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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  by SANDRA GAIL WALKER B . S c , 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 © S a n d r a Gail Walker, 1980  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of B r i t i s h 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 B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date  \1  XH  /J?0  -iiABSTRACT Interaction of metalloporphyrins, p a r t i c u l a r l y 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 b i s ( a c e t o n i t r i l e ) complex RuOEP(CH CN) , 3  2  (OEP = the dianion of octaethylporphyrin) with or without excess a c e t o n i t r i l e present, are i r r e v e r s i b l y 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 a c e t o n i t r i l e concentration are consistent with a d i s s o c i a t i v e mechanism: k  l  k  2  RuOEP(L) <=> RuOEP(L)<=?RuOEP(L)(CO)  (I)  2  k  _l  k  _2  The k i n e t i c rate constants, k-j, k_  2  and k_^/k and the overall 2  equilibrium constant were determined at 30°C in toluene. The Ru0EP(P(n-Bu) ) 3  toward 0  2  2  complex, in toluene, i s completely unreactive  at 30°C over a period of several days; although again a  monocarbonyl i s formed under a CO atmosphere.  In the presence of excess  P(n-Bu) , under CO, an equilibrium mixture of RuOEP(P(n-Bu) ) 3  3  RuOEP(CO)(P(n-Bu) ) i s formed. 3  (II)  2  and  The equilibrium constant K for reaction  and the thermodynamic parameters AH (3.7 Kcal/mole) and AS (10.3 e.u.)  are determined along with the rate constants for the d i s s o c i a t i v e mechanism (cf. Equation I).  The low AH value implies comparable bond  K + CCW=l RuOEP(CO)(P(n-Bu) ) + P(n-Bu)  3  strengths between ruthenium and the two ligands P(n-Bu)  3  RuOEP(P(n-Bu) ) 3  (II)  >  2  3  and CO.  The k -|/l<2 values for the a c e t o n i t r i l e 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 systems.  iron  The major difference between the a c e t o n i t r i l e and phosphine . 5  systems is in the k  2  value which varies by 10 , p a r t i a l l y due to the  difference in i r - a c i d i t y of the two axial Toluene solutions of RuOEP(CH CN) 3  2  ligands. bind N  2  and C H 2  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 s i t u from the  b i s ( a c e t o n i t r i l e ) complex in pyridine, are completely unreactive toward CO.  Even toluene solutions with small amounts of pyridine react only  p a r t i a l l y (^15% in three days at 25°C) to give the monocarbonyl. Upon dissolving the RuOEP(CH CN) 3  2  complex in DMA, DMF and THF, the  species formed seem to be RuOEP(CH CN)(solvent). 3  These species react  with CO at 30°C in a two step r e a c t i o n , 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  -ivare possibly two species present when RuOEP(CH CN) 3  p y r r o l e , RuOEP(pyrrole) d i f f e r e n t rates.  2  2  is dissolved in  and RuOEP(CH CN)(pyrrole), which react at 3  -V-  TABLE OF CONTENTS  Page  ABSTRACT  ii  TABLE OF CONTENTS  v  LIST OF TABLES  vii  LIST OF FIGURES  '  viii  ABBREVIATIONS  xi  ACKNOWLEDGEMENTS CHAPTER I.  xiv  INTRODUCTION  1  1.1  General  1.2  Hemoglobin and Myoglobin  2  1.3  Iron Model Systems  5  1.4  Ruthenium Model Systems  7  CHAPTER II.  '.  1  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 CHAPTER III.  Complexes  ,  12  THE REACTION OF RuOEP(CH CN) 3  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  AND CO  2  27  IV.1  Spectral Characteristics  27  IV.2  Treatment of Data  30  IV. 3  Discussion  39  CHAPTER V.  THE REACTIONS OF RuOEP(CH CN) 3  2  WITH OTHER GASES IN  TOLUENE AND WITH CO IN OTHER SOLVENTS V. l  The Reaction of RuOEP(CH CN) 3  2  With N  2  42  and With C H 2  4  in  Toluene  V.2  42  V.l.l  The Reaction of RuOEP(CH CN)  2  and N  V.l.2  The Reaction of RuOEP(CH CN)  2  With C H  3  3  The Reaction of RuOEP(CH CN) 3  V.2.1  2  42  2  2  4  With CO in Other Solvents  The Reaction of RuOEP(CH CN) 3  2  49  With CO in  Pyridine (py) V.2.2  46  50  The Reaction of CO in N,N-Dimethylacetamide (DMA), N,N-Dimethylformamide (DMF) and Tetrahydrofuran (THF) With.RuOEP(CH CN) 3  V.2.3 CHAPTER VI.  52  2  The Reaction of RuOEP(CH CN)  CONCLUSIONS  3  2  With CO i n Pyrrole  62 66  -vi i -  LIST OF TABLES Table 111.1  Page Rate or reaction of RuOEP(CH CN) with CO in toluene at 3  2  various a c e t o n i t r i l e concentrations and CO pressures, at 30°C 111.2  21  Kinetic and equilibrium data for the reaction of RuOEP(CH CN) with CO at 30°C in toluene 3  111.3  Kinetic and equilibrium data for the reaction of RuOEP(pyrrole)  111.4  23  2  2  with 0  2  at 20°C in pyrrole  24  Kinetic and equilibrium data for the reaction of Fe(porphyrin)(piperidine)  2  complexes with CO in toluene at  23°C IV. 1  24  Equilibrium constant values from 21-41°C for the reaction of RuOEP(P(n-Bu) ) 3  IV.2  2  with one atmosphere CO, in toluene  Rate of reaction of RuOEP(P(n-Bu) ) 3  2  ..  with CO in toluene at  various ligand concentrations and CO pressures at 31°C IV.3  Rate of reaction of RuOEP(P(n-Bu) )(CO) with P(n-Bu) 3  3  ..  37  Kinetic data for the reaction of RuOEP(P(n-Bu) ).(CO) and 3  P(n-Bu) IV.5  36  in  toluene at 31 °C IV.4  31  3  in toluene at 31°C  37  Kinetic data for the reaction of RuOEP(P(n-Bu) ) 3  at 31 °C in toluene  2  and CO 39  -vi i i LIST OF FIGURES Figure 1.1  Page 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 c e l l  11  II. 2  Photolysis  14  III. 1  Typical spectral changes for the reaction of  cell  RuOEP(CH CN) with CO in toluene at 30°C 3  111.2  17  2  F i r s t - o r d e r plots for the reaction of RuOEP(CH CN) 3  CO in toluene with 1.91 x 10  with  2  M a c e t o n i t r i l e added at  30°C 111.3  19  Plot of k  _ 1 Q b s d  vs  [CH CN]/[C0] 3  for the reaction of  Ru0EP(CH CN) with CO in toluene with 1.91 x 1 0 " M 2  3  2  a c e t o n i t r i l e 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  with CO in toluene with no added P(n-Bu) IV.2  3  2  at 31°C  28  Spectral changes for the reaction of RuOEP(P(n-Bu) ) 3  with CO in toluene containing 2.84 x 10~ M P(n-Bu)  2  at  4  3  31°C IV.3  29  Equilibrium plots for the reaction of Ru0EP(P(n-Bu) ) 3  with 1 atm CO in toluene  2  32  -ixFigure IV.4  Page Van't Hoff plot for the reaction of RuOEP(P(n-Bu) ) 3  with  2  1 atm CO in toluene IV.5  33  F i r s t - o r d e r plot f o r the reaction of RuOEP(P(n-Bu) ) 3  with  2  1 atm CO in toluene containing 7.08 x 10~ M P(n-Bu)  at  4  3  31°C IV. 6  35  Plot of k  - 1 o b s d  vs  [C0]/lP(n-Bu) ] 3  . Ru0EP(P(n-Bu) )(C0) with P(n-Bu)  ..  38  in toluene containing 1.9 x 10~ M CH CN at 30°C  43  3  V. l  in toluene at 31°C  3  2  with  2  2  3  F i r s t - o r d e r plot for the reaction of RuOEP(CH CN) 3  1 atm N V.3  3  Spectral changes f o r the reaction of RuOEP(CH CN) 1 atm N  V.2  for the reaction of  2  in toluene containing 1.9 x 1 0 "  2  3  3  2  4  with  M CH CN at 30°C  Spectral changes for the reaction of RuOEP(CH CN) 3/4 atm of C H  2  in toluene containing 1.9 x 1 0 "  2  2  45  with  M CH CN 3  at 30°C  47  V.4  Possible structures for ethylene complex  48  V.5  Spectral changes for the reaction of Ru0EP(CH CN) 3  2  with  1 atm CO in toluene containing 0.15 M pyridine at 25°C V.6  Spectral changes for the photolysis of RuOEP(CO)(DMA) forming RuOEP(DMA)  2  V.7  in DMA  53  Spectral changes for the reaction of species 'X' with 1 atm CO in DMA at 29°C  V.8  51  54  F i r s t - o r d e r plot of the reaction of species 'X' with 1 atm CO in DMA at 29°C  56  \  -X-  Figure V.9  Page Spectral changes f o r the reaction of species 'X' with 1 atm CO in DMF at 29°C  V.10  59  Spectral changes for the reaction of species 'X' with 1 atm CO in THF at 30°C  V.ll  Possible scheme to explain the observed spectral changes of RuOEP(CH CN) 3  V.12  60  2  with CO in DMA, DMF and THF  Spectral changes for the reaction of species  61 'Y' with  1 atm CO in pyrrole at 30°C V.13  F i r s t - o r d e r plot of the reaction of species 1 atm CO in pyrrole at 30°C  63 'Y' with 64  -xi -  ABBREVIATIONS The following l i s t of abbreviations, most of which are commonly adopted in chemical research l i t e r a t u r e , w i l l be employed in this  atm  atmosphere  A  absorbance at any time, t  A  e  A  o  A  t  absorbance at the equilibrium position absorbance of the reactant absorbance at any time, t  A  oo C  2 4 H  CH  2  absorbance of the product ethylene methylene  CH CN  acetonitrile  °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  3  k  l  k  -l  k k  2  -2  kinetic rate constant kinetic rate constant k i n e t i c rate constant kinetic rate constant  thesis.  -xii-  overall rate constant for the forward reaction overall rate constant for the reverse reaction pseudo-first-order rate constant  obsd M  molarity  M-CO  metal-carbonyl  M(porphyrin)L  five-coordinate metal porphyrin complex  M(porphyrin)L  bond  six-coordinate metal porphyrin complex  2  M(porphyrin)L(CO)  carbonylated six-coordinate metal porphyrin complex  M(porphyrin)LL  mixed axial  1  mg  milligram  N  nitrogen  2  nm  ligand six-coordinate metal porphyrin complex  nanometre dioxygen  °2  octaethylporphyrin dianion  OEP  octamethyltetrabenzoporphyri n di an i on  P  0MB  phthalocyanine  Pc P(n-Bu)  n-butylphosphine  3  PpIX  protoporphyrin  py  pyridine  Ru (C0) 3  1  dianion  2  IX  ruthenium dodecacarbonyl  RuMb  rutheni um(11)-reconstituted myoglobin  + RuMb  rutheni um(111)-reconsti tuted myoglobi n  AS  entropy change f o r the reaction  s  spin state  sec  second  T  temperature  -XT  11-  t  time  TCNE  tetracyanoethylene  THF  tetrahydrofuran  TPP  tetraphenylporphyrin dianion  E  molar e x t i n c t i o n c o e f f i c i e n t  v  frequency (cm~^)  0  - x i vACKN0WLED6EMENTS I would l i k e to thank Dr. B. R. James f o r his supervision over the years and his assistance i n the w r i t i n g of t h i s t h e s 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, B r i a n , f o r his patience and understanding during the w r i t i n g of t h i s t h e s i s and my parents f o r the encouragement they have always given me during my academic endevours.  -1-  CHAPTER I INTRODUCTION 1.1  General The i n t e r a c t i o n of molecular dioxygen (O2) with metalloporphyrin  species has been of i n t e r e s t ever since such species were recognized as being the important centres in n a t u r a l l y occurring oxygen-storage -transport systems.  and  An iron porphyrin moiety, c a l l e d a heme u n i t , is the  p r o s t h e t i c group present in myoglobin and hemoglobin which are involved in oxygen-storage and oxygen-transportation, r e s p e c t i v e l y . are also components of various oxygenases and oxidases.  Heme units  Oxygenases  catalyze the incorporation of one or two atoms of dioxygen i n t o a substrate, while oxidases are enzymes that convert both atoms of dioxygen i n t o water or hydrogen peroxide^. These enzyme systems contain proteins which can be d i f f i c u l t to work w i t h , so s c i e n t i s t s have been searching f o r simpler, p r o t e i n - f r e e co-ordination compounds that can mimic the oxygen-carrying and - a c t i v a t i o n a b i l i t y of the natural species.  Simple metalloporphyrins seem obvious  candidates s i n c e , in n a t u r a l l y occurring systems, they are often found at the a c t i v e s i t e .  A study of metalloporphyrin-dioxygen complexes  should lead to an increased understanding of the structure and function of c e r t a i n b i o l o g i c a l systems employing dioxygen. extensively reviewed  This subject has been  1 -8 , sometimes in context with the more general coverage  -2/  of other (non-porphyrin) 1.2  x  synthetic oxygen c a r r i e r s  2-4  Hemoglobin and Myoglobin Hemoglobin and myoglobin combine r e v e r s i b l y with dioxygen and they bind  one dioxygen f o r 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 v e r t e b r a t e s , the porphyrin i s 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 t e t r a m e r i c , 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 c a l l e d 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 i s shown in Figure 1.2.  The protoheme p r o s t h e t i c group l i e s in a  crevice between E and F h e l i c e s of the polypeptide, held in place by nonbinding i n t e r a c t i o n s with the p r o t e i n .  The s i n g l e covalent attachment to  the protein occurs by coordination of the heme iron to the imidazole o  nitrogen of the ' p r o x i m a l ' h i s t i d i n e residue . In the deoxygenated s t a t e , the ferrous i r o n i s f i v e - c o o r d i n a t e with one vacant a x i a l p o s i t i o n .  In t h i s conformation, the iron i s in a high s p i n , 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 a x i a l ligand.  Upon oxygenation, the s i x t h coordination s i t e i s occupied by  dioxygen and the iron atom now i s found in a low s p i n , S=0, state and moves into the mean plane of the p o r p h y r i n ^ . The a f f i n i t y of a subunit in hemoglobin to add a s i n g l e molecule of dioxygen i s 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).  -5subunits in the tetramer.  This is known as the 'cooperativity e f f e c t '  and is of great biological  importance . 10  The 'Bohr effect* i s another  important interaction in hemoglobin and relates the change in a f f i n i t y of the heme s i t e 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 t r a n s i t i o n metals are known to bind  dioxygen; these include complexes of cobalt  12  , manganese  13 14 , titanium  15 and rhodium  }  but only iron and ruthenium species w i l l be discussed here.  At ambient temperatures, the Fe(porphyrin)l_2 (L = any ligand) complexes in a variety of solvents a r e , in most cases, i r r e v e r s i b l y oxidized by dioxygen, often quite rapidly to the f i n a l y-oxo F e ( l I I ) species ( F e ( I I I ) - O - F e ( I I I ) ) ^ .  This most l i k e l y 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 i n deoxymyoglobin, f o r example, a five-coordiante high spin species i s present. 20 Three recent synthetic approaches  based on supressing formation of  the y-oxo d i i r o n complex have led to the formation and detection of 1:1 iron:dioxygen adducts.  These methods are 1) use of s t e r i c a l l y hindered  porphyrins that prevent dimerization, 2) use of low temperatures thatslow down the dimerization process, and 3) the use of a r i g i d surface onto which the iron porphyrin complex can be attached to prevent dimerization. Two other features are desirable to simulate the deoxyheme centre: coordinate geometry and a non-polar hydrophobic environment.  a five-  -6-  Wang  21  f i r s t demonstrated that simple porphyrins could be reversibly 22  oxygenated when immobilized in s o l i d , polymer films.  Chang and Traylor  then extended this work using s o l i d films of ferrous porphyrins with appended axial ligands, and these systems revealed oxygenation reactions 23 with a 1:1 Fe:0 stoichiometry. There also were many reports describing r e v e r s i b l e , stoichiometric oxygenation of six-coordinate iron(II) porphyrins 24 in solution at low temperatures. Baldwin prepared a capped ferrous 2  porphyrin which reversibly oxygenated in solution at room temperature, as 25 did Collman's more well-known ' p i c k e t - f e n c e ' porphyrins  .  These picket-  fence porphyrins are synthesized to incorporate a s t e r i c 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 d i s s o c i a t i v e mechanism, equation (1): l 2 Fe(porphyrin)L < = F e ( p o r p h y r i n ) L < = = Fe(porphyrin)(L)(X) (1) k  k  >  >  2  k  -l  k  -2  (X= CO or 0 ) 2  The analysis of the kinetic and equilibrium data y i e l d s values of k-j, k_  2  and k_-|/k and these may be compared with data for myoglobin systems. 2  example, k_  2  For  is d i r e c t l y 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 w i l 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 p r i n c i p l e , a good chance  of detecting and i s o l a t i n g dioxygen complexes, hopefully under less demanding conditions (see above), since the chemistry of the second row t r a n s i t i o n metals is generally  'slowed down'.  31 It was found  that solutions of bis(acetonitrile)octaethylporphyrinato-  ruthenium(II), RuOEP(CH CN) , (Figure 1.3 shows the structure of OEP) in 3  2  N,N,-dimethylformamide or pyrrole could absorb 1.0 mole of dioxygen per ruthenium atom reversjbly at ambient conditions. carbon monoxide reversibly (cf. equation Interestingly,  The system s i m i l a r l y bound  (1)).  however, ruthenium(II)-reconstituted  horse heart  apomyoglobin (RuMb) treated with dioxygen in phosphate buffers at 0°C gave only i r r e v e r s i b l e 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 -oxidation proceeds via an 2  29 e f f i c i e n t outer sphere mechanism before loss of an axial ligand can occur  .  It was of i n t e r e s t , 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 itself.  -8-  Figure 1.3.  The structure of octaethylporphyrin.  -9-  CHAPTER II EXPERIMENTAL 11.1  Instrumentation U l t r a v 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 c e l l compartment.  Quartz  c e l l s of pathlength 1 cm were used. Infrared spectra were recorded on a Perkin Elmer 457 grating spectrophotometer.  S o l i d state spectra were obtained as Nujol mulls between  NaC£ p l a t e s . Nuclear magnetic resonance spectra were recorded on a Varian XL-100 spectrometer. Microanalyses were performed by Mr. P. Borda of t h i s department. 11.2  Spectrophotometric K i n e t i c Measurements Due to the extreme oxygen s e n s i t i v i t y of many of the ruthenium species  in s o l u t i o n , i t was necessary to perform spectrophotometric studies in a s t r i c t l y anaerobic system.  A l l o p t i c a 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 c a r r i e d out in the type of c e l l shown in Figure II.1.  The c e 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 c u l a t i n g thermostating bath, the temperature of which was adjusted appropriately. In a t y p i c a l experiment, the s o l i d ruthenium complex was placed in  -10the quartz part of the c e l l through A (Figure II.1) through B.  and the solvent was added  The solvent was degassed by repeatedly freezing i t in the f l a s k  of the c e l l , pumping o f f any uncondensed gas and then thawing the s o l v e n t , being careful not to wet the s o l i d during t h i s process. could then be added to the s o l i d sample.  The degassed solvent  The c e l l was then placed in the  thermostated compartment to allow the s o l u t i o n temperature to e q u i l i b r a t e . A f t e r 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 c e l l was shaken in order to ensure complete mixing of the gas in the s o l u t i o n .  The corresponding reaction was then monitored  u n t 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 i n s o l u t i o n and the p a r t i a l  pressure of the gas remained e s s e n t i a 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  P u r i f i e d argon, nitrogen and oxygen were supplied by Canadian L i q u i d A i r Limited.  The argon was f u r t h e r p u r i f e d by passing i t through a drying  tower containing fresh phosphorus pentoxide and molecular sieves type 5A).  (BDH,  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 t e c h 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 o f f . The frozen gas was then warmed to room temperature and t h i s freeze-pump-warm  -11-  A  B.  t<-4  Fitted w i t h a high v a c u u m teflon stopcock  Fitted with B - U c a p  To v a c u u m line  Quartz c e l l  Figure 1 1 . "I. Anaerobic Spectral  Cell.  -12process was repeated for several cycles until a l l  uncondensed materials were  removed. 11.3.2  Solvents  A l l solvents were freshly d i s t i l l e d prior to use and in a l l except toluene and a c e t o n i t r i l e , were d i s t i l l e d under vacuum. once p u r i f i e d , were handled under an argon atmosphere using  cases,  All  solvents,  Schlenk  33 techniques Toluene and tetrahydrofuran (Fisher S c i e n t i f i c Co., spectral grade) were dried over and d i s t i l l e d from sodium-benzophenone k e t y l , the toluene being d i s t i l l e d under nitrogen. Manufacturing  A c e t o n i t r i l e (Matheson, Coleman and Bell  Chemists, spectral grade) was dried over phosphorus  and d i s t i l l e d from calcium hydride under nitrogen.  pentoxide  N,N-Dimethylacetamide  (Fisher S c i e n t i f i c Co., analytical grade) and pyrrole (Aldrich Chemical Co. Limited, reagent grade) were dried over and d i s t i l l e d from calcium hydride. N,N-Dimethylformamide  (Fisher S c i e n t i f i c Co., analytical grade) was dried  over and d i s t i l l e d from anhydrous copper sulphate.  Pyridine  (American  Chemical and S c i e n t i f i c 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 was vacuum d i s t i l l e d .  (Aldrich Chemical Co. Limited, analytical  grade)  Tetracyanoethylene (Eastman Kodak Co.) was p u r i f i e d by  sublimation. II.4  Complexes Carbonyloctaethylporphyrinatoruthenium(II)-ethanol  (RuOEP(CO)(EtOH)) OA  was prepared by a method similar to that of Tsutsui et al octaethylporphyrin, provided by J . B. Paine III,  .  and 500 mg of  500 mg of Ru^C0  19  -13(Strem Chemical Inc.) N , for 24 hours.  were refluxed in 100 ml of degassed toluene, under  The toluene was removed and the s o l i d dissolved in 25 ml  2  of methylene chloride and 25 ml of absolute ethanol. refluxed under N  2  This solution was  for t h i r t y minutes before the solvent was removed and the  s o l i d was p u r i f i e d by chromatography.  A deactivated alumina  (Fisher  S c i e n t i f i c 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 r e c r y s t a l l i z e d from methylene  chloride/ethanol, washed with pentane and dried Analysis:  (64% y i e l d ) ; v .Q=1930 cm~1 r  Calculated for C H N 0 R u : C, 66.19%; H, 7.07%; N, 7.92%. 3g  5  4  2  Found: C, 66.11%; H, 7.15%; N, 7.92%. Nuclear Magnetic Resonance data in CDC£ : 0EP; CH , 1.98 t r i p l e t ; 3  CH , 4.09 quartet; p y r r o l e , 9.98 s i n g l e t ; 2  3  Ethanol; CH , -1.06 t r i p l e t ; 2  CH , -0.07 quartet. 3  Bis(acetonitrile)octaethylporphyrinatoruthenium(II)  (Ru0EP(CH CN) ) 3  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 a c e t o n i t r i l e and toluene under argon in a photolysis II.2).  cell  (Figure  Argon was bubbled through the s t i r r i n g 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 l i n e and the s o l i d was washed -1 31 with cold pentane and dried Analysis:  (72% y i e l d ) j  VQ-^=2260 cm"  .  %  Calculated for C H N R u : C, 67.13%; H, 6.99%; N, 11.75%. 40  5Q  6  Found: C, 67.41%; H, 6.96%; N, 11.25%. Nuclear Magnetic Resonance data in CDC£ : 0EP; CH , 1.90 t r i p l e t ; 3  3  CH , 4.00 quartet; pyrrole, 9.90 s i n g l e t ; A c e t o n i t r i l e ; CrL, 0.64 2  singlet.  -14-  Water inlet Water outlet  A r g o n outlet  A r g o n inlet  C a v i t y for Lamp  S o l u t i o n outlet  Figure II.2.  Photolysis C e l l .  -15Bi s(tri(n-butyl)phosphi ne)octaethyloornhyri natorutheni um(11) (RuOEP(P(n-Bu) ) ) was generously provided by Dr. George Domazetis. 3  2  Dilute solutions of RuOEPCL)^ SDecies situ. cell  Solutions of 1 0 "  5  (L = solvent) can be made in  M RuOEP(CO)(EtOH) are made up in the spectral  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(CH CN) 3  III.l  AND CO  2  Spectral Characteristics Toluene was chosen as a solvent to study the reactions of 0 and CO 2  with the RuOEP(CH CN) 3  2  complex.  However, when the i n i t i a l spectrum of the  b i s a c e t o n i t r i l e complex was recorded, under argon in d i l u t e solution (^10~^ M), the v i s i b l e bands were very broad and not t y p i c a l of s i x coordinate, low spin Ru(II)  .  Since a c e t o n i t r i l e , as an axial l i g a n d , may  be quite l a b i l e , and not strongly coordinated, a c e t o n i t r i l e was added to the toluene solution in order to generate and s t a b i l i z e the six-coordinate species in solution and achieve the corresponding spectrum. Toluene solutions of RuOEP(CH CN) 3  2  under an atmosphere of 0  2  slowly  undergo i r r e v e r s i b l e oxidation; the product i s l i k e l y a y-oxo Ru(III) dimer as i s usually observed with the corresponding six-coordinate p r o t e i n free iron porphyrin systems, The RuOEP(CH CN) 3  2  species under an atmosphere of CO underwent a  series of spectral changes to give a f i n a l spctrum i d e n t i c a l to that of Ru0EP(C0)(CH CN) (made by dissolving ^5 x 1 0 " M RuOEP(CQ)(EtOH) 5  3  10  M solution of a c e t o n i t r i l e in toluene).  the RuOEP(CH CN) 3  2  Figure III.l  in a  Measurements of CO uptake by  species showed that 1.0 mole of CO/Ru atom was absorbed shows typical spectral changes, as a function of time,  for the addition of a known amount of CO to RuOEP(CHoCN) ; a number of 9  Figure I I I . l .  Typical Spectral Changes for the Reaction of RuOEP(CH CN)  with CO in Toluene at 30°C.  3  -18isosbestic points are generated. nm (  = 1.70 x 10 M" c m ) and 496 nm ( 4  e  In the v i s i b l e region, the bands at 527  1  to positions at 549 nm (  = 1.05 x 10  -1  4  M" cm" ) red s h i f t 1  1  1  M"  1  cm" ).  M"  1  cm" ) and smaller side bands at 394 nm (e = 8.46 x 10  1  1  = 2.29 x 10 M" cm" ) and 518 nm ( 4  e  e  e  =1.31  x 10  The Soret region with an intense band at 405 nm ( e = 2.20 x 1 0  1  4  M" cm" ) and 1  1  385 nm (e = 6.93 x 10 M" cm" ) changed to a major band at 395 nm (e = 4  1.76 x 10  5  1  1  M" cm" ) with a small shoulder at 375 nm. 1  For a fixed CO  1  pressure, the length of time required for each reaction increased with increasing added concentration of a c e t o n i t r i l e i n the solution. III.2  Treatment of Data The k i n e t i c data were obtained by following the increase i n spectral  i n t e n s i t y of the 549 nm band of the carbonyl.  Plots of log(A - A ) versus ro  t  time gave good straight l i n e s , Figure III.2; A^ i s the absorbance of the RuOEP(CO)(CH CN) species 3  and A.J. i s 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 i s much larger than that  of the porphyrin(see below).  An inverse dependence on a c e t o n i t r i l e  concentration at a fixed CO pressure and a less than f i r s t - o r d e r dependence on CO at a fixed a c e t o n i t r i l e  concentration are readily interpreted in  terms of a d i s s o c i a t i v e mechanism(Eq. 1, Ch. 1):  l 2 RuOEP(CH CN) ^ZZ=l RuOEP(CH CN) < ' k  k  >  3  2  3  k  -l  k  >RuQEP (C0)(Ch* CN) 3  -2  Since the reaction i s judged, by the spectral changes, to go to completion, k_ i s assumed to be n e g l i g i b l e . 2  Assuming a steady state  (2)  4  5  -19-  TIME  Figure III.2.  (min)  First-Order Plots for the Reaction of RuOEP(CH CN)  CO in Toluene With 1.91 x 1 0 "  3  2  M A c e t o n i t r i l e added at 30°C.  2  With  -20-  concentration of five-coordinate intermediate leads to the rate law: rate = ^ ^ [ C O ] [RuOEP(CH CN) ] 3  2  (  3  )  k_ 1CH CN] + k [C0] 1  3  2  For any one experiment i n which the CO and a c e t o n i t r i l e concentrations remain e f f e c t i v e l y constant, this may be rewritten as: rate = k where k obsd  k  1  log(A  ro  Qbsd  [RuOEP(CH CN) ] 3  = k k lC0]/(k_  Q b s d  S  t  '  i  2  1  P  e  s e u  2  1  [CH3CNJ + k [C0.])  (4)  2  d o - f i r s t - o r d e r rate constant measured in the plots of  - A^.) versus time.  The data are given in Table I I I . l .  In agreement with equation (4), at  high a c e t o n i t r i l e concentrations, the dependence on CO pressure approaches f i r s t - o r d e r but becomes less than f i r s t - o r d e r and approaches zero order as the a c e t o n i t r i l e concentration decreases.  The a c e t o n i t r i l e dependence  remains inverse over the small pressure range of CO studied.  There were no  complications i n the system due to the presence of displaced a c e t o n i t r i l e in the forward reaction since added a c e t o n i t r i l e was at least i n a hundredfold excess. The inverse of expression ( 4 ) gives: k  obsd  _ 1  =  k  l  _  1 +  k_i[CH CN]/(k k [C03) 3  1  (5)  2  The CO pressure can be converted to molarity using the known s o l u b i l i t y of CO i n toluene at 30°C (6.5 x 1 0 " M a t m " ) 3  [CH CN]/[C0] 3  k_ /k k 1  1  f o r a l l data in Table III.l  3 7  A plot of k  gives a straight  and an intercept of k-," (e.g. Figure III.3). 1  2  1  _ 1 o b s d  vs  l i n e of slope  The value of k_ was 2  estimated by placing the s o l i d RuOEP(CO)(EtOH) adduct into a large excess of a c e t o n i t r i l e in toluene solution and following spectral changes f o r the CO displacement by a c e t o n i t r i l e .  The overall equilibrium constant K  -21-  T  a  b  l  e  ni.l.  Rate of Reaction of RuOEP(CH CNj 3  ?  With CO in Toluene at  Various A c e t o n i t r i l e Concentrations and CO Pressures, at 30°C  CO Pressure  3  [CH3CN]  k  Q b s d  x 10  (atm)  (moles/litre)  (sec )  0.963  0.375  1.95  0.963 0.713 0.463 0.213  0.190 0.190 0.190 0.190  3.70 2.77 1.97 1.18  4 b  - 1  0.971 0.721 0.501 0.221  9.52 9.52 9.52 9.52  x x x x  10" , 10", 10", 10"*  6.47 4.37 3.08 2.12  0.971 0.721 0.471 0.241  5.72 5.72 5.72 5.72  x x x x  10"?, 10, 10", 10"*  9.33 6.97 5.63 3.48  0.971 0.721 0.471 0.221  3.82 3.82 3.82 3.82  x x x x  10" 10", 10", 10"*  10.53 9.12 7.47 4.35  0.971 0.721 0.471 0.221  1.91 1.91 1.91 1.91  x x x x  10" 10", 10"* 10"*  15.72 14.58 11.57 7.00  0.971 0.721 0.471 0.221  3.83 3.83 3.83 3.83  x x x x  10" 10'^ 10"^ 10^  23.98 21.92 20.03 16.67  2  2  2  3  Pressures were corrected for the p a r t i a l pressure of toluene at 30°C; R. C. Weast, Ed., 'Handbook of Chemistry and P h y s i c s ' , 56 standard ed The Chemical Rubber Company Co., Cleveland, Ohio, 1975, p D198. b. estimated error ±5%.  Figure III.3. RuOEP(CrLCN)  9  Plot of k  o b s d  "'  vs  [CH CN]/[-C0] For The Reaction of 3  With CO in Toluene With 1.91 x 1 0 "  2  M A c e t o n i t r i l e Added at 30°C.  -23(k-|k /k -jk ) can then be readily estimated (see below). 2  2  Table III.2.  Kinetic and Equilibrium Data f o r the Reaction of RuOEP(CH CN) 3  With CO at 30°C in Toluene.  k  k_ /k  a  1  1 (sec" )  k_  b  K  2  2  1  (sec ) - 1  1  2.41 x 1 0 "  a. estimated error ±25%. III.3  3.4 x 1 0  .176  3  4.0 x TO  - 7  4  b. estimated error ±10%.  Discussion From the data, the six-coordinate b i s ( a c e t o n i t r i l e ) complex i s seen  to lose an a c e t o n i t r i l e ligand about 10 times faster than the mixed ligand 4  species gives up a CO molecule and this i s the major factor governing the equilibrium constant.  The k_-|/k value.shows that the five-coordinate 2  intermediate prefers to bind CO over a c e t o n i t r i l e k i n e t i c a l l y by a factor of about f i v e . Some rough calculations based on unpublished data from these l a b o r a t o r i e s ^ , were d o n e 3  RuOEP(pyrrole)  39  (Table III.3) f o r oxygen binding of  in pyrrole, which i s a solvent in which oxygenation occurs  2  without appreciable oxidation.  The values f o r k.j and k_-j/k are comparable 2  to the CO reaction in toluene but there i s a difference of about a hundred i n k_ and the values suggest that the strong binding of CO 2  (compared to 0 ) i s reflected i n i t s much lower o f f - r a t e .  Attempts to  2  measure the kinetics of the CO reaction with RuOEP(CH CN) 3  for a more d i r e c t comparison with the 0 Chapter 5).  2  2  i n pyrrole  system were unsuccessful (see  2  -24-  Table III.3.  Kinetic and Equilibrium Data f o r the Reaction of RuOEP(pyrrole) With 0 at 20°C i n Pyrrole. ?  k_ /k 1  K  2  (sec" )  (sec )  1  - 1  %0.003  It  ^0.06  ^10  'x/ICf  5  i s also of interest to compare the Ru0EP(CH CN) /C0 3  2  those f o r the CO binding to some Fe(porphyrin)(amine) (Table III.4).  2  4  data with  systems  In terms of porphyrin properties, OEP i s considered much  closer to protoporphyrin IX (PpIX) than octamethyltetrabenzoporphyrin (OMBP) or tetraphenylporphyrin (TPP) or phthalocyanine  (Pc).  30 Table III.4.  Kinetic and Equilibrium Data  f o r the Reaction of  Fe(porphyrin)(piperidine)o Complexes With CO i n Toluene at 23°C.  Porphyrin  k_ /k ]  (sec )  1020  0.25  1.7  2340  490  0.09  26  209  a  - 1  a  a  a  PpIX  20  0.06  0.002  230000  TPP  11  0.52  0.002  150000  0.5  0.13  3.3  0.85  Pc a.  K  (sec ) - 1  OMBP  2  Fe(0MBP)(py)  2  -25The k_-|/l<2 value f o r RuOEP(CH CN) 3  2  i n toluene l i e s within the range  of data f o r the iron systems and i s some 100 times the value f o r the PpIX system.  The k-j and k_ values are quite d i f f e r e n t f o r the ruthenium and 2  iron systems.  The k-j value f o r the FePpIX system i s some 10 times that 5  of the ruthenium complex and 10 times the k  2  value.  As expected, k i n e t i c  l a b i l i t y i s slowed down considerably when using the second row elements. The k_ value f o r Ru0EP(CH CN) /C0 2  3  2  can also be compared to the o 39  decarbonylation rate of COMb in aqueous solution at pH 7, 20 C %0.02 s e c ) . - 1  (k  2  Although the k_ value f o r COMb i s similar to the k_ 2  2  values of the iron protein-free systems, once again the ruthenium complex binds CO much tighter k i n e t i c a l l y than the naturally occurring heme group does Based on the findings i n the iron systems  (Table III.4), a hypothesis  40 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 f o r the five-coordinate intermediate are shown in Figure III.4.  N N 1  2  0/  Figure III.4  Possible Structures of the Five-Coordinate Intermediate.  When considering s t e r i c i n t e r a c t i o n s , the addition of a bulky ligand to a high spin intermediate, ^ , w i l l be less favourable than the corresponding  -26addition to the low spin species, £ , e s p e c i a l l y r e l a t i v e to the rate of addition of a non-bulky ligand such as CO. If the assumption is made that the intermediate l i e s close to the 41 t r a n s i t i o n 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 i t e 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/k value of 0.176 for the ruthenium system might imply a 2  structure more analagous to £ than ^ for the RuOEP(CH CN) intermediate, 3  but c l e a r l y much more data are needed for other ruthenium systems (especially with Ru(porphyrin)(amine) can be drawn.  2  species) before such a conclusion  An axial pi peri dine ligand in an iron porphyrin system 42  does give r i s e to s t e r i c interaction due to the 2,6-CH  2  groups  and thus  could well give r i s e to movement of the iron atom out of the plane in the five-coordinate intermediate.  The k_-j/k  2  value for the FePpIX(py) /C0 2  system with no such s t e r i c problem is l i k e l y to be greater than the 0.002 value for the piperidine system. (Table III.4), the k_^/k  2  Using the OMBP data as a guide,  value could be increased to ^0.02, a factor of  about ten smaller than the ruthenium system:  the data again t e n t a t i v e l y  suggest a more in-plane structure for the ruthenium intermediate.  -27-  CHAPTER 4 THE REACTION OF RuOEP(P(n-Bu) ) AND CO 3  IV.1  3  Spectral Characteristics Toluene was again used as the solvent f o r t h i s system.  However, i t  was not necessary to add an excess of phosphine ligand to the solvent in order to generate the correct spectrum f o r the six-coordinate bis(phosphine) system.  This contrasts with the b i s ( a c e t o n i t r i l e ) system in toluene  (Chapter 3). When one atmosphere of 0  2  was added to the bis(phosphine)  30°C, no appreciable reaction occurred within 24 hours.  system at  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 carbonylphosphine 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 c h a r a c t e r i s t i c of the reaction.  The product, RuOEP(P(n-Bu) )(CO), was never isolated so 3  i t s extinction c o e f f i c i e n t s 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) )2 w i t h ! atm  CO in Toluene with no added P(n-Bu), at 31°C-  3  -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. CO in Toluene  Spectral Changes for the Reaction of RuOEP(P(n-Bu) ) 3  Containing 2.84 x 1 0 "  4  M P(n-Bu), at 31°C.  2  w i t h l atm  -30In the i n i t i a l spectrum of RuOEP(P(n-Bu) ) , there are bands at 3  535 nm (  = 1.95 x 10  e  «\460 nm (  e  M"  4  = 0.51 x 10  M'  4  c m " ) , 511 nm (  1  1  1  e  2  = 2.72 x 10  M"  4  c m " ) , 428 nm ( E = 3.20 x 10 1  M"  5  417 nm (  = 7.98 x 10  4  M"  1  e  c m " ) , 405 nm (e = 4.94 x 10  360 nm (  = 7.72 x 10  4  M"  1  e  cm" ) and <341 nm (e = 5.06 x 10  1  4  M"  1  cm" ),  1  1  1  cm" ), 1  cm" ),  1  1  M"  4  1  cm" ). 1  The f i n a l spectrum of RuOEP(P(n-Bu) )(CO) has bands at 555 nm (e = 1.70 3  x 10 M"  1  M"  1  4  M"  1  c m " ) , 528 nm(  = 2.39 x 10  1  c m " ) , 388 nm (  e  = 6.74 x 10 M"  1  4  e  cm" ) and ^,325 nm ( 1  e  1  = 7.62 x 10  4  4  M'  c m " ) , 409 nm (  1  1  c m " ) , 358 nm ( 1  M"  1  e  e  = 3.49 x 10  = 5.84 x 10  5  4  cm" ). At any p a r t i c u l a r 1  equilibrium p o s i t i o n , there were bands of both the starting and f i n a l 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 i s consistent with the equilibrium:  RuOEP(P(n-Bu) ) 3  2  K + C0<=> RuOEP(P(n-Bu) )(CO) + P(n-Bu) 3  (6)  3  [RuOEP(P(n-Bu) )(CO)][P(n-Bu) ] 3  K  =  3  [RuOEP(P(n-Bu) ) ][CO] 3  (  7  )  2  Using spectral data to find the various concentrations of i n i t i a l and f i n a l species, one can rewrite the equilibrium expression as:  log K = log A - A Q  " A T A ~  oo  - log[C0]  +  log[P(n-Bu) l 3  (8)  -31A  Q  is the absorbance of the R u O E P ^ n - B u ) . ^  soecies  i s the absorbance of the RuOEP(P(n-Bu) )(CO) species estimated by 3  extinction c o e f f i c i e n t data A is the absorbance at the equilibrium p o s i t i o n . 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 A -A  vs  Q  A^A~ CO  log[P(n-Bu) ] at a fixed pressure (Figure IV.3). 3  l i n e plots of slope -1.0 ± .1 were obtained. Table IV.1.  straight  The K values are l i s t e d in  A plot of ln(K) vs 1/T (Figure IV.4)  from which the thermodynamic parameters, AH AS  In a l l cases,  gave a straight  line  = 3.7 ± 0.5 Kcal/mole and  = 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) Ka a.  "21 0,425  26  31  36  0,506  0.536  0.589  41 0.650  estimated error ± 10%.  As well as calculating a value for K and i t s 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 d i s s o c i a t i v e machanism is once more assumed to be occurring, i . e .  -32-  Figure IV.3.  Equilibrium Plots for the Reaction of RuOEP(P(n-Bu) )2 with  1 atm CO in Toluene.  3  -33-  Fiqure IV.4.  Van't Hoff Plot f o r the Reaction of RuOEP(P(n-Bu) )  1 atm CO in Toluene.  3  2  with  -34l RuOEP(P(n-Bu) ) <== k  3  k  2  k  2  RuOEP(P(n-Bu) ) <  >  :> RuOEP(P(n-Bu) )(CO)  3  -l  k  -2  but since an equilibrium is obtained in a l l cases, k assumed n e g l i g i b l e .  (9)  3  cannot be  2  Therefore, when the rate law is derived, the  expression becomes: rate = l 2 f k  k  C 0  J [RuOEP(P(n-Bu) ) ] 3  k_-, {P(n-Bu) ] + k [C0] 3  k_-,k_ [P(n-Bu) ] lRuOEP(P(n-Bu) (CO)]  2  2  "  2  3  (10)  3  k_-,[ P(n-Bu) ] + k [C0] 3  2  which can be rewritten: rate = k [RuOEP(P(n-Bu) ) ] f  3  2  - k [RuOEP(P(n-Bu) )(CO)] r  (11)  3  k^r is the overall rate constant for the forward reaction and k  is the overall rate constant for the reverse reaction.  r  This expression can now be i n t e g r a t e d (k  A  + k ) t = In A - A  f  r  Q  43  to give: (12)  e  is the absorbance at the equilibrium position  g  and A is the absorbance at any time, t . This then gives the expression: ^k k [C0] 1  + k_ k_ [P(n-Bu) ] ^ t  2  1  k_ [P(n-Bu) ] 1  2  + k [C0]  3  Q  k k [C0] 1  s l  k  °P  e  obsd  2  1  S  t  ^  1 e  + k ^ 3  P  s e u  A-A  e  (  1  3  e  versus time (Figure IV.5) yielded straight l i n e s of  k_ lP(n-Bu) j"  =  1  e  Q  j  2  Plots of In A - A  In A - A  3  +  2  lP(n-Bu) ] 3  "k [C0] 2  =  k  obsd  d o - f i r s t - o r d e r rate constant for the reaction.  Table IV.2 gives the k i n e t i c data,  (  1  4  )  )  -35-  Figure IV.5.  First-Order Plot for the Reaction of RuOEP(P(n-Bu) )  1 atm CO in toluene containing 7.08 x 1 0 "  3  4  M P(n-Bu), at 31°C.  2  with  -36Table 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  (atm)  P(n-Bu)  k  3  (moles/litre)  0.971 0.721 0.471 0.221  1.057 1.057 1.057 1.057  0.971 0.721 0.471 0.221  7.083 7.083 7.083 7.083  Q b s d  x 10  k  3 b  (sec )  d  x 10  -1  3  (calc)  (sec ) -1  X  10"? 10", 10"^ 10""  6.67 7.77 7.95 11 .0  6.08 6.98 7.41 10.45  X  1 0  1 ioi  5.67 5.84 6.11 8.75  5.69 5.96 6.59 8.66  X X X  X X X  3  10"  4  c  a. and b. see Table I I I . 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 y i e l d s the k i n e t i c rate constants.  Therefore, alternative  procedures were used. Since, in the ease of RuOEP(P(n-Bu) )2 and 1 or h atmosphere of CO 3  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  Chap 3).  This i s thus a direct measure of k-| (k-| = 2.11 x 10"  -1 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) ) (Table IV.3). Under these conditions (k-j being n e g l i g i b l e ) , the rate of the reaction is 3  rate = k_-,k_ [P(n-Bu) ] [RuOEP(P(n-Bu) ) (CO)] 2  k [C0J + k_-, 2  3  3  [P(n-Bu) ] 3  which can be rearranged to give:  2  (  1  5  )  -37-  •Wi"  1  =  k  -2  _ 1  +  k [C0)/k_ k_ [P(n-Bu) ] 2  k  Therefore, a plot of l i n e of slope  2  _ 1  vs  o b s d  k /k_-|k_ 2  1  2  (16)  3  [CO]/[Ptn-Bu)^  and an intercept of  should give a straight  k_  _1  (Figure IV.6 and Table  2  IV.4).  Table IV.3.  Rate of Reaction of RuOEP(P(n-Bu) )(CO) With P(n-Bu), in 3  Toluene at 31°C.  CO Pressure  P(n-Bu)  3  x 10  3  2  obsd><  ™  k  (atm)  (moles/1itre)  (sec )  0.971 0.971 0.971 0.971  5.02 5.73 7.15 8.57  1.79 1.92 2.21 2.47  2  b  -1  a. and b. see Table I I I . l .  Table IV.4.  Kinetic Data For the Reaction of RuOEP(P(n-Bu) )(CO) and 3  P(n-Bu)  3  in Toluene at 31°C.  (sec ) -1  0.061  5.35 x 1 0 "  2  a. estimated error ± 10%. b. estimated error ± 25%.  Taking the rate constants l i s t e d in Table IV.4 and substituting them back into the expression for  k  obsc  |  (14) f o r the overall r e a c t i o n , rates  can be calculated for the conditions l i s t e d in Table IV.2  (see t a b l e ) .  -39-  The complete set of k i n e t i c parameters is l i s t e d in Table IV.5. calculated by K = k k / k _ k _ 1  2  1  2  K was  and is within 15% of the d i r e c t l y  measured K at 31°C.  Table IV.5.  Kinetic Data for the Reaction of RuOEP(P(n-Bu) ) 3  and  2  CO at 31°C in Toluene.  k_ /k 1  K  2  ^ 1 (sec )  (sec" )  -1  1  2.11 x 1 0 "  IV.3  0.061  3  5.35 x 1 0 "  0.647  2  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 d i f f e r e n t from the previous b i s ( a c e t o n i t r i l e ) system (see Chap 3).  The k_^/k  2  value shows that the  five-coordinate intermediate prefers to bind CO over P(n-Bu) factor of 16, however, the Ru-CO and Ru-P(n-Bu)  3  3  by a  bond strengths are s i m i l a r  ( A H value). These data can also be compared to the data of Table 111.3. the oxygenation of Ru0EP(pyrrole) are quite similar but the k_  2  2  in pyrrole.  The k  ]  and k_ /k  value is very d i f f e r e n t .  1  2  values  The o f f - r a t e f o r  CO seems to be 1000 times that f o r oxygen, again quite d i f f e r e n t to the b i s ( a c e t o n i t r i l e ) 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_^/k values, here too, are very s i m i l a r , k 2  2  is  -40very d i f f e r e n t , resulting in a rather dramatic variation in the value of K.  The two k_i/l<2 values d i f f e r by a factor of only three which implies  that the structure of the five-coordinate RuOEP(P(n-Bu) ) and RuOEP(CH CN) 3  are quite similar(see Chap 3).  3  Further work on the RuOEPI_2 systems and othe  Ru(porphyrin)l_2 systems i s necessary to get a clearer picture of the nature 44 of the five-coordinate species.  At t h i s time, work  study of RuTPP(CH CN) , RuTPP(phosphine) 3  2  2  has started on the  and other RuOEP(phosphine)  2  systems. The two k_2 values in the systems studied here vary by ^10^, a very dramatic d i f f e r e n c e .  The phosphine trans to the-CO molecule seems to l a b i l i  the CO molecule much more readily than an a c e t o n i t r i l e molecule can. Since CH CN is not such a good ir-acid as P(n-Bu) ^, the CO i s l i k e l y to 4  3  3  accept more of the ir-electron density from the metal centre in the a c e t o n i t r i l e 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 w i l l be competition for the iT-electron  density between the P(n-Bu)  3  and CO and thus the M-CO bond i s not as strong  as in the previous case (solution infrared spectrum taken in hexane, ^10" M V  C0  =  c m ) and the CO i s now much more e a s i l y l o s t . -1  correlation between CO l a b i l i t y and v  co  Such a  seems reasonable f o r two such 30  c l o s e l y 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 i n i t i a t e d in the area of c a t a l y s i s  in  which this system and RuTPP(phosphine)2 species are used to c a t a l y t i c a l l y decarbonylate aldehydes.  The main thrust of the work, so f a r , has been  in the use of RuTPP(P(Ph) ) 3  ?  in a c e t o n i t r i l e .  A CO atmosphere seems to be  -41necessary to i n i t i a t e the decarboxylation reaction. has been decarbonylated with turnover  Phenylacetaldehyde  lumbers of 10 /hour at 20°C. 3  However, the actual mechanism of the reaction is far from completely understood. These ruthenium(porphyrin)(phosphine) successful  systems seem to be quite  in this area due to the l a b 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 w i l l probably develop out of  these systems in the f i e l d s of catalysis  and bioinorganic  chemistry.  -42-  CHAPTER 5 THE REACTIONS OF RuOEP(CH CN)o WITH OTHER GASES IN TOLUENE 3  AND WITH CO IN OTHER SOLVENTS V.l  The Reaction of RuOEP(CH CN) 3  2  With N  Since the reaction of RuOEP(CH CN) 3  2  and With C Q H ^ in Toluene  2  in toluene with CO had been  studied, reactions with other gaseous ligands were of i n t e r e s t . and W h i t t e n  Hopf  had ' a c t i v a t e d ' a ruthenium(II) mesoporphyrin IX system by  47  using surfactant complexes in monolayer assemblies; the system reacted with C0,0  2  and N  Although 0  2>  2  was known to oxidize the RuOEP(CH CN) 3  in toluene, i t seemed worthwhile investigating C H , i s o e l e c t r o n i c with 0 . 2  4  Its  2  V.1.1  3  Toluene solutions of 1 0 "  5  and N  2  2  was also tested.  2  M RuOEP(CH CN) 3  added were reacted with one atmosphere of N ' s u c c e s s f u l ' run (see below).  system  i t s r e a c t i v i t y towards  r e a c t i v i t y toward N  The Reaction of RuOEP(CH CN)  2  2  2  with 1.9 x 1 0 "  2  M CH CN 3  at 30°C; Figure V.l shows a  The i n i t i a l spectrum was that of  with extinction c o e f f i c i e n t s stated in Chapter 3.  As N  2  RuOEP(CH CN) 3  reacted, the v i s i b l e  bands broadened, the f i n a l spectrum having a shoulder at 555 nm (e = 1.0 x 10 M"  1  1  M  - 1  cm ). -1  x 10 M'  4  5  M"  1  cm" ) and the main band centred around 525 nm (e = 1.3 x 10 1  cm" ) with small shoulders appearing at 388 nm(e = 6.67 x 10  cm" ) and 378 nm (e = 5.87 x 10 1  4  In the Soret region, the band blue shifted to 398 nm (e = 1.67 1  4  M"  1  cm" ). 1  2  4  -44When one atmosphere of N bands of RuOEP(CH CN) 3  2  2  was used in the r e a c t i o n , the o r i g i n a l  in the Soret region completely disappeared, suggesting  that the reaction had gone to completion.  When \ an atmosphere of N  2  was  used, bands from the b i s ( a c e t o n i t r i l e ) species could s t i l l be seen. Therefore, an equilibrium process seems to be occurring, presumably: K  RuOEP(CH CN) 3  2  + N < = i RuOEP(CH CN)(N ) + CH CN 2  3  2  (17)  3  The forward reaction could be p a r t i a l l y 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 r e p r o d u c i b i l i t y . Many times, while scanning the spectrum during a run, isosbestic points were lost.  The collapse of the v i s i b l e bands was very similar to the reaction of  RuOEP(CH CN) 3  Chap 3).  2  and 0 , in which the product is some oxidized species (see 2  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(CH CN)(N ) was found to be very 3  2  l i g h t - s e n s i t i v e and i f one wavelength is scanned f o r too long, some of the N  2  w i l l photolyze o f f the complex to regenerate the RuOEP(CH CN) 3  2  species. Of the reactions with good isosbestic points, inconsistent k i n e t i c data were obtained.  For example, though good f i r s t - o r d e r plots were  obtained (Figure V.2) for the reaction of RuOEP(CH CN) 3  atmosphere of N  2  2  with one  at 30°C (from data obtained by monitoring the decrease  in i n t e n s i t y 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 p a r t i c u l a r system was abandoned.  -45-  Figure V.2. 1 atm N  2  First-Order Plot for the Reaction of RuOEP(CH CN)  in Toluene Containing 1.9 x 1 0 "  3  2  M CH CN at 30°C. 3  2  with  -46-  /  The l i g h t s e n s i t i v i t y 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 N ruthenium porphyrin complex. RuOEP(THF)  also seems to bind to a  By photolyzing RuOEP(CO)(EtOH) in THF,  is formed in s i t u .  2  2  The THF was evaporated o f f by bubbling  N through the solution and a red s o l i d was isolated which is believed to be the N adduct, RuOEP(THF)(N ). The s o l i d had a v = 2110 c m " , -1 which can be compared to a = 2088 cm for the complex 2  1  2  2  N  2  2+  2  48  trans-[Ru(NH ) (H 0)(N )] 3  4  2  .  2  However, no kinetic studies have been  carried out on this system. V. 1.2  The Reaction of RuOEP(CH,CN)  2  Toluene solutions of 1 0 "  5  With  CQH  M RuOEP(CH CN) 3  4  with 1.9 x 1 0 "  2  2  M CH CN 3  added were reacted with 3/4 atmosphere of C,,H at 30°C(Figure V.3). 4  Again, from examining the bands in the Soret region, the reaction appears to have gone to completion.  The spectrum of the f i n a l product is very  similar to that of the proposed RuOEP(CH CN)(ft,) species, showing a 3  broad band in the v i s i b l e region. 3 1 1 548 nm (e = 9.24 x 10 (e = 1.18 x 10  M"  The f i n a l spectrum has a shoulder at  cm" ), a broad band centred around 525 nm  M"  1  cm" ) and in the Soret region, a main band at 398 nm  (e = 2.04 x 10 M"  1  cm" ) with shoulders at 388 nm (  4  5  1  1  and at 378 nm (e = 6.77 x 10  4  M"  1  cm" ). 1  e  = 9.37 x 10  4  M'  Some reversal of the reaction  could be seen by degassing the solvent. As with the case of binding N , the kinetic runs were very 2  inconsistent.  1  Often the spectral curves would lose t h e i r isosbestic  points partway through the r e a c t i o n , and sometimes the reaction would  cm" ) 1  -47-  30NV9U0S8V 1  (NJ  ^  f g  §  T -  CD  ABSORBANCE Figure V.3.  Spectral Changes for the Reaction of RuOEP(CH CN) 3  3/4 atm of C H 2  4  in Toluene Containing 1.9 x 1 0 "  2  2  with  M CH CN at 30°C. 3  -48never s t a r t at a l l . When the i n i t i a l amount of added CH CN was doubled to 0.038 M and 3  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(CH CN) + C H <-=^.RuOEP(CH CN)(C H ) + CH CN 3  2  2  4  3  This r e a c t i o n , as in the N oxygen-sensitive, the C H 2  4  2  2  4  (18)  3  reaction, seemed to be extremely photo- and not being bound very t i g h t l y .  The use of  tetracyanoethylene, TCNE, was considered because activated o l e f i n s should coordinate more strongly and s t a b i l i z e any Ru-olefin complex.  However,  TCNE in toluene produced intense colours due to the formation of a charge49 transfer complex  ; the intense colour covers the absorption bands of  the porphyrin complex in the v i s i b l e region. Reversible binding of C H 2  4  to RuOEP(THF)  2  in THF at 20°C has  also been demonstrated by spectroscopy by another worker in t h i s 39 laboratory  .  The exact nature of the ethylene compl-ex is of p a r t i c u l a r interest. The species presumably contains a ir-bonded o l e f i n i c moiety but i t is not known i . e . whether one or both CH^CN ligands come o f f when the C H„ is bound: 0  Figure V.4  Possible structures for ethylene complex,  Complex 3 is considered as formally seven-coordinate, system that binds 0  ?  A Mn(IT) porphyrin  (and TCNE) does lose an axial ligand in forming  -49complexes 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 , I r , 1  1  Pt^ ). 1  The evidence suggests then that perhaps instead of  binding dioxygen as a bent superoxide ( R u IV -2 side-on peroxide (Ru oxidation state. found  51  1 1 1  ^ ) , the 0 -  2  is bound as a  - 0 ~ ) with the ruthenium being formally in the +4 2  One isolated Ru(IV) complex, H R u ( P ( P h ) ) , has been 4  3  3  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(CH CN) 3  V.2  The Reaction of RuOEP(CH CN) 3  2  2  in toluene.  With CO in Other Solvents  Since the reaction of RuOEP(CH CN) 3  2  and CO in toluene had gone so  cleanly, the same reaction in other solvents was also t r i e d , p a r t i c u l a r l y  31 since the reversible 0 -binding had been demonstrated 2  polar solvents DMA, DMF and pyrrole.  On dissolving the  in the a p r o t i c , RuOEP(CH CM) 3  2  complex in the coordinating solvents used, (DMF, DMA, THF, py and p y r r o l e ) , both CHgCN ligands were believed to be displaced by the solvent ligands (see below).  The bis species could c e r t a i n l y be formed in s i t u by  photolyzing the RuOEP(CO)(EtOH) adduct in the appropriate solvent  (see  Experimental), but then there was always the p o s s i b i l i t y of some dissolved CO remaining in the solvent, and this could possibly have interfered with the CO reaction being studied. RuOEP(CH CN) , 3  2  The only useful isolated s o l i d was  and since a c e t o n i t r i l e ligands are f a i r l y l a b i l e  (as  -50-  judged by the reaction with CO in toluene-Chap. I l l ) ,  the solvent  ligands,  at s u f f i c i e n t l y high concentrations, should e a s i l y displace the a c e t o n i t r i l e , 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(CH CN) 3  The RuOEP(CH CN) 3  2  2  With CO in Pyridine (py).  complex in neat pyridine gives the bis(pyridine)  species, but the system is completly unreactive towards CO, which is quite consistent with a d i s s o c i a t i v e mechanism involving i n i t i a l loss of a pyridine ligand. Dissolution of RuOEP(CH CN) 3  2  in toluene containing 0.15 M p y r i d i n e , 5?  again, gave a spectrum similar to that reported in benzene. 495 nm (  V i s i b l e bands appear at 521 nm (e = 3.80 x 10  = 1.48 x 10  e  for s o l i d  4  M"  1  c m " ) , 450 nm ( 1  a Soret band at 395 nm ( E = 1.02 X 10  5  M"  1  e  = 1.58 x 10 cm" ). 1  4  reaction of the Ru0EP(py)  2  M"  4  M"  1  1  2  cm ), - 1  cm" ) and 1  However, under these  conditions, based on the known spectrum of'RuOEP(CO)(py) by a method similar to that of Ru0EP(C0)(Et0H)-see  RuOEP(py)  ( s o l i d prepared  Experimental), the  with one atmosphere of CO at 25°C was only  ^15% complete a f t e r 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 r e f l e c t 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.  RuOEP(py)  2  K + C 0 ^ = ± R u 0 E P ( C 0 ) ( p y ) + py  Surprisingly, toluene solutions of the b i s ( a c e t o n i t r i l e ) complex containing 0.015 M pyridine did not completely form the bis(pyridine)  (19)  -51-  Figure V.5.  Spectral Changes for the Reaction of RuOEP(CH CN)  1 atm CO in Toluene Containing 0.15 M pyridine at 25°C.  3  2  with  - 5 2 -  species, which has a c h a r a c t e r i s t i c band at 4 5 0 nm.  Presumably, the  mixed ligand species RuOEP(CH CN)(py) must be present.  Studies on the-  3  pyridine systems were not pursued further p a r t i a l l y due to this added complication. The Reaction of  V.2.2  RUOEP(CHQCN)  N,N-Dimethylformamide  2  With CO in N,N-Dimethylacetamide (DMA),  (DMF) and Tetrahydrofuran (THF).  Since the s o l i d RuOEP(DMA) has not been i s o l a t e d , the species was 2  _5  formed in s i t u by photolyzing a 1 0 complex in DMA for x 1 0 M"  1  x 1 0 M"  1  4  5  ^2  min.  c m " ) , 4 9 8 nm ( 1  cm" ). 1  M solution of the RuOEP(CO)(EtOH)  Spectral bands were found at = 1 . 1 5 x 1 0 M' 4  e  1  521  nm  cm' ) and 3 9 5 nm ( 1  e  (e  =3.52  = 1.68  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 M"  1  ( e = 2 . 1 6 x 1 0 M"  1  4  5  c m " ) , 5 1 7 nm ( 1  = 1 . 4 9 x 1 0 M" 4  e  cm )and a shoulder at 3 7 3 nm ( _1  1  c m " ) , 3 9 4 nm 1  = 3 . 8 5 x 1 0 M" 4  e  cm" )  1  1  (Figure V . 6 ) . Of i n t e r e s t , when the s o l i d RuOEP(CH CN) 3  2  is dissolved in DMA, a  spectrum (trace #1 on Figure V . 7 ) d i f f e r e n t to that of RuOEP(DMA)  is  observed.  and the  2  The v i s i b l e bands of this species  'X' are much broader  band at 5 2 1 nm is only 1 . 4 times more intense than the 4 9 8 nm band; the r a t i o of these band i n t e n s i t i e s in the bis(DMA) species is about 3 .  The  spectrum resembles the type of spectrum normally attributed to a f i v e 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 a c e t o n i t r i l e must be playing a  r o l e , and, as in the pyridine system, a mixed snecies, in this case, RuOEP(CH-CN)(DMA),  is strongly indicated.  The p o s s i b i l i t y of  Figure V.7.  Spectral Changes for the Reaction of Species 'X' with  1 atm CO in DMA at 29°C.  -55-  Tr-bonded a c e t o n i t r i l e cannot be completely ruled out  53 .  When one atmosphere of CO i s added to the RuOEP(DMA) species, 2  formed in s i t u , 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 i e l d isosbestic points over a period of several hours (Figure V.7), the f i n a l spectrum resembling that of RuOEP(CO)(DMA). A plot of 1og(A -A ) versus time, for the slower changes, based on the t  oo  increase in intensity of the 548 nm band, gives a straight l i n e (Figure V.8) of slope = 1.09 x 1 0 "  4  sec"  1  at 29°C.  When Ru0EP(CH-CN) 3  o  was dissolved  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 s o l u t i o n , the same sort of spectral changes, as those i l l u s t r a t e d in occurred.  Figure V.7,  A f i r s t - o r d e r plot also gave a straight l i n e of slope = 1.03  -4 -1 x 10 sec , which suggests that the measurable, slower part of the reaction i s 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  to 7.43 x 10  -1 sec  , indicating a f i r s t - o r d e r 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 i s i b l e and Soret bands in the same positions, The second, slower step could be the formation of a bis(carbonyl) species.  There has been a r e p o r t  5 4  of the formation of the bis(carbonyl)  -56-  0.9-  "1.V  1.5-  32  lb  TIME (min)  Figure V  .8.  First-Order Plot of the Reaction of Species  CO in DMA at 29 C. U  'X' w i t h ' l atm  -57complex 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 r i s e to a V C Q = 1990 c m , higher than that of the mono- 1  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 i s i b l e spectrum can  only be obtained in a non-coordinating solvent, since one CO molecule is rapidly replaced in a coordinating solvent such as DMA, p y r i d i n e , etc. The v i s i b l e spectrum of the bis(carbonyl)  species in toluene d i f f e r s from  the monocarbonyl (EtOH adduct) in toluene in that the 548 nm band sharpens and i n t e n s i f i e s s l i g h t l y and the 517 nm band develops hyperfine side bands at 508 nm and 513 nm. bis(carbonyl)  At room temperature, toluene solutions of the  species are not stable with respect to loss of CO and  spectral studies must be carried out at sub-zero temperatures.  Considering  these f a c t s , a second CO molecule adding on to 'RuOEP(CO)(DMA)  at  1  29°C in DMA to give RuOEP(CO)  2  seems highly u n l i k e l y .  If species 'X' or RuOEP(DMA) is l e f t in DMA for long periods, the 2  species w i l l abstract CO from the solvent.  When RuOEP(DMA) is formed in 2  s i t u and the solution is thoroughly degassed and l e f t under argon, over a period of 24 hours there is a gradual increase in i n t e n s i t y of the band at 548 nm and a large decrease in i n t e n s i t y of the 521 nm  and 498 nm bands;  the changes appear consistent with formation of RuOEP(CO)(DMA). have been other r e p o r t s  5 6  There  of ruthenium complexes abstracting CO from DMA.  DMF was also studied as a solvent system.  The RuOEP(DMF)  species  2  formed is s i t u was found to have bands at 521 nm ( E = 5.38 x 10  4  M  - 1  cm ), - 1  -58493 nm (  e  = 1.97 x 10  4  M"  cm" ) and 391 nm (  1  1  E  = 2.29 x 10  5  M"  cm" ).  1  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 (e = 2.44 x 10 M" 4  1  c m " ) , 394 nm ( 1  at 374 nm (E =6.00 x 10  M"  4  1  = 2.96 x 10 M" 5  e  cm" ).  M"  4  1  1  c m " ) , 517 nm 1  cm" ) and a shoulder 1  Again, when Ru0EP(CH CN)  1  3  2  is  dissolved  in DMF, a species d i f f e r e n t to RuOEP(DMF) is attained and this reacts 2  wtth one atmosphere of CO as seen in Figure V.9. that whtch occurred in DMA.  The reaction is similar to  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 with a rate constant of 1.9x10  -5  sec  -1  o at 29 C.  The corresponding study in THF gave very similar findings. RuOEP(THF)  2  species has bands at 521 nm (•£ = 6.84 X 10  M"  1  c m " ) , 494 nm 1  ( E = 2.03 x 10 M"  1  c m " ) , 388 nm ( E = 2.55 x 10  ( E = 7.87 x 10 M"  1  cm" ).  ( E = 4.10 x 10 M"  1  c m " ) , 518 nm ( E = 2.60 x 10  ( E = 4.98 x 10 M '  1  cm" ) and a broad band at <320 nm ( E = 3.89 x 10  4  4  4  5  M"  1  cm" ).  1  The RuOEP(CO)(THF)  1  1  1  c m ) and 296 nm -1  species has bands at 549 nm 4  M"  1  c m " ) , 396 nm 1  1  When the RuOEP(CH CN)  1  5  M"  4  The  3  2  4  was dissolved in the THF (the THF had to  be d i s t i l l e d on the vacuum l i n e , d i r e c t l y into the c e l l , avoiding any contact with a i r ) 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 1 0 "  4  sec"  1  at 30°C.  When the DMA, DMF and THF systems, the species dissolution of RuOEP(CH CN) 3  into the RuOEP(solvent)  in any of these solvents could be converted  species by less than 2 minutes of photolysis.  2  Also, the RuOEP(solvent)  2  'X' present on  ?  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  1 atm CO in DMF at 29°C.  'X' wi  -60-  33NV9eJ0S8V  ABSORBANCE  Figure V.10.  Spectral Changes for the Reaction of Species 'X' with  1 atm CO in THF at 30°C.  -61with one atmosphere of CO to give the RuOEP(CO)(solvent)  spectrum, while  the corresponding species 'X' react quite d i f f e r e n t l y . One thing these solvents have in common is that they are susceptible 56-58 to metal-catalyzed decarbonylation coincidence.  .which may be more than a  It is unlikely that 'X' is a carbonyl, since the spectra  are more typical of RuOEP(L)  rather than RuOEP(CO)L.  2  l i k e l y RuOEP(CH CN)(solvent).  Species  'X'  is most  As mentioned in Chapter 4, the bis(phosphine)  3  ruthenium porphyrin complexes have been found to c a t a l y t i c a l l y decarbonylate aldehydes, and this was i n i t i a t e d by exposure to CO with subsequent 46 very high turn-over numbers for the c a t a l y s i s i n i t i a l exposure of RuOEP(CH CN)(solvent)  .  It  is f e a s i b l e that the  to CO could give rapid  3  decarbonylation of the solvent to give an amine (at least in the cases of DMA and DMF).  The product would l i k e l y be, for the DMA system,  RuOEP(CO)(N(CH ) ), and the spectrum after the rapid CO reaction is that 3  of a carbonyl.  3  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) * slow 1  >RuOEP(CO)'(N(CH-),) fast  6  slow CO  RuOEP(DMA), * Figure V . l l .  Possible scheme to explain the observed spectral changes  of RuOEP(CH CN) 3  >RuOEP(CO)(DMA) fast  2  with CO in DMA, DMF and THF.  The spectrophotometric data could be consistent with such a scheme.  The  -62-  minimal k i n e t i c data indicate that the slow step is f i r s t - o r d e r in CO, and this is d i f f i c u l t to r a t i o n a l i z e , however, since the slow spectral  changes  look very much l i k e the conversion of one monocarbonyl into another. More work needs to be done on these systems before this series of reactions can be f u l l y understood. V.2.3  The Reaction of RuOEP(CH,CN)o With CO in Pyrrole. 31 Since  some of the o r i g i n a l reversible oxygenation work  was done  in p y r r o l e , this was also t r i e d as a solvent f o r the reaction with CO. As in the case of the DMA, DMF and THF systems, the species  'Y' obtained  when RuOEPCCH^CN^ i s dissolved in pyrrole i s not the Ru0EP(pyrrole) species. 495 nm (  Ru0EP(pyrrole) =1.61  e  x 10  M"  4  has bands at 522 nm(  2  c m ) and 395 nm (  1  -1  The carbonyl, RuOEP(CO)(pyrrole), M"  1  c m " ) , 518 nm ( 1  e  = 1.36 x 10  e  = 6.76 x 10  Species  4  M"  1  = 3.25 x 10 = 1.09 x 10  5  4  M" M"  1  1  cm" ), 1  cm" ). 1  has bands at 550 nm ( e = 2.05 x 10 4  M"  a shoulder at 375 nm ( e = 4.01 x 10 <310 nm (  E  E  4  1  c m " ) , 397 nm ( 1  M"  1  E  2  = 2.23 x 10  5  4  M"  1  cm" ),  cm" ) and a broad band at 1  cm" ). 1  'Y' has a less intense and broader Soret band  than the  bis(pyrrole) complex and a difference in peak height ratios in the v i s i b l e region.  When one atmosphere of CO was added to species  no sudden spectral change;  *Y' there is now  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 l e f t overnight to get a f i n a l spectrum.and when less than one atmosphere is used, the reaction is less complete suggesting a reversible equilibrium. When a f i r s t - o r d e r plot was done for the reaction with one atmosphere (Figure V.13), though, the log plot starts out in a l i n e a r fashion, but  1  -63-  33NV8eJ0S8V  i  p Figure V.12.  1  o  1  o  ^ ABSORBANCE"  Spectral Changes for the Reaction of Species  1 atm CO in pyrrole at 30°C.  ho on~> 'Y'  with  -64-  Figure V.13.  First-Order Plot of the Reaction of Species  1 atm CO in pyrrole at 30°C.  'Y' with  -65-  about one % - l i f e , the plot curves away from l i n e a r i t y .  For a f i r s t - o r d e r  reaction, the log plot is normally l i n e a r for at least 3 h a l f - l i v e s . 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 a c e t o n i t r i l e . The data could result from CO reacting with two d i f f e r e n t species present in solution at d i f f e r e n t rates (cf. eq. 20), one species reacting much more slowly and this could complicate the k i n e t i c s .  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 CN) 3  2  in toluene, excess a c e t o n i t r i l e was  needed in order to s t a b i l i z e 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 d i s s o c i a t i v e mechanism: k  RUOEP(L)  l  k  2 (21)  -ZII=. RUOEP(L) ZZ=!RUOEP(CO)L >  2  <  <  k  -l  k  With the L = P(n-Bu)  3  -2  system in toluene, no excess phosphine was necessary  to maintain the six-coordinate species which, under these conditions, reacted with CO to f u 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 k i n e t i c s . RuOEP(P(n-Bu) ) 3  2  Under these conditions, the reaction of  with 1 atm CO gave an equilibrium mixture with  Ru0EP(C0)(P(n-Bu) ), the CO being e a s i l y displaced by the excess of,, 3  phosphine ligand. Kinetic and thermodynamic parameters are presented for both systems (L  =  CH^CN,  P(n-Bu) ), and the data compared within the systems and with 3  those f o r some Fe(II)(porphyrin) systems. for  these M(porphyrin)L,>  Based on the k ^/k  2  values  species, a hypothesis as to the structure of  -67the corresponding five-coordinate intermediate was made, which suggests, for the RuOEP(CH CN)  and RuOEP(P(n-Bu) ) intermediates, that the metal  3  3  centres are more in the porphyrin plane than out of i t . The RuOEP(CH CN) 3  complex in toluene also binds both N  2  2  and CgH^,  but the systems proved d i f f i c u l t to study, one factor being the extreme photosensitivity of the products, the coordinated gas molecules being photolabile. When RuOEP(CH CN) was dissolved in coordinating solvents 3  DMF, THF and p y r r o l e ) , the anticipated RuOEP(solvent) only in pyridine.  (py, DMA,  2  However, RuOEP(py)  2  species was formed  does not react with 1 atm CO in  2  neat pyridine; on d i l u t i n g the pyridine with toluene, a slow p a r t i a l reaction occurs to give the monocarbonyl, RuOEP(CO)(py). On dissolution of s o l i d RuOEP(CH CN) 3  in DMA, DMF or THF, the spectrum  2  achieved is not that of the RuOEP(solvent)  2  species, which can be formed  in s i t u by the photolysis of RuOEP(CO)(EtOH) in the solvent; the much broader v i s i b l e spectrum is believed to be that of species ' X ' .  This species  RuOEP(CH CN)(solvent), 3  -X' can be photolyzed to give  which slowly reverts back thermally to species  'X'.  RuOEP(solvent)  Species  "X  1  2  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 t e n t a t i v e l y suggested to involve a decarbonylation of the solvent to give, for example with DMA, RuOEP(CO)(N(CH ) ); the 3  3  subsequent slow reaction could be replacement of the amine by the solvent. In the case of dissolution of the b i s ( a c e t o n i t r i l e ) complex in pyrrole, again the i n i t i a l spectrum is not that of the RuOEP(pyrrole) species.  2  Reaction with CO gives a series of spectral changes to give what  -68-  appears to be RuOEP(CO)(pyrrole).  However, a f i r s t - o r d e r k i n e t i c plot  of this reaction is only l i n e a r for about one h a l f - l i f e . species, RuOEP(CH CN)(pyrrole) 3  Perhaps two  and RuOEPtpyrrole^, are present in solution  and they react with CO at d i f f e r e n t rates. The presence of the a c e t o n i t r i l e ligands ( i n i t i a l l y chosen to be an innocent ligand in strongly coordinating solvents) e f f e c t on the chemistry of the RuOEP species.  is having a pronounced  A major problem in studying  these systems, is that most RuOEP(L)(L') complexes show v i s i b l e and Soret bands at wavelengths that are independent of L, thus making i d e n t i f i c a t i o n of the species in solution d i f f i c u l t .  One worthwhile e f f o r t would be  i s o l a t i o n of other R u O E P d ^ species, f o r example, with L = DMA, DMF, THF and pyrrole.  -69REFERENCES 1.  B. R. James, in 'The Porphyrins', D. Dolphin, Ed., V o l . V, Academic Press, New York, 1978, p. 205.  2.  R. W. Erskine and B. 0. F i e l d , Struct. Bonding, 28, 1 (1976).  3.  G. McLendon and A. E. M a r t e l l , Coord, Chem. Rev., 19, 1 (1976).  4.  L. Vaska, Acc. Chem. Res., 9, 175 (1976).  5.  J . P. Collman, Acc. Chem. Res., K>, 265 (1977).  6.  J . W. Buchler, Angew. 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