Alkane-Soluble Bis[tris(alkylphenyl)carbenium] Diborate Cocatalyst for Olefin Polymerizations

Binuclear dianionic cocatalysts can bring cationic active metal centers into close proximity to study center–center enchainment cooperativity effects in olefin polymerization catalysis. The previously reported binuclear diborate cocatalyst, (Ph3C+)2[1,4-(C6F5)3BC6F4B(C6F5)3]2– (B2,H), is poorly soluble in alkane and aromatic solvents and requires undesirable haloaromatic additives to fully solubilize it for efficient olefin polymerizations. Here, two binuclear diborate-based cocatalysts, (Ar3C+)2[1,4-(C6F5)3BC6F4B(C6F5)3]2– (B2,t-Bu; Ar = 4-t-Bu-C6H4-; B2,n-octyl; Ar = 4-n-octyl-C6H4-), are synthesized and characterized by multinuclear NMR spectroscopy, density functional theory computation, and by single-crystal diffraction for B2,t-Bu. B2,n-octyl exhibits good solubility in low-polarity solvents such as toluene and methylcyclohexane (MeCy), enabling the study of (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si(tBuN)](ZrMe+)2 [EBICGC(ZrMe+)2]-catalyzed ethylene homo- and co-polymerizations in solvent systems of decreasing polarity (toluene/difluorobenzene → toluene → MeCy). Product Mws are bimodal and sensitive to the above solvent progression, with the high-Mw fraction (wt %) increasing from 41 → 92 → 100%, respectively, for ethylene homopolymerization, and from 15 → 53 → 93%, respectively, for ethylene + 1-hexene copolymerization. Under scaled/industrial high temperature, higher pressure operating conditions, the same soluble binuclear diborate is an active olefin copolymerization cocatalyst, giving high polymer Mws and similar dispersity, D̵.