Coordinative chain transfer homopolymerization and copolymerization of bio‐sourced β ‐myrcene and butadiene promoted by iminopyridine iron complexes

Abstract

A family of iron complexes bearing iminopyridine (ImPy) ligands with systematic variations on the N ‐aryl and pyridine moieties was evaluated as pre‐catalysts for the coordinative polymerization of β‐myrcene and butadiene. Upon activation with Al ⁱ Bu ₃ and trityl borate, these complexes were further assessed under coordinative chain transfer polymerization (CCTP) conditions using ZnEt ₂ as chain transfer agent (CTA). Several complexes exhibited high activities in both polymerization regimes, with regioselectivities strongly dependent on the monomer nature. Polymyrcenes with moderately to highly 1,4‐regular microstructures were obtained, whereas butadiene polymerization generally led to 1,2 units with variable 1,4 incorporations, except for Fe1 which yielded significant 1,4‐polybutadiene. The addition of 10 equivalents of ZnEt ₂ as CTA uncovered pronounced differences in catalyst performance arising from their steric and electronic characteristics. Non‐fluorinated complexes (Fe1–Fe4) exhibited clear CCTP signatures, including substantial reductions of M _n and narrower dispersities, while fluorinated analogues (Fe5–Fe8) were essentially unaffected. A second series of iron complexes supported by ImPy derivative ligands (Fe9–Fe12) further emphasized the critical role of steric hindrance near the pyridine nitrogen and of chelate ring size. Finally, statistical copolymerization of butadiene/myrcene and under chain transfer conditions proceeded efficiently with Fe2–Fe4. © 2026 Society of Chemical Industry.