Oxidation of Möbius type Ni(II) and Pd(II) Hexaphyrin- Cyclodextrin complexes. The Oak and the Reeds fable.
Résumé
We have previously developed a family of hexaphyrin-cyclodextrin (HCD) [1] hybrids and in particular one that is doubly linked which incorporates specific chiral communications involving central, planar and Möbius chiralities. [2] The metalation of this latter with either Ni(II) or Pd(II) afforded two pairs of pseudo-enantiomers (Rp/M and Sp/P) featuring quasi-mirror ECD spectra. Chemical oxidation to [26] π systems led to behaviors reminiscent to “The Oak and the Reeds” fable, due to a stronger coordination of Ni(II) than that of Pd(II). Oxidation of the robust Ni(II) complexes (“the Oak”) interrupts the π-conjugation pathways, but preserves the Möbius-like conformations which display marked ECD signatures. In contrast, oxidation of the more flexible Pd(II) complexes (“the Reeds”) converts the [28] aromatic Möbius systems into rectangular [26] aromatic ones losing their chiroptical intensities. However, the cyclodextrin linking pattern maintains a planar chiral environment (Rp or Sp), allowing the original Möbius configuration to be regenerated by reduction with a full chiral retention.These stereo-shape-memory processes will be disclosed in more details in this communication.