Este trabalho investigou a influência das propriedades estéricas e eletrônicas de ligantes ancilares em complexos do tipo [RuCl2(PR3)3] e [RuCl2(PR3)xLy], onde R = p-toluil e L = piperidina, N-butilamina e isonicotinamida, em reações de polimerização via metátese por abertura de anel (ROMP) e de copolimerização via metátese por abertura de anel (ROMCP) de norborneno (NBE) e norbornadieno (NBD). O objetivo foi observar como o efeito estéreo (dado em função do ângulo de cone, &theta;) e eletrônico (dado em função de pKa) da PpTol3 pode influenciar a reatividade em ROMP e ROMCP quando está sozinha ou combinada com amina. <br /> O complexo [RuCl2(PpTol3)3] (1) produziu rendimentos melhores que 70% por 10 min a 23 &deg;C, com Mw na ordem de 104 g.mol-1 e IPD de 2,2. O melhor rendimento obtido quando o complexo [RuCl2(PpTol3)2(pip)] (2) é utilizado foi observado nas reações por 30 min a 50 &deg;C (80,2%) com Mw de 1,5 x 105 g.mol-1. IPD de 2,0 foi obtido com 2 por 60 min a 23 &deg;C. O complexo 2 demonstrou ser mais reativo que o complexo 1 nas reações de ROMP de NBD, com rendimento de 60,1% por 60 min a 50 &deg;C. O impedimento estéreo de PpTol3 em 1, provavelmente é o responsável pelo melhor desempenho com NBE, com um período de indução mais curto para iniciar a ROMP. Por outro lado, o sinergismo amina&rarr;Ru&rarr;olefina deve contribuir para a ativação de NBD com 2. <br /> Os rendimentos para poliNBE com os complexos contendo N-butilamina e isonicotinamida foram de 68 e 35%, respectivamente, por 60 min a 50 &deg;C, isso mostra que a atividade catalítica para estes complexos sobrepõe o baixo ângulo de cone da Nbutilamina e a capacidade de retrodoação da isonicotinamida. Os rendimentos para o poliNBD foram de 30,9 e 9,1, respectivamente. <br /> As reações de copolimerizações com NBE e NBD (ROMCP) foram realizadas com uma quantidade fixa de NBE ([NBE]/[Ru] = 5000) e diferentes concentrações de NBD ([NBD]/[Ru] = 1000, 2000 ou 3000), por 60 min a 50&deg;C. Para ambos os complexos 1 e 2, os rendimentos foram acima de 80% quando aumentou-se a [NBD] e os materiais poliméricos apresentaram microestruturas lisas. Os valores de Tg (acima de 60 &deg;C) obtidos quando o complexo 1 foi utilizado, sugerem a presença de NBD nas cadeias poliméricas. Com o complexo 2, os valores de Tg foram entre 33 e 37 &deg;C, indicando a possibilidade de polimerização apenas do NBE. / This study investigated the influence of steric and electronic properties of ancillary ligands in complexes of the type [RuCl2(PR3)3] and [RuCl2(PR3)xLy], with R = p-tolyl and L = piperidine, N-butylamine and isonicotinamide, for ring-opening metathesis polymerization (ROMP) and ring-opening metathesis copolymerization of norbornene (NBE) and norbornadiene (NBD). The aim was to observe how the steric (in terms of the cone angle, &theta;) and electronic (in terms of pKa) effects of PpTol3 can tune the reactivity in ROMP and ROMCP when alone or combining with an amine. <br /> The [RuCl2(PpTol3)3] complex (1) produced yields better than 70% for 10 min at 23 &deg;C, with Mw in the order of 104 g.mol-1 and PDI of 2,2. The best yields obtained when the complex [RuCl2(PpTol3)2(pip)] (2) was used was observed in the reactions 30 min at 50 &deg;C (80%), with Mw of 1.5 x 105 g.mol-1. PDI of 2.0 was obtained with 2 for 60 min at 23 &deg;C. The complex 2 proved to be more reactive than complex 1 for ROMP of NBD, with yield of 60.1% for 60 min at 50 &deg;C. The steric hindrance of PpTol3 in 1 probable provided the difference in the reactive for NBE, with a short induction period to initiate the ROMP. However, the amine&rarr;Ru&rarr;olefin synergism in 2 probable contributed to the better activation of NBD. <br /> The yields for polyNBE with the N-butylamine and isonicotinamide derivative complexes were 68 and 35%, respectively, for 60 min at 50 &deg;C., it shows that the catalytic activity of these complexes to overlap the low cone angle of the N-butylamine and the ability of the backdonation of the isonicotinamide. Proceeds to poliNBD were 30.9 and 9.1, respectively. <br /> Copolymerizations with NBE and NBD (ROMCP) were performed with a fixed quantity of NBE ([NBE]/[Ru] = 5000) and different concentrations of NBD ([NBD]/[Ru] = 1000, 2000 or 3000), for 60 min at 50 &deg; C. The yields were better than 80% when increasing the [NBD] and the polymeric materials showed smooth microstructures. The obtained Tg values (60 &deg;C) obtained when the complex 1 was used, indicated the presence of NBD in the polymer chains. With the complex 2, the Tg values were in the range of 33 - 37 &deg;C, indicating the possibility of polymerization of only NBE.

Les polyuréthanes (PUs) sont utilisés comme adhésifs depuis des décennies, mais l’utilisation d’isocyanates durant leur synthèse les place aujourd’hui dans la visée de nouvelles réglementations. Dans ces travaux, nous décrivons trois technologies alternatives potentielles aux Pus, basés sur la métathèse d’oléfines. La première technologie repose sur la synthèse de polyuréthanes sans isocyanates (NIPUs) à partir de motifs carbonate de vinylène (VC). Des polyoléfines VC2-téléchéliques ont été synthétisées par polymérisation par ouverture de cycle par métathèse / métathèse croisée (ROMP/CM) de cyclooléfines en présence d’un agent de transfert (CTA) de type VC. Cependant, la polyaddition avec une diamine a mis en évidence des reactions secondaires empêchant d’obtenir le matériaux désiré. La seconde technologie considérée est la synthèse de polyamides (PA). Des polyoléfines diazlactone (AZL)2-téléchéliques ont été synthétisées par ROMP/CM en presence d’un CTA de type AZL, puis ouvertes par une diamine. Des PAs ont ainsi été obtenus avec succès, mais en faibles quantités, ne permettant pas d’étudier leurs propriétés mécaniques ou adhésives. La dernière approche utilise les polymères silylés (SMPs). Trois types de SMPs ont été synthétisés par diverses stratégies de métathèse : des polypropylèneglycols (PPGs), des copolymères polycyclooctène (PCOE)/PPG et des copolymères polybutadiène (PBD)/PPG. La polycondensation de ces SMPs par différents systèmes catalytiques a été étudiée, ainsi que les propriétés mécaniques et adhésives des matériaux résultants. Parmi ceux-ci, les copolymères PCOE/PPG SMPs ont démontré de remarquables propriétés mécaniques et adhésives, meilleures que la plupart des SMPs commerciaux d’aujourd’hui. / Polyurethanes (PUs) have been used as adhesives for decades, but the toxic isocyanates needed for their synthesis is now on the scope of regulations. In this work, we describe three potential alternative technologies to classic PUs, based on a powerful polymerization tool: olefin metathesis. The first technology relies on the synthesis of nonisocyanate polyurethanes from vinylene carbonate (VC) functionalities. Telechelic VC polyolefins were synthesized by ring-opening metathesis polymerization/cross-metathesis (ROMP/CM) of cycloolefins with a VC chain-transfer agent (CTA). However, polyaddition attempts with a diamine evidenced side-reactions, preventing the isolation of the expected material The second technology considered is the synthesis of polyamide (PA). Following a similar strategy, telechelic azlactone (AZL) polyolefins were synthesized by ROMP/CM of cycloolefins with an AZL CTA, then, were subsequently opened by a diamine. PA were successfully obtained through this strategy, however in small quantities, thus, no mechanical nor adhesive tests were carried out. The last technology uses silyl modified polymers (SMPs). Three type of SMPs were synthesized, using diverse olefin metathesis strategies : polypropylene (PPG), polycylooctene (PCOE)/PPG copolymers and polybutadiene (PBD)/PPG copolymers. Curing of the trimethoxysilyl or triethoxysilyl groups inside these SMPs was studied using different catalytic systems, as well as the mechanical and adhesive properties of the materials obtained. Among them, PCOE/PPG copolymers displayed remarkable good mechanical and adhesive properties, better than the majority of commercial SMPs available today.

Abstract: Metal-Organic Frameworks (MOFs) are a class of highly porous, hybrid, functional and crystalline extended coordination compounds. Their exceptional properties renders them ideal for a wide range of applications including gas storage and catalysis. Especially for catalysis, MOFs are receiving attention as well-defined supports for organometallic heterogeneous catalysis with noticeably the post-synthetic grafting of transition metal complexes on secondary building units (SBU) containing hydroxides moieties. The objective of this dissertation is to explore the synthesis, reactivity and functionalization of MOFs with SBU containing hydroxides units by transition metal catalyst using the Surface Organometallic Chemistry (SOMC) approach. Chapter 1, gives an introduction to the field of MOF and their applications to catalysis through the functionalization of hydroxide containing SBUs. This chapter introduces also the SOMC strategy with an overview of its catalytic application for olefin metathesis and CO2 conversion. Chapter 2 and 3 give a detailed application of SOMC to MOFs with the selective grafting of the W(≡CtBu)(CH2tBu)3 complex on the highly crystalline and mesoporous Zr-NU-1000 MOF. The obtained single site material, Zr-Nu-1000-W, is fully characterized using state of the art experimental methods and all the steps leading to the final grafted moieties were identified by DFT. Zr-NU-1000-W is active for olefin metathesis and is further fine-tuned by activation with EtAlCl2 giving a more selective and stable catalyst. Moreover, the nature of the grafted species could be modulated by pre-activation of the initial W(≡CtBu)(CH2tBu)3 complex with dmpe giving W(≡CtBu)(=CHtBu)(CH2tBu)(dmpe) also grafted on Zr-NU-1000. Chapter 4 and 5, describe the deliberate design and bulk synthesis of a new zirconium MOF, Zr-she-MOF-2, and highlight the discovery of a new highly connected MOF, RE-urx-MOF-1, based on a careful combination of rare earth (RE) metals with heterobifunctional triangular tetrazolate-based ligand. Additionally, the replacement of the tetrazolate functionality by carboxylate, leads to the formation of a different MOF structure RE-gea-MOF-4 having the gea topology with the presence of 18-connected nonanuclear RE cluster. Both Zr-she-MOF-2 and RE-gea-MOF-4 are active for the coupling of epoxides with CO2 to form cyclic carbonate in the presence of Bu4NBr. Finally, Chapter 6 will discuss the conclusions and perspectives of this dissertation.

The general objective of this thesis is the analysis of selective reactions for group VI grafted metal complexes via methods and principles of SOMC. For this objective, three approaches have been chosen. The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing heterogeneous catalysis and more specifically the different approaches to support catalysts on surfaces. The concept of catalysis by design is introduced as a new way to use the surface as a ligand. Chapter 2 presents the results of a library of well-defined catalysts of group VI with identical catalytic functionality, but different ligand environment. The results reveal, that metal-carbynes are able to switch their catalytic reactivity based on the substrate that they are contacted with. The difference in reaction mechanisms and the differing reactivities towards the substrates are presented. It can be concluded that the classical ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas cyclic alkanes yield exclusively higher and lower homologues of the substrate without polymeric products. Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products is analyzed. It is presented, that the ligand environment of the catalysts is showing an influence in the selectivity. Rates of cis/trans isomerization of the products are high and are approaching thermodynamic equilibrium at high conversion. Product isomerization, thermodynamic equilibrium and reactivity differences between liquid phase and gas phase products are analyzed. Chapter 4 presents the full characterization of tungsten-hydrides by selective transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show, that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes. Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the generated tungsten-hydroxides of chapter 4.

Catalysis, which is primarily a molecular phenomenon, is an important field of chemistry because it requires the chemical conversion of molecules into other molecules. It also has an effect on many fields, including, but not limited to, industry, environment and life Science[1]. Surface Organometallic Chemistry is an effective methodology for Catalysis as it imports the concept and mechanism of organometallic chemistry, to surface science and heterogeneous catalysis. So, it bridges the gap between homogenous and heterogeneous catalysis[1]. The aim of the present research work is to study the effect of Nitrogen surface ligands on the activity of Alkane, Propane in particular, metathesis. Our approach is based on the preparation of selectively well-defined group (VI) transition metal complexes supported onto mesoporous materials, SBA15 and bearing amido and/or imido ligands. We choose nitrogen ligands because, according to the literature, they showed in some cases better catalytic properties in homogenous catalysis in comparison with their oxygen counterparts[2]. The first section covers the modification of a highly dehydroxylated SBA15 surface using a controlled ammonia treatment. These will result in the preparation of two kind of Nitrogen surface ligands: - One with vicinal silylamine/silanol, (≡SiNH2)(≡SiOH), noted [N,O]SBA15 and, - Another one with vicinal bis-silylamine moieties (≡SiNH2)2, noted [N,N]SBA15[3]. The second section covers the reaction of Schrock type Tungsten Carbyne [W(≡C- tBu)(CH2-tBu)3] with those N-surface ligands and their characterizations by FT-IR, multiple quantum solid state NMR (1H, 13C), elemental analysis and gas phase analysis. The third section covers the generation of the active site, tungsten hydride species. Their performance toward propane metathesis reaction using the dynamic reactor technique PID compared toward previous well-known catalysts supported on silica oxide or mesoporous materials[4]. A fairly good turn over number (TON = 43) has been obtained following hydrogen treatment of tungsten alkylidyne supported on [N,O] SBA151100, in comparison with TON of zero in the obtained with [N,N] SBA15 and classical SiO2 silica support. Therefore, the cooperation between silylamine and silanol in close vicinity are required to improve the efficiency of the catalyst in the metathesis of propane.

Ce travail de thèse s’intéresse à la synthèse totale d'alcaloïdes de la famille des Lycorines, produits naturels isolés à partir de plantes des Amaryllidaceae qui possèdent de multiples activités biologiques. Leurs structures sont caractérisées par un squelette commun tétracyclique azoté : le galanthane. L’accès rapide au squelette galanthane a été développé via une étape clé de métathèse tandem cyclisante permettant d’obtenir deux cycles fonctionnalisés en une seule étape. La première partie de ce travail a conduit au développement d’une voie de synthèse asymétrique des (–)-α et (–)-β-lycoranes à partir d’un même intermédiaire, une sulfinylaldimine α-chirale, obtenue par réduction d’un N-sulfinylthioimidate α-chiral grâce à des conditions développées au laboratoire. La seconde partie de ce travail a porté sur la synthèse asymétrique de la (+)-kirkine, nécessitant une révision de la stratégie pour former le cycle B du squelette galanthane de manière précoce dans la synthèse. Nous avons réalisé la première synthèse totale asymétrique de la structure décrite de la (+)-kirkine. L’obtention des lycoranes et de la kirkine prouve la flexibilité ainsi que l'efficacité de la voie de synthèse, en particulier de l'étape clé de métathèse tandem et des N-sulfinylthioimidates comme intermédiaires clés. Cette voie est donc très prometteuse pour accéder à d'autres composés naturels de la famille des Lycorines. / This thesis work focuses on the total synthesis of alkaloids of the Lycorine family, natural products isolated from the plants of Amaryllidaceae, owning many biological properties such as anticancer, antiviral, antimicrobial or anti-inflammatory. Their structure is characterized by a nitrogen-containing tetracyclic galanthan skeleton. A fast access to the galanthan skeleton was developed by a key tandem ring closing metathesis step to obtain two cycles in a single step. The first part of this work concerns the development of an asymmetric synthetic pathway to obtain the (–)-α and (–)-β-lycoranes from a common central intermediate, an α-chiral sulfinylaldimine, obtained by reduction of the corresponding α-chiral sulfinylthioimidate. The second part of this work focuses on the asymmetric synthesis of (+)-kirkine, which required a strategy revision for the formation of the B cycle of the galanthan skeleton earlier in the synthesis. We have succeeded in realising the first asymmetric total synthesis of the described structure for (+)-kirkine. The asymmetric synthesis of lycoranes and kirkine proves the flexibility and efficiency of the synthetic route, in particular of the tandem metathesis step and the N-sulfinylthioimidates as key intermediates. This synthetic pathway is therefore very promising to obtain other natural products of the Lycorine family.

Surface Organometallic Chemistry (SOMC) is an excellent approach to erase the gap between homogeneous and heterogeneous catalysis by grafting the molecular organometallic complex on various oxide surfaces, forming well-defined and single-site catalysts. This strategy allows for better characterization as well as the improvement and development of existing and new catalysts. These surface species could promote a wide range of catalytic applications (i.e., metathesis of hydrocarbons, hydrogenolysis of alkanes, and olefin polymerization reactions) depending on the metal center and its coordination sphere. In particular, the grafting of alkylated organometallic complexes of groups 4, 5, and 6 metals on the surface oxide is a thermodynamically favored reaction generally leading to strongly bonded well-defined surface species, which are highly reactive catalysts. This thesis has focused on the preparation, characterization, and catalytic investigation of different supported complexes that contain methyl, alkyl, and alkylidyne ligands. The first part compares the catalytic activity of [(≡Si−O−)W(-CH3)5] and [(≡Si-O-)Mo(≡CtBu)(-CH2tBu)2] surface species experimentally and by DFT calculations in the metathesis reactions of linear classical and functionalized olefins. Both pre-catalysts perform almost equally in the α-olefin metathesis reaction. However, in the functionalized olefin metathesis reaction, W pre-catalyst provides selective metathesis products and performs much better than Mo that gives a range of isomerization products. The second part deals with the synthesis and characterization of [(THF)2Zr(-CH3)4] and its grafting on silica support for the first time. The generated surface species [(≡Si−O−)Zr(CH3)3(THF)2] and [(≡Si−O−)2Zr(CH3)2(THF)2] are used for the conversion of CO2 and propylene oxide to cyclic propylene carbonates achieving a TON of 4227. The third part describes the first synthesis and characterization of the highly unstable homoleptic [Ti(-CH3)4] without any coordinating solvent. This complex was stabilized by grafting on SiO2-700, yielding two fully characterized surface species [(≡Si-O-)TiMe3] and [(≡Si-O-Si≡)(≡Si-O-)TiMe3], which were used in the hydrogenolysis reaction of propane and n-butane, with TONs of 419 and 578, respectively. Finally, the fourth part reports the immobilization and characterization of [TiMe2Cl2], an intermediate in the synthesis of [Ti(-CH3)4], on SiO2-700 resulting in [(≡Si-O-)TiMeCl2] and [(≡Si-O-)TiMe2Cl] surface species. These complexes reacted with a demethylating Lewis acid agent (BARF), forming the corresponding cationic Ti species [(≡Si-O-)TiMeCl]+ and [(≡Si-O-)TiCl2]+. Both neutral and cationic complexes were tested in the ethylene polymerization reaction affording linear HDPE with high molecular weights of 500,367 and 486,612 g/mol.

With its unrivaled versatility and atom economy, olefin metathesis is arguably the most powerful catalyst methodology now known for the construction of carbon-carbon bonds. When compared to palladium-catalyzed cross-coupling methodologies, however, catalyst productivity lags far behind, even for the “robust” ruthenium metathesis catalysts. Unexpected limitations to the robustness of these catalysts were first widely publicized by reports describing the implementation of metathesis in pharmaceutical manufacturing. Recurring discussion centered on low catalyst productivity resulting from decomposition of the Ru catalysts by impurities, including ppm-level contaminants in the technical-grade solvent. Over the past 7 years, a series of mechanistic studies from the Fogg group has uncovered the pathways by which common contaminants (or indeed reagents) trigger catalyst decomposition. Two principal pathways were identified: abstraction of the alkylidene or methylidene ligand by nucleophiles, and deprotonation of the metallacyclobutane intermediate by Bronsted base. Emerging applications, however, notably in chemical biology, highlight new challenges to catalyst productivity. The first part of this thesis emphasizes the need for informed mechanistic insight as a guide to catalyst redesign. The widespread observation of a cyclometallated N-heterocyclic carbene (NHC) motif in crystal structures of catalyst decomposition products led to the presumption that activation of a C-H bond in the NHC ligand initiates catalyst decomposition. Reducing NHC bulk has therefore been proposed as critical to catalyst redesign. In experiments designed to probe the viability of this solution, the small NHC ligand IMe4 (tetramethylimidazol-2-ylidene) was added to the resting-state methylidene complexes formed in metathesis by the first- and second-generation Grubbs catalysts (RuCl2(PCy3)2(=CH2) GIm or RuCl2(H2IMes)(PCy3)(=CH2) GIIm, respectively). The intended product, a resting-state methylidene species bearing a truncated NHC, was not formed, owing to immediate loss of the methylidene ligand. Methylidene loss is now shown to result from nucleophilic attack by the NHC – a small, highly potent nucleophile – on the methylidene. Density functional calculations indicate that IMe4 abstracts the methylidene, generating the N-heterocyclic olefin H2C=IMe4. The latter is an even more potent nucleophile, which attacks a second methylidene, resulting in liberation of [EtIMe4]Cl. These findings report indirectly on the original question concerning the impact of ligand truncation. The ease with which a small, potent nucleophile can abstract the key methylidene ligand from GIm and GIIm underscores the importance of increasing steric protection at the [Ru]=CH2 site. This chemistry also suggests intriguing possibilities for efficient, selective, controlled methylidene abstraction to terminate metathesis activity while leaving the “RuCl2(H2IMes)(PCy3)” core intact. This could prove an enabling strategy for tandem catalysis applications in which metathesis is the first step. The second part of this thesis, inspired by the potential of olefin metathesis in chemical biology, focuses on the impact of hydroxide ion and water on the productivity of phosphine-free metathesis catalysts. In reactions with the important second-generation Hoveyda catalyst HII, hydroxide anion is found to engage in salt metathesis with the chloride ligands, rather than nucleophilic attack. The resulting Ru-hydroxide complex is unreactive toward any olefins larger than ethylene, while ethylene itself causes rapid decomposition. Proposed as the decomposition pathway is bimolecular coupling promoted by the strong H-bonding character of the hydroxide ligands. Lastly, the impact of the water on Ru-catalyzed olefin metathesis is examined. In a survey of normally facile metathesis reactions using state-of-the-art catalysts, even trace water (0.1% v/v) is found to be highly detrimental. The impact of water is shown to be greater at room temperature than previously established at 60 °C. Preliminary evidence strongly suggests that the mechanism by which water induces decomposition is temperature-dependent. Thus, at high temperature, decomposition of the metallacyclobutane intermediate appears to dominate, but this pathway is ruled out at ambient temperatures. Instead, water is proposed to promote bimolecular decomposition. Polyphenol resin, which can sequester water by H-bonding, is shown to offer an interim solution to the presence of trace water in organic media. These findings suggest that major avenues of investigation aimed at reducing intrinsic catalyst decomposition may likewise be relevant to the development of water-tolerant catalysts.

Olefin metathesis is a powerful tool for the making and breaking of carbon-carbon double bonds. Among well-defined homogenous catalysts for olefin metathesis, ruthenium-based alkylidenes stand out for their robustness and relative ease-of-use. Synthesis of the most active Ru-based metathesis catalysts remains challenging, however, and there is continued interest in new and improved routes to alkylidene installation as metathesis begins to see wide uptake in industry. The first part of this thesis focuses on developing new routes to known catalysts. Magnesium carbenoids are investigated as a potential alkylidene source, and in the process a novel route to benzylmagnesium carbenoids is developed. Initially promising results showing ca. 40% conversion to first generation metathesis catalysts failed to lead to a viable high-yield route to Ru-alkylidenes. A high yield route to RuCl2(H2IMes)(py)4 (previously reported in low yields as a decomposition product of the third-generation Grubbs’ metathesis catalyst) is developed and this complex is investigated as a precursor to indenylidene-based catalysts. Although RuCl2(H2IMes)(py)4 is shown to be substitutionally labile, indenylidene installation could not be achieved. Finally, zinc aryloxides are investigated as an alternative to thallium and silver reagents for the installation of aryloxide ligands. Initial results indicate that zinc aryloxides are kinetically, though not thermodynamically, competent for the installation of the challenging aryloxide C6F5O- on the second-generation Hoveyda catalyst. The second part of this thesis concerns progress towards the development of a new low-valent catalyst platform. Initial experiments involving treating the second-generation Hoveyda catalyst with various reducing agents fail to produce low-valent alkylidenes, leading instead to decomposition of alkylidene. Drawing inspiration from early transition metal systems, the remainder of the second part focuses on alpha-hydride elimination from a RuII alkyl as a means of accessing low-valent alkylidenes. To this end, a novel benzylruthenium complex as well as bis-benzyl and mono-aryloxide derivatives are developed. While attempts to induce benzyl-to-benzyl hydride abstraction or intramolecular deprotonation of the benzyl ligand failed to produce alkylidenes, ligand-induced benzyl-to-aryloxide hydride abstraction appears to be successful, leading to the observation of a broad 1H NMR signal in the region characteristic for low-valent Ru-alkylidenes.

No description available.