Martin Čapka

Hydrogenation activity of homogeneous and heterogenized rhodium(i) complexes containing (ω-triethoxy-silylalkyl)-diphenylphosphines

Abstract Kinetics of liquid phase hydrogenation of alkenes catalysed by homogeneous rhodium(I) complexes prepared in situ from μ, μ′-dichloro-bis-[di(alkene)rhodium] and phosphines of the type RPPh 2 (R = −(CH 2 ) n (OEt) 3 n = 1 − 6 and R = −CH 2 SiMe 3− m (OEt) m ; m − 3) and by their heterogenized analogues anchored to silica have been studied at 1.1 atm hydrogen pressure and 37 − 67 °C. The hydrogenations catalysed by catalysts of both types were found to be first order in the alkenes. The reaction rates are discussed in relation to the deactivation of the rhodium catalysts due to the dimerisation of catalytically active species. It is proposed that the dimerisation takes place also on the surface of the support and depends on the length of the spacer group separating the diphenylphosphino group from the surface.

Silica-supported rhodium complexes. relation between catalyst structure and activity

Abstract A series of heterogenized catalysts has been prepared by the reaction of chlorobis(ethylene)rhodium(I) dimer and phosphinated silica. The structures of these catalysts have been varied by changing the length of the phosphine-alkylene chain, -(CH2)nPPh2, used to couple the rhodium center to the silica surface. The dependence of the activity of the silica-attached catalysts on the structure has been studied in the hydrosilylation of hexene-1. It was found that the activity was ten times higher for the complex linked to silica through a short chain, containing one methylene group, than for the other rhodium complexes linked via alkylene chains containing two to six carbon atoms. Variatons in the activity have been attributed to the differences in the nature of the catalytic species formed on the surface. A binuclear structure for the catalysts of lower activity and a mononuclear one for the catalyst of higher activity have been postulated and confirmed by e.s.c.a. and i.r. measurements.

Carbohydrate phosphinites as chiral ligands for asymmetric syntheses catalyzed by complexes: Part VIII1: Immobilization of cationic rhodium(I) chelates of phenyl 4,6-O-(R)-benzylidene-2,3-bis(O-diphenylphosphino)-β- D-glucopyranoside on silica

Abstract The application of silica-based cation exchangers (SiO2)-O-Si(CH2)3-O-C6H4SO3H for immobilization of the cationic rhodium(I) chelate 5 of phenyl 4,6-O-(R)-benzylidene-2,3-bis(O-diphenylphosphmo)-β-D-glucopyranoside (Ph-β-glup) in methanol gives rise to hetrogenized solvolyzed species 6a carrying two hydroxy groups and showing enhanced enantioselectivity in the hydrogenation of N-acetylamino-acrylic acid esters of up to 95% e.e. compared with 91% e.e. for the homogeneous catalyst 5. The high activity of the heterogenized catalyst may be increased more than five-fold by preloading the exchanger with alkali or ammonium ions, thus approaching the level of homogeneous ones. The high leaching of rhodium may be minimized by using supports preloaded with aniline. Application of solvents of different polarity is possible.

Selective Phosphination of (3-Chloropropyl)triethoxysilane. A New Route to Alkoxysilyl-Substituted Phosphines1

Abstract Tertiary phosphines of the type (C2Hj5O)3Si(CH2)3-P(C6H5)R /R = phenyl (Ia) and menthyl (Ib)/ were prepared by phosphination of the title compound with LiP(C6H5)R.

Catalytic activity of homogeneous and silica-anchored rhodium complexes

Using recently synthesized [1] (C2H5O)3Si(CH2)3CH(COCH3)2 (1) and (CH3O)3Si(CH2)2−Py (2) (Py=2-pyridyl), a series of homogeneous and silica-anchored rhodium carbonyl complexes were prepared. Their catalytic performance was studied in hydrogenation, hydrosilylation and methanol carbonylation.

Effect of the Pore Size of a Support on Activity and Action Pattern of Immobilized Endopolygalacturonase

Endopolygalacturonase (E.C. 3.2.1.15) was covalently bound to silica supports of different porosity treated with 3-(2′,3′-epoxypropoxy)propyltrimethoxysilane. The activity and action pattern on sodium pectate and tetra(D-galactosiduronic acid) were investigated in batch and continuous flow-reactors. Pore size of the supports affected the loading of the enzyme as well as its action pattern and kinetics. A decrease in randomness of degradation of D-galacturonan, loss of specificity of (3 + 1) splitting of tetra(D-galactosiduronic acid) and decrease in Km value were found with the supports containing predominantly micropores. The extent of the changes decreased with increasing pore size of the support. The catalytic behaviour of endopolygalacturonase bound on the supports with large pores was quite analogous to that of the free enzymes.

Catalysis by Metal Complexes. VIII. An Improved Synthesis of 1-Trichlorosilyl-2-Butene and 1-Trichlorosilyl-2-Methyl-2-Butene

Abstract The title compounds were prepared in high yields under mild conditions by the reaction of the appropriate dienes with trichlorosilane catalysed with bis (benzonitrile) palladium dichloride.

Endopolygalacturonase immobilized on epoxide-containing supports

SummaryEndopolygalacturonase was immobilized onto 3-(2′,3′-epoxypropoxypropyl)-silica and oxirane-acrylic beads. Optimum conditions of immobilization and catalytic properties of the immobilized enzyme preparations are described.

Immobilization and nonspecific adsorption of proteins to pyrogeneous highly dispersed silicon dioxide

SummaryA support based on pyrogeneous silicon dioxide of particle size 0.01 to 0.1/um, modified by 3-(amino)propyltriethoxysilane and activated by glutaraldehyde was employed for the immobilization of concanavalin A, immunoglobulins, basic pancreatic trypsin inhibitor, and chymotrypsin. Its binding capacity is comparable with that of porous supports while the biological activity of the proteins immobilized is retained. Nonspecific adsorption of these proteins to the support is low compared to its binding capacity.

Methyl 4,6-O-benzylidene-2,3-bis-O-(diphenylphosphino)-α-D-glucopyranoside —A new efficient ligand for asymmetric hydrosilylation of ketones

A rhodium (I) complex with the title ligand has been found to be an efficient catalyst for enantioselective hydrosilylation of ketones. The optical yields of alcohols (47%) obtained compare this system favorably with the most effective catalysts so far reported.AbstractБыло найдено, что комплекс родия (I) с заглавным лигандом является эффективным катализатором энантиоселективного гидросилилирования кетонов. На основе полученных оптических выходов спиртов (47%) эти системы следует относить к самым эффективным катализаторам среди до сих пор известных.