Metal-organic frameworks supported iron catalysts for isoprene polymerization

Immobilization of active site on solid support plays great roles in improving catalyst performance. In this study, a series of solid supported iron precatalysts via the immobilization of iron halides (FeX n , X = Cl, Br or I, n = 2 or 3) on the metal-organic frameworks of UiO type bearing bipyridine moiety (bpy-UiO) were synthesized and used for isoprene polymerization. These bpy-UiO supported iron precatalysts (bpy-UiO-FeX n ) were also well characterized by the powder X-ray diffraction, elemental analysis and N 2 adsorption measurement. Upon activation with trialkylaluminums (AlEt 3 , Al(i-Bu) 3 and AlOct 3 ), bpy-UiO-FeX n exhibited excellent catalytic activity for isoprene polymerization. Interestingly, the iron(III) precatalysts had higher activity than the iron(II) precatalysts, and the highest activity was 1726.4 Kg⋅P/(mol⋅Fe⋅h) for bpy-UiO-FeBr 3 with AlEt 3 . Moreover, the activity gradually increased as the polymerization temperature increased from 0 °C to 50 °C, reflecting the fact that the MOFs supported iron catalysts had excellent thermal stability. Notably, the obtained polyisoprene had the ultrahigh molecular weight ( M w = 1.20×10 6 –3.13×10 6 Daltons), and predominantly consisted of 38.5–54.4 mol % cis -1,4 configuration and 45.6–61.5 mol % 3,4-configuration. This work offers an opportunity to design the high active and stable iron catalyst for conjugated diene polymerization based on the solid support.