Download or read book Electronic Structure and Reactivity of Transition Metal Complexes Incorporating Pro radical Bis phenoxide Ligands written by Ryan Michael Clarke and published by . This book was released on 2018 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Transition metal complexes with pro-radical ligands have received considerable research attention due to their interesting electronic structures, photophysical properties, and applications in catalysis. The relative ordering of metal and ligand frontier orbitals in a complex incorporating pro-radical ligands dictates whether oxidation/reduction occurs at the metal centre or at the ligand. Many metalloenzymes couple redox events at multiple metal centres or between metals and pro-radical ligands to facilitate multielectron chemistry. Owing to the simplicity of the active sites, many structural and functional models have been studied. One class of pro-radical ligand that has been investigated extensively are bis-imine bis-phenoxide ligands (i.e. salen) due to their highly modular syntheses. In this thesis, projects related to the synthesis, electronic structure, and reactivity of mono and bimetallic complexes incorporating the salen framework are explored. Chapter 2 presents a systematic investigation of the effects of geometry on the electronic structure of four bis-oxidized bimetallic Ni salen species. The tunability of their intense intervalence charge transfer (IVCT) transitions in the near infrared (NIR) by nearly 400 nm due to exciton coupling in the excited states is described. For the first time, this study demonstrates the applicability of exciton coupling to ligand radical systems absorbing in the NIR region. Chapter 3 investigates the ground-state electronic structure of a bis-oxidized Co dimer. Enhanced metal participation to the singly occupied molecular orbitals results in both high spin Co(III) and Co(II)-L• character in the ground state, and no observable band splitting in the NIR due to exciton coupling. Finally, Chapter 4 describes a series of oxidized nitridomanganese(V) salen complexes with different para ring substituents (R = CF3, tBu, and NMe2), demonstrating that nitride activation is dictated by remote ligand electronics. Upon one-electron oxidation, electron deficient ligands afford a Mn(VI) species and nitride activation, whereas an electron-rich ligand results in ligand based oxidation and resistance to N coupling of the nitrides. This study highlights the alternative reactivity pathways that pro-radical ligands impose on metal complexes and represents a key step in the use of NH3 as a hydrogen storage medium. The results presented herein provide a starting point for further efforts in reactivity with the salen platform.

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.

Download or read book Molecular Electronic Structures of Transition Metal Complexes I written by David Michael P. Mingos and published by Springer Science & Business Media. This book was released on 2012-01-13 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: J.P. Dahl: Carl Johan Ballhausen (1926–2010).- J.R. Winkler and H.B. Gray: Electronic Structures of Oxo-Metal Ions.- C.D. Flint: Early Days in Kemisk Laboratorium IV and Later Studies.- J.H. Palmer: Transition Metal Corrole Coordination Chemistry. A Review Focusing on Electronic Structural Studies.- W.C. Trogler: Chemical Sensing with Semiconducting Metal Phthalocyanines.- K.M. Lancaster: Biological Outer-Sphere Coordination.- R.K. Hocking and E.I. Solomon: Ligand Field and Molecular Orbital Theories of Transition Metal X-ray Absorption Edge Transitions.- K.B. Møller and N.E. Henriksen: Time-resolved X-ray diffraction: The dynamics of the chemical bond.

Download or read book The Effects of Ligand Electronics on the Properties and Reactivity of Late Transition Metal Complexes written by David Shaffer and published by . This book was released on 2012 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: The overarching theme of the work herein is the investigation of the effects of ligand electronics on the electronic structure and reactivity of non-innocent late transition metal complexes. Chapter 2 describes the electronic structure of (nacnacR[supercript]) Rh II[superscript] (phdisq) (nacnacR[superscript] = CH[C(R)(N-i [superscript] Pr2 C6 H3)]2, -[superscript], R = CH3, CF3; phdisq = 9,10-phenanthrenediiminosemiquinone *[superscript]-[superscript]), which incorporates both a reducible diimine ligand and a reducing [beta]-diketiminate ligand. The complex is assigned as having highly delocalized, closed shell frontier orbitals. One-electron oxidation of (nacnacCH3[superscript]) RhII[superscript] (phdisq) produces a delocalized ligand-based radical, while one-electron reduction gives (nacnac CH3[superscript]) RhII[superscript]) (phda). Chapter 3 studies the oxidative addition of halogen substrates to (nacnacR[superscript]) Rh(phdisq). Chlorine and bromine are observed to add in a normal trans fashion, but the addition of iodine is found to be dependent on the electronic properties of the ligands, forming either an [eta]1 -I2 complex or the oxidative addition product. Chapter 4 reports the reactions of (nacnacCH3[superscript])Rh(phdisq) with haloacids. The addition of HCl quickly produces the product [(nacnacH[superscript]CH3[superscript] RhCl2 (phdaH2)]+[superscript] (phdaH2 = 9,10-phenanthrenediamine), which is the result of protonation of the (nacnacCH3[superscript]) ligand, oxidative addition to the rhodium center, and hydrogenation of the phdi ligand. This reaction is reversible, and the deprotonated (nacnacCH3[superscript])RhCl2 (phdaH2) is also isolable but undergoes slow disproportionation. All phdaH2 complexes are dehydrogenated by oxygen to give the corresponding phdi products. Chapter 5 examines the differences between (nacnacCH3[superscript])Co(phdisq) and (nacnacCH3[superscript])Rh(phdisq). The solid state structures are completely analogous, suggesting analogous electronic ground states. Differences in the solution spectroscopic characterization between the rhodium and cobalt complexes suggest the existence of a thermally accessible triplet state for (nacnacCH3[superscript])Co(phdisq). Chapter 6 addresses the question of how the introduction of a reducible ligand will affect the electrocatalytic potential of a catalyst for proton reduction. The complexes (adi)M(bdt) (M = Ni, Co; adi = N-N'-bis(2,4,6-trimethylphenyl)-acenapthene-1,2-diimine, bdt = 1,2-benzenedithiolate2-[superscript] are described, and the cobalt complex is evaluated as an electrocatalyst for H+[superscript] reduction. Results indicate that the [eta]-acidic nature of the adi ligand makes the cobalt center less basic, thus reducing its catalytic efficiency. Chapter 7 compares tungsten complexes of the well-known redox active bis(3,5-di- tert- butyl-phenolate)amido3-[superscript] ligand (ONO3-[superscript]) and the novel bis(4-methyl-thiophenolate)amido3-[superscript] (SNS3-[superscript]) ligand. While W(ONO)2 is found to be an `innocent' tungsten(VI) complex, W(SNS)2 is described as tungsten(IV) with partially oxidized (SNS) ligands. W(SNS)2 has a highly distorted geometry that is ascribed to [eta]-[eta] interactions in the solid state.

Download or read book Molecular Electronic Structures of Transition Metal Complexes II written by David Michael P. Mingos and published by Springer Science & Business Media. This book was released on 2012-01-11 with total page 247 pages. Available in PDF, EPUB and Kindle. Book excerpt: T. Ziegler: A Chronicle About the Development of Electronic Structure Theories for Transition Metal Complexes.- J. Linderberg: Orbital Models and Electronic Structure Theory.- J.S. and J.E. Avery: Sturmians and Generalized Sturmians in Quantum Theory.- B.T Sutcliffe: Chemistry as a “Manifestation of Quantum Phenomena” and the Born–Oppenheimer Approximation?- A.J. McCaffery: From Ligand Field Theory to Molecular Collision Dynamics: A Common Thread of Angular Momentum.- M. Atanasov, D. Ganyushin, K. Sivalingam and F. Neese: A Modern First-Principles View on Ligand Field Theory Through the Eyes of Correlated Multireference Wavefunctions.- R.S. Berry and B.M. Smirnov: The Phase Rule: Beyond Myopia to Understanding.

Download or read book Electronic Structure and Properties of Transition Metal Compounds written by Isaac B. Bersuker and published by John Wiley & Sons. This book was released on 2010-12-01 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt: With more than 40% new and revised materials, this second edition offers researchers and students in the field a comprehensive understanding of fundamental molecular properties amidst cutting-edge applications. Including ~70 Example-Boxes and summary notes, questions, exercises, problem sets, and illustrations in each chapter, this publication is also suitable for use as a textbook for advanced undergraduate and graduate students. Novel material is introduced in description of multi-orbital chemical bonding, spectroscopic and magnetic properties, methods of electronic structure calculation, and quantum-classical modeling for organometallic and metallobiochemical systems. This is an excellent reference for chemists, researchers and teachers, and advanced undergraduate and graduate students in inorganic, coordination, and organometallic chemistry.

Download or read book Synthesis and Ligand Enabled Reactivity of Transition Metal Complexes Bearing a Redox Active Bis phenoxy amide Ligand written by Aaron M. Hollas and published by . This book was released on 2016 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work described herein focuses on the ability of redox-active ligands to enable multi-electron reactivity at transition metal centers. A parallel theme is the effect of ancillary ligands on controlling and modulating the electronic structure of the redox-active ligand and metal center in addition to ancillary ligand effects as they relate to controlling the primary coordination sphere of the metal. (Abstract shortened by ProQuest.).

Download or read book Synthesis and Reactivity of Late Transition Metal Complexes Featuring a Bis 8 quinolyl methylsilyl Ligand written by Preeyanuch Sangtrirutnugul and published by . This book was released on 2007 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Reactions of First row Transition Metal Complexes in Bis alkoxide Ligand Environments with Diazoalkanes written by Amanda Grass and published by . This book was released on 2020 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation focuses on the design and reactions of novel late transition metal carbene complexes featuring alkoxide ligand environments. The high-valent cobalt carbene Co(OR)2(=CPh2) (OR = OCtBu2Ph), featuring short Co=C bond of 1.773(3) ©5, was previously reported from the reaction of Co(OR)2(THF)2 with diphenyldiazoalkane. Magnetic and spectroscopic (EPR) studies demonstrated Co(OR)2(=CPh2) to be a low-spin S = ℗ư complex. Computational studies, in agreement with experimental data, suggested that the electronic structure of Co(OR)2(=CPh2) lies between intermediate spin Co(III) anti-ferromagnetically coupled to a carbene radical and a Co(IV) alkylidene. This dissertation began with investigation of this complex in carbene transfer reactivity. Stoichiometric ketenimine formation occurs upon reaction with various isocyanides CNR0́ø (CNR0́ø =2,6-dimethylphenyl isocyanide, 4-methoxyphenyl isocyanide, 2-chloro-6-methylphenyl isocyanide, adamantyl isocyanide). The reaction is accompanied by the formation of a cobalt bis(alkoxide) bis(isocyanide) complexes Co(OR)2(CNR)2, which were independently synthesized and characterized. Excess isocyanide was required to form ketenimine due to formation of the bis(isocyanide) complex. DFT calculations suggest the mechanism proceeds through isocyanide binding to cobalt, in contrast to nucleophilic attack at the carbene carbon. This is followed by intramolecular insertion into the Co-carbene bond to form the ketenimine complex. Dissociation of free ketenimine from cobalt then leads to the bis(isocyanide) complex. Catalytic formation of ketenimines was investigated at room temperature by exposing the mixtures of the carbene precursors and isocyanides to Co(OR)2(THF)2. The carbene precursors investigated included both diazoalkane (diphenyldiazomethane) and diazoesters (methyl phenyldiazoacetate, and ethyl diazoacetate).

Download or read book Molecular Electronic Structures of Transition Metal Complexes written by David Michael Patrick Mingos and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electronic Structure of Transition Metal Ions and Clusters written by W. M. C. Sameera and published by . This book was released on 2008 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis uses density functional theory (DFT) to explore the electronic structure and reaction mechanisms of open-shell transition metal ions and clusters. The early part of the thesis (Chapters 2 and 3) is devoted to high-valent metal-oxo species, both mono- and bimetallic, while Chapter 4 describes some aspects of copper-catalysed carbon-carbon bond formation. Finally, Chapter 5 highlights the role of DFT in computing magnetic and spectroscopic properties of exchange-coupled iron clusters. Whilst the chemistry contained in the thesis is rather diverse, the underlying theme of open-shell transition metal ions is common to all chapters. Moreover, we are primarily concerned with the ways in which interactions between two or more adjacent open-shells (either two metals or a metal and a ligand radical) control structure and reactivity. After a brief introduction to relevant theoretical aspects in Chapter 1, we use Chapter 2 to establish a link between the electronic structure of the high-valent Mn(V)=O porphyrin monomer species and their ability to perform oxidation reactions. The reaction profiles for oxidation of a range of substrates depend critically on the electronic structure of the isolated oxidant. Where the electronic ground state is genuinely best described as Mn(V)=O, the interaction between oxidant and substrate is repulsive at large separations, only becoming attractive when the incoming nucleophile approaches close enough to drive an electron out of oxide p manifold. In contrast, where the ground state is better described as an oxyl radical form, Mn(IV)-O, the oxidation occurs in sequential one-electron steps, the first of which is barrierless. In Chapter 3, we extend these ideas to bimetallic systems, where the presence of two high-valent manganese centres allows the system to oxidise water. Specifically, we focus on two model systems which have been shown to oxidise water, a Mn-porphyrin-based system synthesised by Naruta and a Mn-based system reported by McKenzie where the ligands contain a mixture of pyridine and carboxylate donors. In both cases, we again find that the emergence of oxyl radical character is the key to the reaction chemistry. However, the radical character is 'masked' in the electronic ground states, either by transfer of an electron from the porphyrin ring (Naruta) or by formation of a di-[mu]-oxo bridge (McKenzie system). In Chapter 4 we turn our attention to copper chemistry, and the role of copper complexes in catalysing atom transfer radical additions (Kharasch additions). In this reaction, the copper cycles between Cu(I) and Cu(II) oxidation states, and the result is the formation of a new C-C bonds. This Chapter makes extensive use of hybrid QM/MM techniques to model the environment of the copper centre in the target polypyrazolylborate-copper complexes (TpxCu). Finally, in Chapter 5 we consider the electronic structure, magnetic and spectroscopic properties of a pair of exchange-coupled Fe3 clusters, [Fe3([mu]3-O)([mu]-4-O2N-pz)6X3]2− (where pz=pyrazolato, X=Cl, Br). Our primary goal was to establish how well broken-symmetry DFT is able to reproduce the observed Mössbauer spectroscopic parameters, which are extensively used to identify the chemical environments of iron species and, in the case of mixed-valence clusters, to establish the degree of delocalisation of the additional electrons. In recent years DFT has proved able to compute these parameters with encouraging accuracy, but it is not clear to what extent the known deficiencies in broken-symmetry wavefunctions will compromise this ability. Our work suggests that neither the isomer shift nor the quadrupole splitting are strongly influenced by the nature of the coupling between the metal ions, suggesting that broken-symmetry solutions can be used as a basis for computing these parameters in more complex clusters.

Download or read book Magnetism and Structure in Transition Metal Complexes written by Michael Harry Dickman and published by . This book was released on 1984 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electronic Structure of Transition Metal Complexes written by Catherine M. Redfern and published by . This book was released on 1988 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Characterization and Reactivity of Novel Bis phosphinoamide Zr Co Heterobimetallic Complexes Bearing N isopropyl Phosphinoamide Ligands written by Nathaniel C. McCutcheon and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In light of growing environmental and economic concerns, there is a motivated effort to mimic the two-electron reactivity of precious transition metal complexes using more abundant, affordable, and non-toxic first row transition metals. The main challenge in this effort is that more sustainable first row transition metals do not readily undergo two-electron redox processes, which comprise many industrially relevant catalytic mechanisms, instead preferring to participate in one-electron reactions. One of several ways the Thomas group has approached this challenge is by tethering a Lewis acidic early metal to an electron-rich late metal via a bifunctional phosphinoamide ligand framework, allowing access to highly reduced late metal centers that have been shown to more favorably undergo two-electron redox processes. This thesis explores how the electron-donating properties of the phosphinoamide ligand impact the structure and reactivity of a novel series of bis(phosphinoamide) Zr/Co complexes. This series employs a more electron-donating iPrNPiPr2- ligand, as opposed to the XylNPiPr2- ligand previously featured in the group’s bis(phosphinoamide) Zr/Co systems. The relative electron density at the cobalt center is qualified using multiple spectroscopic and computational methods, and structural comparisons are made between analogous Zr/Co complexes bearing different ligands. These data are used to determine how increasing the electron-donating ability of the bis(phosphinoamide) framework impacts the thermodynamics of bond activation and the overall structure-reactivity relationship of Zr/Co complexes.

Download or read book Electronic Structure of Open shell Transition Metal Complexes written by Tobias Kramer and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents electronic structure calculations on problems related to the bonding in inorganic coordination compounds and clusters. A wide range of molecules with the ability to exist in different structural forms or electronic states has been selected and density functional theory is systematically applied in order to gain detailed insight into their characteristics and reactivity at the electronic level. First, we address the question of redox non-innocent behaviour of bipyri- dine in a series of 1st row transition metal complexes. Complexes of the type [M(2,2'-bipyridine)(mesh]O (M = Cr, Mn, Fe, Co, Ni; mes = 2,4,6-Me3C6H2) and their one-electron reduced forms have been explored. The results clearly show that the anions are best described as complexes of the monoanionic bipyridine radi- cal (Sbpy = 1/2), giving a rationale for the observed structural changes within the ligand. Likewise, we have identified dianionic bipyridine in both the complexes [Zn2( 4,4'-bpy) (mes)4J2- and [Fe(2,2'-bpyh]2-. In no case have we found evidence for significant metal-to-ligand backbonding. The subject of redox-noninnocence is further revisited in a comparative study of the two complexes [M(o-Clpap)3] (M = Cr, Mo; o-Clpap = 2-[(2-chlorophenyl)azo]-pyridine), and their associated elec- tron transfer series. The results indicate that all electron transfer processes are primarily ligand-based, although in the case of the Mo analogue these are cou- pled to substantial electron density changes at the metal. The ability of pap to form radical anions finds a contrasting case in the dinuclear Rh complex [Rh2 (f-L- p-Clpaph(cod)CI2], where the two ligand bridges act as acceptors of strong dz" backbonding from a formally Rh -I centre. We then direct our attention to the endohedral Zintl clusters [Fe@GelOP- and [Mn@Pbd3-, which reveal peculiar topologies. "\lVe have probed the electronic factors that influence their geomet- ric preferences, and propose a model based on the shift of electron density from the endohedral metal to the cage to account for the observed geometries. Subsequently, we reassess the electronic structure of the xenophilic clusters Mn2(thf)4(Fe(CO)4)2 and [Mn(Mn(thf)2)3(Mn(CO)4)3]-' We conclude that these are best viewed as exchange coupled Mn II centres bridged by closed-shell carbonylate fragments. In the closing chapter the reduction of N02- to NO by the complex [Cu(tct)(N02)]+ (tct = cis,cis-1,3,5-tris(cinnamylideneamino)cyclohexane) is studied, a process that mimics the enzyme-catalysed reaction. Two viable pathways for the reaction have been traced and key intermediates identified. Both direct release of NO or via de- composition of a Cu-NO complex are kinetically and thermodynamically feasible.

Download or read book Electronic Structure of Transition Metal Complexes written by Catherine M. Redfern and published by . This book was released on 1988 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electronic structure and excited state properties of some transition metal complexes having a lowest energy metal to ligand charge transfer state written by Peter C. Servaas and published by . This book was released on 1991 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: