Dative or coordinative carbon−boron bond in boron trapped N-heterocyclic carbenes (NHCs)? An answer given on the magnetic criterion

The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of isolated as well as B–C bond length varied model compounds (BR3 trapped NHCs) 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 the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the present dative vs. coordinative bond character of the boron−carbon bond in the trapped NHCs. Results are confirmed by bond lengths and 11B/13C chemical shift variations in the BR3 trapped NHCs. [Display omitted] •The electron configuration of the ylide-stabilized carbene moiety of NHC-boranes does not change when compared with the free carbene.•Weak changes in δ(13C)/ppm of the carbene carbon atom and extremely strong high field shifts of δ(11B)/ppm of the boron atom in NHC-boranes sensitively attend the boron re-hybridization.•On both the structural and magnetic criterion the Ccarbene−BR3 bond prove to be completely covalent and of same quality as usual C–B bonds. .•The application of the dative bond arrow (Ccarbene.→BR3) is not justified.