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Heterocyclic Carbene (heterocyclic + carbene)
Selected AbstractsAdducts of Aluminum and Gallium Trichloride with a N -Heterocyclic Carbene and an Adduct of Aluminum Trichloride with a ThioneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2004Andreas Stasch Abstract The reactions of AlCl3 and GaCl3 with 1,3,4,5-tetramethylimidazole-2-ylidene in toluene at room temperature affords the 1:1 adducts 5 and 6, respectively. The use of a bulky N -heterocyclic carbene (NHC) in toluene/THF and AlCl3 results in the formation of an imidazolium salt 7 with the tetrachloroaluminate anion. A 1:1 adduct 8 of 1,3,4,5-tetramethylimidazole-2(3H)-thione with AlCl3 is obtained in toluene. The crystal structures of 5·0.5C7H8, 7·THF and 8 were determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Rh(I) and Pd(II) complexes of methoxy functionalized heterocyclic carbene: Synthesis and characterizationCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2006M. E. Günay Abstract A new methoxy functionalized 2-(trichloromethyl)-1,3-diarylimidazolidin (6) was synthesized as the precursor for N-heterocyclic carbene complexes of Pd(II) and Rh(I) by the condensation of N,N'-bis(2,4-dimethoxyphenyl)-1,2-diaminoethane with chloral. The structures of all compounds have been elucidated by a combination of multinuclear NMR spectroscopy, elemental analysis and in one instance, by single crystal X-ray diffraction. Compound 8, C27H34N2O4ClRh, crystallizes in the triclinic space group P-1 with cell dimensions a = 9.7642(12)Å, b = 11.1914(11)Å, c = 13.0102(14)Å, , = 104.034(9)°, , = 106.658(9)°, , = 99.658(9)° with Z = 2. The molecular structure of 8 shows the geometry around the Rh metal to be a slightly distorted square planar. The crystal structure shows the formation of centrosymmetric dimers via intermolecular C-H...Cl hydrogen bonds. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reactions of the Aluminum(I) Monomer LAl [L = HC{(CMe)(NAr)}2; Ar = 2,6- iPr2C6H3] with Imidazol-2-ylidene and Diphenyldiazomethane.EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2004A Hydrogen Transfer from the L Ligand to the Central Aluminum Atom, Formation of the Diiminylaluminum Compound LAl(N=CPh2) Abstract The solid-state reaction of LAl and imidazol-2-ylidene at elevated temperature (120 °C) yielded the aluminum monohydride N -heterocyclic carbene adduct [{HC[C(CH2)NAr] (CMeNAr)}AlH-{CN(R)C2Me2N(R)}] [R = iPr (1), Me (2)]. Compounds 1 and 2 have been characterized by spectroscopic (IR, and 1H and 13C NMR), mass spectrometric, and elemental analyses, and 1 was further characterized by X-ray structural analysis. These experimental data indicate that the Al,H bond is formed by hydrogen migration from one of the methyl groups of the ,-diketiminato ligand backbone. The reaction of LAl with two equivalents of diphenyldiazomethane afforded the diiminylaluminum compound LAl(N=CPh2)2 (3), while an excess of diphenyldiazomethane resulted in the formation of Ph2C=N,N=CPh2. This suggests that Ph2C=N,N=CPh2 is initially generated and then reacts further by oxidative addition to yield 3. The X-ray structural analysis reveals that compound 3 contains the shortest Al,Niminyl bond among those with a four-coordinate aluminum center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Adducts of Aluminum and Gallium Trichloride with a N -Heterocyclic Carbene and an Adduct of Aluminum Trichloride with a ThioneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2004Andreas Stasch Abstract The reactions of AlCl3 and GaCl3 with 1,3,4,5-tetramethylimidazole-2-ylidene in toluene at room temperature affords the 1:1 adducts 5 and 6, respectively. The use of a bulky N -heterocyclic carbene (NHC) in toluene/THF and AlCl3 results in the formation of an imidazolium salt 7 with the tetrachloroaluminate anion. A 1:1 adduct 8 of 1,3,4,5-tetramethylimidazole-2(3H)-thione with AlCl3 is obtained in toluene. The crystal structures of 5·0.5C7H8, 7·THF and 8 were determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Sulfonated N -Heterocyclic Carbenes for Pd-Catalyzed Sonogashira and Suzuki,Miyaura Coupling in Aqueous SolventsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Sutapa Roy Abstract The reactions of the N,N, -diarylimidazolium and N,N, -diarylimidazolinium salts with chlorosulfonic acid result in the formation of the respective disulfonated N -heterocyclic carbene (NHC) precursors in reasonable yields (46,77%). Water-soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na2PdCl4) and potassium hydroxide (KOH) in water, were successfully applied in the copper-free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2,mol% catalyst loading. The preformed (disulfonatedNHC)PdCl(cinnamyl) complex was used in aqueous Suzuki,Miyaura reactions at 0.1,mol% catalyst loading. The coupling protocol reported here is very useful for Sonogashira reactions of N - and S -heterocyclic aryl bromides and chlorides with aryl- and alkylacetylenes. [source] Rapid Screening of New Polymer-Supported Palladium (II) Bis(3,4,5,6-tetrahydropyrimidin-2-ylidenes),MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2004Monika Mayr Abstract Summary: The synthesis of two 1,3-diaryl-3,4,5,6-tetrahydropyrimidin-2-ylidene-based N -heterocyclic carbene- (NHC) derived palladium complexes, Pd(5-hydroxy-1,3-bis-(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (Ag2Br2Cl4) (10) and Pd(5-(bicyclo[2.2.1]hept-5-ene-2-carbonyloxy)-1,3-bis-(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (Ag2Br2Cl4) (11) is described. 10 was supported on a PS-DVB and a Wang resin, respectively, to yield catalysts 12 and 13, while 11 was used for the synthesis of a ring-opening metathesis precipitation polymerization-derived support 14. All supports were tested for their activity in Heck-type reactions using a combinatorial approach. Structure of polymer supported Pd-catalysts. [source] A facile route to ruthenium,carbene complexes and their application in furfural hydrogenationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2010Zea Strassberger Abstract A number of new N -heterocyclic carbene (NHC) ligands were synthesized via a multicomponent reaction, wherein an aldehyde or ketone, a primary amine and an ,-acidic isocyanide were reacted, giving the corresponding 2H -2-imidazolines. These were easily alkylated with an alkyl halide at position N-3, yielding the final NHC precursors, that were then complexed with Ru in situ. The resulting complexes are shown to be active and selective catalysts for the transfer hydrogenation of furfural to furfurol, using isopropanol as the hydrogen source. Importantly, the carbene ligand remains coordinated to the ruthenium center throughout the reaction. Copyright © 2009 John Wiley & Sons, Ltd. [source] Palladium(0) pre-catalysts with heteroditopic NHC,amine ligands by transmetallation from their silver(I) complexesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2009Stefan Warsink Abstract The synthesis of an air-stable series of Pd0 complexes with dissymmetric bidentate N -heterocyclic carbene,amine ligands has been performed. The key step is an unprecedented carbene transfer from AgI to obtain electron-rich zero-valent palladium precatalysts. The coordination behavior of the ligands was determined with X-ray crystallography. Surprising results were obtained in the catalysis of transfer semi-hydrogenation, where the addition of base appeared not to be necessary to obtain the desired product stereoselectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Asymmetric transfer hydrogenation catalyzed by a novel planar chiral N -heterocyclic carbene,rhodium(I) complexAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2009Ru Jiang Abstract A novel chelated ferrocene-based planar chiral N-heterocyclic carbene-Rh(I) complex was synthesized by a simple method. It was applied to the asymmetric transfer hydrogenation of prochiral ketones. Enantioselectivities of up to 67% ee were observed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation of novel axially chiral NHC,Pd(II) complexes and their application in oxidative kinetic resolution of secondary alcoholsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2009Shi-Jia Liu Abstract Novel axially chiral N -heterocyclic carbene (NHC) Pd(II) complexes were prepared from optically active 1,1,-binaphthalenyl-2,2,-diamine (BINAM) and H8 -BINAM and their crystal structures were unambiguously determined by X-ray diffraction. These chiral N -heterocyclic carbene (NHC) Pd(II) complexes were applied in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant or under aerobic conditions, affording the corresponding sec -alcohols in good yields with moderate to good enantioselectivities. Copyright © 2009 John Wiley & Sons, Ltd. [source] Chiral Concave Imidazolinium Salts as Precursors to Chiral Concave N -Heterocyclic Carbenes,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2007Ole Winkelmann Abstract Imidazolinium moieties have been incorporated into bimacrocycles to generate precursors for concave N -heterocyclic carbenes (NHCs). By using one symmetrically substituted benzene bridgehead and one naphthalene bridgehead devoid of local C2 -symmetry, axially chiral concave imidazolinium ions have been obtained. Starting from 2,7-dihydroxy-1-nitronaphthalene (7), the phenol groups have been transformed to 4-pentenyl ethers 8, and the nitro group was then reduced to the corresponding amine 9. Next, 9 and a 2,6-bis(alkenyloxy)aniline 10 were connected by an oxalic acid linker. After reduction of the diamide 13 to diamine 14, a bridge was installed with triethyl orthoformate to give a tetraalkenyl-substituted imidazolinium salt 15. Ring-closing metathesis of 15 followed by hydrogenation of the products 16 yielded the bimacrocyclic salts 17 in 9,18,% overall yield (based on 7), giving amounts up to >300 mg. The configurational stability of 17 was investigated by NMR using chiral enantiopure anions TRISPHAT 18 and BINPHAT 19 as stereodynamic probes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Suzuki reaction of aryl chlorides using saturated N -heterocarbene ligandsHETEROATOM CHEMISTRY, Issue 7 2005Ismail Özdemir From readily available starting materials, six 1,3-dialkyl-imidazolinium bromides (2a,f) have been prepared and characterized by conventional spectroscopic methods and elemental analyses. The incorporation of saturated N -heterocyclic carbenes into palladium precatalysts gives high catalyst activity in the Suzuki coupling of deactivated aryl chloride substrates in aqueous media. The complexes were generated in the presence of Pd(OAc)2 by in situ deprotonation of 2a,f. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:557,561, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20140 [source] Chiral iridium(I) bis(NHC) complexes as catalysts for asymmetric transfer hydrogenationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010Claus Diez Abstract The common use of NHC complexes in transition-metal mediated C,C coupling and metathesis reactions in recent decades has established N -heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes bearing NHC-containing chiral ligands is dominated by mixed carbene/oxazoline or carbene/phosphane chelating ligands. In contrast, applications of complexes with chiral, chelating bis(NHC) ligands are rare. In the present work new chiral iridium(I) bis(NHC) complexes and their application in the asymmetric transfer hydrogenation of ketones are described. A series of chiral bis(azolium) salts have been prepared following a synthetic pathway, starting from L -valinol and the modular buildup allows the structural variation of the ligand precursors. The iridium complexes were formed via a one-pot transmetallation procedure. The prepared complexes were applied as catalysts in the asymmetric transfer hydrogenation of various prochiral ketones, affording the corresponding chiral alcohols in high yields and moderate to good enantioselectivities of up to 68%. The enantioselectivities of the catalysts were strongly affected by the various, terminal N -substituents of the chelating bis(NHC) ligands. The results presented in this work indicate the potential of bis-carbenes as stereodirecting ligands for asymmetric catalysis and are offering a base for further developments. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||