Pyridine‐oxazoline ligated iron complexes: Synthesis, characterization, and catalytic activity for isoprene polymerization

• Published in: Applied organometallic chemistry Vol. 36; no. 10
• Main Authors: Zhao, Mengmeng, Zhang, Xianhui, Wang, Ledong, Wang, Liang, Zhu, Guangqian, Wang, Qinggang
• Format: Journal Article
• Language: English
• Published: Chichester Wiley Subscription Services, Inc 01.10.2022
• Subjects: Catalytic activity; Chemical synthesis; Chemistry; Covalent bonds; Crystallography; Dichlorides; Iron; iron complex; Isoprene; isoprene polymerization; Polymerization; Pyridines; pyridine‐oxazoline ligand; Selectivity
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.6848

A series of iron(II) dichloride complexes (Fe1–Fe3) bearing 2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L1), 4‐isopropyl‐2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L2), and 4‐(t‐butyl)‐2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L3) and iron(II) acetylacetonate complex (Fe4) bearing L1 were synthesized and characterized by elemental and spectroscopic analyses. Determined by single‐crystal X‐ray crystallography, complex Fe3 adopts an unusual unsymmetrical binuclear core. Upon activation with methylaluminoxane (MAO), the pyridine‐oxazoline (Py‐ox) ligated iron complexes (Fe1–Fe4) showed excellent activity towards isoprene polymerization. Complex Fe1 displayed the highest activity of 8160 kg (mol·h)−1 with 54% of 3,4‐polyisoprene. The ligand environment and counter anion on iron center all displayed significant effects on polymerization activity and selectivity, which reflected the special performance compared with pyridine‐imine. And we propose the possible mechanism through cis‐η4 mode following the σ bond rotation because of the steric effect of t‐butyl substituent of Fe4 to give high trans‐1,4‐polymers. Furthermore, the effects of reaction parameters on the catalytic activity and selectivity were investigated in detail. Four iron(II) complexes bearing pyridine‐oxazoline were synthesized and characterized, and displayed high catalytic performance for polymerization of isoprene, in which the substituents at oxazoline showed crucial effects on activity and selectivity.