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.

Synthesis, Structural and Electronic Properties, and Reactivity of Group 5 Metal Complexes Incorporating the Redox-active [ONO] Ligand Platform

Synthesis, Structural and Electronic Properties, and Reactivity of Group 5 Metal Complexes Incorporating the Redox-active [ONO] Ligand Platform
Author: Steven Paul Hananouchi
Publisher:
Total Pages: 67
Release: 2014
Genre:
ISBN: 9781303814730
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This thesis describes the synthesis, electronic and structural properties, and reactivity of Group 5 metal complexes incorporating the [ONO] ligand platform. A study of the electronic and structural properties of the Group 5 metal complexes incorporating the [ONO] ligand is performed. Once the electronic properties of the complexes are known, the reactivity of the complexes is compared. Chapter 1 describes a brief history of redox-active ligands. The previously published results of redox-active ligands acting as an electron source are discussed. In Chapter 2, the synthesis and electronic and structural properties of metal dichlorides and trichlorides of Group 5 metal complexes incorporating the [ONO] ligand and comparing the metal-ligand cooperativity are performed. In Chapter 3, the synthesis and reactivity of [ONO]NbMe2 and the reactivity of reduced species of [ONO]V(L)n are discussed.

Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center

Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center
Author: Ryan A. Zarkesh
Publisher:
Total Pages: 150
Release: 2012
Genre:
ISBN: 9781267171108
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This dissertation describes the synthesis and reactivity of tantalum metal complexes containing a tridentate redox-active ligand. Fundamental studies have focused on utilizing the redox-active ligand to store multiple electron equivalents for oxidative addition and reductive elimination reactions. Chapter 1 provides an introduction to the characteristics of redox-active ligands and provides an overview of group transfer reactions involving redox-active ligands. The previous published results of bidentate redox-active ligands coordinated to Group IV d0 metals are discussed in terms of their decomposition side reactions. Chapter 2 describes the coordination of a known tridentate redox-active bis(phenoxy)amide ligand, (ONO), to a d0 tantalum(V) metal center and the examination of the redox properties of the resulting chloro oxidation products by electrochemical and spectroscopic methods. Chapter 3 examines the reactivity of the (ONO)TaR2 complexes in the general context of organometallic chemistry with a focus on protonolysis and reactivity with aryl azides, a known source of nitrene fragments upon oxidation. Chapter 4 examines the reactivity of the (ONO)TaX2 (X = Me, Cl) compounds with bulky diazoalkanes, a known carbene transfer reagent. The (ONO)TaCl2 complex proved to be a competent catalyst to generate cyclopropanes from styrene and the corresponding diazoalkane. Chapter 5 explores the utilization of the (ONO) ligand to store electron equivalents for the catalytic nitrene-nitrene coupling reactions with organoazides to afford organodiazenes. Finally, Chapter 6 addresses the electronic considerations of a related redox-active triamido ligand in an effort to tune the ligand's redox potentials.

Synthesis of Reactive Metal Complexes Supported by 1,1'-disubstituted Ferrocene Ligands

Synthesis of Reactive Metal Complexes Supported by 1,1'-disubstituted Ferrocene Ligands
Author: Jonathan Lee Brosmer
Publisher:
Total Pages: 155
Release: 2017
Genre:
ISBN:
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Reliable transformation of low-cost rare-earth metal oxides to organometallic rare-earth metal complexes is a prerequisite for the advancement of non-aqueous rare-earth metal chemistry. We have recently developed an in situ method to prepare rare-earth alkyl and halide precursors supported by a diamidoferrocene NNfc, 1,1'-fc(NSiMe2Bu)2, as an ancillary ligand. We extended the scope of this method to other lanthanide ions including those that are redox active, such as cerium, praseodymium, samarium, terbium, thulium, and ytterbium. Specifically, samarium trisbenzyl could be generated in situ and then converted to the corresponding samarium benzyl or iodide complexes in good yield. However, it was found that ytterbium trisbenzyl could not be formed cleanly and the consequent conversion to ytterbium iodide complex was low yielding. By adapting an alternative route, the desired ytterbium chloride precursor could be obtained in good yield and purity. The synthesis and characterization of two yttrium alkyl complexes supported by a bisphosphinimine ferrocene ligand, NPfc (1,1 -di(2,4-di-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), were accomplished. Although (NPfc)Y(CH2Ph) and (NPfc)Y(CH2SiMe3) could be structurally characterized, these compounds are thermally sensitive and decompose at ambient temperature within hours. Their characterization was accomplished by NMR spectroscopy, electrochemical measurements, and elemental analysis. Reactivity studies were also carried out; however, the lack of prolonged thermal stability at ambient temperature of these molecules led to decomposition before a clean transformation to reaction products could be observed. The synthesis and characterization of Ln-C4Ph4-K, [(NNTBS)Ln( 2-C4Ph4)][K(THF)x] (Ln = Sc, Y, Lu), rare-earth metal complexes supported by a ferrocene diamide ligand, NNTBS (NNTBS = fc(NSitBuMe2)2, fc = 1,1 -ferrocenediyl), were accomplished. The preparation of the half-sandwich compounds, Ln-naph-K, [(NNTBS)Ln( -C10H8)][K(THF)2] (Ln = Sc, Y, Lu, La), was necessary in order to obtain high yields of rare-earth metallacyclopentadienes. Unlike Y and Lu, La did not show the same reactivity toward PhCCPh. The characterization of the new metal complexes was accomplished by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes

Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes
Author: Padmapriya Srinivasan
Publisher:
Total Pages: 0
Release: 2022
Genre: Green chemistry
ISBN:
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Green Chemistry initiatives have recently been at the forefront of both industrial and academic communities in order to address fundamental scientific challenges of protecting human health and the environment. The Twelve Principles of Green Chemistry, of which catalysis is a primary tenet and the main motivation for this project, has led the path to reduce waste production in the chemical industry. The principle of catalysis states that catalytic reactions necessarily produce less waste than stoichiometric reactions. Traditionally, precious and toxic heavy transition metals such as platinum and palladium have been used as metal centres in catalysts because of their stability, favourable redox properties, and ease of characterization. These concerns prompted this research in finding more environmentally friendly alternatives as metal centres in catalysis, such as main group complexes. Indium is a heavy main group metal that is environmentally benign. It is most stable in the +3 oxidation state and, notably, does not possess other readily accessible oxidation states. To make indium complexes redox-active, so-called "non-innocent" redox-active ligands are being explored. The current work seeks to synthesize a series of redox-active indium catalysts with varied steric bulk about the indium centre and different redox-active ligands. The goals of this study are to first synthesize and structurally characterize organometallic indium compounds with the redox-active ligand 2-amninobenzenethiol, and then test the reactivity of indium complexes with dithiolate ligands using mild oxidizing agents. A third goal is to use DFT methods to rationalize the synthesized complexes in terms of structure, reactivity, bonding motifs, and in interpreting the experimental spectroscopic data.

Redox-Active Ligands

Redox-Active Ligands
Author: Marine Desage-El Murr
Publisher: John Wiley & Sons
Total Pages: 373
Release: 2024-01-31
Genre: Science
ISBN: 352783088X
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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.

Redox Activity of Early Metal Complexes Supported by N, N'-bis(arylimino)acenaphthylene Ligands

Redox Activity of Early Metal Complexes Supported by N, N'-bis(arylimino)acenaphthylene Ligands
Author: Kensha Marie Clark
Publisher:
Total Pages: 195
Release: 2010
Genre:
ISBN: 9781124209203
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Redox-active ligands have been previously shown to enhance reactivity at metal centers by serving as electron reservoirs. This class of ligand facilitates intramolecular electron transfer, enabling reactivity pathways such as oxidative addition and reductive elimination at d0 metal centers. Towards the goal of coupling ligand promoted reactivity with the known reactivity of low-coordinate Group IV imido complexes, the sterics, electronics, and reactivity of the N, N'-bis(arylimino)acenaphthylene (BIAN) ligand set were explored. Initially, the coordination geometry enforced by three BIAN ligand derivatives, dpp-BIAN, tmp-BIAN, and dmp-BIAN (dpp = 2,6-diisopropylphenyl; tmp = 2,4,6-trimethylphenyl; dmp = 3,5-dimethylphenyl), in titanium imido complexes was evaluated. These three ligands present different steric profiles, with dpp-BIAN providing the most steric bulk, while dmp-BIAN ligand offers the least steric protection. In these studies, it was observed that the bulkier ligands, dpp-BIAN and tmp-BIAN, stabilize coordinatively unsaturated imido complexes, (dpp-BIAN)TiCl2(=NR) and (tmp-BIAN)TiCl2(=NR) (R = tBu or 2,6-dimethylphenyl). The dmp-BIAN ligand exclusively forms the six-coordinate amino-imido complexes, (dmp-BIAN)TiCl2(=NR)(NH2tBu). Neutral tris-semiquinonate complexes, M(dmp-BIAN isq)3, of titanium, vanadium, and chromium were structurally, spectroscopically, and electrochemically characterized. From these data, the ability of the BIAN ligand to facilitate intramolecular charge redistribution in early metals was determined. In these complexes, the ligand not only enables reversible redox processes, but antiferromagnetic exchange coupling is observed between the radical ligands and metal ions. The bulky dpp-BAAN ligand, which is the two electron reduced form of dpp-BIAN, was used to make unprecedented mixed-valence cluster complexes of zirconium and hafnium, [(dpp-BAAN)3M3(u2-Cl)3(u3-Cl)2] (M = Zr or Hf). In these complexes the metal centers act as non-discrete redox sites, and an unpaired electron is considered delocalized over the entire molecule. The synthesis and subsequent isolation of these complexes demonstrates the stability that the electronically flexible BIAN ligand set provides. After considering the ligand sterics and electronics, Group IV synthons (dpp-BAAN)MCl2 and (dpp-BAAN)MR2 (M = Ti or Zr; R = Np, CH2Si(CH3)3, or OtBu) were synthesized and characterized. The reactivity of (dpp-BAAN)TiCl2 towards oxidants was evaluated. It was found that this complex successfully undergoes oxidative chloride addition and nitrene addition. Nitrene addition to the (dpp-BAAN)TiNp2 complex results in the unexpected extrusion of bineopentyl from the metal center to generate a putative imido species. Protonolysis of the same synthon similarly forms a putative imido species. The addition of chloride to this species yields a five-coordinate imido complex, (dpp-BIAN)TiCl2(=NR) (R = p-MeCH6), and establishes the basis for further reactivity studies.