Trimethylamine-dibromoborane

Trimethylamine-dibromoborane has been reported in the literature only once.7 It was prepared by the reaction of boron tribromide with trimethylamine-borane, in carefully controlled 

A two-step process, using HBr for the first replacement, and then a stoichiometric amount of Br2 for the second, avoids the difficulties. 

The compound is soluble in acetone, chloroform, methylene chloride, and nitromethane. It is insoluble in alkanes and cold water and stable toward water in the cold but gives an acidic solution when boiled with water. The infrared spectrum shows a single band at 2510 cm.-1, about 50 cm.-1 higher wave number than in the monobromo compound. The nB spectrum gives a doublet 18.9 p.p.m. upfield from trimethyl borate Jb-h = 155 Hz. The proton spectrum in methylene chloride shows a sharp singlet at 2.91 p.p.m. downfield from external tetramethylsilane and 0.20 p.p.m. farther downfield than the monobromo compound. Boron-attached hydrogens are not detectable. 

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