Enantioselective hydrolysis of amino acid esters by non-chiral copper complexes equipped with bis (β-cyclodextrin)s

Preparation and chiral resolution properties of bridged bis(cyclodextrin)s hybrid spheres for high performance liquid chromatography

Selenium-bridged bis(β-cyclodextrin)s organic-inorganic hybrid silica material with regular spherical shape as new type of chiral stationary phase was directly synthesized under the one-pot hydrothermal synthesis method, and the chiral stationary phase was further characterized by infrared spectroscopy, scanning electron microscopy, thermogravimetry, and elemental analysis. The results of chiral separation showed that eight chiral compounds including various types of chiral alcohols and flavanone were successfully separated in the reversed-phase separation mode by high performance liquid chromatography, which showed the better chiral resolution effect than that on the C2 position of single β-cyclodextrin. The mechanism of chiral separation was likely due to multiple interactions such as inclusion, hydrogen bonding, electrostatic interaction, dipole-dipole interaction, and the synergistic effect of two cyclodextrins during the chiral resolution process. The synergy of the two cyclodextrins has great potential for development in chiral resolution.

Crystal structures of two CuII compounds: catena-poly[[chlorido-copper(II)]-μ-N-[eth-oxy(pyridin-2-yl)methyl-idene]-N'-[oxido(pyridin-3-yl)methyl-idene]hydrazine-κ4 N,N',O:N''] and di-μ-chlorido-1:4κ2 Cl:Cl-2:3κ2 Cl:Cl-di-chlorido-2κCl,4κCl-bis[μ3-eth-oxy(pyridin-2-yl)methano-lato-1:2:3κ3 O:N,O:O;1:3:4κ3 O:O:N,O]bis-[μ2-eth-oxy(pyridin-2-yl)methano-lato-1:2κ3 N,O:O;3:4κ3 N,O:O]tetracopper(II)

Two CuII complexes [Cu(C14H13N4O2)Cl] n , I, and [Cu4(C8H10NO2)4Cl4] n , II, have been synthesized. In the structure of the mononuclear complex I, each ligand is coordinated to two metal centers. The basal plane around the CuII cation is formed by one chloride anion, one oxygen atom, one imino and one pyridine nitro-gen atom. The apical position of the distorted square-pyramidal geometry is occupied by a pyridine nitro-gen atom from a neighbouring unit, leading to infinite one-dimensional polymeric chains along the b-axis direction. Each chain is connected to adjacent chains by inter-molecular C-H⋯O and C-H⋯Cl inter-actions, leading to a three-dimensional network structure. The tetra-nuclear complex II lies about a crystallographic inversion centre and has one core in which two CuII metal centers are mutually inter-connected via two enolato oxygen atoms while the other two CuII cations are linked by a chloride anion and an enolato oxygen. An open-cube structure is generated in which the two open-cube units, with seven vertices each, share a side composed of two CuII ions bridged by two enolato oxygen atoms acting in a μ3-mode. The CuII atoms in each of the two CuO3NCl units are connected by one μ2-O and two μ3-O atoms from deprotonated hydroxyl groups and one chloride anion to the three other CuII centres. Each of the penta-coordinated CuII cations has a distorted NO3Cl square-pyramidal environment. The CuII atoms in each of the two CuO2NCl2 units are connected by μ2-O and μ3-O atoms from deprotonated alcohol hy-droxy groups and one chloride anion to two other CuII ions. Each of the penta-coordinated CuII cations has a distorted NO2Cl2 square-pyramidal environment. In the crystal, a series of intra-molecular C-H⋯O and C-H⋯Cl hydrogen bonds are observed in each tetra-nuclear monomeric unit, which is connected to four tetra-nuclear monomeric units by inter-molecular C-H⋯O hydrogen bonds, thus forming a planar two-dimensional structure in the (01) plane.

Highly Efficient Method for Suzuki Reactions in Aqueous Media

Herein, we report the crystal structure and characterization of mono-6-(l-aminopropanol)-deoxy-β-cyclodextrin (L _n @β-CD). A highly efficient, in situ generated catalyst, PdCl₂(L _n @β-CD), was synthesized for palladium-catalyzed cross-coupling reactions under mild reaction conditions, and the use of this catalyst in Suzuki cross-couplings was investigated. Low palladium loadings of 0.01 mol % PdCl₂(L _n @β-CD) (Pd accounted for approximately 8.4% of the catalyst by mass) were found to be highly efficient for Suzuki cross-couplings in water and afforded the corresponding biaryl compounds in excellent yields. The catalyst can be recycled and reused.