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Journal articles on the topic "Precatalyst"
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Takahashi, Rina, Koji Kubota, and Hajime Ito. "Air- and moisture-stable Xantphos-ligated palladium dialkyl complex as a precatalyst for cross-coupling reactions." Chemical Communications 56, no. 3 (2020): 407–10. http://dx.doi.org/10.1039/c9cc06946a.
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A Xantphos-ligated palladium dialkyl complex can serve as a high performance precatalyst for various cross-coupling reactions, thus providing a convenient alternative to previously developed classes of precatalysts.
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Borré, Etienne, Frederic Caijo, Christophe Crévisy, and Marc Mauduit. "New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations." Beilstein Journal of Organic Chemistry 6 (December 6, 2010): 1159–66. http://dx.doi.org/10.3762/bjoc.6.132.
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Seven novel Hoveyda–Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda’s precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions.
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Imazu, Haruna, Kakeru Masaoka, Saki Uike, and Masamichi Ogasawara. "Molybdenum-Catalyzed Enantioselective Ring-Closing Metathesis/Kinetic Resolution of Racemic Planar-Chiral 1,1′-Diallylferrocenes." Catalysts 14, no. 2 (2024): 123. http://dx.doi.org/10.3390/catal14020123.
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The molybdenum-catalyzed enantioselective ring-closing metathesis/kinetic resolution of a series of racemic planar-chiral 1,1′-diallylferrocene derivatives was reinvestigated utilizing the method of generating catalytically active chiral molybdenum-alkylidene species in situ, which allowed us to examine a variety of chiral molybdenum-alkylidene metathesis precatalysts in the present asymmetric reaction. With the catalyst screening experiments conducted in this study, the more practical reaction conditions, including a choice of a proper chiral molybdenum precatalyst, giving planar-chiral ferrocenes of higher enantiomeric purity and better chemoselectivity could be optimized.
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Yang, Yi, Qinghai Zhou, Junjie Cai, et al. "Exploiting the trifluoroethyl group as a precatalyst ligand in nickel-catalyzed Suzuki-type alkylations." Chemical Science 10, no. 20 (2019): 5275–82. http://dx.doi.org/10.1039/c9sc00554d.
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Rahman, Md Mahbubur, Qun Zhao, Guangrong Meng, Roger Lalancette, Roman Szostak, and Michal Szostak. "[IPr#–PEPPSI]: A Well-Defined, Highly Hindered and Broadly Applicable Pd(II)–NHC (NHC = N-Heterocyclic Carbene) Precatalyst for Cross-Coupling Reactions." Molecules 28, no. 15 (2023): 5833. http://dx.doi.org/10.3390/molecules28155833.
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In this Special Issue, “Featured Papers in Organometallic Chemistry”, we report on the synthesis and characterization of [IPr#–PEPPSI], a new, well-defined, highly hindered Pd(II)–NHC precatalyst for cross-coupling reactions. This catalyst was commercialized in collaboration with MilliporeSigma, Burlington, ON, Canada (no. 925489) to provide academic and industrial researchers with broad access to reaction screening and optimization. The broad activity of [IPr#–PEPPSI] in cross-coupling reactions in a range of bond activations with C–N, C–O, C–Cl, C–Br, C–S and C–H cleavage is presented. A comprehensive evaluation of the steric and electronic properties is provided. Easy access to the [IPr#–PEPPSI] class of precatalysts based on modular pyridine ligands, together with the steric impact of the IPr# peralkylation framework, will facilitate the implementation of well-defined, air- and moisture-stable Pd(II)–NHC precatalysts in chemistry research.
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Hausmann, Jan Niklas, Stefan Mebs, Konstantin Laun, et al. "Understanding the formation of bulk- and surface-active layered (oxy)hydroxides for water oxidation starting from a cobalt selenite precursor." Energy & Environmental Science 13, no. 10 (2020): 3607–19. http://dx.doi.org/10.1039/d0ee01912g.
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Starting from a cobalt selenite precatalyst, we obtained a bulk and a near-surface active oxygen evolution catalyst and connected their structural properties to the precatalyst structure, the transformation conditions, and the catalytic activity.
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Jung, S.-C., and W.-S. Yoon. "Modelling and parametric investigation of NOx reduction by oxidation precatalyst-assisted ammonia-selective catalytic reduction." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 223, no. 9 (2009): 1193–206. http://dx.doi.org/10.1243/09544070jauto1099.
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Nitrogen oxide (NO x) reduction by the selective catalytic reduction (SCR) system assisted by an oxidation precatalyst is modelled and analytically investigated. The Langmuir—Hinshelwood SCR kinetic scheme with vanadium-based catalyst and ammonia (NH3) reductant in conjunction with the NO—NO2 conversion reaction over a platinum-based catalyst is used. The effects of the ratio of the oxidation precatalyst to the SCR monolith volume, the gas temperature, the space velocity, and the NH3-to-NO x concentration ratio on the de-NO x performance are parametrically examined. The oxidation precatalyst promotes NO x conversion at low temperatures. At intermediate temperatures, the NO x reduction is either activated or deactivated with increase in the space velocity. A higher oxidation precatalyst-to-SCR monolith volume ratio tends to promote the NO x reduction of higher space velocities. At high temperatures, the de-NO x efficiency is very high and insensitive to the space velocity. The NO x conversion efficiency depends on the NH3-to-NO x ratio at low temperatures.
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Gupta, Saswata, Siyuan Su, Yu Zhang, Peng Liu, Donald J. Wink, and Daesung Lee. "Ruthenabenzene: A Robust Precatalyst." Journal of the American Chemical Society 143, no. 19 (2021): 7490–500. http://dx.doi.org/10.1021/jacs.1c02237.
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Roque, Jose B., Alex M. Shimozono, Tyler P. Pabst, Gabriele Hierlmeier, Paul O. Peterson, and Paul J. Chirik. "Kinetic and thermodynamic control of C(sp 2 )–H activation enables site-selective borylation." Science 382, no. 6675 (2023): 1165–70. http://dx.doi.org/10.1126/science.adj6527.
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Catalysts that distinguish between electronically distinct carbon-hydrogen (C–H) bonds without relying on steric effects or directing groups are challenging to design. In this work, cobalt precatalysts supported by N -alkyl-imidazole–substituted pyridine dicarbene (ACNC) pincer ligands are described that enable undirected, remote borylation of fluoroaromatics and expansion of scope to include electron-rich arenes, pyridines, and tri- and difluoromethoxylated arenes, thereby addressing one of the major limitations of first-row transition metal C–H functionalization catalysts. Mechanistic studies established a kinetic preference for C–H bond activation at the meta -position despite cobalt-aryl complexes resulting from ortho C–H activation being thermodynamically preferred. Switchable site selectivity in C–H borylation as a function of the boron reagent was thereby preliminarily demonstrated using a single precatalyst.
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Chouki, Takwa, Manel Machreki, Jelena Topić, et al. "Iron Phosphide Precatalyst for Electrocatalytic Degradation of Rhodamine B Dye and Removal of Escherichia coli from Simulated Wastewater." Catalysts 12, no. 3 (2022): 269. http://dx.doi.org/10.3390/catal12030269.
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Electrocatalysis using low-cost materials is a promising, economical strategy for remediation of water contaminated with organic chemicals and microorganisms. Here, we report the use of iron phosphide (Fe2P) precatalyst for electrocatalytic water oxidation; degradation of a representative aromatic hydrocarbon, the dye rhodamine B (RhB); and inactivation of Escherichia coli (E. coli) bacteria. It was found that during anodic oxidation, the Fe2P phase was converted to iron phosphate phase (Fe2P-iron phosphate). This is the first report that Fe2P precatalyst can efficiently catalyze electrooxidation of an organic molecule and inactivate microorganisms in aqueous media. Using a thin film of Fe2P precatalyst, we achieved 98% RhB degradation efficiency and 100% E. coli inactivation under an applied bias of 2.0 V vs. reversible hydrogen electrode in the presence of in situ generated reactive chlorine species. Recycling test revealed that Fe2P precatalyst exhibits excellent activity and reproducibility during degradation of RhB. High-performance liquid chromatography with UV-Vis detection further confirmed the electrocatalytic (EC) degradation of the dye. Finally, in tests using Lepidium sativum L., EC-treated RhB solutions showed significantly diminished phytotoxicity when compared to untreated RhB. These findings suggest that Fe2P-iron phosphate electrocatalyst could be an effective water remediation agent.
Dissertations / Theses on the topic "Precatalyst"
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Bray, Joshua. "Rationalising Pd-precatalyst design for efficient arylcyanation reactions." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/17038/.
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This thesis describes the use of in situ infrared spectroscopy to investigate the kinetics and mechanism of Pd-catalysed arylcyanation. These studies probe the formation of small Pd nanoclusters in the Pd catalysed cyanation of aryl halides. Initially, an overview of the role of Pd nanoparticles and Pd nanoparticle precursor complexes in Pd-catalysed reactions is provided. The application of the established precatalyst in extensive kinetic studies of arylcyanation has revealed that there is clear evidence for heterogeneous catalytic behaviour (Chapter 4). A significant change in kinetic profile supports a change in precatalyst activation mechanism. Pd concentration and catalyst loading data, along with computational analysis, support a role for small Pd clusters in catalysis (Chapter 5).
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Loock, Monique Marié. "The alkene metathesis reactivity of the PUK-Grubbs 2-precatalyst / Monique Marié Loock." Thesis, North-West University, 2009. http://hdl.handle.net/10394/5032.
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Metathesis reactions are of great value for industrial processes e.g. Shell Higher Olefin Process (SHOP) to form new alkenes. A lot of catalytic systems were developed to optimize the activity, stability and selectivity of these precatalysts. In a previous study a Grubbs 2-type precatalyst (Gr2Ph (3)) which had a N^O hemilabile ligand with two phenyl groups coordinated to the Ru-metal was developed. This Grubbs 2-type precatalyst, known as the Puk-Grubbs 2-precatalyst (Gr2Ph (3)) was used for 1-octene metathesis reactions and showed an increase in the selectivity, thermal stability, activity and lifetime In comparison to Grubbs 1 (Gr1 (1)) and Grubbs 2 (Gr2 (2)). In order to determine if the precatalyst is of value to metathesis reactions it was used for different 1-alkenes (1-hexene, 1-heptene, 1-nonene and 1-decene) and the conditions optimized.
The Gr2Ph (3) precatalyst was successfully synthesized (43% yield) in this study and used for the metathesis reactions of the different 1-alkenes. The metathesis reactions of each 1-alkene was conducted at different temperatures, 55°C and 60°C for 1-hexene reactions, 60°C, 70°C and 80°C for 1-heptene reactions and 60°C, 80°C and 100°C for 1-decene reactions, except 1-nonene, while the Ru:1-alkene ratios were varied for 1-hexene and 1-heptene (1:7000 and 1:9000). The results of the 1-alkene metathesis reactions showed that the Gr2Ph (3) precatalyst increased the lifetime to 35 days and thermal stability when compared to Gr1 (1) (1 hour lifetime) and Gr2 (2) (3 hours lifetime). The TON, selectivity and activity is comparable to those of the Gr2 (2) reaction results, whilst an improvement on the Gr1 (1) results was obtained. The optimum conditions in terms of TON, PMP formation and selectivity for Gr2Ph (3) was found to be at 80°C with a 1:7000 Ru:1-alkene ratio for 1-heptene and 1-decene, but the ethylene accumulation In the mini reactors had an impact on the results. The ethylene accumulation resulted in the conversion of the already formed PMPs into SMPs and IPs during the course of the reaction. The optimum temperature for the 1-hexene reactions were determined to be at 60°C for Gr2Ph (3) with a Ru:1alkene ratio of 1:7000, with a high PMP formation, selectivity and TON.
The 1H-NMR investigation of the metathesis reactions of 1-octene and 1-hexene with Gr2Ph (3) in CDCI3 at 30°C with a Ru:1-alkene ratio of 1:40, showed that only one carbene signal was present. Metathesis products were formed and confirmed with GC-MS and a larger amount of SMPs and IPs were formed by the competing isomerization reactions. These results indicate that metathesis does occur but that another mechanism was present or that the ligand was not hemilabile as suspected.<br>Thesis (Ph.D. (Chemistry))--North-West University, Potchefstroom Campus, 2010.
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Beck, John Frederick. "orthoMetallated Acetophenone Imines as Ligands for Transition and Main Group Metals: Synthesis and Organometallic Reactivity and the Hydroamination of Allenes using a Palladium Allyl Triflate 3-Iminophosphine Precatalyst." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1311613955.
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Standley, Eric A. (Eric Alan). "Nickel precatalysts as enabling tools for catalytic coupling reactions." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97984.
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Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>[Chemical formula] A series of air-stable nickel complexes of the form L₂Ni(aryl)X (L = monodentate phosphine, X = Cl, Br) and LNi(aryl)X (L = bis-phosphine) have been synthesized and are presented as a library of precatalysts suitable for a wide variety of nickel-catalyzed transformations. These complexes are easily synthesized from low-cost NiCl₂-6H₂O or NiBr₂-3H₂O and the desired ligand followed by addition of 1 equiv of Grignard reagent. A selection of these complexes were characterized by single-crystal X-ray diffraction, and an analysis of their structural features is provided. [Chemical formula] The air-stable nickel(II) complex trans-(PCy₂Ph)₂Ni(o-tolyl)Cl was employed as a precatalyst for the Mizoroki-Heck-type, room temperature, internally selective coupling of substituted benzyl chlorides with terminal alkenes. This reaction, which employs a terminal alkene as an alkenylmetal equivalent, provides rapid, convergent access to substituted allylbenzene derivatives in high yield and with regioselectivity greater than 95:5 in nearly all cases. The reaction is operationally simple, can be carried out on the benchtop with no purification or degassing of solvents or reagents, and requires no exclusion of air or water during setup. Synthesis of the precatalyst is accomplished through a straightforward procedure that employs inexpensive, commercially available reagents, requires no purification steps, and proceeds in high yield. [Chemical formula] The nickel-catalyzed cross-coupling of aliphatic N-tosylaziridines with aliphatic organozinc reagents is described. The reaction protocol displays complete regioselectivity for reaction at the less hindered C-N bond, and the products are furnished in good to excellent yield for a broad selection of substrates. An air-stable nickel(II) chloride/ligand precatalyst was also developed and employed for the reaction. In addition to increasing the activity of this catalyst system, this also greatly improves the practicality of this reaction, as the use of the very air-sensitive Ni(cod)₂ is avoided. Finally, mechanistic investigations, including deuterium-labeling studies, show that the reaction proceeds with overall inversion of configuration at the terminal position of the aziridine by way of aziridine ring opening by Ni (inversion), transmetallation (retention), and reductive elimination (retention).<br>by Eric A. Standley.<br>Ph. D. in Organic Chemistry
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Paradiso, Veronica. "Ruthenium metathesis precatalysts with unsymmetrical Nheterocyclic carbene (NHC) ligands." Doctoral thesis, Universita degli studi di Salerno, 2018. http://hdl.handle.net/10556/3017.
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2016 - 2017<br>Olefin metathesis is one of the most important chemical transformations for the formation
of carbon-carbon double bonds. The possibility to build up highly funtionalised alkenes
starting from simple olefins makes this reaction indispensable in modern organic synthesis,
giving access to a wide range of molecules that would be barely obtained through other
synthetic routes.
The success of metathesis is due to the development of new and efficient catalysts which can
be used in a wide variety of research fields, both in industry and in academia. In this
context, the research of the ‘perfect’ metathesis complex still impassions scientists all over
the word, and several research papers regarding the development of new catalytic systems
are published every year.
The group I am part of focuses its attention on the development of new ruthenium
metathesis catalysts. Our interest lies in the influence that nature and configuration of
substituents on the N-heterocyclic carbene (NHC) ligand could have on the performances of
the corresponding metal complexes.
In this doctoral thesis, the field of unsymmetrical N-heterocyclic carbene (u-NHC)
ruthenium catalysts will be explored. Synthesis and characterisation of several novel
complexes will be discussed. Catalytic performances will be evaluated in model metathesis
reactions as well as in more attractive metathesis transformations. The relationship between
NHC structure and complexes’ behaviours will be investigated using NMR, X-Ray, IR, cyclic
voltammetry and DFT calculations. ..[edited by Author]<br>XXX ciclo
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Raymakers, Maria de Fatima Marques. "Modelling of Grubbs type precatalysts with bidentate hemilabile ligands / Fatima Raymakers." Thesis, North-West University, 2012. http://hdl.handle.net/10394/9199.
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Metathesis is a valuable reaction for the production of new alkenes. In the last 50 years, heterogeneous as well as homogeneous catalysts have been used for this reaction. In the homogeneous category are the very successful catalysts designed by the Grubbs group. The first generation Grubbs precatalyst (Gr1) bearing two phosphine ligands was followed after extensive studies by the more active second generation Grubbs precatalyst (Gr2). In Gr2, one of the phosphine ligands is replaced with an N-heterocyclic carbene. Grubbs type precatalysts bearing pyridynyl-alcoholato chelating ligands are pertinent to this study.
Scheme 1: The synthesis of Grubbs type precatalysts bearing a pyridynyl-alcoholato ligand.
In two previous studies, both supported by computational methods, Grubbs type precatalysts with N^O chelating ligands were synthesised. These investigations were motivated by the fact that chelating ligands bearing different donor atoms can display hemilability. The loosely bound donor atom can de-coordinate to make available a coordination site to an incoming substrate “on demand”, whilst occupying the site otherwise and hence preventing decomposition via open coordination sites. In the first investigation, the incorporation of an O,N-ligand with both R1 and R2 being phenyl groups into the Gr2 precatalyst, resulted in an increase in activity, selectivity and lifetime of the precatalyst in comparison to Gr2 in the metathesis reaction with 1- octene. In the second study, three synthesised complexes were found to be active for the metathesis of 1-octene.
This computational study sought to better understand the structural differences and thermodynamic properties of these Grubbs type precatalysts with bidentate/hemilabile ligands. A large number of structures were constructed in Materials Studio by varying the R groups of the bidentate/hemilabile ligand attached to both the Gr1 and Gr2 catalysts. The majority of structures were Gr1-type complexes. For each ligand selected, a group of structures consisting of closed precatalyst, open precatalyst, and where applicable a precatalyst less PCy3, closed metallacycle, open metallacycle and where applicable a metallacycle less PCy3, was constructed and optimised using DMol3. Bond lengths, bond angles, HOMO and LUMO energies and Hirshveld charges of structures were compared with one another. PES scans were performed on the metallacycles of four groups. The purpose of the PES scans was to ascertain whether these bidentate ligands were hemilabile and to illuminate the preferred reaction mechanism for these types of precatalysts.
The major finding of this study was that the possibility of an associative mechanism cannot be ruled out for some Gr2-type precatalysts with bidentate ligand. For some precatalysts hemilability is energetically expensive and possibly not viable. No evidence of a concerted mechanism was found. The dissociative mechanism was found to be the preferred mechanism for most of the structures that were subjected to PES scans.
The HOMO-LUMO energies of a complex can be used, as a predictive tool, to assess the reactivity and stability of a complex, as well as its preference for substrates.<br>Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2013.
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Siangwata, Shepherd. "Monometallic and multimetallic complexes as precatalysts in the hydroformylation of olefins." Doctoral thesis, Faculty of Science, 2020. http://hdl.handle.net/11427/32348.
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A series of new aryl ether salicylaldimine-based monomeric, dimeric, trimeric and hexameric triazolyl ligands have been synthesised. The N,O-chelating ligands were synthesised via Schiff base condensation reactions of salicylaldehyde with the bromopropylamine hydrobromide salt, followed by the azidation of the resultant N-3-bromopropylsalicylaldimine. Click chemistry reactions of the azido propyl salicylaldimine with the appropriate phenolic-alkyne afforded the mono-, di-, tri- and hexameric aryl ether salicylaldimine-based triazolyl ligands. The ligands were characterised using various analytical and spectroscopic techniques. Complexation of the monomeric and trimeric ligands with the dimeric rhodium precursor [RhCl(COD)]2 yielded new aryl ether N,O-chelate mononuclear and trinuclear Rh(I) complexes. The complexes were characterised using nuclear magnetic resonance spectroscopy, infrared spectroscopy, mass spectrometry and melting point determinations. The mononuclear and trinuclear complexes were successfully evaluated as catalyst precursors in the hydroformylation of higher olefins. The reaction conditions were optimised using the mononuclear precatalyst at 85 ℃, 40 bar syngas pressure for 4 h with 2.87 x 10-3 mmol Rh loading and a substrate (1-octene) to catalyst ratio of 2500 : 1. These conditions gave good aldehyde chemoselectivity (90%), excellent conversion of the substrate (99%) and good catalytic activity (554 h-1 ). Comparable catalytic performance of both precatalysts was obtained when milder reaction conditions (85 ℃, 20 bar for 4 h) were adopted in the evaluation of the mononuclear complex against the low generation dendritic trinuclear complex. The mercury poisoning experiments revealed a dual catalytically influenced system, emanating from a combination of homogeneous and heterogeneous catalytic species. The mononuclear catalyst precursor was also evaluated successfully in the hydroformylation of internal olefins 7- tetradecene and trans-4-octene. The catalyst precursor gave good conversions of both internal olefins (> 80%) under the optimum reaction conditions (85 ℃, 40 bar for 4 h). Catalyst recyclability studies in the hydroformylation of 1-octene conducted using the Organic Solvent Nanofiltration (OSN) strategy demonstrated five successful recycles with consistently good catalytic performance from both catalyst precursors. Inductively coupled plasma optical emission spectrometry (ICP-OES) experiments revealed a near perfect (99%) membrane retention of the rhodium metal. Kinetic studies using the mononuclear precatalyst were investigated by evaluating the effect of temperature, syngas total pressure and catalyst loading on the rate of hydroformylation. The activation energy for the hydroformylation of 1-octene was calculated to be 62 kJ mol-1 and the experimental rate constants were found to be in good agreement with the predicted rate data obtained using a modified fundamental mechanismbased rate model. The synthesis and characterisation of new water-soluble, sulfonated aryl ether salicylaldiminebased mono- and trimeric ligands has also been described. The ligands were prepared following a series of amine and Boc-protection and deprotection procedures, Schiff base condensation reactions and Williamson ether synthesis. The water-soluble N,O-chelating aryl ether ligands were characterised using various spectroscopic and analytical techniques. Subsequently, complexation reactions of the ligands with the dimeric [RhCl(COD)]2 gave the corresponding new water-soluble mononuclear and trinuclear Rh(I) complexes. The complexes were characterised using nuclear magnetic resonance spectroscopy, infrared spectroscopy, mass spectrometry and melting point determinations. The complexes show appreciably good solubility in water, 15.7 mg/mL (mononuclear complex) and 8.6 mg/mL (trinuclear complex). The new water-soluble mono- and trinuclear complexes were successfully evaluated as precursors in the aqueous biphasic hydroformylation of higher olefins. Optimisation experiments using the mononuclear precatalyst gave the best results at 85 ℃, 50 bar syngas pressure for 4 h with 2.87 x 10-3 mmol Rh loading and a substrate (1-octene) to catalyst ratio of 2500 : 1. Both catalyst precursors gave near quantitative catalytic conversion of 1-octene, good activities (> 550 h -1 ) and attractive aldehyde chemoselectivity (> 85%). A substrate and product-distribution time study showed a positive dendritic effect in relation to the trinuclear complex over the mononuclear complex. The mercury poisoning experiments were suggestive of a system that is catalysed by a dual effect of homogeneous and heterogeneous catalytic species. Recyclability experiments were successfully conducted over 5 cycles, with a gradual decline in catalytic performance for both complexes. The dendrimer stabilised trinuclear precatalyst showed improved recyclability in “neat”, monophasic hydroformylation experiments, while the mononuclear precatalyst showed a reduced overall performance. The bias towards the linear aldehyde for the dendritic trinuclear complex was tunable by addition of excess bulkier trimeric water-soluble ligand into the catalytic system. Inductively coupled plasma optical emission spectrometry experiments showed moderate losses of the metal from the aqueous phase to the organic layer. Both catalyst precursors also showed good catalytic activity (> 450 h-1 ) and a total bias to aldehyde chemoselectivity (no hydrogenation products) in the aqueous biphasic hydroformylation of styrene.
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Arrowsmith, Merle. "Intramolecular hydroamination of aminoalkenes with group 2 precatalysts : mechanistic insights and ligand design." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538274.
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Long relegated to the background by the pre-eminence of magnesium-based, stoichiometric Grignard reagents, a distinct chemistry of the heavier alkaline earth metals, calcium, strontium and barium, is only now starting to emerge. As similarities have been drawn between the large, electropositive, redox-inert and d0 alkaline earth Ae2+ dications and the Ln3+ cations of the lanthanide series, a growing group 2-mediated catalytic chemistry has developed over the last decade, including polymerisation reactions, heterofunctionalisation reactions of multiple bonds and some rare examples of dehydrocoupling reactions. Among these catalytic reactions the magnesium- and calcium-catalysed intramolecular hydroamination of aminoalkenes has attracted particular interest. Mechanistic studies have demonstrated many parallels with the lanthanide-mediated catalytic cycle based upon successive σ-bond metathesis and insertion steps. In the first part of this thesis, further investigations into the hydroamination/cyclisation reaction have demonstrated the prominent role of the charge density of the catalytic group 2 cation (M = Mg, Ca, Sr, Ba), the beneficial influence of stabilising spectator ligands, and the importance of the choice of the reactive co-ligand for efficient catalyst initiation. Kinetic analyses of reactions monitored by NMR spectroscopy have given new insight into activation energies, entropic effects, substrate and product inhibition, and kinetic isotope effects, leading to a review of the previously suggested lanthanide-mimetic mechanism. In a second part, this study seeks to address two of the main challenges posed by the intramolecular hydroamination reaction in particular, and heavier alkaline earth-catalysed reactions in general: (i) The need to design new monoanionic spectator ligands capable of stabilising heteroleptic heavier alkaline earth complexes and preventing deleterious Schlenk-type ligand redistribution processes in solution; (ii) The stabilisation of highly reactive heteroleptic group 2 alkyl functionalities for fast, irreversible catalyst initiation and novel reactivity.
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Shahane, Saurabh. "Design of olefin metathesis precatalysts for organic solvent nanofiltration : acceptorless dehydrogenation of alcohols." Rennes 1, 2012. http://www.theses.fr/2012REN1S104.
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This work deals with two independent research topics with the common goal of finding ways to render catalytic processes more efficient and sustainable by lowering their environmental impact. The first part of this thesis deals with the design of ruthenium-based olefin metathesis pre-catalysts for organic solvent nanofiltration (OSN). OSN is an environmentally friendly separation process attracting academic and industrial interests for the removal of organometallic residues as well as for catalysts recycling. For this work, new pre-catalysts based on the Hoveyda-Grubbs architecture containing modifications on the isopropoxystyrene as well as on the N-heterocyclic carbene (NHC) ligands were prepared and fully characterized. The catalysts were evaluated for their catalytic activities under standard conditions and were then subjected to Nanofiltration (NF) studies. In the second part of this work, the catalytic, acceptorless dehydrogenation of alcohols was explored. In the first instance, [RuCl₂(p-cymene) IMes] was evaluated in the dehydrogenation of alcohols in the presence of a base co-catalyst and optimizations were carried out in order to obtain maximum conversions. In the second instance, a series of three arene-ruthenium-carboxylato catalysts were subjected to dehydrogenation studies and the catalyst [Ru(OAc)₂(p-cymene)] operating under acidic conditions was found to be the best amongst the three. In both cases, primary alcohols were converted to the corresponding esters while secondary alcohols rendered ketones on oxidation. Particular emphasis was placed on methyl ricinoleate, a renewable fatty acid methyl ester (FAME) obtained from castor oil. The dehydrogenation of this ester furnished in high yields the saturated keto-ester methyl 12-oxostearate via a hydrogen borrowing alcohol dehydrogenation-alkene hydrogenation tandem reaction<br>Ce travail comporte deux volets de recherche indépendants qui ont pour objectifs communs de rendre certains procédés catalytiques plus efficaces et plus acceptable d'un point de vue environnemental. La première partie des travaux de thèse concerne le design et la synthèse de pré-catalyseurs du ruthénium pour la métathèse des oléfines en vue de leurs Nanofiltration (NF) en milieu organique. La nanofiltration en milieu organique est un procédé de séparation qui suscite un grand intérêt à la fois académique et industriel pour la purification de mélanges réactionnels contenant des résidus organométalliques et pour le recyclage de catalyseurs. Au cours de ce travail, plusieurs pré-catalyseurs basés sur l'architecture des complexes de type Hoveyda ont été préparés en apportant des modifications stériques et polaires sur les ligands isopropoxystyrene ou NHC. Ces complexes ont été caractérisés et leur activité catalytique en métathèse ainsi que leur nanofiltration ont été étudié. Dans une seconde partie, la déshydrogenation d'alcool sans accepteur d'hydrogène a été étudié. Dans un premier temps le complexe [RuCl₂(p-cymene) IMes] a été évalué en présence d'une base et de nombreux paramètres expérimentaux ont été optimisés. De la même manière, un autre catalyseur à ligand carboxylate [Ru(OAc)₂2(p-cymene)] et opérant en milieu acide a été étudié et s'est montré plus actif que le catalyseur précédemment cité. Dans les deux cas, les alcools secondaires ont été oxydés en cétones alors que les alcools primaires ont conduit à la formation d'esters. Une attention particulière a été apportée à la déshydrogénation du ricinoléate de méthyle, un composé renouvelable issu de l'huile de ricin. Ce substrat a pu être transformé efficacement en méthyl 12-oxostéarate, un produit à haute valeur ajoutée, par un processus tandem dit ‘d'emprunt d'hydrogène' consistant en la déshydrogénation d'alcool/hydrogénation d'alcène
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Payne, Philippa Robyn. "Synthesis, structure, and reactivity of early transition metal precatalysts bearing (N,O)-chelating ligands." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45597.
Full textBooks on the topic "Precatalyst"
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Jon, McLeod, and Society of Automotive Engineers, eds. A sampling system for the measurement of precatalyst emissions from vehicles operating under transient conditions. Society of Automotive Engineers, 1993.
Find full textBook chapters on the topic "Precatalyst"
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Lao, Zhiqi, and Patrick H. Toy. "Use of Phosphine Oxides as Catalysts and Precatalysts." In Nonnitrogenous Organocatalysis. CRC Press, 2017. http://dx.doi.org/10.1201/9781315371238-6.
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Huang, Lin, and Pui Kwan Wong. "Nature of the True Catalytic Species in CarbonCarbon Coupling Reactions with Heterogeneous Palladium Precatalysts." In Palladium-Catalyzed Coupling Reactions. Wiley-VCH Verlag GmbH & Co. KGaA, 2013. http://dx.doi.org/10.1002/9783527648283.ch10.
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Malacria, M., C. Aubert, and J. L. Renaud. "Tris(acetylacetonato)cobalt(III) as a Precatalyst." In Compounds with Transition Metal-Carbon pi-Bonds and Compounds of Groups 10-8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os). Georg Thieme Verlag KG, 2001. http://dx.doi.org/10.1055/sos-sd-001-00375.
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Gupta, V. K. "Stereoregulating effects of alkoxysilanes in propylene polymerization." In Chemistry and Technology of Silicon and Tin. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780198555803.003.0038.
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Abstract There is great interest in the development of new generation Ziegler-Natta catalysts supported on magnesium compounds for the stereospecific polymerization of propylene. Such a catalytic system includes a solid precatalyst with mainly magnesium chloride as the support, an organic ‘internal’ Lewis base, titanium tetrachloride, and a co-catalyst solution consisting of a trialkylaluminium and an ‘external’ Lewis base. The activity and stereospecificity of the catalytic system are highly dependent on the details of preparation and the nature of the components used as pre-catalyst and co-catalyst.
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Taber, Douglass. "Organocatalytic C-C Ring Construction: (+)-Ricciocarpin A (List) and (-)-Aromadendranediol (MacMillan)." In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0073.
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Yoshiji Takemoto of Kyoto University designed (Organic Lett. 2009, 11, 2425) an organocatalyst for the enantioselective conjugate addition of alkene boronic acids to γ-hydroxy enones, leading to 1 in high ee. Attempted Mitsunobu coupling led to the cyclopropane 2, while bromoetherification followed by intramolecular alkylation delivered the cyclopropane 3. Jeffrey W. Bode of the University of Pennsylvania demonstrated (Organic Lett. 2009, 11, 677) a remarkable dichotomy in the reactivity of N-heterocyclic carbenes. A triazolium precatalyst combined 4 and 5 to give 6, whereas an imidazolium precatalyst combined 4 and 5 to give 7. Xinmiao Liang of the Dalian Institute of Chemical Physics and Jinxing Ye of the East China University of Science and Technology devised (Organic Lett. 2009, 11, 753) a Cinchona -derived catalyst that converted the prochiral cyclohexenone 8 into the diester 10 in high ee. Rich G. Carter of Oregon State University found (J. Org. Chem. 2009, 74, 2246) a simple sulfonamide-based proline catalyst that effected the Mannich condensation of the prochiral ketone with ethyl glyoxalate 12 and the amine 13, leading to the amine 14. In the first pot of a concise, three-pot synthesis of (-)-oseltamivir, Yujiro Hayashi of the Tokyo University of Science combined (Angew. Chem. Int. Ed. 2009, 48, 1304) 15 and 16 in the presence of a catalytic amount of diphenyl prolinol TMS ether to give an intermediate nitro aldehyde. Addition of the phosphonate 17 led to a cyclohexenecarboxylate, that on the addition of the thiophenol 18 equilibrated to the ester 19. Ying-Chun Chen of Sichuan University used (Organic Lett. 2009, 11, 2848) a related diaryl prolinol TMS ether to direct the condensation of the readily-prepared phosphorane 20 with the unsaturated aldehyde 21 to give the cyclohexenone 22. Armando Córdova of Stockholm University also used (Tetrahedron Lett. 2009, 50, 3458) diphenyl prolinol TMS ether to mediate the addition of 24 to 23. The subsequent intramolecular aldol condensation proceeded with high diastereocontrol, leading to 25. Benjamin List of the Max-Planck Institut, Mülheim employed (Nat. Chem. 2009, 1, 225) a MacMillan catalyst for the reductive cyclization of 26.
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Rosales, Merlin, Federico Arrieta, Jéssica Castillo, Angel González, Janeth Navarro, and Regina Vallejo. "Regioselective homogeneous hydrogenation of heteroaromatic nitrogen compounds by use of [OsH(CO)(NCMe)2(PPh3)2]BF4 as the Precatalyst." In Studies in Surface Science and Catalysis. Elsevier, 2000. http://dx.doi.org/10.1016/s0167-2991(00)80541-8.
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Malacria, M., C. Aubert, and J. L. Renaud. "Cobalt(II) Complexes as Precatalysts." In Compounds with Transition Metal-Carbon pi-Bonds and Compounds of Groups 10-8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os). Georg Thieme Verlag KG, 2001. http://dx.doi.org/10.1055/sos-sd-001-00376.
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"Density Functional Theory Computational Study of Phosphine Ligand Dissociation versus Hemilability in a Grubbs-Type Precatalyst Containing a Bidentate Ligand during Alkene Metathesis." In Industrial Applications of Molecular Simulations. CRC Press, 2016. http://dx.doi.org/10.1201/b11485-17.
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Lambert, Tristan H. "Functional Group Protection." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0014.
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Alfonso Iadonisi at the University of Naples Federico II developed (Eur. J. Org. Chem. 2013, 3137) a procedure for the selective acetolysis of the perbenzylated sugar 1 to furnish 3 using isopropenyl acetate (2) instead of the more typical and high-boiling acetic anhydride. The (3,4-dimethoxylphenyl)benzyl (DMPBn) protecting group, which is removed (cf. 4 → 5) under acidic conditions in the presence of the cation scavenger 5, was developed (J. Org. Chem. 2013, 78, 5264) by David S. Larsen at the University of Otago as an alternative to the p-methoxybenzyl (PMB) group. Another new hydroxyl-protecting group, the AzDMB group, which can be installed by simple acylation of (7 + 8 → 9) and removed under reductive conditions, was developed by Gijsbert A. van der Marel and Jeroen D.C. Codée of Leiden University. Stefan Grimme at the University of Bonn and Armido Studer at Westfälische-Wilhelms-Universität Münster found (Chem. Sci. 2013, 4, 2177) that NHC precatalyst 11 in the presence of NaH, benzaldehyde, and the oxidant 12 allows for the selective O-acylation of aminoalcohol 10 to 13. The reductive deprotection of benzyl carbamate 14 using the strong organic reductant 15 under photolytic conditions was achieved (Angew. Chem. Int. Ed. 2013, 52, 2239) by John A. Murphy at the University of Strathclyde. Liang-Qiu Lu and Wen-Jing Xiao at Central China Normal University found (Chem. Asian J. 2013, 8, 1090) that mixed imide 17 could be detosylated under visible light photoredox catalysis in the presence of Hantzsch ester 18. Frank Glorius at Westfälische-Wilhelms-Universität Münster developed (Org. Lett. 2013, 15, 1776) a ruthenium-catalyzed procedure for the N-formylation of amine 20 using methanol as the source of the formyl group. Protection of the thymine derivative 22 with a 2-(methoxycarbonyl)ethenyl (MocVinyl) group to produce 23 was developed (J. Org. Chem. 2013, 78, 5832) by Jaume Vilarrasa at the University of Barcelona. Deprotection of the MocVinyl group is readily achieved by treatment with a nucleophilic reagent such as pyrrolidine. Robert H. Grubbs at Caltech demonstrated (Chem. Sci. 2013, 4, 1640) that ether 24 could be demethylated with triethylsilane and potassium t-butoxide at high temperatures.
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Rama, Raquel J., M. Trinidad Martín, Auxiliadora Prieto, and M. Carmen Nicasio. "Developing Ni and Pd precatalysts for demanding cross-coupling reactions." In Advances in Inorganic Chemistry. Elsevier, 2024. http://dx.doi.org/10.1016/bs.adioch.2024.05.002.
Full textConference papers on the topic "Precatalyst"
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McLeod, Jon, Don Nagy, Pat Schroeder, et al. "A Sampling System for the Measurement of PreCatalyst Emissions from Vehicles Operating Under Transient Conditions." In International Congress & Exposition. SAE International, 1993. http://dx.doi.org/10.4271/930141.
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