Rigid Triptycene-Based Di- and Trinuclear Salicylaldiminato Nickel Cooperative Polymerization Catalysts

Abstract

A multimetallic structure with a rigid linker can poise more than one catalytically active site in close proximity to control their reaction pathways in ethylene (co)polymerization by intermetallic cooperativity. This elegant concept was mainly limited to bimetallic systems. We report the synthesis of a series of mono-, bi-, and trinuclear salicylaldiminato Ni(II) catalysts based on a triptycene backbone. In ethylene (co)polymerization, the bimetallic nickel catalyst not only showed higher activity than the mononickel catalyst but also achieved an enhanced incorporation rate of α-olefin and the polar amino olefin, while the trimetallic nickel catalysts were thermally robust up to 100 °C and achieved a unique long-chain branching level up to an 81% mole ratio of all. Trinuclear nickel catalysts were found to be very less active for ethylene copolymerization with 1-hexene due to the increased steric hindrance. Although the catalytic result is worse than expected, especially for trinickel complexes, this work is still meaningful for the development of multinuclear catalysts that can mediate important catalytic reactions with enhanced efficiency and cooperativity.