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41.
[structure: see text] The addition of oligothiophene into a dendritic structure causes a self-association behavior by intermolecular pi-pi interactions in a solution and in a solid state. Increasing the generation of the dendritic structure gives not only a high association constant but also sufficient field-effect hole mobility, which indicates that the charge-transporting passes are formed by the strong pi-pi interactions. 相似文献
42.
Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism. 相似文献
43.
Oligothiophenes with the length of ca.10 nm bearing anchor units (a protected thiol group or trimethylsilylethynyl) at both terminal positions in the conjugated backbone have been synthesized by the block-coupling synthetic strategy. Their electronic properties were clarified by spectroscopic and electrochemical measurements. 相似文献
44.
We investigated the effects of methanol on the two rheological properties, dynamic modulus and flow behaviour, for an aqueous
solution of hydrophobically ethoxylated urethane (HEUR). When the added methanol constitutes 0–10 mol% of the sample, the
gel relaxation time shortens; when it constitutes 20 mol% of the sample, the distribution of relaxation times broadens. Relaxation
of the physical gel formed by a transient network is directly related to the lifetime of the crosslink points, i.e. flower
micelles. We speculate that methanol addition shortens the relaxation time by changing the hydrophobic interactions in the
flower micelles. The changed hydrophobic interactions then affect not only the relaxation time but also the shape of the HEUR-chain
molecular associating structures which in turn affects the mechanical spectrum. Under constant shear flow, shear thickening
increases with increasing methanol concentration, and the increase in stress under constant shear flow shows unusual behaviour.
A possible contributing factor to this behaviour may be the non-cosolvency of methanol with polyethyleneoxide (PEO). At some
critical concentration, methanol in PEO aqueous solution becomes a poor solvent, which then affects the properties of the
PEO chains in the transient networks of HEUR aqueous solution. The rheological properties of the transient networks clearly
affect the properties of both the crosslink points and the chains. In short, methanol addition induces complicated changes
in gel mechanical properties. 相似文献
45.
46.
The elastic properties of alkali germanate glasses, xR2O?(100 ? x)GeO2 (R = Li, Na, K, Rb, Cs ; x = 14, 28), have been studied by Brillouin scattering in the wide temperature range up to 1200 °C. The remarkable aging effect of Brillouin shift ΔνL has been observed below a glass transition temperature Tg ≈ 500 °C. The temperature dependence of longitudinal sound velocity VL of well annealed glasses shows the gradual decrease below Tg, while on further heating the remarkable decrease is observed above Tg. The scaled temperature dependence of VL is nearly independent on alkali metals below the melting temperature Tm. While on further heating above Tm, the drastic decrease of VL and increase of αL show the remarkable alkali dependence. It may be attributed to the appearance of dynamic process related to ionic hopping of alkali metals released from glass network above Tm. 相似文献
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49.
Controlled synthesis of hydroxyapatite-supported palladium complexes as highly efficient heterogeneous catalysts 总被引:5,自引:0,他引:5
Mori K Yamaguchi K Hara T Mizugaki T Ebitani K Kaneda K 《Journal of the American Chemical Society》2002,124(39):11572-11573
Achieving precise control of active species on solid surfaces is one of the most important goals in the development of highly functionalized heterogeneous catalysts. The treatment of hydroxyapatites with PdCl(2)(PhCN)(2) gives two new types of hydroxyapatite-bound Pd complexes. Using the stoichiometric hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), we found that monomeric PdCl(2) species can be grafted on its surface, which are easily transformed into Pd(0) particles with narrow size distribution in the presence of alcohols. Such metallic Pd species can effectively promote alcohol oxidation using molecular oxygen and are shown to give a remarkably high TON of up to 236 000. Another monomeric Pd(II) phosphate complex can be generated at a Ca-deficient site of the nonstoichiometric hydroxyapatite, Ca(9)(HPO(4))(PO(4))(5)(OH), affording a catalyst with Pd(II) structure and high activity for the Heck and Suzuki reactions. To the best of our knowledge, the PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date. These Pd catalysts are recyclable in the above organic reactions. Our approach to catalyst preparation based on the control of Ca/P ratios of hydroxyapatites represents a particularly attractive method for the nanoscale design of catalysts. 相似文献
50.
Highly efficient esterification of carboxylic acids with alcohols by montmorillonite-enwrapped titanium as a heterogeneous acid catalyst 总被引:1,自引:0,他引:1
Tomonori KawabataTomoo Mizugaki Kohki EbitaniKiyotomi Kaneda 《Tetrahedron letters》2003,44(51):9205-9208
Montmorillonite-enwrapped titanium catalyst was found to efficiently promote the esterification of carboxylic acids with alcohols. In comparison to other catalysts reported to date, this heterogeneous catalyst offers a remarkably simple workup procedure, and is reusable without any appreciable loss in its activity and selectivity. 相似文献