Neutral, Noncoordinating, and Hydrocarbon-Soluble Protic Cocatalyst for Olefin Polymerization
Tomoya Nakashima, Yuushou Nakayama, Takeshi Shiono, Ryō Tanaka
Abstract
Active species for coordination polymerization usually consist of a transition-metal cation and a noncoordinating counteranion. Such species are often generated in situ from neutral metal precursors and cocatalysts, such as fluoroaryl-substituted borate salts. However, these salts are scarcely soluble in solvents with low dielectric constants, which are often necessary for the highly stereospecific polymerization of olefins. Here, we have prepared a neutral fluoroarylborane that is converted into a boratabenzene anion in the presence of a base due to its highly protic C–H bond at the 10-position. This borane served both as a conventional Lewis acid and a Bro̷nsted acid when reacted with Cp2ZrMe2 to give cationic zirconocene species. Although its Lewis acidity was lower than that of B(C6F5)3, this species successfully activated the catalyst Me2Si(Flu)(NtBu)TiMe2 and promoted the polymerization of propylene in both toluene and heptane to give polypropylene with a ultrahigh molecular weight (>106).