Encapsulation of an Electron in a Diborencine Macrocycle: Synthesis, Structure, and Reactivity

Encapsulation of a single electron within the internal cavity of a host system poses significant challenges, as the electron tends to delocalize over the surface. In this study, we successfully trap a single electron through a B-B one-electron σ-bond in a diborencine macrocycle (compound 4). The structure of this one-electron σ-bond has been characterized using X-ray single-crystal analysis and EPR studies, indicating that this bond exhibits considerable s-character, with the boron atoms adopting sp³ hybridization, as supported by DFT computations. Additionally, compound 4 demonstrates rich reactivity: it can facilitate O₂ cleavage, generating a B-O-B cyclic product; its reaction with PhSSPh produces a B-S-B linked ring-expansion product, while reactions with PhSeSePh and quinone yield ring-contraction products. The resulting products have been fully characterized through X-ray single-crystal analysis, NMR, and HRMS spectroscopy. Finally, DFT computational studies have been performed to elucidate the reaction mechanism of this one-electron B-B bond.