ESR studies of the state of Ti3+ and Ti2+ in Ti?Mg catalysts for olefin polymerization

ESR studies have revealed that in Ti–Mg catalysts after interaction with organoaluminium compounds, the Ti³⁺ ions formed are present mainly as TiCl₃ associates. Isolated Ti³⁺ ions of various types are also detected. Part of titanium ions is in the divalent state and provides an ESR signal after oxidation by water to the trivalent state in the form of Ti³⁺ ordered by cooperative Jahn-Teller interaction.

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, - , Ti³⁺ TiCl₃. Ti³⁺ . Ti³⁺ - -.

     

Transport properties and electroanalytical response characteristics of drotaverine ion-selective sensors

The construction and electroanalytical response characteristics of poly(vinyl chloride) matrix ion-selective sensors (ISSs) for drotaverine hydrochloride are described. The membranes incorporate ion-association complexes of drotaverine with tetraphenylborate, picrate, tetraiodomercurate, tetraiodobismuthate, Reinecke salt, and heteropolycompounds of Keggin structure—molybdophosphoric acid, tungstophosphoric acid, molybdosiliconic acid and tungstosiliconic acid as electroactive materials for ionometric sensor controls. These ISSs have a linear response to drotaverine hydrochloride over the range 8×10^–6 to 5×10^–2 mol L^–1 with cationic slopes from 51 to 58 mV per concentration decade. These ISSs have a fast response time (up to 1 min), a low determination limit (down to 4.3×10^–6 mol L^–1), good stability (3–5 weeks), and reasonable selectivity. Permeabilities and ion fluxes through a membrane were calculated for major and interfering ions. Dependences of the transport properties of the membranes on the concentrations of the ion exchanger and near-membrane solution and their electrochemical characteristics are presented. The ISSs were used for direct potentiometry and potentiometric titration (sodium tetraphenylborate) of drotaverine hydrochloride. Results with mean accuracy of 99.1±1.0% of nominal were obtained which corresponded well to data obtained by use of high-performance liquid chromatography.     

Synthesis of 6H-pyrrolo[3',4':2,3][1,4]diazepino[6,7,1-hi]indole-8,10(7H,9H)-diones using 3-bromo-4-(indol-1-yl)maleimide scaffold

Series of 3-arylalkyl- or 3-alkylamino-4-(indol-1-yl)maleimides and bis(indol-1-yl)maleimides were synthesised. The cyclization of the 3-substituted 4-(indol-1-yl)maleimides under the action of acids resulted in the formation of diazepine[1,4] derivatives with indoline and maleimide nuclei annelated. These compounds readily produced the corresponding indolomaleimidodiazepines[1,4] after dehydrogenation.     

Partition constants of α-aminophosphonates in two-phase aqueous-organic solvent systems

Two-phase potentiometric titration was used to determine partition constants for a series of -aminophosphonates (RO)₂P(O)CH₂NR¹R² [R = Alk (C₂-C₅), R¹, R² = Me, Et, (CH₂)₅] between water and organic solvents, such as chloroform, carbon tetrachloride, toluene, octane, n-octanol, nitrobenzene, o-xylene, and cyclohexane. Correlations between the partition constants and the number of carbon atoms in substrate molecules were obtained. Solvent effects on partition constants were discussed, and solution parameters of -aminophosphonates were calculated.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 12, 2004, pp. 1998–2002.Original Russian Text Copyright © 2004 by Garifzyanov, Nuriazdanova, Zakharov, Cherkasov.This revised version was published online in April 2005 with a corrected cover date.     

General and efficient insertion of carbons carrying benzotriazole

Anions formed from the lithiation of 1-(1-benzotriazolylalkyl)benzotriazoles (1, 6) and 1-(1-methylthioalkyl)benzotriazoles (10 and 10a) with n-BuLi underwent additions to cyclic and acyclic ketones giving intermediates 3a-f, 7b-f, and 11b-d, respectively, in excellent yields. Thermal rearrangements of intermediates 3a,b,d-f and 7b-d,f in the presence of zinc bromide provided one-carbon chain-extended or ring-expanded alpha-benzotriazolyl ketones 4a,b,d-f and 8b-d,f in moderate yields with excellent regioselectivity. By contrast, intermediates 11b-d on treatment with zinc bromide loose a molecule of benzotriazole followed by intramolecular cyclization of the resulting intermediates 12b-d to provide the 2,3- and 1,2,3-substituted indenes 13b-d in good yields.     

Catalytic properties of monomeric and oligomeric Cu(II) phenylhydrazono imine chelates immobilized on zeolite with a topological anchor

Heterogeneous catalysts for liquid-phase oxidation of cyclohexene with molecular oxygen were prepared by topological-anchor immobilization on CaA zeolite of a monomeric Cu(II) chelate with N,N′-trimethylenebis(2-methyl-1-benzoylglyoxal 1-phenylhydrazone 2-imine) and of an oligomeric product of its condensation with ethylenediamine. The samples prepared contain surface monomeric and oligomeric Cu(II) chelates oriented toward the reaction medium, which makes them accessible to reactant molecules. The catalytic properties of the above monomeric chelate are preserved in going to the oligomers. The apparent rate constants per metal center for both homogeneous (soluble monomeric chelate) and heterogeneous modes coincide, suggesting the pseudohomogeneous behavior of the supported samples. The topological-anchor immobilization of insoluble oligomeric Cu(II) polychelates on zeolite leads to their more efficient utilization as heterogeneous catalysts and can be considered as one of examples of combining advantages of homogeneous and heterogeneous catalysis.     

Silver-catalyzed [2 + 2] cycloadditions of siloxy alkynes

We have described the first [2 + 2] cycloadditions of siloxy alkynes with a range of unsaturated carbonyl compounds. The reactions are efficiently promoted by substoichiometric amount of silver trifluoromethanesulfonimide and display excellent regio- and diastereoselectivity combined with a broad substrate scope. Our studies have established unambiguously the stepwise mechanism of this process and provided evidence for a novel role of silver in the catalytic cycle of the reaction, which involves silver-based complexation and activation of siloxy alkyne toward the subsequent 1,4-addition.     

Investigation of n-hexane dehydrocyclization over supported Pt catalyst modified by adsorbed rhenium

A -Al₂O₃ supported Re–Pt bimetallic catalyst prepared by electrochemical adsorption has been studied in n-hexane dehydrocyclization, using the slug-pulse method. The activity of the Re–Pt/Al₂O₃ catalyst treated only in hydrogen was low, but markedly increased by a calcination step before hydrogen treatment. The modified catalyst showed higher activity and increased selectivities for benzene and iso-hexanes than the base Pt/Al₂O₃ catalyst.

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Pd/Pt, -Al₂O₃, -. Pd–Pt/Al₂O₃, , , . Pd–Pt/Al₂O₃ , Pt/Al₂O₃.

     

Dithiane additions to vinyl epoxides: steric control over the SN2 and SN2' manifolds

High chemoselectivity can be achieved in the addition of lithium dithiane anions to vinyl epoxides exploiting the steric nature of the dithiane substituent. Unencumbered dithiane anions afford SN2 adducts, whereas sterically encumbered anions lead primarily to SN2' adducts. Furthermore, the SN2' addition occurs syn to the vinyl epoxide.     

Bis(m-phenylene)-32-crown-10-based cryptands, powerful hosts for paraquat derivatives

Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF(6) anion in analogous complexes exhibited the highest association constant K(a) = 5.0 x 10(6) M(-1) in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the beta-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats.