Single-atom catalysis for organic reactions

Metal-based catalysis,including homogeneous and heterogeneous catalysis,plays a significant role in the modern chemical industry.Heterogeneous catalysis is widely used due to the high efficiency,easy catalyst separation and recycling.However,the metal-utilization efficiency for conventional heterogeneous catalysts needs further improvement compared to homogeneous catalyst.To tackle this,the pursing of heterogenizing homogeneous catalysts has always been attractive but challenging.As a recently emerging class of catalytic material,single-atom catalysts(SACs)are expected to bridge homogeneous and heterogeneous catalytic process in organic reactions and have arguably become the most active new frontier in catalysis field.In this review,a brief introduction and development history of single-atom catalysis and SACs involved organic reactions are documented.In addition,recent advances in SACs and their practical applications in organic reactions such as oxidation,reduction,addition,coupling reaction,and other organic reactions are thoroughly reviewed.To understand structure-property relationships of single-atom catalysis in organic reactions,active sites or coordination structure,metal atom-utilization efficiency(e.g.,turnover frequency,TOF calculated based on active metal)and catalytic performance(e.g.,conversion and selectivity)of SACs are comprehensively summarized.Furthermore,the application limitations,development trends,future challenges and perspective of SAC for organic reaction are discussed.

Recent Advances in Organic Reactions Catalyzed by Lanthanide(III) Complexes

Lanthanide compounds have been attracting much attention in organic synthesis. Chiral Ln substituted BINOL have been widely studied in several asymmetric organic reactions. LnCl 3 and Ln(OTf) 3 have been expected to serve as Lewis acids and have been applied to many important synthetic reactions in a one pot manner. Ln(O i Pr) 3 exhibits some basic characters, which also can be utilized in some special organic transformation. This article deals with some lanthanides(III) complexes promoted organic reactions, which we have recently developed.

Organic reactions in chiral micelles 7.The structural effects on the asymmetric oxidation of prochiral sulfides in chiral micelles

A variety of phenyl alkyl sulfides were oxidized enantioselectively with NaIO_4 in chiral micellar systems formed from eight chiral surfactants,to give optical active sulfoxides.The enantiomer excesses ranged from 1.6 to 15.0%.To understand the mechanistic detail of this asymmetric oxi- dation in chiral micelle,the effects of structure both in substrates and surfactants on the optical yield of the oxidation were studied and discussed.Generally,increasing the alkyl chain length both in sur- factants and in substrates enhances the optical yield,also the surfactant with hydroxy group at its appropriate position gives better enantioselectivity,suggesting the enzymic characteristics of the chiral micelle.

Adiabatic Decomposition of Two Kinds of Organic Peroxides by Accelerating Rate Calorimeter

The accelerating rate calorimeter was applied to study the thermal hazard of two kinds of organic peroxides, i.e. methyl ethyl ketone peroxide (MEKPO) and benzoyl peroxide (BPO). And their thermal decomposition characteristics were discussed. Meanwhile, thermal decomposition characteristics of MEKPO and BPO vvere compared. The result indicated that MEKPO is more sensitive to thermal effect than BPO. While once the thermal decomposition takes place. BPO will be more hazardous than MEKPO due to its serious pressure effect. Thermal kinetic analysis of these two kinds of organic peroxides was also taken, and the kinetic parameters for them were calculated. The study of thermal decomposition of MEKPO solution with different initial concentrations indicated that, the lower concentration MEKPO solution is, the higher onset temperature will be. And with the addition of organic solvent, it becomes more difficult for MEKPO to reach a thermal decomposition. Therefore, its thermal hazard is reduced.

Investigation of the Photosensitized Mechanisms of PCBs in the Presence of Natural Organic Matter

The structures of 26 different congeners of polychlorinated biphenyls（PCBs, including monothrough deca-chlorinated） were optimized using density functional theory（DFT） calculations with the 6-31＋G（d,p） basis set. The activation energies for the dechlorination of these systems were calculated for direct photodegradation and photosensitized degradation reaction pathways in the presence of natural organic matter（NOM）. The dechlorination mechanism of these PCBs and the ring-opening reaction mechanisms（using QST3 method） of the photosensitive degradation products were analyzed. The results showed that（i） the activation energy for the photosensitized degradation of PCBs was much lower than that of direct photodegradation;（ii） the degradation activities（i.e., C–Cl bond cleavage energies） were the same for both degradation pathways and followed the order ortho 〉 meta 〉 para;（iii） the degradation activities of asymmetric PCBs were higher than those of the corresponding symmetrical PCBs for the direct photodegradation and it was completely opposite in the photosensitive degradation;（iv） there was no correlation between the dissociation energy and the number of C–Cl bonds for the direct photodegradation and dechlorination products were all biphenyl;（v） the degradation activity of PCBs decreased as the number of C–Cl bonds increased in the presence of NOM; and（vi） even when the dechlorination reaction was incomplete, it produced chlorophenol. Furthermore, the free radicals of NOM led to the ring-opening reactions of PCBs via an initial addition step. The main site of these ring-opening reactions was the ortho position. Notably, the likelihood of ring-opening reactions occurring involving the degradation products increased as the degradation degree of PCBs increased.

Enhanced Acid/Base Catalysis in High Temperature Liquid Water

Two novel and environmentally benign solvent systems, organic acids-ennchea high temperature liquid water （HTLW） and NH3-enriched HTLW, were developed, which can enhance the reaction rate of acid/base-catalyzed organic reactions in HTLW. We investigated the decomposition of fructose in organic acids-enriched HTLW, hydrolysis of cinnamaldehyde and aldol condensation of phenylaldehyde with acetaldehyde in NH3-enriched HTLW. The experimental results demonstrated that organic acids-enriched or NH3-enriched HTLW can greatly accelerate acid/base-catalyzed organic reactions in HTLW.

POLYMER-SUPPORTED LEWIS ACID CATALYSTS. Ⅵ. POLYSTYRENE-BONDED STANNIC CHLORIDE CATALYST

A polystyrene-bonded stannic chloride catalyst was synthesized by the method of lithium polystyryl combined with stannic chloride. This catalyst is a polymeric organometallic compound containing 0.25 mmol Sn (Ⅳ)/g catalyst. The catalyst showed sufficient stability and catalytic activity in organic reaction such as esterification, acetalation and ketal formation, and it could be reused many times without losing its catalytic activity.

ESR studies on reactions of dicyclopentadienyl dicarbonyl titanium with organic halides

ESR method was used to elucidate the mechanism of the reactions of alkyl,allyl or benzyl halides with dicyclopentadienyldicarbonyl titanium.The paramagnetic intermediates of the reac- tions were identified during the course of the reactions.The reaction mechanism based on ESR find- ings and the products analyses is postulated to operate on radical pathways.When alkyl halides were used to react with the organometallic compound 1,the intermediate found was[Cp_2Ti(CO)X](C), and the main product was identified to be dicyclopentadienyl-acyl-halo titanium(3),an insertion of TiCO into R-X,i.e.[Cp_2Ti-C(O)R]X.When allyl or benzyl halidcs were used,the intermediate found was[Cp_2TiX](B),and the main products were identified to be the dicyclopentadienyl titanium dihalides and the coupling products of allyl or benzyl groups.

Heterogeneous Cu catalyst in organic transformations

Copper catalysis plays a crucial role in organic synthesis providing a wide spectrum of important transformations over decades.Success in homogeneous copper catalysis has often relied on the appropriate modulation of coordinating ligands,whereas the development of the corresponding heterogeneous variant has relatively gained less attentions.In this review,we aim to deliver a comprehensive summary of a number of seminal heterogenized Cu-catalyzed homogenous catalysis reported over the last decade.The scope of this review is classified by the type of transformations in which the catalyst’s preparation and activity including the relationship between structure and activity are underscored.In this way,this review highlights the potential and synthetic perspectives of heterogeneous copper catalysis in both academic and industry.

Suzuki Reactions in Water Catalyzed by an Active and Reus- able PMO-Type Pd（ll） Organometal Catalyst with Cage-Like Mesoporous Structure

A novel Pd（ll） organometal catalyst with three-dimensional （3D） cage-like la3d cubic mesoporous structure and high surface area was prepared. In comparison with the corresponding catalyst with two-dimensional （2D） P6mm hexagonal mesoporous structure, the as-prepared catalyst exhibited higher activities in the water-medium Suzuki coupling reactions owing to the diminished diffusion limit. It showed comparable efficiencies with the Pd（PPh3）2C12 homogeneous catalyst and could be easily recycled and reused for five times without significant loss of activity.

Homogeneous and heterogeneous reactions of anthracene with selected atmospheric oxidants

The reactions of gas-phase anthracene and suspended anthracene particles with O3 and O3-NO were conducted in a 200-L reaction chamber, respectively. The secondary organic aerosol （SOA） formations from gas-phase reactions of anthracene with O3 and O3-NO were observed. Meanwhile, the size distributions and mass concentrations of SOA were monitored with a scanning mobility particle sizer （SMPS） during the formation processes. The rapid exponential growths of SOA reveal that the atmospheric lifetimes of gas-phase anthracene towards O3 and O3-NO are less than 20.5 and 4.34 hr, respectively. The particulate oxidation products from homogeneous and heterogeneous reactions were analyzed with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer （VUV-ATOFMS）. Gas chromatograph/mass spectrometer （GC/MS） analyses of oxidation products of anthracene were carried out for assigning the time-of-flight （TOF） mass spectra of products from homogeneous and heterogeneous reactions. Anthrone, anthraquinone, 9,10- dihydroxyanthracene, and 1,9,10-trihydroxyanthracene were the ozonation products of anthracene, while anthrone, anthraquinone, 9-nitroanthracene, and 1,8-dihydroxyanthraquinone were the main products of anthracene with O3-NO.

Sonication method synergism with rare earth based nanocatalyst:preparation of NiFe_(2–x)Eu_xO_4 nanostructures and its catalytic applications for the synthesis of benzimidazoles,benzoxazoles,and benzothiazoles under ultrasonic irradiation

A simple and practical ultrasonically synthetic strategy for the preparation of rare-earth based catalyst, nanostructured NiFe2-xEuxO4 was developed. The structtre of NiFe2-xEuxO4 was characterized by various analyses such as X-ray diffraction （XRD）, scanning electron microscopy （SEM） and fourier transform infrared spectroscopy （FT-IR）. The catalytic performance of NiFe2-xEuxO4 was evaluated for the synthesis of benzimidazoles, benzoxazoles and benzothiazoles under ultrasonic irradiation. All reactions were completed in short times and all products were obtained in good to excellent yields in presence of the rare-earth based catalyst. Besides, NiFe2-xEuxO4 could be recovered for 6 times without noticeably decreasing the catalytic activity.

Visible-light-induced photoredox-catalyzed synthesis of benzimidazo[2,1-a]iso-quinoline-6(5H)-ones

A simple and efficient visible-light-induced photo redox-catalyzed diarylation of N-methacryloyl-2-arylbenzoimidazoles with aryl diazonium salts was developed.The reaction provides a conve nient access to a variety of benzimidazoisoquinolinones through the construction of two C-C bonds in one step under mild reaction conditions.