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Ligand Precursors (ligand + precursor)
Selected AbstractsChiral Polyamino Alcohols via Hydroaminomethylation: A New Class of Polyamines for Dendritic Cores and Ligand PrecursorsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Muhammad Afzal Subhani Abstract In this contribution, the synthesis of a new class of chiral polyamino alcohols (PAA) via a two-step hydroaminomethylation/hydrolysis procedure is reported. The chiral polyamines are obtained by hydroaminomethylation of N -olefinic oxazolidinones with different amines in first step followed by hydrolysis of the resulting polyamines to give the chiral PAA in the second step. The dendritic chiral PAA (Mw=1300,1400,g,mol,1) are also synthesized efficiently through a multifold hydroaminomethylation/hydrolysis procedure. Furthermore, chiral PAA are investigated as ligands in ruthenium-catalyzed asymmetric hydrogen transfer reduction of acetophenone to 1-phenyl alcohol. [source] ChemInform Abstract: Unsymmetrical, Oxazolinyl-Containing Achiral and Chiral NCN Pincer Ligand Precursors and Their Complexes with Palladium(II).CHEMINFORM, Issue 16 2010Xin-Qi Hao 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] ChemInform Abstract: Sterically Demanding, Zwitterionic Trialkylphosphonium Sulfonates as Air-Stable Ligand Precursors for Efficient Palladium-Catalyzed Cross-Couplings of Aryl Bromides and Chlorides.CHEMINFORM, Issue 43 2008William S. Brown 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] Assessing the Potential of Zwitterionic NHC·CS2 Adducts for Probing the Stereoelectronic Parameters of N-Heterocyclic CarbenesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009Lionel Delaude Abstract Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and electronic properties of NHC ligands. Because of their outstanding ability to crystallize, the five NHC·CS2 betaines were found to be highly suitable for probing the steric influence of nitrogen atom substituents on imidazolylidene-based ligand precursors via XRD analysis, while the corresponding NHC·CO2 adducts were deemed more appropriate for evaluating the ,-donating properties of carbene ligands.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] gem -Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Michael G. Edwards The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem -dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C23H26O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry. [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. 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