(673c) On the Mechanism of Ethylene Di- and Oligomerization on Uniform d8 Metal Cations in Zeolites

Activation of the strong C–H bonds in ethylene is demonstrated on d⁸ single atoms in the cationic positions of zeolites H-FAU and H-BEA under ambient conditions. The oxidative addition of C₂H₄ to the metal center occurs with the formation of a d⁶ metal vinyl hydride, explaining the initiation of the olefin-polymerization cycle on d⁸ M(I/II) sites in the absence of pre-existing M–H bonds. Post-reaction characterization of the two materials reveals that the active metal cations remain site-isolated whereas deactivation occurs due to the formation of carbonaceous deposits on the zeolites. Our findings solve a 50-year old mystery as to how ethylene di- and oligomerization occurs on metal ions in zeolites.