Ruthenium-mediated regio- and stereoselective alkenylation of pyridine

A novel alkenylation reaction of pyridine is developed. Heating a cationic ruthenium vinylidene complex [CpRu(=C=CHR)(PPh(3))(2)]PF(6) in pyridine at 100-125 degrees C for 24 h affords (E)-2-alkenylpyridine. Initially, pyridine coordinates to ruthenium by displacement of one of the phosphine ligands. Then, [2 + 2] heterocycloaddition occurs to form a four-membered ruthenacyclic complex. Deprotonation of the beta-hydrogen affords a neutral pi-azaallyl complex. Protonolysis furnishes the product. As a result, a vinylidene group is inserted into the alpha C-H bond of pyridine. The alkenylation reaction is made catalytic in ruthenium by the use of (alkyn-1-yl)silane as the vinylidene source. Treatment of (alkyn-1-yl)trimethylsilane with pyridine in the presence of a cationic ruthenium complex [CpRu(PPh(3))(2)]PF(6) affords the corresponding (E)-2-alkenylpyridine in good yield in a regio- and stereoselective manner.     

Thermodynamic properties of binary mixtures: Hexamethylphosphoric triamide (HMPA) with a non-polar liquid at 25°C

Excess isobaric heat capacities C _p ^E , densities and speeds of sound u of HMPA+heptane and+benzene were measured at 25°C. C _p ^E of both mixtures were positive in the range of small x and negative in the other region. The mixture containing benzene showed higher C _p ^E than the heptane mixture. They both exhibited considerably smaller C _V ^E than C _p ^E . V^E was positive for HMPA+heptane and negative for HMPA+benzene. The compressibilities K _s ^E and K _p ^E of both mixtures were negative. In both mixtures, non-random mixing is expected and [(CH₃)₂N]₃PO molecules are inhomogeneously distributed.     

Self-organization and photoreactivity of anthryl dendron having perfluoroalkyl chains at the terminals

A newly designed anthryl dendron having perfluoroalkyl chains at terminals showed thermotropic liquid crystallinity, which was characterized using polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. The anthryl dendron forms S_B phase at room temperature below 53 °C, at which temperature a phase transition to Col_rd takes place. In a fluorous solvent, regioselective photodimerization of the anthryl dendron occurred to give head-to-head photodimers, although photodimerization in the S_B phase and chloroform gave both head-to-head and head-to-tail photodimers.     

Synthesis and properties of polyacetylenes with adamantyl groups

Three disubstituted acetylenes with an adamantyl group—1-(p-adamantylphenyl)-2-chloroacetylene (ClpAdPA), 1-(p-adamantylphenyl)-1-propyne (pAdPP), and 1-(p-adamantylphenyl)-2-phenylacetylene (pAdDPA)—polymerized in good yields in the presence of MoCl₅- or TaCl₅-based catalysts. The highest weight-average molecular weights of poly(ClpAdPA), poly(pAdPP), and poly(pAdDPA) reached 3.6 × 10⁵, 1.1 × 10⁶, and 6.0 × 10⁶, respectively. The polymers were yellow to white solids and completely soluble in toluene, chloroform, and so forth. These polymers thermally were fairly stable, and the onset temperatures of weight loss in air were over 360 °C. Poly(pAdPP) and poly(pAdDPA) provided free-standing films by solution casting, and their oxygen permeability coefficients (P_O2) at 25 °C were 8.6 and 55 barrers [1 barrer = 1 × 10⁻¹⁰ cm³ · (STP) · cm/(cm² · s · cm Hg)], respectively, which are relatively small compared to those of other substituted polyacetylenes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4546–4553, 1999     

Effects of L-tyrosine esters on quenching and photosensitized charge separation using polymers containing ruthenium(II) complex

A series of ruthenium(II) complex-containing partially quaternized poly(1-vinylimidazole)s with various alkyl side chains such as hexyl (C₆RuQPIm), dodecyl (C₁₂RuQPIm), and hexadecyl (C₁₆RuQPIm) were synthesized. The effects of L -tyrosine esters with hexyl (C₆Tyr), octyl (C₈Tyr), and dodecyl (C₁₂Tyr) on the quenching with methylviologen and photosensitized charge separation reactions were investigated using these metallopolymers as polymer photosensitizers. The quenching reaction took place through both a dynamic quenching process and a static quenching one mediated by the L -tyrosine esters. The kinetic parameters for these processes were obtained from a computed curve fitting using a Stern–Volmer equation derived from a combination of dynamic quenching and static quenching. The parameters had a significant dependence on the lengths of the alkyl groups in the L -tyrosine esters and the alkyl side chains on these metallopolymers. During photosensitized charge separation, the reaction proceeded through these quenching processes, referred to as direct and mediated processes. The initial rates of methylviologen radical formation also depended on these lengths; they increased when the lengths of the alkyl side chain on these metallopolymers and alkyl groups in the L -tyrosine esters were long. Such a dependence was caused by a change in the balance of some effects such as the electrostatic and steric effects. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4360–4367, 1999     

Arsenobetaine-decomposing Ability of Marine Microorganisms Occurring in Particles Collected at Depths of 1100 and 3500 Meters

The arsenobetaine-decomposing ability of microorganisms occurring in sinking particles, which play a main role in the vertical transport of organic substances produced in the photic zone, was investigated. The microorganisms in particles collected in the deep sea, 1100 and 3500 m in depth, clearly showed decomposing ability. With the particles from 1100 m, the degradation products were the same as those produced by microorganisms occurring in sources in the photic zone, i.e. trimethylarsine oxide (TMAO), dimethylarsinic acid (DMA) and inorganic arsenic(V). At 3500 m, the degradation activity was diminished, smalls amount of DMA and TMAO being produced. These results suggest that arsenobetaine contained in the animals starts to degrade immediately after the death of the animals and their transformation to particles. The degradation of arsenobetaine to inorganic arsenic in our tentative arsenic cycle in marine ecosystems (inorganic arsenic to inorganic arsenic via the biosynthesis of arsenobetaine) may apply to the deep sea as well as to the photic zone. © 1997 by John Wiley & Sons, Ltd.     

Molecular motion of ends of isolated poly(isobutylene) chains tethered on the poly(tetrafluoroethylene) surface in vacuo

Poly(isobutylene) (PIB) chains with a radical at the chain end were graft-copolymerized on the poly(tetrafluoroethylene) (PTFE) surface in vacuo at 77 K. The PIB chains tethered on the PTFE surface in vacuo were regarded as isolated chains from neighboring tethered PIB chains. The molecular motion of the ends of the isolated PIB chains was observed by an electron spin resonance (ESR) spectrometer in the temperature range from 3 to 125 K, which was lower than T_g of PIB, 200 K,¹ and two motion modes were found: One is a quantum tunneling of the methyl group located at the chain end at 3 K, and the other is an interconformation transition with freely rotating methyl group at the end at 77 K, where the transition rate was estimated to be 15 MHz at that temperature. The transition rate increased with an increase in temperature. The activation energy of the transition was estimated to be 370 J/mol. The high mobility and low activation energy was attributed to the isolation of PIB chains in vacuo. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2095–2102, 1998     

Rhodium-Catalyzed Intermolecular [4+2] Cycloaddition of Unactivated Substrates

No electron-withdrawing or electron-releasing substituents are necessary for the substrates in the rhodium-catalyzed [4+2] cycloaddition reaction between a vinylallene and an ordinary alkyne under mild conditions [Eq. (1)]. The use of the strongly electron-accepting P[OCH(CF₃)₂]₃ ligand affords the optimal rhodium catalyst. cod = 1,5-cyclooctadiene.     

Structural and Spectroscopic Characterization of a Mononuclear Hydroperoxo–Copper(II) Complex with Tripodal Pyridylamine Ligands

A model for the key intermediate in copper oxygenase reactions, the Cu(II )–OOH complex, was prepared with the novel tripodal pyridylamine ligand, bis(6-pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine. The HOO⁻ moiety is stabilized by hydrogen bonding to two amine H atoms (see structure on the right).