Catalyst Nuclearity Effects in Olefin Polymerization. Enhanced Activity and Comonomer Enchainment in Ethylene plus Olefin Copolymerizations Mediated by Bimetallic Group 4 Phenoxyiminato Catalysts

This contribution describes the synthesis, characterization, and catalytic implementation of the binuclear {2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato group 4 metal complexes {1,8-(O)(2)C10H4-2,7-[CH=N(2,6-(Pr2C6H3)-Pr-i)](2)}Zr2Cl6(THF)(2) (FI2-Zr-2) and {1,8-(O)(2)C10H4-2,7-[CH=N(2,6-(Pr2C6H3)-Pr-i)](2)}Ti2Cl6(THF)(2) (FI2-Ti-2) in comparison to the mononuclear analogues {3-Bu-t-2-(O)C6H3CH=N(2,6-(Pr2C6H3)-Pr-i)}ZrCl3(THF) (FI-Zr-1) and {3-Bu-t-2-(O)C6H3CH=N(2,6-(Pr2C6H3)-Pr-i)} TiCl3(THF) (FI-Ti-1), in ethylene homopolymerization and ethylene + olefin copolymerization processes. The comonomers studied include 1-hexene, 1-octene, 1,5-hexadiene (1,5-HD), 1,4-pentadiene (1,4-PD), and highly hindered 1,1-disubstituted methylenecyclopentane (MCP) and methylenecyclohexane (MCH). In ethylene + 1-hexene copolymerizations, FI2-Zr-2 enchains 1.5x more 1-hexene than FI-Zr-1, and FI2-Ti-2 enchains 2.2x more 1-hexene than FI-Ti-1. While ethylene + 1,5-HD and ethylene + 1,4-PD copolymerizations mediated by FI2-Zr-2 and FI-Zr-1 produce ethylene + 1,4-PD and ethylene + 1,5-HD copolymers at respectable activities, FI2-Ti-2 and FI-Ti-1 are virtually inactive. While MCP and MCH are efficiently coenchained with ethylene via a ring-unopened pathway by both FI2-Ti-2 and FI-Ti-1, FI2-Zr-2 and FI-Zr-1 produce only polyethylene. These examples represent the first olefin copolymerizations reported for monophenoxyiminato group 4 complexes, and in general the bimetallic catalysts incorporate between 1.8x and 3.4x more comonomer in ethylene + olefin copolymerizations than their monometallic counterparts. In comparison to mono- and binuclear group 4 constrained geometry catalysts (CGCs), the mono- and binuclear FI catalysts: (1) enchain significantly greater densities of alpha-olefins, (2) display enhanced binuclear catalyst polymerization activity versus their mononuclear analogues, and (3) produce predominantly linear polyethylenes as opposed to the branched polyethylenes produced by CGCs.