Nickel, ligands

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

Fig. 7.4 Isomer shift (relative to Ni metal and corrected for SOD) as a function of ligand electronegativity (plot A) and as a function of nickel-ligand ionicity (plot B) (from [9])...

Cationic latexes, 19 855 Cationic metallocene complexes, 16 90 Cationic monomers, of water-soluble polymers, 20 475-482 Cationic nickel ligand complexes,... 

Table 23. Selected nickel-ligand bond enthalpy contributions, D[(CpNi-L)+] kJ mol-1 determined by ion cyclotron resonance (Ref.93 )...

Figure 9.3 pictures the oligomerisation reaction Ni is an abbreviation for the nickel-ligand moiety, kg stands for the rate of the growth reaction, and kt for the rate of the termination reaction. These rate constants are the same for all intermediate nickel alkyls, except perhaps for the first two or three members of the sequence owing to electronic and steric effects. Interestingly, a simple kinetic derivation leads to an expression for the product distribution. One can... 

Interestingly, the catalysts used here are similar to the nickel-ligand complexes used by Shell for their commercial ethene oligomerization process. Similar catalysts for making polyketone have also been patented by Keim et al. 

Cyclodimerization of Butadiene with Nickel-ligand Catalystsa-b... 

Butadiene and butyne, in a 2-to-l ratio, react with both the naked-nickel and nickel-ligand catalyst to form 4,5-dimethyl-cb,m,tram-1,4,7-cyclodecatriene (DMCDeT) (94). The yield with naked-nickel, however, never exceeds 25% and will not be discussed further. 

Table X, however, shows clearly that, in contrast to the butadiene-ethylene system, triphenylphosphine is the most successful ligand. We will return to this point later. The preparation of DMCDeT on a laboratory scale can be conveniently carried out by dissolving the nickel-ligand catalyst [which may be prepared by reduction of nickel acetylacetonate or directly from bis(cyclooctadiene)nickel and triphenylphosphine] in a solution of butadiene in toluene. Butyne is then added to give a butadiene-to-butyne ratio of 5-10 1. The reaction is conducted at 20° C and the contraction in volume is observed. The reaction is terminated at the break in the contraction curve (Fig. 3).

Fig. 3. Volume contraction in the co-oligomerization of butadiene with 2-butyne (nickel-ligand catalyst) (94) I = P(C6H5)3, II = P(OC6H5)3.

Synthesis of Methyl-Substituted 1,5-Cyclooctadienes We will first consider the formation of substituted eight-membered ring systems using the dimerization catalyst (nickel-ligand). Two routes are available either two molecules of substituted butadiene may dimerize... 

The products formed by the co-oligomerization of acrylic esters with butadiene (102,106) provide useful information concerning the nature and configuration of the intermediates involved. Naked-nickel, methyl acrylate, and butadiene do not react together.7 However, reaction does occur if the nickel-ligand system is used. The formation of the Diels-Alder adduct between the diene and olefin (a cyclohexene derivative) can be suppressed by adding the reactants dropwise to the catalyst (Table XVI footnote C). 

At normal temperatures methyl crotonate does not react with butadiene in the presence of either naked-nickel or the nickel-ligand catalyst. Moreover, since no oligomerization of the butadiene occurs, it is probable that the formation of a stable nickel complex renders the catalyst inactive. 

In the presence of alcohols, butadiene is oligomerized by the nickel ligand catalyst to open chain hydrocarbons (110-112). The product, an isomer of octatriene, is dependent on the ligand attached to the nickel (113). 

We have already shown that the formation of a four-membered ring from cis- and trans-piperylene with a nickel-ligand, catalyst is not consistent with... 

Table 1. Composition of the oligomerization products of butadiene with nickel-ligand catalysts .

In the presence of suitable cocatalysts such as alcohols, phenols, or secondary amines, 1,3-diolefins are oligomerized to linear dimers or trimers by the same nickel-ligand systems, which are effective for cyclooligomerization (see 14.5.2.5.1). Reactions may be accompanied by telomerization. Typical examples are given in Table 1. 

Cyclodimerization of 1,3-Diolefins. The nickel-ligand catalysts effective in the cyclodimerization of 1,3-diolefins are composed of preformed complexes such as [Ni(CO) L4 ] or [Ni(cod)2]/L [L = PR3, P(OR)3] or are prepared in situ by reducing a Ni(II) compound such as [Ni(acac)2] in the presence of L and the diolefin . Orga-noaluminum compounds are most commonly used reducing agents, but various other systems have also been investigated . ... 

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