Flash Communication: Mononuclear Metallacycle Mechanism in Binuclear Cr/PNCNP Catalyst May Trigger the Switch from Ethylene Trimerization into Tetramerization

An interesting switch from ethylene trimerization to
tetramerization
induced by the length of carbon linkers with the Cr/PNCNP catalyst
has been investigated by density functional theory (DFT) methods.
Structural analysis suggested that incorporating an additional methylene
group into the ligand backbone may facilitate the generation of binuclear
Cr species with a binding mode of (η2-P,N). Instead of the previously proposed bimetallic
route, further DFT calculations indicated that a monomeric ring expansion
mechanism might be responsible for the selective formation of 1-octene,
which is consistent with the previous deuterium labeling experiment
and crystallographic characterization.