V. A. Likholobov

New carbon material as support for catalysts

Structure and adsorption properties of new carbon carriers obtained on the basis of carbon black have been examined. These carriers possess largely mesoporous structure, developed surface and high mechanical strength and contain hollow globules. Walls of these globules have pores, whose size is several hundreds Å. The new material is of interest for fundamental studies of carbon-supported catalysts.AbstractИсследована структура и адсорбционные свойства новых углеродных носителей, полученных на основе технического углерода, которые обладают преимущественно мезопористой структурой, развитой поверхностью и высокой механической прочностью. Носитель состоит из глобул. Глобуль внутри пустье и стенки глобул имеют отверстия размером несколько сотен Å. Новый углеродный материал представляет интерес для фундаментального исследования катализаторов на углеродных носителях.

Determination of key intermediates for homogeneous water-gas shift reaction and hydrocarbonylation of ethylene to diethyl ketone catalyzed by the ‘Pd(OAc)2-PPh3-CF3COOH/H2O’ system

Abstract The homogeneous water-gas shift reaction (WGSR) and hydrocarbonylation of ethylene to diethyl ketone (DEK) catalyzed by the ‘Pd(OAc) 2 -PPh 3 -CF 3 COOH/H 2 O’ system have been studied. The main kinetic regularities of these reactions have been elucidated, and the catalytically active palladium species have been detected and characterized by 1 H, 13 C and 31 P NMR. The key palladium intermediate for both catalytic reactions is the cationic hydride complex [(PPh 3 ) 3 PdH] + 1. In the case of the WGSR, this complex serves as a source of dihydrogen, and in the case of the hydrocarbonylation of ethylene it undergoes transformations via consecutive rapid insertions of C 2 H 4 into a Pd-H bond and then of CO into a Pd-C bond to form, respectively, palladium ethyl and propionyl complexes. All the kinetic and NMR data obtained support the mechanism involving the phosphinepalladium(II) complex reduction with CO to form CO 2 as the rate-determining step for the WGSR, and the mechanism involving formation of the species 1 and the palladium propionyl complex interaction with C 2 H 4 as slow steps for the hydrocarbonylation of ethylene with CO/H 2 to give DEK. The possible reasons for the relative stability of the palladium hydride, ethyl and propionyl complexes in strongly acidic medium and the high selectivity of DEK formation in the hydrocarbonylation reaction are discussed.

Formation and reactivity of palladium hydride complexes, [(PPh3)3PdH]+ and [(PPh3)2Pd(μ-H)(μ-CO)Pd(PPh3)2]+, in aqueous trifluoroacetic acid solutions

Abstract Interaction of H2 with P2PdX2 complex (P = PPh3, X = CF3COO) in aqueous trifluoroacetic acid solution at 70°C in excess triphenylphosphine results in the formation of the palladium hydride complex [P3PdH]+. The same complex is formed by protonation of PdP4 at 25°C in aqueous CF3COOH. When treated by carbon monoxide, [P3RdH]+ is changed to the binuclear palladium carbonyl hydride complex [P2Pd(μ-H)(μ-CO)PdP2]+.

Synthesis of Pd(II) nitro and nitrate complexes and studies of their reactivity towards oxidation of olefins in organic solvents

Complexes of the composition Pd(NOn)2−mClmL2 (n=2, 3; m=0, 1, 2; L=CH3CN) have been synthesized and their reactivity in ethylene and propylene oxidation has been examined. Data on the influence of the ligands, solvents and olefins on the composition of reaction products are reported.AbstractСинтезированы комплексы состава Pd(NOn)2−mClmL2 (n=2, 3; m=0, 1, 2; L=CH3CN) и изучены их реакционные свойства в окислении этилена и пропилена. Получены данные о влиянии природы лигандов, растворителя и олефина на скорость и состав продуктов реакции.

Effect of dentate number of anchored phosphine ligands on the composition and catalytic properties of their palladium complexes

Mono-, di- and triphosphine ligands anchored by a Si−C bond to the surface of silica have been synthesized. Complexes of Pd(II) and Pd(O) with these ligands have been obtained. On the basis of elemental analysis and UV spectroscopy, structures of the complexes formed are suggested. The catalytic properties of the above complexes in the selective hydrogenation of cyclopentadiene are compared.AbstractПроведён синтез моно-, ди- и трифосфиновых литандов, закр еплённых связью Si−C с поверхностью силикагеля. Получены комплексные соедине ния Pd(II) и Pd(O) с этими лигандами. На основании данных элементного анализа и УФ-спектроскопии предложены структуры образуюшихся комплексов. Сопоставлены катал итические свойства полученных комплексов в реакции селективного гидриров ания циклопентадиена.

Study on the mechanism of ethylene oxidation by a nitrite complex of palladium in chloroform medium

Abstract A detailed mechanism of ethylene oxidation by a palladium nitrite complex Pd(NO 2 )Cl(CH 3 CN) 2 in chloroform solution is studied using IR and 1 H NMR spectroscopy. Kinetic and spectral data obtained indicate the formation of a number of intermediates. The structure and routes of decomposition of the intermediates to end products are suggested.

Mechanism of catalytic oxidation of olefins by periodic acid in acetic solutions of palladium acetate

Abstract Oxidation of C2-C4 olefins by periodic acid, catalyzed with palladium acetate, is studied. During oxidation, glycol esters are formed with high selectivity. The process is accompanied by oxygen atom transfer from the periodate anion to the olefin. Results of the kinetic study of ethylene oxidation are reported. The structure of intermediate palladium complexes is studied using NMR and IR spectroscopy. The mechanism of the reaction is also discussed.

Formation of glycol esters from olefins in acetic acid solutions containing Pd(II) and LiXO3 as oxidizing agent

A study was made of the formation of glycol derivatives from ethylene and other olefins in acetic acid solutions containing Pd(OAc)2 and LiXO3 (X=Cl, Br, I). On the basis of the data obtained an assumption of the processes taking place in the system was made.AbstractПроведено исследование реакции образования производных глик лей из этилена и некоторых других олефинов в уксуснокислом растворе, содержащем Pd(OAc)2 и LiXO3 (X=Cl, Br, I). На основании полученных данных сделано предположение о юсительно происходящих в системе процессов.

Ethylene oxidation by lithium nitrate in the presence of palladium acetate in acetic acid

Data are reported on variations of the gas phase volume and product accumulation in ethylene oxidation by lithium nitrate in acetic acid solutions, catalyzed by palladium acetate. An assumption is made on the routes of nitrate ion reduction.AbstractПолучены данные об изменении обьема газовой фазы и накопления продуктов в реакции окисления этилена нитратом лития, катализируемой ацетатом палладия, в растворах уксусной кислоты. На основании этих данных сделано предположение о путях восстановления нитрат-иона.

Studies of the reasons for the deactivation of palladium(II)-nitrate catalytic systems

Studies of the reasons for the deactivation of palladium-nitrate catalytic systems indicate that this process is due to the formation of insoluble palladium complexes with side products of catalytic reactions, e.g. cyanide ion, oxalic and nitrolic acids. The deactivation is decreased by the addition of ions of transition metals Ru, Rh, Ni and Fe.AbstractИсследованы причины, приводящие к дезактивации палладий-нитратных каталитических систем. Установлено, что процесс дезактивации обусловлен образованием нерастворимых комплексов палладия с продуктами побочных окислительновосстановительных реакций, такими, как цианид-ион, щавелевая кислота и нитроловые кислоты. Показано, что введение в раствор ионов переходных металлов Ru, Rh, Ni и Fe приводит к замедлению процесса дезактивации.