Synthesis, structure and transition metal ion complexation property of lariat azacalix[4]pyridines

Lariat azacalix[4]pyridines that contain a chelating group such as pyridine and thiophene in the lariat arm were synthesized by means of highly efficient coupling reactions to the bridging nitrogen atom of macrocycles. Based on absorption spectrophotometric titrations and NMR spectroscopy, the lariat azacalix[4]pyridines were found to act as powerful and selective hosts to form 1:1 complexes with the transition metal ions, giving binding constants in the range of 5.28–10.6 (log K). X-ray molecular structures of the complexes indicated that the N-lariat arm comes over the face of azacalix[4]pyridine macrocycle to bind metal ion from the axial position, producing lasso azacalix[4]pyridine–metal complexes, which are the structural mimics of the Fe-containing nitrile hydratase.

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