Chain Transfer to Toluene in Styrene Coordination Polymerization

• Published in: Angewandte Chemie International Edition Vol. 59; no. 11; pp. 4324 - 4328
• Main Authors: Lin, Fei, Liu, Zhaohe, Wang, Meiyan, Liu, Bo, Li, Shihui, Cui, Dongmei
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 09.03.2020; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkyl compounds; Aluminum; Chain transfer; Chains (polymeric); Chemistry; Chemistry, Multidisciplinary; Coordination; coordination polymerization; C−H activation; Fluorine; Ligands; Magnesium; Molecular structure; Molecular weight; NMR; Nuclear magnetic resonance; Physical Sciences; Polymerization; rare earths; Science & Technology; Styrene; styrene polymerization; Styrenes; Toluene; Two dimensional analysis; Zinc; C-H activation; ETHYLENE; COMPLEXES; styrene polymerization; SYNDIOTACTIC POLYMERIZATION; chain transfer; coordination polymerization; CYCLOPENTADIENYL; COPOLYMERIZATION; ANCILLARY LIGAND; CATALYSTS; rare earths; C−H activation
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201914603

The chain‐transfer reaction is rather important in coordination polymerization regarding catalytic efficiency, adjustment of molecular weight, and control of chain structure. To date, chain transfer to H2 and Al, Mg, and Zn alkyl compounds and β‐H elimination are the commonly encountered modes. Now a novel chain transfer to toluene is reported. By introducing fluorine atoms into the β‐diketimine ligands, an inert catalytic system for styrene (St) coordination polymerization was transferred into the highly active one. The activity increased with an increase in the number of fluorines in the ligands. Surprisingly, the molecular weights of resultant polystyrenes are very low (Mn=2000–6600 Da) despite of St loadings, corresponding up to 121 chains per active species. The mechanisms were investigated by DFT simulation, MALDI‐TOF MS, isotope tracing experiment and 2D NMR spectrum analyses, which revealed that the fluorine activated the polymerization and directed chain transfer to toluene. Taking on toluene: Highly efficient chain transfer to toluene has been achieved for the first time in styrene coordination polymerization by using rare‐earth metal precursors. The higher polymerization activity is attributed to the fluorine substitutents on the β‐diiminato ligands lowering the LUMO energy of the active metal center and also directing the chain transfer to the ortho‐proton of toluene.