It is well noticed that hydrogen promotes catalyst activity in
Cr/PNP-catalyzed ethylene tetramerization, but the mechanism of this
boost is unclear. A density functional theory (DFT) study devoted to
exploring this effect was conducted, and conformation changes were
carefully taken into consideration to build a clear reaction pathway.
Three components in the catalytic cycle was examined in detail: the
production of 1-hexene from the metallacycloheptane, the production of
1-octene from metallacyclononane, and the formation of active center on
the catalyst. The result indicates that the formation of active center
on the catalyst becomes more favorable upon imposition of hydrogen,
where hydrogen function as a second ligand. This easing effect could be
the key factor leading to the outperformed catalyst activity.