Tungsten promoter

A tungsten-promoted intramolecular [3-1-2] cycloaddition reaction of an alkyne and epoxide leads to the formation of air-isomers of reduced furo[3,4-c]pyrans, as shown in Equation (68) <2001JA7427>. The alkynyltungsten complexes were prepared in good yields from the corresponding alkynes upon treatment with CpWlCOlsCl and diethylamine <1997JA4404>. 

In Thermotoga maritima, the most thermophilic organism known, tungsten promotes synthesis of an Fe-contain-ing hydrogenase as well as some other enzymes but seems to have a regulatory rather than a structural role.688... 

Y., Seraji, M.S.I., and Suib, S.L. (2014) Tungsten promoted mesoporous group 4 (Ti, Zr, Hf) transition metal oxides for room temperature, solvent free acetalization and ketalization reactions. Chem. Mater., 26 (9), 2803 2813. 

Ha2ards encountered with tungsten may be caused by substances associated with the production and use of tungsten, eg. As, Sb, Pb, and other impurities in tungsten ores, Co aerosols and dust in the carbide industry, and thoria used in welding electrodes. Lanthanum is being promoted as a substitute for thoria in this appHcation. 

The route to carbene initiation for systems catalyzed solely by transition metal salts (55, 54), or their combinations with Lewis acids such as A1C13 (55), is not well established. Nevertheless, some evidence suggests reduction of the metal by the olefinic substrate (55). Zero-valent (56) and hexavalent (57, 55) tungsten complexes that promote metathesis when activated by UV radiation are the least-understood metathesis systems. 

With Cr(C0) , base clearly promotes the WGSR. However, unlike ruthenium carbonyl, chromium and tungsten carbonyls demonstrate less activity with trimethylamine than with carbonate as base. 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

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