Olefin Binding Research Articles

Selectivity in the Polymerization of Olefins with Cyclopentadienyl Chromium Catalysts: A Density Functional Study

The chromium-based Union Carbide catalyst exhibits high activity for the homopolymerization of ethylene. However, it fails to catalyze the homopolymerization of α-olefins or even the copolymerization of the latter with ethylene. To understand the origins of this selectivity, density functional theory calculations are used to model the olefin polymerization reactions of a cyclopentadienylchromium(III) complex whose properties recommend it as a structural and functional model for the Union Carbide catalyst. We find that this chromium alkyl binds both ethylene and propene weakly and therefore reversibly, and that the barrier for insertion of propene is significantly higher than that for inserting ethylene. Because olefin binding is reversible, the insertion step discriminates against the incorporation of α-olefin into the polymer chain.

A stable salt of the tris(ethene)silver cation: structure and characterization of [Ag(eta2-C2H4)3]+[Al[OC(CF3)3]4]-.

More than 50 yr. after the proposal of the Dewar-Chatt-Duncanson model for the binding of olefins to transition-metal atoms, the first structurally characterized example of a silver-C2H4 complex [Ag(h2-C2H4)3]+ was obtained with the help of the very weakly coordinating [Al{OC(CF3)3}3]- ion. By contrast, earlier gas-phase investigations only suggested the existence of [Ag(h2-C2H4)x]+ ions (x = 1 and 2). The crystal structure of the title compd. is given and it was compared with DFT calcd. structure. [on SciFinder (R)]

Olefin Binding in a Binuclear Iridium Complex as a Function of Fluorine Substitution: Ethylene to Tetrafluoroethylene

The reactions of the diiridium methyl complex [Ir2(CH3)(CO)(μ-CO)(dppm)2][CF3SO3] (1) with ethylene, fluoroethylene, Z-1,2-difluoroethylene, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene have been investigated. Reaction of 1 with ethylene at −78 °C yields [Ir2H(η2-C2H4)(CO)2(μ-CH2)(dppm)2][CF3SO3] (2a), resulting from C−H activation of the methyl group induced by ethylene coordination, whereas reaction at higher temperatures yields the simple ethylene adduct [Ir2(CH3)(CO)(η2-C2H4)(μ-CO)(dppm)2][CF3SO3] (2b). Reactions of 1 with fluoroethylene and Z-1,2-difluoroethylene yield only the olefin adducts analogous to 2b. At −78 °C reaction with 1,1-difluoroethylene yields the methylene-bridged hydride product [Ir2H(η2-C2F2H2)(CO)2(μ-CH2)(dppm)2][CF3SO3] (5a), which upon warming, yields first the olefin adduct [Ir2(CH3)(CO)(η2-C2F2H2)(μ-CO)(dppm)2][CF3SO3] (5b) followed by the olefin-bridged product [Ir2(CH3)(CO)2(μ-C2F2H2)(dppm)2][CF3SO3] (5c). Trifluoro- and tetrafluoroethylene yield only th...

Sorptive reconstruction of the CuAlCl(4) framework upon reversible ethylene binding.

Three ethylene adducts to CuAlCl(4) have been characterized by single crystal and/or powder X-ray diffraction, (13)C, (27)Al and (63)Cu MAS NMR and diffuse reflectance UV-vis spectroscopy. (C(2)H(4))(2)CuAlCl(4), a = 7.1274(5) b = 12.509(1) c = 11.997(3) beta = 91.19 degrees, Pc, Z = 4; alpha-(C(2)H(4))CuAlCl(4), a =7.041(3) b = 10.754(8) c =11.742(9) beta = 102.48(6), P2(1), Z = 4 and beta-(C(2)H(4))CuAlCl(4), a = 7.306(2), b = 16.133(3), c = 7.094(1), Pna2(1), Z = 4. Up to 2 equiv of ethylene ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperatures and pressures as low as 300 Torr. The ethylene ligands are bound to copper (I) primarily through a sigma-interaction, because the AlCl(4)(-) groups also bound to copper prevent any significant pi-back-bonding. The olefin binding is reversible and has been characterized by gravimetric and volumetric adsorption analysis and by time and pressure resolved synchrotron powder X-ray diffraction. Comparison of the parent crystal structure to those of the adduct phases provide an atomistic picture of the sorptive reconstruction reactions. These are proposed to proceed by a classic substitution mechanism that is directed by the van der Waals channels of the parent crystalline lattice.

Structural dependence of thermodynamics of alkene binding to yttrium alkyl complexes and of kinetics of alkyl migration to coordinated alkenes.

Agostic interactions in yttrium alkyls are structure dependent. Primary alkyl yttrium complexes have beta-CH(2) agostic interactions at low temperature, but a shift toward alpha-agostic interactions occurs on warming. For the more crowded beta-disubstituted yttrium alkyls, an alpha-CH(2) agostic interaction is seen. The thermodynamics of alkene binding to the primary alkyl yttrium complex Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) depend strongly on the structure of the alkene. A single allylic substituent on the alkene has a small effect on alkene binding, but a second allylic substituent has a large destabilizing effect. Propene binding to yttrium alkyls is largely independent of the nature of the alkyl ligand. Equilibrium constants for propene binding to n-, gamma-substituted, beta-substituted, and secondary alkyl yttrium complexes are similar. The rate of migration of an alkyl group to a coordinated alkene depends strongly on the structure of the alkyl group: n-alkyl approximately gamma-substituted >> beta-substituted >> alpha-substituted. The approximately 200-fold slower insertion of propene into Cp(2)YCH(2)CH(CH(3))(2) (6) than that into Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) is therefore due to kinetically slow migration of the beta-disubstituted alkyl group of 6 and not to differences in the equilibrium binding of propene. Processes related to chain transfer and site epimerization at the metal center are also reported.

Activation of alkenes and H2 by [Fe]-H2ase model complexes.

The established ability of the Fe(II) bridging hydride species (micro-H)(micro-pdt)[Fe(CO)2(PMe3)]2+, 1-H+, to take-up and heterolytically activate dihydrogen, resulting in H/D scrambling of H2/D2 and H2/D2O mixtures (Zhao et al. Inorg. Chem. 2002, 41, 3917) has prompted a study of simultaneous alkene/H2 activation by such [Fe]H2ase model complexes. That the required photolysis produced an open site was substantiated by substitution of CO in 1-H+ by CH3CN with formation of structurally characterized [(micro-H)(micro-pdt)[Fe(CO)2(PMe3)][Fe(CO)(CH3CN)(PMe3)]]+[PF6]-. Under similar photolytic conditions, H/D exchange reactions between D2 and terminal alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, were catalyzed by 1-H+ and the edt (SCH2CH2S) analogue, 2-H+. Substantial regioselectivity for H/D exchange at the internal vinylic hydrogen was observed. The extent to which the olefins were deuterium enriched vs deuterated was catalyst dependent. The stabilizing effect of the binuclear chelating ligands, SCH2CH2CH2S, pdt, and SCH2CH2S, edt, is required for the activity of binuclear catalysts, as the mono-dentate micro-SEt analogue decomposed to inactive products under the photolytic conditions of the catalysis. Reactions of 1 and 2 with EtOSO2CF3 yielded the S-alkylated products, [(micro-SCH2CH2CH2SEt)[Fe(CO)2(PMe3)]2]+[SO3CF3]- (1-Et+), and 2-Et+, rather than micro-C2H5 analogues to the micro-H of 1-H+. The stability and lack of reactivity toward H2 of 1-Et+ and 2-Et+, indicates they are not on the reaction path of the olefin/D2 H/D exchange process. A mechanism with olefin binding to an open site created by CO loss and formation of an Fe-(CH2CHDR) intermediate is indicated. A likely role of a binuclear chelate effect is implicated for the unique S-XXX-S cofactor in the active site of [Fe]H2ase.

Heavy-atom kinetic isotope effects, cocatalysts, and the propagation transition state for polymerization of 1-hexene using the rac-(C(2)H(4)(1-indenyl)(2))ZrMe(2) catalyst precursor.

Using 13C NMR techniques, the 12C/13C kinetic isotope effects (KIEs) for the polymerization of 1-hexene catalyzed by rac-(C2H4(1-indenyl)2)ZrMe2 in the presence of four different cocatalysts (tris(pentfluorophenyl)borane, tris(pentafluorophenyl)alane, anilinium tetrakis(pentafluorophenyl)borate, and methylalumoxane) have been determined. All cocatalysts yield similar KIEs within experimental uncertainty, with values of 1.009(1) and 1.017(2) at C1 and C2, respectively. Ab initio DFT computational modeling of the polymerization KIE indicates that alkene binding to the catalyst must be reversible, with the majority of the KIE developing in the subsequent migratory insertion reaction.

Enantioselective ruthenium-catalyzed ring-closing metathesis.

[reaction: see text] The first enantioselective ruthenium olefin metathesis catalysts have been prepared, and high enantiomeric excesses (up to 90%) are observed in the desymmetrization of achiral trienes. A model consistent with the stereochemical outcome of the reactions is described and suggests side-on olefin binding and reorganization of the halide ligands.

Toward separation and purification of olefins using dithiolene complexes: an electrochemical approach.

The complex Ni[S2C2(CF3)2]2 reacts with light olefins, including ethylene and propylene, selectively and reversibly. The reaction is not poisoned by hydrogen gas, carbon monoxide, acetylene, or hydrogen sulfide, which are commonly present in olefin streams, presumably because olefin binding occurs through the sulfur ligand rather than the metal center. The reversible reaction of olefins with Ni[S2C2(CN)2]2n (n = 0, -1, -2) can be controlled electrochemically, where the oxidation state-dependent binding and release of olefins are fast on the electrochemical time scale. The observed tolerance to poisons and controllable electrochemical reactivity present an alternative approach to the separation of olefins from complex streams.

Switched-On Nickel

The separation of mixtures of chemical compounds is often a laborious task, especially on an industrial scale. In his Perspective, Crabtree highlights a new concept introduced by Wang and Stiefel for the separation of olefins from refinery mixtures. The authors have discovered an electrochemical switch that can selectively separate olefins and is not prone to poisoning by common impurities. The key to the discovery lies in using an unusual complex that is derived more from biological concepts than from the complexes commonly used for olefin binding.

Kinetics and Thermodynamics of Alkene Complexation in d0Metal−Alkyl−Alkene Complexes

Alkene dissociation from the yttrium chelate Cp*2Y[η1,η2-CH2CH2CH2CHCH2] (7-on) became slow enough below −100 °C to be measured by dynamic 1H NMR spectroscopy [ΔG⧧(−110 °C) = 7.5 kcal mol-1, ΔH⧧ = 9.3 kcal mol-1]. Coalescence of the Cp* resonances of Cp*2Y[η1,η2-CH2CH2CH(CH3)CHCH2] (8-on) requires alkene dissociation plus inversion at yttrium and occurred substantially slower than simple alkene dissociation [ΔG⧧(−72 °C) = 9.6 kcal mol-1, ΔH⧧ = 10.8 kcal mol-1]. The binding energy of a disubstituted alkene to a d0 yttrium center was determined to be ΔH° = 2.6 kcal mol-1 by direct observation of the equilibrium between Cp*2Y(η1,η2-CH2CH2CH2C(CH3)CH2) (6-on) and Cp*2Y(η1-CH2CH2CH2C(CH3)CH2) (6-off). The significantly greater ΔH⧧ of alkene dissociation compared with ΔH° of alkene binding can be attributed either to stabilization of the dissociated yttrium alkyl by a β-agostic interaction or to destabilization of the transition state leading to alkene dissociation by increased strain in the chelate tether. Bin...

Coordinated carbenes from electron-rich olefins on RuHCl(PPr3i)2

Dehydrohalogenation of RuH2Cl2L2 (L=PPr3i) gives (RuHClL2)2, shown to be a halide-bridged dimer by X-ray crystallography; the fluoride analog is also a dimer. (RuHClL2)2 reacts with N2, pyridine and C2H4 (L′) to give RuHClL′L2, but with vinyl ether and vinyl amides, H2CCH(E) [E=OR, NRC(O)R′] such olefin binding is followed by isomerization to the heteroatom-substituted carbene complex L2HClRuC(CH3)(E). The reaction mechanism for such rearrangement is established by DFT(B3PW91) computations, for C2H4 as olefin (where it is found to be endothermic), and the structures of intermediates are calculated for H2CC(H)(OCH3) and for cyclic and acyclic amide-substituted olefins. It is found, both experimentally and computationally, that the amide oxygen is bonded to Ru, with a calculated bond energy of approximately 9 kcal mol−1 for an acyclic model. Less electron-rich vinyl amides or amines form η2-olefin complexes, but do not isomerize to carbene complexes. Calculated ΔE values for selected ‘‘ competition’’ reactions reveal that donation by both Ru and the heteroatom-substituted X are necessary to make the carbene complex L2HClRuC(X)(CH3) more stable than the olefin complex L2HClRu(η2-H2CCHX). This originates in part from a diminished endothermicity of the olefin→carbene transformation when the sp2 carbon bears a π-donor substituent. The importance of a hydride on Ru in furnishing a mechanism for this isomerization is discussed. The compositional characteristics of Schrock and Fischer carbenes are detailed, it is suggested that reactivity will not be uniquely determined by these characteristics, and these new carbenes RuHCl[C(X)CH3]L2 are contrasted to Schrock and Fischer carbenes.

Probing the mechanisms of enantioselective hydrogenation of simple olefins with chiral rhodium catalysts in the presence of anions

The strong influence of various anions upon the hydrogenation of 2-phenyl-1-butene, catalyzed by chiral rhodium catalysts was investigated. Both sulfonates and halides exert large increases in the enantioselectivity when [Rh[(-)-bdpp](NBD)]ClO4 (bdpp = 2,4-bis(diphenylphosphino)pentane, NBD = 2,5-norbornadiene) is used as the catalyst precursor at high pressures (70 atm) of dihydrogen in nonpolar solvents. A dihydride mechanism similar to that for Wilkinson's catalyst [RhCl(PPh3)3] was shown to be operating at both high- and low-pressure conditions through a combination of catalytic studies, 31P, 1H and parahydrogen-induced polarization (PHIP) NMR experiments. With sulfonate and in neat methanol, however, a mechanistic switch takes place from a dihydride route (dihydrogen addition before olefin binding) at high pressure to an unsaturate route (olefin binding before dihydrogen addition) at low pressures (<30 atm). Olefin isomerization is inhibited by halide addition, but occurs with sulfonate and in neat methanol through what is most likely a pi-allyl mechanism. A detailed understanding of the effects of addition of these anions is crucial for development of new classes of catalysts capable of efficient enantioselective reduction of prochiral olefins lacking a secondary polar binding group.

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid)(PE-g-AA) and the olefin reversible coordinates with the PE-g-AA-Ag + complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag + ion. Also, the Ag + ion in PE-g-AA-Ag + membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag + ( olefin ) complex was proposed. The coordination number of Ag + ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag + in the PE-g-AA-Ag + complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA-Ag + complex membranes were studied. The equilibrium, association, and dissociation constants were also presented.

Polymeric complex membranes for olefin/paraffin separation

AbstractSemi‐crystalline polyethylene (PE), rubbery silicone rubber (SR) and glassy poly[(l‐trimethylsilyl)‐l‐propyne] (PTMSP) were modified for olefin/paraffin separation. The polymers were first grafted with the acrylic acid (AA) and then incorporated with silver ions for forming the complex membranes such as PE‐g‐AA‐Ag+, SR‐g‐AA‐Ag+ and PTMSP‐g‐AA‐Ag+ The complex membranes were activated by glycerol solvation and subsequently showed high selectivity in olefin/paraffin separation. The silver ion distribution, the kinetics of olefin binding to PE‐g‐AA‐Ag+, the gas permeation properties and the sorption behaviors were studied. A novel dry complex membrane for olefin/paraffin separation based on AgClO4 complexing with PTMSP main‐chain was also studied.

Kinetic Studies of Olefin Binding to Sulfido Sites in Dinuclear Molybdenum Complexes

The reactions of olefins with a series of molybdenum complexes of the formula (R-CpMo-({mu}-S)){sub 2}S{sub 2}CHX, where R = H, CH{sub 3}, CO{sub 2}Na, and X = H, CN, CMe{sub 3}, have been studied. Olefin reagents have included propene, 1-butene, cis- and trans-2-butene, and isomers of hexene. Olefin additions to the sulfido ligands in the dimers result in alkanedithiolate complexes. The rates of these reactions have been monitored by visible spectroscopy, and rate constants, k{sub on}, have been compared as dimer substituent and olefin structure have been varied. The rate constants for olefin dissociation from the alkanedithiolate complexes, k{sub off}, have also been determined by NMR spectroscopy. The studies have permitted us to probe the relative contributions of k{sub on} and k{sub off} to the equilibrium constants for reversible olefin binding as inductive and steric effects are varied. The potential for using these systems in olefin separation schemes is discussed. 20 refs., 3 figs., 6 tabs.

Stereoselective binding of olefins to a molybdenum center and synthesis of a chiral molybdenum-olefin complex

Stereoselective binding of olefins to a molybdenum center and synthesis of a chiral molybdenum-olefin complex

A mechanistic approach to the asymmetric epoxidation of allylic alcohols and osmylation of alkenes

A mechanistic study of the oxidation of allylic alcohols to allylic epoxides catalyzed by titanium-tartrate complexes and the cis -dihydroxylation of alkenes by osmium tetraoxide and osmium tetraoxide-chiral diamine ligand complexes is presented. The structure of the titanium-tartrate complexes, and the oxygen transfer in relation to asymmetric epoxidation of allylic alcohols catalyzed by titanium-tartrate complexes are discussed on the basis of the frontier orbital approach; in a similar way is the binding of alkenes to the oxo ligands in osmium tetraoxide and osmium tetraoxide-chiral diamine ligand complexes presented. The results are discussed in relation to the experimental suggested mechanisms.

ChemInform Abstract: Binding of Alkenes to the Ligands in OsO2X2 (X: O and NR) and CpCo(NO)2. A Frontier Orbital Study of the Formation of Intermediates in the Transition‐Metal‐Catalyzed Synthesis of Diols, Amino Alcohols, and Diamines.

Chemischer InformationsdienstVolume 17, Issue 32 Physical Organic Chemistry ChemInform Abstract: Binding of Alkenes to the Ligands in OsO2X2 (X: O and NR) and CpCo(NO)2. A Frontier Orbital Study of the Formation of Intermediates in the Transition-Metal-Catalyzed Synthesis of Diols, Amino Alcohols, and Diamines. K. A. JOERGENSEN, K. A. JOERGENSENSearch for more papers by this authorR. HOFFMANN, R. HOFFMANNSearch for more papers by this author K. A. JOERGENSEN, K. A. JOERGENSENSearch for more papers by this authorR. HOFFMANN, R. HOFFMANNSearch for more papers by this author First published: August 12, 1986 https://doi.org/10.1002/chin.198632076AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue32August 12, 1986 RelatedInformation

Binding of alkenes to the ligands in OsO2X2 (X = O and NR) and CpCo(NO)2. A frontier orbital study of the formation of intermediates in the transition-metal-catalyzed synthesis of diols, amino alcohols, and diamines

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBinding of alkenes to the ligands in OsO2X2 (X = O and NR) and CpCo(NO)2. A frontier orbital study of the formation of intermediates in the transition-metal-catalyzed synthesis of diols, amino alcohols, and diaminesKarl Anker. Joergensen and Roald. HoffmannCite this: J. Am. Chem. Soc. 1986, 108, 8, 1867–1876Publication Date (Print):April 1, 1986Publication History Published online1 May 2002Published inissue 1 April 1986https://doi.org/10.1021/ja00268a026RIGHTS & PERMISSIONSArticle Views478Altmetric-Citations92LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1018 KB) Get e-Alerts Get e-Alerts