The nickel indenyl compounds md(PR3)Ni-X (Ind = indenyl and its substituted
derivatives; R = Ph, Cy, Me; X = Cl, Me, CCPh) can dimerize and/or polymer
ize ethylene in the presence of suitable activators. For example, poly(meth
ylaluminoxanes) (PMAO) combine with these Ni precursors to produce catalyti
cally active species for both the dimerization and polymerization of ethyle
ne. The polymers obtained from these reactions;are mostly linear polyethyle
nes which contain a small number of ethyl branches and exhibit molecular we
ights in the range of M-w = 10(5) (M-w/M-n ca. 2). On the other hand; using
activators such as AgBF4, AlCl3, and B(C6F5)(3) leads to the exclusive for
mation of butenes. It is proposed that the latter activators convert the Ni
-precursors to the highly electrophilic cations [IndNi(PR3)](+), which effi
ciently catalyze the dimerization of ethylene to butenes; in contrast, Ni/P
MAO combinations- give both the aforementioned cationic species as well as
neutral species bearing a Ni(mu -Me)Al core, which is thought to be the act
ive site for the polymerization reactions.