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1.
O. N. Babkina O. M. Chukanova E. E. Faingol"d N. M. Bravaya 《Russian Chemical Bulletin》2004,53(4):785-790
Quantitative characteristics of changes in the energy of charge transfer from -bonded ligands to metal are presented for the series of structurally similar ansa-metallocene complexes of IVB Group elements. The changes are caused by the solvation effect, replacement of -bonded chlorine ligands by methyl groups and of bridging ethylene groups by dimethylsilylene moieties, introduction of the methyl substituent into position 2 and phenyl substituent into position 4 of the indenyl system, variation of the transition metal in metallocene, and formation of complexes with polymethylalumoxane (MAO) at different AlMAO/Zr ratios. These effects are found to be additive. 相似文献
2.
Complexes of azobisisobutyronitrile (AIBN) with titanium tetrachloride and vanadium tetrachloride have been synthesized and characterized. It was demonstrated that Ti(IV) and V(IV) form equimolar complexes with AIBN, with nitrile ligands located incis positions in the coordination spheres of metal atoms. Kinetics of thermal decomposition of free and complexed AIBN were studied and compared. The gas evolution rate was measured in the presence of tetrabutoxytitanium, which does not react with AIBN. It was demonstrated that complexing leads to a marked increase of the rate constant of AIBN thermal decomposition.Institute of Chemical Physics, Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1746–1754, August, 1992. 相似文献
3.
E. A. Sanginov A. N. Panin S. L. Saratovskikh N. M. Bravaya 《Polymer Science Series A》2006,48(2):99-106
For two stereospecific metallocene catalysts, namely, syndiospecific Ph2CCpFluHfMe2 and isospecific rac-Me2SiInd2ZrMe2, the introduction of Lewis bases into a reaction medium was shown to promote a marked rise in the efficiency of catalytic systems. In the case of the syndiospecific metallocene, the maximum effect of the base (a 10-fold increase in activity) was achieved using the (Ph2CCpFluHfMe2 + Ph3N)/CPh3B(C6F5)4 catalytic system in the presence of Al-i-Bu3 at a molar ratio of Al: Hf: B: N = 15: 1: 1: 1. When the polymerization of propylene was carried out in the presence of Al-i-Bu3 and Ph3N, an elastomeric stereoblock syndio/atactic polypropylene was produced. For the (rac-Me2SiInd2ZrMe2 + amine)/CPh3B(C6F5)4 catalytic system, a 15-to 30-fold increase in activity was observed upon introduction of amines of the aniline type: Me2NPh, Me-n-BuNPh, and NPh3. 相似文献
4.
N. M. Bravaya E. E. Faingol’d A. N. Galiullin O. N. Babkina S. L. Saratovskikh A. V. Chernyak V. D. Makhaev 《Russian Chemical Bulletin》2015,64(9):2076-2082
1H NMR method showed that in systems based on triisobutylaluminum (TIBA) and triphenylcyclopropenylium [Ph3C3]+[B(C6F5)4]–(CPB) or triphenylmethylium [Ph3C]+[B(C6F5)4]–(TB) perfluorophenylborates in a toluene–dichloromethane mixture the Friedel–Crafts process occurs with the formation of ditolylmethane (DTM) accompanied by the complete decomposition of TIBA to form isobutane. 19F NMR spectroscopy showed that the [B(C6F5)4]–anion decomposes in the systems to form B(C6F5)3 and HC6F5. The short-living [AlBu2 i]+ cation formed in the reaction of perfluorophenylborates with TIBA is assumed to be the species initiating the process. It has been shown that CPB is less reactive than TB. The addition of a stoichiometric amount of Ph2CCpFluHfMe2 exerts no effect on the process with the CPB-containing system but inhibits the reaction in the case of TB. 相似文献
5.
A theoretical study of the electronic structure of the photoactive yellow protein (PYP) model chromophore, para-coumaric acid (p-CA), is presented. Electronically excited states of the phenolate and carboxylate isomers of the deprotonated p-CA are characterized by high-level ab initio methods including state-specific and multistate multireference pertrubation theory (SS-CASPT2, and MS-CASPT2), equation-of-motion coupled-cluster methods with single and double substitutions (EOM-CCSD) and with an approximate account of triple excitations (CC3). We found that the two isomers have distinctly different patterns of ionization and excitation energies. Their excitation energies differ by more than 1 eV, in contradiction to the experimental report [Rocha-Rinza et al., J. Phys. Chem. A 113, 9442 (2009)]. The calculations confirm metastable (autoionizing) character of the valence excited states of both phenolate and carboxylate isomers of p-CA(-) in the gas phase. The type of resonance is different in the two forms. In the phenolate, the excited state lies above the detachment continuum (a shape resonance), whereas in the carboxylate the excited π→π(*) state lies below the π-orbital ionization continuum, but is above the states derived from ionization from three other orbitals (Feshbach resonance). The computed oscillator strength of the bright electronic state in the phenolate is higher than in the carboxylate, in agreement with Hu?ckel's model predictions. The analysis of photofragmentation channels shows that the most probable products for the methylated derivatives of the phenolate and carboxylate forms of p-CA(-) are CH(3), CH(2)O and CH(3), CH(2)O, CO(2), respectively, thus suggesting an experimental probe that may discriminate between the two isomers. 相似文献
6.
The products of the reactions of polymethylalumoxane (MAO) with triisobutylaluminum (TIBA), rac-Me2Si(2-Me,4-PhInd)2ZrCl2 (1) with MAO (1 + MAO), and (1 + MAO) + TIBA were studied by 1H NMR at different molar ratios of the components. When the ratio AlTIBA/AlMAO is ∼6, the reaction between MAO and TIBA involves the replacement of the methyl group of MAO by isobutyl groups and the formation
of isobutylmethylalumoxane or mixed isobutylmethylalumoxane structures. When the TIBA content in the system increases to 30
mol.%, these structures are rearranged to form products with a low degree of association. With the equimolar ratio of the
reactants, the main reaction products are tetraisobutylalumoxane and polyisobutylalumoxane. The 1 + MAO system with the molar ratio AlMAO/Zr = 50 affords a MAO-bonded monomethyl monochloride derivative [L2ZrCl-μ-Me]δ+[MAO]δ−. An increase in this ratio to 150 produces intermediate binuclear complexes [L2ZrCl-μ-Me-MeZrL2]+[MAO]− and [Me2Al-(μ-Me)2-ZrL2]+[MAO]−. The addition of TIBA induces the replacement of the ZrMe groups by isobutyl groups at the first step of the interaction
and formation of nonidentified reaction products at the subsequent steps.
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Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 934–940, April, 2005. 相似文献
7.
K. B. Bravaya A. V. Bochenkova A. A. Granovskii A. V. Nemukhin 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(5):671-675
The structure and electronic absorption spectra of a model green fluorescent protein chromophore were studied in the neutral, cationic, and anionic forms in the isolated state. The energies of S 0-S 1 vertical transitions were calculated using a new method based on a modified multiconfiguration quasi-degenerate perturbation theory (aug-MCQDPT2). This method was used to obtain quantitative estimates of S 0-S 1 vertical transition energies for chromophores in the isolated state, 2.54, 3.12, and 3.11 eV (the experimental values were 2.59, 3.05, and 2.99 eV) for the anionic, cationic, and neutral forms, respectively. 相似文献
8.
Kessel L Nielsen IB Bochenkova AV Bravaya KB Andersen LH 《The journal of physical chemistry. A》2007,111(42):10537-10543
The aging process of the human lens is associated with accumulation of chromophores and fluorophores that impair visual function. In the present study, we examined the photodissociation of 3-OH-kynurenine and argpyrimidine. Furthermore, absorption spectra obtained in gas phase using an electrostatic ion storage ring were studied as gas phase absorption have been shown to be more similar to the in vivo condition than absorption spectra obtained in the liquid phase. Experimental results were compared to theoretical modeling using the multistate, multireference perturbation theory approach combined with advanced molecular modeling tools to account for the solvent effects and to provide direct support for band assignments. Absorption maxima were determined both experimentally and theoretically and significant differences between the two chromophores were found. In particular, 3-OH-kynurenine demonstrated a blue-shift of more than 130 nm in the aqueous phase compared to the gas-phase due to the existence of different 3-OH-kynurenine conformers, which are stable under different conditions and originate from the interplay between intra- and intermolecular interactions. Photodissociation of argpyrimidine and 3-OH-kynurenine was observed in vacuum thus confirming the results previously obtained in liquid phase demonstrating that the photodestruction takes place in both media. 相似文献
9.
A. N. Panin T. A. Sukhova N. M. Bravaya 《Journal of polymer science. Part A, Polymer chemistry》2001,39(11):1901-1914
Ethylene polymerizations with catalytic systems Me2SiCp*NtBuZrX2 ( 1 ) [Cp* = C5(CH3)4; X = Cl ( 1Cl ), Me ( 1Me )], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C6F5)4 [Cat = CPh3 ( 3 ), Me2NHPh ( 4 )], or Me2SiCp2ZrX2 [X = Cl ( 2Cl ), Me ( 2Me )]/TIBA/ 3 ( 4 ) were performed within a wide range of ethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl ( 2Cl )/TIBA/ 3 led to the formation of very high linear molecular weight polyethylene (PE) of Mη ∼2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: kp/ktr ∼20–30 for 1Me /TIBA/ 3 and kp/ktr ∼350–500 for 2Me /TIBA/ 3 . It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr–Al bridged complex followed by the formation of a partially polarized Zr–Al(Cl)R2 (R = iBu) or an unreactive Zr–AlR3 cationic complex by abstraction of the alkyl ligand under the action of borate. It was concluded that AlR3 from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated α-olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl ( 1Me )/TIBA/ 3 /Ph2NH, 1Cl ( 1Me )/TIBA/ 4, 2Cl ( 2Me )/TIBA/ 3 /Ph2NH, and 2Cl ( 2Me )/TIBA/ 4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a σ-donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated α-olefin into trans-vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2Me relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1901–1914, 2001 相似文献
10.
The catalytic properties of the zirconium complex with “constrained geometry” Me2SiCp*NBu1ZrX2 (Cp*=C5Me4, X=Cl (1a), Me (1b)) and bridged bis(cyclopentadienyl)zirconocene Me2SiCp2ZrX2 (X=Cl (2a), Me (2b)) during their activation with triisobutylaluminum/perfluorophenyl borates (TIBA/LB(C6F5)4, L=CPh3 (3), Me2HNPh (4)) in ethylene polymerization under a monomer pressure of 2–20 atm were studied by comparison. Both dichloride complexes exhibit
moderate activity under the action of the combined TIBA/3 activating agent and give linear high-molecular-weight polyethylene (PE). The interaction of the dimethyl complexes with
TIBA/3(4) afford active sites in which the growing polymeric chain is intensely transferred to the monomer, due to which low-molecular-weight
PE is formed. The dichloride complexes affected by TIBA/4 also afford low-molecular-weight PE. Analysis of the structure of the polymeric products (1H NMR spectrometry, IR spectroscopy), molecular-weight parameters of the PE samples (gel permeation chromatography (GPC)),
and kinetics of polymerization suggested that the active site contains AlBui
3 as a heteronuclear bridged cationic complex. The influence of various basic substrates (the products of chain transfer with
the terminal vinyl groups, the dimethylaniline fragment of borate4 or other amine specially introduced into the reaction mixture) on the catalytic properties of the Zr−Al site was revealed.
The polymerization rate and molecular-weight parameters of PE as functions of the reaction temperature, ethylene pressure,
and modifying additives were studied.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1189–1198, July, 2000. 相似文献