Reactions at Coordinated Ligands: Redox-active Ligands and Coordination of Lewis Acids

Reactions at Coordinated Ligands: Redox-active Ligands and Coordination of Lewis Acids
Author: Mark R. Ringenberg
Publisher:
Total Pages:
Release: 2011
Genre:
ISBN:

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The theme of this study is reactivity at the ligand and how remote, relative to the metal, activation affects the metal center. The three approaches were the use of redox-active ligands, ligand protonation and Lewis acid coordination to ligands. The focus is on ligand design rather than substrate or metal optimization with a primary interest in reactivity with dihydrogen. The main thrust of the work has been the investigation of redox-active ligands in which redox occurs at the ligand. Redox-active ligands have been generally a curiosity in organometallic chemistry and have only recently been realized in catalysis. Presented here is one of the first examples of a system that incorporates redox-active ligands as a critical component to the catalysts. The complexes utilizing redox-active ligands became Lewis acidic upon oxidation, similar in behavior to the Noyori type catalyst that became Lewis acidic upon protonation. The catalysts containing redox-active ligand were used for the oxidation of H2. The interest in H2 oxidation is the hope that it will fulfill the need for a new fuel source. This interest has lead to the development of soluble catalyst that can oxidize H2 to protons and electrons, in order to further study the mechanism. Redox-active ligands have lower reorganizational barriers because redox at organic substituents are typically lower than for inorganic centers. Furthermore, redox-active ligands can supplement the electrons/holes transferred from the metal, which can facilitate reactions that require multi-electron transfers. The next theme was the use of borane Lewis acids bound to a coordinated ligand, which dramatically changed the ligands from a donor to an acceptor. This type of reaction at the ligand fundamentally changes the reactivity at the metal, however, the affects are not as dramatic as say substituting the ligand. A largh enough change in ligand polarity can affect oxidation-state at the metal. The oxidation state of a metal becomes very difficult to assign when multiple electronic structures exist between the metal and the ligand. In fact in many ways the concept of metal oxidation state becomes meaningless as the electronic structure of the ligand becomes more complicated. These subtler changes in ligand oxidation state and the affects they have on reactivity at metal have not been as widely explored in catalysis. Remote activation of a metal center through reacts at coordinated ligands will be explored here in. The coordination of boranes to cyanide ligands is well know, however, this theme has not been applied to hydrogenase models. Cyanide is an essential component of the [FeFe]- and [NiFe]-hydrogenase active sites, both enzymes feature two cyanide ligands, however, models using cyanides ligands are plagued by undesirable side reactions such as metal-cyanide bridged polymers and decomposition. The bound boranes are used to simulate the hydrogen bonding found in the enzymes. The complexation of Lewis acids to cyanides offers an advantage over alkylation, in that the inductive affect of the borane can be tuned to better approximate the correct level of hydrogen bonding found in the enzyme.

Reactions of Coordinated Ligands

Reactions of Coordinated Ligands
Author: P.S. Braterman
Publisher: Springer Science & Business Media
Total Pages: 419
Release: 2012-12-06
Genre: Science
ISBN: 1461307554

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This, the second and final volume of Reactions of Coordinated Ligands, describes the chemistry of ligands bound through non-carbon atoms, and of coordinated carbon dioxide. As before, emphasis is on the underlying mechanisms, which provide a unity of understanding for superficially disparate processes. The wide range of topics covered illustrates well both the versatility and the usefulness of coordination chemistry in the controlled activation of ligands. Looking to the future, carbon dioxide is the feedstock of last resort. The homogeneous reduction of dinitrogen to ammonia now seems unlikely to replace the Haber process, but solution reactions also lead to more complex, varied, and valuable products. Nitrogen monoxide, a "non innocent" ligand, impinges as pollutant and reagent. Its rich chemistry stems from its linked roles as three-electron donor, and as extremely powerful -acceptor. In the hydrolysis and condensation of complexed amides, esters etc. , metals act both as templates and as tunable and poly functional Lewis acids. Here the control of hydrophobic and steric interactions begins to model the subtle mechanisms of biological specificity. Finally, phosphorus and sulfur are imporant both as ligand atoms in themselves, and as anchors for other functionalities. I would like to thank all those who have been involved in the writing and production of this work, and also my colleagues old and new, at Glasgow and the University of North Texas, for their support. Paul S. Braterman v CONTENTS 1. Reactions of Coordinated Carbon Dioxide 1 J. D. Miller 1.

Reactions of Coordinated Ligands

Reactions of Coordinated Ligands
Author: P.S. Braterman
Publisher: Springer
Total Pages: 1072
Release: 1986
Genre: Gardening
ISBN:

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This book is aimed at graduate students and research workers in aU branches of ohemistry, who wish to gain insight into what continues'to be one of the fastest growing areas of the subject. Aonding to a metal center may stabilize a ligand towards some reagents, activate it towards others, or modify its chemical behavior in more subtle ways. AU these effects have their uses, and aU invite understanding in terms of mechanism. Thus mechanistic insight is linked to control of reaction pathways. The detailed working out of this relationship provides the central theme of the book. The effect of the metal may be electronic or steric, and may involve the energy or the entropy of activation. It may depend on changes induced in the initial state of the ligand, or on those that only arise further along the reaction pathway. It may involve one coordination site or several, and the effects may be more, or less, specific to the metal involved and more, or less, amenable to control through the other Jigands. These remarks apply equaUy strongly to the carbon-bound ligands which occupy the major part of this work, and to those attached by other atoms. Thus the reactions discussed here are relevant in such diverse areas as bulk homogeneous catalysis, stereoselective stoichiometric synthesis, and bioinorganic chemistry.

Redox-Active Ligands

Redox-Active Ligands
Author: Marine Desage-El Murr
Publisher: John Wiley & Sons
Total Pages: 373
Release: 2024-02-05
Genre: Science
ISBN: 3527348506

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Redox-Active Ligands Authoritative resource showcasing a new family of ligands that can lead to better catalysts and promising applications in organic synthesis Redox-Active Ligands gives a comprehensive overview of the unique features of redox-active ligands, describing their structure and synthesis, the characterization of their coordination complexes, and important applications in homogeneous catalysis. The work reflects the diversity of the subject by including ongoing research spanning coordination chemistry, organometallic chemistry, bioinspired catalysis, proton and electron transfer, and the ability of such ligands to interact with early and late transition metals, lanthanides, and actinides. The book is divided into three parts, devoted to introduction and concepts, applications, and case studies. After the introduction on key concepts related to the field, and the different types of ligands and complexes in which ligand-centered redox activity is commonly observed, mechanistic and computational studies are described. The second part focuses on catalytic applications of redox-active complexes, including examples from radical transformations, coordination chemistry and organic synthesis. Finally, case studies of redox-active guanidine ligands, and of lanthanides and actinides are presented. Other specific sample topics covered include: An overview of the electronic features of redox-active ligands, covering their historical perspective and biological background The versatility and mode of action of redox-active ligands, which sets them apart from more classic and tunable ligands such as phosphines or N-heterocyclic carbenes Preparation and catalytic applications of complexes of stable N-aryl radicals Metal complexes with redox-active ligands in H+/e- transfer transformations By providing up-to-date information on important concepts and applications, Redox-Active Ligands is an essential reading for researchers working in organometallic and coordination chemistry, catalysis, organic synthesis, and (bio)inorganic chemistry, as well as newcomers to the field.

Reactions of Coordinated Ligands

Reactions of Coordinated Ligands
Author: Paul S. Braterman
Publisher:
Total Pages: 1052
Release: 1986
Genre: Coordination compounds
ISBN:

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The Age of Noninnocence

The Age of Noninnocence
Author: Seth N. Brown
Publisher: Wiley
Total Pages: 368
Release: 2017-01-24
Genre: Science
ISBN: 9781118646854

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This book presents a comprehensive introduction to the unique and fundamental features of redox-active ligands, the preparation and characterization of their coordination complexes, and finally the importance of this class of molecules to biology, catalysis and materials. The book aims to provide a broadly accessible introduction to the particular features and opportunities unique to redox-active ligands. It begins with an introduction to the intellectual challenges posed by redox-active ligands and descriptions of the types of ligands and complexes in which ligand-centered redox activity are commonly observed. Following this, the book is divided into two sections as follows: The first section focuses on electronic structure and bonding, which has historically dominated this field and continues to be actively researched. The spectroscopic and other physical measurements that have been used to elucidate the electronic structure of these compounds are described. The interplay between synthesis, bonding models, and physical measurements has often been critical in shaping our understanding of these compounds. This interplay is illustrated by a number of case studies. The second section focuses on the use of redox-active complexes in stoichiometric and catalytic reactions. The scope of known reactions is presented, including examples from bioinorganic chemistry (both enzymes and model compounds). Where possible, the significance of the redox-active ligand is discussed, with an eye both to summarizing existing knowledge and pointing out possibilities for future research. This book explains the underpinnings of physical and theoretical techniques of redox-active ligands, providing up to date information on definitions, scope and applications for research scientists and graduate students working in organic and inorganic chemistry, organometallics and coordination chemistry.

Metals and Ligand Reactivity

Metals and Ligand Reactivity
Author: Edwin C. Constable
Publisher: Wiley-VCH
Total Pages: 332
Release: 1996-01-18
Genre: Science
ISBN:

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Edwin C. Constable Metals and Ligand Reactivity An Introduction to the Organic Chemistry of Metal Complexes New, revised and expanded edition This book is a highly readable introduction to the reactions of coordinated ligands, which have become a useful tool in organic synthesis. Bridging the gap between the traditional fields, this text presents the basic concepts of ligand reactivity as well as synthetic applications of these reactions. Topics covered include Principles of metal-ligand interaction Reactions of coordinated ligands with nucleophiles and electrophiles Oxidation and reduction of coordinated ligands Cyclic and encapsulating ligands, template effects and supramolecular chemistry Carefully selected examples, lucidly designed figures and schemes as well as numerous study problems make this book an ideal guide for students and practitioners of organic synthesis. References to further reading are also included.

The Organometallic Chemistry of the Transition Metals

The Organometallic Chemistry of the Transition Metals
Author: Robert H. Crabtree
Publisher: John Wiley & Sons
Total Pages: 600
Release: 2005-06-14
Genre: Science
ISBN: 0471718750

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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.

Selectivities in Lewis Acid Promoted Reactions

Selectivities in Lewis Acid Promoted Reactions
Author: Dieter Schinzer
Publisher: Springer Science & Business Media
Total Pages: 326
Release: 2012-12-06
Genre: Science
ISBN: 940092464X

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The ASI workshop on "Selectivities in Lewis Acid Promoted Reactions" held in the Emmantina-Hotel in Athens-Glyfada, Greece, October 2-7, 1988 was held to bring some light into the darkness of Lewis acid induced processes. As such the workshop reflects some current trends in organic synthesis, where Lewis acids are becoming a powerful tool in many different modern reactions, e.g. Diels-Alder reactions, Ene reactions, Sakurai reactions, and in general silicon and tin chemistry. The objective of this meeting was to bring together most of the world experts in the field to discuss the major reactions promoted by Lewis acids. Organic synthesis will play a major role in this book connected with some fundamental mechanistic work on allylsilane and -tin chemistry. Both natural product synthesis and unnatural molecules are presented in the chapters. The book presents all the 15 invited lectures and the contributions of 15 posters. I am confident that the material presented in this book will stimulate the chemistry, which has been discussed on our meeting, around the world. The meeting and the book were only possible through a grant of the NATO Scientific Affairs Devision and financial support by the following companies: Kali Chemie (Hannover, W-Germany), E. Merck (Darmstadt, W-Germany), Sandoz (Basel, Switzerland), Schering (Berlin, W-Germany).