Conformational analysis of N→BH3, N→BF3, and N‐CH3+ complexes with ibuprofen‐derivative amides

The synthesis and structural characterization of novel amine-borane adducts of ibuprofen derivatives are presented. The changes of the electron density on the carbonyl and pyridine ring after formation of N→BH3, N→BF3, and N-CH3+ have been confirmed by 1H, 11B, 13C, and 19F NMR, further supported by homonuclear and heteronuclear correlations. Moreover, electrostatic interactions —H+···−F and the nonclassical H+···−H— were identified by NMR spectra. The analysis of the resulting molecular structures offered insights on the 2-aminopyridine N→B adducts. The N→BH3 adduct formed a single molecular arrangement, both in C6D6 and CDCl3. The same behavior was observed for the N→BF3 adduct in CDCl3. However, two conformers of this adduct were detected in C6D6. All adduct geometries were corroborated by density functional theory computational calculations.