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NITROSYLMETALLOPORPHYRIN COMPLEXES AS MODELS for /C URED MEAT

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NITROSYLMETALLOPORPHYRIN COMPLEXES AS MODELS for /C URED MEAT NITROSYLMETALLOPORPHYRIN COMPLEXES AS MODELS FOr /c URED MEAT PIGMENTS s' A Thesis Presented to the University of Surrey for the Degree of Doctor of Philosophy in the Faculty of Chemical and Biological Sciences hy Russell Martin Thompson, B.Sc. The Joseph Kenyon Research Laboratories, Department of Chemistry, University of Surrey, Guildford, SURREY GU2 5XH England September 1988 5 - <=\o5 3 ci ProQuest Number: 10804592 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10804592 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ABSTRACT A range of nitrosylmetalloporphyrin complexes, M(porph)NO [M = Fe, Co; porph = TPP, OEP, TpivPP], some labelled with 1 5NO, has been synthesised and investigated as structural and spectroscopic models of the cured meat pigment, nitrosylmyoglobin. The nitrosylmetalloporphyrins were found to be unstable in solution (and some in the solid state) with respect to loss or further reaction of the nitrosyl ligand. The diamagnetic cobalt (III) porphyrin^nitrosyIs and a range of other square pyramidal complexes of cobalt(III) with an apical nitrosyl ligand have been further investigated by 15 59 N and Co NMR spectroscopy to establish whether the CoNO group is bent or linear and to study nephelauxetic and spectrochemical effects at the metal. In all cases studied the CoNO group is bent (CoNO ^120°). The basal ligands were dithiocarbamate, tetradentate Schiff base, porphyrin, and bidentate diamine and oximate giving S^, S2N2' N4' ®ONN, or ONON coordination in the equatorial plane. The shielding of both cobalt and nitrogen tends to decrease with decrease in M(d) to n (NO) back-bonding as indicated by M-N and N-0 bond distances, and the MNO angle and the NO stretching frequencies. The shieldings decrease with electron withdrawal by ring substituents and also in going from sulphur to nitrogen to oxygen coligands, i.e. with decrease in ligand field splitting and in the nephelauxetism of the coligands. The bent nitrosyls of cobalt can function as oxygen transfer catalysts via a nitrosyl-nitro couple. Consequently, a range of Co(III) porphyrin nitro complexes, (L)Co(porph)N02 (porph = TPP, OEP; L = py, iMelm) and several nitro complexes containing the other basal ligands have been synthesised and 15 59 investigated by the N and Co NMR technique. The coordinated nitro ligand is labile and linkage isomerism and ligand exchange have been observed. These observations may be related to the deterioration of cured meat colour which is of importance to the food industry. The crystal structure of (py)Co (TPP)N02 is presented; the nitro group of which is rotationally disordered. Recrystallisation of (1MeIm)Co- (TPP)NC> 2 gave [Co(TPP) (1Melm)2 ]N02 , the crystal structure of which has been determined. Formation of this nitrite is further evidence for the lability of the nitro ligand. The known complex Fe(salphen)NO was prepared using ascorbic acid for the first time to prevent contamination with the oxo-bridged iron(III) dimer. Variable temperature 57 Fe Mossbauer effect studies of the S = 1/2 to S = 3/2 spin transition for Fe(salphen)NO show that the crossover is continuous and centred at T c^181 K, and that the electronic transition between the two spin states is rapid on the Mossbauer timescale. The fluxionality of CoCl2 (^NO) (PPh2Me)2 was studied by -I c o-i n variable temperature N and P NMR. An O NMR study of the 1 7 ji-peroxo complex [(NH^J^Co 02Co(NH2 ),_ ] (NO^ ) ^. 2H20 is pres- ented. An attempt to measure 1 5N NMR spectra of the dia- magnetic 18 electron species, Fe (porph)( 14 N0)( 15NO) (porph = TPP, OEP) presumably containing linear FeNO+ and bent FeNO" was unsuccessful. ACKNOWLEDGEMENTS The author expresses his sincere thanks to Academic Supervisor Dr. Leslie F. Larkworthy for his patience and friendly supervision. Thanks are also expressed to Industrial Supervisor Dr. Cliff L. Walters of the Leatherhead Food Research Association, and also to Dr. Joan Mason of the Open University for provision of nitrogen-15 labelled reagents. Mr Glen Smith, Dr. David C. Povey, and Mr Andy Golder are thanked for help in X-ray crystallography. Prof. E. Konig and colleagues at the University of Erlangen-Nurnberg, West Germany are acknowledged for the Mossbauer measurements, as are Drs. 0. Howarth, A. Harrison, and E. Curzon of Warwick University for the high field NMR measurements. The help of the Technical Staff of the Chemistry Department is gratefully acknowledged, especially Mrs Ruth Archer and Mr Tony Hill for constantly allowing the author to borrow the odd bit of essential glassware when the Chemistry Stores was closed. The speedy service of the University Glassblowers is also acknowledged. The author would like to thank the SERC and the Leatherhead FRA for the provision of a CASE award. Thanks are also due to the many friends and colleagues at Surrey and especially for the regular games of 5-a-side football enjoyed during the time there. Finally the author would like to express his sincere thanks to his wife Anne for her love and constant patience during the work. CONTENTS CHAPTER 1 INTRODUCTION Page No. 1.1 Formation and Deterioration of Cured Meat Colour 1 1.1.1 Meat Colour and the Consumer 1 1.1.2 Meat, Muscle, and Myoglobin 1 1.1.3 Formation of Cured Meat Colour 7 1.1.4 Cooked Cured Meat Colour 15 1.1.5 Deterioration of Cured Meat Colour 19 1.1.5.1 Oxidation 21 1.1.5.2 Reducing Agents 23 1.1.5.3 Radiation and the Role of Light 24 1 .1 .5.4 pH 27 1 .1 .5.5 Temperature 28 1.1.5.6 Heavy Metal Contamination 29 1.1.6 Preservation of the Cured Meat Colour 30 1.2 Nitrosyl Chemistry 33 1.2.1 Nitric Oxide and the Coordinated Nitrosyl Group 33 1.2.1.1 Transition Metal Nitrosyl Complexes 34 1.2.2 Bonding Theories 40 1.3 Nitrosylmetalloporphyrins 48 i CHAPTER 2 EXPERIMENTAL TECHNIQUES AND BACKGROUND TO SPECTROSCOPIC INVESTIGATIONS 66 2.1 Preparative Methods 66 . 2.1.1 Technique for Manipulation of Air-sensitive Compounds 66 2.1.2 General Method for Synthesis of Metal Nitrosyl Complexes 71 Page No. 2.1.2.1 Preparation and Purification ofNitric Oxide 71 2.1.2.2 Use of the Nitric Oxide Line in Preparation of Nitrosyl Complexes 73 1 5 2.1.3 Synthesis of N Nitrosyl Complexes 76 1 5 2.1.3.1 From Gaseous NO 76 2.1.3.2 Synthesis of ^NO from Na^NC > 2 77 2.2 Purification of Solvents and Reagents 80 2.2.1 Reagents 80 2.2.2 Solvents 80 2.2.3 Chromatographic Materials 81 2.3 Experimental Methods 82 2.3.1 Microanalyses 82 2.3.2 Mass Spectroscopy 82 2.3.3 Magnetochemistry 82 2.3.4 Single Crystal X-Ray Crystallography 82 2.3.5 Mossbauer Spectroscopy 83 2.3.6 Infrared Spectroscopy 83 2.3.6.1 IR Spectroscopy of Nitrosyls and Coordinated Nitrite 83 2.3.7 Visible Absorption Spectroscopy 88 2.3.7.1 Visible Absorption Spectroscopy of Porphyrins and Metalloporphyrins 88 2.3.8 Nuclear Magnetic Resonance Spectroscopy 94 2.3.8.1 Sealed NMR Tube Experiments 94 1R 17 2 13.8•2 NMR Nuclei ( N, Co, O) 95 2.3.8.2.1 Nitrogen ( ^ N and ^ N ) NMR 98 2.3.8.2.1.1 Simplified Theory of Nuclear Magnetic Shielding for Nitrogen Nuclei 99 Page No. 59 2.3.8.2.2 Cobalt ( Co) NMR Spectroscopy 111 2.3.8.2.2.1 Theoretical Basis for Nuclear Magnetic Shielding in Cobalt(III) Complexes 114 59 2.3.8.2.2.2 Other Relevant Co NMR Studies 120 1 7 2.3.8.2.3 Oxygen ( 0) NMR Spectroscopy 121 CHAPTER 3 PREPARATIONS OF LIGANDS AND COMPLEXES 12 2 3.1 Introduction 122 3.1.1 Porphyrin Synthesis 122 3.1.2 Metalloporphyrin Complexes 130 3.1.3 Nitrosyl Complexes 130 3.1.4 Nitro Complexes 131 3.1.5 ji-Peroxo Complexes 131 3.2 Ligand Synthesis 131 3.3 Preparation of Metalloporphyrin Complexes 144 3.3.1 Iron Porphyrin Complexes 144 3.3.2 Cobalt Porphyrin Complexes 146 3.4 Preparation of Nitrosylmetalloporphyrin Complexes 148 3.4.1 Cobalt Nitrosyl Porphyrin Complexes 148 3.4.2 Iron Nitrosyl Porphyrin Complexes 150 3.5 ji-Oxo-bis[porphyrinatoiron(III) ] Complexes 153 3.6 Preparation of Cobalt(III) Nitro Complexes 154 3.7 Preparation of 1 5N-Labelled Cobalt Porphyrin Complexes 157 1 5 3.7.1 N-Nitrosyl Cobalt Porphyrin Complexes 157 1 5 3.7.2 N-Nitro Cobalt Porphyrin Complexes 158 Page No. 3.8 Miscellaneous Work 159 3.8.1 Miscellaneous Cobalt(III) Nitrosyls 159 14 15 3.8.2 Miscellaneous Cobalt(III) ' N-Nitro Complexes 161 3.8.3 Preparation of Fe(salphen)NO 163 3.8.4 |i-Peroxo Bridged Binuclear Cobalt(III) Complexes 164 3.8.5 Starting Materials 165 CHAPTER 4 RESULTS AND DISCUSSION 16 7 4.1 Starting Materials; Porphyrins and Metalloporphyrins 167 4 4.1.1 Magnetochemistry of Co( a -TpivPP) and Fe(OEP)Cl 173 4.2 Nitrosyl(porphyrinato)cobalt(III) Complexes 176 15 59 15 4.2.1 N and Co NMR Investigations of N-Nitrosyl- (porphyrinato)cobalt(III) Complexes 183 4.3 Oxidation of Cobalt Nitrosyl Complexes to Cobalt Nitro Complexes 190 4.3.1 Single Crystal X-Ray Structural Determination of (py)Co(TPP)N02 and [Co(TPP)(lMeIm)2]N02 198 4.3.1.1 (py)Co(TPP)N02 198 4.3.1.2 [Co(TPP)(lMeIm)2 ]N02 204 4.3.2 Relationship of the Molecular Structures of (py)Co(TPP)N02 and [Co(TPP)(lMeIm)2]N02 to Other Structures of Cobalt Porphyrin Complexes Containing Axially Coordinated Nitrogenous Bases 212 4.4 Nitrosyl(porphyrinato)iron(II) Complexes 220 4.5 ji-Oxo-bis[ (porphyrinato)iron(III) ] Dimers 225 4.6 Sealed NMR Tube Experiments 225 Page No.
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