Pd (II)‐catalyzed vinyl addition polymerization of novel functionalized norbornene bearing dimethyl carboxylate groups

Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007     

MODELING HARVEST SCHEDULING IN MULTIFUNCTIONAL PLANNING OF FORESTS FOR LONGTERM WATER YIELD OPTIMIZATION

In this study, wood production and hydrologic functions of forests were accommodated within a planning procedure for separate working circles (areas dedicated to certain forest functions) that were delineated according to an Ecosystem‐Based Functional Planning approach. Mixed integer goal programming was used as the optimization technique. The timing and scheduling of a maintenance cutting (partial harvest) was the decision variable in the modeling effort, and an original formulation was developed as a multiobjective planning procedure. Four sample planning strategies were developed and model outputs were evaluated according to these strategies. Spatial characteristics of stands were considered, and used to prohibit the regeneration of adjacent stands during the same time period. Because of the positive relationship between qualified water production and standing timber volume in the forest, the model attempts to maximize qualified water production levels by increasing standing volume stocks in the forest through the delay of regeneration activities.     

The porosity, acidity, and reactivity of dealuminated zeolite ZSM-5 at the single particle level: the influence of the zeolite architecture

A combination of atomic force microscopy (AFM), high‐resolution scanning electron microscopy (HR‐SEM), focused‐ion‐beam scanning electron microscopy (FIB‐SEM), X‐ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron‐based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM‐5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol‐to‐olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM‐5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM‐5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5–50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.     

Effect of chemical modification on oligomerization capacity of alumina support for Pd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Effect of modification with an alkali metal on the acid properties of alumina supports and on the oligomerization capacity and working stability of Pd-Al₂O₃ catalysts was studied.     

Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies

The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) ?) and Fe-O distances (1.941(2)/1.949(2) ?) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mo?ssbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 ?, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 ?) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.     

Rearrangements in the electron-impact induced fragmentation of some β-aroyl-α-methylpropionic acids

A complex rearrangement on electron-impact for β-aroyl-α-methylpropionic acids, involving both hydrogen and hydroxy migration followed by loss of carbon monoxide and allyl radical, is described and discussed. The rearrangement process, resulting in an ion [ArCOOH₂]⁺, is favoured by electron-withdrawing substituents in the aromatic ring.     

Iron(II) complexes with bio-inspired N,N,O ligands as oxidation catalysts: olefin epoxidation and cis-dihydroxylation

The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis-dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [Fe(II)(PrL1)(2)](BPh(4))(2) (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [Fe(II)(PrL1)(2)(MeOH)(2)](OTf)(2) (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15-15'-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [Fe(II)(PrL1)(2)](OTf)(2) (2) and [Fe(II)(PrL1)(2)](BPh(4))(2) (3) were tested in olefin oxidation reactions with H(2)O(2) as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis-dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.     

Synthesis and cytotoxicity of 28-carboxymethoxy lupane triterpenoids.Preference of 28-O-acylation over 28-O-alkylation of betulm by ethyl bromoacetate

28-Carboxymethoxy lupane tritepenoids 3 and 4 were synthesized by alkylation of betulin with the THP protected 2- hydroxyethyl iodide followed by oxidation and reduction.Direct reaction of betulin(5) or betulone(10) with ethyl bromoacetate led to 28-O-acylation,instead of 28-O-alkylation.The targeted compounds 3 and 4 were not cytotoxic at the highest concentration tested(75μmol/L),suggesting that elongation of the chain length at the 28-position in both betulinic acid(1) and betulonic acid(2) was detrim...     

Theoretical study on the electronic,structural, properties and reactivity of a series of mono-, di-, tri- and tetrachlorothiophenes as well as corresponding radical cation forms as monomers for conducting polymers

In this paper, electrical and structural properties of mono-, di-, tri- and tetrachlorothiophenes and their radical cations have been studied using the density functional theory and B3LYP method with 6-311++G** basis set. The effects of the number and position of the substituent of chlorine atoms on the properties of the thiophene ring for all chlorothiophenes and their radical cations have been studied. Vibrational frequencies, nuclear chemical shielding constants, spin-density distribution, size and direction of dipole moment vector, ionization potential, electric polarizabilities and NICS values of these compounds have been calculated as well. The analysis of these data showed that double bonds in 3-chlorothiophene are more delocalized and it is the best possible candidate monomer among all chlorothiophenes for the synthesis of corresponding conducting polymers with modified characteristics.