Chirality-Driven Self-Assembly of Discrete, Homochiral FeII 2 L3 Cages

Coordination chemistry is a powerful method to synthesize supramolecular cages with distinct features that suit specific applications. This work demonstrates the synthesis of discrete, homochiral Fe^II ₂ L₃ cages via chirality-driven self-assembly. Specifically, the installation of chirality - at both the vertices and ligand backbones - allows the formation of discrete, homochiral Fe^II ₂ L₃ cages of different sizes via stereochemical control of the iron(II) centers. We observed that larger cages require multiple chiral centra (chiral ligands and vertices). In contrast, the formation of smaller cages is stereoselective with solely chiral ligands. The latter cages can also be formed from two chiral subcomponents, but only when they have matching chirality. Single-crystal X-ray diffraction of these smaller Fe^II ₂ L₃ cages revealed several non-covalent interactions as a driving force for narcissistic chiral self-sorting. This expected behavior was confirmed utilizing the shorter ligands in racemic form, yielding discrete, homochiral Fe^II ₂ L₃ cages formed in enantiomeric pairs.

Chiral Self-Sorting Effects in the Self-Assembly of Metallosupramolecular Aggregates Comprising Ligands Derived from Tröger's Base

Five ligands with either nitrile or isonitrile metal binding motifs have been synthesized based on the 2,8- or 3,9-disubstituted Tröger's base scaffold, respectively. These ligands self-assemble into dinuclear cyclic metallosupramolecular aggregates upon coordination to [(dppp)Pd(OTf)₂ ] in a highly diastereoselective manner, by heterochiral self-sorting in a chiral self-discriminating manner as shown by ESI mass spectrometry, NMR spectroscopy, and single crystal XRD analysis. This observation is in contrast to earlier studies with ligands derived from Tröger's base that have larger metal binding motifs and bis(nitrile) and bis(isonitrile) ligands based on other rigid dissymmetric cores such as [2.2]paracyclophanes. Thus, the combination of these slim metal binding motifs with the rigid v-shaped 2,8- or 3,9-disubstituted Tröger's base scaffolds seems to be especially well preorganized to ensure high-fidelity social self-sorting behavior.

Influencing the Self-Sorting Behavior of [2.2]Paracyclophane-Based Ligands by Introducing Isostructural Binding Motifs

Two isostructural ligands with either nitrile (L^nit) or isonitrile (L^iso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ligand itself (L^nit) or its precursors (L^iso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)₂] differ in their composition: whereas L^nit forms dinuclear complexes, L^iso exclusively forms trinuclear ones. Furthermore, they also differ in their chiral self‐sorting behavior as (rac)‐L^iso undergoes exclusive social self‐sorting leading to a heterochiral assembly, whereas (rac)‐L^iso shows a twofold preference for the formation of homochiral complexes in a narcissistic self‐sorting manner as proven by ESI mass spectrometry and NMR spectroscopy. Interestingly, upon crystallization, these discrete aggregates undergo structural transformation to coordination polymers, as evidenced by single‐crystal X‐ray diffraction.

Chiral self-sorting behaviour of [2.2]paracyclophane-based bis(pyridine) ligands

[2.2]Paracyclophane-based bis(pyridine) ligands form dinuclear complexes upon coordination to palladium(ii) ions, however, with distinct differences concerning their chiral self-sorting ability.

Making a Right or Left Choice: Chiral Self-Sorting as a Tool for the Formation of Discrete Complex Structures

This review discusses chiral self-sorting-the process of choosing an interaction partner with a given chirality from a complex mixture of many possible racemic partners. Chiral self-sorting (also known as chiral self-recognition or chiral self-discrimination) is fundamental for creating functional structures in nature and in the world of chemistry because interactions between molecules of the same or the opposite chirality are characterized by different interaction energies and intrinsically different resulting structures. However, due to the similarity between recognition sites of enantiomers and common conformational lability, high fidelity homochiral or heterochiral self-sorting poses a substantial challenge. Chiral self-sorting occurs among natural and synthetic molecules that leads to the amplification of discrete species. The review covers a variety of complex self-assembled structures ranging from aggregates made of natural and racemic peptides and DNA, through artificial functional receptors, macrocyles, and cages to catalytically active metal complexes and helix mimics. The examples involve a plethora of reversible interactions: electrostatic interactions, π-π stacking, hydrogen bonds, coordination bonds, and dynamic covalent bonds. A generalized view of the examples collected from different fields allows us to suggest suitable geometric models that enable a rationalization of the observed experimental preferences and establishment of the rules that can facilitate further design.

Self-assembly of heteroleptic dinuclear metallosupramolecular kites from multivalent ligands via social self-sorting

A Tröger's base-derived racemic bis(1,10-phenanthroline) ligand (rac)-1 and a bis(2,2'-bipyridine) ligand with a central 1,3-diethynylbenzene unit 2 were synthesized. Each of these ligands acts as a multivalent entity for the binding of two copper(I) ions. Upon coordination to the metal ions these two ligands undergo selective self-assembly into heteroleptic dinuclear metallosupramolecular kites in a high-fidelity social self-sorting manner as evidenced by NMR spectroscopy and mass spectrometry.

Synthesis, chiroptical and SHG properties of polarizable push–pull dyes built on π-extended binaphthyls

Novel binaphthyl push–pull dyes extend their π-bridge and incorporate as acceptors pyridine units, useful for further supramolecular polarization.

Self-assembly of metallosupramolecular rhombi from chiral concave 9,9'-spirobifluorene-derived bis(pyridine) ligands

Two new 9,9'-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands act as concave templates and form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd](2+) and [(dppp)Pt](2+) ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp)2M2{(R)-L}2](OTf)4, [(dppp)2M2{(S)-L}2](OTf)4, and [(dppp)2M2{(R)-L}{(S)-L}](OTf)4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies could also be characterised by single crystal X-ray diffraction.