Hexaphyrin-cyclodextrin hybrids: Getting larger, getting confused

François Robert (1) , Bernard Boitrel (1) , Mickaël Ménand (2) , Stéphane Le Gac (1)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 IPCM - Institut Parisien de Chimie Moléculaire

The diversity of hexaphyrin-cyclodextrin hybrids (HCD), previously formed from the covalent assembly of regular hexaphyrin and [Formula: see text]-cyclodextrin subunits, has been increased following two main directions: enlarging the confined space provided by the cyclodextrin and tuning the N-core of the hexaphyrin aiming at bimetallic complexes. The larger [Formula: see text]-cyclodextrin unit was selectively functionalized with aldehyde linkers on its primary rim which were further reacted with 2 eq. of pentafluorophenyl tripyrrane in acidic conditions, followed by DDQ oxidation. Doubly-linked HCD hybrids were obtained with structural variations in the hexaphyrin macrocycles depending on the MSA concentration (2 vs. 200 mM) producing either regular ([26] rectangular/[28] Möbius) or doubly N-confused dioxo ([26] rectangular) scaffolds. For the latter, two isomers were isolated featuring mirror transoid skeletons and long-side meso-linking patterns, giving rise to planar chirality at the origin of intense and opposite electronic circular dichroism (ECD) spectra. Zn(II) complexation was then investigated leading to two main findings. (i) The regular [28] Möbius HCD afforded a mixture of monometallic Möbius Zn(II) complexes in the presence of acac ligand. ECD spectroscopy indicated a chirality transfer from the [Formula: see text]-cyclodextrin favoring a [Formula: see text] Möbius twist, but opposite to that arising from the narrower [Formula: see text]-cyclodextrin congener ([Formula: see text] twist favored). (ii) Owing to N 3 O coordination boxes, dissymmetric bimetallic Zn(II) complexes were readily formed with the doubly N-confused dioxo HCDs through a positive cooperative process. Both metal centers bind a DMAP ligand in axial positions, which is of interest for the

Keywords: hexaphyrin; cyclodextrin; conformation; aromaticity; Möbius; N-confused

Domains: Chemical Sciences

François Robert, Bernard Boitrel, Mickaël Ménand, Stéphane Le Gac. Hexaphyrin-cyclodextrin hybrids: Getting larger, getting confused. Journal of Porphyrins and Phthalocyanines, 2021, 25 (10n12), pp.1022-1032. ⟨10.1142/S1088424621500929⟩. ⟨hal-03366069⟩