Ethylene Polymerization at High Temperatures Catalyzed by Double-Decker-Type Dinuclear Iron and Cobalt Complexes: Dimer Effect on Stability of the Catalyst and Polydispersity of the Product

Dinuclear
Fe and Co complexes with a double-decker structure were
synthesized by using macrocyclic ligands having two bis­(imino)­pyridine
groups. X-ray crystallography of the dinuclear Co complex revealed
that the two bis­(imino)­pyridine Co moieties stack in an antiparallel
manner with a distance of 7.74 Å. A dinuclear Fe complex catalyzes
ethylene polymerization at 80–120 °C (5 atm ethylene)
to produce polymers with a relatively narrow molecular weight distribution
(Mw/Mn = 1.75–2.77);
its highest activity is 975 g (mmol Fe)−1 h–1 atm–1 at 100 °C. Ethylene
polymerization at room temperature under 1 atm ethylene catalyzed
by the dinuclear Co and Fe complexes produces polymers with much higher
molecular weight (Mn up to 15.5-fold increase)
than the corresponding mononuclear complexes.