20348-51-0Relevant academic research and scientific papers
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.
Switching the Reactivity of Palladium Diimines with “Ancillary” Ligand to Select between Olefin Polymerization, Branching Regulation, or Olefin Isomerization
Jones, Glen R.,Basbug Alhan, Hatice E.,Karas, Lucas J.,Wu, Judy I.,Harth, Eva
supporting information, p. 1635 - 1640 (2020/11/30)
Coordinating solvents are commonly employed as ancillary ligands to stabilize late transition metal complexes and are conventionally considered to have little effect on the reaction products. Our work identifies that the presence of ancillary ligand in Pd-diimine catalyzed polymerizations of α-olefins can drastically alter reactivity. The addition of different amounts of acetonitrile allows for switching between distinct reaction modes: isomerization–polymerization with high branching (0 equiv.), regular chain-walking polymerization (1 equiv.), and alkene isomerization with no polymerization (>20 equiv.). Optimization of the isomerization reaction mode led to a general set of conditions to switch a wide variety of diimine complexes into efficient alkene isomerization catalysts, with catalyst loading as low as 0.005 mol %.
Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism
Kim, Daniel,Pillon, Guy,Diprimio, Daniel J.,Holland, Patrick L.
supporting information, p. 3070 - 3074 (2021/03/08)
Double-bond transposition in alkenes (isomerization) offers opportunities for the synthesis of bioactive molecules, but requires high selectivity to avoid mixtures of products. Generation of Z-alkenes, which are present in many natural products and pharmaceuticals, is particularly challenging because it is usually less thermodynamically favorable than generation of the E isomers. We report a β-dialdiminate-supported, high-spin cobalt(I) complex that can convert terminal alkenes, including previously recalcitrant allylbenzenes, to Z-2-alkenes with unprecedentedly high regioselectivity and stereoselectivity. Deuterium labeling studies indicate that the catalyst operates through a π-allyl mechanism, which is different from the alkyl mechanism that is followed by other Z-selective catalysts. Computations indicate that the triplet cobalt(I) alkene complex undergoes a spin state change from the resting-state triplet to a singlet in the lowest-energy C-H activation transition state, which leads to the Z product. This suggests that this change in spin state enables the catalyst to differentiate the stereodefining barriers in this system, and more generally that spin-state changes may offer a route toward novel stereocontrol methods for first-row transition metals.
Selective Isomerization of Terminal Alkenes to (Z)-2-Alkenes Catalyzed by an Air-Stable Molybdenum(0) Complex
Becica, Joseph,Glaze, Owen D.,Wozniak, Derek I.,Dobereiner, Graham E.
, p. 482 - 490 (2018/02/17)
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.
Normal Alpha Olefin Synthesis Using Metathesis and Dehydroformylation
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, (2018/05/24)
The present invention discloses processes for producing normal alpha olefins, such as 1-hexene, 1-octene, and 1-decene, in a multistep synthesis scheme. Generally, a first normal alpha olefin is subjected to an olefin metathesis step to form a linear internal olefin, which is then subjected to an isomerization-hydroformylation step to form a linear aldehyde, which is then subjected to a dehydroformylation step to form a second normal alpha olefin.
Careful investigation of the hydrosilylation of olefins at poly(ethylene glycol) chain ends and development of a new silyl hydride to avoid side reactions
Shin, Hyunseo,Moon, Bongjin
, p. 527 - 536 (2018/01/27)
Hydrosilylation of olefin groups at poly(ethylene glycol) chain ends catalyzed by Karstedt catalyst often results in undesired side reactions such as olefin isomerization, hydrogenation, and dehydrosilylation. Since unwanted polymers obtained by side reactions deteriorate the quality of end-functional polymers, maximizing the hydrosilylation efficiency at polymer chain ends becomes crucial. After careful investigation of the factors that govern side reactions under various conditions, it was related that the short lifetime of the unstable Pt catalyst intermediate led to the formation of more side products under the inherently dilute conditions for polymers. Based on these results, two new chelating hydrosilylation reagents, tris(2-methoxyethoxy)silane (5) and 2,10-dimethyl-3,6,9-trioxa-2,10-disilaundecane (6), have been developed. It was demonstrated that the hydrosilylation efficiency at polymer chain ends was significantly increased by employing the internally coordinating hydrosilane 5. In addition, employment of the internally coordinating disilane species 6 in an addition polymerization with 1,5-hexadiene by hydrosilylation reaction yielded a polymer with high molecular weight (Mn = 9300 g/mol), which was significantly higher than that (Mn = 2600 g/mol) of the corresponding polymer obtained with non-chelating dihydrosilane, 1,1,3,3-tetramethyldisiloxane.
CATALYSTS AND CATALYTIC PROCESSES
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Page/Page column 20, (2017/05/28)
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.
An Agostic Iridium Pincer Complex as a Highly Efficient and Selective Catalyst for Monoisomerization of 1-Alkenes to trans-2-Alkenes
Wang, Yulei,Qin, Chuan,Jia, Xiangqing,Leng, Xuebing,Huang, Zheng
supporting information, p. 1614 - 1618 (2017/02/05)
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.
Fischer-Tropsch synthesis: effect of ammonia on product selectivities for a Pt promoted Co/alumina catalyst
Rao Pendyala, Venkat Ramana,Shafer, Wilson D.,Jacobs, Gary,Martinelli, Michela,Sparks, Dennis E.,Davis, Burtron H.
, p. 7793 - 7800 (2017/02/05)
The effects of co-fed ammonia in synthesis gas on the activity and product selectivities of a typical cobalt catalyst (0.5% Pt-25% Co/Al2O3) were investigated during the Fischer-Tropsch synthesis using a continuously stirred tank reactor (CSTR). The product selectivities were compared at a similar CO conversion level for various concentrations (10-1000 ppmv) of ammonia, as well as clean (un-poisoned) conditions. The addition of 10-1000 ppmv ammonia (concentration of ammonia with respect to the syngas feed) significantly decreased activity; the percentage of deactivation was similar (～40%) for the various concentrations of ammonia used. At similar CO conversions, the addition of ammonia caused an increase in olefin selectivity and the corresponding paraffin and alcohol selectivities were decreased compared to the ammonia free synthesis conditions. Olefin selectivity increased with increasing concentration of ammonia, and the paraffin and alcohol selectivities were decreased with increasing ammonia concentration. At similar CO conversions, ammonia addition exhibited a positive effect on hydrocarbon selectivity (i.e., lower light gas products and higher C5+) and also light gas product selectivities (C1-C4) were decreased and C5+ selectivity increased with increasing concentration of ammonia compared to ammonia free conditions.
Effect of the presence of ionic liquid during the NiMoS bulk preparation in the transformation of decanoic acid
Leyral, Géraldine,Brillouet, Soizic,Rousseau, Julie,Richard, Frédéric,Mamede, Anne Sophie,Courthéoux, Laurence,Pradel, Annie,Ribes, Michel,Brunet, Sylvette
, p. 120 - 132 (2017/01/11)
The impact of the presence and amount of [BMIM][NTf2] ionic liquid during the preparation of bulk NiMoS catalysts was investigated. It was clearly shown that these factors have a strong influence on both the morphology and specific surface area of the obtained NiMoS samples. Most interestingly the catalytic activity for the transformation of decanoic acid increased up to three times when IL was present during synthesis. In the same time, a greater selectivity towards hydrocarbons was observed. On the whole a clear relationship between catalytic activity, selectivity and NiMoS morphology was demonstrated. Consequently, it is possible to modify the morphology of the materials and impact the catalytic properties by changing the synthesis conditions.
