NMR study of the sigmatropic [1,3]-B shift in 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene

Abstract

Activation parameters of the interconversion of geometric isomers6a and6b were determined by a complete lineshape analysis of the temperature-dependent13C NMR spectra of 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene (6). For the reaction6a →6b, ΔG≠298 = 52.2±0.1 kJ mol−1, ΔH≠ = 27.9±0.5 kJ mol−1, ΔS≠ = −82±8 J mol−1 K−1; For the reaction6b →6a, ΔG≠298 = 52.6±0.1 kJ mol−1, ΔH≠ = 24.7±0.5 kJ mol−1, ΔS≠ = −93±10 J mol−1 K−1. The interconversion of deuteropyridine complexes9a and9b proceedsvia their dissociation, which indicates that the rearrangement of borane6 occurs according to the [1,3]-B shift mechanism.