Active in ethylene oligomerizations

Sm(II) amides display extraordinary reactivity in catalytic caprolactone polymerization [298]. Among other complexes Yb(btsa)2(AlEt3)2 and Y(C3H5)2[N (SiMe2CH2PMe2)2] exhibit catalytic activity in ethylene oligomerization [144, 169]. 

It should be noted that the heterogeneous complexes on Ni[P(NEt2)3]2 base, showing at the early stage of work higher activity in ethylene oligomerization and better selectivity in respect to butene-1, are less steady in comparison with such complexes on Ni(PPh3) base. 

Sulfonated nickel ylide complex is a potent single-component catalyst for ethylene oligomerization in aromatic and polar solvents [226]. The modification of this complex with various organoaluminum compounds (AlEtjCl/AlEtCU or AlEt-O-Et) results in the formation of a new catalytic system with 10-20 times higher activity in ethylene oligomerization in aromatic solvents compared with that of the original ylide [201,227-229]. 

The propylene oligomerization literature is considerably poorer than that for the ethylene oligomerization. The catalysts for oligomerization of propylene are also active in ethylene oligomerization. Also in this case, the titanium, zirconium, and nickel complexes are the most popular catalysts. Propylene oligomers are more structurally diverse than ethylene oligomers. 

The complex [(methallyl)NiPh2PCH2PPh2(0)][SbF6] was found to be stable and active for ethylene oligomerization in PF -containing ionic liquids. The high elect-rophilicity of an unaltered Ni center in the liquid was suggested to be responsible for the activity of the catalyst 210). 

Table 2. The activity and selectivity of Ni - HMC and their homogenous analogues in ethylene oligomerization.

An excellent review on soluble systems, including also the more recent progresses in ethylene polymerization, is that of Sinn and Kaminsky who even developed soluble catalytic systems with extremely high activities by using alumoxane and biscyclopentadienyl-titanium or-zirconium compounds. Interesting results have also been obtained in ethylene oligomerization and in propylene dimerization... 

It is largely accepted that the active species in ethylene oligomerization is a nickel hydride species like 8. The mechanism for the hydride formation is supported by the reactions depicted in eqs. (7)-(9). Complex 9 eliminates butadiene at low temperatures and becomes active at 40 °C. Insertion of ethylene and elimination of styrene from structure 4 at 70 °C causes the complex to become active, while the more strongly bound cyclopentadienyl ligand in structure 10 needs 130 °C [49]. The elimination products of these reactions could be detected by GLC. 

The Ni salt was supported on non-porous alumina either by impregnation or ion exchage. Increased activity and selectivity in ethylene oligomerization was observed for the ion-exchanged catalyst in comparison with the impregnated catalyst. 

Work in this area has focused on nonphosphine supports. Polymerization of ethylene was reported with TiCU on a homopolymer or copolymer of vinylphenylphosphine AIR3 was added to activate the catalyst. With a nickel salt on a phosphinated polystyrene, addition of NaBH4 resulted in a catalyst active in the oligomerization and polymerization of acetylenic monomers (see Table 7). 

Complexes I and III are ethylene oligomerization-active centers. Compound II is inert in ethylene oligomerization. 

The effects of various organoaluminum compounds on ethylene oligomerization with Ni-ylide were evaluated in toluene solution at 30-120°C and ethylene at pressure 6.6—14.6 atm. An excess of AlEtj (20 1) reduces Ni-ylide to Ni(0) under these conditions, resulting in a complete loss of oligomerization activity. Tetraethylaluminoxane (produced in the reaction between AlEt3 and water in toluene solution) also deactivates Ni-ylide in ethylene oligomerization. 

Various compounds of the complex organo-Ni types show activity in olefin oligomerization processes. Ni-chelates [235] and bis(l,5-cyclooctadiene)Ni(0) deposited on omega zeolites or Y-type zeolite support [236] have high reactivity in the oligomerization of ethylene to form higher olefins. 

Green, M., Active species in ethylene oligomerization in the presence of transition metal complexes, Pure Appl. Chem., 50, 27, 1978. 

In addition to the neutral nickel/phosphine complexes used in the Shell Higher Olefins Process (SHOP), cationic Ni-complexes such as [(mall)Ni(dppmo)][SbF6] (see Figure 5.2-7) have attracted some attention as highly selective and highly active catalysts for ethylene oligomerization to HAOs [106]. 

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

In contrast, data on the characterization and the catalytic properties of hafnium surface complexes are very scarce [42, 43]. Yet, some papers describe the hafnium complexes as more active than the zirconium analog, in the polymerization of ethylene [44], more selective in the oligomerization of propene [45, 46] and faster... 

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