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This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: • This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. • A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. • This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. • The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. • When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Transition-Metal-Hydrogen Systems at Extreme Conditions I V N E R U S E I T H Y T O H F G E R D I N B U Thomas Scheler A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the University of Edinburgh March 2013 Abstract The application of extreme conditions offers a general route for the synthesis of materials under equilibrium conditions. By finely tuning the thermodynamic variables of pressure and temperature one can manipulate matter on an atomic scale, creating novel compounds or changing the properties of existing materials. In particular, the study of hydrogen and hydrogen compounds has attracted the attention of researchers in the past. Although hydrogen readily reacts with many elements at ambient conditions, there is a significant “hydride gap” covering the d-metals between the Cr-group and Cu-group elements. At elevated pressures however, the chemical potential of hydrogen rises steeply. At sufficient pressures, hydrogen overcomes the dissociation barrier at the metal surface and atomic hydrogen diffuses into the metal, usually occupying interstitial sites in the host matrix. These interstitial hydrogen alloys can exhibit interesting physical properties, such as modified crystalline structures, different compressibility, altered microstructure (nanocrystallinity), hydrogen mediated superconductivity or potential hydrogen storage capabilities. Furthermore, theory predicts that hydrogen confined in a host matrix might undergo the elusive transition to a metallic groundstate at considerably lower pressures than pure hydrogen. Most d-metals have been found to exhibit hydride phases at extended conditions of pressure and temperature. However, besides rhenium, the 6th row metals between tungsten and gold, as well as silver, have not or only very recently been found to form bulk hydrides. In the course of this PhD-thesis, several of the missing metal- hydrides were successfully synthesized in the diamond anvil cell and characterized by in-situ x-ray diffraction using synchrotron radiation. i Declaration Except where otherwise stated, the research undertaken in this thesis was the unaided work of the author. Where the work was done in collaboration with others, a significant contribution was made by the author. T. Scheler March 2013 ii Acknowledgements In a way, writing these acknowledgements was the most difficult part of completing this thesis. So many people contributed to this work on various levels and it would be impossible to name you all. First and foremost, I would like to thank my supervisor Eugene Gregoryanz who has been a great mentor over the past few years and was always available when I needed help. Although it is difficult for me now to drink a Radler (Alster) without feeling a tiny amount of guilt. I would like to thank my colleagues Christophe Guillaume, Ross Howie, Phil Simpson and Donna Morton who helped a lot with the preparation of diamond anvil cells and with experiments during beamtimes. The memory of all of us sitting in the Dreyer in Hamburg is still fresh. A big Thank You also goes to everyone who was involved in the hydride projects: Miriam Marqu´es, who did calculations for the platinum and iridium projects, Yanming Ma and his group for calculations in the tungsten project, Christian Donnerer who took over the copper project and brought it to a nice conclusion, Zuzana Konˆopkov´a who spent several nights alone at the beamline at PETRA-III laser-heating our iridium samples, Olga Degtyareva for teaching me the basics of crystallographic data analysis, Thomas Cornelius and Tobias Sch¨ulli for giving me a few days of their inhouse beamtime at the ESRF for testing in-situ scanning x- ray diffraction microscopy. Additionally, there were so many people in CSEC who contributed with helpful discussions, by looking over data with me or simply during fantastic lunchtime conversations. Thank you Graham, Ingo, John, Emma, Craig, Mungo, Wanaruk, Chris, Rachel, Julian, Michal, Lucy, Alex. Looking back over the past three years, I would have never managed to get anywhere without the help of Jane Patterson. I would also like to extend my thanks to everyone in the CM-DTC, in particular Prof. Andy Mackenzie, Dr. Chris Hooley, Christine Edwards and Dr. Julie Massey and also Prof. Malcolm McMahon, who made it possible for me in the first place to come to Edinburgh. I am grateful to my examiners Prof. Paul Attfield and Dr. Michael Hanfland for their time and for providing constructive criticism which helped to improve this thesis significantly. Finally, the biggest (and I mean that) Thank You goes to Mirjam - for simply everything. iii Contents Abstract i Declaration ii Acknowledgements iii Contents iv List of figures v List of tables xiii 1 Introduction 1 1.1IntroductionandMotivation..................... 1 1.2 Thesis Outline ............................. 5 2 The Metal-Hydrogen System 9 2.1PropertiesofFreeHydrogen..................... 9 2.2HydrogeninHostMatrices...................... 13 2.3TransitionMetal-Hydrides:AReview................ 19 3 Review of High-Pressure Equipment and Techniques 31 3.1TheDiamondAnvilCell....................... 31 3.2 Pressure Scales ............................ 34 3.2.1 The Ruby Pressure Scale ................... 35 3.2.2 Equations of State as Pressure Scales ............ 37 3.2.3 TheDiamondRamanGauge................. 38 3.2.4 TheHydrogenVibronGauge................ 40 3.3 X-ray Diffraction at High Pressures ................. 41 3.3.1 BasicDiffractionTheory................... 42 3.3.2 In-situ Synchrotron X-ray Diffraction at High Pressure . 46 3.3.3 Determination of Hydrogen Content with X-rays ...... 48 3.4 Other Techniques . ......................... 50 3.4.1 RamanSpectroscopy..................... 50 iv CONTENTS 3.4.2 NeutronDiffraction...................... 50 3.4.3 TransmissionElectronMicroscopy.............. 51 3.4.4 FocusedIonBeams...................... 51 4 Transition Metal-Hydrogen Systems at Extreme Conditions 54 4.1Platinum................................ 54 4.2 Rhenium ................................ 64 4.3Tungsten................................ 73 4.4 Iridium ................................. 90 4.5Copper................................. 104 4.6Othermetals............................. 106 4.6.1 Gold.............................. 106 4.6.2 Silver .............................. 109 4.6.3 Osmium ............................ 110 5 Conclusions and Future Prospects 112 A Data Tables 116 Bibliography 130 Publications 143 v List of Figures 2.1 Raman spectrum of hydrogen at ∼5 GPa (fluid state) in a diamond anvil cell. The peaks denoted D1 and D2 are first and second order diamond Raman peaks (see chapter 3.2). The hydrogen rotons are seen at Raman shifts below D1 (So(1) and So(3)belongtootho-, So(0) and So(2) to para-hydrogen), the main hydrogen vibron mode −1 ν1 at shifts above 4000 cm .DatacourtesyofR.Howie...... 10 2.2 PT-Phase-diagram of hydrogen (see [Howie 12] and references therein (annexed to this thesis)). The thick solid line denotes the proposed melting curve. Coloured dashed lines with open triangles and crosses are theoretical transition boundaries between the molecular and atomic state. Thin solid lines are established phase boundaries between solid phases I, II and III. Thin dashed lines are the recently proposed phase boundaries including phase IV. 13 2.3 The Cr-group to Cu-group elements and their reactions with hydrogen (arrows). α denotes a bcc configuration, an hcp and γ an fcc configuration. Fully green fields denote the formation of a stoichiometric hydride. Ruthenium is only known to form a substoichiometric hydride with low hydrogen content, while no hydride phases are known for silver and osmium. The existence of a hydride phase in gold is in dispute (see chapter 2.3). The blue frame indicates the scope of the present work, i.e. elements investigated during the course of this thesis. For comparison, the state of knowledge prior to this work is included next to the respectivesymbols........................... 15 3.1 A) Schematic drawing of a typical DAC. B) Photograph of a closed symmetric DAC (“doughnut” type). C) Close-up schematic of the sample confined between the gasket (drawing) and the two diamondanvils............................. 32 vi LIST OF FIGURES 3.2 Gasket Preparation: A) A sheet of Re is placed between the aligned diamonds. B) The diamonds are pressed into the metal to create an indent. C) A centered hole is drilled into the indent. D) The metal sample is placed with a sharp needle in the hole. E) The cell is closed with one diamond leaving a small gap. F) Air in the cell is replaced with hydrogen gas and the cell is closed. G)-H) Optical micrograph of the sample hole taken through the diamonds. The metal sample and a ruby-sphere can be seen in the 50 μmhole. 34 3.3 A) Energy levels in the Cr3+ ion, taken from [Syassen 08]. B) Fluorescence spectrum from ruby showing the R1 and R2 lines. 36 3.4 Equations of state for the metals listed in Table 3.1 (see there for references). Inset shows EoS for copper. .............. 38 3.5 Equation of state of hydrogen. Inset shows d-spacings of hydrogen Bragg peaks vs. pressure. The values are derived from the EoS given in [Loubeyre 96]. For practical purposes, the data can be foundinTableA.1........................... 39 3.6 The Akahama pressure scale for the diamond Raman edge [Akahama 07]. InsetshowstheobservedRamanspectrumat123GPa......
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  • Using Alcohols As Simple H2-Equivalents for Copper-Catalysed Transfer Semihydrogenations of Cite This: Chem

    Using Alcohols As Simple H2-Equivalents for Copper-Catalysed Transfer Semihydrogenations of Cite This: Chem

    ChemComm View Article Online COMMUNICATION View Journal | View Issue Using alcohols as simple H2-equivalents for copper-catalysed transfer semihydrogenations of Cite this: Chem. Commun., 2019, 55,13410 alkynes† Received 26th August 2019, Accepted 15th October 2019 Trinadh Kaicharla, Birte M. Zimmermann, Martin Oestreich and Johannes F. Teichert * DOI: 10.1039/c9cc06637c rsc.li/chemcomm Copper(I)/N-heterocyclic carbene complexes enable a transfer copper hydride-based catalytic transformation, namely the semi- semihydrogenation of alkynes employing simple and readily available reduction of internal alkynes to alkenes.10–12 alcohols such as isopropanol. The practical overall protocol circumvents The alkyne semihydrogenation poses challenges in stereo- theuseofcommonlyemployedhighpressureequipmentwhenusing selectivity (E vs. Z) and chemoselectivity (overreduction of the 10 Creative Commons Attribution 3.0 Unported Licence. dihydrogen (H2) on the one hand, and avoids the generation of stoichio- formed alkene to the corresponding alkane, Scheme 1), and thus metric silicon-based waste on the other hand, when hydrosilanes are serves as an ideal model reaction for catalyst development. To probe used as terminal reductants. a possible transfer of a hydrogen atom from the a-position of an alcohol by means of a copper(I) catalyst, we investigated the transfer Catalytic transfer hydrogenations (TH) are attractive for the semihydrogenation of internal alkyne 1,usinga,a-dideuterated reduction of a variety of functional groups, as they offer practical benzyl alcohol (2-d2, Scheme 1). Employing readily available [SIMes- protocols circumventing the need for high pressure equipment.1 CuCl]13 in catalytic amounts (10 mol%) and NaOtBu as base, full In general, for catalytic TH there is a need for easy-to-use and safe conversion either with microwave or conventional heating to the dihydrogen (H2) sources, as these reactants are associated with the corresponding alkene 3 was found.