Boron trihalide-amine adducts

Mixed boron trihalide adducts of amines must have been present as intermediates in earlier halogen displacement studies 40,124), but the experimental methods used led to detection of only the final unmixed-halogen product. 

The near-random redistribution of fluorine and chlorine in oxygen-donor boron trihalide adducts (27, 29) might be rationalized using this principle since oxygen is between fluorine and chlorine on the hard-soft scale (140), and there is less discontinuity of ligands in terms of hard-soft properties. However, amine adducts of BHF2 do tend to disproportionate to give the BF3 and BH3 adducts (130). 

The classical method of preparation of amine-trihaloboranes involves the direct addition of the amine to the boron trihalide.1,2 However, when this method is used in an attempt to prepare boron trihalide adducts of secondary amines, one obtains a mixture of... 

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