Azomethine derivatives. Part XI. Monomeric and dimeric arylmethyleneamino- and diarylmethyleneamino-boron compounds

Abstract

Details are given for the preparation of the monomeric aryl- and diaryl-methyleneaminoboranes Ph₂C:NBPh₂, p-tolyl₂C:NBPh₂, (p-CIC₆H₄)₂C:NBPh₂, p-BrC₆H₄(Ph)C:NBPh₂, Ph₂C:NB(mesityl)₂, PhCH:NB(mesityl)₂, and 2,2′- biphenylylC:NBPh₂ by one or more of the following routes: (1) R¹₂C:NSiMe₃+ R²₂BX; (2) R¹₂C:NLi + R²₂BX; (3) 2R¹₂C:NH + R²₂BX (4) R¹₂C:NBX₂+ 2R²Li (5) R¹₂C:NH₂+Cl-+ NaBPh₄(X = halogen). The intermediate adduct (p-tolyl)₂C:NH,BPh₃ was isolated in a reaction of type (5). The associated alkylideneaminoboranes (Ph₂C:NBPhCl)_n, (PhCH:NBPhCl)₂, (PhCH:NBPh₂)₂, [Ph₂C:NB(2,2′-biphenylyl)]_n, and (Ph₂C:NBO₂C₆H₄)_n were similarly prepared. The monomeric alkylideneamino-boranes are apparently prevented from dimerising by the bulk of the substituents, particularly on boron, which also inhibit approach of potential donor molecules. Except for the air-stable Ph₂C:NB (mesityl)₂, they are hydrolysed by moist air. Their i.r. spectra have characteristic absorptions, assigned ν(CNB), in the range 1765–1820 cm.^–1. ¹H n.m.r. and mass spectroscopic details of several of the compounds are given and discussed.