DOCSLIB.ORG

And Dianionic Carbaborane Ligands and Their Transition Metal Complexes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
And Dianionic Carbaborane Ligands and Their Transition Metal Complexes Mono- and Dianionic Carbaborane Ligands and Their Transition Metal Complexes Ewan J. M. Hamilton Thesis Presented for the Degree of Doctor of Philosophy University of Edinburgh 1990 Declaration Except where specific reference is made to other sources, the work presented in this thesis is the original work of the author. It has not been submitted, in whole or in part, for any other degree. Certain of the results have been published, or have been accepted for publication (see Appendix 2). Ewan J. M. Hamilton U Dedicated to my parents and family for their unfailing support. 'U I devoted a day to a coarse sifting of the chicken shit, and another two trying to oxidize the acid contained in it into alloxan. The virtue and patience of ancient chemists must have been superhuman, or perhaps my inexperience with organic preparations was boundless. All I got were foul vapors, boredom, humiliation, and a black and murky liquid which irremediably plugged up the filters and displayed no tendency to crystallize, as the text declared it should. The shit remained shit, and the alloxan and its resonant name remained a resonant name. That was not the way to get out of the swamps: by what path would I therefore get out, I the discouraged author of a book which seemed good to me but which nobody read? Best to return among the colorless but safe schemes of inorganic chemistry. Primo Levi, from The Periodic Table Iv Acknowledgements First and foremost, I would like to thank my supervisor, Dr. Alan Welch, without whose assistance, encouragement, enthusiasm and optimism this work could not have been done. Thanks are also due to John Millar, Heather Grant and Dr. David Reed, who obtained n.m.r. spectra, and Elaine M'Dougall, who performed the elemental analyses. The help of Dr. Ruth Sorbie and Ken Taylor was invaluable in obtaining and interpreting electrochemical and spectroelecirochemical data. Assistance and encouragement have always been readily forthcoming from those who have worked over the years in laboratories 290-293, and although space limits a full "roll of honour" here, all help and advice has been greatly appreciated. Finally, thanks are due to the University of Edinburgh for the use of facilities and to S.E.R.C. for financial support. V Abstract Chapter 1 consists of a brief overview of transition metal cyclopentadienyl chemistry and of the chemistry of carbametailaborane species derived from [7,8-nido-C2B9H11 ]2 , with specific reference to the bonding modes commonly adopted by each ligand to transition metal fragments. The forms of the it-MO's of [C5H5], [C2B9H 11]2 and of the monoanionic ligand [9-SMe2-7,8-C2B9H10} (or [carb'] ), as obtained by extended Huckel molecular orbital (EHMO) calculations, are also presented. In Chapter 2, the structure of [7,8-C2B9H 12], (1), is presented, showing an endo -H atom, rather than the commonly accepted ji-H, associated with the open ligand face.This result is supported by those of n.m.r. and theoretical studies. Isolobal replacement of the endo-terminal hydrogen atom by a fPPh 3Au) fragment leads to complex (2), [10-endo-(PPh 3Au)-7,8-nido-C2B9H 11 ], which has also been studied crystallographically. Structural trends within the series (1), (2) and [PPh3Cu(C2B9H11)] have been rationalised via the results of EHMO calculations. Chapter 3 presents the structure of [10,1 1-i-H-9-SMe 2-7,8-nido-C2B9H10], (3)1 the protonated precursor to the monoanionic ligand [carb']. The molecule possesses an asymmetric bridging H atom on its open face, a structural feature whose origin may be traced using MO calculations at the extended Huckel level. The (triphenyiphosphine) gold(I) and (triphenylphosphine)copper(I) derivatives of [carb'], (4) and(S), have been prepared, and their structures determined by X-ray methods. In all three compounds, the SMe 2 substituent appears to adopt a preferred conformation, and it is suggested that this is allied to an intramolecular electrostatic interaction. Analysis of structural patterns within (3), (4) and (5) reveals different trends to those observed for the related series in the previous chapter. These differences may be rationalised by frontier MO considerations. vi Chapter 4 comprises a comparative structural, spectral and theoretical study of the analogous complexes (carb')Mn(CO) 3 , (6), and CpMn(CO) 3 , (7). The net electronic properties of the anionic ligands in the two complexes are shown to be highly similar, by consideration of infra-red carbonyl stretching frequencies and C-O distances determined by X-ray experiments. Extended Huckel and extended Huckel/fragment MO calculations suggest that the very slightly lower v 0 observed for (6) is a result of slightly greater e-donation into (primarily) the e acceptor orbitals of the (Mn(CO) 3 } fragment by the carbaborane ligand than by Cp. This results in limitation of a-donation by the carbonyl ligands, giving the slightly lower v 0 observed. Chapter 5 details the preparation of the bis(carb') analogue of ferrocene, Fe(carb')2, (8), and its structural characterisation as the E-isomer, where both (chiral) ligands are of the same optical isomer. The isomeric nature of (8) has been shown to be dependent on its method of preparation. Electrochemical work on Fe(carb') 2 again shows the net electron-donating properties of [carb'] to be comparable to those of Cp. (8) may also be readily oxidised chemically to give the 1 monocation. [Fe(carb') 2 ] . A second product, Fe(carb')(C2B9H 10SMe), (9), has also been isolated and its structure determined as the 0-isomer (where the two ligands are of opposite handedness). This, allied to the results of electrochemical studies, allow a mechanism for the formation of (9) to be proposed, involving loss of (Me) from [Fe(carb') 2]. Chapter 6 gives details of the experimental procedures leading to the results discussed in the body of the work, and comprises four sections: 1. Synthetic Methods and Spectral Data, 2. Crystallographic Techniques, 3. Molecular Orbital Calculations, and 4. Electrochemical and Spectroelectrochemical Techniques. VII Abbreviations AO atomic orbital BTMA benzyltrimethylammonium COSY correlation speciroscopy Cp cyclopentadienyl Cp* pentamethylcyclopentadienyl dmso dimethylsulphoxide EHMO extended Huckel molecular orbital EHMO/FMO extended Huckel/fragment molecular orbital e.s.d. estimated standard deviation Et ethyl eV electron volts Fc ferrocene FMO fragment molecular orbital HOMO highest occupied molecular orbital LCAO linear combination of atomic orbitals LUMO lowest unoccupied molecular orbital Me methyl MO molecular orbital n.m.r. nuclear magnetic resonance Ph phenyl p.p.m. parts per million PSEPT polyhedral skeletal electron pair theory SEP skeletal electron pair TBA tetra(n-butyl)ammonium THF tetrahydrofuran viii Abbreviations for Specific Complexes [7,8-nido-C2B9H121- [10-endo-(PPh3Au)-7,8-nido-C 2B9H1 i] [10,1 1-JL-H-9-SMe2-7,8-nido-C2B9Hi& [10,11 -J.L-(PPh3Au)-9-SMe2-7,8-nido-C2B9H1& [3-PPh3-4-SMe2-3, 1 ,2-CuC2B9H10] [3,3,3-(CO) 3-4-SMe2-3, 1 ,2-MnC2B9H rn' [(i-05H5)Mn(CO)3] [com,no-3,3'-Fe-4,4'-(SMe2)2- 1,1 ',2,2'-(C2B9H10)2] [com,no-3,3'-Fe-4-SMe2-4'-SMe- 1,1 ',2,2'-(C2B9H10)2] ix Contents Page Chapter 1: Introduction 1 Introduction 1 Chemistry of the Cyclopentadienyl Ligand 2 Carbametallaboranes: A Brief Introduction 11 Monoanionic Carbaboranes, [C2B9H10L] 19 Comparison of the it-MO's of [C 5H5]-, [C2B9H1 and [carb'] 20 Scope of the Work Presented 23 Chapter 2: [7,8-C2B9H12] and Group lb Derivatives 25 Introduction 25 Synthesis and Characterisation of [BTMA](1) 26 Synthesis and Characterisation of [drnsoH.dmso](1) 29 Structural Study of (1) 30 Synthesis and Characterisation of [BTMA](2) 43 Structural Study of (2) 45 Structural Patterns in (1), (2) and [PPh 3Cu(C2B9H11 )] - 55 Conclusions 64 Chapter 3: carb'H and Group lb Derivatives 65 [10,1 1-I.t-H-9-SMe2-7,8-nido-C2B9H1&, (3): Introduction 65 Structural Study of (3) 67 Deprotonation of (3) 81 Synthesis and Characterisation of (4) 83 Structural Study of (4) 84 Synthesis and Characterisation of (5) 94 Structural Study of (5) 95 Structural Patterns in (3), (4) and (5) 104 Conclusions 109 Chapter 4: (carb')Mn(CO) 3 versus CpMn(CO)3: A Comparative Study 110 Introduction 110 Synthesis and Characterisation of (6) 111 Structural Study of (6) 113 x Synthesis and Characterisation of (7) 122 Structural Study of (7) -. 122 Structural and Spectral Comparison between (6) and (7) 130 Electronic Structures of (6) and (7) 131 Conclusions 140 Chapter 5: The Bis(cage) Iron System 142 Introduction 142 Synthesis and Characterisation of (8) 142 Structural Study of (8) 144 Electrochemical Study of (8) 156 Chemical Oxidation of (8) 158 Spectroelectrochemical Study of (8) 160 Introduction to (9) 162 Synthesis and Characterisation of (9) 163 Structural Study of (9) 165 Electrochemical Study of (9) 182 Reaction of (9) with [Me30]BF4 183 Spectroelectrochemical Study of (9) 186 Conclusions 188 Chapter 6: Experimental 189 Introduction 189 Section 1: Synthetic Methods and Spectral Data 190 Section 2: Crystallographic Techniques 201 Section 3: Molecular Orbital Calculations 213 Section 4: Electrochemical and Spectroelectrochemical Techniques 221 References 227 Appendices 236 Appendix 1: Lectures and Courses Attended 237 Appendix 2: Published Work 238 xi Chapter 1 Introduction Since the inception of carhametallaborane (or metallacarborane) chemistry in 1.2 the mid-1960's there has been drawn an analogy between the IC13 9 11 1 (dicarhollide) ligand and the cyclopentadienide (IC5 H 5 1 or Cp) anion. A more recent modification of this analogy suggests that 1C2B 9 H 1 j may he better compared to the pentamethyl derivative of Cp, C 5 Me5 (or Cp*_), on account of its steric requirements.
Load more

Recommended publications
  • Application of Metallocenes for the Synthesis of Multiwalled Carbon Nanotubes
    APPLICATION OF METALLOCENES FOR THE SYNTHESIS OF MULTIWALLED CARBON NANOTUBES by Nonjabulo Philile Dominica Ngidi Submitted in fulfilment of the academic requirement for the degree of Master of Science in the School of Chemistry and Physics University of KwaZulu-Natal, Durban, Westville campus February 2016 ABSTRACT Multiwalled carbon nanotubes (MWCNTs) are carbon materials which have one-dimensional structure. They possess unique properties such as semi-conductor and high tensile strength that allow them to be widely used in many applications. MWCNTs and other shaped carbon nanomaterials (SCNMs) were synthesized by chemical vapour deposition (CVD) method. Three factors that affect the morphology, thermal, chemical, mechanical and electrical properties of SCNMs were investigated. The parameters are: carbon source, catalyst (metallocenes), and growth temperature. Two different carbon sources were studied for the synthesis of MWCNTs i.e., toluene and acetonitrile (also used as a nitrogen source). The metallocenes: nickelocene, cobaltocene and ruthenocene were used as catalysts (2.5 wt.%) while ferrocene was employed as control. These metallocenes were investigated because they have similar structure as ferrocene, a well-known catalyst for the synthesis of SCNMs. The synthesis was carried out at five different growth temperatures, 800, 850, 900, 950 and 1000 °C. As-synthesized MWCNTs and other SCNMs were further purified, in order to remove amorphous carbon and this was performed by testing different methods of purification. The effective method for purification of MWCNTs was method 2 which involved refluxing for 24 hours. It was chosen to be the best method because it produced purer MWCNTs as compared to other methods which caused damage to the MWCNTs.
    [Show full text]
  • Synthesis and Reactivity of Cyclopentadienyl Based Organometallic Compounds and Their Electrochemical and Biological Properties
    Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Sasmita Mishra Department of Chemistry National Institute of Technology Rourkela Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties Dissertation submitted to the National Institute of Technology Rourkela In partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry by Sasmita Mishra (Roll Number: 511CY604) Under the supervision of Prof. Saurav Chatterjee February, 2017 Department of Chemistry National Institute of Technology Rourkela Department of Chemistry National Institute of Technology Rourkela Certificate of Examination Roll Number: 511CY604 Name: Sasmita Mishra Title of Dissertation: ''Synthesis and reactivity of cyclopentadienyl based organometallic compounds and their electrochemical and biological properties We the below signed, after checking the dissertation mentioned above and the official record book(s) of the student, hereby state our approval of the dissertation submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Chemistry at National Institute of Technology Rourkela. We are satisfied with the volume, quality, correctness, and originality of the work. --------------------------- Prof. Saurav Chatterjee Principal Supervisor --------------------------- --------------------------- Prof. A. Sahoo. Prof. G. Hota Member (DSC) Member (DSC) ---------------------------
    [Show full text]
  • First-Principles Simulations of the Interaction of Metal-Organic Molecules with a Surface and As Building Blocks for Nanodevices
    Universite´ de Strasbourg IPCMS: CNRS - UMR 7504 These` de Doctorat FIRST-PRINCIPLES SIMULATIONS OF THE INTERACTION OF METAL-ORGANIC MOLECULES WITH A SURFACE AND AS BUILDING BLOCKS FOR NANODEVICES par Burak Ozdamar¨ pr´esent´eeen vue d'obtenir le grade de Docteur de l'Universit´ede Strasbourg Sp´ecialit´e:Physique de la mati`erecondens´eeet des mat´eriaux Soutenue publiquement le 28/10/2016 `al'IPCMS devant le jury compos´ede: Prof. Dr. Roberto Marquardt UdS-LCQ Pr´esident Prof. Dr. J¨urg Hutter UZH-CMSZH Rapporteur Prof. Dr. Andres Saul AMU-CINaM Rapporteur Prof. Dr. Fabrizio Cleri UL1-IEMN Rapporteur Dr. S´ebastien Le Roux UdS-IPCMS Examinateur Prof. Dr. Mauro Boero UdS-IPCMS Directeur de th`ese Tired of lying in the sunshine staying home to watch the rain You are young and life is long and there is time to kill today And then one day you find ten years have got behind you No one told you when to run, you missed the starting gun. Roger Waters iii Abstract UNIVERSITE´ DE STRASBOURG Institut de Physique et Chimie des Mat´eriauxde Strasbourg Doctor of Philosophy FIRST-PRINCIPLES SIMULATIONS OF THE INTERACTION OF METAL-ORGANIC MOLECULES WITH A SURFACE AND AS BUILDING BLOCKS FOR NANODEVICES by Burak Ozdamar¨ The purpose of this study is to investigate the interaction of organometallic com- plexes with transition metals. This topic in question has a broad array of applica- tions in a number of domain; realization of nanojunctions for molecular nanoelec- tronics, biological imaging and nanocatalysis. Within this general framework, this PhD project aims to model the fundamental interactions of molecular building blocks at the atomic level in order to understand their role in the assembly and functionalization of nanostructures.
    [Show full text]
  • Metalation Studies on Titanocene Dithiolates
    inorganics Article Metalation Studies on Titanocene Dithiolates Tilmann G. Kießling and Karlheinz Sünkel * ID Department of Chemistry, Ludwig-Maximilians University Munich, 81377 Munich, Germany; [email protected] * Correspondence: [email protected]; Tel.: +49-89-2180-77773 Received: 18 July 2018; Accepted: 22 August 2018; Published: 24 August 2018 Abstract: Titanocene bis-arylthiolates [(C5H4X)(C5H4Y)Ti(SC6H4R)2] (X,Y = H, Cl; R = H, Me) can be prepared from the corresponding titanocene dichlorides by reacting with the thiols in the presence of DABCO as a base. They react with n-butyl lithium to give unstable Ti(III) radical anions. While the unsubstituted thiolates (X = Y = R = H) react with lithium Di-isopropylamide by decomposing to dimeric fulvalene-bridged and thiolate-bridged Ti(III) compounds, the ring-chlorinated compounds can be deprotonated with LDA and give appropriate electrophiles di-substituted and tri-substituted titanocene dithiolates. Keywords: titanocene thiolates; metalation; chlorocyclopentadienyl ligands 1. Introduction Titanocene compounds, i.e., compounds of the type “Cp2TiXn” where “Cp” stands for a substituted or unsubstituted cyclopentadienyl ligand and “X” for any anionic or neutral ligand and n = 0–2 are arguably the second-most studied metallocenes after ferrocene. Soon after the first synthesis of (C5H5)2TiCl2 in 1954 [1], its potential for acting as a polymerization catalyst when combined with certain aluminum compounds was discovered [2]. Further studies showed that a judicious choice of substituents on the cyclopentadienyl ring had a great influence on the stereochemistry of the produced polymers, which gave rise to an enormous number of publications and also many review articles [3–8].
    [Show full text]
  • Formation from Chlorophenols 82
    FORMATION OF AROMATIC COMPOUNDS BY CYCLOPENTADIENE MOIETIES IN COMBUSTION PROCESSES A Thesis Presented to The Academic Faculty by Do Hyong Kim In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the School of Civil and Environmental Engineering Georgia Institute of Technology August 2005 FORMATION OF AROMATIC COMPOUNDS BY CYCLOPENTADIENE MOIETIES IN COMBUSTION PROCESSES Approved by: Dr. James A. Mulholland, Advisor Dr. Armistead G. Russell School of Civil and Environmental School of Civil and Environmental Engineering Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Michael H. Bergin Dr. C. David Sherrill School of Civil and Environmental School of Chemistry and Biochemistry Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Kurt D. Pennell School of Civil and Environmental Engineering Georgia Institute of Technology Date Approved: 06/29/2005 This dissertation is dedicated to my family ACKNOWLEDGEMENTS I would like to thank the following people for their help and support throughout my program at Georgia Tech. First of all, I would like to especially thank Dr. James. A. Mulholland, my advisor, for his endless and excellent guidance. Words cannot be good enough to express my gratitude toward him. It was always my pleasure to work and spend time with him during last seven years. My gratitude also goes to Drs. Ted Russell, Kurt D. Pennell, Michael H. Bergin and David Sherrill for their guidance, helpful comments and time spent serving on my thesis committee. I like to thank Dr. Guangxuan Zhu, our lab manager, who has fixed many a problem and given excellent advice on analytical techniques in the lab.
    [Show full text]
  • Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)
    NOMENCLATURE OF INORGANIC CHEMISTRY IUPAC Recommendations 2005 IUPAC Periodic Table of the Elements 118 1 2 21314151617 H He 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 3456 78910 11 12 Na Mg Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 * 57− 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba lanthanoids Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 87 88 ‡ 89− 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra actinoids Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo * 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ‡ 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr International Union of Pure and Applied Chemistry Nomenclature of Inorganic Chemistry IUPAC RECOMMENDATIONS 2005 Issued by the Division of Chemical Nomenclature and Structure Representation in collaboration with the Division of Inorganic Chemistry Prepared for publication by Neil G.
    [Show full text]
  • CURRICULUM VITAE WILLIAM E. GEIGER, JR. Professor Of
    CURRICULUM VITAE WILLIAM E. GEIGER, JR. Professor of Chemistry University of Vermont, Burlington VT 05405 802-656-0268; EMAIL [email protected] FAX 802-656-8705 Education B.S. Canisius College 1965 Chemistry Ph.D. Cornell University 1969 Analytical Chemistry Positions Research Associate, Univ. of California at Riverside 1968-69 Postdoctoral Research Associate, Northwestern Univ. 1969-70 Assistant Professor, Southern Illinois Univ. 1970-74 Assistant Professor, Univ. of Vermont 1974-77 Associate Professor, Univ. of Vermont 1977-82 Professor, Univ. of Vermont 1982-Present Pomeroy Professor, Univ. of Vermont 1997-Present Chair, Department of Chemistry, University of Vermont 1998-2001 Honors University of Vermont Scholar 1984 James Crowdle Award, Canisius College 1995 Dean’s Lecturer, UVM 2009 Vermont Academy of Science and Engineering 2009 William Geiger Research Laboratory (Free State University) 2011 Professional Organizations Member, American Chemical Society (ACS) Division of Analytical Chemistry Division of Inorganic Chemistry Society for Electroanalytical Chemistry (SEAC) Vermont Academy of Science and Engineering Selected Professional Activities Professeur Associe, Univ. of Bordeaux 1986 Editor, Newsletter of SEAC 1985-88 Editorial Advisory Board, Organometallics 1989-91 Board of Directors, SEAC 1992-95 Graduiertenkolleg Lecturer, Univ. of Freiburg 1996 Editorial Board, Chemtracts 1997-98 Leverhulme Fellow, University of Bristol 1998 Erskine Fellow, University of Canterbury 2000 Advisory Board, Center for Molecular Electrocatalysis 2009-present INVITED LECTURES AND COLLOQUIA Canisius College 10/70 Univ. Maryland at Baltimore 9/71 Franklin and Marshall College 9/71 Univ. of Missouri at St. Louis 2/73 Brown University 10/75 Univ. of Massachusetts at Amherst 12/75 Univ. of Massachusetts at Boston 2/76 SUNY at Buffalo 11/76 SUNY at Plattsburgh 1/77 Providence College 2/78 Wesleyan University 2/78 St.
    [Show full text]
  • AROMATIC HYDROCARBONS: Part I
    AROMATIC HYDROCARBONS: Part I DR SUNIL K. SINGH Assistant Professor in Chemistry SK SINGH, KMC Concept of Aromaticity Aromatic compounds apparently contain alternate double and single bonds in a cyclic structure and resemble benzene in chemical behaviour. They undergo substitution rather than addition reactions. This characteristic behaviour is known as aromaticity. Addition reaction: Substitution reaction: Br Br 2 H E CCl + 4 Br E + H+ Br2 No Reaction SK SINGH, KMC CCl4 Following are the main criteria of aromaticity: Chemical behaviour: electrophilic aromatic substitution. Structural: bond length equalization due to cyclic delocalization of electrons. C-C bond length in benzene id 139 pm. SK SINGH, KMC Contd……………….. Enhanced stability (large resonance energy). Heat of hydrogenation of Benzene is 49.8 Kcal/mole. Heat of hydrogenation of 1,3,5- hexatriene is 85.8 Kcal/ mole. Smaller the heat of hydrogenation Magnetic: "ring current" effects. more is the stability. Benzene is ~36 Kcal/mole more stable than the 1,3,5- • anomalous chemical shifts in NMR. hexatriene. • large magnetic anisotropies • high diamagnetic susceptibility. SK SINGH, KMC Huckel’s Rule and aromaticity A molecule is aromatic if all the following conditions are fulfilled: It is cyclic, planar and it has continuous delocalization of p electrons (electrons in p orbitals) with or without the participation of lone pair(s)/ -ve charge/ +ve charge. Huckel’s rule: The delocalised p-electron system must contain a total of (4n+2)p electrons, where n is a whole number (i.e., n = 0,1,2,3,………). Note that the p-orbitals in which the electrons are delocalizing must be parallel to each other so that a continuous overlap of electrons is possible along the ring.
    [Show full text]
  • Synthesis of the Metallocenes for the Production of Exotic High Energy Ion Beams
    Synthesis of the Metallocenes for the Production of Exotic High Energy Ion Beams Ntombizonke Yvonne Kheswa A thesis is submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the Department of Physics & Astronomy, University of the Western Cape, South Africa. Supervised by: Prof. J. N. Orce, Department of Physics & Astronomy University of the Western Cape Prof. S. Titinchi, Department of Chemistry, University of the Western Cape Dr. R. Thomae Accelerator and Engineering Department iThemba LABS March 2019 https://etd.uwc.ac.za DECLARATION I declare that Synthesis of the Metallocenes for the Production of Exotic High Energy Ion Beams is my own work, that it has not been submitted for any degree or examination in any other university, and that all the sources I have used or quoted have been indicated and acknowledged by complete references. Signed: Ntombizonke Kheswa Date: 1 March 2019 i https://etd.uwc.ac.za Synthesis of the Metallocenes for the Production of Exotic High Energy Ion Beams Department of Physics and Astronomy, University of the Western Cape, Private Bag X17, 7535 Bellville, South Africa. ABSTRACT The Subatomic Physics Department of iThemba Laboratory for Accelerated Based Sciences (iThemba LABS) conducts experiments that require a variety of particle beams in order to study nuclear properties (reaction, structure, etc.) of various nuclides. These particle beams are accelerated using the K-200 Separated Sector Cyclotron (SSC) and delivered to different physics experimental vaults. Prior to acceleration, the particle beam is first ionised using an Electron Resonance Ion Source (ECRIS). The main goal of this study is the production of exotic metallic beams of 60Ni8+ and 62Ni8+ using ECRIS4, which are required for the Coulomb excitation experiments approved by the Programme Advisory Committee (PAC) at iThemba LABS.
    [Show full text]
  • MITOCW | 2. the Ferrocene Lecture
    MITOCW | 2. The Ferrocene Lecture [SQUEAKING] [RUSTLING] [CLICKING] JOHN DOLHUN: Welcome to the ferrocene lecture. We are going to do a demonstration at the start because I'm going to be talking about additional reactions during this lecture. And I want you to actually see one happen. So I've got Amanda Trainor, who is manning the fire extinguisher. Amanda just had her fire extinguisher testing. So she is ready to go. And Dr. Sarah Hewett will actually assist me with the bromine that we're using. Bromine and me go way back because I made bromine when I was in high school. In the parents of my-- in my parents' home-- in the basement. The whole place filled up with reddish brown gas. And back in those days, the chemistry sets had real chemicals in them. So what we're going to do is we are going to cook some bacon. And we are going to crack the glycerol. And we going to make this unsaturated compound acrolein. Then we're going to throw it into the bromine. And the bromine should add across the double bond-- an addition reaction. This is the acrid smelly stuff that you smell when you cook bacon. This is the burned bacon fat smell that you smell. It's colorless, flammable, and very poisonous. So let's go. We're going to start this. So I'm using a creme brulee torch. It's my wife's. She's probably out of her mind now looking for it. So we're cooking the bacon.
    [Show full text]
  • Differentiation Between Spin State, Electrostatic and Covalent Bonding
    Inorganica Chimica Acta 360 (2007) 179–189 www.elsevier.com/locate/ica Metal–ligand bonding in metallocenes: Differentiation between spin state, electrostatic and covalent bonding Marcel Swart Institucio´ Catalana de Recerca i Estudis Avanc¸ats (ICREA), 08010 Barcelona, Spain Institut de Quı´mica Computacional, Universitat de Girona, Campus Montilivi, 17071 Girona, Spain Received 16 June 2006; received in revised form 26 July 2006; accepted 26 July 2006 Available online 5 August 2006 Inorganic Chemistry – The Next Generation. Abstract We have analyzed metal–ligand bonding in metallocenes using density functional theory (DFT) at the OPBE/TZP level. This level of theory was recently shown to be the only DFT method able to correctly predict the spin ground state of iron complexes, and similar accuracy for spin ground states is found here. We considered metallocenes along the first-row transition metals (Sc–Zn) extended with alkaline-earth metals (Mg, Ca) and several second-row transition metals (Ru, Pd, Ag, Cd). Using an energy decomposition analysis, we have studied trends in metal–ligand bonding in these complexes. The OPBE/TZP enthalpy of heterolytic association for ferrocene (À658 kcal/mol) as obtained from the decomposition analysis is in excellent agreement with benchmark CCSD(T) and CASPT2 results. Covalent bonding is shown to vary largely for the different metallocenes and is found in the range from À155 to À635 kcal/mol. Much smaller variation is observed for Pauli repulsion (55–345 kcal/mol) or electrostatic interactions, which are however strong (À480 to À620 kcal/mol). The covalent bonding, and thus the metal–ligand bonding, is larger for low spin states than for higher spin states, due to better suitability of acceptor d-orbitals of the metal in the low spin state.
    [Show full text]
  • N-Metal Compounds
    31 N-METAL COMPOUNDS n the 85 years following Kekulk's brilliant proposal for the structure of ben- zene, organic chemistry underwent a tremendous expansion, and in the process a wide variety of paradigms or working hypotheses were developed about what kinds of compounds could "exist" and what kinds of reactions could occur. In many cases, acceptance of these hypotheses appeared to stifle many possible lines of investigation and caused contrary evidence to be pigeonholed as "interesting but not conclusive." As one example, the paradigm of angle strain was believed to wholly preclude substances that we know now are either stable or important reaction intermediates, such as cubane (Section 12- 1O), cyclo- propanone (Section 17-1 I), and benzyne (Sections 14-6C and 23-8). No paradigm did more to retard the development of organic chemistry than the notion that, with a "few" exceptions, compounds with bonds between carbon and transition metals (Fe, Co, Ni, Ti, and so on) are inherently un- stable. This idea was swept away in 1951 with the discovery of ferrocene, (C,H,),Fe, by P. L. Pauson. Ferrocene has unheard of properties for an organoiron compound, stable to more than 500" and able to be dissolved in, and recovered from, concentrated sulfuric acid! Pauson's work started an avalanche of research on transition metals in the general area between organic and inorganic chemistry, which has flourished ever since and has led to an improved understanding of important biochemical processes. 31-1 Metallocenes 31-1 METALLOCENES The discovery of ferrocene was one of those fortuitous accidents that was wholly unforeseeable- the kind of discovery which, over and over again, has changed the course of science.
    [Show full text]