ORGANOBORANES .8. STRUCTURE OF THERMALLY ISOMERIZED ORGANOBORANE FROM REACTION OF BORANE AND 1,3-BUTADIENE IN A 1 - 1 MOLAR RATIO . EVIDENCE FOR AN EXCEPTIONALLY STABLE TRANSANNULAR BORON-HYDROGEN BRIDGE

Distillation of the largely polymeric product produced in the reaction of equimolar quantities of borane and 1,3-butadiene produces a material, C8H16B2H2, with extraordinary properties for a tetrasubstituted diborane (dinner of a dialkylborane). Thus this material is stable to water and methanol at room temperature, and fails to hydroborate simple olefins without heating. It is not oxidized by cold alkaline hydrogen peroxide, and this treatment can be used to prepare the pure material, free of the usual small amounts of more reactive impurities. These characteristics do not appear to be compatible with the proposed formulation as bisborolane, (CH2)4BH2B(CH2)4. Accordingly, the alternative formulation as 1,6-diboracyclodecane, with a transannular boron-hydrogen bridge, was investigated. Reaction with methanol occurs slowly in refluxing tetrahydrofuran, liberating hydrogen, and forming methoxy derivatives. However, glpc examination of the reaction mixture revealed the essential absence of B-methoxyborolane, (CH2)4BOCH3, in the initial phases of the reaction. Similarly, protonolysis with acetic acid forms 1,4-butanediboronic acid, isolated and identified as the bisdiethanolamine derivative, mp 261-263°. Both of these observations are compatible with the formulation of the compound as 1,6-diboracyclodecane, but not with the bisborolane structure. Finally, it is pointed out that the highly unusual characteristics of the compound are readily understood in terms of the formulation as 1,6-diboracyclodecane, where the transannular structure could greatly stabilize the boron-hydrogen bridge and render this moiety relatively inert toward reagents which usually attack it with ease. © 1969, American Chemical Society. All rights reserved.