Showing papers on "Double bond published in 1992"

Comprehensive handbook on hydrosilylation

Abstract: Chapter headings and selected sections. Introduction. Catalytic Aspects of Hydrosilylation. Free-radical addition. Methods of silyl radical generation. Hydrosilylation of the C=C bond: mechanism, stereochemistry and examples. Addition of silicon hydrides to other multiple bonds. Nucleophilic-electrophilic catalysis. Homogeneous catalysis by transition metal complexes. Catalysis by supported transition metal complexes. The Reactivity in Hydrosilylation of Particular Types of Organic Compounds With Multiple Bonds. Hydrocarbons with an isolated C=C bond. Dienes with isolated double bonds. Alkene and cycloalkene derivatives with functional groups. Alkyne derivatives with functional groups. Saturated carbonyl compounds. Unsaturated carbonyl compounds. The Effect of Substituents at Silicon on the Reactivity of the Si-H Bond in Hydrosilylation. Effect of the structure of silicon hydrides on the rate and yield in hydrosilylation processes. Influence of the structure of the silicon hydride on regio- and stereoselectivity in hydrosilylation. Practical choice of silicon hydride in the hydrosilylation reaction. The Hydrosilylation of Unsaturated Organosilicon Compounds. Addition of substituted hydrosilanes to carbon-carbon double bonds in unsaturated silanes. Curing organosilicon polymers by hydrosilylation. Intra- and intermolecular hydrosilylation. The Application of Hydrosilylation Processes. Silanes as coupling agents. Reduction of organic compounds by hydrosilylation. Modification of polymers via hydrosilylation. A Compilation of Information on Hydrosilylation Studies Over the Period from 1965 to 1990. List of tables. Abbreviations. Tables/Figures.Bibliography. Reviews. Papers. Patents. Index.

Preparation and characterization of C 60 Br 6 and C 60 Br 8

Abstract: BUCKMINSTERFULLERENE (C60) is much more reactive than was originally anticipated, because resonance structures that place double bonds in the pentagonal rings are energetically unfavourable1 and lead to restricted electron delocalization. C60 therefore behaves as an electron-deficient 'super-alkene' rather than as a 'super-aromatic', as demonstrated by the addition of osmium tetroxide2, platinum3, dipolar molecules4, alkyl radicals5and amines6. Reaction of anions derived from C60 with iodomethane results in up to 24 methyl groups becoming attached to the cage, although compounds containing either eight or six methyl groups are dominant in the mass spectrum7. Here we report the synthesis of crystalline C60Br6 (which forms magenta plates) and C60Br8 (dark brown prisms) by mixing solutions of C60 with bromine. The structures of these compounds, which contain occluded bromine when precipitated from the brominating medium, have been determined by single-crystal X-ray diffraction. Reaction of C60 with bromine in the absence of solvent gives C60Br24 (which also contains occluded bromine). We propose a configuration for C60Br24 (and sterically hindered C60X24 compounds) based on that for C60Br8. On being warmed in solution, C60Br6 rearranges and disproportionates to C60Br8, and all three bromo derivatives revert to C60 on strong heating. These results provide an insight into the pattern of addition of bulky reagents to C60.

Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C60 Derivative, C60Br24

Abstract: C(60) and liquid bromine react to form C(60)Br(24), a crystalline compound isolated as a bromine solvate, C(60)Br(24)(Br(2))(x), The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C(60) framework is recognizable in C(60)Br(24), but sp(3) carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 degrees to 200 degrees C there is effectively quantitative reversion of C(60)Br(24) to C(60) and Br(2).

Photophysics of donor-acceptor substituted stilbenes. A time-resolved fluorescence study using selectively bridged dimethylamino cyano model compounds

Abstract: Several selectively bridged 4-(dimethylamino)-4'-cyanostilbenes are investigated. All of them show strongly red-shifted fluorescence spectra connected with a considerable dynamical Stokes shift in polar solvents. Bridging, however, photophysics (fluorescence quantum yields and lifetimes) dramatically. Blocking of the double bond twist by a sufficiently rigid bridge (-CH 2 -) leads to quantum yields near 1, although the anilino group is free to rotate

Tris(trimethylsilyl)silane: an efficient hydrosilylating agent of alkenes and alkynes

Abstract: tris(trimethylsilyl)silane adds across the double bond of a variety of mono-, di-, and trisubstituted under free-radical conditions in good yields. The reaction, which proceeds via a free-radical chain mechanim, is highly regioselective (anti-Markovnikov). Addition to prochiral olefins bearing an ester group is highly stereoselective. The factors that control the stereochemistry have been discussed in term of preferred conformations of the intermediate carbon-centered radicals and are thought to be of steric origin

Polymerization of silicon-containing diphenylacetylenes and high gas permeability of the product polymers

Abstract: 1-Phenyl-2-[p-(trimethylsilyl)phenyl]acetylene and 1-phenyl-2-[m-(trimethylsilyl)phenyl]acetylene polymerized with TaCl 5 cocatalyst systems to provide new polymers with over 70% yields having a weight-average molecular weight over 1×10 6 . As cocatalysts, n-BuSn 4 , Et 3 SiH and 9BBN were especially effective. The polymers were yellow solids with the alsternating double bond structure [CPh=C(PhSiMe 3 )] n . They completely dissolved in toluene, CHCl 3 , etc., and formed tough films by solution casting The onset temperatures of weight loss in TGA in air were as high as ca.400°C. Their oxygen permeability coefficients were both high, ca. 1000 barrers

Oxo-hydrido and imido-hydrido derivatives of permethyltantalocene. Structures of (.eta.5-C5Me5)2Ta(:O)H and (.eta.5-C5Me5)2Ta(:NC6H5)H: doubly or triply bonded tantalum oxo and imido ligands?

Abstract: The syntheses of the complexes Cp*{sub 2}Ta({double bond}O)H, Cp*{sub 2}Ta({double bond}NH)H and Cp*{sub 2}Ta({double bond}NC{sub 6}H{sub 5})H and the solid-state structures for Cp*{sub 2}Ta({double bond}O)H and Cp*{sub 2}Ta({double bond}NC{sub 6}H{sub 5})H are reported (Cp* = ({eta}{sup 5}-C{sub 5}Me{sub 5})). These are formally 18-electron complexes with the oxo or imido ligands donating only one {pi}-electron pair to tantalum. Since these ligands commonly donate both {pi}-electron pairs (i.e. they triply bond) to transition-metal centers, at issue are the Ta-O and Ta-N bond orders. Cp*{sub 2}Ta({double bond}NC{sub 6}H{sub 5})H crystallizes in the monoclinic space group. The solid-state structure reveals a linear Ta-N-C unit for Cp*{sub 2}Ta({double bond}NC{sub 6}H{sub 5})H. This feature is accommodated on both steric and electronic grounds. Cp*{sub 2}Ta({double bond}O)H crystallizes in the monoclinic space group. The Ta-N and Ta-O bond distances are intermediate between the values expected for double and triple bonds, and the {nu}(Ta-O) for Cp*{sub 2}Ta({double bond}O)H is considerably less than that for other metal oxo compounds. Thus, the tantalum-nitrogen and tantalum-oxygen bond orders for these two compounds are anomalously low.

Total synthesis of (-)-nummularine F

Abstract: The first total synthesis of the 14-membered para ansa cyclopeptide alkaloid (-)-nummularine F is reported. The pivotal transformations of the synthetic strategy are (1) a stereocontrolled approach for introducing the absolute stereochemistry at the α- and β-carbons of the parent β-hydroxyproline utilizing D-serine as a source of chirality; (2) cyclization to a rigid 14-membered ring; and (3) introduction of the enamide double bond. The synthesis began with the conversion of D-serine to (2S,3S)-3-(4-cyanophenoxy)-1-[(1,1-dimethylethoxy)carbonyl]proline.After conversion of the cyano function to a formyl group, a Henry reaction between the 4-formylphenoxy group and the anion of nitromethane gave a mixture of epimeric benzyl alcohols containing a terminal nitro group.The nitro group was reduced to an amine and coupled to Z-protected L-isoleucine to afford the desired acyclic precursor.Cyclisation was achieved by the coupling of the proline pentafluorophenyl ester and the amino group of the L-isoleucine.The enamide bond was introduced after cyclisation,via thermal selenoxide elimination

NADPH-dependent beta-oxidation of unsaturated fatty acids with double bonds extending from odd-numbered carbon atoms

Abstract: The mitochondrial metabolism of 5-enoyl-CoAs, which are formed during the beta-oxidation of unsaturated fatty acids with double bonds extending from odd-numbered carbon atoms, was studied with mitochondrial extracts and purified enzymes of beta-oxidation. Metabolites were identified spectrophotometrically and by high performance liquid chromatography. 5-cis-Octenoyl-CoA, a putative metabolite of linolenic acid, was efficiently dehydrogenated by medium-chain acyl-CoA dehydrogenase (EC 1.3.99.3) to 2-trans-5-cis-octadienoyl-CoA, which was isomerized to 3,5-octadienoyl-CoA either by mitochondrial delta 3,delta 2-enoyl-CoA isomerase (EC 5.3.3.8) or by peroxisomal trifunctional enzyme. Further isomerization of 3,5-octadienoyl-CoA to 2-trans-4-trans-octadienoyl-CoA in the presence of soluble extracts of either rat liver or rat heart mitochondria was observed and attributed to a delta 3,5,delta 2,4-dienoyl-CoA isomerase. Qualitatively similar results were obtained with 2-trans-5-trans-octadienoyl-CoA formed by dehydrogenation of 5-trans-octenoyl-CoA. 2-trans-4-trans-Octadienoyl-CoA was a substrate for NADPH-dependent 2,4-dienoyl-CoA reductase (EC 1.3.1.34). A soluble extract of rat liver mitochondria catalyzed the isomerization of 2-trans-5-cis-octadienoyl-CoA to 2-trans-4-trans-octadienoyl-CoA, which upon addition of NADPH, NAD+, and CoA was chain-shortened to hexanoyl-CoA, butyryl-CoA, and acetyl-CoA. Thus we conclude that odd-numbered double bonds, like even-numbered double bonds, can be reductively removed during the beta-oxidation of polyunsaturated fatty acids.

Synthesis of the monooxoruthenium(V) complexes containing the aminopolycarboxylic acid ligands EDTA and PDTA and their reactivities in the oxidation of organic substrates. X-ray crystal structures of K[RuIII(EDTA-H)Cl].cntdot.2H2O and K[RuIII(PDTA-H)Cl].cntdot.0.5H2O

Abstract: The syntheses and characterization of K[Ru[sup V][double bond]O(EDTA)] (3) and K[Ru[sup V][double bond]O(PDTA)] (4) are described. The kinetics of the formation of 3 and 4 by the interaction of the corresponding chloro complexes K[Ru[sup III](EDTA-H)Cl] (1) and K[Ru[sup III](PDTA-H)Cl] (2) with the oxygen atom donor NaOCl was investigated in the temperature range 30-50C. The activation parameters of the oxygenation reaction of 1 and 2 to 3 and 4, respectively, are consistent with an associatively activated process. The O atom transfer reaction from 3 and 4 to the unsaturated and saturated hydrocarbons were studied spectrophotometrically in the temperature range 30-50C by following the disappearance of the characteristic oxo peak of the complexes at 393 nm and by product analysis. The activation parameters for the oxidation of the substrates corresponding to the rate-determining oxygen atom transfer step were determined, and a suitable mechanism was proposed. The crystal and molecular structures of the precursor complexes 1 and 2 were determined using single-crystal X-ray diffraction technique.

Influence of strain on chemical reactivity. Relative reactivity of torsionally distorted double bonds in MCPBA epoxidations

Abstract: The second-order reaction rata were measured for the MCPBA epoxidation in CH 2 Cl 2 for a series of cyclic olefins including bridgehead olefins and trans-cycloalkenes. As expected, strained bridgehead alkenes and trans-cycloalkenes showed faster reaction rates than nonstrained cis-cycloalkenes. The MM-2 steric energies of alkenes, alkanes, and their corresponding epoxides were calculated to evaluate the strain energy released in each reaction (ΔSE). Plots of log k rel vs olefin strain didnot show a good correlation

Polymerizable compositions containing olefin metathesis catalysts and cocatalysts, and methods of use therefor

Abstract: Polymerization of ring-strained cyclic olefins takes place in the presence of a one-part or two-part catalyst which is air and moisture stable and which comprises a transition metal-containing compound. The one-part transition metal-containing catalyst is selected from the group consisting of (a) compounds of the formula: (L1) (L2)Q wherein Q represents Mo or W; L1 represents one to six CO (carbonyl) ligands; L2 represents none to 5 ligands, each of which is a non-ionic compound or unit of a polymer which can be the same or different, each contributes two, four, or six electrons to the metal and is different from L1; wherein the sum of the valence electrons of Q and the electrons contributed by the ligands L?1 and L2? is 18, (b) at least one of cationic ruthenium and osmium-containing organometallic salts having at least one polyene ligand, and (c) [Ir(RO?2?CHC=CHCO2R)2Cl]2 wherein each R independently is hydrogen or lower alkyl (C1 to C4), provided that the oxidation state of the metal is in the range of +3 to 0, and that cocatalysts containing C-halogen bonds are not present. The two-part catalyst comprises (a) a transition metal-containing catalyst, provided that the oxidation state of the transition metal is in the range of +3 to 0, and (b) a cocatalyst selected from the group consisting of (i) terminal or silyl alkynes, (ii) organosilanes containing at least one of α and β groups, (iii) oxidative salts or oxidative compounds containing an oxygen atom to non-oxygen atom double bond, and (iv) heteroatom-containing alkenes. The polymerized composition is useful to provide molded articles, elastomers, dielectric supports, ionophoric or biologically active materials, composite materials, and the like.

Highly enantioselective alkylation of carbon–nitrogen double bonds. Catalytic and stoichiometric asymmetric synthesis of optically active amines by the enantioselective addition of dialkylzinc reagents to N-diphenylphosphinoylimines

Abstract: The first highly enantioselective alkylation of carbon–nitrogen double bonds (of N-diphenylphosphinoylimines) with dialkylzinc reagents promoted by chiral amino alcohols afforded optically active phosphoramides (precursors of amines) in up to 91% enantiomeric excess.

Products and mechanism of the reaction of ozone with phospholipids in unilamellar phospholipid vesicles

Abstract: While considerable effort has been expended on determining the health effects of exposure to typical urban concentrations of O3, little is known about the chemical events responsible for toxicity. Phospholipids containing unsaturated fatty acids in the cell membranes of lung cells are likely reaction sites for inhaled ozone (O3). In this study, we examined the reaction of O3 with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in unilamellar phospholipid vesicles. Reaction of ozone with the carbon-carbon double bond of POPC yielded an aldehyde and a hydroxy hydroperoxide. The hydroxy hydroperoxide eliminated H2O2 to yield a second aldehyde. Upon further ozonolysis, the aldehydes were oxidized to the corresponding carboxylic acids. A material balance showed that no other reaction consumed POPC and O3 or produced these products. As a mechanistic probe, we measured incorporation of oxygen-18 from 18O3 into aldehyde, carboxylic acid, and H2O2. Approximately 50% of the aldehyde oxygen atoms were derived from O3. Oxygen in H2O2 was derived solely from O3, where both oxygen atoms in a molecule of H2O2 were from the same molecule of O3. One of the carboxylic acid oxygen atoms was derived from the precursor aldehyde, while the other was derived from O3. These results support the following mechanism. Cleavage of the carbon-carbon double bond of POPC by O3 yields a carbonyl oxide and an aldehyde. Reaction of H2O with the carbonyl oxide yields a hydroxy hydroperoxide, preventing formation ozonide by reaction of the carbonyl oxide and aldehyde. Elimination of H2O2 from the hydroxy hydroperoxide yields a second aldehyde. Oxidation of the aldehydes by O3 yields carboxylic acids.

Methane activation by Group IVB imido complexes

Abstract: An ab initio study of methane activation by group IVB imido complexes, when coupled with available experimental data, reveals an interesting picture of this important reaction. Initial interaction of methane and (H)[sub 2]M[double bond]NH leads to the formation of alkane complexes bound by [approx]9 kcal mol[sup [minus]1]. Experiment indicates that the polarity of the metal-ligand bond upon which the C-H is activated plays an important role in facilitating subsequent scission. Calculations support this hypothesis and suggest that formation of the alkane complex acts to increase C[sup [delta][minus]]H[sup [delta]+] polarization, setting the stage for C-H cleavage. Calculated methane elimination barriers for (H)[sub 2]M(CH[sub 3])(NH[sub 2]) (M = Ti, Zr, Hf) are in good agreement with experimental models in terms of absolute numbers and trends as a function of metal. Calculated geometries indicate a late transition state for methane elimination, in agreement with experimentally determined activation parameters. The TSs have a kite-shaped geometry with an obtuse angle about the H of the C-H bond being activated (H[sub t]) and a short MH[sub t] distance, 1-2% greater than normal. The short MH[sub t] distance suggests a stabilizing interaction, supported by a positive bond overlap population. Calculation of the intrinsic reaction coordinate demonstrates themore » importance of agostic interactions between N-H and M along the reaction coordinate. 43 refs., 3 figs., 1 tab.« less

Structure and dispersion of molybdenum oxide supported on alumina and titania

Abstract: Samples of molybdenum oxide supported on alumina and titania have been studied by oxygen chemisorption, X-ray diffraction and laser Raman spectroscopy. The three techniques gave a consistent picture of the dispersion of molybdenum oxide on the supports. For the alumina-supported samples it was found that reduction and reoxidation at 673 K were appropriate for titrating surface molybdenum atoms. This temperature was found to be lowered to 623 K for the titania-supported materials. The structure of the dispersed phase on both supports was found to be the same. In the absence of water, it consisted of a monomeric OMoO4 species with a single OMo double bond, four O—Mo links to the surface, and a possible long O⋯Mo bond opposite the double bond. With the introduction of water vapour, this species became a dioxo species with two OMo double bonds and two O—Mo links to the surface. The interaction of the oxide with the support was of an acid–base nature.

Influence of strain on chemical reactivity. Relative reactivity of torsionally strained double bonds in 1,3-dipolar cycloadditions

Abstract: The addition of picryl azide to a series of mono- and bicyclic olefins including trans-cycloalkenes and bridgehead alkenes is reported. Secondary reaction products were identified, and their mechanism of formation was explained by an analysis relating the transition state energies to the conformation of the reaction intermediates. Bridgehead alkenes showed reversed regiochemistry of cycloaddition when compared with model alkenes. It is proposed that the reversal of regiochemistry is caused by the out of plane bending of the bridgehead double bond

Carbon-Oxygen Bond Activation by Transition Metal Complexes

Abstract: Publisher Summary This chapter provides an overview of Carbon–0xygen bond cleavage reactions promoted by transition metal complexes, particularly the conceptual and mechanistic aspects of C–0 bond activation by transition metal complexes. Carbon–oxygen single bonds as well as carbon–oxygen double bonds may be cleaved by transition metal complexes. The chapter deals with the cleavage of the carbon–oxygen single bonds in organic compounds and treats the carbon–oxygen double-bond cleavage later. Two types of processes have been recognized regarding allylic oxygen bond cleavage. One is the process giving products, resulting from the net oxidative addition of allylic compounds and the other is the consecutive-type process initiated by transition metal complexes having ligands such as hydride, alkyl, or alkoxide that may add to the allylic double bond to cause reactions. The C–0 bond cleavage of alkenyloxiranes to π-ally1 complexes can be accomplished with transition metal complexes other than palladium. For example, on treatment of alkenyloxiranes with iron, cobalt, or manganese carbonyls, various η3 allyloxycarbonycl omplexes have been obtained.

New pentacyclic compounds and their use as absorption or fluorescence dyes

Abstract: Pentacyclic derivatives have general formulae (Ia), (Ib) and (Ic), in which R?1 and R13? are the same or different and stand for: hydrogen, alkyl with 1 to 20 carbon atoms, polyoxyhydrocarbyl, phenyl, phenylalkyl with 1 to 3 carbon atoms in the alkyl chain, in which the alkyl and/or phenyl residues may be substituted by one or several hydroxyl, halogen, sulfo, carboxyl or alkoxycarbonyl groups, and alkoxyl may have 1 to 4 carbon atoms; R7 stands for an alkyl group with 1 to 7 carbon atoms substituted by at least one halogen or for a carboxylalkyl group or for a phenyl group substituted by a carboxyl or alkoxycarbonyl group and by at least one halogen located at the 0 position on the carbon atom bound to the pentacyclic ring system, in which alkoxy can have 1 to 4 carbon atoms, or R7 stands for a carboxymethylen-oxy-alkyloxyl group; the residues R?14 and R15?, as well as the positions in the rings non designated by specific symbols may stand for any desired, possibly mutually bridged, substituents; both bonds marked by a dotted line indicate that both carbon atoms connected by the dotted line can be bonded to each other by a simple or double bond; and X- stands for a counterion. Also disclosed are their derivatives activated at at least one of the residues R1, R7 and/or R13. These compounds are useful as absorption or fluorescence dyes, in particular as markers for hapten/antibody/protein-conjugates, as laser dyes and as absorption media for solar collectors.

Reactions of ML4Cl2 (M = Mo, W; L = PMe3, PMePh2) with epoxides, episulfides, carbon dioxide, heterocumulenes, and other substrates: a comparative study of oxidative addition by oxygen atom, sulfur atom, or nitrene group transfer

Abstract: A comparative survey of the reactivity of the divalent molybdenum and tungsten chloro-phosphine complexes MLPCl 2 (M=Mo, W; L=PMe 3 , PMePh 2 ) toward oxidation by a variety of oxygen atom, sulfur atom, and nitrene donors is presented. In general, reactions result in net two-electron oxidation of the metal center, producing metal oxo, sulfido, and imido complexes. The reactions can also be described as oxidative addition reactions, in many cases oxidative addition of C=X double bonds.