Syndiospecific Polymerization of o‑Methoxystyrene and Its Silyloxy or Fluorine-Substituted Derivatives by HNC-Ligated Scandium Catalysts: Synthesis of Ultrahigh-Molecular-Weight Functionalized Polymers

A scandium dication active species [(IPr)­Sc­(μ-CH2SiMe3)­(μ-CH2CHMe2)­AliBu2]2+[B­(C6F5)4]2– (IPr = (2,6-C6H3iPr2NCH)2C) in situ generated from the reaction of an N-heterocyclic carbene-ligated scandium trialkyl complex (IPr)­Sc­(CH2SiMe3)3 (2) with 1–3 equiv of cocatalyst [Ph3C]­[B­(C6F5)4] and an excess of AliBu3 exhibits unprecedentedly high activity (up to 2.2 × 106 g·molSc–1·h–1) and syndiotactic selectivity (rrrr > 99%) in the polymerization of o-methoxystyrene (oMOS) and its silyloxy- or fluorine-substituted derivatives, affording syndiotactic poly­(oMOS)­s and their silyloxy or fluorine-substituted derivatives with ultrahigh molecular weight (Mn up to 4.6 × 106) and moderate molecular weight distributions (Mw/Mn = 1.37–2.21) unavailable by the traditional catalysts. Based on in situ NMR spectroscopy, matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) spectroscopy, and density functional theory (DFT) calculations, a plausible coordination polymerization mechanism has been proposed for the syndiotactic polymerization of oMOS by such a Sc dication active species.