Synthesis of tris(4-amino-2,6-dimethylphenyl)borane and facile extension of its π-conjugated system by utilizing the reactivity of the amino groups

Tris(4-amino-2,6-dimethylphenyl)borane (1), a triarylborane bearing an unsubstituted amino group on all of its aryl substituents, and related triarylboranes were synthesized via Ullmann condensation. The facile dehydration reactions of 1 with benzaldehyde and nitrosobenzene gave tris[4- (benzylidenamino)-2,6-dimethylphenyl]borane and tris[2,6-dimethyl-4-(phenylazo) phenyl]borane, respectively. These triarylboranes bear an extended π-conjugated system bridged by a nitrogen-containing π-linker on each of their aryl groups. UV-vis absorption spectra and theoretical calculations revealed that the π-conjugated system of the triarylborane was effectively extended by utilizing the reactivity of the amino groups.