Bridge of Si: Intramolecular direct arylation of 2‐(arylsilyl)aryl triflates is catalyzed smoothly by Pd(OAc)2/PCy3 in the presence of Et2NH in dimethylacetamide (DMA), giving rise to the corresponding silicon‐bridged biaryls in good to excellent yields. The new approach has led to the synthesis of a silicon‐bridged 2‐phenylindole (see scheme) that exhibits blue photoluminescence in the solid state with extremely high quantum yields.

We have discovered that the combination of Pd(OAc)(2)/o-chloranil can catalyze the direct C-H bond arylation of polycyclic aromatic hydrocarbons (PAHs) with arylboroxins that occurs selectively at the K-region. The sequential integration of Pd-catalyzed direct arylation of PAHs and FeCl(3)-mediated cyclodehydrogenation is effective in rapidly extending a parent PAH π-system with high directionality.

Palladium-catalyzed intramolecular direct arylation of 2-[(2-pyrrolyl)silyl]aryl triflates gives 3,2'-silicon-bridged 2-arylindoles and -pyrroles in good to high yields. The reaction proceeds through cleavage of C-OTf, C-Si, and C-H bonds to result in the formation of C-C and C-Si bonds. Various kinds of functional groups such as OMe, CN, Cl, F, and SiMe(3) tolerated the conditions. The new reaction allows synthesis of functionalized Si-bridged 2-arylindoles that emit intense and efficient blue fluorescence in the solid state.

The preparation of 4,5-dimethylsilylene- or 4,5-tetramethyldisilylene-bridged 9-silafluorenes was achieved by lithiation of 2,2',6,6'-tetrabromobiphenyls followed by silylation with dichlorodimethylsilane or 1,2-dichloro-1,1,2,2-tetramethyldisilane, respectively. X-ray analysis of the silylene-bridged silafluorene revealed that the molecular framework was perfectly planar and four Si-C(methyl) sigma bonds were completely orthogonal to the plane. Both the silicon atoms and the benzene rings were significantly deformed from the normal tetrahedral and hexagon shapes, respectively. The silicon bridge at the 4,5-positions was found to induce a red shift of the absorption and fluorescence spectra measured in cyclohexane, compared with 9-silafluorenes. It is remarkable that the disilylene-bridged silafluorene emitted blue light (lambda(em)=450 nm) with a large Stokes shift. The emission maxima of the silicon-bridged silafluorenes in thin films were similar to those measured in cyclohexane solution. DFT calculations suggested that introduction of the silicon bridge led to increases in both the HOMO and LUMO levels compared with 9-silafluorene.

Recently, π-conjugated molecules containing a 9-silafluorene moiety have attracted considerable attention owing to their potential applications in organic electronics. While most studies focus on the oligomers and (co)polymers of 9-silafluorenes, functionalized 9-silafluorenes themselves remain unexplored. In this paper, we describe the preparation, photophysical properties, and theoretical calculations of 2-amino-7-acceptor-9-silafluorenes and we show that these silafluorenes can potentially be used as novel chromophores for functional organic materials. The D-π-A type silafluorenes were prepared by Pd-catalyzed intramolecular coupling of 2-(3-aminophenyldiisopropylsilyl)aryl triflates and the subsequent functional group conversion through reduction of the cyano group to a formyl and Knoevenagel condensation of the formyl group with malonitrile. The UV−visible absorption and fluorescence spectra of the D-π-A type silafluorenes exhibited a red-shift when the electron-withdrawing nature of the acceptor increased. The emission maxima of the fluorescence were highly dependent on the solvent. In the cases of formyl- and dicyanoethenyl-substituted silafluorenes, the emission colors ranged from blue to yellow for the formyl derivatives and from green to red for the dicyanoethenyl derivatives. The noticeable fluorescence solvatochromism suggests the intramolecular charge-transfer character of the excited states. The silafluorenes also exhibited fluorescence in the solid state (e.g., a neat thin film and a doped polymer film), and the emission color was dependent on the polarity of the polymer. In the solid state, the quantum yields of diphenylamino derivatives were generally higher than those of dimethylamino derivatives, presumably because the bulky diphenylamino group prevented chromophores from assembling close to each other. A comparison of the photophysical properties and theoretical calculations of D-π-A type silafluorenes with those of the corresponding fluorenes revealed that the silicon bridge contributed to the extension of the effective conjugation length of the biphenyl moiety when the acceptor was either hydrogen, trifluoromethyl, or a cyano group, whereas there was no contribution of the silicon bridge to the π-extension in silafluorenes substituted by strong electron acceptors such as formyl and dicyanoethenyl groups. White photoluminescence was demonstrated with an excellent quantum yield of 0.81 in the solid state from the poly(methyl methacrylate) (PMMA) film doped with Ph2N/CHO- and Ph2N/CH(CN)2-substituted silafluorenes. This work reveals the potential of D-π-A type silafluorenes as versatile organic emitting materials.

Pd(OAc)(2)/o-chloranil/M(OTf)(n) can effectively promote the C-H arylation of fluoranthene with arylboron compounds or arylsilanes. The reaction takes place with high regioselectivity at the C3 position of fluoranthene. Moreover, the new catalytic system allows the use of unfunctionalized arenes as coupling partners in the arylation of polycyclic aromatic hydrocarbons.

Double Horner-Wadsworth-Emmons reaction of (E)-2,3-diaryl-1,4-bis(diethylphosphonyl)but-2-ene with (p-substituted) benzaldehydes gave (1E,3E,5E)-1,3,4,6-tetraarylhexa-1,3,5-trienes in moderate to good yields. Substitution of electron-withdrawing or -donating groups at the para position of the 1,6-diphenyl groups induced a slight bathochromic shift of UV spectra measured in CHCl(3) compared with that of the parent 1,3,4,6-tetraphenylhexa-1,3,5-triene. Although fluorescence was not observed with all the trienes in CHCl(3), they markedly emitted visible light in powder forms with quantum yields of 0.15-0.44. Introduction of amino groups at the para position of the 3,4-diphenyl groups induced a bathochromic shift of emission maxima with good solid-state quantum yields. Thus, the tetraarylated triene framework is found to serve as a new class of fluorophores that exhibit aggregation-induced emission.

Die intramolekulare direkte Arylierung von 2‐(Arylsilyl)aryltriflaten wird glatt von Pd(OAc)2/PCy3 in Gegenwart von Et2NH in Dimethylacetamid (DMA) katalysiert, wobei die entsprechenden Si‐verbrückten Biaryle in guten bis hervorragenden Ausbeuten entstehen. Dieser Ansatz ermöglicht die Synthese eines Si‐verbrückten 2‐Phenylindols (siehe Schema; PMMA=Poly(methylmethacrylat)), das im Festkörper eine blaue Photolumineszenz mit sehr hohen Quantenausbeuten zeigt.