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Substitution and Redox Chemistry of Ruthenium Complexes

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Substitution and Redox Chemistry of Ruthenium Complexes iJ il r¿ SUBSTITUTION AND REDOX CHEMISTRY OF RUTHENIUM COMPLEXES by Paul Stuaft Moritz, B. Sc. (Hons) * A Thesis submitted for the Degree of Doctor of Philosophy. The Department of Physical and lnorganic Chemistry, The University of Adelaide. JUNE 1987 lìr.+:-c{,¡l I /tz lZ]' STATEMENT. This Thesis conta¡ns no materialwhich has been accepted for the award of any other Degree or Diploma in any University and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference is made in the text. I give consent that, if this Thesis is accepted for the award of the Degree of Doctor of Philosophy, it may be made available for photocopying and, if applicable, loan. Moritz. SUMMARY The coordination chemislry of ruthenium is domínated by the oxidation states, +2 and +3. Within these oxidation states, the ammine complexes form a large and welt- characterized group. This thesis reports on the chemistry of lhe hitherto neglected triammine complexes, with particular reference to their redox chemistry, and the possible formation of Ru(lV) triammine complexes with terminal oxo ligands. The chemistry of the +4 oxidation state is further explored through the formation of stable chelate complexes. The salt, [Ru(NH3)3(OH2)31(CFgSO3)3, was prepared by hydrotysis of Ru(NHs)sCts in triflic acid solution. lts spectra, electrochemistry and substitution reactions are similar to those of the well-known hexa-, penta-, and tetraammine complexes. At freshly polished platinum and glassy carbon electrodes, a quasi reversible redox wave was detected, corresponding to a proton-coupled reduction involving the pu3+7pu2+ couple. At anodically-activated glassy carbon electrodes, an additional, irreversible cV wave was delected,which was attributed to the pug2+7gugHr3+ couple. The uv/vis spectrum of the Ru(lll) complex was also pH-dependent, and the pK" values associated with two proton disssociation steps were measured. Solvolysis of the aqua ligands by organic solvents was studied electrochemically and spectroscopically. Coordination of methanol is favoured by the +3 oxidation state, and acetonitrile can coordinate to either the +3 or +2 oxidation state, with the reaction occurring more rapdily on the +2 state. Dimethylsulphoxide can coordinate to either oxidation state, through a s-bound, r-bonding interaction. Acetone appears to coordinate through the carbonyl oxygen alom to the +3 state, and to the +2 state lhrough an î2 æ-interaction involving both atoms of the carbonyl group. Substitution reactions were carried out with a variety of ligands to give three types of complexes: (1) substituted triammineaquaruthenium(lll) complexes, where the ligands are uni- or dinegative bidentate ligands, such as diketonates and dicarboxylic acids. (2) substituted triammineruthenium(ll) complexes with mono- and bidentate r¡- acceptor ligands such as pyridines and nitriles. (3) triammineruthenium(ll) complexes with tripodal, tridentate ligands containing three pyridine molecules bound to a central heteroatom. The spectra and electrochemistry of these complexes showed features similar to those of the analogous Ru(lll) and Ru(ll) tetra- and pentaammine complexes. ln all three cases, the complexes exhibited reversible or quasi reversible electron lransfers attributable to the gu3+7pu2+ couple. ln the cases where an aqua ligand was present, pH-dependent electron transfers were evident. At anodically-activated glassy carbon electrodes, irreversible waves attributable to the RuOHr3+¡gug2+ oxidation were also observed. ln the case of the complex, IRu(NH3)3(C2Od(OH2)]+, this latter redox couple was also quasi-reversible at a highly polished glassy carbon electrode. The chemistry of the triammine series was further extended by the isolation and characterization of a triammine nitrosyl complex, and the reaction of this complex to give dinitrogen complexes. Complexes with dinegative, tridentate ligands based on aromatic hydrazones, were formed by the reaction of Rucl3.3H20 with two equivalents of the appropriate protonated ligand in the presence of base. Depending on the ligand used, either a Ru(lll) or Ru(lV) complex was obtained. The spectra, magnetochemistry, and electrochemistry of these complexes were studied. The oxidation state of the complex, and the E172 potential of the gu4+¡gu3+ couple were shown to be dependent on the electronic properties of the ligand. ln some cases, two reversible electron lransfer reactions could be detected in DMSO, corresponding to lhe gu4+79u3+ and Ru3+/Ru2+ couples. ACKNOWLEDGEMENTS. I acknowledge and thank my supervisor, Dr. Alex Diamantis. without his encouragement, guidance and friendship this work would not have come to fruition. I would also like to thank Dr. B. J. steel, who was always willing to discuss electrochemical aspects of my work, and Dr. J. H. Coates, who acted as my Supervisor during Dr. Díamantis's absence on study leave. Dr. F. R. Keene of James Cook University kindly supplied ligands and preprints of his publications, and Dr. G. A. Healh, formerly of Edinburgh University, provided a copy of some recent, unpublished, results. Thanks are also due to Dr. E. R. T. Tiekink, who determined the crystal struclures, Mr. T. Blumenthal and Mr. M. Liddell, who recorded the mass spectra and Ms. Andrea Hounslow who recorded the NMR spectra. Mr. Michael Hounslow provided invaluable advice on the finer points of Macintosh word processing. Dr. Md. Abdus Salam, Tom Horr, Robert Jones (who proof read this Thesis) and Mary Manikas patiently humoured me while we shared the laboratory. They, and the rest of my friends and fellow students, gave much me much support and many hours of f ru itfu I conversation. I also thank the Technical, Laboratory and Secretarial staff of the Department of Physical and lnorganic Chemistry. The financial assistance of a Commonwealth Postgraduate Research Award and a short term University of Adelaide Scholarship is acknowledged. ABBREVIATIONS acac penta-2,4-dione ampy 2(aminomethyl)pyridine BH benzoylhydrazine bzac 1 -phenylbuta-1,3-dione dbm 1,3-diphenylpropa-1,3-dione DMSO dimethylsulphoxide dpm 2,2,6, 6-tetramethylhepta-3,5-dione EtOH ethanol hap 2-hydroxyacetophenone hna 2 -hy dr oxy an ap ht h ald e h yd e HTFMS trif luoromethanesulphonic acid MeCN aceto nitrile(cyanomethane) MEK butanone MeOH methanol MeSO3 methanesulphonate anion MeSOsH methanesulphonic acid OAP 2-aminophenol oxine 8-hydroxyquinoline phen 1 ,10-phenanthroline PPh3 triphenylphosphine py pyridine py3OOH tris(pyridyl) methanol pyscH tris(pyridyl)methane PYgN tris(pyridyl)amine RuAn Ru(NHs)n sal salicylaldehyde SalH salicyloylhydrazinze terpy 2,2',2"-lerpyridine TFMS trif luoromethanesulphonate anio n The abbreviations for the dinegative tridentate ligands are derived from the trivial names of the ketone-type and amine-type portions which make up the schiff's base ligand. For example, bzacBH = benzoylacetonebenzoylhydrazone. (Systematic name = ¡rl'-(1-methyl- 3-oxo-3-phenylpropyl idene) benzo hyd razide. ABBREVIATIONS (cont.) ELECTROCHEMISTRY. SPECTRA CV cyclic voltammetry A absorbance DPV differentialpulse voltammetry B.M. Bohr magneton Êln half-wave potential FAB fast atom Ep peak potential (subscript c refers to cathodic bombardment peaks, subscript a refers to anodic peaks ir infrared GCE glassy carbon electrode sh shoulder LSV linear sweep voltammetry uv/vis ultra violet/ OSWV Osteryoung square wave voltammetry visible SCE saturated calomel electrode (D) stretching mode SCP sampled current polarography (õ) bending mode ì. wavelength 1) frequency "It is beter to ask soÍne of the questions than to know all the an.sril'ers." (James Thurter, "Fables of Our Time a¡rd Illustrated Poems. ") TABLE OF CONTENTS. PAGE STATEMENT SUMMARY ACKNOWLEDGEMENTS ABBREVIATIONS CHAPTER 1. ¡NTRODUCT¡ON. 1.1 Aims of the Project. 1 1.2 Factors Affecting the Stability of Ruthenium Oxidation States 2 1.4. Oxoruthenium(lV) Complexes With N-Donor Ligands. 5 1.4. Ruthenium(lV) Complexes With Bidentate Ligands. 8 1.5. Ruthenium(lV) Complexes With Chloro Ligands. 10 1.6. Ruthenium(lV)edtaComplexes. 11 1 .7. Tridentate Dinegative Ligands. 12 1.8. ElectrochemicalTechniquesandMaterials. 12 References. 17 CHAPTER 2. AMMINE AQUA RUTHENIUM COMPLEXES. 2.1. lntroduction. 20 2.2. lsolation of Triamminetriaquaruthenium(lll). 21 2.3 Acid-BaseProperties. 21 2.4 Electronic Spectra. 24 2.5. ElectrochemicalStudies. 25 2.6. Redox Chemislry. 31 2.7. Electrochemistry in Organic Solvents. 33 References. 37 CHAPTER 3. SUBSTITUTED TRIAMMINERUTHENIUM COMPLEXES. 3.1. lntroduction. 40 3.2. Ruthenium(lll)Complexes. 42 Preparation of Complexes 42 Electronic Spectra 43 Vibrational Spectra 45 The Electrochemistry of IRu(NHs)s(LL)(OH2)]2+ Complexes. 46 The Electrochemistry of IRu(NH3)s(C2Od(OH2)l+. 52 Discussion of Electrochemical Results. 53 Comparison of E¡¡2with pK". 56 Electrolytic Reduction of Ru(lll) Complexes. 57 Description of the Crystal Structure of [Ru (NH3)3(acac) (OH2)](S206).2H2O. 58 3.3. Ruthenium(ll)Complexes. 59 Preparation of Complexes 59 Electronic Spectra 61 Vibrational Spectra 63 Electrochemical Studies 65 3.4. Triammine(tripod)ruthenium(ll) Complexes. 68 Preparation of Complexes 68 Electronic Spectra 69 Vibrational Spectra 71 Electrochemical Studies 71 Description of the Crystal Structure of [Ru(NH3)3{(py)3COH)]812. 71 3.5. Conclusions. 73 References. 75 CHAPTER 4. RUTHENIUM COMPLEXES WITH TRIDENTATE LIGANDS. 4.1. lntroduction. 80 4.2. Preparationof bis-(Tridentate) RutheniumComplexes. 80 4.3. ElectrochemicalStudies.
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