One-Electron Boron–Carbon Triel Bonding

Abstract

Aiming to interrogate the possibility of heteronuclear B–C one-electron σ-bonding, we have prepared a naphthalene-based platform ([5]+) decorated at its peri-positions by a carbenium and a boryl unit separated by a B–C distance of 2.994(4) Å. Reduction of this cationic platform by one electron affords a radical (5•) with a shortened B–C distance of 2.874(3) Å, suggesting the onset of B–C one-electron bonding. This radical, which was also characterized by EPR spectroscopy, undergoes a second reduction, affording a borate ([5]−) with a long, polar covalent B–C bond of 1.793(8) Å. These compounds have been structurally, spectroscopically, and computationally investigated, shedding light on the polarization and weakness of the B–C bond of 5•, which is best described as a noncovalent one-electron B···C triel bond rather than a covalent one-electron σ-bond.