I. the Low Temperature Photochemistry of Iron Pentacarbonyl and Disubstituted Acetylenes, II
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New Applications of Cyclobutadiene Cycloadditions: Diversity and Target Oriented Synthesis
New Applications of Cyclobutadiene Cycloadditions: Diversity and Target Oriented Synthesis Author: Jason Joseph Marineau Persistent link: http://hdl.handle.net/2345/1741 This work is posted on eScholarship@BC, Boston College University Libraries. Boston College Electronic Thesis or Dissertation, 2010 Copyright is held by the author, with all rights reserved, unless otherwise noted. Boston College The Graduate School of Arts and Sciences Department of Chemistry NEW APPLICATIONS OF CYCLOBUTADIENE CYCLOADDITIONS: DIVERSITY AND TARGET ORIENTED SYNTHESIS a dissertation by JASON JOSEPH MARINEAU submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2010 © Copyright by JASON JOSEPH MARINEAU 2010 New Applications of Cyclobutadiene Cycloadditions: Diversity and Target Oriented Synthesis Jason J. Marineau Thesis Advisor: Professor Marc. L. Snapper Abstract Cyclobutadiene cycloadditions provide rapid access to rigid polycyclic systems with high strain energy and unusual molecular geometries. Further functionalization of these systems allows entry into unexplored chemical space. A tricarbonylcyclobutadiene iron complex on solid support enables exploration of these cycloadditions in a parallel format amenable to diversity oriented synthesis. Modeling of the cycloaddition transition states with density functional calculations provides a theoretical basis for analysis of the regioselectivity observed in generation of these substituted bicyclo[2.2.0]hexene derivatives. The high strain energy accessible in cyclobutadiene cycloadducts and their derivatives renders them useful synthons for access to medium-ring natural products through ring expansion. Torilin, a guaiane sesquiterpene isolated from extracts of the fruits of Torilis japonica, exhibits a range of biological activities including testosterone 5 -reductase inhibition, hKv1.5 channel blocking, hepatoprotective, anti-inflammatory and anti-cancer effects. -
CHEMISTRY 412/512 MIDTERM # 1 – Answer Key February 14, 2007 1
CHEMISTRY 412/512 MIDTERM # 1 – answer key February 14, 2007 1. (8 pts) Acyl cations ( RCO ) are key intermediates in Friedel – Crafts acylation reactions. They are stabilized by the presence of oxygen and this can be demonstrated through either resonance or MO analysis. a. Consider the formyl cation, shown below. Show how it is stabilized, using appropriate resonance structures. HCO formyl cation HCO HCO Acyl cations are stabilized by conjugation of one of the lone pairs at the oxygen center. b. Construct the orbital mixing diagram for the formyl cation, starting with group orbitals for CH and O-atom. Consider only first order mixing. Place the appropriate number of valence electrons and demonstrate how QMOT explains the stabilization of the cation. O HC The mixing diagram clearly shows the formation of TWO equivalent π-bonds, which is analogous to the resonance structure on the right, i.e. there is significant contribution by the O-atom. 2. (6 pts) Antiaromatic molecules avoid antiaromaticity by structural distortion. For example, cyclobutadiene is not square (and antiaromatic) but rectangular. Show, using π-group orbital analysis, that such distortion would indeed be stabilizing. square rectangular Solution: Instability of square cyclobutadiene is due to the presence of two degenerate, half-filled π-molecular orbitals (π2 and π3). In the rectangular form, qualitatively, the MOs remain the same, but the strength of some bonding/antibonding interactions is affected and it causes the degeneracy to be lifted. Focus on π2 and π3. Upon stretching, the antibonding interaction in π2 is reduced, while the same geometric distortion leads to reduction of the bonding interaction in π3. -
An Indicator of Triplet State Baird-Aromaticity
inorganics Article The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity Rabia Ayub 1,2, Kjell Jorner 1,2 ID and Henrik Ottosson 1,2,* 1 Department of Chemistry—BMC, Uppsala University, Box 576, SE-751 23 Uppsala, Sweden; [email protected] (R.A.); [email protected] (K.J.) 2 Department of Chemistry-Ångström Laboratory Uppsala University, Box 523, SE-751 20 Uppsala, Sweden * Correspondence: [email protected]; Tel.: +46-18-4717476 Received: 23 October 2017; Accepted: 11 December 2017; Published: 15 December 2017 Abstract: Baird’s rule tells that the electron counts for aromaticity and antiaromaticity in the first ππ* triplet and singlet excited states (T1 and S1) are opposite to those in the ground state (S0). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T1 state so as to retain T1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T1 state support our hypothesis. The SCB ring should indicate T1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief. Keywords: Baird’s rule; computational chemistry; excited state aromaticity; Photostability 1. Introduction Baird showed in 1972 that the rules for aromaticity and antiaromaticity of annulenes are reversed in the lowest ππ* triplet state (T1) when compared to Hückel’s rule for the electronic ground state (S0)[1–3]. -
Chemical Intercalation of Zerovalent Metals Into 2D Layered Bi2se3 Nanoribbons † † ‡ † † † § Kristie J
Article pubs.acs.org/JACS Chemical Intercalation of Zerovalent Metals into 2D Layered Bi2Se3 Nanoribbons † † ‡ † † † § Kristie J. Koski, Colin D. Wessells, Bryan W. Reed, Judy J. Cha, Desheng Kong, and Yi Cui*, , † Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States ‡ Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States § SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, 2575 Sand Hill Road, Menlo Park, California 94025, United States *S Supporting Information ABSTRACT: We have developed a chemical method to intercalate a variety of zerovalent metal atoms into two-dimen- sional (2D) layered Bi2Se3 chalcogenide nanoribbons. We use a chemical reaction, such as a disproportionation redox reaction, to generate dilute zerovalent metal atoms in a refluxing solution, which intercalate into the layered Bi2Se3 structure. The zerovalent nature of the intercalant allows superstoichiometric intercalation of metal atoms such as Ag, Au, Co, Cu, Fe, In, Ni, and Sn. We foresee the impact of this methodology in establishing novel fundamental physical behaviors and in possible energy applications. 1. INTRODUCTION Ni, and Sn. Some interesting effects that could arise with − 7−10 intercalation are superconductivity, such as in Cu Bi2Se3, Intercalation is the insertion of a guest species into a host 6 lattice. Intercalation into layered materials is essential to battery enhanced conductivity, or possibly opening a surface state gap electrodes, electrochromics, detergents, and solid lubricants and in topological insulator Bi2Se3. This method of zerovalent metal is important in exotic fundamental two-dimensional (2D) intercalation may also be extended to other layered materials. -
Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc
Metal-Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc Richard H. Duncan Lyngdoh*,a, Henry F. Schaefer III*,b and R. Bruce King*,b a Department of Chemistry, North-Eastern Hill University, Shillong 793022, India B Centre for Computational Quantum Chemistry, University of Georgia, Athens GA 30602 ABSTRACT: This survey of metal-metal (MM) bond distances in binuclear complexes of the first row 3d-block elements reviews experimental and computational research on a wide range of such systems. The metals surveyed are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, representing the only comprehensive presentation of such results to date. Factors impacting MM bond lengths that are discussed here include (a) n+ the formal MM bond order, (b) size of the metal ion present in the bimetallic core (M2) , (c) the metal oxidation state, (d) effects of ligand basicity, coordination mode and number, and (e) steric effects of bulky ligands. Correlations between experimental and computational findings are examined wherever possible, often yielding good agreement for MM bond lengths. The formal bond order provides a key basis for assessing experimental and computationally derived MM bond lengths. The effects of change in the metal upon MM bond length ranges in binuclear complexes suggest trends for single, double, triple, and quadruple MM bonds which are related to the available information on metal atomic radii. It emerges that while specific factors for a limited range of complexes are found to have their expected impact in many cases, the assessment of the net effect of these factors is challenging. -
Using SMILES Strings for the Description of Chemical Connectivity in the Crystallography Open Database
Quirós et al. J Cheminform (2018) 10:23 https://doi.org/10.1186/s13321-018-0279-6 RESEARCH ARTICLE Open Access Using SMILES strings for the description of chemical connectivity in the Crystallography Open Database Miguel Quirós1* , Saulius Gražulis2,3 , Saulė Girdzijauskaitė3, Andrius Merkys2 and Antanas Vaitkus2 Abstract Computer descriptions of chemical molecular connectivity are necessary for searching chemical databases and for predicting chemical properties from molecular structure. In this article, the ongoing work to describe the chemical connectivity of entries contained in the Crystallography Open Database (COD) in SMILES format is reported. This col- lection of SMILES is publicly available for chemical (substructure) search or for any other purpose on an open-access basis, as is the COD itself. The conventions that have been followed for the representation of compounds that do not ft into the valence bond theory are outlined for the most frequently found cases. The procedure for getting the SMILES out of the CIF fles starts with checking whether the atoms in the asymmetric unit are a chemically accept- able image of the compound. When they are not (molecule in a symmetry element, disorder, polymeric species,etc.), the previously published cif_molecule program is used to get such image in many cases. The program package Open Babel is then applied to get SMILES strings from the CIF fles (either those directly taken from the COD or those produced by cif_molecule when applicable). The results are then checked and/or fxed by a human editor, in a computer-aided task that at present still consumes a great deal of human time. -
Iron Pentacarbonyl
Poison Facts: Low Chemicals: Iron Pentacarbonyl Properties of the Chemical Iron carbonyl (pentacarbonyl iron), C5FeO5, is a yellow, oily liquid. It is pyrophoric in air and burns to Fe2O3 (Iron[III] oxide) and decomposes by light to Fe2(CO)9 and CO. It is practically insoluble in water, readily soluble in most organic solvents (ether, acetone, ethyl acetate) and slightly soluble in alcohol. The vapor is heavier than air and may travel along the ground. Distant ignition is possible, and it may explode on heating. It may also spontaneously ignite in contact with air. Iron pentacarbonyl is a strong reducing agent and reacts violently with oxidants. Uses of the Chemical Iron pentacarbonyl is prepared from iron (and iron compounds) and CO. It is used in the manufacture of powdered iron cores for high-frequency coils used in the radio and television industries. It is also used as an anti-knock agent in motor fuels and as a catalyst in organic reactions. Absorption, Distribution, Metabolism and Excretion (ADME) Iron pentacarbonyl can be absorbed into the body by inhalation of the vapor, through the skin or by ingestion. No other pharmacokinetic data is available. Clinical Effects of Acute Exposure • Ocular exposures: Iron pentacarbonyl is a local irritant and may cause irritation and injury to eyes. • Dermal exposures: The chemical may irritate the skin and mucous membranes. It may be absorbed through the skin. • Inhalation exposures: If inhaled, iron pentacarbonyl is a local irritant to the lungs and gastrointestinal tract. Symptoms of acute exposure to high concentrations resemble those of exposures to nickel carbonyl. -
Cyclobutadiene
View metadata, citation and similar papers at core.ac.uk brought to you by CORE Published in "Angewandte Chemie International Edition 45(40): 6616 - 6619, 20 provided by RERO DOC Digital Library which should be cited to refer to this work. Cyclobutadiene: The Antiaromatic Paradigm? Thomas Bally* Keywords: In memory of Satoru Masamune antiaromaticity · cyclobutadiene · thermochemistry (1928–2003) There is probably no other single widely accepted (and hardly disputed) London proposed in 1937 a very appeal- molecule that has fascinated experimen- that benzene, with its six cyclically ing model that accounts for these effects tal and theoretical chemists so consis- delocalized p electrons, represents the in terms of ring currents that are in- tently over the past 40 years as has paradigm of aromaticity. In view of the duced by the external magnetic field in cyclobutadiene (CBD). On average, famous Hckel 4n/4n + 2 electron rule, the system of cyclically delocalized 16 publications which deal, in one form one is tempted to rush to the conclusion p electrons.[5] or another, with the parent compound that CBD, with its four cyclically delo- There has been a vigorous debate in p C4H4 and 40 which deal with cyclo- calized electrons, is therefore the recent years about whether and to what butdienes in general have appeared in paradigm of antiaromaticity. extent these ring currents contribute to every year of this time span, and there However, this conclusion is not as the deshielding or shielding of protons are probably many more on derivatives straightforward as it might seem, be- attached to aromatic or antiaromatic and metal complexes. -
The Relation Between Ring Currents and Aromatic Stabilization Energies for Assessing the Degree of Aromaticity
The Relation Between Ring Currents and Aromatic Stabilization Energies for Assessing the Degree of Aromaticity Chandan Kumar,y Heike Fliegl,∗,y and Dage Sundholm∗,z yCentre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O.Box 1033, N-1315 Blindern, Norway zDepartment of Chemistry, University of Helsinki, P.O. Box 55 (A. I. Virtanens Plats 1), FIN-00014, Finland E-mail: heike.fl[email protected]; [email protected].fi 1 Abstract Magnetically induced ring-current strength susceptibilities and nucleus independent chemical shifts (NICS) have been studied for 15 single-ring aromatic, antiaromatic and nonaromatic molecules. The current densities have been calculated at the density func- tional theory (DFT), Hartree-Fock (HF), and second-order Møller-Plesset perturbation theory (MP2) levels using the gauge-including magnetically induced current method (GIMIC). The ring-current strength susceptibilities have been obtained by numerical integration of the current density flowing around the molecular ring. The calculated ring-current strength susceptibilities are almost independent of the level of theory. The relative degree of aromaticity deduced from the magnetic properties has been compared with the ones deduced from hydrogenation enthalpies that are considered to be propor- tional to aromatic stabilization energies (ASE). For the studied single-ring molecules, GIMIC, NICS and ASE calculations yield similar trends. The study shows that there is a linear correlation between the magnetic and energetic criteria of aromaticity. The largest uncertainty originates from the accuracy of the energy data, because they are much more dependent on the employed computational level than the calculated mag- netic properties. Thus, ring-current strength susceptibilities can be used for assessing the degree of aromaticity. -
Some Reactions of Tris(Triphenylphosphine )-Dicarbonyliron( 0)
Indian Journal of Chemistry Vol. 21A, June 1982, pp. 579·582 Some Reactions of Tris(Triphenylphosphine )-dicarbonyliron( 0) S. VANCHEESAN Chemistry Department, Indian Institute of Technology, Madras 600 036 Received 20 October 1981; revised and accepted 15 February 1982 Tris(triphenylphospbine)-dicarbonyliron(O)(I) undergoes substitution reactions with trimethylphosphite, pyri- dine, dimethyl sulphoxide and methylisocyanide. Substitution takes place via dissociation of I to a 1 coordinativel1 unsaturated 16 electron complex, which is a highly reactive unstable intermediate. Both steric and electronic factors playa prominent role in deciding the feasibility of the reaction. Steric factor is expressed in terms of e, the cone angle of the ligand, and electronic factor in terms of Al mode of CO stretching frequency in Ni(CO)aL, where L is the ligand for which the electronic factor is expressed in terms of "CO. Ligands with cone angle e, greater than that of triphenyl- phosphine e.g. t-butylphosphine, do not react. In the reaction of I with molecular hydrogen and bromine, oxidative addition takes place. Diphenylacetylene forms two isomers, whereas carbon disulphide forms a n-complex on reaction with L MONG the d8 iron-phosphine complexes of (PPh3)2]+BF~ in absolute ethanol was allowed to the type fe(CO)6_" (PPh3) •• (where x = 1 to react overnight with triphenylphosphine in the A 3), the complexes with x = 1 and 2 had been presence of lithium metal. The resulting micro- studied to some extent>", Mono- and bis-phosphine crystalline solid was filtered and freed from phos- complexes can be prepared= by the reaction of phos- phine using hot ethanol and filtered. -
Organo-Transition Metal Chemistry Some Studies
ORGANO-TRANSITION METAL CHEMISTRY SOME STUDIES IN ORGANO-TRANSITION METAL CHEMISTRY By COLIN CRINDROD, B.Sc. A Thesis Submitted to the Faculty of Graduate Studies in Partial Fulfilment of the Requirements for the Degree Master of Science McMaster University October 1966 MASTER OF SCIENCE (1966) MCMASTER UNIVERSITY (Chemistry) Hamilton, Ontario TITLE: Some Studies in Organo-Transition Metal Chemistry AUTHOR: Colin Grindrod, B.Sc. (Manchester University) SUPERVISOR: Dr. P. M. Maitlis NUMBER OF PAGES: iv, 71 SCOPE AND CONTENTS: The work described is an extension of the ligand-transfer reactions of substituted cyclobutadienes and cyclopentadienyls previously carried out by Maitlis et al. Efforts were directed particularly to ligand transfer reactions of n-allyl-transition metal complexes. The reactions of organic halides with metal carbonyls were also studied in attempts to isolate new organometallic derivatives. (ii) ACKNOWLEDGEMENTS The author wishes to express his sincere gratitude for the stimulating advice and constant encouragement provided by Dr. P. M. Maitlis, under whose guidance this work was carried out. Thanks are also extended to Imperial Oil Co. Ltd. for providing the financial support which made this study possible. (iii) CONTENTS Page INTRODUCTION Historical................................... 1 Cyclobutadiene-transition metal oompeeees... 7 Ligand-transfer reactions................... 10 Allyl-transition metal complexes............ 13 Reactions of metal carbonyls with organic halides.... ..................... 25 DISCUSSION -
Metal Carbonyls
MODULE 1: METAL CARBONYLS Key words: Carbon monoxide; transition metal complexes; ligand substitution reactions; mononuclear carbonyls; dinuclear carbonyls; polynuclear carbonyls; catalytic activity; Monsanto process; Collman’s reagent; effective atomic number; 18-electron rule V. D. Bhatt / Selected topics in coordination chemistry / 2 MODULE 1: METAL CARBONYLS LECTURE #1 1. INTRODUCTION: Justus von Liebig attempted initial experiments on reaction of carbon monoxide with metals in 1834. However, it was demonstrated later that the compound he claimed to be potassium carbonyl was not a metal carbonyl at all. After the synthesis of [PtCl2(CO)2] and [PtCl2(CO)]2 reported by Schutzenberger (1868) followed by [Ni(CO)4] reported by Mond et al (1890), Hieber prepared numerous compounds containing metal and carbon monoxide. Compounds having at least one bond between carbon and metal are known as organometallic compounds. Metal carbonyls are the transition metal complexes of carbon monoxide containing metal-carbon bond. Lone pair of electrons are available on both carbon and oxygen atoms of carbon monoxide ligand. However, as the carbon atoms donate electrons to the metal, these complexes are named as carbonyls. A variety of such complexes such as mono nuclear, poly nuclear, homoleptic and mixed ligand are known. These compounds are widely studied due to industrial importance, catalytic properties and structural interest. V. D. Bhatt / Selected topics in coordination chemistry / 3 Carbon monoxide is one of the most important π- acceptor ligand. Because of its π- acidity, carbon monoxide can stabilize zero formal oxidation state of metals in carbonyl complexes. 2. SYNTHESIS OF METAL CARBONYLS Following are some of the general methods of preparation of metal carbonyls.