Iridium Complexes As Highly Active Catalysts For Hydrogen Isotope Exchange And Hydrogen Borrowing Processes
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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.
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.
Iridium I Complexes For The Functionalisation Of Carbon Hydrogen Bonds
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Author : Renan Zorzatto
language : en
Publisher:
Release Date : 2018
Iridium I Complexes For The Functionalisation Of Carbon Hydrogen Bonds written by Renan Zorzatto 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.
The development of catalytic systems for the functionalisation of carbon-hydrogen bonds has been an intensive area of research for the last 5 decades. In this context, transition metal complexes play a crucial role in reaction discovery, mechanistic evaluation and synthetic applications. In the Kerr group, this technology has been explored in the context of hydrogen isotope exchange, resulting in the development of highly active iridium(I) complexes bearing phosphines and NHC ligands. Despite their broad functional group compatibility, existing methods for isotope exchange are ineffective in the labelling of sterically encumbered directing groups. Hence, in the first chapter we investigate the synthesis of three new iridium(I) complexes bearing chelating phosphine-functionalised NHC ligands, and their application in the isotope exchange of sterically hindered carbamates. Our initial studies revealed high catalytic efficiency and tolerance for steric encumbrance, prompting us to perform a combined theoretical and experimental investigation of the reaction mechanism.Therefore, by conducting DFT calculations and kinetic experiments, we were able to identify a rich dynamic behaviour in solution and ultimately propose a reaction mechanism. Additionally, our interest in the activation of carbon-hydrogen bonds resulted in the exploration of a theoretical model for the prediction of enthalpies of activation, resulting in the identification of relevant electronic and steric descriptors.From the knowledge gathered in our initial studies, the second chapter describes the application of our novel iridium catalysts in the functionalisation of carbon-hydrogen bonds in the context of hydroarylation of olefins. Thus, we identified carboxylic acids as suitable directing groups for this transformation and employed Design of Experiments to optimise the reaction conditions. Synthetic studies were focused on the preparation of 14 substrates, enabling quick assessment of the capabilities and limitations of this reaction. These investigations resulted in a synthetic method suitable for the synthesis of bi- and tricycles featuring tertiary and quaternary benzylic stereocentres in a racemic fashion.Finally, we investigated the mechanism of this process by DFT calculations, which led us to identify a plausible reaction pathway which should guide future kinetic evaluations.
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.
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.
Computationally Guided Rational Ligand Design Of Novel Iridium I Complexes For Elevated Substrate Applicability In Hydrogen Isotope Exchange Processes
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Author : Gary J. Knox
language : en
Publisher:
Release Date : 2018
Computationally Guided Rational Ligand Design Of Novel Iridium I Complexes For Elevated Substrate Applicability In Hydrogen Isotope Exchange Processes written by Gary J. Knox 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.
Using a computationally guided rational ligand design approach, a novel chelated NHC-P iridium(I) catalyst system has been identified for the directed hydrogen isotope exchange (HIE) of aryl sulfones. The catalyst design process was aided primarily through DFT binding energy calculations. The solvent scope of the reaction was studied, and the optimised conditions applied to the successful deuterium labelling of a broad range of 20 aryl sulfones. The catalyst system was also shown to be highly active in the HIE of aryl sulfones at sub-atmospheric pressures of deuterium. Additionally, the catalyst system was applied in the tritiation of aryl sulfones, affording tritiated samples of methylphenyl sulfone, as well as a GPR119 agonist, in high levels of specific activity.This chelated catalyst system was then further refined for the labelling of highly substituted sulfonamides. A more focussed approach to the catalyst design process was taken at this stage, with a combination of binding energy calculations and binding mode analysis being used to guide the modification of the ligand. This resulted in a novel, chelated NHC-Py system, which proved to be highly active in the HIE of a broad range of highly substituted sulfonamides. A total of 22 sulfonamide substrates were synthesised, and labelled using this novel catalyst system. Additionally, this complex was shown to be highly effective in the deuteration of sulfoximines, for which the means of labelling are severely under met.Finally, our studies in the labelling of aryl sulfones led us to the serendipitous discovery of ether-directed HIE. This process was investigated with our novel NHC-P catalyst system, and a substrate scope established. Additionally, a potential application in form of labelling natural products, and natural product-like molecules has been proposed, with a series of three natural product-like molecules having been synthesised for attempts towards labelling.
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 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.
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.
Oxide And Zeolite Supported Molecular Iridium Complexes And Clusters
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Author : Jing Lu
language : en
Publisher:
Release Date : 2012
Oxide And Zeolite Supported Molecular Iridium Complexes And Clusters written by Jing Lu 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.
The stability and performance of supported catalysts are influenced by the size and structure of the metal species, the ligands bonded to the metal, and the support. Resolution of these effects has been lacking because of the lack of investigations of catalysts with uniform and systemically varied catalytic sites. Starting with a molecular iridium complex precursor, Ir(C2H4)2(acac) (acac is acetylacetonate), highly uniform isostructural supported Ir(C2H4)2 complexes were prepared on MgO, [gamma]-Al2O3, zeolite HY zeolite H[beta], and zeolite HSSZ-53 supports. The structure and transformation of these supported iridium complexes were characterized with infrared (IR) spectroscopy, X-ray absorption spectroscopy (XAS), and scanning transmission electron microscopy (STEM). By treatments in H2, the supported iridium complexes were converted into: (a) small clusters consisting of only a few atoms (~Ir4) at 353 K, and (b) bigger clusters approximately 1 nm in diameter (~Ir40) at 673 K. Moreover, the isostructural Ir(C2H4)2 complexes were transformed into Ir(CO)2, Ir(CO)(C2H4), Ir(CO)(C2H4)2 and Ir(CO)2(C2H4) complexes on supports by treatments in various mixtures of flowing C2H4, CO, and helium. Thus, this set of samples provides supported iridium species with systematically varied supports, ligands and nuclearities. The catalytic performances of these iridium complexes and clusters were evaluated for ethylene hydrogenation and H-D exchange in the conversion of H2 and D2. Furthermore, the cluster formation (sintering) process from supported iridium complex catalysts in contact with H2 was also investigated. The data identify support and ligand effects in catalytic reaction mechanisms and in sintering behavior of the metal species. The results are expected to contribute to fundamental understanding of structure, bonding, and reactivity of supported catalysts, suggesting further opportunities for design and discovery of hydrocarbon conversion catalysts.