Cycloaliphatic Polymers via Late Transition Metal Catalysis - Late Transition Metal Polymerization Catalysis - page 125

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Scheme 4.1 Multi-component catalyst for norbornene polymerization.
the Ni to form a “wrap-around” ligand. This complex, while being highly active
for butadiene polymerization in toluene (10 4 turnovers), is completely inactive to-
ward norbornene polymerization under the same conditions. If the reaction dilu-
ent is changed from toluene to 1,2-dichloroethane (presumably favoring the for-
mation of an unidentified ionic species) good yields of poly(norbornene) are ob-
tained (70%) in a reaction time of 60 min at ambient temperature. However, if
hexafluoroantimonic acid (1 : 1 molar ratio on nickel) is added to the system, a
highly exothermic reaction ensues and the yield of polymer under otherwise simi-
lar conditions becomes quantitative within 2-3 min.
The reaction of HSbF 6 with Ni(C 12 H 18 ) has been reported to form cationic
[Ni(C 12 H 19 )]SbF 6 , wherein the C 12 wrap-around ligand has been protonated to
yield a single allyl and two olefin moieties [49]. Note the structural similarities be-
tween this complex (Scheme 4.1) and the naked nickel complex (Fig. 4.4).
The cationic complex, [Ni(C 12 H 19 )]SbF 6 can be made independently from
Ni(cyclo-1,5-octadiene) 2 , butadiene, and HSbF 6 . This material exhibited similarly
high activity toward norbornene polymerization.
Ultimately it was discovered that introduction of butadiene into the catalyst sys-
tem was not necessary. Simply adding an equimolar mixture of HSbF 6 to
Ni(O 2 CR) 2 in 1,2-dichloroethane solution of norbornene-type monomers followed
by introduction of BF 3 ·Et 2 O and AlEt 3 (1 : 9 : 10 Ni : B : Al molar ratio) produced an