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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.
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.
It has long been recognized that metal spin states play a central role in the reactivity of important biomolecules, in industrial catalysis and in spin crossover compounds. As the fields of inorganic chemistry and catalysis move towards the use of cheap, non-toxic first row transition metals, it is essential to understand the important role of spin states in influencing molecular structure, bonding and reactivity. Spin States in Biochemistry and Inorganic Chemistry provides a complete picture on the importance of spin states for reactivity in biochemistry and inorganic chemistry, presenting both theoretical and experimental perspectives. The successes and pitfalls of theoretical methods such as DFT, ligand-field theory and coupled cluster theory are discussed, and these methods are applied in studies throughout the book. Important spectroscopic techniques to determine spin states in transition metal complexes and proteins are explained, and the use of NMR for the analysis of spin densities is described. Topics covered include: DFT and ab initio wavefunction approaches to spin states Experimental techniques for determining spin states Molecular discovery in spin crossover Multiple spin state scenarios in organometallic reactivity and gas phase reactions Transition-metal complexes involving redox non-innocent ligands Polynuclear iron sulfur clusters Molecular magnetism NMR analysis of spin densities This book is a valuable reference for researchers working in bioinorganic and inorganic chemistry, computational chemistry, organometallic chemistry, catalysis, spin-crossover materials, materials science, biophysics and pharmaceutical chemistry.
The work described herein focuses on the ability of redox-active ligands to enable multi-electron reactivity at transition metal centers. A parallel theme is the effect of ancillary ligands on controlling and modulating the electronic structure of the redox-active ligand and metal center in addition to ancillary ligand effects as they relate to controlling the primary coordination sphere of the metal. (Abstract shortened by ProQuest.).
In this thesis a number of projects involving the design and characterization of complexes bearing redox active ligands are described. Focusing on the phenolate containing ligands, the properties and electronic structure of their corresponding metal complexes were studied by a series of experimental (i.e. electrochemistry, UV-Vis-NIR, EPR, rR etc.) and theoretical (DFT) methods. Specifically, the redox processes of these metal complexes were tuned by varying the para-ring substituents. In one study, nickel-salen (salen is a common abbreviation for N2O2 bis-Schiff-base bis-phenolate ligands) complexes were investigated, where the oxidation potentials of the ligand were predictably decreased as the electron donating ability of the para-ring substituents was increased (NMe2 > OMe > tBu > CF3). Interestingly, the oxidation of these geometrically-symmetric complexes afforded an asymmetric electronic structure in a number of cases, in which the ligand radical was localized on one phenolate rather than delocalized across the ligand framework. This difference in electronic structure was found to be dependent on the electron donating ability of the substituents; a delocalized ligand radical was observed for electron-withdrawing substituents and a localized ligand radical for strongly donating substituents. These studies highlight that para-ring substituents can be used to tune the electronic structure (metal vs. ligand based, localized vs. delocalized radical character) of metallosalen complexes. To evaluate if this electronic tuning can be applied to the metal center, a series of cobalt complexes of these salen ligands were prepared. Indeed, the electronic properties of the metal center were also significantly affected by para-ring substitution. These cobalt-salen complexes were tested as catalysts in organometallic radical-mediated polymerizations, where the most electron rich complexes displayed the best conversion rates. With a firm understanding of the role that the para-ring substituent can play in influencing the electronic structure and reactivity of metallosalen complexes in catalysis, two novel iron complexes, which contain a number of redox active phenolate fragments, were prepared. In addition, these iron-complexes feature a chiral bipyrrolidine backbone. Ligands with this chiral diamine backbone bind metals ions diastereoselectively owing to its increased rigidity, which is critical to stereoselectivity in catalysis. A symmetric (with two phenolates) ligand was prepared by reported methods, and a novel route to synthesize an asymmetric ligand (one phenolate and one pyridine) from symmetric starting materials was established. The neutral iron-complexes were found to be high spin (S = 5/2), and can undergo ligand based oxidation to form an antiferromagnetically-coupled (Stotal = 2) species. The results presented will serve as the basis for catalyst development using complexes of similar ligands.
Authored by one of the world's leading experts in the field, this treatment of a core topic in coordination chemistry discusses the fundamentals, including the physical properties and chemical reactivity, followed by interesting applications in catalysis and biochemistry. The result is a perfect overview for all newcomers to the field as well as more experienced researchers.
Transition metal complexes incorporating redox-active ligands have the potential to facilitate controlled multielectron chemistry, enabling their use in catalysis and energy storage applications. Moreover, the use of transition metal complexes containing redox-active ligands has been extended to two- (2D) and three-dimensional (3D) materials, such as supramolecular assemblies (i.e., metallacycles, molecular cages, or macrocycles) and metal-organic frameworks (MOFs) for catalytic, magnetic, electronic, and sensing applications. Salens (N2O2 bis(Schiff-base)-bis(phenolate) are an important class of redox-active ligands, and have been investigated in detail as they are able to stabilize both low and high metal oxidation states for the above-mentioned applications. The work in this thesis focuses on the synthesis and electronic structure elucidation of metal salen complexes in monomeric form, as discrete supramolecular assemblies and 3D MOFs. Structural and spectroscopic characterization of the neutral and oxidized species was completed using mass spectrometry, cyclic voltammetry, X-ray diffraction, NMR, UV-Vis-NIR, and EPR spectroscopies, as well as theoretical (DFT) calculations. Chapter 2 discusses the synthesis and electronic structure evaluation of a series of oxidized uranyl complexes, containing redox-active salen ligands with varying para-ring substituents (tBu, OMe, NMe2). Chapters 3 and 4 discuss the incorporation of a redox-active nickel salen complex equipped with pyridyl groups on the peripheral positions of the ligand framework into supramolecular structures via coordination-driven self-assembly. The self-assembly results in formation of a number of distinct metallacycles, affording di-, tetra-, and octa-ligand radical species. Finally, the design, synthesis, and incorporation of metal salen units into MOFs is discussed in Chapter 5. Preliminary assembly and oxidation experiments are presented as an opportunity to explore the redox-properties of salen complexes incorporated into a solid-state 3D framework. Overall, the work described in this thesis provides a pathway for salen ligand radical systems to be used in redox-controlled host-guest chemistry, catalysis, and sensing.