Active template rotaxane synthesis through the Ni-catalyzed cross-coupling of alkylzinc reagents with redox-active esters

Synthesis of Interlocked and Non-Interlocked Deca(para-phenylene) Derivatives by Ni-mediated Biaryl Coupling

Oligo(para-phenylene) (PPn) is a compound composed of directly connected 1,4-phenylene moieties. The synthesis of PPn composed of six or more phenylene moieties with no substituent at the internal phenylene moiety has been challenging because of its low solubility. Herein we synthesized oligo(para-phenylene)[2]rotaxanes, including a deca(para-phenylene)[2]rotaxane, with a defined number of phenylene moieties. Biaryl coupling of iodoarenes mediated by macrocyclic dibenzodihydrophenanthroline-Ni complex was utilized for the first time to synthesize the [2]rotaxanes. Compared to the non-interlocked deca(para-phenylene), the deca(para-phenylene)[2]rotaxane showed higher solubility. The properties of the oligo(para-phenylene)[2]rotaxanes and non-interlocked oligo(para-phenylene)s were analyzed by spectroscopic methods.

Macrocyclic host molecules with aromatic building blocks: the state of the art and progress

Macrocyclic host molecules play the central role in host-guest chemistry and supramolecular chemistry. The highly structural symmetry of macrocyclic host molecules can meet people's pursuit of aesthetics in molecular design, and generally means a balance of design, synthesis, properties and applications. For macrocyclic host molecules with highly symmetrical structures, building blocks, which could be described as repeat units as well, are the most fundamental elements for molecular design. The structural features and recognition ability of macrocyclic host molecules are determined by the building blocks and their connection patterns. Using different building blocks, different macrocyclic host molecules could be designed and synthesized. With decades of developments of host-guest chemistry and supramolecular chemistry, diverse macrocyclic host molecules with different building blocks have been designed and synthesized. Aromatic building blocks are a big family among the various building blocks used in constructing macrocyclic host molecules. In this feature article, the recent developments of macrocyclic host molecules with aromatic building blocks were summarized and discussed.

Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes

The mechanical interlocking of molecular components can lead to the appearance of novel and unconventional properties and processes, with potential relevance for applications in nanoscience, sensing, catalysis, and materials science. We describe a [3]rotaxane in which the number of recognition sites available on the axle component can be changed by acid–base inputs, encompassing cases in which this number is larger, equal to, or smaller than the number of interlocked macrocycles. These species exhibit very different properties and give rise to a unique network of acid–base reactions that leads to a fine pK_a tuning of chemically equivalent acidic sites. The rotaxane where only one station is available for two rings exhibits a rich coconformational dynamics, unveiled by an integrated experimental and computational approach. In this compound, the two crown ethers compete for the sole recognition site, but can also come together to share it, driven by the need to minimize free energy without evident inter-ring interactions.

Recent Progress in Radical Decarboxylative Functionalizations Enabled by Transition-Metal (Ni, Cu, Fe, Co or Cr) Catalysis

Aliphatic carboxylic acids are abundant in natural and synthetic sources and are widely used as connection points in many chemical transformations. Radical decarboxylative functionalization promoted by transition-metal catalysis has achieved great success, enabling carboxylic acids to be easily transformed into a wide variety of products. Herein, we highlight the recent advances made on transition-metal (Ni, Cu, Fe, Co or Cr) catalyzed C–X (X = C, N, H, O, B, or Si) bond formation as well as syntheses of ketones, amino acids, alcohols, ethers and difluoromethyl derivatives via radical decarboxylation of carboxylic acids or their derivatives, including, among others, redox-active esters (RAEs), anhydrides, and diacyl peroxides.

1 Introduction

2 Ni-Catalyzed Decarboxylative Functionalizations

3 Cu-Catalyzed Decarboxylative Functionalizations

4 Fe-Catalyzed Decarboxylative Functionalizations

5 Co- and Cr-Catalyzed Decarboxylative Functionalizations

6 Conclusions

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

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 weak - or are disfavored compared to other binding modes - to 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.

Fluorophoric [2]rotaxanes: post-synthetic functionalization, conformational fluxionality and metal ion chelation

Fluorophoric [2]rotaxanes form an exciplex upon interpenetration and the exciplex signals are used to monitor the chelation properties of the interlocked systems.