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Steven Kealey Synthesis and Coordination Chemistry of Scorpionate Ligands and their Applications in 11C—Positron Emission Tomography Steven Kealey Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy Supervisor: Prof. N. J. Long Department of Chemistry Imperial College London April 2008 STATEMENT OF COPYRIGHT The copyright of this thesis rests with the author. No quotation from it should be published without the prior written consent of the author and information derived from it should be acknowledged appropriately. DECLARATION The work described in this thesis was carried out in the Department of Chemistry, Imperial College London, between October 2004 and December 2007. The entire body of work is my own unless otherwise stated to the contrary and has not been submitted previously for a degree at this or any other university. i ABSTRACT This thesis is concerned with the synthesis and coordination chemistry of a range of poly(pyrazolyl)borate scorpionate' ligands and examines their suitability in facilitating rapid [11C]carbonylation reactions to form radiotracers for application in positron emission tomography (PET). The synthesis of a series of tris(pyrazolyl)borate (Tp) ligands and their corresponding copper(I) carbonyl complexes is described. The copper(I) carbonyls were formed by reaction of potassium Tp salts with copper chloride in the presence of carbon monoxide. The second part of this thesis concerns the use of a copper(I)-Tp system for selectively solubilising "CO from nitrogen-rich gas streams for subsequent use in palladium-catalysed carbonylation reactions between amines and aryl-halides to form amides. These reactions were performed on a microfluidic device and in Schlenk apparatus using unlabelled carbon monoxide. These reactions were transferred to the radiochemical laboratory whereby efficient "CO trapping was observed prior to the formation of 11C-radiolabelled amides. The third part of this thesis explores the coordination chemistry of palladium(II) towards a novel hybrid ligand consisting of pyrazolyl and triphenylphosphine moieties. The potential hemilabile behaviour of this ligand and its derivatives towards palladium was investigated and the use of these complexes as catalysts for carbonylation reactions is described. The final part of this thesis examines the coordination chemistry of poly(pyrazolyl)borates bearing additional coordinating groups appended to the 3- or 5-position of the pyrazolyl rings. Reactions of the 3-substituted derivatives were carried out with a range of metals and found to display varied coordination behaviour depending on the specific coordination requirements of the metal. ii PUBLICATIONS Publications resulting from this work are listed below and are reproduced in full in the appendix (Chapter 8). Variable Coordination Behaviour of Pyrazole-Containing N,P and N,P(0) Ligands Towards Palladium(H), Steven Kealey, Nicholas J. Long, Philip W. Miller, Andrew J. P. White, Peter B. Hitchcock, Antony D. Gee. Dalton Transactions, 2007, 2823. A Novel Tetrakis(pyrazolyl)borate Ligand Bearing Triphenylphosphine Oxide Substituents, Steven Kealey, Nicholas J. Long, Andrew J. P. White and Antony D. Gee. Dalton Transactions, 2007, 4763. ScorpoPhos: A Novel Phosphine-Nitrogen Ligand Containing a Tris(pyrazolyl)borate Ligand Core, Steven Kealey, Nicholas J. Long, Philip W. Miller, Andrew J. P. White and Antony D. Gee. Dalton Transactions, 2008, 2677. iii ABBREVIATIONS A angstrom, 1040 m AD Alzheimer's disease ADME absorption, distribution, metabolism and excretion AIBN azobis(isobutyronitrile) Ani anilinyl Ar aryl Bp bis(pyrazolyl)borate Bp* bis(3,5-dimethyl(pyrazoly1))borate Bq Becquerel (one disintegration per second) tBu tert-butyl, C(CH3)3 COD 1,5-cyclooctadiene CORM CO-releasing molecule CT computed tomography DCEA bis(2-cyanoethyl)amine DCM dichloromethane DRIFT diffuse reflectance infrared fourier transformation DMA-DMA dimethylacetamide dimethylacetal DMF dimethylformamide DMF-DMA dimethylformamide dimethylacetal DMSO dimethylsulphoxide dppp 1 ,3 -bi s (diphenylpho sphino)prop ane EGDMA ethylene glycol dimethacrylate EI electron ionization EOB end of bombardment ESI electrospray ionisation Et ethyl, CH2CH3 eV electron volt FAB fast atom bombardment FDG fluoro-2-deoxy-D-glucose GC gas chromatography HOMO highest occupied molecular orbital HPLC high performance liquid chromatography iv IR infra red 'Pr iso-propyl, CH(CH3)2 1 litre L ligand LUMO lowest unoccupied molecular orbital M metal Me methyl, CH3 MeCN acetonitrile MLCT metal to ligand charge transfer MO molecular orbital MRI magnetic resonance imaging m/z mass to charge ratio NMR nuclear magnetic resonance s singlet d doublet dd double doublet t triplet Hz hertz 8 chemical shift ppm parts per million OAc acetate, CH3C00" PET positron emission tomography Ph phenyl Py pyridyl pz pyrazolyl TACN 1,4-diisopropy1-1,4,7-triazacyclononane THE tetrahydrofuran Tim tris(imidazole-2-ylidene)borate TMPA tris(2-pyridylmethyl)amine Tp tris(pyrazolyl)borate Tp* tris(3,5-dimethyl(pyrazoly1))borate Tkp tetrakis(pyrazolyl)borate UV-vis ultra violet-visible vibrational frequency, cm-1 ACKNOWLEDGEMENTS Probably the most challenging aspect of any thesis is to construct an acknowledgements section that is not overwhelmingly cringe-worthy when re-read in years to come. Having failed at this in less than two lines I shall carry on regardless. Firstly, I would like to thank my supervisors Nick and Tony who have provided me with so much support throughout my project and for allowing me to work with a fantastic amount of freedom. Thanks to Nick and Phil for putting up with my constant knocking on their doors to provide the tiniest update on the progress of any given reaction. My thanks to Phil especially for so much help with syntheses and for those countless discussions which usually started with 'I think you should try making...'. Sometimes I did, and sometimes it worked, so for that, I am most grateful. Obviously I'd like to thank all the members of the Long group, past and present, whom I have been most fortunate to work with, and go to the Holland Club with, over the years. I'm very grateful to GSK, EPSRC and the Department of Chemistry for providing funding for my project. Within the chemistry department I would like to thank Dick and especially Pete for going above-and-beyond their duties in helping me with all matters NMR. Thanks to Andrew White for X-ray analysis of my compounds, without which my thesis would be substantially barer. I am also grateful to John Barton and Stephen Boyer for mass spectrometry and elemental analysis. Outside the department there are so many people who have made my last few years in London so enjoyable that I can't possibly name them all — In my head I am very grateful to you. More specifically, I would like to thank my housemates of years gone by, especially Mark, Dan and Dom for so many good laughs and probably an equal number of unaccountable headaches the next day. I would like to thank my family for being brilliant all of the time and for coming to visit me, taking me to concerts and buying me dinner. Finally, and this almost goes without saying, thank you Sophie for being so loving and supportive and managing to do so even when sharing the same living space as me. I feel extremely lucky. vi TABLE OF CONTENTS Declaration i Abstract ii Publications iii Abbreviations iv Acknowledgements vi 1. Introduction 1 1.1 Positron Emission Tomography 2 1.1.1 Positron Emitting Isotopes 4 1.1.2 Applications of PET 5 1.1.3 "C-Radiolabelling 9 1.2 Carbon Monoxide 10 1.2.1 [11C]Carbon Monoxide as a Reagent 10 1.2.2 Palladium—Mediated [11C] Carbonyl ations 11 1.2.3 Alternative [11C]Carbonylation Methods 17 1.2.4 Coordination Chemistry of Carbon Monoxide 18 1.2.5 Metal Carbonyl Complexes in Nature 19 1.3 Copper(I) Carbonyl Complexes 25 1.3.1 Background 25 1.3.2 No Supporting Ligand 27 1.3.3 Bidentate Ligands 28 1.3.4 Tridentate Ligands 30 1.3.5 Flexible Tetradentate Ligands 31 1.3.6 Macrocyclic Tetradentate Ligands 34 1.3.7 Immobilized Copper(I) Complexes 35 1.3.8 Summary 37 1.4 Poly(pyrazolyl)borate Ligands 37 1.4.1 Background 37 1.4.2 Features 38 1.4.3 Naming of Scorpionates 39 1.4.4 Tris(pyrazolyl)borates 40 1.4.5 Tp-Supported Copper Carbonyls 41 vii 1.4.6 Applications of Tp Ligands 43 1.5 Research Objectives 45 1.6 References 46 2. Synthesis and Copper Coordination Chemistry of Scorpionate Ligands 51 2.1 Synthesis of Known Scorpionates 53 2.1.1 Tris(pyrazolyl)borates 53 2.1.2 Bis(pyrazolyl)borates 55 2.2 Synthesis of Novel Tp Ligands 56 2.2.1 Background 56 2.2.2 Attempted Synthesis of Alkoxy-Substituted Tp 57 2.2.3 Synthesis of Methylthio-Substituted Tp 59 2.2.4 Summary 65 2.3 Synthesis of Copper Carbonyls 66 2.3.1 Synthesis of CuTpCO (2.10) 67 2.3.2 Synthesis of CuTp*CO (2.11) 68 2.3.3 Synthesis of Cu[TpPh'sme]C0 (2.12) 69 2.3.4 Summary of Carbonyls 74 2.4 Rapid Carbonylation Reactions 75 2.4.1 Background 75 2.4.2 Rapid Carbonylation with Tp* 75 2.5 CO Displacement Reactions 77 2.5.1 Decarbonylation of CuTp*C0 78 2.5.2 Decarbonylation of Cu[TpPh'smeiC0 80 2.5.3 Summary 81 2.6 Future Work 81 2.6.1 Novel Electron-Rich Tps 81 2.6.2 Carbene Chemistry 83 2.6.3 UV-Triggered Decarbonylation 84 2.7 References 85 3. Palladium-Mediated Carbonylation Reactions 87 3.1 "CO Trapping Reactions 88 3.1.1 Background 88 viii 3.1.2 Reaction Setup 90 3.1.3 Calculations 91 3.1.4 Results and Discussion 92 3.2 'Cold' Amide Syntheses 93 3.2.1 Background 93 3.2.2 Microfluidic Reactions 94 3.2.3 Schlenk Reactions 98 3.2.4 Carbonylation Summary 100 3.3 'Hot' Amide Syntheses 101 3.3.1 Reaction Setup 101 3.3.2 Results and Discussion 102 3.3.3 Summary 105 3.4 Future Work 107 3.4.1 [11C]Carbonylations 107 3.5 References 108 4.
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