Nickel sulfide catalysts reactions catalyzed

An exhaustive review of the extensive patent literature on reactions catalyzed by nickel sulfide is beyond the scope of this chapter. The section on reactions catalyzed by nickel sulfide contains a number of selected reactions for illustrative purposes. The conditions under which nickel sulfide acts as a catalyst are mentioned. 

It is evident that many of the older ideas about the poisoning of nickel catalysts must be re-examined in the light of data now available. The two nickel sulfides, NisSa and NiS, which can exist under the conditions prevailing in some catalytic systems, are catalysts for some reactions also catalyzed by metallic nickel and for other reactions not yet found to be catalyzed by the metal. Explanations of this behaAuor in terms of band theory (or Brillouin zones) can be expected in the near future. 

There is a substantial body of literature on the palladium- and nickel-catalyzed formation of aryl sulfides, selenides, and phosphines from aromatic and heteroaromatic halides. Progress on these reactions has continued with several recent contributions [47-50]. A review in 1997 covered the types of transformations that can be conducted and the types of catalysts used [51]. Particularly useful examples are the conversions ofbinaphthol to binaphthylphosphines... 

Vinyl sulfides have been prepared by the catalytic addition of the S—H bond of thiols (85) to terminal alkynes (86) under solvent-free conditions using the nickel complex Ni(acac)2 (47). High alkyne conversions (up to 99%) were achieved after 30 min at 40 °C in favor of the corresponding Markovnikov products (87) (equation 23). Other metal acetylacetonate complexes were examined for this reaction, but none showed any improvement over the nickel catalyst. Mechanistic details suggest that alkyne insertion into the Ni—S bond is important to the catalytic cycle and that nanosized structural units comprised of [Ni(SAr)2] represent the active form of the catalyst. Isothiocyanates and vinyl sulfides have been produced in related Rh(acac)(H2C=CH2)2 (6) and VO(acac)2 (35) catalyzed sulfenylation reactions of aryl cyanides and aryl acetylenes, respectively. 

The hydroformylation of alkenes is commonly run using soluble metal carbonyl complexes as catalysts but there are some reports of heterogeneously catalyzed reactions of olefins with hydrogen and carbon monoxide. Almost all of these are vapor phase reactions of ethylene or propylene with hydrogen and carbon monoxide catalyzed by rhodium, " 20 ruthenium,nickel, 22,123 cobalt, 23,124 and cobalt-molybdenum 23 catalysts as well as various sulfided metal catalysts. 23,125,126... 

Nickel- or palladium-catalyzed coupling reactions of alkyl Grignard or zinc reagents can be applied to heteroaromatic halides and sulfides. The characteristic features are, therefore, based on those described in the preceding sections and hence details are not repeated in this section. Aspects are summarized by the types of heteroaromatic compounds NiCh(DPPP) is used as catalyst, unless stated otherwise hereafter. 

There were a few isolated examples of coupling reactions that form C—and C—S bonds.f Tunney and Stille had reported the Pd-catalyzed formation of the C—P bonds in aromatic phosphines, and several groups had reported the formation of C—S bonds in sulfides using catalysts based on both palladium and nickel. In addition there were suggestions that simple procedures for C—bond formation could be developed and that palladium complexes could act as catalysts for C—N bond-forming cross-coupling processes. For example, Boger and co-workers used stoichiometric amounts of palladium to form aromatic C—N bonds in a /3-carbolide natural product by an intramolecular process (Eq. 1). Perhaps more closely related to the work discussed in detail here. 

Originally Bergius felt that coal hydrogenation could not be catalyzed because the large quantities of sulfur present would poison the catalysts. He added luxmasse simply to absorb sulfur from the products although, coincidentally, the combination of iron oxide with titania and alumina was an excellent choice of catalyst. Since his first tests, however, the industrial use of the process has depended on catalysts that were developed more or less empirically. It was soon realized that the processes involved in hydrogenating coal were more complex than the simple reactions described by Sabatier and Ipatieff. Different catalysts such as iron oxide or iron snlfide, probably with traces of other metal oxides, were reqnired. These catalysts could be used in the presence of snUhr and were, in fact, even more active when sulfided. Several studies reported that iron, nickel, cobalt, tin, zinc, and copper chlorides were effective catalysts and claimed that aimnoninm molybdate was particularly active. 

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