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1.
Chemistry ; 2020 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-32840913

RESUMO

Dynamic covalent chemistry (DCC) is a powerful synthetic tool to construct large defined molecules in one step from rather simple precursors. The advantage of the intrinsic dynamics of the applied reversible reaction steps is a self-correction under the chosen conditions, to achieve high yields of the target compound. To date, only a few examples are known, in which DCC was used to build up a molecular defined but larger product that was chemically transferred to a more stable congener in a second (irreversible) step. Here, we present a nanometer-sized [8+12] boronic ester cage containing 48 peripheral terminal alkene units which allows to put a hydrocarbon exoskeleton around the cage via alkene metathesis.

2.
Chemistry ; 2020 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-32648593

RESUMO

By applying a chirality-assisted synthesis (CAS) approach enantiopure diaminodibromotriptycenes were converted to rigid chiral helical diazadibenzoanthracenes, which show besides pronounced Cotton effects in circular dichroism spectra a higher photoluminescence quantum yields as comparable carbacyclic analoga. For the enantiopure building blocks, a protocol was developed allowing the large scale synthesis without the necessity of separation via HPLC.

3.
Chemistry ; 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32539193

RESUMO

Since a few years, the interest in negatively curved fused polycyclic aromatic hydrocarbons (PAHs) has significantly increased. Recently, the first chiral negatively curved PAH with the topology of a monkey saddle was introduced. Herein the synthesis of its triaza congener is reported. The influence of this CH↔N exchange on photophysical and electrochemical properties is studied as well as isomerization process of the enantiomers. The aza analogue has a significantly higher inversion barrier, which makes it easier to handle at room temperature. All experimental results are underpinned by theoretical DFT calculations.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32521080

RESUMO

Porous shape-persistent organic cages have become the object of interest in recent years because they are soluble and thus processable from solution. A variety of cages can be achieved by applying dynamic covalent chemistry (DCC), but they are less chemically stable. Here the transformation of a salicylimine cage into a quinoline cage by a twelve-fold Povarov reaction as the key step is described. Besides the chemical stability of the cage over a broad pH regime, it shows a unique absorption and emission depending on acid concentration. Furthermore, thin films for the vapor detection of acids were investigated, showing color switches from pale-yellow to red, and characteristic emission profiles.

5.
Chemistry ; 2020 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-32459010

RESUMO

Five different di- and tetracyano substituted pyrene-fused pyrazaacenes have been synthesized and studied as potential electron acceptors in the solid state. Therefore, from all compounds single crystals were grown and the crystal packing studied by DFT calculations (transfer integrals and reorganization energies) to get an insight in possible use for semiconducting charge transport.

6.
Chemistry ; 2020 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-32368815

RESUMO

Previously it was demonstrated that triptycene end-capping can be used as a crystal engineering strategy to direct the packing of quinoxalinophenanthrophenazines (QPPs) towards cofacially stacked π dimers with large molecular overlap resulting in high charge transfer integrals. Remarkably, this packing motif was formed under different crystallization conditions and with a variety of derivatives bearing additional functional groups or aromatic substituents. Benzothienobenzothiophene (BTBT) and its derivatives are known as some of the best performing compounds for organic field-effect transistors. Here, the triptycene end-capping concept is introduced to this class of compounds and polymorphic crystal structures are investigated to evaluate the potential of triptycene end-caps as synthons for crystal engineering.

7.
Chemistry ; 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32314830

RESUMO

A new synthetic route to tetraindenopyrene (TIP)-a bowl-shaped cut-out structure of C70 -is reported. The key step in this approach is a fourfold palladium-catalyzed C-H activation that increases the yield more than 50 times in comparison to the approach originally described by Scott and co-workers. Besides examination of its optoelectronic properties and study of its aggregation in solution, TIP was also re-investigated by dispersion-corrected DFT methods, which showed that dispersion interactions significantly increase the bowl-to-bowl inversion barrier. Furthermore, TIP was used as a semiconductor in p-channel thin-film transistors (TFTs).

8.
J Org Chem ; 85(5): 3981-3989, 2020 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-31990546

RESUMO

A racemic C3-symmetric trihydroxytribenzotriquinacene was resolved on a large scale by fractional crystallization of the corresponding (1S)-camphanic esters, achieving both enantiopure enantiomers (>99% ee) in 35% and 32% yields. The method relies on a distinct solvent-controlled discrimination process between the diastereomers. The enantiopure trihydroxytribenzotriquinacenes were converted into four other enantiopure building blocks, which are valuable precursors for supramolecular and materials chemistry to illustrate the utility of the synthesized compounds.

9.
Angew Chem Int Ed Engl ; 59(1): 270-274, 2020 01 02.
Artigo em Inglês | MEDLINE | ID: mdl-31613416

RESUMO

A contorted polycyclic aromatic hydrocarbon (PAH) in the shape of a monkey saddle has been synthesized in three steps from a readily available truxene precursor. The monkey saddle PAH is consisting of three five-, seven six-, and three eight-membered rings and has been unambiguously characterized by single-crystal X-ray diffraction. Owing to the three biaryl axes the monkey saddle PAH is inherently chiral. The inversion of the two enantiomeric structures into each other preferably occurs through a twisting of peripheral rings rather than by a fully planar intermediate, as has been calculated by DFT methods. Enantiomers were separated by chiral HPLC and inversion barriers determined by variable temperature circular dichroism spectroscopy, supporting the twisting mechanism.

10.
Angew Chem Int Ed Engl ; 58(49): 17577-17582, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31550407

RESUMO

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.

11.
Chemistry ; 25(47): 11121-11134, 2019 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-31210369

RESUMO

Triptycene end-capped quinoxalinophenanthrophenazine reveals a coplanar arrangement with a high overlap of the π planes. Four structurally related model compounds bearing electron-withdrawing or -donating groups were synthesized, and their optoelectronic properties were characterized by using cyclovoltammetry, absorption- and emission spectroscopy as well as theoretical calculations. The directional robustness of the triptycene end-capping of these compounds was tested by using single-crystal X-ray diffraction. The impact of solvents and crystallization conditions has also been investigated. In total, 17 single-crystal structures were obtained. Each structure was evaluated for its potential charge-transfer capability taking into account the overall molecular packing, solvent enclathration and the structural overlap of the π planes of adjacent molecules. For this purpose, charge-transfer integrals were also calculated for every π-stacked dimer.

12.
Angew Chem Int Ed Engl ; 58(31): 10650-10654, 2019 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-31125478

RESUMO

The oxidative cyclodehydrogenation (often named the Scholl reaction) is still a powerful synthetic tool to construct even larger polycyclic aromatic hydrocarbons (PAHs) by multiple biaryl bond formations without the necessity of prior installation of reacting functional groups. Scholl-type reactions are usually very selective although the resulting products bear sometimes some surprises, such as the formation of five-membered instead of six-membered rings or the unexpected migration of aryl moieties. There are a few examples, where chlorinated byproducts were found when FeCl3 was used as reagent. To our knowledge, the direct functionalization of PAHs during Scholl-type cyclization by triflyloxylation has not been observed. Herein we describe the synthesis of functionalized PAHs by the formation of five-membered rings and a regioselective triflyloxylation in one step. The triflyloxylated PAHs can be used as reactants for further transformation to even larger contorted PAHs.

13.
Angew Chem Int Ed Engl ; 58(26): 8819-8823, 2019 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-30964597

RESUMO

In recent years, interest in shape-persistent organic cage compounds has steadily increased, not least because dynamic covalent bond formation enables such structures to be made in high to excellent yields. One often used type of dynamic bond formation is the generation of an imine bond from an aldehyde and an amine. Although the reversibility of the imine bond formation is advantageous for high yields, it is disadvantageous for the chemical stability of the compounds. Amide bonds are, in contrast to imine bonds much more robust. Shape-persistent amide cages have so far been made by irreversible amide bond formations in multiple steps, very often accompanied by low yields. Here, we present an approach to shape-persistent amide cages by exploiting a high-yielding reversible cage formation in the first step, and a Pinnick oxidation as a key step to access the amide cages in just three steps. These chemically robust amide cages can be further transformed by bromination or nitration to allow post-functionalization in high yields. The impact of the substituents on the gas sorption behavior was also investigated.

14.
Angew Chem Int Ed Engl ; 58(6): 1768-1773, 2019 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-30557460

RESUMO

In contrast to organic cages which are formed by exploiting dynamic covalent chemistry, such as boronic ester cages, imine cages, or disulfide cages, those with a fully carbonaceous backbone are rarer. With the exception of alkyne metathesis based approaches, the vast majority of hydrocarbon cages need to be synthesized by kinetically controlled bond formation. This strategy implies a multiple step synthesis and no correction mechanism in the final macrocyclization step, both of which are responsible for low overall yields. Whereas for smaller cages the intrinsic drawbacks are not always obvious, larger cages are seldom synthesized in yields beyond a few tenths of a percent. Presented herein is a three-step method to convert imine cages into hydrocarbon cages. The method has been successfully applied to even larger structures such as derivatives of C72 H72 , an unknown cage suggested by Fritz Vögtle more than 20 years ago.

15.
Chempluschem ; 84(9): 1239-1244, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31944043

RESUMO

Triptycene-based organic molecules of intrinsic microporosity (OMIMs) with extended functionalized π-surfaces are excellent materials for gas sorption and separation. In this study, the affinities of triptycene-based OMIM affinity materials on 195 MHz high-fundamental-frequency quartz crystal microbalances (HFF-QCMs) for hazardous and illicit compounds such as piperonal and (-)-norephedrine were determined. Both new and existing porous triptycene-based affinity materials were investigated, resulting in very high sensitivities and selectivities that could be applied for sensing purposes. Remarkable results were found for safrole - a starting material for illicit compounds such as ecstasy. A systematic approach highlights the effects of different size of π-surfaces of these affinity materials, allowing a classification of the properties that might be optimal for the design of future OMIM-based affinity materials.

16.
Org Lett ; 20(22): 7270-7273, 2018 11 16.
Artigo em Inglês | MEDLINE | ID: mdl-30394096

RESUMO

A facile three-step synthetic route to heteroannulated extended coronenes via a selective bromination of diarenoperylenes as the key step is presented. The heteroannulated coronenes were characterized by X-ray crystallography and by photophysical and electrochemical means.

17.
Acc Chem Res ; 51(10): 2411-2422, 2018 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-30203648

RESUMO

The interest in shape-persistent organic cages is nearly as old as the interest in supramolecular chemistry. In the beginning, organic cages have often been synthesized in a stepwise manner, which is not only laborious but very often also accompanied by low overall yields. In 1988, MacDowell published the one pot high-yielding synthesis of [2 + 3] imine cages based on TREN and aromatic dialdehydes, exploiting the reversible condensation of amines and aldehydes to  imines, which was later used by others to make even larger cages on the basis of resorcinarenes. In 2008, the synthesis and characterization of an adamantoid [4 + 6] imine cage by condensation of a C3 v-symmetric triaminotriptycene and commercially available 4- tert-butyl salicyldialdehyde was introduced by the author, which was the ignition of our group activities in this research area. In 2011, we published the first gas-sorption data for this [4 + 6] imine cage: with a measured specific surface area of SABET = 1377 m2/g according to the model of Brunauer-Emmett-Teller (BET) this was twice as high as for the reported smaller cages of Cooper. For a second desolvated polymorph of the same cage, an even higher SABET = 2071 m2/g was determined; still one of the highest surface areas until date for porous organic molecular materials. Subsequently, the influence of the substituent in 4-position of the salicyldialdehyde for the reaction to [4 + 6] imine cages was investigated as well as the role of the phenolic hydroxyl group. It turned out that the phenolic hydroxyl group is crucial as directing group to increase the formation of the cage as well as stabilize the structure by cyclic six-membered intramolecular hydrogen bonds. The concept was extended to other imine-based cages of different geometry and size. For instance, a [4 + 4] cubic structure from triptycene trissalicylaldehyde and triptycene triamine was accessible as an amorphous insoluble solid, able to adsorb 18.2 wt % CO2 at ambient conditions. To gain further insight into the structural needs of the molecular precursors, rigidity and preorientation of reacting sites were investigated on prismatic [2 + 3] and truncated tetrahedral [4 + 4] imine cages, showing that rigidity and preorientation is beneficial or even crucial for cage formation. Furthermore, chiral self-sorting was studied on the basic of racemic triamines. Besides imine condensation, we explored the reversible formation of boronic esters from boronic acids and diols. Triptycene tetraol with its 120° angle between the aromatic units has been used in the condensation with benzene triboronic acid to achieve a large cuboctahedral [12 + 8] cage with pore dimensions of 2 nm, which are by IUPAC definition mesoporous. After activation the measured specific surface area was SABET = 3758 m2/g, a number rarely achieved even for other porous compounds such as threedimensional framework materials. Smaller tetrahedral [4 + 6] boronic ester cages were synthesized too. These cages show a selective gas sorption with preference of saturated hydrocarbon ethane over ethylene and acetylene. What distinguishes porous materials derived from molecular cages from three-dimensional frameworks or networks the most is their solubility; thus, the cages are soluble porous units (SPUs) in a broader sense. Taking advantage of this, [4 + 6] imine cages were postfunctionalized in solution to change the gas sorption properties in the crystalline state. Furthermore, cage solutions were spray-coated onto quartz crystal microbalances to enhance affinity and selectivity for sensing of airborne analytes. In this Account, the contributions from our lab on porous organic cages are presented.

18.
Chemistry ; 24(44): 11438-11443, 2018 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-29897652

RESUMO

In recent years the interest of shape-persistent organic cage compounds synthesized by dynamic covalent chemistry (DCC) has risen, because these cages are potentially interesting for gas sorption or -separation. One such reaction in DCC is the condensation of boronic acids with diols to form boronic esters. Most interestingly, the variety of geometries and sizes for boronic ester cages is much lower than that of, for example, imine-based cages. Here, a small series of shape-persistent [4+6] tetrahedral boronic ester cages is introduced. One cage has a high specific surface area of 511 m2 g-1 and selectively adsorbs ethane over ethylene and acetylene.

19.
Angew Chem Int Ed Engl ; 57(35): 11321-11324, 2018 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-29938890

RESUMO

Tribenzotriquinacene (TBTQ) is a bowl-shaped molecule that has been widely used as a molecular building block in supramolecular and materials chemistry. Especially C3 -symmetric threefold-substituted TBTQs are interesting for these purposes. Until now a general and selective synthetic approach to those C3 -symmetric products was lacking, mainly because the typically used electrophilic aromatic substitution reactions of the parent TBTQ hydrocarbons produce predominantly the C1 isomer over the C3 isomer (3:1 statistical ratio). Herein we introduce a threefold borylation of TBTQ with the C3 isomer as the main product (2.6:1 C3 /C1 ratio). The borylated TBTQ can be converted in good yields into other C3 -symmetric TBTQs, thus allowing straightforward synthetic access to new building blocks for supramolecular and materials chemistry.

20.
Chemistry ; 24(44): 11433-11437, 2018 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-29846023

RESUMO

In 2013 the concept of OMIMs (organic molecules of intrinsic microporosity) was introduced by McKeown et al. These OMIMs are constructed on the basis of rigid molecular cores such as triptycene, spirobifluorenes, and others. Like shape-persistent organic cages, these are soluble discrete molecules and therefore an interesting alternative to 3D, insoluble porous materials, such as metal-organic frameworks, covalent-organic frameworks, or zeolites. OMIMs are chemically and thermally robust because the formation of strong covalent bonds has been used for their synthesis. To date, a few OMIMs have been reported, though most of them did not contain any functional unit to enhance gas sorption properties. This work introduces an isostructural series of metal-salphene based OMIMs with different metal ions (Zn2+ , Ni2+ , Cu2+ , Pd2+ , and Pt2+ ) integrated into the backbone. The influence of the metal centers on interaction with gas molecules has been investigated by gas sorption experiments.

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