Gas-Phase Reactivity of AuSiO3– Anion Clusters with n-Alkanes (C1–C4): Distinguishing Capture, Stabilized Association, and C–H Bond Activation

Abstract

The reactivity of heteronuclear gold-silicon oxide cluster anion AuSiO3– toward small alkanes (C1–C4) has been experimentally investigated at room temperature by employing a homemade reflectron time-of-flight mass spectrometer. Experimental results reveal distinct reaction channels for these systems, which produce hydrogen-containing dissociation products (SiO3H–) and associative adducts (AuSiO3CnH2n+2–, n = 1–4). While the total depletion (capture) rate increases with increasing chain length, the branching ratio of dissociation products correspondingly decreases. Density functional theory calculations demonstrate that the two-fold-coordinated gold ion (Au+) anchored on the AuSiO3– cluster proceeds via an oxidative addition mechanism involving homolytic bond cleavage. Both RRKM calculations and MESMER master-equation simulations reveal that for larger alkanes such as C4H10, the rapidly growing density of vibrational states with increasing chain length shifts the competition from product dissociation toward collisional stabilization, thereby favoring associative adduct formation over dissociation pathways─a stark contrast to the behavior observed in the AuSiO3––CH4 reaction. This work provides novel insights into the competition among collisional capture, stabilized association, and C–H bond activation in small-molecule alkanes.