Reactivity of Stoichiometric Lanthanum Oxide Cluster Cations in C-H Bond Activation

Lanthanum oxide cluster cations are prepared by laser ablation and reacted with alkane molecules (n-butane and methane) in a fast flow reactor under thermal collision conditions. A reflectron time-of-flight mass spectrometer is used to detect the cluster distributions before and after the reactions. Hydrogen atom abstraction (HAA) from n-butane by (La2O3)(N)(+) (N = 1-8, N not equal 6) is observed, while the HAA from methane is only observed for (La2O3)(5)(+). The experimentally determined rate constants for HAA vary significantly with the cluster sizes. Density functional theory (DFT) calculations are performed to study the structures and reactivity of (La2O3)(N)(+) (N = 1-6) dusters. The DFT results suggest that the experimentally observed C-H bond activation by (La2O3)(N)(+) is facilitated by oxygen-centered radicals. The position of oxygen-centered radicals binding onto the clusters can heavily influence the reactivity in C-H bond activation. This gas-phase study improves our understanding about the chemistry of oxygen-centered radicals.