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Synthesis Structural And Electronic Properties And Reactivity Of Group 5 Metal Complexes Incorporating The Redox Active Ono Ligand Platform
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Book Synopsis Synthesis, Structural and Electronic Properties, and Reactivity of Group 5 Metal Complexes Incorporating the Redox-active [ONO] Ligand Platform by : Steven Paul Hananouchi
Download or read book Synthesis, Structural and Electronic Properties, and Reactivity of Group 5 Metal Complexes Incorporating the Redox-active [ONO] Ligand Platform written by Steven Paul Hananouchi and published by . This book was released on 2014 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Synthesis, Characterization, and Reactivity Studies of Iron Complexes Supported by the Redox-active [ONO] Ligand by : Janice Lin Wong
Download or read book Synthesis, Characterization, and Reactivity Studies of Iron Complexes Supported by the Redox-active [ONO] Ligand written by Janice Lin Wong and published by . This book was released on 2014 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center by : Ryan A. Zarkesh
Download or read book Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center written by Ryan A. Zarkesh and published by . This book was released on 2012 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Controlling Redox Processes in Metal Complexes and Multifunctional Materials by : Khrystyna Herasymchuk
Download or read book Controlling Redox Processes in Metal Complexes and Multifunctional Materials written by Khrystyna Herasymchuk and published by . This book was released on 2020 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Elucidating the Electronic Structure of Transition Metal Complexes Featuring Redox Active Ligands by : Linus Kai Ho Chiang
Download or read book Elucidating the Electronic Structure of Transition Metal Complexes Featuring Redox Active Ligands written by Linus Kai Ho Chiang and published by . This book was released on 2014 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Organic Redox Systems by : Tohru Nishinaga
Download or read book Organic Redox Systems written by Tohru Nishinaga and published by John Wiley & Sons. This book was released on 2015-12-30 with total page 624 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands by : Romain Kunert
Download or read book Synthesis, Characterization and Applications of Complexes Involving Redox-active Ligands written by Romain Kunert and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Synthesis of Metal Complexes Supported by Ferrocene-based Ligands for Tandem Catalysis and Applications Toward Liquid Cell Quantum Sensing by : Yi Shen
Download or read book Synthesis of Metal Complexes Supported by Ferrocene-based Ligands for Tandem Catalysis and Applications Toward Liquid Cell Quantum Sensing written by Yi Shen and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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).
Book Synopsis Synthesis, Structure, and Reactivity of Group 5 and 6 Metallocene Complexes Containing Organosilicon Ligands by : Timothy S. Koloski
Download or read book Synthesis, Structure, and Reactivity of Group 5 and 6 Metallocene Complexes Containing Organosilicon Ligands written by Timothy S. Koloski and published by . This book was released on 1991 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Redox Activity of Early Metal Complexes Supported by N, N'-bis(arylimino)acenaphthylene Ligands by : Kensha Marie Clark
Download or read book Redox Activity of Early Metal Complexes Supported by N, N'-bis(arylimino)acenaphthylene Ligands written by Kensha Marie Clark and published by . This book was released on 2010 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Synthesis, Structures, Bonding, and Reactivity of Group 4 Metal Alkyl Complexes Incorporating 8-quinolinolato Ligands by : Xiaohong Bei
Download or read book Synthesis, Structures, Bonding, and Reactivity of Group 4 Metal Alkyl Complexes Incorporating 8-quinolinolato Ligands written by Xiaohong Bei and published by . This book was released on 1997 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Redox-Active Ligands by : Marine Desage-El Murr
Download or read book Redox-Active Ligands written by Marine Desage-El Murr and published by John Wiley & Sons. This book was released on 2024-01-31 with total page 373 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Oxidation State Roulette by : Brandon Fitchett
Download or read book Oxidation State Roulette written by Brandon Fitchett and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of rare and expensive noble metals in the chemical industry as organometallic catalysts has grown exponentially in the past few decades due to their high activity, selectivity and their ability to catalyze a wide range of reactions. With this growth in use has also come a proportional growth in concern as these toxic metals inevitably leach into the environment and their negative effects on public health and our ecosystems are becoming better understood. First-row transition metal catalysts provide both environmental and economic benefits as alternatives to these noble metals due to their lower toxicity and cheaper costs. The two-electron chemistry that makes the noble metals so attractive however, is more challenging to accomplish with first-row transition metals. Intelligently designing the ligand scaffold which surrounds the metal can mitigate or even eliminate some of the shortfalls of these first-row metals. Some key features that should be considered when designing a ligand are: 1) a strong chelating ability so the ligand can stay attached to the metal, 2) incorporation of strong donors to favour low-spin complexes, 3) inclusion of hemilabile groups to allow for substrate activation and metal stabilization throughout various oxidation states, 4) redox activity to be able to donate or accept electrons, and 5) inclusion of Lewis base functionalities which are able to assist the substrate activation. Ligands which incorporate these features are known as bifunctional ligands as they can accomplish more than one function in the catalytic cycle. Developing first-row transition metal complexes containing these ligands may enable these species to replicate the reactivity and selectivity generally associated with the precious metals. Being able to replace the noble metals used in industry with these catalysts would have tremendous environmental and economic benefits. The objective of this thesis is to advance the field of bifunctional catalysis by examining the behaviour of two sterically svelte, tridentate SNS ligands containing hard nitrogen and soft sulphur donors when bonded to cobalt. Previous work with iron provides a template of the ligand behaviour to which cobalt can be compared, allowing us to contrast the effects exerted by the different metals. After an introduction to bifunctional catalysis in Chapter 1, Chapter 2 describes the reactivity of the amido ligand, SMeNHSMe, with precursors ranging from Co(I) to Co(III), all of which yielded the 19e- pseudooctahedral cobalt(II) bis-amido complex, Co(SMeN-SMe)2 characterized by 1H NMR spectroscopy, single-crystal X-ray crystallography and cyclic voltammetry. Although this complex has a similar structure as the Fe analogue, the cobalt bis-amido complex did not exhibit the same hemilabile behaviour that allowed for simple ligand substitution of one of the thioether groups. Instead it reacted reversibly with 2,2'-bipyridine while 1,2-bis(dimethylphosphino)ethane (DMPE) and 2,6-dimethylphenyl isocyanide both triggered additional redox chemistry accompanied by the loss of protonated SMeNHSMe. In contrast, protonation gave the cobalt(II) amido-amine cation, [Co(SMeNSMe)(SMeNHSMe)](NTf2), which allowed for substitution of the protonated ligand by acetonitrile, triphenylphosphine and 2,2'-bipyridine based on 1H NMR evidence. The ability of Co(SMeNSMe)2 to act as a precatalyst for ammonia-borane dehydrogenation was also probed, revealing that it was unstable under these conditions. Addition of one equivalent of DMPE per cobalt, however, resulted in better activity with a preference for linear aminoborane oligomers using ammonia-borane and, surprisingly, to a change in selectivity to prefer cyclic products when moving to methylamine-borane. Chapter 3 delves into the chemistry of the thiolate ligand, SMeNHS, which formed a new 18e- cobalt(III) pseudooctahedral complex, Co(S-NC-)(SMe)(DEPE), from oxidative addition of the Caryl-SMe bond. Scaling up this reaction resulted instead in formation of an imine-coupled [Co(N2S2)]- anion which was characterized by 1H NMR/EPR spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry and DFT studies. The latter revealed an interesting electronic structure with two electrons delocalized in the ligand, demonstrating the non-innocent nature of the N2S2 ligand. While the analogous iron complex proved to be an effective pre-catalyst for the hydroboration of aldehydes with selectivity against ketones, this behaviour was not observed with [Co(N2S2)]- which gave a slower rate and less selectivity. The knowledge acquired from this thesis work has advanced the field of bifunctional catalysis by extending the application of these two SNS ligands from iron to cobalt, revealing unpredictable differences in reactivity between the metals. By comparing the behaviour of these ligands with iron and cobalt, we gain a better understanding of the chemistry that is accessible by these ligands and the applications for which they may be used. This increased knowledge contributes to our long-term goal of replacing expensive and toxic noble metals with more benign first-row transition metals, improving the sustainability of the chemical industry.
Book Synopsis The Great Potential of Redox Active Ligands by : Meredith Miles
Download or read book The Great Potential of Redox Active Ligands written by Meredith Miles and published by . This book was released on 2018 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal N-heterocyclic carbene (NHC) complexes have recently gained much popularity due to their tunable, steric, and electronic properties. Applications for such versatile molecules include organocatalysis1 2 3, olefin metathesis4 5 6, sundry cyclization reactions7 8 9, and materials chemistry10 11. Redox active NHCs are of special interest due to their ability to alter the electronic properties of the metal centers they are ligated to.12 In the first chapter, Au(I)-NHC complexes were synthesized and tested for biological activity in human cancer cell lines. Increasing reactive oxygen species (ROS) in cellular systems has proven to be a successful pathway for treating cancer13 14 15. The redox active group in this case was naphthoquinone which contributed to the oxidative stress applied to the tumor cells. Three Au(I)-NHC complexes were synthesized and analyzed structurally utilizing 1H NMR, 13C NMR, and X-ray crystallography. Biological studies including IC50 cell culture lines and cell proliferation analyses were performed to determine the complexes' efficiency and success as a cancer treatment drug. The second chapter describes a theoretical approach to synthesize a redox active tetrathiafulvalene (TTF) fused with an iridium-NHC complex to serve as a redox switchable catalyst. The first compound in this synthetic route was successfully synthesized and analyzed structurally with 1H and 13C NMR, UV-Vis spectroscopy, and IR spectroscopy. The electrochemical properties were also investigated. Tetrathiafulvalene possesses the ability to undergo multiple one electron reversible redox transformations. This unique characteristic paired with the catalytic properties of iridium-NHC could produce a catalyst capable of accessing three or more catalytic species based upon the oxidation state of TTF.
Book Synopsis Reactivity of the Five-coordinate Transition Metal Complexes Toward Oxygen, Carbon Monoxide, and Nitrogen by : Vahdat Jahed
Download or read book Reactivity of the Five-coordinate Transition Metal Complexes Toward Oxygen, Carbon Monoxide, and Nitrogen written by Vahdat Jahed and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In biological systems, O2 interaction with iron centers in enzyme structure occurs during respiration and the metabolic process. To fully understand the interaction mechanism, each step of the O2 reduction process is important and needs to be characterized. To this goal, we have synthesized and characterized a series of cationic five-coordinate iron complexes, [FeII(L)(L')]+ where L is TpMe, Me = hydrotris{3,5-dimethylpyrazol-1-yl}borate; TpPh, Me = hydrotris{3-phenyl-5-methylpyrazol-1-yl}borate; L'= 2,2'-bipyridine; 4,4'-dimethoxy-2,2'-bipyridine; 4,4'-dimethyl-2,2'-bipyridine; 4,4′-bis(trifluoromethyl)-2,2′-bipyridine; 4,4'-dibromo-2,2'-bipyridine. These complexes were utilized to activate O2 to isolate iron-oxygen intermediate species. The electronic spectra indicate intense absorption at 390 nm consisting of O2 binding to the mononuclear iron complex that generates an iron oxygen intermediate. In addition, the effect of the ligand on the stability of the potential intermediate was studied by altering the ligand substitute. We also treated the high-spin iron(II) reaction with CO to generate the corresponding adduct of low-spin iron(II). 1HNMR analysis reveals a diamagnetic complex arising from a spin-state change from S = 2 to S = 0. Furthermore, infrared spectroscopy has been used to support CO binding empirically. In chapter 3, my research studies nitrene chemistry. Nitrenes are chemically analogous to a single oxygen atom (i.e., NR vs. O). Therefore, nitrene can insert into other chemical bonds. Such reactivity can install synthetically valuable carbon-nitrogen bonds into hydrocarbon substrate. Affording shorter routes to high-value commodity chemicals. However, free nitrenes are generated with difficulty and often display rapid and unselective reactivity. Some degree of control can be achieved through the coordination of nitrene within the ligand field of a metal complex. Structural and electronic modifications affect nitrene reactivity and enable catalyst optimization by characterizing reactive intermediates. We provided a rare example of an octahedral high valent iron imido complex. In chapter 4, polydentate ligand systems have been used to synthesize a new series of late first-row transition metal complexes. We employed Tp hydrotris(pyrazolyl)borates and Bp hydrobis(pyrazolyl)borates to synthesize five-coordinate complexes, [(L)M(L')] where (L is TpPh, Me, TpMe, Me; L'= BpPh, Me, BpH, H; and M= Fe, Co, Ni) to investigate their coordination chemistry. Various sterically hindered ligand systems show an interesting effect on the ligand orientation in the complex structure.
Book Synopsis Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes by : Padmapriya Srinivasan
Download or read book Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes written by Padmapriya Srinivasan and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Expanding the Chemistry of D0 Transition Metals Through Redox-active Ligands by : Nicole Annette Ketterer
Download or read book Expanding the Chemistry of D0 Transition Metals Through Redox-active Ligands written by Nicole Annette Ketterer and published by . This book was released on 2008 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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