Sebastian Beil

Nature Chemistry, Published online: 24 August 2020; doi:10.1038/s41557-020-0526-0

Cucurbit[8]uril can stabilize discrete host:guest n:n oligomers of controlled size and shape in water with properties specific to the oligomers. We collected more than 50 examples and identified several factors explaining the formation of linear or cyclic oligomers and provide some rational to design new assemblies and target advanced properties.

Abstract

Proteins are an endless source of inspiration. By carefully tuning the amino‐acid sequence of proteins, nature made them evolve from primary to quaternary structures, a property specific to protein oligomers and often crucial to accomplish their function. On the other hand, the synthetic macrocycles cucurbiturils (CBs) have shown outstanding recognition properties in water, and a growing number of (host)_n:(guest)_n supramolecular polymers involving CBs have been reported. However, the burgeoning field of discrete (n:n) host:guest oligomers has just started to attract attention. While 2:2 complexes are the major oligomers, 3:3 and up to 6:6 oligomers have been described, some associated with emerging applications, specific to the (n:n) arrangements. Design rules to target (n:n) host:guest oligomers are proposed toward new advanced host:guest systems.

Round round get around: A highly efficient metal‐catalyzed tandem cycloaddition reaction enables benzannulation to access cyclopolyarene nanorings of varied sizes from poly(arylene‐butadiynylene) macrocyclic precursors. Unique Möbius topology is manifested by the cyclopolyarene nanorings composed of an odd number of repeat units, whereas cylindrical tubular structures with radial conjugation are formed with an even number of repeat units.

Abstract

By harnessing a highly efficient metal‐catalyzed tandem cycloaddition reaction as the key benzannulation step, a series of cyclopolyarene nanorings of varied sizes are obtained from poly(arylene‐butadiynylene) macrocyclic precursors, which can be synthesized relatively conveniently. Interestingly, due to the nonparallel bond connectivity of the repeat unit, unique Möbius topology is manifested by the cyclopolyarene nanorings composed of an odd number of repeat units, whereas cylindrical tubular structures with radial conjugation are formed with those consisting of an even number of repeat units.

Fine mechanics: A systematic experimental and computational study explains why tiny structural changes in the extremities of a molecular axle can allow or prevent its insertion in the cavity of a macrocycle. These results provide guidelines to design interlocked molecules with predetermined dynamic features, that can be used to make nanostructured machines, motors and materials.

Abstract

The general principles guiding the design of molecular machines based on interlocked structures are well known. Nonetheless, the identification of suitable molecular components for a precise tuning of the energetic parameters that determine the mechanical link is still challenging. Indeed, what are the reasons of the “all‐or‐nothing” effect, which turns a molecular “speed‐bump” into a stopper in pseudorotaxane‐based architectures? Here we investigate the threading and dethreading processes for a representative class of molecular components, based on symmetric dibenzylammonium axles and dibenzo[24]crown‐8 ether, with a joint experimental–computational strategy. From the analysis of quantitative data and an atomistic insight, we derive simple rules correlating the kinetic behaviour with the substitution pattern, and provide rational guidelines for the design of modules to be integrated in molecular switches and motors with sophisticated dynamic features.

This Review discusses synthetic approaches to fullerene‐based hybrids with low‐dimensional (LD) materials and their properties. Recent advances in the design of fullerene‐based LD nanomaterials for (photo)electrocatalytic applications are emphasized. The relationship between the electronic structures and the catalytic functions of the heterostructures is addressed to provide an understanding of these emerging materials at the molecular level.

Abstract

An emerging class of heterostructures with unprecedented (photo)electrocatalytic behavior, involving the combination of fullerenes and low‐dimensional (LD) nanohybrids, is currently expanding the field of energy materials. The unique physical and chemical properties of fullerenes have offered new opportunities to tailor both the electronic structures and the catalytic activities of the nanohybrid structures. Here, we comprehensively review the synthetic approaches to prepare fullerene‐based hybrids with LD (0D, 1D, and 2D) materials in addition to their resulting structural and catalytic properties. Recent advances in the design of fullerene‐based LD nanomaterials for (photo)electrocatalytic applications are emphasized. The fundamental relationship between the electronic structures and the catalytic functions of the heterostructures, including the role of the fullerenes, is addressed to provide an in‐depth understanding of these emerging materials at the molecular level.

The digold(I) complex [Au₂Cl₂(Cy₂PCH₂PCy₂)] reacts with 4,4′‐diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au‐P‐C‐P‐Au groups at the three corners. The synthesis of the complex and its chemical oxidation produced [6]cycloparaphenylene ([6]CPP) in 59 % overall yield.

Abstract

The digold(I) complex [Au₂Cl₂(Cy₂PCH₂PCy₂)] reacts with 4,4′‐diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au‐P‐C‐P‐Au groups at the three corners. The synthesis of the complex and its chemical oxidation produced [6]cycloparaphenylene ([6]CPP) in 59 % overall yield.

We report the synthesis of all‐cis 1,2,4,5‐tetrakis (trifluoromethyl)‐ and all‐cis 1,2,3,4,5,6‐hexakis (trifluoromethyl)‐ cyclohexanes by direct hydrogenation of precursor tetrakis‐ or hexakis‐ (trifluoromethyl)benzenes. The resultant cyclohexanes have a stereochemistry such that all of the CF 3 groups are on the same face of the cyclohexyl ring. All‐cis 1,2,3,4,5,6‐hexakis(trifluoromethyl)cyclohexane is the most sterically demanding of the all‐cis hexakis substituted cyclohexanes prepared to date with a barrier ( ΔG) to ring inversion calculated at 27 kcal mol ‐1 . The X‐ray structure of all‐cis 1,2,3,4,5,6‐hexakis(trifluoromethyl)cyclohexane displays a flattened chair conformation and the electrostatic profile of this compound reveals a large diffuse negative density on the fluorine face and a focused positive density on the hydrogen face. The electropositive hydrogen face has the ability to co‐ordinate chloride (K = ~10 3 ) and to a lesser extent fluoride and iodide (K = ~10 2 ) ions. Dehydrofluorination promoted decomposition occurs with fluoride ion acting as a base.

A freestanding porphyrin‐based monoatomic layer can be easily synthesized from the nanometer scale to the millimeter scale via bottom‐up growth. Both its structure and property are analogous to graphene. The monoatomic layers show remarkable metal center dependence of the catalytic activity and selectivity for CO₂ electroreduction.

Abstract

Developing two‐dimensional (2D) and single atomic layered materials is a fascinating challenge. Here we successfully synthesize porphyrin‐based monoatomic layer (PML), a freestanding 2D porphyrin‐based material of monomer‐unit thickness (2.8 Å). The solvothermal method provides a bottom‐up approach for tailoring the monoatomic layer from the nanoscale to the milliscale. PMLs containing accurately tailorable M‐N₄ units (M=Cu and Au) were synthesized, which present metal center‐dependent performance for CO₂ electrocatalysis. PML with Cu‐N₄ centers performs high faradaic efficiencies of HCOO⁻ and CH₄ (80.86 % and 11.51 % at −0.7 V, respectively) while PML with Au‐N₄ centers generates HCOO⁻ and CO as major products (40.90 % and 34.40 % at −0.8 V, respectively). Irreversible restructuring behavior of Cu sites is also observed. Based on the graphene‐like properties and metal center‐selectivity relationships, we believe that PML will play a distinct role in various applications.

Nature, Published online: 15 July 2020; doi:10.1038/s41586-020-2445-z

Cu nanowire arrays formed in situ are efficient catalysts for controllable deuteration of halides using D₂O as a cheap and safe deuterated donor. A cross‐coupling of carbon and deuterium free radicals might be involved in this reaction. High compatibility with easily reducible functional groups, one‐pot C−H to C−D transformation, and paired synthesis of valuable chemicals at both electrodes showed the potential utility.

Abstract

Precise deuterium incorporation with controllable deuterated sites is extremely desirable. Here, a facile and efficient electrocatalytic deuterodehalogenation of halides using D₂O as the deuteration reagent and copper nanowire arrays (Cu NWAs) electrochemically formed in situ as the cathode was demonstrated. A cross‐coupling of carbon and deuterium free radicals might be involved for this ipso‐selective deuteration. This method exhibited excellent chemoselectivity and high compatibility with the easily reducible functional groups (C=C, C≡C, C=O, C=N, C≡N). The C−H to C−D transformations were achieved with high yields and deuterium ratios through a one‐pot halogenation–deuterodehalogenation process. Efficient deuteration of less‐active bromide substrates, specific deuterium incorporation into top‐selling pharmaceuticals, and oxidant‐free paired anodic synthesis of high‐value chemicals with low energy input highlighted the potential practicality.

Nature Chemistry, Published online: 10 July 2020; doi:10.1038/s41557-020-0510-8

Turn and flip : A C₅₉N⁺ cation has been trapped by ethanol or water in a tubular host to fix an oxy substituent on the fullerene guest. The substituent was found to modulate the guest motion, with the up‐and‐down flipping motions of the guest facilitated by the OH group sliding along the inner wall of the host while staying attached through OH‐π hydrogen bonds, whereas an ethoxy substituent halted such motions.

Abstract

A supramolecular/synthetic method has been devised to affix a sterically hindered substituent onto a fullerene guest encapsulated in a tubular host. A two‐wheeled complex of (C₅₉N)‐(C₅₉N) with a tubular host was oxidatively bisected to afford a C₅₉N⁺ cation captured in the tube. The C₅₉N⁺ cation in the tube was then trapped by ethanol or water, which led to an oxy substituent pinned on the guest. The guest motions within the tube were modulated by the pinned substituent, and up‐and‐down flipping motions were halted by an ethoxy substituent. A hydroxy substituent, however, was ineffective in halting the flipping motions, despite the tight‐fitting relationship between the tubular host and the spherical guest. Theoretical calculations of the dynamics revealed that the flipping motions were assisted by OH‐π hydrogen bonds between the guest and the carbon‐rich wall and that sliding motions of the OH group were also facilitated by deformations of the tube.