NMR assignments of [6-R-nido-5,6-C2B8H10]- anions (where R = H, Me, and n-C6H13).: An irreversible 5 → 6 alkyl migration via a B9 vertex-swing mechanism

Deprotonation by "proton sponge" (PS = 1,8-dimethylaminonaphthalene) of the parent dicarbaborane nido-5,6-C2B8H12 (1) and its 6-R-substituted derivatives (where R = Me and n-C6H13) leads to the anions [nido-5,6-C2B8H11](-) [1](-) and [6-R-nido-5,6-C2B8H10](-) [6-R-1](-) respectively. In contrast, the deprotonation of the 5-substituted isomers, 5-R-nido-5,6-C2B8H11 (5-R-1), results in irreversible conversion into the 6-substituted anions [6-R-1]-, from which the neutral compounds 6-R-1 can be obtained via reprotonation. This 5 --> 6 alkyl migration can be explained by the B9 vertex-swing mechanism previously proposed for the interenantiomeric fluxionality of [1]-, but now with the product dictated by the higher thermodynamic stabilities of the 6-substituted derivatives. The work has also resulted in complete assignments of B-11 and H-1 NMR spectra of the [nido-5,6-C2B8H11](-) anion and of 11B NMR spectra of the [6-R-nido-5,6-C2B8H10]- anions.