Synthesis of Skeletally Labeled 3-Methylhexaborane(12) and 2-Methylpentaborane(9): 10B and 11B NMR Spectral Studies of Base-Catalyzed Intramolecular Rearrangements in 2-Methylpentaborane(9)

Article abstract of DOI:10.1021/ja00297a036

Selectively 10B labeled 3-MeB6H11 has been synthesized from 1-MeB5H8 and 96percent 10B labeled B2H6 by modification of a previously published procedure.Positions B(1), B(2), and B(6) of the labeled 3-MeB6H11 each contain 46 +/- 5percent 10B while B(3), B(4), and B(5) are isotropically normal (19percent 10B).Reaction of this compound with dimethyl ether produces 2-MeB5H8 which is 10B enriched at B(4) (47 +/- 5percent 10B) and, to a lesser extent, at B(3,5) (30 +/- 5percent 10B).In the presence of 2,6-lutidine the 10B label in the 2-MeB5H8 equilibrates into all boron positions except the methyl-substituted B(2).These are the first direct observations of the movement of cluster boron atoms in the isomerization of pentaborane(9) derivatives.Several proposed isomerization mechanisms are examined in light of these results.