Evidence of reversibility in azo-coupling reactions between 1,3,5-tris(N,N-dialkylamino)benzenes and arenediazonium salts

The reactions between strongly electron-rich aromatic substrates (1,3,5-tris(N,N-dialkylamino)benzenes, neutral carbon super nucleophiles) and diazonium salts produce moderately stable sigma complexes (Wheland complexes). The reactivity of Wheland complexes with electrophiles (other diazonium salts, or 4,7-dinitrobenzofuroxan) produces exchange reactions in the electrophilic part: the better electrophile replaces the less powerful electrophile. In the same way, in Wheland complexes with the 1,3,5-tris(morpholinyl)benzene, the 1,3,5-tris(piperidinyl)benzene replaces the less powerful nucleophile 1,3,5-tris(morpholinyl)benzene. Evidence is reported here indicating that for the title system the reaction of the attack of the electrophilic reagent producing Wheland complexes is a reversible process. The final products of the diazo-coupling reactions undergo a further attack of some diazonium salts. From the final products of the double diazo-coupling reactions (diazo compounds), we collected evidence that is a clear instance of complete reversibility of the diazo-coupling reaction.