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The novel dialkylzirconium complexes L′ZrR2, (R = CH3, Bn = benzyl, CH2SiMe3, L′ = Me2Si{η5-tetramethylcyclopentadienyl}{6-[2-(dimesitylboryl)phenyl]pyrid-2-ylamido}) were synthesized. Upon activation with 1 equiv. of [Ph3C]+[B(C6F5)4]−, both L′Zr(CH3)2 and L′Zr(Bn)2 are quantitatively converted in situ into [L′Zr(CH3)]+[B(C6F5)4]− and [L′Zr(Bn)]+[B(C6F5)4]− while only 28 mol% conversion is observed with L′Zr(CH2SiMe3)2. The aluminum-free cationic catalysts [L′Zr(CH3)]+[B(C6F5)4]−, [L′Zr(Bn)]+[B(C6F5)4]− and [L′Zr(CH2SiMe3)]+[B(C6F5)4]− initiate ring-opening metathesis polymerization (ROMP) of NBE to form predominantly cis-poly(NBE)ROMP. Upon activation with [Ph3C]+[B(C6F5)4]− and AliBu3, L′Zr(CH3)2, L′Zr(Bn)2 and L′Zr(CH2SiMe3)2 also exhibit moderate catalytic activity in the copolymerization of ethylene (E) with NBE. The resulting copolymers do not contain any ROMP-derived poly(NBE), which is in stark contrast to the complexes’ homopolymerization propensity for NBE. Upon activation with methylalumoxane (MAO), L′Zr(CH3)2 and L′Zr(Bn)2 produce pure vinyl-insertion polymerization-derived poly(NBE)-co-poly(E) while L′Zr(CH2SiMe3)2 allows for the synthesis of predominantly trans-poly(NBE)ROMP-co-poly(NBE)VIP-co-poly(E)-based copolymers via an α-H+ elimination/addition process. Our findings are discussed on the basis of the instability of the alkylidenes in the presence of E and the blocking effect of aluminum alkyls on ROMP via coordination to the pyridyl-moiety in the cationic complexes.

polymer chemistry

Tandem vinyl insertion-/ring-opening metathesis copolymerization with ansa-6-[2-(dimesitylboryl)-phenyl]pyrid-2-ylamido zirconium complexes: role of trialkylaluminum and MAO