New p-aminophenol-based dendritic melamines. Iterative synthesis, structure, and electrochemical characterisation

Avoiding any protective-deprotective step, the synthesis of new (G-0, -1, -2) dendritic melamines is reported. Their construction consisted of chemoselective SN2-Ar amination of cyanuric chloride with p-aminophenol (peripheral unit) and piperazine or 4,4′-bipiperidine (linkers). This novel class of amino-s-triazines is primarily investigated by DFT calculations (optimal geometry and electronic structure) in tandem with (VT) 1H NMR spectroscopy providing details of the rotational diastereomerism about the C(s-triazine)-N(exocyclic) partial double bonds, solvation effects and conformation of the linkers. These data are subsequently exploited in electrochemical investigations (cyclic voltammetry on the Pt electrode/DMSO, 0.1 M KCl). Two reversible electron-transfer phenomena have been observed. Thus, depending on the variable π-deficiency strength of the s-triazine ring acting as the EWG on the adjacent NH group and the ability of the latter to undergo redox processes in tandem with the phenolic p-HO group, two electrochemical pathways are proposed, namely the p-benzoquinonimine route and the electropolymerization route.