scholarly journals Online HPLC Analysis of Buchwald-Hartwig Aminations from Within an Inert Environment

2020 ◽  
Author(s):  
Thomas C. Malig ◽  
Lars P. E. Yunker ◽  
Sebastian Steiner ◽  
Jason E. Hein
Keyword(s):  
Hplc Analysis ◽  
A Priori ◽  
Underlying Mechanism ◽  
Small Subset ◽  
Coupling Reactions ◽  
Chemical Transformations ◽  
Automated Sampling ◽  
Catalyst Systems ◽  
Temporal Profiles ◽  
Monitoring Platform

We have developed a reaction monitoring platform capable of automated sampling and online HPLC analysis to generate temporal profiles for reactions performed from within a glovebox. The device allows for facile reaction progress analysis to aid in mechanistic studies of air-sensitive chemical transformations. The platform has demonstrated high reproducibility regarding sample mixing, dilution, delivery, and analysis. We employed the sampling platform to acquire temporal profiles for a series of Buchwald-Hartwig aminations. Parallel coupling reactions using iodobenzene and bromobenzene both exhibit complex kinetics. A competition reaction including both aryl halides demonstrated high selectivity for iodobenzene indicative of catalyst monopoly. The temporal profile for the difunctionalized substrate 1,4-iodobromobenzene was unexpected based <i>a priori </i>and is indicative of a distinct underlying mechanism. We attribute this unanticipated reactivity to intramolecular catalysts transfer through the π system as seen in “living” polymerization transfer catalyst systems. This automated sampling platform has greatly increased mechanistic understanding by performing only a small subset of experiments.

scholarly journals Online HPLC Analysis of Buchwald-Hartwig Aminations from Within an Inert Environment

2020 ◽  
Author(s):  
Thomas C. Malig ◽  
Lars P. E. Yunker ◽  
Sebastian Steiner ◽  
Jason E. Hein
Keyword(s):  
Hplc Analysis ◽  
A Priori ◽  
Underlying Mechanism ◽  
Small Subset ◽  
Coupling Reactions ◽  
Chemical Transformations ◽  
Automated Sampling ◽  
Catalyst Systems ◽  
Temporal Profiles ◽  
Monitoring Platform

We have developed a reaction monitoring platform capable of automated sampling and online HPLC analysis to generate temporal profiles for reactions performed from within a glovebox. The device allows for facile reaction progress analysis to aid in mechanistic studies of air-sensitive chemical transformations. The platform has demonstrated high reproducibility regarding sample mixing, dilution, delivery, and analysis. We employed the sampling platform to acquire temporal profiles for a series of Buchwald-Hartwig aminations. Parallel coupling reactions using iodobenzene and bromobenzene both exhibit complex kinetics. A competition reaction including both aryl halides demonstrated high selectivity for iodobenzene indicative of catalyst monopoly. The temporal profile for the difunctionalized substrate 1,4-iodobromobenzene was unexpected based <i>a priori </i>and is indicative of a distinct underlying mechanism. We attribute this unanticipated reactivity to intramolecular catalysts transfer through the π system as seen in “living” polymerization transfer catalyst systems. This automated sampling platform has greatly increased mechanistic understanding by performing only a small subset of experiments.

Synthesis of Phosphonates, Phosphinates and Tertiary Phosphine Oxides by Pd- or Ni-Catalyzed Microwave-Assisted P–C Coupling Reactions without the Addition of Conventional Ligands

2021 ◽  
Vol 25 ◽  
Author(s):  
Réka Henyecz ◽  
György Keglevich
Keyword(s):  
Tautomeric Form ◽  
Catalyst Precursor ◽  
Coupling Reactions ◽  
Optimum Conditions ◽  
Pd Catalysts ◽  
Catalyst Complex ◽  
Two Factors ◽  
Dialkyl Phosphites ◽  
Catalyst Systems ◽  
P Ligands

Abstract: Microwave (MW)-assistance may be a powerful tool also in the Hirao P–C coupling reactions of vinyl/aryl halides with dialkyl phosphites in the presence of Pd-catalysts/P-ligands elaborated forty years ago. This review surveys the development of this reaction by showing the expansion of the reagents and catalysts, as well as the information accumulated. The stress was laid on the “green” aspects, the simplification of the catalyst systems, and the reliable mechanistic details in order to be able to establish the optimum conditions. The best protocol involves the use of some excess of the >P(O)H reagent to ensure the PdII→Pd0 reduction and, via its trivalent tautomeric form (>POH) also the P-ligand. The overall rate is the result of two factors, the activity of the catalyst complex formed, and the reactivity of the reactants in the P–C coupling reactions. Both components are influenced by the nature of the aryl substituents in Ar2P(O)H. NiII salts may also be used as the catalyst precursor, however, despite the PdII→Pd0→PdII route, in this case, a NiII→NiIV→NiII sequence was proved.

Character selection and the quantification of morphological disparity

Paleobiology ◽  
2016 ◽  
Vol 43 (1) ◽  
pp. 68-84 ◽  
Author(s):  
Bradley Deline ◽  
William I. Ausich
Keyword(s):  
A Priori ◽  
Morphological Diversity ◽  
Small Subset ◽  
Early Paleozoic ◽  
Data Set ◽  
Rarefaction Analysis ◽  
Morphological Studies ◽  
Body Regions ◽  
Scientific Hypotheses

AbstractA priori choices in the detail and breadth of a study are important in addressing scientific hypotheses. In particular, choices in the number and type of characters can greatly influence the results in studies of morphological diversity. A new character suite was constructed to examine trends in the disparity of early Paleozoic crinoids. Character-based rarefaction analysis indicated that a small subset of these characters (~20% of the complete data set) could be used to capture most of the properties of the entire data set in analyses of crinoids as a whole, noncamerate crinoids, and to a lesser extent camerate crinoids. This pattern may be the result of the covariance between characters and the characterization of rare morphologies that are not represented in the primary axes in morphospace. Shifting emphasis on different body regions (oral system, calyx, periproct system, and pelma) also influenced estimates of relative disparity between subclasses of crinoids. Given these results, morphological studies should include a pilot analysis to better examine the amount and type of data needed to address specific scientific hypotheses.

scholarly journals DFT Study of Unstrained Ketone C-C Bond Activation via Rhodium(I)-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions

2019 ◽  
Author(s):  
Dengmengfei Xiao ◽  
Lili Zhao ◽  
Diego Andrada
Keyword(s):  
Density Functional ◽  
Bond Activation ◽  
Chemical Reactivity ◽  
Cross Coupling ◽  
Underlying Mechanism ◽  
Reductive Elimination ◽  
Coupling Reactions ◽  
Co Catalysts ◽  
Cross Coupling Reactions ◽  
Strain Model

Unstrained cyclic ketones can participate in cooperative Suzuki-Miyaura cross-coupling type reaction using rhodium(I)-based catalyst via C-C bond activation. The regioselectivity indicates a trend where the most substituted side is activated and it is controlled by the beta-substituents. In this work, Density Functional Theory (DFT) calculations have been carried out to disclose the underlying mechanism in the reaction of a ketone series and arylboronate using ylidene as ancillary ligand and pyridine as co-catalysts. The computed energies suggest the reductive elimination step with the highest energy while the reductive elimination has the highest energy barrier. By the means of the Activation Strain Model (ASM) of chemical reactivity, it is found that the ketone strain energy released on the oxidative addition does not control the relativity of the OA reactivity, but indeed is the interaction energy between Rh(I) and C-C bond the ruling effect. The effect of the beta-substituents on regioselectivity has been additionally studied.

scholarly journals Tailored Catalysis for the F&F Industry

2021 ◽  
Vol 75 (7) ◽  
pp. 634-641
Author(s):  
Denis Jacoby
Keyword(s):  
Aldol Condensation ◽  
Cost Effective ◽  
Coupling Reactions ◽  
Chemical Transformations ◽  
Bond Forming ◽  
Heterogeneous Catalytic ◽  
Cross Coupling Reactions ◽  
Carbon Carbon Bond ◽  
The Difference ◽  
Insight Into

Over the past decades, scientists at Firmenich have focused their efforts on continuously improving chemical transformations for the production of F&F ingredients in order to make them safer, cleaner, more efficient and consequently cost effective, through the implementation of the Green Chemistry principles. Numerous examples of innovative catalytic technologies could be cited, particularly in the field of homogeneous and heterogeneous catalytic hydrogenation. Nevertheless, we chose here to provide a rare insight into the industrial application of some very useful and atom-economic carbon–carbon bond forming reactions. We selected two examples among others as a good illustration of how catalysis makes the difference compared to conventional stoichiometric approaches. The first example deals with catalysed cross-aldol condensation and the second example concerns catalysis of cross-coupling reactions.

scholarly journals A domino reaction for generating β-aryl aldehydes from alkynes by substrate recognition catalysis

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Weiwei Fang ◽  
Felix Bauer ◽  
Yaxi Dong ◽  
Bernhard Breit
Keyword(s):  
Substrate Recognition ◽  
Domino Reaction ◽  
Chemical Transformations ◽  
Reaction Sequence ◽  
Reaction Conditions ◽  
Consecutive Reaction ◽  
Aryl Aldehydes ◽  
Rh Catalyst ◽  
Catalyst Systems ◽  
Step Control

Abstract The development of universal catalyst systems that enable efficient, selective, and straightforward chemical transformations is of immense scientific importance. Here we develop a domino process comprising three consecutive reaction steps based on the strategy of supramolecular substrate recognition. This approach provides valuable β-aryl aldehydes from readily accessible α-alkynoic acids and arenes under mild reaction conditions, employing a supramolecular Rh catalyst containing an acylguanidine-bearing phosphine ligand. Furthermore, the synthesis of a key intermediate of Avitriptan using this protocol is accomplished. The first step of the reaction sequence is proved to be the regioselective hydroformylation of α-alkynoic acids. Remarkably, molecular recognition of the ligand and the substrate via hydrogen bonding plays a key role in this step. Control experiments indicate that the reaction further proceeds via 1,4-addition of an arene nucleophile to the unsaturated aldehyde intermediate and subsequent decarboxylation.

Application of Bimetallic and Trimetallic Nanoparticles Supported on Graphene as novel Heterogeneous Catalysts in the Reduction of Nitroarenes, Homo-coupling, Suzuki-Miyaura and Sonogashira Reactions

2020 ◽  
Vol 24 (19) ◽  
pp. 2216-2234
Author(s):  
Seyede Mahdiye Hoseini Chopani ◽  
Shima Asadi ◽  
Majid M. Heravi
Keyword(s):  
Graphene Oxide ◽  
Metal Nanoparticles ◽  
Heterogeneous Catalysts ◽  
Bimetallic Nanoparticles ◽  
Solid Surfaces ◽  
Coupling Reactions ◽  
Chemical Transformations ◽  
Organic Transformations ◽  
Conductive Surface ◽  
Sonogashira Reactions

In the last decade, the use of heterogeneous catalysts based on Metal Nanoparticles (MNPs) has attracted increasing attention due to their prominence as nanocatalysts in several key chemical transformations. Notably, it is well identified that supporting Metal Nanoparticles (MNPs) with suitable solid surfaces can protect the MNPs from leaching, deactivation, and also increasing its ease of separation and possible reusability. Graphene oxide (GO) as a conductive surface could have non-covalent bonding interactions like hydrogen bonding, electrostatic and π –π* stacking interactions with substrate leading to activation of the substrate. Remarkably, it is recognized that bimetallic nanoparticles supported on graphene oxide often show novel properties that are not present on either of the parent metal or surfaces. In this review, we tried to reveal the potential advantages of bimetallic and trimetallic nanoparticles supported on graphene oxide in organic transformations, including the reduction of nitroarenes, Suzuki-Miyaura and Sonogashira coupling reactions.

Gold Nanoparticles as Efficient Catalysts in Organic Transformations

2021 ◽  
Vol 22 ◽  
Author(s):  
Irshad A. Wani ◽  
Sapan K. Jain ◽  
Huma Khan ◽  
Abul Kalam ◽  
Tokeer Ahmad
Keyword(s):  
Carbon Monoxide ◽  
Gold Nanoparticles ◽  
Fuel Cells ◽  
Liquid Phase ◽  
Industrial Applications ◽  
Coupling Reactions ◽  
Chemical Transformations ◽  
Organic Transformations ◽  
Catalytic Materials

Abstract: This review summarizes the utilization of gold nanoparticles as efficient catalysts for a variety of chemical transformations like oxidation, hydrogenation and coupling reactions as compared to the conventional catalytic materials. This review explores the gold nanoparticles based catalysts for the liquid phase chemo-selective organic transformations which are proving to be evergreen reactions and has importance for industrial applications. Apart from organic transformation reactions gold nanoparticles has been found to be applicable in removing the atmospheric contaminants and improving the efficiency of the fuel cells by removing the impurities of carbon monoxide.

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