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

Identification of the metal-containing products of reactions of the neutral transition metal atom Zr(4d 2 5s 2, 3 F) 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/N 2 buffer gas at 0.6 Torr. Mass spectra of the products of both Zr + C 2 H 4 and Zr + C 3 H 6 indicate that H 2 elimination occurs as the primary reaction step. The efficiency of the Zr + C 2 H 4 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 H 2 elimination by ground-state Zr. For the secondary reactions ZrC 2 H 2 + C 2 H 4 and ZrC 3 H 4 + C 3 H 6 and for the reactions ZrO + C 2 H 4 and ZrO + C 3 H 6, mass spectra again indicate that H 2 elimination occurs. Rate constant measurements using photoionization detection show that the presence of the C 2 H 2 and C 3 H 4 ligands enhances the reaction efficiency over that of the bare Zr atom, while ZrO reacts at essentially the same rate as Zr.