Organoboranes : XXV. Hydridation of dialkylhaloboranes. New practical syntheses of dialkylboranes under mild conditions

Practical methods for the synthesis of dialkylboranes (R₂BH) via the hydridation of dialkylhaloboranes (R₂BX) have been developed. Convenient methods available for the preparation of R₂BX via the hydroboration of alkenes with monohaloborane complexes (H₂BX · SMe₂) make this approach valuable for the preparation of various dialkylboranes, R₂BH, many of which are not available by direct hydroboration of alkenes with borane itself. The suitability of various hydriding agents, such as borane derivatives, complex metal hydrides, and alkoxy metal hydrides, for the hydridation of R₂BX was examined, utilizing B-halo-9-borabicyclo[3.3.1]nonane as a representative dialkylhaloborane. In this case, the unusual stability of the resulting dialkylborane, 9-BBN, permits direct estimation of the reaction products by ¹¹B NMR spectroscopy. The generality of the procedure has been demonstrated.