E. A. Karakhanov

Pd Nanoparticles in Dendrimers Immobilized on Silica–Polyamine Composites as Catalysts for Selective Hydrogenation

New heterogeneous hydrogenation catalysts, based on Pd nanoparticles and polypropyleneimine (PPI) dendrimers of the third generation that have been covalently grafted to a silica surface modified with polyallylamine (PAA) have been synthesized. The final products were characterized by TEM, XPS, and solid-state NMR spectroscopy. The synthesized materials are effective catalysts for selective hydrogenation of dienes to monoenes and phenyl acetylene to styrene at very high substrate/Pd ratios with turnover rates higher than related Pd nanoparticle catalysts. The synthesized catalysts can be reused without any loss of activity in the case of styrene and isoprene.

New catalytic systems for selective oxidation of aromatic compounds by hydrogen peroxide

Abstract Some new water-soluble catalytic systems based on iron complexes of polyethylene oxide and block copolymers of ethylene oxide and propylene oxide functionalized by catechol or β-cyclodextrin have been developed. These complexes were examined as catalysts for biomimetic hydroxylation of benzene and phenol by hydrogen peroxide. It is shown that the introduction of β-cyclodextrin into the polyethylene oxide molecule is favourable for rate and selectivity of hydroxylation of aromatic compounds in a two-phase system.

Substrate selectivity in byphasic Wacker-oxidation of alkenes in the presence of water-soluble calixarenes

Abstract Biphasic Wacker-oxidation of higher olefins, catalyzed by palladium complexes with water-soluble sulfonated calix[4]arene- and calix[6]arene-derived ligands have been studied. Complexes showed high catalytic activity under mild conditions and can be multiply reused. Catalysts display substrate selectivity in oxidation of C 6 and C 8 olefins—internal cavity of calixarenes recognizes the size of the substrates. The correlation between binding constants of inclusion complexes and selectivity has been established.

Nanocatalysts based on dendrimers

Nanostructured regular materials based on dendrimers bound by covalent or coordination bonds between surface functional groups were synthesized. Bimetallic Cu(II) and Pd(II) metal complexes with nitrile-based dendrimers demonstrated high activity in Wacker oxidation of terminal alkenes along with good selectivity for methylketone formation. New heterogeneous catalysts based on Pd nanoparticles and cross-linked polypropylene imine (PPI) and polyamidoamine (PAMAM) dendrimers were prepared and examined for selective hydrogenation of unsaturated compounds.

Biphasic Wacker-oxidation of 1-octene catalyzed by palladium complexes with modified β-cyclodextrins

New water-soluble palladium complexes with molecular recognition abilities based on β-cyclodextrin (β-CD) modified by nitrile-containing groups have been designed. Complexes display high catalytic activity and selectivity in two-phase Wacker-oxidation of 1-octene under mild conditions. The correlation between binding constants for inclusion complexes of β-CD-based compounds with substrate and the reaction rates has been established.

Macrocomplexes on the basis of functionalized polyethylene glycols and copolymers of ethylene oxide and propylene oxide: synthesis and catalysis

Water soluble catalysts combining the properties of metal complexes and surfactants on the basis of terminally functionalized polyethylene glycols and block-copolymers of ethylene oxide and propylene oxide with various combinations of ethylene and propylene oxide fragments were investigated. Polymers, functionalized by dipyridyl and acetylacetone were used as ligands for preparation of Fe(III) and Co(II) complexes, which showed a high activity and selectivity in oxidation of cyclohexane and ethylbenzene by both hydrogen peroxide and oxygen. An aqueous phase hydroformylation rhodium catalyst was prepared on the basis of polyethylene glycols functionalized by phosphine groups.

Ruthenium Nanoparticles Stabilized in Cross‐Linked Dendrimer Matrices: Hydrogenation of Phenols in Aqueous Media

Novel catalysts consisting of ruthenium nanoparticles encapsulated in cross‐linked matrices based on the poly(propylene imine) dendrimers of the 1st and 3rd generations have been synthesized with a narrow particle size distribution (3.8 and 1.0 nm, respectively). The resulting materials showed high activity for the hydrogenation of phenols in aqueous media (specific catalytic activity reached turnover frequencies of 2975 h−1 with respect to hydrogen uptake). It has been shown that the use of water as a solvent leads to a 1.5 to 50‐fold increase in the reaction rate depending upon the nature of the substrate. It has been established that unlike the traditional heterogeneous catalysts based on ruthenium, during the hydrogenation of dihydroxybenzenes, the hydrogenation rate decreases in the order: resorcinol>hydroquinone≫catechol. The maximum specific activity for resorcinol was a turnover frequency of 243150 h−1 with respect to hydrogen uptake. The catalyst based on the dendrimer of the 3rd generation containing finer particles has significantly inferior activity to the catalyst based on the dendrimer of the 1st generation by virtue of steric factors, as well as the need for prereduction of the ruthenium oxide contained on the surface. These catalysts showed resistance to metal leaching and may be reused several times without loss of activity.

Surface active rhodium catalysts for hydroformylation of higher alkenes in two-phase systems

Abstract A variety of water-soluble phosphine and phosphite ligands with phase-transfer ability based on functionalized polyethylene oxide has been synthesized. The corresponding rhodium complexes show high catalytic activity in aqueous biphasic hydroformylation of higher alkenes under mild conditions. The catalysts can be easily separated from products and reused. The effect of ligands structure, temperature, ligand-to-rhodium ratio, addition of free PPh3 and P(OPh)3 on catalytic stability and activity is studied.

Design of dendrimer-based nanostructured catalyst systems and their catalytic activity in hydrogenation: Synthesis of ruthenium nanoparticles immobilized in dendrimer networks

A new method has been proposed for immobilization of 3-nm ruthenium nanoparticles on special supports synthesized for this purpose, polymer networks based on poly(propylene imine) dendrimers. It has been shown that the structure of the support has a substantial effect on the size of particles and their catalytic activity in the hydrogenation reactions of unsaturated and aromatic compounds. The catalysts can be reused without loss of activity.

Iron and copper complexes with nitrogen-containing ligands as catalysts for cyclohexane oxidation with hydrogen peroxide under mild reaction conditions

Oxidation of cyclohexane (CH) with hydrogen peroxide under mild reaction conditions in the presence of systems containing in situ generated iron complexes with nitrogen-containing ligands (2,2′-bipyridyl and o-phenanthroline) and chlorinated (Cl15) copper phthalocyanine (CuPcCl15) have been studied. It has been shown that in water-acetonitrile blends under optimum conditions, CH is oxidized with the formation of cyclohexanol, cyclohexanone, and acids involving cyclohexane hydroperoxide. High total selectivity for ketone and alcohol is reached in the excess of ligands and the substrate.