardo nuove applicazioni tecnologiche di complessi di oro(I) e oro(III) con leganti NHC. Ad oggi, la maggior parte di questi esempi riguarda complessi di oro con leganti mono(carbenici N-eterociclici). Il lavoro svolto in questa tesi di dottorato è invece incentrato sulla sintesi e caratterizzazione di nuovi complessi di oro con leganti di(NHC) (di(NHC) = di(carbene N-eterociclico)) e sulla ricerca di una possibile relazione tra la loro struttura molecolare, le loro proprietà e la loro reattività. I risultati ottenuti sono divisi in tre capitoli principali: i) Sintesi e caratterizzazione di nuovi complessi di oro(I) con leganti di(NHC); ii) Ossidazione dei complessi di oro(I) con leganti di(NHC); iii) Sintesi e reattività di complessi di oro e argento con nuovi leganti di(NHC) funzionalizzati mediante click chemistry. i) Sintesi e caratterizzazione di nuovi complessi di oro(I) con leganti di(NHC). Nuovi complessi di oro(I) con leganti di(NHC) differentemente funzionalizzati sono stati ottenuti mediante deprotonazione diretta dei corrispondenti sali di diimidazolio, precursori dei leganti carbenici, in presenza di AuCl(SMe2) e di una base debole (NaOAc). Nelle condizioni di reazione impiegate sono stati ottenuti, con buone rese, complessi dinucleari di oro(I) caratterizzati da una struttura metallamacrociclica con due leganti di(NHC) a ponte fra i due centri metallici. Le proprietà fotochimiche ed elettrochimiche dei complessi di oro(I) ottenuti sono fortemente influenzate dalla struttura del legante di(NHC) utilizzato e in particolare, dal ponte (Y) presente tra i due anelli imidazol-2-ilidenici. È stato identificato un complesso (3, Y = (CH2)3) caratterizzato da una fotoemissione allo stato solito molto intensa con una resa quantica di emissione quasi unitaria (Фem = 96 %). Il legante di(NHC) presente nella struttura del complesso 3 è stato successivamente funzionalizzato sugli atomi di azoto in posizione 1,1’ con sostituenti contenenti catene alifatiche di diversa lunghezza con l’obiettivo di ottenere complessi con caratteristiche di cristalli liquidi luminescenti. I nuovi complessi ottenuti, a differenza del complesso di riferimento 3, si comportano come materiali termotropici. ii) Ossidazione dei complessi di oro(I) con leganti di(NHC). La reattività dei complessi di oro(I) nella reazione di addizione ossidativa di alogeno è fortemente influenzata dall’alogeno e dalla struttura del legante di(NHC) impiegati. Nella maggior parte dei casi sono stati ottenuti complessi dinucleari di oro(III) stabili; tuttavia utilizzando come ossidante un alogeno relativamente ingombrante come lo iodio è stato possibile isolare anche un complesso a valenza mista Au(III)/Au(I). Inoltre la presenza del ponte propilene nella struttura dei complessi di(NHC) favorisce la formazione di complessi in cui l’oro è presente nel poco comune stato di ossidazione Au(II)/Au(II). La struttura e la geometria dei prodotti ottenuti è stata in molti casi confermata dalla risoluzione della relativa struttura ai raggi X. iii) Sintesi e reattività di complessi di oro e argento con nuovi leganti di(NHC) funzionalizzati mediante click chemistry. La reazione di cicloaddizione tra azide e alchino catalizzata da sali di Cu(I) (CuAAC) è stata utilizzata per introdurre nuovi gruppi funzionali (anelli triazolici recanti rispettivamente un gruppo benzile o una catena di polietilenglicole) nelle posizioni 5,5’ degli anelli imidazolici del precursore carbenico a ponte propilenico. Utilizzando le condizioni di reazione ottimizzate è stato quindi possibile ottenere i corrispondenti complessi dinucleari di oro(I), oro(III) e argento(I). L’attività citotossica in vitro dei complessi di oro(III) con leganti di(NHC) funzionalizzati è stata determinata su una serie di differenti linee cellulari neoplastiche e su due linee cellulari sane. I complessi funzionalizzati presentano un’attività maggiore rispetto ai complessi con leganti non funzionalizzati ed esprimono la loro citotossicità in maniera preferenziale verso le cellule tumorali.

Ces travaux de thèse se situent dans un domaine au cœur des préoccupations actuelles qui est le développement de nouveaux complexes photoactifs utilisant des métaux abondants pour remplacer les métaux nobles dans les dispositifs à énergie renouvelable. De nouvelles familles de complexes précurseurs ou sensibilisateurs potentiels pour les cellules DSSC (Dye-sensitized solar cells) à base de fer et de ligands tridentates pyridyl-carbènes (FeNHC) ont été préparées et caractérisées. L’objectif, à côté de l’aspect applicatif pour l’énergie, est d’accroître les connaissances dans l’étude des relations structure-propriétés dans les complexes homoleptiques Fe-NHC portant des ligands pyridyl-bisimidazolylidènes par modification du noyau central, du groupe de greffage et de la géométrie de coordination. Après mise au point de la synthèse, les complexes ont fait l’objet de différentes caractérisations photophysiques, électrochimiques et théoriques. Un nouveau record de durée de vie des états excités MLCT a été obtenu avec des complexes à noyau pyrazine (32 ps). L’optimisation géométrique, c’est-à-dire le design de ligands permettant d’obtenir une géométrie de coordination octaédrique idéale pour induire un champ de ligand fort a été étudiée. Nous avons obtenu les complexes recherchés (structure attestée par diffraction RX) en accroissant la distance entre le cœur pyridine et les carbènes latéraux. Cette modification induit un décalage bathochrome, mais la conjugaison électronique ainsi que la rigidité du complexe restent à optimiser. Nous avons aussi développé une nouvelle voie de synthèse permettant d’introduire des groupes d’accroche Π-étendus dans le but de limiter la recombinaison de charge après injection dans le semi-conducteur TiO2. Enfin, Le rendement des cellules DSSC a été optimisé par l’incorporation d’un nouvel additif MgI2 dans la composition de l’électrolyte permettant d’atteindre une efficacité de 0.5% inédite pour un complexe de fer. Au final ces travaux de thèse mettent à la disposition de la communauté des outils synthétiques pour la conception de complexes FeII-NHC à durée de vie prolongée à l'état excité, et représentent une étape supplémentaire dans la compréhension des processus photophysiques opérés au sein de ces complexes
This thesis is part of a current concern and high interest research field, which is the development of new photoactive complexes using abundant metals to replace noble metals in renewable energy devices. Novel families of potential sensitizers for DSSC (Dye-sensitized solar cells) based on iron and tridentate pyridyl-carbene ligands (FeNHC) have been prepared and characterized. The aim, besides the application aspect for energy, is to increase the understanding of the structure-property relationships in Fe-NHC homoleptic complexes carrying pyridyl-bisimidazolylidene ligands by modification of the central core, anchoring group and coordination geometry. Once synthesized, the complexes were submitted to various photophysical, electrochemical and theoretical characterizations. A new MLCT excited state lifetime record was obtained with a pyrazine-based complexes (32 ps). The geometric optimization, which means the design of ligands to obtain an ideal octahedral coordination geometry to induce a strong ligand field was studied. X-ray diffraction measurements attested that the desired complexes were obtained by increasing the distance between the pyridine core and the lateral carbenes. This modification induces a bathochromic shift, but the electronic conjugation as well as the rigidity of the complexes remain to be optimized further. We have also developed a novel synthetic route for introducing Π-extended anchoring groups in order to limit the charge recombination after the injection into the TiO2 semiconductor. The efficiency of the DSSC cells was optimized by the incorporation of a new MgI2 additive in the electrolyte composition which led to an unprecedented efficiency of 0.5% for an iron complex. Finally, this thesis offers new synthetic tools for the design of FeII-NHC complexes with extended excited state lifetimes and represents a further step in the understanding of the photophysical processes operated within this type of iron complexes

The chapter one introduces the reported examples of rare earth metal (RE) complexes with different oxidation states. It also reviews the synthesis and reactivity study of N-heterocyclic carbene (NHC) supported transition metal and RE metal complexes. Chapter two focusses on the synthesis and characterisation of a series of tetraaryloxide Ce and Pr complexes. With the reaction of bulky tetraphenol proligand H4LR(R = P, PT, M) with four equivalents of KN"(N" = N(SiMe3)2), a dimerised complex of [K4LP]2(thf)11 was synthesised and characterised. The salt metathesis reactions of this complex with RECl3(thf)2 afford bimetallic aryloxide complexes of K2L2RE2(thf)11 (RE = Ce, Pr), which display divergent structures under different conditions. Reactions of the CeIII complex of K2L2Ce2(thf)11 with a variety of oxidants(I2, CuCl2 and O2, etc.) lead to the oxidation of CeIII to CeIV, affording purple ceric dimer of L2Ce2. The reaction of the PrIII complexes with I2 under 60 °C affords a mixture from which PrIII iodide (LPr2I2) has been isolated and characterised. This chapter also discusses the reactivity of the bimetallic aryloxide complexes towards different substrates, such as MeLi, KC8 and KBn (Bn = benzyl). Bimetallic complexes of L(REX)2(py)8 (RE = Ce, Pr; X = Cl, BH4) are synthesised and characterised. The preliminary study on the copolymerization of cyclohexene oxide (CHO) and CO2 is conducted for CeIII and PrIII complexes. Chapter three details the work on two different types of NHC ligand. The first ligand is the β-ketoimidazolinium salts H2LBr {L = RC(O)CH2{CH[NCH2CH2NMes], R = tBu, naphth} which reacts with MHBEt3 (M = Na, K) to form carbene-borane adducts RC(O)CH2{C(BEt3[NCH2CH2NMes]}. This type of reactivity differs from the previous work on imidazole derivatives. The possible mechanism of these reactions is provided and discussed. The other ligand is p-aryloxy-tethered imidazolinium salt H2LX (L = N-3,5-di-tert-butyl-4-hydrooxyphenyl-N’-mesityl-imidazolinium, X = Cl, Br, PF6 ), which have been synthesised and characterised. The reactions of these salts with MN"(M = Na, K) enabled the characterisation of polymerised complexes of [NaL]n and [KL(thf)2]n. The yttrium complex YL3 is synthesised and its reactivity towards small molecules such as boranes, CO2 and CS2 is discussed. Chapter four presents the primary results on the study of macrocyclic NHC based cyclophane ligand H6LPF6 (L = calix[4]imidazolylidene[2]pyrazolato). Investigations on the reactivity of the ligand towards different bases (NaN", KN", KBn etc.) are examined and subsequent metathesis reactions with RE complexes are explored. Chapter five concludes the work presented in this thesis. Chapter six contains all experimental and characterisation details.

Une méthode simple et efficace a été développée pour la préparation de ligands bifonctionnels associant les motifs phosphine ou phosphite d'une part, et carbène Nhétérocyclique(NHC) ou imidazolium d'autre part. Dans un premier temps, une série de ligands diphénylphosphine-carbène chiraux portant un centre stéréogène en a de la phosphinea été développée à partir b-hydroxyesters. Une famille de ligands a ainsi été développée afin d'évaluer l'influence de l'encombrement stérique de différents groupements alkyles en a de la phosphine et de la nature des groupements aromatiques portés sur l'imidazole sur leur activité catalytique. L’étude s’est ensuite étendue à la synthèse de ligands de type dialkylphosphine carbène et phosphite-carbène. Ces différents ligands ont été complexés avec des métaux tels que l’iridium ou le rhodium de manière à en étudier l’activité en hydrogénation asymétrique
A straightforward method for the preparation of new bidentate ligands containing aphosphine or a phosphite and a carbene function was developed. Different phosphorus-imidazolium compounds were prepared according to this method. First, diphenylphosphine-NHC ligands featuring a stereogenic center a to the phosphine were synthesized from b-hydroxyesters. This strategy was then extended to the preparation of phosphite-imidazoliumand dialkylphosphine-imidazolium compounds. Complexation of these phosphorus-NHCligands with different metals like Ir or Rh was performed in order to study there catalytic properties in asymmetric hydrogenation