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)2C6H3], 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)2CF3CO, CH3(CF3)2CO, or Ph(CF3)2CO] prepared in situ significantly increases the polymerization rate while preserving selectivity. The resulting polymers were characterized by 1H and 13C NMR spectroscopy and gel‐permeation chromatography. A homoleptic iron complex catalyzes the ring‐opening metathesis polymerization of norbornene to yield highly stereoregular polynorbornene (99 % cis, syndiotactic). The influence of solvent, temperature, and additives was examined.