Stereoselective trans -1,4 Polymerization of Isoprene and β -Myrcene Mediated by Iron Complexes Bearing 1,1-Diaryl- N -(quinolin-8-yl)methanimine Ligands

Abstract

Although iron has emerged as an earth-abundant alternative for 1,3-diene coordinative polymerization, stereoselective iron systems remain uncommon and are often associated with limited catalytic activity. Here, we report three iron(II) complexes supported by 1,1-diaryl-N-(quinolin-8-yl)methanimine ligands, which upon activation with Al(iBu)3/[CPh3][B(C6F5)4] or methylaluminoxane (MAO), promote trans-1,4-selective polymerization of isoprene and β-myrcene with high activity (TOF up to 5700 h–1 at room temperature) and trans-1,4 contents of up to 95 and 99%, respectively. These systems operate under mild conditions and afford polymers with tunable molar masses by varying the monomer-to-Fe ratio. Beyond homopolymers, the catalyst platform allows the synthesis of poly(isoprene-block-myrcene) through sequential copolymerization, yielding trans-1,4-stereoregular materials. Density functional theory (DFT) calculations provide mechanistic insights into the origin of the trans-1,4 selectivity, rationalizing the experimentally observed selectivity. This work demonstrates that well-defined iron catalysts can efficiently mediate trans-selective 1,3-diene polymerization with high activity, highlighting the potential of iron for the development of precision polymerization catalysts.