N-heterocyclic Carbenes

N-heterocyclic Carbenes
Author: Silvia Díez-González
Publisher: Royal Society of Chemistry
Total Pages: 469
Release: 2011
Genre: Science
ISBN: 1849730423

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Over the last fifteen years, N-heterocyclic carbenes (NHCs) have mostly been used as ancillary ligands for the preparation of transition metal-based catalysts. Compared to phosphorus-containing ligands, NHCs tend to bind more strongly to metal centres, avoiding the necessity for the use of excess ligand in catalytic reactions. The corresponding complexes are often less sensitive to air and moisture, and have proven remarkably resistant to oxidation. Recent developments in catalysis applications have been facilitated by the availability of carbenes stable enough to be bottled, particularly for their use as organocatalysts. This book shows how N-heterocyclic carbenes can be useful in various fields of chemistry and not merely laboratory curiosities or simple phosphine mimics. NHCs are best known for their contribution to ruthenium and palladium-catalysed reactions but the scope of this book is much broader. The synthesis of NHC ligands and their corresponding metal complexes are covered in depth. Moreover, the biological activity of NHC-containing complexes, as well as an overview of their theoretical aspects are included. Such metal species are further examined, not only in terms of their catalytic applications, but also of their stereoelectronic parameters and reactivity/stability. Finally, special attention is given to the hot topic of organocatalysis. The book will be of interest to postgraduates, academic researchers and those working in industry.

Functionalised N-Heterocyclic Carbene Complexes

Functionalised N-Heterocyclic Carbene Complexes
Author: Olaf Kühl
Publisher: John Wiley & Sons
Total Pages: 364
Release: 2010-02-02
Genre: Science
ISBN: 0470685840

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N-heterocyclic carbenes (NHCs) have found increasing use as reagents for a range of organic transformations and in asymmetric organocatalysis. The performance of these molecules can be improved and tuned by functionalisation. Functionalised carbenes can anchor free carbenes to the metal site, introduce hemilability, provide a means to immobilise transition metal carbene catalysts, introduce chirality, provide a chelate ligand or bridge two metal centres. NHC can be attached to carbohydrates and campher, derived from amino acids and purines, they can be used as organocatalysts mimicking vitamin B1 or as weak “solvent” donors in lanthanide chemistry. Functionalised N-Heterocyclic Carbene Complexes describes major trends in functionalised NHC ligands, aiming to assist readers in their attempts to develop and apply their own functionalised carbenes. After an introduction to the chemistry and behaviour of NHC, the book gives a detailed description of functionalised carbenes and their complexes according to a range of functional groups, each with a discussion of the synthetic route, structure, stability and performance. Functionalised N-Heterocyclic Carbene Complexes is an essential guide to fine-tuning this important class of compounds for practitioners, researchers and advanced students working in synthetic organometallic and organic chemistry and catalysis.

N-Heterocyclic Carbenes

N-Heterocyclic Carbenes
Author: Steven P. Nolan
Publisher: John Wiley & Sons
Total Pages: 690
Release: 2014-07-07
Genre: Science
ISBN: 3527671242

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This comprehensive reference and handbook covers in depth all major aspects of the use of N-heterocyclic carbene-complexes in organic synthesis: from the theoretical background to characterization, and from cross-coupling reactions to olefin metathesis. Edited by a leader and experienced scientist in the field of homogeneous catalysis and use of NHCs, this is an essential tool for every academic and industrial synthetic chemist.

N-Heterocyclic Carbenes in Synthesis

N-Heterocyclic Carbenes in Synthesis
Author: Steven P. Nolan
Publisher: John Wiley & Sons
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.

Exploratory Research Into Atypical N-heterocyclic Carbenes

Exploratory Research Into Atypical N-heterocyclic Carbenes
Author:
Publisher:
Total Pages: 127
Release: 2013
Genre: Electronic books
ISBN:

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The objective of this research is to create unique and highly functional N-heterocyclic carbene complexes that provide maximum catalytic features in close proximity to the metal centers. The N-heterocyclic carbenes created over the past 20 years have generally consisted of imidazole moieties substituted at both nitrogen atoms with alkyl and aryl substitutents. These typical N-heterocylic carbenes have presented many highly stable and tunable complexes used in catalysis, however, some beneficial features would be imparted on these N-heterocyclic carbenes if one of the alkyl and aryl substituted sites were allowed to remain un-substituted. These unique atypical protic N-heterocyclic carbenes allow for acid base chemistry to occur in close proximity to the metal center while simultaneously providing the tunable, highly sigma-donating features of a typical N-heterocyclic carbene. The research presented in this thesis explores the synthetic approach to atypical protic N-heterocyclic carbene ligand precursors as well as their complexation and subsequent catalytic capabilities. Two ligand precursor families were created: one consisting of an iodobenzene moiety attached to a tert-butyl imidazole group, and one in which a pyridine ring moiety is attached to a tert-butyl imidazole group. The iodobenzene group yielded two ligand precursors, 2a and 2b, both containing methylene spacers between the auxiliary moiety and tert-butyl groups. The pyridine-containing family consisted of 3a, where the tert-butyl imidazole was directly attached to the pyridine ring, and 3c, where the tert-butyl imidazole was attached to the ring by a methylene spacer. Attempts to complex the first ligand precursor family 2a and 2b were unsuccessful and lead to the synthesis of the pyridine analogues 3a and 3c which were successfully complexed to both iridium and rhodium metal centers yielding: Ir-Phos- 3a, Ir-Phos-3c, Ir-S0-3a, Ir-S1-3c, Rh-S0-3a, and Rh-S1-3c. Catalytic studies carried out with the six complexes above consisted of the oxidation of alcohols to their corresponding ketones. These catalytic tests revealed a higher degree of successful turnover with the 3c containing complexes. Crystallographic data suggests that bond angles and bond distances found in 3c containing complexes give inherent advantages to the 3c containing complexes due to the flex allowed by the methylene spacer. Additionally, catalytic comparisons of methylated analogues of 3c with the atypical protic 3c complexes showed a decrease in catalytic activity suggesting that the presences of the un-substituted nitrogen in close proximity to the metal center yields the predicted benefit of using atypical protic N-heterocyclic carbenes.

N-Heterocyclic Carbenes in Organocatalysis

N-Heterocyclic Carbenes in Organocatalysis
Author: Akkattu T. Biju
Publisher: John Wiley & Sons
Total Pages: 556
Release: 2019-03-04
Genre: Science
ISBN: 3527809074

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Summarizing the emerging field of N-heterocyclic carbenes used in organocatalysis, this is an excellent overview of the synthesis and applications of NHCs focusing on carbon-carbon and carbon-heteroatom bond formation. Alongside comprehensive coverage of the synthesis, characteristics and applications, this handbook and ready reference also includes chapters on NHCs for polymerization reactions and natural product synthesis.

The Organometallic Chemistry of N-heterocyclic Carbenes

The Organometallic Chemistry of N-heterocyclic Carbenes
Author: Han Vinh Huynh
Publisher: John Wiley & Sons
Total Pages: 352
Release: 2017-01-23
Genre: Science
ISBN: 1118698800

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The Organometallic Chemistry of N-heterocyclic Carbenes describes various aspects of N-heterocyclic Carbenes (NHCs) and their transition metal complexes at an entry level suitable for advanced undergraduate students and above. The book starts with a historical overview on the quest for carbenes and their complexes. Subsequently, unique properties, reactivities and nomenclature of the four classical NHCs derived from imidazoline, imidazole, benzimidazole and 1,2,4-triazole are elaborated. General and historically relevant synthetic aspects for NHCs, their precursors and complexes are then explained. The book continues with coverage on the preparation and characteristics of selected NHC complexes containing the most common metals in this area, i.e. Ni, Pd, Pt, Ag, Cu, Au, Ru, Rh and Ir. The book concludes with an overview and outlook on the development of various non-classical NHCs beyond the four classical types. Topics covered include: Stabilization, dimerization and decomposition of NHCs Stereoelectronic properties of NHCs and their evaluation Diversity of NHCs Isomers of NHC complexes and their identification NMR spectroscopic signatures of NHC complexes normal, abnormal and mesoionic NHCs The Organometallic Chemistry of N-heterocyclic Carbenes is an essential resource for all students and researchers interested in this increasingly important and popular field of research.

Synthetic and Catalytic Studies of Group 11 N-heterocyclic Carbene Complexes

Synthetic and Catalytic Studies of Group 11 N-heterocyclic Carbene Complexes
Author: David Stephen Laitar
Publisher:
Total Pages: 216
Release: 2006
Genre:
ISBN:

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(Cont.) Carbon dioxide also inserts into the Cu-Si bond of a copper silyl complex. The resulting complex evolves CO to give a copper siloxide complex. Mesitaldehyde inserts cleanly and selectively into the Cu-B bond of (NHC)CuB(pin), to form a B-O and a copper-carbon bond. This complex reacts with bis(pinacolato)diboron to regenerate (NHC)CuB(pin) and produce an aldehyde diboration product, in which a diboron reagent has been added across the C=O bond of mesitaldehyde. A copper boryl complex with a smaller NHC supporting ligand proved to be a much more effective diboration catalyst and a wide range of aldehydes react cleanly with bis(pinacolato)diboron. The insertion of alkenes into an (NHC)copper(I) boryl affords isolable -boroalkyl complexes in high yields; competition experiments using substituted styrenes show that electron-donating substituents slow the reaction. Although the insertion products are stable at ambient temperature, a P-hydride elimination/reinsertion sequence affords a rearranged a-boroalkyl complex on heating.