Patent ID: 8686209

Claim:
An improved process for the oligomerization of ethylene to provide a series of Î±-olefins of formula CH 2 â•CH 2 (CH 2 CH 2 ) n H wherein n is an integer of 1 or more, in the presence of a catalyst system comprising an iron complex of a symmetrical diimine of a 2,6-diacylpyridine or a 2,6-pyridinedicarboxaldehyde of the formula wherein: X 1 and X 2 are each independently carbon or nitrogen; R 1 and R 2 are independently hydrogen, hydrocarbyl, substituted hydrocarbyl or a functional group, provided that when X 1 is nitrogen R 1 is not present, and when X 2 is nitrogen R 2 is not present; R 3 is hydrocarbyl, substituted hydrocarbyl, a functional group or hydrogen; R 4 and R 5 are each independently hydrogen, hydrocarbyl, or substituted hydrocarbyl; R 6 and R 7 are the same, and are aryl groups in which a first ortho position is substituted by hydrocarbyl, substituted hydrocarbyl or a functional group, and a second ortho position is hydrogen or fluorine; wherein the improvement comprises: said symmetrical diimine of a 2,6-diacylpyridine or a 2,6-pyridinedicarboxaldehyde is made with a primary aromatic amine which contains no more than 0.5 mol percent of impurities which are themselves primary aromatic amines and in which one of said second ortho positions is not hydrogen or fluorine; and/or said symmetrical diimine of a 2,6-diacylpyridine or a 2,6-pyridinedicarboxaldehyde contains no more than 0.5 mol percent of diimines in which said one of said second ortho positions is not a hydrogen or fluorine; and wherein said mol percent is based on the total amount of primary aromatic amines present.