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, D.