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 NBH3, NBF3, and N-CH3+ have been confirmed by H-1, B-11, C-13, and F-19 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 NB adducts. The NBH3 adduct formed a single molecular arrangement, both in C6D6 and CDCl3. The same behavior was observed for the NBF3 adduct in CDCl3. However, two conformers of this adduct were detected in C6D6. All adduct geometries were corroborated by density functional theory computational calculations.