Nickel catalyst system

In comparison to the Ziegler catalyst, the use of the nickel catalyst system offers the following advantages [34] ... 

Fig. 7. Cocatalyst effect on nickel catalyst systems. Curve a, Ni°CODj + Ph3P + 5i-Bu2A1C1 curve b, Ni°COD2 + Ph3P + 5i-BuAlCI2 curve c, addition of 2i-BuAlCl2 to (a) after 40 minutes of reaction.

The isomer distribution of the nickel catalyst system in general is similar qualitatively to that of the Rh catalyst system described earlier. However, quantitatively it is quite different. In the Rh system the 1,2-adduct, i.e., 3-methyl-1,4-hexadiene is about 1-3% of the total C6 products formed, while in the Ni system it varies from 6 to 17% depending on the phosphine used. There is a distinct trend that the amount of this isomer increases with increasing donor property of the phosphine ligands (see Table X). The quantity of 3-methyl-1,4-pentadiene produced is not affected by butadiene conversion. On the other hand the formation of 2,4-hexadienes which consists of three geometric isomers—trans-trans, trans-cis, and cis-cis—is controlled by butadiene conversion. However, the double-bond isomerization reaction of 1,4-hexadiene to 2,4-hexadiene by the nickel catalyst is significantly slower than that by the Rh catalyst. Thus at the same level of butadiene conversion, the nickel catalyst produces significantly less 2,4-hexadiene (see Fig. 2). 

In the literature there are many reports of the formation of active catalyst for the 1 1 codimerization or synthesis of 1,4-hexadiene employing a large variety of Co or Fe salts, in conjunction with different kinds of ligands and organometallic cocatalysts. There must have been many structures, all of which are active for the codimerization reaction to one degree or another. The scope of the catalyst compositions claimed to be active as the codimerization catalysts is shown in Table XV (69-82). As with the nickel catalyst system discussed earlier, the preferred Co or Fe catalyst system requires the presence of phosphine ligands and an alkylaluminum cocatalyst. The catalytic property can be optimized by structural control of these two components. 

Even though Ziegler catalysts have been known for almost half a century, rare earth metals (Ln), particularly neodymium (Nd)-based Ziegler catalyst systems, only came into the focus of industrial and academic research well after the large scale application of titanium, cobalt and nickel catalyst systems. As a direct consequence of the late recognition of the technological potential of rare earth metal Ziegler catalysts, these systems have attracted much attention. 

Promising results have been reported by various laboratories since 1990 on catalysis in molten salts, notably for catalytic hydrogenation, hydroformylation, oxidation, alkoxycarbonylation, hydrodimerization/telomerization, oligomerization, and Trost-Tsuji coupling [113]. A continuous-flow application to the linear dimerization of 1-butene on an ionic-liquid nickel catalyst system reached activities with TON > 18000 [116]. 

Most of the homodimerization and -oligomerization reactions of substituted methylenecyclopropanes have been performed with nickel catalyst systems. The product composition is additionally complicated by the formation of regioisomers. With an increasing number of substituents, some general changes in the product distribution have been observed ... 

Manufacturing process Several methods exist for reduction of o-anisic aldehyde to o-anisic alcohol, however, direct reduction by hydrogen using Raney-Nickel catalyst system at 90-100° C and 5-7 atm pressure has been commercially most attractive. Most of the key players of p-anisic alcohol such as BASF, Givaudan, Koffoeks, etc. also produce some quantities of o-anisyl alcohol. Application areas include flavor and fragrance, pharmaceuticals, etc. Global demand has been estimated at 300-350 tpa. 

In earlier investigations, asymmetric nickel-catalyzed isomerization and cyclodimerization of methylenecyclopropane was found to give l-methylene-2-vinylcyclopentane44. The nickel catalyst system was prepared by reduction of NiBr2L2 with butyllilhium. With tributylphosphane as ligand a 91% yield of the dimerization product was obtained. With dibromobis(( - )-methyl(phenyl)propylphosphane]nickel and butyllithium, optically active (no enantiomeric excesses given) l-methylene-2-vinylcyclopentane of unknown absolute configuration was obtained in 30% yield. Involvement of a n-allyl intermediate is proposed (loc. cit. 141 in ref 45). 

Other nickel-catalyst systems were also demonstrated to catalyse amina-tion of phenol derivatives, such as Ni(COD)2/SIPr-catalysed amination of aiyl carbamates, Ni(COD)2/dppf-catalysed amination of aryl sulfamates, and (dppf)Ni(o-tolyl)Cl-catalysed amination of aiyl sulfamates, mesylates, and triflates/ ... 

Other nickel catalyst systems can cyclodimerize butadiene to 2-methylene-vinylcyclopentane (Kiji et a ., 1970a, b) or linearly dimerize it to (E,E)-1,3,6-octatriene in high yield [Eq. (85) (Pittman and Smith, 1975)]. 

Catalytic Reactions under Nickel Catalysis. Nickel catalyst systems allow 1,1-dimethylsilacyclobutane to be a reagent for hydrosilane-free reductive silylation of aldehydes. Treatment of benzaldehyde with 1,1-dimethylsilacyclobutane in the presence of 10 mol % of Ni(cod)2 and 20 mol % of PPh2Me provides allyl-benzyloxydimethylsilane in good yield (eq 11). Divalent nickel precatalysts such as NiCl2 and Ni(acac)2 show no catalytic activity. 

Diamanti, S.J., Ghosh, P, Shimizu, E., and Bazan, G.C. (2003) Ethylene homopolymerization and copolymerization with functionalized 5-norbomen-2-yl monomers by a novel nickel catalyst system. Macromolecules, 36,9731-9735. 

Suzuki Coupling reactions of secondary alkyl halides were not effective using the palladium catalysts described above. However, these latter transformations can be achieved using nickel catalyst systems." " For example the Ni/prolinol-catalyzed coupling of 45 with phenylboronic acid gave 46 in 84% yield. 

As the developed nickel catalyst system proved to be excellent for the stereoselective transformation of monosaccharide trichloroacetimidate substrates, its... 

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