Sebastian Beil

Pile, oligomerize, and tangle: The complexation of a twisted triarylmethane ligand with Cu^I or Ag^I ions afforded M₆L₄, M₁₂L₈, and M₁₈L₁₂ coordination polyhedra that can be considered as cross‐linked and tangled oligomers of a hypothetical double‐propeller M₃L₂ subunit supported by weak acetylene–π coordination.

Abstract

The self‐assembly of nanostructures is dominated by a limited number of strong coordination elements. Herein, we show that metal–acetylene π‐coordination of a tripodal ligand (L) with acetylene spacers gave an M₃L₂ double‐propeller motif (M=Cu^I or Ag^I), which dimerized into an M₆L₄ interlocked cage (M=Cu^I). Higher (M₃L₂) _n oligomers were also selectively obtained: an M₁₂L₈ truncated tetrahedron (M=Cu^I) and an M₁₈L₁₂ truncated trigonal prism (M=Ag^I), both of which contain the same double‐propeller motif. The higher oligomers exhibit multiply entangled facial structures that are classified as a trefoil knot and a Solomon link. The inner cavities of the structures encapsulate counteranions, revealing a potential new strategy towards the synthesis of functional hollow structures that is powered by molecular entanglements.

Crystal clear colours: Selective expression of chromophores is achieved in a soft organic molecule. In response to various external stimuli, full‐colour emissions from ten different individual single crystals and dynamic triplet‐exciton behaviours can be realized via the competition between different chromophores for emission.

Abstract

Soft luminescent materials are attractive for optoelectronic applications, however, switching dominant chromophores for property enrichment remains a challenge. Herein, we report the first case of a soft organic molecule (DOS) featuring selective expression of chromophores. In response to various external stimuli, different chromophores of DOS can take turns working through conformation changes, exhibiting full‐colour emissions peaking from 469 nm to 583 nm from ten individual single crystals. Dynamic triplet‐exciton behaviours including thermally activated delayed fluorescence (TADF), room‐temperature phosphorescence (RTP), mechanoluminescence (ML), and distinct mechano‐responsive luminescence (MRL) can all be realized. This novel designed DOS molecule provides a multifunctional platform for detection of volatile organic compounds (VOCs), multicolour dynamic displays, sensing, anticounterfeiting, and hopefully many others.

Nature, Published online: 17 February 2020; doi:10.1038/s41586-020-2060-z

Corannulene and a tetragold(I) rectangle‐like metallocage mutually adapt their shapes to maximize shape complementarity upon formation of a host–guest complex.

Abstract

A tetragold(I) rectangle‐like metallocage containing two pyrene‐bis‐imidazolylidene ligands and two carbazolyl‐bis‐alkynyl linkers is used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs), including corannulene. The binding affinities obtained for the encapsulation of the planar PAHs guests in CD₂Cl₂ are found to exponentially increase with the number of π‐electrons of the guest (1.3 > logK >6.6). For the bowl‐shaped molecule of corannulene, the association constant is much lower than the expected one according to its number of electrons. The molecular structure of the host–guest complex formed with corannulene shows that the molecule of the guest is compressed, while the host is expanded, thus showing an interesting case of artificial mutual induced‐fit arrangement.

Gadolinium photocatalysis: A highly regioselective, intermolecular [2+2] photocycloaddition/ring‐expansion sequence with indoles is introduced, which could provide divergent access to cyclopenta[b]indoles and indolines. A simple and commercially available Gd(OTf)₃ salt is sufficient for this visible‐violet‐light‐induced transformation.

Abstract

Lanthanide photocatalysts are much less investigated in synthetic chemistry than rare and expensive late transition metals. We herein introduce Gd^III photocatalysis of a highly regioselective, intermolecular [2+2] photocycloaddition/ring‐expansion sequence with indoles, which could provide divergent access to cyclopenta[b]indoles and indolines. A simple and commercially available Gd(OTf)₃ salt is sufficient for this visible‐violet‐light‐induced transformation. The reaction proceeds either through a transient or start‐to‐end dearomatization cascade and shows excellent regioselectivity (usually >95:5 r.r.), broad scope (59 examples), good functional group tolerance and facile scale‐up under mild, direct visible‐light‐excitation conditions. Mechanistic investigations reveal that direct excitation of the Gd(OTf)₃/indole mixture gives an excited state intermediate, which undergoes the subsequent [2+2] cycloaddition and cyclobutane‐expansion cascade.

Same but different: A new generation of saturated benzene mimetics, 2‐oxabicyclo[2.1.1]hexanes, was developed. These compounds were designed as analogues of bicyclo[1.1.1]pentane with an improved water solubility. Crystallographic analysis of the compounds revealed that they occupy a novel chemical space but resemble meta‐disubstituted benzenes at the same time.

Abstract

A new generation of saturated benzene mimetics, 2‐oxabicyclo[2.1.1]hexanes, was developed. These compounds were designed as analogues of bicyclo[1.1.1]pentane with an improved water solubility. Crystallographic analysis of 2‐oxabicyclo[2.1.1]hexanes revealed that they occupy a novel chemical space, but, at the same time, resemble the motif of meta‐disubstituted benzenes.

Give me a ring: A palladium‐catalyzed dearomative cyclization was developed that provides facile access to eight types of bridged tetracyclic skeletons bearing various ring sizes and heterocycles. Several skeletons or analogues of natural products, including tubingensin B and dracaenones, were synthesized. Asymmetric dearomative cyclization with a chiral palladium catalyst provided enantiomerically enriched bridged polycyclic systems with up to 99 % ee.

Abstract

A powerful palladium‐catalyzed dearomative cyclization was developed that provides facile access to eight types of bridged tetracyclic skeletons bearing various ring sizes and heterocycles. With this method, several skeletons or analogues of natural products, including tubingensin B and dracaenones, were synthesized. Asymmetric dearomative cyclization enables the construction of various enantiomerically enriched bridged polycyclic systems with up to 99 % ee by employing a chiral palladium catalyst.

Power of twist : A twisted heptagonal diimide acceptor with well‐balanced structural rigidity and rotatability has been developed for the synthesis of a highly efficient aggregation‐induced delayed fluorescence material, which was used to make state‐of‐the‐art performance non‐doped OLEDs.

Abstract

The development of efficient non‐doped organic light‐emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation‐caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π–π stacking due to well‐balanced rigidity and rotatability of heptagonal structure. The BPI‐based luminogen (DMAC‐BPI ) shows significant aggregation‐induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non‐doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll‐off as low as 1.0 % at 1000 cd m⁻², which represents the state‐of‐the‐art performance for non‐doped OLEDs. In addition, the synthetic route to DMAC‐BPI is greatly streamlined and simplified through oxidative Ar−H/Ar−H homo‐coupling reaction.

Nature Communications, Published online: 14 February 2020; doi:10.1038/s41467-020-14522-7

No beating about the bush: (Hetero)aromatic amines underwent decarboxylative N‐alkylation directly with carboxylic acids with a dual copper/acridine photocatalytic system. The directional character of the acridine photocatalysis facilitates the challenging decarboxylation of unactivated carboxylic acids in the presence of more readily oxidizable anilines, thus enabling the use of a wide range of structurally diverse amine and acid substrates (see scheme).

Abstract

The development of efficient and selective C−N bond‐forming reactions from abundant feedstock chemicals remains a central theme in organic chemistry owing to the key roles of amines in synthesis, drug discovery, and materials science. Herein, we present a dual catalytic system for the N‐alkylation of diverse aromatic carbocyclic and heterocyclic amines directly with carboxylic acids, by‐passing their preactivation as redox‐active esters. The reaction, which is enabled by visible‐light‐driven, acridine‐catalyzed decarboxylation, provides access to N‐alkylated secondary and tertiary anilines and N‐heterocycles. Additional examples, including double alkylation, the installation of metabolically robust deuterated methyl groups, and tandem ring formation, further demonstrate the potential of the direct decarboxylative alkylation (DDA) reaction.

A new and powerful approach for the synthesis of diketopyrrolopyrroles bearing electron‐donating and sterically‐hindered substituents has been developed. This method allows for the regioselective installation of C‐aryl and N‐alkyl substituents in a predictable and programmed manner. Unprecedented control over the optical properties of DPP derivatives has been demonstrated by the creation of a large series of dipolar DPPs, some bearing previously inaccessible substituents.

Abstract

A new, transformative methodology for the preparation of diketopyrrolopyrroles from aldehydes, primary amines, nitriles, and diethyl oxalacetate has been developed. It is now possible to prepare diketopyrrolopyrroles bearing an ordered arrangement of three different substituents from abundant and commercially available materials, allowing the independent regulation of all desired physicochemical properties. For the first time very electron‐rich (carbazol‐3‐yl, dimethylaminophenyl, pyrrolo[3,2‐b]pyrrolyl), and sterically hindered substituents (naphthalen‐1‐yl, quinolin‐4‐yl, acridin‐9‐yl, imidazo[1,5‐a]pyridin‐1‐yl, 2‐bromophenyl etc.) can be appended to the diketopyrrolopyrrole core by condensation of an appropriate nitrile with a pyrrolidin‐2‐one intermediate. Even greater synthetic possibilities are related to the fact that such demanding substituents as 4‐dimethylaminophenyl, indol‐3‐yl, and 2‐methoxyphenyl can be incorporated from aldehyde precursors, bypassing problems with the nitriles reactivity.

More light in chemistry: This Minireview highlights the state‐of‐the‐art and emerging techniques in theoretical and computational photochemistry. This is a challenging and rapidly evolving field that relates time‐dependent spectroscopy with electronic structure theory and molecular dynamics for electronic excited states.

Abstract

Photochemistry is a fascinating branch of chemistry that is concerned with molecules and light. However, the importance of simulating light‐induced processes is reflected also in fields as diverse as biology, material science, and medicine. This Minireview highlights recent progress achieved in theoretical chemistry to calculate electronically excited states of molecules and simulate their photoinduced dynamics, with the aim of reaching experimental accuracy. We focus on emergent methods and give selected examples that illustrate the progress in recent years towards predicting complex electronic structures with strong correlation, calculations on large molecules, describing multichromophoric systems, and simulating non‐adiabatic molecular dynamics over long time scales, for molecules in the gas phase or in complex biological environments.

Play with Lego: A modular synthetic strategy for macrocycles with functional skeletons was demonstrated, involving one‐pot and high‐yielding condensation between bis(2,4‐dimethoxyphenyl)arene monomers and paraformaldehyde. By changing the blocks, variously functional units can be conveniently introduced into the backbone of macrocycles.

Abstract

Reported here is a molecule‐Lego synthetic strategy for macrocycles with functional skeletons, involving one‐pot and high‐yielding condensation between bis(2,4‐dimethoxyphenyl)arene monomers and paraformaldehyde. By changing the blocks, variously functional units (naphthalene, pyrene, anthraquinone, porphyrin, etc.) can be conveniently introduced into the backbone of macrocycles. Interestingly, the macrocyclization can be tuned by the geometrical configuration of monomeric blocks. Linear (180°) monomer yield cyclic trimers and pentamers, while V‐shaped (120°, 90° and 60°) monomers tend to form dimers. More significantly, even heterogeneous macrocycles are obtained in moderate yield by co‐oligomerization of different monomers. This series of macrocycles have the potential to be prosperous in the near future.

Global influence: A stable core‐modified [38]octaphyrin with open‐shell diradical character was synthesized efficiently by Yamamoto coupling followed by oxidative dehydrogenation. The neutral compound has a planar backbone and is globally aromatic, its dication has a distorted geometry and is antiaromatic, and its tetracation has a shallow‐bowl shape and is again aromatic (see scheme).

Abstract

A soluble and stable core‐modified [38]octaphyrin, MC‐T8, containing eight thiophene rings was synthesized by Yamamoto coupling followed by oxidative dehydrogenation. X‐ray crystallographic analysis revealed a nearly planar backbone, and the molecule is globally aromatic with a dominant 38π conjugation pathway. The dication MC‐T8²⁺ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC‐T8⁴⁺ becomes aromatic again, with a shallow‐bowl‐shaped geometry. Both the neutral compound and the dication demonstrated open‐shell diradical character with a small singlet–triplet energy gap (−2.70 kcal mol⁻¹ for MC‐T8 and −3.78 kcal mol⁻¹ for MC‐T8²⁺ ), and they are stable owing to effective spin delocalization.

Excited deracemization: Visible‐light photocatalysis has been utilized to convert racemates into single enantiomers in the presence of a chiral photosensitizer or a pair of chiral catalysts. Mechanistic studies revealed that energy transfer (E_nT) or a sequence of electron transfer (ET), proton transfer (PT), and hydrogen atom transfer (HAT) is operative.

Abstract

Deracemization is an ideal but challenging strategy for the conversion of a racemic mixture into a single enantiomer. Recent studies have demonstrated that visible‐light photocatalysis could be utilized to promote selective deracemization of axially chiral allenes as well as cyclopropylquinolones and cyclic ureas with central chirality either through energy transfer or through a sequence of electron, proton, and hydrogen‐atom transfer.

Anthracene excited: Supramolecular photocatalysis via charge‐transfer excitation of a host–guest complex was realized by use of macrocyclic boronic ester [2+2] _BTH‐F containing highly electron‐deficient difluorobenzothiadiazole moieties. The triplet excited state of anthracene was generated by visible light irradiation, and cycloaddition with several dienes and alkenes proceeded in high yields.

Abstract

Supramolecular photocatalysis via charge‐transfer excitation of a host–guest complex was developed by use of the macrocyclic boronic ester [2+2]_BTH‐F containing highly electron‐deficient difluorobenzothiadiazole moieties. In the presence of a catalytic amount of [2+2]_BTH‐F, the triplet excited state of anthracene was generated from the charge‐transfer excited state of anthracene@[2+2]_BTH‐F by visible‐light irradiation, and cycloaddition of the excited anthracene with several dienes and alkenes proceeded in a [4+2] manner in high yields.

Heterocycle cross‐couplings by sulfur: Addition of heteroaryl nucleophiles onto a simple, readily accessible alkyl sulfinyl(IV) chloride allows formation of a trigonal bipyramidal sulfurane intermediate. Reductive elimination provides bis‐heteroaryl products in a practical and efficient fashion.

Abstract

Despite the tremendous utilities of metal‐mediated cross‐couplings in modern organic chemistry, coupling reactions involving nitrogenous heteroarenes remain a challenging undertaking – coordination of Lewis basic atoms into metal centers often necessitate elevated temperature, high catalyst loading, etc. Herein, we report a sulfur (IV) mediated cross‐coupling amendable for the efficient synthesis of heteroaromatic substrates. Addition of heteroaryl nucleophiles to a simple, readily‐accessible alkyl sulfinyl (IV) chloride allows formation of a trigonal bipyramidal sulfurane intermediate. Reductive elimination therefrom provides bis‐heteroaryl products in a practical and efficient fashion.

Triangular momentum: Synthesis and characterization of the [n]triangulene series (n=3–5) are presented. These open‐shell molecules are predicted to host ferromagnetically coupled edge states with net spin values scaling with molecular size and are therefore considered promising candidates for future molecular spintronics applications.

Abstract

Triangulene and its higher homologues are a class of zigzag‐edged triangular graphene molecules (ZTGMs) with high‐spin ground states. These open‐shell molecules are predicted to host ferromagnetically coupled edge states with net spin values scaling with molecular size and are therefore considered promising candidates for future molecular spintronics applications. Unfortunately, the synthesis of unsubstituted [n]triangulenes and the direct observation of their edge states have been a long‐standing challenge due to a high reactivity towards oxygen. However, recent advances in precursor design enabled the on‐surface synthesis and characterization of unsubstituted [3]‐, [4]‐, and [5]triangulene. In this Minireview, we will highlight key aspects of this rapidly developing field, ranging from the principles of precursor design to synthetic strategies and characterization of a homologous series of triangulene molecules synthesized on‐surface. We will also discuss challenges and future directions.

Chemistry brought to life? Between vitalism and romanticism, often‐forgotten naturalists believed in the spontaneous creation of matter, essential for biological activity to occur. Yet flawed, they opened the door to understanding shape and pattern in nature. That knowledge gives clues to the origin of primitive life and notably fuels our efforts in designing artificial cells.

Abstract

This Essay focuses briefly on early studies elaborated by natural and chemical philosophers, and the once‐called synthetic biologists, who postulated the transition from inanimate to animate matter and even foresaw the possibility of creating artificial life on the basis of physical and chemical principles only. Such ideas and speculations, ranging from soundness to weirdness, paved however the way to current developments in areas like abiotic pattern formation, cell compartmentalization, biomineralization, or the origin of life itself. In particular, the generation of biomorphs and their relationship to microfossils represents an active research domain and seems to be the logical way to bring the historical work up to the future, as some scientists are trying to make artificial cells. The last sections of this essay will also highlight modern science aimed at understanding what life is and, whether or not, it can be redefined in chemical terms.

A new method for the synthesis of carbazoles and related compounds has been reported through either visible light irradiation or rhodium catalysis. Sulfilimines were employed as a safe nitrene source. Compared with aryl azides, aryl sulfilimines are more reactive and thus can be used under milder reaction conditions. The gram‐scale synthesis of Clausine C demonstrated the synthetic potential of this method.

Abstract

While direct nitrene insertions into C−H bonds have become an important tool for building C−N bonds in modern organic chemistry, the generation of nitrene intermediates always requires transition metals, high temperatures, ultraviolet or laser light. We report a mild synthesis of carbazoles and related building blocks through a visible light‐induced intramolecular C−H amination reaction. A striking advantage of this new method is the use of more reactive aryl sulfilimines instead of the corresponding hazardous azides. Different catalysts and divergent light sources were tested. The reaction scope is broad and the product yield is generally high. An efficient gram‐scale synthesis of Clausine C demonstrates the applicability and scalability of this new method.

Enantioselective process: A dicationic bidentate halogen‐bond donor based on iodoimidazolium groups with rigidly attached chiral moieties allowed the NMR‐based enantiodiscrimination of a racemic diamine. It also enabled the first enantioselective reaction catalyzed by a “pure” halogen‐based Lewis acid.

Abstract

Even though halogen bonding—the noncovalent interaction between electrophilic halogen substituents and Lewis bases—has now been established in molecular recognition and catalysis, its use in enantioselective processes is still very rarely explored. Herein, we present the synthesis of chiral bidentate halogen‐bond donors based on two iodoimidazolium units with rigidly attached chiral sidearms. With these Lewis acids, chiral recognition of a racemic diamine is achieved in NMR studies. DFT calculations support a 1:1 interaction of the halogen‐bond donor with both enantiomers and indicate that the chiral recognition is based on a different spatial orientation of the Lewis bases in the halogen‐bonded complexes. In addition, moderate enantioselectivity is achieved in a Mukaiyama aldol reaction with a preorganized variant of the chiral halogen‐bond donor. This represents the first case in which asymmetric induction was realized with a pure halogen‐bond donor lacking any additional active functional groups.