Home About us Contact
|
Home About us Contact | ||
|
|
||
MeCN
Terms modified by MeCN Selected Abstracts[Tris(pyrazolyl)methane]ruthenium Complexes Capable of Inhibiting Cancer Cell GrowthEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2009Jesse M. Walker Abstract The [tris(pyrazolyl)methane]ruthenium complexes [(,3 -tpm)RuCl(solv)2]PF6 [tpm = tris(pyrazolyl)methane; solv = MeCN, dmso] and [(,3 -tpm)RuCl(LL)]PF6 [LL = ,2 -dppe, ,2 -dppp, ,2 -dppb, (PMePh2)2] have been prepared, characterized and screened in vitro for their antiproliferative properties against the MCF-7 (breast) and HeLa (cervical) cancer cell lines by using the MTT assay. Although the MeCN and dmso complexes showed no activity under the conditions used, the phosphane complexes exhibited remarkable cytotoxic behaviour. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Bis(terdentate) Pyrazole/Pyridine Ligands: Synthesis, Crystal Structures and Magnetic Properties of Bridged Binuclear and Tetranuclear Copper(II) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2009Akhilesh Kumar Singh Abstract A new binucleating bis(terdentate) ligand, 3,5-[3-bis(2-pyridyl)pyrazole-1-ylmethyl]pyrazole (HL2), was synthesized. Reaction of the deprotonated ligand L2 with hydrated CuII salts gives (,-pyrazolato)(,-hydroxido)-bridged binuclear and tetranuclear complexes [L2Cu2(,-OH)(ClO4)(MeCN)](ClO4) (2), [L2Cu2(dmf)2(,3 -OH)]2(ClO4)4·4dmf (3·4dmf) and [L2L,Cu2](ClO4)2 [4; HL, = 3-(2-pyridyl)pyrazole]. In these complexes, both ,-OH and ,3 -OH bridges were observed. This contrasts the situation for a dicopper(II) complex of the related bis(terdentate) ligand 3,5-bis[6(2,2,-dipyridyl)]pyrazole (HL1), {L1Cu2(OMe)(MeOH)[,1 - O -(NO3)]}{[Cu2(NO3)2(,-OMe)2]}0.5·MeOH (1·MeOH), where the shorter and more rigid ligand side arms enforce a larger Cu···Cu separation and the formation of a MeO,HOMe moiety within the bimetallic pocket. Molecular structures of all complexes were elucidated by X-ray crystallography. Variable-temperature magnetic susceptibility measurements (295,2 K) for powdered samples of complexes 2,4 reveal strong antiferromagnetic coupling between two copper centres. The magnitude of the coupling is discussed in view of the structural features. During the preparation of complex 4, partial ligand hydrolysis was also observed, but this strongly depends on the reaction conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Tris(dibenzo[a,d]cycloheptenyl)phosphane: A Bulky Monodentate or Tetrapodal LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Urs Fischbach Abstract The tetradendate phosphane tris(5H -dibenzo[a,d]cyclohepten-5-yl)phosphane (trop3P, 1) was synthesized from tris(trimethylsilyl)phosphane and 5-chloro-5H -dibenzo[a,d]cycloheptene. Sulfurization of 1 with elemental sulfur led to trop3P=S. Complexes of 1 with AgI, AuI, RhI, IrI, and PdII were prepared. The structures of trop3P (1), trop3P=S (2), [AgCl(trop3P)] (3), [Au(trop3P)(MeCN)]PF6 (5), [RhCl(trop3P)] (6) and [Pd(trop3P)(H2O)](OTf)2 (9) were determined by X-ray diffraction studies. In the coinage metal complexes, 1 serves as monodentate extremely bulky ,1 -phosphane ligand (cone angle ca. 250°). In the RhI, IrI, and PdII complexes, 1 acts as tetradendate ligand. CP MAS NMR spectroscopy shows that the span of the chemical shift tensor increases in 7, 6, and 9 in this order (, = 310 ppm, 410 ppm, 465 ppm) and contains two strongly deshielded components, which are responsible for the unusual high frequency isotropic shift of the 31P resonances. This property correlates inversely with the metal to olefin backbonding (M,C=Ctrop) and ,(31P) decreases with increasing M,C=Ctrop in the order 9 (, = 260 ppm) > 7 (, = 196 ppm) > 6 (, = 135 ppm) > 3 (, = ,30.9 ppm). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Theoretical Studies on Metal,Metal Interaction and Intrinsic 1,3[,*(d),(s/p)] Excited States of Dinuclear d10 Complexes with Bridging Phosphane LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2006Qing-Jiang Pan Abstract To explore the metal,metal interaction and spectroscopic properties, the ground- and excited-state structures of [M2(dpm)2]2+ [M = Ag (2), Cu (3), dpm = bis(diphosphanyl)methane] and their solvated species [M2(dpm)2]2+·(MeCN)2 were optimized by the MP2 and CIS methods, respectively. In the ground states, the calculated M,M distances and their corresponding M,M stretching frequencies for 2 and 3 indicate the presence of metallophilic attraction; there is strong N,Cu/Ag coordination in acetonitrile, which is different from the case in previous studies of [Au2(dpm)2]2+ (1). CIS calculations show that 2 and 3 have 1,3[,*(d),(s/p)] as their lowest-energy excited state, as is also the case for 1, confirmed by unrestricted MP2 calculations. On the basis of the CIS-optimized structures, the TD-DFT (B3LYP) method was employed to calculate the emission spectra of such complexes. For 3, the phosphorescent emissions were calculated at 424 and 514 nm in the solid state and acetonitrile, which is comparable to the experimental data of 475 and 480 nm, respectively. The comparison between the gas-phase and solution emissions for 1,3 reveals that the N,M coordination results in a large red-shift of the emission wavelength. Taking previous studies into account , we found that the M,M distances are linearly correlated with the M,M stretching frequencies for the dinuclear d10 complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Nitrate- and Nitrite-Assisted Conversion of an Acetonitrile Ligand Into an Amidato Bridge at an {Mo2(Cp)2(,-SMe)3} Core: Electrochemistry of the Amidato Complex [Mo2(Cp)2(,-SMe)3{,-,1,,1 -OC(Me)NH}]+EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Marc Le Hénanf Abstract Treatment of [Mo2(Cp)2(,-SMe)3(MeCN)2]+ (1+) with NO3, or NO2, results in the conversion of one terminally bound acetonitrile ligand into an amidato bridge. The reaction produces [Mo2(Cp)2(,-SMe)3{,-,1,,1 -OC(Me)NH}]0/+ (20/+) and involves the formation of an intermediate, which was detected by cyclic voltammetry but which could not be isolated, and which likely arises from the substitution of the NOx anion for one MeCN ligand. The electrochemical behaviour of 2+ was studied by cyclic voltammetry in THF and MeCN. The reduction of 2+ in the presence of acid (HBF4/H2O or HBF4/Et2O) in these solvents leads to the release of the amidate bridge. Controlled-potential electrolysis of 2+ in MeCN in the presence of acid produces 1+ quantitatively; the charge consumed (>1 F,mol,1 of 1+) indicates that electrons are also used to reduce protons. This was confirmed by the formation of 2+ (in variable amounts depending on the conditions) on treating 2 with acid. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis of (1,2,4-Oxadiazole)palladium(II) Complexes by [2 + 3] Cycloaddition of Nitrile Oxides to Organonitriles in the Presence of PdCl2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2005Nadezhda A. Bokach Abstract The reaction between the nitrile oxides 2,4,6-R3C6H2CNO (R = Me, OMe) and trans -[PdCl2(RCN)2], or RCN (R = Me, Et, CH2CN, NMe2, Ph) in the presence of PdCl2, proceeded smoothly under mild conditions and allowed the isolation of the 1,2,4-oxadiazole complexes trans -[PdCl2{Na=C(R)-ON=Cb(C6H2R3)(Na,Cb)}2] (1,8) in 40,85,% yields. In CH2Cl2, the reaction between 2,4,6-R3C6H2CNO and [PdCl2(MeCN)2] furnishes [PdCl2(ONCC6H2R3)2] (9 and 10), which are the first representatives of metal compounds where nitrile oxides act as ligands. The 1,2,4-oxadiazole complexes 1,8 were characterized by elemental analysis, FAB mass spectrometry, and IR, 1H and 13C{1H} NMR spectroscopy, while 2, 3, 7, and 8 were additionally characterized by X-ray crystallography. The liberation of the heterocyclic species from 1,8 was successfully performed by substitution reaction either with 1,2-bis(diphenylphosphanyl)ethane or with an excess amount of Na2S·7H2O in MeOH; the liberated 1,2,4-oxadiazoles (11,18) were characterized by positive-ion FAB mass spectrometry and 1H and 13C{1H} NMR spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Structure-Dependent Electrochemical Behavior of Thienylplatinum(II) Complexes of N,N-HeterocyclesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2004Feng Zhao Abstract trans -[Pt(MeCN)(PPh3)2(2-thienyl)]BF4 (1) serves as a convenient precursor to bifunctional mononuclear trans -[Pt(PPh3)2(,1 - N - N)(2-thienyl)]BF4 [N - N = pyrazine (2); 2-chloropyrazine, (3)] and dinuclear trans,trans -[Pt2(PPh3)4(,- N - N)(2-thienyl)2](BF4)2 [(N - N = 4,4, -bipyridine (4); 4,4, -vinylenedipyridine (5)] complexes. The nuclear selectivity is conveniently controlled by the choice of the heterocyclic ligands or spacers. Both structural types 3 and 5 were confirmed by single-crystal X-ray crystallographic analyses. Their solution identities were established by positive-ion Electrospray Mass Spectrometry (ESMS). The electroactivities of these complexes were studied by cyclic voltammetry (CV). Continuous CV scans of 4 and 5 revealed variations in the redox waves with the number of scans. While the initial oxidative scan exhibited only a broad, irreversible wave, further cycling showed the growth of two additional redox couples up to about the tenth cycle. The peak currents of these redox couples began to decay with prolonged potential cycling beyond the tenth cycle. These findings are consistent with the formation of electroactive oligomers/polymers, and this conclusion is supported by visible thin film formation on the electrodes. In contrast, the mononuclear complexes (2 and 3) do not show such behavior. The films formed were further studied by repetitive potential cycling and XPS. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis and Structure of Two New High Nuclearity Ru/Pt Mixed-Metal ClustersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2003Brian F. G. Johnson Abstract The reaction of the dianion [Ru5C(CO)14]2, with [PtCl2(MeCN)2] in the presence of silica yields [Ru5PtC(CO)16] (1) and the new compound [PPN]2[Ru10Pt2C2(CO)28] (2), while, in a related reaction, [Ru6C(CO)16]2, undergoes addition of [PtCl2(MeCN)2] to yield the cluster [Ru12PtC2(CO)32(MeCN)2] (3). The high nuclearity compounds 2 and 3 have been fully characterized and their structures determined by single crystal X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Nucleophilic Reactivities of Azulene and Fulvenes,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Mariusz K, dziorek Abstract The kinetics of the reactions of azulene (1), 6,6-dimethylfulvene (2), 6-[4-(dimethylamino)phenyl]fulvene (3) and 6-(julolidin-9-yl)fulvene (4) with a set of benzhydrylium ions (reference electrophiles) have been investigated in MeCN. The second-order rate constants for these reactions correlate linearly with the electrophilicity parameters (E) of the benzhydrylium ions. According to the linear free-enthalpy relationship log,k2(20 °C) = s(N + E), the nucleophilicity parameters N and s of the ,-nucleophiles 1,4 were determined and compared with those of other types of nucleophiles. Azulene (1, N = 6.66) is about 10 times more nucleophilic than N -methylpyrrole and comparable to 2-methylindole. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Basicity of Guanidines with Heteroalkyl Side Chains in AcetonitrileEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 30 2008Mirjana Eckert-Maksi Abstract The pKa values of seven novel guanidine derivatives, six of them possessing heteroalkyl substituents capable of forming intramolecular hydrogen bonds, were determined in acetonitrile (MeCN) by using the UV/Vis spectrophotometric titration method. The obtained pKa values range from 24.7 to 27.2. The most basic among the studied guanidines was found to be by ca. 4 pKa units more basic than thewell-known superbase N1,N1,N3,N3 -tetramethylguanidine (TMG). The trends in the changes in the measured pKa values were compared with the experimental (determined by the extended kinetic method) and theoretical [B3LYP/6-311+G(2df,p)//B3LYP/6-31G(d)] gas-phase proton affinities. It was shown that basicity ordering of the bases with dimethylaminopropyl substituents in acetonitrile follows the trend encountered in the gas phase. However, this is not the case for the methoxypropyl-substituted guanidines indicating that in these molecules formation of the intramolecular hydrogen bonds is to large extent hindered due to solvation by acetonitrile.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Polystyrene-Supported 1,5,7-Triazabicyclo[4.4.0]dec-5-ene as an Efficient and Reusable Catalyst for the Thiolysis of 1,2-Epoxides under Solvent-Free ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2006Francesco Fringuelli Abstract Polystyrene-supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene (PS-TBD) is an effective basic catalyst for the thiolysis of the 1,2-epoxides 1a,e by the aryl- and alkyl-substituted thiols 2A,E under solvent-free conditions while its activity is remarkably reduced in MeCN. The reactions are totally anti -diastereoselective and generally highly C-, regioselective. The corresponding hydroxy sulfides have been isolated in excellent yields and the catalyst has been easily recovered and reused with no loss in terms of efficiency and selectivity of the process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of 2,4-Furanophanes by Palladium-Catalyzed Macrocyclization Reactions of 1,n -Diallenyl DiketonesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2004A. Stephen K. Hashmi Abstract The 1,n -diallenyl diketones 8a,j were prepared and subjected to reactions with the [PdCl2(MeCN)2] catalyst. Upon decreasing the length of the bridge between the allenyl ketone units, first we obtained the (E) isomer 10 as the macrocyclic product and then the (Z) isomer 11 accompanied by the exocyclic double bond isomer 12. In all cases, the open-chained 1,n -difuryl alkanes were isolated as side-products. The analogous preparation and conversion of the diallenyl diketones 19 and 24, which have even longer bridges and ether-functionalities, delivered the 20- to 52-membered macrocycles 21a, 21b, 26a, and 26b with only the expected (E) configuration of the double bond. The ring closure of a furan derivative, having vinyl groups in its substituents at the 2- and 4-positions, to a related product by Ru-catalyzed olefin metathesis delivered yields similar to the Pd-catalyzed macrocyclization, but provided a mixture of both double bond isomers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Ring-Expansion of MCPs in the Presence of DIAD or DEAD and Lewis AcidsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2004Li-Xiong Shao Abstract Treatment of methylenecyclopropanes (MCPs) with DIAD or DEAD in MeCN under mild conditions in the presence of Lewis acid Zr(OTf)4 gave the cyclobutanone ring-expansion products in good to high yields based on the employed DIAD or DEAD. From a deuterium labeling experiment, the oxygen atom is derived from ambient water. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Photoinduced Shuttling Dynamics of Rotaxanes in Viscous Polymer SolutionsADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Dhiredj C. Jagesar Abstract The effect of external friction, caused by medium viscosity, on the photoinduced translational motion in a rotaxane-based molecular shuttle 1 is investigated. The shuttle is successfully operated in solutions of poly(methacrylonitrile) (PMAN) of different molecular weights in MeCN and PrCN. The viscosity of the medium is tuned by changing the PMAN concentration. The rheological behavior of the polymer solution gives insight into the structure of the polymer solution on the microscopic scale. In PrCN, the entanglement regime is reached at lower concentration than in MeCN. This is also reflected by the effect on the shuttling: in the PrCN/PMAN system, a larger viscosity effect is observed compared to MeCN/PMAN. The shuttle is found to be slowed down in the polymer solutions but is still active at high viscosities. The observed retardation effect on the kinetics of shuttling in MeCN/PMAN and PrCN/PMAN can be correlated to the PMAN concentration through the hydrodynamic scaling model. The Stokes,Einstein relationship proves inadequate to correlate the shuttling rates to macroscopic viscosity, but the dependence of the shuttling rate on the bulk viscosity fits well to a commonly observed power-law relationship. The viscosity effect on the shuttling is found to be weak in all cases. [source] Physicochemical Properties of a New Multicomponent Cosolvent System for the pKa Determination of Poorly Soluble Pharmaceutical CompoundsHELVETICA CHIMICA ACTA, Issue 8 2007Abstract A mixture of cosolvents is described that significantly improves the solubility of most pharmaceutical compounds. The mixture consists of equal volumes of MeOH, 1,4-dioxane, and MeCN, thereby containing polar and nonpolar solvents, and is referred to as MDM (from MeOH, dioxane, and MeCN). MDM is mixed with H2O until the required composition is reached. The utility of this system is that it enables analytical measurements to be performed on a wide range of compounds where measurements would be impaired in aqueous solution. We present the physicochemical characteristics of MDM/H2O mixtures (density, dielectric constant, psKw) and the principles of pKa measurement in this solvent/H2O mixture. We also present pKa values in H2O of several drug compounds determined from values measured in MDM/H2O mixtures. [source] Quenching of Singlet Oxygen by Tertiary Aliphatic Amines.HELVETICA CHIMICA ACTA, Issue 10 2006Products, Structural Effects on Rates Abstract A kinetic and product study of the reaction of a series of , -methyl-substituted N -methylpiperidines with thermally generated 1O2 in MeCN was carried out. It was found that as the number of , -methyl groups (Me in , -position relative to the N-atom) increases, the rate of 1O2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N -demethylation products and N -formyl derivatives. The same trend was observed for the ratio between N -demethylation and formation of the N -formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme,1 where an exciplex is first formed that by a H-atom transfer process produces an , -amino-substituted C-radical. The latter forms the product of N -demethylation by one electron oxidation, or affords the N -formyl derivative by radical coupling (Scheme,1). Similar results were obtained with N,N -dimethylcyclohexanamine. However, this ,acyclic' amine exhibited behaviors quite distinct from those of the N -methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio. [source] A Rapid and Efficient Stereoselective Synthesis of (Z)- and (E)-Allyl Bromides from Baylis,Hillman Adducts Using Bromo(dimethyl)sulfonium Bromide,HELVETICA CHIMICA ACTA, Issue 7 2006Biswanath Das Abstract Treatment of Baylis,Hillman adducts 1 with bromo(dimethyl)sulfonium bromide, Br(Me2)S+Br,, in MeCN was found to stereoselectively afford (Z)- and (E)-allyl bromides 2. The reaction is rapid at room temperature, high-yielding, and highly stereoselective. [source] Cycloadditions of Bifunctional Vinyl Ethers with Electrophilic Alkenes through Tetramethylene Zwitterion IntermediatesHELVETICA CHIMICA ACTA, Issue 6 2005Bifunctional vinyl ethers react with electron-poor alkenes to cyclobutanes in good yields. The second CC bond reacted with neither the cyclobutane nor its zwitterion intermediate, even on heating. Cyclobutanes formed from ,tetracyanoethylene' (8) were transformed into tetrahydropyridines by reaction of the corresponding zwitterion with MeCN as the solvent. In contrast, cyclobutanes formed from dimethyl (dicyanomethylidene)propanedioate (9) did not react with MeCN, which is ascribed to diminished stabilization of the zwitterion intermediate, and increased steric effects. These results extend the classical studies of Huisgen and his co-workers. [source] Syntheses and structures of sulfilimine, sulfone diimine, and sulfoximine derivatives of a monocyclic thiophene, 3,4-di- tert -butylthiopheneHETEROATOM CHEMISTRY, Issue 5 2001Juzo Nakayama The reaction of 3,4-di-tert-butylthiophene (6a) with N-[(p-tolylsulfonyl)imino]-phenyliodinane (TsN=IPh) in the presence of Cu(MeCN)4PF6 in MeCN at room temperature provided 3,4-di-tert-butyl-1-[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (3b),3,4-di-tert-butyl-1,1-bis[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (5a), and 1-(p-tolylsulfonyl)-3,4-di-tert-butylpyrrole (7a) as the principal products. The use of 20 molar amounts of 6a gave 3b in an increased yield of 61%. Treatment of 3,4-di-tert-butylthiophene 1-oxide (1a) with (CF3CO)2O or (CF3SO2)2O, followed by reactions with RSO2NH2, ROC(=O)NH2, or RCONH2, furnished a series of S-imino derivatives (3b,c,e,h) of 6a, which carry an electron-withdrawing substituent on the imino nitrogen atom. Treatment of the S-imino derivative 3f (substituent on the nitrogen atom = COBu) with CF3CO2H gave an aminosulfonium salt (13), whose deprotonation led to the parent N-unsubstituted 1-imide derivative (3n). Treatment of 2,4-di-tert-butylthiophene 1-oxide (1b) with TsN=IPh in the presence of Cu(MeCN)4PF6 in MeCN at room temperature provided 2,4-di-tert-butyl-1-[(p-toluenesulfonyl)imino]-1,1-dihydrothiophene 1-oxide (4e) in 81% yield. Hydrolysis of 4e by concentrated H2SO4 at room temperature furnished 2,4-di-tert-butyl-1-imino-1,1-dihydrothiophene 1-oxide (4f) in 89% yield. A pair of enantiomers of 4f were separated by high-performance liquid chromatography (HPLC) on a chiral column, and their absolute configurations were determined by an X-ray crystallographic analysis. Structures of sulfilimine, sulfone diimine, and sulfoximine derivatives of monocyclic thiophenes, obtained in these ways, are discussed based on spectroscopies (IR and 1H and 13C NMR) and X-ray crystallographic analyses. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:333,348, 2001 [source] Mechanism of interaction of DNA bases with dichloro-[1-alkyl-2-(naphthylazo)imidazole]palladium(II) complexes: A cytosine caseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2009Pradip Kumar Ghosh Interaction of cytosine (C) with dichloro-[1-alkyl-2-(,-naphthylazo)imidazole]-palladium(II) [Pd(,-NaiR)Cl2, 1] and dichloro-[1-alkyl-2-(,-naphthylazo)imidazole]-palladium(II) [Pd(,-NaiR)Cl2, 2] complexes {where alkyl R = Me (a), Et (b) or Bz (c)} in acetonitrile (MeCN)-water (50% v/v) medium to yield [{1-alkyl-2-(,-naphthylazo)-imidazole}bis(cytosine)]palladium(II)dichloride (3a, 3b, 3c) and [{1-alkyl-2-(,-naphthylazo)-imidazole}bis(cytosine)]palladium(II)dichloride (4a, 4b, 4c) was studied. The products were characterized by microanalytical data and spectroscopic techniques (FT-IR, UV,vis, and NMR). The reaction kinetics show first-order dependence of the rate on each of the concentration of Pd(II) complex and C. External addition of Cl, ion (LiCl) did not influence this nucleophilic substitution rate process and has proved the cleavage of first PdCl bond is the rate-determining step. Thermodynamic parameters standard enthalpy of activation (,,Ho) and standard entropy of activation (,,So) were determined from variable temperature kinetic studies. The negative values of ,,So indicate that the reaction proceeds through an associative inner sphere mechanism. The magnitude of the second-order rate constant k2 increases in the following order: Pd(NaiEt)Cl2 (b) < Pd(NaiMe)Cl2 (a) < Pd(NaiBz)Cl2 (c) as well as Pd(,-NaiR)Cl2 (1) < Pd(,-NaiR)Cl2 (2), which corroborates with the experimental ,,Ho values. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 463,472, 2009 [source] An empirical approach to study the occurrence of ion exchange in the ionic micellar-mediated semi-ionic reactions: Kinetics of the rate of reaction of piperidine with ionized phenyl salicylate in the presence of cationic micellesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2001M. Niyaz Khan Pseudo-first-order rate constants (kobs),obtained for the cleavage of ionized phenyl salicylate (PS,) at constant [NaOH], [MeCN], [CTAZ]T (total concentration of cetyltrimethylammonium chloride and bromide), [Pip]T (total concentration of piperidine), and varying concentrations of sodium cinnamate, acetate, and butanoate ([NaX]),follow the relationship: kobs = (k0 + , K[NaX])/(1 + K[NaX]), where , and K are empirical parameters. The values of , are almost independent of [CTAZ]T, while K values decrease with the increase in [CTAZ]T within its range 0.006,0.020 M. The values of , and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: KS = KS0/(1 + ,X/S [NaX]), where KS is the CTAZ micellar binding constant of PS, in the presence of NaX. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 288,294, 2001 [source] Ruthenium Catalysts for Controlled Mono- and Bis-Allylation of Active Methylene Compounds with Aliphatic Allylic SubstratesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Hui-Jun Zhang Abstract The allylation of 1,3-dicarbonyl compounds and malononitrile with aliphatic allylic substrates is achieved under mild conditions in the presence of new ruthenium catalysts. The ruthenium complex [Ru(C5Me5)(2-quinolinecarboxylato)(CH2CHCH- n -Pr)],[BF4] as a precatalyst, allows the synthesis of mono-allylated branched derivatives. On the other hand, the parent complex [Ru(C5Me5)(MeCN)3],[PF6] as a precatalyst, straightforwardly favours the bis-allylation of the procarbonucleophiles leading to bis-allylated bis-linear products. The involvement of the two precatalysts provides a sequential synthesis of unsymmetrical mixed linear-branched bis-allylated derivatives. [source] Oxidation of thioanisole by hydrogen peroxide: activation by nitrilesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2003Nicholas D. Gillitt Abstract The oxidation of thioanisole (PhSMe) by H2O2 is activated by acetonitrile (MeCN) and propionitrile (EtCN) and involves the formation of a transient peroxyimidate, 1, by reaction of and RCN, and 1 can be rapidly trapped by PhSMe. The rate of oxidation of PhSMe is then independent of the concentrations of PhSMe and of H2O2, but varies linearly with and [RCN]. In very dilute PhSMe it and H2O2 compete in reacting with 1, and the rate then depends on [PhSMe]. The initial reaction gives PhSOMe, and subsequent formation of PhSO2Me is slow. The rates of oxidation are slightly higher than that expected from the MeCN-activated decomposition of H2O2, which involves a second molecule of H2O2 in conversion of the peroxyimidate into amide and oxygen. Copyright © 2003 John Wiley & Sons, Ltd. [source] Reactions of 1,2,5-thiadiazole 1,1-dioxide derivatives with nitrogenated nucleophiles.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 20031-dioxide, 4-diphenyl-, 5-thiadiazole , Addition of amines, Part , amides to Abstract The addition reactions of some amides and aromatic amines to a CN double bond of 3,4-diphenyl-1,2,5-thiadiazole 1,1-dioxide (1) were studied in aprotic solvent solutions [N,N -dimethylformamide (DMF) and acetonitrile (MeCN)]. Equilibrium constants for the reactions of 1 with acetamide, 2-fluoroacetamide, butyramide, benzamide, aniline and 3-aminopyridine were measured using a previously reported cyclic voltammetric (CV) method. Aliphatic amines gave unstable solutions, probably owing to reactions of anionic species derived from 1. Other N nucleophiles tested (formamide, succinimide, thioacetamide and cyanamide) yielded different products that have not yet been characterized. DMF, N,N -dimethylacetamide (DMA) and N -methylacetamide did not react. The addition thiadiazoline produced in the reaction of acetamide with 1 was characterized by IR and 1H and 13C RMN NMR spectroscopy as a prototype compound. For this system, the equilibrium constant could also be measured by a standard UV,VIS method and was found to be in agreement with the value obtained by CV. The reaction of 1 with urea produced a bicyclic product, identified as 3a,6a-diphenyltetrahydroimidazo[4,5- c]-1,2,5-thiadiazol-5-one 2,2-dioxide. Copyright © 2003 John Wiley & Sons, Ltd. [source] Ring-opening reactions of 5-(aryl)thianthrenium bromides with aryl thiolatesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2002Ding-Quan Qian Abstract A series of 5-(aryl)thianthrenium bromides (6a,e) with aryl (Ar) groups phenyl (a), p -tolyl (b), p -anisyl (c), p -chlorophenyl (d) and p -bromophenyl (e) was prepared by reaction of thianthrene 5-oxide with the appropriate Grignard reagent ArMgBr. Reactions of 6a,e with aryl thiolates (Ar,SNa, Ar,,=,phenyl, p -tolyl and p -chlorophenyl, 7a,c) were carried out in MeCN at room temperature. Products from 6a,c were a small amount of arene [benzene (8a) and toluene (8b)], and substantial amounts of ArSAr, (9), thianthrene (Th) and a trisulfide, namely a 2-(ArS)-2,-(Ar,S)-diphenyl sulfide (10). Products from reactions of 6d,e were smaller amounts of 9 and 10 but substantial amounts of 1,4-di(Ar,S)benzene (11) and a tetrasulfide (12a,c). The reactions that lead to products 9,12 are attributed to ligand coupling (LC) pathways in sulfuranes formed by attack of Ar,S, at the sulfonium S atom of 6. In the formation of 11 and 12 the halogen atom (Cl, Br) is first displaced from 6d,e by Ar,S,, giving a new thianthrenium ion (14) from which sulfurane formation (15) follows. Products 10 and 12 result from opening of the thianthrenium ring of sulfuranes 13 and 15 through LC. Products were assayed with a combination of GC and isolation with TLC, and were identified with a combination of GC (authentic compounds), x-ray crystallography (10a), elemental analyses and high-resolution mass spectrometry. The reactions of 6 are compared with earlier reactions of 5-(alkoxy)-and 5-(alkyl)thianthrenium salts (1 and 2). Copyright © 2002 John Wiley & Sons, Ltd. [source] Cyclometalated 2-phenylpyridine complex [RuII(o -C6H4 -py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008F. Diaz Camacho Abstract The cyclometalated complex [RuII(o -C6H4 -py)(MeCN)4]PF6 (1) with a ,-RuC bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n -butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2-bromoisobutyrate, methyl 2-bromopropionate, and 1-phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion-dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst (1), when the added amount of (1) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the (1)-catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193,4204, 2008 [source] Development and validation of a method based on a QuEChERS procedure and heart-cutting GC-MS for determination of five mycotoxins in cereal productsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 4-5 2010Sara C. Cunha Abstract A new analytical method for the rapid and simultaneous determination of five mycotoxins (zearelenone, deoxynivalenol, Fusarenon X, 15-acetyldeoxynivalenol and nivalenol) in breakfast cereals and flours by heart-cutting GC-MS has been developed and validated. Extraction was performed with MeCN, applying a modified QuEChERS (QUick, Easy, CHeap, Effective, Rugged and Safe) procedure, and the extracts were analyzed after a silylation of the analytes under study. Careful optimization of the parameters of Deans Switch device and GC-MS was achieved in order to attain a fast separation in SIM mode, allowing a total run time of only 8,min. Acceptable recoveries for all mycotoxins at two different spiking levels (20 and 100,,g/kg) were achieved with good repeatability (from 9 to 21%). LOD ranged from 2 to 15,,g/kg and LOQ ranged from 5 to 50,,g/kg, which were lower than the maximum limit legal established by the European Union (EU). The method developed was applied to commercial breakfast cereals and flours; among the mycotoxins studied, deoxynivalenol and zearalenone were the most predominant. [source] Reinvestigation of the Mechanism of the Free Radical Polymerization Photoinitiation Process by Camphorquinone,Coinitiator Systems: New ResultsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2004Ilona Pyszka Abstract Summary: Comparative studies of photoinitiation processes using camphorquinone (CQ) and benzophenone (BP) as light absorbers were performed. The experimental results show that after the transformation of (phenylthio)acetic acid (PTAA) into its tetrabutylammonium salt (PTAA AS), a substantial decrease of the polymerization photoinitiation ability for the CQ,PTAA AS pair in comparison to the CQ,PTAA pair is observed. The mechanism of the photoinitiated polymerization for the tested photoredox pair was clarified based on laser flash photolysis experiments obtained using benzophenone as an electron acceptor and (phenylthio)acetic acid and its tetrabutylammonium salt as electron donors in solution in MeCN. It is documented and deduced that the photoreduction of benzophenone in the presence of (phenylthio)acetic acid and its tetrabutylammonium salt occurs by a photoinduced electron transfer process, while for CQ as initiator, the free radicals are formed by hydrogen atom abstraction by the triplet state of camphorquinone. Schematic of the transients formed after an electron-transfer process for benzophenone,PTAA and benzophenone,PTAA AS pairs. [source] Synthesis and characterizations of N,N,-bis(diphenylphosphino)-2-(aminomethyl)aniline derivatives: application of a palladium(II) complex as pre-catalyst in Heck and Suzuki cross-coupling reactionsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2009Murat Aydemir Abstract The reaction of 2-(aminomethyl)aniline with 2 equivalents of PPh2Cl in the presence of Et3N, proceeds in CH2Cl2 to give N,N,-bis(diphenylphosphino)-2-(aminomethyl)aniline 1 in good yield. Oxidation of 1 with aqueous H2O2, elemental sulfur or gray selenium gave the corresponding oxide, sulfide and selenide dichalcogenides [Ph2P(E)NHC6H4CH2NHP(E)Ph2] (E: O, 2a; S, 2b; Se, 2c), respectively. The reaction of [Ph2PNHC6H4CH2NHPPh2] with PdCl2(cod), PtCl2(cod) and [Cu(MeCN)4]PF6 gave the corresponding chelate complexes, PdCl21, PtCl21 and [Cu(1)2]PF6. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzes the Suzuki coupling and Heck reaction, affording biphenyls and stilbenes respectively, in good yields. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||