Cis-1,4-Enhanced Polymerization of Isoprene Catalyzed by Iminopyridine-Iron(II) Complexes

(Imino)pyridine late transition-metal complexes have been well-explored in olefin polymerization. Among them, iron-based (imino)pyridine complexes stand out due to their abundance, low toxicity, and versatility in conjugated diene polymerization. While ligand modifications have predominantly focused on N_imine-substituents, direct pyridine ring functionalization remains underexplored despite emerging evidence of its potential influence. This study introduces a family of 6-methoxy-substituted (imino)pyridine iron catalysts for isoprene polymerization with high cis-1,4 selectivity (up to 91%). Unlike conventional isolated modification strategies that use steric hindrance substituents of N_imine, this work highlights the necessity of considering the ligand framework as an integrated system where interactions between distinct structural units govern polymerization behavior. These well-defined iron complexes challenge prior assumptions that pyridine ring modifications lack utility in conjugated diene polymerization and redefine future approaches to ligand optimization by emphasizing holistic over isolated structural adjustments in (imino)pyridine late transition-metal complexes.