Cyclic boron compounds. Part IX. Aldiminoboranes and their cyclic dimers

Abstract

Di-n-butyl-(t-butylaldimino)borane (Buⁿ₂B–NCHBu^t)_n has been prepared from t-butyl cyanide and tri-n-butylborane by two methods. It is monomeric in the vapour (at ca. 110°), when the i.r. spectrum shows a strong band at 1850 cm.^–1, assigned to the asymmetric BNC stretching frequency of a linear, pseudo-cumulative BN π-bonding system [graphic omitted]. It is mainly dimeric in benzene, as are the dihalogeno-(t-butylaldimido)boranes (Hal₂B–NCHBu^t)₂(Hal = Cl or Br), obtained from the di-n-butyl compound by heating with BHal₃; they are believed to belong to the BNBN 4-membered ring system. Spectroscopic and other physical data are reported. Monomeric and dimeric forms of (Buⁿ₂BNCHBu^t)_n are characterised (variable temperature experiments) by ¹¹B nuclear magnetic resonances at –38·8 ± 0·5 and –7·4 ± 0·4 p.p.m. relative to BF₃,OEt₂.