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. 2025 Oct 1;147(39):35227-35231.
doi: 10.1021/jacs.5c13589. Epub 2025 Sep 17.

One-Electron Boron-Carbon Triel Bonding

Paula Castro Castro  1 , Wei-Chun Liu  1 , François P Gabbaï  1
Affiliations

One-Electron Boron-Carbon Triel Bonding

Paula Castro Castro et al. J Am Chem Soc. .

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.

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Figures

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Top: Formation of [R···BF3]• intermediates by oxidation of organotrifluoroborates and representation of the computed structure and B–C distance of [H3C···BF3]•. Bottom: Examples of systems featuring one-electron B–B or C–C σ-bonds, with corresponding bond lengths.
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Synthetic scheme leading to the formation of [5]­[BF4]. The crystal structures of 4 and [5]­[BF4] are also shown. For all crystal structures, the ellipsoids are drawn at the 50% probability level; the solvent molecules, counterions and H atoms are omitted for clarity.
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Top: Cyclic voltammogram of [5]­[BF4] recorded under N2 in CH2Cl2 with TBAPF6 as supporting electrolyte (0.25 M) at a scan rate of 0.1 V/s. Bottom: Synthesis and crystal structure of [K­(18-c-6)]­[5]. Ellipsoids are drawn at the 50% probability level. Solvent molecules and H atoms are omitted for clarity.
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Synthesis, EPR spectrum, spin density map, and crystal structure of 5 •. Inset shows NBO and Pipek-Mezey orbitals corresponding to the C···B interaction in 5 •. Contour plots are drawn at an isovalue of 0.05. Ellipsoids are drawn at the 50% probability level. H atoms are omitted for clarity.
See this image and copyright information in PMC

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