Sebastian Beil

A pair of molecular tweezers: A redox‐active coordination tweezer constructed from the dithiol‐fluorene framework spontaneously dimerizes in solution due to favorable geometric and electronic parameters. The interpenetrated dimer can dissociate upon forming a 1:1 host–guest complex in the presence of an electron‐poor guest, which can be reversibly released upon oxidation through an exchange process.

Abstract

Developing methodologies for on‐demand control of the release of a molecular guest requires the rational design of stimuli‐responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination‐tweezers has been less explored. Herein, we report the first example of a redox‐triggered guest release from a metalla‐assembled tweezer. This tweezer incorporates two redox‐active panels constructed from the electron‐rich 9‐(1,3‐dithiol‐2‐ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron‐poor planar unit, forming a 1:1 host–guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox‐triggered molecular delivery pathway.

An inorganic salt is used for the multicomponent reductive cross‐coupling for the straightforward construction of sulfones. Both intramolecular and intermolecular reductive cross‐couplings were comprehensively explored, and diverse sulfones were accessible from the corresponding alkyl and aryl halides.

Abstract

Conventionally, sulfones are prepared by oxidation of sulfides with strong oxidants. Now, a multicomponent reductive cross‐coupling involving an inorganic salt (sodium metabisulfite) for the straightforward construction of sulfones is disclosed. Both intramolecular and intermolecular reductive cross‐couplings were comprehensively explored, and diverse sulfones were accessible from the corresponding alkyl and aryl halides. Intramolecular cyclic sulfones were systematically obtained from five‐ to twelve‐membered rings. Naturally occurring aliphatic systems, such as steroids, saccharides, and amino acids, were highly compatible with the SO₂‐insertion reductive cross‐coupling. Four clinically applied drug molecules, which include multiple heteroatoms and functional groups with active hydrogens, were successfully prepared via a late‐stage SO₂ insertion. Mechanistic studies show that alkyl radicals and sulfonyl radicals were both involved as intermediates in this transformation.

Nature Reviews Chemistry, Published online: 29 October 2019; doi:10.1038/s41570-019-0140-0

Easy on, easy off: 5‐(aryl)dibenzothiophenium triflates were prepared by highly selective metal‐free C−H sulfenylation of arenes. Interestingly, these salts undergo site‐selective Suzuki–Miyaura coupling in the presence of C−I bonds, enabling the iterative synthesis of polyaromatics.

Abstract

A synthetic protocol for the preparation of 5‐(aryl)dibenzothiophenium salts starting from inexpensive dibenzothiophene S‐oxide and simple arenes is reported. The scope of the method regarding the nature of the arene is evaluated, intermediates along the reaction sequence have been trapped, and side‐reactions identified. In addition, the X‐ray structures of a complete set of these salts are reported and their reactivities studied. Specifically, chemoselective Suzuki coupling is observed at the dibenzothiophenium in the presence of iodides.

Fantastic twelve naphthochromenone photocatalysts (PCs) that absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) were synthesized on gram scale. Their excited‐state redox potentials, PC*/PC^.− (up to 1.65 V) and PC^.+/PC* (up to −1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching.

Abstract

Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC^.− (up to 1.65 V) and PC^.+/PC* (up to −1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis.

Polarizability is driven to the extreme and harnessed for anion–π catalysis. Multi‐walled carbon nanotubes i) outperform single‐walled ones (polarizable beyond one tube), ii) are inactivated by π‐basic competitors (active sites are on tube surface), iii) prefer covalent, linker‐sensitive interfacing over non‐covalent strategies (pyrene), and iv) activate existing anion‐π catalysts by electron sharing (NDIs > fullerenes).

Abstract

Induced π acidity from polarizability is emerging as the most effective way to stabilize anionic transition states on aromatic π surfaces, that is, anion–π catalysis. To access extreme polarizability, we propose a shift from homogeneous toward heterogeneous anion–π catalysis on higher carbon allotropes. According to benchmark enolate addition chemistry, multi‐walled carbon nanotubes equipped with tertiary amine bases outperform single‐walled carbon nanotubes. This is consistent with the polarizability of the former not only along but also between the tubes. Inactivation by π‐basic aromatics and saturation with increasing catalyst concentration support that catalysis occurs on the π surface of the tubes. Increasing rate and selectivity of existing anion–π catalysts on the surface of unmodified nanotubes is consistent with transition‐state stabilization by electron sharing into the tubes, i.e., induced anion–π interactions. On pristine tubes, anion–π catalysis is realized by non‐covalent interfacing with π‐basic pyrenes.

Nature, Published online: 23 October 2019; doi:10.1038/d41586-019-03176-1

Nature, Published online: 23 October 2019; doi:10.1038/s41586-019-1655-8

Nature, Published online: 23 October 2019; doi:10.1038/s41586-019-1661-x

Deep Blue! Soluble contorted PAHs with two embedded azulene moieties with different degrees of curvature are synthesized and spectroscopically compared.

Abstract

Polycyclic aromatic hydrocarbons (PAHs) that contain both five‐ and seven‐membered rings are rare, and those where these rings are annulated to each other and build azulene units have, to date, mainly been generated in minute amounts on surfaces. Herein, a rational approach to synthesize soluble contorted PAHs containing two embedded azulene units in the bulk is presented. By stepwise detachment of tert‐butyl groups, a series of three azulene embedded PAHs with different degrees of contortion has been made to study the impact of curvature on aromaticity and conjugation. Furthermore, the azulene PAHs showed high fluorescence quantum yields in the NIR regime.

All the colors of the rainbow: Ultralong organic phosphorescence (UOP) was enabled in a set of amorphous polymers by ionization under ambient conditions. The UOP emission color could be controllably manipulated from blue to red over the entire visible region (see photographs) by varying the excitation wavelength.

Abstract

Amorphous purely organic phosphorescence materials with long‐lived and color‐tunable emission are rare. Herein, we report a concise chemical ionization strategy to endow conventional poly(4‐vinylpyridine) (PVP) derivatives with ultralong organic phosphorescence (UOP) under ambient conditions. After the ionization of 1,4‐butanesultone, the resulting PVP‐S phosphor showed a UOP lifetime of 578.36 ms, which is 525 times longer than that of PVP polymer itself. Remarkably, multicolor UOP emission ranging from blue to red was observed with variation of the excitation wavelength, which has rarely been reported for organic luminescent materials. This finding not only provides a guideline for developing amorphous polymers with UOP properties, but also extends the scope of room‐temperature phosphorescence (RTP) materials for practical applications in photoelectric fields.

Networking: The synthesis of host phenolic building blocks, consisting of macrocyclic host rings and phenolic coordinating functions, enables the rapid assembly of adherent conformal metal–phenolic network coatings on diverse substrates with modular and tunable interfacial properties using host–guest chemistry.

Abstract

The manipulation of interfacial properties has broad implications for the development of high‐performance coatings. Metal–phenolic networks (MPNs) are an emerging class of responsive, adherent materials. Herein, host–guest chemistry is integrated with MPNs to modulate their surface chemistry and interfacial properties. Macrocyclic cyclodextrins (host) are conjugated to catechol or galloyl groups and subsequently used as components for the assembly of functional MPNs. The assembled cyclodextrin‐based MPNs are highly permeable (even to high molecular weight polymers: 250–500 kDa), yet they specifically and noncovalently interact with various functional guests (including small molecules, polymers, and carbon nanomaterials), allowing for modular and reversible control over interfacial properties. Specifically, by using either hydrophobic or hydrophilic guest molecules, the wettability of the MPNs can be readily tuned between superrepellency (>150°) and superwetting (ca. 0°).

A porphyrin‐based molecular sensor for selective detection of anions is described by M. O. Senge and co‐workers in their Communication (DOI: https://doi.org/10.1002/anie.20190792910.1002/anie.201907929). The acid‐activated interface between the specially designed binding cavity and corresponding substrates results in distinct spectroscopic alterations with vibrant colorimetric response. The cover picture by Ella Marushchenko illustrates chemically re‐engineered pigments to act like tiny Venus flytraps luring anions disguised as flies.

I can Si clearly now: The ability of silicon to stabilize vinyl cationic species enables a redox arylation of alkynes whereby the poor reactivity and regioselectivity of alkyl‐substituted alkynes are lifted. This enables the synthesis of a range of α‐silyl‐α′‐arylketones under mild conditions in good to excellent yields. The silicon moiety of the products can either be removed or harnessed for additional C−C bond formation.

Abstract

The ability of silicon to stabilize vinyl cationic species leads to a redox arylation of alkynes whereby the stringent limitations of reactivity and regioselectivity of alkyl‐substituted alkynes are lifted. This allows the synthesis of a range of α‐silyl‐α′‐arylketones under mild conditions in good to excellent yields and with high functional group tolerance, whereby the silicon moiety in the final products can either be removed for a formal acetone monoarylation transform, or capitalized upon for subsequent electrophilic substitutions at either side of the carbonyl group.