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Версия для печати | Главная > Центр > Научные советы > Научный совет по катализу > ... > 2003 год > № 27

№ 27

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Краткая информация о конференциях в области катализа:

  • Российско-американский семинар "Достижения в области исследования и применения катализаторов"
  • 2-й Всероссийский семинар "Топливные элементы и энергоустановки на их основе" )

А.Д. Гохштанд
"Методы оценки стоимости объектов интеллектуальной собственности".

Новые конкурсы ИНТАС

За рубежом

Российско-американский семинар "Достижения в области исследования и применения катализаторов"


2-й Всероссийский семинар "Топливные элементы и энергоустановки на их основе"


А.Д. Гохштанд "Методы оценки стоимости объектов интеллектуальной собственности."


Новые конкурсы ИНТАС


За рубежом

Simple, direct indole synthesis

A remarkable metal-catalyzed reaction of nitroaromatic compounds with alkynes (shown) goes through N-centered reduction, C-H activation, and the formation of both C-N and C-C bonds to give indoles in moderate yields [Chem. Commun, 2002, 484]. Kenneth M. Nicholas, professor of chemistry and biochemistry, postdoc Andrea Penoni, and undergraduate Jerome Volkmann at the University of Oklahoma, Norman, find that nitrosoaromatics also yield indoles when reacted with alkynes, suggesting that the nitroso compounds are intermediates in this catalytic reductive annulation [Org. Lett., 4,699 (2002)]. The reactions are regioselective, selectively forming 3-substituted indoles with terminal alkynes. The researchers currently are exploring the scope and mechanism of the reactions and plan to use them in the synthesis of some of the many bioactive indoles.

C & EN / MARCH 11, 2002

Nornicotine catalyzes aldol reactions in H2O

A metabolite of nicotine can catalyze aldol reactions under physiological conditions, according to chemists at Scripps Research Institute [J. Am. Chem. Soc., 124, 3220 (2002)]. The intriguing finding has potentially large implications for understanding the physiology of cigarette addiction and for nicotine replacement therapy. Chemistry professor Kim D. Janda and graduate student Tobin J. Dickerson find that nornicotine (shown) catalyzes the reaction of acetone with 4-nitrobenzaldehyde in aqueous phosphate buffer, giving the aldol addition product in 81% yield. Nornicotine also catalyzes aldol reactions of other compounds, including pyruvate, an important player in metabolism. Such aldol reactions usually proceed only in organic solvents; in water, they require enzymes or Lewis acid catalysts.
A constituent of tobacco and a minor metabolite of nicotine, nornicotine has a longer half-life than its parent compound, and heavy smokers can have fairly constant levels in their blood. The Scripps researchers are investigating the physiological relevance of their findings.

C & EN / APRIL 1, 2002

Reduction of ligated N2 to ammonia

Yandulov and Schrock have been exploring the chemistry of triamidoamine ([(RNCH2CH2)3N]3-=[RN3N]3-) molybdenum complexes with the aim of understanding how catalytic reduction of dinitrogen might be achieved on a single-site homogeneous catalyst. These workers now have made the study of the process more transparent, with the development of a complex having a highly protected molybdenum reaction site (D Yandulov & R Schrock, J Am Chem Soc 2002. 124. 6252).

When R is an aryl group substituted in the 3 and 5 positions, it is possible to isolate complexes (see Figure 1) in which dinitrogen binds to molybdenum to form a monomeric species (avoiding formation of relatively stable [RN3N]Mo-Nº N-Mo[RN3N] complexes). The figure outlines some of the substitution, protonation and redox reactions that surround the synthesis and reactivity of [RN3N]Mo-Nº N complexes, but the reduction of dinitrogen to ammonia reported by these authors still requires reduction by CoCp2. Nevertheless, this ligand system allows the isolation of several intermediates in the reduction process - and knowledge that may be invaluable in the search for the ultimate objective: catalytic reduction of dinitrogen to ammonia.

Timothy Hughbanks Texas A&M University

arbon-free precursor to BN-nanotubes

The synthesis of carbon nanotubes led quickly to the investigation of corresponding boron nitride analogues. However, methods of synthesising carbon nanotubes have not been adaptable to the reliable synthesis of BN nanotubes. Thus, there is no way to obtain BN nanotubes in reasonable quantity or, especially, purity. Tang's group (C Tang Y Bando, T Sato & K Kurashima, Chem Commun 2002. 1290) has exploited the fact that boron reacts with MgO at elevated temperatures (11000C) to yield gaseous magnesium and B2O2. The latter reacts with ammonia that is flowed into the chamber, to produce the boron nitride product:

B (s) + MgO (s) ® B2O2(g) + Mg (g)
B2O2 (g) + NH3 (g) ® 2BN(s) + 2H2O (g) + H2 (g)

Catalysed additions of triphenylphosphine

In Chemistry Letters (2002. 272) Arisawa, Momozuka & Yamaguchi describe a rhodium-mediated process where triphenylphosphine adds to dienes (see Reaction 1). The regioselectivities observed are usually highly in favour of addition of the phosphine to the diene terminus. Where the regioselectivity of the addition is imperfect, then many products can be recrystallised to purity.

Z-Alkenes are less reactive than the E-isomers, hence the addition process can be used to remove the latter from mixtures of diene starting materials.

Kevin Burgess Texas A&M University

Palladium-catalysed arylation of thiophenesM

Continuing their work on arylation of electron-rich aromatic compounds. Miura and coworkers have investigated palladium-catalysed reactions of thiophenes with aryl halides. They find that 2-thiophene carboxamides undergo triarylatlon with loss ofthe amide functionality, 3-substituted thiophenes can be triarylated (especially if the 3-substituent is an electron withdrawing group), and the reaction conditions may be controlled such that diarylation of them is possible (reactions 3-5, respectively).

reaction 3

reactions 4 and 5

Hydrogenation of hindered alkenes

There are not many homogeneous catalysts that mediate hydrogenations of tri-and tetra-substituted, unfunctionalised alkenes. The gold standard in this field is Crabtree's catalyst, [Ir(PCy3)(py)(COD)]+PF6¯ which can achieve this at ambient temperature and pressure. In Organometallic. Weller and coworkers have reported a rhodium-based complex that has hydrogenation activities marginally inferior to Crabtree's catalyst (2002, in press). They report good evidence that the rhodium complex 1, under hydrogen, is transformed into 2 in which the [closo-CB11H6Br6]¯ anion complexes the metal as shown. The stated rationale behind investigation of this complex was that, '... the weakly coordinating carborane anion could ... move to one side to allow olefin and dihydrogen to coordinate the rhodium, while remaining available in order to stabilise reactive cationic species.' This hypothesis seems to be born out by the results. Under 1 atm of hydrogen at room temperature, complex 1 catalysed the hydrogenation of 1-methylcyclohexane and of 2,3-dimethylbut-2-ene, with turnover frequencies that are not significantly less than those measured for Crabtree's catalyst.

Complex 1 and 2

Chemistry & Industry - 15 July 2002

Calalytic epoxidation of alkenes by NO2

Nitrous oxide, often overlooked as an oxidant, has the obvious advantage of generating only a very innocuous by product on reduction. It now appears that it can be used to epoxidise alkenes in a process catalysed by the polyoxometalate [n-Oct3MeN]10[MnIII2ZnW(ZnW9O34)2]. Unfortunatuly, the process requires temperatures of 150oC and only proceeds at a rate of about one turnover/hour. However, the reaction is 100% stereoselective in that cis-stilbene only gives cis-stilbene oxide. It is also interesting from a mechanistic standpoint as, surprisingly appreciable quantities of Mn11 are formed reversibly in the reaction (EPR).

Fig. Allylis oxidation - typical reaction, catalyst and product

Chemistry & Industry - 16 September 2002

1-D zeolites trap hydrocarbons

One-dimensional zeolites, a class of porous solids with relatively low interconnectivity, may be useful as hydrocarbon traps in automotive catalysis, according to a study conducted at Northwestem University. At engine start-up catalytic converters are cold and ineffective in catalyzing reactions of hydrocarbons and other exhaust stream components - resulting in a couple of minutes of high-level tailpipe emissions. A proposed solution to the "cold start" problem involves trapping the hydrocarbons up-stream of the converter and releasing them after the converter is warm enough to cause the gases to react. Success with that approach, however, has been limited by a lack of suitable adsorbent materials, particularly for lightweight hydrocarbons. Now, chemical engineering associate professor Randall Q. Snurr, graduate student Kenneth F. Czaplewski, and coworkers have found that when test mixtures of propane and toluene are adsorbed in EUO and mordenite-1-D zeolites characterized by nonintersecting narrow channels-propane's desorption temperature is raised by 35 to 100oC compared to the desorption temperature of pure propane [Microporous Mesoporous Mater., 56, 55 (2002)]. The group explains that low concentrations of tightly adsorbed toluene are sufficient to clog the narrow pores at low temperatures.

C&EN / OCTOBER 28 2002/ 33

Combinatorial materials finding catalysts faster

Symyx-Dow collaboration yields new class of polyolefin catalysts

A four-year collaboration between Symyx Technologies and Dow Chemical has borne fruit in the discovery of a new class of single-site catalysts for olefin polymerization. The new amide-ether-based hafnium catalysts were found using a fully integrated high-throughput screening methodology [J. Am. Chem. Soc., 125, 306 (2003)].

"The results are stunning," says one of the coauthors, Dow chemist James C. Stevens, because the new screening methodology enabled them to do in days or weeks what used to take many months or years.

The Dow-Symyx researchers set out to discover new catalysts with potential for the production of linear low-density polyethylene, which is a copolymer of ethyiene and an α-olefin, such as 1-octene. They first synthesized a library of hafnium and zirconium complexes containing 23 different bidentate and tridentate ligands. To screen these complexes under different activation conditions, they carried out 384 polymerization experiments in just a few hours.

The work uncovered many catalytically active metal-ligand combinations. One hafnium catalyst (complex 1) was found capable, under the right conditions, of polymerizing 1-octene with 100% conversion. Further experiments demonstrated that this complex can produce high-molecular-weight ethylene-1-octene copolymers.

In the course of one day, the researchers then studied the activity at 130oC of 96 other hafnium complexes containing related amine-ether ligands. They found that many of these catalysts are even better at copolymerizing ethylene and 1-octene than complex 1.

In larger scale batch reactor experiments, complex 1 and a closely related hafnium complex were found to perform as well as or better than Dow's workhorse metallocene polyolefin catalyst system.

Dow isn't necessarily "marching to commercialization" with any of the catalysts reported in the JACS paper, Stevens tells C&EN. "But we will be talking soon, I think, about another catalyst that's come out of this procedure that is going to be commercialized. "-RON DAGANI.

C&EN / APRIL 7, 2003

Co catalysts, CO insertion, and bioplastics

Poly[(R)]-β-hydroxybutyrate] (PHB) is a biodegradable polyester that is made by bacteria and has properties similar to polypropylene. Its environmentally friendly nature is attractive, but high fermentation production costs make it impractical for many commercial applications. Chemistry professor Geoffrey W. Coates and his group at Cornell University have now come up with a new class of catalysts, [Lewis acid]+[Co(CO)4]-, which they believe could be part of a potentially economical chemical route to PHB. The researchers have shown that the Co catalysts readily insert CO into epoxides and aziridines to make β-lactones and β-lactams, respectively. For example, they have made multigram quantities of (R)-β -butyrolactone from (R)- propylene oxide with 95% yield and complete retention of configuration. The R isomer is critical to make PHB, Coates notes, since a mix of isomers leads to polymers with poor properties. Coates's group also has developed di-iminate zinc alkoxide catalysts for ring-opening polymerization of the β-lactones to PHB and related poly (β-hydroxy-alkanoates) [J. Am. Chem. Soc., 124, 15239 (2002)]. Other aspects of the work include using the catalysts to make substituted lactones, lactams, and other heterocycles for pharmaceutical building blocks.

C&EN / APRIL 14, 2003

First catalytic, asymmetric Passerini reaction devised

Chemists have found a way to carry out the Passerini reaction both catalytically and enantioselectively [J. Am. Chem. Soc., 125, 7825 (2003)]. The Passerini reaction is a carbon-carbon bond-forming process that's widely used to synthesize natural products and diverse libraries of drug candidates. It involves the formation, in one step, of an α-acyloxy carboxamide from three components: an isocyanide, a ketone or an aldehyde, and a carboxylic acid. Chemistry professor Scott E. Denmark and graduate student Yu Fan at the University of Illinois, Urbana-Champaign, show that, in the presence of silicon tetrachloride, a chiral bisphosphor-amide (shown) catalyzes the Passerini reaction enantioselectively. The catalyst, a Lewis base, promotes the ionization of SiCl4, a weak Lewis acid. The resulting catalyst-SiCl3+ adduct affords highly enandomerically enriched α-hydroxy amides and esters from a wide range of aldehyde and isocyanide starting materials.

Atmospheric' direct route to propylene oxide

A significant research problem in industrial chemistry has been to find a direct oxidation process to make propylene oxide, a versatile chemical intermediate. In theory, combining O2 with propylene should work, but the conversion is low. So instead, a pair of two-step processes currently are used to manufacture propylene oxide - the chlorohydrin process and the peroxidation process - but both have major coproducts. Now, Torsten Berndt of the Institute for Tropospheric Research in Leipzig, Germany, and coworkers have uncovered a potentially viable direct route to propylene oxide by reacting propylene with nitrogen(V) oxides such as nitrate radicals in the gas phase - chemistry the researchers observed while conducting atmospheric studies [Ind. Eng. Chem. Res., 42, 2870 (2003)]. The researchers combine NO2 with O3 and add the mixture to propylene in a flow-through gas reactor. The nitrogen (V) oxides formed act as an oxygen-transfer agent to convert propylene to propylene oxide with yields and selectivity comparable with the current industrial routes, Berndt notes. This noncatalytic nitrate oxidation route would be a lucrative alternative if it can be successfully scaled up, the researchers believe.

C&EN / June 23, 2003

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