Browsing by Author "Baro, Angelika"

Now showing 1 - 5 of 5

Open Access
Columnar propeller‐like 1,3,5‐triphenylbenzenes : probing the effect of chlorine on the Suzuki cross‐coupling and liquid crystalline properties
(2020) Grunwald, Marco André; Wöhrle, Tobias; Forschner, Robert; Baro, Angelika; Laschat, Sabine
Suzuki cross‐couplings either between chlorinated N‐methyliminodiacetic acid (MIDA)‐protected aryl boronates and 1,3,5‐tribromobenzene or between chlorinated aryl bromides and phenyltrisboronic species to star‐shaped 1,3,5‐triphenylbenzenes with different substitution patterns and chloro substituents at the outer phenyl rings were studied. The chlorinated precursors required for the respective reaction were synthesized and characterized. Depending on the used coupling reaction target triphenylbenzenes were isolated in yields between 42 % and 88 %. Their mesomorphic properties were influenced by the substitution pattern and number of peripheral chlorine atoms. Triphenylbenzene with 3,5‐alkoxy substitution and H in para‐position self‐assembled into either columnar hexagonal (Colh) mesophases or a soft crystal. While threefold chloro substitution in meta‐position of the outer phenyl rings led to stable room temperature Colho phases, triphenylbenzenes with threefold para‐chloro or 3,5‐dichloro substitution were non‐mesomorphic. Based on X‐ray diffraction data a helical packing model for the observed phases similar to that of related alkoxy‐substituted triphenylbenzenes was proposed.
Open Access
Efficient and spatially controlled functionalization of SBA‐15 and initial results in asymmetric Rh‐catalyzed 1,2‐additions under confinement
(2021) Beurer, Ann‐Katrin; Kirchhof, Manuel; Bruckner, Johanna R.; Frey, Wolfgang; Baro, Angelika; Dyballa, Michael; Giesselmann, Frank; Laschat, Sabine; Traa, Yvonne
Selectively functionalized mesoporous silica may considerably advance heterogeneous catalysis through the controlled immobilization of highly selective complex catalysts inside the mesopores. However, spatially controlled functionalization and the precise analytical verification are still a challenge. In this publication, we report a method, which ensures a selective functionalization of the mesopore surface with a clickable linker and thus makes it possible to study confinement effects during catalyzed reactions. First, we passivate the silanol groups on the particle surface and in the pore entrances of the mesoporous silica material SBA‐15 with 1,1,1‐trimethyl‐N‐(trimethylsilyl)silanamine. Then we remove the template by solvent extraction and functionalize the pore walls with 3‐azidopropyltriethoxysilane before we click the catalyst. In initial experiments of asymmetric Rh‐catalyzed 1,2‐addition, we investigate the performance of a catalyst clicked selectively in the mesopores and compare it to the dissolved catalyst as well as to the catalyst immobilized exclusively on the external surface of SBA‐15.
Open Access
Novel discotic boroxines : synthesis and mesomorphic properties
(2014) Wöhrle, Tobias; Baro, Angelika; Laschat, Sabine
Discotic liquid crystals have attracted the attention of many research groups worldwide. Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications could be realized. Aryl boronic acids are valuable reagents for a number of metal-catalyzed reactions, and boroxines, the cyclic trimers of organoboronic acids, may serve as useful building blocks. However, surprisingly little is known about liquid crystalline boroxines. We described a new synthetic approach to highly substituted triphenylboroxines and investigated their liquid crystalline properties. The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives showed broad mesophases for a minimum alkyl chain length of C9. Textures observed under polarizing optical microscope indicated a columnar hexagonal (Colh) mesophase geometry that was confirmed by X-ray diffraction experiments.
Open Access
Synthesis and biological evaluation of a library of AGE‐related amino acid triazole crosslinkers
(2020) Icik, Esra; Jolly, Anthony; Löffler, Paul; Agelidis, Nektarios; Bugdayci, Bakiye; Altevogt, Luca; Bilitewski, Ursula; Baro, Angelika; Laschat, Sabine
Three N‐Boc‐protected amino acids, l‐serine, l‐aspartic, and l‐glutamic acid, were either converted into their methyl azidoalkanoates or various alkynes via Bestmann‐Ohira strategy or via reaction with propargylamine and propargyl bromide, respectively. The Cu‐catalyzed click reaction provided a library of amino acid based triazoles, which were further N‐methylated to triazolium iodides or deprotected and precipitated as free amino acid triazole dihydrochlorides. The biological properties of all derivatives were investigated by cytotoxicity assay (against L929 mouse fibroblasts) and broth microdilution method (E. coli ΔTolC and S. aureus). First results reveal complete inactivity for triazolium iodides with cell viabilities and microbial growths nearly 100 %, indicating them as possible analogs of advanced glycation endproducts (AGEs).
Open Access
Synthesis and liquid crystalline self‐assembly of concave diindoles with a hydropentalene core
(2021) Bühlmeyer, Andrea; Ehni, Philipp; Ullmann, Dustin; Frey, Wolfgang; Baro, Angelika; Laschat, Sabine
Fischer indole reaction of Weiss diketone with 4‐bromophenylhydrazine provided the 2,8‐dibromo‐hexahydropentaleno[2,1‐b:5,4‐b’]diindole key intermediate, which was converted to the target compounds by N‐protection/Suzuki cross‐coupling. Variation of protecting groups, mesogenic units, and their alkoxy substitution gave calamitic diindole mesogens. Both N‐protection and alkoxy chain influenced the mesomorphic properties of phenyl diindoles. Among the differently N‐protected derivatives only ethylcarbamate‐protected ones formed enantiotropic mesophases. Mesophase range and type were controlled by the chain lengths: chains≤C12 gave nematic (N) phases, diindoles with side chains≥C14 formed additional lower temperature smectic (SmA) phases. Irrespective of the chain lengths 4′‐alkyloxybiphenyl diindoles formed N and SmA phases upon first heating but tended to decomposition below their clearing points. X‐ray crystal structure analysis of bis(4′‐decyloxy)biphenyl diindole reveals that in the solid‐state the folding angle of the hydropentalene core caused an almost perpendicular orientation of the two indole/biphenyl parts with respect to each other.