- UTILIZATION OF SUPERCRITICAL FLUID SOLVENT-EFFECTS IN HETEROGENEOUS CATALYSIS.
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Comparative studies on fixed-bed catalytic isomerization of 1-hexene and disproportionation of 1,4-diisopropylbenzene were performed under liquid, gaseous or supercritical conditions. The kinetic measurements show that by variation of pressure in the different fluid states catalytic surface reactions as well as mass transfer effects between catalyst and fluid phase and/or transport processes inside porous catalysts can be influenced in a very sensitive way. Conclusions are drawn in view of new possibilities for the direction of yield and selectivity of multiple reactions, for the prolongation of catalyst lifetime, and the study of deactivation mechanisms on heterogeneous catalysts.
- Tiltscher,Wolf,Schelschshorn
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- Formation and Subsequent Reactivity of a N2-Stabilized Cobalt-Hydride Complex
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The reduced heterobimetallic Co/Zr complex N2Co(iPr2PNMes)3Zr(THF) (1) has been previously reported to react with the C=O bonds of CO2 and benzophenone to generate Zr/Co μ-oxo complexes OC-Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (1-CO2) and Ph2C=Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (1-Ph2CO), respectively. Herein, we report a similar reaction of 1 with pyridine-N-oxide to form an analogous complex (pyridine)Co(iPr2PNMes)2(-O)Zr(iPr2PNMes) (2) with a more labile ligand bound to cobalt. Much like 1-CO2 and 1-Ph2CO, compound 2 reacts with Ph3SiH via formation of a Si-O linkage to form (N2)(H)Co(iPr2PNMes)3ZrOSiPh3 (5). The dinitrogen ligand in 5 is weakly bound and can be readily removed in vacuo or displaced by other L-type ligands. This allows complex 5 to undergo insertion reactions with unsaturated substrates, including diphenyldiazomethane, CO2, benzonitrile, and phenylacetylene to give hydrazonato (Ph2C=NNH)Co(iPr2PNMes)3ZrOSiPh3 (7), formate (OC(H)O)Co(iPr2PNMes)3ZrOSiPh3 (8), ketimide (PhHC=N)Co(iPr2PNMes)3ZrOSiPh3 (9), and ylide Co(PhHC=CHPiPr2NMes)(iPr2PNMes)2ZrOSiPh3 (10) products, respectively. Compound 5 was also found to catalyze the isomerization of 1-hexene to internal isomers.
- Krogman, Jeremy P.,Foxman, Bruce M.,Thomas, Christine M.
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- METAL COMPLEXES IN THE CATALYTIC TRANSFORMATIONS OF OLEFINS. 5. CATALYTIC SYNTHESIS OF C9-C24 OLEFINS FROM PROPYLENE
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The optimum conditions for the production of C9-C24 olefins with yields of 20-25percent (remainder hexenes) by oligomerization of liquid propylene at the Ni(PPh3)n (n = 2-4)-Et3Al2Cl3 catalytic system were determined by simplex design of experiments.It was shown that the obtained hexenes undergo secondary di- and trimerization reactions.Key words: oligomers, propylene, triphenylphosphinenickel, triethylaluminum.
- Furman, D. B.,Ivanov, A. O.,Belyankin, A. Yu.,Pogorelov, A. G.,Yanchevskaya, T. V.,Bragin, O. V.
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- Microporous Heteropoly Compound as a Shape Selective Catalyst: Cs2.2H0.8PW12O40
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The pore size of acidic Cs salts (CsxH3-xPW12O40) was precisely controlled by the Cs content.Cs2.2H0.8PW12O40 possesses micropores in the range from 6.2 to 7.5 Angstroem (in diameter) and exhibits efficient shape selective catalysis toward decomposition of ester, dehydration of alcohol, and alkylation of aromatics in liquid-solid system.This is the first example of shape-selective solid superacid.
- Okuhara, Toshio,Nishimura, Toru,Misono, Makoto
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- A balancing act: Manipulating reactivity of shape-controlled metal nanocatalysts through bimetallic architecture
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Manipulating the electronic structure of metal nanocrystals is one way of altering their catalytic activities. This ability is demonstrated here by introducing a Au interior to shape-controlled Pd nanocrystals, producing core@shell Au@Pd nanoparticles with varying shell thicknesses. As revealed by X-ray photoelectron spectroscopy, the electronic structure of the Pd shell depends on its thickness. These core@shell nanocrystals were used to catalyze two model reactions: selective hydrogenation of 2-hexyne and oxidation of formic acid, where different reactivities were found also as a function of shell thickness. The comparison of particles with varying bimetallic architecture but identical geometric features provides insight into how electronic regulation in a catalytic reaction can be achieved. It is concluded that a balance in binding interaction between the molecular substrate and catalyst surface is necessary to design an efficient catalyst and can be achieved with shape-controlled core@shell nanocrystals.
- Laskar,Skrabalak
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- The catalytic effect of boron substitution in MCM-41-type molecular sieves
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A series of B-MCM-41 samples has been synthesized with a wide range of boron content (SiO2:B2O3 ratio from 20 to 200), using ethyl silicate ester-40 (ES-40) as the silica source and characterized by XRD, BET, FT-IR, 11B-MAS NMR, SEM, pyridine adsorption, TPDA, and chemical analysis. The interplanar d100 spacing varies from 40 to 45 A, depending on the Si:B ratio. On calcination, a significant amount of four-coordinated boron is converted into less stable three-coordinated boron, and some boron is removed from the framework. The degree of deboronation increases with an increase of boron content of the sample. The B substitution in the MCM-41 framework results in only weak and mild acid sites. The isomerization of 1-hexene is found to be influenced by the boron content in the framework. The isomerization leads to both a hydrogen shift and skeletal rearrangement. The selectivity ratios of cis-2-hexene to trans-2-hexene and 2-hexene to 3-hexene were found to decrease with an increase of temperature and a decrease of the SiO2:B2O3 ratio of the catalysts. Skeletal isomerization starts at 250°C, forming secondary products, and increases with an increase of temperature and an increase of boron content of the catalysts.
- Sundaramurthy,Eswaramoorthi,Lingappan
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- A high (Z)/(E) ratio obtained during the 3-hexyne hydrogenation with a catalyst based on a Rh(I) complex anchored on a carbonaceous support
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The (Z)/(E) ratio was analyzed for the 3-hexyne semi-hydrogenation at 275, 290 and 303 K. [RhCl(NH2(CH2)12CH 3)3] pure and supported on a carbonaceous material were used as catalysts. The supported complex showed high values of conversion and selectivity, and its behaviour was much better than the Lindlar catalyst used as a reference. Graphical abstract: Conversion to (Z)-3-hexene versus 3-hexyne total conversion as a function of temperature for: (1) Lindlar catalyst, (2) homogeneous complex and (3) anchored complex on RX3.[Figure not available: see fulltext.]
- Liprandi, Domingo A.,Cagnola, Edgardo A.,Paredes, Jose F.,Badano, Juan M.,Quiroga, Monica E.
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- Exohedral functionalization: Vs. core expansion of siliconoids with Group 9 metals: Catalytic activity in alkene isomerization
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Taking advantage of pendant tetrylene side-arms, stable unsaturated Si6 silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)2Cl]2 inserts into an endohedral Si-Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si6 benzpolarene motif. In the case of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) a similar Si-Si insertion leads to the contraction of the Si6 cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes.
- Giarrana, Luisa,Huch, Volker,Poitiers, Nadine E.,Scheschkewitz, David,Zimmer, Michael
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- Metallacarboranes in Catalysis. 8. I: Catalytic Hydrogenolysis of Alkenyl Acetates. II: Catalytic Alkene Isomerization and Hydrogenation Revisited
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Part I of this study describes the facile hydrogenolysis (and deuteriolysis) of alkenyl acetates, such as isopropenyl acetate (D) and 1-phenylvinyl acetate (E), with rhodacarborane catalyst precursors to yield acetic acid and the corresponding alkene.The catalyst precursors employed were (I), (II), and (III).The hydrogenolysis of alkenyl acetates D and E produced propene and styrene, respectively, along with acetic acid in essentially quantitativeyields.Deuterium at Rh was demonstrated not to enter the hydrogenolysis reaction.Use of D2 as the reducing agent with I and E resulted in the incorporation of deuterium into reactant E and products.Styrene produced in these reactions was predominantly d1 with appreciable quantities of d0 and d2.Ethylbenzene, a byproduct resulting from the hydrogenation of styrene, contained only traces of d0 species and was largely d1, d2, and d3.The acetic acid formed in these reactions was isotopically pure CH3COOD.The rate law for E hydrogenolysis with I contained no term showing hydrogen dependence.These results suggest a reaction mechanism for hydrogenolysis that is based upon the relatively slow formation and decomposition of a very reactive rhodium(III) monohydride formed through the regioselective oxidative addition of Rh(I) (in the exo-nido tautomer of the rhodacarborane) to terminal B-H bonds.The monohydride produced in this fashion then enters a cyclic heterolysis process with H2 which leads to rapid product formation.This mechanism suggests that slow B-D/C-H exchange should occur between I-d9 (B-D at all vertices of I) and anisotopically normal alkane, such as 1-hexene (B), during alkene isomerization.Such exchange was observed and shown to be regioselective.This new information predicated part II of this study, which is devoted to a modification of previously advanced proposals for the mechanisms of alkene isomerization and hydrogenation with rhodacarborane precursors.The facile and regioselective exchange of B-H in (IV) with D2 was examined and shown to be electrophilic in character and to apparently proceed through very reactive monohydride intermediates.These new data coupled with previously reported results allow the formulation of unified mechanisms for B-H/D2 and B-H/C-D exchange, alkenyl acetate hydrogenolysis, alkene isomerization, and alkene hydrogenation based upon the key B-Rh(III)-H species formed by the regioselective oxidative addition of terminal B-H bonds to Rh(I) centers.Thus, the effective catalytic sites in all of these reactions appear to be an array of B-Rh(III)-H centers formed reversibly from the Rh(I) present in exo-nido-rhodacarborane tautomers which are, in turn, in equilibrium ...
- Belmont, James A.,Soto, Jorge,King, Roswell E.,Donaldson, Andrew J.,Hewes, John D.,Hawthorne, M. Frederick
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- Komplexkatalyse XXIX. Kationische Allylbis(ligand)nickel(II)hexafluorophosphate PF6 und die Kombination /Et2AlCl als Katalysatoren fuer die Propendimerisation
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The cationic allylbis(ligand)nickel(II) complexes PF6 with L=P(OPh)3, P(OThym)3 and SbPh3 were found to be efficient catalysts for the oligomerization of propene under a l0 bar pressure of the monomer.The main products are dimers, and specifically the methylpentenes.The /Et2AlCl system catalyzes propene dimerization at atmospheric pressure with high activity, and selectivity similar to that of the cationic allylbis(ligand)nickel(II) complexes.In a kinetic analysis the rate law and the activation parameters ΔH and ΔS were determined for the propene dimerization with this catalytic system.
- Balbolov, Entscho,Mitkova, Magdalena,Kurtev, Kurty,Gehrke, Joerg-Peter,Taube, Rudolf
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- 1-Hexene isomerization over sulfated mesoporous Ta oxide: The effects of active site and confinement
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The isomerization of 1-hexene at 343 K was conducted over a series of sulfated mesoporous Ta oxides with pore sizes ranging from 12 to 30 A. The results were compared to the popular industrial catalysts HY-zeolite, H-ZSM5, and Amberlyst 15. The conversion of 1-hexene to trans/cis-2-isomers can reach 95.89% in 4 h, which is roughly 2 times faster than Amberlyst 15 and 20 times faster than HY-zeolite and H-ZSM5. GC analysis confirmed that trans- and cis-2-hexene isomers formed through a double bond shift process as the only two principal products. The molar ratio of trans/cis-2-hexene isomers varies with pore size, clearly showing confinement effects in this process. The selectivity of our best material toward the trans-isomer is at least 3 times greater than that of either zeolite or Amberlyst 15. The best catalytic results in this studywere achieved when using C12 H2SO4 mesoporous Ta oxide, which possesses a pKa of -8.2 and 19.8 mmol/g acid sites. The X-ray diffraction pattern showed complete retention of the mesostructure throughout catalysis as evidenced by a single broad reflection. Pyridine adsorption and infrared spectroscopy (IR) suggest that both Bronsted sites (1538 cm-1) and Lewis sites (~1443 cm-1) coexist on the surface of these materials. The large amount of Bronsted acid sites, high BET surface areas, high acid strength Ho, and superior diffusion properties of C12 H2SO4 mesoporous Ta oxide are probably responsible for its extremely high catalytic activity and selectivity. Copyright
- Rao, Yuxiang,Kang, Junjie,Antonelli, David
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- Alkylation of toluene with 1-hexene over macroreticular ion-exchange resins
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The macroreticular acidic ion-exchange resins Amberlyst 35, Amberlyst 46 and Purolite CT 275 were investigated as catalysts for the alkylation of toluene with 1-hexene and simultaneous dimerization and isomerization of the olefin at 373 K. After six hours
- Cadenas, Madelin,Bringué, Roger,Fité, Carles,Iborra, Montserrat,Ramírez, Eliana,Cunill, Fidel
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- Geometrically Constrained Cationic Low-Coordinate Tetrylenes: Highly Lewis Acidic σ-Donor Ligands in Catalytic Systems
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A novel non-innocent ligand class, namely cationic single-centre ambiphiles, is reported in the phosphine-functionalised cationic tetrylene Ni0 complexes, [PhRDippENi(PPh3)3]+ (4 a/b (Ge) and 5 (Sn); PhRDipp={[Ph2PCH2SiR2](Dipp)N}?; R=Ph, iPr; Dipp=2,6-iPr2C6H3). The inherent electronic nature of low-coordinate tetryliumylidenes, combined with the geometrically constrained [N?E?Ni] bending angle enforced by the chelating phosphine arm in these complexes, leads to strongly electrophilic EII centres which readily bind nucleophiles, reversibly in the case of NH3. Further, the GeII centre in 4 a/b readily abstracts the fluoride ion from [SbF6]? to form the fluoro-germylene complex PhRDippGe(F)Ni(PPh3)3 9, despite this GeII centre simultaneously being a σ-donating ligand towards Ni0. Alongside the observed catalytic ability of 4 and 5 in the hydrosilylation of alkynes and alkenes, this forms an exciting introduction to a multi-talented ligand class in cationic single-centre ambiphiles.
- Keil, Philip M.,Hadlington, Terrance J.
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supporting information
(2022/01/13)
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- Allylnickel(II) complexes of bulky 5-substituted-2-iminopyrrolyl ligands
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The optimized reaction between [Ni(COD)2] (COD = 1,5-cyclooctadiene) and ligand precursor 5-(2,4,6-triisopropylphenyl)-2-[N-(2,6-diisopropylphenyl)-formimino]-1H-pyrrole yielded the η3-cyclooctenyl-Ni(II) complex [Ni{κ2N,N’-5-(2,4,6-iPr3C6H2)-NC4H2-2-C(H) = N(2,6-iPr2C6H3)}(η3-C8H13)] 1. Subsequently, the η3-allyl complexes [Ni{κ2N,N’-5-R-NC4H2-2-C(H)=N(2,6-iPr2C6H3)}(η3-C3H5)] (R = 3,5-(CF3)2C6H3 (2a), 2,6-Me2C6H3 (2b), 2,4,6-iPr3C6H2 (2c) and CPh3 (2d)) were prepared in good yields via metathesis of [Ni(η3-C3H5)(μ-Br)]2 with the respective potassium 5-R-2-[N-(2,6-diisopropylphenyl)formimino]pyrrolyl salt (KLa-d). Complexes 1 and 2a-d were characterized by NMR spectroscopy, elemental analysis and complex 2d further analyzed by single crystal X-ray diffraction. Addition of excess pyridine to solutions of complexes 2a-d led to the observation of a fluxional process that, according to VT-NMR experiments, corresponds to a pyridine-assisted cis–trans isomerization process occurring in these complexes, via a η3-η1-η3 haptotropic shift of the allyl ligand, with ΔG? values in range of 9.5–17.3 kcal mol?1. Additionally, complexes 2a-d, when activated by B(C6F5)3, slowly catalyzed the isomerization of hex-1-ene to mixtures of internal olefins.
- Cruz, Tiago F. C.,Gomes, Pedro T.,Lopes, Patrícia S.
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- Designing and synthesis of phosphine derivatives of Ru3(CO)12 – Studies on catalytic isomerization of 1-alkenes
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A comparative investigation on the isomerization reactions of 1-alkenes to their corresponding 2-alkenes catalyzed Ru3(CO)12 (1), Ru3(CO)9(PEt3)3 (2) and Ru3(CO)10(dppe) (3), (where dppe = 1,2-bis(diphenylphosphino)ethane) is described. Both the complexes of types 2 and 3 were characterized by all analytical and spectroscopic data. The molecular structure of 2 was confirmed by single-crystal X-ray analysis. It is observed that the nature of phosphine ligands plays an important role in the isomerization of 1-alkenes. When the chelated diphosphine is used, the internal isomerization reaction by [Ru3(CO)10(dppe)] (3) is completed relatively in less time compared to other derivatives. As per the DFT calculations, the observed reaction rate for the alkene isomerization may be explained based on the relative stability of 1, 2, and 3. The CO abstraction step is highly feasible in 3, the least stable among the three, thus the reaction occurs at the highest rate. Due to the increased relative stability from 2 to 1, the reaction requires more time at elevated temperatures and the rate decreases as a consequence.
- Pandya, Chayan,Panicker, Rakesh R.,Senjaliya, Parth,Hareendran, M.K. Hima,Anju,Sarkar, Sibasis,Bhat, Haamid,Jha, Prakash C.,Rao, Koya Prabhakara,Smith, Gregory S.,Sivaramakrishna, Akella
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- Immobilized Platinum Hydride Species as Catalysts for Olefin Isomerizations and Enyne Cycloisomerizations
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Platinum hydride species catalyze a number of interesting organic reactions. However, their reactions typically involve the use of high loadings of noble metal and are difficult to recycle, making them somewhat unsustainable. We have synthesized surface-immobilized Pt-H species via oxidative addition of surface OH groups to Pt(PtBu3)2 (1), a rarely used immobilization technique in surface organometallic chemistry. The hydride species thus made were characterized by infrared, magic-angle spinning nuclear magnetic resonance, and X-ray absorption spectroscopies and catalyzed both olefin isomerization and cycloisomerization of a 1,6 enyne (5) with a high selectivity and low Pt loading.
- Bauer, Matthias,Cronin, Steve P.,Dyballa, Michael,Estes, Deven P.,Li, Zheng,Maier, Sarah,Nowakowski, Michal,Vu Dinh, Manh-Anh
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supporting information
p. 1751 - 1757
(2021/06/28)
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- Comparative Study of Homogeneous and Silica Immobilized N^N and N^O Palladium(II) Complexes as Catalysts for Hydrogenation of Alkenes, Alkynes and Functionalized Benzenes
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Abstract: This work reports the use of homogeneous and silica immobilized palladium(II) complexes of ligands (2-phenyl-2-((3(triethoxysilyl)propyl)imino)ethanol) (L1), (4-methyl-2-((3(triethoxysilyl)propyl)imino)methyl)phenol) (L2), [L1-MCM-41] (L1im), and [L2-MCM-41] (L2im) as catalysts in molecular hydrogenation of alkenes, alkynes and functionalized benzenes. The homogeneous complexes [Pd(L1)2] (Pd1), [Pd(L2)2] (Pd2), [Pd(L1)(Cl2)] (Pd3),?and [Pd(L2)(Cl2)] (Pd4), and their respective silica immobilized?complexes [Pd(L1)2]-MCM-41] (Pd1im), [Pd(L2)2)-MCM-4] (Pd2im), [Pd (L1)(Cl2)-MCM-41] (Pd3im) and [Pd(L2)(Cl2)]-MCM-41] (Pd4im) formed active catalysts in?the molecular hydrogenation of these substrates. The catalytic activities and product distribution in these reactions were largely dictated by the nature of the substrate. The kinetic studies revealed a pseudo-first order dependence on styrene substrate for both the homogeneous and immobilized catalysts. Significantly, the selectivity of both homogeneous and immobilized catalysts were comparable in the hydrogenation of both?alkynes and multi-functionalized benzenes. The supported catalysts could be recycled up to four times with minimum loss of catalytic activity and showed absence of any leaching from hot filtration experiments. Kinetics and poisoning studies established that complexes Pd1–Pd4 were largely homogeneous in nature, while the immobilized complexes Pd1im–Pd4im formed Pd(0) nanoparticles as the main active species. Graphic Abstract: [Figure not available: see fulltext.].
- Akiri, Saphan O.,Ngcobo, Nondumiso L.,Ojwach, Stephen O.
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p. 2850 - 2862
(2020/03/30)
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- Bis(phosphine)hydridorhodacarborane Derivatives of 1,1′-Bis(ortho-carborane) and Their Catalysis of Alkene Isomerization and the Hydrosilylation of Acetophenone
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Deprotonation of [7-(1′-closo-1′,2′-C2B10H11)-nido-7,8-C2B9H11]- and reaction with [Rh(PPh3)3Cl] results in isomerization of the metalated cage and the formation of [8-(1′-closo-1′,2′-C2B10H11)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (1). Similarly, deprotonation/metalation of [8′-(7-nido-7,8-C2B9H11)-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10]- and [8′-(7-nido-7,8-C2B9H11)-2′-Cp*-closo-2′,1′,8′-CoC2B9H10]- affords [8-{8′-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10}-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (2) and [8-(8′-2′-Cp*-closo-2′,1′,8′-CoC2B9H10)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (3), respectively, as diastereoisomeric mixtures. The performances of compounds 1-3 as catalysts in the isomerization of 1-hexene and in the hydrosilylation of acetophenone are compared with those of the known single-cage species [3-H-3,3-(PPh3)2-closo-3,1,2-RhC2B9H11] (I) and [2-H-2,2-(PPh3)2-closo-2,1,12-RhC2B9H11] (V), the last two compounds also being the subjects of 103Rh NMR spectroscopic studies, the first such investigations of rhodacarboranes. In alkene isomerization all the 2,1,8-or 2,1,12-RhC2B9 species (1-3, V) outperform the 3,1,2-RhC2B9 compound I, while for hydrosilylation the single-cage compounds I and V are better catalysts than the double-cage species 1-3.
- Chan, Antony P. Y.,Parkinson, John A.,Rosair, Georgina M.,Welch, Alan J.
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supporting information
(2020/02/04)
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- Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance
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A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.
- Lutz, Sean A.,Hickey, Anne K.,Gao, Yafei,Chen, Chun-Hsing,Smith, Jeremy M.
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supporting information
p. 15527 - 15535
(2020/10/20)
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- Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates
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We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes (1 a: (S)-BINAP; 1 b: (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex (1 c: (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]2 and [Rh(cod)2]+[BF4]? upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.
- Higashida, Kosuke,Brüning, Fabian,Tsujimoto, Nagataka,Higashihara, Kenya,Nagae, Haruki,Togni, Antonio,Mashima, Kazushi
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p. 8749 - 8759
(2020/07/04)
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- NNNO-Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins
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The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et2AlCl, Et3Al2Cl3, EtAlCl2, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg·mol (Ni)?1·h?1·atm?1) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh3 as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)?1·h?1·atm?1 and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl2 produce up to 5 mol. percent of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β-alkyl elimination.
- Zubkevich, Sergey V.,Tuskaev, Vladislav A.,Gagieva, Svetlana Ch.,Kayda, Anatoliy S.,Khrustalev, Victor N.,Pavlov, Alexander A.,Zarubin, Dmitry N.,Bulychev, Boris M.
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- Dynamic ?-Bonding of Imidazolyl Substituent in a Formally 16-Electron Cp Ru(2-P, N)+ Catalyst Allows Dramatic Rate Increases in (E)-Selective Monoisomerization of Alkenes
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Alkene isomerization can be an atom-economical approach to generating a wide range of alkene intermediates for synthesis, but fully equilibrated mixtures of disubstituted internal alkenes typically contain significant amounts of the positional as well as geometric (E and Z) isomers. Most classical catalyst systems for alkene isomerization struggle to kinetically control either positional or E/Z isomerism. We report coordinatively unsaturated, formally 16-electron Cp Ru catalyst 5, which facilitates simultaneous regio- A nd stereoselective isomerization of linear 1-alkenes to their internal analogues, providing consistent yields of (E)-2-alkenes greater than 95%. Because nitrile-free catalyst 5 is more than 400 times faster than previously published nitrile-containing analogues 2 + 2a, very reasonable 0.1-0.5 mol % loadings of 5 complete ambient-temperature reactions within 15 min to 4 h. UV-vis, NMR, and computational studies depict the imidazolyl fragment on the phosphine as a hemilabile, four-electron donor in 2-P,N coordination. For the first time, we show direct experimental evidence that the PN ligand has accepted a proton from the substrate by characterizing the intermediate Cp Ru[??3-allyl][1-P)P-N+H], which highlights the essential role of the bifunctional ligand in promoting rapid and selective alkene isomerizations. Moreover, kinetic studies and computations reveal the role of alkene binding in selectivity of unsaturated catalyst 5.
- Paulson, Erik R.,Moore, Curtis E.,Rheingold, Arnold L.,Pullman, David P.,Sindewald, Ryan W.,Cooksy, Andrew L.,Grotjahn, Douglas B.
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p. 7217 - 7231
(2019/08/27)
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- Potassium Yttrium Ate Complexes: Synergistic Effect Enabled Reversible H2 Activation and Catalytic Hydrogenation
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A potassium yttrium benzyl ate complex was generated simply by mixing an yttrium amide and potassium benzyl. The benzyl ate complex could undergo peripheral deprotonation to produce a cyclometalated complex or hydrogenation to give a hydride ate complex. The latter hydride ate complex features a (KH)2 structure protected by two yttrium amide complexes. The synergistic effect between potassium hydride and the amide ligand enables the complex to deprotonate a methyl C-H bond. The combination of intramolecular deprotonation of the hydride ate complex and hydrogenation of the cyclometalated complex constitutes a reversible H2 activation process. Using this process involving formal addition and elimination of H2, we accomplished the catalytic hydrogenation of alkenes, alkynes, and imines.
- Zhai, Dan-Dan,Du, Hui-Zhen,Zhang, Xiang-Yu,Liu, Yu-Feng,Guan, Bing-Tao
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p. 8766 - 8771
(2019/09/30)
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- Selective hydrothermal reductions using geomimicry
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Reduction of carbon-carbon π-bonds has been demonstrated using iron powder as the reductant and simple powdered nickel as the catalyst in water as the solvent at 250 °C and the saturated water vapor pressure, 40 bars. Stereochemical, kinetic and electronic probes of the mechanism suggest reaction via a conventional Horiuti-Polyani process for hydrogenation at the nickel metal surface. Selective reduction of carbon-carbon π-bonds is observed in the presence of other functional groups. The reactions use benign and Earth-abundant reagents that are at low depletion risk and take place in water as the only solvent under conditions that are characteristic of many geochemical processes.
- Bockisch, Christiana,Lorance, Edward D.,Shaver, Garrett,Williams, Lynda B.,Hartnett, Hilairy E.,Shock, Everett L.,Gould, Ian R.
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p. 4159 - 4168
(2019/08/07)
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- Nickel(II) complexes with tripodal NNN ligands as homogenous and supported catalysts for ethylene oligomerization
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Four new coordination compounds of nickel (II) with derivatives of N,N-bis(pyrazol-1-ylmethyl)propylamine were synthesized; their composition and structure were confirmed with IR-spectroscopy and elemental analysis. The structures of products 13 and 15 were unambiguously established in an X-ray diffraction study. Compounds 13 and 15 crystallize in the orthorhombic space groups Pna21 and P212121 correspondingly and represent a monomeric octahedral nickel complexes, that are typical for tridentate scorpion-type ligands. New method for immobilization of nickel complexes with derivatives of N,N-bis(pyrazol-1-ylmethyl)propylamine on silica gel modified with aminopropyl groups was proposed. The EXAFS/XANES analysis indicated that Ni atom in the supported complexes adopt almost octahedral geometry, being partly surrounded by nitrogen atoms from organic ligand and partly grafted to silica surface through silanol groups, with Br? in outer coordination sphere. Both the original and the supported complexes, when activated with Et2AlCl or Et3Al2Cl3, catalyze ethylene oligomerization with the predominant formation of butene isomers. Generally, the immobilized complexes show higher activity and better selectivity towards 1-butene formation.
- Tuskaev, Vladislav A.,Zubkevich, Sergei V.,Saracheno, Daniele,Gagieva, Svetlana Ch.,Dorovatovskii, Pavel V.,Kononova, Elena G.,Khrustalev, Victor N.,Zarubin, Dmitry N.,Bulychev, Boris M.,Kissin, Yury V.
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- Catalyst versus Substrate Control of Forming (E)-2-Alkenes from 1-Alkenes Using Bifunctional Ruthenium Catalysts
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Here we examine in detail two catalysts for their ability to selectively convert 1-alkenes to (E)-2-alkenes while limiting overisomerization to 3- or 4-alkenes. Catalysts 1 and 3 are composed of the cations CpRu(κ2-PN)(CH3CN)+ and Cp?Ru(κ2-PN)+, respectively (where PN is a bifunctional phosphine ligand), and the anion PF6-. Kinetic modeling of the reactions of six substrates with 1 and 3 generated first- and second-order rate constants k1 and k2 (and k3 when applicable) that represent the rates of reaction for conversion of 1-alkene to (E)-2-alkene (k1), (E)-2-alkene to (E)-3-alkene (k2), and so on. The k1:k2 ratios were calculated to produce a measure of selectivity for each catalyst toward monoisomerization with each substrate. The k1:k2 values for 1 with the six substrates range from 32 to 132. The k1:k2 values for 3 are significantly more substrate-dependent, ranging from 192 to 62 000 for all of the substrates except 5-hexen-2-one, for which the k1:k2 value was only 4.7. Comparison of the ratios for 1 and 3 for each substrate shows a 6-12-fold greater selectivity using 3 on the three linear substrates as well as a >230-fold increase for 5-methylhex-1-ene and a 44-fold increase for a silyl-protected 4-penten-1-ol substrate, which are branched three and five atoms away from the alkene, respectively. The substrate 5-hexen-2-one is unique in that 1 was more selective than 3; NMR analysis suggested that chelation of the carbonyl oxygen can facilitate overisomerization. This work highlights the need for catalyst developers to report results for catalyzed reactions at different time points and shows that one needs to consider not only the catalyst rate but also the duration over which a desired product (here the (E)-2-alkene) remains intact, where 3 is generally superior to 1 for the title reaction.
- Paulson, Erik R.,Delgado, Esteban,Cooksy, Andrew L.,Grotjahn, Douglas B.
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supporting information
p. 1672 - 1682
(2019/01/04)
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- Kinetics and chemoselectivity studies of hydrogenation reactions of alkenes and alkynes catalyzed by (benzoimidazol-2-ylmethyl)amine palladium(II) complexes
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A series of (benzoimidazol-2-ylmethyl)amine palladium(II) complexes have been employed as catalysts in the homogeneous hydrogenation of alkenes and alkynes under mild conditions. A correlation between the catalytic activity and the nature of the ligand was established. Kinetic studies of the hydrogenation reactions of styrene established pseudo-first-order dependence on styrene substrate. On the other hand, partial orders with respect to H2 and catalyst concentrations were obtained. The nature of the solvent used influenced the hydrogenation reactions, where coordinating solvents resulted in lower catalytic activities. Kinetics and mechanistic studies performed were consistent with the formation of palladium monohydride intermediates as the active species.
- Tshabalala, Thandeka A.,Ojwach, Stephen O.
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supporting information
p. 148 - 155
(2018/08/23)
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- Selective Isomerization of Terminal Alkenes to (Z)-2-Alkenes Catalyzed by an Air-Stable Molybdenum(0) Complex
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Positional and stereochemical selectivity in the isomerization of terminal alkenes to internal alkenes is observed using the cis-Mo(CO)4(PPh3)2 precatalyst. A p-toluenesulfonic acid (TsOH) cocatalyst is essential for catalyst activity. Various functionalized terminal alkenes have been converted to the corresponding 2-alkenes, generally favoring the Z isomer with selectivity as high as 8:1 Z:E at high conversion. Interrogation of the catalyst initiation mechanism by 31P NMR reveals that cis-Mo(CO)4(PPh3)2 reacts with TsOH at elevated temperatures to yield a phosphine-ligated Mo hydride (MoH) species. Catalysis may proceed via 2,1-insertion of a terminal alkene into a MoH group and stereoselective β-hydride elimination to yield the (Z)-2-alkene.
- Becica, Joseph,Glaze, Owen D.,Wozniak, Derek I.,Dobereiner, Graham E.
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p. 482 - 490
(2018/02/17)
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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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- An Ion-Responsive Pincer-Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization
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Rapid, selective, and highly controllable iridium-catalyzed allylbenzene isomerization is described, enabled by tunable hemilability based on alkali metal cation binding with a macrocyclic “pincer-crown ether” ligand. An inactive chloride-ligated complex can be activated by halide abstraction with sodium salts, with the resulting catalyst [κ5-(15c5NCOPiPr)Ir(H)]+ exhibiting modest activity. Addition of Li+ provides a further boost in activity, with up to 1000-fold rate enhancement. Ethers and chloride salts dampen or turn off reactivity, leading to three distinct catalyst states with activity spanning several orders of magnitude. Mechanistic studies suggest that the large rate enhancement and high degree of tunability stem from control over substrate binding.
- Kita, Matthew R.,Miller, Alexander J. M.
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supporting information
p. 5498 - 5502
(2017/05/05)
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- CATALYSTS AND CATALYTIC PROCESSES
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A process for migrating C=C double bonds within an unsaturated organic compound is described. The process involves contacting an unsaturated organic compound starting material with a heteropoly acid catalyst in the presence of light having a wavelength of less than or equal to 700 nm. Also described is a process for the preparation of novel heteropoly acids having markedly increased surface area.
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Page/Page column 18
(2017/05/28)
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- Influence of increasing steric demand on isomerization of terminal alkenes catalyzed by bifunctional ruthenium complexes
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Preparation of a series of cyclopentadienyl- and imidazolyl-phosphine-containing Ru-based complexes bearing a different degree of the Cp-ring methylation has been attempted. According to experimental and structural data the steric factors prevented the formation of the last complex in the series that contains permethylated Cp ring. These complexes were then subjected to alkene isomerization using 1-hexene. The rate of isomerization decreased, in general, with the increase in the Cp-ring methylation suggesting that the initial alkene coordination and/or imidazolyl N decoordination steps are restricted in the overall mechanism.
- Smarun, Alexey V.,Shahreel, Wahyu,Pramono, Steven,Koo, Shin Yi,Tan, Lai Yoong,Ganguly, Rakesh,Vidovi?, Dragoslav
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- Terminal alkene monoisomerization catalysts and methods
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The invention provides novel catalysts and methods of using catalysts for controlling the position of a double bond and cis/trans-selectivity in isomerization of terminal alkenes to their 2-isomers. Catalysts such as (pentamethylcyclopentadienyl)Ru formulas 1 and 3 having a bifunctional phosphine can be used in the methods. A catalyst loading of 1 mol % of formulas 1+3 can be employed for the production of (E)-2-alkenes at 40-70° C.; lower temperatures can be used with higher catalyst loading. Acetonitrile-free catalysts can be used at lower loadings, room temperature, and in less than a day to accomplish the same results as catalysts 1+3. The novel catalyst systems minimize thermodynamic equilibration of alkene isomers, so that the trans-2-alkenes of both non-functionalized and functionalized alkenes can be generated.
- -
-
Page/Page column 49; 50
(2017/08/07)
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- Designing bifunctional alkene isomerization catalysts using predictive modelling
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Controlling the isomerization of alkenes is important for the manufacturing of fuel additives, fine-chemicals and pharmaceuticals. But even if isomerization seems to be a simple unimolecular process, the factors that govern catalyst performance are far from clear. Here we present a set of models that describe selectivity and activity, enabling the rational design and synthesis of alkene isomerization catalysts. The models are based on simple molecular descriptors, with a low computational cost, and are tested and validated on a set of eleven known Ru-imidazol-phosphine complexes and two new ones. Despite their simplicity, these models show good predictive power, with R2 values of 0.60-0.85. Using a combination of principal components analysis (PCA) and partial least squares (PLS) regression, we construct a "catalyst map", that captures trends in reactivity and selectivity as a function of electrostatic charge on the N? atom, EHOMO, polar surface area and the optimal mass substituents on P/distance Ru-P ratio. In addition to indicating "good regions" in the catalyst space, these models also give insight into mechanistic steps. For example, we find that the electrostatic charge on N?, EHOMO and polar surface area are crucial in the rate-limiting step, whereas the optimal mass of substituents on P/distance Ru-P is correlated with the product selectivity.
- Landman, Iris R.,Paulson, Erik R.,Rheingold, Arnold L.,Grotjahn, Douglas B.,Rothenberg, Gadi
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p. 4842 - 4851
(2017/10/23)
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- Rhodium(III) Catalyzed Solvent-Free Tandem Isomerization–Hydrosilylation From Internal Alkenes to Linear Silanes
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The selective synthesis of linear silanes from internal alkenes or alkene mixtures is reported. Unsaturated 16 electrons hydrido–silyl–RhIII complexes are efficient catalysts for a tandem catalytic alkene isomerization–hydrosilylation reaction at room temperature under solvent-free conditions. Such a process would be of value to the chemical industry, as mixtures of internal aliphatic olefins are substantially cheaper and more readily available than the pure terminal isomers.
- Azpeitia, Susan,Garralda, María A.,Huertos, Miguel A.
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p. 1901 - 1905
(2017/06/13)
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- Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene
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Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals.
- Witt, Timo,H?u?ler, Manuel,Kulpa, Stefanie,Mecking, Stefan
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supporting information
p. 7589 - 7594
(2017/06/13)
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- Alkene Isomerization by “Sandwich” Diimine-Palladium Catalysts
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In contrast to traditional diimine-palladium complexes, sterically hindered “sandwich” diimine-palladium adducts act as olefin isomerization catalysts. Terminal olefins are selectively converted to 2-olefins by a sequence of migratory insertion, β-hydride elimination, and olefin displacement. The reaction is performed at 0 °C with 1 mol % of an air-stable precatalyst and tolerates functional groups such as ketones, silyl ethers, and halogens. The isomerization may be used to produce silyl enol ethers from protected allylic alcohols.
- Kocen, Andrew L.,Klimovica, Kristine,Brookhart, Maurice,Daugulis, Olafs
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supporting information
p. 787 - 790
(2017/04/21)
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- Regio- and Chemoselective Hydrogenation of Dienes to Monoenes Governed by a Well-Structured Bimetallic Surface
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Unprecedented surface chemistry, governed by specific atomic arrangements and the steric effect of ordered alloys, is reported. Rh-based ordered alloys supported on SiO2 (RhxMy/SiO2, M = Bi, Cu, Fe, Ga, In, Pb, Sn, and Zn) were prepared and tested as catalysts for selective hydrogenation of trans-1,4-hexadiene to trans-2-hexene. RhBi/SiO2 exhibited excellent regioselectivity for the terminal C=C bond and chemoselective hydrogenation to the monoene, not to the overhydrogenated alkane, resulting in a high trans-2-hexene yield. Various asymmetric dienes, including terpenoids, were converted into the corresponding inner monoenes in high yields. This is the first example of a regio- and chemoselective hydrogenation of dienes using heterogeneous catalysts. Kinetic studies and density functional theory calculations revealed the origin of the high selectivity: (1) one-dimensionally aligned Rh arrays geometrically limit hydrogen diffusion and attack to alkenyl carbons from one direction and (2) adsorption of the inner C=C moiety to Rh is inhibited by steric repulsion from the large Bi atoms. The combination of these effects preferentially hydrogenates the terminal C=C bond and prevents overhydrogenation to the alkane.
- Miyazaki, Masayoshi,Furukawa, Shinya,Komatsu, Takayuki
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supporting information
p. 18231 - 18239
(2017/12/27)
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- Alkanethiolate-capped palladium nanoparticles for selective catalytic hydrogenation of dienes and trienes
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Selective hydrogenation of dienes and trienes is an important process in the pharmaceutical and chemical industries. Our group previously reported that the thiosulfate protocol using a sodium S-alkylthiosulfate ligand could generate catalytically active Pd nanoparticles (PdNP) capped with a lower density of alkanethiolate ligands. This homogeneously soluble PdNP catalyst offers several advantages such as little contamination via Pd leaching and easy separation and recycling. In addition, the high activity of PdNP allows the reactions to be completed under mild conditions, at room temperature and atmospheric pressure. Herein, a PdNP catalyst capped with octanethiolate ligands (C8 PdNP) is investigated for the selective hydrogenation of conjugated dienes into monoenes. The strong influence of the thiolate ligands on the chemical and electronic properties of the Pd surface is confirmed by mechanistic studies and highly selective catalysis results. The studies also suggest two major routes for the conjugated diene hydrogenation: the 1,2-addition and 1,4-addition of hydrogen. The selectivity between two mono-hydrogenation products is controlled by the steric interaction of substrates and the thermodynamic stability of products. The catalytic hydrogenation of trienes also results in the almost quantitative formation of mono-hydrogenation products, the isolated dienes, from both ocimene and myrcene.
- Chen, Ting-An,Shon, Young-Seok
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p. 4823 - 4829
(2017/10/19)
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- Polymer-modified supported palladium catalysts for the hydrogenation of acetylene compounds
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Palladium catalysts supported on zinc oxide modified with polyethylene glycol or pectin were synthesized and investigated in the hydrogenation of acetylene compounds. It was established that the polymercontaining catalysts reduce acetylene hyrbons to olefins with high activity, selectivity, and stability. The composition and structure of the obtained composites were studied by elemental analysis, transmission electron microscopy, and XPS spectroscopy. It was found that the nanosized particles of palladium uniformly immobilized on the surface of zinc oxide were formed in the course of the synthesis of a supported polymer/oxide complex.
- Zharmagambetova,Seitkalieva,Talgatov,Auezkhanova,Dzhardimalieva,Pomogailo
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p. 360 - 367
(2016/07/06)
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- (Pyridyl)benzoazole palladium(II) complexes as homogeneous catalysts in hydrogenation of alkenes and alkynes
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Reactions of 2-(2-pyridyl)benzimidazole (L1), 2-(2-pyridyl)benzothiazole (L2) and 2-(2-pyridyl)benzoxazole (L3) with either [PdCl2(NCMe)2] or [PdClMe(COD)] produced complexes [(PdCl2(L1)] (1), [(PdCl2(L2)] (2), [(PdCl2(L3)] (3) and [(PdClMe(L1)] (4) in good yields. Treatment of 1 with PPh3 gave the cationic complex [(Pd(L1)ClPPh3]Cl (5), while reactions of 4 with one equiv. of PPh3 and NaBAr4 (Ar = 3,5-(CF3)2C6H3) produced the cationic complex [(Pd(L1)MePPh3]BAr4 (6). Single-crystal X-ray analysis has been used to elucidate the structure of complex 6. The complexes formed active catalysts in hydrogenation reactions of alkenes and alkynes. Hydrogenation of terminal alkenes was accompanied by isomerization to the internal isomers, while alkyne reactions involved a two-step process producing alkenes and the respective alkanes. While the kinetics data and formation of inactive palladium nanoparticles support the homogeneous nature of the active species, mercury drop experiments indicated a possible role of the nanoparticles in the re-generation of the active species.
- Ojwach, Stephen O.,Ogweno, Aloice O.,Akerman, Matthew P.
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p. 5069 - 5078
(2016/07/07)
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- Neutral and cationic (pyrazolylmethyl)pyridine palladium(II) complexes: kinetics and chemoselectivity studies in hydrogenation of alkenes and alkynes
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Reactions of (3,5-dimethylpyrazolylmethyl)pyridine (L1) and (3,5-diphenylpyrazolylmethyl)pyridine (L2) with either [PdCl2(NCMe)2] or [PdClMe(COD)] afforded the respective neutral palladium complexes, [PdCl2(L1)] (1), [PdCl2(L2)] (2) and [PdClMe(L1)] (3). Treatment of complex 1 with equimolar amounts of PPh3 or PPh3/NaBAr4 produced the corresponding cationic complexes [Pd(L1)ClPPh3]Cl (4) and [Pd(L1)ClPPh3]BAr4 (5), respectively. Complexes 1–5 formed active catalysts in hydrogenation of alkenes and alkynes. Isomerization reactions were predominant in the hydrogenation reactions of terminal alkenes, while hydrogenation of alkynes involved a two-step process via alkene intermediates prior to the formation of the respective alkenes. The lack of induction periods in the hydrogenation reactions in addition to pseudo-first-order kinetics with respect to the substrates established the homogeneous nature of the active species.
- Ojwach, Stephen O.,Ogweno, Aloice O.
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p. 539 - 546
(2016/07/20)
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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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- Synthesis, characterization, and reactivities of molybdenum and tungsten PONOP pincer complexes
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A new series of molybdenum and tungsten tricarbonyl pincer complexes, bearing pyridine-based PONOP-type pincer ligands, have been synthesized and fully characterized. Addition of HBF4·Et2O to these tricarbonyl complexes generated seven-coordinate molybdenum and tungsten hydride complexes, and these compounds have been isolated in good yields. These metal hydrides show fluxional behavior in solution. The hydride ligands on these metal complexes are acidic in nature and are readily deprotonated by bases. The molybdenum hydride complex is shown to catalyze isomerization of 1-hexene to internal isomers under mild conditions.
- Castro-Rodrigo, Ruth,Chakraborty, Sumit,Munjanja, Lloyd,Brennessel, William W.,Jones, William D.
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p. 3124 - 3131
(2016/10/09)
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- Molybdenum and Tungsten Alkylidene Complexes That Contain a 2-Pyridyl-Substituted Phenoxide Ligand
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In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (~150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3C6H2 (Trip) in the other ortho position ([MesON]- or [TripON]-, respectively). The alkylidene (neophylidene) complexes that were prepared include W(O)(CHCMe2Ph)(Me2Pyr)(RON) (R = Mes or Trip), Mo(NC6F5)(CHCMe2Ph)(RON)Cl, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(RON)Cl, Mo(N-t-Bu)(CHCMe2Ph)(RON)Cl, and M(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(TripON)(OTf) (M = Mo or W). The reaction between Mo(NAr)(CHCMe2Ph)(TripON)(OTf) and ethylene yielded an ethylene complex, Mo(NAr)(C2H4)(TripON)(OTf)(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W(O)(CHCMe2Ph)(Me2Pyr)(MesON) also stereoselectively polymerized several substituted norbornadienes at 100 °C.
- Sues, Peter E.,John, Jeremy M.,Bukhryakov, Konstantin V.,Schrock, Richard R.,Müller, Peter
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supporting information
p. 3587 - 3593
(2016/11/06)
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- 2-iminopyridine nickel(II) complexes bearing electron-withdrawing groups in the ligand core: Synthesis, characterization, ethylene oligo- and polymerization behavior
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A series of novel 2-[(arylimino)alkyl]pyridine derivatives, containing electron-withdrawing groups (F, Cl, Br, CF3, NO2, CN) in the aryl rings, have been synthesized and characterized by1H,13C and19F NMR spectroscopy. The corresponding nickel(II) complexes (24 complexes) have been prepared in good yields. The nature of the Ni complexes has been established by elemental analysis, paramagnetic1H NMR and X-ray diffraction studies. Those complexes, activated with MAO, have been found to be highly active in the oligomerization and polymerization of ethylene (up to 9600?kg (mol of Ni)?1?h?1?bar?1), affording highly branched low-MW PE or ethylene oligomers, predominantly butenes and hexenes. The dependence of content and ratio of ethylene oligomers as well as of the polymer characteristics (molecular weight, degree of branching) on the nature of the substituents in the aryl(imino) and pyridine rings has been analyzed systematically. (E)-N-(1-(pyridin-2-yl)ethylidene)-2-(trifluoromethyl)aniline Ni complex supported on silica-alumina affords polyethylene with higher molecular weights, broader molecular weight distribution, and lower level of branching than the homogeneous catalyst.
- Antonov, Artem A.,Semikolenova, Nina V.,Talsi, Evgenii P.,Matsko, Mikhail A.,Zakharov, Vladimir A.,Bryliakov, Konstantin P.
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p. 241 - 249
(2016/09/19)
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- N-Phosphanyl- and N,N′-Diphosphanyl-Substituted N-Heterocyclic Carbene Chromium Complexes: Synthesis, Structures, and Catalytic Ethylene Oligomerization
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The chromium(II) complexes [CrCl2(t-BuNHC,P-κC)2] (1), [CrCl2(MesNHC,P-κC)2] (2), [CrCl2(DippNHC,P-κC)2] (3), and [CrCl2(P,NHC,P-κC)2] (4) containing the N-phosphanyl- or N,N′-diphosphanyl-substituted N-heterocyclic carbene (NHC) hybrid ligands t-BuNHC,P (1-(di-tert-butylphosphino)-3-tert-butylimidazol-2-ylidene), MesNHC,P (1-(di-tert-butylphosphino)-3-mesitylimidazol-2-ylidene), DippNHC,P (1-(di-tert-butylphosphino)-3-(2,6-diisopropylphenyl)imidazol-2-ylidene), and P,NHC,P (1,3-bis(di-tert-butylphosphino)imidazol-2-ylidene), respectively, were prepared from CrII ([CrCl2(thf)2]) or CrIII ([CrCl3(thf)3] or [Cr(Me)Cl2(thf)3]) precursors. The solid-state structures of these four complexes show square-planar CrII centers, with two trans chloride and two monodentate CNHC donors. Alkylation of 3 and 4 with [Mg(benzyl)2(thf)2] led to the formation of the σ complexes [Cr(benzyl)3(DippNHC,P-κC,κP)] (5) and [Cr(benzyl)3(P,NHC,P-κC,κP)] (6), respectively, with five-coordinate distorted-square-pyramidal CrIII coordination, comprising a chelating ligand through the CNHC and one P donor and three benzyl groups. These complexes were used as precatalysts in ethylene oligomerization, and it was found that the nature of the cocatalyst used and the metal oxidation state have a remarkable influence on the catalytic properties. The CrIII/MAO systems displayed superior catalytic performance (TOF values up to 16320 mol of C2H4/((mol of Cr) h) for 6) and gave mostly oligomers. Interestingly, the oligomers obtained with complex 3 were almost exclusively 1-hexene and 1-butene when the reaction was initiated at 30 °C. The overall activities and selectivities were also affected by the initial reaction temperature and the nature of the solvent. With AlEtCl2 (EADC) as cocatalyst, polyethylene was predominately formed. (Chemical Equation Presented).
- Ai, Pengfei,Danopoulos, Andreas A.,Braunstein, Pierre
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p. 4109 - 4116
(2015/09/01)
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- Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
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We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products.
- Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hlne,Reek, Joost N. H.,Breuil, Pierre-Alain R.
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p. 3754 - 3762
(2015/05/05)
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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.
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Paragraph 0082
(2015/03/28)
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- Z -selective alkene isomerization by high-spin cobalt(II) complexes
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The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
- Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
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p. 945 - 955
(2014/02/14)
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- A one-pot tandem olefin isomerization/metathesis-coupling (ISOMET) reaction
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A tandem catalytic reaction has been developed as part of a process to discover tungsten-based olefin metathesis catalysts that have a strong preference for terminal olefins over cis or trans internal isomers in olefin metathesis. This tandem isomerization/terminal olefin metathesis reaction (ISOMET) converts Cn trans internal olefins into C2n-2cis olefins and ethylene. This reaction is made possible with Ru-based "alkene zipper" catalysts, which selectively isomerize trans olefins to an equilibrium mixture of trans and terminal olefins, plus tungsten-based metathesis catalysts that react relatively selectively with terminal olefins to give Z homocoupled products. The most effective catalysts are W(NAr)(C3H6)(pyr)-(OHIPT) (Ar = 2,6-diisopropylphenyl; pyr = pyrrolide; OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) and various [CpRu(P - N)(MeCN)]X (X-= [B(3,5-(CF3)2C6H3)4]-, PF6-, B(C6F5)4-) isomerization catalysts.
- Dobereiner, Graham E.,Erdogan, Gulin,Larsen, Casey R.,Grotjahn, Douglas B.,Schrock, Richard R.
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p. 3069 - 3076
(2015/02/19)
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- General catalyst control of the monoisomerization of 1-alkenes to trans -2-alkenes
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After searching for the proper catalyst, the dual challenges of controlling the position of the double bond, and cis/trans-selectivity in isomerization of terminal alkenes to their 2-isomers are finally met in a general sense by mixtures of (C5Me5)Ru complexes 1 and 3 featuring a bifunctional phosphine. Typically, catalyst loadings of 1 mol % of 1 and 3 can be employed for the production of (E)-2-alkenes at 40-70 C. Catalyst comprising 1 and 3 avoids more than any other known example the thermodynamic equilibration of alkene isomers, as the trans-2-alkenes of both nonfunctionalized and functionalized alkenes are generated.
- Larsen, Casey R.,Erdogan, Gulin,Grotjahn, Douglas B.
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supporting information
p. 1226 - 1229
(2014/02/14)
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- Synthesis and reactivity of a masked PSiP pincer supported nickel hydride
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Tridentate PSiP pincer ligands featuring two phosphine donors and an anionic Si donor have attracted considerable attention in recent years. Here, we report the synthesis of the η3-cyclooctenyl complex, (PhPSiP)Ni(η3-cyclooctenyl) (1; PhPSiP = Si(Me)(2-PPh2-C6H4)2) through the reaction of Ni(COD)2 with PhPSiHP (PhPSiHP = HSi(Me)(2-PPh2-C6H4)2). We propose, that as a result of β-hydride elimination of 1,3-COD, 1 can act as a synthetic equivalent for (PhPSiP)NiH. The reaction of 1 with a variety of different reagents including another equivalent of PhPSiHP to form (PhPSiP)2Ni (2), 1,3-COD and H2, PPh3 to form the Ni(0) species (PhPSiHP)Ni(PPh3) (3) and 1,3-COD and 2,6-lutidine·HCl to generate (PhPSiP)NiCl (4), 1,3-COD and H2 are in agreement with this hypothesis. In addition, in the reaction of 1 with BH3·THF, (PhPSiP)Ni(κ2-BH4) (5) was observed but could not be isolated. This reaction presumably proceeds via (PhPSiP)NiH. This is supported by the observation that the reaction of (CyPSiP)NiH (CyPSiP = Si(Me)(2-PCy2-C6H4)2) with BH3·THF formed (CyPSiP)Ni(κ2-BH4) (6). Catalytic reactions such as alkene isomerization and CO2 reduction using 1 as precatalyst are also consistent with a nickel hydride being accessible. Compounds 1, 2 and 6 were characterized by X-ray crystallography.
- Suh, Hee-Won,Guard, Louise M.,Hazari, Nilay
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supporting information
p. 37 - 43
(2015/02/19)
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- Applications of PC(sp3)P iridium complexes in transfer dehydrogenation of alkanes
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Iridium ethylene complexes based on the PC(sp3)P pincer-type triptycene ligand have been synthesized. Complexes bearing various substituents on the phosphines have been investigated as catalysts in transfer dehydrogenation of alkanes. The complex 8a, which bears isopropyl groups, has demonstrated high stability and activity when used as a catalyst in the disproportionation of 1-hexene at 180 °C and in the transfer dehydrogenation of linear and cyclic alkanes with tert-butylethylene as a hydrogen acceptor at 200°C. A similar complex bearing a CH2NMe2 group, 33, allowed support of the catalyst on γ-alumina for operation in a heterogeneous mode.
- Bzier, David,Brookhart, Maurice
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p. 3411 - 3420
(2015/02/19)
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- Metal-free deoxygenation of carbohydrates
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The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C-O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6F5)3) is shown to catalyze the metal-free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products. A spoonful of sugar: The Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbohydrates to give a mixture of hexane and hexene isomers, with diethylsilane (Et2SiH2) providing the hydride equivalent. A variety of carbohydrates including methyl cellulose can be deoxygenated by this metal-free method, and the system can be tuned for selective deoxygenation at certain sites. Copyright
- Adduci, Laura L.,McLaughlin, Matthew P.,Bender, Trandon A.,Becker, Jennifer J.,Gagne, Michel R.
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supporting information
p. 1646 - 1649
(2014/03/21)
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- Olefin isomerization and hydrosilylation catalysis by lewis acidic organofluorophosphonium salts
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Organofluorophosphonium salts of the formula [(C6F 5)3-xPhxPF][B(C6F5) 4] (x = 0, 1) exhibit Lewis acidity derived from a low-lying σ* orbital at P opposite F. This acidity is evidenced by the reactions of these salts with olefins, which catalyze the rapid isomerization of 1-hexene to 2-hexene, the cationic polymerization of isobutylene, and the Friedel-Crafts-type dimerization of 1,1-diphenylethylene. In the presence of hydrosilanes, olefins and alkynes undergo efficient hydrosilylation catalysis to the alkylsilanes. Experimental and computational considerations of the mechanism are consistent with the sequential activation and 1,2-addition of hydrosilane across the unsaturated C-C bonds.
- Perez, Manuel,Hounjet, Lindsay J.,Caputo, Christopher B.,Dobrovetsky, Roman,Stephan, Douglas W.
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supporting information
p. 18308 - 18310
(2014/01/06)
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- (POP)Rh pincer hydride complexes: Unusual reactivity and selectivity in oxidative addition and olefin insertion reactions
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We report on the synthesis and reactivity of rhodium complexes featuring bulky, neutral pincer ligands with a "POP" coordinating motif, tBuxanPOP, iPrxanPOP, and tBufurPOP ( tBuxanPOP = 4,5-bis(di-tert-butylphosphino)-9,9-dimethyl-9H-xanthene; iPrxanPOP = 4,5-bis(diisopropylphosphino)-9,9-dimethyl-9H-xanthene; tBufurPOP = 2,5-bis((di-tert-butylphosphino)methyl)furan). The (POP)Rh complexes described in this work are, in general, more reactive than their (PNP)Rh and (PCP)Rh analogues, which allows for the generation of several new species under relatively mild conditions. Thus, monomeric (POP)RhCl complexes oxidatively add H2 to form (POP)Rh(H)2Cl, from which the coordinatively unsaturated hydride complexes (POP)Rh(H) 2+ and (tBuxanPOP)Rh(H) can be obtained. In the case of the new ligand tBufurPOP, a major kinetic product of the reaction with H2 is, surprisingly, the trans dihydride, i.e. trans-(tBufurPOP)Rh(H)2Cl; this is most likely attributable to reversible decoordination of one of the pincer coordinating groups, followed by addition of H2 to a highly reactive three-coordinate species. Ethylene is hydrogenated by (tBuxanPOP) Rh(H)2+ at 25 °C, but propylene is not, even at elevated temperatures. Ethylene undergoes insertion into the Rh-H bond of ( tBuxanPOP)RhH; this reaction is reversible, allowing for an experimental determination of the equilibrium constant for this hydrometalation. The less bulky iPrxanPOP ligand affords a dihydride complex which functions as a modestly active alkane dehydrogenation catalyst, the first such example for a cationic pincer complex of any metal.
- Haibach, Michael C.,Wang, David Y.,Emge, Thomas J.,Krogh-Jespersen, Karsten,Goldman, Alan S.
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p. 3683 - 3692
(2013/11/19)
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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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