Hypervalency
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Planar Cyclopenten‐4‐Yl Cations: Highly Delocalized Π Aromatics
Angewandte Research Articles Chemie How to cite: Angew.Chem. Int. Ed. 2020, 59,18809–18815 Carbocations International Edition: doi.org/10.1002/anie.202009644 German Edition: doi.org/10.1002/ange.202009644 Planar Cyclopenten-4-yl Cations:Highly Delocalized p Aromatics Stabilized by Hyperconjugation Samuel Nees,Thomas Kupfer,Alexander Hofmann, and Holger Braunschweig* 1 B Abstract: Theoretical studies predicted the planar cyclopenten- being energetically favored by 18.8 kcalmolÀ over 1 (MP3/ 4-yl cation to be aclassical carbocation, and the highest-energy 6-31G**).[11–13] Thebishomoaromatic structure 1B itself is + 1 isomer of C5H7 .Hence,its existence has not been verified about 6–14 kcalmolÀ lower in energy (depending on the level experimentally so far.Wewere now able to isolate two stable of theory) than the classical planar structure 1C,making the derivatives of the cyclopenten-4-yl cation by reaction of bulky cyclopenten-4-yl cation (1C)the least favorable isomer.Early R alanes Cp AlBr2 with AlBr3.Elucidation of their (electronic) solvolysis studies are consistent with these findings,with structures by X-raydiffraction and quantum chemistry studies allylic 1A being the only observable isomer, notwithstanding revealed planar geometries and strong hyperconjugation the nature of the studied cyclopenteneprecursor.[14–18] Thus, interactions primarily from the C Al s bonds to the empty p attempts to generate isomer 1C,orits homoaromatic analog À orbital of the cationic sp2 carbon center.Aclose inspection of 1B,bysolvolysis of 4-Br/OTs-cyclopentene -
On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and Its Application to Heteroatomic Π-Electron Systems
Symmetry 2010, 2, 1485-1509; doi:10.3390/sym2031485 OPEN ACCESS symmetry ISSN 2073-8994 www.mdpi.com/journal/symmetry Article On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems Ewa D. Raczyñska 1, *, Małgorzata Hallman 1, Katarzyna Kolczyñska 2 and Tomasz M. Stêpniewski 2 1 Department of Chemistry, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 159c, 02-776 Warszawa, Poland 2 Interdisciplinary Department of Biotechnology, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska 166, 02-776 Warszawa, Poland * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +48-22-59-37623; Fax: +49-22-59-37635. Received: 23 April 2010; in revised form: 19 May 2010 / Accepted: 7 July 2010 / Published: 12 July 2010 Abstract: The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for mono- and polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe properly various resonance effects (σ-π hyperconjugation, n-π conjugation, π-π conjugation, and aromaticity) possible for heteroatomic π-electron systems, some modifications, based on the original HOMA idea, were proposed and tested for simple DFT structures containing C, N, and O atoms. An abbreviation HOMED was used for the modified index. Keywords: geometry-based index; π -electron delocalization; σ - π hyperconjugation; n-π conjugation; π-π conjugation; aromaticity; heteroatomic compounds; DFT 1. -
Lactide/^Caprolactone Polymerization Behavior of Monomeric Aryloxytitanatrane
698 Bull. Korean Chem. Soc. 2007, Vol. 28, No. 4 Notes Synthesis, X-ray Structure, and /-Lactide/^Caprolactone Polymerization Behavior of Monomeric Aryloxytitanatrane Sang-deok Mun, Younjin Hong, and Youngjo Kim* Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 361-763, Korea. *E-mail: 가[email protected] Received February 2, 2007 Key Words : Titanatrane, Mononuclear, Ring opening polymerization, Polylactide, Polycaprolactone The chemistry of atrane coordinated by the central nitro polymerization (ROP) of l-lactide (l-LA) or ^caprolactone gen atom as well as all three arms of deprotonated triethanol 任-CL) are now one of popular research fields in the homo amine ligand, imino-2,2',2''-triethanolate, has been inten geneous catalysis. In this regard, a new mononuclear tita- sively studied over the past few decades and its examples are natrane obtained was used as a catalyst for the ROP of l-LA now known across the periodic table.1 Most studies have and £-CL. focused on the use of main group elements such as silicon, The treatment of Ti(O-i-Pr)4 with 1 equivalent of 2,6-di- phosphorus, aluminum, and tin in the formation of atrane.1 tert-butylphenol and 1 equivalent of triethanolamine in THF In view of the well known significant number of similarities gave, after workup, novel mononuclear titanatranes 1 as in the chemistries of tin and titanium, relatively few reports orange-yellow crystals in 81% isolated yield. After recrystal have appeared concerning metallic titanatranes with a lization using toluene, 1 was used as a catalyst for making transannular N—Ti bond from bridgehead N atom in polylactide (PLA) and polycaprolactone (PCL). -
Electron Transfer and Modification of Oligosilanylsilatranes and Related
This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Article pubs.acs.org/Organometallics Electron Transfer and Modification of Oligosilanylsilatranes and Related Derivatives † ‡ § Mohammad Aghazadeh Meshgi, Judith Baumgartner,*, Viatcheslav V. Jouikov,*, † and Christoph Marschner*, † Institut für Anorganische Chemie, Technische Universitaẗ Graz, Stremayrgasse 9, 8010 Graz, Austria ‡ Institut für Chemie, Universitaẗ Graz, Stremayrgasse 9, 8010 Graz, Austria § UMR 6226, Chimie et Photonique Moleculaires,́ Universitéde Rennes 1, 35042 Rennes, France *S Supporting Information ABSTRACT: Several silatranyl -substituted oligosilanes were prepared starting from bis(trimethylsilyl)silatranylsilanide. Electrochemical and theoretical investigations of some oligosilanes revealed that electrooxidation occurs by formation of a short-lived cation radical. This species undergoes structural relaxation to form a pair of conformers, with endo and exo relationships with respect to the Si−N interaction. Reaction of a 1,4-disilatranyl-1,4-disilanide with 1,2- dichlorotetramethyldisilane gave a mixture of cis and trans diastereomers of a cyclohexasilane with the trans isomer showing a diminished Si−N distance. ■ INTRODUCTION along the Si−N dative bond reflects the nature of Si−N − Among hypercoordinated silicon compounds silatranes (Figure bonding. In fact the Si N bonding neither is covalent nor is − 8 1) occupy a prominent position.1 4 The suffix “atrane” was based on intermolecular charge transfer. What happens with this unusual bond upon electron withdrawal, for instance during electrooxidation, is of a great interest (for classical bonds see ref 9) but is not known so far. -
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Understanding the role of Ti-rich domains in the stabilization of gold nanoparticles on mesoporous silica-based catalysts Alaina Moragues a, Begoña Puértolas b, Álvaro Mayoral c,d, Raúl Arenal c,d, Ana B. Hungría e, Sonia Murcia-Mascarós a, Stuart H. Taylor f, Benjamín Solsona g,*, Tomás Garcíab,*, Pedro Amorós a,* a Institut de Ciència dels Materials, Universitat de València, P.O. Box 22085, 46071 Valencia, Spain. b Instituto de Carboquímica (ICB-CSIC), C/ Miguel Luesma Castán 4, 50018 Zaragoza, Spain. c Laboratorio de Microscopias Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA), Universidad de Zaragoza, Mariano Esquillor, 50018 Zaragoza, Spain. d Fundación Agencia Aragonesa para la Investigación y el Desarrollo (ARAID), María de Luna 11, 50018 Zaragoza, Spain. e Departamento de Ciencia de Materiales, Ingeniería Metalúrgica y Química Inorgánica, Universidad de Cádiz, Campus Río San Pedro, 11510 Puerto Real, Spain. f Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT Cardiff, United Kingdom. g Departamento de Ingenieria Quimica, Universitat de València, Avenida de la Universitat, 46071 Valencia, Spain. *Corresponding authors at: Institut de Ciència dels Materials, Universitat de València, P.O. Box 22085, 46071 Valencia, Spain (Pedro Amorós). E-mail addresses: [email protected], [email protected], [email protected] 1 ABSTRACT The preparation and stabilization of gold nanoparticles with a precise control of size and dispersion is highly attractive for a variety of applications, and a key aspect is thermal stability of the nanoparticles. This paper focuses on understanding the effect of TiO2-based nanodomains, dispersed on mesoporous silicas, and how they control gold nanoparticle stability. -