Alternating Diene Metathesis Polycondensation (ALTMET) – Opitimizing Catalyst Loading

Summary: Olefin metathesis polymerization is a flexible and easy way to prepare highly functionalized macromolecules with high precision. Within this context, the efficiency of a series of ruthenium based catalysts in the polycondensation of dienes with diacrylates yielding alternating copolymers is studied. Previous works with Grubbs 2^nd generation catalyst are compared with Hoveyda 2^nd generation catalyst that was found to be much more efficient in these reactions giving reasonable conversions and thus high molecular weights at low catalyst loading. Additionally the performance of several other Hoveyda type catalysts has been studied.     

Indium (III) Tribromide : An Excellent Catalyst for Biginelli Reaction

A highly efficient catalyst indium (III) tribromide is used to synthesize 5-alkoxy- carbonyl-4-hydrocarbyl-3,4-dihydropyrimidin-2(1H)-ones by a three-component coupling of β-keto ester, aldehydes and urea through improved Biginelli reaction.     

A (31) P NMR Investigation of the CoPi Water-Oxidation Catalyst

Beneath the sheets: (31) P?NMR data suggests that phosphates are liberated freely in the interlayer of a cobalt-hydroxide water-oxidation catalyst. The cobalt-hydroxide sheets are separated by an interlayer region with water, counterions and phosphate, which help to shuttle protons as the layer develops charge.     

A Homogeneous Chiral Manganese(III)–Salphe Catalyst for Enantioselective Epoxidation of Olefins

A new chiral Mn(III)–Salphe catalyst was synthesized from natural amino acid (R)-phenylalanine and 3,5-di-tert-butyl-hydroxybenzaldehyde and applied to the asymmetric epoxidations of unfunctionalized olefins in ionic liquids. Satisfactory enantioselectivities (79% < ee < 93%) and good yields were achieved when NaClO was used as oxidant. We found that both the pH value (11.3) and reaction temperature (15 °C) were crucial for the epoxidation reactions. In our reaction system, NH₄OAc was unnecessary. We proposed that alcoholic hydroxyls in the Mn(III)–Salphe compound played the role of axial ligand. However, the reaction time was longer than when using Jacobsen's catalyst because of the structure of the Mn(III)–Salphe compound, in which coordination geometries by the two alcoholic hydroxyls with certain angles affected the substrate approaching the Mn(V) = 0 center. The chiral ligand was characterized by the combination of infrared, ultraviolet, and visible spectra and ¹H NMR.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Dehydrocoupling Polymerization: Poly(silylether) Synthesis by Using an Iron β-Diketiminate Catalyst

We describe the iron-catalyzed polymerizations of diol and silane monomers to obtain fourteen different poly(silylether) products with number average molecular weights (M_n) up to 36.3 kDa. The polymerization reactions developed in this study are operationally simple and applicable to 1° and 2° silane monomer substrates and a range of benzylic and aliphatic diol substrates as well as one polyol example. The polymers were characterized by IR spectroscopy, DSC and TGA and, where solubility allowed, ¹H, ¹³C{¹H}, ²⁹Si{¹H} NMR spectroscopies, GPC and MALDI-TOF were also employed. The materials obtained displayed low T_g values (−70.6 to 19.1 °C) and were stable upon heating up to T_–5%,Ar 421.6 °C. A trend in T_–5%,Ar was observed whereby use of a 2° silane leads to higher T_–5%,Ar compared to those obtained using a 1° silane. Reaction monitoring was undertaken by in situ gas evolution studies coupled with GPC analysis to follow the progression of chain-length growth which confirmed a condensation polymerization-type mechanism.     

Electrocatalysis of Metalloporphyrins(Ⅷ)——Electrocatalytic Reduction of Molecular Oxygen with Water-Soluble Cobalt (Ⅱ) Tetrakis(4-Trimethyl Ammonium Phenyl) Porphyrin Catalyst

Reported here is the electrocatalytic reduction of molecular oxygen in the presence of water-soluble cobalt(Ⅱ) tetrakis(4-trimethyl ammonium phenyl) porphyrin (Co(Ⅱ)TTAPP) as catalyst in solutions of various pH values. The overpotential of molecular oxygen reduction is reduced by ca. 200-400 mV in acidic and neutral solutions compared with several decades of millivolts in alkaline solutions, indicating that Co(Ⅱ)TTAPP possesses much higher catalytic activity in acidic and neutral solutions than in alkaline. H2TTAPP in solutions of various pH exhibits no significant catalytic activity for oxygen reduction. The significant difference in the electrocatalytic activity of Co(Ⅱ)TTAPP from that of H2TTAPP for oxygen reduction indicates that the electrocatalytic activity of Co(Ⅱ)TTAPP should be attributed to the central cobalt atom (Co(Ⅱ)) coordinated by N4 internal ring in Co(Ⅱ)TTAPP. The total number of electrons involved in oxygen reduction electrocatalyzed by Co (Ⅱ)TTAPP is 2, and the product of suc     

Thermoregulated Phase-separable Ru_3(CO)_(12)/PETPP Complex Catalyst for Hydrogenation of Styrene

The basic problem in homogeneous catalysis is the separation of catalyst from the reaction mixtures. To overcome this drawback, a number of methods have been developed. One of them is to attach homogeneous catalyst to supports 1. An alternative and well used approach involves liquid/liquid biphasic catalysis in which the catalyst and product reside in different phases and separation of the products is achieved simply by phase separation2. Recently, a concept of thermoregulated phase transf…     

Metal 2-Hydroxy-1-Naphthaldehyde Thiosemicarbazone (Me-HNT) Complexes-A New Kind of Biomimic Enzyme Catalyst

Enzymes have been widely used in analytical biochemistry and have considerableadvantages of rapidity and high selectivity'-', but they are expensive and their solutions arequite unstable. So study of biomimic enzyme become an important branch of enzyme,analysis'-'. Metal complexes are important mimetic resources, e-g. the metalloporphyrins.(MPs) system has been used as the model of mimic peroxidase'. As common ligands,Schiffbases are easy to be synthesized, dissolved and are widely used in me…     

Hydrocarboxylation of Styrene in Water-Soluble Catalyst System Pd(OAc)_2-TPPTSH-HOAc-H_2O

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Reduction of Sulphur-containing Aromatic Nitro Compounds with Hydrazine Hydrate over Iron(III) Oxide-MgO Catalyst

Sulphur-containing aromatic amines were prepared efficiently in good to excellent yields by reduction of the corresponding sulphur-containing aromatic nitro compounds with hydrazine hydrate in the presence of iron(III) oxide-MgO catalyst. The catalyst exhibited high activity and stability for the reduction of sulphur-containing aromatic nitro compounds. The yields of sulphur-containing aromatic amines were up to 91-99 % at 355 K after reduction for 1-4 h over this catalyst.     

Pd Close Coupled Catalyst

Europe III standards require significantly higher emissions reduction, especially for hydrocarbon (HC). For a typical vehicle, a large portion (up to 80 %) of the HC emissions occurs during cold start. A variety of technologies are under development to reduce cold start HC emissions, including close coupled catalysts1; electrically heated catalysts2 and hydrocarbon absorbers3. Among them, the close coupled catalyst gradually dominated the technologies4. A high performance close coupled cat…     

Catalytic Asymmetric Cyclopropanation using a New Chiral β-Diketone Cu (Ⅱ) Complex as a Catalyst

ManytransitionmetalcomPlexescatalyzethedecomPositionofa-diazoesterbythemethylenetransferreactiontoolefins,givingthecorrespondingcyclopropaneadductsl'z.Thismethodhasbeenwidelyusedinthesynthesisofnaturalproducts.Sofar,variouskindsoftransitionmetalcomPlexeshavebeenusedintheasymmetriccyclopropanation"'.6-diketonecomplexessuchasCu(acac)2(acac=acetylacetone)areamongthemostpopuIarcatalystsforthecyclopropanationofalkeneswithdiazocomPounds,butthefirstchiralo-diketonecomplexwasreportedonlyinl9845.Wesy…     

High Trans-1,4(Co)Polymerization of β-Myrcene and Isoprene with an Iminophosphonamide Lanthanum Catalyst

β-Iminophosphonamide ligated lanthanum bis(benzyl) complex(NPNDipp)La(CH2Ph-4-Me)2(THF)(NPNDipp = Ph2P(NC6H3iPr2-2,6)2), upon activation of Al Et3 and [Ph3C][B(C6F5)4], exhibited high catalytic activity and high trans-1,4 stereoselectivity for the polymerization of bio-sourced b-myrcene(MY). Based on which, a series of novel trans-1,4 regulated elastomers could be generated by random/block copolymerization of MY and isoprene(IP).     

The Polymerization of Methyl Methacrylate with a New Nd(O—i-Pr)_3—AI(i-Bu)_3Catalyst System

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Copolymerization of Ethylene/1-Butene with Heterogeneous TiCl4/(α-Diimine)nickel(Ⅱ) Complex Combined Catalyst

The new type heterogeneous combined catalyst system TiCl4-(α-diimine)nickel(Ⅱ) complexes/MgCl2-SiO2/AlR3 was prepared. Ethylene and 1-butene were copolymerized with the catalysts in slurry phase. It was found that with combined catalyst, the copolymers with lower density and higher branched degree were obtained. 13CNMR results showed that in the obtained copolymers existed not only ethyl but also some other kinds of branches due to the fact that ethylene exhibits the behavior of oligomerization and copolymerization in-situ with combined catalysts.     

Synthesis of 4-Methyl-2-Isopropyl-1,3-Dioxolane by TiSiW_(12)O_(40)/TiO_2 as Catalyst

Acetals and ketals are a kind of the important compounds and used to protect carbonyl, middle material of the organic synthesis. What’s more, they are a sort of the widely use flavor substance. 4-Methyl-2-isopropyl-1,3-dioxolane has fresh fruit odor and apple note. It is used to producing many sorts of essence. And the conventional method to synthesize 4-methyl-2-isopropyl-1,3-dioxolane makes use of sulfuric acid as catalyst in factories. But it causes many problems, such as the erosion of p…     

Scandium(III) Triflate as an Efficient and Reusable Catalyst for Synthesis of 3,4‐Dihydropyrimidin‐2(1H)‐ones

Sc(III) triflate efficiently catalyzes the three‐component condensation reaction of an aldehyde, a β‐ketoester, and urea in refluxing acetonitrile to afford the corresponding 3,4‐dihydropyrimidin‐2(1H)‐ones in excellent yields. The catalyst can be recovered and reused, making this method friendly and environmentally acceptable.     

Synthesis and Characterization of Poly(isoprene-b-butyl methacrylate) Block Copolymer in the Presence of Rare Earth Catalyst

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Methylalumoxane (MAO)-Derived MeMAO− Anions in Zirconocene-Based Polymerization Catalyst Systems – A UV-Vis Spectroscopic Study

Reaction of Me₂Si(Ind)₂ZrCl₂ with excess methylalumoxane (MAO) gives rise to ion pairs containing zirconocenium cations of the type [Me₂Si(Ind)₂ZrMe]⁺ in contact with two types of anions, MeMAO _A ⁻ and MeMAO _B ⁻, which differ in their coordinative strengths: More strongly coherent contact-ion pairs [Me₂Si(Ind)₂ ZrMe^+..MeMAO _B ⁻] are converted by a sufficiently high excess of MAO to more easily separable contact-ion pairs [Me₂Si(Ind)₂ZrMe^+..MeMAO _A ⁻], which react with AlMe₃ to form the outer-sphere ion pairs [Me₂Si(Ind)₂Zr(µ-Me)₂AlMe₂]⁺ MeMAO _A ⁻, and are likely to be required also for the formation of the olefin-containing reaction complexes responsible for catalytic activity.