{"Affiliation":[{"label":"Affiliation","value":"Science, Faculty of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."},{"label":"Affiliation","value":"Chemistry, Department of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."}],"AggregatedSourceRepository":[{"label":"Aggregated Source Repository","value":"DSpace","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","classmap":"ore:Aggregation","property":"edm:dataProvider"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","explain":"A Europeana Data Model Property; The name or identifier of the organization who contributes data indirectly to an aggregation service (e.g. Europeana)"}],"Campus":[{"label":"Campus","value":"UBCV","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","classmap":"oc:ThesisDescription","property":"oc:degreeCampus"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","explain":"UBC Open Collections Metadata Components; Local Field; Identifies the name of the campus from which the graduate completed their degree."}],"Creator":[{"label":"Creator","value":"Ng, Flora Tak Tak","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/creator","classmap":"dpla:SourceResource","property":"dcterms:creator"},"iri":"http:\/\/purl.org\/dc\/terms\/creator","explain":"A Dublin Core Terms Property; An entity primarily responsible for making the resource.; Examples of a Contributor include a person, an organization, or a service."}],"DateAvailable":[{"label":"Date Available","value":"2011-07-06T20:41:51Z","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"edm:WebResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"DateIssued":[{"label":"Date Issued","value":"1968","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"oc:SourceResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"Degree":[{"label":"Degree (Theses)","value":"Master of Science - MSc","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","classmap":"vivo:ThesisDegree","property":"vivo:relatedDegree"},"iri":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","explain":"VIVO-ISF Ontology V1.6 Property; The thesis degree; Extended Property specified by UBC, as per https:\/\/wiki.duraspace.org\/display\/VIVO\/Ontology+Editor%27s+Guide"}],"DegreeGrantor":[{"label":"Degree Grantor","value":"University of British Columbia","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","classmap":"oc:ThesisDescription","property":"oc:degreeGrantor"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the institution where thesis was granted."}],"Description":[{"label":"Description","value":"A kinetic study was undertaken to investigate the potentiality of rhodium chioro complexes containing diethyl sulphide ligands as homogeneous catalysts. Preliminary studies have also been carried out on the analogous iridium complexes and some rhodium complexes containing arsenic ligands.\r\nUnder mild conditions of temperature and pressure (70-85\u00b0C and upto one atmosphere of hydrogen), it was found that cis RhCl\u2083(Et\u2082S)\u2083 in dimethylacetamide solution is an active catalyst for the homogeneous hydrogenation of maleic acid, trans cinnamic acid and ethylene. In benzene solution, no homogeneous hydrogenation occurred. The kinetics of the maleic acid hydrogenation have been studied in detail and it was found that the hydrogenation process consisted of two rate determining steps: the initial hydrogen reduction of Rh(III) to Rh(I) which complexed rapidly with the maleic acid present and the subsequent hydrogenation of the Rh(I) - maleic acid complex to yield succinic acid and Rh(I) again. The detailed mechanisms of these steps, with particular emphasis on solvent effects are discussed.\r\nThe corresponding IrCl\u2083(Et\u2082S)\u2083 complex and Rh(III) complexes with \"difars\" and \"diars\" (two chelating arsenic ligands) were inactive as homogeneous hydrogenation catalysts, however reactions with H\u2082 were observed with the iridium complex itself and also the rhodium difars complex; these reactions are also discussed.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/description","classmap":"dpla:SourceResource","property":"dcterms:description"},"iri":"http:\/\/purl.org\/dc\/terms\/description","explain":"A Dublin Core Terms Property; An account of the resource.; Description may include but is not limited to: an abstract, a table of contents, a graphical representation, or a free-text account of the resource."}],"DigitalResourceOriginalRecord":[{"label":"Digital Resource Original Record","value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/35913?expand=metadata","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","classmap":"ore:Aggregation","property":"edm:aggregatedCHO"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","explain":"A Europeana Data Model Property; The identifier of the source object, e.g. the Mona Lisa itself. This could be a full linked open date URI or an internal identifier"}],"FullText":[{"label":"Full Text","value":"ACTIVATION.OF HYDROGEN BY RHODIUM AND IRIDIUM CHLORO COMPLEXES CONTAINING SULPHIDE OR ARSirE TYPE LIGANDS by FLORA TAK TAK NG B.Sc. The U n i v e r s i t y of Hong Kong, 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of CHEMISTRY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1968 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n -t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t n f Chemistry  The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a D a t e 19th A p r i l , 1968. ABSTRACT A kinetic study was undertaken to investigate the potentiality of rhodium chioro complexes containing diethyl sulphide ligands as homogeneous catalysts. Preliminary studies have also been carried out on the analogous iridium complexes and some rhodium complexes containing arsenic ligands. Under mild conditions of temperature and pressure (70-85\u00b0C and upto one atmosphere of hydrogen), i t was found that cis RhCl^(Et2S)^ in dimethylacetamide solution is an active catalyst for the homogeneous hydrogenation of maleic acid, trans cinnamic acid and ethylene. In benzene solution, no homogeneous hydrogenation occurred. The kinetics of the maleic acid hydrogenation have been studied in detail and i t was found that the hydrogenation process consisted of two rate determining steps: the i n i t i a l hydrogen reduction of Rh(III) to Rh(I) which complexed rapidly with the maleic acid present and the subsequent hydrogenation of the Rh(I) - maleic acid complex to yield succinic acid and Rh(I) again. The detailed mechanisms of these steps, with particular emphasis on solvent effects are discussed. The corresponding IrCl^CEt^S)^ complex and Rh(III) complexes with \"difars\" and \"diars\" (two chelating arsenic ligands) were inactive as homogeneous hydrogenation catalysts, however reactions with were observed with the iridium complex i t s e l f and also the rhodium difars complex; these reactions are also discussed. TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGMENTS i x CHAPTER I . INTRODUCTION 1 A. Aim of the work. 1 B. T r a n s i t i o n metal complexes as homogeneous c a t a l y s t s . 1 C. Mechanism of hydrogen a c t i v a t i o n i n homogeneous 1 hydrogenation r e a c t i o n s . ( i ) Inorganic s u b s t r a t e s . ,3 ( i i ) Organic s u b s t r a t e s . 4 D. L i t e r a t u r e r e p o r t s on rhodium complexes as 8 homogeneous hydrogenation c a t a l y s t s . E. General. 10 CHAPTER I I . EXPERIMENTAL t A. P r e p a r a t i o n of rhodium complexes. B. Other m a t e r i a l s . C. Hydrogenation apparatus. D. Experimental procedure f o r a t y p i c a l gas uptake experiment. 12 12 13 13 16 i v Page E. E x t r a c t i o n o f r e a c t i o n p r o d u c t s . r 17 F. S p e c t r o s c o p i c work. 17 CHAPTER I I I . THE R h C l 3 ( E t 2 S ) 3 CATALYSED HYDROGENATION OF 18 .,- \u2022 OLEFINIC COMPOUNDS. A. S t o i c h i o m e t r y . 18 B. K i n e t i c s . 20 ( i ) I n i t i a l r e g i o n . 20 ( i i ) L i n e a r r e g i o n . 25 C. E f f e c t o f added d i e t h y l s u l p h i d e . 32 D. E f f e c t o f added c h l o r i d e . 32 E. F u r t h e r gas u p t a k e e x p e r i m e n t s . 39 F. S p e c t r o p h o t o m e r i c s t u d i e s . 39 G. D i s c u s s i o n . 46 ( i ) I n i t i a l r e g i o n . 46 ( i i ) E f f e c t o f added E t 2 S on i n i t i a l r a t e . 49 ( i i i ) E f f e c t o f added c h l o r i d e on i n i t i a l r a t e . 53 ( i v ) S o l v e n t e f f e c t s on t h e i n i t i a l r e d u c t i o n p r o c e s s . 54 ( v ) C a t a l y t i c h y d r o g e n a t i o n o f m a l e i c a c i d . 55 CHAPTER I V . CATALYTIC PROPERTIES OF SOME RELATED I r AND 62 Rh COMPLEXES. A. I r C l 3 ( E t 2 S ) 3 s y s t e m s . 62 B. R h ( I I I ) d i f a r s and R h ( I I I ) d i a r s s y s t e m s . 64 Page C. D i s c u s s i o n . 64 Ci) I r C l 3 ( E t 2 S ) 3 systems. 64 ( i t ) R h ( I I I ) d i f a r s and Rh ( I I I ) d i a r s systems. 67 \\ \u2022 REFERENCES. . 7 0 LIST OF TABLES Page RhCl_(Et~S)~ c a t a l y s e d hydrogenation of maleic a c i d i n DMA. I V a r i a t i o n of i n i t i a l slope w i t h [ ? J h C l 3 ( E t 2 S ) J . 21 I I V a r i a t i o n of i n i t i a l slope w i t h p a r t i a l pressure of R^. 23 I I I Temperature dependence of k^. 26 IV V a r i a t i o n of second slope w i t h [ R h C l 3 ( E t 2 S ) 3 ] . 28 V V a r i a t i o n of second slope w i t h p a r t i a l pressure of . 30 VI Temperature dependence of k^. 33 V I I V a r i a t i o n of r a t e s w i t h added [ E ^ S ] , 35 \u2022> V I I I V a r i a t i o n of r a t e s w i t h added [ L i C l ] . 38 L I S T O F F I G U R E S 1. Apparatus for constant pressure gas-uptake measurements. RhCl. ( E t . S ) _ catalysed hydrogenation of maleic acid in DMA. , 3 2 3 2. Rate plots for the reaction at 80\u00b0C. 3. Dependence of i n i t i a l slope on [Rh] . 4. Dependence of i n i t i a l slope on partial pressure of H^ . 5. Arrhenius plot for the Rh(I)-maleic acid complex formation. 6. Dependence of second slope on [Rh]. 7. Dependence of second slope on partial pressure of H2-8. Arrhenius plot for the RhCl^CEt^S)^ catalysed hydrogenation of maleic acid. 9. Dependence of i n i t i a l slope on added [ E ^ S ] . 10. Rate plots for the reaction in the presence of added E t 2 S at 80\u00b0C. 11. Dependence of i n i t i a l slope on added [chloride]. Absorption spectra of R h C l 3 ( E t 2 S ) 3 . 12. Absorption spectra of R h C l 3 ( E t 2 S ) 3 in DMA. 13. Effect of time on the absorption spectra of R h C l 3 ( E t 2 S ) 3 in DMA at 426 nyx. 1 4 . Effect of added LiCl on the absorption spectra of RhCl 3(Et 2S) 3 in D M A . 1 5 . Absorption spectra of R h C l 3 ( E t 2 S ) 3 in D M A in the presence of maleic acid. 1 6 . Absorption spectra of R h C l 3 ( E t 2 S ) 3 in benzene. Plot of l \/ ( i n i t i a l rate) against added [ E ^ S ] for the Rh(I)-maleic acid complex formation. Rate plot for the reaction between H 2 and I r C l 3 ( E t 2 S ) 3 in D M A at 80\u00b0C. Rate plot and the corresponding log plot for the reaction between K 0 and Rh(III) difars in D M A at 80\u00b0C. ACKNOWLEDGMENTS I wish to thank Dr. B.R. James for his advice, guidance and encouragement during the preparation of the thesis and throughout the course of research. I also wish to express my gratitude to G. L. Rempel for many valuable suggestions and discussions. C H A P T E R I I N T R O D U C T I O N A. Aim of the work. The main object of the work was to investigate the potentiality of some rhodium complexes containing sulphide or arsine type ligands as homogeneous hydrogenation catalysts for the reduction of organic and inorganic substrates. Where catalytic activity was observed, detailed kinetic studies have been made in an attempt to elucidate the reaction mechanisms. B. Transition metal complexes as homogeneous catalysts. In the last few years, great advancement has been made in the 1-3 f i e l d of homogeneous catalysis , This includes the discovery and elucidation of a variety of new and often unusual, catalytic reactions of transition metal ions and coordination compounds. Examples of these reactions include homogeneous hydrogenation, hydroformylation, oxidation and isomerisation of olefins, hydration of acetylene compounds and polymerisations. The Group V I I I platinum metal complexes have been found to be particularly active for these kinds of reactions in both aqueous and nonaqueous solvents. C . Mechanism of hydrogen activation in homogeneous hydrogenation reactions. In general, transition metal complexes seem to activate molecular 2 1-3 hydrogen f o r homogeneous hydrogenation through three d i f f e r e n t ways , namely, h e t e r o l y t i c s p l i t t i n g of hydrogen, homolytic s p l i t t i n g of hydrogen or d i h y d r i d e formation. In each case, r e a c t i v e hydride intermediates of the t r a n s i t i o n metal c a t a l y s t are producec . I t i s thought that c a t a l y t i c a c t i v i t y of t r a n s i t i o n metal complexes depends very much on the l a b i l i t y and thermodynamic s t a b i l i t y of these hydride intermediates *. Hydrogen i n such intermediates commonly ac t s as an a n i o n i c l i g a n d . H e t e r o l y t i c s p l i t t i n g i n v o l v e s no change i n the formal o x i d a t i o n number of the metal e.g. ML + H. -1 ML .H\" + H + + L b n 2 n-1 where M and L represent the metal and l i g a n d r e s p e c t i v e l y . I t i s e s s e n t i a l l y a s u b s t i t u t i o n a l process. R e a c t i v i t y i s ' t h u s governed by : the s u b s t i t u t i o n l a b i l i t y of the complex ML^, the s t a b i l i t y of the hydride formed, and by the presence of s u i t a b l e base to s t a b i l i s e the released proton. In homolytic s p l i t t i n g e.g. 2ML + H_ , 2ML .H + 2L n 2 n-1 and d i h y d r i d e formation e.g. ML + R 0 * ML H. the hydride formation i s accompanied by change i n the formal o x i d a t i o n number of the metal and hence the r e a c t i v i t y may a l s o depend on the 3 susceptibility of the metal to oxidation, (i) Inorganic substrates. Literature reports show that homolytic and heterolytic splitting of hydrogen have been observed in the activation step for the reduction of inorganic substrates. 4 Calvin showed that Cu(I) acetate, in quinoline solution, catalyses homogeneously the hydrogenation of Cu(II). The rate determining homolytic splitting of ^ is followed by a fast step involving reduction of the substrate. I k l II -2 C u + H_ * . 2 C u H 2 _ k_! \u201e I T - \u201e II fast t,+ Cu H + Cu > 2 C u + H In the case of reduction of Fe(III) catalysed by RhCl^.S^O in aqueous 3 M HCI, heterolytic sp l i t t i n g of is postulated as the rate determining step The hydride intermediate, Rh***H , then reduces Fe(III) in a fast step regenerating the starting Rh(III) species: Rh 1 1 1 + H, Rh nV + H + 2 k , \u201e . I I I , - , O T , H I fast \u201e , I I I . o n ' 1 1 \u2022 u + Rh H + 2 F e > Rh + 2 F e * H Direct evidence for the equilibrium in the i n i t i a l step has been obtained in the corresponding Ru(III) system by isotopic exchange studies with deuterium ^\u2022 C u ( I I ) , A g ( I ) , R u ( I I I ) P d ( I I ) and Co(II) have a l s o been reported to a c t i v a t e hydrogen f o r r e d u c t i o n of in o r g a n i c s u bstrates by e i t h e r or both of the above mechanisms. ( i i ) Organic s u b s t r a t e s . Although many t r a n s i t i o n metal complexes had been found to a c t i v a t e molecular hydrogen, u p t i l about 1964 r e l a t i v e l y few had been found to c a t a l y s e homogeneously the hydrogenation of organic s u b s t r a t e s . Since then there has been a s i g n i f i c a n t amount of l i t e r a t u r e on t h i s t o p i c . The three d i f f e r e n t routes of hydrogen a c t i v a t i o n recognised w i l l be e x e m p l i f i e d below. The Ru(II) c a t a l y s e d homogeneous hydrogenation of fumaric a c i d 8 i n aqueous s o l u t i o n has been i n t e r p r e t e d by Halpern, Harrod and James i n terms of h e t e r o l y t i c s p l i t t i n g of by a Ru(II) - o l e f i n TT complex i n the r a t e determing step. The hydrido Ru - o l e f i n 7T complex then rearranges to a Ru - a l k y l cr complex which then p i c k s up a proton to give the p a r a f f i n The mechanism can be p i c t u r e d as f o l l o w s : CT complex f a s t \/ \u2014 Ru 1 II c 4- A _ B where A de n o t e s COOH and B denotes H. ^Co(CN)^]^ i s found t o c a t a l y s e homogeneously t h e h y d r o g e n a t i o n 3 9 o f c o n j u g a t e d o l e f i n s s u c h as b u t a d i e n e i n aqueous s o l u t i o n ' . D e t a i l e d 9 k i n e t i c s t u d i e s by K w i a t e k and c o w o r k e r s s u g g e s t e d t h a t t h e r e a c t i o n p r o c e e d s by the f o l l o w i n g mechanism. The i n i t i a l s t e p i n v o l v e s h o m o l y t i c s p l i t t i n g o f H_ by [co(CN) , f o l l o w e d by c o m p l e x i n g o f the b u t a d i e n e t o g i v e t h e i n t e r m e d i a t e : [ c H 3 C H = CHCH 2 10 C o ( C N ) ^ ] ^ w h i c h has been p r e p a r e d and c h a r a c t e r i s e d T h i s then may undergo r e a c t i o n w i t h the h y d r i d o s p e c i e s by two d i f f e r e n t ways, depe n d i n g on t h e c y a n i d e c o n c e n t r a t i o n , t o g i v e 1 or 2 - butene: 2[co(CN) ] + H 0 ^ [HCo(CN) ] [HCo(CN) ]' + CH_ = CHCH =*CH, -> CH\u201eCH = CHCH\u201eCo (CN)J : [ C H 3CH = CHCH 2Co(CN) 5] 3 _ [H C O (C M 5 ] 3-5J v CH^CH^CH = CH -CN 3 2 2 2(co(CN).] 3\"' +CN CH; ,CH2 [co(CN) 4] 2* [HCo(CN) 5]3 ^ CH3CH=CHCH3+2[co(CN)5] 3-CH CH\u201e I t has been suggested however that the (co(CN) ] 3~ ca t a l y s e d hydrogenation of cinnamate [c^H^CH = CHC02J i n v o l v e s a r a d i c a l anion intermediate: [HCo(CN)5]3\" + [c6H5CH = CHC0 2]\" > (Co(CN) 5) 3\" + [c 6H 5CH 2CHC0 2] [HCoCCN)^ 3\" + [c 6H 5CH 2CHC0 2] -> [co(CN) 5] 3\" + [c 6H 5CH 2CH 2C0 2]' 12 13 Wilk i n s o n and coworkers ' . r e c e n t l y reported that c h l o r o t r i s ( triphenylphosphine) rhodium ( I ) i n benEene s o l u t i o n i s an a c t i v e c a t a l y s t f o r homogeneous h y d r o g e n a t i o n of o l e f i n s c o n t a i n i n g i s o l a t e d double bonds, but not ethylene i t s e l f . A s a l i e n t feature i n t h i s system i n v o l v e s the formation of the d i h y d r i d e R h C l ( P h 3 P ) 2 H 2 ; t h i s then re a c t s w i t h the o l e f i n i n the r a t e determining step. N.M.R. stud i e s i n d i c a t e d that the t r a n s f e r of hydrogen to the o l e f i n i n v o l v e s a metal c i s - d i h y d r i d e species. The a c t i v i t y of the R h C l ( P h 3 P ) 3 complex depends on i t s a b i l i t y to d i s s o c i a t e i n s o l u t i o n to form the a c t i v e species R h C l ( P h 3 P ) 2 S , where S i s solvent molecule which can be e a s i l y d i s p l a c e d by o l e f i n or hydrogen. 7 The mechanism c o n s i s t e n t w i t h k i n e t i c data i s as f o l l o w s : R h C l ( P h 3 P ) 3 =? RhC l ( P h 3 P ) 2 S + Ph 3P RhCl(Ph 3P) 2S+H 2 o l e f i n R h C l ( P h 3 P ) 2 o l e f i n K, k\" H 2RhCl(Ph 3P) 2S k' o l e f i n R h C l ( P h 3 P ) 2 S + p a r a f f i n I t was shown that the r e a c t i o n k\" R h C l ( P h 3 P ) 2 o l e f i n H, -> R h C l ( P h 3 P ) 2 S + p a r a f f i n i s of n e g l i g i b l e s i g n i f i c a n c e under the experimental c o n d i t i o n s and the p a r a f f i n i s produced s o l e l y by the a t t a c k of the o l e f i n on the d i h y d r i d e s p e c i e s . Metal complexes reported to c a t a l y s e the r e d u c t i o n of o l e f i n i c compounds now i n c l u d e those of Ru(II) ^,14,15^ p t ( j j j 14,16^ P d ( I I ) 1 6 , Co(II) 9 ' 1 1 ' 1 7 , Co(I) 1 8 , Fe(0) 1 9 , I r ( I ) \" . 2 \u00b0 ' 2 1 > 2 2 , N i ( I I ) 1 6 , R h ( I I I ) 1 2 ' 2 3 , and Rh(I) 5 ' 1 2 ' 2 3 . In the homogeneous hydrogenation of o l e f i n s , the question a r i s e s as to whether both the o l e f i n and hydrogen or j u s t the hydrogen need to be a c t i v a t e d by the c e n t r a l metal atom. The R h C l ( P h 3 P ) 3 system i n d i c a t e s p o s s i b l y that only hydrogen needs to be a c t i v a t e d whereas i n the Ru(II) system both hydrogen and o l e f i n are a c t i v a t e d . Nevertheless, i n homogeneous hydrogenation, at some stage of the r e a c t i o n there must be a d d i t i o n of metal 8 hydride to the o l e f i n , i . e . \\ \/ \\ \/ MH -f- C ===== C : \u2014 y M C C H and many such h y d r o m e t a l l a t i o n r e a c t i o n s have been observed d i r e c t l y , e.g. w i t h H P t C l ( P E t 3 ) 2 ' , HMn(C0>5 , [HCc(CN) 5J \" , [RhH(CN) 4H 20j 29 and R h H C l 2 ( P h 3 P ) 2 , Hydrometallation i s an example of a much wider c l a s s 30 of \" i n s e r t i o n \" type r e a c t i o n s which are q u i t e common i n many c a t a l y t i c r e a c t i o n s . D. L i t e r a t u r e r e p o r t s on rhodium complexes as homogeneous hydrogenation c a t a l y s t s . 23 A recent review, by James , covered the r e a c t i o n s and c a t a l y t i c p r o p e r t i e s g e n e r a l l y of rhodium complexes i n s o l u t i o n up to the middle of 1966. The r e l e v a n t l i t e r a t u r e data from t h i s , and more r e c e n t l y reported work w i l l be summarised below. I g u t i 3 1 f i r s t reported that (Rh(NH 3) 5(H 2 oJc i 3, [ R h ^ H ^ C l J CI and R h C l 3 i n aqueous acetate s o l u t i o n s a c t i v a t e d molecular hydrogen f o r r e d u c t i o n of quinone, fumaric a c i d and sodium n i t r i t e . However, i n more recent s t u d i e s traces of m e t a l l i c rhodium, a powerful heterogeneous c a t a l y s t , were found during some s i m i l a r r e a c t i o n s , and the above systems may have been heterogeneously c a t a l y s e d . Halpern and Harrod ^ found that chlororhodate (III) species i n aqueous a c i d s o l u t i o n s c a t a l y s e d homogeneously the hydrogen re d u c t i o n of f e r r i c i o n . Further i n v e s t i g a t i o n of t h i s system by James and Rempel ^ showed that only the a n i o n i c , l a b i l e , chlororhodate (III) species were e f f e c t i v e c a t a l y s t s . These chlororhodate (III) species i n aqueous a c i d s o l u t i o n s were not e f f e c t i v e f o r homogeneous hydrogenation of 9 o l e f i n i c s u b s t a n c e s ~\\ However, RhCl^.SH^O i n d i m e t h y l a c e t a m i d e i s found t o c a t a l y s e t h e hydrogen r e d u c t i o n o f c e r t a i n s u b s t i t u t e d e t h y l e r e s 5 3 2 as w e l l as e t h y l e n e i t s e l f 12 13 3 3 3A-W i l k i n s o n and c o w o r k e r s ' ' ' have r e p o r t e d the h y d r o g e n a t i o n of o l e f i n s and a c e t y l e n e s u s i n g a number o f r h o d i u m ( I I I ) and r h o d i u m ( I ) complexes as homogeneous c a t a l y s t s i n e t h a n o l , benzene o r e t h a n o l ^ b e n z e n e 1 34 33 34 m i x t u r e s . The complexes i n c l u d e R h C l 3 . 3 H 2 0 , 1,2,6, R h ( p y ) 3 C l 3 ' , the s o l v a t e d r h o d i u m ( I ) c h l o r i n e - b r i d g e d s t a n n o u s c h l o r i d e complex, 33 R h 2 C l 2 ( S n C l 2 . E t O H ) ^ and t h e t r i p h e n y l p h o s p h i n e d e r i v a t i v e s , 1,2,3 R h ( P h 3 P ) 3 C l 3 3 3 ' 3 5 } R h C l ( P h 3 P ) 3 1 2 ' 1 3 ' 3 6 , 3 7 and ['RhCN(Ph P) ] 2 2 8 . The k i n e t i c s o f most o f t h e s e systems have not been r e p o r t e d i n d e t a i l . The 12 a c t i v i t y o f R h C l ( P h 3 P ) 3 i n benzene has been s t u d i e d i n d e t a i l and i t i s f o und t o be a v e r y e f f i c i e n t c a t a l y s t , ( s e e s e c t i o n C ( i i ) ) . O t her 38 39 rhodium complexes w i t h t r i p h e n y l p h o s p h i n e as l i g a n d , R h C O C l ( P h 3 P ) 2 ' 40 41 and R h H C O ( P h 3 P ) 3 , ' a l s o c a t a l y s e t h e h y d r o g e n a t i o n o f o l e f i n s and 20 36 a c e t y l e n e s ' , but t h e s e complexes t h e m s e l v e s , u n l i k e R h C l ( P h 3 P ) 3 ( s e e C ( i i ) ) show l i t t l e r e a c t i o n w i t h h y d r o g e n . o r o l e f i n a l o n e . The o x i d a t i o n s t a t e o f rhodium i n t h e s e a c t i v e complexes i s ( I I I ) o r ( I ) and i t has been found t h a t r h o d i u m ( I ) c o m p l e x e s , when . v , - 'A v u v . . , \u2022 A 1 2 , 1 3 , 2 8 , 3 3 , 3 5 - 4 1 . . . s t a b i l i s e d by p h o s p h i n e t y p e l i g a n d s , a r e p a r t i c u l a r l y e f f e c t i v e f o r homogeneous h y d r o g e n a t i o n . C o r r e s p o n d i n g systems u s i n g rhodium complexes c o n t a i n i n g s i m i l a r s u l p h i d e or a r s i n e t y p e l i g a n d s have n o t been r e p o r t e d , a l t h o u g h r e c e n t l y B a i l a r and Tayim ^ r e p o r t e d t h a t complexes of t h e t y p e M X 2 ( Q P h n ) 2 (M = P t or Pd ; X = H a l i d e ; , Q = P or As when n = 3 and S or Se when n = 2 ; Ph = p h e n y l ) c a t a l y s e the h y d r o g e n a t i o n of n o n a r o m a t i c p o l y o l e f i n s but only i n the presence of SnCl^. No d e t a i l e d k i n e t i c data were given. E. General. Very few rhodium complexes c o n t a i n i n g sulphur ligands have 42 been c h a r a c t e r i s e d . James and Rempel i n t h i s l a b o r a t o r y were studying the c a t a l y t i c a c t i v i t y of rhodium c h l o r i d e complexes, and i t was i n i t i a l l y decided to study other c h l o r o complexes c o n t a i n i n g a l s o d i e t h y l sulphide ( E t 2 S ) as a coordinated l i g a n d (see I below) since these had been 43 44 prepared some years ago by other workers ' Some experiments have a l s o been c a r r i e d out using two complexes c o n t a i n i n g a r s i n e l i g a n d s ; one was the well-known ' d i a r s ' complex (see I I 45 below) o r i g i n a l l y described by Nyholm and coworkers , and the other 46 was a complex prepared i n t h i s Department by C u l l e n and Dhaliwal which has been correspondingly c a l l e d a ' d i f a r s ' complex (see I I I below). CI ( I ) c i s 1,2,3 t r i c h l o r o t r i s ( d i e t h y l s u l p h i d e ) rhodium ( I I I ) 11 ( I I I ) d i c h l o r o d i (1,2 - d i m e t h y l a r s i n o t e t r a f l u o r o c y c l o b u t e n e ) rhodium ( I I I ) c h l o r i d e . CHAPTER II EXPERIMENTAL A. Preparation of rhodium complexes. The cis 1,2,3 trichlorotris (diethyl sulphide) rhodium (III) 44 complex was prepared according to the literature by refluxing diethyl sulphide with rhodium trichloride trihydrate in ethanol. The orange crystalline compound obtained had the correct melting point of 127\u00b0C and microanalysis carried out by Schwarzkoff Microanalytical Laboratory and Mr. Borda of this Department (C \u00ab 28.87, H = 6.44, S = 19.33, Cl = 22.3%) agreed well with that calculated for RhCl 3(Et 2S) 3 (C = 30.2, H = 6.30, S = 19.42, Cl = 22.3%). Visible and ultraviolet spectra recorded in ethanol gave peaks at 421 nyj- ( \u20ac = 330) and 292 m\/i (\u00a3 = 20100) slightly different from those reported, 424 mjx ( 6 = 370) and 292 m\/t ( e-= 25800). A small amount of dichlorodi (1,2, - dimethylarsinotetrafluoro-cyclobutene) - rhodium (III) chloride, \"Rh(III) difars\", was kindly given to us by Dr. Cullen of this Department and a further amount was prepared by refluxing 1,2, dimethylarsinotetrafluorocyclobutene in ethanol with 46 rhodium trichloride trihydrate . The difars ligand, also donated by Dr. Cullen, was purified by d i s t i l l a t i o n under reduced pressure in an inert atmosphere of nitrogen (120\u00b0C, 47mm). The complex was identified from its properties and analysis (C = 23.29, H = 3.71, Cl = 12.0, Rh = 8.39%; C a l : C \u00ab= 22, H = 2.74, CI = 12.1, Rh = 11.5%). o-Phenylene-bis ( d i m e t h y l a r s i n e ) rhodium ( I I I ) c h l o r i d e \" R h ( I I I ) d i a r s \" was prepared by r e f l u x i n g o-phenylene-bis ( d i m e t h y l a r s i n e ) 45 i n ethanol w i t h sodium hexachlororhodate using however a Rh : A r s i n e r a t i o of 1 : 2. The complex was i d e n t i f i e d from i t s p r o p e r t i e s and a n a l y s i s (C = 30.36, H = 4.4%; C a l : C = 30.36, H = 4.1%). RhCl,.3H o0 was obtained from Platinum Chemicals, Na RhCl,.12H.0 from K & K L a b o r a t o r i e s and ( N H . ) _ I r C l , from Johnson and Matthey L t d . H i. b D i e t h y l sulphide (Eastman Organic Chemicals) and o-phenylene-bis (dimethyl-a r s i n e ) (Strem Chemicals) were used without f u r t h e r p u r i f i c a t i o n . B. Other m a t e r i a l s . Research grade hydrogen was obtained from Matheson Co. and was passed through a \"deoxo\" c a t a l y t i c p u r i f i e r before use. Deuterium and ethylene were obtained as C P . grade from Matheson Co. N,N - dimethyl-acetamide (DMA) was obtained from Eastman Organic Chemicals. I t was p u r i f i e d by s t i r r i n g over calcium hydride under a N^ atmosphere overnight -then d i s t i l l i n g i n a atmosphere at 58\u00b0C, 11 mm. The d i s t i l l a t e was c o l l e c t e d d i r e c t l y onto Linde 4A molecular sieve and stored under n i t r o g e n before use. Maleic,and trans cinnamic acids were obtained from Eastman Organic Chemicals. Maleic a c i d was r e c r y s t a l l i s e d from water before use and i t s p u r i t y was checked by m e l t i n g - p o i n t determination. L i t h i u m c h l o r i d e and l i t h i u m p e r c h l o r a t e were A.R. grade obtained from A l l i e d Chemical Co. C. Hydrogenation apparatus. The hydrogenation apparatus used i n the k i n e t i c s t u d i e s was a constant pressure gas uptake type apparatus, as shown d i a g r a m a t i c a l l y i n Fig u r e 1. The pyrex r e a c t i o n v e s s e l (A), which could be c l i p p e d to a metal rod shaken by a motor ( I ) during a r e a c t i o n , was connected by a s p i r a l g l a s s arrangement w i t h tap (C) to the o i l manometer (D) through tap -(H). The o i l manometer which c o n s i s t e d of a c a p i l l a r y U tube f i l l e d w i t h b u t y l p h t h a l a t e (a l i q u i d of n e g l i g i b l e vapour pressure) was connected to the gas measuring burette c o n s i s t i n g of a mercury r e s e r v o i r (E) and a p r e c i s i o n bored tube (N) of known diameter. The gas measuring burette was i n turn connected through an Edward's high vacuum needle valve (M) t o i t h e gas handling part of the apparatus, which c o n s i s t e d of a mercury manometer ( F ) , the gas i n l e t (Y) and connections to the Welch Duo Seal r o t a r y vacuum pump (G). The r e a c t i o n f l a s k (A) was thermostated i n a s i l i c o n o i l (Dow Corning 550 f l u i d ) bath (B). I t c o n s i s t e d of a four l i t r e g l a s s beaker i n s u l a t e d by polystyrene foam on a l l sides and enclosed by a wooden box w i t h a small c i r c u l a r hole f o r observing the colour changes of the r e a c t i o n mixture. The top of the o i l bath v\/as w e l l covered by stereo foam. The gas burette was immersed i n a thermostated water bath made from a perspex r e c t a n g u l a r tank. Both thermostat baths were operated using \"Jumo\" thermo r e g u l a t o r s w i t h \"mere to mere\" r e l a y c o n t r o l c i r c u i t s and heating provided by 25 watt elongated l i g h t b ulbs. These together w i t h mechanical s t i r r i n g ensured temperature c o n t r o l to w i t h i n about + 0.1\u00b0C. A v e r t i c a l l y mounted t r a v e l l i n g telescope was used to f o l l o w the gas uptake. A lab-chron 1400 timer was used to record the time during the k i n e t i c experiments. 16 D. Experimental procedure f o r a t y p i c a l gas uptake experiment. For each experiment, the required amount of rhodium complex was weighed out i n s i d e the r e a c t i o n f l a s k (A; and the s o l u t i o n was made up w i t h the r e q u i r e d amount of DMA. A stock s o l u t i o n of maleic a c i d i n DMA. was added to the above s o l u t i o n i f r e q u i r e d . The f l a s k (A) was then connected by the s p i r a l and tap (C) to the gas handling part of the apparatus at (0) . The reactant s o l u t i o n was degassed by a l t e r n a t e c o o l i n g w i t h pumping and warming. Hydrogen was admitted at a pressure somewhat l e s s than that r e q u i r e d f o r the experiment and then taps (C) and (P) were c l o s e d . The whole system up to tap (H) was then pumped down w i t h taps ( K ) , ( L ) , (J) and (M) open. The f l a s k and s p i r a l arrangement were disconnected from (0) and t r a n s f e r r e d i n t o the thermostated o i l bath w i t h the s p i r a l connected to the o i l manometer through tap (H). Tap (H) was opened and a f t e r the a i r between tap (H) and (C) was pumped out tap (Q) was c l o s e d . Hydrogen was admitted to the r e s t of the gas uptake apparatus up to tap (C) which was then opened so that the pressure i n the whole system was e q u a l i s e d . The r e a c t i o n pressure r e q u i r e d was adjusted by using the mercury manometer. Tap ( J ) and needle v a l v e (M) were closed w h i l e the i n i t i a l reading of the mercury l e v e l i n (N) was taken. Taps (K) and (L) were closed and the timer and shaker were s t a r t e d simultaneously. As a r e s u l t of any hydrogen uptake, the o i l l e v e l on the l e f t hand s i d e of the manometer rose and to maintain zero d i f f e r e n c e i n the l e v e l s , hydrogen was admitted i n t o the gas measuring burette through tap (J) and needle v a l v e (M) to give a corresponding r i s e of mercury i n (N). The change i n height of the mercury was noted as a f u n c t i o n of time. Since the diameter of (N) was known, the corresponding N.T.P. volume of hydrogen used was found and an uptake plot of gas consumption in moles\/litre against time could be drawn. . The use of a small volume of solution ( ~~ 5 ml) in a relatively large indented vessel ( \u2014 30 ml) and a high shaking rate ensured the absence.of diffusion control in the rate of gas consumption. E. Extraction of reaction products. At the end of some experiments involving hydrogenation of maleic acid, the succinic acid was recovered from solution by pumping off the DMA solvent through a cold trap; the acid was collected as a sublimate. It was identified from i t s melting point and infrared spectrum. F. Spectroscopic work. Some studies involving the RhCl.j(Et2S).j system were carried out spectrophotometrically in the visible range using a thermostated Perkin Elmer Model 202 spectrophotometer. Matched Beckman standard s i l i c a cells of 1 cm or 1 mm optical path length were.used. Infrared spectra were recorded on a Perkin Elmer Model 21 spectrophotometer using KBr discs. N.M.R. studies were done on a Varian HR-100 spectrophotometer. CHAPTER III THE RhCl 3(Et 2S) 3 CATALYSED HYDROGENATION OF OLEFINIC COMPOUNDS A. Stoichiometry. A solution of about 10 M RhCl 3(Et 2S> 3 in DMA, yellow at room temperature and orange at 80\u00b0C, was found to homogeneously hydrogenate maleic acid (MA) under an atmosphere or less of hydrogen. A three to ten fold excess of maleic acid was used. In the absence of maleic acid, the RhCl 3(Et 2S) 3 complex was reduced by H 2 to the metal. No rhodium hydrides were detected in the course of these reactions. The kinetics of the hydrogenation of maleic acid were followed by using the constant pressure gas uptake apparatus (Figure 1) described in Chapter II. Typical gas uptake plots are shown in Figure 2. The i n i t i a l more rapid uptake of hydrogen steadily decreased to a constant value which persisted upto regions approaching the end-point. At later stages metallic rhodium was observed and this coincided with the observation of an unexpected increase in the hydrogenation rate (see the upper curve of Figure 2); no deviations from the linear rate were observed unless metal began to precipitate. The final end-point was reached when a l l the rhodium had precipitated as metal and gas uptake ceased. The H 2 stoichoimetry of the reaction corresponded to the reduction of Rh(III) to Rh(0) and complete hydrogenation of maleic acid to succinic acid. Most experiments were followed 4.0 0 1000 2000 3000 4000 5000 Time, sec Figure 2. Rate p l o t s f o r the R h C l 3 ( E t 2 S ) 3 c a t a l y s e d hydrogenation of maleic a c i d , (80\u00b0C, DMA, 725 mm H\u201e, 3.0 x 10~ 2 M maleic a c i d , [Rh]: <0> 8.79 x 10\" 3 M, ( ^ ) 5.145 x 10\" 3 M). well into the region of constant rate but were concluded before metal precipitated. B. Kinetics. The gas uptake plots clearly did not analyse for any simple overall 1st order or 2nd order reaction. However, the rate law could be arrived at by examining the i n i t i a l region and linear region separately. The kinetics for the system were investigated over a concentration range of (0.2 - 1.0) x 10\"2 M in RhCl 3(Et 2S) 3, (0.5 - 2.7) x 10\"3 M in H 2 and -2 (3.0 - 6.0) x 10 M in maleic acid. (i) I n i t i a l region. The rate of uptake of hydrogen in this region was obtained by measuring the i n i t i a l slope. This could be done quite easily. The variation of i n i t i a l slope with rhodium concentration is shown in Table I and Figure 3. The straight line obtained indicates a 1st order dependence on the RhCl 3(Et 2S) 3 complex. There is also an approximate 1st order dependence of rate on hydrogen concentration as shown in Table II and -2 Figure 4. Doubling the maleic acid concentration from 3.0 to 6.0 x 10 M had no effect on either the i n i t i a l rate or linear rate (see later). Thus the i n i t i a l rate is independent of maleic acid and leads to the rate lav; -d[\"21 dt = k L [H 2)[Rh] (1) where k^ is a 2nd order rate constant. From equation (1) values of k^ were computed for particular values of [Rh] and [H 2] . The average value of k^ wa found to be 1.91 M * sec * (Table I and II). Alternatively, the value of k^ 2 1 Table I V a r i a t i o n of i n i t i a l slope w i t h [ R h C l 3 ( E t 2 S ) 3 ] ( 8 0 \u00b0 C , [ H 2 ) = 2 . 3 2 x 1 0 * 3 M , [MA] = 3 . 0 x 1 0 \" 2 M , DMA) [ R h C l 3 ( E t 2 S ) 3 ] I n i t i a l slope k x 1 0 3 M x 1 0 ^ M sec * M ^ sec * 2 . 5 4 0 . 9 1 . 5 3 5 . 1 4 5 2 . 2 1 . 8 5 7 . 6 4 3 . 2 1 . 8 1 1 0 . 1 9 4 . 5 1 . 9 0 Average 1 . 7 7 Table I I V a r i a t i o n of i n i t i a l slope v i t h p a r t i a l pressure of hydrogen (p'H 2) (80\u00b0C, ( R h C l 3 ( E t 2 S ) 3 ) =5.145 x 10\" 3 M , [ K A] = 3.0 x 10\" 2 M , DMA) p'H 2 [ ^ l I n i t i a l slope 3 5 - 1 - 1 mm x 10 M * x 10 M sec M sec 194 0.62 0.74 2.30 377 1.22 1.18 1.87 531 1.70 2.19 2.50 725 2.32 2.17 1.83 842 2.70 2.55 1.83 Average 2.06 * G.L. Rempel, Ph.D. Thesis, U n i v e r s i t y of B r i t i s h Columbia, A p r i l 1968. 24 was obtained from the slope of the graph of i n i t i a l slope against [fthj - 3 - 1 (Figure 3). The slope gave a pseudo rate constant k| = 4.33 x 10 sec , where II ' = ^ [ H J . The solubility of H 2 in DMA at 725mm is 2.32 x :0~3 M 4 7 , hence the value of k^ was found to be 1.86 M * sec Similarly from the plot of i n i t i a l slope against p'H,, (Figure 4), another pseudo rate constant k^\" ** 3.15 x 10 ^ M sec * mm * where k^\" = \u00ab*kjjRh] was obtained. <* is Henry's constant for the solubility of H_ in DMA and has the value of 3.2 x 10 ^ M -1 4 7 -3 mm . Since the RhCl.j(Et2S).j concentration used was 5.145 x 10 M , k^ was found to be 1.91 M * sec Measurement of k^ over a temperature range of 70.5 - 85 C yielded a good Arrhenius plot. (Table III, Figure 5). From the slope, the activation energy was found to be 13.5 kcal\/mole. AH* was estimated to be about 12.9 kcal\/mole and AS * to be about -21.4 e.u. ( i i ) Linear region. The linearity in the uptake plot indicated a pseudo zero order reaction. The rate of hydrogen uptake was obtained by measuring the linear slope (2nd slope). Variation of this 2nd slope with rhodium concentration (Table IV, Figure 6) is reasonably linear. There is also a 1st order dependence of the 2nd slope on [H 2] (Table V, Figure 7). The rate is independent of the [KA] over the range (3.0 - 6.0) x 10 2 M. The rate law consistent with the kinetic data is dt 2 J = k 2 [ H 2 ] [ R h T l ( 2 ) where [RhJ = total i n i t i a l [RhCl_(Et-S),] . At constant H 2 pressure this Table ; i l Temperature dependeace of k 7.Q.5 738 2.37 1.30 1.07 75.0 742 2.38 1.68 1.37 80.0 725 .2.32 2.20 1.85 85.0 715 2.29 2.77 2.34 * Assuming the s o l u b i l i t y of H 2 in DMA remains the same over the temperature range 70 - 85\u00b0C. 28 Table ;v Var ia t ion of 2nd slope with [.IhCl ( E t 2 S ) 3 ] (80\u00b0C, [H 2 ] = 2.32 x 10\" 3 M, [KA] = 3.0 x 10\" 2 M, DMA) [RhC l 3 (E t 2 S) 3 ] 2nd slope k 2 x 10\"* M x 10^ M sec M * sec * 2.54 5.145 7.64 10.19 2.92 4.25 5.84 7.60 0.49 0.36 0.33 0.31 Average 0.37 29 Table V V a r i a t i o n of 2nd slope w i t h p'H 2 (80\u00b0C J R h C l 3 ( E t 2 S ) 3 ] - 5.145 x l O * 3 M , [MAJ = 3.0 X 10\" 2 M , DMA) p'H 2 [ H 2 ] 2nd slope k 2 3 6 - 1 - 1 mm x 10 M * x 10 M sec M sec 194 0.62 1.16 0.36 377 1.22 2.11 0.34 531 1.70 2.91 0.33 725 2.32 4.34 0.36 842 2.70 4.97 0.36 Average 0.35 * G.L. Rempel, Ph.D. Thesis, U n i v e r s i t y of B r i t i s h Columbia, A p r i l , 1968. gives r i s e to a constant r a t e (pseudo zero order k i n e t i c s ) only i f the ^Rh^,j term remains constant; i n t h i s system t h i s i s b e l i e v e d to represent a c o n c e n t r a t i o n of a Rh( l ) - maleic a c i d complex. (See d i s c u s s i o n ) . The values of c a l c u l a t e d using equation (2) are shown i n Tables IV and V. The average value of was found to be 0.36 M ^ sec ^ . Values of k^ -1 -1 obtained from the slopes of the graphs (Figure 6 and 7) , were 0.34 M sec and 0.32 M * sec * r e s p e c t i v e l y . K i n e t i c measurements of k^ over the range of temperature 70.5 -85\u00b0C gave a reasonable Arrhenius p l o t (Table VI, Figure 8) w i t h the a c t i v a t i o n parameters A ^21.4 kcal\/mole and A S \u2014- 1.0 e.u. C. E f f e c t of added d i e t h y l s u l p h i d e . Added d i e t h y l sulphide slowed down the i n i t i a l part of the r e a c t i o n but d i d not appear to a f f e c t the rate i n the l i n e a r r e g i o n . (Table V I I ) . The i n i t i a l r a t e decreased r a p i d l y at f i r s t w i t h added Et^S and then tended to l e v e l o f f (Figure 9 ) . I t i s i n t e r e s t i n g to note that the r e a c t i o n s at 0.15 and 0.20 M added Et^S gave e s s e n t i a l l y l i n e a r uptake p l o t s throughout (Figure 10) which i n themselves i n c o r r e c t l y suggest an o v e r a l l simple mechanism. D. E f f e c t of added c h l o r i d e . A d d i t i o n of L i C l a l s o i n h i b i t e d the r a t e of hydrogen uptake i n the i n i t i a l r e g i o n , but l e f t the r a t e i n the l i n e a r region v i r t u a l l y u n a f f e c t e d . This i n h i b i t i o n i s not a s a l t e f f e c t s i n c e a d d i t i o n of LiC10 A.3H 20 d i d not a f f e c t the i n i t i a l r a t e (Table V I I I ) . Up to about a 1 : 1 mole r a t i o of [cf] : [Rh], a marked inverse dependence on added Table VI Temperature dependence of k 2 (1 [ R h C l 3 ( E t ? S ) q ] = 5.145x 10\" 3 M, [MA] = 3.0 x 10\" 2 M, DMA) T\u00b0C P'H 2 w 2nd slope k 2 mm x 10 3 M * 6 -1 x 10 M sec -1 -1 M sec 70.5 738 2.37 2.08 0.17 75.0 742 2.38 3.00 0.25 80.0 725 2.32 4.25 0.36 85.0 715 2.29 7.20 0.61 * Assuming the s o l u b i l i t y of H 2 i n DMA remains the same over the temperature range 70 - 85\u00b0C. 34 2.78 2.82 . 2.86 2.90 (1\/T) x 1 0 3 , K - 1 Figure 8. Arrhenius p lot for the RhC l 3 (E t 2 S> 3 catalysed -3 -2 hydrogenation of maleic a c i d , (DMA, 5.145 x 10 M Rh, 3.0 x 10 M maleic ac i d ) . \u2022 35 Table VII V a r i a t i o n of rates w i t h added [ E ^ S ] i n DMA (80\u00b0C, J R h C l 3 ( E t 2 S ) 3 ) = 5.145 x 10\" 3 M , [MA)= 3.0 x 10\" 2 M , [ H 2 ] = 2.32 x l O * 3 M ) E t 2 S j I n i t i a l slope l \/ ( i n i t i a l slope) 2nd slope M x 10~* M sec * x 10 ~* M * sec x 10^ M sec Q.00 2.20 0.46 4.25 0.02 1.57 0.64 4.92 0.05 1.16 0.86 4.80 0.10 0.76 1.31 5.16 0.15 0.59 1.69 5.00 0.20 0.44 2.27 4.72 36 37 Xi U O n 0 4000 2000 Time, sec Figure 10. Rate p lots for the R h C l 3 ( E t 2 S ) 3 catalysed hydrogenation of maleic acid in the presence of added E t 2 S , 3 2 (80\u00b0C, DMA, 725 mm H 2 , 5.145 x 10* M Rh\u201e 3.0 x 10\" M maleic a c i d , E t 2 S ( Q ) \u00b0 - 1 5 M - ( A ) 0.20 M) Table V I I I V a r i a t i o n of ra t e s w i t h added [ L i C l ] i n DMA at 80\u00b0C ( [ R h C l 3 ( E t 2 S ) 3 ] = 5.145 x 10\" 3 M, [MA] = 3.0 x 10\" 2 M, (H ] = 2.32 x 10\" 3 M) [ci~] [ci0 4~] I n i t i a l slope 2nd slope 2 2 5 - 1 6 - 1 x 10 M x 10 M x 10 M sec x 10 M s e c 0.00 00.125 0.25 0.50 1.00 30.00 0.00 30.00 0.00 0.375 0.25 0.00 0.00 0.00 30.00 30.00 2.20 1.40 0.92 0.66 0.64 0.64 2.08 0.60 4.30 4.32 4.48 4.28 4.60 5.40 6.60 5.60 39 c h l o r i d e r e s u l t e d ; at higher c h l o r i d e c o n c e n t r a t i o n the i n i t i a l slope apparently decreased to a constant va.\\ue (Figure 11). E. Further gas uptake experiments. When w a s used instead of f o r the MA re d u c t i o n a s i m i l a r gas uptake p l o t was obtained. The rat e s i n d i c a t e small isotope e f f e c t s ( k ^ \/ k ^ 2 = 1.10 and k 2 H 2 \/ k 2 D 2 = 1.05). -3 For r e a c t i o n s of 5 x 10 M R h C l 3 ( E t 2 S ) 3 w i t h H 2 ( l atm t o t a l o \u2014 2 pressure) i n benzene at 55 C no gas uptake was apparent. When 5 x 10 M trans cinnamic a c i d was used as substrate under the same co n d i t i o n s no uptake of hydrogen occurred. However t h i s s ubstrate was homoseneously hydrogenated i n DMA w i t h a r a t e comparable to that of MA. When a ll^\/C^ti.^ mixed atmosphere (400 mm and 357 mm H 2) and -3 a 5 x 10 M R h C l 3 ( E t 2 S ) 3 were used ethylene underwent c a t a l y t i c hydrogenation af 80\u00b0C but the k i n e t i c s of t h i s system have not been studied further..No hydrogenation of ethylene occurred i n benzene at 50\u00b0C using (200 mm C^^, 200 mm H 2) and 5 x 10\" 3 M R h C l 3 ( E t 2 S ) 3 . F. Spectrophotomeric s t u d i e s . The v i s i b l e spectrum of R h C l 3 ( E t 2 S ) 3 i n DMA was recorded at room temperature (Figure 12). Absorption peaks appear at 370 m\/x ( e = 389) and 426 mjn. ( e = 308). On standing at room temperature the o p t i c a l d e n s i t y (O.D.) of the peak at ^ 26 m\/\/- very slowly decreased. O.D. changes were ac c e l e r a t e d by heating to 80\u00b0C (Figure 12). The change i n O.D. at 426 nux can r e a d i l y be followed as a f u n c t i o n of time. A p l o t of O.D. against time 41 0 I I I I j 350 450 550 Wave le n g t h , mjx. Figure 12. Absorption s p e c t r a of R h C l 3 ( E t 2 S ) 3 i n DMA. Immediately a f t e r d i s s o l v i n g R h C l - ( E t 9 S ) ~ i n DMA at room temperature; ' : \u2014 On heating the s o l u t i o n to 80\u00b0C f o r 15 min. at 80\u00b0C i s shown i n Figure 13. When excess d i e t h y l sulphide (10 : 1 r a t i o of Et^S : Rh) was a d d e d ; e s s e n t i a l l y the same absorption peaks appeared at 370 m>o( e = 380) and 426 m\/i. ( e = 317) but the O.D. d i d not change on standing at room temperature or heating to 80\u00b0C. When L i C l was added i n a 6 : 1 r a t i o ( L i C l : Rh) to a s o l u t i o n of RhCl-^Et^S).j i n DMA the spectrum obtained immediately a f t e r mixing at room temperature showed absorption peaks at 369 mju- ( \u00a3 = 394) and 421 mju- ( \u00a3 = 301). On standing f o r 20 minutes, the peaks were s h i f t e d s l i g h t l y to higher wavelengths. On heating to 80\u00b0C, the spectrum changed c o n s i d e r a b l y and showed absorption peaks at 381 mjx ( \u00a3 * 191) , 453 m\/x. ( \u20ac = 163) and a shoulder at 530 mjiX. ( \u00a3 1 1 46.7); the spectrum remained p r a c t i c a l l y constant on f u r t h e r standing or heating (Figure 14). On adding MA to a s o l u t i o n of R h C l 3 ( E t 2 S ) 3 i n DMA there was e s s e n t i a l l y no change i n the absorption peaks, (370 m\/t, \u00a3 = 381, 426 nju, \u00a3 = 298), even on heating to 80\u00b0C (Figure 15). The spectrum of a s o l u t i o n ( R h C l 3 ( E ^ S ) ^ and MA i n DMA) during the l i n e a r hydrogenation region i s shown i n Figure 15; an absorption peak at 359 mjx ( \u20ac~317) and a shoulder at 430 m\/x. ( 6-218) were observed. Samples taken at d i f f e r e n t stages throughout the l i n e a r uptake r e g i o n e x h i b i t e d e s s e n t i a l l y the same spectrum. The sp e c t r a of these s o l u t i o n s remained unchanged i n a i r f o r s e v e r a l days. The spectrum of R h C l - ^ E t ^ S ^ and cinnamic a c i d 5.n DMA a f t e r r e a c t i o n w i t h hydrogen showed e s s e n t i a l l y the same spectrum which remained p r a c t i c a l l y constant over a considerable period of time i n a i r . a 0 I I J I 350 400 450 500 Wave length, mju. Figure 14. Effect of added LiCl (6:1 ratio of Cl : 1 on the absorption spectra of RhCl.j(Et 2S) 3 in DMA. \u2022 Immediately after dissolving RhCl.j(Et 2S) 3 and LiCl in DMA at room temperature. On heating the solution to 80\u00b0C for 15 min. 45 o I L : i ; i 350 400 450 500 Wave le n g t h , mjx F i g u r e 15. Absorption s p e c t r a of RhCl ^ C E t , ^ ) ^ i n DMA i n the presence of maleic a c i d . The s o l u t i o n heated i n a i r to 80\u00b0C. \u2022 S o l u t i o n taken from the l i n e a r hydrogenation r e g i o n . 46 The v i s i b l e spectrum of R h C l 3 ( E t 2 S ) 3 recorded i n benzene showed absorption peaks at 370 m\/x ( 6 = 424) and 429 m\/x. ( \u00a3 = 344). On heating the spectrum was e s s e n t i a l l y unchanged. The spectrum of a benzene s o l u t i o n of RhCl^CEt^S)^, and trans cinnamic a c i d or ethylene which had been subjected to H 2 at 60 C gave the same spectrum as the i n i t i a l s o l u t i o n of the R h C l 3 ( E t 2 S ) 3 i n benzene (Figure 16) G. D i s c u s s i o n , The r e s u l t s i n d i c a t e that R h C l 3 ( E t 2 S ) 3 i n DMA s o l u t i o n i s an e f f i c i e n t c a t a l y s t f o r the homogeneous hydrogenation of maleic a c i d , trans cinnamic a c i d and ethylene. The only other sulphur c o n t a i n i n g metal complex reported to a c t i v a t e molecular hydrogen i s P t C l 2 ( S P h 2 ) 2 which however r e q u i r e s the presence of stannous c h l o r i d e as c o c a t a l y s t . This system reduces p o l y o l e f i n s to the monoene stage. ( i ) I n i t i a l r e g i o n . When MA was used as s u b s t r a t e , the i n i t i a l r a t e was given by the r a t e law dl\"2' - k j H 2 ] H (1) dt In analogy w i t h the RhCl 3.3H 20\/H 2\/MA 5 ' 4 7 system i n DMA, the i n i t i a l r e a c t i o n i s thought to i n v o l v e the r e d u c t i o n of R h ( I I I ) to R h ( I ) . The Rh(I) i s s t a b i l i s e d by complexing w i t h MA i n a r a p i d step preventing d i s p r o p o r t i o n a t i o n to the metal. This step i s f a s t since i n the absence of MA, metal i s r a p i d l y produced. The point of metal p r e c i p i t a t i o n i n the uptake experiments (Figure 2) i n d i c a t e s that the complex i s probably 1 : 1 species. The spectroscopic s t u d i e s (Figure 12 and 15) i n d i c a t e that there % 3 2 0 - 160 w 0 | I _ _ J I 350 400 450 500 Wave length, nui Figure 16. Absorption spectra of RhCl^CEt^S)^ in benzene at room temperature. 48 i s n o ' i n i t i a l c o m p l e x i n g o f R h ( I I I ) w i t h MA. The r e d u c t i o n o f R h ( I I I ) t o R h ( I ) must i n v o l v e hydrogen a c t i v a t i o n . 1-3 Among the t h r e e d i f f e r e n t ways of hydrogen a c t i v a t i o n ( C h a p t e r I , s e c t i o n C) h e t e r o l y t i c s p l i t t i n g , h o m o l y t i c s p l i t t i n g and d i h y d r i d e f o r m a t i o n ; h e t e r o l y t i c s p l i t t i n g w i t h the f o r m a t i o n o f R h ( I I I ) H i n t e r m e d i a t e i s most l i k e l y . The hydrogen l i g a n d s i n a d i h y d r i d e s p e c i e s a r e p r e s e n t as a n i o n i c l i g a n d s . D i h y d r i d e f o r m a t i o n w i t h R h ( I I I ) complexes would e f f e c t i v e l y i n c r e a s e t h e o x i d a t i o n s t a t e from I I I t o V, w h i c h i s q u i t e u n s t a b l e and r a r e f o r r h odium. Hence a c t i v a t i o n o f H.^ R h C l ^ C E t ^ S ) ^ 12> y i a t h i s mechanism i s h i g h l y u n l i k e l y . Some sq u a r e p l a n a r R h ( I ) and 22 A-8 I r ( I ) ' complexes a r e w e l l known t o r e a c t w i t h H^ t o g i v e o c t a h e d r a l R h ( I I I ) and I r ( I I I ) d i h y d r i d e s . Energy c a l c u l a t i o n s f o r h o m o l y t i c and h e t e r o l y t i c s p l i t t i n g o f 49 H 2 i n w a t e r f a v o u r the l a t t e r . I n DMA, a s o l v e n t o f m o d e r a t e l y h i g h p o l a r i t y , i t i s e x p e c t e d t h a t i o n i c s p l i t t i n g ( h e t e r o l y t i c s p l i t t i n g ) w o u l d be f a v o u r e d . H e t e r o l y t i c s p l i t t i n g i s s i m i l a r l y t h o ught t o be i n v o l v e d i n the RhCl 3.3H 20\/H 2\/MA ~ * s y s t e m i n DMA and aqueous s o l u t i o n s . H e t e r o l y t i c s p l i t t i n g i s o b s e r v e d i n the a c t i v a t i o n o f H 2 by R h C l 3 ( p y ) 3 . The Rh-H bond i n R h C l 2 H ( p y ) 3 has been d e t e c t e d by N.M.R. 5 0 . Other R h ( I I I ) h y d r i d e s such as [ R h ( C N ) 4 ( H 2 0 ) H ] 2 \" , [ R M N H ^ H ] 2 * , [ R h ( t r i e n ) C l H ] + 23 have been r e p o r t e d The f o l l o w i n g mechanism f o r t h e i n i t i a l r e a c t i o n i s s u g g e s t e d and i s c o n s i s t e n t w i t h the o b s e r v a t i o n s and k i n e t i c d a t a , ( i . e . 1 s t o r d e r 49 dependences on [Rh] and [H_] a n c* zero order dependence on [M A ] ) R h 1 1 1 + H 2 \u2014 > Rh I X IH\" + H + (3) Rh H \u00bb Rh + H (4) I f a s t - T Rh + MA \u2014 ) Rh ( M A ) (5) In absence of M A , 2 Rh 1 + H 2 > 2 Rh\u00b0 + 2H + (6) and\/or 2 Rh 1 -> R h 1 1 + Rh\u00b0 (7) The absence of any appreciable isotope e f f e c t ( k j ^ 2 \/ k ^2 _ i . i g ) suggests that the process i n v o l v i n g breaking of H-H bonds and making of Rh-H bonds i s synchronous. ( i i ) E f f e c t of added E t 2 S on i n i t i a l r a t e . The observed inverse dependence of the i n i t i a l r a t e on added E t 2 S (Figure 9) can be explained by assuming that H 2 reacts w i t h an i n t e r -mediate species ( I ) produced by d i s s o c i a t i o n of the i n i t i a l complex K Y \u2022' R h C l 3 ( E t 2 S ) 3 ; ^ * R h C l 3 ( E t 2 S ) 2 + E t 2 S (8) b (I ) R e a c t i v i t y of H 2 w i t h the i n i t i a l complex must be very low since the r e a c t i o n i s i n h i b i t e d on a d d i t i o n of E t 2 S . 50 I t i s l i k e l y that DMA, a c o o r d i n a t i n g s o l v e n t , w i l l occupy the vacant s i t e produced by d i s s o c i a t i o n of the i n i t i a l complex to give RhCl 3(Et 2 S) 2DMA. ' Evidence f o r the d i s s o c i a t i o n i s obtained from the spectroscopic s t u d i e s : on standing or heating the O.D. of a s o l u t i o n of R h C l 3 ( E t 2 S ) 3 i n DMA changed w i t h a corresponding s h i f t i n Xmax, whereas on adding E t 2 S to the same s o l u t i o n no change i n O.D. was observed. The f i n d i n g s 43 of Dwyer and Nyholm suggest that the d i s s o c i a t i o n of E t 2 S from t h i s complex i n aqueous a c i d a l c o h o l i c s o l u t i o n occurs much more r e a d i l y than the d i s s o c i a t i o n of the C l l i g a n d . The value of the e q u i l i b r i u m constant fo r the d i s s o c i a t i o n can be estimated from the k i n e t i c data. Taking i n t o account the suggested e q u i l i b r i u m ( 8 ) , the mechanistic scheme f o r the i n i t i a l r e d u c t i o n of R h ( I I I ) to Rh(I) now becomes : K RhCl (Et S) r ' R h C l 3 ( E t 2 S ) 2 + E t 2 S (8) k b R h C l 3 ( E t 2 S ) 2 + H 2 ~g > R h m C l 3 ( E t 2 S ) 2 H ~ + H + (9) determining and hence \" ^\"2) = k [ RhCl (Et S) ] [ H ) (10) dt The e q u i l i b r i u m i n (8) must be reached r e l a t i v e l y q u i c k l y compared w i t h the r a t e of r e a c t i o n (9) to give the observed 1st order dependence on [ H 2 ] ; the r a p i d s p e c troscopic changes observed at 80\u00b0C are i n agreement w i t h t h i s . 51 Since K =\u2022 [RhCl (Et S) ] [ E t S] [ R h C l 3 ( E t 2 S ) 3 ] and where Hence [ R h C l 3 ( E t 2 S ) 3 ] + [ R h C l 3 ( E t 2 S ) 2 ] = [ R h T ] [Rh T] = t o t a l s t a r t i n g [ R h C l 3 ( E t 2 S ) 3 ] K[Rh ] the r e f o r e [ R h C l 3 ( E t 2 S ) 2 ] = [ E t 2 s ] + K Rate = - d [ H 2 ] K k t [ H 2 l [ R h T ] dt [ E t ? s ] + K (11) (12) which accounts f o r the observed 1st order dependence on [Rh^,] and [ H 2 ] , and the inverse dependence on [ E ^ S ] . Equation (12) may be rearranged to give Rate Ks1 Kkt[H2]Kl + kt [ H 2 ] l R h T ] (13) ( I f the e q u i l i b r i u m i n (8) i s not r a p i d , a steady s t a t e treatment f o r the R h C l 3 ( E t 2 S ) 2 s p e c i e s , i n the above mechanism y i e l d s the r a t e law - d [ H 2 ] VtWKl dt kt[H2]'-+ k b [ E t 2 S l + k f (14) which i n d i c a t e s between zero and 1st order dependence on [ H \u201e ] . ) A p l o t of l \/ ( i n i t i a l r a t e ) against added[Et sjshown i n Figure (17), o U J 1 i I l 0 0.08 0.16 Added E t 2 S , M Figure 17. P l o t of l \/ ( i n i t i a l slope) against added [Et2s] , (80\u00b0C, DMA, 725 mm H 2, 5.145 x 10\" 3 M Rh, 3.0 x 10\" M maleic a c i d ) . 53 gives, a good s t r a i g h t l i n e i n accordance w i t h equation (13). This gives a value f or K at 80\u00b0C of 0.047M and f o r kfc of 1.97 M 1 sec : The average - 1 -1 value of k^ (1.89 M x sec ) evaluated, using equation ( 1 ) , i s a composite of the e q u i l i b r i u m constant, the r a t e constant and the [Et\u201es]. k i \" [ E ^ } \\ ~ <15> For k i n e t i c r e a c t i o n s using [^h^] of about 5.x 10 3 M, the value of K i n d i c a t e s that the complex d i s s o c i a t e s to the extent of ~90%. The magnitude of K i s thus large compared w i t h [ E ^ S ] . In the absence of added E t 2 S , and as shown by equation (15), k^ should then approximate to k^ as found. Thus the measured r a t e corresponds to r e a c t i o n of H 2 w i t h a R h C l . j ( E t 2 S ) 2 species and the determined a c t i v a t i o n parameters i H ^ = 12.9 kcal\/mole and & S * = -21.4 e^u. r e f e r to t h i s r e a c t i o n . ( i i i ) E f f e c t of added c h l o r i d e on i n i t i a l r a t e . The inverse dependence of the i n i t i a l r a t e w i t h added c h l o r i d e i s shown i n Figure 11. A lower l i m i t i n g r a t e i s reached at about a 1 : 1 r a t i o of | c i ] : [ R h | . This together w i t h the s p e c t r a l evidence (Figure 14) suggest that the i n h i b i t i o n i s due to the presence of a new higher c h l o r o species w i t h a lower r e a c t i v i t y . The i n h i b i t i o n upto the 1 : 1 r a t i o s t r o n g l y suggests that 1 mole of E t 2 S d i s s o c i a t e s per mole of R h C l ^ E t ^ S ^ ( S e c t i o n G ( i i ) above) and that the vacant c o o r d i n a t i o n s i t e i s probably replaced completely by c h l o r i d e . In the presence of added L i C l , both C l and DMA w i l l compete f o r the vacant c o o r d i n a t i o n s i t e . The l i m i t i n g r a t e at higher [ c l ], which i s about 1\/3 of that when no C l was added, i s thought to be due to r e a c t i v i t y of a [RhCl (Et S) ] \" sp e c i e s . The R h C l 3 ( E t 2 S ) 2 DMA species i s expected to be more e f f i c i e n t towards h e t e r o l y t i c s p l i t t i n g of than the [RhCl^CEt^S)^] species because of the e a s i e r displacement of the DMA molecule. I t should be noted that the data i n v o l v i n g the c h l o r i d e v a r i a t i o n do not analyse too w e l l q u a n t i t a t i v e l y f o r the scheme o u t l i n e d above. For example, the r a t e at 0.0025 M added CI should be at l e a s t equal toxthe sum of the r a t e at no added CI and the lower l i m i t i n g r a t e , that i s 1.42 M sec * (see F i g u r e 11); the a c t u a l r a t e i s about 0.92 M sec The data could be c o n s i s t e n t w i t h an o v e r a l l process i n which the i n i t i a l R h C l 3 ( E t 2 S ) 3 complex on d i s s o l u t i o n r a p i d l y l o s t some CI ion as w e l l as Et2S. Further experiment would be necessary to e l u c i d a t e more p r e c i s e l y the nature of the species i n s o l u t i o n . ( i v ) Solvent e f f e c t s on the i n i t i a l r e d u c t i o n process. When benzene was used as solvent i n s t e a d of DMA, no hydrogen r e d u c t i o n of R h ( I I I ) was observed e i t h e r i n the absence or presence of a sub s t r a t e (trans cinnamic a c i d or e t h y l e n e ) . .Hence i n the reduction of R h C l 3 ( E t 2 S ) 3 , the solvent plays a c r i t i c a l r o l e . Both p o l a r i t y and the c o o r d i n a t i n g a b i l i t y of the solvent i s l i k e l y to be important here. In g e n e r a l , r e a c t i o n s which produce ions i n s o l u t i o n are favoured i n more p o l a r s o l v e n t s . The increase i n r a t e i s governed l a r g e l y by the change i n entropy of a c t i v a t i o n during the formation of a polar t r a n s i t i o n s t a t e . DMA i s a p o l a r solvent w i t h d i e l e c t r i c constant 3 7 . 8 , a n d benzene i s non-polar, the d i e l e c t r i c constant being 2.3. As i n d i c a t e d e a r l i e r , the red u c t i o n i s thought to i n v o l v e h e t e r o l y t i c s p l i t t i n g of H,. and the formation 55 of i o n i c species (equation 3 ) ; t h i s r e a c t i o n w i l l c l e a r l y be more favourable i n DMA. The changes i n spectra of the RhCl ( E t ^ S ) ^ complex i n DMA were i n t e r p r e t e d i n ;\".erms of d i s s o c i a t i o n of the i n i t i a l complex (see equation 8 ) ; no s p e c t r a l changes were observed f o r benzene s o l u t i o n s of the complex. This d i s s o c i a t i o n i s not an i o n i c one so presumably the c o o r d i n a t i n g a b i l i t y and donor strength of the DMA solvent are important. Solvent a s s i s t e d 52 d i s s o c i a t i o n of octahedral complexes i s w e l l s u b s t a n t i a t e d . A number of t r a n s i t i o n metal complexes have been prepared which cont a i n DMA as a 53 l i g a n d , i n which i t i s thought to be coordinated through the oxygen The a c t i v a t i o n parameters f o r the r e d u c t i o n step (AH^ =12.9 2 kcal\/mole and = - 2 1 . 4 e.u.) are c l o s e to those reported f o r the H r e d u c t i o n of R h C l 3 . 3 H 2 0 i n DMA ( A H * = 1 7 . 3 kcal\/mole, = - 9 . 2 e.u.) under s i m i l a r c o n d i t i o n s . The negative value and magnitude of AS* i s of the order expected f o r a r e a c t i o n i n v o l v i n g the formation of ions from n e u t r a l 5 4 molecules i n such a solvent (v) C a t a l y t i c hydrogenation of maleic a c i d . I t i s thought that the Rh(I)-MA complex formed i n the hydrogen re d u c t i o n of R h ( I I I ) to Rh(I) ( G ( i ) equations 3 to 5) i s the a c t i v e species f o r homogeneous hydrogenation. Metal deposited when the amount of uncomplexed MA present was i n s u f f i c i e n t to s t a b i l i s e the R h ( I ) . The complexing of. MA w i t h Rh(I) occurs r a p i d l y and the r a t e determining hydrogenation step i s thought to be the subsequent r e a c t i o n of 56 the Rh(I)*MA complex w i t h to y i e l d s u c c i n i c a c i d and the Rh(I) species again which r a p i d l y complexes w i t h f u r t h e r maleic a c i d . F o l l o w i n g production of Rh(I) from R h ( I I I ) , the mechanistic scheme c o n s i s t e n t wi;h the k i n e t i c data i s shown below I k 2 I Rh (MA) + H 2 > Rh + SA (16) Rh 1 + MA f a S t > Rh I(MA) (17) SA = s u c c i n i c a c i d , other coordinated ligands are omitted. The above mechanism gives the r a t e law observed i n the l i n e a r region of the uptake p l o t - d ! H 2 ] f I I f l \u00b1- = k [Rh (MA)J [H_ J ^ v ^ J L . < 2 , (2) dt The c o n c e n t r a t i o n of the Rh(I)-MA complex i s equal to the t o t a l Rh c o n c e n t r a t i o n once a l l the R h ( I I I ) i s reduced. Hence at constant H 2 pressure, the r e a c t i o n becomes one of pseudo zero order. The Rh(I) species produced i n the i n i t i a l r e d u c t i o n v \/ i l l be l a b i l e and of the form R h C l x ( E t 2 S ) ^ ( D M A ) z where xVy+z i s probably 4. This hydro-genation may thus be compared to the homogeneous hydrogenation of o l e f i n s 12 c a t a l y s e d by R h C l ( P h 3 P ) 3 which d i s s o c i a t e s i n s o l u t i o n to give R h C l ( P h 3 P ) 2 ~ ( s o l v e n t ) . In the l a t t e r system no metal has been observed at any stage of the r e a c t i o n . The E t 2 S l i g a n d i s a weaker -jr acceptor than Ph 3P and the Rh(I) s u l f i d e species i s not so h i g h l y s t a b i l i s e d as i s seen by i t s f a c i l e r e d u c t i o n by H 2 to the metal. A f u r t h e r coordinated ir acceptor o l e f i n 57 i s necessary f o r s t a b i l i s a t i o n . The mechanism f o r c a t a l y t i c hydrogenation can be thought of as i n v o l v i n g three b a s i c steps (a) substrate a c t i v a t i o n (b) hydrogen a c t i v a t i o n (c) hydrogen t r a n s f e r . For the present system these 3 b a s i c steps are l i k e l y to be present. The s u b s t r a t e a c t i v a t i o n occurs through r a p i d c o o r d i n a t i o n of MA to Rh(I) to give a Rh(I)-MA complex. For reasons mentioned e a r l i e r i n s e c t i o n ( G ( i ) ) homolytic s p l i t t i n g of hydrogen i s u n l i k e l y . The f o l l o w i n g scheme i n v o l v i n g a h e t e r o l y t i c s p l i t t i n g of can be w r i t t e n i n analogy w i t h the Ru(II)-MA complex i n 3M HCI system H\" \\ \/ C Rh-H, V slow Rh-C \/ \\ f a s t \\ \/ + C = C \/ \\ C \/ \\ \\ \/ \u2014 R h \u2014 + H \u2014 C \u2014 C \u2014 H <r \/ \\ H* Rh-\"A Rh\u2014C C\u2014H \/ \\ Such a s p l i t t i n g of R would r e s u l t i n the i n i t i a l formation of a Rh(I)-hydrido 7? o l e f i n complex. I n s e r t i o n of o l e f i n i n t o the Rh-H bond then produces a Rh(I) <r a l k y l complex and hydrogenation i s completed by e l e c t r o p h i l i c a t t a c k on the metal bonded carbon atom by a proton. A Rh(I)-hydrido TT o l e f i n complex i s not unreasonable e s p e c i a l l y i n view of the presence of the TT acceptor l i g a n d s . Intermediates as such have been detected 25 i n l t h e platinum metal systems . Some Rh(I) <r a l k y l complexes have a l s o 55 been c h a r a c t e r i s e d 8 In the Ru(II)-MA system i t has been shown by t r a c e r s t u d i e s that the H + which completes the r e a c t i o n comes from the 3M HCI s o l v e n t . DMA i s a non-protonic solvent and the proton c o n c e n t r a t i o n w i l l be low, being governed by the h e t e r o l y t i c s p l i t t i n g of the H 2\u2022 Hence the step i n v o l v i n g e l e c t r o p h i l i c a t t a c k by a proton i s thought to be rat h e r u n l i k e l y . An a l t e r n a t i v e mechanism i n v o l v i n g h e t e r o l y t i c s p l i t t i n g of H 2 and c o n s i s t e n t w i t h the k i n e t i c data could i n v o l v e a r a t e determining r e a c t i o n w i t h ky t n e \u00b0~ a l k y l complex H~ \\ - \/ slow I \\ \/ R h \u2014 C \u2014 C \u2014 H + H\u201e > \u2014 R h \u2014 + H \u2014 C \u2014 C \u2014 H \/ \\ 2 I \/ \\ > f a s t \/ C \\ Such r e a c t i o n s of rhodium phenyls w i t h hydrogen to y i e l d metal hydrides have 55 been po s t u l a t e d . However t h i s i m p l i e s a qui t e k i n e t i c a l l y and a i r s t a b l e Rh(I) <r a l k y l complex; a more l i k e l y mechanism i n v o l v i n g the pe r s i s t e n c e of a square planar Rh(I) o l e f i n complex - w e l l s u b s t a n t i a t e d g e n e r a l l y - i s given below. H e t e r o l y t i c s p l i t t i n g of H 2 i s not too probable and the most l i k e l y mechanism f o r hydrogen a c t i v a t i o n i s thought to be through d i h y d r i d e formation. Dihydride formation has been observed and proposed i n the 12 c a t a l y t i c hydrogenation of o l e f i n s by the square planar RhClCPh^P)^ and I r C l C O ( P h 3 p ) 2 2 0 > 2 2 complexes. The hydrogenation would then proceed by o x i d a t i v e - a d d i t i o n of H 2 to the square planar RhL^ ( o l e f i n ) complex followed by subsequent h y d r o m e t a l l i t i o n of the o l e f i n i c bond: (where L \u2014 C I , E t 2 S or s o l v e n t ) 12 The a c t u a l step i n v o l v i n g t r a n s f e r of hydrogen i s u n c e r t a i n . W i l k i n s o n has suggested that i n the s i m i l a r RhCl(Ph.jP) 3 system the t r a n s f e r of both hydrides i s simultaneous, each by a 3 centre t r a n s i t i o n s t a t e i f the o l e f i n occupies a p o s i t i o n c i s to both the Rh-H bonds. H ? D2 The low k i n e t i c i s o t o p e e f f e c t o b t a i n e d ( k 2 = 1-05) s u g g e s t s the s y n c h r o n o u s b r e a k i n g o f R h - H bonds and making o f C - H bonds, t a k i n g p l a c e p o s s i b l y v i a t h e t r a n s i t i o n s t a t e i n v o l v i n g two s i m u l t a n e o u s 3 c e n t r e bonds. The a c t i v a t i o n p a r a m e t e r s A = 2 1.4 k c a l \/ m o l e and A S 2 = - 1 . 0 e.u. a r e i n a range t y p i c a l of a b i m o l e c u l a r r e a c t i o n i n s o l u t i o n between 54 an i o n and a n e u t r a l m o l e c u l e ; t h i s s u g g e s t s t h e R h ( I ) s p e c i e s i s a n i o n i c and l i k e l y t o be t h e [ R h * C l 2 ( E t 2 S ) ( M A ) ] s p e c i e s . S i m i l a r a c t i v a -t i o n p a r a m e t e r s ( A H ^ = 1 8.4 k c a l \/ m o l e , A S * = - 6 . 1 e.u.) were o b t a i n e d f o r a c o r r e s p o n d i n g s t e p i n t h e c a t a l y t i c h y d r o g e n a t i o n o f m a l e i c a c i d by 5 47 c h l o r o r h o d a t e ( I ) s p e c i e s i n D M A a t h i g h c h l o r i d e c o n c e n t r a t i o n ' . The a c t i v i t y o f t h e d i e t h y l s u l p h i d e c o n t a i n i n g complex i s about l \/ 5 t h t h a t o f t h e c h l o r o complex. R e a c t i o n s o f t h i s t y p e a r e e x p e c t e d t o be f a v o u r e d i n a medium o f lower d i e l e c t r i c c o n s t a n t . The f a c t t h a t i n benzene t h e r e i s no h y d r o g e n a t i o n o f t h e s u b s t r a t e s r e s u l t s from t h e i n h i b i t i o n o f the i n i t i a l r e d u c t i o n p r o c e s s w h i c h depends on the a v a i l a b i l i t y o f a v a c a n t s i t e f o r p r o d u c t i o n , o f t h e R h ( I ) s p e c i e s . (See S e c t i o n G ( i v ) ) . Ah i n t e r m e d i a t e or a c t i v a t e d complex i n w h i c h b o t h o l e f i n and H 2 a r e c o o r d i n a t e d t o t h e m e t a l atom seems n e c e s s a r y f o r h y d r o g e n a t i o n t o 22 o c c u r . F o r example, I r C l C 0 ( P h 3 P ) 2 i n benzene ' and R h C l ( P h 3 P ) 3 i n 12 p y r i d i n e o r a c e t o n i t r i l e f orm d i h y d r i d c s v e r y r e a d i l y and r e v e r s i b l y , but a r e u n a b l e t o h y d r o g e n a t e o l e f i n s a t 25\u00b0C and 1 atmosphere s i n c e t h e y a r e c o o r d i n a t i v e l y s a t u r a t e d and have no v a c a n t s i t e f o r o l e f i n c o o r d i n a t i o n . I f a s o l v e n t a s s i s t e d d i s s o c i a t i o n o f one of t h e Ph^P l i g a n d s o c c u r s , the 12 22 complexes become a c t i v e f o r h y d r o g e n a t i o n ' . A d d i t i o n o f e x c e s s Ph^P i n t h e above systems r e v e r s e s t h e d i s s o c i a t i o n and h y d r o g e n a t i o n i s i n h i b i t e d , A d d i t i o n of L i C l upto 0.3 M or Et^S up to 0.2 M d i d not a f f e c t the hydrogenation r a t s . The MA l i g a n d must then compete e f f e c t i v e l y w i t h CI or Et^S ligands f o r a s i t e on the square planar complexes. As expected the a f f i n i t y of Rh(I) f o r a Et^S l i g a n d i s not as high as f o r Ph\u201eP, a stronger IT acceptor. CHAPTER IV CATALYTIC PROPERTIES OF SOME RELATED Ir AND Rh COMPLEXES A few preliminary experiments have been carried out with a number of related and relevant iridium and rhodium complexes. The results are summarized below. A. IrCl 3(Et 2S> 3 systems. Small amounts of the cis and trans isomers of the I r C l 3 ( E t 2 S ) 3 complex were prepared and identified from their m.p. and colour. A solution of the cis isomer in DMA (4 x 10 2 M [ir]) reacted very slowly with H2(730mm) at 80\u00b0C in the absence of substrate. The uptake seemed to level off at a stage corresponding to reduction of Ir(III) to Ir(II) but further experiments are necessary to substantiate this (Figure 18). The f i n a l solution at this stage however did not act as homogeneous hydrogenation catalyst for maleic acid. Studies with the cis isomer of I r C l 3 ( E t 2 S ) 3 in benzene solution at 56\u00b0C (4 x 10~2 M [ir] , 409 mm H2> in absence of substrate showed no hydrogen uptake over a period of 4 hours. -3 The trans isomer (7 x 10 M) in DMA showed no reaction with hydrogen (730 mm) at 80\u00b0C over a period of 3 hours. It did not act as a homogeneous hydrogenation catalyst for maleic acid under the same conditions, 1 . 5 0 4000 8000 12,000 Time, sec Fig u r e 18. Rate' p l o t f o r the r e a c t i o n between and IrCl.j(Et2S) (80\u00b0C, DMA, 725 mm H 2, 4 x 10~ 2 M I r ). 64 B. R h ( I I I ) d i f a r s and R h ( I I I ) d i a r s systems. At 80\u00b0C and 730 mm H 2 , a s o l i t i o n of R h ( I I I ) d i f a r s (3.18 x 10~ 3 M) i n DMA underwent r e a c t i o n w i t h hydrogen. The st o i c h i o m e t r y of the r e a c t i o n corresponded approximately to 2 moles of H 2 uptake f o r every mole of Rh used and the uptake p l o t s gave good 1st order l o g p l o t s . (Figure 19). However, R h ( I I I ) d i f a r s i n DMA was not a c t i v e f o r hydrogenation of maleic or fumaric a c i d s . P r e l i m i n a r y s t u d i e s i n d i c a t e d that the hydrogen r e a c t i o n i s 1st order i n [^h] arid between zero and 1st order i n [H 2 ] \u2022 No hydrides were detected by N.M.R. stud i e s at the end of the r e a c t i o n s . The R h ( I I I ) d i a r s complex was not very s o l u b l e i n DMA even at 80\u00b0C but d i s s o l v e d e a s i l y i n dimethyl sulphoxide. K i n e t i c studies i n d i c a t e d that the complex d i d not undergo r e a c t i o n w i t h hydrogen i t s e l f . C. D i s c u s s i o n . ( i ) I r C l 3 ( E t 2 S ) 3 systems. The c i s and trans I r C l 3 ( E t 2 S ) 3 complexes do not homogeneously hydrogenate o l e f i n s i n benzene or DMA. There are as yet no re p o r t s of I r ( I I I ) complexes being a c t i v e f o r homogeneous hydrogenation. Both c a t i o n i c and a n i o n i c complexes of I r ( I I I ) are s u b s t i t u t i o n i n e r t ^ and t h i s w i l l be an important f a c t o r i f c o o r d i n a t i o n s i t e s f o r both hydrogen and o l e f i n are to be made a v a i l a b l e . The only I r complexes that have been found to e f f e c t i v e l y hydrogenate o l e f i n s 22 20 are the more l a b i l e I r ( C O ) C l ( P h 3 P ) 2 i n DMA, or benzene and IrHCQ(Ph 3P) 3 i n benzene. 65 Time, sec Figure 19. Rate p l o t and the corresponding log p l o t f o r the r e a c t i o n between H 2 and R h ( I I I ) d i f a r s , (80\u00b0C, DMA, 362 mm H 2, 3.18 x 10\" 3 M Rh ) . ( Q ) H 2 absorbed; ( A ) L\u00b08 [ R h I 1 1 ] \u2022 66 In analogy w i t h the RhCl ( S t 2 S ) system i n DMA (see Chapter I I I ) i t would appear that r e d u c t i o n of I r ( l I I ) to I r ( I ) i s necessary f o r the production of a l i k e l y c a t a l y s t . This v,ould presumably occur through h e t e r o l y t i c s p l i t t i n g of H^: I r + H 2 \u00bb I r K + H I r i d i u m ( I I I ) hydrides can be formed q u i t e r e a d i l y but u n l i k e t h e i r 58 rhodium analogues, they do not r e a d i l y transform to the u n i v a l e n t s t a t e according to the equation I r H > I r + H This d i f f e r e n c e can be a s c r i b e d to the somewhat increased strength of Ir-H bonds compared to the Rh-H bonds and the higher energy r e q u i r e d f o r the 12 conversion of Rh(I) to R h ( I I I ) -2 A 4 x 10 M s o l u t i o n of c i s I r C l . j ( E t 2 S ) 3 undergoes a slow r e a c t i o n w i t h hydrogen i n the absence of substrate i n DMA but not i n benzene s o l u t i o n . This solvent e f f e c t could again be r a t i o n a l i s e d i n terras of donor s t r e n g t h , p o l a r i t y and s o l v a t i o n power. The H 2 uptake appears to be approaching an amount corresponding to r e d u c t i o n of I r ( I I I ) to I r ( I I ) but t h i s seems to be an u n l i k e l y product from an intermediate I r * * * H species. I r ( I I ) has been reported to occur i n some complexes i n c l u d i n g ammines ( i r ( N H ^ ) ^ ] C l ^ and a s u l f i t o complex, N a ^ [ i r ( S O ^ ) ^ ] . l O i ^ O , but none of these are u n e q u i v o c a l l y 59 e s t a b l i s h e d . Further s t u d i e s would be necessary to i n v e s t i g a t e the nature of t h i s hydrogen r e a c t i o n . 67 The f a c t that the trans I r C l ^ E ^ S ) ^ complex does not undergo r e a c t i o n \\ ' i t h may be r e l a t e d to s t e r i c f a c t o r s . The d i f f e r e n c e i n c a t a l y t i c hydrogenation a c t i v i t y between rhodium and i r i d i u m sulphur complexes i l l u s t r a t e s the importance of the o x i d a t i o n s t a t e of the metal atom and the l a b i l i t y and s t a b i l i t y of the hydrido intermediate formed. ( i i ) R h ( I I I ) d i f a r s and R h ( I I I ) d i a r s systems. The r e s u l t s i n d i c a t e that i n the R h ( I I I ) d i f a r s system., 2 moles of H 2 a t e consumed f o r every mole of Rh used although the complex does not act as a homogeneous hydrogenation c a t a l y s t f o r maleic a c i d . The s t o i c h i o m e t r y suggests 2 a l t e r n a t i v e s ; (1) r e d u c t i o n of R h ( I I I ) to Rh(I) followed by f u r t h e r o x i d a t i o n - a d d i t i o n of H 2 to form a d i h y d r i d e : -,+ (1) As As Rh C l I I I \" C l As 'As H, - i + As As Rh As +H, As -1 + 6 8 The intermediate i n v o l v e d i n e i t h e r scheme would be The 1st a l t e r n a t i v e seems to be somewhat l e s s l i k e l y s i n c e no Rh-H bond s i g n a l was detected by N.M.R. stud i e s and the R h ( I I I ) d i f a r s complex which contains 2 c h e l a t i n g ligands i s expected to be l e s s s u s c e p t i b l e to r e d u c t i o n by H att a c k . The 2nd a l t e r n a t i v e i s thus favoured; the hydrogenation of the o l e f i n i c bond i n the d i f a r s l i g a n d could be compared. w i t h . t h s c a t a l y t i c hydrogenation of o l e f i n s v i a an intermediate hydride produced by h e t e r o l y t i c s p l i t t i n g of the R^, but i n t h i s case the o l e f i n i s already present as part of a coordinated l i g a n d . The f a c t that the Rh ( I I I ) d i a r s complex does not undergo r e a c t i o n w i t h under s i m i l a r c o n d i t i o n s .(DMA and DMSO have very s i m i l a r solvent p r o p e r t i e s ) lends f u r t h e r support f o r the 2nd a l t e r n a t i v e . I t i s 45 known that the R h ( I I I ) d i a r s c a t i o n i s very s t a b l e i n s o l u t i o n and hence i s very u n l i k e l y to be reduced by E^ t o R h ( I ) . The greater s t a b i l i t y of the double bonds i n the phenyl r i n g s of the d i a r s complex r e l a t i v e to those i n the t e t r a f l u o r o c y c l o b u t e n e r i n g s of the d i f a r s complex could account f o r the l a c k of hydrogenation of the former. The i n a b i l i t y of the R h ( I I I ) d i f a r s complex to homogeneously hydrogenate maleic a c i d cannot be discussed i n any d e t a i l because i t i s not known whether the l a c k of i n i t i a l formation of a Rh(I) species i s re s p o n s i b l e f o r the i n a c t i v i t y of the complex. I f process (1) i s o c c u r r i n g , the r e s u l t i n g R h ( I I I ) d i h y d r i d e w i l l i n any case have no vacant s i t e f o r c o o r d i n a t i o n of an o l e f i n arid i t would not be expected to be c a t a l y t i c a l l y a c t i v e . These experiments were c a r r i e d out w i t h a view to i n v e s t i g a t e the e f f e c t of c h e l a t i n g ligands on c a t a l y t i c a c t i v i t y . Recently ^ a square planar Rh(I) complex w i t h the c h e l a t i n g diphosphine Me2PCH2CH2PMe2 (dmpe) has been shown to undergo r e v e r s i b l e o x i d a t i v e - a d d i t i o n r e a c t i o n s : H However no informa t i o n about i t s c a t a l y t i c a c t i v i t y was reported. REFERENCES 1. J . Halpern, Ann. Rev. Phys. Chem., IS, 103 (1965). 2. J . Halpern, Proc. 3rd I n t e r n . C a t a l y s i s Amsterdam, 1964; North Holland, Amsterdam, V o l . 1, 1965, p.146. 3. J . Halpern, Chem. Eng. News, 44, (45), 68 (1966). 4. M. C a l v i n and W.K. Wilmarth, J . Am. Chem. S o c , 78, 1301 (1956), 5. B.R. James and G.L. Rempel, Can. J . Chem., 44, 233 (1966). 6. J.F. Harrod and J . Halpern, Can. J . Chem., 37, 1933 (1959). 7. B.R. James and J . Halpern, Can. J . Chem., 44, 671 (1966). 8. J . Halpern, J.F. 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