Quantification of Stereochemical Communication in Metal–Organic Assemblies

Abstract

The derivation and application of a statistical mechanical model to quantify stereochemical communication in metal–organic assemblies is reported. The factors affecting the stereochemical communication within and between the metal stereocenters of the assemblies were experimentally studied by optical spectroscopy and analyzed in terms of a free energy penalty per “incorrect” amine enantiomer incorporated, and a free energy of coupling between stereocenters. These intra‐ and inter‐vertex coupling constants are used to track the degree of stereochemical communication across a range of metal–organic assemblies (employing different ligands, peripheral amines, and metals); temperature‐dependent equilibria between diastereomeric cages are also quantified. The model thus provides a unified understanding of the factors that shape the chirotopic void spaces enclosed by metal–organic container molecules.

Synthesis and Characterization of Self‐Assembled Chiral FeII2L3 Cages

“…This was thoroughly investigated by the Nitschke group, who introduced a very powerful subcomponent self‐assembly strategy based on pyridylimine ligands . They reported that for some systems the stereoselectivity at the coordination complexes at the corners of their tetrahedral cage was controlled by stereochemical communication by the chirality at either the vertices or the ligands used for coordination . For example, during the formation of the coordination centers in Fe II 4 L 4 cages, additional chiral moieties were introduced to force the metal centers to adopt a single stereoisomer, which led to enantiopure cage structures.…”

Embedding and Positioning of Two FeII4L4 Cages in Supramolecular Tripeptide Gels for Selective Chemical Segregation

“…[23] Tr ipeptides of syndiotactic l-d-l stereochemistry have been shown only recently to adopt an amphipathic conformation, with side chains in an isotactic configuration that enables their long-range self-organization into gel-forming fibers.A n exception to this design rule is l-Phe-d-Ala-l-Phe,w hich does not meet the expected requirements of hydrophobicity and steric hindrance and was thus not observed to form ag el. [25] Thet ripeptide (p-aminobenzoyl)-l-Phe-d-Ala-l-Phe-NH 2 ( Figure 1) was thus synthesized and probed for gelation in various solvents,a mong which CH 3 CN was chosen as the most suitable choice for stable gels and cages (see Table S2 in the Supporting Information). [25] Thet ripeptide (p-aminobenzoyl)-l-Phe-d-Ala-l-Phe-NH 2 ( Figure 1) was thus synthesized and probed for gelation in various solvents,a mong which CH 3 CN was chosen as the most suitable choice for stable gels and cages (see Table S2 in the Supporting Information).…”

“…[24] We hypothesized that the addition of a p-aminobenzoyl moiety at the N-terminus could address both issues to yield anew gelator,which would also be potentially useful in cases where the presence of ap rimary aliphatic amine is undesirable.I ndeed, af ree N-terminus could result in unwelcome substitution of MOC amine subcomponents and reduce MOC stability,whereas an aniline substituted with an electron-deficient amide group would not be expected to substitute more electron-rich aniline residues incorporated into the periphery of acage. Tw oM OCs ( Figure 1) were prepared [25] to encapsulate different guests in CH 3 CN;MOC 1 binds trifluoroacetate (TFA À )m oderately and perrhenate (ReO 4 À )strongly,asevidenced by 1 Hand 19 FNMR spectroscopy (see Figures S13-S17 in the Supporting Information), whereas MOC 2 encapsulates fluoroadamantane (FA; see Figures S18 and S19). Tw oM OCs ( Figure 1) were prepared [25] to encapsulate different guests in CH 3 CN;MOC 1 binds trifluoroacetate (TFA À )m oderately and perrhenate (ReO 4 À )strongly,asevidenced by 1 Hand 19 FNMR spectroscopy (see Figures S13-S17 in the Supporting Information), whereas MOC 2 encapsulates fluoroadamantane (FA; see Figures S18 and S19).…”

Dynamic Covalent Chemistry within Biphenyl Scaffolds: Reversible Covalent Bonding, Control of Selectivity, and Chirality Sensing with a Single System

“…Through induced helicity as aresult of central-to-axial chirality transfer,t he handedness and ee values of chiral monoalcohol and monoamine analytes were reported by circular dichroism. [5] Atropisomeric receptors have also been used in av ariety of analytical applications, [6] such as chiroptical assays for enantiomeric composition, [7] which can be employed to rapidly analyze chiral samples for catalyst development. [3] Despite the long history of exploring axial chirality,t here is continued interest in discovering novel strategies for communication between central and axial chirality.…”

“…[3] Despite the long history of exploring axial chirality,t here is continued interest in discovering novel strategies for communication between central and axial chirality. [5] Atropisomeric receptors have also been used in av ariety of analytical applications, [6] such as chiroptical assays for enantiomeric composition, [7] which can be employed to rapidly analyze chiral samples for catalyst development. [4] Moreover,t he chirality of metalorganic or organic frameworks and cages has been modulated through the incorporation of atropisomeric motifs.…”