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Disparate symmetries in head-to-tail Schiff-base macrocycles Chen, Zhengyu

Abstract

Two new Schiff-base macrocycles (called campestarenes) with 5-fold symmetry were prepared with bulky triphenylsilyl and triisopropylsilyl substituents. A single crystal structure of one campestarene showed an almost flat conformation of campestarenes are in their extreme enol-imine form. Tautomerization within the campestarene between the enol-imine and keto-enamine form was investigated by variable-temperature NMR and UV-vis spectroscopy. It was found that the molecule displays strong solvent- and temperature-dependent tautomerization that leads to large changes in color. These results were supported by computational investigations that showed the possibility of tautomerization between keto-enamine form and enol-imine form. The experimental studies showed the relative permittivity of solvents has a large influence on the relative stability of different campestarene tautomers in solution. Some methyl/phenyl substituted campestarene precursors were prepared for macrocyclization of methyl/phenyl substituted campestarenes. Different synthetic conditions were tested to facilitate the formation of campestarens. One phenyl substituted campestarene was synthesized under acid condition. Two new Pt₃ Schiff-base macrocycles with 3-fold symmetry were synthesized following a head-to-tail approach. Computational investigations showed an almost flat conformation of Pt₃ macrocycles. Aggregation of Pt₃ macrocycles in solid state was studied by MALDI-TOF, TEM and PXRD. It was found that Pt₃ macrocycles displays nanotubular structures due to aggregation. Aggregation of Pt₃ macrocycles in solution was investigated by variable-temperature 1D NMR and 2D NMR. The experimental results showed aggregation of Pt3 macrocycles at both high and low temperatures. Errata: http://hdl.handle.net/2429/60786

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