Ethylene nickel-catalyzed oligomerization

Butene. Commercial production of 1-butene, as well as the manufacture of other linear a-olefins with even carbon atom numbers, is based on the ethylene oligomerization reaction. The reaction can be catalyzed by triethyl aluminum at 180—280°C and 15—30 MPa ( 150 300 atm) pressure (6) or by nickel-based catalysts at 80—120°C and 7—15 MPa pressure (7—9). Another commercially developed method includes ethylene dimerization with the Ziegler dimerization catalysts, (OR) —AIR, where R represents small alkyl groups (10). In addition, several processes are used to manufacture 1-butene from mixed butylene streams in refineries (11) (see BuTYLENEs). 

Coordination-catalyzed ethylene oligomerization into n-a-olefins. The synthesis of homologous, even-numbered, linear a-olefins can also be performed by oligomerization of ethylene with the aid of homogeneous transition metal complex catalysts [26]. Such a soluble complex catalyst is formed by reaction of, say, a zero-valent nickel compound with a tertiary phosphine ligand. A typical Ni catalyst for the ethylene oligomerization is manufactured from cyclo-octadienyl nickel(O) and diphenylphosphinoacetic ester ... 

The oligomerization of ethylene to higher a-olefins is catalyzed by nickel(II) chelate complexes such as (22-XXXIV). The active species is a nickel hydride, generated in situ,... 

Scheme 3 Condensed Gibbs free-energy profile (kcal mol ) of the complete catalytic cycle of the co-oligomerization of 1,3-butadiene and ethylene catalyzed by zerovalent bare nickel complexes affording linear and cyclic Cio-olefins, focused on viable routes for individual elementary steps. The favorable [Ni (ri -frans-butadiene)2(ethylene)] isomer of the active catalyst species lb was chosen as reference. Activation barriers for individual steps are given relative to the favorable stereoisomer of the respective precursor (given in italics)...

Perfluormated oligoethers with the acetylacetonate group at the end of the polymer formed complexes 56 with nickel(I), which catalyzed ethylene oligomerization. The turnover number in the reaction reached 2460 in a perfluorinated ether-toluene two-phase system, and the catalyst, which was in the fluorine-containing phase, was readily separable [169]. 

Figure 29 Ethylene oligomerization is catalyzed by a nickel-containing catalyst Pi, pq.p = propagation steps ...

The mechanism of Ni-catalyzed ethylene oligomerization involves both nickel hydride and nickel alkyl species. The mechanism is known in the literature as the metal-hydride mechanism, Cossee-Arlman mechanism, or ethylene insertion - -hydride elimination mechanism and results in a Schulz-Flory distribution of the oligomerization products. The mechanism is depicted in Figure 6.16.4. Note that two other coordination sites at the nickel are occupied by one bidentate ligand or two monodentate ligands (see Section 2.4 for details) that have been omitted in Figure 6.16.4 for clarity. 

It is possible to oligomerize ethylene by nickel in the absence of a Lewis acid. Butenes are formed by heating nickelocene to 200°C in the presence of ethylene 1193]. In this process, homolytic decomposition of nickelocene produces excited nickel atoms, which catalyze dimerization. This is similar to heterogeneous catalysis. To explain the nickelocene-catalyzed dimerization of ethylene, Tsutsui [194] has proposed a three-step mechanism represented in the following reactions ... 

The subsequent development of the process for high-density polyethylene was the result of careful systematic observation by the experiment team. Further work on the oligomerization of ethylene to the commereially-valuable Ce and Cs a-olefins led to the discovery that the displacement reaction was catalyzed by traces of nickel in the reactor. The displacement reaction became faster than the growth reaction as the concentration of nickel was increased, and at 120°C, only the dimer was produced. In subsequent investigations of other metals as co-catalysts in conjunction with triethylaluminium, it was shown that zirconium acetylacetonate inhibited the displacement reaction completely, and that polyethylene was the only product. Further work led to the development of the well-known titanium chloride/triethyl alununum catalyst, which operated at low temperatures and atmospheric pressure. The reaction became known as the Mul-heim Atmospheric Polyethylene Process. ... 

Lecocq Olivier-Bourbigou, 2007) Chloroaluminate ILs Biphasic Ni-Catalyzed Ethylene Oligomerization in ILs Chloroaluminate ILs are highly active catalysts either for the biphasic ethylene oligomerization or for polymerization depending on the buUdness of the diimine ligand. The activation of Ni(0) with a Bronsted add in different non-chloroaluminate ILs is also reported. The nickel catalysts are immobilized and stabilized in the Ils and can be recycled. 

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