Synthesis and characterization of aminopyridine iron() chloride catalysts for isoprene polymerization: sterically controlled monomer enchainment

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 48; no. 22; pp. 7862 - 7874
• Main Authors: Jing, Chuyang, Wang, Liang, Mahmood, Qaiser, Zhao, Mengmeng, Zhu, Guangqian, Zhang, Xianhui, Wang, Xiaowu, Wang, Qinggang
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 14.06.2019
• Subjects: Bearing; Catalysis; Catalysts; Chemical analysis; Coordination compounds; Crystallography; Infrared spectroscopy; Iron chlorides; Isoprene; Monomers; Polymerization; Selectivity; Spectrum analysis; Steric hindrance; X-ray diffraction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt00452a

In this study, a series of 2-R-6-(1-(alkylamino)methyl)pyridine-iron complexes [alkyl: (CPh 3 ) Fe1 H ; (CHPh 2 ) Fe2 H ; (CHPh 2 ) Fe3 Me ; (CHMePh) Fe4 H ; (CH 2 Ph) Fe5 H ; (CHMe 2 ) Fe6 H ; (C 6 H 11 ) Fe7 H ; (CH 2 (4-OMe)Ph) Fe8 H ; (CH 2 (4-CF 3 )Ph) Fe9 H ; (CH 2 (2,4,6-Me 3 )Ph) Fe10 H ; (CH 2 Ph) Fe11 Me ] were synthesized and well characterized by ATR-IR spectroscopy, HRMS spectroscopy and elemental analysis. In addition, Fe3 Me , Fe4 H , Fe7 H and Fe11 Me were characterized by X-ray diffraction analysis: Fe3 Me and Fe11 Me adopted distorted tetrahedral geometries in the solid state while Fe4 H and Fe7 H were found in dimeric or polymeric forms respectively in which chlorides acted as bridging ligands. The catalytic capacities of these iron complexes were investigated for isoprene polymerization. Upon activation with a MAO cocatalyst, the catalytic activities of complexes varied as a function of the steric and electronic influences of substituents. In general, the catalysts bearing the least steric groups and electron-withdrawing groups exhibited relatively high activities. An outstanding activity of 190.6 × 10 4 g·mol −1 ·h −1 was obtained by Fe5 H [CH 2 Ph]. Moreover, changes in the steric hindrance around the metal center showed a notable effect on the selectivity of monomer enchainment. In particular, most of the polymers obtained by these complexes bearing flexible frameworks were in favor of 3,4-enchainment. Aminopyridine iron( ii ) chloride complexes coordinating a type of flexible ligand are reported as precursors for controlled polymerization of isoprenes.