Alexandra Friedrich

Preparing (Multi)Fluoroarenes as Building Blocks for Synthesis: Nickel-Catalyzed Borylation of Polyfluoroarenes via C–F Bond Cleavage

The [Ni(IMes)2]-catalyzed transformation of fluoroarenes into arylboronic acid pinacol esters via C-F bond activation and transmetalation with bis(pinacolato)diboron (B2pin2) is reported. Various partially fluorinated arenes with different degrees of fluorination were converted into their corresponding boronate esters.

NHC Nickel-Catalyzed Suzuki–Miyaura Cross-Coupling Reactions of Aryl Boronate Esters with Perfluorobenzenes

An efficient Suzuki-Miyaura cross-coupling reaction of perfluorinated arenes with aryl boronate esters using NHC nickel complexes as catalysts is described. The efficiencies of different boronate esters (p-tolyl-Beg, p-tolyl-Bneop, p-tolyl-Bpin, p-tolyl-Bcat) and the corresponding boronic acid (p-tolyl-B(OH)2) in this type of cross-coupling reaction were evaluated (eg, ethyleneglycolato; neop, neopentylglycolato; pin, pinacolato; cat, catecholato). Aryl-Beg was shown to be the most reactive boronate ester among those studied. The use of CsF as an additive is essential for an efficient reaction of hexafluorobenzene with aryl neopentylglycolboronates.

Preparation, Properties, and Structures of the Radical Anions and Dianions of Azapentacenes

A series of diazapentacenes (5,14-diethynyldibenzo[b,i]phenazine, 6,13-diethynylnaphtho[2,3-b]phenazine) and tetraazapentacenes (7,12-diethynylbenzo[g]quinoxalino[2,3-b]quinoxaline, 6,13-diethynylquinoxalino[2,3-b]phenazine) were reduced to their radical anions and dianions, employing either potassium anthracenide or lithium naphthalenide in THF. The anionic species formed were investigated by UV-vis-NIR, fluorescence and EPR spectroscopy, spectroelectrochemistry, and quantum chemical calculations. Single crystal X-ray structures of three of their radical anions and of three of their dianions were obtained. In contrast to the acenes, the anions of the azapentacenes are persistent and, in some cases, even moderately stable toward air, and were characterized.

Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals

We show that by judicious choice of substituents at the 2- and 7-positions of pyrene, the frontier orbital order of pyrene can be modified, giving enhanced control over the nature and properties of the photoexcited states and the redox potentials. Specifically, we introduced a julolidine-like moiety and Bmes2 (mes=2,4,6-Me3 C6 H2 ) as very strong donor (D) and acceptor (A), respectively, giving 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, in which the donor destabilizes the HOMO-1 and the acceptor stabilizes the LUMO+1 of the pyrene core. Consequently, for 2,7-substituted pyrene derivatives, unusual properties are obtained. For example, very large bathochromic shifts were observed for all of our compounds, and unprecedented green light emission occurs for the D/D system. In addition, very high radiative rate constants in solution and in the solid state were recorded for the D-π-D- and D-π-A-substituted compounds. All compounds show reversible one-electron oxidations, and Jul2 Pyr exhibits a second oxidation, with the largest potential splitting (ΔE=440 mV) thus far reported for 2,7-substituted pyrenes. Spectroelectrochemical measurements confirm an unexpectedly strong coupling between the 2,7-substituents in our pyrene derivatives.

Synthesis, Photophysical, and Electrochemical Properties of Pyrenes Substituted with Donors or Acceptors at the 4- or 4,9-Positions

We report herein an efficient and direct functionalization of the 4,9-positions of pyrene by Ir-catalyzed borylation. Three pinacol boronates (-Bpin), including 4-(Bpin)-2,7-di( tert-butyl)pyrene (5), 4,9- bis(Bpin)-2,7-di( tert-butyl)pyrene (6), and 4,10- bis(Bpin)-2,7-di( tert-butyl)pyrene (7), were synthesized. The structures of 6 and 7 have been confirmed by single-crystal X-ray diffraction. To demonstrate the utility of these compounds, donor (NPh2)-substituted compounds 4-diphenylamino-2,7-di( tert-butyl)pyrene (1) and 4,9- bis(diphenylamino)-2,7-di( tert-butyl)pyrene (2) have been synthesized on a gram scale. Acceptor (BMes2)-substituted compounds 4,9- bis(BMes2)pyrene (3) and 4,9- bis(BMes2)-1,2,3,6,7,8-hexahydropyrene (4) were synthesized for comparison. The photophysical and electrochemical properties of compounds 1-4 have been studied both experimentally and theoretically. The S0 → S1 transitions of the 4- or 4,9-disubstituted pyrenes, 1-3, are allowed, with moderate fluorescence quantum yields and radiative decay rates. The photophysical and electrochemical properties of 1-3 were compared with the 2,6-naphthalenylene-cored compound 4 as well as the previously reported 2,7- and 1,6- pyrenylene-cored compounds.

Bromination Improves the Electron Mobility of Tetraazapentacene

A cyclocondensation of TIPS-ethynyl-substituted diaminoarenes with in situ obtained 4,5-dibromocyclohexa-3,5-diene-1,2-dione has led to the synthesis of tetrabromotetraazapentacene (BrTAP). BrTAP is easily reduced to its air-stable radical anion and electron mobilities >0.56 cm2  V-1  s-1 can be achieved in thin-film transistors.

CCDC 1529577: Experimental Crystal Structure Determination

Related Article: Martin Eck, Sabrina Wurtemberger-Pietsch, Antonius Eichhorn, Johannes H. J. Berthel, Rudiger Bertermann, Ursula S. D. Paul, Heidi Schneider, Alexandra Friedrich, Christian Kleeberg, Udo Radius, Todd B. Marder|2017|Dalton Trans.|46|3661|doi:10.1039/C7DT00334J