Stereospecific Ring-Opening Metathesis Polymerization of Norbornene Catalyzed by Iron Complexes

Developing well-defined iron-based catalysts for olefin metathesis would be a breakthrough achievement in the field not only to replace existing catalysts by inexpensive metals but also to attain a new reactivity taking advantage of the unique electronic structure of the base metals. Here, we present a two-coordinate homoleptic iron complex, Fe(HMTO)(2) [HMTO=O-2,6-(2,4,6-Me3C6H2)(2)C6H3], that is capable of performing ring-opening metathesis polymerization of norbornene to produce highly stereoregular polynorbornene (99 % cis, syndiotactic). The use of heteroleptic Fe(HMTO)(RO) [RO=(CH3)(2)CF3CO, CH3(CF3)(2)CO, or Ph(CF3)(2)CO] prepared in situ significantly increases the polymerization rate while preserving selectivity. The resulting polymers were characterized by H-1 and C-13 NMR spectroscopy and gel-permeation chromatography.

Automated summary

The study explores the capability of an iron-based catalyst in performing ring-opening metathesis polymerization of olefins, demonstrating that the use of in situ prepared heteroleptic iron catalysts significantly enhances polymerization rate and selectivity.