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

Abstract

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.