Catalytic Small Molecule Reduction Using Late Transition Metal Complexes of Carbon and Nitrogen Donor Chelates PDF Download
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Author: Sopheavy Siek
Publisher:
ISBN:
Category :
Languages : en
Pages : 772
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Book Description
Hydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible that energy can be released on demand. A new bidentate chelating ligand was designed and synthesized for this project, using an N-heterocyclic carbene ring bound directly to a pyridinol ring (NHC-pyOR). This new ligand was used to make iridium complexes that were studied as catalysts for the hydrogenation of CO2 and dehydrogenation of formic acid. For comparison, analogous bipy derived iridium and ruthenium complexes were also tested. In general, the NHC-pyOR complexes demonstrated modest activity, where hydroxyl-pyridines found in the bipy derived systems are more active for CO2 hydrogenation under basic conditions. However, the trends were quite different for formic acid dehydrogenation reaction which will be discussed in Chapter 2. Other ruthenium (II) and iridium (III) complexes of the NHC-pyOR ligand with difference counter anions from above complexes were also synthesized. The ruthenium complexes were tested for their ability to accelerate CO2 (de)hydrogenation, but our studies show that these complexes all undergo transformations in solution and thus they are not true catalysts, but rather pre-catalysts. The use of new tridentate pincer ligands derived from NHC and pyridinol is also described. A new ligand containing (NHC-pyOR-NHC) rings binding to a metal with the pyridinol derivative were synthesized. A series of metal complexes of the type LnM were synthesized (n = 1 and 2; M = Fe2+, Co3+, and Ru2+). Preliminary results of photocatalytic reduction of CO2 to CO show that ruthenium complexes are the most active catalysts followed by cobalt and iron, respectively. The activation of carbon dioxide and nitrite utilizing bio-inspired and proton responsive catalysts were also studied with tris(triazolyl)hydroborate (Ttz) complexes of zinc(II) and copper(II). For the biomimetic zinc complexes for CO2 activation, the synthetic result was found to be greatly depend on the steric bulk of Ttz ligand which will be discussed in detail in Chapter 6. Moreover, the electrochemical reduction of Ttz-Cu(II) complexes in the presence and absence of a proton source shows processes that are relevant to enzymatic nitrite reduction which also will be studied in Chapter 7.
Author: Sopheavy Siek
Publisher:
ISBN:
Category :
Languages : en
Pages : 772
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Book Description
Hydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible that energy can be released on demand. A new bidentate chelating ligand was designed and synthesized for this project, using an N-heterocyclic carbene ring bound directly to a pyridinol ring (NHC-pyOR). This new ligand was used to make iridium complexes that were studied as catalysts for the hydrogenation of CO2 and dehydrogenation of formic acid. For comparison, analogous bipy derived iridium and ruthenium complexes were also tested. In general, the NHC-pyOR complexes demonstrated modest activity, where hydroxyl-pyridines found in the bipy derived systems are more active for CO2 hydrogenation under basic conditions. However, the trends were quite different for formic acid dehydrogenation reaction which will be discussed in Chapter 2. Other ruthenium (II) and iridium (III) complexes of the NHC-pyOR ligand with difference counter anions from above complexes were also synthesized. The ruthenium complexes were tested for their ability to accelerate CO2 (de)hydrogenation, but our studies show that these complexes all undergo transformations in solution and thus they are not true catalysts, but rather pre-catalysts. The use of new tridentate pincer ligands derived from NHC and pyridinol is also described. A new ligand containing (NHC-pyOR-NHC) rings binding to a metal with the pyridinol derivative were synthesized. A series of metal complexes of the type LnM were synthesized (n = 1 and 2; M = Fe2+, Co3+, and Ru2+). Preliminary results of photocatalytic reduction of CO2 to CO show that ruthenium complexes are the most active catalysts followed by cobalt and iron, respectively. The activation of carbon dioxide and nitrite utilizing bio-inspired and proton responsive catalysts were also studied with tris(triazolyl)hydroborate (Ttz) complexes of zinc(II) and copper(II). For the biomimetic zinc complexes for CO2 activation, the synthetic result was found to be greatly depend on the steric bulk of Ttz ligand which will be discussed in detail in Chapter 6. Moreover, the electrochemical reduction of Ttz-Cu(II) complexes in the presence and absence of a proton source shows processes that are relevant to enzymatic nitrite reduction which also will be studied in Chapter 7.
Author: David Morales-Morales
Publisher: Elsevier
ISBN: 0128129328
Category : Science
Languages : en
Pages : 756
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Book Description
Pincer Compounds: Chemistry and Applications offers valuable state-of-the-art coverage highlighting highly active areas of research—from mechanistic work to synthesis and characterization. The book focuses on small molecule activation chemistry (particularly H2 and hydrogenation), earth abundant metals (such as Fe), actinides, carbene-pincers, chiral catalysis, and alternative solvent usage. The book covers the current state of the field, featuring chapters from renowned contributors, covering four continents and ranging from still-active pioneers to new names emerging as creative strong contributors to this fascinating and promising area. Over a decade since the publication of Morales-Morales and Jensen's The Chemistry of Pincer Compounds (Elsevier 2007), research in this unique area has flourished, finding a plethora of applications in almost every single branch of chemistry—from their traditional application as very robust and active catalysts all the way to potential biological and pharmaceutical applications. - Describes the chemistry and applications of this important class of organometallic and coordination compounds - Includes contributions from global leaders in the field, featuring pioneers in the area as well as emerging experts conducting exciting research on pincer complexes - Highlights areas of promising and active research, including small molecule activation, earth abundant metals, and actinide chemistry
Author: Edward Mason Gordon
Publisher:
ISBN:
Category :
Languages : en
Pages : 456
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
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Book Description
In modern era of scarce resources, developing chemical processes that can eventually generate useful materials and fuels from readily available, simple, cheap, renewable starting materials is of paramount importance. Small molecules, such as dioxygen, dinitrogen, water, or carbon dioxide, can be viewed as ideal sources of oxygen, nitrogen, or carbon atoms in synthetic applications. Living organisms perfected the art of utilizing small molecules in biosynthesis and in generating energy; photosynthesis, which couples carbohydrate synthesis from carbon dioxide with photocatalytic water splitting, is but one impressive example of possible catalytic processes. Small molecule activation in synthetic systems remains challenging, and current efforts are focused on developing catalytic reactions that can convert small molecules into useful building blocks for generating more complicated organic molecules, including fuels. Modeling nature is attractive in many respects, including the possibility to use non-toxic, earth-abundant metals in catalysis. Specific systems investigated in our work include biomimetic catalytic oxidations with dioxygen, hydrogen peroxide, and related oxygen atom donors. More recently, a new direction was been also pursued in the group, fixation of carbon dioxide with transition metal complexes. Mechanistic understanding of biomimetic metal-catalyzed oxidations is critical for the design of functional models of metalloenzymes, and ultimately for the rational synthesis of useful, selective and efficient oxidation catalysts utilizing dioxygen and hydrogen peroxide as terminal oxidants. All iron oxidases and oxygenases (both mononuclear and dinuclear) utilize metal-centered intermediates as reactive species in selective substrate oxidation. In contrast, free radical pathways (Fenton chemistry) are common for traditional inorganic iron compounds, producing hydroxyl radicals as very active, non-selective oxidants. Recent developments, however, changed this situation. Growing families of synthetic iron complexes that resemble active sites of metalloenzymes produce metal-based intermediates (rather than hydroxyl radicals) in reactions with oxygen donors. These complexes are very promising for selective oxygen and peroxide activation. In order to understand the mechanisms of metal-based small molecule activation, kinetically competent metal-oxygen intermediates must be identified. One of the grand challenges identified by the Department of Energy workshop "Catalysis for Energy" is understanding mechanisms and dynamics of catalyzed reactions. The research summarized herein focuses on detailed characterization of the formation and reactivity of various iron-peroxo- and iron-oxo intermediates that are involved in catalysis. Rates of rapid reactions were studied at low temperatures by a specialized technique termed cryogenic stopped-flow spectrophotometry. These measurements identified reaction conditions which favor the formation of catalytically competent oxidants. Chemical structures of reactive complexes was determined, and new, efficient catalysts for hydrocarbon oxidation were synthesized. Importantly, these catalysts are selective, they promote oxidation of hydrocarbons at a specific site. The catalysts are also efficient and robust, hundreds of cycles of substrate oxidation occur within minutes at room temperature. Furthermore, they enable utilization of environmentally friendly oxidants, such as hydrogen peroxide, which produces water as the only byproduct. Mechanistic insights uncovered the role of various acid-containing additives in catalytic oxidations. Proton delivery to the active catalytic sites facilitated oxidations, similarly to the catalytic pathways in metal-containing enzymes. Under certain conditions, two metals in one complex can act in concert, modeling the reactivity of a bacterial enzyme which converts methane into methanol. In related studies, a family of nickel complexes that react with carbon ...
Author: Robert H. Crabtree
Publisher: John Wiley & Sons
ISBN: 0471718750
Category : Science
Languages : en
Pages : 600
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Book Description
Fully updated and expanded to reflect recent advances, this Fourth Edition of the classic text provides students and professional chemists with an excellent introduction to the principles and general properties of organometallic compounds, as well as including practical information on reaction mechanisms and detailed descriptions of contemporary applications.
Author: Xi-Jie Dai
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"This thesis advances the knowledge in two fundamentally important organic chemical transformations: (1) cleavage of carbon-oxygen bonds and (2) formation of carbon-carbon bonds. Such advancement consists of four late transition metal-catalyzed reactions based on the oxygenated chemical feedstock, which will be discussed on a chapter-by-chapter basis. Chapter 2 introduces our initial attempts to address a 40-year-old scientific challenge in the field of alcohol deoxygenation: how to selectively and efficiently remove hydroxyl groups in organic molecules without affecting other existing functional groups. We hypothesize a single-step, redox process to solve this problem, whereby the dehydrogenative oxidation of alcohols and the Wolff-Kishner reduction are combined. As a proof-of-concept discovery, the early development of this reaction is catalyzed by iridium complexes and mediated by hydrazine under forcing reaction conditions. This deoxygenation protocol proves effective for many simple activated substrates such as benzylic and allylic alcohols. The major limitation, however, is the poor reactivity and selectivity seen in aliphatic alcohol substrates. Chapter 3 describes the adaptation of ruthenium(II) catalysis for the direct deoxygenation of primary aliphatic alcohols in a completely chemo- and regio-selective manner. Such a robust catalytic system, comprising [Ru(p-cymene)Cl2]2 and 1,2-bis(dimethylphosphino)ethane, is vital to lower the activation energy barriers to the dehydrogenative oxidation of aliphatic alcohols, and makes this step more kinetically favorable. Equally important is the combination of KOt-Bu, DMSO and t-BuOH, which promotes the subsequent Wolff-Kishner reduction at low temperature. This method is thus more practical compared with the iridium-based protocol, proceeding under milder thermal conditions. Its synthetic utility is demonstrated by the selective cleavage of carbon-oxygen bonds in both simple and complex organic molecules such as steroids and alkaloids. Chapter 4 presents a synthetic approach to utilize naturally occurring carbonyl compounds (i.e. aldehydes and ketones) as more sustainable alkyl carbanion equivalents for formation of carbon-carbon bonds via carbonyl addition reactions. Traditionally, such transformations depend on organometallic reagents which are made from petroleum-derived chemical feedstocks and a stoichiometric quantity of metal. Accessing this new chemical reactivity of carbonyl compounds attributes to the ruthenium(II) catalytic system discovered in the early deoxygenation chemistry. By controlling the basicity, preformed carbonyl-derived hydrazones can intercept another carbonyl compounds to form new carbon-carbon bonds via a Zimmerman-Traxler chair-like transition state. This chemical transformation delivers a wide range of synthetically valuable secondary and tertiary alcohols. Additional highlights include excellent functional group compatibility and good stereochemical control governed by chiral amido and phosphine ligands. Chapter 5 focuses on the further exploration of such unique 'umpolung' reactivity for formation of carbon-carbon bonds via conjugate addition reactions. Inspired by the softness of ruthenium(II) pre-catalyst, which bears a resemblance to that of 'soft' transition metals in the classical 1,4-conjugate addition, we presume that this ruthenium(II)-based catalytic system may be more effective for conducting nucleophilic conjugate additions. Indeed, a variety of highly functionalized aromatic carbonyl compounds are used as latent benzyl carbanions, to couple with electron-deficient [alpha],[beta]-unsaturated compounds including esters, ketones, sulfones, phosphonates, and amides. Two bidentate phosphine ligands (dppp and dmpe) are found to facilitate this process in a complementary manner, largely depending on electronic profiles of the carbonyl compounds. Chapter 6 summarizes all research present in this thesis and contributions to knowledge advancement. " --
Author: Aaron Pierpont
Publisher:
ISBN:
Category : Methane
Languages : en
Pages : 116
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Book Description
Author: L. Brandsma
Publisher: Springer Science & Business Media
ISBN: 3642603289
Category : Science
Languages : en
Pages : 349
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Book Description
Homogeneous catalysis is an important strategy for the synthesis of high-valued chemicals. L. Brandsma has carefully selected and checked the experimental procedures illustrating the catalytic use of copper, nickel, and palladium compounds in organic synthesis. All procedures are on a preparative scale, make economic use of solvents and catalysts, avoid toxic substances and have high yields.
Author:
Publisher: Elsevier
ISBN: 0443140049
Category : Science
Languages : en
Pages : 270
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Book Description
Earth-Abundant Transition Metal Catalyzed Reactions, Volume 74 in the Advances in Catalysis series, highlights new advances in the field, with this new volume presenting interesting chapters. Each chapter is written by an international board of authors. Chapters in this new release include in Chiral Iron Complexes for Asymmetric Catalysis, Recent advances in Ni-catalyzed Functionalization of Strong C-O and C-H Bonds, Low-valent Molecular Cobalt Complexes for Reductive Chemistry, Iron-catalyzed group-transfer reactions with hypervalent iodine reagents, and Iron Porphyrins for Mediating Atom Efficient C–C Bond Formations. - Provides the authority and expertise of leading contributors from an international board of authors - Presents the latest release in Advances in Catalysis serials - Updated release includes the latest information in the field
Author: Walter Kaminsky
Publisher: Wiley-VCH
ISBN: 9783527317424
Category : Technology & Engineering
Languages : en
Pages : 0
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Book Description
With an enormous velocity, olefin polymerization has expanded to one of the most significant fields in polymers since the first industrial use about 50 years ago. In 2005, 100 million tons of polyolefins were produced - the biggest part was catalyzed by metallorganic compounds. The Hamburg Macromolecular Symposium 2005 with the title "Olefin Polymerization" involved topics such as new catalysts and cocatalysts, kinetics, mechanism and polymer reaction engineering, synthesis of special polymers, and characterization of polyolefins. The conference combined scientists from different disciplines to discuss latest research results of polymers and to offer each other the possibility of cooperation. This is reflected in this volume, which contains invited lectures and selected posters presented at the symposium.
