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The reactions of various ruthenium octaethylporphyrin complexes with small gas molecules Walker, Sandra Gail 1980

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THE REACTIONS OF VARIOUS RUTHENIUM OCTAETHYLPORPHYRIN COMPLEXES WITH SMALL GAS MOLECULES B.Sc , The University of Guelph, 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1980 ©Sandra Gail Walker, 1980 by SANDRA GAIL WALKER In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C?H£M v The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date \1XH /J?0 - i i -ABSTRACT Interaction of metalloporphyrins, particularly of the iron subgroup, with gas molecules such as 0 2 and CO, remains of considerable interest in terms of comparison with natural heme protein systems. This thesis describes studies on ruthenium(II) porphyrin complexes, the second row analogues of the heme systems. Toluene solutions of the bis(acetonitri le) complex RuOEP(CH3CN)2, (OEP = the dianion of octaethylporphyrin) with or without excess acetonitri le present, are irreversibly oxidized by 0 2 at 30°C. However, with CO, the complex undergoes a clean reaction to give RuOEP(CO)(CHgCN) with several isosbestic points observed in the UV/VIS spectrum. The kinetic dependence on the CO pressure and acetonitr i le concentration are consistent with a dissociative mechanism: k l k 2 RuOEP(L)2<=> RuOEP(L)<=?RuOEP(L)(CO) (I) k _ l k_2 The kinetic rate constants, k-j, k_2 and k_^/k2 and the overall equilibrium constant were determined at 30°C in toluene. The Ru0EP(P(n-Bu)3)2 complex, in toluene, is completely unreactive toward 0 2 at 30°C over a period of several days; although again a monocarbonyl is formed under a CO atmosphere. In the presence of excess P(n-Bu) 3, under CO, an equilibrium mixture of RuOEP(P(n-Bu)3)2 and RuOEP(CO)(P(n-Bu)3) is formed. The equilibrium constant K for reaction (II) and the thermodynamic parameters AH (3.7 Kcal/mole) and AS (10.3 e.u.) are determined along with the rate constants for the dissociative mechanism (cf. Equation I). The low AH value implies comparable bond K RuOEP(P(n-Bu)3)2 + CCW=l>RuOEP(CO)(P(n-Bu)3) + P(n-Bu) 3 (II) strengths between ruthenium and the two ligands P(n-Bu) 3 and CO. The k -|/l<2 values for the acetonitri le and phosphine systems are thought to relate to the structure of the five-coordinate intermediate, RuOEP(L); the data suggest the ruthenium is probably more in the porphyrin plane than out of plane, al least compared to analogous iron systems. The major difference between the acetonitr i le and phosphine . 5 systems is in the k 2 value which varies by 10 , part ia l ly due to the difference in ir-acidity of the two axial ligands. Toluene solutions of RuOEP(CH3CN)2 bind N2 and C 2 H 4 very weakly. However, due to the extreme photo- and oxygen-sensitivity of the products, no consistent kinetic data could be obtained. Solutions of RuOEP(py)2 in neat pyridine, formed in situ from the bis(acetonitri le) complex in pyridine, are completely unreactive toward CO. Even toluene solutions with small amounts of pyridine react only part ia l ly (^ 15% in three days at 25°C) to give the monocarbonyl. Upon dissolving the RuOEP(CH3CN)2 complex in DMA, DMF and THF, the species formed seem to be RuOEP(CH3CN)(solvent). These species react with CO at 30°C in a two step reaction, an instantaneous part followed by a much slower one; the reactions appear to involve the rapid formation of one monocarbonyl followed by decomposition to the expected monocarbonyl, RuOEP(CO)(solvent). Decarbonylation of the amide solvent to give an amine ligand may be involved in the fast reaction. Judging by the reaction with CO (non-first-order in ruthenium) there - i v -are possibly two species present when RuOEP(CH3CN)2 is dissolved in pyrrole, RuOEP(pyrrole)2 and RuOEP(CH3CN)(pyrrole), which react at different rates. - V -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS v LIST OF TABLES v i i LIST OF FIGURES ' v i i i ABBREVIATIONS xi ACKNOWLEDGEMENTS xiv CHAPTER I. INTRODUCTION 1 1.1 General '. 1 1.2 Hemoglobin and Myoglobin 2 1.3 Iron Model Systems 5 1.4 Ruthenium Model Systems 7 CHAPTER II. EXPERIMENTAL 9 11.1 ^Instrumentation 9 11.2 Spectrophotometric Kinetic Measurements 9 11.3 Materials 10 11.3.1 Gases 10 11.3.2 Solvents 12 11.3.3 Nongaseous Ligands 12 11.4 Complexes , 12 CHAPTER III. THE REACTION OF RuOEP(CH3CN)2 AND CO 16 111.1 Spectral Characteristics 16 111.2 Treatment of Data 18 111.3 Discussion 23 -vi -CHAPTER IV. THE REACTION OF RuOEP(P(n-Bu)3)2 AND CO 27 IV.1 Spectral Characteristics 27 IV.2 Treatment of Data 30 IV. 3 Discussion 39 CHAPTER V. THE REACTIONS OF RuOEP(CH3CN)2 WITH OTHER GASES IN TOLUENE AND WITH CO IN OTHER SOLVENTS 42 V. l The Reaction of RuOEP(CH3CN)2 With N2 and With C 2 H 4 in Toluene 42 V . l . l The Reaction of RuOEP(CH3CN)2 and N2 42 V.l.2 The Reaction of RuOEP(CH3CN)2 With C 2 H 4 46 V.2 The Reaction of RuOEP(CH3CN)2 With CO in Other Solvents 49 V.2.1 The Reaction of RuOEP(CH3CN)2 With CO in Pyridine (py) 50 V.2.2 The Reaction of CO in N,N-Dimethylacetamide (DMA), N,N-Dimethylformamide (DMF) and Tetrahydrofuran (THF) With.RuOEP(CH3CN)2 52 V.2.3 The Reaction of RuOEP(CH3CN)2 With CO in Pyrrole 62 CHAPTER VI. CONCLUSIONS 66 -vi i -LIST OF TABLES Table Page 111.1 Rate or reaction of RuOEP(CH3CN)2 with CO in toluene at various acetonitri le concentrations and CO pressures, at 30°C 21 111.2 Kinetic and equilibrium data for the reaction of RuOEP(CH3CN)2 with CO at 30°C in toluene 23 111 .3 Kinetic and equilibrium data for the reaction of RuOEP(pyrrole)2 with 0 2 at 20°C in pyrrole 24 111 .4 Kinetic and equilibrium data for the reaction of Fe(porphyrin)(piperidine) 2 complexes with CO in toluene at 23°C 24 IV. 1 Equilibrium constant values from 21-41°C for the reaction of RuOEP(P(n-Bu)3)2 with one atmosphere CO, in toluene .. 31 IV.2 Rate of reaction of RuOEP(P(n-Bu)3)2 with CO in toluene at various ligand concentrations and CO pressures at 31°C .. 36 IV.3 Rate of reaction of RuOEP(P(n-Bu)3)(CO) with P(n-Bu) 3 in toluene at 31 °C 37 IV.4 Kinetic data for the reaction of RuOEP(P(n-Bu)3).(CO) and P(n-Bu) 3 in toluene at 31°C 37 IV.5 Kinetic data for the reaction of RuOEP(P(n-Bu)3)2 and CO at 31 °C in toluene 39 -vi i i -LIST OF FIGURES Figure Page 1.1 The structure of the heme unit of hemoglobin and myoglobin 3 1.2 The structure of the beta chain of hemoglobin 4 1.3 The structure of octaethylporphyrin 8 IT.l Anaerobic spectral ce l l 11 II. 2 Photolysis cel l 14 III. 1 Typical spectral changes for the reaction of RuOEP(CH3CN)2 with CO in toluene at 30°C 17 111.2 First-order plots for the reaction of RuOEP(CH3CN)2 with CO in toluene with 1.91 x 10 M acetonitr i le added at 30°C 19 111 .3 Plot of k Q b s d _ 1 vs [CH3CN]/[C0] for the reaction of Ru0EP(CH3CN)2 with CO in toluene with 1.91 x 10" 2 M acetonitr i le added at 30°C 22 111.4 Possible structures of the five-coordinate intermediate 25 IV.1 Spectral changes for the reaction of RuOEP(P(n-Bu)3)2 with CO in toluene with no added P(n-Bu) 3 at 31°C 28 IV.2 Spectral changes for the reaction of RuOEP(P(n-Bu)3)2 with CO in toluene containing 2.84 x 10~4 M P(n-Bu) 3 at 31°C 29 IV.3 Equilibrium plots for the reaction of Ru0EP(P(n-Bu)3)2 with 1 atm CO in toluene 32 - i x -Figure Page IV.4 Van't Hoff plot for the reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO in toluene 33 IV.5 First-order plot for the reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO in toluene containing 7.08 x 10~4 M P(n-Bu) 3 at 31°C 35 IV. 6 Plot of k o b s d - 1 vs [C0]/lP(n-Bu)3] for the reaction of . Ru0EP(P(n-Bu)3)(C0) with P(n-Bu) 3 in toluene at 31°C .. 38 V. l Spectral changes for the reaction of RuOEP(CH3CN)2 with 1 atm N2 in toluene containing 1.9 x 10~2 M CH3CN at 30°C 43 V.2 First-order plot for the reaction of RuOEP(CH3CN)2 with 1 atm N2 in toluene containing 1.9 x 10" 2 M CH3CN at 30°C 45 V.3 Spectral changes for the reaction of RuOEP(CH3CN)2 with 3/4 atm of C 2 H 4 in toluene containing 1.9 x 10" 2 M CH3CN at 30°C 47 V.4 Possible structures for ethylene complex 48 V.5 Spectral changes for the reaction of Ru0EP(CH3CN)2 with 1 atm CO in toluene containing 0.15 M pyridine at 25°C 51 V.6 Spectral changes for the photolysis of RuOEP(CO)(DMA) forming RuOEP(DMA)2 in DMA 53 V.7 Spectral changes for the reaction of species 'X' with 1 atm CO in DMA at 29°C 54 V.8 First-order plot of the reaction of species 'X' with 1 atm CO in DMA at 29°C 56 -X-\ Figure Page V.9 Spectral changes for the reaction of species 'X' with 1 atm CO in DMF at 29°C 59 V.10 Spectral changes for the reaction of species 'X' with 1 atm CO in THF at 30°C 60 V . l l Possible scheme to explain the observed spectral changes of RuOEP(CH3CN)2 with CO in DMA, DMF and THF 61 V.12 Spectral changes for the reaction of species 'Y' with 1 atm CO in pyrrole at 30°C 63 V.13 First-order plot of the reaction of species 'Y' with 1 atm CO in pyrrole at 30°C 64 -xi -ABBREVIATIONS The following l i s t of abbreviations, most of which are commonly adopted in chemical research l i terature, wil l be employed in this thesis. atm atmosphere A absorbance at any time, t A e absorbance at the equilibrium position A o absorbance of the reactant A t absorbance at any time, t A oo absorbance of the product C 2 H 4 ethylene CH2 methylene CH3CN acetonitr i le °C degrees centigrade cm centimetre CO carbon monoxide COMb carbonylated myoglobin DMA N,N-dimethylacetamide DMF N,N-dimethylformamide AH enthalpy change for the reaction °K degrees Kelvin K equilibrium constant k l kinetic rate constant k - l kinetic rate constant k 2 kinetic rate constant k -2 kinetic rate constant - x i i -obsd M M-CO M(porphyrin)L M(porphyrin)L2 M(porphyrin)L(CO) M(porphyrin)LL1 mg N 2 nm °2 OEP 0 M B P Pc P(n-Bu) 3 PpIX py R u 3 ( C 0 ) 1 2 RuMb RuMb AS s sec T + overall rate constant for the forward reaction overall rate constant for the reverse reaction pseudo-first-order rate constant molarity metal-carbonyl bond five-coordinate metal porphyrin complex six-coordinate metal porphyrin complex carbonylated six-coordinate metal porphyrin complex mixed axial ligand six-coordinate metal porphyrin complex milligram nitrogen nanometre dioxygen octaethylporphyrin dianion octamethyltetrabenzoporphyri n di an i on phthalocyanine dianion n-butylphosphine protoporphyrin IX pyridine ruthenium dodecacarbonyl rutheni um(11)-reconstituted myoglobin rutheni um(111)-reconsti tuted myoglobi n entropy change for the reaction spin state second temperature -XT 11-t time TCNE tetracyanoethylene THF tetrahydrofuran TPP tetraphenylporphyrin dianion E molar ext inct ion coe f f i c i en t v frequency (cm~^) 0 -x i v-ACKN0WLED6EMENTS I would l i k e to thank Dr. B. R. James for his supervision over the years and his assistance in the wr i t ing of th i s thes i s . I also would l i k e to thank the various members of the 'James Gang' whom I have come to know and without whom, these three years would not have been as enjoyable. F i n a l l y , I wish to thank my husband, Br ian, for his patience and understanding during the wr i t ing of th i s thesis and my parents for the encouragement they have always given me during my academic endevours. - 1 -CHAPTER I  INTRODUCTION 1.1 General The interact ion of molecular dioxygen (O2) with metalloporphyrin species has been of interest ever since such species were recognized as being the important centres in natura l ly occurring oxygen-storage and -transport systems. An iron porphyrin moiety, ca l led a heme un i t , is the prosthetic group present in myoglobin and hemoglobin which are involved in oxygen-storage and oxygen-transportation, respect ively. Heme units are also components of various oxygenases and oxidases. Oxygenases catalyze the incorporation of one or two atoms of dioxygen into a substrate, while oxidases are enzymes that convert both atoms of dioxygen into water or hydrogen peroxide^. These enzyme systems contain proteins which can be d i f f i c u l t to work wi th , so s c ien t i s t s have been searching for simpler, protein-free co-ordination compounds that can mimic the oxygen-carrying and -act i vat ion a b i l i t y of the natural species. Simple metalloporphyrins seem obvious candidates s ince, in natura l ly occurring systems, they are often found at the act ive s i t e . A study of metalloporphyrin-dioxygen complexes should lead to an increased understanding of the structure and function of certain b io log ica l systems employing dioxygen. This subject has been 1 -8 extensively reviewed , sometimes in context with the more general coverage - 2 -/ x 2-4 of other (non-porphyrin) synthetic oxygen carr iers 1.2 Hemoglobin and Myoglobin Hemoglobin and myoglobin combine revers ib ly with dioxygen and they bind one dioxygen for each heme unit present. The iron atom in the heme unit i s chelated to the four core nitrogen atoms of the protoporphyrin IX dianion (Figure 1.1). In the hemeproteins of vertebrates, the porphyrin is embedded in a polypeptide chain having a molecular weight of 16,000 to 18,000. Myoglobins are monomeric, being composed of only one of these protein chains, while most hemoglobins are tetrameric, containing four such polypeptide subunits held together in a tetrahedral array. Each molecule of hemoglobin contains two subunits known as the a chains and two subunits ca l led the 6 chains. The t e r t i a r y structure of the 3 unit of hemoglobin as deduced from X-ray data is shown in Figure 1.2. The protoheme prosthetic group l i e s in a crevice between E and F hel ices of the polypeptide, held in place by non-binding interact ions with the protein. The s ingle covalent attachment to the protein occurs by coordination of the heme iron to the imidazole o nitrogen of the 'proximal ' h i s t i d i ne residue . In the deoxygenated s ta te , the ferrous iron i s f ive-coordinate with one vacant ax ia l pos i t ion. In th i s conformation, the iron is in a high sp in, 9 10 S=2, configuration and i t has been found ' that the metal l i e s several tenths of an angstrom out of the plane of the porphyrin, towards the axial l igand. Upon oxygenation, the s ix th coordination s i t e is occupied by dioxygen and the iron atom now i s found in a low sp in, S=0, state and moves into the mean plane of the porphyr in^ . The a f f i n i t y of a subunit in hemoglobin to add a s ingle molecule of dioxygen is apparently dependent upon the number of other oxygenated - 3 -Figure 1.1. The stucture of the heme unit of hemoglobin and myoglobin. -4-Figure 1.2. The structure of the beta chain of hemoglobin. Taken from M. F. Perutz and L. F. TenEyck, Cold Spring Habor Symp. Quant. B i o l . , 36, 295 (1971). -5-subunits in the tetramer. This is known as the 'cooperativity ef fect ' and is of great biological importance 1 0. The 'Bohr effect* is another important interaction in hemoglobin and relates the change in a f f in i ty of the heme site towards the binding of dioxygen as a function of phP"'. Neither of these effects are present in myoglobin. 1.3 Iron Model Systems Many porphyrin complexes of transition metals are known to bind 12 13 14 dioxygen; these include complexes of cobalt , manganese , titanium 15 and rhodium } but only iron and ruthenium species wi l l be discussed here. At ambient temperatures, the Fe(porphyrin)l_2 (L = any ligand) complexes in a variety of solvents are, in most cases, irreversibly oxidized by dioxygen, often quite rapidly to the f inal y-oxo Fe(lII) species (Fe(III)-O-Fe(III))^. This most l ike ly occurs by a 'dimerization 1 process involving the interaction of an oxygenated and a deoxy-iron(II) 17 18 porphyrin ' . . These oxo-bridged species are usually five-coordinate 19 and high spin . Another problem in mimicking the protein systems is that ferrous porphyrins tend to form six-coordinate low spin complexes with any 5 ligand present , while in deoxymyoglobin, for example, a five-coordiante high spin species is present. 20 Three recent synthetic approaches based on supressing formation of the y-oxo diiron complex have led to the formation and detection of 1:1 iron:dioxygen adducts. These methods are 1) use of s ter ica l ly hindered porphyrins that prevent dimerization, 2) use of low temperatures that-slow down the dimerization process, and 3) the use of a r ig id surface onto which the iron porphyrin complex can be attached to prevent dimerization. Two other features are desirable to simulate the deoxyheme centre: a f i ve -coordinate geometry and a non-polar hydrophobic environment. -6-21 Wang f i r s t demonstrated that simple porphyrins could be reversibly 22 oxygenated when immobilized in so l id , polymer films. Chang and Traylor then extended this work using sol id films of ferrous porphyrins with appended axial ligands, and these systems revealed oxygenation reactions 23 with a 1:1 Fe:0 2 stoichiometry. There also were many reports describing reversible, stoichiometric oxygenation of six-coordinate iron(II) porphyrins 24 in solution at low temperatures. Baldwin prepared a capped ferrous porphyrin which reversibly oxygenated in solution at room temperature, as 25 did Collman's more well-known 'picket-fence' porphyrins . These picket-fence porphyrins are synthesized to incorporate a steric bulk on one side of the porphyrin, thereby creating a non-protic cavity for the coordination of ligands such as dioxygen. The geometry protects these complexes from subsequent dimerization reactions. Two such dioxygen adducts have been 25 26 isolated as solids ' and are diamagnetic as is oxymyoglobin. The X-ray 27 crystallographic results show that the dioxygen binding is end-on with a bent Fe-(K° bond H 3 6 ° ) . Six-coordinate, low spin Fe(porphyrin)l_2 complexes have been shown to 28 react with carbon monoxide at ambient temperatures or with dioxygen at low 29 temperatures , to give the carbonyl or dioxygen adduct, respectively, via a dissociative mechanism, equation (1): k l k2 Fe(porphyrin)L 2 < = > F e ( p o r p h y r i n ) L < = = > Fe(porphyrin)(L)(X) (1) k - l k -2 (X= CO or 0 2) The analysis of the kinetic and equilibrium data yields values of k-j, k_2 and k_-|/k2 and these may be compared with data for myoglobin systems. For example, k_2 is directly comparable with deoxygenation of oxymyoglobin or - 7 -decarbonylation of carbonyl-myoglobin, while the five-coordinate 28 30 intermediate is considered to be a kinetic model for deoxymyoglobin ' . These data wil l be discussed in more detail together with data obtained in the present studies on ruthenium systems (Chapters 3 and 4). 1.4 Ruthenium Model Systems The use of ruthenium instead of iron is a logical extension in both model and protein studies and this has been of prime concern within the Bioinorganic Group here at U.B.C. There seemed, in pr inciple, a good chance of detecting and isolating dioxygen complexes, hopefully under less demanding conditions (see above), since the chemistry of the second row transition metals is generally 'slowed down'. 31 It was found that solutions of bis(acetonitrile)octaethylporphyrinato-ruthenium(II), RuOEP(CH3CN)2, (Figure 1.3 shows the structure of OEP) in N,N,-dimethylformamide or pyrrole could absorb 1.0 mole of dioxygen per ruthenium atom reversjbly at ambient conditions. The system similarly bound carbon monoxide reversibly (cf. equation (1)). Interestingly, however, ruthenium(II)-reconstituted horse heart apomyoglobin (RuMb) treated with dioxygen in phosphate buffers at 0°C gave only irreversible oxidation to the metmyoglobin, RuMb+, though RuMb did 32 bind CO . Unlike the iron centre, ruthenium is incorporated into myoglobin as a six-coordinate low-spin species and the 0 2-oxidation proceeds via an 29 ef f ic ient outer sphere mechanism before loss of an axial ligand can occur . It was of interest, then, to study the kinetics of the binding of gas molecules (especially CO and 0 2) to the protein-free ruthenium(II) porphyrin complexes for comparison with corresponding iron(II) systems and myoglobin i t se l f . - 8 -Figure 1.3. The structure of octaethylporphyrin. -9-CHAPTER II  EXPERIMENTAL 11.1 Instrumentation U l t r av i o l e t and v i s i b l e absorption spectra were recorded on a Cary 17 spectrophotometer f i t t e d with a thermostated ce l l compartment. Quartz ce l l s of pathlength 1 cm were used. Infrared spectra were recorded on a Perkin Elmer 457 grating spectrophotometer. So l id state spectra were obtained as Nujol mulls between NaC£ plates. Nuclear magnetic resonance spectra were recorded on a Varian XL-100 spectrometer. Microanalyses were performed by Mr. P. Borda of th i s department. 1 1 . 2 Spectrophotometric K inet ic Measurements Due to the extreme oxygen s e n s i t i v i t y of many of the ruthenium species in so lut ion, i t was necessary to perform spectrophotometric studies in a s t r i c t l y anaerobic system. A l l opt ica l density measurements in the u l t r a -v i o l e t - v i s i b l e region were carr ied out in the type of c e l l shown in Figure II.1. The ce l l was maintained at a constant temperature by placing i t in a thermostated c e l l compartment which was attached to a Haake model FK c i r cu l a t i ng thermostating bath, the temperature of which was adjusted appropriately. In a typ ica l experiment, the s o l i d ruthenium complex was placed in -10-the quartz part of the c e l l through A (Figure II.1) and the solvent was added through B. The solvent was degassed by repeatedly freezing i t in the f lask of the c e l l , pumping of f any uncondensed gas and then thawing the solvent, being careful not to wet the s o l i d during th i s process. The degassed solvent could then be added to the s o l i d sample. The c e l l was then placed in the thermostated compartment to allow the solut ion temperature to equ i l i b ra te . After an i n i t i a l spectrum was recorded, a known amount of gas was admitted into the c e l l and the ce l l was shaken in order to ensure complete mixing of the gas in the so lut ion. The corresponding reaction was then monitored unt i l completion. Since the concentrations of the ruthenium porphyrin complexes used were very low (%1 x 10"^ M) and the s o l u b i l i t i e s of the gases are of the order -3 -1 of 1 x 10 M atm , the gas concentrations in solut ion and the pa r t i a l pressure of the gas remained e s sent ia l l y constant throughout the experiment. The pressure of the gas was measured by a mercury manometer. II.3 Materials II.3.1 Gases Pur i f i ed argon, nitrogen and oxygen were supplied by Canadian Liquid A i r Limited. The argon was further purifed by passing i t through a drying tower containing fresh phosphorus pentoxide and molecular sieves (BDH, type 5A). Nitrogen was passed through an 'Oxisorb ' c a t a l y t i c p u r i f i e r (A l l tech Associates) before use. C P . Grade carbon monoxide and ethylene were obtained from the Matheson Gas Co. In order to remove any oxygen present from the ethylene, i t was frozen in l i q u i d nitrogen and any uncondensed material was pumped of f . The frozen gas was then warmed to room temperature and th i s freeze-pump-warm -11-A t<-4 B. Fitted w i th a high v a cuum tef lon stopcock Fitted with B -Ucap To vacuum line Quartz c e l l Figure 1 1 . "I. Anaerobic Spectral Ce l l . -12-process was repeated for several cycles until a l l uncondensed materials were removed. 11.3.2 Solvents Al l solvents were freshly d i s t i l l ed prior to use and in a l l cases, except toluene and acetonitr i le, were d i s t i l l ed under vacuum. Al l solvents, once puri f ied, were handled under an argon atmosphere using Schlenk 33 techniques Toluene and tetrahydrofuran (Fisher Sc ient i f ic Co., spectral grade) were dried over and d i s t i l l ed from sodium-benzophenone ketyl, the toluene being d i s t i l l e d under nitrogen. Acetonitr i le (Matheson, Coleman and Bell Manufacturing Chemists, spectral grade) was dried over phosphorus pentoxide and d i s t i l l ed from calcium hydride under nitrogen. N,N-Dimethylacetamide (Fisher Sc ient i f ic Co., analytical grade) and pyrrole (Aldrich Chemical Co. Limited, reagent grade) were dried over and d i s t i l l ed from calcium hydride. N,N-Dimethylformamide (Fisher Sc ient i f ic Co., analytical grade) was dried over and d i s t i l l ed from anhydrous copper sulphate. Pyridine (American Chemical and Sc ient i f ic Co., reagent grade) was dried over and d i s t i l l e d from potassium hydroxide. 11.3.3 Nongaseous Ligands Tri(n-butyl)phosphine (Aldrich Chemical Co. Limited, analytical grade) was vacuum d i s t i l l ed . Tetracyanoethylene (Eastman Kodak Co.) was purif ied by sublimation. II.4 Complexes Carbonyloctaethylporphyrinatoruthenium(II)-ethanol (RuOEP(CO)(EtOH)) OA was prepared by a method similar to that of Tsutsui et al . 500 mg of octaethylporphyrin, provided by J . B. Paine III, and 500 mg of Ru^C019 -13-(Strem Chemical Inc.) were refluxed in 100 ml of degassed toluene, under N 2, for 24 hours. The toluene was removed and the sol id dissolved in 25 ml of methylene chloride and 25 ml of absolute ethanol. This solution was refluxed under N 2 for thirty minutes before the solvent was removed and the solid was purified by chromatography. A deactivated alumina (Fisher Sc ient i f ic Company, 80-200 mesh) column was made up in petroleum ether (reagent grade, 65°-110°C) and the product was eluted using petroleum ether, toluene and ethanol. The complex was recrystal l ized from methylene chloride/ethanol, washed with pentane and dried (64% yield); vr.Q=1930 cm~1 Analysis: Calculated for C 3 g H 5 N 4 0 2 Ru: C, 66.19%; H, 7.07%; N, 7.92%. Found: C, 66.11%; H, 7.15%; N, 7.92%. Nuclear Magnetic Resonance data in CDC£ 3: 0EP; CH 3, 1.98 t r i p l e t ; CH 2, 4.09 quartet; pyrrole, 9.98 singlet; Ethanol; CH 2, -1.06 t r i p l e t ; CH 3, -0.07 quartet. Bis(acetonitrile)octaethylporphyrinatoruthenium(II) (Ru0EP(CH3CN)2) was prepared based on a general photolysis method described by Whitten et a l 3 5 . 200 mg of Ru0EP(C0)(Et0H) was dissolved in 100 ml each of degassed acetonitr i le and toluene under argon in a photolysis cel l (Figure II.2). Argon was bubbled through the st i rr ing solution as i t was irradiated for 18 hours with a Hanovia medium pressure 450-W mercury vapour bulb. . The solvent was then removed on a vacuum line and the sol id was washed -1 31 with cold pentane and dried (72% yield)j VQ-^=2260 cm" . % Analysis: Calculated for C 4 0 H 5 Q N 6 Ru: C, 67.13%; H, 6.99%; N, 11.75%. Found: C, 67.41%; H, 6.96%; N, 11.25%. Nuclear Magnetic Resonance data in CDC£ 3: 0EP; CH 3, 1.90 t r i p l e t ; CH 2, 4.00 quartet; pyrrole, 9.90 singlet; Acetonitr i le; CrL, 0.64 singlet. -14-Water inlet Water outlet A r gon outlet Argon inlet Cav i t y for Lamp So lut ion outlet Figure II.2. Photolysis Ce l l . -15-Bi s(tri(n-butyl)phosphi ne)octaethyloornhyri natorutheni um(11) (RuOEP(P(n-Bu)3)2) was generously provided by Dr. George Domazetis. Dilute solutions of RuOEPCL)^ SDecies (L = solvent) can be made in s i tu. Solutions of 10" 5 M RuOEP(CO)(EtOH) are made up in the spectral cel l in the appropriate solvent. The solution is then irradiated with a 600 W Bl-PIN tungsten halogen lamp until the spectrum observed is that of the RuOEP(L)2 species (%2 min). The solution can then be degassed to remove some of the CO released during the photolysis. CHAPTER 3 THE REACTION OF RuOEP(CH3CN)2 AND CO III.l Spectral Characteristics Toluene was chosen as a solvent to study the reactions of 0 2 and CO with the RuOEP(CH3CN)2 complex. However, when the i n i t i a l spectrum of the bisacetonitri le complex was recorded, under argon in dilute solution (^10~^ M), the vis ib le bands were very broad and not typical of s ix-coordinate, low spin Ru(II) . Since acetonitr i le, as an axial l igand, may be quite l ab i le , and not strongly coordinated, acetonitri le was added to the toluene solution in order to generate and stabi l ize the six-coordinate species in solution and achieve the corresponding spectrum. Toluene solutions of RuOEP(CH3CN)2 under an atmosphere of 0 2 slowly undergo irreversible oxidation; the product is l ike ly a y-oxo Ru(III) dimer as is usually observed with the corresponding six-coordinate protein-free iron porphyrin systems, The RuOEP(CH3CN)2 species under an atmosphere of CO underwent a series of spectral changes to give a final spctrum identical to that of Ru0EP(C0)(CH3CN) (made by dissolving ^5 x 10" 5 M RuOEP(CQ)(EtOH) in a 10 M solution of acetonitri le in toluene). Measurements of CO uptake by the RuOEP(CH3CN)2 species showed that 1.0 mole of CO/Ru atom was absorbed Figure III.l shows typical spectral changes, as a function of time, for the addition of a known amount of CO to RuOEP(CHoCN) 9; a number of Figure III.l. Typical Spectral Changes for the Reaction of RuOEP(CH3CN) with CO in Toluene at 30°C. -18-isosbestic points are generated. In the v is ib le region, the bands at 527 nm ( e = 1.70 x 10 4 M"1 cm - 1) and 496 nm ( e = 1.05 x 10 4 M"1 cm"1) red shift to positions at 549 nm ( e = 2.29 x 10 4 M" 1 cm"1) and 518 nm ( e =1.31 x 10 4 M"1 cm" 1). The Soret region with an intense band at 405 nm (e = 2.20 x 10 5 M"1 cm"1) and smaller side bands at 394 nm (e = 8.46 x 10 4 M"1 cm"1) and 385 nm (e = 6.93 x 10 4 M"1 cm"1) changed to a major band at 395 nm (e = 1.76 x 10 5 M"1 cm"1) with a small shoulder at 375 nm. For a fixed CO pressure, the length of time required for each reaction increased with increasing added concentration of acetonitr i le in the solution. III.2 Treatment of Data The kinetic data were obtained by following the increase in spectral intensity of the 549 nm band of the carbonyl. Plots of log(A r o- A t ) versus time gave good straight l ines, Figure III.2; A^ is the absorbance of the RuOEP(CO)(CH3CN) species and A.J. is the absorbance at any time, t , during the reaction. This shows that the reaction follows pseudo-first-order kinetics under the conditions of the experiment. The CO concentration is much larger than that of the porphyrin(see below). An inverse dependence on acetonitr i le concentration at a fixed CO pressure and a less than f i rst -order dependence on CO at a fixed acetonitr i le concentration are readily interpreted in terms of a dissociative mechanism(Eq. 1, Ch. 1): k l k 2 RuOEP(CH3CN)2^ZZ=l> RuOEP(CH3CN) '< >RuQEP (C0)(Ch*3CN) (2) k - l k - 2 Since the reaction is judged, by the spectral changes, to go to completion, k_2 is assumed to be negligible. Assuming a steady state -19-TIME (min) Figure III.2. First-Order Plots for the Reaction of RuOEP(CH3CN)2 With CO in Toluene With 1.91 x 10" 2 M Acetonitri le added at 30°C. -20-concentration of five-coordinate intermediate leads to the rate law: rate = ^^[CO] [RuOEP(CH3CN)2] ( 3 ) k_1 1CH3CN] + k2[C0] For any one experiment in which the CO and acetonitri le concentrations remain effect ively constant, this may be rewritten as: rate = kQ b s d[RuOEP(CH 3CN) 2] where k Q b s d = k 1 k 2 lC0 ] / (k_ 1 [CH3CNJ + k 2[C0.]) (4) kobsd 1 S t ' i e P s e u do- f i r s t -o rder rate constant measured in the plots of log(A r o - A^ .) versus time. The data are given in Table III.l. In agreement with equation (4), at high acetonitr i le concentrations, the dependence on CO pressure approaches f i rst -order but becomes less than f i rst -order and approaches zero order as the acetonitri le concentration decreases. The acetonitr i le dependence remains inverse over the small pressure range of CO studied. There were no complications in the system due to the presence of displaced acetonitr i le in the forward reaction since added acetonitr i le was at least in a hundred-fold excess. The inverse of expression (4) gives: k obsd _ 1 = k l _ 1 + k_i[CH 3CN]/(k 1k 2[C03) (5) The CO pressure can be converted to molarity using the known so lubi l i ty of CO in toluene at 30°C (6.5 x 10" 3 M a tm" 1 ) 3 7 - A plot of k o b s d _ 1 vs [CH3CN]/[C0] for a l l data in Table III.l gives a straight l ine of slope k_ 1/k 1k 2 and an intercept of k-,"1 (e.g. Figure III.3). The value of k_2 was estimated by placing the solid RuOEP(CO)(EtOH) adduct into a large excess of acetonitri le in toluene solution and following spectral changes for the CO displacement by acetonitr i le. The overall equilibrium constant K -21-T a b l e n i . l . Rate of Reaction of RuOEP(CH3CNj? With CO in Toluene at Various Acetonitri le Concentrations and CO Pressures, at 30°C CO Pressure 3 [CH3CN] k Q b s d x 10 4 b (atm) (moles/litre) ( sec - 1 ) 0.963 0.375 1.95 0.963 0.190 3.70 0.713 0.190 2.77 0.463 0.190 1.97 0.213 0.190 1.18 0.971 9.52 x 10"2, 6.47 0.721 9.52 x 10", 4.37 0.501 9.52 x 10", 3.08 0.221 9.52 x 10"* 2.12 0.971 5.72 x 10"?, 9.33 0.721 5.72 x 1 0 , 6.97 0.471 5.72 x 10", 5.63 0.241 5.72 x 10"* 3.48 0.971 3.82 x 10" 2 10.53 0.721 3.82 x 10", 9.12 0.471 3.82 x 10", 7.47 0.221 3.82 x 10"* 4.35 0.971 1.91 x 10" 2 15.72 0.721 1.91 x 10", 14.58 0.471 1.91 x 10"* 11.57 0.221 1.91 x 10"* 7.00 0.971 3.83 x 10" 3 23.98 0.721 3.83 x 10'^ 21.92 0.471 3.83 x 10"^ 20.03 0.221 3.83 x 1 0 ^ 16.67 Pressures were corrected for the partial pressure of toluene at 30°C; R. C. Weast, Ed., 'Handbook of Chemistry and Physics', 56 standard ed The Chemical Rubber Company Co., Cleveland, Ohio, 1975, p D198. b. estimated error ±5%. Figure III.3. Plot of k o b s d " ' vs [CH3CN]/[-C0] For The Reaction of RuOEP(CrLCN)9 With CO in Toluene With 1.91 x 10" 2 M Acetonitri le Added at 30°C. -23-(k-|k2/k -jk 2 ) can then be readily estimated (see below). Table III.2. Kinetic and Equilibrium Data for the Reaction of RuOEP(CH3CN)2 With CO at 30°C in Toluene. k a 1 1 (sec" 1) k_ 1 /k 2 b k_2 K ( sec - 1 ) 2.41 x 10" 3 .176 3.4 x 1 0 - 7 4.0 x TO4 a. estimated error ±25%. b. estimated error ±10%. III.3 Discussion From the data, the six-coordinate bis(acetonitri le) complex is seen to lose an acetonitr i le ligand about 10 4 times faster than the mixed ligand species gives up a CO molecule and this is the major factor governing the equilibrium constant. The k_-|/k2 value.shows that the five-coordinate intermediate prefers to bind CO over acetonitri le k inet ical ly by a factor of about f ive. Some rough calculations based on unpublished data from these laboratories 3^, were done 3 9 (Table III.3) for oxygen binding of RuOEP(pyrrole)2 in pyrrole, which is a solvent in which oxygenation occurs without appreciable oxidation. The values for k.j and k_-j/k2 are comparable to the CO reaction in toluene but there is a difference of about a hundred in k_2 and the values suggest that the strong binding of CO (compared to 0 2) is reflected in i ts much lower off -rate. Attempts to measure the kinetics of the CO reaction with RuOEP(CH3CN)2 in pyrrole for a more direct comparison with the 0 2 system were unsuccessful (see Chapter 5). -24-Table III.3. Kinetic and Equilibrium Data for the Reaction of RuOEP(pyrrole)  With 0 ? at 20°C in Pyrrole. (sec" 1) k_ 1/k 2 ( sec - 1 ) K %0.003 ^0.06 'x/ICf 5 ^10 4 It is also of interest to compare the Ru0EP(CH3CN)2/C0 data with those for the CO binding to some Fe(porphyrin)(amine)2 systems (Table III.4). In terms of porphyrin properties, OEP is considered much closer to protoporphyrin IX (PpIX) than octamethyltetrabenzoporphyrin (OMBP) or tetraphenylporphyrin (TPP) or phthalocyanine (Pc). 30 Table III.4. Kinetic and Equilibrium Data for the Reaction of Fe(porphyrin)(piperidine)o Complexes With CO in Toluene at 23°C. Porphyrin ( sec - 1 ) ( sec - 1 ) k_ ]/k 2 K OMBP 1020 0.25 1.7 2340 490a 0.09 a 26 a 209a PpIX 20 0.06 0.002 230000 TPP 11 0.52 0.002 150000 Pc 0.5 0.13 3.3 0.85 a. Fe(0MBP)(py)2 -25-The k_-|/l<2 value for RuOEP(CH3CN)2 in toluene l ies within the range of data for the iron systems and is some 100 times the value for the PpIX system. The k-j and k_2 values are quite different for the ruthenium and iron systems. The k-j value for the FePpIX system is some 10 times that 5 of the ruthenium complex and 10 times the k 2 value. As expected, kinetic l ab i l i t y is slowed down considerably when using the second row elements. The k_2 value for Ru0EP(CH3CN)2/C0 can also be compared to the o 39 decarbonylation rate of COMb in aqueous solution at pH 7, 20 C (k 2 %0.02 s e c - 1 ) . Although the k_2 value for COMb is similar to the k_2 values of the iron protein-free systems, once again the ruthenium complex binds CO much tighter kinetical ly than the naturally occurring heme group does Based on the findings in the iron systems (Table III.4), a hypothesis L was advanced dealing with the geometry of the five-coordinate intermediate and such consideration should also be extended to the ruthenium systems. The two possible extreme structures for the five-coordinate intermediate are shown in Figure III.4. 40 N N 1 2 0/ Figure III.4 Possible Structures of the Five-Coordinate Intermediate. When considering steric interactions, the addition of a bulky ligand to a high spin intermediate, ^, wil l be less favourable than the corresponding -26-addition to the low spin species, £, especially relative to the rate of addition of a non-bulky ligand such as CO. If the assumption is made that the intermediate l ies close to the 41 transition state, both in free energy and geometry , then some statement about the structure of the intermediate can be made, based on the kinetic data. In Table III.4, there is a range of 10 for the k_i/k 2 values and this variation may arise from a difference in structure and spin state of the intermediate. The five-coordinate intermediate of the PpIX and TPP systems was considered to have a structure similar to that of 1 which resembles the active s ite of hemoglobin and myoglobin, with the iron atom out of the plane and in a high spin state. The larger values of •<_-|/kg for OMBP and Pc would be consistent with an intermediate species that is low or intermediate spin with a structure closer to that of 2. The k_-j/k2 value of 0.176 for the ruthenium system might imply a structure more analagous to £ than ^ for the RuOEP(CH3CN) intermediate, but clearly much more data are needed for other ruthenium systems (especially with Ru(porphyrin)(amine)2 species) before such a conclusion can be drawn. An axial pi peri dine ligand in an iron porphyrin system 42 does give rise to steric interaction due to the 2,6-CH2 groups and thus could well give rise to movement of the iron atom out of the plane in the five-coordinate intermediate. The k_-j/k2 value for the FePpIX(py)2/C0 system with no such steric problem is l i ke ly to be greater than the 0.002 value for the piperidine system. Using the OMBP data as a guide, (Table III.4), the k_^/k2 value could be increased to ^0.02, a factor of about ten smaller than the ruthenium system: the data again tentatively suggest a more in-plane structure for the ruthenium intermediate. -27-CHAPTER 4 THE REACTION OF RuOEP(P(n-Bu)3)3 AND CO IV.1 Spectral Characteristics Toluene was again used as the solvent for this system. However, i t was not necessary to add an excess of phosphine ligand to the solvent in order to generate the correct spectrum for the six-coordinate bis(phosphine) system. This contrasts with the bis(acetonitr i le) system in toluene (Chapter 3). When one atmosphere of 0 2 was added to the bis(phosphine) system at 30°C, no appreciable reaction occurred within 24 hours. Upon addition of one atmosphere of CO, however, a series of spectral changes were observed as a function of time. There were several clean isosbestic points and the reaction appeared to go to completion to form the carbonyl-phosphine complex. To establish pseudo-first-order conditions with respect to ligand concentration, small amounts of phosphine were added to the toluene in a l l reactions. However, under these conditions, the reaction did not go to completion, the position of the equilibrium being dependent upon the CO pressure used and the amount of excess phosphine added. Figures IV.1 and IV.2 show typical spectral changes characteristic of the reaction. The product, RuOEP(P(n-Bu)3)(CO), was never isolated so i t s extinction coefficients were based on the spectrum achieved when the reaction went to completion with no added phosnhine ligand. -28-30NV9cJ0S8V ABSORBANCE Figure IV.1. Spectral Changes for the Reaction of RuOEP(P(n-Bu)3)2 with! atm CO in Toluene with no added P(n-Bu), at 31°C--29-a o N v a c J o s a v A B S O R B A N C E Figure IV.2. Spectral Changes for the Reaction of RuOEP(P(n-Bu)3)2 withl atm CO in Toluene Containing 2.84 x 10" 4 M P(n-Bu), at 31°C. -30-In the i n i t i a l spectrum of RuOEP(P(n-Bu)3)2, there are bands at 535 nm ( e = 1.95 x 10 4 M"1 cm" 1), 511 nm ( e = 2.72 x 10 4 M"1 cm" 1), «\460 nm ( e = 0.51 x 104 M' 1 cm" 1), 428 nm ( E = 3.20 x 105 M"1 cm" 1), 417 nm ( e = 7.98 x 104 M"1 cm" 1), 405 nm (e = 4.94 x 104 M"1 cm" 1), 360 nm ( e = 7.72 x 10 4 M"1 cm"1) and <341 nm (e = 5.06 x 10 4 M"1 cm" 1). The f inal spectrum of RuOEP(P(n-Bu)3)(CO) has bands at 555 nm (e = 1.70 x 10 4 M"1 cm" 1), 528 nm(e = 2.39 x 10 4 M' 1 cm" 1), 409 nm ( e = 3.49 x 10 5 M"1 cm" 1), 388 nm ( e = 6.74 x 104 M"1 cm" 1), 358 nm ( e = 5.84 x 10 4 M"1 cm"1) and ,^325 nm ( e = 7.62 x 10 4 M"1 cm" 1). At any particular equilibrium position, there were bands of both the starting and f inal species (cf. Figure IV.2). In most cases, reactions were over within twenty minutes. IV.2 Treatment of Data The dependence of the reaction on CO pressure and the concentration of added phosphine is consistent with the equilibrium: K RuOEP(P(n-Bu)3)2 + C0<=> RuOEP(P(n-Bu)3)(CO) + P(n-Bu) 3 (6) [RuOEP(P(n-Bu)3)(CO)][P(n-Bu)3] K = [RuOEP(P(n-Bu)3)2][CO] ( 7 ) Using spectral data to find the various concentrations of i n i t i a l and f inal species, one can rewrite the equilibrium expression as: log K = log A Q - A - log[C0] + log[P(n-Bu) 3l " A T A ~ oo (8) -31-AQ is the absorbance of the RuOEP^n-Bu).^ soecies is the absorbance of the RuOEP(P(n-Bu)3)(CO) species estimated by extinction coefficient data A is the absorbance at the equilibrium position. The CO pressure is again converted to molarity units . Temperature dependence studies were done over a range of 21-41°C. The equilibrium constants were obtained from plots of log AQ-A vs A^A~ CO log[P(n-Bu)3] at a fixed pressure (Figure IV.3). In a l l cases, straight l ine plots of slope -1.0 ± .1 were obtained. The K values are l i s ted in Table IV.1. A plot of ln(K) vs 1/T (Figure IV.4) gave a straight l ine from which the thermodynamic parameters, AH = 3.7 ± 0.5 Kcal/mole and AS = 10.3 ± 5 e.u., were calculated. Table IV.1 Equilibrium Constant Values from 21-41°C for the Reaction  of RuOEP(P(n-Bu).,);, with one Atmosphere CO, in Toluene. Temperature (°C) "21 26 31 36 41 Ka 0,425 0,506 0.536 0.589 0.650 a. estimated error ± 10%. As well as calculating a value for K and i ts thermodynamic parameters, some individual kinetic rate constants were also determined. Kinetic data were obtained by following the increase in spectral intensity at 555 nm as CO was bound by the ruthenium. In these cases, though, since the reactions did not go to completion, the rate law expression used in Chapter 3 cannot be used. The dissociative machanism is once more assumed to be occurring, i .e . -32-Figure IV.3. Equilibrium Plots for the Reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO in Toluene. -33-Fiqure IV.4. Van't Hoff Plot for the Reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO in Toluene. -34-k l k 2 RuOEP(P(n-Bu) 3 ) 2 <== > RuOEP(P(n-Bu)3) < :> RuOEP(P(n-Bu)3)(CO) (9) k - l k -2 but since an equilibrium is obtained in a l l cases, k 2 cannot be assumed negligible. Therefore, when the rate law is derived, the expression becomes: rate = k l k 2 f C 0 J [RuOEP(P(n-Bu)3)2] k_-,k_2[P(n-Bu)3] lRuOEP(P(n-Bu)3(CO)] (10) k_-, {P(n-Bu)3] + k2[C0] " k_-,[ P(n-Bu)3] + k2[C0] which can be rewritten: rate = k f [RuOEP(P(n-Bu)3)2] - kr[RuOEP(P(n-Bu)3)(CO)] (11) k^ r is the overall rate constant for the forward reaction and k r is the overall rate constant for the reverse reaction. This expression can now be integrated 4 3 to give: (k f + k r ) t = In A Q -A e (12) A g is the absorbance at the equilibrium position and A is the absorbance at any time, t. This then gives the expression: ^k1k2[C0] + k_1k_2[P(n-Bu)3] ^t In A Q -A e ( 1 3 ) k_1 [P(n-Bu)3] + k2[C0] j A-A e Plots of In A Q -A e versus time (Figure IV.5) yielded straight l ines of k 1k 2[C0] + k ^ 2 lP(n-Bu) 3] s l ° P e = k_1lP(n-Bu)3j" +"k 2[C0] = kobsd ( 1 4 ) kobsd 1 S t ^ 1 e P s e u do- f i r s t -o rder rate constant for the reaction. Table IV.2 gives the kinetic data, -35-Figure IV.5. First-Order Plot for the Reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO in toluene containing 7.08 x 10" 4 M P(n-Bu), at 31°C. -36-Table IV.2. Rate of Reaction of RuOEP(P(n-Bu)3)., with CO in Toluene at Various Ligand Concentrations and CO Pressures at 31°C. CO Pressure 9 P(n-Bu) 3 k Q b s d x 10 3 b k d ( c a l c ) c (atm) (moles/litre) ( sec - 1 ) x 10 3 ( sec - 1 ) 0.971 1.057 X 10"? 6.67 6.08 0.721 1.057 X 10", 7.77 6.98 0.471 1.057 X 10"^ 7.95 7.41 0.221 1.057 X 10""3 11 .0 10.45 0.971 7.083 X 1 0 1 5.67 5.69 0.721 7.083 X 5.84 5.96 0.471 7.083 X i o i 6.11 6.59 0.221 7.083 X 10" 4 8.75 8.66 a. and b. see Table III.l. c. see text for explanation,•agreement with measured rate constants within 10%. However, due to the complicated nature of the rate law, no simple graphical method yields the kinetic rate constants. Therefore, alternative procedures were used. Since, in the ease of RuOEP(P(n-Bu)3)2 and 1 or h atmosphere of CO in toluene with no added phosphine, the reaction went to completion, with the same measured k ^ ^ , this means that k^  is rate determining (see -3 -1 Chap 3). This is thus a direct measure of k-| (k-| = 2.11 x 10" sec" ). Once such a reaction had been carried to completion, a large excess of phosphine was added, under the CO atmosphere, and the reaction was pushed back completely to the l e f t , reforming RuOEP(P(n-Bu)3)2(Table IV.3). Under these conditions (k-j being negl igible), the rate of the reaction is rate = k_-,k_2 [P(n-Bu)3] [RuOEP(P(n-Bu)3) (CO)] ( 1 5 ) k2[C0J + k_-, [P(n-Bu)3] which can be rearranged to give: -37-• W i " 1 = k - 2 _ 1 + k2[C0)/k_ 1k_2[P(n-Bu)3] (16) Therefore, a plot of k o b s d _ 1 vs [CO]/[Ptn-Bu)^ should give a straight l ine of slope k2/k_-|k_2 and an intercept of k_2_1 (Figure IV.6 and Table IV.4). Table IV.3. Rate of Reaction of RuOEP(P(n-Bu)3)(CO) With P(n-Bu), in Toluene at 31°C. CO Pressure 3 (atm) P(n-Bu) 3 x 10 2 (moles/1itre) kobsd>< ™ 2 b ( sec - 1 ) 0.971 5.02 1.79 0.971 5.73 1.92 0.971 7.15 2.21 0.971 8.57 2.47 a. and b. see Table III.l. Table IV.4. Kinetic Data For the Reaction of RuOEP(P(n-Bu)3)(CO) and  P(n-Bu) 3 in Toluene at 31°C. ( sec - 1 ) 0.061 5.35 x 10" 2 a. estimated error ± 10%. b. estimated error ± 25%. Taking the rate constants l i sted in Table IV.4 and substituting them back into the expression for k o b s c| (14) for the overall reaction, rates can be calculated for the conditions l i sted in Table IV.2 (see table). -39-The complete set of kinetic parameters is l i s ted in Table IV.5. K was calculated by K = k 1 k 2 /k_ 1 k_ 2 and is within 15% of the direct ly measured K at 31°C. Table IV.5. Kinetic Data for the Reaction of RuOEP(P(n-Bu)3)2 and CO at 31°C in Toluene. ^ 1 ( sec - 1 ) k_ 1/k 2 (sec" 1) K 2.11 x 10" 3 0.061 5.35 x 10" 2 0.647 IV.3 Discussion From the data, Table IV.5, the six-coordinate bis(phosphine) complex loses a phosphine ligand 25 times slower than the mixed ligand species gives up a CO molecule, very different from the previous bis(acetonitri le) system (see Chap 3). The k_^/k2 value shows that the five-coordinate intermediate prefers to bind CO over P(n-Bu) 3 by a factor of 16, however, the Ru-CO and Ru-P(n-Bu)3 bond strengths are similar ( A H value). These data can also be compared to the data of Table 111.3. the oxygenation of Ru0EP(pyrrole)2 in pyrrole. The k ] and k_ 1/k 2 values are quite similar but the k_2 value is very dif ferent. The off-rate for CO seems to be 1000 times that for oxygen, again quite different to the bis(acetonitri le) system, showing that the phosphine has marked effects on the solution chemistry of the systems. The data of Table IV.5 can also be compared to those of Table III.2 Though the k-j and k_^/k2 values, here too, are very s imilar, k 2 is -40-very di f ferent, resulting in a rather dramatic variation in the value of K. The two k_i/l<2 values d i f fer by a factor of only three which implies that the structure of the five-coordinate RuOEP(P(n-Bu)3) and RuOEP(CH3CN) are quite similar(see Chap 3). Further work on the RuOEPI_2 systems and othe Ru(porphyrin)l_2 systems is necessary to get a clearer picture of the nature 44 of the five-coordinate species. At this time, work has started on the study of RuTPP(CH3CN)2, RuTPP(phosphine)2 and other RuOEP(phosphine)2 systems. The two k_2 values in the systems studied here vary by ^10^, a very dramatic difference. The phosphine trans to the-CO molecule seems to l ab i l i the CO molecule much more readily than an acetonitr i le molecule can. Since CH3CN is not such a good ir-acid as P(n-Bu) 3 4^, the CO is l i ke ly to accept more of the ir-electron density from the metal centre in the acetonitri le system, therefore strengthening the M-CO bond (solution -3 -1 infrared spectrum taken in hexane, ^10" M, = 1935 cm - ). In the case of the P(n-Bu) 3 system, there wi l l be competition for the iT-electron density between the P(n-Bu)3 and CO and thus the M-CO bond is not as strong as in the previous case (solution infrared spectrum taken in hexane, ^10" M VC0 = cm - 1) and the CO is now much more easi ly lost. Such a correlation between CO l ab i l i t y and v c o seems reasonable for two such 30 closely related systems, but i t does not hold more generally . Due to the ease that the RuOEP(phosphine)(CO) system was found to 46 lose a CO molecule, work has been init iated in the area of catalysis in which this system and RuTPP(phosphine)2 species are used to cata lyt ica l ly decarbonylate aldehydes. The main thrust of the work, so far , has been in the use of RuTPP(P(Ph)3) ? in acetonitr i le. A CO atmosphere seems to be -41-necessary to in i t ia te the decarboxylation reaction. Phenylacetaldehyde has been decarbonylated with turnover lumbers of 103/hour at 20°C. However, the actual mechanism of the reaction is far from completely understood. These ruthenium(porphyrin)(phosphine) systems seem to be quite successful in this area due to the l ab i l i t y of the Ru-CO bond, that results from the presence of the phosphine ligand in the trans axial position. Much more interesting chemistry wil l probably develop out of these systems in the f ields of catalysis and bioinorganic chemistry. -42-CHAPTER 5 THE REACTIONS OF RuOEP(CH3CN)o WITH OTHER GASES IN TOLUENE  AND WITH CO IN OTHER SOLVENTS V.l The Reaction of RuOEP(CH3CN)2 With N2 and With CQH^ in Toluene Since the reaction of RuOEP(CH3CN)2 in toluene with CO had been studied, reactions with other gaseous ligands were of interest. Hopf and Whitten 4 7 had 'activated' a ruthenium(II) mesoporphyrin IX system by using surfactant complexes in monolayer assemblies; the system reacted with C 0 , 0 2 and N 2 > Although 0 2 was known to oxidize the RuOEP(CH3CN)2 system in toluene, i t seemed worthwhile investigating its reactivity towards C 2 H 4 , isoelectronic with 0 2 . Its reactivity toward N2 was also tested. V.1.1 The Reaction of RuOEP(CH3CN)2 and N2 Toluene solutions of 10" 5 M RuOEP(CH3CN)2 with 1.9 x 10" 2 M CH3CN added were reacted with one atmosphere of N2 at 30°C; Figure V.l shows a 'successful' run (see below). The i n i t i a l spectrum was that of RuOEP(CH3CN)2 with extinction coefficients stated in Chapter 3. As N2 reacted, the v is ib le bands broadened, the f inal spectrum having a shoulder at 555 nm (e = 1.0 x 10 4 M - 1 cm"1) and the main band centred around 525 nm (e = 1.3 x 10 4 M"1 cm - 1 ) . In the Soret region, the band blue shifted to 398 nm (e = 1.67 x 10 5 M"1 cm"1) with small shoulders appearing at 388 nm(e = 6.67 x 104 M' 1 cm"1) and 378 nm (e = 5.87 x 10 4 M"1 cm" 1). -44-When one atmosphere of N2 was used in the reaction, the original bands of RuOEP(CH3CN)2 in the Soret region completely disappeared, suggesting that the reaction had gone to completion. When \ an atmosphere of N2 was used, bands from the bis(acetonitri le) species could s t i l l be seen. Therefore, an equilibrium process seems to be occurring, presumably: K RuOEP(CH3CN)2 + N 2 <= i RuOEP(CH3CN)(N2) + CH3CN (17) The forward reaction could be part ia l ly reversed by freeze-thaw-degassing the solution to remove the N 2. However, the system proved d i f f i c u l t to study in terms of reproducibi l ity. Many times, while scanning the spectrum during a run, isosbestic points were lost. The collapse of the v is ib le bands was very similar to the reaction of RuOEP(CH3CN)2 and 0 2 , in which the product is some oxidized species (see Chap 3). Other times, the reaction would apparently either stop partway through a run or in some cases, never begin at a l l . Eventually the solution product, thought to be RuOEP(CH3CN)(N2) was found to be very l ight-sensit ive and i f one wavelength is scanned for too long, some of the N2 wil l photolyze off the complex to regenerate the RuOEP(CH3CN)2 species. Of the reactions with good isosbestic points, inconsistent kinetic data were obtained. For example, though good f i rst -order plots were obtained (Figure V.2) for the reaction of RuOEP(CH3CN)2 with one atmosphere of N2 at 30°C (from data obtained by monitoring the decrease in intensity of the 525 nm band),pseudo-first-order rate constants -4 -1 -4 -1 from 5.70 x 10 sec to 2.14 x 10 sec were obtained. Therefore, the study of this particular system was abandoned. -45-Figure V.2. First-Order Plot for the Reaction of RuOEP(CH3CN)2 with 1 atm N2 in Toluene Containing 1.9 x 10" 2 M CH3CN at 30°C. -46- / The l ight sensit iv ity coupled with possible trace oxygen impurities rendered the system impractical to study from a kinetic viewpoint. 39 Closely related work has been done in this laboratory in another solvent, tetrahydrofuran (THF), in which N2 also seems to bind to a ruthenium porphyrin complex. By photolyzing RuOEP(CO)(EtOH) in THF, RuOEP(THF)2 is formed in s i tu. The THF was evaporated off by bubbling N2 through the solution and a red solid was isolated which is believed to be the N2 adduct, RuOEP(THF)(N2). The solid had a v N = 2110 cm" 1 , -1 2 which can be compared to a = 2088 cm for the complex 2+ 248 trans-[Ru(NH 3) 4(H 20)(N 2)] . However, no kinetic studies have been carried out on this system. V. 1.2 The Reaction of RuOEP(CH,CN)2 With C Q H 4 Toluene solutions of 10" 5 M RuOEP(CH3CN)2 with 1.9 x 10" 2 M CH3CN added were reacted with 3/4 atmosphere of C,,H4 at 30°C(Figure V.3). Again, from examining the bands in the Soret region, the reaction appears to have gone to completion. The spectrum of the f inal product is very similar to that of the proposed RuOEP(CH3CN)(ft,) species, showing a broad band in the v is ib le region. The f inal spectrum has a shoulder at 3 1 1 548 nm (e = 9.24 x 10 M" cm" ), a broad band centred around 525 nm (e = 1.18 x 10 4 M"1 cm"1) and in the Soret region, a main band at 398 nm (e = 2.04 x 10 5 M" 1 cm"1) with shoulders at 388 nm ( e = 9.37 x 10 4 M' 1 cm"1) and at 378 nm (e = 6.77 x 10 4 M"1 cm" 1). Some reversal of the reaction could be seen by degassing the solvent. As with the case of binding N 2, the kinetic runs were very inconsistent. Often the spectral curves would lose their isosbestic points partway through the reaction, and sometimes the reaction would -47-30NV9U0S8V 1 § f g (NJ ^ T - CD ABSORBANCE Figure V.3. Spectral Changes for the Reaction of RuOEP(CH3CN)2 with 3/4 atm of C 2 H 4 in Toluene Containing 1.9 x 10" 2 M CH3CN at 30°C. -48-never start at a l l . When the i n i t i a l amount of added CH3CN was doubled to 0.038 M and spectral changes were observed, the extent of C ^ r l ^ binding seemed to be very small, consistent with some sort of equilibrium such as: K RuOEP(CH3CN)2 + C2H4<-=^.RuOEP(CH3CN)(C2H4) + CH3CN (18) This reaction, as in the N2 reaction, seemed to be extremely photo- and oxygen-sensitive, the C 2 H 4 not being bound very t ightly. The use of tetracyanoethylene, TCNE, was considered because activated olefins should coordinate more strongly and stabi l ize any Ru-olefin complex. However, TCNE in toluene produced intense colours due to the formation of a charge-49 transfer complex ; the intense colour covers the absorption bands of the porphyrin complex in the v is ib le region. Reversible binding of C 2 H 4 to RuOEP(THF)2 in THF at 20°C has also been demonstrated by spectroscopy by another worker in this 39 laboratory . The exact nature of the ethylene compl-ex is of particular interest. The species presumably contains a ir-bonded o lef in ic moiety but i t is not known whether one or both CH C^N ligands come off when the C0H„ is bound: i .e . Figure V.4 Possible structures for ethylene complex, Complex 3 is considered as formally seven-coordinate, A Mn(IT) porphyrin system that binds 0 ? (and TCNE) does lose an axial ligand in forming -49-complexes of type 4 1 3 ' 3 . Information on the ruthenium system could relate back to the ruthenium complexes that bind oxygen. There is no report of any metal centre that binds both dioxygen as an end-on superoxide and also TT-bonded ethylene. 4 50 Ethylene complexes are usually formed with systems that give peroxides ' (eg. Rh 1, I r 1 , Pt^1). The evidence suggests then that perhaps instead of binding dioxygen as a bent superoxide ( R u 1 1 1 ^ - ) , the 0 2 is bound as a IV -2 side-on peroxide (Ru -0 2 ~ ) with the ruthenium being formally in the +4 oxidation state. One isolated Ru(IV) complex, H 4Ru(P(Ph) 3) 3, has been found 5 1 to be seven-coordinate. Unfortunately, an oxygenated ruthenium porphyrin complex has not been isolated yet and due to the noted inconsistencies, no further work was done on the ethylene binding by RuOEP(CH3CN)2 in toluene. V.2 The Reaction of RuOEP(CH3CN)2 With CO in Other Solvents Since the reaction of RuOEP(CH3CN)2 and CO in toluene had gone so cleanly, the same reaction in other solvents was also t r i ed , particularly 31 since the reversible 0 2-binding had been demonstrated in the aprotic, polar solvents DMA, DMF and pyrrole. On dissolving the RuOEP(CH3CM)2 complex in the coordinating solvents used, (DMF, DMA, THF, py and pyrrole), both CHgCN ligands were believed to be displaced by the solvent ligands (see below). The bis species could certainly be formed in situ by photolyzing the RuOEP(CO)(EtOH) adduct in the appropriate solvent (see Experimental), but then there was always the poss ib i l i ty of some dissolved CO remaining in the solvent, and this could possibly have interfered with the CO reaction being studied. The only useful isolated solid was RuOEP(CH3CN)2, and since acetonitr i le ligands are f a i r l y labi le (as -50-judged by the reaction with CO in toluene-Chap. I l l ) , the solvent ligands, at suff ic ient ly high concentrations, should easily displace the acetonitr i le, whose concentration would be low (twice that of the Ru-porohyrin) and not interfere with the CO reaction to be studied. V.2.1 The Reaction of RuOEP(CH3CN)2 With CO in Pyridine (py). The RuOEP(CH3CN)2 complex in neat pyridine gives the bis(pyridine) species, but the system is completly unreactive towards CO, which is quite consistent with a dissociative mechanism involving i n i t i a l loss of a pyridine ligand. Dissolution of RuOEP(CH3CN)2 in toluene containing 0.15 M pyridine, 5? again, gave a spectrum similar to that reported for solid RuOEP(py)2 in benzene. Visible bands appear at 521 nm (e = 3.80 x 10 4 M"1 cm - 1 ) , 495 nm ( e = 1.48 x 10 4 M"1 cm" 1), 450 nm ( e = 1.58 x 10 4 M"1 cm"1) and a Soret band at 395 nm (E = 1.02 X 10 5 M"1 cm" 1). However, under these conditions, based on the known spectrum of'RuOEP(CO)(py) (solid prepared by a method similar to that of Ru0EP(C0)(Et0H)-see Experimental), the reaction of the Ru0EP(py)2 with one atmosphere of CO at 25°C was only ^15% complete after 3 days (Figure V.5). This would give K for the reaction (19) at 25°C as ^25, some 50 times greater than for the analogous RuOEP(P(n-Bu)3)2 system; this could ref lect the stronger 45 Ru-CO bond of the pyridine system due to the weaker iT-acceptor properties of the trans pyridine compared to the phosphine. K RuOEP(py)2 + C0^=±Ru0EP(C0)(py) + py (19) Surprisingly, toluene solutions of the bis(acetonitri le) complex containing 0.015 M pyridine did not completely form the bis(pyridine) -51-Figure V.5. Spectral Changes for the Reaction of RuOEP(CH3CN)2 with 1 atm CO in Toluene Containing 0.15 M pyridine at 25°C. - 5 2 -species, which has a characteristic band at 4 5 0 nm. Presumably, the mixed ligand species RuOEP(CH3CN)(py) must be present. Studies on the-pyridine systems were not pursued further part ia l ly due to this added complication. V . 2 . 2 The Reaction of R U O E P ( C H Q C N ) 2 With CO in N,N-Dimethylacetamide (DMA), N,N-Dimethylformamide (DMF) and Tetrahydrofuran (THF). Since the solid RuOEP(DMA)2 has not been isolated, the species was _5 formed in situ by photolyzing a 1 0 M solution of the RuOEP(CO)(EtOH) complex in DMA for ^ 2 min. Spectral bands were found at 5 2 1 nm ( e = 3 . 5 2 x 1 0 4 M"1 cm" 1), 4 9 8 nm ( e = 1 . 1 5 x 1 0 4 M' 1 cm' 1) and 3 9 5 nm ( e = 1 . 6 8 x 1 0 5 M"1 cm" 1). The RuOEP(CO)(DMA) species, which is considered to be formed when RuOEP(CO)(EtOH) is dissolved in DMA, has bands at 5 4 8 nm ( e = 2 . 9 0 x 1 0 4 M"1 cm" 1), 5 1 7 nm ( e = 1 . 4 9 x 1 0 4 M" 1 cm" 1), 3 9 4 nm ( e = 2 . 1 6 x 1 0 5 M"1 cm_ 1)and a shoulder at 3 7 3 nm ( e = 3 . 8 5 x 1 0 4 M"1 cm"1) (Figure V . 6 ) . Of interest, when the solid RuOEP(CH 3CN) 2 is dissolved in DMA, a spectrum (trace #1 on Figure V . 7 ) different to that of RuOEP(DMA)2 is observed. The vis ib le bands of this species 'X' are much broader and the band at 5 2 1 nm is only 1 . 4 times more intense than the 4 9 8 nm band; the ratio of these band intensities in the bis(DMA) species is about 3 . The spectrum resembles the type of spectrum normally attributed to a f i ve -coordinate species (Chapter 3 ) . If this solution is photolyzed for ^ 2 min, the bis(DMA) species can be generated but this gradually collapses back to the species 'X' spectrum. The acetonitr i le must be playing a role, and, as in the pyridine system, a mixed snecies, in this case, RuOEP(CH-CN)(DMA), is strongly indicated. The poss ib i l i ty of Figure V.7. Spectral Changes for the Reaction of Species 'X' with 1 atm CO in DMA at 29°C. -55-53 Tr-bonded acetonitri le cannot be completely ruled out . When one atmosphere of CO is added to the RuOEP(DMA)2 species, formed in s i tu, there is an immediate spectral change to one that is identical to that of the RuOEP(CO)(DMA) species which is stable as such. When species 'X' is reacted with one atmosphere of CO, there is again an 'instantaneous' spectral change, but this is followed by a series of slower spectral changes that also y ie ld isosbestic points over a period of several hours (Figure V.7), the f inal spectrum resembling that of RuOEP(CO)(DMA). A plot of 1og(A t-Aoo) versus time, for the slower changes, based on the increase in intensity of the 548 nm band, gives a straight l ine (Figure V.8) of slope = 1.09 x 10" 4 sec" 1 at 29°C. When Ru0EP(CH-CN)o was dissolved 3 2 in toluene containing 0.21 M DMA, the same i n i t i a l broad spectrum of species 'X' was achieved and when one atmosphere of CO was added to the solution, the same sort of spectral changes, as those i l lustrated in Figure V.7, occurred. A f i r s t -order plot also gave a straight l ine of slope = 1.03 -4 -1 x 10 sec , which suggests that the measurable, slower part of the reaction is independent of the amount of DMA present. Further, when species 'X' in neat DMA was reacted with 3/4 atmosphere of CO, the rate decreased -5 -1 to 7.43 x 10 sec , indicating a f i rs t -order dependence on CO. As to what is actually occurring in solution is s t i l l unknown. There is a very fast reaction, followed by a much slower reaction. The data suggest that f i r s t one species is formed rapidly in solution and this slowly rearranges or reacts further with the CO, both reactant and product species having v is ib le and Soret bands in the same positions, The second, slower step could be the formation of a bis(carbonyl) species. There has been a repor t 5 4 of the formation of the bis(carbonyl) -56-0.9-"1.V 1.5-32 TIME (min) lb Figure V .8. First-Order Plot of the Reaction of Species 'X' with' l atm CO in DMA at 29UC. -57-complex of RuOEP in benzene. The complex precipitates out of solution when CO is bubbled through a benzene solution of RuOEP(CO)(EtOH). The trans carbonyls give rise to a V C Q = 1990 c m - 1 , higher than that of the mono-carbonyl. Attempts made to get a solution infrared spectrum of the product from the slow reaction were unsuccessful, since DMA absorbs very 55 strongly in this region. Work has been done recently within the Bioinorganic Group on the RuOEP(CO)2 complex. A v is ib le spectrum can only be obtained in a non-coordinating solvent, since one CO molecule is rapidly replaced in a coordinating solvent such as DMA, pyridine, etc. The v is ib le spectrum of the bis(carbonyl) species in toluene di f fers from the monocarbonyl (EtOH adduct) in toluene in that the 548 nm band sharpens and intensif ies s l ight ly and the 517 nm band develops hyperfine side bands at 508 nm and 513 nm. At room temperature, toluene solutions of the bis(carbonyl) species are not stable with respect to loss of CO and spectral studies must be carried out at sub-zero temperatures. Considering these facts, a second CO molecule adding on to 'RuOEP(CO)(DMA)1 at 29°C in DMA to give RuOEP(CO)2 seems highly unlikely. If species 'X' or RuOEP(DMA)2 is l e f t in DMA for long periods, the species wi l l abstract CO from the solvent. When RuOEP(DMA)2 is formed in situ and the solution is thoroughly degassed and le f t under argon, over a period of 24 hours there is a gradual increase in intensity of the band at 548 nm and a large decrease in intensity of the 521 nm and 498 nm bands; the changes appear consistent with formation of RuOEP(CO)(DMA). There have been other report s 5 6 of ruthenium complexes abstracting CO from DMA. DMF was also studied as a solvent system. The RuOEP(DMF)2 species formed is situ was found to have bands at 521 nm (E = 5.38 x 10 4 M - 1 cm - 1 ) , -58-493 nm ( e = 1.97 x 10 4 M"1 cm"1) and 391 nm ( E = 2.29 x 10 5 M"1 cm" 1). The RuOEP(CO)(DMF) species formed from the carbonyl-ethanol adduct dissolved in DMF has bands at 548 nm (E = 3.60 x 10 4 M"1 cm" 1), 517 nm (e = 2.44 x 104 M"1 cm" 1), 394 nm ( e = 2.96 x 10 5 M"1 cm"1) and a shoulder at 374 nm (E =6.00 x 10 4 M"1 cm" 1). Again, when Ru0EP(CH3CN)2 is dissolved in DMF, a species different to RuOEP(DMF)2 is attained and this reacts wtth one atmosphere of CO as seen in Figure V.9. The reaction is similar to that whtch occurred in DMA. There is rapid i n i t i a l spectral changes followed by a slow reaction which takes ^12 hours to go to completion -5 -1 o with a rate constant of 1.9x10 sec at 29 C. The corresponding study in THF gave very similar findings. The RuOEP(THF)2 species has bands at 521 nm (•£ = 6.84 X 10 4 M"1 cm" 1), 494 nm ( E = 2.03 x 10 4 M"1 cm" 1), 388 nm ( E = 2.55 x 10 5 M"1 cm - 1) and 296 nm ( E = 7.87 x 10 4 M"1 cm" 1). The RuOEP(CO)(THF) species has bands at 549 nm ( E = 4.10 x 10 4 M"1 cm" 1), 518 nm ( E = 2.60 x 10 4 M"1 cm" 1), 396 nm ( E = 4.98 x 10 5 M' 1 cm"1) and a broad band at <320 nm ( E = 3.89 x 10 4 M"1 cm" 1). When the RuOEP(CH3CN)2 was dissolved in the THF (the THF had to be d i s t i l l ed on the vacuum l ine , d irect ly into the c e l l , avoiding any contact with air) a broad spectrum was once again achieved. The addition of one atmosphere of CO yielded again a two-step reaction (Figure V.10). The slower reaction was complete in ^30 minutes with a rate constant of 6.45 x 10" 4 sec" 1 at 30°C. When the DMA, DMF and THF systems, the species 'X' present on dissolution of RuOEP(CH3CN)2 in any of these solvents could be converted into the RuOEP(solvent)2 species by less than 2 minutes of photolysis. Also, the RuOEP(solvent) ? species react very quickly (less than 2 minutes) -59-B O N V Q c J O S a v A B S O R B A N C E Figure V.9. Spectral Changes for the Reaction of Species 'X' wi 1 atm CO in DMF at 29°C. -60-33NV9eJ0S8V ABSORBANCE Figure V.10. Spectral Changes for the Reaction of Species 'X' with 1 atm CO in THF at 30°C. -61-with one atmosphere of CO to give the RuOEP(CO)(solvent) spectrum, while the corresponding species 'X' react quite di f ferent ly. One thing these solvents have in common is that they are susceptible 56-58 to metal-catalyzed decarbonylation .which may be more than a coincidence. It is unlikely that 'X' is a carbonyl, since the spectra are more typical of RuOEP(L)2 rather than RuOEP(CO)L. Species 'X' is most l i ke ly RuOEP(CH3CN)(solvent). As mentioned in Chapter 4, the bis(phosphine) ruthenium porphyrin complexes have been found to cata lyt ica l ly decarbonylate aldehydes, and this was in i t iated by exposure to CO with subsequent 46 very high turn-over numbers for the catalysis . It is feasible that the i n i t i a l exposure of RuOEP(CH3CN)(solvent) to CO could give rapid decarbonylation of the solvent to give an amine (at least in the cases of DMA and DMF). The product would l ike ly be, for the DMA system, RuOEP(CO)(N(CH3)3), and the spectrum after the rapid CO reaction is that of a carbonyl. The subsequent slow step could then be replacement of the amine by the solvent ligand. The suggested scheme is outlined below using DMA as the solvent system: CO RuOEP(CrLCN)9 + DMA<=2RuOEP(CH.CN) (DMA) >RuOEP(CO)'(N(CH-),) 1 * fast 6 slow slow CO RuOEP(DMA), >RuOEP(CO)(DMA) * fast Figure V . l l . Possible scheme to explain the observed spectral changes of RuOEP(CH3CN)2 with CO in DMA, DMF and THF. The spectrophotometric data could be consistent with such a scheme. The -62-minimal kinetic data indicate that the slow step is f i rst -order in CO, and this is d i f f i cu l t to rat ional ize, however, since the slow spectral changes look very much l ike the conversion of one monocarbonyl into another. More work needs to be done on these systems before this series of reactions can be fu l l y understood. V.2.3 The Reaction of RuOEP(CH,CN)o With CO in Pyrrole. 31 Since some of the original reversible oxygenation work was done in pyrrole, this was also tr ied as a solvent for the reaction with CO. As in the case of the DMA, DMF and THF systems, the species 'Y' obtained when RuOEPCCH^CN^ is dissolved in pyrrole is not the Ru0EP(pyrrole) 2 species. Ru0EP(pyrrole)2 has bands at 522 nm(E = 3.25 x 10 4 M"1 cm" 1), 495 nm ( e =1.61 x 10 4 M"1 cm - 1) and 395 nm ( E = 1.09 x 10 5 M"1 cm" 1). The carbonyl, RuOEP(CO)(pyrrole), has bands at 550 nm ( e = 2.05 x 10 4 M"1 cm" 1), 518 nm ( e = 1.36 x 10 4 M"1 cm" 1), 397 nm ( E = 2.23 x 10 5 M"1 cm" 1), a shoulder at 375 nm ( e = 4.01 x 10 4 M"1 cm"1) and a broad band at <310 nm ( e = 6.76 x 104 M"1 cm" 1). Species 'Y' has a less intense and broader Soret band than the bis(pyrrole) complex and a difference in peak height ratios in the vis ible region. When one atmosphere of CO was added to species *Y' there is now no sudden spectral change; gradual changes occur as a function of time and excellent isosbestic points are noted (Figure V.12). The reaction at 30°C appears to be ^70% complete in an hour but the solution had to be le f t overnight to get a f inal spectrum.and when less than one atmosphere is used, the reaction is less complete suggesting a reversible equilibrium. When a f i rst -order plot was done for the reaction with one atmosphere (Figure V.13), though, the log plot starts out in a l inear fashion, but -63-33NV8eJ0S8V i 1 1 ho p o o on~> ^ ABSORBANCE" Figure V.12. Spectral Changes for the Reaction of Species 'Y' with 1 atm CO in pyrrole at 30°C. -64-Figure V.13. First-Order Plot of the Reaction of Species 'Y' with 1 atm CO in pyrrole at 30°C. -65-about one % - l i f e , the plot curves away from l inear i ty . For a f i rst -order reaction, the log plot is normally l inear for at least 3 ha l f - l ives . Again the reaction does not seem to be a simple equilibrium as exemplified in equation 20, even though good isosbestic points were obtained throughout the reaction. K RuOEP(L)(L') + C0<—*Ru0EP)(C0)L(or !_') + L' (or L) (20) where L and L' can be pyrrole and/or acetonitr i le. The data could result from CO reacting with two different species present in solution at different rates (cf. eq. 20), one species reacting much more slowly and this could complicate the kinetics. Some sort of rearrangement could also be occurring but the spectrum of the reaction product is similar to RuOEP(CO)(pyrrole) so this is doubtful. Again, more work must be done to straighten out the problems of what are the species in solution. -66-CHAPTER 6  CONCLUSIONS In the case of RuOEP(CH 3CN) 2 in toluene, excess acetonitr i le was needed in order to stabi l ize the six-coordinate RuOEPCCH^CN^ species in solution. Under these conditions at 30°C, in a l l cases, the reaction with up to 1 atmosphere CO went to completion qiving RuOEP(CO)(CHgCN) via a dissociative mechanism: k l k2 R U O E P ( L ) 2 < - Z I I = . > R U O E P ( L ) < Z Z = ! R U O E P ( C O ) L (21) k - l k -2 With the L = P(n-Bu) 3 system in toluene, no excess phosphine was necessary to maintain the six-coordinate species which, under these conditions, reacted with CO to fu l l y form the carbonyl. However, in order to do kinetic studies on this system, excess phosphine was necessary to maintain pseudo-first-order kinetics. Under these conditions, the reaction of RuOEP(P(n-Bu)3)2 with 1 atm CO gave an equilibrium mixture with Ru0EP(C0)(P(n-Bu)3), the CO being easily displaced by the excess of,, phosphine ligand. Kinetic and thermodynamic parameters are presented for both systems ( L = CH^CN, P(n-Bu) 3), and the data compared within the systems and with those for some Fe(II)(porphyrin) systems. Based on the k ^/k 2 values for these M(porphyrin)L,> species, a hypothesis as to the structure of -67-the corresponding five-coordinate intermediate was made, which suggests, for the RuOEP(CH3CN) and RuOEP(P(n-Bu)3) intermediates, that the metal centres are more in the porphyrin plane than out of i t . The RuOEP(CH3CN)2 complex in toluene also binds both N 2 and CgH^, but the systems proved d i f f i cu l t to study, one factor being the extreme photosensitivity of the products, the coordinated gas molecules being photolabile. When RuOEP(CH3CN)2 was dissolved in coordinating solvents (py, DMA, DMF, THF and pyrrole), the anticipated RuOEP(solvent)2 species was formed only in pyridine. However, RuOEP(py)2 does not react with 1 atm CO in neat pyridine; on diluting the pyridine with toluene, a slow partial reaction occurs to give the monocarbonyl, RuOEP(CO)(py). On dissolution of solid RuOEP(CH3CN)2 in DMA, DMF or THF, the spectrum achieved is not that of the RuOEP(solvent)2 species, which can be formed in situ by the photolysis of RuOEP(CO)(EtOH) in the solvent; the much broader v is ib le spectrum is believed to be that of RuOEP(CH3CN)(solvent), species 'X'. This species -X' can be photolyzed to give RuOEP(solvent)2 which slowly reverts back thermally to species 'X'. Species "X1 reacts with CO to give an instantaneous spectral change, followed by slower changes, that suggest that RuOEP(CO)(solvent) is being formed. The sudder. spectral change is tentatively suggested to involve a decarbonylation of the solvent to give, for example with DMA, RuOEP(CO)(N(CH3)3); the subsequent slow reaction could be replacement of the amine by the solvent. In the case of dissolution of the bis(acetonitri le) complex in pyrrole, again the i n i t i a l spectrum is not that of the RuOEP(pyrrole)2 species. Reaction with CO gives a series of spectral changes to give what -68-appears to be RuOEP(CO)(pyrrole). However, a f i rst -order kinetic plot of this reaction is only l inear for about one h a l f - l i f e . Perhaps two species, RuOEP(CH3CN)(pyrrole) and RuOEPtpyrrole^, are present in solution and they react with CO at different rates. The presence of the acetonitr i le ligands ( i n i t i a l l y chosen to be an innocent ligand in strongly coordinating solvents) is having a pronounced effect on the chemistry of the RuOEP species. A major problem in studying these systems, is that most RuOEP(L)(L') complexes show vis ib le and Soret bands at wavelengths that are independent of L, thus making identif icat ion of the species in solution d i f f i c u l t . One worthwhile effort would be isolation of other RuOEPd^ species, for example, with L = DMA, DMF, THF and pyrrole. -69-REFERENCES 1. B. R. James, in 'The Porphyrins', D. 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