C-H bond activation by nanosized scandium oxide clusters in gas-phase

Scandium oxide cluster cations are prepared by laser ablation and reacted with n-butane in a fast flow reactor. A reflectron time-of-flight mass spectrometer is built to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) products (Sc2O3)(N)H+ (N = 1-22), (Sc2O3)(N)O4H+ (N = 4-22) and their deuterated compounds are observed upon the cluster interactions with n-C4H10 and n-C4D10, respectively. This indicates that C-H bond activation of n-butane over atomic clusters as large as Sc44O66+ and Sc44O70+ can take place in gas phase. The experimentally determined rate constants and values of kinetic isotopic effect for HAA vary significantly with the cluster sizes. Density functional theory (DFT) calculations are performed to study the structures and reactivity of small clusters (Sc2O3)(1-3)(+). The DFT results suggest that the experimentally observed C-H bond activation by (Sc2O3)(N)(+) is facilitated by oxygen-centred radicals bridgingly bonded in the clusters. The nature of unpaired spin density distributions within the clusters may be responsible for the experimentally observed size-dependent reactivity. (C) 2011 Elsevier B.V. All rights reserved.