Synthesis of conformationally stable 1,8-diarylnaphthalenes: development of new photoluminescent sensors for ion-selective recognition

Highly constrained 1,8-diarylnaphthalenes exhibiting stability to isomerization have been prepared utilizing two consecutive CuO-promoted Stille cross-couplings of 1,8-dibromonaphthalene and 4-alkyl-9-trimethylstannylacridines. Screening of Pd catalysts Pd(PPh(3))(4), PdCl(2)dppf, or Pd(2)(dba)(3)/t-Bu(3)P and bases such as Cy(2)NMe, t-BuOK, K(3)PO(4), and Cs(2)CO(3) in DME or DMF revealed superior results of Stille over Suzuki coupling with acridylboronic acids or pinacolate derivatives. The meso syn- and C(2)-symmetric anti-isomers of 1,8-bis(4,4'-dimethyl-9,9'-diacridyl)naphthalene, 2, and 1,8-bis(4,4'-diisopropyl-9,9'-diacridyl)naphthalene, 3, did not show any sign of syn/anti-interconversion after heating to 180 degrees C for 24 h. Using the Eyring equation, we calculated the Gibbs standard activation energy for isomerization, DeltaG degrees (), to be higher than 180 kJ/mol. PM3 calculations of 2 and 3 suggest a highly congested structure exhibiting two parallel acridyl moieties perpendicular to the naphthalene ring. UV and fluorescence spectroscopy studies of 2 and 3 revealed remarkable quantum yields of these blue and green light emitters. Fluorescence titration experiments with the syn-isomer of 2 showed highly efficient quenching by Cu(II) ions, whereas almost no quenching effects were observed with Cu(I) and Zn(II) salts. The striking difference in fluorescence quenching was attributed to significant photoinduced electron transfer, resulting in nonradiative relaxation of excited Cu(II)-syn-2. Stern-V?lmer plots of syn-2 in the presence of CuCl(2) showed a sigmoidal quenching curve indicating cooperative recognition, whereas a linear response was observed with CuCl and ZnCl(2). Fluorescence experiments in the presence of various amounts of CuCl, CuBr, and Cu(ACN)(4)BF(4) proved that the quenching is cation selective and independent of the nature of counteranions.     

Synthesis and characterization of new π‐conjugated polymers containing 1,8‐naphthyridine in the main chain: Role of the 1,8‐naphthyridine unit in π‐conjugated polymers

Alternating π‐conjugated copolymers of 1,8‐naphthyridine‐2,6‐diyl ( 1,8‐Nap ) with 9,9‐dioctylfluorene‐2,7‐diyl ( P(Flu‐Ph‐1,8‐Nap) ) and 2,5‐didodecyloxy‐1,4‐phenylene ( P(ROPh‐Ph‐1,8‐Nap) ) have been synthesized by Pd‐catalyzed organometallic polycondensation. The copolymers showed UV‐vis absorption peaks at around 390 nm in o‐dichlorobenzene. The polymers were photoluminescent both in o‐dichlorobenzene and in the solid state. In o‐dichlorobenzene, the emission peaks of P(Flu‐Ph‐1,8‐Nap) and P(ROPh‐Ph‐1.,8‐Nap) appeared at λ_EM = 440 and 471 nm, with quantum yields of 87% and 66%, respectively. Electrochemical data revealed that 1,8‐Nap behaved as a typical electron‐accepting unit. When P(Flu‐Ph‐1,8‐Nap) was treated with 10‐camphorsulfonic acid, the emission peak shifted to λ_EM = 598 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Pd-catalyzed amidation of 2-chloro- and 2,7-dichloro-1,8-naphthyridines

[reactions: see text] The catalytic amidation between 2-chloro- and 2,7-dichloro-1,8-naphthyridines and primary amides bearing functional groups is reported. When Pd(OAc)2, xantphos, and K2CO3 are used, it is possible to obtain symmetric as well as nonsymmetric 2,7-diamido-1,8-naphthyridines in 50-90% yield with good functional-group tolerance. Monoamidation of 2,7-dichloro-1,8-naphthyridine using 0.9 equiv of the amide proceeded with good selectivity compared to the formation of the diamide, but as a result of the difficult isolation of the product, isolated yields were poor to moderate (22-42%).     

Synthesis of a sterically crowded atropisomeric 1,8-diacridylnaphthalene for dual-mode enantioselective fluorosensing

An efficient synthetic route to a sterically crowded 1,8-diheteroarylnaphthalene-derived enantioselective fluorosensor that operates in two different detection modes utilizing fluorescence lifetime and intensity has been developed. Screening of palladium-catalyzed Negishi, Kumada, Suzuki, Hiyama, and Stille coupling methods showed that the latter affords highly congested 1,8-diarylnaphthalenes in superior yields. Despite severe steric hindrance, axially chiral 1,8-bis(3-(3',5'-dimethylphenyl)-9-acridyl)naphthalene, 1, was obtained in 68% yield from 1,8-dibromonaphthalene, 14, and 3-(3',5'-dimethylphenyl)-9-tributylstannylacridine, 13, via two consecutive Stille cross-coupling steps using tetrakis(triphenylphosphine)palladium(0) as catalyst in the presence of copper(II) oxide. The preparation of 1 involved formation of 4-(3',5'-dimethylphenyl)-2-chlorobenzoic acid, 7, through microwave-assisted Suzuki coupling of 4-bromo-2-chlorobenzoic acid, 10, and 3,5-dimethylphenylboronic acid, 11, followed by regioselective amination with aniline and acridine ring construction in phosphorus oxybromide. Lithiation, subsequent treatment with trimethylstannyl chloride, and Stille cross-coupling then completed the five-reaction sequence providing 1 in 57% overall yield. The enantiomers of 1 were separated by semipreparative HPLC on a (R,R)-Whelk-O 1 column and successfully employed in enantioselective fluorosensing of N-t-Boc-protected serine, 20, glutamine, 22, proline, 23, and 2-hydoxy-2-methylsuccinic acid, 21. Fluorescence titration experiments with 23 revealed that both static and dynamic quenching occur with distinctive enantioselectivity. Addition of (R)-23 to a solution of (+)-1 in acetonitrile resulted in stronger fluorescence quenching than titration with the (S)-enantiomer of 23. The fluorescence lifetime, tau, of 1 was determined as 18.8 ns and steadily decreased to 7.5 and 6.8 ns in the presence of 0.1 M of (S)-23 and (R)-23, respectively.     

Pd/Cu catalyzed homo-coupling reactions of 2-iodo-3-iodomethyl-1,4-diarylnaphthalene in the presence of arylacetylene

Palladium/CuI catalyzed reactions of 2-iodo-3-iodomethyl-1,4-diarylnaphthalenes in the presence of arylacetylenes produced the corresponding sp³-sp³ homo-coupling products 1,2-bis(3-iodonaphthalen-2-yl)ethane in moderate to good yields.     

Synthesis of a novel potential tridentate anthracene ligand, 1,8-bis(dimethylamino)-9-bromoanthracene,and its application as chelate ligand for synthesis of the corresponding boron and palladium compounds

A novel potential tridentate ligand, 1,8-bis(dimethylamino)-9-bromoanthracene, was synthesized. The key steps are as follows: 1) dimethylamination of 1,8-dibromo-9-methoxyanthracene by a modified Buchwald's method to afford 1,8-bis(dimethylamino)-9-methoxyanthracene, and 2) reduction of the methoxy group by LDBB (lithium di-tert-butylbiphenylide) followed by treatment with BrCF2CF2Br. The corresponding 1,8-bis(dimethylamino)-9-lithioanthracene, which should be a useful versatile tridentate ligand, could be generated by treatment of the bromide with one equivalent of nBuLi. The lithioanthracene reacted with B-chloroborane derivatives to give three 9-boryl derivatives. Although we recently reported that the crystal structure of 1,8-dimethoxy-9-B-catecholateborylanthracene was a symmetrical compound with the almost identical two O-B distances (2.379(2) and 2.441(2) A), the newly prepared 1,8-bis(dimethylamino)-9-borylanthracene derivatives clearly have unsymmetrical structures with coordination of only one NMe2 group toward the central boron atom. However, the energy difference between the unsymmetrical and symmeterical structures was found to be very small based on 1H NMR measurements, in which symmetrical anthracene patterns in the aromatic region (two kinds of doublets and a triplet) and a sharp singlet signal of the two NMe2 groups were observed even at -80 degrees C. 1,8-Bis(dimethylamino)-9-bromoanthracene itself can be a versatile ligand for transition metal compounds. In fact, direct palladation of the bromide took place by the reaction with [Pd2(dba)3].CHCl3 in THF to give the 9-palladated product. X-ray crystallographic analysis of the Pd compound showed that the square planar palladium atom was coordinated in a symmetrical fashion by both NMe2 groups (Pd-N bonds are 2.138(5) and 2.146(5) A).     

Convenient Synthesis of 1,8-Diiodoanthracene and Its Coupling with Thianthrene Boronic Acids

1,8-Diiodoanthracene has been prepared from commercially available 1,8-dichloroanthraquinone; it was shown to couple twice under Pd(0)-catalysis, with thianthrene 1- and 2-boronic acids giving 1,8-bis(thianthrenyl)anthracenes.     

1,8-Dimethylnaphthalene-bridged diphosphine ligands: synthesis and structural comparison of their palladium complexes

The synthesis of a new series of ligands with a 1,8-dimethylnaphthalene backbone is reported, 1,8-(R2PCH2)2C10H6, where R = (t)Bu 1 (dbpn), (i)Pr 2 (dippn), Cy 3 (dchpn) and Ph 4 (dphpn). The ligand 1 is structurally characterised by X-ray crystallography. A comparative structural study of the respective (diphosphine)Pd(dba) and (diphosphine)PdCl2 complexes is carried out, comparing the X-ray crystal structures of complexes 6, 7, 8, 10, 11 and 12. It is shown that the geometry at the metal is affected by not only ligand demands, but also by the palladium oxidation state and the electronic properties of the ligands. Two qualitative stability series are also identified: 9 < 10 < 11 approximately 12 is observed, and P2Pd(dba) complexes are more stable than the corresponding P2PdCl2 complexes towards opening of the chelate ring. It is also concluded that the bite angle is heavily influenced by the electron donating properties of the ligand.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–XVI. ISPERSE BLUE 35

The photochemistry (Type I and II) of the phototoxic textile dye Disperse Blue (DB-35) and its purified components has been studied using electron spin resonance in conjunction with spin trapping technique and the direct detection of singlet oxygen (1O2) luminescence. The main components of DB-35 (which is synthesized by the successive nitration, reduction and methylation of 1,8-dihydroxy-anthraquinone) were separated by HPLC and identified by mass spectrometry and 2-D NMR as 4,5-diamino-1,8-dihydroxyanthraquinone (4,5-DDHAQ; 62% of total dye) and 2,7-diamino-1,8-dihydroxyanthraquinone (2,7-DDHAQ; 31% of total dye). Minor components included 2,5-diamino-1,8-dihydroxyanthraquinone (2,5-DDHAQ) and a monomethylated derivative of either 4,5-DDHAQ or 2,7-DDHAQ. Irradiation (624 nm) of 4,5-DDHAQ and 2,7-DDHAQ in dimethylsulfoxide resulted in the generation of superoxide which was trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Visible light irradiation of the components in ethanol generated 1O2 with the yields decreasing in the following order: 4,5-DDHAQ greater than 2,5-DDHAQ greater than 2,7-DDHAQ. These findings indicate that upon irradiation by visible light DB-35 can generate active oxygen species which may be responsible for the photocontact dermatitis caused by this dye.     

Evidence of Transannular Bonding Interaction between Two Sulfur Atoms on Photolysis of Naphtho[1,8-ef][1,4]dithiepins

Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3 with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithiepin (5a) revealed that the S.S distance is shorter than the sum of their van der Waals radii, indicating that compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields of the consumption of 5a and the formation of 6aand 1 were 0.34. The mechanism of this reaction was investigated by examining the effect of sensitization and light intensity. The results indicate that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio calculations were carried out on model compound 7, and it was shown that the excitation to the S(1) state causes a bonding interaction between the two sulfur atoms, making the reaction possible.     

Naphthalene proton sponges as hydride donors: diverse appearances of the tert-amino-effect

It has been shown that the 1-NMe(2) group in the 2-substituted 1,8-bis(dimethylamino)naphthalenes (proton sponges) can intramolecularly donate a hydride ion to an appropriate electron-accepting ortho-substituent such as diarylcarbenium ion, β,β'-dicyanovinyl or methyleneiminium group. This produces the 1-N(+)(Me)=CH(2) functionality and triggers a number of further transformations (tert-amino effect) including peri-cyclization, ortho-cyclization or hydrolytic demethylation. In each particular case, the course of the reaction is determined by the nature of the ortho-substituent and the most potent nucleophile presenting in the reaction mixture. For 2,7-disubstituted 1,8-bis(dimethylamino)naphthalenes, two types of tandem tert-amino effect with the involvement of both peri-NMe(2) groups have been registered. The conclusion was made that proton sponges are generally more active in the tert-amino reactions than the corresponding monodimethylaminoarenes. This is ascribed both to higher electron donor ability of proton sponges and markedly shortened distance between electrophilic C(α)-atom in the ortho-substituent and hydrogen atoms of the nearest NMe(2) group. Most conversions observed proceed in good to high yields and are useful for the preparation of derivatives of benzo[h]quinoline, quino[7,8:7',8']quinoline, 2,3-dihydroperimidine, N,N,N'-trimethyl-1,8-diaminonaphthalene and proton sponge itself.     

Biosynthesis of Pd/MnO2 nanocomposite using Solanum melongena plant extract and its application for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides

In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO₂ nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO₂) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO₂ nanocomposite was used as a heterogeneous catalyst for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing various electron‐donating or electron‐withdrawing groups in the presence of K ₄ [Fe (CN) ₆ ] as non‐toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work‐up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity.     

Greener approach for synthesis of monodispersed palladium nanoparticles using aqueous extract of green tea and their catalytic activity for the Suzuki–Miyaura coupling reaction and the reduction of nitroarenes

A facile and green route for the synthesis of palladium nanoparticles (NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@G.Tea extract was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The Pd‐NPs@G.Tea extract could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties, and also for the reduction of nitroarenes using sodium borohydride in an environmentally friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity.     

A very efficient synthesis of 1,8-diazaanthraquinones

The reaction between 1-dimethylamino-1-azadienes and 2,6-dibromobenzoquinone gave excellent yields of the corresponding double hetero Diels-Alder cycloadducts. 3-Substituted azadienes directly gave aromatic 1,8-diazaanthraquinone derivatives, while 4-substituted azadienes led to 1,8-dimethylamino-1,4,5,8-tetrahydro-1,8-diazaanthraquinones, which were aromatized under thermal conditions.     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Theoretical Study on the Electronic Structures and Spectral Properties of 1,8-Naphthalimide Derivatives

The molecular geometries, frontier molecular orbital properties, and absorption and emission properties of three 4-phenoxy-1,8-naphthalimide derivatives, namely 4-phenoxy-N-（2-hydroxyethyl）-1,8-naphthalimide（1）,4-（2-tert-butylphenoxy）-N-（2-hydroxyethyl）-1,8-naphthalimide（2）, and 4-[2,4-di（tert-butyl）]phenoxy-N-（2-hydroxyethyl）-1,8-naphthalimide（3）, are investigated by density functional theory（DFT） and time-dependent density functional theory（TD-DFT） calculations in conjunction with polarizable continuum models（PCMs）. Four functionals and ten basis sets are employed for 1 to calculate the electron transition energies, which were compared with the experimental observations. Our results reveal that the B3LYP/6-311＋G（d,p） method is the best choice to reproduce the experimental spectra. Moreover, the effects of substituents on the molecular geometries, electronic structures, absorption and emission spectra are also studied at the B3LYP/6-311＋G（d,p） level. We find that the gap between the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） decreases with increasing the number of tert-butyl substituents onto the phenoxy groups, suggesting red-shift of the absorption and emission bands. This is related to the increase of conjugation from 1 to 2 and 3. Our calculations are in good agreement with the experimental results.     

Palladium Nanoparticles Immobilized on Individual Calcium Carbonate Plates Derived from Mussel Shell Waste: An Ecofriendly Catalyst for the Copper‐Free Sonogashira Coupling Reaction

The conversion of waste into high‐value materials is considered an important sustainability strategy in modern chemical industries. A large volume of shell waste is generated globally from mussel cultivation. In this work, mussel shell waste (Perna viridis ) is transformed into individual calcium carbonate plates (ICCPs) and is applied as a support for a heterogeneous catalyst. Palladium nanoparticles (3–6 nm) are deposited with an even dispersion on the ICCP surface, as demonstrated by X‐ray diffraction and scanning electron microscopy. Using this system, Sonogashira cross‐coupling reactions between aryl iodides and terminal acetylenes were accomplished in high yields with the use of 1 % Pd/ICCP in the presence of potassium carbonate without the use of any copper metal or external ligand. The Pd/ICCP catalyst could also be reused up to three times and activity over 90 % was maintained with negligible Pd‐metal leaching. This work demonstrates that mussel shell waste can be used as an inexpensive and effective support for metal catalysts in coupling reactions, as demonstrated by the successful performance of the Pd‐catalyzed, copper‐free Sonogashira cross‐coupling process.     

Efficient anchorage of Pd nanoparticles on carbon nanotubes as a catalyst for hydrazine oxidation

A simple method is devised to deposit well-dispersed Pd nanoparticles on multi-walled carbon nanotubes (CNTs). Pd nanoparticles (1–3 nm) prepared in ethanol were transferred to toluene solution and modified by organic molecule benzyl mercaptan which acts as a cross linker between Pd nanoparticles and CNTs. The morphology and structure of the resulting Pd/CNT nanocomposite were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Pd nanoparticles were highly dispersed and effectively anchored on CNTs. The excellent electrocatalytic activity of the Pd/CNT nanocomposite for the oxidation of hydrazine was demonstrated by cyclic voltammetry.     

Evaluation of nonlinear modeling based on artificial neural networks for the spectrophotometric determination of Pd(II) with CPA-mK

A new method is proposed for the spectrophotometric determination of Pd(II), based on the reaction of Pd(II) with 2-(4-chloro-2-phosphonophenylazo)-7-(3-carboxyphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid(CPA-mK) in sulfuric acid without heating. Beer’s law is obeyed for 1.0–4.0 μg of Pd (II) in 10 mL of solution. The calibration curve from 1.0 to 42.0 μg in 10 mL of solution is modeled successfully by artificial neural networks (ANNs). The maximum relative error between experimental values and the values predicted by ANNs is 1.5%. In comparison with some mathematical functions, ANNs show better ability for curve fitting, thus greatly extending the applicable range of the calibration curve of this new system. The method has been applied to determine Pd (II) in ore and catalyst samples with a relative error of less than 4% and with a recovery range between 94% and 103%.     

1,8-dihydroxyanthraquinone-Mg(II) complex: II. Spectrophotometric study. Determination of Mg(II)

The 1,8-dihydroxyanthraquinone (1,8-DHAn) shows a colored and fluorescent reaction with the ion Mg(II) in a hydroalcoholic and ammonical medium.In the present work we have studied spectrophotometrically the 1,8-DHAn-Mg(II) complex in a hydroethanolic and ammonical, 8 × 10^?4M medium. We found that the complex shows a maximum absorbance at 510 nm, and obeys a 1:1 stoichiometry with log K of 4.08.We propose a new method for the spectrophotometric determination of Mg(II) which is valid for concentrations between 0.25 and 2.00 ppm, and yields an error of 1.32%.