Abstract
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.