Activation of the C–I and C–OH bonds of 2-iodoethanol by gas phase silver cluster cations yields subvalent silver-iodide and -hydroxide cluster cations

Abstract

The gas phase ion–molecule reactions of silver cluster cations (Ag_n⁺) and silver hydride cluster cations (Ag_mH⁺) with 2-iodoethanol have been examined using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. These clusters exhibit size selective reactivity: Ag₂H⁺, Ag₃⁺, and Ag₄H⁺ undergo sequential ligand addition only, while Ag₅⁺ and Ag₆H⁺ also promote both C–I and C–OH bond activation of 2-iodoethanol. Collision induced dissociation (CID) of Ag₅HIO⁺, the product of C–I and C–OH bond activation by Ag₅⁺, yielded Ag₄OH⁺, Ag₄I⁺ and Ag₃⁺, consistent with a structure containing AgI and AgOH moieties. Ag₆H⁺ promotes both C–I and C–OH bond activation of 2-iodoethanol to yield the metathesis product Ag₆I⁺ as well as Ag₆H₂IO⁺. The metathesis product Ag₆I⁺ also promotes C–I and C–OH bond activation.

DFT calculations were carried out to gain insights into the reaction of Ag₅⁺ with ICH₂CH₂OH by calculating possible structures and their energies for the following species: (i) initial adducts of Ag₅⁺ and ICH₂CH₂OH, (ii) the subsequent Ag₅HIO⁺ product, (iii) CID products of Ag₅HIO⁺. Potential adducts were probed by allowing ICH₂CH₂OH to bind in different ways (monodentate through I, monodentate through OH, bidentate) at different sites for two isomers of Ag₅⁺: the global minimum “bowtie” structure, 1, and the higher energy trigonal bipyramidal isomer, 2. The following structural trends emerged: (i) ICH₂CH₂OH binds in a monodentate fashion to the silver core with little distortion, (ii) ICH₂CH₂OH binds to 1 in a bidentate fashion with some distortion to the silver core, and (iii) ICH₂CH₂OH binds to 2 and results in a significant distortion or rearrangement of the silver core. The DFT calculated minimum energy structure of Ag₅HIO⁺ consists of an OH ligated to the face of a distorted trigonal bipyramid with I located at a vertex, while those for both Ag₄X⁺ (X = OH, I) involve AgX bound to a Ag₃⁺ core. The calculations also predict the following: (i) the ion–molecule reaction of Ag₅⁺ and ICH₂CH₂OH to yield Ag₅HIO⁺ is exothermic by 34.3 kcal mol⁻¹, consistent with the fact that this reaction readily occurs under the near thermal experimental conditions, (ii) the lowest energy products for fragmentation of Ag₅HIO⁺ arise from loss of AgI, consistent with this being the major pathway in the CID experiments.