DOCSLIB.ORG

Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
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". They only low oxidation state metals; exist in the singlet state. middle and late transition metals Fe(0), Mo(0), Cr(0), W(0); pi-electron acceptor metal ligands; Rolf Gleiter, Ronald Hoffman J. Am. Chem. Soc. 1968, 90, 5457 - 5460. pi-donor substituents on methylene group such as alkoxy and Jean-Luc Mieusset and Udo H. Brinker J. Am. Chem. Soc. 2006, 128, 15843 - 15850. amino groups. 1 Baran Group Meeting Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007 Advantages over regular carbenes 2. Excellent functional group compatibility - serving as blocking groups - From fleeting intermediates to powerful reagents in organic synthesis. 1. Improved stability OTMS OMe Ph O H OMe o Typical carbenes such as diphenyl carbene have lifetimes in the BuLi, THF, -78 C [Cr] nanosecond regime. [Cr] Ph Et 75 % Et 3 equiv of CH2CHCH2Li, THF [Cr] O Most Fischer carbene complexes are stable to air and water and to -78 oC to RT, then SiO dilute acids and bases. Despite the high dipole moment of these 2 complexes (~ 4 - 5 Debye), most complexes can be purified by 71 % H chromatography on silica gel with hexane as eluent and are usually Ph Et the first compounds to elute. Identification of the fractions from the column containing the carbene complex can simply be done by eye on the basis of their color. The colors of complexes bearing alkoxy J. Barluenga. J. Am. Chem. Soc. 2002, 124, 9056 -9057. groups as the heteroatom-stabilizing group tend to correlate with the hybridzation of the carbon substituent of the carbene carbon. Those 3. Improved reactivity and selectivity with sp3 carbons usually are yellow, those with sp2 carbons are normally red and those with sp hybridized carbon substituents are Cr(CO)5 Cr(CO)5 invariably an intense purple/black color. Cr(CO)5 RT, 3 h MeO MeO MeO 70 % 92 : 8 O O O MeO MeO MeO thermal conditions: RT, 7 months, 54 % 70 : 30 AlCl3, 0.5 h , 50 % 95 : 5 W. Wulff. J. Am. Chem. Soc. 1990, 112, 3642. http://www.chemistry.msu.edu/faculty/wulff/myweb26/research/carbenes.htm 2 Baran Group Meeting Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007 Synthesis of Fischer carbene complexes: 2. Hegedus-Semmelhack approach 1. Standard Fischer route O OK OR2 OLi OR C8K R1 Cl R X R Li RX 2 K [M(CO) ] (OC) M 2 M(CO) 1 M(CO)6 2 5 5 (OC)5M 6 (OC)5M (OC)5M R1 R1 R1 R1 O M = Cr, Mo, W R3 R1 = alkyl, aryl, vinyl HN R1 NR3R4 2 + - HS R3 RX = R 3O BF4 , R2OSO3F R4 R3, R4 = H, alkyl - O NR3R4 SR3 NR3R4 TMSCl (OC)5M NR3R4 (OC)5M (OC)5M (OC)5M R1 R1 R1 R1 This is the most direct and general approach to Fischer carbene M = Cr, W complexes; R1 = alkyl, aryl, vinyl Limitations are the availability of organolithium compound R X = R2 O+BF -, R OSO F and the alkylation reagent. 2 3 4 2 3 R3, R4 = H, alkyl O R2 This strategy combining an organoelectrophile and a metal nucleophile - + OLi + - O NMe4 O can be extended to the synthesis of aminocarbene complexes. Me4N Br X R2 (OC)5M (OC)5M O R1 R1 (OC)5M R1 Recent reviews: M = Cr, W R1 = alkyl, aryl, vinyl W. D. Wulff, in Comprehensive Organometallic Chemistry II, ed. R3OH R2 = Me, tBu A. W. Abel, F. G. A. Stone and G. Wilkinson, pergamon Press, Oxford, 1995, vol. 12, p. 469 X = Br, Cl L. S. Hegedus, ibid., vol. 12, p. 549. R = terpene, sugar skeletons 3 OR3 (OC)5M R1 This is the standard approach to optically active Fischer carbene complexes bearing alkoxy substituents. 3 Baran Group Meeting Fischer Carbene Complexes in Organic Synthesis Ke Chen 1/31/2007 Reaction pattern of carbene complexes: Pattern B: Bond formation via metal carbene anions Part I: Ligand-centered OR OR OMe OMe (OC)5M (OC)5M (OC)5Cr O R R pKa = 12 pKa = 25 C H3C OH O O OC CO O R A E CH3 N 1. nBuLi OC Cr O 2. PhCHO Ph N CH OC CO N 3 CR2 Nu N 3. HOAc / Ce(IV) Ph H B (OC)4Cr Ph B 60 %, > 96 % de CH3 CH3 W. Wulff, J. Org. Chem., 1994, 6882. Pattern A: Addition of nucleophiles OMe OMe 1. nBuLi O OMe (OC)5Cr (OC)5Cr (OC)5Cr OMe NHR H - MeOH 2. O (OC)5Cr NH2R (OC) Cr 5 NHR (OC)5Cr Ph OLi Ph Ph B. A. Anderson, J. Am. Chem. Soc., 1993, 115, 4602. OMe O (OC) Cr OLi 5 THF, -80 oC to RT Ph Li Pattern C: Transformation of metal carbenes to metal carbynes Ph O O 50 % Cr(CO)5 J. Barluengal, J. Chem. Soc., Chem. Commun. 1993, 1068 Ph OMe ? (OC)5Cr N N MeO For reviews on reaction pattern of carbene complexes, see "Carbene Chemistry : From Fleeting Ph Intermediates to Powerful Reagents", chapter 8. Cr(CO)5 H. Fischer, Chem. Ber. 1980, 113, 193 4 Baran Group Meeting Ke Chen 1/31/2007 Fischer Carbene Complexes in Organic Synthesis Reaction pattern of carbene complexes: Diels-Alder reaction of boroxycarbene complexes: Part I: Ligand-centered 1. t-BuLi, Et2O F Cycloaddition reactions: (OC)5Cr O Ph OMe Br 2. Cr(CO)6, Et2O B F OMe N [2 + 2] CH3 N OMe (OC)5W . N Me RT, 12 h 3. BF3 Et2O, RT (OC)5W H3CO 87 % 1.THF, -78 oC to RT 85% CH3 K. L. Faron, J. Am. Chem. Soc. 1988, 110, 8727 -8729. 2. 3N HCl, THF, RT 95 % [3 + 2] TMSCHN2 F OMe OMe (OC)5Cr O hexanes, RT CHO B F (OC)5W (OC)5W HBr, DCM, RT N 4.5 h, 87 % NH N 85 % N H3C O O CH3 W. D. Wulff, J. Am. Chem. Soc. 1986, 108, 5229 -5236. [4 + 2] J. Barluenga. J. Am. Chem. Soc. 1998, 120, 2514 -2522. H3C H3C CH TBSO CH N 3 N 3 Miscellaneous cases O O Ipc N OCH3 N Ph OLi O B Ph (-) -Ipc2BCl, Et2O Ph H (OC)4Cr (OC)4Cr CH3 DCM, RT, 12 h (OC)5W 80 %,single isomer -78 oC to RT CH O 3 Ph CH3 OTBS W. D. Wulff, J. Am. Chem. Soc. 1997, 119, 6438 -6439. J. Barluenga, J. Am. Chem. Soc,, 1996, 118, 6090 -6091. H2O2, NaOH Intramolecular Pauson -Khand reaction: 83 %, > 99 % de NH (OC) W Ph (OC) W 5 OH OH 5 [Co2(CO)8] Ph 75 % O Ph J. M. Moreto. Angew. Chem. Int. Engl. 1991, 11,1470. 5 Baran Group Meeting Ke Chen 1/31/2007 Fischer Carbene Complexes in Organic Synthesis Reaction pattern of carbene complexes: OMe OMe Part II: Metal-centered DMF, 152 oC (OC)5Cr H 1. Reaction with olefins Fe 88 %, 97 % de Fe OR 1 OR1 OR1 (OC)5Cr (OC)4Cr (OC)4Cr R2 R 2 R2 "The functionalized Ru Fischer-type complexes are active in a variety of Cr(CO) H 5 THF, 100oC Me olefin metathesis reactions, although Et with significantly lower rates than the Olefin Metathesis Me OMe 55 % MeO corresponding carbon analogues." Cyclopropanation Et favored R, H. Grubbs, Organometallics. 2002, 21, 2153 -2164. H H General carbene complexes used in cyclopropanation reactions: Et Et Cr R R MeO MeO Cp Cp (CO)4 Cr(CO) Cr(CO) Cr(CO)5 Cr(CO)4 R*Ph2P OC 5 5 Fe H Fe H H OC OC CH 2 Me OMe Ph OMe OMe Me H Me MeO Cr R MeO R Et MeO (CO) Et W(CO)5 W(CO) Mo(CO) 4 Et 5 5 Cr(CO)4 disfavored Ph OMe Ph H Bu OMe J. Am. Chem. Soc. , 113, 23, 1991, 8916-8921 (leads to olefin (less stable ) metathesis product) O O Cr(CO)5 Suitable olefins: O Cl 85oC,12 h Alkyl R1 OMe intermediate A O Alkyl R 85 % EWG EWG 1 O EWG R2 R2 R1 R1, R2 = akyl, aryl R1, R2 and R3 = alkyl R3 Chemtracts - Organic Chemistry.
Load more

Recommended publications
  • Common Names for Selected Aromatic Groups
    More Nomenclature: Common Names for Selected Aromatic Groups Phenyl group = or Ph = C6H5 = Aryl = Ar = aromatic group. It is a broad term, and includes any aromatic rings. Benzyl = Bn = It has a -CH2- (methylene) group attached to the benzene ring. This group can be used to name particular compounds, such as the one shown below. This compound has chlorine attached to a benzyl group, therefore it is called benzyl chloride. Benzoyl = Bz = . This is different from benzyl group (there is an extra “o” in the name). It has a carbonyl attached to the benzene ring instead of a methylene group. For example, is named benzoyl chloride. Therefore, it is sometimes helpful to recognize a common structure in order to name a compound. Example: Nomenclature: 3-phenylpentane Example: This is Amaize. It is used to enhance the yield of corn production. The systematic name for this compound is 2,4-dinitro-6-(1-methylpropyl)phenol. Polynuclear Aromatic Compounds Aromatic rings can fuse together to form polynuclear aromatic compounds. Example: It is two benzene rings fused together, and it is aromatic. The electrons are delocalized in both rings (think about all of its resonance form). Example: This compound is also aromatic, including the ring in the middle. All carbons are sp2 hybridized and the electron density is shared across all 5 rings. Example: DDT is an insecticide and helped to wipe out malaria in many parts of the world. Consequently, the person who discovered it (Muller) won the Nobel Prize in 1942. The systematic name for this compound is 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane.
    [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]
  • 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.
    [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]
  • 23.5 Basicity and Acidity of Amines
    23_BRCLoudon_pgs5-0.qxd 12/8/08 1:22 PM Page 1122 1122 CHAPTER 23 • THE CHEMISTRY OF AMINES alkylamines, this resonance occurs at rather small chemical shift—typically around d 1. In aromatic amines, this resonance is at greater chemical shift, as in the second of the preceding examples. Like the OH protons of alcohols, phenols, and carboxylic acids, the NH protons of amines under most conditions undergo rapid exchange (Secs. 13.6 and 13.7D). For this reason, split- ting between the amine N H and adjacent C H groups is usually not observed. Thus, in the NMR spectrum of diethylamine,L the N H resonanceL is a singlet rather than the triplet ex- pected from splitting by the adjacent CHL2 protons. In some amine samples, the N H resonance is broadened and, like the OL H protonL of alcohols, it can be obliterated fromL the spectrum by exchange with D2O (the “DL2O shake,” p. 611). The characteristic 13C NMR absorptions of amines are those of the a-carbons—the carbons attached directly to the nitrogen. These absorptions occur in the d 30–50 chemical-shift range. As expected from the relative electronegativities of oxygen and nitrogen, these shifts are somewhat less than the a-carbon shifts of ethers. PROBLEMS 23.4 Identify the compound that has an M 1 ion at mÜz 136 in its CI mass spectrum, an IR 1 + = absorption at 3279 cm_ , and the following NMR spectrum: d 0.91 (1H, s), d 1.07 (3H, t, J 7Hz), d 2.60 (2H, q, J 7Hz), d 3.70 (2H, s), d 7.18 (5H, apparent s).
    [Show full text]
  • 2 Reactions Observed with Alkanes Do Not Occur with Aromatic Compounds 2 (SN2 Reactions Never Occur on Sp Hybridized Carbons!)
    Reactions of Aromatic Compounds Aromatic compounds are stabilized by this “aromatic stabilization” energy Due to this stabilization, normal SN2 reactions observed with alkanes do not occur with aromatic compounds 2 (SN2 reactions never occur on sp hybridized carbons!) In addition, the double bonds of the aromatic group do not behave similar to alkene reactions Aromatic Substitution While aromatic compounds do not react through addition reactions seen earlier Br Br Br2 Br2 FeBr3 Br With an appropriate catalyst, benzene will react with bromine The product is a substitution, not an addition (the bromine has substituted for a hydrogen) The product is still aromatic Electrophilic Aromatic Substitution Aromatic compounds react through a unique substitution type reaction Initially an electrophile reacts with the aromatic compound to generate an arenium ion (also called sigma complex) The arenium ion has lost aromatic stabilization (one of the carbons of the ring no longer has a conjugated p orbital) Electrophilic Aromatic Substitution In a second step, the arenium ion loses a proton to regenerate the aromatic stabilization The product is thus a substitution (the electrophile has substituted for a hydrogen) and is called an Electrophilic Aromatic Substitution Energy Profile Transition states Transition states Intermediate Potential E energy H Starting material Products E Reaction Coordinate The rate-limiting step is therefore the formation of the arenium ion The properties of this arenium ion therefore control electrophilic aromatic substitutions (just like any reaction consider the stability of the intermediate formed in the rate limiting step) 1) The rate will be faster for anything that stabilizes the arenium ion 2) The regiochemistry will be controlled by the stability of the arenium ion The properties of the arenium ion will predict the outcome of electrophilic aromatic substitution chemistry Bromination To brominate an aromatic ring need to generate an electrophilic source of bromine In practice typically add a Lewis acid (e.g.
    [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]
  • Los Premios Nobel De Química
    Los premios Nobel de Química MATERIAL RECOPILADO POR: DULCE MARÍA DE ANDRÉS CABRERIZO Los premios Nobel de Química El campo de la Química que más premios ha recibido es el de la Quí- mica Orgánica. Frederick Sanger es el único laurea- do que ganó el premio en dos oca- siones, en 1958 y 1980. Otros dos también ganaron premios Nobel en otros campos: Marie Curie (física en El Premio Nobel de Química es entregado anual- 1903, química en 1911) y Linus Carl mente por la Academia Sueca a científicos que so- bresalen por sus contribuciones en el campo de la Pauling (química en 1954, paz en Física. 1962). Seis mujeres han ganado el Es uno de los cinco premios Nobel establecidos en premio: Marie Curie, Irène Joliot- el testamento de Alfred Nobel, en 1895, y que son dados a todos aquellos individuos que realizan Curie (1935), Dorothy Crowfoot Ho- contribuciones notables en la Química, la Física, la dgkin (1964), Ada Yonath (2009) y Literatura, la Paz y la Fisiología o Medicina. Emmanuelle Charpentier y Jennifer Según el testamento de Nobel, este reconocimien- to es administrado directamente por la Fundación Doudna (2020) Nobel y concedido por un comité conformado por Ha habido ocho años en los que no cinco miembros que son elegidos por la Real Aca- demia Sueca de las Ciencias. se entregó el premio Nobel de Quí- El primer Premio Nobel de Química fue otorgado mica, en algunas ocasiones por de- en 1901 al holandés Jacobus Henricus van't Hoff. clararse desierto y en otras por la Cada destinatario recibe una medalla, un diploma y situación de guerra mundial y el exi- un premio económico que ha variado a lo largo de los años.
    [Show full text]
  • Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of  Electrons Above and Below Its Sigma Bond Framework
    Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product.
    [Show full text]
  • Small Molecule
    National School on Neutron and X-ray Scattering June 24, 2010 Xiaoping Wang Neutron Scattering Science Division Oak Ridge National Laboratory Outline • Small Molecule Crystallography • Accurate Molecular Structural Determination – Impact on Science • Structure and Bonding – Metal-Metal Multiple Bonds – From Small Molecule to Superamolecular Assembly • Case Studies – Gas Adsorption Dynamic in a Meal-Organic Framework – Electronic Communications Between Dimetal Centers – Effects of Crystallization on Molecular Structure – Single Crystal to Single Crystal Chemical Reaction • Future Directions – Single Crystal Crystallography in Higher Dimensions – Charge and Spin Density – Time Resolved Diffraction – Bridging the Gap in Small Molecule and Macromolecule Crystallography Small Molecule Crystallography • Small molecule A neutral or ionic compound of synthetic or biological origin but it is not a polymer, protein or nucleic acid: – Inorganic and Organic Compounds – Catalysts – Natural Products – Pharmaceuticals – Synthetic Chemicals • Small Molecule Crystallography – Use single crystal X-ray/Neutron diffraction methods to determine the three dimensional structure of small molecules at atomic resolution. Chemical Crystallography – The relationship between molecular structure and chemical, biochemical or biological properties. Cambridge Structural Database Stores data for organic molecules & metal-organic compounds http://www.ccdc.cam.ac.uk/ Basic Research at CCDC Mean molecular dimensions Studies of substituent effects Statistical and numerical
    [Show full text]
  • Facts & Figures 2014
    Technische Universität München Facts & Figures 2014 Portrait TUM combines top-class facilities for cutting-edge research with unique learning opportunities for students. TUM scientists are committed to finding solutions to the major challenges facing society as we move forward: • Health & Nutrition • Energy & Natural Resources • Environment & Climate • Information & Communications • Mobility & Infrastructure. TUM thinks and acts with an entrepreneurial spirit. Its aim is ambitious: to create lasting value for society through excellence in education and research, the active promotion of next-generation talent and a strong entre- preneurial spirit. All of which combine to make TUM one of Europe’s leading universities. Departments Locations & Networks 154 programs - 13 departments - 3 locations TUM science network Freising • Max Planck Institutes: Garching Munich Freising 13 Martinsried • Architecture • TUM School of 99 Munich Life Sciences • Civil, Geo and Environ- • Helmholtz Zentrum Weihenstephan mental Engineering 11 München • iwb Anwenderzentrum • Electrical, Electronic and Augsburg Computer Engineering 13 • Fraunhofer Institutes: • TUM School of Medicine Garching 471 Holzkirchen • Sport and Health Freising Sciences 99 99 471 • TUM School of 13 TUM locations Education • Munich • TUM School of 99 • Garching Management • Freising Munich • Iffeldorf Garching 94 • Obernach • Chemistry • Straubing • Wettzell • Informatics • Singapore: TUM Asia • Mathematics 471 • Beijing • Brussels • Mechanical 99 Engineering • Cairo • Mumbai • Physics •
    [Show full text]