Match-mismatch effects in two-fold transfer of chirality within a Möbius metallo-receptor

Parallel Chirality Inductions in Möbius Zn(II) Hexaphyrin Transformation Networks

Networked chemical transformations are key features of biological systems, in which complex multicomponent interactions enable the emergence of sophisticated functions. Being interested in chirality induction phenomena with dynamic Möbius π-systems, we have designed a pair of Möbius [28]hexaphyrin ligands in order to investigate mixtures rather than isolated molecules. Thus, a hexaphyrin bearing a chiral amino arm was first optimized and found to bind a ZnOAc moiety, triggering an impressive quasi-quantitative chirality induction over the Möbius π-system. Second, this amino-type hexaphyrin was mixed with a second hexaphyrin bearing a chiral carboxylate arm, affording at first ill-defined coordination assemblies in the presence of zinc. In contrast, a social self-sorting behavior occurred upon the addition of two exogenous achiral effectors (AcO- and BuNH2), leading to a well-defined 1:1 mixture of two Möbius complexes featuring a sole Möbius twist configuration (parallel chirality inductions). We next successfully achieved compartmentalized switching, i.e., a single-component transformation from such a complex mixture. The BuNH2 effector was selectively protected with Boc2O, owing to a lower reactivity of the arm's NH2 function intramolecularly bound to zinc, and subsequent addition of BuNH2 restored the initial mixture, retaining parallel chirality inductions (five cycles). By changing the nature and twist configuration of only one of the two complexes, at initial state or by switching, this approach enables a "two-channel" tuning of the chiroptical properties of the ensemble. Such multiple dynamic chirality inductions, controlled by selective metal-ligand recognition and chemical reactivity, set down the basis for Möbius-type stereoselective transformation networks with new functions.

Möbius ZnII -Hexaphyrins Bearing a Chiral Coordinating Arm: A Chiroptical Switch Featuring P/M Twist Inversion Controlled by Achiral Effectors

By their conformational flexibility, Möbius aromatic hexaphyrins provide a dynamic chirality attractive to develop stimuli responsive systems such as chiroptical switches. A regular [28]hexaphyrin has been equipped with a chiral coordinating arm to achieve transfer of chirality from a fix stereogenic element to the dynamic Möbius one. The arm allows straightforward formation of labile monometallic Zn^II complexes with an exogenous ligand, either a carboxylato or an amino with opposite inwards/outwards orientations relative to the Möbius ring. As a corollary, the chiral coordinating arm is constrained over the ring or laterally, inducing opposite P and M Möbius configurations with unprecedented high stereoselectivity (diast. excess greater than 95 %). By tuning the transfer of chirality, these achiral effectors generate electronic circular dichroism spectra with bisignate Cotton effect of opposite signs. Switching between distinct chiroptical states was ultimately achieved in mild conditions owing to ligand exchange, with high robustness (10 cycles).

Interconversion between Möbius chiroptical states sustained by hexaphyrin dynamic coordination

Harnessing the chiroptical properties of molecular Möbius rings is motivated by fundamental aspects while challenged by synthetic difficulties. Focusing on Möbius aromatic Zn(ii) hexaphyrin complexes, interconversion between two chiral states was achieved through binding and release of an amino ligand (forward/backward stimuli), leading to different chiroptical switching phenomena (amplification, on-off, inversion). The amine either supplies the chirality or behaves as an achiral effector regulating the Zn(ii)-binding of a second (chiral) carboxylato ligand. These results highlight the Möbius [28]hexaphyrin scaffold as an attractive chiral switchable unit.