1003-64-1Relevant articles and documents
Regioselective Isomerization of Terminal Alkenes Catalyzed by a PC(sp3)Pincer Complex with a Hemilabile Pendant Arm
De-Botton, Sophie,Filippov, D.Sc. Oleg A.,Shubina, Elena S.,Belkova, Natalia V.,Gelman, Dmitri
, p. 5959 - 5965 (2020)
We describe an efficient protocol for the regioselective isomerization of terminal alkenes employing a previously described bifunctional Ir-based PC(sp3)complex (4) possessing a hemilabile sidearm. The isomerization, catalyzed by 4, results in a one-step shift of the double bond in good to excellent selectivity, and good yield. Our mechanistic studies revealed that the reaction is driven by the stepwise migratory insertion of Ir?H species into the terminal double bond/β-H elimination events. However, the selectivity of the reaction is controlled by dissociation of the hemilabile sidearm, which acts as a selector, favoring less sterically hindered substrates such as terminal alkenes; importantly, it prevents recombination and further isomerization of the internal ones.
Liquid phase hydrodeoxygenation of anisole, 4-ethylphenol and benzofuran using Ni, Ru and Pd supported on USY zeolite
Gamliel, David P.,Karakalos, Stavros,Valla, Julia A.
, p. 20 - 29 (2018)
The objective of this work is to understand the role of metals on the hydrodeoxygenation (HDO) reaction pathways of three bio-oil model compounds. Ni, Ru and Pd were impregnated on USY zeolite, and the catalysts were characterized to determine metal reduction profile, surface concentration and nanoparticle size. Ru-USY and Pd-USY were completely reduced at a temperature below 450 °C, but Ni-USY still contained surface metal oxides after reduction. There was no indication of strong interactions between the metals and USY support. Anisole, 4-ethylphenol and benzofuran were used as bio-oil model compounds, in order to determine the effects of each metal on deoxygenation of methoxy-, phenol and furan functional groups, respectively. Pd-USY was the most effective HDO catalyst, exhibiting the highest turnover frequency for HDO of all three model compounds, in addition to and high selectivity to deoxygenated products. A mechanism was proposed for each model compound, and the kinetics of hydrogenation, dehydration, C–C coupling and ring-opening reactions were determined.
Geminal dialkylation, alkylative reduction and olefination of aliphatic aldehydes. Reaction of gem-bistriflates with higher order dialkylcyanocuprates
Garcia Martinez,Osio Barcina,Ruiz Diez,Subramanian
, p. 13231 - 13238 (1994)
gem-Dialkylation or alkylative reduction of α-unbranched aliphatic aldehydes 1 is advantageously achieved by reaction of the corresponding gem-bistriflates 2 with di-n-alkylcyanocuprates or di-sec- and di-tert-alkylcyanocuprates respectively. The reaction of α-branched gem-bistriflates 2 with dialkylcyanocuprates in the presence of boron trifluoride affords the olefins 6 in good yield.
Mechanistic studies of alkene isomerization catalyzed by CCC-pincer complexes of iridium
Knapp, Spring Melody M.,Shaner, Sarah E.,Kim, Daniel,Shopov, Dimitar Y.,Tendler, Jennifer A.,Pudalov, David M.,Chianese, Anthony R.
, p. 473 - 484 (2014)
Iridium complexes containing CCC-pincer m-phenylene-bridged N-heterocyclic carbene ligands were examined as catalysts for alkene isomerization. Complexes containing either mesityl or adamantyl side groups were found to catalyze the isomerization of a number of alkenes to the internal isomers, including 1-octene, vinylcyclohexane, and allylbenzene. Mechanistic studies indicate a surprising dichotomy, apparently caused by ligand steric effects. For the mesityl-substituted catalyst, several lines of evidence provide strong support for isomerization via an iridium allyl hydride intermediate: (1) H-D crossover experiments indicate that 1,3-hydrogen migration is exclusively intramolecular, (2) the catalyst resting state, a π-allyl hydride species, was isolated and serves as a kinetically competent catalyst, (3) NMR experiments indicate that the π-allyl hydride resting state undergoes reversible C-H reductive elimination that is rapid relative to catalytic turnover, and (4) kinetic studies indicate that the isomerization reaction is first order in substrate and catalyst, consistent with turnover-limiting ligand substitution. H-D crossover experiments for alkene isomerization catalyzed by the adamantyl-substituted complex show selectivity for a 1,3-deuterium shift, as well as the intermolecular transfer of hydrogen. These results are consistent with an insertion/elimination mechanism proceeding selectively through a secondary metal-alkyl or with a π-allyl-type mechanism with an unknown pathway for intermolecular hydrogen crossover.
Regioselective hydroalumination of allenes and their synthetic application
Nagahara,Maruoka,Yamamoto
, p. 3783 - 3789 (1993)
The hydroalumination of a terminal allene, 1,2-nonadiene, with LiAlH4 in THF using [TiCl2(Cp)2], TiCl4, TiCl3, ZrCl4, and [ZrCl2 (CP)2] catalyst afforded a wide variet
Dilithiated phosphazenes: Scaffolds for the synthesis of olefins through a new class of bicyclic 1,2-oxaphosphetanes
Garcia-Lopez, Jesus,Peralta-Perez, Emma,Forcen-Acebal, Angela,Garcia-Granda, Santiago,Lopez-Ortiz, Fernando
, p. 856 - 857 (2003)
The first examples of the PN-directed dilithiation of (N-methoxycarbonyl)phosphazenes in the Cα and Cortho to the phosphorus, and the use of these dianions in the formation of tri- and tetra-substituted olefins through stereospecific thermolysis of a new type of isolable bicyclic 1,2-oxaphosphetanes are described.
Benign catalysis with iron: Unique selectivity in catalytic isomerization reactions of olefins
Jennerjahn, Reiko,Jackstell, Ralf,Piras, Irene,Franke, Robert,Jiao, Haijun,Bauer, Matthias,Beller, Matthias
, p. 734 - 739 (2012)
The use of noble metal catalysts in homogeneous catalysis has been well established. Due to their price and limited availability, there is growing interest in the substitution of such precious metal complexes with readily available and bio-relevant catalysts. In particular, iron is a "rising star" in catalysis. Herein, we present a general and selective iron-catalyzed monoisomerization of olefins, which allows for the selective generation of 2-olefins. Typically, common metal complexes give mixtures of various internal olefins. Both bulk-scale terminal olefins and functionalized terminal olefins give the corresponding products under mild conditions in good to excellent yields. The proposed reaction mechanism was elucidated by in situ NMR studies and supported by DFT calculations and extended X-ray absorption fine structure (EXAFS) measurements.
Superbase catalysts from thermally decomposed sodium azide supported on mesoporous γ-alumina
Bota, Roxana M.,Houthoofd, Kristof,Grobet, Piet J.,Jacobs, Pierre A.,Leuven
, p. 99 - 103 (2010)
Mesoporous g-alumina because of its homogeneous pore size distribution, represents a good support for alkali metals. Controlled thermal decomposition of impregnated sodium azide on such support yields a superbasic catalyst for the double bond migration of
Photochemical Dehydrogenation of Alkanes Catalyzed by trans-Carbonylchlorobis(trimethylphosphine)rhodium: Aspects of Selectivity and Mechanism
Maguire, John A.,Boese, William T.,Goldman, Alan S.
, p. 7088 - 7093 (1989)
The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate.The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane.In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130.A kinetic isotope effect, kH/kD=5.3, is found for thedehydrogenation of C6H12/C6D12.Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution.The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics.On the basis of these results, a mechanism is proposed in which the enrgy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
Modular Ni(0)/Silane Catalytic System for the Isomerization of Alkenes
Chang, Alison Sy-Min,Cook, Amanda K.,Kawamura, Kiana E.,Martin, Daryl J.,Morris, Parker T.,Smith, Haley M.
supporting information, p. 486 - 496 (2022/03/02)
Alkenes are used ubiquitously as starting materials and synthetic targets in all areas of chemistry. Controlling their geometry and position along a chain is vital to their reactivity and properties yet remains challenging. Alkene isomerization is an atom-economical process to synthesize targeted alkenes, and selectivity can be controlled using transition metal catalysts. The development of mild, selective isomerization reactivity has enabled efficient tandem catalytic systems for the remote functionalization of alkenes, a process in which a starting alkene is isomerized to a new position prior to the functionalization step. The key challenges in developing isomerization catalysts for remote functionalization applications are (i) a lack of modularity in the catalyst structure and (ii) the requirement of nonmodular and/or harsh additives during catalyst activation. We address both challenges with a modular (NHC)Ni(0)/silane catalytic system (NHC, N-heterocyclic carbene), demonstrating the use of triaryl silanes and readily accessible (NHC)Ni(0) complexes to form the proposed active (NHC)(silyl)Ni-H species in situ. We show that modification of the steric and electronic nature of the catalyst via modification of the ancillary ligand and silane partner, respectively, is easily achieved, creating a uniquely versatile catalytic system that is effective for the formation of internal alkenes with high yield and selectivity for the E-alkene. The use of silanes as mild activators enables isomerization of substrates with a variety of functional groups, including acid-labile groups. The broad substrate scope, enabled by catalyst design, makes this catalytic system a strong candidate for use in tandem catalytic applications. Preliminary mechanistic studies support a Ni-H insertion/elimination pathway.
