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C Bond (c + bond)
Terms modified by C Bond Selected AbstractsMolecular Library Obtained by Allene Insertion into the Pd,C Bond of Cyclopalladated Complexes: Biological and Pharmacological EvaluationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2004Claude Sirlin Abstract A minilibrary of cationic N-heterocycles has been prepared and evaluated. The potential for the preparation was a result of the high versatility of palladium-mediated chemistry. The synthesis of the novel molecules was based on intramolecular quaternization of tertiary amine attached allylpalladium complexes. The steric and electronic factors of the reaction are discussed. The structures of the synthesized molecules made them candidates for precise biological and pharmacological evaluations. Of the various N-heterocyclic compounds, 2,2-dimethyl-3-methylenenaphtho[def]quinolizinium showed antibacterial activity at micromolar concentrations. This compound also proved to be a nanomolar competitive antagonist for the channel site of the nicotinic acetylcholine receptor. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Alkyne and Ketone Induced Novel Cleavage of a C,C Bond and a C,Si Bond in Zirconacyclobutene,Silacyclobutene Fused Ring Compounds.CHEMINFORM, Issue 18 2003Tao Yu Abstract For Abstract see ChemInform Abstract in Full Text. [source] Borrowing Hydrogen: Indirect "Wittig" Olefination for the Formation of C,C Bonds from AlcoholsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Phillip J. Black Abstract The successful development of an indirect three-step domino sequence for the formation of C,C bonds from alcohol substrates is described. An iridium-catalysed dehydrogenation of alcohol 1 affords the intermediate aldehyde 2. The desired C,C bond can then be formed by a facile Wittig olefination, yielding the intermediate alkene 3. In the final step the alkene is hydrogenated to afford the indirect Wittig product, the alkane 4. The key to this process is the concept of borrowing hydrogen; hydrogen removed in the initial dehydrogenation step is simply borrowed by the iridium catalyst. Functioning as a hydrogen reservoir, the catalyst facilitates C,C bond formation before subsequently returning the borrowed hydrogen in the final step. Herein we present full details of our examination into both the substrate and reaction scope and the limitations of the catalytic cycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Facile Cleavage of Si,C Bonds during the Sol-Gel Hydrolysis of Aminomethyltrialkoxysilanes , A New Method for the Methylation of Primary AminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2004Augustin Adima Abstract The reaction of chloromethyltriethoxysilane with (1R,2R)-bis(methylamino)cyclohexane (1) afforded the corresponding bis-silylated compound 2. The sol-gel hydrolysis of 2 did not give the expected bridged silsesquioxane owing to quantitative Si,C-bond cleavage. Instead, silica and (1R,2R)-bis(dimethylamino)cyclohexane (3) were obtained. This reaction was exploited to propose a new route for the methylation of amines. Such methylation reaction of amines could be extended to other amines and provides a new method for the selective monomethylation of primary amines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Direct Addition of Zr,C Bonds of Alkylzirconocenes to Activated Alkenes.CHEMINFORM, Issue 11 2003Yuanhong Liu No abstract is available for this article. [source] Mechanism-Based Inactivation of Coenzyme B12 -Dependent 2-Methyleneglutarate Mutase by (Z)-Glutaconate and Buta-1,3-diene-2,3-dicarboxylateEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006Wolfgang Buckel Abstract In the presence of holo 2-methyleneglutarate mutase, buta-1,3-diene-2,3-dicarboxylate and (Z)-glutaconate [(Z)-pent-2-ene-1,5-dicarboxylate], but not (E)-glutaconate, each induced homolysis of the Co,C bond of coenzyme B12 to afford cob(II)alamin and the 5,-deoxyadenosyl radical. The latter probably added to the double bond in (Z)-glutaconate and one of the double bonds in buta-1,3-diene-2,3-dicarboxylate to afford a corresponding "radical adduct". The formation of new radicals and cob(II)alamin was diagnosed by UV/Visible and EPR spectroscopy. (Z)-Glutaconate rapidly inactivated the mutase with formation of aquocobalamin, which was possibly derived by electron transfer from cob(II)alamin to the radical adduct. In contrast, buta-1,3-diene-2,3-dicarboxylate was a much slower inactivator. In this case, the spectroscopic data revealed a relatively stable complex of the radical adduct with cob(II)alamin in the active site of the enzyme. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Syntheses, Crystal Structures, and Characterizations of a Series of New Layered Lanthanide Carboxylate-PhosphonatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2006Si-Fu Tang Abstract Hydrothermal reactions of different lanthanide(III) salts with (H2O3PCH2)2NCH2COOH (H5L1) led to two new layeredlanthanide(III) carboxylate-diphosphonates, namely La(H2L1)(H2O)2·H2O (1) and La(H2L1)(H2O) (2). The structure of compound 1 features a layered architecture in which the nine-coordinate La3+ ions are bridged by phosphonate groups of the ligands. The carboxylate group of the phosphonate ligand remains protonated and is involved in the interlayer hydrogen bonding. Compound 2 features a double layer structure in which the La3+ ion is eight-coordinated and the carboxylate group of the ligand is chelated to a La3+ ion in a bidentate fashion. Hydrothermal reactions of lanthanide(III) salts with 4-HOOC,C6H4,CH2N(CH2PO3H2)2 (H5L2) afforded three new compounds, namely, La(H4L2)(H3L2)(H2O)·2H2O (3), Er(H3L2)(H4L2) (4), and Er(HL3)(H2L3)(H2O) (5) [H2L3 = H2O3PCH2N(CHO)(CH2,C6H4,COOH)]. H2L3 was formed by the in situ oxidation of one P,C bond of the H5L2 ligand. Compound 3 features a (002) lanthanum(III) phosphonate layer in which the seven-coordinate La3+ ions are bridged by diphosphonate moieties of the ligands. The carboxylate group remains protonated and is involved in the interlayer hydrogen bonding. The structure of compound 4 contains a 1D chain along the a axis in which each pair of ErO6 octahedra is bridged by a pair of phosphonate groups. These 1D chains are further interconnected by hydrogen bonds between noncoordinated phosphonate oxygen atoms into a (002) layer with the phenyl carboxylate groups hanging on the interlayer space. The structure of compound 5 is also layered. The interconnection of Er3+ ions by bidentate and tetradentate bridging phosphonate groups resulted in a (002) inorganic layer with the organic groups orientated to the interlayer space. Luminescence properties of compounds 4 and 5 have also been studied.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Regiospecific Cyclometalation of Diphenyl(2-substituted phenyl)phosphane with Methyltetrakis(trimethylphosphane)cobalt(I)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2003Hans-Friedrich Klein Abstract The pre-chelate molecules 2-(diphenylphosphanyl)- N,N -dimethylaniline, [2-(diphenylphosphanyl)benzyl]dimethylamine, 1-(diphenylphosphanyl)-2-ethylbenzene, 1-(diphenylphosphanyl)-2-isopropylbenzene, and 2-(diphenylphosphanyl)benzonitrile, in a reaction with [CoMe(PMe3)4], eliminate methane to afford the selectively 6- ortho -metalated complexes 1,5 that contain four-membered metallacycles. The molecular structure of 3 shows a tbp-coordinated cobalt atom, with axial C and PMe3 donor groups. Metalation in the aliphatic side-chain occurs with 2-(diphenylphosphanyl)toluene, giving complex 6 that contains a five-membered metallacycle. Benzyldiphenylphosphane is selectively ortho -metalated in the benzyl group, affording 7. As shown by the molecular structures, complex 7 is a true ligand isomer of 6. Substitution of a trimethylphosphane group in compounds 4 and 6 by ethene gives the pentacoordinate complexes 8 and 9, respectively. The ethene ligand is ,-coordinated in the equatorial plane of a trigonal bipyramid. Under 1 bar of CO, complex 6 forms monocarbonyl complex 10. Carbonylation of complexes 3 and 4 proceeds by insertion of CO into the Co,C bond under ring expansion, affording the aroylcobalt complexes 11 and 12, respectively. Complex 6 reacts with iodomethane in an oxidative substitution reaction yielding a structurally characterized octahedral complex mer - 13, which eliminates a methyl group in THF at 20 °C to form a pentacoordinate cobalt(II) complex 14. Complex 3 oxidatively adds iodomethane in a stereoselective cis addition to give the cobalt(III) complex mer - 15, which retains its four-membered metallacycle and the CoCH3 group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Permanganate Oxidation Revisited: Synthesis of 3-Deoxy-2-uloses via Indium-Mediated Chain Elongation of CarbohydratesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Christoph Schmölzer Abstract Application of the Barbier-type indium-mediated allylation method to suitable substrates offers access to carbohydrates bearing a terminal olefin moiety. The C,C bond forming reaction generates a defined stereochemistry of the new chiral center and tolerates a wide variety of starting aldehydes thus allowing modifications in the carbohydrate backbone. Further transformations of the alkene moiety via an environmentally benign and subtle controlled protocol using potassium permanganate gives rise to the structural motif of 3-deoxy-2-uloses in good yields. The final part of the reaction sequence focuses on the deprotection of the acetyl groups essential for the success of the oxidation step. The acidic and labile 3-deoxy position of the target molecule is prone to elimination applying standard deacetylation conditions and therefore demands derivatisation of the molecule. The introduction of a thioketal moiety using microwave conditions shows promising results and subsequent standard transformations are applicable leading to the desired products. [source] Ex-Chiral-Pool Synthesis of ,-Hydroxyphosphonate Nucleoside AnaloguesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2007Franck Gallier Abstract A new series of mononucleotide analogues bearing a nonhydrolysable P,C bond instead of the P,O phosphate linkage is presented. We intend to set up an approach that allows the synthesis of ,-hydroxyphosphonate nucleoside analogues as a single diastereoisomer. In this respect, the key "sugar-phosphonate" intermediate was obtained through an Arbusov reaction from an iodosugar derivative in which the stereochemistry of the ,-hydroxy group is determined by the choice of the starting material and remains in the resulting nucleotide analogues. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Borrowing Hydrogen: Indirect "Wittig" Olefination for the Formation of C,C Bonds from AlcoholsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Phillip J. Black Abstract The successful development of an indirect three-step domino sequence for the formation of C,C bonds from alcohol substrates is described. An iridium-catalysed dehydrogenation of alcohol 1 affords the intermediate aldehyde 2. The desired C,C bond can then be formed by a facile Wittig olefination, yielding the intermediate alkene 3. In the final step the alkene is hydrogenated to afford the indirect Wittig product, the alkane 4. The key to this process is the concept of borrowing hydrogen; hydrogen removed in the initial dehydrogenation step is simply borrowed by the iridium catalyst. Functioning as a hydrogen reservoir, the catalyst facilitates C,C bond formation before subsequently returning the borrowed hydrogen in the final step. Herein we present full details of our examination into both the substrate and reaction scope and the limitations of the catalytic cycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] A family of thioxanthato ruthenium and osmium arylsISRAEL JOURNAL OF CHEMISTRY, Issue 3 2001Swarup Chattopadhyay The title complexes of type M(RL2)(PPh3)2(CO)(S2CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL1)(PPh3)2(CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL2 ligand in 2 is the imine-phenol tautomer of N-C6H4R(p)-4-methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic-C2 atom only while RL1 in 1 is the iminium-phenolato tautomer chelated via carbanionic-C2 and phenolato-O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ,180° around the M,C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ,40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL2)(PPh3)2(CO)(O2CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru,P bonds in 2a (R = Me) differ in length by as much as 0.06 Å. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate. [source] High-performance liquid chromatographic/tandem mass spectrometric identification of the phototransformation products of tebuconazole on titanium dioxideJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2002Paola Calza Abstract Tebuconazole is a widely used fungicide. The formation of by-products on irradiated titanium dioxide as a photocatalyst was evaluated. Several species derived from tebuconazole degradation were identified and characterized by HPLC/MSn. A pattern of reactions accounting for the observed intermediates is proposed. Different parallel pathways are operating (and through these pathways the transformation of the molecule proceeds), leading to a wide range of intermediate compounds. All these molecules are more hydrophylic than tebuconazole. The main steps involved are (1) the hydroxylation of the molecule with the formation of three species having [M + H]+ 324; the hydroxylation occurs on the C-1 carbon and on the aromatic ring in the two ortho -positions; (2) the cleavage of a C,C bond with the release of the tert -butyl moiety and the formation of a species having m/z 250; analogously to step 1, also on this species a further hydroxylation reaction occurs; (3) through the loss of the triazole moiety with the formation of a structure with m/z 257. Copyright © 2002 John Wiley & Sons, Ltd. [source] Direct observation of deuterium migration in crystalline-state reaction by single-crystal neutron diffraction.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2001The H atoms bonded to the chiral C atoms (stereogenic center) of the 1-cyanoethyl groups in two cobalt complexes, [(R)-1-cyanoethyl]bis(dimethylglyoximato)(pyridine)cobalt(III) (2) and [(R,S)-1-cyanoethyl]bis(dimethylglyoximato)(piperidine)cobalt(III) (3), were replaced with D atoms, such as Co,C*D(CH3)CN. The crystals of the two cobalt complexes were irradiated with a xenon lamp for 72,h and 27,d, respectively. The unit-cell dimensions were gradually changed with retention of the single-crystal form. The crystal structures after irradiation were determined by neutron diffraction. In each crystal the chiral 1-cyanoethyl group of one of the two crystallographically independent molecules was partly inverted to the opposite configuration, whereas that of the other molecule kept the original configuration. The C*,D bond in the inverted group was completely conserved in the process of the inversion of the chiral alkyl group. This suggests that the inversion of the chiral 1-cyanoethyl group proceeds with the rotation of the cyanoethyl radical after the Co,C bond cleavage by photo-irradiation so that the opposite side of the radical faces the Co atom. This is followed by recombination of the Co,C bond to form the inverted 1-cyanoethyl group. [source] Insight into the structures of [M(C5H4I)(CO)3] and [M2(C12H8)(CO)6] (M = Mn and Re) containing strong I...O and ,(CO),,(CO) interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Alexander S. Romanov The compounds tricarbonyl(,5 -1-iodocyclopentadienyl)manganese(I), [Mn(C5H4I)(CO)3], (I), and tricarbonyl(,5 -1-iodocyclopentadienyl)rhenium(I), [Re(C5H4I)(CO)3], (III), are isostructural and isomorphous. The compounds [,-1,2(,5)-acetylenedicyclopentadienyl]bis[tricarbonylmanganese(I)] or bis(cymantrenyl)acetylene, [Mn2(C12H8)(CO)6], (II), and [,-1,2(,5)-acetylenedicyclopentadienyl]bis[tricarbonylrhenium(I)], [Re2(C12H8)(CO)6], (IV), are isostructural and isomorphous, and their molecules display inversion symmetry about the mid-point of the ligand C[triple-bond]C bond, with the (CO)3M(C5H4) (M = Mn and Re) moieties adopting a transoid conformation. The molecules in all four compounds form zigzag chains due to the formation of strong attractive I...O [in (I) and (III)] or ,(CO),,(CO) [in (I) and (IV)] interactions along the crystallographic b axis. The zigzag chains are bound to each other by weak intermolecular C,H...O hydrogen bonds for (I) and (III), while for (II) and (IV) the chains are bound to each other by a combination of weak C,H...O hydrogen bonds and ,(Csp2),,(Csp2) stacking interactions between pairs of molecules. The ,(CO),,(CO) contacts in (II) and (IV) between carbonyl groups of neighboring molecules, forming pairwise interactions in a sheared antiparallel dimer motif, are encountered in only 35% of all carbonyl interactions for transition metal,carbonyl compounds. [source] 6,-Hydroxy-5,-methyl-20-oxo-19-norpregn-9(10)-en-3,-yl acetateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009R. M. A. Pinto In the title compound, C23H34O4, which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion-inducing activity, the conformation of ring B is close to half-chair due to the presence of both the C=C double bond and the axial 5,-methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C,C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum-mechanical ab initio Roothan Hartree,Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule. [source] Bromido(,5 -carboxycyclopentadienyl)dinitrosylchromium(0) and (,5 -benzoylcyclopentadienyl)bromidodinitrosylchromium(0)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Yu-Pin Wang In the structures of each of the title compounds, [CrBr(C6H5O2)(NO)2], (I), and [CrBr(C12H9O)(NO)2], (II), one of the nitrosyl groups is located at a site away from the exocyclic carbonyl C atom of the cyclopentadienyl (Cp) ring, with twist angles of 174.5,(3) and 172.5,(1)°. The observed orientation is surprising, since the NO group is expected to be situated trans to an electron-rich C atom in the ring. The organic carbonyl plane is turned away from the Cp ring plane by 5.6,(8) and 15.2,(3)°in (I) and (II), respectively. The exocyclic C,C bond in (I) is bent out of the Cp ring plane towards the Cr atom by 2.8,(3)°, but is coplanar with the Cp ring in (II); the angle is 0.1,(1)°. [source] 4,6-Dinitro- N,N,-di- n -octylbenzene-1,3-diamine, 4,6-dinitro- N,N,-di- n -undecylbenzene-1,3-diamine and N,N,-bis(2,4-dinitrophenyl)octane-1,8-diamineACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Gary Teng 4,6-Dinitro- N,N,-di- n -octylbenzene-1,3-diamine, C22H38N4O4, (I), 4,6-dinitro- N,N,-di- n -undecylbenzene-1,3-diamine, C28H50N4O4, (II), and N,N,-bis(2,4-dinitrophenyl)octane-1,8-diamine, C20H24N6O8, (III), are the first synthetic meta -dinitroarenes functionalized with long-chain aliphatic amine groups to be structurally characterized. The intra- and intermolecular interactions in these model compounds provide information that can be used to help understand the physical properties of corresponding polymers with similar functionalities. Compounds (I) and (II) possess near-mirror symmetry, with the octyl and undecyl chains adopting fully extended anti conformations in the same direction with respect to the ring. Compound (III) rests on a center of inversion that occupies the mid-point of the central C,C bond of the octyl chain. The middle six C atoms of the chain form an anti arrangement, while the remaining two C atoms take hard turns almost perpendicular to the rest of the chain. All three molecules display intramolecular N,H...O hydrogen bonds between the amine and nitro groups, with the same NH group forming a bifurcated intermolecular hydrogen bond to the nitro O atom of an adjacent molecule. In each case, these interactions link the molecules into one-dimensional molecular chains. In (I) and (II), these chains pack so that the pendant alkyl groups are interleaved parallel to one another, maximizing nonbonded C,H contacts. In (III), the alkyl groups are more isolated within the molecular chains and the primary nonbonded contacts between the chains appear to involve the nitro groups not involved in the hydrogen bonding. [source] Poly[diaqua(,-4,4,-bipyridine-,2N:N,)bis(,-cyanido-,2C:N)bis(cyanido-,C)nickel(II)copper(II)]: a metal,organic cyanide-bridged frameworkACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008Olha Sereda The structure of the title compound, [NiCu(CN)4(C10H8N2)(H2O)2]n or [{Cu(H2O)2}(,-C10H8N2)(,-CN)2{Ni(CN)2}]n, was shown to be a metal,organic cyanide-bridged framework, composed essentially of ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains (4,4,-bpy is 4,4,-bipyridine) linked by [Ni(CN)4]2, anions. Both metal atoms sit on special positions; the CuII atom occupies an inversion center, while the NiII atom of the cyanometallate sits on a twofold axis. The 4,4,-bpy ligand is also situated about a center of symmetry, located at the center of the bridging C,C bond. The scientific impact of this structure lies in the unique manner in which the framework is built up. The arrangement of the ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains, which are mutually perpendicular and non-intersecting, creates large channels running parallel to the c axis. Within these channels, the [Ni(CN)4]2, anions coordinate to successive CuII atoms, forming zigzag ,Cu,N[triple-bond]C,Ni,C[triple-bond]N,Cu, chains. In this manner, a three-dimensional framework structure is constructed. To the authors' knowledge, this arrangement has not been observed in any of the many copper(II),4,4,-bipyridine framework complexes synthesized to date. The coordination environment of the CuII atom is completed by two water molecules. The framework is further strengthened by O,H...N hydrogen bonds involving the water molecules and the symmetry-equivalent nonbridging cyanide N atoms. [source] (1-Pyridinio)perfluorophenacylide: a new stable pyridinium ylide in the enol formACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2008Shinji Yamada The title compound, C13H6F5NO, exists in the enol form and adopts the E configuration about the enol double bond. It is the first example of an enol-type pyridinium ylide. The enol structure was unambiguously determined on the basis of the significantly longer C,O bond and shorter C,C bond. Intramolecular C,H...O and C,H...F hydrogen bonds are responsible for promotion of the enol form and for the stability of this compound. [source] 1,2,4,5-Tetrakis(2-vinylpyridyl)benzene,dichloromethane (1/2)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2003Brian T. Holmes The title compound, C34H26N4·2CH2Cl2, lies about an inversion center. The solvent molecules interact with the benzene molecule both through C,H,N hydrogen bonding to span pyridine N atoms of adjacent vinyl groups, possibly stabilizing the rotational conformation observed, and through a , interaction between a dichloromethane Cl atom and a pyridyl ring C,C bond of a c -glide-related molecule. The benzene molecules form stacks along the a axis such that two of the four olefin groups are properly oriented for photoreactivity (2+2 cyclodimerization). [source] Calcium(II) meso -2,3-diphenylsuccinate heptahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000Gregory Morin The title compound, [Ca(C16H12O4)(H2O)6]·H2O, adopts a conformation about the central C,C bond that places the two carboxylate groups in an anti orientation. The crystal consists of layers of two-dimensional arrays of 2,3-diphenylsuccinate dianions which are linked by bridging Ca2+ cations. The unit cell contains two Ca2+ cations in an unusual four-membered Ca,O,Ca,O ring in which the bridging O atoms belong to water molecules rather than carboxylates, i.e. poly[[[di-,-aqua-bis[pentaaquacalcium(II)]]-,-(meso -2,3-diphenylsuccinato- O:O,)] succinate dihydrate]. [source] Synthesis and Characterization of Linear Tetranuclear Silver(I) Complexes Bridged by Tetraphosphane LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2009Yukie Takemura Abstract Reactions of AgOTf with meso -bis[(diphenylphosphanylmethyl)phenylphosphanyl]methane (dpmppm) afforded[Ag4(OTf)2(,-OTf)(,-dpmppm)2{(CH3)2CO}](OTf) (1) and [Ag4(OTf)2(,-OTf)(,-dpmppm)2(RNC)2](OTf) {R = Xyl (2a), Mes (2b), tBu (2c)}. When AgOTf was treated with dpmppm in air in the presence of tBuNC, cleavage of the C,Cl and P,C bonds occurred to give [Ag4(,-Cl)(,-dpmppm)2(tBuNC)4](OTf)3 (3) and [Ag4(,-Ph2PO2)(,-dpmppm)2(tBuNC)3](OTf)3 (4). Reaction of AgOCOCF3 with dpmppm resulted in [Ag4(OCOCF3)2(,-OCOCF3)(,-dpmppm)2](CF3COO) (5). By treatment of AgPF6 with dpmppm, [Ag4(,-dpmppm)2(tBuNC)4](PF6)4 (6) and [Ag4(PO2F2)2(,-dpmppm)2(tBuNC)2] (PF6)2 (7) were obtained. Wheareas complexes 1,3 possess a {Ag4(,-dpmppm)2}4+ core in which the Ag4 strings are rather bent with two dpmppm ligands arranged in a syn fashion, complexes 4,7 have linear Ag4 strings supported by two dpmppm ligands arranged in an anti fashion. These results suggest that the dpmppm-supported tetrasilver(I) strings are quite flexible and labile and thus are potentially important in promoting organic reactions as a result of the multimetallic centers.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Borrowing Hydrogen: Indirect "Wittig" Olefination for the Formation of C,C Bonds from AlcoholsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Phillip J. Black Abstract The successful development of an indirect three-step domino sequence for the formation of C,C bonds from alcohol substrates is described. An iridium-catalysed dehydrogenation of alcohol 1 affords the intermediate aldehyde 2. The desired C,C bond can then be formed by a facile Wittig olefination, yielding the intermediate alkene 3. In the final step the alkene is hydrogenated to afford the indirect Wittig product, the alkane 4. The key to this process is the concept of borrowing hydrogen; hydrogen removed in the initial dehydrogenation step is simply borrowed by the iridium catalyst. Functioning as a hydrogen reservoir, the catalyst facilitates C,C bond formation before subsequently returning the borrowed hydrogen in the final step. Herein we present full details of our examination into both the substrate and reaction scope and the limitations of the catalytic cycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] UV-Light-Driven Immobilization of Surface-Functionalized Oxide Nanocrystals onto Silicon,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007E. Fanizza Abstract TiO2 nanorods (NRs) and ,-Fe2O3 nanocrystals (NCs) passivated with unsaturated long-chain carboxylic acids, namely 10-undecylenic acid (10UDA) and oleic acid (OLEA), are covalently anchored to Si(100) at room temperature by UV-light-driven reaction of hydrogenated silicon with the carbon,carbon double bond (,CC,) moieties of the capping surfactants. The high reactivity of vinyl groups towards Si provides a general tool for attaching particles of both materials via Si,C bonds. Interestingly, TiO2 NRs were efficiently attached to silicon even when capped by OLEA. This latter finding has been explained by a photocatalytic mechanism involving the primary role of hydroxyl radicals that can be generated upon bandgap TiO2 photoexcitation with UV light. The increased oxide coverage achievable on Si opens access to further surface manipulation, as demonstrated by the possibility of depositing an additional film of Au nanoparticles onto TiO2 via TiO2 -catalyzed visible-light-driven reduction of aqueous AuCl4, ions. Extensive morphological and chemical characterization of the obtained NC-functionalized Si substrates is provided to support the effectiveness of proposed photochemical approaches. [source] Concerning the Structure of [18]AnnuleneHELVETICA CHIMICA ACTA, Issue 8 2005Otto Ermer A recent computational study of Schleyer and co-workers [1] is reviewed, which led these authors to the firm conclusion that [18]annulene has a localized structure with alternating single and double C,C bonds, contrary to earlier crystallographic analyses of X-ray-diffraction data favoring a delocalized non-alternating form. It is pointed out i) that deceptive orientational disorder phenomena in the crystal might be subject to experimental resolution in this case, and ii) that, in contrast to gas and solution phases, [18]annulene might possibly assume the non-alternating structure in the crystalline solid state. [source] Bond cutting in K-doped tris(8-hydroxyquinoline) aluminiumJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008Hsin-Han Lee A series of Al 2p, K 2p, O 1s and N 1s core-level spectra have been used to characterize the interaction between potassium (K) and tris(8-hydroxyquinoline) aluminium (Alq3) molecules in the K-doped Alq3 layer. All core-level spectra were tuned to be very surface sensitive in selecting various photon energies provided by the wide-range beamline at the National Synchrotron Radiation Research Center, Taiwan. A critical K concentration (x = 2.4) exists in the K-doped Alq3 layer, below which the K-doped atoms generate a strained environment near the O and N atoms within 8-quinolinoline ligands. This creates new O 1s and N 1s components on the lower binding-energy side. Above the critical K coverage, the K-doped atoms attach the O atoms in the Al,O,C bonds next to the phenoxide ring and replace Al,O,C bonds by forming K,O,C bonds. An Alq3 molecule is disassembled into Alq2 and Kq by bond cutting and bond formation. The Alq2 molecule can be further dissociated into Alq, or even Al, through subsequent formations of Kq. [source] Sol-Gel-Derived Silicon-Boron Oxycarbide Glasses Containing Mixed Silicon Oxycarbide (SiCxO4,x) and Boron Oxycarbide (BCyO3,y) UnitsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Christel Gervais The introduction of B atoms in SiOC glass networks has been achieved through the pyrolysis of sol-gel-derived polyborosiloxanes under an inert atmosphere. The starting gels were obtained from hydrolysis-condensation reactions of triethylborate (B(OEt)3) and an organically modified trialkoxysilane (EtSi(OEt)3). The resulting hybrid EtSiO1.5 -B2O3 gels showed a homogeneous dispersion of the B atoms in the siloxane network via ,Si,O,B, bonds. The presence of such borosiloxane bridges prevents the formation of cyclic or cage siloxane entities and leads to relatively high ceramic yields (,80%). The transformation of the polyborosiloxanes into amorphous SiBOC glasses was followed using Fourier transform infrared spectroscopy and multinuclear magic-angle spinning-nuclear magnetic resonance (MAS-NMR) (11B, 13C, and 29Si). An important change in the carbon, silicon, and boron environments occurs during pyrolysis. Interestingly, the 11B MAS-NMR spectra suggest a progressive replacement of the B,O bonds by B,C bonds, which leads to a distribution of trigonal BCxO3,x sites in the glass that was pyrolyzed at 1000°C, with a residual amount of B(OSi)3 sites. The resulting glasses can thus be described as silicon-boron oxycarbide networks that are based on SiCxO4,x and BCyO3,y mixed environments. [source] On the origin of topological differences between experimental and theoretical crystal charge densitiesACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2000Anatoliy Volkov Topological analysis of experimental and theoretical (molecular and crystal) electron densities of p -nitroaniline and p -amino- p,-nitrobiphenyl reveals considerable discrepancies between experiment and theory for the bond critical points properties. Particularly large differences occur for the positive curvature along the bond path (,3). The differences become somewhat smaller when more extended basis sets and correlation effects are introduced in the theoretical calculations. The effect of the crystal matrix on the properties of bond critical points is evaluated for the p -nitroaniline molecule using the 6-21G** and 6-31G** basis sets. The differences between the isolated molecule and the molecule in the crystal are too small to explain the quantitative disagreement between the theoretical and experimental topologies reported in the literature and found in the current study. For most bonds, the observed changes in the properties of the electron density agree well for both basis sets but some discrepancies are found for changes in ,3 for N,H and aromatic C,C bonds. When the theoretical densities are projected into the multipole density functions through refinement of the theoretical structure factors, the topological properties change and differences between theory and experiment are reduced. The main origin of the observed discrepancies is attributed to the nature of the radial functions in the experimental multipole model. [source] Bond catastrophes in rhodium complexes: experimental charge-density studies of [Rh(C7H8)(PtBu3)Cl] and [Rh(C7H8)(PCy3)Cl]ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Hazel A. Sparkes Rhodium complexes have potential uses in both catalysis and promoting the cleavage of C,C bonds. In order to further our understanding of these species and their potential applications, it is vital to obtain insight into the bonding within the species, particularly the Rh,C interactions, and to this end experimental charge-density studies have been undertaken on the title complexes. High-resolution single-crystal datasets to sin,,/, = 1.06,Å,1 were obtained at 100,K and analysed using Bader's `Atoms in Molecules' (AIM) approach. The results of the studies have provided unique insights into the bonding involving rhodium and highlight the importance of undertaking such investigations for transition metal compounds. [source] | ||||||||||||||||||||||||||||