Dynamic NMR as a Nondestructive Method for the Determination of Rates of Dissociation. XVIII. Factors Affecting the Rates of Dissociation of N–B Bond in the Coordinated Form of 9-[2-(Dialkylaminomethyl) phenyl]-9-borabicyclo[3.3.1] nonanes

NMR spectra of the title compounds reveal that they exist in the intramolecularly N–B coordinated form. The NMR signals exhibited dynamic behaviors accompanied with the dissociation of the N–B bond and total line shape analyses of the exchanging nuclei afforded kinetic parameters for the topomerization. Entropies of activation are large and positive, typical for the dissociation of coordination bonds. Examination with the multiple probes shows that the nitrogen inversion requires additional energy after the N–B bond dissociation. The barrier for the topomerization is affected by N-alkyl groups due to their F-strain. The barrier height is reduced in nonpolar solvents and not influenced by nucleophilicity of solvents. These solvent effects are discussed in connection with polarity of the N–B bond and steric hindrance of the boron atom.