A highly active Ni(II)-triadamantylphosphine catalyst for ultrahigh-molecular-weight polyethylene synthesis

Abstract

Here we report that the tri-1-adamantylphosphine-nickel complex [Ad₃PNiBr₃]^-[Ad₃PH]⁺ upon activation with an alkylaluminoxane catalyzes the polymerization of ethylene to ultrahigh-molecular-weight, nearly linear polyethylene (M_n up to 1.68 × 10⁶ g mol^-1) with initial activities reaching 3.7 million turnovers per h^-1 at 10 °C. Copolymerizations of ethylene with α-olefins such as 1-hexene and 1-octadecene, as well as tert-butyldimethyl(dec-9-en-1-yloxy)silane give the corresponding copolymers with no decrease in activity.

Fig. 1

Monodentate trialkylphoshine-nickel catalysts for olefin dimerization and polymerization. a Propylene dimerization with exceptionally high initial turnover frequencies (Wilke). b Ethylene polymerization using tri-t-butylphoshine-nickel complex (Wilke). c Olefin cross-dimerization using tri-cyclohexylphosphine nickel catalyst. d Ethylene polymerization using tri-t-butylphoshine-nickel-acac catalyst generated in situ

Fig. 2

Synthesis of catalyst 6. Reaction of tri-1-adamanylphosphine with nickel bromide hydrate in 1,2-dimethoxyethane forms complex 6

Fig. 3

ORTEP view of the molecular structure of 6. Thermal ellipsoids are drawn to encompass 50% probability. Hydrogens and co-crystallized chlorobenzene are omitted for clarity. Selected bond distances (Å) and angles (deg.): P(1)-Ni(1) 2.3821(8); Ni(1)-Br(1) 2.4002(6); P(1)-Ni(1)-Br(1) 111.52(3); Br(3)-Ni(1)-Br(2) 110.12(2)