Efficient Proton-Templated Synthesis of 18- to 38-Membered Tetraimino(amino)diphenol Macrocyclic Ligands: Structural Features and Spectroscopic Properties

A whole range of Robson-type tetraiminodiphenol macrocyclic ligands have been prepared as their
perchlorate salts [H4L](ClO4)2 in high yield (ca. 90%) by a single-step [2 + 2] condensation reaction
between 4-methyl(or tert-butyl)-2,6-diformyl(or diacyl)phenols and α,ω-diaminoalkanes (C2−C12)
in the presence of acetic acid and NaClO4. The reduction of these 18- to 38-membered macrocyclic
salts with NaBH4 have afforded corresponding tetraaminodiphenol macrocycles H2L‘. The X-ray
crystal structures of two of the tetraiminodiphenol macrocycles with the C2 and C4 lateral chains
have been determined, and the optimized configurations for all of the macrocycles have been obtained
by molecular mechanics calculations. The macrocycles have been characterized by elemental analysis
and by IR, absorption, emission, and NMR spectroscopic study. The protonated tetraiminodiphenol
macrocycles exhibit strong fluoroscence in methanol, acetonitrile, and nitromethane and undergo
quenching when treated with triethylamine. The neutral macrocycles H2L, isolated by treating
[H4L](ClO4)2 with excess of triethylamine, lack luminescence, as do the reduced tetraaminodiphenol
macrocycles H2L‘. The hydrolytic cleavage of [H4L](ClO4)2 has been studied.