First examples of bispidine-ferrocene cyclophanes

Abstract

Two approaches for the syntheses of bispidine-ferrocene cyclophanes were reported. Both include the acylation of 1,5-dimethylbispidin-9-one (H2Bp) or its pendant amino-armed derivative by 1,1’-ferrocenoyl (Fc(CO)2) dichloride. The first approach allowed to isolate di-, tri- and pentameric cyclic oligomers of composition (BpFc(CO)2)n. The second one included the preliminary functionalization of H2Bp by N-protected glycine followed by deprotection and cyclization with Fc(COCl)2. The crystal structure of two new bispidine-ferrocene cyclophanes was established by single-crystal X-ray study. This study revealed the anti-conformation of amido-groups attached to the bispidine nitrogen atoms for both molecules. Various NMR techniques were applied to study the solution behavior of the macrocycles; the predominant anti-conformation in solution was also proved. The acyclic model compound Bp(FcCO)2 also showed only anti-conformer as revealed by VT-NMR and X-ray studies. Cyclic voltammetry study showed the difference in oxidation potentials of the Fc moiety within the row Bp(FcCO)2 – (BpFc(CO)2)2 – (BpFc(CO)2)3 with splitting of the oxidation curve in two later cases. The results obtained in this work will find an application in design and study of novel bispidine-ferrocene cyclophanes for the purposes of supramolecular sensing and catalysis.