Selective Hydrogenation of Azobenzene to Hydrazobenzene via Proton-Coupled Electron Transfer from a Polyoxotungstate Cluster

Zhou Lu; Shannon E Cooney; James R McKone; Ellen M Matson

doi:10.1021/jacsau.4c00127

Selective Hydrogenation of Azobenzene to Hydrazobenzene via Proton-Coupled Electron Transfer from a Polyoxotungstate Cluster

JACS Au. 2024 Mar 21;4(4):1310-1314. doi: 10.1021/jacsau.4c00127. eCollection 2024 Apr 22.

Authors

Zhou Lu¹, Shannon E Cooney¹, James R McKone², Ellen M Matson¹

Affiliations

¹ Department of Chemistry, University of Rochester, Rochester, New York 14627, United States.
² Departments of Chemical and Petroleum Engineering and Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.

Abstract

In this report, we describe proton-coupled electron transfer (PCET) reactivity at the surface of the Keggin-type polyoxotungstate cluster [ⁿBu₄N]₃[PW^VI₁₂O₄₀] (PW₁₂) in acetonitrile. Bond dissociation free energies (BDFEs) of the O-H groups generated upon reduction of PW₁₂ in the presence of acid are determined through the construction of a potential-pK_a diagram. The surface O-H bonds are found to be weak (BDFE(O-H)_avg < 48 kcal mol^-1), comparable to the BDFE of H₂. This is consistent with the observed formation of H₂ upon addition of a suitably strong organic acid, H₂NPh₂⁺ (pK_{a MeCN} = 5.98), to the reduced form of the cluster. The one-electron reduced form of PW₁₂ is isolated and used in conjunction with acid to realize the stoichiometric semihydrogenation of azobenzene via PCET from the surface of the reduced cluster.