- Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)
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The Co(I) complex, [Co(N2)(CyPNP)] (CyPNP = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of internal alkynes under 2 bar of H2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E- and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, [Co(PMe3)(CyPNP)], results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, [CoH(CyPNP)], can also be generated by treatment of degassed solutions of [Co(N2)(CyPNP)] with H2. The CoII-hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.
- Alawisi, Hussah,Arman, Hadi D.,Tonzetich, Zachary J.
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p. 1062 - 1070
(2021/04/09)
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- Selecting double bond positions with a single cation-responsive iridium olefin isomerization catalyst
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The catalytic transposition of double bonds holds promise as an ideal route to alkenes of value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, normally requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst selectively produces either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on noncovalent modifications.
- Camp, Andrew M.,Kita, Matthew R.,Blackburn, P. Thomas,Dodge, Henry M.,Chen, Chun-Hsing,Miller, Alexander J.M.
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supporting information
p. 2792 - 2800
(2021/03/01)
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- Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert
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The metal-free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal-free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron-ligand cooperation.
- Wech, Felix,Hasenbeck, Max,Gellrich, Urs
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supporting information
p. 13445 - 13450
(2020/09/23)
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- A General Strategy for Open-Flask Alkene Isomerization by Ruthenium Hydride Complexes with Non-Redox Metal Salts
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A homogenous metal hydride (M?H) catalyst for isomerization normally requires rigorous air-free techniques. Here, we demonstrate a highly efficient protocol in which simple non-redox metal ions as Lewis acids can promote olefin isomerization dramatically with a commercially available RuH2(CO)(PPh3)3 complex in an open-flask system. Isomerization can be accomplished within a short time, and a satisfactory selectivity for different types of unsaturated compounds can be obtained. Meanwhile, an excellent turnover number up to 17208 was achieved under air, and open-flask gram-scale experiments further demonstrated the efficiency of the RuH2(CO)(PPh3)3/non-redox-metals system. We used FTIR spectroscopy, GC–MS, NMR spectroscopy and kinetics studies to evidence that in the sluggish RuH2(CO)(PPh3)3 catalyst, bloated PPh3 ligands cause steric hindrance for the coordination of the free alkene. Alternatively, the addition of non-redox metal ions could induce the dissociation of the PPh3 ligand to offer unoccupied coordination sites for the alkene and to form the Mg-bridged adduct OC?Ru?H2?Mg2+ as the highly active species, which benefited the isomerization significantly through the metal hydride addition–elimination pathway. Finally, this strategy was demonstrated as an impactful approach for hydride catalysts of other transition metals such as Os.
- Lv, Zhanao,Chen, Zhuqi,Hu, Yue,Zheng, Wenrui,Wang, Haibin,Mo, Wanling,Yin, Guochuan
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p. 3849 - 3859
(2017/09/18)
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- An Agostic Iridium Pincer Complex as a Highly Efficient and Selective Catalyst for Monoisomerization of 1-Alkenes to trans-2-Alkenes
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A unique Ir complex (tBuNCCP)Ir with the pyridine–phosphine pincer as the sole ligand, featuring a dual agostic interaction between the Ir and two σ C?H bonds from a tBu substituent, has been prepared. This complex exhibits exceptionally high activity and excellent regio- and stereoselectivity for monoisomerization of 1-alkenes to trans-2-alkenes with wide functional-group tolerance. Reactions can be performed in neat reactant on a more than 100 gram scale using 0.005 mol % catalyst loadings with turnover numbers up to 19000.
- Wang, Yulei,Qin, Chuan,Jia, Xiangqing,Leng, Xuebing,Huang, Zheng
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supporting information
p. 1614 - 1618
(2017/02/05)
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- Nonredox Metal-Ion-Accelerated Olefin Isomerization by Palladium(II) Catalysts: Density Functional Theory (DFT) Calculations Supporting the Experimental Data
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Redox metal-ion-catalyzed olefin isomerization represents one of the important chemical processes. This work illustrates that nonredox metal ions can sharply accelerate Pd(II)-catalyzed olefin isomerization, while Pd(II) alone is very sluggish. Nuclear magnetic resonance (NMR) and ultraviolet-visible light (UV-vis) characterizations disclosed that the acceleration effect originates from the formation of heterobimetallic Pd(II) species with added nonredox metal ions, which improves the C-H activation capability of the Pd(II) moiety. Density functional theory (DFT) calculations further confirmed the sharp decrease of the energy barrier in C-H activation by the heterobimetallic Pd(II)/Al(III) species.
- Senan, Ahmed M.,Qin, Shuhao,Zhang, Sicheng,Lou, Chenling,Chen, Zhuqi,Liao, Rong-Zhen,Yin, Guochuan
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p. 4144 - 4148
(2016/07/12)
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- CATALYST AND PROCESS FOR THE CO-DIMERIZATION OF ETHYLENE AND PROPYLENE
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Disclosed are novel catalyst solutions comprising an organic complex of nickel, an alkyl aluminum compound, a solvent, and a phosphine compound, that are useful for the preparation of butenes, pentenes and hexenes by the co-dimerization or cross-dimerization of ethylene and propylene. Also disclosed are processes for the dimerization of ethylene and propylene that utilize these catalyst solutions. The catalyst systems described herein demonstrate that, depending on the choice of phosphine compound used with the catalytically active nickel, it is indeed possible to lower the concentration of hexene olefins relative to butenes and pentenes, even in the presence of excess propylene. The selectivity to the linear or branched pentene product can also be controlled by the selection of the phosphine compound. The catalyst solutions may be used with mixtures of olefins.
- -
-
Paragraph 0082
(2015/03/28)
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- Magnetic core-shell nanoparticles as carriers for olefin dimerization catalysts
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We report the covalent support of functionalized nickel complexes on magnetic core-shell hybrid particles γ-Fe2O3/ SiO2. Two completely different ways of connecting the particle with these nickel complexes were carried out. The first approach used the hydrosilylation method between the alkene-substituted nickel complex and a silane. In a second approach, the particles were connected with the complexes by means of click chemistry (copper-catalyzed Huisgen 1,3-dipolar cycloaddition). For this purpose, the nickel complexes were substituted with an alkyne moiety. Transmission and scanning electron microscopies, energy-dispersive X-ray diffraction, and FTIR spectroscopy were the methods employed to characterize the successful heterogenization of the nickel complexes. Copyright
- Ruhland, Thomas M.,Lang, Julian R.V.,Alt, Helmut G.,Mueller, Axel H.E.
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p. 2146 - 2153
(2013/06/26)
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- Homogeneous Dimerization Catalysts Based on Vanadium
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A series of new bis(imino)pyridine vanadium(III) complexes was synthesized according to formula: They were tested for the homogeneous catalytic dimerization of propylene after activation with MAO and showed excellent selectivity for dimerization. The catalysts can be used with or without PPh3 as an additive to produce ≧80% dimerized alkenes.
- -
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Page/Page column 4; 6
(2011/04/18)
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- Homogeneous catalytic dimerization of propylene with bis(imino)pyridine vanadium(III) complexes
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A series of new bis(imino)pyridine vanadium(III) complexes was synthesized. They were tested for the homogeneous catalytic dimerization of propylene after activation with MAO. The activity and selectivity depend on the ligand structure of the corresponding organic coordination compound. The influence of PPh3 as an additive was investigated and high dependency could be observed.
- Lang, Julian R.V.,Denner, Christine E.,Alt, Helmut G.
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experimental part
p. 45 - 49
(2010/07/08)
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- High yield of liquid range olefins obtained by converting i-propanol over zeolite H-ZSM-5
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Methanol, ethanol, and i-propanol were converted under methanol-to-gasoline (MTH)-like conditions (400°C, 1-20 bar) over zeolite H-ZSM-5. For methanol and ethanol, the catalyst lifetimes and conversion capacities are comparable, but when i-propanol is use
- Mentzel, Uffe V.,Shunmugavel, Saravanamurugan,Hruby, Sarah L.,Christensen, Claus H.,Holm, Martin S.
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experimental part
p. 17009 - 17013
(2010/03/23)
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- Insight into cis-to-trans olefin isomerisation catalysed by group 4 and 6 cyclopentadienyl compounds
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Intramolecular isomerisation of the pendant allyl unit present in the model compound [MoH(eta;5-C5H4SiMe 2CH2CH=CH2)- (CO)3] reported before was investigated by DFT calculations.
- Chahboun, Ghaita,Petrisor, Cristina E.,Gomez-Bengoa, Enrique,Royo, Eva,Cuenca, Tomas
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experimental part
p. 1514 - 1520
(2009/07/10)
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- Kinetics of the thermal isomerization of 1,1,2-trimethylcyclopropane
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The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2-trimethylcyclopropane to three isomeric methylpentenes and two dimethyl-butenes have been determined over a wide range of temperatures, 688-1124 K, using both static and shock tube reactors. For the overall loss of reactant. Ea =63.7 (±0.5) kcal/mol and log10 A= 15.28 (±0.12). These values are higher by 2.6 kcal/mol and 0.7-0.8 than previously reported from experimental work or predicted from thermochemical calculations. Ea for the formation of trans-4-methyl-2-pentene is 1.5 kcal/mol higher than Ea for the formation of the cis isomer, which is identical to the Ea difference previously reported for the formation of trans- and cis-2-butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the C - C ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclo-propanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1, 1-or 1,2-dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in C - C bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes.
- Lewis, David K.,Hughes, Steven V.,Miller, Justine D.,Schlier, Jessica,Wilkinson, Kevin A.,Wilkinson, Sara R.,Kalra, Bansi L.
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p. 475 - 482
(2008/02/09)
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- Synthesis, molecular structure and catalytic activity of chiral benzamidinate nickel complexes
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Two new nickel complexes containing the chiral benzamidinate ligation: [PhC(N-SiMe3)(N′-myrtanyl)]2Ni(py)2 (3) and {[PhC(NH)(N′-myrtanyl)]2Ni}2 (6) have been synthesized and characterized. The solid-state molecular structures of these complexes have been determined by low-temperature X-ray diffraction analysis. Complex 3 was obtained via two different procedures. In complex 3, the metal adopts a nearly ideal octahedral environment, whereas in complex 6 the two divalent nickel metals are coordinated in a square-planar geometry, forming a dimer. Complex 3 activated with MAO has been found to oligomerize propylene producing a mixture of dimers, trimers and tetramers with a turnover frequency of 5200 h-1, whereas complex 6 being activated with MAO oligomerizes ethylene to a mixture of dimers and trimers with a high turnover frequency of 15,400 h-1. In addition, when activated with MAO both complexes showed a good activity for the vinyl-type polymerization of norbornene.
- Nelkenbaum, Elza,Kapon, Moshe,Eisen, Moris S.
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p. 3154 - 3164
(2007/10/03)
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- Novel neutral arylnickel(II) phosphine catalysts containing 2-oxazolinylphenolato N-O chelate ligands for ethylene oligomerization and propylene dimerization
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A series of new neutral arylnickel(II) phosphine complexes 1 bearing 2-oxazolinylphenolato ligands [2-(4-R1-5-R2-C3H2NO) -C6H4O]Ni (2-R4-4-R3-C6H3 (PPh3) were synthesized by reactions of sodium salts of 2-(4,5-dihydro-2-oxazolyl)phenol derivatives with trans-Ni(Ar)(Cl (PPh3)2 or by direct reactions of the ligands with trans-Ni(Ar)(Cl)(PPh3)2 in the presence of NEt3. These neutral Ni(II) complexes 1 exhibited high activities and selectivities in ethylene oligomerization and propylene dimerization. The catalytic activities and the product distributions were dependent on the selection of various organoaluminum cocatalysts and phosphine scavenger (Ni(COD)2). The effects of various reaction conditions on ethylene oligomerization were also examined. The highest activity of 5.51×105 g oligomers/(mol Ni · h) and 83% selectivity of C6 internal olefins were obtained in 1a/MAO catalytic system in ethylene oligomerization. The oligomers consisted mainly of lower carbon olefins in the range of C4-C8. Complexes 1 showed the moderate tolerance of polar additives in ethylene oligomerization. The highest activity of 1a/MAO in propylene dimerization reached to 1.32×105 g oligomers/(mol Ni · h).
- Zhao, Wei,Qian, Yanlong,Huang, Jiling,Duan, Jianjun
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p. 2614 - 2623
(2007/10/03)
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- Debrominations of vic-Dibromides with Diorganotellurides. 1. Stereoselectivity, Relative Rates, and Mechanistic Implications
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Debrominations of vic-dibromides with diaryl tellurides 1-4 and di-n-hexyl telluride (9) are described. A mechanistic explanation of the debromination is offered which accounts for several key experimental observations: (1) the reaction is highly stereoselective with erythro-dibromides giving trans-olefins and threo-dibromides giving cis-olefins, (2) the reaction is accelerated by more electron-rich diorganotellurides, (3) the reaction is accelerated in a more polar solvent, (4) the reaction is accelerated by the addition of carbocation-stabilizing substituents to the carbons bearing the bromo substituents, and (5) erythro-dibromides are much more reactive than threo-dibromides. It is proposed that bromonium ion formation from the vic-dibromide is slow and rate-determining. Bromonium ion formation is followed by rapid scavenging of "Br-" by the diorganotelluride. The bromonium ion formation provides stereoselectivity and eclipsing interactions lower the reactivity of threo-dibromides. No intermediate species were observed by 1H NMR.
- Butcher, Timothy S.,Zhou, Feng,Detty, Michael R.
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p. 169 - 176
(2007/10/03)
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- A Dynamic Equilibrium of Oxaphosphetanes
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The course of the Wittig reaction was investigated by rapid injection NMR spectroscopy.Rate constants for the formation of oxaphosphetanes were determined.A new dynamic equilibrium of oxaphosphetanes was observed for the first time.The solvent and substituent dependence of the new effect was investigated.By labeling various oxaphosphetanes with 13C and 17O the lithium salt dependence of the new equilibrium was shown.A lithium adduct of oxaphosphetanes under these conditions is proposed. - Key Words: Wittig reaction / Rapid injection NMR / Dynamic NMR / Oxaphosphetanes
- Geletneky, Christian,Foersterling, Frank-Holger,Bock, Willi,Berger, Stefan
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p. 2397 - 2402
(2007/10/02)
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- Acid-Base Properties of Modified Aluminas
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The acid-base properties of modified aluminas (SO42-, PO43-, Cl-, F-, Mg2+ and Na+, 0.2-2.0 wt.percent) have been investigated by FTIR spectroscopy of probe molecules (pyridine and CDCl3), CO2 TPD and the dehydration of 4-methyl-pentan-2-ol.The results of these methods and those of previous NH3 TPD studies were compared in order to establish a classification of our aluminas.There is very good agreement between the results of the five methods.The various modifying ions have effects as summarised in the following acidity-basicity scale: Na+ 2+ 3- - 2- , - increasing basicity).Fluorine is distinguished from the other ions as it is able to create Broested-acidic sites.CO2 TPD is an adequate method for basicity measurement.NH3 and CO2 TPD give complementary results.Furthermore, FTIR spectroscopy of adsorbed CDCl3 gives valuable information on the effects of ions on the basic strengths.
- Berteau, Pascal,Kellens, Marie-Ange,Delmon, Bernard
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p. 1425 - 1431
(2007/10/02)
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- METAL COMPLEXES IN CATALYTIC CONVERSION OF OLEFINS. 3. CATALYTIC DIMERIZATION OF ETHYLENE AND PROPYLENE BY Ni(PPh3)n-Et3Al2Cl3 SYSTEM
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The Ni(PPh3)n-Et3Al2Cl3 catalytic system was found to be most effective for the dimerization of ethylene and propylene when the ligands Bu3PO and (BuO)2-PNEt2 were used in the Ni complex.For propylene dimerization in the liquid phase, the yield was 54 kmole/mole Nih at 40 - 55 deg C.Using mathematical planing methods for the experiments the optimum conditions range for the formation of hexanes was found, in which selectivity for dimerization reached 85-96percent at 80-90percent conversion.
- Furman, D. B.,Kudryashev, A. V.,Ivanov, A. O.,Pogorelov, A. G.,Yanchevskaya, T. V.,Bragin, O. V.
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p. 444 - 447
(2007/10/02)
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- Reactivity and Intersystem Crossing of Singlet Methylene in Solution
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Evidence is reported wich demonstrates that singlet methylene, produced from the photolysis of diazomethane or diazirine undergoes intersystem crossing to form triplet methylene in perfluorohexane solvent.The results of triplet sensitized photolysis and of direct photolysis experiments with dilute concentrations of substrate (cis- and trans-2-pentene and chloroform) appear to be essentially identical.Stern-Volmer analyses of the competition kinetics between acetonitrile and 2-pentenes or chloroform for singlet methylene are consistent with the near diffusion controlled reactivity of singlet methylene.With the assumption of diffusion-controlled reactions for singlet methylene, plots of the quantum yield for singlet vs. triplet reaction for methylene allow the first estimate (-1) of the rate of intersystem crossing of singlet methylene in the condensed phase.This value is considerably smaller than the value that is extrapolated to the solution phase from results in the gas phase.The possible reasons for this difference are discussed.
- Turro, Nicholas J.,Cha, Yuan,Gould, Ian R.
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p. 2101 - 2107
(2007/10/02)
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- DIMERISATION DE MONOOLEFINES CATALYSEE PAR DES COMPLEXES DU NICKEL ET DU COBALT GENERES ELECTROCHIMIQUEMENT
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Dimerization of olefins was performed with NiL2X2 and CoL2X2 complexes by an electrochemical reduction process under controlled cathodic potential.The influence of several parameters (choice of anode, supporting electrolyte, ligand, temperature and pressure) was studied in order to increase the dimer production and selectivity.In case of ethylene, with nickel-based catalysts, 2-butenes are formed selectively with a turn-over number of 12 000 within 50 h.With propylene as substrate methylpentenes are the main products, in which case the reaction rate appears to be two orders of magnitude lower than with ethylene under identical conditions.Although less active, cobalt based catalysts show an unusual behaviour, as they are particularly selective for 1-butene production (>90percent).
- Masotti, H.,Wallet, J. C.,Pfeiffer, G.
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p. 241 - 252
(2007/10/02)
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- The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes
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We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes.Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization.This kind of isomerization increases with an increase in the number of alkyl substituents around the double bound.These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1?,?* state is involved in cis-trans isomerization process; (b) the 1?,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state.Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.
- Collin, Guy J.,Deslauriers, Helene
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p. 1424 - 1430
(2007/10/02)
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- ETUDE DE L'ISOMERISATION DU METHYL-4 PENTENE-1 PAR L'HYDRIDO DIAZOTE TRIS(TRIPHENYLPHOSPHINE)COBALT(I): CoHN2(PPh3)3
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At 25 deg C, and under 1 to 7 bar nitrogen pressure, the isomerization of 4-methyl-1-pentene catalyzed in benzene by CoHN2(PPh3)3 involves two active species: HCoN2(S1)(PPh3)2 and HCo(S1)(PPh3)3, respectively, in greater quantities at higher (P(N2) > 7 bars) and small quantities at P(N2) - O nitrogen pressures. The kinetic study shows that the rate of the reaction is always ruled by the equation:
- Petit, F.,Arzouyan, C.,Peiffer, G.,Gaydou, E.
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p. 261 - 272
(2007/10/02)
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