[PDF] Mechanistic Studies Of Palladium Catalyzed Diene Carbocyclization eBook

Author : Pedro Luis Arrechea
Publisher :
Page : 253 pages
File Size : 10,58 MB
Release : 2016
Category :
ISBN :

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Mechanistic studies on the palladium catalyzed C-N bond-forming reaction were carried out to generate a more complete understanding of the catalytic cycle. To understand this reaction, several kinetic studies employing simple aryl halide and amine coupling partners were performed to elucidate unknown reaction pathways. Chapter 1. The resting state for the palladium catalyzed cross-coupling of various diarylamines and aryl halides is found to be the diphenylamido complex. Kinetic studies of the catalytic reaction are used to generate an Eyring plot. Hammett studies were performed for both the aryl halide and diarylamine coupling partners. The rates of reductive elimination for catalysts based on the biaryl ligands XPhos, CyJohnPhos, CPhos, BrettPhos, RuPhos, and SPhos were evaluated. Analogues of SPhos demonstrated that electron-donation of the lower aryl group is key to the stability of the amido complex in accordance with theoretical calculations. The methoxy substituent at the C3 position is demonstrated to retard the overall rate of reductive elimination for a RuPhos-BrettPhos hybrid ligand. These studies demonstrate that reductive elimination is likely not a problematic step for C-N cross-couplings. Chapter 2. Kinetic experiments demonstrated an inverse dependence on the concentration of both amine and aryl halide coupling partners. These observations are demonstrated to be valid for several amine classes, aryl halides, and biaryl ligands. Some work is done to demonstrate mechanistic overlap with other bidentate ligands. Based on these studies, a simplified reaction network for oxidative addition is proposed which reproduces key features of the experimental system.

Author : Hyung Yoon
Publisher : Springer Nature
Page : 236 pages
File Size : 29,81 MB
Release : 2020-09-02
Category : Science
ISBN : 3030540774

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This book presents Pd- and Ni-catalyzed transformations generating functionalized heterocycles. Transition metal catalysis is at the forefront of synthetic organic chemistry since it offers new and powerful methods to forge carbon–carbon bonds in high atom- and step-economy. In Chapter 1, the author describes a Pd- and Ni-catalyzed cycloisomerization of aryl iodides to alkyl iodides, known as carboiodination. In the context of the Pd-catalyzed variant, the chapter explores the production of enantioenriched carboxamides through diastereoselective Pd-catalyzed carboiodination. It then discusses Ni-catalyzed reactions to generate oxindoles and an enantioselective variant employing a dual ligand system. Chapter 2 introduces readers to a Pd-catalyzed diastereoselective anion-capture cascade. It also examines diastereoselective Pd-catalyzed aryl cyanation to synthesize alkyl nitriles, a method that generates high yields of borylated chromans as a single diastereomer, and highlights its synthetic utility. Lastly, Chapter 3 presents a Pd-catalyzed domino process harnessing carbopalladation, C–H activation and π-system insertion (benzynes and alkynes) to generate spirocycles. It also describes the mechanistic studies performed on these reactions.

Author : Liane May Klingensmith
Publisher :
Page : 138 pages
File Size : 50,68 MB
Release : 2005
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ISBN :

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Precatalyst species present in a solution of Pd2(dba)3 and Xantphos were identified as Pd(Xantphos)(dba) and Pd(Xantphos)2 by use of 31p NMR and independent syntheses. Pd(Xantphos)2 was found to form at high ligand concentrations. To determine whether the formation of this species affected reaction rates, reaction calorimetry was used to explore the rate of the palladium-catalyzed coupling of 4-t-butylbromobenzene and morpholine using the ligand Xantphos at varying palladium to ligand ratios. It was found that catalyst activity is dramatically dependent on the concentration of ligand relative to palladium, due to formation of Pd(Xantphos)2. Two plausible hypotheses for the low activity of Pd(Xantphos)2 as a precatalyst are (1) a slow rate of dissociation of a ligand from the bis-ligated species, and (2) the high degree of insolubility of Pd(Xantphos)2. Magnetization transfer experiments were used to probe the rate of dissociation of ligand for the bis-ligated species, and reaction calorimetry experiments were performed using the more soluble t-butylXantphos in comparison to Xantphos to determine whether the insolubility of' Pd(Xantphos)2 causes it to have relatively low activity. It was found that solubility is not the main cause for the low activity of Pd(Xantphos)2, and evidence was given to support the hypothesis that low activity results from the slow dissociation of a ligand from the bis-ligated species.

Author : P. Henry
Publisher : Springer Science & Business Media
Page : 449 pages
File Size : 15,76 MB
Release : 2012-12-06
Category : Science
ISBN : 940099446X

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The field of organometallic chemistry has emerged over the last twenty-five years or so to become one of the most important areas of chemistry, and there are no signs of abatement in the intense current interest in the subject, particularly in terms of its proven and potential application in catalytic reactions involving hydrocarbons. The development of the organometallic/ catalysis area has resulted in no small way from many contributions from researchers investigating palladium systems. Even to the well-initiated, there seems a bewildering and diverse variety of organic reactions that are promoted by palladium(II) salts and complexes. Such homogeneous reactions include oxidative and nonoxidative coupling of substrates such as olefins, dienes, acetylenes, and aromatics; and various isomerization, disproportionation, hydrogenation, dehydrogenation, car bonylation and decarbonylation reactions, as well as reactions involving formation of bonds between carbon and halogen, nitrogen, sulfur, and silicon. The books by Peter M. Maitlis - The Organic Chemistry of Palladium, Volumes I, II, Academic Press, 1971 - serve to classify and identify the wide variety of reactions, and access to the vast literature is available through these volumes and more recent reviews, including those of J. Tsuji [Accounts Chem. Res. , 6, 8 (1973); Adv. in Organometal. , 17, 141 (1979)], R. F. Heck [Adv. in Catat. , 26, 323 (1977)], and ones by Henry [Accounts Chem. Res. , 6, 16 (1973); Adv. in Organometal. , 13, 363 (1975)]. F. R. Hartley's book - The Chemistry of Platinum and Palladium, App!. Sci. Pub!.

Author : Montserrat Diéguez
Publisher : John Wiley & Sons
Page : 431 pages
File Size : 23,70 MB
Release : 2018-02-21
Category : Technology & Engineering
ISBN : 3527804072

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An important reference for researchers in the field of metal-enzyme hybrid catalysis Artificial Metalloenzymes and MetalloDNAzymes in Catalysis offers a comprehensive review of the most current strategies, developed over recent decades, for the design, synthesis, and optimization of these hybrid catalysts as well as material about their application. The contributors—noted experts in the field—present information on the preparation, characterization, and optimization of artificial metalloenzymes in a timely and authoritative manner. The authors present a thorough examination of this interesting new platform for catalysis that combines the excellent selective recognition/binding properties of enzymes with transition metal catalysts. The text includes information on the various applications of metal-enzyme hybrid catalysts for novel reactions, offers insights into the latest advances in the field, and contains an informative perspective on the future: Explores the development of artificial metalloenzymes, the modern and strongly evolving research field on the verge of industrial application Contains a comprehensive reference to the research area of metal-enzyme hybrid catalysis that has experienced tremendous growth in recent years Includes contributions from leading researchers in the field Shows how this new catalysis combines the selective recognition/binding properties of enzymes with transition metal catalysts Written for catalytic chemists, bioinorganic chemists, biochemists, and organic chemists, Artificial Metalloenzymes and MetalloDNAzymes in Catalysis offers a unique reference to the fundamentals, concepts, applications, and the most recent developments for more efficient and sustainable synthesis.