Chiral Self‐Discrimination and Guest Recognition in Helicene‐Based Coordination Cages

Abstract

Chiral nanosized confinements play a major role for enantioselective recognition and reaction control in biological systems. Supramolecular self‐assembly gives access to artificial mimics with tunable sizes and properties. Herein, a new family of [Pd2L4] coordination cages based on a chiral [6]helicene backbone is introduced. A racemic mixture of the bis‐monodentate pyridyl ligand L1 selectively assembles with PdII cations under chiral self‐discrimination to an achiral meso cage, cis‐[Pd2L1P2L1M2]. Enantiopure L1 forms homochiral cages [Pd2L1P/M4]. A longer derivative L2 forms chiral cages [Pd2L2P/M4] with larger cavities, which bind optical isomers of chiral guests with different affinities. Owing to its distinct chiroptical properties, this cage can distinguish non‐chiral guests of different lengths, as they were found to squeeze or elongate the cavity under modulation of the helical pitch of the helicenes. The CD spectroscopic results were supported by ion mobility mass spectrometry.

Extended enantiopure ortho-phenylene ethylene (o-OPE)-based helical systems as scaffolds for supramolecular architectures: a study of chiroptical response and its connection to the CISS effect

“…This geometry allows the assembly of well-defined metallosupramolecular entities with metal centres with coordination sites in a 180° orientation, resulting on either linear Ag(I) complexes or on square planar Pd(II) complexes with two additional ligands in trans positions. 12 In the case of the Ag(I) cations, two different binding sites are possible, the alkynes and the pyridines. ECD spectroscopy was highly informative to discriminate between the two alternatives.…”

“…8 Consequently, fully conjugated helical molecules have been theoretically suggested as interesting candidates for spintronics, quantum sensing and quantum information applications. [9][10][11] Moreover, the remarkable geometry of [6]-helicenes have also been used in the context of chiral metallosupramolecular architectures 12,13 as bidentate donors with an angle between the binding sites close to 0°. 14 These systems have emerged as an unique research field owing to their electronic, optical and sensing capabilities.…”

Reaction Monitoring and Structural Characterisation of Coordination Driven Self-Assembled Systems by Ion Mobility-Mass Spectrometry

“…These cages were observed to accommodate two similar aromatic sulfonates, which primarily varied in length. When incorporated into the host guest complex and observed by TIMS-MS, these two host-guest complexes had different mobilities, which could be assigned to a change in the helical pitch of the helicenes within the cage to accommodate the longer guest molecule ( Figure 13 ) ( Schulte et al, 2019 ). This work was used to confirm results obtained via circular dichroism, a technique suited to observation of chiral systems.…”

“… The difference in ion mobility measured by TIMS-TOF of two host-guest complexes can be linked to the change in helical pitch of a constituent ligand as the length of the guest is varied ( Schulte et al, 2019 ). …”

Control and Transfer of Chirality Within Well-Defined Tripodal Supramolecular Cages

“…Aiming at providing a general view about recent progress in the preparation of chiral tripodal cages displaying chirality dynamics, this mini-review summarizes current knowledge on how the chiral information can propagate along such tridimensional architectures. Control of the chirality within tripodal cages upon chiral sorting (Henkelis et al, 2014 ; Schaly et al, 2016 ; Jedrzejewska and Szumna, 2017 ; Schulte et al, 2019 ; Séjourné et al, 2020 ), or guest binding (You et al, 2012 ; Bravin et al, 2019 ; Pavlovic et al, 2019 ) are beyond the scope of this work.…”