Size-dependent reactivity of VO⁺ (n = 1-9) clusters with ethane

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of V⁺ and VO⁺ (n = 1-9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among V⁺ (n = 1-9) clusters, only V_3-5⁺ can react with C₂H₆ to generate dehydrogenation products and the reaction rate constants are below 10^-13 cm³ molecule^-1 s^-1. In contrast, the reaction rate constants for all VO⁺ (n = 1-9) with C₂H₆ significantly increase by about 2-4 orders of magnitude. Theoretical analysis evidences that the addition of ligand O affects the charge distribution of the metal centers, resulting in a significant increase in the cluster reactivity. The analysis of frontier orbitals indicates that the agostic interaction determines the size-dependent reactivity of VO⁺ cluster cations. This study provides a novel approach for improving the reactivity of early 3d TMs.