Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 14 de 14
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Artigo em Inglês | MEDLINE | ID: mdl-31793169

RESUMO

Nitrogen-doped polycyclic aromatic hydrocarbons (aza-PAHs) have found broad applications in material sciences. Herein, a modular electrochemical synthesis of aza-PAHs was developed via a rhodium-catalyzed cascade C-H activation and alkyne annulation. A multifunctional O-methylamidoxime enabled the high chemo- and regioselectivity. The isolation of two key rhodacyclic intermediates made it possible to delineate the exact order of three C-H activation steps. In addition, the metalla-electrocatalyzed multiple C-H transformation is characterized by unique functional group tolerance, including highly reactive iodo and azido groups.

2.
Chemistry ; 2019 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-31875327

RESUMO

Electrophotochemistry has enabled arene C-H trifluoromethylation with the Langlois reagent CF3 SO2 Na under mild reaction conditions. The merger of electrosynthesis and photoredox catalysis provided a chemical oxidant-free approach for the generation of the CF3 radical. The electrophotochemistry was carried out in an operationally simple manner, setting the stage for challenging C-H trifluoromethylations of unactivated arenes and heteroarenes. The robust nature of the electrophotochemical manifold was reflected by a wide scope, including electron-rich and electron-deficient benzenes, as well as naturally occurring heteroarenes. Electrophotochemical C-H trifluoromethylation was further achieved in flow with a modular electro-flow-cell equipped with an in-operando monitoring unit for on-line flow-NMR spectroscopy, providing support for the single electron transfer processes.

3.
J Am Chem Soc ; 141(43): 17198-17206, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31549815

RESUMO

A flow-metallaelectro-catalyzed C-H activation was realized in terms of robust rhodaelectro-catalyzed alkyne annulations. To this end, a modular electro-flow cell with a porous graphite felt anode was designed to ensure efficient turnover. Thereby, a variety of C-H/N-H functionalizations proved amenable for alkyne annulations with high levels of regioselectivity and functional group tolerance, viable in both an inter- or intramolecular manner. The electro-flow C-H activation allowed easy scale up, while in-operando kinetic analysis was accomplished by online flow-NMR spectroscopy. Mechanistic studies suggest an oxidatively induced reductive elimination pathway on rhodium(III) in an electrocatalytic regime.

4.
Angew Chem Int Ed Engl ; 58(19): 6342-6346, 2019 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-30835907

RESUMO

Rapid access to structurally diversified polycyclic aromatic hydrocarbons (PAHs) in a controlled manner is of key significance in materials sciences. Herein, we describe a strategy featuring two distinct electrocatalytic C-H transformations for the synthesis of novel nonplanar PAHs. The combination of rhodaelectrooxidative C-H activation/[2+2+2] alkyne annulation of easily accessible boronic acids with electrocatalytic cyclodehydrogenation provided modular access to diversely substituted PAHs with electricity as a sustainable oxidant. The unique molecular topology as well as the photophysical and electronic properties of the thus obtained PAHs were fully analyzed. The unique power of this metallaelectrocatalysis method was demonstrated by the chemoselective assembly of synthetically useful iodo-substituted PAHs.

5.
Dalton Trans ; 46(9): 3014-3024, 2017 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-28203677

RESUMO

We present a convenient synthesis of the first silylated bistetrazole via a catalyzed twin [2 + 3] cycloaddition of TMS-azide at cyanogen and its application to access bistetrazolatoborates, structurally characterized by a unique unsaturated ten-membered B2N4C4 heterocyclic system. Furthermore, new borate anions with two pyrazine-2,3-diolato ligands were synthesized from tetrafluoroborate salts and structurally characterized. Their organic cation can be exchanged for Li+via cation exchange. The conceptual relation of these new salts to lithium ion battery bisoxalalatoborate additive LiBOB, a prominent solid electrolyte interface (SEI) generator, is discussed.

6.
Angew Chem Int Ed Engl ; 56(11): 3090-3093, 2017 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-28229512

RESUMO

Herein we present the first superbase MHPN with two interacting P-ylide entities. Unlike classical proton sponges, this novel compound class has carbon atoms as basicity centers which are forced into close proximity by a naphthalene scaffold. The bisylide exhibits an experimental pKBH+  value of 33.3±0.2 on the MeCN scale and a calculated gas-phase proton affinity of 277.9 kcal mol-1 (M062X/6-311+G**//M062X/6-31G*+ZPVE method) exceeding that of the corresponding monoylide by nearly 15 kcal mol-1 . The origin of the unexpectedly high basicity of the new bisylide was investigated by NMR spectroscopic methods, single-crystal X-ray diffraction as well as theoretical calculations and can be partly attributed to the rapid exchange of the "acidic" proton between the two basic carbon atoms after protonation.

7.
Chemistry ; 22(45): 16292-16303, 2016 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-27717038

RESUMO

Depending on the amount of methanol present in solution, CO2 adducts of N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO2 Me] and [EMMIm][OCO2 Me]. The reactivity pattern of representative 1-ethyl-3-methyl-NHO-CO2 adduct 4 has been investigated and compared with the corresponding NHC-CO2 zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO-CO2 H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO-CO2 zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]2 cyanomalonate salts formed exemplify the first C-C bond-forming carboxylation reactions with NHO-activated CO2 . The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO-CO2 Me][X]. The first NHO-SO2 adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.

8.
Chem Commun (Camb) ; 52(78): 11646-8, 2016 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-27602991

RESUMO

Herein we report the synthesis of the first ionic liquids with the highly reactive and synthetically valuable phosphaethynolate (PCO(-)) anion. They are simply synthesised by the reaction of organic methylcarbonate salts with P(SiMe3)3. The products are obtained in near to quantitative yields and they are highly viscous liquids at room temperature or have low melting points for symmetric cations. Moreover, extending this synthetic strategy towards Sb(SiMe3)3 we discovered a simple synthesis for [P(nBu)3Me](+)3[Sb11](3-), the first organic cation salt comprising the Zintl-anion [Sb11](3-).

9.
Inorg Chem ; 55(13): 6725-30, 2016 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-27299466

RESUMO

K2Hg6Se7, Na2Hg3S2.51Se1.49, K2Hg3S1.03Se2.97, and K2Hg3S2.69Se1.31 were prepared by ionothermal treatment of K2Hg2Se3, Na2HgSe2, and K2Hg3Se4, respectively, in a nonclassical hydrosulfide ionic liquid (EMIm)(SH). In contrast to their lighter congeners, the title compounds could so far not be synthesized by inorganic polychalcogenide salt flux techniques. The applied method hence mimics polychalcogenide flux conditions, while operating at much lower temperatures below the decomposition temperature of the ionic liquid. It might thus be viewed as a pseudo-flux approach.

10.
Chemistry ; 22(12): 4218-30, 2016 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-26879604

RESUMO

We present the synthesis and thorough characterization of ionic liquids and organic salts based on hydrochalcogenide HE(-) (E=S, Se, Te) anions. Our approach is based on halide-, metal-, and water-free decarboxylation of methylcarbonate precursors under acidic conditions, resulting from the easily dissociating reagents H2 E. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy, thermal and single-crystal XRD analyses. The hydrosulfide salts were investigated with respect to their ability to dissolve elemental sulfur in varying stoichiometry. Thus-prepared polysulfide ILs were also analyzed by UV/Vis spectroscopy and cyclic voltammetry.

11.
Dalton Trans ; 44(46): 20045-55, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26525145

RESUMO

Three deep blue emitting Cu(I) compounds, [Cu(PPh3)tpym]PF6, [Cu(PPh3)tpym]BF4, and [Cu(PPh3)tpym]BPh4 (tpym = tris(2-pyridyl)methane, PPh3 = triphenylphosphine) featuring the tripodally coordinating tpym and the monodentate PPh3 ligands were studied with regard to their structural and photophysical properties. The compounds only differ in their respective counter ions which have a strong impact on the emission properties of the powder samples. For example, the emission quantum yield can be significantly increased for the neat material from less than 10% to more than 40% by exchanging BPh4(-) with PF6(-). These effects can be linked to different molecular packings which depend on the counter ion. In agreement with these results, it was found that the emission properties also strongly depend on the surrounding matrix environment which was elucidated by investigating photophysical properties of the compounds as powders, doped into a polymer matrix, and dissolved in a fluid solution, respectively. The observed differences in the emission behavior can be explained by different and pronounced distortions that occur in the excited state. These distortions are also displayed by density functional theory (DFT) calculations.

12.
Inorg Chem ; 54(19): 9568-75, 2015 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-26371537

RESUMO

A high-yield synthesis of the class of (trimethylsilyl)chalcogenolate organic salts [Cat][TMS-E] (E = S, Se, Te; Cat = BMPyr, DMPyr, NMe4, nBu3MeP) is presented. The title compounds have been prepared by the strictly aprotic reaction between the respective bis(trimethylsilyl)chalcogenide (TMS2E) and methylcarbonate ionic liquids (ILs). This constitutes a novel reaction behavior of methylcarbonate ILs, acting as a nucleophilic desilylating agent and a Lewis base instead of as a Brønsted base. Thus prepared silylchalcogenolate salts represent an activated form of the multifunctional TMS2E reactant series. Pyrrolidinium TMS-S salts have proven to be excellent precursors for the synthesis of pyrrolidinium hexasulfides. The scope of the desilylation reaction can be extended to other silyl-bearing synthons such as (trimethylsilyl)azide and (trimethylsilyl)cyanide.

13.
Dalton Trans ; 44(18): 8506-20, 2015 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-25434594

RESUMO

A new class of emissive and neutral Cu(I) compounds with tripodal ligands is presented. The complexes were characterized chemically, computationally, and photophysically. Under ambient conditions, the powders of the compounds exhibit yellow to red emission with quantum yields ranging from about 5% to 35%. The emission represents a thermally activated delayed fluorescence (TADF) combined with a short-lived phosphorescence which represents a rare situation and is a consequence of high spin-orbit coupling (SOC). In the series of the investigated compounds the non-radiative rates increase with decreasing emission energy according to the energy gap law while the radiative rate is almost constant. Furthermore, a well-fit linear dependence between the experimental emission energies and the transition energies calculated by DFT and TD-DFT methods could be established, thus supporting the applicability of these computational methods also to Cu(I) complexes.

14.
Inorg Chem ; 53(7): 3839-46, 2014 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-24635355

RESUMO

Herein we report on the new NH-acid N-(2,3,4,5,6-pentafluorophenyl)-N-nonafluoro-tert-butylamine, HN(C6F5)(C(CF3)3), bearing two different sterically demanding and strongly electron-withdrawing perfluorinated amine substituents. The title compound and seven of its alkaline and alkaline earth metal salts were synthesized and investigated concerning their thermal, spectroscopic, and structural properties. The Li, Na, K, Cs, and Mg salts were investigated by single-crystal XRD analysis. The molecular structures reveal interesting motifs such as manifold fluorine metal secondary interactions. The lithium and magnesium compounds exhibit a remarkable thermal stability and an unexpectedly high volatility. We believe that this report will provoke investigations to apply the corresponding anion in ionic liquids, in lithium electrolytes, and as a weakly electron-donating ligand in the preparation of highly Lewis-acidic main group, rare earth, or transition metal complexes.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA