Teses / dissertações sobre o tema "Ruthenium-based catalysts"

Two series of new mononuclear ruthenium complexes with hydrophobic or hydrophilic ligands [Ru(bda)L2] and [Ru(pdc)L3] (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) were synthesized and their electrochemical properties and catalytic activity toward water oxidation were examined. It was revealed that the hydrophobic ligands introduced to [Ru(bda)L2 ] improved the catalytic performance, ahnost twofold TON and TOF values were achieved compared to the [Ru(bda)] catalyst with hydrophilic ligands. The cyclic voltammogram of [Ru(bda)L2] exhibited marginal difference between the catalysts with hydrophobic ligands and hydrophilic ones, implying that the hydrophobic ligands promoted the catalytic activity by :lacilitating formation of a reaction intermediate dimer.

As part of a European wide effort to develop metathesis catalysts for use in fine chemical and pharmaceutical compound synthesis, this study focuses on the design and synthesis of ruthenium based catalysts for olefin metathesis. The aim, of this work was simple: to develop new, more active, more stable, easy to synthesise and commercially viable Ruthenium based catalysts, as well trying to rationalize the effect of structural changes on reactivity. Two different approaches were explored in order to develop more active catalysts bearing N-heterocyclic carbene (NHC) ligands: changing the leaving group and the effect of the NHC moiety in indenylidene type complexes. Over 12 new catalysts were developed and their activity compared to that of commercially available catalysts. Overall, the new complexes exhibited superior reactivity compared to previously reported catalysts in several benchmark transformations. However, olefin metathesis is a very substrate specific reaction, and rather than finding one catalyst that is superior to all, a catalogue of catalysts suitable for specific transformations was developed. In addition, the effect of structural changes on substrate activity was investigated in the ring closing metathesis of 1,8-nonadienes. The reaction profiling showcased the presence of a gem-difluoro group as an accelerating group in this incarnation of the olefin metathesis reaction and leads to ring formation over polymerization. In order to rationalize the effect of structural changes on catalyst activity, kinetic studies dealing with the initiation mechanism of ruthenium-indenylidene complexes were examined and compared with that of benzylidene counterparts. It was discovered that not all indenylidene complexes followed the same mechanism, highlighting the importance of steric and electronic properties of so-called spectator ligands, and that there is no single mechanism for the ruthenium-based olefin metathesis reaction. These results highlight the importance of systematic development of catalysts and that as scientists we should not take for granted.

The catalytic activity of ruthenium(II) bis(diimine) complexes cis-[Ru(6,6′-Cl2bpy)2(OH2)2](Z)2 (2, Z = CF3SO3; 3, Z = (3,5-(CF3)2C6H3)4B ,i.e. BArF), cis-[Ru(4,4′-Cl2bpy)2(OH2)2](Z)2 (4, Z = CF3SO3; 5, Z = BArF) and cis-[Ru(bpy)2(PR3)(OH2)](CF3SO3)2 (7, bpy = 2,2’-bipyridine, PR3 = P(C6H4F)3; 8, bpy = 2,2-bipyridine, PR3 = PPh3; 9, bpy = 4,4’-dichloro-2,2’-bipyridine, PR3 = PPh3; 10, bpy = 4,4’-dimethyl-2,2’-bipyridine, PR3 = P(C6H4F)3) for the hydrogenation and hydrogenolysis of furfural (FFR), furfuryl alcohol (FFA) and 5-hydroxymethylfurfural (HMF) was investigated. The compounds 2-5 are active and highly selective catalysts for the hydrogenation of FFR to FFA. Using 2 as catalyst at 100 °C, hydrogenation of FFR proceeded to high conversion (≥98%) and with 100% selectivity to FFA in 2 h. The catalyst cis-[Ru(6,6′-Cl2bpy)2(OH2)2](CF3SO3)2 (2) also showed some activity for hydrogenolysis of FFR and FFA at 130 °C in ethanol, giving up to 25% of 2-methylfuran (MF) yield. The catalyst 3 alsodisplayed high catalytic activity for the hydrogenation of FFA to tetrahydrofurfuryl alcohol. Catalysts 7-10 are also active towards the hydrogenation of furfural (FFR) in NMP giving >90% FFR conversion with 100% selectivity for furfuryl alcohol (FFA) in 12 h. Compounds 7-10 are active C-O bond hydrogenolysis catalysts in presence of bismuth halide Lewis acids. For example, hydrogenolysis of FFA in the presence of 1 mol% of catalyst cis-[Ru(4,4’-Cl2bpy)2(PPh3)(OH2)](CF3SO3)2 (9) and 20 mol% bismuth bromide at 180 °C/51 atm H2 pressure gave >96% conversion of FFA and 55% MF yield. Compounds 7-10 in the presence of bismuth halides, showed almost 100% conversion of HMF with a very high selectivity (65-72%) for 2,5-DMF, along with 10-12% of MF, and trace amount of 5-methylfurfural (MeFFR). In order to test the activity of ruthenium hydrides towards the C-O bond hydrogenation and hydrogenolysis of HMF, series of monocationic ruthenium complexes cis-[Ru(bpy)2(PR3)(H)](CF3SO3) (12, bpy = 2,2’-bipyridine, PR3 = P(C6H4F)3; 13, bpy = 2,2-bipyridine, PR3= PPh3; 14, bpy = 4,4’-dimethyl-2,2’-bipyridine, PR3= P(C6H4F)3) were prepared. The hydrogenation of HMF using catalysts 12-14, produced 70-72% of 2,5-DMF and 11% MF, suggesting that ruthenium hydrides are active and efficient catalysts for HMF hydrogenation.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017.
One of the very promising synthetic fuel production strategies is the Fischer-Tropsch process, founded on the Fischer-Tropsch Synthesis, which owes its discovery to the namesake researchers Franz Fischer and Hans Tropsch. The Fischer-Tropsch Synthesis (FTS) converts via complex polymerisation reaction a mixture of CO and H2 over transition metal catalysts to a complex mixture of hydrocarbons and oxygen containing compounds with water as major by-product. The mixture of CO and H2 (termed syngas) may be obtained by partial oxidation of carbon containing base feedstocks such as coal, biomass or natural gas via gasification or reforming. The Fischer-Tropsch (FT) process thus presents the opportunity to convert carbon containing feedstocks to liquid fuels, chemicals or hydrocarbon waxes, which makes, for instance, the monetisation of stranded gas or associated gas a possibility. The FT-process is typically carried out in two modes of operation: low temperature Fischer-Tropsch (LTFT) and high temperature Fischer-Tropsch (HTFT). LTFT is normally operated at temperatures of 200 – 250 °C and pressures of 10 – 45 bar to target production of high molecular weight hydrocarbons, while HTFT is operated at 300 – 350 °C and 25 bar to target gasoline production. The catalytically active metals currently used commercially are iron and cobalt, since product selectivity over nickel is almost exclusively to methane and ruthenium is highly expensive in addition to requiring very high pressures to perform optimally. Fe is much cheaper, but tends to deactivate more rapidly than Co due to oxidation in the presence of high H2O partial pressures. One of the major drawbacks to using Fe as FT catalyst is the requirement of lower per pass conversion which necessitates tail gas recycle to extend catalyst life and attain acceptable overall conversions. A more active or similarly active but more stable Fe-catalyst would thus be advantageous. For this reason promotion of a self-prepared typical LTFT Fe-catalyst with Ru was investigated. A precipitated K-promoted Fe-catalyst was prepared by combination of co-precipitation and incipient wetness impregnation and a ruthenium containing catalyst prepared from this by impregnation with Ru3(CO)12. The catalysts, which had a target composition of 100 Fe/30 Al2O3/5 K and 100 Fe/30 Al2O3/5 K/3 Ru, were characterised using XRD, SEMEDX, ICP-OES, TPR and BET N2-physisorption, before testing at LTFT conditions of 250 °C and 20 bar in a continuously stirred slurry phase reactor.

In this thesis the author concentrates on the preparation of several novel building blocks based on butadienyl skeleton and their synthetic application for organic synthesis. Stereo-defined 1,1,4,4-tetrahalo-1,3-butadienes could be readily synthesized. The reactions of these butadienes with butyllithium and its Suzuki coupling reactions with aryl boronic acid are unprecedented. Moreover, bis(pinacolato)diboron could react with 1,4,4-trihalo-1-lithiodienes which were obtained in situ by lithiation of our new bis(gem-dihalo)dienes, to afford corresponding novel gem-diboryldienes which serve as good substrates for the Miyaura-Suzuki coupling reaction. Upon treatment with LiAlH₄, 1,4-dicyano-1,4-bis(trimethylsilyl)-1,3-dienes could undergo a novel hydride-induced cyclization to afford multiply functionalized cyclopentadienes in high isolated yields. In a second objective, novel [Ru(C₅Me₄R)(2-quinolinecarboxylato)(CH₂CHCHR')][PF6] and [Ru(C₅Me₅)(2-quinolinecarboxylato)(CH₂CHCHn-Pr)][BF₄], allyl ruthenium(IV) complexes were synthesized. These complexes were used as catalysts in allylation reactions, and it is the first time that high regioselectivity in favor of the branched product was obtained from purely aliphatic allylic substrates and functional vinylsilanes
Un objectif de cette thèse était la préparation de nouveaux fragments organique à partir du squelette butadiényle et leurs applications en synthèse organique. Des 1,1,4,4-tétrahalo-1,3-butadiènes ont été préparés de façon stéréosélective. La réaction de ces butadiènes avec le butyllithium et leur couplage de Suzuki avec des acides arylboroniques constituent des transformations nouvelles et originales. De nouveaux gem-diboryldiènes, également d���excellents agents de couplage de Suzuki, ont été obtenus à partir des gem-dihalodiènes correspondants. Le traitement avec LiAlH₄ de 1,4-dicyano-1,4-bis(triméthylsilyl)-1,3-diènes a conduit à une nouvelle réaction de cyclisation induite par des hydrures pour former des cyclopentadiènes multi-fonctionnalisés avec de très bons rendements. Dans un deuxième objectif, une série de complexes inédits du ruthénium porteurs de nouveaux ligands Cp et N-O chelatants ont été conçus et préparés avec l’objectif d’obtenir de bonnes propriétés catalytiques en allylation de nucléophiles. Ces complexes ont été utilisés comme catalyseurs d’allylation et ont conduit pour la première fois à d’excellentes régiosélectivités en faveur des produits branchés à partir de substrats allyliques purement aliphatiques et à la préparation de dérivés vinylsilanes fonctionnels

Interest in olefin metathesis has increased over the years with the development of ruthenium-based catalysts. Their unique properties have allowed their use in numerous industrial and laboratory processes in relatively mild conditions and in combination with a wide range of solvents. Several studies have provided insights into how these catalysts work, but very little has been done in order to understand why they work that way; an important aspect that has the potential of benefiting chemists while designing new catalysts. The research introduced here has focused on the fundamental understanding of their reactivity by exploring their electronic structure, using a combination of synchrotron-based X-ray-absorption (XAS) techniques in combination with DFT calculations and multiplet simulations. As part of the experimental work, samples from various ruthenium-based catalysts classified as first-generation (whenever the ancillary ligand is a phosphine) or as second-generation analogues (whenever this ligand is an N-heterocyclic carbene, NHC) were used. The Ru K-edge XAS data have revealed that the ruthenium centre in second-generation analogues is more positively charged than the corresponding first-generation counterparts. This offers a rationale for previously observed kinetic results, which have shown a slower initial step for the second-generation Grubbs catalyst. At the same time, they raise questions in a more fundamental level on whether or not NHCs are truly better charge donors than phosphine ligands. DFT results are consistent and the ongoing analyses of the Cl K- and C K-edge XAS data indicate similar overall bonding structures between first- and second- generation analogues. In addition, from preliminary results on these edges, two possible identities of substantially different nature have emerged for the LUMO orbital. In this regard, the final conclusion should provide important insights on through which orbital the metathesis reaction gets started. As a side product, the analyses of the challenging Cl K-edge XAS data have inspired the development of a new methodology and a Matlab-based computer program for fitting. Ultimately, the methods and techniques detailed here can serve as the foundation for the comprehensive study of other related systems relevant to olefin metathesis, or in general, to the field of homogeneous catalysis.

A growing interest towards new sources of energy has led in recent years to the development of a new generation of catalysts for alcohol dehydrogenative coupling (ADC). This green, atom-efficient reaction is capable of turning alcohol derivatives into higher value and chemically more attractive ester molecules, and it finds interesting applications in the transformation of the large variety of products deriving from biomass. In the present work, a new series of ruthenium-PNP pincer complexes are investigated for the transformation of 1-butanol, one of the most challenging substrates for this type of reactions, into butyl butyrate, a short-chain symmetrical ester widely used in flavor industries. Since the reaction kinetics depends on hydrogen diffusion, the study aimed at identifying proper reactor type and right catalyst concentration to avoid mass transfer interferences and to get dependable data. A comparison between catalytic activities and productivities has been made to establish the role of the different ligands bonded both to the PNP binder and to the ruthenium metal center, and hence to find the best catalyst for this type of reaction.

N-heterocyclic carbenes (NHCs) have become a very popular class of ligands, which has found uses in numerous catalytic applications. The use of such compounds in combination with phosphorus-based ligands within metal complexes has enabled the design of very active yet robust catalytic systems. The following chapters will describe the design of novel well-defined palladium- and ruthenium-based pre-catalysts featuring a NHC and a phosphorus-based ligand, referred at as mixed ligand systems. Such species were employed in catalysis where their properties appeared highly beneficial, uses at low catalysts loading and under harsh conditions were then envisioned. The preparation of a series of well-defined palladium mixed NHC/phosphine species is presented in chapter 2. Their catalytic activity in the aqueous Suzuki-Miyaura reaction of aryl chlorides and boronic acids, using low catalyst loadings, is described. The observation of catalytic activity of the latter systems in the hydration of nitriles prompted us to further investigate this reactivity. This reaction appeared to be operative in the absence of palladium species and could be performed under base-catalysed conditions, which was studied in detail and depicted in chapter 3. The combination of a NHC and a phosphite ligand in ruthenium olefin metathesis pre-catalysts has been underexplored. Preliminary results showed that such species could be readily prepared and presented an unusual geometry and a high catalytic activity. Variations in phosphite-containing ruthenium olefin metathesis pre-catalysts are presented. Chapter 4 describes the investigation of various Schrock carbene moieties in such architectures, as well as their implications in structure and catalysis. Chapter 5 depicts attempts to design olefin metathesis Z-selective pre-catalysts by inserting a chelating NHC moiety within phosphite-containing ruthenium species. This dissertation concludes on the potential of such mixed species in catalysis, and armed with the new knowledge provided by this work, proposes potential developments of such chemistry in the design of always more robust and active catalytic systems.

Proton exchange membrane fuel cells are one of the most promising hydrogen energy conversion devices for portable, mobile and stationary applications. For wide spread usage to produce electricity platinum loading has to be decreased by using highly active electrocatalysts. Even 10 ppm carbon monoxide or higher than 30% carbon dioxide cause performance losses via deactivation which can be diminished by using binary catalysts. The aim of this thesis is to develop new platinum based electrocatalysts with high catalytic activity and to overcome the problems due to the deactivation. platinum and platinum-ruthenium based catalysts on different carbon supports have been prepared by supercritical carbon dioxide deposition and microwave irradiation methods. By using supercritical carbon dioxide deposition platinum on Vulcan XC72R (VXR), multi wall carbon nanotube (MWCNT) and Black Pearl 2000 (BP2000) catalysts were prepared and characterized by XRD, TEM and cyclic voltammetry (CV). XRD results showed that in catalysts prepared by using supercritical carbon dioxide deposition method, the particle sizes as low as 1-2 nm can be obtained. From the CV results the electrochemical surface areas obtained were Platinum/VXR>
Platinum/MWCNT>
PlatinumBP2000. By means of the oxygen reduction reaction (ORR), the number of electrons transferred per oxygen molecule was calculated as 3.5, 3.6 and 3.7 for Platinum/BP2000, Platinum/VXR and Platinum/MWCNT, respectively. The microwave irradiation was used to prepare platinum on VX, Regal and BP2000 and platinum-ruthenium on VX. The effects of microwave duration, base concentration, carbon support used and surfactant/precursor ratios were investigated. The particle sizes of the catalysts were ranging between 2-6 nm. The prepared catalysts were characterized by XRD, XPS, and then PEMFC tests were performed. The performance was ordered as Platinum/VX>
Platinum/Regal>
Platinum/BP2000. The power losses arising from carbon dioxide in hydrogen feed were decreased by using prepared platinum-ruthenium based catalysts.

La métathèse des oléfines est une réaction emblématique de la chimie verte pour la formation de nouvelles doubles liaisons carbone-carbone. Permettant une grande économie d’atome et la réduction du nombre d’étapes de synthèse, cette réaction offre des atouts incontestables pour la production de molécules d’intérêts. Ainsi, une multitude de complexes de ruthénium ont été développés depuis les années 1990 avec pour objectif d’étendre les champs d’applications de la métathèse. Si des avancées majeures ont été accomplies au niveau de l’activité et de la stabilité de ces précatalyseurs, le contrôle de la sélectivité de la réaction lors de la formation de centres stéréogènes constitue toujours un réel défi. C’est dans ce contexte que s’inscrivent ces travaux de thèse.Ainsi, deux nouvelles familles de complexes de ruthénium contenant des ligands Carbènes Alkyl Amino Cycliques (CAACs) chiraux ont été développées. Les complexes à base de CAACs associant une chiralité centrée et une chiralité axiale ont permis d’obtenir d’excellentes énantiosélectivités allant jusqu’à 99% ee en métathèse croisée par ouverture de cycle (AROCM). Les complexes CAACs de type Blechert ont, quant à eux, permis de combiner une remarquable activité à des charges catalytiques en deçà de 0.05 mol% et d’excellentes énantiosélectivités (95% ee). Enfin, une nouvelle classe de ligands CAACs contenant un motif barrélène (CABCs) a été développée et évaluée dans diverses réactions de métathèse
Olefin metathesis is an important reaction of green chemistry for the formation of new carbon-carbon double bonds. Allowing a better atom economy and shortening synthetic pathways, this technology offers many advantages for the production of highly valuable molecules. Thus, numerous ruthenium-based complexes have been developed since the 1990s aiming to extend the field of application of metathesis. While major advances were reached in terms of activity and stability of these precatalysts, controlling the selectivity of the reaction during the formation of stereogenic centers is still a major challenge.Hence, in this PhD thesis, two new families of chiral Cyclic alkylaminocarbenes (CAAC)-based ruthenium complexes were developed. Complexes containing CAACs that combined both centered and axial chirality enabled to achieve excellent enantioselectivities up to 99% ee in Asymmetric ring-opening cross metathesis (AROCM). Blechert type CAAC-Ru complexes reached remarkable activity at loadings below 0.05 mol% with very high enantioselectivities (95% ee). Finally, a novel class of CAAC family ligands carrying a barrelene scaffold (CABCs) was studied and the associated Ru complexes were evaluated across various metathesis reactions

特異なルテニウムが触媒する"Borrowing hydrogen"のコンセプトに基づく有機反応を開発した。まず、Ru/JOSIPHOS触媒を用いて、1,2-ジオールとアミンの反応から光学活性β-アミノアルコールを最高99%収率ならびに77% eeで得ることに成功した。本反応は新規であり、その反応機構についても明らかにした。さらに、RuCl2(PPh3)3/DPEphos/K3PO4を組み合わせた触媒を用いることで、アルコールをアルキル化剤に用いるインドールの3位選択的アルキル化反応を達成した。高効率かつ広いタイプの基質に適用できる。
Several novel ruthenium-catalyzed "borrowing hydrogen"-based organic reaction has been developed. For very first time optically active β-amino alcohols can be sinthesized directy by reaction of 1,2-diol and coressponding amine under Ru/JOSIPHOS catalysis in up to 99% yield and 77% ee. Since this reaction is very new, intensive investigation of the reaction mechanism was also carried out. Meanwhile, combination of RuCl2(PPh3)3/DPEphos/K3PO4 was found to be effective catalyst for alkylation of indole with alcohol as an alkylating reagent. This catalysis was highly reactive to give the corresponding alkylated indole in excellent yield for almost all types of indoles and alcohols substrates.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University

Thesis advisor: Amir H. Hoveyda
Chapter 1. In Situ Methylene Capping: A Key Strategy in Catalytic Stereoretentive Olefin MetathesisA general approach for in situ methylene capping that significantly expands the scope of catalyst-controlled stereoselective olefin metathesis is presented. By incorporation of stereodefined 2-butene as the capping reagent, the catechothiolate Ru complex is enabled to catalyze olefin metathesis reactions of terminal alkenes. Substrates bearing a carboxylic acid, an aldehyde, an aryl substituent, an α substituent were thus converted to the desired products in 47–88% yield and 90:10–98:2 Z:E selectivity. The capping strategy was also applied in ring-closing metathesis reactions leading to 14- to 21-membered macrocyclic alkenes (96:4–98:2 Z:E). The utility of this method was highlighted through synthesis of a platelet aggregate inhibitor and two members of the prostaglandin family compounds by cross-metathesis reaction, as well as a strained 14-membered ring stapled peptide by macrocyclic ring-closing metathesis. Examples of the corresponding E-selective cross-processes are provided as well. Chapter 2. Synthesis of Z- or E-Trisubstituted Allylic Alcohols and Ethers by Kinetically Controlled Catalytic Cross-MetathesisKinetically controlled Ru-catalyzed cross-metathesis reactions that generate Z- or E-trisubstituted alkenes are discussed. Reactions were catalyzed by catechothiolate Ru complex to generate trisubstituted allylic alcohols and ethers in up to 81% yield and >98% stereoisomeric purity. The approach is applicable to synthesis of products containing an alcohol, an aldehyde, a carboxylic acid or an alkenyl substituent. Mechanistic models that account for the observed trends in efficiency and stereoselectivity will be provided. Chapter 3. A New Ru-Based Catechothiolate Complex Bearing an Unsaturated NHC Ligand for Synthesis of Z-α,β-Unsaturated Carbonyl Compounds by Cross Metathesis Design and development of a new Ru catechothiolate complex that may be used to promote Z-selective cross-metathesis transformations that afford Z-α,β-unsaturated esters, acids, and amides (including Weinweb amides) are discussed. Comparison between Ru catechothiolate complexes with an unsaturated NHC and a saturated NHC ligand will be provided. Utility of the approach is demonstrated by an eight-step synthesis (15% overall yield) of an intermediate for synthesis of stagonolide E, and a five-step synthesis of a precursor to dihydrocompactin
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

The mechanism of homologation of bioethanol to butanol and higher alcohols via the Guerbet reaction was computationally and experimentally investigated. The catalytic pathway involves a ruthenium-based complex and a base co-catalyst which work simultaneously. Due to selectivity issues, secondary products were formed and high competition between main pathway and side reactions was recorded. Herein, the overall catalytic mechanism for all the processes involved in was investigated, also considering the principal side reactions, using density functional theory (DFT) methods and experiments to confirm theoretical outcomes. Due to the complexity of the reaction network, kinetic simulations were established from DFT results, confirming experimental products distribution and giving insights into the factors governing the reaction mechanism.

Thesis advisor: Amir H. Hoveyda
Chapter 1. Through the use of quantum theory of atoms in molecules (QTAIM) the similarities and differences between transition metal complexes ligated by phosphines and N-heterocyclic carbenes (NHC) were elucidated. Among the key findings, the phosphines were identified as stronger charge donors than NHCs; however, the latter class of ligands exhibits a weaker p-accepting character than the former. Furthermore, Tolman electronic parameter (TEP) was determined to be an inadequate gauge for the total electron donating ability of phosphines and NHCs; rather TEP can serve as a measurement of population of dp set of orbitals of a metal center in question. Computational and experimental studies of the mechanism of NHC-catalyzed boron and silicon addition to a,ß-unsaturated carbonyls reactions were carried out. Through the use of radical traps the mechanisms involving homolytic cleavage of B-B or B-Si bonds were ruled out. Computational (DFT) studies of the mechanism identified two pathways: (1) direct activation of diboron or borosilyl reagents through coordination of NHC to the B atom, (2) net oxidative addition of the diboron or borosilyl reagents to the carbon (II) of the NHC. The insights gained from the aforementioned studies were employed to rationalize the observed lack of reactivity of NHC-activated diboron complexes in the presence of aldehydes. Chapter 2. New C(1)-symmetric chiral monodentate N-heterocyclic carbenes were prepared, and corresponding chiral Ru-carbene complexes were synthesized. These complexes were employed to gain empirical understanding of factors that govern stereoselectivity in Ru-catalyzed enantioselective olefin ring-closing metathesis. The data thus obtained was employed to infer that syn-to-NHC reaction pathways are competitive and non-selective. One plausible mechanism, through which syn-to-NHC pathways can be accessed, involves Berry pseudorotations. Through the use of stereogenic-at-Ru complexes diastereomeric Ru-carbenes were isolated (silica gel chromatography) and spectroscopically characterized in solution phase. The diastereomeric Ru-carbenes were found to undergo non-metathesis stereomutations at Ru center, thereby providing additional support for the above hypothesis regarding accessibility of syn-to-NHC olefin metathesis pathways. Non-metathesis stereomutation at Ru was found to be accelerated in the presence of protic additives, suggesting the plausibility of hydrogen bonding between the acidic proton and the X-type ligands on Ru. Occurrence of hydrogen bonding was corroborated through the use of chiral allylic alcohols in Ru-catalyzed diastereoselective ring-opening/cross metathesis, which was developed into a versatile method for highly diastereoselective functionalization of terminal olefins
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Des catalyseurs Ru supporté sur TiO2 actifs et sélectifs pour l’hydrogénation de l’acide lévulinique en γ-valérolactone en présence d’acide formique comme source interne d’hydrogène ont été développés. L’élaboration d’un nouveau support, TiO2 modifié par Ca2+, permet d’améliorer la production de γ-valérolactone, grâce à la fois à une décomposition de l’acide formique plus sélective en hydrogène et à une hydrogénation de l’acide lévulinique plus efficace. Ces performances améliorées sont associées à l’existence d’interactions Ru/support plus fortes avec une adsorption du CO plus faible, et à une basicité accrue du support. Elles ont été exaltées par la mise en œuvre d’une synthèse photo-assistée sous lumière solaire comme alternative soutenable à l’imprégnation par voie humide, permettant d’obtenir des particules sub-nanométriques de distribution de taille étroite. Il a été montré qu’un profile de type volcano centré sur 1.5 nm relie l’activité catalytique à la taille des particules
Active and selective Ru catalysts based on TiO2 supports have been developed for the combined hydrogenation of levulinic acid to γ-valerolactone with internal hydrogen supply via in-situ formic acid decomposition. A controlled modification of the TiO2 support by Ca2+ improved the catalytic performance in the one-pot hydrogenation, as a result of enhanced performances in both the formic acid dehydrogenation and the levulinic acid hydrogenation. The improved performances were associated to stronger Ru/support interactions with weaker CO adsorption, as well as to an increased support basicity. The performances were further exalted thanks to a one-step solar light photon-assisted synthesis method used as sustainable alternative to classical wet impregnation. It enabled the uniform dispersion of sub-nanometric metallic Ru particles with narrow distribution and fine size monitoring, and a volcano-type profile centered at 1.5 nm was demonstrated between the nanoparticle size and the activity

Le nouveau complexe Cp*La(BH4)2(THF)2 a été utilisé en combinaison avec des alkyles magnésiens et aluminiques pour la (co)polymérisation coordinative par transfert de chaîne (CCTP) du styrène et de l’isoprène. En développant ce concept nous avons obtenu la première croissance de chaîne catalysée du styrène et de l’isoprène avec contrôle de la microstructure. L’application de la CCTP à la copolymérisation statistique est une voie nouvelle et originale pour le contrôle de la composition de copolymères.Par ailleurs, une étude mécanistique a été réalisée pour la polymérisation de l’ ε-caprolactone avec des dérivés cationiques de ruthénium [(η5-C5H5)Ru(η6-arène substitué)][PF6]. Nous avons montré que la polymérisation a lieu selon un mécanisme de type monomère activé avec transfert aux alcools, avec modification de l’hapticité du ligand arène
A newly synthesized Cp*La(BH4)2(THF)2 complex in combination with magnesium or aluminum alkyls was used for the coordinative chain transfer (co)polymerization (CCTP) of styrene and isoprene. Using this concept, we have accomplished the first catalyzed chain growth like reaction of styrene and isoprene, with control of the microstructure. The application of CCTP to statistical copolymerization represents a new and original approach to tune the composition of copolymers. In addition, a mechanistic study of the ring-opening polymerization of ε-caprolactone by [(η5-C5H5)Ru(η6-substituted arene)][PF6] complexes shows that the polymerization proceeds via an activated monomer mechanism by transfer to the alcohol with a change of hapticity of the arene ligand

Dans ce travail, différents systèmes catalytiques nanostructurés ont été synthétisés par une approche organométallique pour obtenir des nanoparticules de petite taille et de distribution de taille étroite, et leur activité catalytique dans la réaction d'oxydation de l'eau a été évaluée. Premièrement, des NPs de fer stabilisées par l'acide oléique ont été synthétisées qui présentaient une taille moyenne d'env. 10 nm ± 1,1 nm. Une couche d'oxyde, gamma-Fe_2O_3, d'env. 2,6 nm d'épaisseur a été formée à leur surface pour obtenir des structures cœur-coquille Fe@FeOx d'env. 11,5 ± 2,3 nm de diamètre. Malgré leur hydrophobicité, ces nanoparticules ont montré une bonne activité électrocatalytique en conditions alcalines. La coquille d'oxyde gamma-Fe_2O_3 étant bien adaptée au greffage de groupements phosphoniques, ces NPs Fe@FeOx ont été greffées avec différents acides aminophosphoniques afin de les transférer dans l'eau. Une évaluation préliminaire de leur activité catalytique montre une amélioration lorsque les NPs sont greffées avec l'acide 3-aminopropyl phosphonique, ce qui ouvre des perspectives prometteuses. En outre, un photosensibilisateur, un complexe Ru-phénanthroline avec un groupe phosphonate pendant, a été synthétisé et greffé sur les NPs Fe@FeOx pour former une photoanode hybride et catalyser la photoélectrodécomposition de l'eau. Des processus mono et biphasiques ont été étudiés pour greffer le complexe à la surface des nanoparticules. Le processus monophasique s'est avéré plus efficace car il a fourni une densité de greffage plus élevée (respectivement 56 et 9 Ru par NP pour les processus mono et biphasiques). Des mesures photoélectrochimiques ont montré que le nanocatalyseur hybride comprenant la teneur en Ru la plus élevée était env. 9 fois plus actif qu'un simple mélange entre un photosensibilisateur au ruthénium sans fonction de greffage et les nanoparticules Fe@FeOx, et env. 40 fois plus actif que les NPs Fe@FeOx. L'amélioration des performances pourrait être attribuée à un transfert d'électrons plus efficace entre le photosensibilisateur et le catalyseur Fe@FeOx grâce à la liaison covalente entre ces deux composants. Le greffage covalent s'est avéré améliorer non seulement l'activité photocatalytique mais également la stabilité du système. Enfin, des NPs NiFe amorphes (diamètre env. 4 nm) avec deux compositions différentes (Ni_0,5Fe_0,5 NPs et Ni_0,68Fe_0,32 NPs) ont été synthétisées, oxydées à l'air et fonctionnalisées avec de l'acide 3-aminopropyl phosphonique. L'activité électrocatalytique de ces NP hydrosolubles a été étudiée en milieu alcalin, en comparaison avec des NPs NiOx, FeOx et Ni_0.1Fe_0.9Ox. Les NPs hydrosolubles contenant 32% de Fe (Ni_0,68Fe_0,32Ox) ont montré l'activité la plus élevée et une bonne durabilité en solution alcaline. Ces caractéristiques rendent ces NP amorphes potentiellement applicables dans les cellules photoélectrochimiques pour la photodécomposition de l'eau
In this work, different nanostructured catalytic systems have been synthesized by an organometallic approach to produce nanoparticles (NPs) of small size and narrow size distribution, and their catalytic activity in the water oxidation reaction has been evaluated. First Fe NPs stabilized by oleic acid were synthesized that displayed an average size of ca. 10 nm ± 1.1 nm. A gamma-Fe_2O_3 oxide layer ca. 2.6 nm thick has been formed at their surface to obtain Fe@FeOx core-shell structure of ca. 11.5 ± 2.3 nm in diameter. Despite their hydrophobicity, these nanoparticles showed good electrocatalytic activity in alkaline conditions. As the gamma-Fe_2O_3 oxide shell is well adapted to the grafting of phosphonic groups, these Fe@FeOx NPs were grafted with different aminophosphonic acids in order to transfer them into water. Preliminary assessment of their catalytic activity showed improved activity for the NPs functionalized by 3-aminopropylphosphonic acid which opens promising prospects. Subsequently, a Ru-phenanthroline light-harvester with a pendant phosphonate group was synthesized and grafted onto the Fe@FeOx core/shell NPs to afford a novel hybrid photoanode for solar-driven water splitting. Mono- and biphasic processes were investigated to graft the Ru-complex at the surface of the NPs. The monophasic process was found to be more efficient as it provided a higher grafting density at the surface of the NPs (respectively 56 and 9 Ru per nanoparticles for the mono and biphasic processes). Photoelectrochemical measurements showed that the hybrid nanocatalyst comprising the highest Ru content was ca. 9-fold more catalytically active than a simple mixture between a ruthenium polypyridyl photosensitizer bearing no grafting group and the Fe@FeOx nanoparticles, and 40-fold more active than the pristine Fe@FeOx NPs. The performance enhancement could be attributed to a more efficient electron transfer between the ruthenium polypyridyl photosensitizer and the Fe@FeOx water oxidation catalyst thanks to the covalent bonding between these two components. The covalent grafting was found to improve not only the photocatalytic activity but also the stability of the system. Finally, amorphous NiFe NPs (diameter ca. 4 nm) with two different ratios between Ni and Fe (Ni_0.5Fe_0.5 NPs and Ni_0.68Fe_0.32 NPs) were synthesized, oxidized in air and grafted with 3-aminopropylphosphonic acid in order to obtain hydrophilic systems. The electrocatalytic activity of these water-soluble NPs was studied in alkaline solution, in comparison with that of crude NiOx NPs, FeOx NPs, and Ni_0.1Fe_0.9Ox NPs. The water soluble NPs containing 32 % of Fe (Ni_0.68Fe_0.32Ox) showed the highest activity and a good durability in alkaline solution. These characteristics make these amorphous NPs potentially applicable in photoelectrochemical cells for water splitting

Tese de mestrado em Química Tecnológica (Química Tecnológica e Qualidade), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011
p-Cymene based ruthenium complexes were employed in the alkylation of tbutylamine with phenethyl alcohol by redox neutral alkylation and in the reduction of acetophenone and benzaldehyde by transfer hydrogenation. A range of in situ generated catalysts formed by [RuX2(p-cymene)]2 dimers (X=Cl or I) with dppf, DPEPhos, dippf or P(i- Bu)3 and a range of p-cymene ruthenium monomers, namely [RuCl(dppf)(p-cymene)]SbF6, [RuI(dppf)(p-cymene)]SbF6, [RuCl(dppf)(p-cymene)]BF4, [RuCl(dppf)(p-cymene)]Cl, [RuI(P(n- Bu)3)2(p-cymene)]SbF6, [RuCl(P(i-Bu)3)2(p-cymene)]SbF6, [RuCl2(P(n-Bu)3)2(p-cymene)], [RuCl(P(CH3)3)2(p-cymene)]SbF6 have been employed in these reactions. These monomers have been synthesised and characterized in this project and only [RuCl2(P(n-Bu)3)2(pcymene)] has been already reported in the literature. Results were compared in terms of conversions and the best ones for the redox neutral alkylation were with the in situ generated catalyst formed by [RuI2(p-cymene) and DPEPhos, giving 96% conversion for a catalyst/substrate ratio of 20 and with [RuI(dppf)(pcymene)] SbF6 which gave 85% conversion for a catalyst/substrate ratio of 40. These reactions have been run out in the open air without degassing or inert gas protection throughout which is not the typical approach found in the literature and that can be very appealing in the industrial point of view. The different halides incorporated in these complexes have been proved to have different effects in the catalytic activity, with iodine usually leading to more active catalysts. Some results and experiments that were performed allowed drawing some conclusions about the mechanism. For the reduction of acetophenone and benzaldehyde by transfer hydrogenation it has been demonstrated that the dimers, the dimer-phosphine pairs and the ruthenium monomers mentioned before are not the most suitable pre-catalysts for these reactions. Overall, conversions up to 73% were obtained which lag far behind the 100% reported in the literature for several other complexes. Some conclusions were drawn about the mechanism and two catalytic cycles were proposed. The brand new dimer [Ru2Cl3(DPEPhos)2(CH3CN)2]SbF6 has been serendipitously synthesised and has shown it forms catalytically active species in both the alkylation of tbutylamine and reduction of acetophenone giving moderate conversions.
Neste projecto foram sintetizados complexos de rutenio e p-cimeno que foram posteriormente avaliados do ponto de vista catalitico em reaccoes de transferencia de hidrogenio. Os complexos de rutenio e p-cimento tem demonstrado ser catalisadores/precatalisadores eficientes em varias reaccoes envolvendo compostos organicos e foi inicialmente sugerido para este projecto pela empresa biofarmaceutica Astra Zeneca o estudo da actividade catalitica do dimero [RuCl2(p-cimeno)]2 na presenca das fosfinas DPEPhos, dippf e P(i-Bu)3 em reaccoes de transferencia de hidrogenio. Esta empresa verificou que este dimero e extremamente activo na alquilacao de morfolina com álcool benzilico na presenca das fosfinas referidas (conversoes acima de 97%). No que respeita aos complexos sintetizados, levaram-se a cabo as sinteses dos dimeros de cloro e iodo de formula molecular [RuX2(p-cimeno)]2 em que X = Cl ou I e ainda de monomeros utilizando os dimeros referidos como compostos de partida. A sintese do dimero de bromo foi tambem tentada mas este revelou-se muito dificil de obter e portanto nao foi utilizado em sinteses posteriores nem nas reaccoes cataliticas. Para obter os monomeros foram ainda utilizadas fosfinas mono ou bidentadas, nomeadamente dppf, DPEPhos, dippf, P(i-Bu)3, P(n-Bu)3, P(CH3)3 ou PhPCl2 que originaram os seguintes complexos neutros ou mono cationicos: [RuCl(dppf)(p-cimeno)]SbF6, [RuI(dppf)(p-cimeno)]SbF6, [RuCl(dppf)(p-cimeno)]BF4, [RuCl(dppf)(p-cimeno)]Cl, [RuCl(P(n-Bu)3)2(p-cimeno)]SbF6, [RuI(P(n-Bu)3)2(p-cimeno)]SbF6, [RuCl(P(i-Bu)3)2(p-cimeno)]SbF6, [RuCl2P(n-Bu)3(p-cimeno)], [RuCl2P(i-Bu)3(p-cimeno)], [RuCl(P(CH3)3)2(p-cymene)]SbF6 e [RuCl2PPh(OCH3)2(p-cymene)]. Entretanto foi ainda sintetizado, por acaso, o dimero [Ru2Cl3(DPEPhos)2(CH3CN)2]SbF6 numa das tentativas de obter o monomero [RuCl(DPEPhos)(p-cymene)]SbF6. Estes compostos foram caracterizados por 1H, 13C e 31P NMR, espectrometria de massa e analise elementar. Entre eles apenas os complexos neutros [RuCl2P(n-Bu)3(p-cimeno)] e [RuCl2P(i-Bu)3(pcimeno)] ja tinham sido referenciados na literatura. As reaccoes aos quais foram submetidos os complexos sintetizados envolvem todas elas, como foi dito, transferencia de hidrogenio. Este tipo de reaccoes envolve normalmente a reducao de cetonas ou iminas e a oxidacao de alcoois ou aminas em que um catalisador transfere hidrogenio entre entre o substrato e o dador ou aceitador de hidrogenio, respectivamente. As reaccoes de transferencia de hidrogenio que aqui foram testadas foram a alquilacao da t-butilamina com alcool feniletilico designada formalmente por “redox neutral alkylation” e a reducao da acetofenona e do benzaldeido aos respectivos alcoois. O potencial catalitico dos complexos sintetizados para com as reaccoes mencionadas foi avaliado maioritariamente por 1H NMR pela percentagem de alcool de partida convertido a produto e num dos casos foi avaliado por cromatografia gasosa pela monitorizacao da concentracao de produto ao longo do tempo. Nomeadamente foi avaliado o potencial catalitico dos dimeros, dos dimeros na presenca de fosfinas e dos monomeros. Na alquilacao da t-butilamina os dimeros por si mesmo revelaram-se inapropriados uma vez que nao foram obtidas conversoes acima de 3%. Ja no caso dos dimeros na presenca de fosfinas os resultados foram significativamente melhores com o par [RuCl2(pcimeno)] 2-DPEPhos a merecer lugar de destaque uma vez que apresentou 96% de alcool de partida convertido a produto com uma proporcao substrato/catalisador de 20. Este resultado foi mesmo o melhor de entre todas as reaccoes de alquilacao levadas a cabo. Relativamente ao uso dos monomeros como pre-catalisadores, o monomero [RuI(dppf)(pcimeno)] SbF6 apresentou o resultado mais promissor com 85% de conversao com uma proporcao substrato/catalisador de 40. Estes resultados tornam-se ainda mais interessantes se levarmos em conta de que estas reaccoes foram levadas a cabo em contacto com a atmosfera, sem desarejamento ou uso de gas inerte durante a reaccao o que nao e a abordagem normalmente encontrada na literatura e que pode ser muito apelativa do ponto de vista industrial. De uma maneira geral as fosfinas bidentadas levaram a resultados promissores tanto quando usadas em combinacao com os dimeros tanto quando foram incorporadas nos respectivos monomeros. O mesmo nao pode ser dito das fosfinas monodentadas. A fosfina P(i-Bu)3 quando na presenca do dimero [RuCl2(p-cimeno)]2 levou a uma conversao de alcool a amina de apenas 28% e quando incorporada no respecivo monomero [RuCl(P(i-Bu)3)2(p-cimeno)]SbF6 nao foi alem dos 9%. Os outros complexos contendo fosfinas monodentadas e que foram testados nesta reaccao de alquilacao, nomeadamente o [RuI(P(n-Bu)3)2(p-cimeno)]SbF6, [RuCl2P(n-Bu)3(p-cimeno)], e o [RuCl(P(CH3)3)2(p-cymene)]SbF6 nao formaram qualquer especia activa cataliticamente uma vez que nao foi detectada a formacao de qualquer amina. Nesta reaccao, para alem da analise do efeito da fosfina, foi analisado o efeito do halogeneto e de uma maneira geral a presenca de iodo em vez de cloro tanto nos dimeros como nos monomeros levou a obtencao de maiores precentagens de produto e/ou reducao na quantidade de alcool por reagir. Foi ainda analisado o efeito do contra-iao, nomeadamente entre os monómeros [RuCl(dppf)(p-cimeno)]SbF6, [RuCl(dppf)(p-cimeno)]BF4 e [RuCl(dppf)(p-cimeno)]Cl e o monomero [RuCl(dppf)(p-cimeno)]Cl parece ser o melhor pre-catalisador apresentando 82% de amina obtida com uma proporcao substrato/catalisador de 20. Os resultados sugerem ainda que os complexos de formula molecular [RuX(LL)(p-cimeno)]+ onde X = halogeneto e LL = ligando bidentado sao os precursores cataliticos nas reaccoes em que sao empregues os dimeros [RuX2(p-cimeno)]2 e fosfinas bidentadas. Uma das reaccoes de alquilacao, como dito anteriormente, foi monitorizada por cromatografia gasosa. Nesta reaccao foi empregue o dimero [RuCl2(p-cimeno)]2 na presença de dppf e a monitorizacao decorreu durante 24h, isto e, o tempo a que todas as alquilações foram submetidas. No entanto esta reaccao apresentou concentracoes de produto/ conversoes muito abaixo das esperadas comparativamente a conversao obtida por 1H NMR para a mesma reaccao. Apesar disso, o padrao de reducao da concentracao de alcool e o padrao de aumento da concentracao de produto ao longo do tempo, corroboram uma das observacoes feitas acerca das conversoes obtidas por 1H NMR, nomeadamente de que durante a reaccao se esta a formar um produto secundario, nomeadamente o ester PhCH2CH2O2CCH2Ph que resulta da reaccao do aldeido formado cataliticamente com o álcool remanescente em solucao que ainda nao reagiu. No entanto, dadas as incoerências encontradas a nivel das concentracoes, da avaria do cromatografo gasoso durante um largo periodo de tempo e de algumas questoes relacionadas com o metodo, a monitorizacao por cromatografia gasosa foi abandonada. Relativamente as reducoes por transferencia de hidrogenio, nomeadamente a reducao da acetofenona e do benzaldeido estas demonstraram padroes de conversao muito semelhantes, nomeadamente os pre-catalisadores que apresentaram percentagens de conversao maiores foram os dimeros sem qualquer adicao de fosfina, ao contrario do que aconteceu nas reaccoes de alquilacao, e a presenca de iodo nos pre-catalisadores nao levou ao aumento, na grande maioria dos casos, da percentagem de produto obtido. No geral, não foram obtidas conversoes acima de 73% o que e um resultado que fica muito aquem dos 100% ja referenciados na literatura para uma larga gama de complexos. Ainda, mais uma vez, as fosfinas monodentadas parecem nao ser apropriadas para serem incorporadas nos pre-catalisadores nas reaccoes de transferencia de hidrogenio uma vez que o monómero [RuI(P(n-Bu)3)2(p-cimeno)]SbF6 nao foi alem dos 3% de acetofenona convertida ao respectivo alcool ou alem dos 12% no caso do benzaldeido. Apesar de tudo, os resultados obtidos permitiram especular um pouco acerca dos mecanismos reaccionais seguidos tendo sido propostos dois mecanismos, um para quando sao empregues apenas os dimeros e outro para quando sao empregues os dimeros na presenca de fosfinas ou empregues os monomeros. Quanto aos resultados obtidos pelo dimero [Ru2Cl3(DPEPhos)2(CH3CN)2]SbF6, este formou especies activas cataliticamente tanto nas alquilacoes como nas reducoes obtendo-se conversoes moderadas em ambos os casos, o que nao deixa de ser um resultado interessante uma vez que, tanto quanto se sabe, ainda nao foi referenciado na literatura o uso de complexos com tres pontes de cloro nas reaccoes em questao.

The development of well-defined ruthenium alkylidene (PCy₃)₂Cl₂Ru=CHPh brought about a revolution in the area of olefin metathesis. The objective of the work presented here is to expand the scope of ruthenium-based olefin metathesis catalysts such as (PCy₃)₂Cl₂Ru=CHPh through the development of novel synthetic organic methods for ring-closing metathesis as well as through modification of the ligand sphere of the ruthenium complexes.

Chapter 2 describes the application of ruthenium alkylidenes to the catalysis of polycyclization reactions. Several acyclic precursors have been synthesized and reacted with (PCy₃)₂Cl₂Ru=CHPh. These precursors vary in topology and contain acetylenic and/or cycloolefinic metathesis relays. The cyclization reactions proceed in good yields to produce polycyclic polyenes.

Chapter 3 focuses on the synthesis of racemic and enantiopure targets containing the 6,8-dioxabicycIo [3.2.1]octane skeleton using an intramolecular ruthenium-catalyzed ring-closing metathesis reaction as the key step. The natural product frontalin is synthesized in racemic and enantiopure forms and in excellent yields using this methodology.

Chapter 4 outlines the preparation of a novel imidazolylidene-substituted ruthenium-based complex starting from (PCy₃)₂RuCl₂(=CHPh). The N-heterocyclic carbene-substituted olefin metathesis initiator exhibits increased ring-closing metathesis activity at elevated temperature compared to that of the parent complex (PCy₃)₂Cl₂Ru(=CHPh). Di-, tri-, and tetra-substituted cycloolefins are successfully prepared from corresponding diene precursors in moderate to excellent yields.

Chapter 5 describes the preparation of a new family of 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene-substituted ruthenium-based complexes. These air and water tolerant systems exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex (PCy₃)₂Cl₂Ru(=CHPh) as well as to the complexes disclosed previously in Chapter 4. In many instances the activity of these new complexes also rivals or exceeds that of the alkoxy-imido molybdenum-based olefin metathesis catalysts. Applications of chiral N-heterocyclic carbene ruthenium complexes to asymmetric ring-closing metathesis are also briefly discussed.

Finally, the synthesis of the Schiff base-substituted ruthenium carbene complexes on a solid support is described in Chapter 6. The activities of the supported complexes are compared to those of their unsupported counterparts. The newly prepared systems are found to be highly stable to air, moisture, and temperature, and exhibit increased catalytic activity in acidic media.

A new hexahydro-s-indacene based NHC ligand and transition metal complexes with Ag, Ir and Ru were prepared. The catalytic behavior of ruthenium complexes with the new NHC ligand in ring-closing metathesis reactions of sterically demanding substrates was investigated. New N-Hoveyda-type and 2-aryloxy-substituted Hoveyda-type complexes were synthesized in the reaction of the Grubbs 3rd generation type complexes [RuCl2(NHC)(3-phenylindeneylidene)(Py)] (NHC = SIMes, SIPr) with 2-ethenyl-N-alkyl-N-phenylaniline (alkyl = Me, Et) and 1-ethenyl-2-phenoxybenzenes (with EWG/EDG groups R para to oxygen).The catalytic activity in various RCM reactions was probed and the new complexes found to be highly efficient. Eight new Hoveyda-type complexes with ferrocenyl substituents were synthesized. Two of these complexes were found to be latent catalysts for ROMP reactions in the reduced state, but are able to polymerize cis-cyclooctene following chemical or electrochemical oxidation of the ferrocenyl group.

碩士
國立中山大學
化學系研究所
106
Grubbs catalyst is one of the most widely used olefin metathesis catalysts. Since ring-opening metathesis（ROM）and ring-closing metathesis（RCM）are the reverse reaction of each other, if the reaction was left for too long, the undesired reverse reaction may occur. In other cases, oligomers may be formed causing the low yield. Metal scavengers can deactivate the catalyst at the right time and can be useful for subsequent purification. In this thesis, silica nanoparticles modified with terminal olefins containing thioether functional groups were investigated as potential scavenger for ruthenium-based metathesis catalysts. We envision that the coordination of the chalcogens and olefins with the ruthenium metal in the catalyst would form a stable cyclic intermediate, which results in the poisoning of the catalyst. The used of modified nanoparticle has the advantages of having larger surface area and ease of separation by centrifugation. The effect of the amount of base and reaction time on particle diameter will be discussed. In addition, the method will be discussed to detectmine the quantity of olefinic functional groups modified on nanoparticles per unit weight. These include the hydroboration with catecholborane, and the indirect analysis of the particles using Ellman''s test. Finally, we will discuss the removal efficiency of the ruthenium metal catalyst.

With the ever expanding utility of transition metal catalysis, there has been a thrust both to develop catalysts with unique selectivites or activites, and to understand the factors which govern these characteristics at both a fundamental and practical level. Olefin metathesis has become an essential reaction for the synthesis of small molecules in addition to polymeric materials. We have pursued two distinct ligand classes based on diaminocarbenes with novel architectures to address specific limitations within this useful class of reactions: 1) limited access to polymeric materials with controlled microstructures and 2) poor stereoselectivity in Ru-catalyzed cross-metathesis (CM) reactions. Numerous phosphines and N-heterocyclic carbenes (NHCs) have been used as ligands for Ru metathesis catalysts, and the resulting activity is very sensitive to their steric and electronic nature. We envisioned that we could take advantage of this dependence by developing a catalyst with tunable ligand donicity. Redox-switchable ligands can lead to catalysts whose selectivity and/or activity are dependent upon the ligand oxidation state. Towards this purpose, we have developed a ligand which incorporates a 1,1’-disubstituted ferrocene moiety into the backbone of a diaminocarbene (FcDAC). Upon ligation of FcDAC to various transition metals, we were able to use cyclic voltammetry and a spectroelectrochemical FT-IR experiment to show electronic communication between FcDAC and the coordinated metal. We then pursued Ru metathesis catalysts incorporating these ligands. The ring-opening metathesis polymerization of 1,5-cyclooctadiene was studied using [(FcDAC)(PPh₃)Cl₂Ru=(3-phenylindenylid-2-ene)] as the catalyst. Chemical redox reactions were used to establish the ability of FcDAC to impart redox-tunable properties to Ru metathesis catalysts. A new ligand class pioneered in our group, N-aryl,N-alkyl acyclic diaminocarbenes (ADCs), was also studied in various Ru metathesis catalysts. To our delight, these catalysts showed lower E : Z ratios than analogous NHC ligands in two representative CM reactions. We also investigated the conformational diversity of these differentially substituted ADCs given their ability to rotate about their C–N bonds, in particular, to determine how this might influence their donicity. Complexes of the type [(ADC)Ir(COD)Cl] and [(ADC)Ir(CO)₂Cl] were studied, given the wealth of structural and spectral data available for analogous compounds incorporating related ligand classes. Different conformations resulted depending on the N-substituents and the nature of the metal complex. Interestingly, the electron donating ability of ADC ligands was found to depend on their conformation, as evidenced by FT-IR and cyclic voltammetry. This established a new avenue for tuning the donor properties of differentially substituted ADC ligands. The unique properties of these novel ligand classes were demonstrated in Ru metathesis catalysts. However, on a broader level, these ligands are expected to have utility in diverse catalytic applications.
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The improved synthesis and olefin metathesis activity of N-heterocyclic carbene (NHC)-coordinated ruthenium alkylidenes of the form (NHC)(L)_x(Cl)₂Ru=CHR (x = 1 or 2) are reported. In order to circumvent the handling of highly sensitive free carbenes, N-heterocyclic carbene "adducts" were prepared in high yields by the reaction of nucleophilic bases with N,N'-diarylimidazolium salts. Most notably, the addition of trichloromethyl anion to N,N'-dimesityl-4,5-dihydroimidazolium chloride produced an air-, moisture-, and temperature-stable crystalline adduct, 2-trichloromethyl-4,5-dihydro-imidazolidine. When this species is heated above the critical temperature of 55 degrees C in the presence of (PCy₃)₂(Cl)₂Ru=CHPh, a single, clean phosphine substitution reaction occurs to form the NHC-coordinated benzylidene (NHC)(PCy)3(Cl)2Ru=CHPh in 84% isolated yield. This procedure has been successfully scaled up to industrial production and remains the most effective catalyst synthesis to date.

The NHC-coordinated catalysts show dramatically expanded activity relative to their bis-phosphine counterparts. The high yielding, trans-stereoselective cross metathesis of various acroyl substrates is the first example of the ruthenium-catalyzed metathesis of olefins directly substituted with electron-withdrawing functionality. Ring-opening cross metathesis of acroyl species with relatively high ring strain cyclooctadiene and norbornene monomers has also been achieved in good yields and perfect regioselectivity when the norbornene is asymmetrically substituted with a bridgehead methyl group.

Further expansion of the substrate scope was achieved when the catalyst's phosphine ligand was replaced with more weakly bound 3-bromopyridine (3-Br-pyr) ligands. The resulting catalyst (NHC)(3-Br-pyr)₂(Cl)₂Ru=CHPh produced synthetically useful yields (>= 67%) in the cross metathesis of acrylonitrile and terminal olefins (as opposed to less than 30% yield with the phosphine-coordinated catalyst). NHC-coordinated catalysts therefore allow both electron-rich and electron-poor olefins to undergo metathesis in the same pot, potentially leading to synthetically valuable products containing electronically differentiated olefins.

The lower activity of phosphine-coordinated catalysts relative to those coordinated with 3-bromopyridine can be addressed by the addition of "phosphine scavengers" to the former. Higher pK_a carboxylic acids (such as acetic and benzoic acids) are capable of accelerating catalysis as effectively as the much stronger hydrochloric acid, without concomitant catalyst decomposition. These properties make carboxylic acids the optimal choice for use with sensitive organic substrates.

Project I: [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 as a Homogeneous Hydrogenation Catalyst for Biomass Derived Substrates. The complex [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 has been shown to be an active ionic hydrogenation catalyst for selected carbonyls, diols and glycerol by the Schlaf group. It was postulated to also be active for other biomass derived substrates such as levulinic acid (LA), furfural and 5-hydroxymethyl furfural (HMF). Synthesis of the complex was optimized and full characterization carried out by 1H/13C –NMR. The complex was tested against LA in aqueous sulfolane medium and the furfural/HMF model system 2,5-hexanedione in water. Activity of the complex was compared to the analogous metal-ligand bifunctional (MLB) system described in Project II. The complex exhibited good thermal stability up to 200 oC in 90/10 wt% sulfolane/water mixtures and was capable of hydrogenation of LA to γ-valerolactone in 95% yield. Addition of protic acids to the reaction mixture and increasing proportions of water decreased the activity of the complex towards the hydrogenation of LA. Project II: [Ru(OH2)3(di(picolyl)amine)](OTf)2 as an acid-, water- stable, metal-ligand bifunctional deoxygenation catalyst. The complex [Ru(OH2)3(di(picolyl)amine)](OTf)2 was postulated to be an active MLB ionic hydrogenation catalyst under acidic aqueous conditions. Using the substantially labile [Ru(DMF)6](OTF)3 ruthenium complex as the precursor, the desired complex was prepared insitu by coordination of the DPA ligand and concomitant reduction of Ru3+ to Ru2+. The complex was characterized by 1H/13C-NMR and tested for the hydrogenation of LA, 2,5-hexanedione, furfural and HMF under acidic aqueous conditions. The complex exhibited thermal stability up to 150 oC and was active for the hydrogenation of carbonyls, as demonstrated by the conversion of 2,5-hexanedione to 2,5-hexanediol in 94% yield in water. Addition of H3PO4 as an acid cocatalyst resulted in nearly complete conversion to dimethyltetrahydrofuran (DMTHF) but further deoxygenation could not be achieved. Direct comparision of [Ru(OH2)3(di(picolyl)amine)](OTf)2 and [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 under identical conditions against LA and 2,5-hexanedione demonstrated that the[Ru(OH2)3(di(picolyl)amine)](OTf)2 catalyst is more active than the [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 complex in all cases, suggesting that the di(picolyl)amine complex operates through a MLB ionic hydrogenation mechanism.
NSERC

碩士
國立交通大學
生物科技學系
107
The non-renewable energy, which is a limited natural energy that comes from the oil, coal, and natural gas, is not likely to continue into the future. A renewable resource such as hydrogen is the fuel of the future, as it has the highest heat energy of combustion compared to the other organic sources and it is eco-friendly. In nature, hydrogen can be generated by the hydrogenase. In recent years, studies on the hydrogenase have been published, and the investigated hydrogen production systems have been applied. In this study, we successfully synthesized an artificial bionic iron-iron [Fe-Fe] hydrogenase's active site and replace the center metal atom iron with ruthenium, Ru2S2(tosyl-adt2-), and characterized the system using UV-visible spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, nuclear magnetic resonance spectroscopy, and X-ray diffraction. In the experiments, the Ru2S2(tosyl-adt2-) activities were obtained, and aqueous/alcohol/formic acid dehydrogenation under a 500 W Xe lamp was optimized. The effects of temperature, concentration, base, p-ligand, and photosensitizers were studied. Lastly, the lamp source irradiation was replaced by solar irradiation in the best condition. Hydrogen as the fuel of the future requires both safe and stable for storage and transportation. Formic acid is produced by the hydrogenation of CO2, and it is an intermediate H2 and CO2 carrier. Furthermore, we also report the development and optimization of an active system of the reversible hydrogenation of CO2 with the Ru2S2(tosyl-adt2-) catalyst.