Dynamic NMR as a Nondestructive Method for the Determination of Rates of Dissociation. XIX. Sulfur Inversion in 9--9-borabicyclononane Proceeds via Dissociative Mechanism

Article abstract of DOI:10.1246/bcsj.64.1563

Kinetic parameters for sulfur inversion in the title compound were determined by the dynamic NMR method in CD2Cl2 as follows: ΔH(excit.) 14.2 +/- 0.1 kcal mol^-1, ΔS(excit.) 11.3 +/- 0.3 cal mol^-1 k^-1. ΔG(excit.)₂₃₃ 11.6 kcal mol^-1.The large and positive entropy of activation suggests that the inversion takes place through dissociative mechanisms.Comparison of the rate constants obtained with multiple probes shows that the rotation about the C_Ph-B bond requires further energy after the dissociation of the S-B bond.The solvent effect on the sulfur inversion is small but distinct; the more polar a solvent, the higher the barrier to the inversion.Dynamic behaviors of a related compound are also discussed.