-
[show abstract]
[hide abstract]
ABSTRACT: Selective CC bond cleavage: A catalyst consisting of nickel(0)/DPEphos and BPh(3) is highly effective for the addition of polyfluorobenzonitriles to alkynes through selective activation of the CCN bond over the CH or CF bonds. The addition reaction is applicable to the sequential insertion of two different alkynes into CCN and CH bonds.
Angewandte Chemie International Edition 11/2012; · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: MAD as an additive: The [Ni(cod)(2) ], (2,6-tBu(2) -4-MeC(6) H(2) O)(2) AlMe (MAD), and N-heterocyclic carbene (NHC) catalytic system effected a highly regioselective alkylation of pyridone derivatives. Substituted pyridones and related heterocycles react with both terminal and internal alkenes to selectively give a range of nitrogen-containing heterocycles with linear alkyl substituents.
Angewandte Chemie International Edition 04/2012; 51(23):5679-82. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: (Z)-1,2-Diaryl-1,2-bis(pinacolatoboryl)ethenes underwent double-cross-coupling reactions with 1-bromo-2-[(Z)-2-bromoethenyl]arenes in the presence of [Pd(PPh(3))(4)] as a catalyst and 3 M aqueous Cs(2)CO(3) as a base in THF at 80 °C. The double-coupling reaction gave multisubstituted naphthalenes in good to high yields. Annulation of 1,2-bis(pinacolatoboryl)arenes with bromo(bromoethenyl)arenes in the presence of a catalyst system that consisted of [Pd(2)(dba)(3)] (dba=dibenzylideneacetone) and 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos) under the same conditions produced fused phenanthrenes in good to high yields. The first annulation coupling occurred regiospecifically at the bromoethenyl moiety. This procedure is applicable to the facile synthesis of polysubstituted anthracenes, benzothiophenes, and dibenzoanthracenes through a double annulation pathway by using the corresponding dibromobis[(Z)-2-bromoethenyl]benzenes as diboryl coupling partners.
Chemistry - An Asian Journal 03/2012; 7(7):1644-51. · 4.50 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Molecular fluorophores of type A-π-D-π-A (D=donor, A=acceptor) demonstrate solid-state emission in the red to near-infrared region with high efficiency. The emission color can be tuned through the substituents on the diarylamino and cyanophenyl moieties. The electroluminescence performance of the designed fluorophore confirms its potential as an emitter for use in organic light-emitting devices.
Angewandte Chemie International Edition 03/2012; 51(17):4095-9. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We prepared a Pd complex by the oxidative addition of 1,1-dibromo-3,3,3-trifluoro-2-tosyloxypropene to [Pd- (PPh3)4]. The atomic distance between Pd and F in the complex was 2.95 ¡, which was shorter than the sum of the van der Waals radii, suggesting that PdF interaction played an important role in determining the stereochemical outcome of the Pd-catalyzed cross-coupling reaction of the propene.
Bulletin of the Chemical Society of Japan 11/2011; 84(12):1339-1341. · 1.44 Impact Factor
-
Bulletin of the Chemical Society of Japan 11/2011; 12:1339-1341. · 1.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Much attention has been paid to the cross-coupling reaction of organosilicon compounds due to their stability, non-toxicity, and natural abundance of silicon. In addition, the silicon-based cross-coupling has many advantages over other cross-coupling protocols. Successful examples of the silicon-based cross-coupling reaction are reviewed, focusing especially on the advances made in the last decade. Having had a number of highly effective palladium catalysts developed mainly for other cross-coupling reactions, the development of the silicon-based protocol owes heavily to the design of organosilicon reagents which effectively undergo transmetalation, a key elemental step of the silicon-based cross-coupling reaction. This tutorial review thus classifies various organosilicon reagents depending on substituents on silicon and surveys their cross-coupling reactions with various electrophiles.
Chemical Society Reviews 07/2011; 40(10):4893-901. · 28.76 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Dimethoxybis(3,3,3-trifluoropropen-1-yl)benzenes were prepared through palladium-catalyzed double cross-coupling reactions of diiododimethoxybenzenes with CF(3)C≡CZnCl, followed by reduction of CF(3)C≡C groups with LiAlH(4) or H(2) in the presence of the Lindlar catalyst. The edges of the absorption spectra of 1,2-(MeO)(2)-4,5-(CF(3)CHC=CH)(2) benzenes 1 and 1,3-(MeO)(2)-4,6-(CF(3)CH=CH)(2) benzenes 2 in cyclohexane ranged from 348 to 360 nm, whereas the absorption spectra of 1,4-(MeO)(2)-2,5-[(E)-CF(3)CH=CH](2) benzene ((E)-3) ended at 406 nm. These findings indicate that the effective conjugation length of (E)-3 was significantly larger than those of 1 and 2. Consistently, 1 and 2 in cyclohexane exhibited fluorescence with emission maxima in the UV region, whereas (E)-3 in cyclohexane emitted violet light with an emission maximum at 407 nm. All the fluorescence spectra of 1-3 in various solvents redshifted as the solvent polarity increased. The photoluminescence of 1-3 in the solid states was also observed with emission maxima in the violet region. It is important to note that the quantum yields of (E)-3 in a neat thin film and in a doped polymer film were 0.37 and 0.49, respectively. Density functional theory calculations suggested that the fluorine atoms contribute to a slight extension of both the HOMOs and the LUMOs, as well as narrowing of the HOMO-LUMO gaps when compared with the corresponding fluorine-free analogues. In the case of (E)-3, it is suggested that the HOMO-LUMO transition includes charge transfer from the ethereal oxygen atoms to the C(sp(2))-CF(3) moieties.
Chemistry - An Asian Journal 06/2011; 6(9):2536-44. · 4.50 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 3,2′-Silylene-bridged 2-phenylindoles were prepared in high yields by palladium-catalyzed silicon-migrative intramolecular coupling of 2-(2-indolylsilyl)aryl triflates. The high thermal stability of the benzosilole-fused indoles was indicated by thermogravimetric analysis (TGA). The absorption spectra revealed that the absorption edges, namely, the HOMO–LUMO energy gaps, could be effectively tuned by substitution with functional groups such as chloro, cyano, methoxy, and phenyl at the meta-positions with respect to nitrogen and silicon, whereas there was no effective conjugation between the core and an aryl group on nitrogen. The changes in the HOMO–LUMO gaps, which were induced by variation of the functional groups, were well reproduced by density functional theory calculation. The indoles exhibited blue fluorescence with high-to-excellent quantum yields both in cyclohexane and in powder as well as in doped poly(methyl methacrylate) (PMMA) films. The emission maxima of each indole exhibited a red-shift, which followed the general order: cyclohexane→PMMA film→powder. X-ray analysis of the diisopropylsilylene-bridged parent indole indicated that there was no close contact like π–π stacking in the crystal, presumably because of the steric effect of the bulky silylene bridge. Examination of the photophysical properties of 3,2-diisopropylmethylene-bridged 2-phenylindole revealed that the quantum yields of the carbon analogue in the solid state were much lower than the corresponding silylene-bridged indole. Thus, the silylene bridge is found to be essential for obtaining high-to-excellent solid-state quantum efficiency using a molecular design based on a 2-phenylindole framework.
05/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Formamides having 1-arylalkyl groups on nitrogen undergo an unprecedented dehydrogenative [4 + 2] cycloaddition reaction with alkynes via nickel/AlMe(3) cooperative catalysis to give highly substituted dihydropyridone derivatives in good yields. Notably, the transformation proceeds through double functionalization of C(sp(2))-H and C(sp(3))-H bonds in the formamides.
Journal of the American Chemical Society 02/2011; 133(10):3264-7. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new molecular design of organic emitters exhibiting efficient solid-state fluorescence, which involves planarity breaking of N,N-diorganoquinacridones, is presented. The new design principle led to the devel- opment of dimethyl 2,5-diaminoterephthalates and 2,5-diamino-1,4-diaroylbenzenes, which emitted green to yellow and yellow to red light with high-to-excellent quantum yields, respectively. In addition, the photoluminescence properties of the diaroylbenzenes were dependent on the morphology and reversibly variable by thermal and solvent vapor stimuli.
Tetrahedron Letters 01/2011; 52(32-doi:10.1016/j.tetlet.2011.05.087):4084-4089. · 2.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Using highly stable, readily accessible, and recyclable 2-(2-hydroxyprop-2-yl)cyclohexyl-substituted arylsilanes activated by a mild carbonate base, nickel-catalysed silicon-based aryl-aryl cross-coupling reaction proceeds for the first time with inexpensive aryl chlorides and tosylates in a highly chemoselective manner.
Chemical Communications 01/2011; 47(1):307-9. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Direct C-4-selective addition of pyridine across alkenes and alkynes is achieved for the first time by nickel/Lewis acid cooperative catalysis with an N-heterocyclic carbene ligand. A variety of substituents on both alkenes and pyridine are tolerated to give linear 4-alkylpyridines in modest to good yields. The addition across styrene, on the other hand, gives branched 4-alkylpyridines. A single example of C-4-selective alkenylation is also described.
Journal of the American Chemical Society 10/2010; 132(39):13666-8. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A combination of Ni(cod)(2) and PCyp(3) is found to be an effective catalyst for chemoselective activation of the C-H bond of fluoroarenes over C-F bonds followed by insertion of alkynes to allow direct alkenylation of the electron-deficient arenes. The characteristics of the reactions are: a C-H bond ortho to a fluorine substituent is selectively activated; the reactivity of fluorobenzenes is roughly proportional to the number of fluorine atoms. The reaction conditions tolerate a broad range of both alkynes and fluoroarenes containing both electron-withdrawing and -donating groups, thus allowing efficient synthesis of a variety of substituted ethenes containing a fluoroaryl motif in high regio- and stereoselective manners. Mechanistic studies including both labeling experiments and stoichiometric reactions reveal that oxidative addition of C-H bonds in fluoroarenes to nickel(0) is kinetically highly facile whereas that of C-F bonds is thermodynamically favoured.
Dalton Transactions 10/2010; 39(43):10483-94. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Alkanenitriles having a heteroatom such as nitrogen, oxygen, and sulfur at the gamma-position are found to add across alkynes stereo- and regioselectively by nickel/Lewis acid catalysis to give highly substituted acrylonitriles. The heteroatom functionalities likely coordinate to the nickel center to make oxidative addition of the C-CN bonds of the alkyl cyanides kinetically favorable, forming a five-membered nickelacycle intermediate and, thus, preventing beta-hydride elimination to allow the alkylcyanation reaction.
Journal of the American Chemical Society 07/2010; 132(29):10024-6. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cyanoformates and cyanoformamides are found to add across alkynes by nickel/Lewis acid (LA) cooperative catalysis to give beta-cyano-substituted acrylates and acrylamides, respectively, in highly stereoselective and regioselective manners. The resulting adducts serve as versatile synthetic building blocks through chemoselective transformations of the ester, amide, and cyano groups as demonstrated by the synthesis of typical structures of beta-cyano ester, beta-amino nitrile, gamma-lactam, disubstituted maleic anhydride, and gamma-aminobutyric acid. The related reactions of cyanoformate thioester and benzoyl cyanide, on the other hand, are found to add across alkynes with decarbonylation in the presence of a palladium/LA catalyst.
Journal of the American Chemical Society 07/2010; 132(29):10070-7. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: There has been extensive research on the development of organic optoelectronic devices, such as organic light-emitting diodes, organic field-effect transistors, and organic solid-state lasers from various viewpoints, ranging from basic studies to practical applications. As organic materials are used as solids in these devices, the importance of organic chromophores that exhibit intense emissions of visible light in the solid state is greatly increasing in the field of organic electronics. However, highly efficient emission from organic solids is very difficult to attain because most organic emitting materials strongly tend to cause concentration quenching of the luminescence in the condensed phase. Therefore, in order to generate and improve organic optoelectronic devices, it is necessary to design novel chromophores that exhibit superior solid-state emission performance. This Focus Review covers the recent development of highly emissive organic small molecules whose photoluminescence quantum yields in the solid state have been reported. Following the introduction, the photophysical processes of excited molecules are briefly reviewed. Subsequently, organic solid fluorophores are described with an emphasis on the characteristics of their molecular structures.
Chemistry - An Asian Journal 07/2010; 5(7):1516-31. · 4.50 Impact Factor
-
Angewandte Chemie International Edition 06/2010; 49(26):4451-4. · 13.45 Impact Factor
-
Angewandte Chemie International Edition 06/2010; 49(26):4447-50. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
05/2010;
