Unexpected Michael Additions on the Way to 2.3,8.9-Dibenzanthanthrenes with Interesting Structural Properties.

The synthesis and properties of a new polycyclic aromatic hydrocarbon containing eight annulated rings and based on the anthanthrene core is described. An unexpected, nucleophile-dependent Michael addition to a dibenzanthanthrene-1,7-dione is found, giving a product with three triisopropylsilylacetylene units and a remarkable solid-state structure (as determined by X-ray crystallography).

Stimuli-responsive chromism in organophosphorus chemistry.

Changes in color are one of the most obvious and easily followed responses that can be induced by an external stimulus. π-Conjugated organophosphorus compounds are on the rise to challenge established systems by opening up new and simple pathways to diversely modified optoelectronic properties--the main challenge for the development of new chromic materials. Relevant stimuli highlighted in this Frontier article include electronic current (electrochromism), light (photochromism), solvent polarity (solvatochromism), aggregation formation (aggregation induced emission, AIE), mechanical force (mechanochromism), temperature (thermochromism), organic solvent vapor (vapochromism), and pH (halochromism).

A Convenient N-Arylation Route for Electron-Deficient Pyridines: The Case of π-Extended Electrochromic Phosphaviologens.

A simple and representative procedure for the synthesis of N,N'-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N'-disubstituted 4,4'-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO-LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corroborated by quantum chemical calculations. Detailed characterizations of the singly reduced radical species by EPR spectroscopy and DFT calculations verified delocalization of the radical over the extended π-system. Finally, to gain deeper insight into the suitability of the new compounds as electroactive and electrochromic materials, multicolored proof-of-concept electrochomic devices were manufactured.

C-Functionalized, air- and water-stable 9,10-dihydro-9,10-diboraanthracenes: efficient blue to red emitting luminophores.

9,10-Dihydro-9,10-diboraanthracene (DBA) provides a versatile scaffold for the development of boron-doped organic luminophores. Symmetrically C-halogenated DBAs are obtained through the condensation of 4-bromo-1,2-bis(trimethylsilyl)benzene or 4,5-dichloro-1,2-bis(trimethylsilyl)benzene with BBr3 in hexane. Unsymmetrically C-halogenated DBAs are formed via an electrophilic solvent activation reaction if the synthesis is carried out in o-xylene. Mechanistic insight has been achieved by in situ NMR spectroscopy, which revealed C-halogenated 1,2-bis(dibromoboryl)benzenes to be the key intermediates. Treatment of the primary 9,10-dibromo-DBAs with MesMgBr yields air- and water-stable C-halogenated 9,10-dimesityl-DBAs (2-Br-6,7-Me2-DBA(Mes)2; 2,6-Br2-DBA(Mes)2; 2,3-Cl2-6,7-Me2-DBA(Mes)2; 2,3,6,7-Cl4-DBA(Mes)2). Subsequent Stille-type C-C-coupling reactions give access to corresponding phenyl, 2-thienyl, and p-N,N-diphenylaminophenyl derivatives, which act as highly emissive donor-acceptor dyads or donor-acceptor-donor triads both in solution and in the solid state. 2-Thienyl was chosen as a model substituent to show that already a variation of the number and/or the positional distribution of the donor groups suffices to tune the emission wavelength of the resulting benchtop stable compounds from 469 nm (blue) to 540 nm (green). A further shift of the fluorescence maximum to 594 nm (red) can be achieved by switching from 2-thienyl to p-aminophenyl groups. A comparison of the optoelectronic properties of selected C-substituted DBA(Mes)2 derivatives with those of the isostructural anthracene analogues unveiled the following: (i) The DBA core is a much better electron acceptor. (ii) The emission colors of DBAs fall in the visible range of the spectrum (blue to orange), while anthracenes emit exclusively in the near-ultraviolet to blue wavelength regime. (iii) DBAs show significantly higher solid-state quantum yields.

Synthesis of bromo-, boryl-, and stannyl-functionalized 1,2-bis(trimethylsilyl)benzenes via Diels-Alder or C-H activation reactions.

1,2-Bis(trimethylsilyl)benzenes are key starting materials for the synthesis of benzyne precursors, Lewis acid catalysts, and certain luminophores. We have developed efficient, high-yield routes to functionalized 4-R-1,2-bis(trimethylsilyl)benzenes, starting from either 1,2-bis(trimethylsilyl)acetylene/5-bromopyran-2-one (2) or 1,2-bis(trimethylsilyl)benzene (1)/bis(pinacolato)diborane. In the first reaction, 5 (R = Br) is obtained through a cobalt-catalyzed Diels-Alder cycloaddition. The second reaction proceeds via iridium-mediated C-H activation and provides 8 (R = Bpin). Besides its use as a Suzuki reagent, compound 8 can be converted into 5 with CuBr(2) in i-PrOH/MeOH/H(2)O. Lithium-bromine exchange on 5, followed by the addition of Me(3)SnCl, gives 10 (R = SnMe(3)), which we have applied for Stille coupling reactions. A Pd-catalyzed C-C coupling reaction between 5 and 8 leads to the corresponding tetrasilylbiphenyl derivative. The bromo derivative 5 cleanly undergoes Suzuki reactions with electron-rich as well as electron-poor phenylboronic acids.