44 results found
Ali C, Blackmond DG, Burés J, 2022, Kinetic Rationalization of Nonlinear Effects in Asymmetric Catalytic Cascade Reactions under Curtin–Hammett Conditions, ACS Catalysis, Pages: 5776-5785, ISSN: 2155-5435
Hutchinson G, Alamillo-Ferrer C, Bures J, 2021, Mechanistically Guided Design of an Efficient and Enantioselective Aminocatalytic alpha-Chlorination of Aldehydes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 143, Pages: 6805-6809, ISSN: 0002-7863
Gesslbauer S, Hutchinson G, White A, et al., 2021, Chirality-Induced catalyst aggregation: insights into catalyst speciation and activity using chiral aluminum catalysts in cyclic ester ring-opening polymerization, ACS Catalysis, Vol: 11, Pages: 4084-4093, ISSN: 2155-5435
A series of chiral-at-metal aluminum complexes have been synthesized using chiral catam ligands. Reactivity studies demonstrate the importance of alkoxide bulkiness and complex chirality in inducing catalyst aggregation. This has been exploited in cyclic ester ring-opening polymerization (ROP). For ε-Cl ROP, enantiopure catalysts were found to outperform a racemic mixture of catalysts, as the racemic mixture resulted in lower activity heterodimeric catalytic species and reduced polymerization rates. In the case of L-LA, one catalyst enantiomer was found to be the most active of the series and outperformed both the other enantiomer and the corresponding achiral catalyst. Very high activities were observed and up to 9,200 equivalents of L-LA were polymerized in 4.5 min at 150 °C with TOF > 100,000 h–1 under industrially relevant conditions. Analysis of the catalyst orders for these reactions provided a meaningful catalyst speciation-activity relationship enabling improved understanding of both catalyst speciation and the activity of each catalytic species involved in cyclic ester ROP using chiral aluminum catalysts.
Alamillo-Ferrer C, Nielsen CD-T, Salzano A, et al., 2021, Understanding the Diastereopreference of Intermediates in Aminocatalysis: Application to the Chiral Resolution of Lactols, JOURNAL OF ORGANIC CHEMISTRY, Vol: 86, Pages: 4326-4335, ISSN: 0022-3263
Hutchinson G, Welsh CDM, Bures J, 2021, Use of Standard Addition to Quantify In Situ FTIR Reaction Data, JOURNAL OF ORGANIC CHEMISTRY, Vol: 86, Pages: 2012-2016, ISSN: 0022-3263
Seppanen O, Aikonen S, Muuronen M, et al., 2020, Dual H-bond activation of NHC-Au(i)-Cl complexes with amide functionalized side-arms assisted by H-bond donor substrates or acid additives, CHEMICAL COMMUNICATIONS, Vol: 56, Pages: 14697-14700, ISSN: 1359-7345
Somerville RJ, Hale LVA, Gomez-Bengoa E, et al., 2019, Intermediacy of Ni-Ni Species in sp(2) C-O Bond Cleavage of Aryl Esters: Relevance in Catalytic C-Si Bond Formation (vol 140, pg 8771, 2018), JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 141, Pages: 20565-20565, ISSN: 0002-7863
Nielsen CD-T, White AJP, Sale D, et al., 2019, Hydroarylation of Alkenes by Protonation/Friedel-Crafts Trapping: HFIP-Mediated Access to Per-aryl Quaternary Stereocenters, JOURNAL OF ORGANIC CHEMISTRY, Vol: 84, Pages: 14965-14973, ISSN: 0022-3263
Martinez-Carrion A, Howlett MG, Alamillo-Ferrer C, et al., 2019, Kinetic Treatments for Catalyst Activation and Deactivation Processes based on Variable Time Normalization Analysis, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 58, Pages: 10189-10193, ISSN: 1433-7851
MartínezCarrión A, Howlett MG, AlamilloFerrer C, et al., 2019, Kinetic Treatments for Catalyst Activation and Deactivation Processes based on Variable Time Normalization Analysis, Angewandte Chemie, Vol: 131, Pages: 10295-10299, ISSN: 0044-8249
Nielsen C, White A, Sale D, et al., 2019, Hydroarylation of Alkenes by protonation/Friedel-Crafts Trapping – HFIP-Mediated Access to Per-Aryl Quaternary Stereocentres, ChemRxiv
<div> <p>Upon treatment with a combination of HFIP and a strong Brønsted acid, alkenes behave as Brønsted bases and protonate to give carbocations which can be trapped by electron rich arenes. The reaction constitutes a Friedel-Crafts (FC) hydroarylation which proceeds with Markovnikov selectivity and is orthogonal to traditional metal catalyzed processes. The products contain polyarylated quaternary carbon atoms which are difficult to obtain <i>via</i> alternative methods. Intermolecular transfer hydrogenation and hydrothiolation are also demonstrated. </p> </div>
Nielsen C, White AJP, Sale D, et al., 2019, Hydroarylation of Alkenes by protonation/Friedel-Crafts Trapping – HFIP-Mediated Access to Per-Aryl Quaternary Stereocentres, ChemRxiv
<jats:p><div><p>Upon treatment with a combination of HFIPand a strong Brønsted acid, alkenes behave as Brønsted bases and protonate to givecarbocations which can be trapped by electron rich arenes. The reaction constitutesa Friedel-Crafts (FC) hydroarylation which proceeds with Markovnikovselectivity and is orthogonal to traditional metal catalyzed processes. Theproducts contain polyarylated quaternary carbon atoms which are difficult toobtain <i>via</i> alternative methods. Intermoleculartransfer hydrogenation andhydrothiolation are also demonstrated. </p></div></jats:p>
Nielsen CD-T, Bures J, 2019, Visual kinetic analysis, Chemical Science, Vol: 10, Pages: 348-353, ISSN: 2041-6520
Visual kinetic analyses extract meaningful mechanistic information from experimental data using the naked-eye comparison of appropriately modified progress reaction profiles. Basic kinetic information is obtained easily and quickly from just a few experiments. Therefore, these methods are valuable tools for all chemists working in process chemistry, synthesis or catalysis with an interest in mechanistic studies. This minireview describes the visual kinetic analyses developed in the last fifteen years and provides answers to the most common queries of new users. Furthermore, a video tutorial is attached detailing the implementation of both VTNA and RPKA.
Nielsen CD-T, Mooij WJ, Sale D, et al., 2019, Reversibility and reactivity in an acid catalyzed cyclocondensation to give furanochromanes - a reaction at the "oxonium-Prins' vs. "ortho-quinone methide cycloaddition' mechanistic nexus, Chemical Science, Vol: 10, Pages: 406-412, ISSN: 2041-6520
Herein we report a combined experimental and computational investigation of the acid catalyzed cyclocondensation reaction between styrenyl homoallylic alcohols and salicylaldehyde to form furanochromanes. We disclose a previously unreported isomerisation of the ‘unnatural’ trans-fused products to the diastereomeric ‘natural’ cis-fused congeners. Notwithstanding the appeal of assuming this corresponds to endo to exo isomerisation of Diels–Alder (D–A) adducts via concerted retro-cycloaddition/cycloaddition reactions of an in situ generated ortho-quinone methide with the styrenyl alkene, our combined Hammett/DFT study reveals a stepwise Prins-like process via discrete benzylic carbocation intermediates for all but the most electron deficient styrenes. As these reactions fortuitously lie at the intersection of these two mechanistic manifolds, it allows us to propose an experimentally determined indicative ρ+ value of ca. −3 as marking this nexus between a stepwise Prins-type pathway and a concerted cycloaddition reaction. This value should prove useful for categorising other reactions formally involving ‘ortho-quinomethides’, without the need for the extensive computation performed here. Logical optimisation of the reaction based upon the mechanistic insight led to the use of HFIP as an additive which enables exclusive formation of ‘natural’ cis-fused products with a ∼100-fold reaction rate increase and improved scope.
Somerville RJ, Hale LVA, Gomez-Bengoa E, et al., 2018, Intermediacy of Ni-Ni Species in sp(2) C-O Bond Cleavage of Aryl Esters: Relevance in Catalytic C-Si Bond Formation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 140, Pages: 8771-8780, ISSN: 0002-7863
Aikonen S, Muuronen M, Wirtanen T, et al., 2018, Gold(I)-Catalyzed 1,3-O-Transposition of Ynones: Mechanism and Catalytic Acceleration with Electron-Rich Aldehydes, ACS CATALYSIS, Vol: 8, Pages: 960-967, ISSN: 2155-5435
Colletto C, Bures J, Larrosa I, 2017, Reaction monitoring reveals poisoning mechanism of Pd-2(dba)(3) and guides catalyst selection, CHEMICAL COMMUNICATIONS, Vol: 53, Pages: 12890-12893, ISSN: 1359-7345
Marais L, Bures J, Jordaan JHL, et al., 2017, A bis(pyridyl)-N-alkylamine/Cu(I) catalyst system for aerobic alcohol oxidation, ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 15, Pages: 6926-6933, ISSN: 1477-0520
Companyo X, Bures J, 2017, Distribution of Catalytic Species as an Indicator To Overcome Reproducibility Problems, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 139, Pages: 8432-8435, ISSN: 0002-7863
Bures J, 2017, What is the order of a reaction?, Topics in Catalysis, Vol: 60, Pages: 631-633, ISSN: 1022-5528
The order of a reaction in some species seems an obvious, trivial concept that all chemists master. However, in complex situations such as catalytic systems, the order of a reaction is not always that simple: it can be partial, negative and function of other parameters. In order to analyze rate laws and experimental orders of complex reaction networks, it is necessary to have a proper mathematical description of what the order of a reaction is. In general, chemists working in catalysis are unaware that such a mathematical description exists and therefore they are restricted to analyzing only extreme limit cases of rate laws. This manuscript offers a description and a simple demonstration of this concept, known as elasticity coefficient or normalized sensitivity. It also presents several examples of applications on classic and usual catalytic scenarios.
Bures J, 2016, Variable Time Normalization Analysis: General Graphical Elucidation of Reaction Orders from Concentration Profiles, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 55, Pages: 16084-16087, ISSN: 1433-7851
Burés J, 2016, Variable Time Normalization Analysis: General Graphical Elucidation of Reaction Orders from Concentration Profiles, Angewandte Chemie, Vol: 128, Pages: 16318-16321, ISSN: 0044-8249
Whitaker D, Burés J, Larrosa I, 2016, Ag(I)-catalyzed C-H activation: the role of the Ag(I) salt in Pd/Ag mediated C-H arylation of electron-deficient arenes, Journal of the American Chemical Society, Vol: 138, Pages: 8384-8387, ISSN: 0002-7863
The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C–H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C–H activation on electron-deficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh3)Ag-carboxylate is responsible for the C–H activation step in the Pd-catalyzed arylation of Cr(CO)3-complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C–H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C–H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C–H functionalization methodologies.
Jimeno C, Günler ZI, Companyó X, et al., 2016, Deciphering the roles of multiple additives in organocatalyzed Michael additions, Chemical Communications, Vol: 52, Pages: 6821-6824, ISSN: 1364-548X
The synergistic effects of multiple additives (water and acetic acid) on the asymmetric Michael addition of acetone to nitrostyrene catalyzed by primary amine-thioureas (PAT) were precisely determined. Acetic acid facilitates hydrolysis of the imine intermediates, thus leading to catalytic behavior, and minimizes the formation of the double addition side product. In contrast, water slows down the reaction but minimizes catalyst deactivation, eventually leading to higher final yields.
Burés J, 2016, A Simple Graphical Method to Determine the Order in Catalyst, Angewandte Chemie, Vol: 128, Pages: 2068-2071, ISSN: 0044-8249
Bures Amat J, Blackmond DG, armstrong A, 2016, Explaining Anomalies in Enamine Catalysis: “Downstream Species” as a New Paradigm for Stereocontrol, Accounts of Chemical Research, ISSN: 1520-4898
Bures Amat J, 2016, A Simple Graphical Method to Determine the Order in Catalyst, Angewandte Chemie - International Edition, ISSN: 1433-7851
A graphical analysis to elucidate the order in catalyst is presented. This analysis uses a normalized time scale, t [cat]Tn, to adjust entire reaction profiles constructed with concentration data. The method is fast and simple to perform because it directly uses the concentration data, therefore avoiding the data handling that is usually required to extract rates. Compared to methods that use rates, the normalized time scale analysis requires fewer experiments and minimizes the effects of experimental errors by using information on the entire reaction profile.
Bures J, Dingwall P, Armstrong A, et al., 2014, Rationalization of an Unusual Solvent-Induced Inversion of Enantio-meric Excess in Organocatalytic Selenylation of Aldehydes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 53, Pages: 8700-8704, ISSN: 1433-7851
Isart C, Bures J, Vilarrasa J, 2014, Electrospray ionization mass spectra of the reactions of NaAuBr4 and related aurates with nucleophiles, JOURNAL OF MASS SPECTROMETRY, Vol: 49, Pages: 331-334, ISSN: 1076-5174
Burés J, Armstrong A, Blackmond DG, 2013, The interplay of thermodynamics and kinetics in dictating organocatalytic reactivity and selectivity, Pure and Applied Chemistry, Pages: 1-1, ISSN: 0033-4545
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