C-Functionalized, Air- and Water-Stable 9,10-Dihydro-9,10-diboraanthracenes: Efficient Blue to Red Emitting Luminophores

Abstract

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.

Reversible Dihydrogen Activation by Reduced Aryl Boranes as Main‐Group Ambiphiles

“…[7] Herein, we show that [DBA] 2À is actually capable of adding H 2 across the two boron atoms under mild conditions.T he ability to undergo this prototypical reaction renders our system unique among main-group ambiphiles (MGAs). In contrast, selective formation of Li 2 [3]w as observed upon the treatment of Li 2 [1]w ith excess HC CtBu (4 equiv) at 50 8 8Cf or 3days.R emarkably,t he crude product gave rise to only one set of signals in the 1 Hand 13 C{ 1 H} NMR spectra, thus ruling out the presence of syn/anti isomers.Inthe majority of crystallographically characterized DBAd erivatives with tetracoordinated boron atoms,t he central B 2 C 4 ring adopts aboat conformation in the solid state (the same is true for Li 2 [5]; Figure 5b;s ee below). In contrast, selective formation of Li 2 [3]w as observed upon the treatment of Li 2 [1]w ith excess HC CtBu (4 equiv) at 50 8 8Cf or 3days.R emarkably,t he crude product gave rise to only one set of signals in the 1 Hand 13 C{ 1 H} NMR spectra, thus ruling out the presence of syn/anti isomers.Inthe majority of crystallographically characterized DBAd erivatives with tetracoordinated boron atoms,t he central B 2 C 4 ring adopts aboat conformation in the solid state (the same is true for Li 2 [5]; Figure 5b;s ee below).…”

“…In the presence of excess H 2 (< 1atm) and at 100 8 8C, solutions of Li 2 [1] product Li 2 [5]i nq uantitative yield after 2days (Scheme 2). Contrary to Li 2 [3], vacuum-sealed solutions of Li 2 [5]inTHF showed no tendencyt ol iberate H 2 at temperatures up to 100 8 8C. Thechemical composition of Li 2 [5]was confirmed by ac omparison of its NMR data with those of as ample independently prepared from 9,10-dihydroxy-DBAa nd LiAlH 4 .…”

“…[12] According to X-ray crystal-structure analysis of [Li(thf) 2 ][Li(thf)] [5], the central B 2 C 4 heterocycle of the dianionic moiety [5] 2À adopts ab oat conformation with adihedral angle C1B1C11//C2B2C12 of 56.2(3)8 8 (Figure 5b). As ab lind test, we also heated solutions of Li 2 [1]i nT HF in the absence of H 2 to 100 8 8C, but observed no formation of Li 2 [5]. As ab lind test, we also heated solutions of Li 2 [1]i nT HF in the absence of H 2 to 100 8 8C, but observed no formation of Li 2 [5].…”

Fundamental and Applied Properties of Borocations

“…13, left) [10]. Furthermore, Wagner and co-workers proposed an analogous intramolecularly activated electrophile 21 in the dehydroboration of arenes [66].…”

Efficient Access to Substituted Silafluorenes by Nickel‐Catalyzed Reactions of Biphenylenes with Et2SiH2

“…We have a long-standing interest in boron-doped aromatics [11][12][13][14][15] and have developed inter alia a protocol for the synthesis of 9-borafluorenes by treatment of the corresponding 9-silafluorene derivatives with BBr 3 . [12,13] However, convenient access to silafluorenes with an asymmetric substitution pattern in the 4-positions is lacking as of yet.…”