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Open AccessArticle

Highly Active Iminopyridyl Iron-Based Catalysts for the Polymerization of Isoprene

UMR 8181–UCCS–Unité de Catalyse et de Chimie du Solide, ENSCL, Centrale Lille, University of Artois, University of Lille, CNRS, F-59000 Lille, France
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Academic Editor: Giovanni Ricci
Molecules 2019, 24(17), 3024; https://doi.org/10.3390/molecules24173024
Received: 5 July 2019 / Revised: 28 July 2019 / Accepted: 7 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Well-Defined Metal Complex Catalysts for Olefin Polymerization)
A series of iminopyridyl-based ligands, 6-[(Ar)N=C(R)]-2-C6H5N [(Ar = 2,6-Me2-C6H3, R = Me (L1); Ar = 2,6-iPr2-C6H3, R = Me (L2); Ar = 2,6-Me2-C6H3, R = H (L3); Ar = 2,6-iPr2-C6H3, R = H (L4); Ar = 3,5-(CF3)2-C6H3, R = Me (L5); Ar = C6F5, R = Me (L6)], and their corresponding iron (II) complexes were developed to investigate their application in the controlled coordinative polymerization of isoprene. The modulation of steric and electronic properties within this family of ligands/pre-catalysts has shown to influence the stereo-selectivity and activity of the polymerization of isoprene after activation. Upon activation with various co-catalysts such as AliBu3/[Ph3C][B(C6F5)4], AlEt3/[Ph3C][B(C6F5)4] or MAO, the resulting catalysts produced polyisoprenes with an excellent conversion (>99% of 500–5000 equiv.) within less than 1 h (TOF > 500 h−1) and having a variety of stereo-/regio-regularities. The presence of electron-donating and withdrawing groups drastically impacted the activity and the stereoselectivity of the catalysts during the course of the polymerization of isoprene. When activated with AliBu3/[Ph3C][B(C6F5)4], the complexes {6-[(2,6-Me2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C1) and {6-[(2,6-iPr2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C2) exhibited moderate trans-1,4 selectivity (>67%) while the iron-based systems bearing related aldiminopyridyl ligands {6-[(2,6-Me2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C3) and {6-[(2,6-iPr2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C4) were found to afford significant cis-1,4 selectivity at low temperature (>86% at −40 °C). On the other hand, the ternary {6-[(3,5-(CF3)2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C5) or {6-[(C6F5)N=C(Me)]-2-C6H5N}FeCl2 (C6)/AliBu3/[Ph3C][B(C6F5)4] catalytic combinations showed exceptional activity for the polymerization of isoprene (TOF > 1,000,000 h−1), albeit providing less stereoselectivity. View Full-Text
Keywords: iminopyridyl ligand; iron (II)-based catalyst; coordination-insertion polymerization; isoprene polymerization iminopyridyl ligand; iron (II)-based catalyst; coordination-insertion polymerization; isoprene polymerization
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MDPI and ACS Style

Hashmi, O.H.; Champouret, Y.; Visseaux, M. Highly Active Iminopyridyl Iron-Based Catalysts for the Polymerization of Isoprene. Molecules 2019, 24, 3024.

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