Chirality induction of π-conjugated chains through chiral complexation

Chirality induction of π-conjugated polyanilines through chiral complexation with the chiral palladium(II) complexes was demonstrated to afford the chiral conjugated polymer complexes. Complexation of the emeraldine base of poly(o-toluidine) (POT) with the chiral palladium(II) complex bearing one labile coordination site led to the formation of the chiral conjugated polymer complex, which exhibited an induced circular dichroism (ICD) based on the chirality induction into a π-conjugated backbone. The mirror image of the CD signal was observed with the chiral conjugated polymer complex, which was obtained from the chiral palladium(II) complex possessing the opposite configuration. The chirality of the podand ligand moieties of the palladium complex is considered to induce a propeller twist of the π-conjugated molecular backbone. The crystal structure of the chiral conjugated complex of N-bis(4′-dimethylaminophenyl)-1,4-benzoquinonediimine (L³) as a model compound of the polyaniline revealed a chiral propeller twist conformation of the π-conjugated backbone. Furthermore, chiral complexation with the cationic palladium(II) complexes provided the ionic chiral conjugated complexes.     

Mechanical activation of catalysts for C-C bond forming and anionic polymerization reactions from a single macromolecular reagent

Coupling of pyridine-capped poly(methyl acrylate)s, PyP(M) (where M corresponds to the number average molecular weight in kDa), to the SCS-cyclometalated dipalladium complex [(1)(CH(3)CN)(2)] afforded organometallic polymers [(1)(PyP(M))(2)] with a concomitant doubling in molecular weight. Ultrasonication of solutions containing [(1)(PyP(M))(2)] effected the mechanical scission of a palladium-pyridine bond, where the liberated PyP(M) was trapped with excess HBF(4) as the corresponding pyridinium salt, harnessed to effect the stoichiometric deprotonation of a colorimetric indicator, or used to catalyze the anionic polymerization of α-trifluoromethyl-2,2,2-trifluoroethyl acrylate. The mechanically induced chain scission also unmasked a catalytically active palladium species which was used to facilitate carbon-carbon bond formation between benzyl cyanide and N-tosyl imines. Spectroscopic and macromolecular analyses as well as a series of control experiments demonstrated that the aforementioned structural changes were derived from mechanical forces that originated from ultrasound-induced dissociation of the polymer chains connected to the aforementioned Pd complexes.     

Synthesis of a [2]rotaxane through first- and second-sphere coordination

In an effort to expand the application of a new template from interpenetrated to interlocked molecular species, we report the synthesis of a new [2]rotaxane by means of both first- and second-sphere coordination of a palladium(II) dichloride subunit.     

Synthesis of palladium nanoparticles by sonochemical reduction of palladium(II) nitrate in aqueous solution

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.     

Synthesis of 1,2- bis (2′-ethynylpyrimidyl) benzene and characterization of the coordination complexes with palladium(II) chloride and silver(I) trifluoromethanesulfonate

Design, synthesis and coordination chemistry of a new trans-coordinating dipyrimidyl ligand are reported. Sonogashira coupling of 2-iodopyrimidine with 1,2-diethynylbenzene yielded the ligand 1,2-bis(2′-ethynylpyrimidyl)benzene (3), in good yield. Coordination complexes were formed with silver(I) and palladium(II) salts. The X-ray crystallographic characterization of the 1?:?1 complex formed between palladium(II) dichloride and 3, and the 4?:?2 complex formed between silver(I) trifluoromethanesulfonate and 3 are reported.     

Cathodic adsorption voltammetry of palladium(II)

The electrochemical behavior of palladium(II) was studied by differential pulse, linear sweep, and alternating-current square-wave voltammetry in HC1, HNO₃, H₂SO₄, and HC1O₄ solutions in the presence of dimethylglyoxime. A peak with a height linearly depending on the concentration of palladium(II) was observed in voltammograms. Typical relationships between the height and potential of a peak and pH, dimethylglyoxime concentration, the potential and time of adsorption accumulation suggested that the observed peak was due to the hydrogen liberation catalyzed by palladium(II) dimethylglyoximate adsorbed on the electrode surface. The detection limits for palladium(II) accumulated for 120 s at -0.2 V were 2 x 10^-8, 5 x 10^-9, and 8 x 10^-10 M for differential pulse, linear sweep, and alternating-current square-wave voltammetry, respectively.     

Propylene Polymerization Catalyzed by Bis(R_3-indenyl) Zirconium Dichloride/Aluminoxane──Synthesis of Metallocenes and Influence ofSolvent Polarity on Polymerization

Three unbridged metallocenes, bis(2,4,7-Me3-indenyl)zirconium dichloride(1) , bis(2-Me-4, 7-Et2-indenyl)zirconium dichloride (2) and bis (2, 4, 6-Me3-indenyl) zirconium dichloride (3) were synthesized. The effect of solvent polarity on propylene polymerization catalyzed by the metallocenes in the presence of methylaluminoxane(MAO) and triisobutylaluminum(TIBA) was investigated in the toluene/CH2Cl2 mixed solvent. Changing the solvent polarity was found to influence the catalytic activity, polymer molecular weight and stereospecificity of the catalysts. The changes in the position of the substituents on the ligand caused the different responses of the catalyst to the changes in solvent polarity. The isotactic stereosequence of polypropylene was found to increase with the increase in the polarity of the reaction medium.     

Heterogeneous metallocene catalysts for ethylene polymerization

The catalyst precursor 9-fluorenylidene-1-cyclopentadienylidene-2-hex-5-enylidene zirconium dichloride proved to be highly active in the heterogeneously catalyzed polymerization of ethylene using silica gel/partially hydrolyzed trimethylaluminum (PHT) as cocatalyst. The substitution of position 4 of the fluorenylidene fragment and position 3 of the cyclopentadienylidene ring improves the catalyst activity. The introduction of a phenyl group into the bridge increases the catalyst activity and the molecular weight of the polymer. The prepolymerization of this catalyst system leads to a major change in catalyst and polymer properties. A significant increase in catalyst activity and a lower molecular weight of the produced polyethylene is observed. The presence of hydrogen during prepolymerization or polymerization of ethylene produces a broader molecular weight distribution indicating a higher number of different active centers.     

H2O/TiCl4/ED 体系引发异丁烯控制正离子聚合中的影响因素研究

在亲核试剂(ED)如吡啶(Py)、N,N-二甲基乙酰胺(DMA)或三乙胺(TEA)存在下,由引发剂H2O和共引发剂TiCl4组成引发体系,在二氯甲烷/正己烷混合溶剂中进行异丁烯(IB)正离子聚合,考察了溶剂极性、聚合温度及异丁烯浓度对聚合反应转化率、产物分子量和分子量分布的影响.试验结果表明,随聚合体系溶剂极性增大,聚合速率加快,相近转化率时聚合产物的分子量分布变窄.随着聚合温度降低,聚合速率明显提高,聚合物的分子量增加,活化能为负值,活性链端发生链转移或链终止等副反应的几率减小,当聚合温度为-60℃时,可以抑制活性链端的β-H脱除反应和链转移副反应,并得到大分子链末端全部为叔氯基团的聚异丁烯(PIB).当[IB]0≤2.5mol/L时,随[IB]0增加,聚合转化率有所增加,聚合产物的GPC谱图均为单峰分布,分子量增大,而分子量分布基本保持不变,对于加入Py的聚合体系,分子量分布指数在1.33~1.45范围内,对于加入TEA的聚合体系,分子量分布指数在1.47~1.60范围内,并求出在加入Py和TEA的聚合体系中活性链向单体的链转移常数CM分别为5.5×10-4和6.6×10-4.     

Spectrophotometric methods for determination of enalapril and timolol in bulk and in drug formulations

Two simple and accurate spectrophotometric methods for determination of timolol and enalapril maleate are described. The first method is based on chelate formation with palladium(II) chloride in buffered medium. The second method is based on the formation of the colored complex between palladium(II), eosin, and the two cited drugs using methylcellulose as surfactant to increase the solubility and intensity of the formed complexes. Under optimum conditions the complexes showed maximum absorption at 369.4 nm and 362.8 nm for timolol and enalapril maleate, respectively, in the first method and 552.2 and 550.6 nm for the second method. Apparent molar absorptivities were 1.8 x 10(3) and 1.3 x 10(3) and Sandell's sensitivities were 5.9 x 10(-4) and 2.7 x 10(-4) for timolol and enalapril maleate in the first method; in the second method molar absorptivities were 2.8 x 10(4) and 1.1 x 10(4) while Sandell's constants were 9.1 x 10(-3) and 2.3 x 10(-3) for timolol and enalapril maleate. The solutions of the complexes obeyed Beer's law in the concentration ranges 20-200 micro g mL(-1) and 50-300 micro g mL(-1) for timolol and enalapril maleate, respectively. In the second method, because the reaction was more sensitive the ranges were reduced to 1.6-16 micro g mL(-1) for timolol 8-56 micro g mL(-1) for enalapril maleate. The proposed methods were applied to the determination of the two drugs in their pharmaceutical formulation.     

Rigid trans-spanning triptycene-based ligands: How flexible they can be?

trans-[1,8-Bis(diisopropylphosphino)triptycene]nickel (II) dichloride, trans-[1,8-bis(diisopropylphosphino)triptycene]carbonylrhodium (I) chloride and cis-[1,8-bis(diisopropyl-phosphino)triptycene] platinum (II) dichloride have been prepared and fully characterized in order to evaluate the coordination diversity of triptycene-based bidentate ligands. Their structural features and coordination preferences were studied and compared to the previously reported palladium complexes. The comparative structural analysis revealed that 1,8-bis(diisopropylphosphino)triptycene is able to access a variety of bite angles and to stabilize metal centers in different geometries. In addition, intramolecular weak C-H?Cl-Pt hydrogen bonding interactions which stabilize [1,8-bis(diisopropyl-phosphino)triptycene] platinum (II) dichloride in a constrained cis form are discussed.     

Evaluation of functionalized silica's for the adsorptive recovery of homogenous catalysts through interaction with the metal centre

The goal of this paper is the evaluation of functionalized silica's for the recovery of homogeneous catalysts by adsorption via its metal centre. As model catalysts, we selected bis(triphenylphosphine)cobalt(II)dichloride (CoCl(2)(PPh(3))(2)), bis(triphenylphosphine)palladium(II)dichloride (PdCl(2)(PPh(3))(2)) and tris(triphenylphosphine)rhodium(I)dichloride (RhCl(PPh(3))(3)). Twelve functionalized groups selected from four classes containing one or more N-, O-, P- or S-atoms were evaluated. A preliminary selection of the adsorbents was done by investigating the adsorption of the metal salts for the cobalt and the palladium complex. The results could be explained by the Hard and Soft Acid Base (HSAB) theory. For the most suitable functionalized adsorbents, these experiments were extended by introducing the ligand in the system which promoted the competition of the functionalized groups on adsorbent and the ligands present in solution. These experiments demonstrated that different complex species are adsorbed. 2-(2pyridyl)ethyl-functionalized silica is selected as a promising adsorbent for adsorption of the CoCl(2)(PPh(3))(2) from acetonitrile, while 3-(mercapto)propyl-functionalized silica is selected as a promising adsorbent for adsorption of the PdCl(2)(PPh(3))(2) and RhCl(PPh(3))(3) from DMF. The presence of a ligand, an increase of the temperature and the presence of a solvent with the donor properties can decrease the adsorption equilibrium and need to be taken into account.     

Highly efficient mechanochemical scission of silver-carbene coordination polymers

The ultrasound-induced scission of silver carbene coordination complexes with polytetrahydrofuran-functionalized N-heterocyclic carbene ligands is reported. In solution, scission is very efficient, with complete conversion within 10 min when the polymers have a molecular weight of 6.7 kDa. The mechanochemical origin of the scission is supported by the molecular weight dependence of the scission rate and by the low reactivity of the silver complex with low molecular weight ligands. The mechanochemical process at room temperature is much faster than thermal scission at 60 degreesC, which has a conversion of 30% in 18 h.     

Thermal stability and degradation of chitosan modified by benzophenone

N-(biphenylmethylidenyl) chitosan polymer was prepared, characterized and thermal stability was compared with chitosan. Thermal degradation products of the modified polymer were identified by GC-MS technique. It seems that the mechanism of degradation of the prepared polymer is characterized by formation of low molecular weight radicals, followed by random scission mechanism along the backbond chain.     

Two-dimensional rhombohedral grid coordination polymers [M(bbbt)(2)(NCS)(2)](n)(M = Co,Mn, or Cd; bbbt = 1,1'-(1,4-butanediyl) bis-1H-benzotriazole): synthesis,crystal structures,and third-order nonlinear optical properties

In this paper, treatment of 1,1'-(1,4-butanediyl) bis-1H-benzotriazole (bbbt) and KSCN with Co(II), Mn(II), or Cd(II) afforded three two-dimensional rhombohedral grid coordination polymers [M(bbbt)(2)(NCS)(2)](n)(M = Co, 1; Mn, 2; Cd, 3). The two-dimensional rhombohedral grids are parallel to the crystallographic ac plane. The rhombohedral grid consists of 44-membered rings of M(4)(bbbt)(4), and gives the dimensions of 12.913 x 10.764 A for polymer 1, 13.106 x 10.797 A for polymer 2, and 13.256 x 10.870 A for polymer 3. The three polymers' third-order nonlinear optical (NLO) properties were determined by Z-scan technique in DMF solution. The results show that all three polymers show very large NLO absorption and strong NLO refraction properties. The third-order NLO absorptive coefficients alpha(2) are 5.4 x 10(-9) m W(-1) for polymer 1, 5.2 x 10(-9) m W(-1) for polymer 2, and 5.0 x 10(-9) m W(-1) for polymer 3. The alpha(2) values are larger than those of all the reported cluster compounds. The NLO refractive index values n(2) of the three polymers are 5.73 x 10(-19), 3.55 x 10(-19), and 3.07 x 10(-19) m(2) W(-1), respectively. Their hyperpolarizability gamma values are calculated to be 2.40 x 10(-30) esu for polymer 1, 1.52 x 10(-30) esu for polymer 2, and 1.50 x 10(-30) esu for polymer 3. The gamma values are comparable to those of clusters and better than those of organometallic compounds, semiconductors, and fullerene.     

Nanostructured polymetallaynes of controlled length: Synthesis and characterization of oligomers and polymers from 1,1′‐bis‐(ethynyl)4,4′‐biphenyl bridging Pt(II) or Pd(II) centers

The reactivity of square planar palladium(II) and platinum(II) complexes in trans or cis configuration, namely trans or cis‐[dichlorobis(tributylphosphine)platinum(II)] and trans‐[dichlorobis(tributylphosphine)palladium(II)] with 1,1′‐bis(ethynyl) 4,4′‐biphenyl, DEBP, leading to π‐conjugated organometallic oligomeric and polymeric metallaynes, was investigated by a systematic variation of the reaction conditions. The formation of polymers and oligomers with defined chain length [? M(PBu₃)₂ (C?C? C₆H₄? C₆H₄? C?C? )]_n (n = 3–10 for the oligomers, n = 20–50 for the polymers) depends on the configuration of the precursor Pt(II) and Pd(II) complexes, the presence/absence of the catalyst CuI, and the reaction time. A series of model reactions monitored by XPS, GPC, and NMR ³¹P spectroscopy showed the route to modulate the chain growth. As expected, the nature of the transition metal (Pt or Pd) and the molecular weight of the polymers markedly influence the photophysical characteristics of the polymetallaynes, such as optical absorption and emission behavior. Polymetallaynes with nanostructured morphology could be obtained by a simple casting procedure of polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3311–3329, 2007     

The thermal degradation of poly(-(d)-β-hydroxybutyric acid): Part 2—Changes in molecular weight

Changes in molecular weight occur in poly(-(d)-β-hydroxybutyric acid) in the temperature range 170–200°C, at which latter temperature evolution of volatile products of degradation becomes significant. Two processes are involved in these changes in molecular weight. The more important is random chain scission at ester groups, which results in the formation of carboxyl and vinyl groups. Although this ultimately results in a drastic reduction in the molecular weight of the polymer, this is delayed in the early stages of the reaction by a condensation reaction between the terminal hydroxyl groups present in the original polymer and the terminal carboxyl groups, which were either originally present or formed in the chain scission process. This delay could have relevance to the industrial processing of this material.     

Ein neues Chloropalladat(II): BaPdCl4

A New Chloropalladate(II): BaPdCl₄ BaPdCl₄ was prepared through reaction of barium chloride and palladium dichloride (molar ratio 2:1) with the aid of the Bridgman technique. According to a X‐ray single crystal investigation, BaPdCl₄ crystallizes with the orthorhombic crystal system (space group Pbcn (No. 60), Z = 4, a = 686.7(1), b = 1258.8(2) pm, c = 750.2(2), R_all = 0.0383). The crystal structure is built up from square planar [PdCl₄] units which are linked together by Ba²⁺ ions in an eightfold coordination.     

Synthesis of 2,3-disubstituted indole using palladium(II)-catalyzed cyclization with alkenylation reaction

The reaction of ethyl 2-ethynylphenylcarbamate derivative with alkenes in the presence of a palladium(II) catalyst, copper dichloride and tetrabutylammonium fluoride (TBAF) produced 2-substituted 3-ethenylindoles during refluxing. The intramolecular cyclization reaction of ethyl 2-ethynylphenylcarbamates, which have an ethenyl part in the ethynyl group, was also used to produce carbazole derivatives.