Tungsten catalysis

I4M. Misono, Heterogeneous Catalysis by Heteropoly Compounds of Molybdenum and Tungsten, Catalysis Reviews, 29,269-321 (1987). 

The 5-endo and 6-endo cyclizations of a,a>-alkynols leading to dihydrofurans and dihydropyrans have been achieved with molybdenum and tungsten catalysis [6]. Transition-metal vinylidene intermediates have been claimed to be involved in these cycloisomerizations [7]. Related cyclizations of bis-homo-propargyl alcohols were recently developed using ruthenium catalysis as shown in Eq. (3) [8]. In the presence of the sodium salt of N-hydroxysuccinimide 9,... 

Tungsten catalysis. A primary amine with the group CH2NH2 on oxidation with 35% hydrogen peroxide in the presence of a catalytic amount of sodium tungstate (Na2W04 2H20, supplied by Fisher) is oxidized via the hydroxylamine to the... 

The massive synthetic potential of the olefin metathesis reaction has yet to be realized in terms of generality and yields. However, since the metallocarbene addition mechanism has been largely accepted, more useful mechanistic studies have appeared this year. The whole area has been adequately reviewed by the timely publication of the proceedings of the international symposium held at Noordwijkerhout in September 1977. The synthetic utility of this transformation has now been extended by tungsten catalysis to the functionalized olefins of aj-olefinic esters (49), to give reasonable yields (35—40%) of the products as isomeric mixtures (50) in which the trans-isomer predominates. Small amounts of the chlorinated starting materials (51) are also present. The complex tungsten... 

Misono, M. 1987. Heterogeneous catalysis by heteropoly compounds of molybdenum and tungsten. Catalysis Reviews Science and Engineering 29(2-3) 269-321. 

Scheme 7.57 Tandem Heck-dihydrotylation reaction catalysed by palladium, osmium, and tungsten catalysis and chiral cinchona alkaloid catalysis.

Rhenium exhibits a greater resistance than tungsten to the water cycle effect, in which lamps and electron tubes become blackened by deposition of metal. This phenomenon involves catalysis by small quantities of water that react with the metal in a hot filament to produce a volatile metal oxide and hydrogen. The oxide condenses on the surface of the bulb and is reduced back to the metal by hydrogen. 

The chemical uses of tungsten have increased substantially in more recent years. Catalysis (qv) of photochemical reactions and newer types of soluble organometaUic complexes for industrially important organic reactions are among the areas of these new applications. 

Reactivity studies of organic ligands with mixed-metal clusters have been utilized in an attempt to shed light on the fundamental steps that occur in heterogeneous catalysis (Table VIII), although the correspondence between cluster chemistry and surface-adsorbate interactions is often poor. While some of these studies have been mentioned in Section ll.D., it is useful to revisit them in the context of the catalytic process for which they are models. Shapley and co-workers have examined the solution chemistry of tungsten-iridium clusters in an effort to understand hydrogenolysis of butane. The reaction of excess diphenylacetylene with... 

Langmuir s research on how oxygen gas deteriorated the tungsten filaments of light bulbs led to a theory of adsorption that relates the surface concentration of a gas to its pressure above the surface (1915). This, together with Taylor s concept of active sites on the surface of a catalyst, enabled Hinshelwood in around 1927 to formulate the Langmuir-Hinshelwood kinetics that we still use today to describe catalytic reactions. Indeed, research in catalysis was synonymous with kinetic analysis... 

Filaments are usually refractory metals such as tungsten or iridium, which can sustain high temperatures for a long time (T > 3000 K). The lifetime of filaments for electron sources can be prolonged substantially if an adsorbate can be introduced that lowers the work function on the surface so that it may be operated at lower temperature. Thorium fulfills this function by being partly ionized, donating electrons to the filament, which results in a dipole layer that reduces the work function of the tungsten. In catalysis, alkali metals are used to modify the effect of the work function of metals, as we will see later. 

Thermal conductivities of two porous catalytic particles are nickel-tungsten, 0.47 W/(m)0C), platinum-alumina, 0.22 (Satterfield, Heterogeneous Catalysis in Practice, 1980). 

Because of their electronic properties, particularly their visible-ultraviolet band gap, tungsten oxides have been the focus of a number of catalysis studies. Kohler and Gopel examined the electrocatalytic properties of W02.72 using spectroscopic surface... 

The reaction of alkynyllithium compounds with alkoxycarbene tungsten complexes leads to anionic propargyl tungsten complexes (Figure 2.33 see also Figure 3.9). These intermediates are stable at low temperatures and react upon Lewis acid catalysis with aldehydes or A -sulfonyl imines to yield five-membered heterocycles [280]. Oxidative methoxycarbonylation [375] of the intermediate vinyl tungsten complex, followed by elimination of methanol leads to pyrroles or furanes (Figure 2.33 Entry 6, Table 2.22). 

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