H₂ Elimination Products from Neutral Zr + Alkene Reactions in the Gas Phase

Abstract

Identification of the metal-containing products of reactions of the neutral transition metal atom Zr(4d25s2, 3F) with ethylene and propylene is accomplished using one-photon ionization at 157 nm and time-of-flight mass spectrometry. The reactions proceed in a fast flow reactor at 298 K with He/N2 buffer gas at 0.6 Torr. Mass spectra of the products of both Zr + C2H4 and Zr + C3H6 indicate that H2 elimination occurs as the primary reaction step. The efficiency of the Zr + C2H4 reaction shows that there is no barrier larger than about 2 kcal/mol above reactants along the entire reaction path. This corroborates an earlier theoretical prediction by Blomberg and Siegbahn of facile H2 elimination by ground-state Zr. For the secondary reactions ZrC2H2 + C2H4 and ZrC3H4 + C3H6 and for the reactions ZrO + C2H4 and ZrO + C3H6, mass spectra again indicate that H2 elimination occurs. Rate constant measurements using photoionization detection show that the presence of the C2H2 and C3H4 ligands enhances the reaction efficiency over that of the bare Zr atom, while ZrO reacts at essentially the same rate as Zr.