Max Martin

Light as air: Visible light and air were used as easily available and inexpensive reagents for direct metal‐free C−H photooxidation of cyclic tertiary amines towards new antiviral δ‐lactams at ambient conditions. This facile and atom‐efficient method is highly appealing for synthesis of versatile Strychnocarpine alkaloid derivatives (see scheme).

Abstract

Air and visible light have been used in facile direct C−H oxidation of cyclic tertiary amines at ambient conditions, employing organic dyes as photocatalysts and LED. Tolerance of this new environmentally compatible protocol to various side‐chain derivatizations of tryptoline and tetrahydroisoquinoline substrates was demonstrated. The developed method provides a straightforward and sustainable route towards δ‐lactams, which feature strong antiviral properties (EC₅₀ down to 4.6±1.8 μm) against human cytomegalovirus (HCMV). The clear advantages, which are easily available and inexpensive reagents, organic dyes, visible light, air/O₂ and atom efficiency, make this system highly appealing for synthesis of versatile Strychnocarpine alkaloid derivatives with antiviral activity.

Sorting carbon nanomaterials requires more than a deft hand. Through the use of shape complimentary π‐concave host molecules, significant strides have been made in the purification and sorting of fullerenes and carbon nanotubes. Even more importantly, the use of π‐concave molecules can open up these carbon nanomaterials to new and exciting applications through their reversible binding, which leaves the electronic structures of these nanomaterials largely unaltered. However, to use π‐concave molecules to great effect, it is imperative to understand what constitutes effective design.

Abstract

Carbon nanomaterials have been at the forefront of nanotechnology since its inception. At the heart of this research are the curved carbon nanomaterial families: fullerenes and carbon nanotubes. While both have incredible properties that have been capitalized upon in a wide variety of applications, there is an aspect that is not commonly exploited by nanoscientists and organic chemists alike: the interaction of curved carbon nanomaterials with curved organic small molecules. By taking advantage of these interactions, new avenues are opened for the use of fullerenes and carbon nanotubes.

An unprecedented 1,4‐cycloadduct of C₆₀ and other sophisticated fullerene architectures were prepared through reductive functionalization. This method, starting with the two‐fold reduction of C₆₀ with potassium, closely resembles related reactions of carbon nanotubides and represents a so far only little explored concept of fullerene chemistry. Investigations on the scope of different electrophiles as addition partners including a series of tether systems with a predefined geometry provide both new insights of fullerene reactivity itself and new types of exohedral derivatives. More information can be found in the Full Paper by A. Hirsch et al. (DOI: https://doi.org/10.1002/chem.20180577710.1002/chem.201805777).

Tailoring synthetic strategies toward complex, but well‐defined molecular architectures is an important aspect of Today’s organic chemistry. Herein, we present designs to build up [3]rotaxanes of Type 2.1 and Type 3 that feature both a polyyne and a cumulene axle in a single mechanically interlocked molecule. The combination of two sp‐hybridized carbon chains was achieved via functionalization of a phenanthroline‐based macrocycle, which allowed the coupling of two [2]rotaxanes toward Type 3 [3]rotaxanes with two polyynes, two cumulenes, or one polyyne and one cumulene axle. The structures have been established via NMR and UV‐vis spectroscopies, as well as high‐resolution mass spectrometry. A [3]rotaxane of Type 3, featuring two [9]cumulene axles, has been assembled and spectroscopically characterized despite expectations that it would be unstable. This represents only the second cumulene rotaxane reported to date. All designs and attempts to form [3]rotaxanes of Type 2.1, which combine a polyyne and cumulene threaded through a single macrocycle, have been unsuccessful.

Sorting carbon nanomaterials requires more than a deft hand. Through the use of shape complimentary π‐concave host molecules, significant strides have been made in the purification and sorting of fullerenes and carbon nanotubes. Even more importantly, the use of π‐concave molecules can open up these carbon nanomaterials to new and exciting applications through their reversible binding, which leaves the electronic structures of these nanomaterials largely unaltered. However, to use π‐concave molecules to great effect, it is imperative to understand what constitutes effective design.

Abstract

Carbon nanomaterials have been at the forefront of nanotechnology since its inception. At the heart of this research are the curved carbon nanomaterial families: fullerenes and carbon nanotubes. While both have incredible properties that have been capitalized upon in a wide variety of applications, there is an aspect that is not commonly exploited by nanoscientists and organic chemists alike: the interaction of curved carbon nanomaterials with curved organic small molecules. By taking advantage of these interactions, new avenues are opened for the use of fullerenes and carbon nanotubes.

Organic electronics: Active ester‐functionalized hexabenzoperylene in field effect transistors has enabled differentiation of tertiary amines from primary and secondary amines in water.

Abstract

Herein, we report two novel derivatives of hexabenzoperylene (HBP) that are functionalized with ester groups. Methyl acetate functionalized HBP (1) in single crystals self‐assembles into a supramolecular nanosheet, which has a two‐dimensional π‐stack of HBP sandwiched between two layers of ester groups. With the same self‐assembly motif, active ester‐functionalized HBP (2) in field effect transistors has enabled differentiation of tertiary amines from primary and secondary amines, in agreement with the fact that active ester reacts with primary and secondary amines but not with tertiary amines to form amides.

New additions to the family: Insights into the reductive functionalization of fullerenes and its application for preparing highly sophisticated fullerene architectures including an unprecedented 1,4‐cycloadduct are presented. Investigations on the exohedral reactivity of fullerenides and the scope of different electrophiles as addition partners leading to a series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns are reported.

Abstract

A systematic screening study of the exohedral reactivity of the reduced fullerenes (fullerenides) C₆₀ ²⁻ and C₆₀ ^⋅− is reported. These doubly and singly negatively charged carbon cages were prepared by two‐fold reduction of C₆₀ with potassium, leading to K₂C₆₀, or by in situ monoreduction with the radical anion of benzonitrile PhCN^⋅−, respectively. Several series of electrophiles, including geminal and distant dihalides, benzyl bromides, and diazonium compounds, were employed as addition partners. In general, the investigated bromides proved to be the most suitable reaction partners. A series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns, depending on the precise architecture and the steric demand of the addends, were synthesized and fully characterized. Some of the reaction products are unprecedented and inaccessible forms of neutral C₆₀. The fullerenide chemistry presented here closely resembles related reactions of graphenides and carbon nanotubides, which are the most powerful methods for the functionalization of these macromolecular forms of synthetic carbon allotropes (SCAs). Activation of C₆₀ by negative charging represents a little explored concept of fullerene chemistry, providing both new insights of fullerene reactivity itself and new types of exohedral derivatives.

The rational synthesis of nanographenes and carbon nanoribbons directly on nonmetallic surfaces has been an elusive goal for a long time. We report that activation of the carbon (C)–fluorine (F) bond is a reliable and versatile tool enabling intramolecular aryl-aryl coupling directly on metal oxide surfaces. A challenging multistep transformation enabled by C–F bond activation led to a dominolike coupling that yielded tailored nanographenes directly on the rutile titania surface. Because of efficient regioselective zipping, we obtained the target nanographenes from flexible precursors. Fluorine positions in the precursor structure unambiguously dictated the running of the "zipping program," resulting in the rolling up of oligophenylene chains. The high efficiency of the hydrogen fluoride zipping makes our approach attractive for the rational synthesis of nanographenes and nanoribbons directly on insulating and semiconducting surfaces.

Concentration matters: Solvent‐ and concentration‐dependent self‐assembly of star‐shaped hexasquarainyl benzenes in well‐defined dimeric H‐type aggregates is described.

Abstract

We describe the aggregate formation and optical properties of a star‐shaped hexaarylbenzene with six squaraine chromophores (=hexasquarainyl benzene). Comprehensive concentration‐dependence studies in acetone/CHCl₃ mixtures reveal a strong propensity to form discrete dimeric aggregates with a high binding constant in excess of 10⁶  m ⁻¹. In this context, a large hypsochromic shift of almost 2700 cm⁻¹ was found in the absorption spectrum, indicating H‐type exciton coupling. The aggregate band is characterised by a very small band width of only 560 cm⁻¹, probably caused by exchange narrowing. Both experimental and computational methods were used to elucidate the supramolecular aggregate structure, which is assumed to consist of two stacked hexasquarainyl benzene monomers.

C−C coupling: It has been found that α‐fluorinated benzophenones undergo unusual fusion under standard McMurry conditions (see figure) leading to the formation anthracene derivatives that necessitate the cleavage of the exceptionally stable aromatic C−F bond. The discovered reaction proves that fluoroorganic chemistry still remains an undeveloped and extremely promising field.

Abstract

By exposure of α‐fluorinated benzophenones to McMurry reaction conditions, we have observed the remarkable formation of 9,10‐diphenylanthracene derivatives. This unexpected transformation necessitates the cleavage of the exceptionally stable aromatic C−F bond under mild McMurry conditions. In this work, the condensation of several related fluorinated benzo‐ and acetophenones has been investigated, which allow us to propose a domino‐like fusion mechanism for this unusual transformation. The scope and limitations of the fluorine‐promoted benzophenone fusion are subsequently discussed.

Pressure on: A unique response of propeller chirality of hexaarylbenzenes (HABs) under pressure is examined. Significantly large differential volumes are obtained for the conformational transition through the crucial solvation and/or desolvation on the propellers.

Abstract

A unique and effective interaction between the peripheral aromatic blades makes hexaarylbenzenes (HABs) attractive in fundamental research as well as for various applications such as molecular wires, sensors, and supramolecular assemblies. The chiroptical responses of HABs are susceptible to environmental factors such as solvent and temperature owing to the dynamic conformational transitions between the conformers. In this study, pressure dependence on the propeller chiral HABs in two different solvents was studied in detail. The effective differential volumes for two different equilibria were determined by quantitative analyses of CD spectra, affording very large differential volumes from the propeller to toroidal conformer (ΔV _T‐C ) of +43 and +42 cm³ mol⁻¹, for H2 and H6, respectively, in methylcyclohexane. The value of H6 was further enhanced to +72 cm³ mol⁻¹ in hexane, the largest value for the typical unimolecular conformational change. Such a response of propeller chirality in HABs is expedient in designing more advanced piezo‐sensitive materials.

Dehydrative π-extension to nanographenes with zig-zag edges

Dehydrative π-extension to nanographenes with zig-zag edges, Published online: 12 November 2018; doi:10.1038/s41467-018-07095-z

Various molecular systems for the quantification of London dispersion of different groups have been reviewed. Each has its benefits and drawbacks. In general, the detailed knowledge of the contribution of London dispersion of specific groups will provide valuable guidelines for the design of molecular structures as well as processes.

In recent years the importance of London dispersion forces as the attractive part of the van der Waals potential has been recognized for structural stability, catalysis and chemical reactivity. Though known for decades, the determination of the strength of dispersive interactions between certain groups remains a challenging task. Geometrically well‐defined molecular model systems offer the possibility to systematically examine and quantify the London dispersion contribution to interaction energies. The incorporation of control systems in the analysis allows dissecting the interaction of interest from other effects. The knowledge gained from these endeavours will provide the necessary basis to include London dispersion in the design of chemical processes and functional materials.

‘Why didn’t we think to do this earlier?’ Chemists thrilled by speedy atomic structures

‘Why didn’t we think to do this earlier?’ Chemists thrilled by speedy atomic structures, Published online: 29 October 2018; doi:10.1038/d41586-018-07213-3

Size, shape and catalysis: Coordination‐driven encapsulation of two pyridyl‐functionalized phosphine ligands in a metal–organic cage yielded a new supramolecular bidentate ligand. The ligands are strongly bound in the cage and when coordinated to rhodium(I), a supramolecular and sterically congested hydroformylation catalyst is obtained, and it displays size selectivity in the conversion of terminal alkenes to the corresponding aldehydes (see figure).

Abstract

Size‐selective hydroformylation of terminal alkenes was attained upon embedding a rhodium bisphosphine complex in a supramolecular metal–organic cage that was formed by subcomponent self‐assembly. The catalyst was bound in the cage by a ligand‐template approach, in which pyridyl–zinc(II) porphyrin interactions led to high association constants (>10⁵  m ⁻¹) for the binding of the ligands and the corresponding rhodium complex. DFT calculations confirm that the second coordination sphere forces the encapsulated active species to adopt the ee coordination geometry (i.e., both phosphine ligands in equatorial positions), in line with in situ high‐pressure IR studies of the host–guest complex. The window aperture of the cage decreases slightly upon binding the catalyst. As a result, the diffusion of larger substrates into the cage is slower compared to that of smaller substrates. Consequently, the encapsulated rhodium catalyst displays substrate selectivity, converting smaller substrates faster to the corresponding aldehydes. This selectivity bears a resemblance to an effect observed in nature, where enzymes are able to discriminate between substrates based on shape and size by embedding the active site deep inside the hydrophobic pocket of a bulky protein structure.