Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Imines

  • boc imine
  • corresponding imine
  • cyclic imine
  • ethylene imine
  • propylene imine

  • Terms modified by Imines

  • imine bond
  • imine derivative
  • imine formation
  • imine ligand
  • imine n atom
  • imine nitrogen
  • imine substrate

  • Selected Abstracts

    Enantioselective Organocatalytic Synthesis of Arylglycines via Friedel,Crafts Alkylation of Arenes with a Glyoxylate Imine

    Dieter Enders
    Abstract The enantioselective organocatalytic synthesis of arylglycines has been developed employing 1,mol% of an enantiopure N -triflyl phosphoramide Brønsted acid as organocatalyst. Various differently substituted phenylglycine derivatives can be synthesized in good to excellent yields and enantiomeric excesses based on a Friedel,Crafts alkylation of electron-rich arenes with a glyoxylate imine. A novel protocol for the deprotection of the N - tert -butylsulfonyl (Bus) group has also been developed. [source]

    Hydrosilylation of Ketone and Imine over Poly-N-Heterocyclic Carbene Particles

    MeiXuan Tan
    Abstract N-Heterocyclic carbene (NHC)-catalyzed ketone/imine hydrosilylation, silane alcohol condensation and asymmetric ketone hydrosilylation reactions were demonstrated for the first time over solid, main-chain poly-NHC particles. The stable and robust poly-NHC particles were easily recovered, and exhibited good catalytic recyclability. A novel chiral induction protocol with a cheap and easily accessible secondary alcohol as the chiral source was also developed in this catalytic system. [source]

    Synthesis and characterization of imine-coupled polyphenols containing carbazole units

    smet Kaya
    Abstract Imine coupled phenolic monomers containing carbazole unit were synthesized in four steps. The monomers were polymerized via oxidative polycondensation by air as oxidant in an aqueous alkaline medium at 50°C. The structures of compounds were confirmed by ultraviolet,visible (UV,vis), Fourier transform infrared, and 1H- and 13C-NMR techniques. The conductivity measurements of these polymers were made by the four-point probe technique and iodine was used as doping agent. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electrochemical and optical band gap values were calculated by the results of the UV,vis and the cyclic voltammetry measurement, respectively. The number-average molecular weight, weight-average molecular weight, and polydispersity index values were determined by the size exclusion chromatography technique. Also, thermal behavior of these polymers was determined by thermogravimetric/differential thermal analysis measurements in a N2 atmosphere between 20 and 1000°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Frustrierte Lewis-Paare: metallfreie Wasserstoffaktivierung und mehr

    ANGEWANDTE CHEMIE, Issue 1 2010
    Abstract Die Kombination sterisch gehinderter Lewis-Säuren und -Basen führt nicht zur üblichen Neutralisationsreaktion unter Bildung der "klassischen" Lewis-Säure/Base-Addukte. Stattdessen stehen die Lewis-Acidität und -Basizität solcher "frustrierten Lewis-Paare" (FLPs) gemeinsam für die Durchführung ungewöhnlicher Reaktionen zur Verfügung. Typische Beispiele für FLPs bestehen aus inter- und intramolekularen Kombinationen sperriger Phosphine und Amine mit stark elektrophilen RB(C6F5)2 -Komponenten. Viele frustrierte Lewis-Paare sind in der Lage, Wasserstoff heterolytisch zu spalten. Die resultierenden H+/H, -Paare (z.,B. stabilisiert in Form der entsprechenden Phosphonium-Kation/Hydridoborat-Anion-Salze) fungieren als metallfreie Katalysatoren für die Hydrierung sperriger Imine, Enamine, Enolether usw. FLPs reagieren auch mit Alkenen, Carbonylverbindungen und einer Vielzahl anderer kleiner Moleküle, darunter auch Kohlendioxid, in vermutlich kooperativen Dreikomponentenreaktionen. Auf dieser Beobachtung lassen sich neue Synthesestrategien aufbauen. [source]

    Enantioselective Total Synthesis of the Marine Toxin (,)-Gymnodimine Employing a Barbier-Type Macrocyclization,

    ANGEWANDTE CHEMIE, Issue 40 2009
    Ke Kong
    Exoten des Meeres: tert -Butyllithium vermittelt bei Umgebungstemperatur eine Barbier-Makrocyclisierung in der ersten Totalsynthese von (,)-Gymnodimin (Ts: Toluol-4-sulfonyl; TBS: tert -Butyldimethylsilyl), einem marinen Toxin aus der Familie der spirocyclischen Imine. Die Synthese enthält außerdem eine vinyloge Mukaiyama-Aldolreaktion zur Kupplung der labilen Butenolidgruppe an eine makrocyclische Keton-Zwischenstufe. [source]

    Catalytic Asymmetric Mannich Reactions of Sulfonylacetates,

    ANGEWANDTE CHEMIE, Issue 31 2009
    Carlo Cassani
    Sulfon gegen Sulfon: Arylsulfonylacetate sind Syntheseäquivalente für eine Vielzahl an ,-Carboxylatanionen. Durch Phasentransferkatalyse (PTC) gelangen ihre milde Deprotonierung und die katalytische asymmetrische Addition an hochreaktive, in,situ aus ,-Amidosulfonen erzeugte Imine (siehe Schema; Pg=Schutzgruppe). Die Nützlichkeit der Produkte in der Synthese wurde mit ihrer einfachen Überführung in eine Reihe von ,-Aminosäurederivate gezeigt. [source]

    ChemInform Abstract: Carbon,Carbon Bond Formations at the Benzylic Positions of N-Benzylxanthone Imines and N-Benzyldi-1-naphthyl Ketone Imine.

    CHEMINFORM, Issue 44 2009
    Takashi Niwa
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Rhodium-Catalyzed Diastereoselective 1,2-Addition of Arylboronic Acids to Chiral Trifluoroethyl Imine.

    CHEMINFORM, Issue 29 2009
    Vouy Linh Truong
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    KCN-Catalyzed C,C Bond Formation Between Imine and gem-Difluoroalkene Moieties: A Facile Synthesis of 2,4-Disubstituted 3-Fluoroquinolines (II).

    CHEMINFORM, Issue 41 2004
    Takashi Mori
    No abstract is available for this article. [source]

    A Novel Three-Component Reaction Catalyzed by Dirhodium(II) Acetate: Decomposition of Phenyldiazoacetate with Arylamine and Imine for Highly Diastereoselective Synthesis of 1,2-Diamines.

    CHEMINFORM, Issue 7 2004
    Yuanhua Wang
    No abstract is available for this article. [source]

    Synthesis of Chiral Phosphorus Reagents and Their Catalytic Activity in Asymmetric Borane Reduction of N-Phenyl Imine of Acetophenone.

    CHEMINFORM, Issue 51 2003
    Kangying Li
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Enzymatic Introduction of Cyanide into Imine for Constructing Optically Active Compound by (R)-Oxy-nitrilase in Almond Meal.

    CHEMINFORM, Issue 12 2003
    Teckheon Lee
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    ChemInform Abstract: Nucleophilic Reactions with ,-Trifluoromethyl Imine and N,O-Disubstituted Aminal: Synthesis of ,-Trifluoromethyl ,-Anilino Esters.

    CHEMINFORM, Issue 20 2002
    Yuefa Gong
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Electric-Field Triggered Controlled Release of Bioactive Volatiles from Imine-Based Liquid Crystalline Phases

    Andreas Herrmann Dr.
    Abstract Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N -(4-methoxybenzylidene)-4-butylaniline (MBBA, 1), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine-based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal. [source]

    Electrochemical, Chemical and Enzymatic Oxidations of Phenothiazines

    ELECTROANALYSIS, Issue 17 2005
    B. Blankert
    Abstract The oxidation of several phenothiazine drugs (phenothiazine, promethazine hydrochloride, promazine hydrochloride, trimeprazine hydrochloride and ethopropazine hydrochloride) has been carried out in aqueous acidic media by electrochemical, chemical and enzymatic methods. The chemical oxidation was performed in acetic acid with hydrogen peroxide or in formate buffers using persulfate. The enzymatic oxidation was performed in acetate or ammonium formate buffer by the enzyme horseradish peroxidase in the presence of H2O2. Molecules with, in the lateral chain, two carbon atoms (2C) separating the ring nitrogen and the terminal nitrogen, showed two parallel oxidation pathways, that is (i) formation of the corresponding sulfoxide and (ii) cleavage of the lateral chain with liberation of phenothiazine (PHZ) oxidized products (PHZ sulfoxide and PHZ quinone imine). Molecules with three carbon atoms (3C) separating the two nitrogens were oxidized to the corresponding sulfoxide. The chemical oxidation of all the studied molecules by hydrogen peroxide resulted in the corresponding sulfoxide with no break of the lateral chain. Oxidation by persulfate yielded, for the 3C derivatives, only the corresponding sulfoxide, but it produced cleavage of the lateral chain for the 2C derivatives. The origin of the distinct oxidation pattern between 2C and 3C molecules might be related to steric effects due to the lateral chain. The data are of interest in drug metabolism studies, especially for the early search. In the case of 2C phenothiazines, the results predict the possibility of an in vivo cleavage of the lateral chain with liberation of phenothiazine oxidized products which are known to produce several adverse side effects. [source]

    The Role of Amine,B(C6F5)3 Adducts in the Catalytic Reduction of Imines with H2: A Computational Study

    Timofei Privalov
    Abstract This study thoroughly examines the potential energy surfaces (PESs) of two possible mechanisms for reduction of imines by B(C6F5)3 and H2. The key reaction steps of the first catalytic mechanism, which is the focus of our study, are: (i) the uptake of H2 by a thermally activated amine,B(C6F5)3 species; (ii) proton transfer from the NH2+ moiety of [RNH2CH2R,]+[HB(C6F5)3], to the imine; (iii) nucleophillic attack of the C-center of the iminium ion by the BH, group. The potential energy barriers of the latter, as determined by calculating the evolution of the H-bonded complex of an imine and [RNH2CH2R,]+[HB(C6F5)3], in toluene, are around 10 kcal,mol,1 each. In the second mechanism, only imines serve as basic partners of B(C6F5)3 in the H2 activation, which affords an [RN(H)CHR,]+[HB(C6F5)3], ion pair; direct reduction then proceeds via nucleophilic attack of the C-center by the BH, in [RN(H)CHR,]+[HB(C6F5)3],. This route becomes catalytic when the product amine is released into the solvent and B(C6F5)3 is re-used for H2 activation. Upon taking into account the association energy of an amine,B(C6F5)3 adduct [,9.5 kcal,mol,1 for tBuN(H)CH2Ph and B(C6F5)3 in toluene], the potential energy barrier for H2 uptake by an imine and B(C6F5)3 increases to 14.5 kcal,mol,1. We report a somewhat lower potential energy barrier for H2 uptake by thermally activated amine,B(C6F5)3 adducts [12.7 kcal,mol,1 for the B-N adduct of tBuN(H)CH2Ph and B(C6F5)3 in toluene], although the difference between the two H2 activationbarriers is within the expected error of the computational method. Two catalytic routes are compared based on B3LYP-computed PESs in solvent (toluene).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Pseudo-Octahedral Schiff Base Nickel(II) Complexes: Does Single Oxidation Always Lead to the Nickel(III) Valence Tautomer?

    Olaf Rotthaus
    Abstract With the aim of establishing correlations between the ligand structure and the oxidation site in nickel complexes from Schiff base ligands, five ligands and their nickel complexes have been synthesized. The prototypical asymmetric Schiff base ligand HL1 contains both phenol and pyridine pendant arms with a pivotal imine nitrogen atom. Ligands HL2,5 differ from HL1 by either their phenolate para substituent, the hybridization of the pivotal nitrogen atom, and/or the N-donor properties of the pyridine moiety. The five complexes [Ni(L1,5)2] are obtained by treating the corresponding ligands with 0.5 equiv. of Ni(OAc)2·4H2O in the presence of NEt3. X-ray crystal-structure diffraction studies as well as DFT calculations reveal that [Ni(L1,5)2] involves a high-spin nickel(II) ion within a pseudo-octahedral geometry. The two ligands are arranged in a meridional fashion when the pivotal nitrogen atom is an imine {as in [Ni(L1,2)2] and [Ni(L4,5)2]}, while the fac isomer is preferred in [Ni(L3)2] (amino pivotal nitrogen atom). [Ni(L1)2] is characterized by an oxidation potential at ,0.17 V vs. Fc+/Fc. The one-electron-oxidized species [Ni(L1)2]+ exhibits an EPR signal at g = 2.21 attributed to a phenoxyl radical that is antiferromagnetically coupled to a high-spin NiII ion. [Ni(L2)2] differs from [Ni(L1)2] by the phenolate para substituent (a tert -butyl instead of the methoxyl group) and exhibits an oxidation potential that is ca. 0.16 V higher. Compared to [Ni(L1)2]+ the cation [Ni(L2)2]+ exhibits a SOMO that is more localized on the metal atom. The EPR and electrochemical signatures of [Ni(L3)2]+ are similar to those of [Ni(L1)2]+, thus showing that an imino to amino substitution compensates for a methoxy to tert -butyl one. Replacement of the pyridine by a quinoline group in [Ni(L4,5)2] makes the complexes slightly harder to oxidize. The EPR signatures of the cations [Ni(L4,5)2]+ are roughly similar to those of the pyridine analogs [Ni(L1,2)2]+. The oxidation site is thus not significantly affected by changes in the N-donor properties of the terminal imino nitrogen atom.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Alcohols for the ,-Alkylation of Methyl Ketones and Indirect Aza-Wittig Reaction Promoted by Nickel Nanoparticles,

    Francisco Alonso
    Abstract Nickel nanoparticles have been found to activate primary alcohols used for the ,-alkylation of ketones or in indirect aza-Wittig reactions. These processes involve hydrogen transfer from the alcohol to the intermediate ,,,-unsaturated ketone or imine, respectively. All these reactions are carried out in the absence of any ligand, hydrogen acceptor or base under mild reaction conditions. For the first time nickel is employed as a potential alternative to noble-metal-based catalysts in both reactions. A reaction mechanism is proposed on the basis of some deuteration experiments. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Synthesis of (R)-(,)-2-Fluoronorapomorphine , A Precursor for the Synthesis of (R)-(,)-2-Fluoro- N -[11C]propylnorapomorphine for Evaluation as a Dopamine D2 Agonist Ligand for PET Investigations

    Kåre Søndergaard
    Abstract 2-Fluoronorapomorphine, the PET labelling precursor to 2-fluoro- N -[11C]propylnorapomorphine, was prepared in 13 steps from codeine in a total yield of 10,%. Codeine was converted in four steps into N -benzylnorcodeine which was oxidised by using the Swern protocol. Subsequent acid-catalysed rearrangement afforded N -benzylnormorphothebaine which was selectively triflylated at the 2-position and pivaloylated at the 11-position. The triflate underwent palladium-catalysed amination with benzophenone imine. Amination conditions required sequential base addition to give substantial conversion of the triflate to the corresponding N -substituted benzophenone imine. After acidic hydrolysis the resulting aniline was transformed into the 2-fluoro compound via the Balz,Schiemann reaction. Hydrogenolysis of the N -benzyl group followed by deprotection of the catechol moiety using BBr3 provided 2-fluoronorapomorphine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    PY181 Pigment Microspheres of Nanoplates Synthesized via Polymer-Induced Liquid Precursors

    Yurong Ma
    Abstract Organic pigments are important crystalline substances, and their properties and applications rely on size and shape control. Pigment Yellow 181 (PY181) is an industrial azo pigment that is light and weatherfast and suitable for high temperature processing. One disadvantage is its needle-like shape in the default , -phase, which makes the pigment difficult to process in industry, e.g., in polymer melts, where a spherical structure would be ideal. Here, we show for the first time, that polymer-induced liquid precursor structures can be formed even in association to a chemical reaction. Furthermore, it is demonstrated that biomineralization principles can be exploited for the generation of advanced functional materials, such as pigments with novel complex morphology and different properties. Stable PY181 microspheres of nanoplates in the , -phase were obtained in mixed solvents of water and isopropanol by direct azo coupling under the directing influence of a designed copolymer additive aminobenzoylaminobenzamide-acetoacetyl-poly(ethylene imine)- block -poly(ethylene glycol) (ABABA-acetoacetyl-PEI- b -PEG). [source]

    Selective mitochondrial glutathione depletion by ethanol enhances acetaminophen toxicity in rat liver

    HEPATOLOGY, Issue 2 2002
    Ping Zhao
    Chronic alcohol consumption may potentiate acetaminophen (APAP) hepatotoxicity through enhanced formation of N -acetyl- p -benzoquinone imine (NAPQI) via induction of cytochrome P450 2E1 (CYP2E1). However, CYP2E1 induction appears to be insufficient to explain the claimed magnitude of the interaction. We assessed the role of selective depletion of liver mitochondrial glutathione (GSH) by chronic ethanol. Rats were fed the Lieber-DeCarli diet for 10 days or 6 weeks. APAP toxicity in liver slices (% glutathione- S -transferase , released to the medium, GST release) and NAPQI toxicity in isolated liver mitochondria (succinate dehydrogenase inactivation, SDH) from these rats were compared with pair-fed controls. Ethanol induced CYP2E1 in both the 10-day and 6-week groups by ,2-fold. APAP toxicity in liver slices was higher in the 6-week ethanol group than the 10-day ethanol group. Partial inhibition of NAPQI formation by CYP2E1 inhibitor diethyldithiocarbamate to that of pair-fed controls abolished APAP toxicity in the 10-day ethanol group only. Ethanol selectively depleted liver mitochondrial GSH only in the 6-week group (by 52%) without altering cytosolic GSH. Significantly greater GSH loss and APAP covalent binding were observed in liver slice mitochondria of the 6-week ethanol group. Isolated mitochondria of the 6-week ethanol group were ,50% more susceptible to NAPQI (25-165 ,mol/L) induced SDH inactivation. This increased susceptibility was reproduced in pair-fed control mitochondria pretreated with diethylmaleate. In conclusion, 10-day ethanol feeding enhances APAP toxicity through CYP2E1 induction, whereas 6-week ethanol feeding potentiates APAP hepatotoxicity by inducing CYP2E1 and selectively depleting mitochondrial GSH. [source]

    Synthesis, characterization and thermal behavior of some Zn(II) complexes with ligands having 1,3,4-thiadiazole moieties

    Nevin Turan
    Some new zinc(II) complexes of the type [Zn(L1)2(C2H5OH)2]·C2H5OH, [Zn(L2)2 Cl2]·H2O, and [Zn2(L3)2(H2O)4Cl4], where HL1 = N-[5,-amino-2, 2,-bis(1,3,4-thiadiazole)-5-yl]-2-hydroxybenzaldehyde imine, L2 = N-(5-ethyl-1,3,4-thiadiazole-2-yl)tereph- thalaldehyde imine, and L3 = N,N,-bis[5-(4-nitro phenyl)-1,3,4-thiadiazole-2-yl]terephthalaldehydedii- mine have been synthesized and characterized by IR, 1H NMR spectra, elemental analyses, magnetic susceptibility, UV,vis. and thermogravimetry-differential thermal analysis (TGA-DTA). On the basis of electronic spectral studies, an octahedral environment around the Zn(II) ion has been suggested. 1H NMR spectra of the metal complexes of ligands were found to be in agreement with the proposed stoichiometry. The presence of water molecules and ethanol in the Zn(II) complexes is also indicated by the thermal studies. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:14,23, 2010; Published online in Wiley InterScience ( DOI 10.1002/hc.20572 [source]

    Covalent Attachment of Low Molecular Weight Poly(ethylene imine) Improves Tat Peptide Mediated Gene Delivery,

    ADVANCED MATERIALS, Issue 16 2006
    F. Alexis
    A polymer-peptide hybrid biomaterial synthesized by coupling poly(ethylene imine) directly to resin-supported Tat peptide takes advantage of the unique features associated with the two original cationic materials and functions as a novel gene-delivery vector with good biocompatibility. The figure shows cells transfected with green fluorescent protein (GFP) using complexes of the polymer-peptide hybrid and GFP (scale bar: 100,,m). [source]

    Enantioselective Organocatalytic Synthesis of Arylglycines via Friedel,Crafts Alkylation of Arenes with a Glyoxylate Imine

    Dieter Enders
    Abstract The enantioselective organocatalytic synthesis of arylglycines has been developed employing 1,mol% of an enantiopure N -triflyl phosphoramide Brønsted acid as organocatalyst. Various differently substituted phenylglycine derivatives can be synthesized in good to excellent yields and enantiomeric excesses based on a Friedel,Crafts alkylation of electron-rich arenes with a glyoxylate imine. A novel protocol for the deprotection of the N - tert -butylsulfonyl (Bus) group has also been developed. [source]

    Intramolecular hydrogen bond in 3-imino-propenylamine isomers: AIM and NBO studies

    H. Raissi
    Abstract The molecular structure and intramolecular hydrogen bond energy of 18 conformers of 3-imino-propenyl-amine were investigated at MP2 and B3LYP levels of theory using the standard 6-311++G** basis set. The atom in molecules or AIM theory of Bader, which is based on the topological properties of the electron density (,), was used additionally and the natural bond orbital (NBO) analysis was also carried out. Furthermore calculations for all possible conformations of 3-imino-propenyl-amin in water solution were also carried out at B3LYP/6-311++G** and MP2/6-311++G** levels of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the imine,amine conformers of this compound are more stable than the other conformers. B3LYP method predicts the IMA-1 as global minimum. This stability is mainly due to the formation of a strong NH···N intramolecular hydrogen bond, which is assisted by ,-electrons resonance, and this ,-electrons are established by NH2 functional group. Hydrogen bond energies for all conformers of 3-imino-propenyl-amine were obtained from the related rotamers methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    Quantum chemical study of penicillin: Reactions after acylation

    Rui Li
    Abstract The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ,-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ,-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ,-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

    Well-Defined Regioselective Iminopyridine Rhodium Catalysts for Anti-Markovnikov Addition of Aromatic Primary Amines to 1-Octyne

    Carlos Alonso-Moreno
    Abstract A series of cationic rhodium(I) complexes of the type [Rh(N-N)(COD)][BPh4], containing the following iminopyridine-based bidentate nitrogen donor ligands (N-N): 2,6-diisopropyl- N -[1-(pyridin-2-yl)ethylidene]aniline (dipea, 1), 2,6-dimethyl- N -[1-(pyridin-2-yl)ethylidene]aniline (dmpea, 2), 2,4,6-trimethyl- N -[1-(pyridin-2-yl)ethylidene]aniline (tmpea, 3) and 2,6-diisopropyl- N -[1-(4-methylpyridin-2-yl)ethylidene]aniline] (dipmpea, 4), were synthesized and fully characterized. The intermolecular hydroamination of a terminal alkyne, such as 1-octyne, with primary aromatic amines in the presence of these cationic rhodium(I) catalysts occurred in an anti-Markovnikov fashion. The rhodium complexes catalyzed the regioselective formation of the E- isomer of the corresponding imine, without the formation of the Z -isomer or the Markovnikov product. These compounds are also presented as efficient regioselective catalysts for the hydroamination of anilines in the presence of air and/or water. [source]

    Immobilisation of the Pyrphos Ligand on Soluble Hyperbranched Supports and Use in Rhodium-Catalysed Hydrogenation in Ionic Liquids

    Abstract The immobilisation of the pyrphos ligand has been extended from highly symmetric dendrimers to less regular structured hyperbranched poly(ethylene imines). Cationic dendritic pyrphos-rhodium(norbornadiene) [pyrphos-Rh(NBD)] complexes have been synthesised using poly(propylene imine) (PPI) and poly(amido amine) (PAMAM) dendrimers as supports bearing between 4 and 64 potential catalytically active sites at their periphery as well as pyrphos-Rh(NBD) complexes tethered to hyperbranched poly(ethylene imines) carrying on average 9 to 139 functionalities located throughout the whole supporting structure. These immobilised systems have been used as catalysts for the hydrogenation of Z -methyl ,-acetamidocinnamate. With the PPI, PAMAM, and hyperbranched poly(ethylene imine)-bound pyrphos-Rh(NBD) omplexes as catalysts, hydrogenations were carried out in methanol, and a decrease in activity and selectivity was observed with increasing size of the macromolecular support. Furthermore, the polycationic catalysts were tested in a liquid/liquid-biphasic system consisting of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate {[BMIM] [BF4]} and isopropyl alcohol. Using the PPI-, PAMAM-, and PEI-immobilised systems, a strong negative "dendritic effect" with increasing molecular size was observed with respect to the catalytic activity, the stereoinduction, and the recyclability. The PPI-bound rhodium(I)-complexes of generations one and two showed good reusability; even after triple recycling, with no loss of activity or selectivity being noted. It has been demonstrated that in this case the catalytic behaviour of hyperbranched systems is essentially similar to that of the related dendritic model system. [source]

    Immobilisation of the BINAP Ligand on Dendrimers and Hyperbranched Polymers: Dependence of the Catalytic Properties on the Linker Unit

    Abstract A series of immobilised Carbo-BINAP ligands has been synthesised using poly(propylene imine) (PPI) dendrimers as soluble supports. They contain up to 64 BINAP ligands at their periphery without an additional linking unit. Despite the high steric requirements of the ligand, all dendrimers could be completely functionalised, resulting in the immobilised systems in good yields. Furthermore, the immobilisation strategy that worked out for the fixation of AMINAP ligands with additional linking units as well as of Carbo-BINAP ligands without additional linking units on dendrimers has thus been extended to less regularly hyperbranched poly(ethylene imines) (PEI) as soluble supports. In that way it has been possible to attach on average 9, 26, and 138 Glutaroyl-AMINAP or Carbo-BINAP ligands to PEIs of different molecular weights. The catalytic properties of these systems in the copper-catalysed hydrosilylation of acetophenone were investigated. The dendritic PPI-bound Carbo-BINAP ligands displayed a strong dependence of enantioselectivity and activity on the generation of the dendrimer. For the Carbo-BINAP and Glutaroyl-AMINAP ligands immobilised on the hyperbranched polymers, however, activities and enantioselectivities comparable to those of the mononuclear catalysts were found. The macromolecular, immobilised BINAP ligands could be recycled several times without any observable loss of activity or enantioselectivity. [source]

    Hybrid Inorganic-Organic Materials Carrying Tertiary Amine and Thiourea Residues Tethered on Mesoporous Silica Nanoparticles: Synthesis, Characterization, and Co-Operative Catalysis

    Alessandra Puglisi
    Abstract Mesoporous silica nanoparticles carrying different loadings of tertiary amine and thiourea residues (residues ratios 53/47, 68/32, and 22/78, respectively) were synthesized by the co-condensation method and fully characterized by CP MAS NMR, powder XRD, SEM, BET, BJH and FT-IR techniques. These materials were tested as bifunctional catalysts in the conjugate addition of acetylacetone to 2-nitrostyrene, a reaction that under solvent-free conditions occurred in quantitative yield. By carrying out several experiments with the bifunctional catalysts featuring different molar ratios of active sites, and with different combinations of monofunctional supported and non-supported catalyst, the co-operativity of the tertiary amine and thiourea residues in catalyzing the reaction was demonstrated. The use of the bifunctional catalyst was extended to the addition of acetylacetone to an activated imine. Catalyst recycling for a total of three reaction cycles was demonstrated without significant erosion of activity. [source]