Salen Complexes (salen + complex)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Resolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic Studies

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008
Pawel Dzygiel
Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


ChemInform Abstract: A Chiral Mn(III) Salen Complex Immobilized onto Ionic Liquid Modified Mesoporous Silica for Oxidative Kinetic Resolution of Secondary Alcohols.

CHEMINFORM, Issue 47 2008
Suman Sahoo
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]


Construction of an Aryliridium,Salen Complex for Highly cis- and Enantioselective Cyclopropanations.

CHEMINFORM, Issue 36 2007
Shigefumi Kanchiku
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]


ChemInform Abstract: Ligand-Assisted Rate Acceleration in Transacylation by an Yttrium,Salen Complex.

CHEMINFORM, Issue 37 2002
Demonstration of a Conceptually New Strategy for Metal-Catalyzed Kinetic Resolution of Alcohols.
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]


Antiferromagnetic Coupling of Stacked CuII,Salen Complexes in DNA,

ANGEWANDTE CHEMIE, Issue 29 2010
Guido
Ein hübsches Pärchen: Die paramagnetischen CuII -Ionen zweier Kupfer-Salen-Metallbasenpaare in benachbarten Positionen in eine DNA-Doppelhelix (siehe Bild) sind antiferromagnetisch gekoppelt, und die Austauschkopplungskonstante ist ,2J=22.4,cm,1. Die dipolare Kopplungskonstante ergab einen Cu,,,Cu-Abstand von 3.7,Å, der dem Basenpaarabstand in natürlicher B-DNA ähnelt. [source]


X-Ray Structures of Copper(II) and Nickel(II) Radical Salen Complexes: The Preference of Galactose Oxidase for Copper(II)

ANGEWANDTE CHEMIE, Issue 29 2010
Maylis Orio Dr.
Kupfer oder Nickel? Der gezeigte CuII -Salen-Komplex, ein Modell des aktiven Zentrums der Galactose-Oxidase (GO), liegt im Festkörper als lokalisiertes Radikal vor, wie an der chinoiden Verteilung der Bindungslängen in einem der Ringe zu erkennen ist. Die Struktur des radikalischen Liganden hängt nicht vom Metall ab, die Zusammensetzung des SOMO dagegen schon. Dies könnte die viel geringere Reaktivität des Ni-Komplexes erklären, ebenso wie die Tatsache, dass natürliche GO ein CuII -Zentrum bevorzugt. [source]


ChemInform Abstract: Exceptionally Active Yttrium,Salen Complexes for the Catalyzed Ring Opening of Epoxides by TMSCN and TMSN3.

CHEMINFORM, Issue 10 2008
Biswajit Saha
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]


Continuous Enantioselective Kinetic Resolution of Terminal Epoxides Using Immobilized Chiral Cobalt,Salen Complexes.

CHEMINFORM, Issue 25 2007
Wladimir Solodenko
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]


Catalytic Aziridinations with Copper(II) Salen Complexes.

CHEMINFORM, Issue 17 2006
Wei Sun
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]


Cyclic Carbonate Synthesis Catalysed by Bimetallic Aluminium,Salen Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010
William Clegg Prof.
Abstract The development of bimetallic aluminium,salen complexes [{Al(salen)}2O] as catalysts for the synthesis of cyclic carbonates (including the commercially important ethylene and propylene carbonates) from a wide range of terminal epoxides in the presence of tetrabutylammonium bromide as a cocatalyst is reported. The bimetallic structure of one complex was confirmed by X-ray crystallography. The bimetallic complexes displayed exceptionally high catalytic activity and in the presence of tetrabutylammonium bromide could catalyse cyclic carbonate synthesis at atmospheric pressure and room temperature. Catalyst-reuse experiments demonstrated that one bimetallic complex was stable for over 60 reactions, though the tetrabutylammonium bromide decomposed in situ by a retro-Menschutkin reaction to form tributylamine and had to be regularly replaced. The mild reaction conditions allowed a full analysis of the reaction kinetics to be carried out and this showed that the reaction was first order in aluminium complex concentration, first order in epoxide concentration, first order in carbon dioxide concentration (except when used in excess) and unexpectedly second order in tetrabutylammonium bromide concentration. Further kinetic experiments demonstrated that the tributylamine formed in situ was involved in the catalysis and that addition of butyl bromide to reconvert the tributylamine into tetrabutylammonium bromide resulted in inhibition of the reaction. The reaction kinetics also indicated that no kinetic resolution of racemic epoxides was possible with this class of catalysts, even when the catalyst was derived from a chiral salen ligand. However, it was shown that if enantiomerically pure styrene oxide was used as substrate, then enantiomerically pure styrene carbonate was formed. On the basis of the kinetic and other experimental data, a catalytic cycle that explains why the bimetallic complexes display such high catalytic activity has been developed. [source]


Noncovalent Modulation of pH-Dependent Reactivity of a Mn,Salen Cofactor in Myoglobin with Hydrogen Peroxide

CHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2009
Jun-Long Zhang Dr.
Abstract To demonstrate protein modulation of metal-cofactor reactivity through noncovalent interactions, pH-dependent sulfoxidation and 2,2,-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) oxidation reactivity of a designed myoglobin (Mb) containing non-native Mn,salen complex (1) was investigated using H2O2 as the oxidant. Incorporation of 1 inside the Mb resulted in an increase in the turnover numbers through exclusion of water from the metal complex and prevention of Mn,salen dimer formation. Interestingly, the presence of protein in itself is not enough to confer the increase activity as mutation of the distal His64 in Mb to Phe to remove hydrogen-bonding interactions resulted in no increase in the turnover numbers, while mutation His64 to Arg, another residue with ability to hydrogen-bond interactions, resulted in an increase in reactivity. These results strongly suggest that the distal ligand His64, through its hydrogen-bonding interaction, plays important roles in enhancing and fine-tuning reactivity of the Mn,salen complex. Nonlinear least-squares fitting of rate versus pH plots demonstrates that 1,Mb(H64X) (X=H, R and F) and the control Mn,salen 1 exhibit pKa values varying from pH,6.4 to 8.3, and that the lower pKa of the distal ligand in 1,Mb(H64X), the higher the reactivity it achieves. Moreover, in addition to the pKa at high pH, 1,Mb displays another pKa at low pH, with pKa of 5.0±0.08. A comparison of the effect of different pH on sulfoxidation and ABTS oxidation indicates that, while the intermediate produced at low pH conditions could only perform sulfoxidation, the intermediate at high pH could oxidize both sulfoxides and ABTS. Such a fine-control of reactivity through hydrogen-bonding interactions by the distal ligand to bind, orient and activate H2O2 is very important for designing artificial enzymes with dramatic different and tunable reactivity from catalysts without protein scaffolds. [source]


Cobalt(II) salen complex with two aza-crown pendants and its analogues as synthetic oxygen carriers

CHINESE JOURNAL OF CHEMISTRY, Issue 6 2004
Xing-Yue Wei
Abstract Salen with two aza-crown ether pendants H2L1 and its analogues H2L2- H2L4 were successfully synthesized starting from benzo-10-aza-15crown-5 (BN15C5) or morpholine. Their structures were characterized by IR, MS, 1H NMR and elemental analysis, and were confirmed by X-ray diffraction analysis of H2L1. Moreover, the saturated oxygen uptake of their cobalt(II) complexes CoL1- CoL4 in diethyleneglycol dimethyl ether was determined at different temperature. The oxygenation contants (KO2 ) and thermodynamic parameters (,H° and ,S°) were calculated. The modulation of O2 -binding capabilities by pendant substituents were investigated as compared with the parent Schiff base complex CoL5 (CoSalen). The results indicate that the dioxygen affinities of CoL have been much more enhanced by aza-crown pendants than that by morpholino pendants, and the O2 -binding capabilities of CoL1 and CoL2 with aza-crown pendants would also be enhanced by adding alkali metal cations. [source]


Improved catalytic activity of homochiral dimeric cobalt,salen complex in hydrolytic kinetic resolution of terminal racemic epoxides

CHIRALITY, Issue 9 2005
Rukhsana I. Kureshy
Abstract Enantiomerically pure epoxides (99%, ee) and diols (98%, ee) from racemic epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane were obtained in 2,12 h by hydrolytic kinetic resolution (HKR) using the recyclable dimeric homochiral Co(III),salen complex 1, (0.2 mol %) derived from 5,5-(2,,2,-dimethylpropane)-di-[(R,R)-{N -(3- tert -butylsalicylidine)- N,-(3,,5,-di- tert -butylsalicylidine)}-1,2-cyclohexanediamine] with cobalt(II) acetate. Unlike its monomeric version, the catalyst could be recycled several times without loss in performance. The use of BF4 as counter ion in HKR reactions was also investigated. © 2005 Wiley-Liss, Inc. Chirality 17:590,594, 2005. [source]


Poly(propylene carbonate), old CO2 Copolymer with New Attractiveness

MACROMOLECULAR SYMPOSIA, Issue 1 2007
Gerrit A. Luinstra
Abstract Summary: The catalytic synthesis of poly(propylene carbonate) (PPC) from propylene oxide and CO2 is mediated by zinc glutarate and chromium salen complexes. The determined solid state structure of the zinc glutarate was taken to model the polymerisation of ethylene oxide. It has a low activation energy for a reaction path involving two zinc atoms, where one binds the nucleophilic alkoxy chain end and one activates the epoxide. A similar pathway may operate in the alternating copolymerization PO/CO2 as is shown in the homogeneous chromium salen catalyst system. The material profile was determined of PPC with 93% carbonate linkages. A study of the transparent blend with poly(lactic acid) (PLA) shows that the polymers are not miscible, but rather compatible as they are finely dispersed and show linear behaviour in the mechanic properties. The permeability of oxygen, carbon dioxide and water of the composite PPC/PLA are also reported. [source]


Cyclic Carbonate Synthesis Catalysed by Bimetallic Aluminium,Salen Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010
William Clegg Prof.
Abstract The development of bimetallic aluminium,salen complexes [{Al(salen)}2O] as catalysts for the synthesis of cyclic carbonates (including the commercially important ethylene and propylene carbonates) from a wide range of terminal epoxides in the presence of tetrabutylammonium bromide as a cocatalyst is reported. The bimetallic structure of one complex was confirmed by X-ray crystallography. The bimetallic complexes displayed exceptionally high catalytic activity and in the presence of tetrabutylammonium bromide could catalyse cyclic carbonate synthesis at atmospheric pressure and room temperature. Catalyst-reuse experiments demonstrated that one bimetallic complex was stable for over 60 reactions, though the tetrabutylammonium bromide decomposed in situ by a retro-Menschutkin reaction to form tributylamine and had to be regularly replaced. The mild reaction conditions allowed a full analysis of the reaction kinetics to be carried out and this showed that the reaction was first order in aluminium complex concentration, first order in epoxide concentration, first order in carbon dioxide concentration (except when used in excess) and unexpectedly second order in tetrabutylammonium bromide concentration. Further kinetic experiments demonstrated that the tributylamine formed in situ was involved in the catalysis and that addition of butyl bromide to reconvert the tributylamine into tetrabutylammonium bromide resulted in inhibition of the reaction. The reaction kinetics also indicated that no kinetic resolution of racemic epoxides was possible with this class of catalysts, even when the catalyst was derived from a chiral salen ligand. However, it was shown that if enantiomerically pure styrene oxide was used as substrate, then enantiomerically pure styrene carbonate was formed. On the basis of the kinetic and other experimental data, a catalytic cycle that explains why the bimetallic complexes display such high catalytic activity has been developed. [source]


Enantioselective cyanosilylation of ketones catalyzed by recyclable polymeric and dimeric MN(III) salen complexes at room temperature

CHIRALITY, Issue 2 2009
Noor-Ul H. Khan
Abstract Recyclable polymeric 1 and dimeric 2 chiral Mn(III) salen complexes catalyzed enantioselective cyanosilylation of various ketones in the presence of triphenylphosphine oxide as an additive proceeded smoothly at room temperature, providing excellent yields (up to 98%) and enantiomeric excess (up to 86%) of respective cyanohydrin trimethylsilyl ether. For most of the substrates, the Catalyst 1 showed slightly better reactivity and enantioselecitivity than the Catalyst 2 nevertheless both the catalysts were easily recovered and reused four times with the retention of their efficiency. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source]


Easily recyclable chiral polymeric Mn(III) salen complexes for oxidative kinetic resolution of racemic secondary alcohols

CHIRALITY, Issue 5 2007
Rukhsana I. Kureshy
Abstract Chiral polymeric Mn(III) salen complexes were used efficiently for oxidative kinetic resolution of racemic secondary alcohols at room temperature. High chiral purity (ee; >99%) was achieved for the oxidative kinetic resolution of racemic secondary alcohols with 0.6 mol % catalyst loading in 60 min. The catalyst was easily recycled for five successive catalytic experiments. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source]