DOCSLIB.ORG

An Investigation of N-Heterocyclic Carbene Carboxylates

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Investigation of N-Heterocyclic Carbene Carboxylates AN INVESTIGATION OF N-HETEROCYCLIC CARBENE CARBOXYLATES: INSIGHT INTO DECARBOXYLATION, A TRANSCARBOXYLATION REACTION, AND SYNTHESIS OF HYDROGEN BONDING PRECURSORS by Bret Ryan Van Ausdall A dissertation submitted to the faculty of The University of Utah in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Chemistry The University of Utah May 2012 Copyright © Bret Ryan Van Ausdall 2012 All Rights Reserved The University of Utah Graduate School STATEMENT OF DISSERTATION APPROVAL The dissertation of Bret Ryan Van Ausdall has been approved by the following supervisory committee members: Janis Louie , Chair 7-8-2011 Date Approved Cynthia Burrows , Member 7-8-2011 Date Approved Thomas Richmond , Member 7-8-2011 Date Approved Matthew S. Sigman , Member 7-8-2011 Date Approved Debra Mascaro , Member 7-8-2011 Date Approved and by Henry S. White , Chair of the Department of Chemistry and by Charles A. Wight, Dean of The Graduate School. ABSTRACT A series of 1,3-disubstituted-2-imidazolium carboxylates, an adduct of CO2 and N-heterocyclic carbenes, was synthesized and characterized using single crystal X-ray, thermogravimetric, IR, and NMR analysis. The TGA analysis of the imidazolium carboxylates shows that as steric bulk on the N-substituent increases, the ability of the NHC-CO2 to decarboxylate increases. Single crystal X-ray analysis shows that the torsional angle of the carboxylate group and the C-CO2 bond length with respect to the imidazolium ring is dependent on the steric bulk of the N-substituent. Rotamers in the t unit cell of a single crystal of I BuPrCO2 (2f) indicate that the C-CO2 bond length increases as the N-substituents rotate toward the carboxylate moiety, which suggests that rotation of the N-substituents through the plane of the C-CO2 bond may be involved in the bond breaking event to release CO2. Combination of N,N-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO2) with the Lewis acids MBPh4, where M=Li or Na, provided two separate complexes, a monomer and dimer, respectively. Combination of N,N-bis(2,4,6- trimethyllphenyl)imidazolum-2-carboxylate (IMesCO2) with LiBPh4 afforded a dimeric species that was similar in global structure to that of the IPrCO2+NaBPh4 dimer. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO2. Kinetic analysis of the transcarboxylation of IPrCO2 to acetophenone with NaBPh4 to yield sodium benzoylacetate was performed. First order dependencies were observed for IPrCO2 and acetophenone while zero order dependence was observed for NaBPh4. Direct t dicarboxylation of MeCN was observed after combination with I BuCO2 in the absence of salts. An imidazolium salt, 1-2,4,6-trimethylphenyl-3-lactamidebenzylimidazolium tosylate was synthesized and characterized by 1H NMR, 13C NMR, and single crystal x- ray analysis. The downfield shift of the amide protons in the 1H NMR spectrum salt relative to the starting material lactamide-OTs indicate that hydrogen bonding was present in solution. The crystal structure of imidazolium tosylate showed a series of intermolecular hydrogen bonds between amide groups and tosylate anions. The amount of hydrogen bonding present in the carbene precursor is promising for attempts to observe intramolecular hydrogen bonding with a carbene and the carboxylate. iv CONTENTS ABSTRACT……………………………………………………………………………………...iii LIST OF ABBREVIATIONS…………………………………………………………………...vii ACKNOWLEDGEMENTS……………………………………………………………………….x Chapter 1. A SYSTEMATIC INVESTIGATION OF FACTORS INFLUENCING THE DECARBOXYLATION OF IMIDAZOLIUM CARBOXYLATES……………………1 Introduction……………………………………………………………………………...1 Results and discussion …………………………………………………………………..2 Conclusion ...…………………………………………………………………………….21 Experimental section…………………………………………………………………….22 References……………………………………………………………………………….27 2. RELEVANCE OF NHC·CO2-BOUND NaBPH4 COMPLEXES IN TRANSCARBOXYLATION REACTIONS…………………………………………...31 Introduction ……………………………………………………………………………..31 Results and discussion…………………………………………………………………..34 Conclusion………………………………………………………………………………55 Experimental section ……………………………………………………………………56 References……………………………………………………………………………….67 3. ADVENTURES IN CARBENE DESIGN: SYNTHESIS OF CHIRAL HYDROGEN BONDING BENZYLIMIDAZOLIUM SALTS, N-HETEROCYLCIC CARBENES, AND NHC·CARBOXYLATES…………………………………………………………71 Introduction………………………………………………………………………………71 Results and discussion …………………………………………………………………...79 Conclusion …………………………………………………………………………….....95 Experimental section……………………………………………………………………..97 References………………………………………………………………………………100 Appendices A. NMR SPECTRA AND CRYSTAL STRUCTURE REPORTS FOR CHAPTER 1………………………………………………………………….104 B. NMR SPECTRA AND CRYSTAL STRUCTURE REPORTS FOR CHAPTER 2………………………………………………………………….193 C. NMR SPECTRA AND CRYSTAL STRUCTURE REPORTS FOR CHAPTER 3………………………………………………………………….224 vi LIST OF ABBREVIATIONS Bn – benzyl Boc – tert-butyl carbamate - BF4 – tetrafluoroborate BPh4 – tetraphenylborate CO2 – carbon dioxide Cy – cyclohexyl d – doublet DMA – N, N – dimethylacetamide DMF – N, N – dimethylformamide DMC - dimethylcarbonate DMSO – dimethylsulfoxide ee – enantiomeric excess Et – ethyl IEt – 1,3-diethylimidazol-2-ylidene IEtCO2 – 1,3-diethylimidazolium-2-carboxylate IEtMe – 1,3-diethyl-4,5-dimethylimidazol-2-ylidene IEtMeCO2 – 1,3-diethyl-4,5-dimethylimidazolium-2-carboxylate i I PrMe – 1,3-isopropyl-4,5-dimethylimidazol-2-ylidene i I PrMeCO2 – 1,3-isopropyl-4,5-dimethylimidazolium-2-carboxylate IMe – 1,3-dimethylimidazol-2-ylidene IMeCO2 – 1,3-dimethylimidazolium-2-carboxylate IMeMe – 1,3,4,5-tetramethylimidazol-2-ylidene IMeMeCO2 – 1,3-tetramethylimidazolium-2-carboxylate IMes – 1,3-bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene IMesCO2 – 1,3-bis-(2,4,6-trimethylphenyl)-imidazolium-2-carboxylate IMesMe – 1,3-bis-(2,4,6-trimethylphenyl)-4,5-dimethylimidazol-2-ylidene IMesMeCO2 – 1,3-bis-(2,4,6-trimethylphenyl)-4,5-dimethylimidazolium-2-carboxylate IMetBu – 1- tert-butylimidazolium-3-methylimidazol-2-ylidene t IMe BuCO2 – 1- tert-butylimidazolium-3-methylimidazolium-2-carboxylate IPr – 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene IPrCO2 – 1,3-bis-(2,6-diisopropylphenyl)-imidazolium-2-carboxylate IPrMe – 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene IPr MeCO2 – 1,3-bis-(2,6-diisopropylphenyl)-4,5-dimethylimidazolium-2-carboxylate ItBu – 1,3-di-tert-butylimidazol-2-ylidene t I BuCO2 – 1,3-di-tert-butylimidazolium-2-carboxylate t I BuPrCO2 – 1- tert-butylimidazolium-3-bis-(2,6-diisopropylphenyl)-imidazolium-2- carboxylate iPr – isopropyl IR – infra-red M – metal m – multiplet MeCN – acetonitrile MeOH – methanol n-Bu – normal-butyl NHC – N-heterocyclic carbene viii NHC·CO2 – N-heterocyclic carbene carboxylate NMR – Nuclear Magnetic resonance OTs- – para-tolylsulfonate Ph – phenyl q – quartet s – singlet SIPr – 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene SIPrCO2 – 1,3-bis(2,6-diisopropylphenyl)-imidazolium-2-carboxylate SIMes – 1,3-bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene SIMesCO2 – 1,3-bis-(2,4,6-trimethylphenyl)-imidazolium-2-carboxylate t – triplet tBu – tert-butyl TEMPOH - 1-hydroxy-2,2,6,6-tetramethyl-piperidine TGA – thermogravimetric analysis THF- tetrahydrofuran TMS – trimethylsilyl X – halogen ix ACKNOWLEDGEMENTS Many thanks to Paul, Yolanda, Marten, and Scott Van Ausdall, my family, for supporting me through this arduous journey; if it were not for their support, finishing this journey would not have been possible. My brother Scott deserves a separate token of gratitude for moving to Salt Lake in his own quest for knowledge and ultimately providing me invaluable brotherhood in times of struggle. It is not possible to thank my family enough. I also thank the many friends through the years helped me in times of good and bad, both in lab and out, who provided me the means to not only grow as a scientist, but as a person. Brendan D’Souza, Kainan Zhang, Jorge de Freitas, and Dave Thomas were lab mates as well as indispensible friends who helped create a lab that was not only a fun place, but a great learning environment where they helped inspire creativity on a daily basis. Dr. Dawn Troast, Dr. Pramod Chopade, and Dr. Rodrigo Cella, post-doctoral researchers at various points in the Louie Lab, helped my development as a researcher and also made life in lab more enjoyable early in my PhD research. The University of Utah and the Chemistry Department must be given thanks as well. The staff that made the Chemistry Department run were invaluable in my research. Dr. Peter Flynn proved to be a bastion of knowledge in designing NMR experiments and also provided key insight into future endeavors. Kevin Teaford, our master glass blower, brought my imagination to life and made several pieces of glassware that were essential in several experiments. Dr. Atta Aarif was a good friend as well as an excellent x-ray crystallographer. Tomi Carr, our groups assistant, proved to be a good friend through the years. My committee members, Dr. Matthew Sigman, Dr. Cynthia Burrows, Dr. Thomas Richmond, and Dr. Debra Mascaro must be given thanks for providing insight and valuable criticism into my research and ideas throughout my PhD. To Dr. Janis Louie, my advisor, I give thanks for providing key advice throughout my graduate student career and providing the funding to perform research. Her focus on the skills to be effective in presenting ideas in a clean and concise manner, as well as allowing for our own individuality
Load more

Recommended publications
  • Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007
    Baran Group Meeting Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007 Ernst Otto Fischer (1918 - ) Other Types of Stabilized Carbenes: German inorganic chemist. Born in Munich Schrock carbene, named after Richard R. Schrock, is nucleophilic on November 10, 1918. Studied at Munich at the carbene carbon atom in an unpaired triplet state. Technical University and spent his career there. Became director of the inorganic Comparision of Fisher Carbene and Schrock carbene: chemistry institute in 1964. In the 1960s, discovered a metal alkylidene and alkylidyne complexes, referred to as Fischer carbenes and Fischer carbynes. Shared the Nobel Prize in Chemistry with Geoffery Wilkinson in 1973, for the pioneering work on the chemistry of organometallic compounds. Schrock carbenes are found with: Representatives: high oxidation states Isolation of first transition-metal carbene complex: CH early transition metals Ti(IV), Ta(V) 2 non pi-acceptor ligands Cp2Ta CH N Me LiMe Me 2 2 non pi-donor substituents CH3 (CO) W CO (CO)5W 5 (CO)5W A.B. Charette J. Am. Chem. Soc. 2001, 123, 11829. OMe O E. O. Fischer, A. Maasbol, Angew. Chem. Int. Ed., 1964, 3, 580. Persistent carbenes, isolated as a crystalline solid by Anthony J. Arduengo in 1991, can exist in the singlet state or the triplet state. Representative Fischer Carbenes: W(CO) Cr(CO) 5 5 Fe(CO)4 Mn(CO)2(MeCp) Co(CO)3SnPh3 Me OMe Ph Ph Ph NEt2 Ph OTiCp2Cl Me OMe Foiled carbenes were defined as "systems where stabilization is Fischer carbenes are found with : obtained by the inception of the facile reaction which is foiled by the impossibility of attaining the final product geometry".
    [Show full text]
  • N-Heterocyclic Carbenes (Nhcs)
    Baran Lab N - H e t e r o c y c l i c C a r b e n e s ( N H C s ) K. J. Eastman An Introduction to N-heterocyclic Carbenes: How viable is resonance contributer B? Prior to 1960, a school of thought that carbenes were too reactive to be smaller isolated thwarted widespread efforts to investigate carbene chemistry. base ! N N N N R R R R Perhaps true for the majority of carbenes, this proved to be an inaccurate X- assessment of the N-heterocyclic carbenes. H longer Kirmse, W. Angerw. Chem. Int. Ed. 2004, 43, 1767-1769 In the early 1960's Wanzlick (Angew. Chem. Int. Ed. 1962, 1, 75-80) first investigated the reactivity and stability of N-heterocyclic carbenes. Attractive Features of NHCs as Ligands for transition metal catalysts: Shortly thereafter, Wanzlick (Angew. Chem. Int. Ed. 1968, 7, 141-142) NHCs are electron-rich, neutral "#donor ligands (evidenced by IR frequency of reported the first application of NHCs as ligands for metal complexes. CO/metal/NHC complexes). Surprisingly, the field of of NHCs as ligands in transition metal chemistry Electron donating ability of NHCs span a very narrow range when compared to remained dormant for 23 years. phosphine ligands In 1991, a report by Arduengo and co-workers (J. Am. Chem. Soc. 1991, Electronics can be altered by changing the nature of the azole ring: 113, 361-363) on the extraodinary stability, isolation and storablility of benzimidazole<imidazole<imidazoline (order of electron donating power). crystalline NHC IAd. NHC-metal complex stability: NaH, DMSO, MeOH N N N N + H2 + NaCl NHCs form very strong bonds with the majority of metals (stronger than Cl- phosphines!) H IAd N-heterocyclic carbenes are electronically (orbital overlap) and sterically (Me vs.
    [Show full text]
  • The Chemistry of Carbene-Stabilized
    THE CHEMISTRY OF CARBENE-STABILIZED MAIN GROUP DIATOMIC ALLOTROPES by MARIHAM ABRAHAM (Under the Direction of Gregory H. Robinson) ABSTRACT The syntheses and molecular structures of carbene-stabilized arsenic derivatives of 1 1 i 1 1 AsCl3 (L :AsCl3 (1); L : = :C{N(2,6- Pr2C6H3)CH}2), and As2 (L :As–As:L (2)), are presented herein. The potassium graphite reduction of 1 afforded the carbene-stabilized diarsenic complex, 2. Notably, compound 2 is the first Lewis base stabilized diatomic molecule of the Group 13–15 elements, in the formal oxidation state of zero, in the fourth period or lower of the Periodic Table. Compound 2 contains one As–As σ-bond and two lone pairs of electrons on each arsenic atom. In an effort to study the chemistry of the electron-rich compound 2, it was combined with an electron-deficient Lewis acid, GaCl3. The addition of two equivalents of GaCl3 to 2 resulted in one-electron oxidation of 2 to 1 1 •+ – •+ – give [L :As As:L ] [GaCl4] (6 [GaCl4] ). Conversely, the addition of four equivalents of GaCl3 to 2 resulted in two- electron oxidation of 2 to give 1 1 2+ – 2+ – •+ [L :As=As:L ] [GaCl4 ]2 (6 [GaCl4 ]2). Strikingly, 6 represents the first arsenic radical to be structurally characterized in the solid state. The research project also explored the reactivity of carbene-stabilized disilicon, (L1:Si=Si:L1 (7)), with borane. The reaction of 7 with BH3·THF afforded two unique compounds: one containing a parent silylene (:SiH2) unit (8), and another containing a three-membered silylene ring (9).
    [Show full text]
  • Photochemical Generation of Carbenes and Ketenes from Phenanthrene-Based Precursors Part I: Dimethylalkylidene Part II: Diphenylketene
    Colby College Digital Commons @ Colby Honors Theses Student Research 2017 Photochemical Generation of Carbenes and Ketenes from Phenanthrene-based Precursors Part I: Dimethylalkylidene Part II: Diphenylketene Tarini S. Hardikar Student Tarini Hardikar Colby College Follow this and additional works at: https://digitalcommons.colby.edu/honorstheses Part of the Organic Chemistry Commons Colby College theses are protected by copyright. They may be viewed or downloaded from this site for the purposes of research and scholarship. Reproduction or distribution for commercial purposes is prohibited without written permission of the author. Recommended Citation Hardikar, Tarini S. and Hardikar, Tarini, "Photochemical Generation of Carbenes and Ketenes from Phenanthrene-based Precursors Part I: Dimethylalkylidene Part II: Diphenylketene" (2017). Honors Theses. Paper 948. https://digitalcommons.colby.edu/honorstheses/948 This Honors Thesis (Open Access) is brought to you for free and open access by the Student Research at Digital Commons @ Colby. It has been accepted for inclusion in Honors Theses by an authorized administrator of Digital Commons @ Colby. Photochemical Generation of Carbenes and Ketenes from Phenanthrene-based Precursors Part I: Dimethylalkylidene Part II: Diphenylketene TARINI HARDIKAR A Thesis Presented to the Department of Chemistry, Colby College, Waterville, ME In Partial Fulfillment of the Requirements for Graduation With Honors in Chemistry SUBMITTED MAY 2017 Photochemical Generation of Carbenes and Ketenes from Phenanthrene-based Precursors Part I: Dimethylalkylidene Part II: Diphenylketene TARINI HARDIKAR Approved: (Mentor: Dasan M. Thamattoor, Professor of Chemistry) (Reader: Rebecca R. Conry, Associate Professor of Chemistry) “NOW WE KNOW” - Dasan M. Thamattoor Vitae Tarini Shekhar Hardikar was born in Vadodara, Gujarat, India in 1996. She graduated from the S.N.
    [Show full text]
  • Carbene Metal Amide Photoemitters: Tailoring Conformationally Flexible Amides for Full Color Range Emissions Including White-Emi
    Chemical Science View Article Online EDGE ARTICLE View Journal | View Issue Carbene metal amide photoemitters: tailoring conformationally flexible amides for full color Cite this: Chem. Sci., 2020, 11,435 † All publication charges for this article range emissions including white-emitting OLED have been paid for by the Royal Society a b b of Chemistry Alexander S. Romanov, * Saul T. E. Jones, Qinying Gu, Patrick J. Conaghan, b Bluebell H. Drummond, b Jiale Feng, b Florian Chotard, a Leonardo Buizza, b Morgan Foley, b Mikko Linnolahti, *c Dan Credgington *b and Manfred Bochmann *a Conformationally flexible “Carbene–Metal–Amide” (CMA) complexes of copper and gold have been developed based on a combination of sterically hindered cyclic (alkyl)(amino)carbene (CAAC) and 6- and 7-ring heterocyclic amide ligands. These complexes show photoemissions across the visible spectrum with PL quantum yields of up to 89% in solution and 83% in host-guest films. Single crystal X-ray diffraction and photoluminescence (PL) studies combined with DFT calculations indicate the important Creative Commons Attribution 3.0 Unported Licence. role of ring structure and conformational flexibility of the amide ligands. Time-resolved PL shows efficient delayed emission with sub-microsecond to microsecond excited state lifetimes at room Received 12th September 2019 À temperature, with radiative rates exceeding 106 s 1. Yellow organic light-emitting diodes (OLEDs) based Accepted 12th November 2019 on a 7-ring gold amide were fabricated by thermal vapor deposition, while the sky-blue to warm-white DOI: 10.1039/c9sc04589a mechanochromic behavior of the gold phenothiazine-5,5-dioxide complex enabled fabrication of the rsc.li/chemical-science first CMA-based white light-emitting OLED.
    [Show full text]
  • On the Road to Carbene and Carbyne Complexes
    ON THE ROAD TO CARBENE AND CARBYNE COMPLEXES Nobel Lecture, 11 December 1973 by ERNST OTTO FISCHER Inorganic Chemistry Laboratory, Technical University, Munich, Federal Republic of Germany Translation from the German text INTRODUCTION In the year 1960, I had the honour of giving a talk at this university* about sandwich complexes on which we were working at that time. I think I do not have to repeat the results of those investigations today. I would like to talk instead about a field of research in which we have been intensely interested in recent years: namely, the field of carbene complexes and, more recently, carbyne complexes. If we substitute one of the hydrogen atoms in a hydrocarbon of the alkane type - for example, ethane - by a metal atom, which can of course bind many more ligands, we arrive at an organometallic compound in which the organic radical is bound to the metal atom by a σ-bond (Fig. la). The earliest compounds of this kind were prepared more than a hundred years ago; the first was cacodyl, prepared by R. Bunsen (1), and then zinc dialkyls were prepared by E. Frankland (2). Later V. Grignard was able to synthesise alkyl magnesium halides by treating magnesium with alkyl halides (3). Grignard was awarded the Nobel Prize in 1912 for this effort. We may further recall the organo-aluminium compounds (4) of K. Ziegler which form the basis for the low pressure polymerisation, for example of ethylene. Ziegler and G. Natta were together honoured with the Nobel Prize in 1963 for their work on organometallic compounds.
    [Show full text]
  • Carbene Rearrangements: Intramolecular Interaction of a Triple Bond with a Carbene Center
    An Abstract OF THE THESIS OF Jose C. Danino for the degree of Doctor of Philosophy in Chemistry presented on _Dcc, Title: Carbene RearrangementE) Intramolecular Interaction of a Triple Bond with aCarbene Center Redacted for Privacy Abstract approved: Dr. Vetere. Freeman The tosylhydrazones of2-heptanone, 4,4-dimethy1-2- heptanone, 6-heptyn-2-one and 4,4-dimethy1-6-heptyn-2- one were synthesizedand decomposed under a varietyof reaction conditions:' drylithium and sodium salt pyrolyses, sodium methoxide thermolysesin diglyme and photolyses of the lithium salt intetrahydrofuran. The saturated ana- logues 2-heptanone tosylhydrazoneand its 4,4-dimethyl isomer afforded the alkenesarising from 6-hydrogeninser- product distribution in the tion. It was determined that differ- dry salt pyrolyses of2-heptanone tosylhydrazone was ent for the lithiumand the sodium salts. However, the product distribution of thedry sodium salt was verysimilar diglyme to product distributionobtained on thermolysis in explained by a with sodium methoxide. This difference was reaction of lithium bromide(present as an impurity inall compound to the lithium salts)with the intermediate diazo afford an organolithiumintermediate that behaves in a some- what different fashionthan the free carbene.The unsaturated analogues were found to produce a cyclic product in addition to the expected acyclic alkenes arising from 3-hydrogen insertion. By comparison of the acyclic alkene distri- bution obtained in the saturated analogues with those in the unsaturated analogues, it was concluded that at leastsome cyclization was occurring via addition of the diazo moiety to the triple bond. It was determined that the organo- lithium intermediateresulting from lithium bromide cat- alyzed decomposition of the diazo compound was incapable of cyclization.
    [Show full text]
  • And Copper–N-Heterocyclic Carbene-Catalyzed C H
    Copper- and copper–N-heterocyclic carbene-catalyzed C─H activating carboxylation of terminal alkynes with CO2 at ambient conditions Dingyi Yu and Yugen Zhang1 Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos, Singapore 138669, Singapore Edited by Jack Halpern, University of Chicago, Chicago, IL, and approved October 4, 2010 (received for review July 26, 2010) The use of carbon dioxide as a renewable and environmentally or an excess amount of organometallic reagents for transmetalla- friendly source of carbon in organic synthesis is a highly attractive tion processes. An alternative possibility to achieve the catalytic approach, but its real world applications remain a great challenge. synthesis of carboxylic acid from CO2 is by direct C─H bond ac- The major obstacles for commercialization of most current proto- tivation and carboxylation. Very recently, Nolan’s group reported cols are their low catalytic performances, harsh reaction conditions, a gold-catalyzed CO2 carboxylation of C─H bonds of highly and limited substrate scope. It is important to develop new reac- activated arenes and heterocycles (32). Herein, we reported a tions and new protocols for CO2 transformations at mild conditions copper- and copper–N-heterocyclic carbene (NHC)-catalyzed and in cost-efficient ways. Herein, a copper-catalyzed and copper– transformation of CO2 to carboxylic acid through C─H bond ac- N -heterocyclic carbene-cocatalyzed transformation of CO2 to car- tivation and carboxylation of terminal alkynes. Various propiolic boxylic acids via C─H bond activation of terminal alkynes with acids were synthesized in good to excellent yields under ambient or without base additives is reported.
    [Show full text]
  • A Benchtop Method for Appending Protic Functional Groups to N‐Heterocyclic Carbene Protected Gold Nanoparticles
    Angewandte Research Articles Chemie International Edition:DOI:10.1002/anie.202001440 Surface Functionalization German Edition:DOI:10.1002/ange.202001440 ABenchtop Method for Appending Protic Functional Groups to N-Heterocyclic Carbene Protected Gold Nanoparticles Joseph F. DeJesus+,Lindy M. Sherman+,Darius J. Yohannan, Jeffrey C. Becca, ShelbyL.Strausser,LeonhardF.P.Karger,Lasse Jensen, David M. Jenkins,* and JonP.Camden* Abstract: The remarkable resilience of N-heterocyclic carbene NHC–CO2 adducts or NHC bicarbonate salts are the most (NHC) gold bonds has quickly made NHCs the ligand of common method for coating noble metal surfaces;[1a, 4,5] choice when functionalizing gold surfaces.Despite rapid however, adding NHCs to nanoparticles in aqueous solutions progress using deposition from free or CO2-protected NHCs, is more challenging.Two complementary approaches for synthetic challenges hinder the functionalization of NHC NHC-protected nanoparticles have been developed. Thefree surfaces with protic functional groups,such as alcohols and NHCs can be added directly to preformed nanoparticles[6] or amines,particularly on larger nanoparticles.Here,wesynthe- gold NHC complexes can be reduced with borohydrides or sizeNHC-functionalized gold surfaces from gold(I) NHC boranes,forming NHC-functionalized gold nanoparticles complexes and aqueous nanoparticles without the need for (AuNPs) under 10 nm in diameter (Figure 1a).[7] Yet, many additional reagents,enabling otherwise difficult functional applications require larger nanoparticles than can be formed groups to be appended to the carbene.The resilience of the with these methods.For example,invivo biological imaging NHC Au bond allows for multi-step post-synthetic modifica- À tion. Beginning with the nitro-NHC,weform an amine-NHC terminated surface,whichfurther undergoes amide coupling with carboxylic acids.The simplicity of this approach, its compatibility with aqueous nanoparticle solutions,and its ability to yield protic functionality,greatly expands the potential of NHC-functionalized noble metal surfaces.
    [Show full text]
  • N-Heterocyclic Carbene Complexes As Antibacterial Agents and Inhibitors of Bacterial Thioredoxin Reductase
    molecules Article Evaluation of Ruthenium(II) N-Heterocyclic Carbene Complexes as Antibacterial Agents and Inhibitors of Bacterial Thioredoxin Reductase Hilke Burmeister 1, Pascal Dietze 2, Lutz Preu 1 , Julia E. Bandow 2 and Ingo Ott 1,* 1 Institute of Medicinal and Pharmaceutical Chemistry, Technische Universität Braunschweig, Beethovenstr. 55, 38106 Braunschweig, Germany; [email protected] (H.B.); [email protected] (L.P.) 2 Applied Microbiology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Universitätsstr. 150, 44801 Bochum, Germany; [email protected] (P.D.); [email protected] (J.E.B.) * Correspondence: [email protected] Abstract: A series of ruthenium(II) complexes with N-heterocyclic carbene (NHC) ligands of the general type (arene)(NHC)Ru(II)X2 (where X = halide) was prepared, characterized, and evaluated as antibacterial agents in comparison to the respective metal free benzimidazolium cations. The ruthenium(II) NHC complexes generally triggered stronger bacterial growth inhibition than the metal free benzimidazolium cations. The effects were much stronger against Gram-positive bacte- ria (Bacillus subtilis and Staphylococcus aureus) than against Gram-negative bacteria (Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa), and all complexes were inactive against the fun- gus Candida albicans. Moderate inhibition of bacterial thioredoxin reductase was confirmed for Citation: Burmeister, H.; Dietze, P.; Preu, L.; Bandow, J.E.; Ott, I. selected complexes, indicating that inhibition of this enzyme might be a contributing factor to the Evaluation of Ruthenium(II) antibacterial effects. N-Heterocyclic Carbene Complexes as Antibacterial Agents and Keywords: antibacterial; N-heterocyclic carbenes; ruthenium; thioredoxin reductase Inhibitors of Bacterial Thioredoxin Reductase. Molecules 2021, 26, 4282.
    [Show full text]
  • Transmetalation from Magnesium–Nhcs—Convenient Synthesis of Chelating -Acidic NHC Complexes
    inorganics Article Transmetalation from Magnesium–NHCs—Convenient Synthesis of Chelating π-Acidic NHC Complexes Julian Messelberger 1, Annette Grünwald 1, Philipp Stegner 2, Laura Senft 3, Frank W. Heinemann 1 and Dominik Munz 1,* 1 Lehrstuhl für Anorganische und Allgemeine Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, 91058 Erlangen, Germany; [email protected] (J.M.); [email protected] (A.G.); [email protected] (F.W.H.) 2 Lehrstuhl für Anorganische und Metallorganische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, 91058 Erlangen, Germany; [email protected] 3 Lehrstuhl für Bioanorganische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, 91058 Erlangen, Germany; [email protected] * Correspondence: [email protected]; Tel.: +49-9131-85-27464 Received: 6 May 2019; Accepted: 19 May 2019; Published: 22 May 2019 Abstract: The synthesis of chelating N-heterocyclic carbene (NHC) complexes with considerable π-acceptor properties can be a challenging task. This is due to the dimerization of free carbene ligands, the moisture sensitivity of reaction intermediates or reagents, and challenges associated with the workup procedure. Herein, we report a general route using transmetalation from magnesium–NHCs. Notably, this route gives access to transition-metal complexes in quantitative conversion without the formation of byproducts. It therefore produces transition-metal complexes outperforming the conventional routes based on free or lithium-coordinated carbene, silver complexes, or in situ metalation in dimethyl sulfoxide (DMSO). We therefore propose transmetalation from magnesium–NHCs as a convenient and general route to obtain NHC complexes. Keywords: NHC; transmetalation; magnesium; palladium; carbene 1. Introduction N-heterocyclic carbene (NHC) ligands have become the powerhouse of modern transition metal chemistry [1–13].
    [Show full text]
  • Carbene-Functionalized Ruthenium Nanoparticles
    Chem. Mater. 2006, 18, 5253-5259 5253 Carbene-Functionalized Ruthenium Nanoparticles Wei Chen, James R. Davies, Debraj Ghosh, Moony C. Tong, Joseph P. Konopelski, and Shaowei Chen* Department of Chemistry and Biochemistry, UniVersity of California, 1156 High Street, Santa Cruz, California 95064 ReceiVed July 11, 2006. ReVised Manuscript ReceiVed August 15, 2006 Stable ruthenium nanoparticles were synthesized by protecting the particles with diazo molecules that reacted readily with the ruthenium surface forming RudC carbene bonds, as manifested in Fourier transform infrared and 1H NMR measurements. The resulting particles, with the core diameter averaged at 2.12 ( 0.72 nm as determined by transmission electron microscopic measurements, showed a Mie scattering profile in optical absorption measurements. In electrochemical studies, the particles exhibited interesting quantized charging characteristics, similar to those observed with alkanethiolate-protected gold (AuSR) nanoparticles. In addition, a proof-of-concept experiment was carried out to demonstrate that metathesis reactions on ruthenium surfaces might be exploited for the chemical functionalization of the particles through efficient surface place exchange reactions. 1H NMR spectroscopy was used to monitor the reaction kinetics which exhibited a rate constant twice that observed with AuSR particles with another thiol ligand. Introduction properties have been demonstrated extensively by alkane- thiolate-protected gold nanoparticles which undergo ex- Metal and semiconductor nanoparticles have stimulated change reactions with other thiol derivatives by taking intensive basic and technological research because of their advantage of the strong affinity of thiols to gold surfaces.14-18 unique chemical and physical properties that differ vastly The resulting surface composition can then be quantitatively from those of bulk materials and molecular species.1 Such evaluated by using a variety of spectroscopic techniques.
    [Show full text]