Reduced transition metal colloids: a novel family of reusable catalysts

Fluorine has received great attention in all fields of science. “Small atom with a big ego” was the title of the Symposium at the ACS meeting in San Francisco in 2000, where a number of the current scientific and industrial aspects of fluorine chemistry made possible by the small size and high electronegativity of the atom were discussed. This small atom has provided mankind with significant benefits in special products such as poly(tetrafluroethylene) (PTFE), freon, fluoro-liquid crystals, optical fiber, pharmaceutical and agrochemical compounds, and so on, all of which have their own unique properties that are otherwise difficult to obtain.1 For instance, at present, up to 30% of agrochemicals and 10% of pharmaceuticals currently used contain fluorine atoms. Therefore, organic fluorine compounds have received a great deal of interest and attention from the scientists involved in diverse fields of science and technology. Now, not only C-F bond formation but also selective C-F bond activation have become current subjects of active investigation from the viewpoint of effective synthesis of fluoroorganic compounds. The former is highlighted by designing a sophisticated fluorinating reagent for regioand stereocontrolled fluorination and developing versatile multifunctional and easily prepared building blocks. C-F bond formation has been treated extensively in several reviews2 and books.3 The latter is a subject that has been less explored but would be promising for selective defluorination of aliphatic fluorides, cross-coupling with aryl fluorides, and * To whom correspondence should be addressed. Phone: 81-78-803-5799. Fax: 81-78-803-5799. E-mail: amii@kobe-u.ac.jp and uneyamak@cc.okayamau.ac.jp. † Kobe University. ‡ Okayama University. Chem. Rev. 2009, 109, 2119–2183 2119

C-F bond activation in organic synthesis.

Metal-mediated reductive hydrodehalogenation of organic halides.

Heterogeneous catalysis on chitosan-based materials: a review

This review highlights various aspects of current palladium membrane research and serves as a comprehensive bibliography covering palladium membrane preparation methods and applications. There are many promising uses for palladium membranes, although widespread use of the available technologies is constrained primarily by the high cost of palladium, lack of durability due to hydrogen embrittlement, and susceptibility to fouling. Various researchers in the field are tackling these problems and fabricating thinner palladium alloy composite membranes that better withstand contaminantion and thermal cycling. What has been accomplished to address these issues and the directions presently being explored are discussed.

Innovations in palladium membrane research

By using a high-resolution solid state nuclear magnetic resonance spectrometer with 27Al and 29Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al2(MoO4)3. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by 27Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The SiAl ratio measured from 29Si MAS NMR further confirms the dealumination process observed by 27Al MAS NMR. The MAS NMR results give us an evidence that Al2(MoO4)3 crystallites are much less active for the reaction.

Methane dehydrogenation and aromatization in the absence of oxygen on MoHZSM-5: A study on the interaction between Mo species and HZSM-5 by using 27Al and 29Si MAS NMR

Polymer-achored monometallic palladium catalyst PVP-PdCl2 (PVP = poly(N-vinyl-2-pyrrolidone)) exhibits very high activity for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN) in the presence of base at 65°C and atmospheric pressure. In this case, the substrate is rapidly hydrodechlorinated to nitrobenzene (NB) which is then reduced to AN. Using the polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, and in the presence of 1.0 mol% of sodium acetate, a strong synergic effect gives rise to a remarkable increase of the selectivity for p-chloroaniline (CAN) and the maximum selectivity of CAN is up to 94%. For the hydrogenation of the non-halo-substituted nitroaromatics to the corresponding aromatic amines, the monometallic PVP-PdCl2 catalyst only shows mild or poor activity, but the colloidal polymer-anchored bimetallic palladium-platinum catalyst, PVP-Pd-1 4Pt , exhibits very high activity and selectivity.

Hydrogenation of nitroaromatics by polymer-anchored bimetallic palladium-ruthenium and palladium-platinum catalysts under mild conditions

A synergic effect of the polymer-anchored bimetallic palladium-ruthenium catalysts can lead to a remarkable increase in the selectivity for p-chloroaniline in the selective hydrogenation of p-chloronitrobenzene under atmospheric pressure and in the presence of a small amount of base.

Yun Xu

Papers

Methane dehydrogenation and aromatization in the absence of oxygen on MoHZSM-5: A study on the interaction between Mo species and HZSM-5 by using 27Al and 29Si MAS NMR

Hydrogenation of nitroaromatics by polymer-anchored bimetallic palladium-ruthenium and palladium-platinum catalysts under mild conditions

A remarkable synergic effect of polymer-anchored bimetallic palladium–ruthenium catalysts in the selective hydrogenation of p-chloronitrobenzene

Catalytic polymeric hollow-fiber reactors for the selective hydrogenation of conjugated dienes

Selective hydrogenation of propadiene and propyne in propene with catalytic polymeric hollow-fiber reactor