By anchoring metal complexes to supports, researchers have attempted to combine the high activity and selectivity of molecular homogeneous catalysis with the ease of separation and lack of corrosion of heterogeneous catalysis. However, the intrinsic nonuniformity of supports has limited attempts to make supported catalysts truly uniform. We report the synthesis and performance of such a catalyst, made from [Rh(C(2)H(4))(2)(CH(3)COCHCOCH(3))] and a crystalline support, dealuminated Y zeolite, giving {Rh(C(2)H(4))(2)} groups anchored by bonds to two zeolite oxygen ions, with the structure determined by extended X-ray absorption fine structure (EXAFS) spectroscopy and the uniformity of the supported complex demonstrated by (13)C NMR spectroscopy. When the ethylene ligands are replaced by acetylene, catalytic cyclotrimerization to benzene ensues. Characterizing the working catalyst, we observed evidence of intermediates in the catalytic cycle by NMR spectroscopy. Calculations at the level of density functional theory confirmed the structure of the as-synthesized supported metal complex determined by EXAFS spectroscopy. With this structure as an anchor, we used the computational results to elucidate the catalytic cycle (including transition states), finding results in agreement with the NMR spectra. 相似文献
Alkynes of reactions : Recent breakthroughs in metal‐catalyzed alkyne reactions, which expand the synthetic utility of alkynes, have been achieved. These approaches broaden the range of alkynes that are accessible by C? N and C? C bond‐forming reactions and demonstrate that the use of bifunctional heterobimetallic catalysts can lead to new reactivity and excellent enantioselectivity (see scheme).
The present review covers the summary of recent progress in designing and developing Biginelli reaction strategies particularly the greener strategies with higher yields, short times and simple work-up, in which the inorganic materials such as alumina, silica gel or zeolite directly or having doped with other reagents were used as catalysts for such a type of transformations. Moreover, several aspects and available references of heterogeneous catalysis using inorganic catalysts in promoting reactions are provided briefly in this review. There is also a concise account covering the better alternative syntheses and some of improved and robust protocols of biginelli reaction for the preparation of dihydropyrimidin-2(1H)-one/thiones analogs. 相似文献
Different dihydroisoindol-4-ols and 8-hydroxytetrahydroisoquinolines were prepared by the gold-catalyzed phenol synthesis. The reaction was investigated with several sterically demanding groups in the 5-position of the furan starting material. The influence of the reaction time and the catalyst on the yield was investigated. 相似文献
Heterogeneous catalysis is one of the fields of modern technology, in which a characterization of structural and chemical
properties of solid surfaces at the microscopic level is of enormous importance. For a long time, such insights have been
precluded by the complexity of most catalytically active materials. Recently, substantial progress has been made, however,
toward a microscopic-level understanding of complex catalyst surfaces. We discuss the driving factors for these advancements,
which are based on the development of new well-defined model systems as well as on advances in experimental technology and
theory. Scrutinizing the example of planar model catalysts, we identify the process of linking structural and chemical information
to microscopic reaction kinetics as a particular challenging aspect of today’s work. We review the kinetic effects which may
have an influence on the reaction kinetics on complex surfaces. As an example how structural and kinetic information can be
correlated at the microscopic level we discuss the case of surface oxidation and oxygen induced restructuring of Pd nanoparticles
as studied by molecular beam methods. 相似文献
Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs. 相似文献
