| Popis: |
An infrared technique was developed to establish the equilibrium involved in the reaction of 9-borabicyclo[3.3.1]nonane with representative amines under standard conditions (25.0°C, cyclohexane or THF solution): (9-BBN)2 + 2 Amine ⇌ 2 9-BBN: Amine. Coordination is complete with primary amines, even as hindered as tert-butylamine. It is complete with diethylamine, but incomplete with diisopropylamine. It is incomplete even with the simple triethylamine. However, the cyclic structure corresponding to triethylamine, namely, quinuclidine, forms a stable adduct. Pyridine is fully coordinated, but the extent of coordination decreases with increasing steric requirements of the 2-alkyl substituent, becoming essentially zero with 2-tert-butylpyridine and 2,6-dimethylpyridine. Thus the results with the unusual Lewis acid, 9-borabicyclo[3.3.1]nonane parallel closely the earlier results for the stability of addition compounds produced by the reaction of such amines with trimethyl-borane, boron trifluoride, and borane. |
