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.     

An M2L4 Molecular Capsule with a Redox Switchable Polyradical Shell

Preparation of molecular nanostructures with polyradical frameworks remains a significant challenge because of the limited synthetic accessibility which is entirely different from that of neutral and ionic ones. Herein we report the quantitative formation of a new M₂L₄ molecular capsule from metal ions and dihydrophenazine‐based ligands. The capsule has a spherical nanocavity (ca. 1 nm in diameter) enclosed by eight redox‐active, dihydrophenazine panels. Electrochemical oxidation of the capsule leads to the generation of multiple radical cations on the shell framework. Moreover, a stable tetra(radical cation) capsule can be reversibly obtained by chemical as well as electrochemical oxidation.     

Anticancer Potencies of PtII‐ and PdII‐linked M2L4 Coordination Capsules with Improved Selectivity

Pt^II‐ and Pd^II‐linked M₂L₄ coordination capsules, providing a confined cavity encircled by polyaromatic frameworks, exhibit anticancer activities superior to cisplatin against two types of leukemic cells (HL‐60 and SKW‐3) and pronounced toxicity against cisplatin‐resistant cells (HL‐60/CDDP). Notably, the cytotoxic selectivities of the Pt^II and Pd^II capsules toward cancerous cells are up to 5.3‐fold higher than that of cisplatin, as estimated through the non‐malignant/malignant‐cells toxicity ratio employing normal kidney cells (HEK‐293). In addition, the anticancer activity of the coordination capsules can be easily altered upon encapsulation of organic guest molecules.     

Photo-activation of Pd-catalyzed Sonogashira coupling using a Ru/bipyridine complex as energy transfer agent

The mixed catalyst system, Pd(CH3CN)2Cl2/P(t-Bu)3/[Ru(2,2'-bipyridine)3].2PF6, promotes the copper-free Sonogashira coupling reaction of aryl bromides at room temperature under irradiation of visible light.     

Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid studied by low-temperature matrix-isolation infrared spectroscopy

Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid has been investigated by low-temperature matrix-isolation infrared spectroscopy with the aid of density functional theory calculation. Infrared spectra of two relatively stable syn isomers, SC and ST, were observed in argon and xenon matrixes. When the matrix samples were annealed after deposition, the isomerization from ST to SC occurred around the benzene-carboxyl bond. Two less stable anti isomers, AT, which has an OH...Cl intramolecular hydrogen bond, and AC, which has no OH...Cl bond, were produced from SC and ST upon UV irradiation. When the matrix samples were kept in the dark after UV irradiation, AT and AC changed to ST and SC, respectively, by spontaneous isomerization around the C-O axis in the carboxyl group. The rate constants of isomerization, AT --> ST, in a Xe matrix were estimated from the absorbance changes at various matrix temperatures. The rate constants showed a drastic decrease in deuteration of the hydrogen atom of the carboxyl group. The relationship between the rate constants and the matrix temperature did not follow the Arrhenius law. These findings lead to the conclusion that the isomerization of AT --> ST and AC --> SC in low-temperature rare-gas matrixes proceeds through intramolecular hydrogen atom tunneling.     

Immobilized triazine-type dehydrocondensing reagents for carboxamide formation: ROMP-Trz-Cl and ROMP(OH)-Trz-Cl

New triazine-type dehydrocondensing reagents, such as ROMP-Trz-Cl and ROMP(OH)-Trz-Cl, were synthesized by a ring opening metathesis polymerization (ROMP) method, and these showed higher loading than conventional polymer-supported condensing reagents. These polymers effect the formation of amides in good yields by addition of a mixture of carboxylic acid, amine and NMM. ROMP(OH)-Trz-Cl, which contains hydroxyl groups in the polymer chain, gave amides in good yields even in MeOH.     

Chiral Sensing Using Circularly Polarized Luminescence of Bis(phenanthroline dicarboxylic acid) EuIII Complex Induced by Allosteric‐type Interaction with Amino Acid Molecules

[Eu(pda)₂]^? and [Eu(bda)₂]^? (pda=1,10‐phenanthroline‐2, 9‐dicarboxylic acid; bda=2,2′ bipyridine 5,5′‐dicarboxylic acid) have an achiral D_2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)₂]^? and [Eu(bda)₂]^? in water solutions containing a mixture of d ‐ and l ‐ amino acids were examined. Plots of g_lum values of the induced CPL as a function of mol‐fraction of l ‐ and d ‐ arginine reveal that [Eu(pda)₂]^? favors homo‐association ([Eu(pda)₂]^?‐(l ‐arginine)₂ or [Eu(pda)₂]^?‐(d ‐arginine)₂) over hetero‐association {[Eu(pda)₂]^?‐(l ‐arginine)?(d ‐arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)₂]^? to promote chiral selective association to another arginine, i.e., homo‐allosteric association. On the other hand, the system of [Eu(pda)₂]^? with histidine favors hetero‐allosteric association over homo‐association. No allosteric effect is recognized in CPL from [Eu(bda)₂]^?.     

Ion–ion interactions of LiPF6 and LiBF4 in propylene carbonate solutions

Self-diffusion coefficients of Li⁺ D_Li⁺, PF₆⁻ D_PF6⁻ and solvent propylene carbonate (PC) D_PC in LiPF₆−PC solutions were determined at 298 K by the pulse gradient spin echo (PGSE) NMR technique over the salt concentration range of 0.1–3.0 M (M = mol dm^– 3). The order of the diffusion coefficients was found to be D_Li⁺ < D_PF6⁻ < D_PC over the concentration range examined, and they were monotonically decreased with increasing the salt concentration. Haven ratio Λ/Λ_NMR, where Λ and Λ_NMR represent the ionic conductivity measured electrochemically and that estimated via the Nernst-Einstein equation using the diffusion coefficient, respectively, was evaluated as the measure of the ion–ion interaction in the LiPF₆–PC solutions. Though Λ/Λ_NMR values for LiPF₆-solutions decrease with increasing the salt concentration, they were greater than those for LiBF₄–PC solutions over the whole concentration range examined, which indicates that the ion pair formation ability of PF₆^– ion is weaker than that of the BF₄^– ion. The smaller value of the ionic conductivity for the highly concentrated LiPF₆–PC solution (above 2.0 M) than that of the LiBF₄-solutions can be attributed to the more rapidly increased viscosity relative to the LiBF₄-solution. Classic molecular dynamics (MD) simulations for the respective LiPF₆ and LiBF₄-solution of 0.5 and 1.0 M were also carried out based on the effective pair potentials. Diffusion coefficients, ionic conductivity and Haven ratio for these solutions were calculated from MD trajectories, and they qualitatively agree with those evaluated by experiments. Pair correlation functions g_LiO(r) (for Li⁺–O (PC) pair) and g_LiPF6(r) (for Li⁺–PF₆^– pair) or g_LiBF4(r) (for Li⁺–BF₄^– pair) revealed that the lithium ion weakly forms the contact ion pairs with PF₆^–, whilst strongly with BF₄^–, which supports the present experimental results. Moreover, the simulation results show that both anions in the contact ion pairs predominantly take the monodentate form, which is in contrast to the multidentate coordination predicted by ab initio calculation in gas phase.     

Purcell effect of GaAs quantum dots by photonic crystal microcavities

We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results.