Homogeneous catalytic systems for the oxidative functionalization of alkanes: design,oxidants, and mechanisms

Russian Chemical Bulletin - The best examples of catalysts and catalytic systems for the oxidative functionalization of alkanes and mechanisms of their action are considered. The prospects for...     

Homo-and copolymerization of vinylcyclohexane with α-olefins in the presence of heterogeneous and homogeneous catalytic systems

The polymerization and copolymerization of vinylcyclohexane with α-olefins in the presence of several heterogeneous and homogeneous catalytic systems were studied. It was shown that, with respect to activity in the polymerization of vinylcyclohexane, the tested catalysts can be arranged in the following order: α-TiCl₃ < titanium-magnesium catalyst < metallocene catalyst. Poly(vinylcyclohexane) prepared with heterogeneous catalytic systems is a solid semicrystalline polymer. The properties of polymers synthesized with homogeneous systems differ substantially depending on the type of the metallocene used. In the presence of metallocenes with a C ₂ symmetry, crystalline powderlike products arise, while in the case of metallocenes with C ₁ and C _s symmetries, polymerization yields amorphous viscous products. Molecular-mass distributions of poly(vinylcyclohexane) samples prepared using both heterogeneous titanium-magnesium catalysts and homogeneous metallocene complexes show a bimodal pattern, indicating the heterogeneity of active centers of these catalysts. Upon introduction of a comonomer (ethylene, propylene, and 1-hexene) into the reaction mixture, the activity of all studied catalytic systems increases. When Me₂C(3-Me-Cp)(Flu)ZrCl₂ and rac-Me₂SiInd₂ZrCl₂ are used as catalysts, the degree of crystallinity of the copolymers grows owing to the presence of ethylene or propylene units in poly(vinylcyclohexane) chains.     

A highly selective catalytic method for the oxidative functionalization of C-H bonds

This communication describes a new and highly practical Pd(II)-catalyzed method for the regio- and chemoselective oxidative functionalization of arenes and alkanes. Carbon-hydrogen bonds of substrates that contain a variety of directing groups (e.g., pyridine, azobenzene, pyrazole, and imine derivatives) are selectively transformed into esters, ethers, and aryl-halides under mild conditions. The scope of this reaction in terms of substrate, directing group, and oxidant is described, and a preliminary catalytic cycle is proposed.     

Carbonylation of methyl acetate in the presence of polymeric rhodium-containing catalysts

New catalytic systems based on RhCl₃ and polymeric nitrogen- and oxygen-containing supports were proposed for the carbonylation of methyl acetate to acetic anhydride. The catalytic systems possess a high activity typical of homogeneous catalysts. The high activity is retained upon the repeated use of the catalyst separated from the reaction products. The nitrogen-containing polymers of the chitosan type serve as cocatalysts. In their presence, the induction period disappears, and the catalytically active species are stabilized, thus enabling the replacement of expensive LiI for cheaper salts of this metal.     

C-H functionalization of 1,4-naphthoquinone by oxidative coupling with anilines in the presence of a catalytic quantity of copper(II) acetate

The oxidative addition of anilines (2) with 1,4-naphthoquinone (3) to give N-aryl-2-amino-1,4-naphthoquinones (1) was found to be catalyzed by copper(II) acetate. In the absence of the catalyst, the reactions are slower and give lower yields with the formation of many colateral products. In the presence of 10 mol % hydrated copper(II) acetate, the reactions are generally more efficient in that they are cleaner, higher yielding, and faster.     

Kinetics of the oxidative coupling of methane in the presence of model catalysts

The kinetics of the oxidative coupling of methane (OCM) in the presence of La/MgO and NaWMn/SiO₂ catalysts in a flow reactor at low reactant conversions was studied. It was found that, in spite of different compositions and properties of the test catalysts, the formation of ethane from methane and ethylene from ethane can be described within the framework of the Mars-van Krevelen redox model in both cases. The rate laws of side reactions, which lead to the formation of carbon oxides, are different from the rate laws of the target reactions of the conversion of methane into ethane and ethane into ethylene. The kinetic parameters required for the numerical simulation of the OCM process were determined for either of the catalysts.     

Non-Cp type homogeneous catalytic systems for olefin polymerization

Development of homogeneous metallocene catalysts for olefin polymerization has been briefly overviewed prior to detailed examination of the chemistry of non-Cp type homogeneous catalytic systems. In order to emphasize the structural characteristics of non-Cp catalysts, they were initially classified according to the coordination numbers of 4-7 and then further subclassified according to the ligand types. Over 100 line drawings and 200 references are utilized.     

Catalytic selective oxidation or oxidative functionalization of methane and ethane to organic oxygenates

Selective oxidation or oxidative functionalization of methane and ethane by both homogeneous and heterogeneous catalysis is presented concerning: (1) selective oxidation of methane and ethane to organic oxygenates by hydrogen peroxide in a water medium in the presence of homogeneous osmium catalysts, (2) selective oxidation of methane to formaldehyde over highly dispersed iron and copper heterogeneous catalysts, (3) selective oxidation of ethane to acetaldehyde and formaldehyde over supported molybdenum cat...     

Dry reforming of methane on porous membrane catalytic systems

A method of high-performance dry reforming of methane into syngas at temperatures below 650 °C on membrane catalytic systems was proposed. The membrane catalytic systems consist of porous inorganic membrane-supports, prepared by self-propagating high-temperature synthesis and modified by nanosized metallocomplex components, which are uniformly distributed inside membrane pores. The influence of the composition of the supported active components, temperature, and flow rate on the activity and selectivity of CH₄ and CO₂ transformations into syngas, as well as the dynamics of CH₄ and CO₂ conversion on the membrane catalytic systems were studied.     

Phosphorylation of heptafluorobutanol in the presence of metal chloride-ether catalytic systems

Catalytic activity of complex catalysts based on Li, Na, K, and Cs chlorides and polydentate ligands, viz., dibenzo-18-crown-6, mono-, di-, and tetraglymes, and poly(ethylene glycols) PEG-600 and PEG-1000 was examined in the phosphorylation of heptafluorobutanol with phosphorus oxychloride. The introduction of an organic ligand into a catalytic system leads to improvement in solubility of the salt used as a catalyst and to an increase in the reaction rate by a factor of 1.3—2.8. The catalytic systems based on LiCl and poly(ethylene glycols) proved to be most efficient.     

Kinetics of the homogeneous catalytic hydrogenation of methacrylic acid in the presence of pentacyanocobaltate(II)

The kinetics and mechanism of the pentacyanocobaltate(II)-catalyzed hydrogenation of methacrylic acid has been investigated by a non-linear programming technique. Three kinetic models have been examined. The best results were obtained with the equation based on a mechanism involving free radicals and organocobalt intermediates.

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ESR studies of Ziegler type catalytic systems in the presence of CO

ESR studies of the interaction between Co(C₅H₇O₂)₂ and Al(C₂H₅)₃ in presence of CO reveal the formation of paramagnetic tri- and tetra-nuclear carbonyl compounds and the consecutive formation of complexes including one, two and three cobalt atoms. Al(C₂H₅)₃ decomposition is suggested to take place on the reduced transition metal to form Co–Al clusters. Structures for the paramagnetic heteronuclear clusters is proposed.

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Cyclodimerization of bicyclo[2.2.1]hepta-2,5-diene in the presence of rhodium-containing zeolite catalysts

It has been shown that norbornadiene is dimerized in the presence of rhodium-containing zeolite catalysts, forming hexacyclic [4+2]dimers preferentially. The effect of the structure and the method of preparation and pretreatment of the catalysts on their activity and selectivity in norbornadiene cycloaddition was studied. The influence of the above parameters on the change in the electronic state of rhodium in the course of the reaction was also investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1913–1919, November, 1994.     

Polymerization of vinyl acetate in homogeneous systems obtained in presence of acrylic acid

The composition ranges over which microemulsions are formed in systems containing vinyl acetate, acrylic acid, water with nonylphenol ethoxylated with 25 mol ethylene oxide monomaleate as surfactant were studied. Conductometric and refractometric investigations have shown the existence of some aqueous/organic, bicontinuous and organic/aqueous microemulsions. The types of precursor microemulsions influence the conversion of monomers. In the presence of a crosslinking agent, diethylene glycol bis maleate, hydrogels are formed whose water absorption depends on the composition of the initial microemulsions. The kinetics of water absorption suggests the modification of polymer network structures as a function of the crosslinked monomer content and the ratio of organic to aqueous phases. Received: 4 March 1998 Accepted in revised form: 8 September 1998     

Glyoxal-promoted homogeneous catalytic oxygenation of cyclohexane with hydrogen peroxide in the presence of V and Co compounds

The efficiency of cyclohexane oxidation with hydrogen peroxide catalyzed by vanadyl acetylacetonate at 40 °C and atmospheric pressure is enhanced by glyoxal additive. The process selectively produces a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone with a high rate (up to 4400 catalyst turnover number). Cobalt(II) acetylacetonate is much less active but more selective with respect to cyclohexyl hydroperoxide.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 307–310, February, 2005.     

Polymerization of ethylene in the presence of novel single-site titanium phenolate catalytic systems

The polymerization of ethylene has been studied in the presence of novel catalytic systems based on various sterically hindered phenol precursor complexes of titanium containing grafted phenoxyammonium ligands. The presence of the grafted ammonium salt in the phenolate ligand leads to an increase in the activity of the catalyst and originates single-site catalytic systems. As evidenced by IR and ¹³C NMR studies and DSC measurements, the resulting polymers are linear, possess a narrow molecular-mass distribution (M _w/M _n = 2–4), and are characterized by a wide range of thermal properties.