Abstract:
Boron trihalide and mixed boron trihalide adducts
of trimethylamine have been prepared, and characterized
by proton and fluorine N.M.R. spectroscopy. The acceptor
power of the boron trihalides was seen to increase in the
order BF3 < BC13 < BBr3 < BI3, corroborating previous
evidence. The mixed boron trihalides had intermediate
Lewis acidities.
Solution reactions between adducts and free boron
trihalides rapidly led to the formation of mixed adducts
when the free boron trihalide is a stronger Lewis acid
than that in the adduct. A slower reaction is observed
when the free BX3 is a weaker Lewis aoid than that complexed.
The mechanism of halogen exchange leading to the
mixed (CH3)3NBX3 adducts was investigated. 10B labelling
experiments precluded B-N bond rupture as a possible
mechanism in solution; results are discussed in terms of
halogen-bridged intermediates. Pre-ionization may be
important for some systems. At higher temperatures, during
gas phase reactions,B-N coordinate bond rupture may be
the initial step of reaction.
Two mixed adduots, namely (CH3)3NBClBr2 and
(CH3)3NBHOIBr were prepared and characterized by Mass
Spectrometry
