Jiří Hetflejš

A rhodium-DIOP complex attached to an inorganic support as catalyst for enantioselective syntheses

A rhodium-DIOP complex attached to a macroporous silica gel has been tested as catalyst for the enantioselective hydrosilylation of acetophenone and hydrogenation of α-acetamidocinnamic acid. The catalyst has been found to be comparable in asymmetric efficiency to homogeneous analogues. In both reactions, the activity of the heterogenized catalyst was by ca. one order of magnitude lower relative to the homogeneous system.AbstractКаталитические свойства комплекса родия с DIOP, связанного на макропористом силикагеле, были проверены в энантиоселективном гидросилилировании ацетофчнона и гидрировании α-ацетамидокоричной кислоты. Было найдено, что катализатор по своей асимметричной эффективности сравним с гомогенными аналогами. В обоих реакциях активность гетерогенного катализатора была приблизительно на один порядок ниже по сравнению с гомогенными системами.

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.

Photodynamic efficiency of porphyrins encapsulated in polysilsesquioxanes

Mesoporous organosilica-porphyrin composites were obtained by entrapment of 5,10,15,20-tetraphenylporphyrin (TPP) and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP) into three polysilsesquioxanes prepared by the sol-gel method from 1,2-bis(triethoxysilyl)ethane, 1,6-bis(triethoxysilyl)hexane, and 1,8-bis(triethoxysilyl)octane. The materials were characterised by their texture and optical properties (fluorescence and absorbance) and by light-induced antimicrobial activity against E. coli BL21(DE3) (pET16bDsRed) strain.

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.

Kinetics of hydrogenation of Z-α-acetamidocinnamic acid catalyzed by rhodium-diphosphine arenesulfonate complexes

Kinetics of the title reaction catalyzed by complexes of the type (Rh(COD)L2)+(O3SC6H4CH3−p)−(L2=Ph2P(CH2)nPPh2, n=2–4, (−)-DIOP) have been studied. With all the catalysts, the reaction proceeds according to the rate law, −d(C=C)/dt=k[Rh]tot[H2] which speaks for the “unsaturate route” to the product.AbstractИсследована кинетика заглавной реакции, катализованной комплексами типа /Rh(COD)L2/+(O3SC6H4CH3−p)−(L2=Ph2P(CH2)nPPh2, n=2–4, (−)-DIOP). Скорость реакции, со всеми катализаторами, подчиняется уравнению: −d(C=C)/dt=k[Rh]tot[H2], что свидетельствует о “ненасьщенном пути”, приводящем к продукту.

Isomerization of 1-pentene catalyzed by Wilkinson's catalyst coordinatively bound to silica

Isomerization of 1-pentene catalyzed by tris-(triphenylphosphine)rhodium(I) chloride coordinatively bound to silica via-O−Si(CH2)nPPh2 (n=1–4,6,9) has been studied. The efficiency of the catalysts depends on the method of their anchoring and spacer length. The best results have been obtained with catalysts containing longer spacers, performing isomerization in the presence of hydrogen.AbstractИзучали изомеризацию 1-пентена, катализированную хлористым трис-(трифенилфосфин)родием(I), координационно связанным с двуокисью кремния через-O−Si(CH2)nPPh2 (n=1–4,6,9). Эффективность катализаторов зависит от метода их сцепления и длины носителя. Наилучшие результаты получены с катализаторами, содержащими длинные носители, проводя изомеризацию в присутствии водорода.

Regioselective Synthesis of Chloro(Methyl)(3-Phenylpropyl)Silanes

Abstract The title compounds of the type C6H5(CH2)3Si(CH3)3-nCln (n = 1–3) have been prepared in good yields by regioselective hydrosilylation of allylbenzene by the corresponding silanes (CH3)3-nSiHCln (n = 1–3), using the H2PtCl6 + P(C6H5)3 system as catalyst.

Hydrogenation of alkenes catalyzed by supported Ziegler catalysts

Supported Ziegler catalysts prepared by the reaction of a Ni(II) 1-butylsalicylaldiminate or Ni(II) 2-ethylhexanoate with Al2O3/SiO2 treated with AlEt3 or NaAlH2 (OCH2CH2OCH3)2 are efficient catalysts for hydrogenation of simple alkenes. The factors influencing their activity are reported.AbstractНанесенные катализаторы Циглера, qpриготовленные взаимо-действием Ni(II) н-бутилсалицилалдимината или Ni(II) 2-этилгексаноата с Al2O3/SiO2, обработанным AlEt3 или NaAlH2 (OCH2CH2OCH3)2, являются эффективными ктализаторами гидрирования алкенов. Приводятся факторы, влияющие на их активность.

The effect of solvent accessible surface on Hammett-type dependencies of infinite dilution 29Si and 13C NMR shifts in ring substituted silylated phenols dissolved in chloroform and acetone

Infinite dilution 29Si and 13C NMR chemical shifts were determined from concentration dependencies of the shifts in dilute chloroform and acetone solutions of para substituted O‐silylated phenols, 4‐R‐C6H4‐O‐SiR′2R″ (R = Me, MeO, H, F, Cl, NMe2, NH2, and CF3), where the silyl part included groups of different sizes: dimethylsilyl (R′ = Me, R″ = H), trimethylsilyl (R′ = R″ = Me), tert‐butyldimethylsilyl (R′ = Me, R″ = CMe3), and tert‐butyldiphenylsilyl (R′ = C6H5, R″ = CMe3). Dependencies of silicon and C‐1 carbon chemical shifts on Hammett substituent constants are discussed. It is shown that the substituent sensitivity of these chemical shifts is reduced by association with chloroform, the reduction being proportional to the solvent accessible surface of the oxygen atom in the Si‐O‐C link. Copyright

SUBSTITUENT EFFECTS IN DEHALOGENATION OF ARYL BROMIDES WITH Naalh2(OCH2CH2OCH3)2

Kinetics of dehalogenation of the bromobenzenes 4-RC6H4Br (R=F, Cl, H, CH3, CH3O and N(CH3)2) with the title hydride (SDMA) and with SDMA in the presence of Co(acac)2 have been examined. The rate constants of the debromination were correlated with Hammett substituent constants σp and E1/2 reduction potentials of the bromobenzenes. ρ values (+4.3 for SDMA reduction and +1.9 for the Co-catalyzed debromination) imply a negative charge concentration effect in transition states of both debrominations. Differences in the course of these reactions are discussed.