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Type Complex (type + complex)
Selected AbstractsEnantioselective Synthesis of , -Blockers via Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2,-[Cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis[phenolato]}(2,)}cobalt ([Co(salen)])-Type ComplexesHELVETICA CHIMICA ACTA, Issue 2 2008Rahul Abstract The synthesis of chirally pure , -blockers was successfully achieved via hydrolytic kinetic resolution of butyl (±)-4-(oxiran-2-ylmethoxy)benzeneacetate ((±)- 1) and (±)-4-(oxiran-2-ylmethoxy)benzeneacetonitrile ((±)- 2) in the presence of bimetallic chiral [Co(salen)]-type complexes. The newly synthesized bimetallic chiral [Co(salen)]-type complexes exhibited excellent enantioselectivities of up to >98% ee in good yields (Tables,1,3). [source] Probing the Mechanism of Olefin Metathesis in Grubbs,Hoveyda and Grela Type Complexes,ANGEWANDTE CHEMIE, Issue 32 2010Tim Vorfalt Dipl.-Ing. Je mehr, desto besser: Kinetische Daten aus UV/Vis-Messungen liefern schlüssige Hinweise für die Beteiligung des olefinischen Substrats am geschwindigkeitsbestimmenden Schritt der Initiierungsreaktion von Olefinmetathesekatalysatoren vom Grubbs-Hoveyda-Typ sowie für einen zweiten, Olefin-unabhängigen Schritt, der nur bei sehr hohen Olefinkonzentrationen geschwindigkeitsbestimmend wird. [source] ChemInform Abstract: Rare [(NHC)2Ni-OH]-Type Terminal Nickel Hydroxo and [(NHC)2Ni]-Type Complexes of N/O-Functionalized N-Heterocyclic Carbenes as Precatalysts for Highly Desirable Base-Free Michael Reactions in Air at Ambient Temperature.CHEMINFORM, Issue 35 2009Manoja K. Samantaray 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: Enantioselective Synthesis of ,-Blockers via Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2,-[Cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis [phenolato]}(2-)}cobalt ([Co(salen)])-Type Complexes.CHEMINFORM, Issue 25 2008Rahul B. Kawthekar 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] The Role of Axial Ligation in Nitrate Reductase: A Model Study by DFT Calculations on the Mechanism of Nitrate ReductionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2008Kuntal Pal Abstract The reactivity differences of the model anionic complexes [Mo(mnt)2(X)(PPh3)], [mnt2, = 1,2-dicyanoethylenedithiolate; X = SPh (1a), SEt (1b), Cl (1c), Br (1b)] towards oxygen atom transfer from nitrate, which is a key step performed by nitrate reductase, has been investigated by density functional theory calculations. Unlike complexes 1a and 1b, complexes 1c and 1d do not react with nitrate. Thermodynamically, all these complexes have a similar ability to generate the pentacoordinate active state [Mo(mnt)2(X)], by dissociation of PPh3, although the inaccessibility of the dxy orbital in 1c,d and the instability of the corresponding nitrate-bound enzyme substrate (ES) type complex contributes to their failure to reduce nitrate. The nature of the ES complex for 1a,b is described. The variation in the experimental data due to the change of axial ligation from SPh to SEt on the catalytic pathway has also been addressed. The gas-phase and solvent-corrected potential energy surface for the reaction of 1a,b with nitrate are established with fully optimized minima and transition states.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Pyrazolate-Based Dinucleating Ligands in L2M2 Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H,C InteractionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Jens C. Röder Abstract A series of nickel(II) and palladium(II) complexes [L2M2]2+ have been prepared and structurally characterized, where L is a pyrazolate ligand with bulky 2,6-dimethyl- or 2,6-di(isopropyl)anilinomethyl side arms. Coordinating counter anions such as chloride can bind to axial sites of the dinickel species in a solvent-dependent process, giving rise to five-coordinate high-spin metal ions. In the case of weakly coordinating anions, the metal ions are found in roughly square-planar environments, and the structures are governed by the tendency of the bulky aryl groups to avoid each other, which forces the methyl or isopropyl substituents in the aryl 2- and 6-positions to approach the metal ions from the axial directions. This leads to drastic low-field shifts of the respective 1H NMR signals, e.g. , = 7.86 ppm for the isopropyl ,CH which comes in close proximity to the low-spin nickel(II) center. The relevance of such low-field NMR resonances of protons close to the axial sites of d8 metal ions for possible three-center four-electron M···H,C hydrogen bonds involving the filled d orbital of the metal ion is discussed. In the present case, attractive M···H interactions are assumed to be of no major significance. This was corroborated by the structure of a further [L2Ni2]2+ type complex where the anilinomethyl side arms bear only a single 2-isopropyl group, which was found rotated away from the metal. Additional spectroscopic and electrochemical properties of the various complexes are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Palladium-Catalyzed Preparation of Propargylic or Allenylic Sulfides from Propargyl Halides or Mesylate and ThiolsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004Ken Tsutsumi Abstract In the presence of a catalytic amount of Pd0 -dppe complex [dppe: 1,2-bis(diphenylphosphanyl)ethane], generated in situ from [Pd2(dba)3·CHCl3] and dppe, propargylic bromide 1a reacted with an equimolar amount of propanethiol at 60 °C in DMF to afford propargylic sulfide 2 in an excellent yield. The reaction occurs readily when carried out in the presence of the weak base triethylamine. The choice of both the phosphane, which is employed as the palladium atom's ligand, and the solvent have a remarkable effect on this reaction. We found that the optimum conditions for the reaction are those using a bidentate phosphane ligand (dppe) in a polar solvent (DMF). Compound 1a reacted smoothly with both aromatic (PhSH) and secondary thiols (CySH) in high yields. The reactions with thiols bearing functional groups (OH or Cl) proceeded selectively in good to moderate yields. Primary chlorides 1b,e were readily converted into their corresponding propargylic sulfides 7,10 in high yields. The Pd0 -dppe catalyst was ineffective in the reaction of the bromide 1g bearing a tBu group at the propargylic position, but the reaction of the corresponding mesylate 1h using the Pd0 -DIOP catalyst [DIOP = O -isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphanyl)butane] at 100 °C afforded the product 11 in good yield. Allenylic sulfides were obtained from 1g,i. We suggest that a cationic ,3 -type complex may be a more reactive intermediate in this catalytic reaction than neutral ,1 - or ,3 -allenyl/propargylpalladium complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Overexpression and Characterization of the Rhodobacter sphaeroides PufX Membrane Protein in Escherichia coli,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2007Shiho Onodera Heterologous expression of the PufX membrane protein from purple photosynthetic bacterium Rhodobacter sphaeroides was attempted by using Escherichia (E.) coli cells. The PufX was overexpressed as a recombinant protein with a histidine tag added to the carboxyl terminus, and can be extracted from the cell membrane by various detergents. Circular dichroism measurements showed that the expressed PufX protein had ,-helix contents of 29% in organic solvents and 22,26% in 0.8,2.0% (w/v) n -octyl ,- d -glucopyranoside solutions, suggesting that the PufX contains a substantial ,-helical region composed of 18,22 amino acids. The PufX expressed in E. coli was examined by reconstitution experiments with LH1 ,- and ,-polypeptides and bacteriochlorophyll a. It was shown that the PufX inhibited not only the reconstitution of the LH1 complex, but also the formation of the B820 subunit type complex at high concentrations, indicating that the expressed PufX is biologically active. Large-scale expression of the functional PufX membrane protein provides sufficient quantity for further biophysical and structural analyses of its biological function, and adds another example for producing highly hydrophobic integral membrane proteins using the E. coli expression system. [source] Controlling the Association of Adamantyl-Substituted Poly{N -[tris(hydroxymethyl)methyl]acrylamide} and a , -Cyclodextrin/Epichlorohydrin Polymer by a Small Drug Molecule , NaproxenCHEMISTRY & BIODIVERSITY, Issue 1 2007Danica Mislovi Abstract Two polymeric substances, a poly{N -[tris(hydroxymethyl)methyl]acrylamide} (THMMA) substituted with adamantyl moieties and a , -cyclodextrin/epichlorohydrin polycondensate, formed a host,guest type complex, which resulted in the gel formation upon mixing of these two compounds at appropriate conditions. Introduction of a drug molecule, i.e., naproxen, that was able to fill the , -cyclodextrin cavities, thus expulsing adamantyl moieties, led to disruption of such association and inhibition of gel formation. The conditions required for the association of the two polymeric components and formation of the gel, as well as the dynamics of its inhibition by addition of naproxen was established. The procedure of using solutions of two associating polymers and an appropriate drug competitor can be used at targeted viscosupplementation. [source] Ethene Polymerization Behavior of MAO-Activated Dichloridotitanium Complexes Bearing Bi- and Tetradentate Salicylaldimine DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2010Antti Pärssinen Abstract New chiral bridged tetradentate (N2O2)TiIVCl2 -type complexes bearing dimethylbiphenyl (1-Ti,3-Ti) and previously published binaphthyl-bridged (4-Ti) complex were synthesized with high yields. This was achieved by treating the corresponding Schiff-base ligand (H2L) precursors with Ti(NMe2)4, followed by conversion of these diamido complexes to LTiCl2 derivatives by the addition of excess of Me3SiCl. A series of unbridged titanium complexes 5-Ti,8-Ti with similar substituents at the phenoxy group were studied and their polymerization properties, after methylaluminoxane (MAO) activation, compared with the above bridged complexes. It was found that the catalysts bearing chiral tetradentate biaryl-bridged salicylaldimine ligands produce multimodal polyethylene (PE) with low activity [below 10 kgPE/(molTi,h,bar)] while their unbridged analogues provide activities that are 10,1000 times greater under similar reaction conditions. The reasons for this dramatic difference in polymerization activities are discussed based on the stabilities of the different cationic species configurations. [source] Modulation of the Communication between Redox Centers in a Tris(ferrocene)-tren Ligand by Complexation of Lanthanide IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2003Marie Heitzmann The tripodal ligand L built on the tren platform and bearing three chemically equivalent ferrocene units was prepared and characterized. Electrochemical investigations indicate that electrostatic communication occurs between the three ferrocene groups in L, which leads to the observation of two distinct voltammetric waves. The electrochemical communication between the three ferrocene moieties is disrupted in 1:1 (L:M3+) type complexes formed between L and Y3+ or Eu3+ metal cations and their electrochemical response tends towards that of a single three-independent-electrons oxidation wave. Modulation of the electrochemical properties of L in the presence of lanthanide ions might be exploited with a view to their electrochemical sensing in organic and aqueous media. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Enantioselective Synthesis of , -Blockers via Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2,-[Cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis[phenolato]}(2,)}cobalt ([Co(salen)])-Type ComplexesHELVETICA CHIMICA ACTA, Issue 2 2008Rahul Abstract The synthesis of chirally pure , -blockers was successfully achieved via hydrolytic kinetic resolution of butyl (±)-4-(oxiran-2-ylmethoxy)benzeneacetate ((±)- 1) and (±)-4-(oxiran-2-ylmethoxy)benzeneacetonitrile ((±)- 2) in the presence of bimetallic chiral [Co(salen)]-type complexes. The newly synthesized bimetallic chiral [Co(salen)]-type complexes exhibited excellent enantioselectivities of up to >98% ee in good yields (Tables,1,3). [source] Two 18, TiIV,5 -Cp-tris(sec -amido)-type complexes derived from 1H -imidazol-2-yl side-chain functionalized cyclopentadienesACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Xiaowu Wang Achiral {2-[2-(,5 -cyclopentadienyl)-2-methylpropyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C12H14N2)], (I), and closely related racemic (SR)-{2-[(,5 -cyclopentadienyl)(phenyl)methyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C15H12N2)], (II), have been prepared by direct reactions of Ti(NEt2)4 and the corresponding 1H -imidazol-2-yl side-chain functionalized cyclopentadienes. In compound (II), there are two crystallographically independent molecules of very similar geometries connected by a noncrystallographic pseudosymmetry operation akin to a 21 screw axis. All Ti-ligating N atoms in both (I) and (II) are in planar environments, which is indicative of an additional N,Ti p,,d, donation. This fact and the 18, nature of both (I) and (II) are additionally supported by quantum chemical single-point density functional theory (DFT) computations. [source] Self-Assembly of [B -SbW9O33]9, Subunit with Transition Metal Ions (Mn2+, Cu2+, Co2+) in Aqueous Solution: Syntheses, Structures and Magnetic Properties of Sandwich Type Polyoxometalates with Subvalent SbIII HeteroatomCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2008Jing-Ping Wang Prof. Abstract Rational self-assembly of Sb2O3 and Na2WO4, or (NH4)18[NaSb9W21O86] with transition-metal ions (Mn2+, Cu2+, Co2+), in aqueous solution under controlled conditions yield a series of sandwich type complexes, namely, Na2H2[Mn2.5W1.5(H2O)8(B -,-SbW9O33)2],32,H2O (1), Na4H7[Na3(H2O)6Mn3(,-OAc)2(B -,-SbW9O33)2],20,H2O (OAc=acetate anion) (2), NaH8[Na2Cu4Cl(B -,-SbW9O33)2],21,H2O (3), Na8K[Na2K(H2O)2{Co(H2O)}3(B -,-SbW9O33)2], 10,H2O (4), and Na5H[{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2],11.5,H2O (5). These structures are determined by using the X-ray diffraction technique and further characterized by obtaining IR spectra and performing elemental analysis. Structure analysis reveals that polyoxoanions in 1 and 5 comprise of two [B -,-SbW9O33]9, building units, whereas 2, 3, and 4 consist of two isomerous [B -,-SbW9O33]9, building blocks, which are all linked by different transition-metal ions (Mn2+, Cu2+, or Co2+) with different quantitative nuclearity. It should be noted that compound 2 represents the first one-dimensional sinusoidal chain based on sandwich like tungstoantimonate building blocks through the carboxylate-bridging ligands. Additionally, 3 is constructed from sandwiched anions [Na2Cu4Cl(B -,-SbW9O33)2]9, linked to each other to form an infinitely extended 2D network, whereas 5 shows an interesting 3D framework built up from offset sandwich type polyoxoanion [{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2]6, linked by Co2+ and Na+ ions. EPR studies performed at 110,K and room temperature reveal that the metal cations (Mn2+, Cu2+, Co2+) reside in a square-pyramidal geometry in 2, 3, and 4. The magnetic behavior of 1,4 suggests the presence of weak antiferromagnetic coupling interactions between magnetic metal centers with the exchange integral J=,0.552,cm,1 in 2. [source] | ||||||||||||||||||||||