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

Gas-phase reactions of atomic gold anions and small gold cluster anions, Au n - ( n = 1-4), with CH 3 I 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. Au n I - identified by mass spectrometry was observed as a common reaction product. Photoelectron spectroscopy and density functional theory calculations revealed that Au 2 I - has a linear structure in which the I atom is bonded to Au 2 , and Au 3 I - and Au 4 I - take a two-dimensional structure in which the I atom is bonded to triangular Au 3 moieties. Pseudo-first-order kinetic analyses of the reaction revealed the inverse correlation of the reactivity of Au n - toward CH 3 I and the electron affinity of Au n , indicating the reductive activation of the C-I bond. Especially, Au 2 - showed the highest reactivity to form Au 2 I - as the main product, whereas the adduct compound Au 2 CH 3 I - 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 Au 2 - 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.