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Richard G Weiss - One of the best experts on this subject based on the ideXlab platform.
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control of pyrene fluorescence intensity by in situ addition of co2 to an amidine amine mixture or co2 removal from an Amidinium carbamate ionic liquid
Photochemical and Photobiological Sciences, 2012Co-Authors: Shibu Abraham, Richard G WeissAbstract:Addition of CO2 to an equimolar amidine/amine mixture leads to formation of a switchable ionic liquid, an Amidinium carbamate, and appearance of strong fluorescence by a solute, pyrene. Passing a ‘displacement gas’, N2, through the ionic liquid or heating it regenerates the amidine/amine mixture and quenches the fluorescence almost totally. No switching or appreciable fluorescence is found when an Amidinium dithiocarbamate is the medium.
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syntheses of cyclic carbonates with Amidinium halide catalysts in reusable reversible room temperature ionic liquids or acetonitrile
ChemInform, 2012Co-Authors: Richard G WeissAbstract:Reaction between epoxides (I) and carbon dioxide (II) in room temperature ionic liquids and in the presence of an Amidinium halide catalyst occurs cleanly to provide the cyclic carbonates (III), exclusively.
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syntheses of cyclic carbonates with Amidinium halide catalysts in reusable reversible room temperature ionic liquids or acetonitrile
Green Chemistry, 2012Co-Authors: Richard G WeissAbstract:In situ-prepared, reversible, room-temperature ionic liquids (RTILs), Amidinium carbamates, have been used as media for the syntheses of cyclic carbonates by cycloaddition of CO2 to epoxides. The Amidinium carbamates were prepared by exposing equimolar mixtures of an easily synthesized amidine and a primary amine to CO2 gas. For comparison purposes, Amidinium dithiocarbamates were also employed as the RTILs in some experiments. Reaction between CO2 and four epoxides in the RTILs, occurs in good yields (> 90% in many cases) at room temperature or 50 °C in the presence of an Amidinium halide catalyst. Product and any unreacted epoxide were extracted easily upon addition of an immiscible, lower density liquid to an RTIL reaction mixture. This process was repeated three times with the same RTIL without any obvious decrease in catalytic activity; presumably, additional transformations could have been conducted. The influences of the type of catalyst, CO2 pressure, reaction time, and temperature on the reaction yields have been investigated. The relatively mild reaction conditions and ease of separation of products, as well as the ability of the Amidinium carbamates to be reused in the presence or absence of water make this an attractive alternative to other procedures for the efficient syntheses of cyclic carbonates.
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reversible room temperature ionic liquids Amidinium carbamates derived from amidines and aliphatic primary amines with carbon dioxide
Chemistry of Materials, 2007Co-Authors: Taisuke Yamada, Paul Joseph Lukac, Mathew George, Richard G WeissAbstract:Reversible, room-temperature ionic liquids, Amidinium carbamates, are made by addition of carbon dioxide to mixtures of an aliphatic amidine and an aliphatic primary amine. The systems can be cycled repeatedly by sequential exposure to CO2 and N2. An example of the utility of such systems is provided.
Michael W Gobel - One of the best experts on this subject based on the ideXlab platform.
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enantioselective synthesis of estrone exploiting a hydrogen bond promoted diels alder reaction
Journal of Organic Chemistry, 2010Co-Authors: Marko Weimar, Gerd Durner, Jan W Bats, Michael W GobelAbstract:Starting from Dane’s diene and methylcyclopentenedione, (+)-estrone is synthesized along the Quinkert−Dane route in 24% total yield. The key step is an enantioselective Diels−Alder reaction promoted by an Amidinium catalyst as efficiently as by a traditional Ti-TADDOLate Lewis acid.
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a c2 chiral bis Amidinium catalyst for a diels alder reaction constituting the key step of the quinkert dane estrone synthesis
European Journal of Organic Chemistry, 2003Co-Authors: Svetlana B Tsogoeva, Gerd Durner, Michael Bolte, Michael W GobelAbstract:A novel C2-chiral bis(Amidinium) salt 12 has been synthesised from 5-(tert-butyl)isophthalic acid. The hydrogen-bond-mediated association of dienophiles 3a and 3b with the chiral host molecule 12 accelerates the Diels−Alder reactions with diene 2 by more than three orders of magnitude. In addition, enantioselective formation of the desired adducts is observed under catalysis with 12. Good ratios of 4a(b) + ent-4a(b)/5a(b) + ent-5a(b) from 1:10 to 1:22 were found in all reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
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catalysis of a diels alder reaction by Amidinium ions
Journal of Organic Chemistry, 2000Co-Authors: Tilmann Schuster, Markus Kurz, Michael W GobelAbstract:Amidines and guanidines are important functional groups in molecular recognition and host-guest chemistry. Here it is shown that lipophilic Amidinium ions catalyze a cycloaddition reaction representing the key step of the Quinkert-Dane estrone synthesis. Hydrogen-bond-mediated association with the organic cation leads to an electrophilic activation of the dienophile and to enhanced rates of the Diels-Alder reaction. The observed effects are similar to those expected from mild Lewis acids. In competition experiments, Amidinium catalysis favors the reaction of the less electron deficient dienophile.
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axially chiral Amidinium ions as inducers of enantioselectivity in diels alder reactions
Organic Letters, 2000Co-Authors: Tilmann Schuster, Gerd Durner, Markus Bauch, Michael W GobelAbstract:[reaction: see text] Enantioselective catalysis of Diels-Alder reactions is mostly achieved by coordinating the dienophile to relatively strong chiral Lewis acids. Here we report on a novel approach employing the hydrogen-bond-mediated association of dienophiles to chiral host molecules. In a reaction forming the steroid skeleton of norgestrel, chiral Amidinium ions induce 5:ent-5 ratios of up to 2.5:1. Improved and simplified Amidinium catalysts may become interesting candidates to perform stereoselective transformations.
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supramolekulare phosphoryl ubertragungsreaktionen vermittelt durch Amidinium phosphat ionenpaarkomplexe
European Journal of Organic Chemistry, 1994Co-Authors: Gilbert Muller, Gerd Durner, Jan W Bats, Michael W GobelAbstract:Supramolecular Phosphoryl Transfer Reactions Mediated by Amidinium Phosphate Ion-Pair Complexes In order to build up simplified synthetic models of staphylococcal nuclease two derivatives of 8-phenylnaphthalene-1-carboxamidine equipped with nucleophilic side chains have been prepared (1,2). After protonation these Amidinium alcohols bind phosphodiester anions via hydrogen bonds and react within the ion-pair complexes to give zwitterionic products 27 and 28. The rate accelerations (DMF, 30°C) compared to the phosphorylation of noncharged alcohols are 2700-fold (2) and 930-fold (1).
Daniel G Nocera - One of the best experts on this subject based on the ideXlab platform.
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comparative pcet study of a donor acceptor pair linked by ionized and nonionized asymmetric hydrogen bonded interfaces
Journal of the American Chemical Society, 2009Co-Authors: Elizabeth R Young, Joel Rosenthal, Justin M Hodgkiss, Daniel G NoceraAbstract:A Zn(II) Amidinium porphyrin is the excited-state electron donor (D) to a naphthalene diimide acceptor (A) appended with either a carboxylate or sulfonate functionality. The two-point hydrogen bond (···[H+]···) formed between the Amidinium and carboxylate or sulfonate functionalities establishes a proton-coupled electron transfer (PCET) pathway for charge transfer. The two D···[H+]···A assemblies differ only by the proton configuration within the hydrogen-bonding interface. Specifically, the Amidinium ion transfers a proton to the carboxylate to form a nonionized amidine−carboxylic acid two-point hydrogen network, whereas the Amidinium retains both protons when bound to the sulfonate functionality, forming an ionized Amidinium−sulfonate two-point hydrogen bond network. These two interface configurations within the dyads thus allow for a direct comparison of the PCET kinetics for the same donor and acceptor juxtaposed by ionized and nonionized hydrogen-bonded interfaces. Analysis of the PCET kinetics ascer...
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structurally homologous β and meso alkynyl Amidinium porphyrins
Inorganic Chemistry, 2007Co-Authors: Joel Rosenthal, Elizabeth R Young, Daniel G NoceraAbstract:AlkynylAmidinium groups have been introduced at the beta and meso positions of a nickel(II) porphyrin (PNi(II)) framework. The modification permits the distance between the Amidinium-amidine acid-base group and porphyrin to be increased while effectively maintaining pi conjugation between the porphyrin macrocycle and the acid-base functionality. Use of an ethynyl spacer as a linker (i) extends the Amidinium functionality away from the sterically bulky mesityl groups of the porphyrin, allowing it to be nearly planar with respect to the porphyrin ring, and (ii) draws the pi-orbital character of the porphyrin out toward the Amidinium functionality, thereby engendering sensitivity of the electronic properties of the porphyrin macrocycle to the protonation state of the Amidinium. The barrier for rotation of the Amidinium group, as calculated by time-dependent density functional theory (TDDFT), is approximately 8.5 kT (5 kcal/mol) for both porphyrins. Analysis of UV-visible absorption profiles for the beta- and meso-alkynylAmidinium PNi(II) upon deprotonation enables accurate determination of the Amidinium acidity constants for the ground state (pK(a)(beta) = 7.03 +/- 0.1, pK(a)(meso) = 7.74 +/- 0.1 in CH(3)CN) and excited state (pK(a)*(beta) = 6.89 +/- 0.1, pK(a)*(meso) = 8.37 +/- 0.1 in CH(3)CN) porphyrins. Whereas pK(a)* pK(a) for the meso-alkynylAmidinium porphyrin, indicating that beta-alkynylAmidinium PNi(II) is a photoacid and meso-alkynylAmidinium PNi(II) is a photobase. These divergent behaviors are supported by analysis of the frontier molecular orbitals of the homologous pair with TDDFT.
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observation of proton coupled electron transfer by transient absorption spectroscopy in a hydrogen bonded porphyrin donor acceptor assembly
Journal of Physical Chemistry B, 2004Co-Authors: Niels H Damrauer, Joel Rosenthal, Justin M Hodgkiss, Daniel G NoceraAbstract:Proton-coupled electron transfer (PCET) kinetics of a Zn(II) porphyrin donor noncovalently bound to a naphthalene-diimide acceptor through an Amidinium-carboxylate interface have been investigated by time-resolved spectroscopy. The S1 singlet excited-state of a Zn(II) 2-Amidinium-5,10,15,20-tetramesitylporphyrin chloride (ZnP-β-AmH+) donor is sufficiently energetic (2.04 eV) to reduce a carboxylate-diimide acceptor (ΔG° = −460 mV, THF). Static quenching of the porphyrin fluorescence is observed and time-resolved measurements reveal more than a 3-fold reduction in the S1 lifetime of the porphyrin upon Amidinium-carboxylate formation (THF, 298 K). Picosecond transient absorption spectra of the free ZnP-β-AmH+ in THF reveal the existence of an excited-state isosbestic point between the S1 and T1 states at λprobe = 650 nm, providing an effective ‘zero-kinetics' background on which to observe the formation of PCET photoproducts. Distinct rise and decay kinetics are attributed to the build-up and subsequent los...
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structurally homologous β and meso Amidinium porphyrins
Inorganic Chemistry, 2001Co-Authors: Chenyu Yeh, Scott E Miller, Scott D Carpenter, Daniel G NoceraAbstract:A synthetic strategy has been developed to afford porphyrins site-derivatized with the same hydrogen-bond synthon attached directly to the macrocyclic ring. Porphyrin homologues derivatized at the β and meso positions with an Amidinium group form 1:1 supramolecular complexes with benzoate acceptors and show notable differences in their excited-state properties that are dependent on the site of the salt bridge.
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formation of porphyrin donor acceptor complexes via an Amidinium carboxylate salt bridge
Tetrahedron Letters, 1995Co-Authors: James P Kirby, Niels A Van Dantzig, C K Chang, Daniel G NoceraAbstract:Abstract Porphyrins have been modified with an amidine functional group and they have been shown to bind carboxylic acids to form a Amidinium-carboxylate salt bridge. These systems offer a new model to probe the mechanism of proton-coupled electron transfer (PCET).
Philip A Gale - One of the best experts on this subject based on the ideXlab platform.
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a new bis Amidinium calix 4 arene difluorophosphinate network an unexpected but not unwelcome guest
Supramolecular Chemistry, 2001Co-Authors: Salvatore Camiolo, Philip A Gale, Mark E Light, Michael B HursthouseAbstract:Abstract A complex hydrogen bonded network is formed between a mono-deprotonated bis-Amidinium calix[4]arene 1 and difluorophosphinate in the presence of methanol. The compound crystallises in the triclinic space group P1 with a=12.0665(5), b=12.5737(6), c=20.0201(15) a, α=86.4098(18), β=79.747(2), γ=66.816(4)°, and D c=1.159 Mgm−3 for Z=4.7824 independent reflections were collected and the final R1 [F 2 > 2α(F 2)] was 0.1243.
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solid state and solution studies of bis carboxylate binding by bis Amidinium calix 4 arenes
Journal of The Chemical Society-perkin Transactions 1, 2001Co-Authors: Salvatore Camiolo, Philip A Gale, Mark I Ogden, Brian W Skelton, Allan H WhiteAbstract:Bis-Amidinium calix[4]arene receptors were shown to coordinate bis-carboxylate anions in DMSO solution; the crystal structure of the malonate salt of one of the receptors revealed a number of different Amidinium–carboxylate interactions, demonstrating the propensity of these species to form complex hydrogen bonding networks.
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bis Amidinium calixarenes templates for self assembled receptors
Tetrahedron Letters, 1998Co-Authors: Philip A GaleAbstract:The synthesis of two bis-Amidinium calixarenes 3 and 4 has been achieved. Compounds 3 and 4 self-assemble with carboxylate salts via Amidinium-carboxylate salt bridges producing ditopic receptor species.
Eiji Yashima - One of the best experts on this subject based on the ideXlab platform.
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Cobalt(II)-Salen-Linked Complementary Double-Stranded Helical Catalysts for Asymmetric Nitro-Aldol Reaction
2016Co-Authors: Daisuke Taura, Shogo Hioki, Junki Tanabe, Naoki Ousaka, Eiji YashimaAbstract:Double-helical, bimetallic chiral Co(II)-salen complexes stabilized by chiral Amidinium–carboxylate salt bridges efficiently catalyzed the asymmetric nitro-aldol (Henry) reaction, producing products with up to an 89% enantiomeric excess (ee); the reactivity and enantioselectivity were higher than those catalyzed by the corresponding single strands. The key role of the chiral double-helical framework for the supramolecular bimetallic catalysis has been revealed by a double-helical catalyst carrying achiral Co(II)-salen units that promoted the Henry reaction, yielding the product with a 50%–45% ee, while the corresponding single strands showed poor or no enantioselectivity
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synthesis of helically twisted 1 1 macrocycles assisted by Amidinium carboxylate salt bridges and control of their chiroptical properties
Organic and Biomolecular Chemistry, 2013Co-Authors: Yuji Nakatani, Yoshio Furusho, Eiji YashimaAbstract:A series of optically active, helically twisted [1 + 1]macrocycles connected via o-, m-, and p-linkages (o-2, m-2, and p-2) was prepared from the corresponding linear duplexes stabilized by complementary Amidinium–carboxylate salt bridges bearing two arms with terminal vinyl groups at both ends through the ring-closing metathesis reaction in the good yields of 67, 92, and 96%, respectively. The chiroptical properties of the macrocycles were dependent on the linker geometries and could be controlled by acid–base interactions and zinc coordination, the changes in which were detected by their CD and absorption spectral changes and fluorescence colors.
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chiral amplification in double stranded helical polymers through chiral and achiral Amidinium carboxylate salt bridges
Polymer Journal, 2012Co-Authors: Wataru Makiguchi, Yoshio Furusho, Shinzo Kobayashi, Eiji YashimaAbstract:A series of m-terphenyl-based random copolymers of chiral and achiral amidines, and their complementary homopolymers of achiral carboxylic acids were prepared by the copolymerization of a p-diiodobenzene derivative, with the diethynyl monomers containing a chiral or achiral amidine group and a carboxyl group using the Sonogashira coupling reaction. The obtained chiral/achiral amidine copolymers assembled into a double-stranded helical structure upon complexation with the complementary achiral homopolymer of carboxylic acids through interstrand Amidinium−carboxylate salt bridges. The complexes exhibited characteristic induced cotton effects in the π-conjugated main-chain chromophore regions, indicating that the interstrand duplexes possess a preferred-handed double-helical structure. The effect of the chiral and achiral amidine contents on the amplification of the helical chirality (‘the sergeants and soldiers effect’) during the interstrand double-helix formation was investigated by comparing the cotton effect patterns and intensities of the duplexes with those of the corresponding all-chiral amidine-based double-helical polymer. m-Terphenyl-based random copolymers of chiral and achiral amidines and its complementary homopolymer of achiral carboxylic acids self-assembled to form complementary double helices with a preferred-handed helical sense via interstrand Amidinium–carboxylate salt bridges, thus showing induced cotton effects in the π-conjugated main-chain chromophore regions. A unique amplification of the helical chirality (‘the sergeants and soldiers effect’) was, for the first time, observed during the double-helix formation.
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Amidinium carboxylate salt bridges as a recognition motif for mechanically interlocked molecules synthesis of an optically active 2 catenane and control of its structure
Angewandte Chemie, 2010Co-Authors: Yuji Nakatani, Yoshio Furusho, Eiji YashimaAbstract:Journal Club 2010.07.22 Eri Nishiyama Amidinium Carboxylate Salt Bridges as a Recognition Motif for Mechanically Interlocked Molecules: Synthesis of an Optically Active [2]Catenane and Control of Its Structure Yuji Nakatani, Yoshio Furusho*, Eiji Yashima* Angew. Chem. Int. Ed. Early view DOI: 10.1002/anie.201002382
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double helix to double helix transformation using platinum ii acetylide complexes as surrogate linkers
Organic Letters, 2006Co-Authors: Yoshio Furusho, Yoshie Tanaka, Eiji YashimaAbstract:We describe novel optically active double helices consisting of complementary strands stabilized by Amidinium-carboxylate salt bridges. The m-terphenyl groups of each strand are joined by trans-Pt(II) acetylide complexes with pendant PPh(3) ligands as the surrogate linker, which converts to cis counterparts by a ligand exchange reaction with cis-1,2-bis(diphenylphosphino)ethylene, resulting in the formation of double helices with different structures. Subsequent iodine-promoted reductive elimination on the Pt(II) atoms generates the fully organic, enantiomerically pure double helices. [structure: see text]