Palladium(0)-Catalyzed Allylation Reaction with Dimethyl 2-fluoromalonate

The palladium(0)-catalyzed allylation reaction of dimethyl 2-fluoromalonate with allylic carbonates proceeds smoothly under neutral conditions to give the S_N2 allylation product. However, using the nucleophile NaCF(CO₂Et)₂ under basic conditions increased the chemical yield. Moreover, the S_N2′ allylation product was increased up to 75% yield.     

金属锰(II)催化臭氧化TNT的机理

以TNT为目标污染物,考察了Mn（Ⅱ）催化臭氧化作用机理,以及HCO3^-、pH值和催化剂投量及投加方式对催化效果的影响。结果表明,Mn（Ⅱ）对臭氧化TNT的催化作用明显。对于一定量的催化剂,一次性投加比多次投加时的催化效果好,催化剂的浓度为0．106mol／L、pH值约为5时效果比较理想,废水溶液的HCO3^-质量浓度为58．1mg／L或290．5mg／L时,对催化效果几乎没有影响。在催化氧化过程中,COD的去除率明显小于TNT,且TNT浓度减小与硝酸盐浓度增加的比例为1：1,说明TNT降解不彻底。Mn（Ⅱ）催化臭氧化过程中产生的水合二氧化锰使胶体表面及溶液-胶体界面增加。臭氧和TNT富集,TNT的氧化分解易于发生。     

Kinetics and Mechanism of the Platinum(II)-Catalyzed Hydroarylation of Vinyl Arenes with 1,2-Dimethylindole

The mechanism of the intermolecular hydroarylation of vinyl arenes ( 1 ) with 1,2-dimethylindole ( 2 ) catalyzed by PtCl₂ has been evaluated through a combination of kinetic analysis, deuterium labeling studies, and stereochemical analysis. The results of these and additional experiments are consistent with a mechanism for hydroarylation involving rapid and reversible complexation of vinyl arene to the catalytically inactive platinum mono(vinyl arene)complex trans-PtCl₂(H₂C=CHAr)(solvent) to form the reactive platinum bis(vinyl arene) complex trans-PtCl₂(H₂C=CHAr)₂, which undergoes turnover-limiting, outer-sphere attack of indole. Rapid protodemetallation of the resulting platinum alkyl complex releases product and regenerates the equilibrating mixture of platinum π-vinyl arene complexes.     

Tricarbonyl(η6-Cycloheptatriene)manganese Hexafluorophosphate: Reactions with Enolate Nucleophiles and Decomplexation of the Product Dienyl Complexes

Reaction of tricarbonylcycloheptatrienemanganese hexafluorophosphate with a wide range of enolate nucleophiles derived from malonic esters, phenylsulfonylesters, β-ketoesters and cyclohexanones proceeds cleanly to give 6-substituted tricarbonyl(1–5-η-cycloheptadienyl)manganese complexes 3 . It was found that demetallation with concomitant stereospecific hydroxylation, to give substituted cycloheptadienes, could be accomplished by direct treatment of the dienyl complexes with ceric ammonium nitrate in buffered wet acetone. Complexes 3a–3c gave mixtures of hydroxy esters and gamma lactones 6 and 7 in proportions which depended on the nature of the substituent present. A novel and potentially useful demetallative cyclofunctionalization was found to occur on treatment of hydroxy ester 3m with excess iodine in acetonitrile, to give the cyclic ether 10 as the only observable product.     

Palladium Nanoparticles in Allylic Alkylations and Heck Reactions: The Molecular Nature of the Catalyst Studied in a Membrane Reactor

A series of palladium nanoparticles stabilized by five chiral sugar‐based oxazolinyl‐phosphite ligands, containing various substituents at the oxazoline and phosphite moieties has been synthesized. They were characterized by transmission electron microscopy (TEM), X‐ray powder diffraction (XRD), infrared spectroscopy (IR) and elemental analysis. These nanoparticles were applied in Pd‐catalyzed asymmetric allylic alkylation and Heck coupling reactions. A detailed study to elucidate the nature of the active species using a continuous‐flow membrane reactor (CFMR), accompanied by TEM observations, classical poisoning experiments, and kinetic measurements have been carried out. Conclusive evidence of the nature of the species involved in the use of PdNPs in asymmetric catalytic reactions has been obtained. The CFMR experiments proved the molecular nature of the true catalysts and all conversions can be justified by the amount of molecular palladium that leached as measured by ICP‐AES.     

Efficient Synthesis of Substituted Selenophenes Based on the First Palladium(0)‐Catalyzed Cross‐Coupling Reactions of Tetrabromoselenophene

Regioselective Suzuki cross‐coupling reactions of tetrabromoselenophene allow a convenient synthesis of aryl‐substituted selenophenes. High yields were obtained using a novel biaryl‐monophosphine ligand. The first tetra(1‐alkynyl)selenophene was prepared in one step by a Sonogashira reaction of tetrabromoselenophene.     

Selective Aerobic Oxidation of Benzyl Alcohols with Palladium(0) Nanoparticles Suspension in Water

Catalysis Letters - This study concerns one of the rare applications of a suspension of palladium nanoparticles in water for oxidation reactions. The aqueous suspension containing well dispersed...     

Regioselective Palladium(0)‐Catalyzed Cross‐Coupling Reactions and Metal‐Halide Exchange Reactions of Tetrabromothiophene: Optimization,Scope and Limitations

The Suzuki reaction of tetrabromothiophene with arylboronic acids provides a regioselective approach to various 5‐aryl‐2,3,4‐tribromothiophenes, symmetrical 2,5‐diaryl‐3,4‐dibromothiophenes, and tetraarylthiophenes. Unsymmetrical 2,5‐diaryl‐3,4‐dibromothiophenes are prepared by Suzuki reaction of 5‐aryl‐2,3,4‐tribromothiophenes. Tetraarylthiophenes containing two different types of aryl groups are obtained by Suzuki reactions of 2,5‐diaryl‐3,4‐dibromothiophenes. During the optimization of the conditions of each individual reaction, the solvent, the catalyst and the temperature play an important role. In several cases, classical conditions [use of tetrakis(triphenylphosphane)palladium(0), Pd(PPh₃)₄, as the catalyst] gave excellent yields. The yields of those transformations which failed or proceeded sluggishly could be significantly improved by application of a new biarylmonophosphine ligand developed by Buchwald and co‐workers. Regioselective metal‐halide exchange reactions of tetrabromothiophene provide a convenient approach to various 2,5‐disubstituted 3,4‐dibromothiophenes. 5‐Alkyl‐2‐trimethylsilyl‐3,4‐dibromothiophenes could be prepared in one pot by sequential addition of trimethylchlorosilane and alkyl bromides. The reaction of tetrabromothiophene with methyl chloroformate and subsequent Suzuki reactions afforded 3,4‐diaryl‐2,5‐bis(methoxycarbonyl)thiophenes.     

Development of Palladium Precatalysts that Efficiently Generate LPd(0) Active Species

Palladium catalysts have become central to modern organic synthesis, particularly in the context of cross-coupling reactions to form C−C and C-heteroatom bonds. The development of highly efficient catalyst systems has seen a transition from the use of in situ-generated catalysts derived from a ligand source and palladium precursor to the use of preformed palladium-ligand complexes that can efficiently generate the active species. The design of these systems has focused on optimizing the generation of the LPd(0) species presumed to be the active catalysts with most state-of-the-art ligand systems. This review will highlight the development of Pd(0), Pd(I), and Pd(II) precatalysts that efficiently generate LPd(0) active species with a focus on their activation mechanisms and applications in catalysis.     

Cu(II)-Catalyzed Ortho-Selective Amination of Simple Phenols with O-Benzoylhydroxylamines

A Cu(II)-catalyzed ortho-selective amination of simple phenols with O-benzoylhydroxylamines has been developed, which provides access to 2-aminophenols under mild conditions. Various functional groups on the phenol and electrophilic amine are compatible, and the protocol typically delivers the products in moderate to good yields. The mechanistic detail of this process are discussed.     

Palladium(0) allylic alkylation in a two-phase system or with a supported aqueous phase catalyst

The reaction of allylic carbonates with various acyclic and cyclic carbonucleophiles is catalyzed by the system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ (or tppts) in a two-phase liquid medium H₂O-nitrile, the activity of the catalyst depending mainly on the nature of the nitrile, the temperature of the reaction and the ratio palladium/tppts. The same system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ supported on silica catalyzes also this reaction. The formation of the active palladium species in the two cases is followed by

Full-size image

NMR spectroscopy and discussed.     

Enantioselective Carbonyl‐Ene Reactions of Arylglyoxals with a Chiral Palladium(II)‐BINAP Catalyst

The palladium(II)‐BINAP‐catalyzed enantioselective carbonyl‐ene reactions between ten arylglyoxals and five alkenes were systematically investigated and demonstrated good to excellent enantioselectivities with high ee values of up to 93.8 %. The results showed that both arylglyoxals and alkenes exert evident effects on the enantioselectivity. Particularly, the ortho‐methyl substituents of the substrates could increase the enantioselectivity. The achieved excellent enantioselectivities may be due to the corresponding substrate matches well fitting the chiral space created by the chiral palladium(II)‐BINAP catalyst. The ortho‐methyl substituents may improve the fitting of the substrate match to the chiral space created by the chiral catalyst, hence the enantioselectivity is improved. When using dienes (1,4‐diisopropenylbenzene and 1,3‐diisopropenylbenzene) as substrates in this reaction, only one of the two carbon‐carbon double bonds participated into the reaction affording tetrafunctional organic compounds with moderate enantioselectivities of up to 83.8 % ee. The chiral Lewis acid palladium(II) catalyst incorporating (R)‐BINAP, which is a conformationally restricted chiral ligand, is very stable in ionic liquids and could be recycled 21 times with retention of the high enantioselectivity.     

Modular Furanoside Phosphite‐Phosphoroamidites,a Readily Available Ligand Library for Asymmetric Palladium‐Catalyzed Allylic Substitution Reactions. Origin of Enantioselectivity

A library of furanoside phosphite‐phosphoroamidite ligands has been synthesized and screened in the palladium‐catalyzed allylic substitution reactions of several substrate types. These series of ligands can be prepared efficiently from easily accessible D ‐xylose and D ‐glucose. Their modular nature enables the position of the phosphoroamidite group, configuration of C‐3 of the furanoside backbone and the substituents/configurations in the biaryl phosphite/phosphoroamidite moieties to be easily and systematically varied. By carefully selecting the ligand components, therefore, high regio‐ and enantioselectivities (ees up to 98%) and good activities have been achieved in a broad range of mono‐ and disubstituted hindered and unhindered linear and cyclic substrates. The NMR studies on the palladium‐π‐allyl intermediates provide a deeper understanding about the effect of the ligand parameters on the origin of enantioselectivity. They also indicate that the nucleophilic attack takes place predominantly at the allylic terminal carbon atom located trans to the phosphoroamidite moiety.     

Kinetics and Mechanism of Ru(III)-Catalyzed Oxidation of Paracetamol by Chloramine-T in Aqueous Acidic Medium

The present paper deals with the kinetics and mechanism of Ru(III)-catalyzed oxidation of paracetamol by chloramine-T (CAT) in aqueous perchloric acid medium at 303 K. The experimental result shows a first order dependence on paracetamol at its low concentrations, but tending towards zeroth order at its higher concentrations. The reactions follow a first order rate dependence with respect to oxidant [CAT] and [Ru(III)]. The reaction showed negative fractional-order dependence on the rate for [H⁺] and p-toluenesulphonamide. Variation in [Cl^?] and ionic strength of the medium did not bring about any significant change on the rate of reaction. The decrease in the reaction rate with decrease in the dielectric constant of the medium was observed in the oxidation of paracetamol. Kinetic and equivalence studies together with product analysis, observed effect of dielectric constant of the medium on the rate of reaction and activation parameters furnished a basis for the formation of a common reaction mechanism for the Ru(III)-catalyzed oxidation of paracetamol by CAT in the acidic medium.     

羧甲基纤维素负载钯催化剂的制备及对Heck反应的催化性能

通过较简单的方法合成了羧甲基纤维素钠负载钯(0)配合物,用XPS、TG、DTA等手段对其进行了表征。该配合物在空气氛围中、较低温度下能很好地催化丙烯酸、苯乙烯与芳基碘的Heck反应,立体选择性地生成取代的反式肉桂酸、1,2-二苯乙烯。羧甲基纤维素钠负载钯(0)配合物能够较方便地从反应体系中分离出来,具有较好的重复使用性能。     

On the Splitting of d.c. Contribution to the Dielectric Loss. Case of Poly(monocyclohexylitaconate)

Abstract

The splitting of the d.c. conductivity on the low frequency side of the dielectric loss has been performed by using the complex dielectric polarizability α, instead of the permittivity. Data dealing with the dielectric loss for poly(monocyclohexylitaconate) have been used to compare both methods. The dielectric relaxation peaks in M″ and α″, are in general in good qualitative agreement. There is a small shift which is attributed to the fact that M is a modulus and α a compliance.     

Thin-Film-Composite Gas Separation Membranes: On the Dynamics of Thin Film Formation Mechanism On Porous Substrates

Abstract

A wide range of gas separations of interest in energy applications are carried out using membranes. Growing attention has been paid to the technology of making thin-film-composites(TFCs) membranes. Understanding the polymer solution and substrate property is key to successfully preparing TFCs membranes. This paper reports on some fundamental issues of coating hollow fibers with polymer from solution by dip coating. Polymeric porous hollow fibers with varying porosities and permeances were coated with polymer solutions of different viscosities in a continuous process. In addition, the fibers were coated dry and by presoaking in the coating solvent. It was found that the thickness of the coating on the low permeance/porosity/wet and dry fibers could be approximated by the Deryaguin model (h/R = 1.33 (Ca) ^0.67). For dry fibers, as the fiber porosity increased, the measured coating thickness was significantly underestimated by the Deryaguin equation. It is believed that the pores in the fiber allow rapid capillary suction of the solvent into the fiber walls and the bore, thus increasing the solution viscosity near the fiber wall, resulting in an increase in the coating thickness. Significant differences in the rate of solvent uptake were observed in these fibers by wicking experiments on a microbalance to support the above hypothesis.     

Extending the Scope of GTFR Glucosylation Reactions with Tosylated Substrates for Rare Sugars Synthesis

Functionalized rare sugars were synthesized with 2-, 3-, and 6-tosylated glucose derivatives as acceptor substrates by transglucosylation with sucrose and the glucansucrase GTFR from Streptococcus oralis. The 2- and 3-tosylated glucose derivatives yielded the corresponding 1,6-linked disaccharides (isomaltose analogues), whereas the 6-tosylated glucose derivatives resulted in 1,3-linked disaccharides (nigerose analogue) with high regioselectivity in up to 95 % yield. Docking studies provided insight into the binding mode of the acceptors and suggested two different orientations that were responsible for the change in regioselectivity.     

On the Palladium(II)‐Catalysed Oxidative Rearrangement of Propargylic Acetates

The catalytic transformation of propargylic acetates into the corresponding α‐acetoxyenones in the presence of palladium(II) chloride is described. Water is a necessary component in this unusual oxidative rearrangement.     

Mercapto-Functionalized MCM-41 Anchored Palladium(0) Complex as an Efficient Catalyst for the Heterogeneous Suzuki Reaction

Mercapto-functionalized MCM-41 anchored palladium(0) complex is an efficient catalyst for the heterogeneous Suzuki reaction of arylboronic acids with aryl halides. Our system not only solves the basic problems of catalyst separation and recovery but also avoids the use of phosphine ligands.