A concise modular synthesis of 2,5-diethynyl-3,4-dibutyl-thiophene-bridged back-to-back terpyridine ligands

The efficient synthesis of soluble and rigid terpyridine-based ditopic ligands bearing an increasing number of 2,5-diethynyl-3,4-dibutylthiophene (DEDBT) modules has demonstrated the advantages of a single convergent strategy based on a double coupling in a final step of monoterpyridine building blocks carrying the adequate number of thiophene modules with a diiodo-substituted thiophene subunit. This protocol enjoys the advantages of both efficiency and versatility and requires pivotal intermediates, which were produced by a step-by-step implementation of monoterpyridine fragments with a key thiophene intermediate carrying an iodo function, a propargylic-protecting group, and two butyl-solubilizing fragments. One set of experimental conditions is required to produce all the intermediates and the final ligands. Oxidative dimerization of monosubstituted terpyridine skeletons bearing one or two thiophene substituents and a terminal alkyne function, in the presence of cupric salts and oxygen, afforded the homotopic ligands with a central dithienylbutadiyne spacer. Optical properties for the new oligomers have been investigated and are discussed in terms of effective conjugation length and pi-electron conjugation. Upon increasing the number of interspersed DEDBT units, a significant lowering in energy of absorption and fluorescence transitions as well as of the quantum yields is observed.     

Polyoxometalates covalently bonded with terpyridine ligands

A terpyridine ligand is covalently linked to a hexamolybdate cluster through the Mo-N imido bond, paving the way for the preparation of hybrids containing covalently bonded transition metal complexes and polyoxometalate clusters.     

Mononuclear and binuclear wirelike ruthenium(II) complexes with oligo-diethynyl-thiophene bridged back-to-back terpyridine ligands: synthesis and electrochemical and photophysical properties

The syntheses, structural features, electrochemical behavior, absorption spectra, and photophysical properties of five mononuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)](2+), RuT(n), and five binuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)Ru(terpy)](4+), RuT(n)Ru, are reported, where n varies from 1 to 5 so that the metal-metal distance is estimated to be 42 A for the largest binuclear complex, RuT(5)Ru (terpy is 2,2':6',2"-terpyridine and DEDBT is 2,5-diethynyl-3,4-dibutylthiophene). The metal-centered oxidation potentials for the mononuclear and binuclear species are slightly more positive than for the reference [Ru(terpy)(2)](2+) complex, owing to the withdrawing nature of the back-to-back terpyridine ligands incorporating the repeat diethynyl-thiophene units. Comparison of the reduction potentials for the mononuclear and binuclear complexes reveals that the reduction steps are localized either at the terpy fragments of the T(n) ligands or at the terpy peripheral ligands. The spectroscopic results (absorption spectra at room temperature, luminescence spectra and lifetimes at room temperature and at 77 K) in acetonitrile solvent are consistent with the establishment of electronic delocalization within the oligomeric diethynyl-thiophene fragments (DEDBT(n)) of the T(n) ligands; however, the results also indicate that the terpy units of these ligands and the DEDBT(n)fragments are not strongly coupled. Both at room temperature and at 77 K, the (3)metal-to-ligand charge-transfer luminescence of RuT(n) and RuT(n)Ru complexes is strongly depressed in the larger species with respect to what happens for n < or = 2 (where the luminescence quantum yield is phi approximately 10(-4)); this is discussed in terms of the possible intervention of triplet levels localized at the oligothiophene DEDBT(n)(fragments.     

Soluble IF-ReS2 nanoparticles by surface functionalization with terpyridine ligands

A major drawback in the application of layered chalcogenide nanoparticles/tubes is their inertness to chemical and biological modification and functionalization. Their potential use in composite materials might be greatly enhanced by improving the chalcogenide/matrix interface bonding. A novel modification strategy for layered chalcogenide nanoparticles based on the chalcophilic affinity of metals and the chelating terpyridine is reported. The terpyridine anchor group can be conjugated to fluorescent tags or hydrophilic/hydrophobic groups that confer solubility in various solvents to the otherwise insoluble chalcogenide nanoparticles. The functionalized particles are characterized using TEM/HRTEM, optical and vibrational spectroscopy, and confocal laser scanning microscopy.     

Rare earth compounds with 3-methoxybenzoic acid and terpyridine ligands

Journal of Thermal Analysis and Calorimetry - Two trivalent rare earth compounds [Ln(3-MOBA)3(terpy)(H2O)]2 (Ln?=?Tb (1), Eu (2); 3-MOBA?=?3-methoxybenzoate,...     

Synthesis of light-harvesting dendrimers focally anchored with crown ethers or terpyridine ligands

Crown ethers and terpyridine ligands have been successfully attached to the focal point of light harvesting phenylacetylene monodendrons through Pd-catalyzed coupling reactions. The structures of these functional monodendrons were characterized by 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis. Such binding-ligand anchored dendrons exhibit broad absorption, large molar extenction coefficients and high fluoresence quantum yields. Coordination of crown ethers with alkali ions results in a significant increase in absorption strength in the UV range, but little alteration in either intensity or position of fluorescence emission. Coordination of terpyridine ligands with Ru2+, however, does efficiently quench the fluorescence from the dendrons,albeit only the smallest dendron exhibits efficient binding.     

Synthesis and properties of novel ditopic polypyridine ligands bridged by one and two acetylenic bonds

Ethynyl substituted bipyridine chelates react with bromo or triflate functionalized bipyridine or terpyridine subunits, in the presence of catalytic amounts of Pd^o(PPh₃)₄ to yield, the new homo- and heteroditopic ethynyl bridge ligands 2a, 4a, 7a and 8. Self coupling of the ethynyl substituted bipyridine species in the presence of CuCl/TMEDA/O₂, yield the symmetric diethynyl bridge ligands 2b, 4b and 7b.     

Tuning the thermotropic and lyotropic properties of liquid-crystalline terpyridine ligands

A rational synthetic strategy is developed to provide compact and simple terpyridine (terpy) mesogens that show liquid-crystallinity both as pure compounds and in organic solution (amphotropic compound). The use of a central 4-methyl-3,5-diacylaminophenyl platform equipped with two lateral aromatic rings, each bearing three appended aliphatic chains, allows connection of a 2,2':6',2'-terpyridine fragment through a polar group such as an ester, amide, or flat conjugated alkyne linker. For the T(12)ester and T(12)amide scaffolds, the mesophase is best described as a lamellar phase, in which the molecules self-assemble into columnar stacks held together in layers. In the T(12)amide case, the additional amide link results in significant stabilization of the lamellar phase. The driving forces for the appearance of columnar ordering are the hydrogen-bonding interactions of the amide groups, which induce head-to-tail pi-stacking of the terpy subunits. Replacing the polar linker by a nonpolarized but linear alkyne spacer, as in the T(12)ethynyl compound, provides a columnar mesophase organized in a rectangular lattice of p2gg symmetry. In this arrangement, two nondiscotic molecules arranged into dimers by hydrogen bonding and pi-pi stacking pile up in a head-to-tail manner to form columns. In addition, the T(12)amide compound proves to be an excellent gelator of cyclohexane, linear alkanes, and DMSO. The resulting robust and transparent gels are birefringent and formed by large aggregates that are readily aligned by shear-flow. TEM and freeze-fracture microscopy reveal that the gels have an original layered morphology made of fibers.     

Synthesis of substituted terpyridine ligands for use in protein purification

A number of 4,4″-disubstituted terpyridines bearing a 4′-thioethanamine linker, and regioisomers thereof, have been synthesised from 4-substituted picolinates. The substituted terpyridines were immobilised onto epoxy-activated Sepharose™ FF gel, creating functionalised solid supports for the fractionation of proteins—including antibodies—by mixed mode affinity chromatography. The metal chelating properties of the immobilised ligand render the stationary phase also amenable for use in immobilised metal-ion affinity chromatography (IMAC), and have been demonstrated with the purification of suitably tagged green fluorescent protein (GFP).     

Synthesis and characterisation of thieno[3,2-b]thiophene-based linear shaped liquid crystals

A series of thieno[3,2-b]thiophene-based liquid crystalline molecules has been synthesised. To investigate the effects of alkyl substituent groups and structure of mesogenic cores, eight kinds of thieno[3,2-b]thiophene-based molecules containing different alkyl substituent groups and mesogenic cores have been synthesised. These molecules were characterised by differential scanning calorimetry, polarising optical microscopy, ultraviolet–visible absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and polarised fluorescence spectroscopy. The results indicated that the thieno[3,2-b]thiophene-based donor-acceptor-donor (D-A-D) type molecules showed the presence of a smectic A phase. Changes in the length of alkyl substituents and mesogenic cores affected the phase transitions, optical and electrochemical properties of the molecules.     

Observation of internal electron transfer in bulky allyl ytterbium complexes with substituted terpyridine ligands

A series of new bulky allyl terpyridyl-ytterbium complexes have been synthesized to determine the effect of allyl ligands on the internal charge-transfer process that exists in these materials. Compared to the pentamethylcyclopentadienyl-ytterbocene compound Cp*2Yb(tpyCN) (nu(C(triple bond)N) = 2172 cm(-1)), the symmetrically substituted allyl complex [1,3-(SiMe3)2C3H3]2Yb(tpyCN) possesses a markedly lowered C(triple bond)N frequency of 2130 cm(-1). Furthermore, the electronic nature of these bulky allyl complexes can be tuned, as demonstrated by the C(triple bond)N frequency of the asymmetric derivatives [1-(SiMe3)C3H4]2Yb(tpyCN) and [1-(SiPh3)-3-(SiMe3)C3H3]2Yb(tpyCN) (2171 and 2164 cm(-1), respectively). The differences in these frequencies can be attributed to differences in the ligands' steric and electronic character. Single-crystal X-ray characterization of [1,3-(SiMe3)2C3H3]2Yb(tpy) reveals that the allyl moiety possesses shorter Yb-C and Yb-N bond distances than the Cp* analogue. The magnetic susceptibility data for [1,3-(SiMe3)2C3H3]2Yb(tpy) departs dramatically from the Curie law, with a room-temperature magnetic moment of 2.95 mu(B).     

Facile construction of novel polycyclic ring systems using a metallocarbenoid-induced cyclization of acetylenic diazo carbonyl compounds

The Rh(II)-catalyzed reaction of diazo 2-propynyl maolonamic acid ester derivatives produce furo[3,4-c]furans in excellent yield. The methodology was applied to the synthesis of several polyheterocyclic systems by first generating a 2-alkoxy-substituted furan and then allowing it to undergo a subsequent intramolecular Diels-Alder cycloaddition. Ring opening of the resulting cycloadduct is followed by deprotonation to furnish a rearranged keto lactone.     

Cobalt complexes of terpyridine ligands: Crystal structure and nuclease activity

Cobalt(II) (1) and cobalt(III) (2) complexes of tridentate ligand, imidazole terpyridine (Itpy), have been synthesized and characterized by both spectroscopic and electrochemical techniques. Single crystal X-ray diffraction studies of complexes 1 and 2 shows that the complexes belong to monoclinic crystal system, with the two Itpy ligands coordinated to the central metal ion. The binding behavior of both the cobalt complexes to calf thymus DNA has been investigated by UV–Vis, fluorescence spectroscopy, viscosity and electrochemical measurements. The results suggest that complexes 1 and 2 bind to DNA through intercalation. The intrinsic DNA binding constant values obtained from absorption spectral titration studies were found to be (5.07 ± 0.12) × 10³ M⁻¹ and (7.46 ± 0.16) × 10³ M⁻¹, respectively, for complexes 1 and 2. Gel electrophoresis studies with the cobalt complexes show that while complex 1 cleaves DNA in the presence of hydrogen peroxide, complex 2 cleaves DNA in the presence of ascorbic acid and hydrogen peroxide.     

Recognition-directed supramolecular assemblies of metal complexes of terpyridine derived ligands with self-complementary hydrogen bonding sites

The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but partially broken grid with a quarter of the H-bonding sites unsaturated (d(N-H-N)=2.984-3.206 A). In the case of the Zn complex 12 with triflate anions, half of the hydrogen bonds are formed. Only one of the two orthogonal ligands has hydrogen bonds (d(N-H-N) = 3.082, 3.096 A) to the neighbouring complexes and thus builds linear, supramolecular, polymeric chains. These structural differences are mainly attributed to crystal-packing effects caused by the different anions. The data presented here may also be regarded as a prototype for the generation of organised arrays through sequential self-assembly processes.     

Synthesis of multicomponent systems composed of one phthalocyanine and four terpyridine ligands

Two phthalocyanine-based multiple ligands were synthesized and characterized. Photochemical and electrochemical properties were measured for zinc(II) phthalocyanines covalently linked with four ruthenium(II) bisterpyridyl complexes. The absorption and electrochemical results are indicative of electronic interaction between two photoactive and redox-active components. Fluorescence spectroscopy of the five nuclear complexes provides evidence of an efficient photoinduced intramolecular energy transfer between the ruthenium-based metal-to-ligand charge-transfer (MLCT) chromophores and the zinc(II) phthalocyanine core. The absorption and fluorescence spectra of the phthalocyanine-based multiple ligands change dramatically as a result of the coordination of metal ions with peripheral terpyridine ligands. This change of fluorescence intensity upon addition of metal ions can apply to an output signal for metal ion sensing. The direct attachment of metal ion receptors with a zinc phthalocyanine core enhanced efficiency of the energy- and electron-transfer reaction from the core to the metal complexes.     

Columnar assembly formation and metal binding of cyclic tri-beta-peptides having terpyridine ligands

[reaction: see text] A novel cyclic tri-beta-peptide having terpyridine (tpy) metal ligands was synthesized to investigate its assembly formation and metal complexation. Microscopic observation revealed that this cyclic peptide formed a rod-shaped molecular assembly. The assembly was able to bind Cu(II) because the tpy ligands covered the surface of the crystal, keeping the tpy plane parallel to the ring plane of the cyclic tri-beta-peptide.     

Syntheses of novel di- and trinucleating ligands having a triethylbenzene core with N,N-bidentate tethers: their complexation toward Pd and Rh organometallic fragments

A series of di- and trinucleating ligands with a 1,3,5-triethylbenzene core connected to N,N-bidentate tethers was synthesized. The ligands readily reacted with monuclear Rh and Pd precursors to give the corresponding di- and trinuclear complexes, which were characterized by using NMR and ESI mass spectroscopy. In the solid state, the trinuclear complexes with ligands having pyridylpyrazolyl tethers adopt the most stable ababab configuration, in which the organometallic fragments are on the same side of the benzene plane. On the other hand, in solution, the linker moieties between the benzene core and the metals are flexible enough to interconvert between other configurations, that is, they exhibit dynamic behavior, and the rotational barrier was dependent on the length of the linkers. From variable temperature (VT) 1H NMR measurements, the rotational barrier for a trinuclear Rh-CO complex with a ligand having methylene linkers was estimated to be approximately 12.6 kcal mol(-1). However, no spectral changes were observed for the ethylene derivative in the temperature range of -60 degrees C to 50 degrees C, indicating that the rotation was not frozen out on the 1H NMR timescale, even at -60 degrees C.     

Photophysical properties and energy transfer pathway of Er(III) complexes with Pt-porphyrin and terpyridine ligands

The photophysical properties of Er(III) complexes coordinated with platinum[5,10,15-triphenyl-20-(4-carboxyphenyl)-porphyrin] (PtP) and terpyridine (tpy) ligands in organic solution were investigated. The Er(III) complex emitted sensitized near-IR (NIR) luminescence when the PtP ligands were excited under deoxygenated conditions. The quantum yield (PhiLn) of the sensitized luminescence was 0.015%, as evaluated from luminescence lifetime. The photophysical studies and theoretical calculations suggest that the F?rster resonance mechanism is very suitable for the energy transfer from PtP to the Er(III) ion and occurred through the first triplet excited state of PtP. The 12.3% energy transfer from the triplet state to the 4F9/2 and 4I9/2 states of Er(III) occurred with a rate distribution of 3.36x10(5) and 6.67x10(4) s(-1), respectively. In addition, the observed triplet quantum yield of the PtP ligand in [Ln(PtP)3(tpy)] proved that the energy transfer from the singlet excited state of the PtP ligand to the Er(III) ion did not take place.