Weak functional group interactions revealed through metal-free active template rotaxane synthesis

Abstract

Modest functional group interactions can play important roles in molecular recognition, catalysis and self-assembly. However, weakly associated binding motifs are often difficult to characterize. Here, we report on the metal-free active template synthesis of [2]rotaxanes in one step, up to 95% yield and >100:1 rotaxane:axle selectivity, from primary amines, crown ethers and a range of C=O, C=S, S(=O) 2 and P=O electrophiles. In addition to being a simple and effective route to a broad range of rotaxanes, the strategy enables 1:1 interactions of crown ethers with various functional groups to be characterized in solution and the solid state, several of which are too weakor are disfavored compared to other binding modesto be observed in typical host-guest complexes. The approach may be broadly applicable to the kinetic stabilization and characterization of other weak functional group interactions.

Breaking through permeability–selectivity trade‐off of thin‐film composite membranes assisted with crown ethers

“…14,38 This hypothesis was validated from FTIR analyses where hydrogen bonding between amine molecules and CEs in the presence of CE were confirmed (Figure S2). [25][26][27][28] Based on the hypothesis above, more CE molecules promoted a higher IP reaction degree as testified by XPS results in Figure S3 and Table 1. Date in Table 1 revealed that O/N ratios of modified membranes were all higher than that of the pristine membrane (N is unique to PA).…”

“…On the other side, the diamine monomer (guest molecule) and the cyclic CE (host molecule) can form the host−guest inclusion F I G U R E 1 Schematic illustration of interfacial polymerization (IP) reaction between diamine and tri-acyl chloride monomers with the presence of crown ethers (CEs) [Color figure can be viewed at wileyonlinelibrary.com] complex via hydrogen-bonding interaction as shown in the Step 1 of Figure 1. [25][26][27][28] After the amidation reaction between the diamine and tri-acyl chloride monomers in IP process, the CE molecules can surround the amide bonds like the neck rings via hydrogen-bonding interaction, as shown in the Step 2 of Figure 1. 25,27,28 Ascribing to these unique characteristics of CE, we hypothesized that CE-assisted IP could significantly impact on the microstructure, morphology as well as FO performances of resulting TFC membranes.…”

A Chiral Interlocking Auxiliary Strategy for the Synthesis of Mechanically Planar Chiral Rotaxanes

“…9,10 Takata and co-workers reported the formation of MPC enantiomers in 4.4% ee using the dynamic kinetic resolution of a pseudo-rotaxane precursor. 9a More recently, Leigh and coworkers reported a direct enantioselective synthesis of MPC rotaxanes under substrate control in an impressive 50% ee using their organocatalytic active template 11 reaction 12 in conjunction with a chiral alcohol leaving group. 9b Such direct enantioselective approaches are extremely attractive but, unless ~90% ee or higher can be achieved, the enantiomeric products still require CSP-HPLC separation for use in applications such as catalysis, 13 sensing 8,14 and materials science.…”

A Chiral Interlocking Auxiliary Strategy for the Synthesis of Mechanically Planar Chiral Rotaxanes

“…11,12 Takata and co-workers reported the formation of MPC enantiomers in 4.4% ee through the dynamic kinetic resolution of a pseudo-rotaxane precursor. 11 Leigh and co-workers recently reported a direct enantioselective synthesis of a MPC rotaxane under substrate control in an impressive 50% ee using their organocatalytic active template 13 reaction 14 in conjunction with a chiral alcohol leaving group. 12 Such direct enantioselective approaches are extremely attractive but, unless ~90% ee or higher can be achieved, the enantiomeric products still require CSP-HPLC separation for use in applications such as catalysis, 15 sensing 10,16 and materials science.…”