Preparation highly reactive nickel

Ullmann coupling. Using the highly reactive nickel which is prepared by electrolysis of a DMF solution in an undivided cell (Pt cathode, Ni anode) at a constant current, aryl halides undergo coupling to give biaryls at 100° (4 examples, 58-90%). 

The dimeric ir-allylnickel halide complexes are most conveniently prepared from allylic halides and nickel(O) species, such as Ni(COD)2 and Ni(CO)4. Although other allylic systems have been used, the most common procedure involves treatment of an allylic bromide with Ni(CO)4 at 50-70 C. ° This gives rise to the moderately air-sensitive dimeric ir-allyl species (equation 46). In polar coordinating solvents, (DMF, HMPA, N-methylpyrrolidone, etc.) these dimeric species are converted into highly reactive monomeric species (equation 47). ... 

Bis(trichlorosilyl)nickel(II) complex 4, having an r/ -arene hgand,is prepared by reaction of hexachloro disilane with highly reactive, vaporized nickel in the presence of toluene (Eq. 2) [12]. Worthy of note is that the arene ligand is displaced by three molecules of carbon monoxide to give 5 [13]. 

Besides various iron and ruthenium complexes [43, 44], nickel-based catalysts have recently been shown to be highly reactive in this respect as well [45]. Thus, a nickel catalyst prepared in situ from equimolar amounts of NiCl2(dppe) (dppe, l,2-bis(diphenylphosphino)ethane) and LiBHEtj (5 mol% each), which presumably resulted in the formation of NiHCl(dppe) as the active catalyst, efficiently catalyzed the isomerization/aldol event of allyl alcohols 82 and aldehydes 83 in combination with the Lewis acid MgBr2 (5 mol%) to furnish aldol products 84 in typically excellent yields and variable isomeric ratios (Table 8.11). Allyl alcohols with a terminal alkene reacted much faster than those with an internal olefin, and the aldol reaction occurred exclusively on the side of the former allyl alcohol. 

Deming, T. J. Novak, B. M. Preparation and reactivity studies of highly versatile, nickel based polymerization catalysts systems. Macromolecules 1993, 26, 7089-7091. 

Previous communications [111] have shown the high reactivity and utility of activated nickel powder prepared by the hthium metal reduction of nickel... 

This sensitivity has inplications for preparation of the surface to be examined. It is very easy for the features of interest to be obscured by deposited impurities or by the consequence of siuface reactions. If the bulk properties of a sample are of interest, then a suitable siuface for examination can be prepared by fracture of a bulk sample under UHV conditions. Some siufaces can be prepared in a controlled environment to avoid contamination and transferred directly to the spectrometer analysis chamber or preparation chamber. Even at the low backgroimd pressures in the analysis chamber, gas molecules wiU adsorb onto and react with surfaces, particularly the often highly reactive surfaces formed by sol-gel. Kim et al. recorded changes to the O Is spectrum from a reduced NiCo204 sanple as a function of time exposed under UHV conditions. The changes to the spectrum (Fig. 6-5) result from reaction with atmospheric H2O and CO. The fit to the O 1 s spectrum shows increased peak intensity at 531.5 and 533.0 eV. Cobalt and nickel hydroxides have... 

Oxidative additions of triethylphosphine-nickel(O) complexes/ or of a specially active slurry of nickel in the presence of EtsP/ to aryl halides give ArNi(PEt3)2Hal CeFsCl and CjEsBr react very rapidly. Highly reactive palladium and platinum slurries have also been prepared which undergo analogous reactions. 

Bis-(N-methyl-N-nitroso)terephthalamide and N,N -dimethyl-N,N -dinitrosooxamide are convenient precursors of diazomethane. From N,N -dinitrosooxamides, other diazoalkanes have been prepared as well . Improved yields in the Schiemann reaction have been obtained with hexafluorophosphoric acid . Reaction of dia-zonium salts with nickel carbonyl and acetic acid may provide a single-step alternative to the Sandmeyer reaction, especially where the nitriles from the latter contain other groups susceptible to hydrolysis . The highly reactive 1,2,4-thiadiazolediazonium salts have permitted an extension of diazonium salt chemistry by new reactions . 

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