N,N',N''-TRIPHENYL-1,3,5-TRIAMINOBENZENE AND ITS SIGMA-COMPLEX ON PROTONATION - A STABLE ,N',N''-TRIPHENYL-2,4,6-TRIAMINOCYCLOHEXADIENYLIUMCATION

Protonation of N,N',N''-triphenyl-1,3,5-triaminobenzene (N,N',N''-trip henyl-1,3,5-benzenetriamine) (1) by p-toluenesulfonic acid occurs at o ne of the C atoms of the central benzene ring, rather than at an N ato m, to form the stable sigma complex ,N',N''-triphenyl-2,4,6-triaminocy clohexadienylium p-toluene-sulfonate (N,N',N''-triphenyl-2,4,6-triamin o-1H-benzenium p-toluenesulfonate) (2). Changes in bond lengths clearl y show the disruption of the aromaticity of the central ring in (1) on protonation and the stabilizing role of the N atoms in the delocaliza tion of the positive charge. One of the outer benzene rings is probabl y involved in electronic stabilization since it approaches planarity w ith the central system. The other outer benzene rings do not show any obvious changes that would indicate a strong electronic contribution t o the stability of (2), but are probably involved sterically.