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– (B
2,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– (B
2,t‑Bu
; Ar = 4-t-Bu-C6H4-; B
2,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 B
2,t‑Bu
. B
2,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(
t
BuN)](ZrMe+)2 [EBICGC(ZrMe+)2]-catalyzed ethylene
homo- and co-polymerizations in solvent systems of decreasing polarity
(toluene/difluorobenzene → toluene → MeCy). Product M
ws are bimodal and sensitive to the above solvent
progression, with the high-M
w 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 M
ws and
similar dispersity, D̵.