Intramolecular carbene stabilization via 3c, 2e bonding on basis of the magnetic criterion. (27th August 2021)

• Record Type: Journal Article
• Authors: Kleinpeter, Erich; Koch, Andreas
• Is Part Of: Tetrahedron. Volume 95(2021)
• Publication Date: 2021-08-27
• Subjects: Cyclobutylcarbene -- 1, 2-diboretane-3-ylidene -- 3c, 2e-bonding -- Through-space NMR shieldings (TSNMRS) -- NICS; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2021.132357
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent cyclobutylcarbene 8, 1, 2-diboretane-3-ylidene 9, and some carbene analogues of boron 14–18 as most intriguing examples of carbenes, which can be stabilized as homoaromatic systems with 3c, 2e bonding, have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually, ring current effect/anisotropy effects as measurable in 1 H NMR spectroscopy) are employed to qualify and quantify the degree of present 3c, 2e-homoaromaticity. Results are confirmed by geometry (bond angles and bond lengths) and spectroscopic data, the δ ( 11 B)/ppm data and the 13 C chemical shifts of the carbene electron-deficient centre. Graphical abstract: Image 1 Highlights: The 13 C chemical shift of the carbene carbon (271.9 ppm) classifies 8 as ylide stabilized carbene. The 3c, 2e-homo-aromaticity with non-classical σ-participation of cyclobutylcarbene is proved. Also the 3c, 2e-homo-aromaticity with non-classical σ-participation of 1, 2-diboretane-. 3-ylidene 9 is proved by the ring current effect. The carbene analogues of boronare intramolecularly stabilized via homoaromatic 2e-delocalization.