The Redox Properties of Germylenes Stabilized by N‐Donor Ligands

Germylenes, organic compounds of divalent germanium, are often considered as promising catalytic systems efficient in reactions of oxidative addition and reductive elimination, including SET reactions. However, the systematic studies of their redox properties, allowing for the quantitative evaluation of the levels of frontier molecular orbitals and the stability of single electron transfer products, are extremely limited in number. In this work, a series of germylenes with various types of stabilization: N−Ge−N, (N→)C−Ge−C(←N), N−Ge−N(←N), O−Ge−O(←N) и (N→)O−Ge−O(←N) (“−“ ‐a covalent bond, stabilization is achieved by p‐donation of a lone pair of electrons of N or O, “→” ‐donor‐acceptor bond) were characterized by cyclic voltammetry. The results were compared with UV/Vis spectroscopy data and DFT calculations. All germylenes studied in MeCN and THF with Bu₄NPF₆ as a supporting electrolyte are chemically irreversibly oxidized in the potential range of 0.5–1.4 V vs. Ag/AgCl. In all cases, as estimated by the quantum chemical calculations, the HOMO remains at the covalently unsaturated germanium center although being significantly redistributed over the molecular system. In turn, electroreduction of germylenes is possible only in the presence of a strong electron‐withdrawing substituent or a pyridine ring depleted in electron density donated to germanium. In both cases, the LUMO is localized exactly on these moieties and is absent on the germanium. Thus, the use of stabilizing groups makes it possible both to improve germylene stability and to fine‐tune their HOMO level that determines their ability to participate in oxidative addition reactions.