A catalytic enantioselective stereodivergent aldol reaction

The aldol reaction is among the most powerful and strategically important carbon-carbon bond-forming transformations in organic chemistry. The importance of the aldol reaction in constructing chiral building blocks for complex small-molecule synthesis has spurred continuous efforts toward the development of direct catalytic variants. The realization of a general catalytic aldol reaction with control over both the relative and absolute configurations of the newly formed stereogenic centers has been a longstanding goal in the field. Here, we report a decarboxylative aldol reaction that provides access to all four possible stereoisomers of the aldol product in one step from identical reactants. The mild reaction can be carried out on a large scale in an open flask, and generates CO₂ as the only by-product. The method tolerates a broad substrate scope and generates chiral β-hydroxy thioester products with substantial downstream utility.

Preferential Enrichment of Enantiomer from Amino Acid Schiff Bases by Coordination Interaction and Crystallization

In this paper, preferential enrichment (PE) is described for three pairs of novel amino acid Schiff base Cu(II)/Cu(I) complexes. Single crystal X-ray diffraction indicated that 1-S/R are one-dimensional coordination polymers (CPs) with helical structures, and 2-S/R and 3-S/R are one-dimensional CPs with auxiliary ligands. By tuning the pH, the solvent and second ligands, the 1-S/R, 3-S/R underwent polymorphic transitions, resulting in enantioselective liberation of excess enantiomers into solution, until the deposited crystals were slightly enriched with the opposite enantiomer, thereby successfully exhibiting PE. However, under the effects of Cu(II), the solvent and low pH, 2-S/R did not exhibit PE and resulted in enrichment of racemic compounds, which was attributed to amino acid Schiff base chiral complex mechanisms of PE. The three pairs of Cu complex structures were characterized by UV-vis, MS and X-ray photoelectron spectroscopy (XPS). All chiral properties were studied by circular dichroism (CD) in the solid and liquid.

The Influence of Electrolyte Type on Kinetics of Redox Processes in the Polymer Films of Ni(II) Salen-Type Complexes

Electrodes modified with polymers derived from the complexes [Ni(salcn)], [Ni(salcn(Me))] and [Ni(salcn(Bu))] were obtained in order to study the kinetics of electrode processes occurring in polymer films, depending on the thickness of the films, the type of electrolyte and the solvent. FTIR and EQCM methods were used to determine the type of mass transported into polymer films during anode processes and the number of moles of ions and solvent. The rate of charge transport through films was determined by the cyclic voltammetry method, by the quantity cD1/2. It was shown that the charge transport was determined by the transport of anions. The kinetics were most efficient for poly[Ni(salcn(Bu))] modified electrodes, obtained from TBAPF6 and working in TBAClO4 and TBABF4. It was also shown that a solvent with a higher DN value and lower viscosity (MeCN) facilitated the transport of the charge through polymer films.

Dinuclear Copper(II) Complexes with Schiff Bases Derived from 2-Hydroxy-5-Methylisophthalaldehyde and Histamine or 2-(2-Aminoethyl)pyridine and Their Application as Magnetic and Fluorescent Materials in Thin Film Deposition

Two Cu(II) complexes, 1 and 2, with tridentate Schiff bases derived from 2-hydroxy-5-methylisophthalaldehyde and histamine HL1 or 2-(2-aminoethyl)pyridine HL2, respectively, were obtained and characterized by X-ray crystallography, spectroscopic (UV-vis, fluorescence, IR, and EPR), magnetic, and thermal methods. Despite the fact that the chelate formed by the NNO ligand donors (C26-C25H2-C24H2-N23=C23H-C22-C19Ph(O1)-C2(Ph)-C3H=N3-C4H2-C5H2-C6 fragment) are identical, as well as the synthesis of Cu(II) complexes (Cu:L = 2:1 molar ratio) was performed in the same manner, the structures of the complexes differ significantly. The complex 1, {[Cu2(L1)Cl2]2[CuCl4]}·2MeCN·2H2O, consists of [Cu2(L1)Cl2]+ units in which Cu(II) ions are bridged by the HL1 ligand oxygen and each of these Cu(II) ions is connected with Cu(II) ions of the next dimeric unit via two bridging Cl- ions to form a chain structure. In the dinuclear [Cu2(L2)Cl3]0.5MeCN complex 2, each Cu(II) is asymmetrically bridged by the ligand oxygen and chloride anions, whereas the remaining chloride anions are apically bound to Cu(II) cations. In contrast to the complex 1, the square-pyramidal geometry of the both Cu(II) centers is strongly distorted. The magnetic study revealed that antiferromagnetic interactions in the complex 2 are much stronger than in the complex 1, which was corresponded with magneto-structural examination. Thin layers of the studied Cu(II) complexes were deposited on Si(111) by the spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The Cu(II) complexes and their thin layers exhibited fluorescence between 489-509 nm and 460-464 nm for the compounds and the layers, respectively. Additionally, DFT calculations were performed to explain the structures and electronic spectral properties of the ligands.

X-ray structure and magnetic and fluorescence characteristics of new Cu(ii) complexes with Schiff bases derived from 2-(2-aminoethyl)pyridine and 2-hydroxy-1-naphthaldehyde; morphology and fluorescence of their thin films

Cu(ii) complexes with tridentate Schiff bases derived from 2-(2-aminoethyl)pyridine and 2-hydroxy-1-naphthaldehyde and COO-, Cl- and NO3- as ligands were obtained and characterized by crystal and molecular, spectroscopic (UV-Vis, fluorescence, IR, and EPR), magnetic and thermal methods. The X-ray crystal structure analysis revealed a distorted square planar geometry for [Cu(ii)(PEMN)CH3COO]CHCl3, 1, and [Cu(ii)(PEMN)Cl], 2, and a distorted square-pyramidal geometry for [Cu(ii)(PEMN)NO3], 3, corresponding to the values of EPR g-matrix diagonal components. The copper(ii) complexes exhibited fluorescence in solution in the range of 370-410 nm. Thin layers of the studied copper(ii) complexes were deposited on Si(111) by a spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM) and fluorescence spectroscopy. For copper(ii) layers (2/Si), the most intense fluorescence band from an intraligand and a d-d transition between 490 and 550 nm was observed.

The mechanism of electropolymerization of nickel(ii) salen type complexes

Ni(ii) complexes with (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediamine ([Ni(salen)]), and its methyl ([Ni(salen(Me))]) and tert-butyl ([Ni(salen(Bu))]) derivatives have been synthesized.

Exploration of biological activities of alkyne arms containing Cu(ii) and Ni(ii) complexes: syntheses, crystal structures and DFT calculations

Several mononuclear Cu(ii) and Ni(ii) Schiff base (N,O-donor) complexes were synthesized and characterized. The binding ability with DNA and BSA and catecholase activity of the complexes were investigated.

Synthesis, spectroscopy, X-ray crystallography, DFT calculations, DNA binding and molecular docking of a propargyl arms containing Schiff base

A propargyl arms containing Schiff base (L) was synthesized by the condensation of 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone with trans-1,2-diaminocyclohexane. The structure of L was characterized by IR, (1)H NMR, (13)C NMR and UV-Vis spectroscopy and by single crystal X-ray diffraction analysis. The UV-Visible spectral behavior of L in different solvents exhibits positive solvatochromism. Density functional calculation of the L in gas phase was performed by using DFT (B3LYP) method with 6-31G basis set. The computed vibrational frequencies and NMR signals of L were compared with the experimental data. Tautomeric stability study inferred that the enolimine is more stable than the ketoamine form. The charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Electronic absorption and emission spectral studies were used to study the binding of L with CT-DNA. The molecular docking was done to identify the interaction of L with A-DNA and B-DNA.

Structural studies of copper(ii) complexes with 2-(2-aminoethyl)pyridine derived Schiff bases and application as precursors of thin organic–inorganic layers

Cu(ii) complexes with Schiff bases derived from 2-pyridin-2-ylethanamine were obtained and characterized by UV-Vis, fluorescence, and IR spectra.