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331.
Jelena Jenter Dipl.‐Chem. Nils Meyer Dr. Peter W. Roesky Prof. Dr. Sven K.‐H. Thiele Dr. Georg Eickerling Dr. Wolfgang Scherer Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5472-5480
The reaction of potassium 2,5‐bis[N‐(2,6‐diisopropylphenyl)iminomethyl]pyrrolyl [(dip2‐pyr)K] with the borohydrides of the larger rare‐earth metals, [Ln(BH4)3(thf)3] (Ln=La, Nd), afforded the expected products [Ln(BH4)2(dip2‐pyr)(thf)2]. As usual, the trisborohydrides reacted like pseudohalide compounds forming KBH4 as a by‐product. To compare the reactivity with the analogous halides, the dimeric neodymium complex [NdCl2(dip2‐pyr)(thf)]2 was prepared by reaction of [(dip2‐pyr)K] with anhydrous NdCl3. Reaction of [(dip2‐pyr)K] with the borohydrides of the smaller rare‐earth metals, [Sc(BH4)3(thf)2] and [Lu(BH4)3(thf)3], resulted in a redox reaction of the BH4? group with one of the Schiff base functions of the ligand. In the resulting products, [Ln(BH4){(dip)(dip‐BH3)‐pyr}(thf)2] (Ln=Sc, Lu), a dinegatively charged ligand with a new amido function, a Schiff base, and the pyrrolyl function is bound to the metal atom. The by‐product of the reaction of the BH4? anion with the Schiff base function (a BH3 molecule) is trapped in a unique reaction mode in the coordination sphere of the metal complex. The BH3 molecule coordinates in an η2 fashion to the metal atom. The rare‐earth‐metal atoms are surrounded by the η2‐coordinated BH3 molecule, the η3‐coordinated BH4? anion, two THF molecules, and the nitrogen atoms from the Schiff base and the pyrrolyl function. All new compounds were characterized by single‐crystal X‐ray diffraction. Low‐temperature X‐ray diffraction data at 6 K were collected to locate the hydrogen atoms of [Lu(BH4){(dip)(dip‐BH3)‐pyr}(thf)2]. The (DIP2‐pyr)? borohydride and chloride complexes of neodymium, [Nd(BH4)2(dip2‐pyr)(thf)2] and [NdCl2(dip2‐pyr)(thf)]2, were also used as Ziegler–Natta catalysts for the polymerization of 1,3‐butadiene to yield poly(cis‐1,4‐butadiene). Very high activities and good cis selectivities were observed by using each of these complexes as a catalyst in the presence of various cocatalyst mixtures. 相似文献
332.
Jelena ?ur?evi? Slavko Radenkovi? Ivan Gutman Svetlana Markovi? 《Monatshefte für Chemie / Chemical Monthly》2009,47(4):1305-1309
Abstract
According to the recently discovered phenylcyclopentadienyl (PCP) rule, the intensity of cyclic conjugation in the five-membered ring of acenaphthylene and fluoranthene-type polycyclic conjugated hydrocarbons increases with the number of PCP fragments present in the molecule. We now tested this rule by DFT calculations at the B3LYP/6-31G(d) level of theory and confirmed its validity. 相似文献333.
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Jelena Golubovi Ana Proti Mira Ze
evi Biljana Otaevi Marija Miki 《Journal of Chemometrics》2014,28(7):567-574
The study of experimental design in conjunction with artificial neural networks for optimization of isocratic ultra performance liquid chromatography method for separation of mycophenolate mofetil and its degradation products has been reported. Experimental design showed to be suitable for selection of experimental scheme, while Kennard‐Stone algorithm was used for selection of training data set. The input variables were column temperature and composition of mobile phase including percentage of acetonitrile, concentration of ammonium acetate in buffer, and its pH value. The retention factor of the most retentive component and selectivity factors were used as the dependent variables (outputs). In this way, artificial neural network has been applied as a predictable tool in solving a method optimization problem using small number of experiments. Network architecture and training parameters were optimized to the lowest root‐mean‐square error values, and the network with 5‐4‐4‐4 topology has been selected as the most predictable one. Predicted data were in good agreement with experimental data, and regression statistics confirmed good ability of trained network to predict compounds retention. The optimal chromatographic conditions included column temperature of 40°C, flow rate of 700 µl min−1, 26% of acetonitrile and 9 mM ammonium acetate in mobile phase, and buffer pH of 5.87. The chromatographic analysis has been achieved within 5.2 min. The validation of the proposed method was also performed considering selectivity, linearity, accuracy, precision, limit of detection, and limit of quantification, and the results indicated that the method fulfilled all required criteria. The method was successfully applied to the analysis of commercial dosage form. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献