Kinetics and Mechanism of the Reactions of Ground-State Y (4d5s, 2D) with Ethylene and Propylene: Experiment and Theory

Abstract

Bimolecular rate constants, primary products, and kinetic isotope effects for the reactions of Y (4d15s2, 2D) with C2H4 and C2D4 and with C3H6 and C3D6 are measured in a fast flow reactor at 300 K with He/N2 buffer gas at 0.8 Torr. The H2 and D2 elimination products and Y(alkene)-stabilized complexes are detected using single photon ionization at 157 nm and time-of-flight mass spectrometry. We find a small normal isotope effect (kH/kD = 1.75 ± 0.12) for the reaction with ethylene but no significant isotope effect (kH/kD = 1.06 ± 0.07) for the reaction with propylene. We use density functional theory in its B3LYP and mPW1PW91 forms with a large basis set to characterize stationary points on the doublet potential energy surface for the reaction Y + C2H4 → YC2H2 + H2. Theory finds no energy barrier to the formation of a long-range Y−ethylene complex. Subsequent steps involving CH bond insertion by metallacyclopropane complexes are consistent with earlier work. However, a new, low-energy path involves concert...