On the synthesis of tetradentate ligands
A modular pathway for the preparation of tetradentate ligands was developed by employment of the nitroaldol reaction (Henry-reaction). Due to the use of basic solids as catalysts, namely the hydrotalcite Syntal 696® and the anion exchange resin Amberlyst A21®, the reactions proceeded at room temperature and the products were obtained by simple work-up procedures. Furthermore, NMR investigations and single crystal X-ray diffraction revealed the stereoselectivity of the developed pathway. In the course of functional group interchanges, the employment of protecting groups was necessary. Protection with trialkylsilyl groups was easily and diastereoselectively achieved. The coordination behavior towards zinc chloride was studied as well as the catalytic activity of a custom-tailored vanadium(V) complex towards sulfoxidation. Moreover, the coordination behavior of carbonyl analogous Schiff-bases towards zinc chloride were examined. The aza-Henry reaction was deployed in the synthesis of a tetradentate diaminobutane and its coordination behavior towards zinc chloride was investigated. Several unexpected reactions, starting from N-alkylpyridylimines were observed and described.