NMR-STUDY OF THE SIGMATROPIC [1,3]-B SHIFT IN 7,8-DIPROPYL-7-BORABICYCLO[4.2.2]DECA-2,4,9-TRIENE

Activation parameters of the interconversion of geometric isomers 6a a nd 6b were determined by a complete lineshape analysis of the temperat ure-dependent C-13 NMR spectra of 7,8-dipropyl-7-borabicyclo[4.2.2]dec a-2,4,9-triene (6). For the reaction 6a --> 6b, Delta G(298)(not equal ) = 52.2+/-0.1 kJ mol(-1), Delta H-not equal = 27.9+/-0.5 kJ mol(-1), Delta S-not equal = -82+/-8 J mol(-1) K-1; For the reaction 6b --> 6a, Delta G(298)(not equal) = 52.6+/-0.1 kJ mol(-1), Delta H-not equal = 24.7+/-0.5 kJ mol(-1), Delta S-not equal = -93+/-10 J mol(-1) K-1. The interconversion of deuteropyridine complexes 9a and 9b proceeds via t heir dissociation, which indicates that the rearrangement of borane 6 occurs according to the [1,3]-B shift mechanism.