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Chiral Complexes (chiral + complex)
Selected AbstractsStructural Analysis of Chiral Complexes of Palladium(0) with 15-Membered Triolefinic Macrocyclic LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2005Anna Pla-Quintana Abstract The complete structural analysis of the palladium complexes of the triolefinic macrocycles (E,E,E)-1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes, which featured from three identical to three different aryl groups, was achieved by performing X-ray diffraction studies, NMR spectroscopy, and other calculations. The stereochemical complexity is determined by the different isomers formed through complexation of the metal to one or other face of each of the three olefins involved. The palladacyclopropane formulation of the palladium,olefin interaction offers a clear picture of the stereogenicity of the olefin carbon atoms that are complexed to the metal. The energetically favorable isomers were identified in the solid-state and in solution by performing X-ray diffraction and NMR spectroscopic analysis, respectively. Els complexos de pal,ladi de macrocicles triolefínics de tipus (E,E,E)-1,6,11-tris(arilsulfonil)-1,6,11-triazaciclopentadeca-3,8,13-triè, contenint des de tres unitats aríliques iguals fins a tres de diferents han estat estudiats mitjançant difracció de Raigs-X, espectroscòpia de RMN i càlculs teòrics. La complexitat estereoquímica deriva dels diferents isomers que es poden formar degut a la complexació del metall amb cadascuna de les dues cares de les tres olefines. La representació dels enllaços metall-olefina com a pal,ladaciclopropans permet una visualització més senzilla de l,estereoquímica dels àtoms de carboni olefínics després de la complexació. Els isomers energèticament possibles han estat determinats en l,estat sòlid i en solució mitjançant difracció de Raigs-X i espectroscòpia de RMN respectivament. [source] Synthesis of Functionalized Indoles with an ,-Stereogenic Ketone Moiety Through an Enantioselective Friedel,Crafts Alkylation with (E)-1,4-Diaryl-2-butene-1,4-dionesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Gonzalo Blay Abstract Chiral complexes of BINOL-based ligands with hafnium tert -butoxide catalyze the enantioselective Friedel,Crafts alkylation of indoles with (E)-1,4-diaryl-2-butene-1,4-diones at room temperature, with good yields and ee up to 94%. Hafnium(IV) was found to be a more effective Lewis acid than other frequently used metal ions such as titanium(IV) or zirconium(IV). Unlike the enantioselective Friedel,Crafts alkylation of indoles with ,,,-unsaturated compounds where the stereogenic center is generated in the ,-position to a carbonyl group, the Friedel,Crafts alkylation with 2-butene-1,4-diones described here generates an ,-stereogenic center with respect to one of the carbonyl groups. This can be regarded as an inversion of the normal reactivity pattern or umpolung. The enantioselective Friedel,Crafts alkylation of indoles with (E)-4-oxo-4-phenylbutenoates using a zirconium(IV)-BINOL catalyst is also reported. This reaction takes place regioselectively at the carbon in the ,-position to the ketone carbonyl group, generating an ,-ester stereogenic center. [source] Synthesis of Functionalized Indoles with a Trifluoromethyl-Substituted Stereogenic Tertiary Carbon Atom Through an Enantioselective Friedel,Crafts Alkylation with ,-Trifluoromethyl-,,,-enonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2010Gonzalo Blay Dr. Abstract Chiral complexes of BINOL-based ligands with zirconium tert -butoxide catalyze the Friedel,Crafts alkylation reaction of indoles with ,-trifluoromethyl-,,,-unsaturated ketones to give functionalized indoles with an asymmetric tertiary carbon center attached to a trifluoromethyl group. The reaction can be applied to a large number of substituted ,-trifluoromethyl enones and substituted indoles. The expected products were obtained with good yields and ees of up to 99,%. [source] Synthesis of optically active hydroxyphosphonatesHETEROATOM CHEMISTRY, Issue 2 2008Irina Guliaiko The reduction of dimenthyl ketophosphonates with sodium borohydride involves asymmetric induction at the ,-carbon atom, resulting in a small excess of the (R)-enantiomer of the ,-hydroxyphosphonate formed. A higher ee purity was achieved if the reduction of chiral dimenthyl ketophosphonates was carried out by the chiral complex of NaBH4 - L -proline, owing to the double asymmetric induction at the ,-carbon atom. The hydroxyphosphonates obtained were isolated in a diastereomerically pure state and were transformed to the optically active, free hydroxyalkylphosphonic acids. The (R)-configuration of one of them was proved by X-ray crystal structure analysis. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:133,139, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20391 [source] Do Trinuclear Triplesalen Complexes Exhibit Cooperative Effects?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010Characterization, Enantioselective Catalytic Sulfoxidation by Chiral Trinuclear FeIII Triplesalen Complexes, Synthesis Abstract The chiral triplesalen ligand H6chand provides three chiral salen ligand compartments in a meta -phenylene arrangement by a phloroglucinol backbone. The two diastereomeric versions H6chandRR and H6chandrac have been used to synthesize the enantiomerically pure chiral complex [(FeCl)3(chandRR)] (3RR) and the racemic complex [(FeCl)3(chandrac)] (3rac). The molecular structure of the free ligand H6chandrac exhibits at the terminal donor sides the O-protonated phenol,imine tautomer and at the central donor sides the N-protonated keto,enamine tautomer. The trinuclear complexes are comprised of five-coordinate square-pyramidal FeIII ions with a chloride at the axial positions. The crystal structure of 3rac exhibits collinear chiral channels of ,11,Å in diameter making up 33.6,% of the volume of the crystals, whereas the crystal structure of 3RR exhibits voids of 560,Å3. Mössbauer spectroscopy demonstrates the presence of FeIII high-spin ions. UV/Vis spectroscopy is in accordance with a large delocalized system in the central backbone evidenced by strong low-energy shifts of the imine ,,,* transitions relative to that of the terminal units. Magnetic measurements reveal weak intramolecular exchange interactions but strong magnetic anisotropies of the FeIII ions. Complexes 3rac and 3RR are good catalysts for the sulfoxidation of sulfides providing very good yields and high selectivities with 3RR being enantioselective. A comparison of 3RR and [FeCl(salen,)] provides higher yields and selectivities but lower enantiomeric excess values (ee values) for 3RR relative to [FeCl(salen,)]. The low ee values of 3RR appeared to be connected to a strong ligand folding in 3RR, opening access to the catalytically active high-valent Fe,O species. The higher selectivity is assigned to a cooperative stabilization of the catalytically active high-valent Fe,O species through the phloroglucinol backbone in the trinuclear complexes. [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] Oxido Pincer Ligands , Exploring the Coordination Chemistry of Bis(hydroxymethyl)pyridine Ligands for the Late Transition MetalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009Axel Klein Abstract Coordination of the 2,6-bis(hydroxymethyl)pyridine-based oxido pincer ligands RR,pydimH2 [R = R, = H (pydimH2); R = R, = Me (pydipH2); R = 2-tolyl, R, = Me (pydotH2)] towards late transition metals CoII, NiII, CuII, ZnII, PdII and PtII allows the formation of molecular species (complexes), which exhibit three main structural motifs in the solid state. The two main species are pentacoordinate [(RR,pydimH2)MCl2] and hexacoordinate [(RR,pydimH2)2M]X2, both of which are stable in solution and can be interconverted by changing the solvent polarity. The disproportionation equilibrium [(RR,pydimH2)MCl2] [rlhar2] [(RR,pydimH2)2M]2+ + [MCl4]2, was studied by optical spectroscopy. The chiral ligand pydotH2 allows the formation of chiral complexes. In the square-planar complexes [(pydimH2)2MCl2] (M = PdII or PtII) the oxido donor functions of the ligands do not take part in the coordination.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Metal-Controlled Stereoselectivity in Complex Formation: Assembly of Tetranuclear Copper(I) Complexes with Four Stereogenic Nitrogen Donor Functions in all-(R) and all-(S) ConfigurationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2003Jörg Schneider Abstract The reaction of N,N, -dialkyl-3,7-diazanonane-1,9-dithiolate (NR2S2) ligands (R = Me, Et) with monovalent copper resulted in the formation of the chiral complexes [Cu4(NMe2S2)2] (1) and [Cu4(NEt2S2)2] (2) which were characterised by means of X-ray diffraction and spectroscopic techniques. They contain copper atoms in both linear {S,Cu,S} fragments, which act as linkers between mononuclear [Cu(NR2S2)], subsites, and in {CuS2N2} units within these building blocks, which can be described as incomplete coordination octahedra of unusual design. Due to favourable interplay between the spatial demands of the ligand system and the electronic requirements of the copper atom, the nitrogen donor atoms within the [Cu(NR2S2)], metallo ligands are restricted to identical absolute configurations. The combination of two [Cu(NR2S2)], metallo ligands with two further CuI ions to give the tetranuclear complexes 1 or 2 via S,Cu,S bridges underlies stereochemical control, resulting in optically active systems with (R,R,R,R) and (S,S,S,S) configurations. Consequently, metallo ligands in their enantiomeric forms cannot combine via S,Cu,S bridges to form optically inactive meso complexes with the (R,R,S,S) configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Binding Studies of Asymmetric Pentacoordinate Copper(II) Complexes Containing Phenanthroline and Ethane-1,2-diamine Ligands with Calf-Thymus DNAHELVETICA CHIMICA ACTA, Issue 9 2005Farukh Arjmand New chiral complexes of the composition [MLL,], where HL=1,2-bis(1H -benzimidazol-2-yl)ethane-1,2-diol=H2bimedol, M=CoII, NiII, CuII, and L,=1,10-phenanthroline (phen) or ethane-1,2-diamine (en), were synthesized and characterized. The ligand L exhibited a coordination mode involving the O-atom of only one OH group, the other one being directed away from the metal center. The complexes [Cu(Hbimedol)(en)]Cl (1), [Cu(Hbimedol)(phen)]Cl (2), [Co(Hbimedol)(phen)]Cl (3), [Ni(Hbimedol)(en)]Cl (4), and [Ni(Hbimedol)(phen)]Cl (5) were ionic in nature and stable at room temperature. The donor sets involved in coordination with the metal ions were the O-atom of one OH group and two N-atoms of the two benzimidazole moieties, besides the two N-atoms of phen or en (Fig.,1.). The proposed five-coordinate geometry of 1,5 was established by analysis of spectroscopic data; the ball-and-stick models supported the proposed structures of 1,5 since they showed apparently no strain on any bond and angle. The interaction of complexes 1 and 2 with calf-thymus DNA were carried out by UV/VIS titration, circular dichroism, electrochemical methods, and viscometry. The intrinsic binding constant Kb of 1 and 2 was determined as 1.57,104 and 1.51,104,M,1, respectively, suggesting that both complexes bind strongly to calf-thymus DNA. [source] Enantioseparation of dansyl amino acids by ligand-exchange capillary electrophoresis with zinc(II)- L -phenylalaninamide complexJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2009Li Qi Abstract A novel method of chiral ligand-exchange CE was developed with L -amino acylamides as a chiral ligand and zinc(II) as a central ion. It has been demonstrated that these chiral complexes, such as Zn(II)- L -alaninamide, Zn(II)- L -prolinamide, and Zn(II)- L -phenylalaninamide, are suitable for use as chiral selectors for the enantioseparation of either individual pair of or mixed dansyl amino acids. The optimal separation running buffer consisted of 5 mM ammonium acetate, 100 mM boric acid, 4 mM ZnSO4·7 H2O, and 8 mM L -amino acylamides at pH 8.2. The experiments showed that apart from the effect of the concentration of the complexes on the resolution and the migration time, the buffer pH also had a sharp influence on resolution. The employed chiral ligands exhibited different enantioselectivities and enantiomer migration orders. D -Amino acids migrate faster than L -amino acids when Zn(II)- L -alaninamide and Zn(II)- L -phenylalaninamide are used as chiral selectors, but it was observed that the migration order is reversed when Zn(II)- L -prolinamide is used as the chiral selector. Furthermore, the amount of dansylated amino acids is found to be highly dependent on the labeling temperature. [source] | ||||||||||||||||||||||