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

Author: Steven Paul Hananouchi
Publisher:
ISBN: 9781303814730
Category :
Languages : en
Pages : 67

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Book Description
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.

Author: Janice Lin Wong
Publisher:
ISBN: 9781321094466
Category :
Languages : en
Pages : 123

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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.

Author: Ryan A. Zarkesh
Publisher:
ISBN: 9781267171108
Category :
Languages : en
Pages : 150

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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.

Author: Khrystyna Herasymchuk
Publisher:
ISBN:
Category :
Languages : en
Pages : 207

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Book Description
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.

Author: Linus Kai Ho Chiang
Publisher:
ISBN:
Category :
Languages : en
Pages : 187

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Book Description
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.

Author: Tohru Nishinaga
Publisher: John Wiley & Sons
ISBN: 1118858743
Category : Science
Languages : en
Pages : 624

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Book Description
Providing a thorough overview of leading research from internationally-recognized contributing authors, this book describes methods for the preparation and application of redox systems for organic electronic materials like transistors, photovoltaics, and batteries. Covers bond formation and cleavage, supramolecular systems, molecular design, and synthesis and properties Addresses preparative methods, unique structural features, physical properties, and material applications of redox active p-conjugated systems Offers a useful guide for both academic and industrial chemists involved with organic electronic materials Focuses on the transition-metal-free redox systems composed of organic and organo main group compounds

Author: Romain Kunert
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
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.

Author: Yi Shen
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
Developing methodologies to synthesize high-value products efficiently from simple substrates with control over the reactivity and selectivity is highly favored by the chemical industry. Employing assisted tandem catalysis, where serial reactions can be carried out in one pot, to achieve streamlined complex syntheses significantly reduces the number of steps and waste. Harnessing spatial and temporal control in catalysis enables approaches toward one-pot transformations and allows the integration of several catalytic processes. Ferrocene-based ligand-supported metal complexes represent a promising class of catalysts that can incorporate redox control over catalytic processes. We have developed a redox-controlled selective hydroamination reaction catalyzed by (thiolfan*)Zr(NEt2)2 (thiolfan*= 1, 1'-bis (2,4-di-tert-butyl-6-thiophenoxy)ferrocene). In situ switching of the catalyst's state during the reaction enables selectivity toward different substrates (Chapter 2).Incorporating the greenhouse gas CO2 into N-carboxyanhydrides (NCAs) followed by subsequent NCA utilization illustrates the possibility of integrating two synthetic steps in one vessel to afford a valuable material with possible CO2 recycling. To demonstrate the immense potential of integrating multi-step transformations in one pot, we developed a set of sustainable conditions for NCA synthesis (Chapter 3). Moreover, several metal catalysts supported by ferrocene-based ligands were found to catalyze NCA polymerization in the presence of a co-catalyst. To establish an integrated system composed of two incompatible processes, we aimed to compartmentalize the active reagents for each step. The structure of the ferrocene-based pro-ligand was modified for surface anchoring. Our efforts toward immobilizing ferrocene-supported metal catalysts onto conductive surfaces pave the way of achieving spatiotemporal control over the processes of NCA synthesis and polymerization (Chapter 4). In addition to the redox-switchable characteristic, ferrocene-based compounds provide a unique platform to support lanthanides and engender distinctive optical properties to them. We synthesized and characterized a series of ytterbium complexes displaying an ultra-narrow absorption in the ultraviolet-visible (UV-Vis) region. The extraordinarily narrow linewidth observed for (thiolfan)YbCl(THF) (thiolfan = 1,1'-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene) allows us to investigate its applications toward magnetic field and liquid cell quantum sensing (Chapter 5).

Author: Timothy S. Koloski
Publisher:
ISBN:
Category :
Languages : en
Pages : 554

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Author: Kensha Marie Clark
Publisher:
ISBN: 9781124209203
Category :
Languages : en
Pages : 195

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Book Description
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.