Abstraction of the I Atom from CH3I by Gas-Phase Au n - (n = 1-4) via Reductive Activation of the C-I Bond.

Abstract

Gas-phase reactions of atomic gold anions and small gold cluster anions, Aun– (n = 1–4), with CH3I were investigated to clarify the effect of the cluster size on C–I bond activation and to elucidate the key properties of Au clusters that govern the reactivity. AunI– identified by mass spectrometry was observed as a common reaction product. Photoelectron spectroscopy and density functional theory calculations revealed that Au2I– has a linear structure in which the I atom is bonded to Au2, and Au3I– and Au4I– take a two-dimensional structure in which the I atom is bonded to triangular Au3 moieties. Pseudo-first-order kinetic analyses of the reaction revealed the inverse correlation of the reactivity of Aun– toward CH3I and the electron affinity of Aun, indicating the reductive activation of the C–I bond. Especially, Au2– showed the highest reactivity to form Au2I– as the main product, whereas the adduct compound Au2CH3I– was hardly formed, in sharp contrast to the reaction of Au– reported previously. On the basis of theoretical calculations, we propose that the reaction proceeded dominantly via the I atom abstraction pathway (attack of Au2– from the I atom side), which is highly preferential from the viewpoint of both the energetics and a steric factor. This study demonstrates that not only the reactivity but also the reaction mechanisms and products are governed by the cluster size in C–I bond activation by Au clusters at the smallest size region.