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Dimeric Structure (dimeric + structure)
Selected AbstractsSynthesis, Characterization, and Properties of Some Copper(II) Complexes of 2-Pyridineformamide Thiosemicarbazone (HAm4DH)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2006María del Carmen Aguirre Abstract Reactions between different copper(II) salts and 2-pyridineformamide thiosemicarbazone (HAm4DH) in neutral ethanolic media led to the formation of complexes with the formulae [Cu(HAm4DH)X2] (X = Cl or Br) (1, 2) and [Cu(HAm4DH)2]X2 (X = NO3 or ClO4) (3, 4). The same reactions carried out in the presence of triethylamine gave rise to new complexes with the general formulae [Cu(Am4DH)X] (X = Cl, Br, AcO, or NO3) (5,8), [Cu(H2O)(Am4DH)](ClO4) (9), and [Cu(Am4DH)2] (10), many of which were isolated with different molecules of crystallization and contain a deprotonated thiosemicarbazone (Am4DH). These complexes were characterized by elemental analysis, and different spectroscopic and magnetic techniques. The thermal and redox behavior of the complexes was also evaluated. Complexes 1, 2, 5, and 6 show better nuclease activity than [Cu(phen)2]2+. Inaddition, crystals were isolated in the cases of [Cu(HAm4DH)Cl2]2 (5a), 1,[Cu(Am4DH)Cl] (5b), 1,[Cu(Am4DH)Br] (6a), and [Cu(HAm4DH)(H2O)(ClO4)2]·MeOH·H2O (9a) and these structures were analyzed by X-ray diffraction. Compound 5a has a dimeric structure with chlorine bridges and shows weak antiferromagnetism (J = ,12.2 cm,1). Complexes 5b and 6a are one-dimensional polymers formed through halogen bridges and the deprotonated thiosemicarbazone in the thiolate form. In compound 9a the copper(II) is in a distorted octahedral environment with two ClO4 units coordinated to the metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Mono-, Di- and Polymeric Calcium and Gadolinium Complexes of the Tripodal Ligand 2,2,,2,,-Nitrilotribenzoic AcidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005Stefan Wörl Abstract Three novel carboxylate-bridged complexes incorporating the tripodal N,O ligand 2,2,,2,,-nitrilotribenzoic acid H3L of formula [CaII(H2L)(OH2)4][(H2L)]·4H2O (1), [CaII(OH2)4]-[CaII(L)(OH2)2]2·7H2O (2) and [GdIII(L)(OH2)3]2[GdIII(L)-(OH2)4]2·13H2O (3) were synthesized and characterized by X-ray crystallography. In all three complexes, the ligand H3L binds to the metal centre only by its three carboxylate donors, leaving the bridgehead nitrogen atom nonbonding. The calcium(II) ion in the monomeric complex 1 is distorted pentagonal-bipyramidal coordinated, the +1 charge of the complex cation [CaII(H2L)(OH2)4]+ is balanced by an H2L, anion and both units are connected by hydrogen bonds. The polymeric compound 2 displays a one-dimensional chain structure, in which two [CaII(L)]2, units form a dimeric structure and are connected by hydrated CaII ions. 3 contains two different [GdIII(L)(OH2)n] dimers. In one of them the two GdIII ions are linked by two monoatomic carboxylate O-bridges showing a short Gd···Gd distance of 3.99 Å. In the second, a syn - anti carboxylate 1,3-bridge with a longer Gd···Gd distance of 4.96 Å is observed. Magnetic measurements of 3 show paramagnetic behaviour with weak antiferromagnetic coupling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Structural model for an AxxxG-mediated dimer of surfactant-associated protein CFEBS JOURNAL, Issue 11 2004Visvaldas Kairys The pulmonary surfactant prevents alveolar collapse and is required for normal pulmonary function. One of the important components of the surfactant besides phospholipids is surfactant-associated protein C (SP-C). SP-C shows complex oligomerization behavior and a transition to ,-amyloid-like fibril structures, which are not yet fully understood. Besides this nonspecific oligomerization, MS and chemical cross-linking data combined with CD spectra provide evidence of a specific, mainly ,-helical, dimer at low to neutral pH. Furthermore, resistance to CNBr cleavage and dual NMR resonances of porcine and human recombinant SP-C with Met32 replaced by isoleucine point to a dimerization site located at the C-terminus of the hydrophobic ,-helix of SP-C, where a strictly conserved heptapeptide sequence is found. Computational docking of two SP-C helices, described here, reveals a dimer with a helix,helix interface that strikingly resembles that of glycophorin A and is mediated by an AxxxG motif similar to the experimentally determined GxxxG pattern of glycophorin A. It is highly likely that mature SP-C adopts such a dimeric structure in the lamellar bilayer systems found in the surfactant. Dimerization has been shown in previous studies to have a role in sorting and trafficking of SP-C and may also be important to the surfactant function of this protein. [source] Molecular modeling of the dimeric structure of human lipoprotein lipase and functional studies of the carboxyl-terminal domainFEBS JOURNAL, Issue 18 2002Yoko Kobayashi Lipoprotein lipase (LPL) plays a key role in lipid metabolism. Molecular modeling of dimeric LPL was carried out using insight ii based upon the crystal structures of human, porcine, and horse pancreatic lipase. The dimeric model reveals a saddle-shaped structure and the key heparin-binding residues in the amino-terminal domain located on the top of this saddle. The models of two dimeric conformations , a closed, inactive form and an open, active form , differ with respect to how surface-loop positions affect substrate access to the catalytic site. In the closed form, the surface loop covers the catalytic site, which becomes inaccessible to solvent. Large conformational changes in the open form, especially in the loop and carboxyl-terminal domain, allow substrate access to the active site. To dissect the structure,function relationships of the LPL carboxyl-terminal domain, several residues predicted by the model structure to be essential for the functions of heparin binding and substrate recognition were mutagenized. Arg405 plays an important role in heparin binding in the active dimer. Lys413/Lys414 or Lys414 regulates heparin affinity in both monomeric and dimeric forms. To evaluate the prediction that LPL forms a homodimer in a ,head-to-tail' orientation, two inactive LPL mutants , a catalytic site mutant (S132T) and a substrate-recognition mutant (W390A/W393A/W394A) , were cotransfected into COS7 cells. Lipase activity could be recovered only when heterodimerization occurred in a head-to-tail orientation. After cotransfection, 50% of the wild-type lipase activity was recovered, indicating that lipase activity is determined by the interaction between the catalytic site on one subunit and the substrate-recognition site on the other. [source] Crystal structure of a staphylokinase variantFEBS JOURNAL, Issue 2 2002A model for reduced antigenicity Staphylokinase (SAK) is a 15.5-kDa protein from Staphylococcus aureus that activates plasminogen by forming a 1 : 1 complex with plasmin. Recombinant SAK has been shown in clinical trials to induce fibrin-specific clot lysis in patients with acute myocardial infarction. However, SAK elicits high titers of neutralizing antibodies. Biochemical and protein engineering studies have demonstrated the feasibility of generating SAK variants with reduced antigenicity yet intact thrombolytic potency. Here, we present X-ray crystallographic evidence that the SAK(S41G) mutant may assume a dimeric structure. This dimer model, at 2.3-Å resolution, could explain a major antigenic epitope (residues A72,F76 and residues K135-K136) located in the vicinity of the dimer interface as identified by phage-display. These results suggest that SAK antigenicity may be reduced by eliminating dimer formation. We propose several potential mutation sites at the dimer interface that may further reduce the antigenicity of SAK. [source] New P-ligands: The aromaticity and reactivity of 2,4,6-trialkylphenylphospholesHETEROATOM CHEMISTRY, Issue 2 2005György Keglevich A further member of 2,4,6-trialkyl-phenyl-phos-pholes, the ditertbutylmethylphenyl derivative (1c) was characterized by Bird index and by the sum of angles at the phosphorus atom to describe the flattening of the P-pyramid. Both numbers suggested a slight aromaticity. The reaction of arylphospholes with phosphorus tribromide was extended to phosphole 1c leading this occasion, after further steps, to the mixture of 3- and 2-substituted products (3c-1 and 3c-2, respectively). A triisopropylphenyl-2H -phosphole (4) formed by sigmatropic rearrangement was utilized in the preparation of new 1-phosphanorbornene derivatives, such as sulfide 6 and hemi-oxides 8-1 and 8-2. Further oxidation of the latter species (8-1 and 8-2) led to the decomposition of the dimeric structure (11). 4 could also be trapped by benzaldehyde to afford the oxaphosphanorbornene (10) as one diastereomer. Finally, the reversible formation of 2H -phosphole 4 from 1H -phosphole 1a at 150°C was proved. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:104,222, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20077 [source] Crystallographic and biochemical studies revealing the structural basis for antizyme inhibitor functionPROTEIN SCIENCE, Issue 5 2008Shira Albeck Abstract Antizyme inhibitor (AzI) regulates cellular polyamine homeostasis by binding to the polyamine-induced protein, Antizyme (Az), with greater affinity than ornithine decarboxylase (ODC). AzI is highly homologous to ODC but is not enzymatically active. In order to understand these specific characteristics of AzI and its differences from ODC, we determined the 3D structure of mouse AzI to 2.05 Å resolution. Both AzI and ODC crystallize as a dimer. However, fewer interactions at the dimer interface, a smaller buried surface area, and lack of symmetry of the interactions between residues from the two monomers in the AzI structure suggest that this dimeric structure is nonphysiological. In addition, the absence of residues and interactions required for pyridoxal 5,-phosphate (PLP) binding suggests that AzI does not bind PLP. Biochemical studies confirmed the lack of PLP binding and revealed that AzI exists as a monomer in solution while ODC is dimeric. Our findings that AzI exists as a monomer and is unable to bind PLP provide two independent explanations for its lack of enzymatic activity and suggest the basis for its enhanced affinity toward Az. [source] Crystal structure of an enhancer of rudimentary homolog (ERH) at 2.1 Å resolutionPROTEIN SCIENCE, Issue 7 2005Ryoichi Arai Abstract The enhancer of rudimentary gene, e(r), of Drosophila melanogaster encodes an enhancer of rudimentary (ER) protein with functions implicated in pyrimidine biosynthesis and the cell cycle. The ER homolog (ERH) is highly conserved among vertebrates, invertebrates, and plants. Xenopus laevis ERH was reported to be a transcriptional repressor. Here we report the 2.1 Å crystal structure of murine ERH (Protein Data Bank ID 1WZ7), determined by the multiwavelength anomalous dispersion (MAD) method. The monomeric structure of ERH comprises a single domain consisting of three ,-helices and four ,-strands, which is a novel fold. In the crystal structure, ERH assumes a dimeric structure, through interactions between the ,-sheet regions. The formation of an ERH dimer is consistent with the results of analytical ultracentrifugation. The residues at the core region and at the dimer interface are highly conserved, suggesting the conservation of the dimer formation as well as the monomer fold. The long flexible loop (44,53) is also significantly conserved, suggesting that this loop region may be important for the functions of ERH. In addition, the putative phosphorylation sites are located at the start of the ,2-strand (Thr18) and at the start of the ,1-helix (Ser24), implying that the phosphorylation might cause some structural changes. [source] Polymerization of the SAM domain of MAPKKK Ste11 from the budding yeast: Implications for efficient signaling through the MAPK cascadesPROTEIN SCIENCE, Issue 3 2005Surajit Bhattacharjya Abstract The sterile ,-motif (SAM) is a protein module ,70 residues long and mainly involved in the protein,protein interactions of cell signaling and transcriptional repression. The SAM domain of the yeast MAPKKK Ste11 has a well-folded dimeric structure in solution. Interestingly, the well-folded dimer of the Ste11 SAM undergoes a time-dependent self-assembly upon lowering of the pH, leading to the formation of high molecular weight oligomers. The oligomeric structures rapidly disassemble to the well-folded dimer upon reversal of the pH to close to neutral conditions. Circular dichroism (CD) and atomic force microscopy (AFM) experiments demonstrate that the oligomeric structure formed at pH 5.0 appears to be highly helical and has architecture akin to proto-fibrils. Residue-specific kinetics of pH-triggered oligomerization obtained from real-time 15N- 1H HSQC experiments indicate that the dimer-oligomer transition appears to involve all residues of the well-folded dimeric structure of the Ste11 SAM. Very interestingly, the interactions of the Ste11 and Ste50 SAM domains also lead to the formation of non-homogeneous hetero-complexes with significant populations of high molecular weight aggregates. AFM imaging shows that the Ste11-Ste50 hetero-polymeric aggregates assume the shapes of circular nano-particles with dimensions of 50,60 nano-meters (nm), in contrast to the proto-fibrils formed by the Ste11 SAM domain alone. Such intrinsic propensity for dimer to oligomer transition of the Ste50-binding SAM domain of Ste11 may endow the MAPKKK Ste11 with unique functional properties required for efficient and high fidelity signal transduction in the budding yeast. [source] Denaturant sensitive regions in creatine kinase identified by hydrogen/deuterium exchangeRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2005Hortense Mazon The GdmHCl-induced unfolding of creatine kinase (CK) has been studied by hydrogen/deuterium (H/D) exchange combined with mass spectrometry. MM-CK unfolded for various periods in different denaturant concentrations was pulsed-labeled with deuterium to identify different conformational intermediate states. For all denaturation times or GdmHCl concentrations, we observed variable proportions of only two species. The low-mass envelope of isotope peaks corresponds to a species that has gained about 10 deuteriums more than native CK, and the high-mass envelope to a completely deuterated species. To localize precisely the unfolded regions in the states highly populated during denaturation, the protein was digested with two proteases (pepsin and type XIII protease) after H/D exchange and rapid quenching of the reaction. The two sets of fragments obtained were analyzed by liquid chromatography coupled to mass spectrometry to determine the deuterium level in each fragment. Bimodal distributions of deuterium were found for most peptides, indicating that these regions were either folded or unfolded. This behavior is consistent with cooperative, localized unfolding. However, we observed a monomodal distribution of deuterium in two regions (1,12 and 162,186). We conclude that the increment of mass observed in the low-mass species of the intact protein (+10,Da) has its origin in these two segments. These regions, which are very sensitive to low GdmHCl concentrations, are involved in the monomer,monomer interface of CK and their perturbation is likely to weaken the dimeric structure. At higher denaturant concentration, this would induce dissociation of the dimer. Copyright © 2005 John Wiley & Sons, Ltd. [source] Bis(,-benzene-1,2-dicarboxylato)bis{aqua[2-(2-chloro-6-fluorophenyl)-1H -imidazo[4,5- f][1,10]phenanthroline]cadmium(II)} and its zinc(II) analogueACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009Xiu-Yan Wang In the isomorphous title compounds, [Cd2(C8H4O4)2(C19H10ClFN4)2(H2O)2] and [Zn2(C8H4O4)2(C19H10ClFN4)2(H2O)2], the CdII centre is seven-coordinated by two N atoms from one [2-(2-chloro-6-fluorophenyl)-1H -imidazo[4,5- f][1,10]phenanthroline (L) ligand, one water O atom and four carboxylate O atoms from two different benzene-1,2-dicarboxylate (1,2-bdc) ligands in a distorted pentagonal,bipyramidal coordination, while the ZnII centre is six-coordinated by two N atoms from one L ligand, one water O atom and three carboxylate O atoms from two different 1,2-bdc ligands in a distorted octahedral coordination. Each pair of adjacent metal centres is bridged by two 1,2-bdc ligands to form a dimeric structure. In the dimer, each L ligand coordinates one metal centre. The dimer is centrosymmetric, with a crystallographic inversion centre midway between the two metal centres. The aromatic interactions lead the dimers to form a two-dimensional supramolecular architecture. Finally, O,H...O and N,H...O hydrogen bonds reinforce the two-dimensional structures of the two compounds. [source] Two novel benzenedicarboxylate-metal complexes: synthesis, crystal structures and fluorescent propertiesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2007Yi-Shan Song Abstract Two novel benzenedicarboxylate,metal complexes, [Sm(nphth)(Hnphth)(H2O)3,H2O]2 and [Zn(nphth)(bipy)(H2O) ,H2O]2 (2) (H2nphth = 3-nitrophthalic acid, bipy = 2,2,-bipyridine), have been synthesized under hydrothermal condition and characterized by single-crystal X-ray diffraction. Both complex 1 and 2 exhibit a dimeric structure, and nphth ligand shows different coordination mode in the f-block and d-block complexes. The fluorescent properties of two complexes are investigated; the results reveal that the two complexes show different kinds of fluorescence. Copyright © 2007 John Wiley & Sons, Ltd. [source] 1.8 Å structure of murine GITR ligand dimer expressed in Drosophila melanogaster S2 cellsACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2009Kausik Chattopadhyay Glucocorticoid-induced TNF receptor ligand (GITRL), a prominent member of the TNF superfamily, activates its receptor on both effector and regulatory T cells to generate critical costimulatory signals that have been implicated in a wide range of T-cell immune functions. The crystal structures of murine and human orthologs of GITRL recombinantly expressed in Escherichia coli have previously been determined. In contrast to all classical TNF structures, including the human GITRL structure, murine GITRL demonstrated a unique `strand-exchanged' dimeric organization. Such a novel assembly behavior indicated a dramatic impact on receptor activation as well as on the signaling mechanism associated with the murine GITRL costimulatory system. In this present work, the 1.8,Å resolution crystal structure of murine GITRL expressed in Drosophila melanogaster S2 cells is reported. The eukaryotic protein-expression system allows transport of the recombinant protein into the extracellular culture medium, thus maximizing the possibility of obtaining correctly folded material devoid of any folding/assembly artifacts that are often suspected with E. coli -expressed proteins. The S2 cell-expressed murine GITRL adopts an identical `strand-exchanged' dimeric structure to that observed for the E. coli -expressed protein, thus conclusively demonstrating the novel quaternary structure assembly behavior of murine GITRL. [source] Structure of a d(TGGGGT) quadruplex crystallized in the presence of Li+ ionsACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2007Christophe Creze A parallel 5,-d(TGGGGT)-3, quadruplex was formed in Na+ solution and crystallized using lithium sulfate as the main precipitating agent. The X-ray structure was determined to 1.5,Å resolution in space group P21 by molecular replacement. The asymmetric unit consists of a characteristic motif of two quadruplexes stacked at their 5, ends. All nucleotides are clearly defined in the density and could be positioned. A single bound Li+ ion is observed at the surface of the column formed by the two joined molecules. Thus, this small alkali metal ion appears to be unsuitable as a replacement for the Na+ ion in the central channel of G-quartets, unlike K+ or Tl+ ions. A well conserved constellation of water molecules is observed in the grooves of the dimeric structure. [source] Intermonomer interactions in dimer of bovine heart cytochrome c oxidaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2001Soo Jae Lee The X-ray structure of bovine heart cytochrome c oxidase solved for orthorhombic crystals showed a dimeric structure stabilized by four subunit,subunit contacts, namely, subunit Vb,subunit Vb on the matrix side, subunit I,subunit VIa, subunit VIa,subunit I in the transmembrane region and subunit VIb,subunit VIb on the intermembrane side. The same intermonomer contacts as in the orthorhombic crystals were observed in both hexagonal and tetragonal crystals, the X-ray structures of which were determined by the molecular-replacement method. These results suggest that the dimeric structure also exists under physiological conditions. These contacts, especially the subunit IVa,subunit I contact, in which the N-terminal portion of subunit IVa is placed on the surface of subunit I near the dioxygen-reduction site, indicate that the function of the bovine heart enzyme is likely to be controlled by perturbation of the monomer,monomer association. [source] The structure of NMB1585, a MarR-family regulator from Neisseria meningitidisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Charles E. Nichols The structure of the MarR-family transcription factor NMB1585 from Neisseria meningitidis has been solved using data extending to a resolution of 2.1,Å. Overall, the dimeric structure resembles those of other MarR proteins, with each subunit comprising a winged helix,turn,helix (wHtH) domain connected to an ,-helical dimerization domain. The spacing of the recognition helices of the wHtH domain indicates that NMB1585 is pre-configured for DNA binding, with a putative inducer pocket that is largely occluded by the side chains of two aromatic residues (Tyr29 and Trp53). NMB1585 was shown to bind to its own promoter region in a gel-shift assay, indicating that the protein acts as an auto-repressor. [source] A Designed Well-Folded Monomeric Four-Helix Bundle Protein Prepared by Fmoc Solid-Phase Peptide Synthesis and Native Chemical Ligation,CHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2006Gunnar T. Dolphin Dr. Abstract The design and total chemical synthesis of a monomeric native-like four-helix bundle protein is presented. The designed protein, GTD-Lig, consists of 90 amino acids and is based on the dimeric structure of the de novo designed helix-loop-helix GTD-43. GTD-Lig was prepared by the native chemical ligation strategy and the fragments (45 residues long) were synthesized by applying standard fluorenylmethoxycarbonyl (Fmoc) chemistry. The required peptide,thioester fragment was prepared by anchoring the free ,-carboxy group of Fmoc-Glu-allyl to the solid phase. After chain elongation the allyl moiety was orthogonally removed and the resulting carboxy group was functionalized with a glycine,thioester followed by standard trifluoroacetic acid (TFA) cleavage to produce the unprotected peptide,thioester. The structure of the synthetic protein was examined by far- and near-UV circular dichroism (CD), sedimentation equilibrium ultracentrifugation, and NMR and fluorescence spectroscopy. The spectroscopic methods show a highly helical and native-like monomeric protein consistent with the design. Heat-induced unfolding was studied by tryptophan absorbance and far-UV CD. The thermal unfolding of GTD-Lig occurs in two steps; a cooperative transition from the native state to an intermediate state and thereafter by noncooperative melting to the unfolded state. The intermediate exhibits the properties of a molten globule such as a retained native secondary structure and a compact hydrophobic core. The thermodynamics of GuHCl-induced unfolding were evaluated by far-UV CD monitoring and the unfolding exhibited a cooperative transition that is well-fitted by a two-state mechanism from the native to the unfolded state. GTD-Lig clearly shows the characteristics of a native protein with a well-defined structure and typical unfolding transitions. The design and synthesis presented herein is of general applicability for the construction of large monomeric proteins. [source] Synthesis, Crystal Structure and Characterization of Two Rare Earth Substituted Keggin-Type GermanotungstatesCHINESE JOURNAL OF CHEMISTRY, Issue 7 2008Jing-Ping WANG Abstract Two germanotungstates based on the dysprosium cations and monovacant Keggin anions [GeW11O39]8,, [(CH3)4N]1.5H3.5[Dy(H2O)2(GeW11O39)]·1.5H2O (1) and [Cu(Hen)(en)]2[Cu(H2O)3]0.5{[Cu(H2en)(Hen)]-[Cu(H2O)3]0.5[Dy(GeW11O39)2]}·1.25H2O (2), have been synthesized and characterized by elemental analysis, inductively coupled plasma (ICP) analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction. Crystal data for 1: monoclinic, space group C2/c with cell dimensions of a=2.8201(5) nm, b=2.2885(3) nm, c=2.4033(4) nm, ,=123.875(2)°, V=12.878(4) nm3, Z=8, µ=21.239 mm,1; and for 2: monoclinic, space group P21/n with cell dimensions of a=2.12808(5) nm, b=1.63834(4) nm, c=3.18074(4) nm, ,=93.760(2)°, V=11.0658(5) nm3, Z=4, µ=24.803 mm,1. The Dy3+/[GeW11O39]8, ratio of compound 1 is 1:1, and it displays an interesting one dimensional chainlike arrangement. And the Dy3+/[GeW11O39]8, ratio of compound 2 is 1:2 , and it shows a typical dimeric structure. [source] An Unusual Reaction of (,-Dimethylaminoethoxy)triethyltin with Phenyltin Trichloride.EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Aryl; X, Symmetrical Dimers [R2SnXY], The First X-ray Structural Evidence of the Existence of Complexes R2SnXY·R2SnXY (R = Alkyl, Y = Hal, Y) Both as Unsymmetrical Adducts [R2SnX2·R2SnY2] Abstract The substituent exchange reaction of PhSnCl3 with [Et3Sn(OCH2CH2NMe2)] gives rise unexpectedly to the unsymmetrical adduct [Ph2SnCl2·Ph2Sn(OCH2CH2NMe2)2] (2). It has been unambiguously proved for the first time that compounds of the RSnX3 type are able to undergo the hydrocarbon substituent redistribution reaction. The analogous tin complexes [Et2SnCl2·Et2Sn(OMe)2] (5) and [Bu2Sn(OAc)2·Bu2Sn(OMe)2] (6), which have ligands other than ,-dimethylaminoethoxy and could be considered as "organotin analogs of Grignard reagents" have symmetrical dimeric structures, i.e., can be formulated as [Bu2Sn(OMe)(OAc)]2 and [Et2Sn(OMe)Cl]2, respectively. Both types of structures, viz., unsymmetrical adduct (2) and symmetrical dimer (5, 6), have been characterized by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Palladium-Catalyzed Suzuki,Miyaura Cross-Coupling Using Phosphinous Acids and Dialkyl(chloro)phosphane LigandsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2006Christian Wolf Abstract The use of eleven palladium complexes having monomeric and ,-chloro-bridged dimeric structures and either bulky dialkyl- and diarylphosphinous acid ligands (POPd, POPd-Br, POPd1, POPd2, POPd6, POPd7, Ph1-Phoxide) or dialkyl(chloro)phosphane ligands (PXPd, PXPd2, PXPd6, PXPd7) for Suzuki,Miyaura coupling reactions has been evaluated. Screening and optimization of catalyst loading, solvent, temperature, and base showed that excellent results can be obtained with electron-deficient and electron-rich aryl iodides, bromides, and chlorides in the presence of 2.5 mol-% of palladium,phosphinous acid POPd, (tBu2POH)2PdCl2, in 1,4-dioxane using cesium carbonate as base. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] | ||||||||||||||||||||||