Refine
Has Fulltext
- yes (12)
Is part of the Bibliography
- yes (12)
Year of publication
- 2021 (12) (remove)
Document Type
- Journal article (12)
Keywords
- inorganic chemistry (4)
- boron (3)
- Boron (2)
- radical (2)
- BN compounds (1)
- Beryllium (1)
- Biradikale (1)
- Bor-Carbonylkomplexe (1)
- Dichtefunktionalrechnungen (1)
- EDA-NOCV (1)
- Reduktionen (1)
- Umlagerungen (1)
- Wade’s rules (1)
- X-ray crystallography (1)
- aminyl radicals (1)
- aromaticity (1)
- azaborinines (1)
- bioimaging (1)
- bismuth amides (1)
- boranes (1)
- boroles (1)
- carborane (1)
- charge transfer (1)
- chromophores (1)
- computational chemistry (1)
- conjugated oligomers (1)
- cyclic alkyl(amino)carbene (1)
- cyclization (1)
- density functional calculations (1)
- diphosphanes (1)
- dual fluorescence (1)
- equilibrium (1)
- heavier pnictogens (1)
- hybrid materials (1)
- isoelectronic analogues (1)
- isomer (1)
- isomerization (1)
- luminescence (1)
- luminescent (1)
- metallacycles (1)
- nitrogen heterocycles (1)
- nucleic acid (1)
- oxidation (1)
- pericyclic reaction (1)
- phosphorus heterocycles (1)
- pnictogen coupling (1)
- polycycles (1)
- pyrenes (1)
- pyridinium (1)
- radical coupling (1)
- radical species (1)
- radicals (1)
- singlet oxygen (1)
- structure elucidation (1)
- tetramers (1)
- thiophene (1)
- threecoordinate boron (1)
- viologens (1)
- weak intermolecular coordination (1)
Institute
Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC\(_{6}\)H\(_{4}\))-closo-1,2-C\(_{2}\)B\(_{10}\)H\(_{10}\)-2-)\(_{2}\)(4-MeC\(_{6}\)H\(_{4}\))B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr\(_{2}\). Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1\(^{.−}\) was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1\(^{.−}\), their calculated geometries, and the S\(_{1}\) excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.
A series of highly substituted 1,2-azaborinines, including a phenylene-bridged bis-1,2-azaborinine, was synthesized from the reaction of 1,2-azaborete rhodium complexes with variously substituted alkynes. 1-Rhoda-3,2-azaborole complexes, which are accessible by phosphine addition to the corresponding 1,2-azaborete complexes, were also found to be suitable precursors for the synthesis of 1,2-azaborinines and readily reacted with alkynyl-substituted 1,2-azaborinines to generate new regioisomers of bi-1,2-azaborinines, which feature directly connected aromatic rings. Their molecular structures, which can be viewed as boron-nitrogen isosteres of biphenyls, show nearly perpendicular 1,2-azaborinine rings. The new method using rhodacycles instead of 1,2-azaborete complexes as precursors is shown to be more effective, allowing the synthesis of a wider range of 1,2-azaborinines.
Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels-Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long-established mechanistic picture of pericyclic rearrangements by demonstrating that seven-membered borepins (i. e., heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels-Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes.
Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen-Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl-Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergestützte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar]\(^{.-}\) Zwischenstufe. Weiterführende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.
Phenylpyridyl-fused boroles [TipPBB1]\(_4\) and TipPBB2 were synthesized and their properties investigated. [TipPBB1]\(_4\) forms a tetramer in both the solid state and solution. TipPBB2 contains a 4-coordinate boron atom in the solid state but dissociates to give a 3-coordinate boron species in solution. TipPBB2 shows interesting temperature-dependent dual fluorescence in solution because of the equilibrium between 3- and 4-coordinate boron species due to weak N⋅⋅⋅B intermolecular coordination.
The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P−P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B−B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.
Dithiophene‐Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics
(2021)
Access to dithiophene‐fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one‐electron reduction processes. The weak aromatic character of the novel 1,2,7‐azadiborepin ring is demonstrated with in‐depth theoretical investigations using nucleus‐independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.
A series of methylene-bridged bis(triarylboranes) has been synthesized via two complementary routes using metal-free catalytic Si/B exchange condensation under mild conditions. The title compounds comprise two borane moieties that show effective internal π-conjugation involving the respective boron centers and the adjacent hetaryl groups. Conjugation between both borane units, however, is disrupted by the aliphatic linker. Cyclic voltammetry revealed minimal electronic communication between the boron centers, as evidenced by two closely spaced reduction processes. The UV-vis spectra showed bathochromic shifted absorption bands compared to related monoboranes, which is attributed to the methylene bridge. A further red-shift results upon introduction of methyl or SiMe\(_3\) groups at the terminal thiophene rings.
The synthesis, photophysical, and electrochemical properties of selectively mono-, bis- and tris-dimethylamino- and trimethylammonium-substituted bis-triarylborane bithiophene chromophores are presented along with the water solubility and singlet oxygen sensitizing efficiency of the cationic compounds Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\). Comparison with the mono-triarylboranes reveals the large influence of the bridging unit on the properties of the bis-triarylboranes, especially those of the cationic compounds. Based on these preliminary investigations, the interactions of Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\) with DNA, RNA, and DNApore were investigated in buffered solutions. The same compounds were investigated for their ability to enter and localize within organelles of human lung carcinoma (A549) and normal lung (WI38) cells showing that not only the number of charges but also their distribution over the chromophore influences interactions and staining properties.
Bismuth Amides Mediate Facile and Highly Selective Pn–Pn Radical‐Coupling Reactions (Pn=N, P, As)
(2021)
The controlled release of well‐defined radical species under mild conditions for subsequent use in selective reactions is an important and challenging task in synthetic chemistry. We show here that simple bismuth amide species [Bi(NAr\(_2\))\(_3\)] readily release aminyl radicals [NAr\(_2\)]. at ambient temperature in solution. These reactions yield the corresponding hydrazines, Ar\(_2\)N−NAr\(_2\), as a result of highly selective N−N coupling. The exploitation of facile homolytic Bi−Pn bond cleavage for Pn−Pn bond formation was extended to higher homologues of the pnictogens (Pn=N–As): homoleptic bismuth amides mediate the highly selective dehydrocoupling of HPnR\(_2\) to give R\(_2\)Pn−PnR\(_2\). Analyses by NMR and EPR spectroscopy, single‐crystal X‐ray diffraction, and DFT calculations reveal low Bi−N homolytic bond‐dissociation energies, suggest radical coupling in the coordination sphere of bismuth, and reveal electronic and steric parameters as effective tools to control these reactions.
The reduction of a cyclic alkyl(amino)carbene (CAAC)-stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, UV/Vis spectroscopy and X-ray crystallography. DFT calculations show significant spin density at beryllium and confirm donor–acceptor bonding between an alkylberyllium radical fragment and a neutral CAAC ligand.
Two N-methylpyridinium compounds and analogous N-protonated salts of 2- and 2,7-substituted 4-pyridyl-pyrene compounds were synthesised and their crystal structures, photophysical properties both in solution and in the solid state, electrochemical and spectroelectrochemical properties were studied. Upon methylation or protonation, the emission maxima are significantly bathochromically shifted compared to the neutral compounds, although the absorption maxima remain almost unchanged. As a result, the cationic compounds show very large apparent Stokes shifts of up to 7200 cm\(^{-1}\). The N-methylpyridinium compounds have a single reduction at ca. −1.5 V vs. Fc/Fc\(^+\) in MeCN. While the reduction process was reversible for the 2,7-disubstituted compound, it was irreversible for the mono-substituted one. Experimental findings are complemented by DFT and TD-DFT calculations. Furthermore, the N-methylpyridinium compounds show strong interactions with calf thymus (ct)-DNA, presumably by intercalation, which paves the way for further applications of these multi-functional compounds as potential DNA-bioactive agents.