N-Heterocyclic Carbenes in Synthesis

N-Heterocyclic Carbenes in Synthesis
Author: Steven P. Nolan
Publisher: Wiley-VCH
Total Pages: 319
Release: 2006-12-13
Genre: Science
ISBN: 3527609407

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This first handbook to focus solely on the application of N-heterocyclic carbenes in synthesis covers metathesis, organocatalysis, oxidation and asymmetric reactions, along with experimental procedures. Written by leading international experts this is a valuable and practical source for every organic chemist.

Synthetic Approaches Towards Gold (I) and Silver (I) Complexes of Functionalised N-heterocyclic Carbene Ligands

Synthetic Approaches Towards Gold (I) and Silver (I) Complexes of Functionalised N-heterocyclic Carbene Ligands
Author: James Laurence Hickey
Publisher:
Total Pages: 311
Release: 2008
Genre: Anti-infective agents
ISBN:

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This work focuses on the design and synthesis of Au(I) and Ag(I) complexes from ligand systems that aim to combine both N-heterocyclic carbene (NHC) and phosphine ligand types. A number of synthetic approaches towards both the ligands and the prepared metal complexes have been developed, with a concerted effort on achieving the desired Au(I) or Ag(I) complexes with minimal reaction steps and synthetic style. The thesis body is divided into two main sections. The first section addresses the preparation of suitable ligand precursors of potential Au(I) and Ag(I) complexes in the form of halo- and phosphino-functionalised imidazolium salts. Several series of haloalkylimidazolium salts were prepared that encompass a range of halogens (Cl, Br, I), alkyl substituents (Me, i-Pr, t-Bu, n-Bu), differing alkyl linker length (n = 0-3), and a variety of organic spacers employed to bridge multi-imidazolium moieties. Novel bidentate and multidentate phosphinoalkylimidazolium salts were synthesised from the various haloalkylimidazolium salts, via the substitution of a halide with nucleophilic diphenylphosphide. A new approach towards rare methylene bridged phosphinomethylimidazolium salts was achieved from the reactions of halomethylimidazolium salts with diphenylphosphine. The second section investigates the preparation of Au(I) and Ag(I) complexes from the halo- and phosphino-functionalised imidazolium salts. A series of dicationic 10, 12, and 14-membered metallacyclic Ag(I) complexes were prepared from the bidentate phosphinoalkylimidazolium salts. The dinuclear Ag(I) metallacycles combine two phosphino-functionalised NHC ligands that are bridged by two coordinated Ag(I) ions in an exclusively head-to-head arrangement. A dinuclear Ag(I) metallacycle was investigated for transmetallation potential to a Au(I) complex and found to selectively transmetallate at the Ag(I) coordinated to the NHC ligands to form a bimetallic metallacycle. Unexpected phosphine oxidation of a 10-membered dinuclear Ag(I) metallacycle resulted in complex disproportionation to an isolable and rare silver(I) trimer. Metal-NHC complexes from haloalkylimidazolium salts have not been reported previously, a novel approach to the synthesis of a series of Au(I) complexes from haloalkylimidazolium salts and a respective gold source was developed and is reported herein. Different synthetic approaches towards Au(I) complexes with the phosphinoalkylimidazolium salts explored a variety of ways to generate the NHC from an imidazolium in the presence of the phosphine. A one-pot, high yielding synthesis of a dinuclear Au(I) complex from PPh3 was also devised, with controlled assembly of the complex resulting in a similar head-to-head ligand arrangement to the dinuclear Ag(I) metallacycles. As an aside, a family of mononuclear [Au(R2NHC)2]+ complexes (R = Me, i-Pr, t- Bu, n-Bu, Cy) prepared previously in our research group, was expanded because of the promising antimitochondrial activity shown by [Au(i-Pr2NHC)2]+. Two new [Au(R2NHC)2]+ complexes with simple alkyl chain functionality were prepared with fine-tuned lipophilicity in close proximity to that of [Au(i-Pr2NHC)2]+.

Part I: Backbone Modification of N-heterocyclic Carbenes: New Ligands and Applications to Catalysis Part II: Large Scale Synthesis of NHC Precursor 2,6-di(3-pentyl)aniline

Part I: Backbone Modification of N-heterocyclic Carbenes: New Ligands and Applications to Catalysis Part II: Large Scale Synthesis of NHC Precursor 2,6-di(3-pentyl)aniline
Author: Matthew Pompeo
Publisher:
Total Pages:
Release: 2013
Genre:
ISBN:

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The first part of this research is focused on the development and application of backbone-modified N-heterocyclic carbene (NHC) ligands in palladium-catalyzed cross-coupling. Various backbone substituted imidazole-2-ylidine NHCs and their corresponding Pd-PEPPSI complexes were synthesized and S.A.R. studies were performed in a series of challenging cross-coupling reactions to determine the effect of backbone substitution on catalyst activity. Pd-PEPPSI-IPentCl, featuring chlorines on the backbone of our IPent NHC, was identified as one of the most active and selective catalysts yet reported in the literature in the secondary alkyl Negishi coupling, an important method for the installation of secondary alkyl groups onto aromatic systems. Mechanistic studies, supported by DFT calculations and IR spectroscopic analyses, indicate that the effect imparted by the backbone substituents is primarily steric in originches Further optimizing the architecture of the trans-ligated pyridine culminated in the development of Pd-PEPPSI-IPentCl-picoline, which we have shown to be a superior catalyst for the unprecedented room temperature Buchwald-Hartwig amination of aryl halides with electronically deactivated anilines using a mild carbonate base. These conditions are milder than any yet reported in the literature for the cross-coupling of anilines and represent a significant advance in the field. The second part of this research deals with the development of a method for the large-scale preparation of 2,6-di(3-pentyl)aniline, a precursor to the IPent family of novel, highly active NHC ligands. Our newly developed synthetic route features a Pd-catalyzed cross-coupling of 3-lithio-2-pentene, derived from 3-pentanone, to readily available 2,6-dibromoaniline. This new sequence represents a significant improvement in overall process efficiency in the form of a lower step count, higher product yield, and increased reproducibility relative to earlier syntheses. Since its inception, this method has been applied successfully towards the synthesis of nearly 0. 7 kg of 2,6-di(3-pentyl)aniline and has the potential for larger scale implementation.

Artificial Metalloenzymes and MetalloDNAzymes in Catalysis

Artificial Metalloenzymes and MetalloDNAzymes in Catalysis
Author: Montserrat Diéguez
Publisher: John Wiley & Sons
Total Pages: 431
Release: 2018-02-21
Genre: 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.

Gold Chemistry

Gold Chemistry
Author: Fabian Mohr
Publisher: John Wiley & Sons
Total Pages: 425
Release: 2009-04-20
Genre: Science
ISBN: 3527320865

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Written by world-class authors, this most recent major book on the topic highlights new and current trends as well as future directions. It is comprehensive in its scope, covering all aspects of gold chemistry -- from homogeneous to heterogeneous catalysis, from supramolecular assemblies to sensors and medicinal applications. The result is an invaluable work for both organic and inorganic chemists working in universities and industry, as well as material scientists.

Phosphorus-31 NMR Spectroscopy

Phosphorus-31 NMR Spectroscopy
Author: Olaf Kühl
Publisher: Springer Science & Business Media
Total Pages: 138
Release: 2008-08-22
Genre: Science
ISBN: 3540791183

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Nuclear Magnetic Resonance is a powerful tool, especially for the identification of 1 13 hitherto unknown organic compounds. H- and C-NMR spectroscopy is known and applied by virtually every synthetically working Organic Chemist. Con- quently, the factors governing the differences in chemical shift values, based on chemical environment, bonding, temperature, solvent, pH, etc. , are well understood, and specialty methods developed for almost every conceivable structural challenge. Proton and carbon NMR spectroscopy is part of most bachelors degree courses, with advanced methods integrated into masters degree and other graduate courses. In view of this universal knowledge about proton and carbon NMR spectr- copy within the chemical community, it is remarkable that heteronuclear NMR is still looked upon as something of a curiosity. Admittedly, most organic compounds contain only nitrogen, oxygen, and sulfur atoms, as well as the obligatory hydrogen and carbon atoms, elements that have an unfavourable isotope distribution when it comes to NMR spectroscopy. Each of these three elements has a dominant isotope: 14 16 32 16 32 N (99. 63% natural abundance), O (99. 76%), and S (95. 02%), with O, S, and 34 14 S (4. 21%) NMR silent. N has a nuclear moment I = 1 and a sizeable quadrupolar moment that makes the NMR signals usually very broad and dif cult to analyse.