One-Electron Boron-Carbon Triel Bonding

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.