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.

Two trinuclear Cu II pyrazolato complexes with a Cu 3 (µ 3-E)-core (E = O 2or OH-) and terminal nitrite ligands in two coordination modes were characterized crystallographically, spectroscopically and electrochemically. One-electron oxidation of the µ 3-O species produces a delocalized, mixed-valent, formally Cu II 2 Cu III-nitrite, but no nitrate. In contrast, under reducing conditions-addition of PhSH as an electron and proton donor-both complexes mediate the reduction of nitrite, releasing NO.