Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands

Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands
Author: Romain Kunert
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:
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We developed a new type of redox-active ligand, involving two N-heterocyclic carbenes and two phenolate units. The strong electron donating properties of the NHC moieties were utilized to stabilize complexes in high oxidation states while the phenolate groups were used as redox-active units. Group 10 metal complexes were developed. Their oxidation chemistry showed the formation of phenoxyl radicals, reaching up to two-electron oxidized, bis(phenoxyl) complexes. We also report the first Ni(III) complex with NHC donors. The ligand was also used to develop metal complexes with nitride ligands. The nitridomanganese complex proved to be unstable and degraded in successive intramolecular nitride-NHC reductive couplings. The degradation afforded a peculiar organic salt with three fused rings forming a central triazone pattern. Conversely, the chromium nitride complex could be isolated and thoroughly characterized. The one-electron oxidized product was generated reversibly at low temperature but readily evolved at room temperature. In a parallel work, we also developed new types of sterically hindered salen ligands to form distorted copper salen complexes as molecular models of galactose oxidase. The copper salen catalysts showed to be effective for the aerobic oxidation of non-activated alcohol substrates.

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.

Synthesis, Characterization, and Reactivity Studies of Iron Complexes Supported by the Redox-active [ONO] Ligand

Synthesis, Characterization, and Reactivity Studies of Iron Complexes Supported by the Redox-active [ONO] Ligand
Author: Janice Lin Wong
Publisher:
Total Pages: 123
Release: 2014
Genre:
ISBN: 9781321094466
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The work reported herein primarily focuses on the development of new platforms for multi-electron reactivity using iron complexes supported by a redox-active pincer-type ligand. This dissertation details the synthesis, characterization, and reactivity of iron complexes coordinated to the redox-active [ONO] ([ONO]H3 = bis(3,5-di-[tert]-butyl-2-phenol)amine) ligand. Chapter 1 provides a general background on ligand-centered and metal-centered redox reactivity. Specifically, the characteristics of redox-active ligands and their ability to promote multi-electron reactivity at redox-inert metal centers is presented. In addition, iron-catalyzed organic transformations in which the metal center undergoes redox changes is also discussed. Finally, ligand-enabled redox reactions mediated by iron complexes containing redox-active ligands is described. Chapter 2 reports on the complexation of bis(3,5-di-[tert]-butyl-2-phenoxy)amine, [ONHO], and the redox-active [ONO] ligands by iron centers to afford a new family of iron complexes. Characterizations of each compound through a battery of analytical techniques reveal the oxidation states of the metal center and ligand. Furthermore, the electronic properties of each complex were investigated in order to evaluate their potential to facilitate multi-electron reactivity. Chapter 3 details the reactivity of the [ONO]Fe platform. Metathesis reactions are conducted with [ONO [superscript q] Fe [superscript III] X2 (X = Cl, N[SiMe3]2 complexes, demonstrating the capability of the fully-oxidized [ONO [superscript q]−1 to act as a two-electron acceptor to generate the fully reduced [ONO [superscript cat]3− that is coordinated to an iron(III) center. Similarly, oxidation of [ONO[superscript cat] Fe [superscript III] (py)3 (py = pyridine) using dihalogens result in two-electron oxidations of the tridentate ligand while the metal oxidation state remains the same. These redox reactions showcase the ability of the [ONO] ligand platform to undergo reversible two-electron oxidation state changes, allowing multi-electron reactivity to occur at the iron center. The synthesis and characterization of two novel bimetallic complexes of the form [ONO]M'[ONO]2 M (M' = Fe, Zn; M = Fe) are presented in Chapter 4. The rich redox profiles of both complexes suggest that they can potentially impart unique cooperative bimetallic reactivity. The synthetic techniques developed to prepare these complexes lay the foundation for a general method to access new bimetallic combinations that could be promising for multi-electron reactivity. Finally, Chapter 5 discusses the synthesis, characterization, and electronic comparisons between two homoleptic tris-iminosemiquinonate chromium(III) compounds. While one is coordinated to three N,N'-bis(3,5-dimethylphenyl)acenapthenediimino-semiquinonate, (dmp-ADI [superscript sq])1−, ligands, the other contains three N,N'-bis(3,5-dimethylphenyl)phenanthrenediimino-semiquinonate, (dmp-PDIsq)1− ligands. The differences in the electronic properties between each complex likely stems from variation in the diimine ligand backbones. However, further investigation is required to completely understand the complicated behaviors of such complexes, both of which apparently exhibit intramolecular anti-ferromagnetic properties.

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.

Vanadium Catalysis

Vanadium Catalysis
Author: Manas Sutradhar
Publisher: Royal Society of Chemistry
Total Pages: 526
Release: 2020-11-05
Genre: Science
ISBN: 1839160896
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Vanadium is one of the more abundant elements in the Earth’s crust and exhibits a wide range of oxidation states in its compounds making it potentially a more sustainable and more economical choice as a catalyst than the noble metals. A wide variety of reactions have been found to be catalysed by homogeneous, supported and heterogeneous vanadium complexes and the number of applications is growing fast. Bringing together the research on the catalytic uses of this element into one essential resource, including theoretical perspectives on proposed mechanisms for vanadium catalysis and an overview of its relevance in biological processes, this book is a useful reference for industrial and academic chemists alike.

Design and Synthesis of a Series of Redox Active Tetrazine and Triazine Based Transition Metal Complexes

Design and Synthesis of a Series of Redox Active Tetrazine and Triazine Based Transition Metal Complexes
Author: Yixin Zhang
Publisher:
Total Pages:
Release: 2018
Genre:
ISBN:
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The use of two different chelating redox active ligands, 2,6-bis(6-methyl-1,2,4,5-3-yl) pyridine (BTZP) and 2,6-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP) in heterometallic first row and second row transition metal chemistry has yielded two new families of redox active metal complexes. These complexes were found to exhibit interesting electrochemical and magnetic properties. In this thesis, Chapter 1 lays the foundation for the research presented within. This section covers the fundamentals of the ligand design, ligand synthesis and related coordination chemistry literature review. Chapters 2 and 3 report the results of the current thesis. In Chapter 2, the synthesis and characterization of a family of discrete molecules and supramolecular arrangements, employing the ligand BTZP, is presented. All of the complexes presented in Chapter 2 are successfully synthesized and characterized with electrochemical and magnetic studies. According to the electrochemical data, it is found that the classic "terpy-like" complexes with [Co(BTZP) 2]2+ formula fosters more stability in the redox process. In Chapter 3, a family of transition metal complexes with [M(BTP) 2]2+ (M=Fe or Co) inorganic cores were obtained through the employment of the ligand BTP with various anions. In addition, dimeric molecules with [CoX4(BTP)2] formula were also obtained by solvothermal synthesis. The complexes were also electrochemically characterized, with all the complexes capable of being reduced, while only [CoII(BTP)2] (ClO4)2 showed reversible redox process. Similar with BTZP, the series of BTP based complexes are also characterized through magnetic measurement. Only cobalt-based BTP complexes are paramagnetic, with [CoII(BTP)2]2+ being spin crossover active when BF4- and ClO4- are present. However, the presence of NCS- and halides lead to either antiferromagnetic interactions and ferromagnetic interactions dominating at different temperature regimes.

Synthesis, Characterization and Coordination Chemistry of Pincer Ligands Based on (benzannulated) Pyridines

Synthesis, Characterization and Coordination Chemistry of Pincer Ligands Based on (benzannulated) Pyridines
Author: Jason Braun
Publisher:
Total Pages: 0
Release: 2020
Genre:
ISBN:
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The idea of 'non-innocent' ligands is that the site of chemical or redox activity on a coordination complex may not be solely limited to the central atom. Ligands may participate either by themselves or in cooperation with a central atom to facilitate electron-transfer and/or chemical reactivity in a more active fashion than in a typical coordination complex. Each of the projects explored in this thesis include the common theme of pyridine-based pincer-type ligands, their coordination to late transition metals and main group elements, and how the reactivity and properties of these complexes involves both the ligand and the ligated element. To do so, a comprehensive investigation of the electronic structure of complexes supported by pincer-type, 'NNN' ligands is also described. Diiminepyridine ligands tend to actively participate in the chemistry of their complexes. Taking advantage of these non-innocent ligands has allowed for the stabilization of unusual oxidation states of transition metal complexes as well as the facilitation of chemical transformations with metals unable to do so using spectator ligands. Pseudo-octahedral iron complexes of these ligands exhibit multiple reversible reductions and are shown to be viable candidates as anolytes for redox flow battery applications. In synthesizing these, a synthetic scheme to prepare these ligands with electron withdrawing groups on the flanking aryl groups was developed, opening up the chemical space for these new ligands in the already well-established field of diiminepyridine ligand chemistry. In addition, bulky analogues engender stabilization of phosphorus complexes in the +1 and +3 oxidations states, not seen before with traditional diiminepyridine ligands. The synthetic route to diarlyamido ligands comprised of flanking quinoline (2,3-benzopyridine) and phenanthridine (3,4-benzoquinoline) donors has also been developed and the coordination of these monoanionic ligands to a variety of late transition metals and main group elements was explored. Several aspects of this ligand can be deemed non-innocent and will be highlighted throughout the course of this thesis. We see an unusual electronic environment of pseudo-octahedral iron complexes of these ligands that exhibit record length charge-transfer excited states and panchromatic absorption. Exchanging the central metal can bring about mixed-valent species upon oxidation evidenced by strong absorption in the near infrared region of the electromagnetic spectrum that significantly depends on metal-ligand orbital overlap.

Molecular Clusters of the Main Group Elements

Molecular Clusters of the Main Group Elements
Author: Matthias Driess
Publisher: John Wiley & Sons
Total Pages: 460
Release: 2008-11-21
Genre: Science
ISBN: 3527614370
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With more than 20 contributions from leading research groups, this book provides essential information for chemists and materials scientists working with molecular clusters. It treats both homonuclear and heteronuclear clusters, including: the theory and concepts in main-group cluster chemistry, * novel boranes and heteroboranes, * silicon/germanium/tin clusters, * alkali metal suboxides, * clusters in alloys with mercury, * chalkogen clusters * and numerous other compound classes. The whole is illustrated by examples of the great potential for technical applications such as electron storage, cancer therapy and in optoelectronic devices. Its systematic coverage of all relevant main group elements makes this the prime reference source in the field.