THE EFFECT OF ALKYL SUBSTITUENTS IN NICKELOCENES ON THE CATALYTIC DIMERIZATION OF ETHYLENE

(C5H4i-Pr)2Ni exhibits the highest catalytic activity in the dimerizat ion of ethylene among the nickelocenes, (C5H4R)2Ni (R = H, Et, n-Pr, i -Pr, or t-Bu) and their analogs (C5H4R)Ni(C3H5) (R = H, i-Pr). The hig her activity is accompanied by lower selectivity with respect to 1-but ene and with higher yields of 1-hexene. It is suggested that the intro duction of an alkyl substituent in the cyclopentadienyl ring of nickel ocene favors the generation of ''hydride sites'' involving the nickel atom. These sites participate in the process of ethylene dimerization.