An investigation of the positional isomeric effect of terpyridine derivatives: Self-assembly of novel cadmium coordination architectures driven by N-donor covalence and π⋯π non-covalent interactions

Four cadmium compounds based on two pyridyl substituted terpyridine isomers, namely {[Cd₃(L1)₂(SCN)₆](THF)₂}_n (1), [Cd₂(L1)(CH₃OH)Cl₄]_n (2), [Cd₂(L2)₂(N₃)₄] (3) and [Cd₂(L2)₂(SCN)₄] (4) (L1 = 4′-(3-pyridyl)-2,2′:6′,2″-terpyridine, L2 = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine) have been synthesized and characterized by IR, elemental analyses, and luminescent spectroscopy with the purpose of investigating the influence of isomeric effect on network assembly. In compounds 1 and 2, L1 as a mono-tridentate bridging ligand links Cd^II atoms into 1D grid-like and 2D wave-like polymers. In contrast, in compounds 3 and 4, L2 as a chelating ligand forms Cd^II dimeric structures. The different coordination behaviors and the positional isomer effect were discussed under the same reaction conditions. In addition, three kind of π?π interactions in the four compounds were summarized, two of which could not be observed on tpy-based complexes.     

Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.     

Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L₁)(L₂) (1) complexes (L₁ = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L₂ = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H₂O₂. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.     

Optically active pentacyclic binuclear diorganotin compounds

Three optically active binuclear diorganotin compounds (2-4) were prepared from an optically active oxalamide: (1S,2R)-(−)-[N-(2-hydroxy-1-methyl-2-phenyl-ethyl)-N′-(2-hydroxy-phenyl)-oxalamide (1). The new compounds [1-(2′,2′-diorganyl-1′-oxa-3′-aza-2′-stanna-indan-3′-yl)-2-(2″,2″-diorganyl-4″-methyl-5″-phenyl[1,3,2]-oxazastannolidin-3″-yl)-ethane-1,2-dione {organyl = methyl (2), n-butyl (3) or phenyl (4)} were characterized by IR, elemental analysis and mass spectrometry. Compounds 3 and 4 were submitted to a detailed NMR study in order to assign their resonances (¹H and ¹³C) and specially the two different ¹¹⁹Sn signals for each compound. The X-ray diffraction analysis of compound 4 showed a planar pentacyclic framework with two penta-coordinated tin atoms with a distorted tbp geometry and 12 intramolecular hydrogen bonds.     

Synthesis of pyrido and pyrazinodithienodipyrimidine-4,8(3H,9H)-dione derivatives by the aza-Wittig methodology

A one-pot synthesis of the hitherto unreported pyrido[5″,6″:4,5;3″2″:4′,5′]dithieno[3,2-d:3′,2′-d′]dipyrimidine-4,8(3H,9H)-dione 6a-o and pyrazino[5″,6″:4,5;3″2″:4′,5′]dithieno[3,2-d:3′,2′-d′]dipyrimidine-4,8(3H,9H)-dione 6p-y pentaheterocyclic systems, based on the tandem aza-Wittig heterocumulene-mediated annulation strategy is described.     

Synthesis of porphyrin-appended terpyridine as a chemosensor for cadmium based on fluorescent enhancement

The design and synthesis of a porphyrin-appended terpyridine, 5-(4-([2,2′:6′,2″]-terpyridin-4-yl-carboxyamidyl)phenyl)-10,15,20-triphenylporphyrin (H₂TPPTPy) and its application as potential fluoroionophore for recognition of metal ions are reported. For preparation of the fluoroionophore, a novel simple strategy with improved total yield has been applied for the synthesis of 2,2′:6′,2″-terpyridine-4′-carboxylic acid as a ligand. H₂TPPTPy shows chelation-enhanced fluorescence effect with cadmium ion via the interruption of photoinduced electron transfer (PET) process, which has been utilized as the basis of the fabrication of the Cd(II)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Cd(II)-sensitive chemosensor were investigated. It shows a linear response toward Cd(II) in the concentration range of 3.2 × 10⁻⁶ to 3.2 × 10⁻⁴ M with a limit of detection of 1.2 × 10⁻⁶ M. The chemosensor shows good selectivity for Cd(II) over a large number of cations, such as alkali, alkali earth and transitional metal ions except Cu(II) and Zn(II). The sensor has been used for determination of Cd(II) in water samples with satisfactory recoveries.     

A new series of potentially hexadentate ligands derived from 2,2′-bipyridine

Reaction of 2,2′-bipyridine-6-carboxaldehyde with the appropriate aliphatic diamine in MeOH and subsequent reduction with NaBH₄ gives the new, potentially hexadentate, ligands N,N′-bis(2,2′-bipyridin-6-ylmethyl)ethane-1,2-diamine (bmet), N,N′-bis(2,2′-bipyridin-6-ylmethyl)propane-1,3-diamine (bmpp) and N,N′-bis(2,2′-bipyridin-6-ylmethyl)hexane-1,6-diamine (bmhx). The syntheses and characterisation of these ligands are reported; the ligands are isolated as the hydrochloride salts, with purification effected by either recrystallisation or cation exchange chromatography. [Co(bmet)](ClO₄)₃ · H₂O is obtained on reaction of bmet · 4.25HCl · 2.5H₂O with Na₃[Co(O₂CO)₃] · 3H₂O, and X-ray structural analysis shows this to have a pair of very short Co–N bonds. The synthesis and characterisation of the first coordination complex containing 6-(aminomethyl)-2,2′-bipyridine (amb) is also described.     

Hydride addition at μ-vinyliminium ligand obtained from disubstituted alkynes

New μ-vinylalkylidene complexes cis-[Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αHN(Me)(R)}(μ-CO)(CO)(Cp)₂] (R = Me, R′ = R″ = Me, 3a; R = Me, R′ = R″ = Et, 3b; R = Me, R′ = R″ = Ph, 3c; R = CH₂Ph, R′ = R″ = Me, 3d; R = CH₂Ph, R′ = R″ = COOMe, 3e; R = CH₂ Ph, R′ = SiMe₃, R″ = Me, 3f) have been obtained b yreacting the corresponding vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2a-f) with NaBH₄. The formation of 3a-f occurs via selective hydride addition at the iminium carbon (C_α) of the precursors 2a-f. By contrast, the vinyliminium cis-[Fe₂{μ-η¹:η³-C_γ (R′) = C_β(R″)C_α = N(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R′ = R″ = COOMe, 4a; R′ = R″ = Me, 4b; R′ = Prⁿ, R″ = Me, 4c; Prⁿ = CH₂CH₂CH₃, Xyl = 2,6-Me₂C₆H₃) undergo H⁻ addition at the adjacent C_β, affording the bis-alkylidene complexes cis-[Fe₂{μ-η¹:η²-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], (5a-c). The cis and trans isomers of [Fe₂{μ-η¹:η³-C_γ(Et)C_β(Et)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4d) react differently with NaBH₄: the former reacts at C_α yielding cis-[Fe₂{μ-η¹:η³-C_γ(Et)C_β(Et)C_αHN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], 6a, whereas the hydride attack occurs at C_β of the latter, leading to the formation of the bis alkylidene trans-[Fe₂{μ-η¹:η²-C(Et)C(H)(Et)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (5d). The structure of 5d has been determined by an X-ray diffraction study. Other μ-vinylalkylidene complexes cis-[Fe₂{μ-η¹:η³-C_γ(R′)C_β(R″)C_αHN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂], (R′ = R″ = Ph, 6b; R′ = R″ = Me, 6c) have been prepared, and the structure of 6c has been determined by X-ray diffraction. Compound 6b results from treatment of cis-[Fe₂{μ-η¹:η³-C_γ(Ph)C_β(Ph)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4e) with NaBH₄, whereas 6c has been obtained by reacting 4b with LiHBEt₃. Both cis-4d and trans-4d react with LiHBEt₃ affording cis-6a.     

A regioselective synthesis of dispiro[oxindole-cyclohexanone]pyrrolidines and dispiro[oxindole-hexahydroindazole]pyrrolidines by sequential 1,3-dipolar cycloaddition and annulation through a microwave induced solvent-free approach

The 1,3-dipolar cycloaddition of an azomethine ylide, generated from isatin and benzylamine by a 1,5-prototopic shift route with various p-substituted 2,6-bis(arylmethylidene)cyclohexanones under different conditions, proceeded regioselectively to give novel dispiroheterocycles. The product on subsequent annulation with hydrazine hydrate afforded 4-aryl-5-phenyl(spiro[2.3″]oxindole)3′-aryl-3′,3a′,4′,5′,6′,7′-hexahydro-2H-indazolospiro[7′.3]pyrrolidines in good yield.     

Oligofluorene-based push-pull type functional materials for blue light-emitting diodes

A series of new oligofluorene-based push-pull type blue light-emitting functional materials, namely, 2-(9H-carbazole-9-yl)-7-(4-cyanophenyl)-9,9-dihexylfluorene (F1), 7-(9H-carbazol-9-yl)-7′-(4-cyanophenyl)-2,2′-bi(9,9-dihexylfluorene) (F2), 7-(9H-carbazole-9-yl)-7″-(4-cyanophenyl)-2,2′:7′,2″-ter(9,9-dihexylfluorene) (F3), and 7-(9H-carbazole-9-yl)-7″′-(4-cyanophenyl)-2,2′:7′,2″:7″,2″′-quarter(9,9-dihexylfluorene) (F4) were synthesized and characterized. Their onset decomposition temperatures for the thermal bond cleavage and the glass-transition temperatures were in general increased with increasing number of fluorene units. In dilute toluene solution, the oligofluorenes exhibited main absorption peaks in the range of 343-370 nm, photoluminescence maxima from 403 to 410 nm, and absolute quantum yields (Φ_PLs) of higher than 87%. In contrast, the absorption spectra of these compounds in the thin films had no large differences from those in the solutions except for the slight peak red-shifts (2-8 nm). The main emission maxima of F1, F2, and F3 in the thin films were located at 418-420 nm, while the main emission of F4 was found to be shifted to 446 nm, followed by a shoulder peak at 421 nm. The Φ_PLs of these thin films were estimated in the range of 59.2-68.7%. The existence of the electron-pull and -push end groups could effectively tune the energy levels of the oligofluorenes. By using the organic light emitting device (OLED) configuration of ITO/PEDOT:PSS/oligofluorenes/TPBi/LiF/Al by solution-process, F4 displayed the best performance: the lowest turn-on voltage (4.1 V) and highest maximum luminance (2180 cd/m²) with maximal current efficiency of 1.17 cd/A. When F4 was fabricated into the optimized device of ITO/MoO₃/NPB/CBP:F4(1:4)/TPBi/LiF/Al by vapor deposition, highest brightness of 5135 cd/m² and current efficiency of 1.76 cd/A were achieved with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.09).     

Cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines): synthesis, structure and mechanism of their formation

Reactions of 3-alkylamino-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones with cyclohexyl- and cycloheptylamines in the presence of AgPy₂MnO₄ produce novel cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines). Detailed information concerning the scope and mechanism of these transformations is discussed.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

Step by step palladium mediated syntheses of new 2-(pyridin-2-yl)-6-R-nicotinic acids and esters

Taking advantage of palladium peculiar “rollover” C,N cyclometallation, it is possible to promote C(3) functionalization of 6-alkyl-substituted-2,2′-bipyridines. The carbonylation reaction of rollover species [Pd(Lⁿ)Cl]₂, (HL¹ = 6-isopropyl-2,2′-bipy, 1; HL² = 6-neopentyl-2,2′-bipy, 2; HL³ = 6-ethyl-2,2′-bipy, 3; HL⁴ = 6-methyl-2,2′-bipy, 4) allowed the synthesis of 2-(pyridin-2-yl)-6-alkyl-nicotinic acids or esters. These nicotinic derivatives are extremely rare and, as far as we know, quite unreported in the case of the 6-substituted molecules.     

The Thorpe-Ziegler-type reaction of 3-cyanopyridine-2(1H)-thiones with Biginelli 6-bromomethyl-3,4-dihydropyrimidin-2(1H)-ones: cascade assembling of tetra- and pentacyclic heterocyclic scaffolds

3-Cyanopyridine-2(1H)-thiones have been shown to react with Biginelli-type ethyl 4-aryl-6-(bromomethyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates upon heating in DMF giving rise to ethyl 4-aryl-6-{[(3-cyanopyridin-2-yl)thio]methyl}-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates. The latter upon treatment with an excess of NaH or t-BuOK in boiling DMF undergo a tandem Thorpe-Ziegler-type heterocyclization to give pyrido[3″,2″:4′,5′]thieno[2′,3′:5,6]pyrido[4,3-d]pyrimidine derivatives in good yields. Selected compounds were tested for antibacterial and antifungal activity.     

Cyanide bridged tetranuclear complex with a novel terthiophene based ligand

A new terthiophene based ligand (L = 3-(2-pryridyl)-5-(2,2′:5′,2″-terthien-3′-yl) pyrazole was synthesized. The reaction of Ni(BF₄)₂·6H₂O, L and nBu₄N[Fe(CN)₃tp^∗] (tp^∗ = tris(3,5-dimethylpyrazol-1-yl)borohyrdide) with NaBPh₄ in MeOH/acetone yielded a cyanide bridged tetranuclear complex [Fe₂Ni₂(CN)₆(tp^∗)₂(L)₄](BPh₄)₂ (1). The electrochemical properties of both 1 and L were investigated, and magnetic susceptibility measurements of 1 were conducted, revealing that ferromagnetic interactions were operative within the tetranuclear core.     

Measurement of oligochitosan-tobacco cell interaction by fluorometric method using europium complexes as fluorescence probes

The interaction of oligochitosan and tobacco cells has been investigated by fluorometric method using two Eu³⁺ complexes as the probes in this work. Based on the reaction of tobacco cells with oligochitosan conjugated to a strongly fluorescent Eu³⁺ complex 4,4′-bis(1″,1″,1″,2″,2″,3″,3″-heptafluoro-4″,6″-hexanedion-6″-yl)chlorosulfo-o-terphenyl-Eu³⁺ (oligochitosan-BHHCT-Eu³⁺ conjugate), the binding kinetic process of oligochitosan-tobacco cells was fluorescently imaged. The results indicate that oligochitosan can be specifically bound to the walls as well as the membranes of tobacco cells. A sensitive and selective Eu³⁺ complex luminescence probe specific for singlet oxygen, [4′-(10-methyl-9-anthryl)-2,2′:6′,2″-terpyridine-6,6″-diyl]bis(methylenenitrilo)tetrakis (acetate)-Eu³⁺, was used for developing a new time-resolved fluorescence assay method for the determinations of indole-3-acetic acid (IAA) and peroxidase produced in the cells during the interaction of oligochitosan and tobacco cells. The assays are sensitive with the detection limits of 32 nM for IAA, and 1.2 nM for peroxidase, respectively. The concentration changes of IAA and peroxidase induced by oligochitosan in tobacco cells reveal that oligochitosan can effectively induce the increase of IAA concentration, accompanied by the decrease of peroxidase concentration. These results give a primary and reliable evidence to explain the growth-promoting mechanism of oligochitosan on the plants at molecular level.     

1-(2′-Pyridylazo)-2-naphtholate complexes of ruthenium: Synthesis,characterization, and DNA binding properties

Reaction of 1-(2′-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)₄Cl₂] (dmso = dimethylsulfoxide), [Ru(trpy)Cl₃] (trpy = 2,2′,2″-terpyridine), [Ru(bpy)Cl₃] (bpy = 2,2′-bipyridine) and [Ru(PPh₃)₃Cl₂] in refluxing ethanol in the presence of a base (NEt₃) affords, respectively, the [Ru(pan)₂], [Ru(trpy)(pan)]⁺ (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh₃)₂(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]⁺ and [Ru(bpy)(pan)(pic)]⁺ complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d⁶, S = 0) and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)–Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)₂] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO₄, [Ru(bpy)(pan)(py)]ClO₄ and [Ru(bpy)(pan)(pic)]ClO₄ complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation.     

Synthesis of 3,3′-disubstituted-2,2′-biindolyls through sequential palladium-catalysed reactions of 2,2,2-trifluoro-N-(2-(4-[2,2,2-trifluoro-acetylamino)-phenyl]-buta-1,3-diynyl)-phenyl)-acetamide with organic halides/triflates

Palladium-catalysed reactions of aryl iodides/vinyl triflates with 2,2,2-trifluoro-N-(2-(4-[2,2,2-trifluoro-acetylamino)-phenyl]-buta-1,3-diynyl)-phenyl)-acetamide provide a straightforward entry into 3,3′-disubstituted-2,2′-biindolyls. Subsequent application of the procedure to homochiral aryl iodides affords the corresponding chiral 3,3′-disubstituted-2,2′-biindolyls. The methodology can also be applied to the synthesis of benzo[c]indolo[2,3-a]carbazoles.     

Rhodium and iridium complexes of N-heterocyclic carbenes: Structural investigations and their catalytic properties in the borylation reaction

Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)₂Cl]₂ to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)₂][Cl,I] [COD = 1,5-cyclooctadiene, NHC =  1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η⁴-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η⁴-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.