Direct Asymmetric Mannich‐Type Reaction of α‐Isocyanoacetates with Ketimines using Cinchona Alkaloid/Copper(II) Catalysts

The enantioselective direct Mannich‐type reaction of ketimines with α‐isocyanoacetates has been developed. Excellent yields and enantioselectivity were observed for the reaction of various ketimines and α‐isocyanoacetates using cinchona alkaloid/Cu(OTf)₂ and a base. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α,β‐diamino acids.     

Ultrafast Encapsulation of Metal Nanoclusters into MFI Zeolite in the Course of Its Crystallization: Catalytic Application for Propane Dehydrogenation

Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM-5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn-ZSM-5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity.     

C-S bond cleavage of pyridine-2-thiol: a new functionality of quadruply bridged dinuclear platinum and palladium complexes

Treatment of pyridine-2-thiol (pytH) with H(2) (60 atm) in the presence of 5-methylpyridine-2-thiolate (5-mpyt)-bridged dinuclear Pt(III), Pt(II), or Pd(II) complexes (1 mol %) in DMF at 150 degrees C for 72 h leads to the formation of pyridine in 3-51% yield. From the (1)H NMR study of the exchange reactions and of the products under D(2) pressure, it is suggested that the catalytic reaction involves bimetallic activation of the pyt ligand followed by the liberation of pyridine and H(2)S.     

Spectroscopic and crystallographic studies on the stability of self-assembled coordination nanotubes

On complexation with (en)Pd(NO3)2, tetrakis(3,5-pyridine) ligand gives two isomeric coordination nanotubes, which are in slow equilibrium despite the presence of sixteen Pd-N bonds in the tube framework.     

Reaction of 2,3-dichloro-5,6-dicyanopyrazine with enamines and some tertiary amines

The reaction of 2,3-dichloro-5,6-dicyanopyrazine ( 1 ) with enamines as well as a few tertiary amines as enamine precursors was investigated. Both reactions gave aminovinyl-substituted pyrazine derivatives. During the attempted purification of 3c or 3d by column chromatography on silica gel, 2-chloro-5,6-dicyano-3-(1′-oxocyclopent-2′-yl)pyrazine ( 4 ) was obtained, apparently by hydrolytic cleavage. The products prepared are all of interest as potential pesticides.     

Immobilization of microbial cells by radiation-induced polymerization of glass-forming monomers and immobilization ofStreptomyces phaeochromogenes cells by polymerization of various hydrophobic monomers

The immobilization ofStreptomyces phaeochromogenes cells was studied by the radiation-induced polymerization of various hydrophobic glass-forming monomers at low temperatures. The glucose isomerase activity of cells immobilized in hydrophobic polymers showed no decrease in activity with repeated use (batch enzyme reaction). Activity increased with increasing monomer concentration in contrast to results with the immobilized enzyme. The hydrophobic polymer composite was microspheric in form. The particle diameter of the composite increased with the increasing monomer concentration.K _m values of the immobilized cells were close to that of intact cells. It was deduced that the cells were trapped on the surface part of the hydrophobic polymer ready to react with the substrate, and not within the matrix where diffusion would play an important role in reaction rates.     

Molecular vibrations and force fields of alkyl sulfides: Part XV. C-S stretching vibrations of aliphatic alkyl sulfides

The C-S stretching vibrations of 28 aliphatic sulfides including one thiol are summarized, and all of the C-S stretching bands are classified into several groups. An extraordinarily low frequency associated with the ethyl group is discussed briefly.     

Heats of pyridine intercalation with α- and γ-zirconium phosphates

Calorimetric measurements at 25°C were made to determine the thermodynamic quantities for the intercalation of pyridine with α- and γ-zirconium phosphates. These phosphates showed exothermic reactions with ΔH⁰ = ?59.3 and ?21.9 kJ mole^?1, respectively. The large difference between the depyridination temperatures for both intercalates is rediscussed with the aid of the ΔG⁰ data obtained.