W Tungsten

The efficient, regioselective synthesis of functionalized/annulated quinolines was achieved by the coupling of 2-aminoaryl ketones with alkynes/active methylenes/α-oxoketene dithioacetals promoted by InCl₃ in refluxing acetonitrile as well as under solvent-free conditions in excellent yields. This transformation presumably proceeded through the hydroamination–hydroarylation of alkynes, and the Friedländer annulation of active methylene compounds and α-oxoketene dithioacetals with 2-aminoarylketones. In addition, simple reductive and oxidative cyclization of 2-nitrobenzaldehyde and 2-aminobenzylalcohol, respectively, afforded substituted quinolines. Systematic optimization of the reaction parameters allowed us to identify two-component coupling (2CC) conditions that were tolerant of a wide range of functional groups, thereby providing densely functionalized/annulated quinolines. This approach tolerates the synthesis of various bioactive quinoline frameworks from the same 2-aminoarylketones under mild conditions, thus making this strategy highly useful in diversity-oriented synthesis (DOS). The scope and limitations of the alkyne-, activated methylene-, and α-oxoketene dithioacetal components on the reaction were also investigated.

In it to wIn it: The regioselective synthesis of functionalized/annulated quinolines involved the coupling of 2-aminoaryl/alkyl ketones with alkynes/activated-methylenes/α-oxoketene-dithioacetals promoted by InCl₃ in MeCN as well as under solvent-free conditions. Simple reductive and oxidative cyclization of 2-nitrobenzaldehyde and 2-aminobenzyl alcohol, respectively, has also been performed to give substituted quinolines.

Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host–guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.

Tioeetterisilloitettuja tetrametoksiresorsinareeneja valmistettiin sitomaan pehmeitä metallikationeja kuten hopeaa. Sitoutumisominaisuuksia tutkittiin sekä liuoksessa että kiinteässä tilassa hyödyntäen NMR-spektroskopiaa ja yksikideröntgenkristallografiaa. Tutkimuksissa huomattiin bistiakruunujen sitovan hopeakationeja huomattavalla affiniteetilla ja liuoksessa 1:2 isäntä-vieraskompleksit muodostuivat nopeasti. Kiinteän tilan rakenteet paljastivat yllättävän hopeakationin endo- ja ekso-sitoutumisen samassa resorsinareenimolekyylissä, jossa toinen hopeakationi oli sitoutuneena resorsinareenin onkalon sisään ja toinen sen ulkopuolelle. Sekä liuos- että kiinteätilan tutkimuksissa huomattiin rikkiatomien muodostavan merkittävimmät sitomisvuorovaikutukset hopeakationin kanssa.

Binding it soft but strong: Resorcinarene bis-thiacrowns containing soft sulfur donor atoms are shown to be ideal host molecules for high-affinity encapsulation of silver inside the resorcinarene cavity. A 1:2 host–guest binding was observed both in solution and in the solid state.

We have developed a ladder-type dithienocyclopentathieno[3,2-b]thiophene (DTCTT) hexacyclic unit in which the central thieno[3,2-b]thiophene ring was covalently fastened to two adjacent thiophene rings through carbon bridges, thereby forming two connected cyclopentadithiophene (CPDT) units in a hexacyclic coplanar structure. This stannylated Sn-DTCTT building block was copolymerized with three electron-deficient acceptors, dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD), dibromo-benzothiadiazole (BT), and dibromo-phenanthrenequinoxaline (PQX), by Stille polymerization, thereby furnishing a new class of alternating donor–acceptor copolymers: PDTCTTTPD, PDTCTTBT, and PDTCTTPQX, respectively. Field-effect transistors based on PDTCTTPQX and PDTCTTBT yielded high hole mobilities of 0.017 and 0.053 cm² V⁻¹ s⁻¹, respectively, which are among the highest performances among amorphous donor–acceptor copolymers. A bulk heterojunction solar cell that incorporated PDTCTTTPD with the lower-lying HOMO energy level delivered a higher V_oc value of 0.72 V and a power conversion efficiency (PCE) value of 2.59 %.

Snakes and ladders: Donor–acceptor polymers based on the ladder-type dithienocyclopentathieno[3,2-b]thiophene (DTCTT) unit has promising performance for solution-processed organic transistors and photovoltaics.

Triquinacene is a concave tricyclic hydrocarbon with diverse photoreactivity. In the cavity of an electron-accepting molecular host, triquinacene was specifically photooxidized at the peripheral allylic position into an alcohol, 1-hydroxytriquinacene, via guest-to-host electron transfer. The unusual reactivity stems from the extremely electron-deficient triazine panel ligand of the host cage, which allows the cage to function as a good electron acceptor. Thus, self-assembled coordination cages can serve not only as molecular-sized reaction vessels but also function electronically as redox media. Dissolved molecular oxygen is indispensable for the photoreaction and immediately traps a photogenerated radical.

Electron-withdrawing cage: A self-assembled coordination cage accommodates triquinacene (1) to allow a specific photooxidation of the peripheral allylic position via guest-to-host electron transfer. The host cage consists of electron-deficient triazine panels and thus serves as a photochemically active molecular container.

Golden donuts: Polystyrene-block-poly(2-vinylpyridine) block copolymer (BCP) corpuscle templates were prepared on PS-modified substrates. Subsequent metal–polymer complexation and reduction resulted in the formation of gold double-ring structures.

The hydrofullerene C₅₀H₁₀ is synthesized by low-pressure benzene–oxygen diffusion combustion. The structure of C₅₀H₁₀ is identified through NMR, mass spectrometry, and IR and Raman spectroscopy as a D_5h symmetric closed-cage molecule with five pairs of fused pentagons stabilized by ten hydrogen atoms. UV/Vis and fluorescence spectrometric analyses disclose its optical properties as comparable with those of its chloride cousin (C₅₀Cl₁₀). Cyclic and square-wave voltammograms reveal that the first reduction potential of C₅₀H₁₀ is more negative than that of C₅₀Cl₁₀ as well as C₆₀, with implications for the utilization of C₅₀H₁₀ as a promising electron acceptor for photovoltaic applications.

Hydrofullerene electron acceptor: The small hydrofullerene C₅₀H₁₀ with D_5h symmetry was synthesized by low-pressure benzene–oxygen diffusion combustion, and identified by NMR, mass spectrometry, and IR and Raman spectroscopy. In comparison with its chlorofullerene cousin, C₅₀H₁₀ shows similar optical properties and potentially useful electrochemical properties (see figure).

A series of rhenium(I) diimine complexes cis,trans-[Re(dmb)(CO)₂(PR¹R²R³)(PR⁴R⁵R⁶)]⁺ (dmb=4,4′-dimethyl-2,2′-bipyridine, Rⁿ=phenyl or alkyl), each of which bears two phosphine ligands with various numbers of phenyl groups, has been synthesized by using the photochemical ligand-substitution reaction. Detailed studies of the structural features, not only in the crystal but also in solution, indicate that the number of phenyl groups is a crucial factor in controlling the rotational conformation of the phosphine ligands, which in turn determines the extent of the π–π interaction between the aromatic diimine ligand and the phenyl group(s). The π–π interaction strongly affected both electrochemical and photophysical properties: 1) the oxidation power of the Re complex became stronger, 2) the lifetime of the excited state became longer, and 3) the Stokes shift between the ¹MLCT absorption band and emission from the corresponding ³MLCT excited state became smaller. In particular, the diphenyl and triphenyl phosphine had much greater influence on the properties than the monophenyl phosphine ligand. Dual emission was observed from the different rotational conformers of the complexes with an intermediate number of phenyl groups in the phosphine ligands.

A group effort: Several rhenium(I) diimine complexes that bear two phosphine ligands with various numbers of phenyl groups exhibited dual emission modulated by the π–π interaction between the aromatic diimine ligand and the phenyl group(s) (see figure). The number of phenyl groups is crucial in controlling the rotational conformation of the phosphine ligands.

Polynuclear single-molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso-oriented magnetic units. Crystalline solid solutions of an Fe₄ SMM and its Ga₄ analogue were prepared with no metal scrambling for Fe₄ molar fractions x down to 0.01. According to high-frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high-temperature spin dynamics found in the pure Fe₄ phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe₄ phase exhibits additional steps which are firmly ascribed to two-molecule QT transitions. Studies on the field-dependent relaxation rate showed that the zero-field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe₄ concentration: the zero-field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment.

Single-molecule magnets (SMMs) as dopants: Crystals of a diamagnetic Ga₄ complex have been doped with the Fe₄ analogue to afford arrays of independent and iso-oriented SMMs. Suppression of intermolecular communication has a strong influence on magnetic relaxation in the low-temperature regime, leading to the disappearance of two-molecule quantum tunneling effects and to profound reshaping of hysteresis loops (see figure; Hdpm=dipivaloylmethane).

A supramolecular system that can activate an enzyme through photo-isomerization was constructed by using a liposomal membrane scaffold. The design of the system was inspired by natural signal transduction systems, in which enzymes amplify external signals to control signal transduction pathways. The liposomal membrane, which provided a scaffold for the system, was prepared by self-assembly of a photoresponsive receptor and a cationic synthetic lipid. NADH-dependent L-lactate dehydrogenase, the signal amplifier, was immobilized on the liposomal surface by electrostatic interactions. Recognition of photonic signals by the membrane-bound receptor induced photo-isomerization, which significantly altered the receptor’s metal-binding affinity. The response to the photonic signal was transmitted to the enzyme by Cu²⁺ ions. The enzyme amplified the chemical information through a catalytic reaction to generate the intended output signal.

trans-formers: A supramolecular system that is capable of activating an enzyme through photoisomerization was constructed on a liposomal membrane. Quantitative evaluation of the present system by using CD and UV spectroscopy showed that enzyme activity was effectively regulated by the specific recognition of the photonic signal by the receptor and its response (see Scheme).

Ruthenium(III)-substituted α-Keggin-type silicotungstates with pyridine-based ligands, [SiW₁₁O₃₉Ru^III(Py)]⁵⁻, (Py: pyridine (1), 4-pyridine-carboxylic acid (2), 4,4′-bipyridine (3), 4-pyridine-acetamide (4), and 4-pyridine-methanol (5)) were prepared by reacting [SiW₁₁O₃₉Ru^III(H₂O)]⁵⁻ with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X-ray absorption near-edge structure (XANES) analysis (Ru K-edge and L₃-edge). Single-crystal X-ray analysis of compounds 2, 3, and 4 revealed that Ru^III was incorporated in the α-Keggin framework and was coordinated by pyridine derivatives through a RuN bond. In the solid state, compounds 2 and 3 formed a dimer through ππ interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru^III–Py was reversibly oxidized into the Ru^IV–Py derivative and reduced into the Ru^II–Py derivative.

Py in the sky: Preparation, structural characterization, and redox studies of Ru^III–pyridine-substituted α-Keggin-type silicotungstate hybrid molecules, [SiW₁₁O₃₉Ru^III(Py)]⁵⁻, are reported. Ru^IV was stabilized in silicotungstate.