Para-hydrogen-induced polarization in rhodium complex-catalyzed hydrogenation reactions

The homogeneous hydrogenation of PhCCH catalyzed by RhClL₃, Rh(COD)L₂⁺, and Rh(COD)dppe⁺ (L  PPh₃; COD1,5-cyclooctadiene; dppe = 1,2-bis(diphenylphosphino)ethane) has been investigated using para-hydrogen-induced polarization (PHIP) which allows that in accord with earlier studies, for RHClL₃ the addition of H₂ is reversible, whereas for Rh(CO)(dppe)⁺ and Rh(COD)L₂⁺, H₂ addition in hydrogenation catalysis is irreversible.     

On the phenomena of temperature hysteresis in hydrogenation reactions over heterogeneous catalysts

For the first time the phenomenon of a temperature hysteresis in the exothermic heterogeneous catalytic reactions of CO hydrogenation (methanation) and propene is discussed; the assumption is made, that the reason of hysteresis is the local overheating of the active centers caused by the complicated dissipation of the released energy through the dispersed particles of the catalyst. Dedicated to Professor Pál Tétényi on the occasion of his 70^th birthday     

用于生物质水相加氢多相负载型金属催化剂的稳定策略

生物质是天然的可再生能源和资源,具有来源广泛、储量丰富、价格低廉的优点以及可转化为高附加值化学品的多功能性,因此作为传统化石能源替代材料受到广泛关注和研究.将生物质通过催化转化为平台化合物再进一步利用是生物质利用的重要途径,其中催化加氢是常用的反应之一.由于绝大多数生物质平台化合物分子中都含氧元素,其加氢过程中会不可避...     

Enantioselective hydrogenation on heterogeneous metal catalysts

The rate of formation of the excess of one enantiomeric product in the enantioselective hydrogenation of ethyl acetoacetate (EAA) and acetylacetone (acac) on a Raney copper catalyst modified with chiral aminoacids (AmA) correlates with the formation constants of the mixed complexes [CU EAA AmA] and [Cu acac AmA].

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() - () , () [Cu··] [Cu··].

     

Self-supported heterogeneous catalysts for enantioselective hydrogenation

"Self-supported" catalysts were prepared by the reaction of bis-MonoPhos ligand with rhodium(I) metallic ion on the basis of molecular assembling through coordination. These polymeric metal-organic assemblies are insoluble in common organic solvents and, as a result, provide an excellent opportunity for running asymmetric catalysis heterogeneously. The application of the self-supported Rh(II) catalysts in the asymmetric hydrogenation of olefin derivatives afforded a variety of enantioenriched amino acid and amine derivatives with high yields and enantioselectivities. This strategy might provide a new direction in asymmetric catalysis, particularly for the development of practical heterogeneous asymmetric synthesis of optically active compounds.     

Selection of heterogeneous catalysts for acetophenone hydrogenation

The electronic structures of acetophenone species adsorbed on supported mono- and polymetallic catalysts have been calculated by the simple LCAO MO method. A correlation between the catalyst selectivity and the order of the -bond formed upon adsorption has been found, from which the selectivity of several polymetallic catalysts has been predicted and experimentally confirmed.

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- . -. , .

     

Alumina‐supported nickel catalyst for liquid‐phase reactions: an expedient and efficient heterogeneous catalyst for hydrogenation reactions

The preparation of a new nickel(0)/Al₂O₃ catalyst for hydrogenation reactions is described. The nickel(0)/Al₂O₃ catalysts were prepared by impregnation of alumina with a solution of a nickel(II) salt. After drying, the nickel(II) salt was reduced under mild conditions into nickel(0) using t‐BuONa‐activated sodium hydride in tetrahydrofuran at 65 °C. The nickel(0)/Al₂O₃ catalysts obtained were characterized by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The supported catalysts were successfully used in solution‐phase hydrogenation of double and triple bonds. Although the activity of the nickel(0)/Al₂O₃ is comparable to non‐supported nickel(0) reagents, it has the advantage of being reusable more than ten times with only a slight decrease of reactivity. Copyright © 2003 John Wiley & Sons, Ltd.     

Nuclear spin polarization in radical reactions

An extension of the Closs-Kaptein-Oosterhoff theory concerning nuclear spin polarization resulting during free radical reactions is presented. This extension is based on the Merrifield model for the magnetic field dependence of triplet-triplet annihilation.     

Mechanism of hydrogenation of carbon dioxide and the relationships governing the selection of heterogeneous catalysts for these reactions

On the basis of the established mechanism of the hydrogenation of CO₂ the main physicochemical factors that determine the variation of chemical reactivity and selectivity with change in the chemical nature of the metal and the oxide support were identified. Methods for calculated control of the catalytic characteristics were determined, and the main principles of the selection and development of metal-containing catalysts for the selective hydrogenation of carbon dioxide were formulated.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 252039 Kiev, Prosp. Nauki, 31. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 134–142, May–June, 1996. Original article submitted December 6, 1995.     

Bulk condensation during heterogeneous reactions

Using the methods of the classical theory of nucleation and an assumed reaction mechanism, the expressions for the rates of nucleation and growth of condensed particles in a particular heterogeneous reaction are derived to describe the kinetics of volume condensation in some complex systems.     

Magnesium bromide mediated highly diastereoselective heterogeneous hydrogenation of olefins

Palladium on carbon combined with magnesium bromide catalyzed hydrogenation of Baylis-Hillman olefins to afford the corresponding aldol derivatives in a highly syn-diastereoselective manner is described. [reaction: see text]