Process for dimerizing lower .alpha.-olefins

A process for dimerizing lower .alpha.-olefins, which comprises dimerizing a lower .alpha.-olefin in the presence of a catalyst system comprising the following components:

• (A) an organic acid salt or complex of nickel,
• (B) a trialkylaluminum,
• (C) at least one trivalent phosphorus compound of the following formula (I), (II) or (III):
• PR.sup.1 R.sup.2 R.sup.3 (I)
• P(NR.sup.1.sub.2).sub.3 (II)
• P(OR.sup.1).sub.3 (III)
• wherein R.sup.1, R.sup.2 and R.sup.3 are independently an alkyl, a cycloalkyl, an aryl, or an aralkyl, and
• (D) a fluorinated isopropanol of the following formula (IV):
• ##STR7## wherein m and n are each an interger satisfying the formula:
• 4.ltoreq.m+n.ltoreq.6, and
• (E) a catalyst co-activator of at least one compound selected from halogenated compounds of the following formulae (V) and (VI):
• ##STR8## wherein X is a halogen atom, R.sup.4, and R.sup.5 and R.sup.6 are each an alkyl, and n is an integer of 1 to 3, in an amount of 0 mole to less than equimolar to the trialkylaluminum.