| Abstrakt: |
The coordination sphere and steric variations in iron catalysts present a fascinating strategy for adjusting monomer regio- and stereoselective enchainment, leading to the development of novel polymer structures in isoprene polymerization. This study investigates a range of iron complexes with variations in the coordination spheres (bidentate and tridentate) and steric/electronic properties of side arms to evaluate their impact on isoprene polymerization. X-ray analysis revealed that the tridentate Fe-NMe2 complex has a dinuclear structure with a μ2-O bridge, where each iron center is monoligated in an octahedral geometry. In contrast, the bidentate Fe-NHPh crystallizes as an ion pair, consisting of a trisligated [L3Fe]2+ cation and counteranions [FeCl4]− and [Cl]−. Toward isoprene polymerization, iron complexes with tridentate ligands bearing NMe2 or NiPr2 side arms exhibited high catalytic activity, whereas those with NH2 or OH side arms showed significantly lower activity. In addition, both bidentate iron complexes were also highly active precatalysts, with activities reaching up to 1.8 × 105 g (IP) per mol (Fe) per h. Variations in the ligand framework led to significant differences in polymer molecular weights, ranging from 37.5 × 103 g mol−1 to 272.8 × 103 g mol−1, with narrow to broad dispersities. Of significant note, tridentate iron complexes were particularly effective for 3,4 monomer addition (up to 63%), resulting in isopropenyl-enriched polyisoprene. In contrast, bidentate complexes showed a nearly equal preference for both 1,4 and 3,4 additions (1,4/3,4 ≈ 50/50). Polyisoprenes with a high number of isopropenyl pendant groups are highly sought after for post-functionalization and the production of high-performance resins. [ABSTRACT FROM AUTHOR] |
