Forming Linear Oligomers from Ethylene

CATALYSTS FORMING LINEAR OLIGOMERS FROM ETHYLENE (TABLE VI) 

Titanium and zirconium based catalysts oligomerize ethylene into a mixture of a-olefin ranging from C4 to C30 with a Schulz—Flory type distribution. The content of linear a-olefin is nearly 100% provided conversion is low enough (a high concentration of ethylene has to be maintained during the whole reaction). 

Besides their comparatively low activity, the main drawback of these catalysts is the difficulty to maximize the sought-after C12-U olefins. This is partly overcome by using nickel containing chelating ligands of P O combination. The addition of triphenylphosphine modifies the distribution as reported in Table VII. Linearity is 99% and a-olefin content higher than 98% (the catalyst does not practically isomerize a-olefins). 

Alkylidene tantalum complex C affords with low yield a-olefins ranging from C40 to C2oo- Its importance lies in its mechanistic implications vide infra). 

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Substitution on the ethylene imine ring hinders polymerization. The 2,3- and 1,2-substituted aziridines fail to polymerize. Only low molecular weight linear and cyclic oligomers form from 1-and 2-substituted ethylene imines. 

This reaction occurred in all cases of ethylene-higher a-olefin oligomerization the added a-olefin was partially isomerized to cis- and trans-2-olefins. Conversions in these isomerization reactions varied from 2.5 to 6%. Cis- and trans-2-olefins with linear chains are also formed in ethylene homooligomerization reaction [227]. Their presence in ethylene oligomers can be similarly explained as a secondary reaction (reaction 81) with the participation of the ethylene oligomers. Olefins with other internal double bonds cannot be formed in reaction (14) from a-olefins. Their possible formation from other olefins with internal double bonds (e.g., formation of 3-olefins from 2-olefins, etc.) in reactions analogous to reaction... 

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