Reversible haptotropic shift in zirconocene-hexapentaene complexes

Low-valent zirconocene species reacted with 1,1,6,6-tetraalkyl-1,2,3,4,5-hexapentaenes to form both 1-zirconacyclopent-3-ynes and eta2-pi-coordinated complexes according to the alkyl groups (R) and the existence of the neutral ligand (L). Haptotropic interconvertion between these two complexes was observed. It was proposed that double insertion of isocyanide into the Zr-C bond of 1-zirconacyclopent-3-ynes takes place via the isocyanide adduct of the eta2-pi-complex as an intermediate.     

One-pot concise syntheses of benzimidazo[2,1-a]isoquinolines by a microwave-accelerated tandem process

Direct, efficient syntheses of the benzimidazo[2,1-a]isoquinoline ring system have been achieved with 2-bromoarylaldehydes, terminal alkynes, and 1,2-phenylenediamines by a microwave-accelerated tandem process in which a Sonogashira coupling, 5-endo cyclization, oxidative aromatization, and 6-endo cyclization can be performed in a single synthetic operation.     

Allosteric coextraction of sodium and metal ions with calix[4]arene derivatives 1

Solvent extraction of three alkali metal ions with p-t-octylcalix[6]arene hexacarboxylic acid, p-t-octylcalix[4]arene tetracarboxylic acid, corresponding linear trimeric and monomeric analogs was investigated. Cyclic tetramer selectively extracts sodium ion among alkali ions at extremely low pH, while the corresponding cyclic hexamer, the trimer, and the monomer exhibited only poor extraction ability for all alkali metals examined. The detailed extractive investigation of sodium ions with the cyclic tetramer was carried out. It was found that two sodium ions are simultaneously extracted by a single molecule of calix[4]arene derivative and that the second sodium extraction is facilitated by the uptake of the first sodium. The self-coextraction mechanism of sodium ions proposed in the present paper also strongly supports allosteric coextraction of sodium and other metal ions. In the competitive extraction of four alkali metal ions, potassium ion was slightly extracted as the second ion at low pH region, whereas it was hardly extracted in the individual extraction system. The result also supports the coextraction mechanism and role of the first-extracted sodium ion as an allosteric trigger. The extraction equilibrium constants of the cyclic tetramer and two sodium ions, K _ex1 and K _ex2, were estimated.     

Preparation of calix[4]arene methylene crosslinked resins with 2-pyridyl pendant group and their adsorption behavior towards silver ion

Three different resins namely 1:5 MC-resin, 1:3 MC-resin and 1:1 MC-resin have been synthesized by methylene crosslinking of 2-pyridylcalix[4]arene. Adsorption behavior of these resins towards the metal ions existing in photographic waste was investigated. The resins show absolute efficiency for adsorption of silver ion with no affinity for other coexisting ions. First two resins form 1:1 complex whereas the third one forms 2:1 complex with silver ion. Maximum loading capacity of silver ion on the present resins was found to be 1.15, 1.29 and 0.69 mol kg^?1, respectively. Column chromatographic separation of silver ion in presence of excess of sodium ions was also carried out with 1:5 MC-resin. Selective adsorption of silver ions over excess of sodium ions was achieved.     

Low-temperature heat capacity of triangle antiferromagnetic molecular clusters K12[(VO)3(SbW9O33)2]·15H2O and K12[(VO)3(BiW9O33)2]·29H2O

Energy level diagrams have been determined for two molecular clusters, K₁₂[(VO)₃(SbW₉O₃₃)₂]·15H₂O and K₁₂[(VO)₃(BiW₉O₃₃)₂]·29H₂O, by low-temperature heat capacity measurements down to 85 mK under magnetic field strengths up to 9 T. Both compounds exhibit a broad heat capacity peak dependent upon the magnetic field, which can be explained by the thermal excitation in the magnetic energy levels. A detailed analysis based on the numerical calculation reveals that the spin-spin interaction between the V⁴⁺ ions includes a Dzyaloshinskii-Moriya interaction.     

Influence of shell strength on shape transformation of micron-sized,monodisperse, hollow polymer particles

Micron-sized, monodisperse, non-spherical polymer particles with "rugby ball" and "red blood corpuscle"-like shapes were produced by seeded polymerization of the dispersion of (divinylbenzene/vinylbiphenyl/xylene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method which the authors proposed in 1991. Their non-spherical shapes were based on buckling of the shell of the resultant hollow particles. In this article, the reversible shape transformation of the hollow composite polymer particle between spherical and such non-spherical shapes was studied in detail by controlling the shell strength. A part of the shell was buckled by external pressure which was caused by evaporation of xylene from the hollow when the shell had the tensile modulus below the critical value calculated from the pressure-buckling relationship of a spherical shell proposed by Uemura. The plasticization of the shell by a good solvent was one of key factors for the shape transformation.     

Addition of alkyl radicals, generated from carboxylic acids via photochemical decarboxylation, to glyoxylic oxime ether: a mild and efficient route to α-substituted α-aminoesters

Radical addition to a glyoxylic oxime ether was accomplished under mild conditions using an alkyl radical generated from a free carboxylic acid via photochemical decarboxylation. The photoreaction provided an efficient route to α-substituted α-aminoesters from carboxylic acids and oxime ether.     

Oxygen‐sensing properties of 5,10,15,20‐tetraphenylporphinato platinum(II) and palladium(II) covalently bound on poly(isobutyl‐co‐2,2,2‐trifluoroethyl methacrylate)

A novel methacrylate monomer bearing 5,10,15,20‐tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a ) was synthesized and copolymerized with isobutyl methacrylate (IBM) and 2,2,2‐trifluoroethyl methacrylate (TFEM) to give poly (IBM‐co‐TFEM) bearing PdTPP (copolymer 2a ) as a dye‐conjugated oxygen‐permeable polymer for pressure‐sensitive paint applications. The introduction of PdTPP into copolymer 2a was confirmed by UV–vis spectroscopy and extended X‐ray absorption fine structure analysis. The Stern–Volmer plots of the copolymer 2a and a mixture of PdTPP and poly(IBM‐co‐TFEM) both showed downward curvature, unlike that of the platinum complex analogue (copolymer 2b ) previously reported. The plots were successfully fitted with a two‐site model to give two distinct Stern–Volmer constants (K_SV1 and K_SV2) and the partition ratio f₁. Interestingly, the f₁ values for the copolymer 2a were almost constant at about 0.98, whereas those of the mixture of PdTPP and poly(IBM‐co‐TFEM) increased from 0.889 to 0.967 as the temperature was increased. This finding suggests that there are two distinct microheterogeneities, one temperature‐dependent and the other temperature‐independent, in the mixture of PdTPP and poly(IBM‐co‐TFEM). The dye‐conjugation approach effectively eliminates the temperature‐dependent, but not the temperature‐independent microheterogeneity. The luminescence decays of copolymers 2a and 2b and the corresponding mixtures in the absence of oxygen indicated that the temperature‐dependent microheterogeneity involves an oxygen diffusion process, whereas the temperature‐independent one appears to be inherent nature in PdTPP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 663–670, 2010