Home About us Contact
|
Home About us Contact | ||
|
|
||
Chiral Ligands (chiral + ligand)
Kinds of Chiral Ligands Selected AbstractsStructural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Sequential Stereoselective Catalysis: Two Single-Flask Reactions of a Substrate in the Presence of a Bifunctional Chiral Ligand and Different Transition MetalsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2003Rita Annunziata Abstract A new bifunctional ligand capable of promoting different stereoselective catalytic transformations in combination with different transition metals has been prepared by connecting with a spacer a bis(oxazoline) to dihydroquinidine; this ligand was employed in a one-flask procedure in which methyl (E)-3-(4-vinylphenyl)propenoate underwent first cyclopropanation at the electron-rich double bond and then dihydroxylation at the electron-poor alkene to afford a product containing four stereocenters with complete regiocontrol and high stereoselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] ChemInform Abstract: Enantiotopic Discrimination in Palladium-Mediated Nucleophilic Substitutions on Achiral Substrates: Chiral Ligand versus Chiral Nucleophile.CHEMINFORM, Issue 4 2010Olivier Jacquet 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: Chiral Ligand Derived from (1S,2R)-Norephedrine as a Catalyst for Enantioselective Prochiral Ketone Reduction.CHEMINFORM, Issue 45 2009Umesh Balakrishnan 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] Chiral Ligand Controlled Asymmetric Conjugate Amination of Enoates with Lithium Mesitylmethyl(trimethylsilyl)amide.CHEMINFORM, Issue 52 2006Takeo Sakai 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, please click on HTML or PDF. [source] Asymmetric, Catalytic Synthesis of ,-Chiral Amines Using a Novel Bis(phosphine) Monoxide Chiral Ligand.CHEMINFORM, Issue 12 2004Alessandro A. Boezio Abstract For Abstract see ChemInform Abstract in Full Text. [source] Kinetic Resolution of Racemic Ferrocenylphosphine Compounds by Enantioselective Oxidation Using Cyclic Selenoxides Having a Chiral Ligand.CHEMINFORM, Issue 18 2003Yoshihiro Miyake No abstract is available for this article. [source] BINOLAM, a Recoverable Chiral Ligand for Bifunctional Enantioselective Catalysis: The Asymmetric Synthesis of Cyanohydrins.CHEMINFORM, Issue 48 2002Jesus Casas Abstract For Abstract see ChemInform Abstract in Full Text. [source] Enantioselective Aziridination of Alkenes with N-Aminophthalimide in the Presence of Lead Tetraacetate Mediated Chiral Ligand.CHEMINFORM, Issue 35 2002Kung-Shou Yang Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Synthesis of Enantiomerically Enriched Amines by Chiral Ligand Mediated Addition of Organolithium Reagents to Imines.CHEMINFORM, Issue 4 2002Sonia Arrasate 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] Ketopinic Acid Derived Bis(hydroxy amides) as Cheap, Chiral Ligands for the Enantioselective Ethylation of Aromatic AldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2010Tomás de las Casas Engel Abstract Readily accessible, C2 - and pseudo- C2 -symmetric bis(hydroxy amides), derived from commercially available (+)-ketopinic acid and protic diamines, are promising, cheap, chiral ligands for the synthetically valuable, enantioselective addition of organozinc reagents to carbon electrophiles. A series of ligands of this type, having key structural differences, has been synthesized and tested in the enantioselective ethylation of benzaldehydes and (E)-cinnamaldehyde, in order to gain information on the origin of ligand efficiency. The results obtained allow for the definition of a privileged structural pattern for the design of improved cheap ligands and support interesting models proposed for both the acting catalytic species and the controlling transition states. The most efficient ligands proved to be less efficient than commercially available (,)-MIB; nevertheless, an impressive efficiency level was obtained, which should sustain interest in this cheap type of ligands. [source] Simple Derivatives of Natural Amino Acids as Chiral Ligands in the Catalytic Asymmetric Addition of Phenylacetylene to AldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2005Zhi-jian Han Abstract Optically active propargylic alcohols are important chiral building blocks in asymmetric synthesis, and asymmetric addition of terminal alkynes to aldehydes is one of the most important and interesting procedures by which to prepare these chiral building blocks. In this work we have identified some simple derivatives of (S)-proline and other natural amino acids as chiral ligands that can be combined with Ti(OiPr)4 and then used to catalyze the asymmetric addition of zinc acetylide, produced in situ by the reaction of phenylacetylene with diethylzinc, to aldehydes. The ee value was as high as 90,%. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] tert -Butanesulfinylphosphines: Simple Chiral Ligands in Rhodium-Catalyzed Asymmetric Addition of Arylboronic Acids to Electron-Deficient OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Feng Lang Abstract An efficient rhodium complex catalyst system was developed by using a class of simple tert -butanesulfinylphosphines as bidentate ligands, which solely bear sulfur chirality and combine the advantages of both sulfoxide and phosphine ligands. Excellent activities (in 0.5 hour, up to 99% yield) and enantioselectivities (up to 98% ee) were displayed in Rh-catalyzed asymmetric 1,4-additions under mild conditions. [source] Application of Ferrocenyl-Substituted Aziridinylmethanols (FAM) as Chiral Ligands in Enantioselective Conjugate Addition of Diethylzinc to Enones.CHEMINFORM, Issue 34 2007Alper Isleyen 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, please click on HTML or PDF. [source] New Chiral Ligands Derived from Mandelic Acid: Synthesis and Application in the Asymmetric Phenyl Transfer Reaction to an Aromatic Aldehyde.CHEMINFORM, Issue 4 2005Carsten Bolm Abstract For Abstract see ChemInform Abstract in Full Text. [source] Use of Diamines Containing the ,-Phenylethyl Group as Chiral Ligands in the Asymmetric Hydrosilylation of Prochiral Ketones.CHEMINFORM, Issue 23 2004Virginia M. Mastranzo Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Novel Planar Chiral Ferrocene and Cyclopentadienyl Manganese Tricarbonyl Derivatives and Their Use as Chiral Ligands in the Palladium-Catalyzed Asymmetric Allylic Alkylation.CHEMINFORM, Issue 44 2003Jae Hoon Lee Abstract For Abstract see ChemInform Abstract in Full Text. [source] Derivatives of (S)-{[2-(Methoxymethyl)pyrrolidin-1-yl]methyl}ferrocene , New Planar Chiral Ligands.CHEMINFORM, Issue 23 2003Radovan Sebesta Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Screening of New Chiral Ligands for the Copper-Catalyzed Enantioselective Allylic Substitution.CHEMINFORM, Issue 11 2003Sandrine Ongeri Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Asymmetric Chelated Claisen Rearrangements in the Presence of Chiral Ligands , Scope and Limitations.CHEMINFORM, Issue 34 2002Uli Kazmaier 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: Practical Synthesis of Chiral Ligands for Catalytic Enantioselective Cyanosilylation of Ketones.CHEMINFORM, Issue 32 2002Shuji Masumoto 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: 2-Amino-Substituted 1-Sulfinylferrocenes as Chiral Ligands in the Addition of Diethylzinc to Aromatic Aldehydes.CHEMINFORM, Issue 29 2002Julian Priego 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: Mono- and Bidentate Phosphinanes , New Chiral Ligands and Their Application in Catalytic Asymmetric Hydrogenations.CHEMINFORM, Issue 27 2002Markus Ostermeier 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: A Versatile Synthesis of Planar Chiral Ligands.CHEMINFORM, Issue 40 2001Susan E. Gibson 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: Chiral C2 -Symmetric 2,3-Disubstituted Aziridine and 2,6-Disubstituted Piperidine as Chiral Ligands in the Addition Reaction of Diethylzinc with Arylaldehydes.CHEMINFORM, Issue 25 2001Min Shi 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: Chiral Ligands with Pyridine Donors in Transition Metal Catalyzed Enantioselective Cyclopropanation and Hydrosilylation Reactions.CHEMINFORM, Issue 6 2001Giorgio Chelucci 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] Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral LigandsCHEMISTRY - AN ASIAN JOURNAL, Issue 8 2009Sanzhong Luo Prof. Abstract By judiciously anchoring functional groups onto chiral ionic liquids, functionalized chiral ionic liquids (FCILs) are emerging as a new type of asymmetric organocatalysts and nonclassical chiral ligands. This Focus Review highlights the applications of FCILs from the viewpoint of asymmetric catalysis. We focus mainly on the de,novo designed and synthesized FCILs which likely still maintain the typical ionic liquids properties, and in a few cases relevant ionic liquid immobilized chiral catalysts are briefly discussed. [source] Chiral CE of aromatic amino acids by ligand-exchange with zinc(II),L -lysine complexELECTROPHORESIS, Issue 15 2007Li Qi Abstract A novel method of chiral ligand-exchange CE was developed with either L - or D -lysine (Lys) as a chiral ligand and zinc(II) as a central ion. This type of chiral complexes was explored for the first time to efficiently separate either individual pairs of or mixed aromatic amino acid enantiomers. Using a running buffer of 5,mM ammonium acetate, 100,mM boric acid, 3,mM ZnSO4·7H2O and 6,mM L -Lys at pH,7.6, unlabeled D,L -tryptophan, D,L -phenylalanine, and D,L -tyrosine were well separated, giving a chiral resolution of up to 7.09. The best separation was obtained at a Lys-to-zinc ratio of 2:1, zinc concentration of 2,4,mM and running buffer pH,7.6. The buffer pH was determined to have a strong influence on resolution, while buffer composition and concentration impacted on both the resolution and peak shape. Boric acid with some ammonium acetate was an adoptable buffer system, and some additives like ethylene diamine tetraacetic acid capable of destroying the complex should be avoided. Fine-tuning of the chiral resolution and elution order was achieved by regulating the ratio of L -Lys to D -Lys; i.e. the resolution increased from zero to its highest value as the ratio ascended from 1:0 to 1:infinitive, and L -isomers eluted before or after D -isomers in excessive D - or L -Lys, respectively. [source] Chiral Half-Sandwich Ruthenium(II) Complexes as Catalysts in 1,3-Dipolar Cycloaddition Reactions of Nitrones with Methacrolein,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2006Daniel Carmona Abstract Ruthenium complexes of formula [(,6 -arene)Ru(LL*)(H2O)][SbF6]2 (arene = C6H6, p -MeC6H4iPr, C6Me6; LL* = bidentate chelate chiral ligand with PN, PP or NN donor atoms) have been tested as catalyst precursors for the asymmetric 1,3-dipolar cycloaddition of nitrones to methacrolein. The reaction occurs quantitatively with perfect endo selectivity and moderate enantioselectivity (up to 74,% ee). The ruthenium aqua complexes can be prepared from the corresponding chlorides, [(,6 -arene)RuCl(LL*)][SbF6]. Dipolarophile intermediates [(,6 -arene)Ru(PNiPr)(methacrolein)][SbF6]2 {PNiPr = (4S)-2-(2-diphenylphosphanylphenyl)-4-isopropyl-1,3-oxazoline} as well as nitrone-containing complexes [(p -MeC6H4iPr)Ru(PNiPr)(nitrone)][SbF6]2 (nitrone = N -benzylidenephenylamine N -oxide, N -benzylidenemethylamine N -oxide, 3,4-dihydroisoquinoline N -oxide) have been also isolated and characterised. The crystal structures of the chlorides (RRu)-[(,6 -C6Me6)RuCl(PNiPr)][SbF6], (RRu)-[(,6 -C6H6)RuCl(PNInd)][SbF6] {PNInd = (3aR,8aS)-2-[2-(diphenylphosphanyl)phenyl]-3a,8a-dihydroindane[1,2- d]oxazole} and those of the aqua solvates (RRu)-[(,6 -arene)Ru(PNiPr)(H2O)][SbF6]2 (arene = C6H6, C6Me6) were determined by X-ray diffraction methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Structural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] | |||||||||||||||||||||||||||||||