Transition metal nickel

Keywords Alpha-diimine, Catalyst, Late transition metal, Nickel, Olefin, Palladium,... 

Like many late transition metals, nickel has featured, albeit briefly, in the pursuit of poly(pyrazolyl)borate-metal-carbollide complexes. Thus, [c/oso-3-(r 2-Ph2Bp)-3,l,2-NiC2B9H11] (90 ) has been obtained as the tet-ramethylammonium salt,39 via the reaction of [Me4N][Ph2Bp] with the neutral bisphosphine nickel dicarbollide [doso-3,3-(PhEt2P)2-3,l,2-... 

This scheme was confirmed by the presence of n-butenes In the reaction gases, and the close similarity of the products obtained from ethylene and n-butenes over zeolite CaMEY, as Indicated In Table IV. ME represents a transition metal nickel, chromium, and cobalt were all found effective for ethylene alkylations. Nickel was the metal used for experiments reported In Tables IV and V. 

Other transition metals, nickel and cobalt, also promoted gasification (Figure 14) with their activity being comparable to that of iron. Nickel was effective from the onset of the exposure to water vapour, as the hydrogen released by the oxidation was sufficient to ensure that the element was completely reduced. In contrast, cobalt oxide, formed by decomposition of the acetate with which the sample was treated, was only reduced to the elemental state on the addition of hydrogen to the gas phase such that PH2/pH20 exceeded that (0.04) at which the oxide was no longer thermodynamically stable. 

The study reported in this chapter examines the interactions of the alkali metal lithium and the transition metal nickel with various TT-bonded hydrocarbons to determine the value of such metal interactions for forming new C-C a-bonds in aromatic systems through preliminary disruption of C-C TT-bonds. From the foregoing considerations, pronounced solvent or ligand effects are expected in such reactions. 

Another valuable transition metal, nickel, is purified by a process first formulated by Ludwig Mond in the 1890s. In the Mondprocess, the impure nickel metal is subjected to a warm (approximately 75°C) stream of carbon monoxide gas. The gaseous, tetrahedral tetracarbonylnickel(O), Ni(CO)4 (often commonly called nickel tetracarbonyl), is immediately formed and allowed to pass into another chamber at about 225°C. (Other transition metals present as impurities are not similarly complexed.) At the higher temperature, the equilibrium between soHd nickel, carbon monoxide, and the nickel carbonyl [as shown in Equation (6.7)] is reversed, and pure nickel is deposited. 

Using a stoichiometric amount of 22, i.e. six equivalents, afforded a mixture of mono- to hexa-alkylated species from which the ligand 23 was isolated by crystallization. The hexa-alkylation process could be enhanced reacting a twofold excess of 22 with the hexaphenol. The ligand CTV(bipy)6 was then isolated in 71 % yield. Again, the H-NMR provided evidence for the hexasubstitution and the Cat, symmetry of the isolated ligand. The compound obtained can accommodate either three square planar (copper(II)) or tetrahedral (copper(I)) transition metals, or, two octahedral transition metals (nickel(II)). The corresponding complexes are of interest in order to study, metal-metal interactions either by electrochemistry, EPR or photochemistry [39]. 

The copolymerization of ethene with TIBA-precomplexed allyl ethyl ether and allyl propyl ether has been catalyzed by 38/ MAO (Figure 19) and related zirconocenes. While the incorporation level of the allyl ethyl ether was highly dependent on the TIBA ether ratio, in case of the allyl propyl ether, the TIBA concentration had a negligible effect. However, for the latter case, the polymerization temperature had a high influence with an optimum at 45 °C. Furthermore, the copolymerization of TlBA-protected 2,7-octadienyl methyl ether with ethene has been reported recently. Different catalysts were employed, with the sterically protected zirconocene 38 (Figure 19) as the most active upon MAO activation. In this case, the catalyst even outperforms a late transition metal nickel a-diimine catalyst system (Section 3.24.4.2). 

The reaction of [2+2+2] cycloaddition of acetylenes to form benzene has been known since the mid-nineteenth century. The first transition metal (nickel) complex used as an intermediate in the [2+2+2] cycloaddition reaction of alkynes was published by Reppe [1]. Pioneering work by Yamazaki considered the use of cobalt complexes to initiate the trimer-ization of diphenylacetylene to produce hexasubstituted benzenes [54]. Vollhardt used cobalt complexes to catalyze the reactions of [2+2+2] cycloaddition for obtaining natural products [55]. Since then, a variety of transition complexes of 8-10 elements like rhodium, nickel, and palladium have been found to be efficient catalysts for this reaction. However, enantioselective cycloaddition is restricted to a few examples. Mori has published data on the use of a chiral nickel catalyst for the intermolecular reaction of triynes with acetylene leading to the generation of an asymmetric carbon atom [56]. Star has published data on a chiral cobalt complex catalyzing the intramolecular cycloaddition of triynes to generate a product with helical chirality [57]. 

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