FaFrit

Tighten your belt: The first aromatic nanobelt has been prepared by Itami and co-workers. This synthesis of a truncated Vögtle belt constitutes a milestone in long-standing efforts of numerous chemists. The realization of such a molecule provides not only new opportunities in materials science, but also paves the way to the rational synthesis of carbon nanotubes.

Hierarchical functional materials with properties encoded for a defined functionality such as light-induced charge separation are highly desirable targets of numerous synthetic efforts. In the field of reticular chemistry, 2D covalent organic frameworks are an emerging class of porous and crystalline materials obtained by bottom-up condensation of molecular building blocks assisted by non-bonding interactions. In this research news article, an overview is provided on newly emerging photoactive and conducting 2D covalent organic frameworks, sketching the creative trajectory from subunit design strategies to framework construction and resulting functionalities.

Hierarchical functional materials with properties encoded for a defined functionality such as light-induced charge separation are highly desirable targets of numerous synthetic efforts. In this research news article, an overview is provided on newly emerging photoactive and conducting 2D covalent organic frameworks, sketching the creative trajectory from subunit design strategies to framework construction and resulting functionalities.

In spite of wide-ranging previous studies on synthetic macrocycles, the installation of open–close functions into the frameworks remains a challenge. We present a new polyaromatic macrocycle capable of switching between open and closed forms in response to external stimuli, namely, base and acid. The macrocycle, which is prepared in three steps, has a well-defined hydrophobic cavity with a length of around 1 nm, surrounded by four pH-responsive acridinium panels. The open and closed structures were confirmed by single-crystal X-ray analysis. The cylindrical cavity can bind long hydrophilic molecules up to 2.7 nm in length in neutral water and then release the bound guests through a reversible open-to-closed structural change upon simple addition of base.

A Dynamic Short Tube: A polyaromatic macrocycle capable of switching between open and closed forms in response to external stimuli is presented. The macrocycle has a well-defined hydrophobic cavity around 1 nm in length, surrounded by four pH-responsive acridinium panels. The cylindrical cavity can bind long hydrophilic molecules in neutral water and then release them through an open-to-closed structural change upon addition of base.

Bowl me over! A breathtaking bowl-shaped oligoarylene has been created. The structure is analogous to that of corranulene, but instead of twenty sp²-hybridized carbon atoms, the new nanometer-sized molecule has been constructed using twenty 1,3,5-trisubstituted benzene rings.

To a large extent, the field of “molecular machines” started after several groups were able to prepare, reasonably easily, interlocking ring compounds (named catenanes for compounds consisting of interlocking rings and rotaxanes for rings threaded by molecular filaments or axes). Important families of molecular machines not belonging to the interlocking world were also designed, prepared, and studied but, for most of them, their elaboration was more recent than that of catenanes or rotaxanes. Since the creation of interlocking ring molecules is so important in relation to the molecular machinery area, we will start with this aspect of our work. The second part will naturally be devoted to the dynamic properties of such systems and to the compounds for which motions can be directed in a controlled manner from the outside, that is, molecular machines. We will restrict our discussion to a very limited number of examples which we consider as particularly representative of the field.

Magic rings: The field of molecular machines has its origins in the synthesis of catenanes and rotaxanes. J.-P. Sauvage describes in his Nobel Lecture the beginnings of this research and the developments that led to the first molecular muscles and machines whose movement can be directed ′′from the outside′′ in a controlled manner.

DOSY is an NMR spectroscopy technique that resolves resonances according to the analytes’ diffusion coefficients. It has found use in correlating NMR signals and estimating the number of components in mixtures. Applications of DOSY in dilute mixtures are, however, held back by excessively long measurement times. We demonstrate herein, how the enhanced NMR sensitivity provided by SABRE hyperpolarization allows DOSY analysis of low-micromolar mixtures, thus reducing the concentration requirements by at least 100-fold.

How low can DOSY go? DOSY analysis of a low-micromolar mixture is achieved by combining DOSY with nuclear spin hyperpolarization. SABRE hyperpolarization enhances NMR signals by two orders of magnitude, resolving six dilute analytes in a 35 min SABRE-DOSY experiment.

Interlocked molecules, such as catenanes, rotaxanes, and molecular knots, have become interesting candidates for the development of sophisticated chemical catalysts. Herein, we report the first application of a catenane-based catalyst in asymmetric organocatalysis, revealing that the catenated catalyst shows dramatically increased stereoselectivities (up to 98 % ee) in comparison to its non-interlocked analogues. A mechanistic rationale for the observed differences was developed by DFT studies, suggesting that the involvement of two catalytically active groups in the stereodetermining reaction step is responsible for the superior selectivity of the interlocked catalyst.

Two rings to catalyze them: A bifunctional [2]catenane catalyst gave drastically increased stereoselectivities in the asymmetric transfer hydrogenation of quinolines compared to two non-interlocked reference catalysts (see picture). DFT calculations point at the involvement of both catalytically active groups as the reason for the high stereoselectivities.

Integrative self-sorting of palladium(II) metal ions and banana-shaped ligands is driven by the interplay of complementary ligand geometries to form cis- or trans-[Pd₂L₂L′₂] heteroleptic cage structures (1–3 in the picture). In their Communication (10.1002/anie.201702573), G. H. Clever and co-workers report a topologically unprecedented “doubly bridged figure eight” assembly in which one of the ligands is forced to adopt an anti-conformation. The extent of the geometric constraints in the heteroleptic cage system is further demonstrated through highly selective ligand-substitution reactions.