Investigations Into The Selectivity Of Iridium Catalysts In The Hydrogen Isotope Exchange Of Aromatic Aldehydes And In Hydroxyl Directed Stereoselective Hydrogenation
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Investigations Into The Selectivity Of Iridium Catalysts In The Hydrogen Isotope Exchange Of Aromatic Aldehydes And In Hydroxyl Directed Stereoselective Hydrogenation
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Author : Giorgia Kidd
language : en
Publisher:
Release Date : 2022
Investigations Into The Selectivity Of Iridium Catalysts In The Hydrogen Isotope Exchange Of Aromatic Aldehydes And In Hydroxyl Directed Stereoselective Hydrogenation written by Giorgia Kidd and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with categories.
Hydrogenation And Hydrogen Isotope Exchange
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Author : Richard J. Mudd
language : en
Publisher:
Release Date : 2016
Hydrogenation And Hydrogen Isotope Exchange written by Richard J. Mudd and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
The field of iridium(I)-mediated processes has expanded over the past 50 years, with new avenues of research constantly opening. To this end, the Kerr group has developed a series of cationic iridium(I) catalysts bearing a bulky NHC/phosphine ligand sphere that can effectively mediate mild hydrogen isotope exchange and olefin hydrogenation processes.Having said this, with the ever-expanding scope of NHCs and the increasing ease of access to phosphines, the possibility still exists to further improve upon these complexes with lower catalyst loadings, faster reaction times, and an improved substrate scope. To this end, this thesis details some of the work achieved throughout the last 3.5 years.Within the first chapter, progress towards more efficient olefin hydrogenation is discussed. In the first instance, highly selective hydrogenation, through the use of a directing group was targeted. Initial investigations focussed upon manipulating the counterion to the cationic iridium(I) complexes in question, and manipulating the ligand sphere through changing the nature of the phosphine and NHC. This process generated new methods for the synthesis of NHC/phosphine catalysts, and was applied to the production of a number of novel complexes. Following on from this, a highly efficient reduction process was optimised, and the selectivity therein investigated.Following on from this, the equivalent asymmetric reaction was then studied, thus entering a new field of research within the group, and therefore, requiring the development of a completely new catalyst system. This process was guided by the non-asymmetric system, and synthesis of a number of model non-chiral complexes. After thoroughly testing the newly synthesised complexes, greater understanding was gained of the requirements for a highly enantioselective reaction, and, through this, to propose a plausible selectivity model and mechanism.In chapter two, we discuss the development of NHC/phosphine catalysts in hydrogen isotope exchange, with a partiular focus on the selectivity of the exchange process. Following on from previous work in the group, this first targets the use of weakly coordinating acids as a directing group, and the impact that addition of base has upon the selectivity of the reaction.Furthermore, understanding that drug design is moving away from planar molecules, towards non-planar, sp3-rich compounds, we also investigated the possibility of exchange at positions in a molecule other than an sp2 aryl ring. This was initially observed when developing the hydrogenation methods discussed in chapter one, enabling selective sp2 exchange in conjugated olefins. This new, highly selective method of labelling was examined through a combined experimental and computational investigation, leading to a thorough understanding of the mechanism and factors governing reaction selectivity. Having progressed from sp2-aryl to sp2-non-aryl exchange, the logical progression was to next investigate sp3 exchange. Through a detailed study three protocols were developed, enabling exchange on a wide range of sp3 hybridised sites, in pharmaceutically relevant systems. These new processes were investigated mechanistically and computationally to ascertain the mechanism and selectivity of exchange.
Iridium Complexes As Highly Active Catalysts For Hydrogen Isotope Exchange And Hydrogen Borrowing Processes
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Author : Philippa Kate Owens
language : en
Publisher:
Release Date : 2018
Iridium Complexes As Highly Active Catalysts For Hydrogen Isotope Exchange And Hydrogen Borrowing Processes written by Philippa Kate Owens and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
Over the last several decades, the organic chemistry community has become increasingly reliant upon iridium catalysis, with applications reported across a number of research areas. In recent years, the Kerr group has developed a series of iridium complexes, which were found to be excellent catalysts for hydrogen isotope exchange and olefin hydrogenation processes. The work described within this thesis centres upon the expansion of these catalysts' reactivity in hydrogen isotope exchange, as well as the synthesis and application of a series of novel iridium complexes, designed for use in hydrogen borrowing catalysis. Chapter one focuses on the development of three efficient and selective methods for hydrogen isotope exchange. Iridium(I) catalysts previously developed within the group have been employed in the successful deuteration of N-heterocycles, which represent an important and relatively underexplored class of labelling substrates. The labelling of a large range of indole, pyrrole, and quinoline derivatives is reported, in which the regioselectivity can be controlled through careful choice of N-protecting group. Extensive practical and computational mechanistic investigations offered insight into the mechanism of indole C3 labelling, which is believed to proceed via an iridium-indoline intermediate. In chapter two, the design and synthesis of a series of novel unsymmetrical NHC ligands, functionalised with electron donating substituents, is described. The corresponding neutral iridium NHC/halide complexes were prepared, and the steric and electronic properties of the ligands were investigated using a number of techniques. These novel complexes were then tested in the catalysis of hydrogen borrowing processes. Extensive optimisation led to the development of an efficient method for the room-temperature N-alkylation of anilines. This methodology was also expanded to include the synthesis of N-heterocycles viaintramolecular C-N bond formation, albeit using more forcing conditions. Lastly, a small series of chiral NHC ligands was designed, and their corresponding iridium complexes prepared and used in a preliminary screening of asymmetric hydrogen borrowing.
Iridium Catalysts For Organic Reactions
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Author : Luis A. Oro
language : en
Publisher: Springer Nature
Release Date : 2021-03-29
Iridium Catalysts For Organic Reactions written by Luis A. Oro and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-03-29 with Science categories.
This new volume “Iridium Catalysts for Organic Reactions” in the series “Topics in Organometallic Chemistry” intends to update several representative well-known reactions and to introduce other less known or new reactions in particular covering sustainability aspects. Iridium complexes are efficient in many catalytic homogeneous transformations providing high efficiency in both results, activity and selectivity. The interest of the book lies in the presentation of the advances, new perspectives and application in a variety of representative iridium-catalysed reaction. All chapters in the volume are contributed by relevant international experts in the field. The book is aimed at researchers, graduate students and synthetic chemists at all levels in academia and industry.
Highly Active Iridium I Complexes For Catalytic Hydrogen Isotope Exchange And Selective Hydrogenation
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Author : Stephanie Irvine
language : en
Publisher:
Release Date : 2009
Highly Active Iridium I Complexes For Catalytic Hydrogen Isotope Exchange And Selective Hydrogenation written by Stephanie Irvine and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Advances In The Synthesis And Application Of Iridium I Complexes For Use In Hydrogen Isotope Exchange
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Author : Alison R. Cochrane
language : en
Publisher:
Release Date : 2012
Advances In The Synthesis And Application Of Iridium I Complexes For Use In Hydrogen Isotope Exchange written by Alison R. Cochrane and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
Investigations into the application of catalysts of the type [Ir(COD)(PR3)(IMes)]PF6 in the field of hydrogen isotope exchange have been undertaken. In particular, the use of alternative solvents has been examined, resulting in the identification of reaction media considered more industrially acceptable than those currently utilised in isotopic labelling processes. Following a series of optimisation studies, the newly developed conditions for H-D exchange were applied to a range of substrates containing a variety of functional groups. In the majority of instances, high levels of deuteration were achieved in reactions employing low catalyst loadings and short reaction times. With regards to the iridium complexes themselves, focus has centred on the introduction of alternative NHC ligands, leading to the synthesis of six novel Ir(I) catalysts. These complexes have been employed in hydrogen isotope exchange reactions, demonstrating high activity in the isotopic labelling of numerous substrates. As a result of such explorations, increased levels of selectivity have been achieved in compounds offering multiple sites of labelling, with catalysts displaying a greater preference for exchange via a 5-mmi over the less energetically favourable 6-mmi. In addition, a catalyst capable of facilitating higher levels of isotope incorporation adjacent to a sulfonamide moiety has been accomplished. A series of DFT studies have also been undertaken. The calculation of solvent binding energies to the iridium complex has revealed a broad correlation between the strength with which solvent molecules coordinate to the metal centre, and the degree of isotope incorporation observed. Further theoretical investigations were performed regarding our novel Ir(I) complexes bearing alternative NHC ligands. More specifically, computational experiments have identified the relative energies of the key processes which occur within the catalytic cycle.
Iridium Catalysis
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Author : Pher G. Andersson
language : en
Publisher: Springer Science & Business Media
Release Date : 2011-01-05
Iridium Catalysis written by Pher G. Andersson and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-01-05 with Science categories.
From the contents: Robert H Crabtree: Introduction and History. - Montserrat Diéguez, Oscar Pàmies and Carmen Claver: Iridium-catalysed hydrogenation using phosphorous ligands. - David H. Woodmansee and Andreas Pfaltz: Iridium Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands. - Ourida Saidi and Jonathan M J Williams: Iridium-catalyzed Hydrogen Transfer Reactions. - John F. Bower and Michael J. Krische: Formation of C-C Bonds via Iridium Catalyzed Hydrogenation and Transfer Hydrogenation. - Jongwook Choi, Alan S. Goldman: Ir-Catalyzed Functionalization of CH Bonds. - Mark P. Pouy and John F. Hartwig: Iridium-Catalyzed Allylic Substitution. - Daniel Carmona and Luis A. Oro: Iridium-catalyzed 1.3-dipolar cycloadditions.
New Subtrate Classes In Iridium Catalyzed Asymmetric Hydrogenation
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Author : Maurizio Bernasconi
language : en
Publisher: Cuvillier Verlag
Release Date : 2014-01-30
New Subtrate Classes In Iridium Catalyzed Asymmetric Hydrogenation written by Maurizio Bernasconi and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014-01-30 with Science categories.
The main aim of the research presented in this thesis was to expand the substrate scope of the iridium-catalyzed asymmetric hydrogenation, which represents an extremely useful methodology for the enantioselective synthesis of chiral molecules.While this chemistry has been developed and investigated mainly for the hydrogenation of unfunctionalized olefins, so far only little attention has been given to functionalized olefins. Therefore, the different research projects presented in this thesis dealt with the application of iridium catalysts to the reduction of particularly valuable substrates that are difficult to hydrogenate enantioselectively with other methods. The first chapter of this thesis gives a general introduction on asymmetric hydrogenation and the role of iridium catalysts in this context. The following two chapters deal with the investigation of new substrates in the iridium-catalyzed asymmetric hydrogenation using various N,Pligands developed in the Pfaltz group,and give an account of the superior results that have been obtained with such catalysts compared to thoserepresenting the state-of-the-art. In particular, chapter twoconcerns the reduction of vinylsilanes, for which the judicious choice of the best catalyst for each specific substrate was required to achieve good results in term of both chemical and optical yield. On the contrary, a pyridinyl phosphitine bearing a 2,6-difluorophenyl group on the oxazoline ringwas best suited for a broad array of 2-alkyl- and aryl- substituted maleic acid dimethyldiester, as reported in chapter three. Such process turned out to be enantioconvergent, allowing the hydrogenation of mixtures of maleates and fumarates in high enantiomeric excesses. In chapter fourthe deployment of environmentally friendly solvents such as THF and 2-MeTHF in the iridium-catalyzed asymmetric hydrogenation of 3,3-disubstituted allylic alcohols is described. Finally, chapter five of this dissertation deals with the development of new NHC ligands for the iridium-catalyzed asymmetric hydrogenation of acid-labile substrates such as tert-butyloxycarbonyl protected allylic alcohols. Experimental details and characterization of the substances discussed in the main body of this manuscript is reported in the experimental section that constitutes chapter six.
On The Design And Further Applications Of Iridium I Complexes In Hydrogen Isotope Exchange Processes
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Author : Marc Reid
language : en
Publisher:
Release Date : 2015
On The Design And Further Applications Of Iridium I Complexes In Hydrogen Isotope Exchange Processes written by Marc Reid and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
A new synthetic procedure for isolation of three established Kerr group catalysts has been successfully developed. The final yield of these catalysts has now been improved beyond those published in the literature, and has allowed for the commercialisation of such catalysts for the first time. The synthesis of a series of iridium(I) complexes of the type [(COD)Ir(IMes)(PPh3)]X (X = BF4, OTf, and BArF) has been established. Application of these species in hydrogen isotope exchange (HIE) processes revealed more efficient catalysis and a wider solvent scope when X = BArF. Additionally, these findings have allowed for the development of a novel method for ortho-HIE in unprotected tetrazoles under basic conditions, revealing a rare account of N-H tetrazole C-H activation and a new mode of reactivity for Kerr group HIE catalysts. Towards predictive catalyst design, a combined experimental and theoretical model has been developed to describe the impact of ligand combinations on catalyst performance. Experimentally, this has resulted in a further broad range of novel NHC/phosphine iridium carbonyl complexes, as well as a catalyst 'quick screen' method based on in-situ formation of Ir dihydride complexes. Computationally, novel parameters have been assessed, culminating in a combined ligand map derived from Principal Component Analysis (PCA) of 140 DFT-optimised iridium complexes. Ligand mapping methods have been employed to assess the use of natural product Lepidiline A as a NHC ligand precursor in novel HIE catalysts, revealing the almost purely electronic influence of 4,5-dimethyl substitution on the imidaz-2-ylidene ring. The PCA model has also highlighted complexes of the type [(COD)Ir(NHC)Cl] to be promising in delivering orthogonal reactivity to the now traditional NHC/phosphine pairing. This analysis has led to the realisation of the first regio- and chemoselective catalytic labelling methods for primary sulfonamides and aldehydes. Finally, a novel, one-parameter approach has been developed to describe chelating and monodentate ligand spheres on the same comparable and quantifiable footing. Chelating NHC/phosphine-ligated iridium catalysts have been designed, synthesised, and successfully applied to ortho-labelling of previously inaccessible sulfones, secondary sulfonamides, and bulky tertiary amides.
Synthetic And Mechanistic Investigations Of Iridium Catalysed Imine Hydrogenation
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Author : York Schramm
language : en
Publisher: Cuvillier Verlag
Release Date : 2013-08-13
Synthetic And Mechanistic Investigations Of Iridium Catalysed Imine Hydrogenation written by York Schramm and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-08-13 with Science categories.
The goal of this doctoral thesis was to gain a better understanding of the reaction course in imine hydrogenation as well as to develop an efficient protocol for the iridium-catalysed asymmetric hydrogenation of aliphatic imines. In the course of these studies, cyclometalation of a chiral imine to an achiral iridium complex generated a chiral catalyst. The structure of the cyclometalated imine was demonstrated to influence the enantioselectivity of the catalyst as well as to be involved in the enantiodiscriminating step of the hydrogenation. The iridacycles were investigated in further detail by two-dimensional NMR studies and their preparation was improved by counterion metathesis. Deuterium labelling experiments depicted addition of hydrogen along the C-N double bond. Optimisation studies for an efficient asymmetric hydrogenation protocol for purely aliphatic imines are described. Hydrogenations could be conducted at -5 °C achieving full conversion and improving enantioselectivities up to 92%. Cyclic aliphatic imines could also be hydrogenated with these iridacycles, but required elevated reaction temperatures as well as hydrogen pressures to achieve turnover. These studies concluded that iridium-catalysed imine hydrogenation is commenced by cyclometalation of the imine substrate to form an active iridium(III) catalyst prior to hydrogenation.