Dynamic NMR as a Nondestructive Method for the Determination of Rates of Dissociation. XIX. Sulfur Inversion in 9-[2-(Ethylthiomethyl)phenyl]-9-borabicyclo[3.3.1]nonane Proceeds via Dissociative Mechanism

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Abstract
Kinetic parameters for sulfur inversion in the title compound were determined by the dynamic NMR method in CD2CL2 as follows: ΔH≠ 14.2±0.1 kcal mol−1, ΔS≠ 11.3±0.3 cal mol−1 K−1, ΔG233≠ 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 Cph–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.

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