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Complexation and hydrogenation of olefins by chlororuthenate (II) in aqueous acid solution King, Roy James 1973

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COMPLEXATION AND HYDROGENATION OF OLEFINS BY CHLORORUTHENATE(II) IN AQUEOUS ACID SOLUTION BY ROY JAMES KING B.Sc. (Hons.), U n i v e r s i t y of B r i t i s h Columbia, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In the Department of CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1973 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 the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the 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 study. I f u r t h e r agree 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 purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of 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 not be a llowed without my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada - i i -ABSTRACT The formation of 1:1 ir-complexes between chlororuthenate(II) and a s e r i e s of substituted ethylenes i n aqueous hydrochloric acid s o l u t i o n i s described. K i n e t i c studies of the complexation f o r maleic, a c r y l i c and c r o t o n i c a c i d substrates are presented. The l i k e l y mechanism i s a two step process i n v o l v i n g an i n i t i a l S ^ l d i s s o c i a t i o n of a chlororuthenate(II) complex or complexes. The nature of the blue chlororuthenate(II) species i s uncertain and th i s prevents r e s o l u t i o n of some questions about the mechanism; however, observations on the behavior of the blue solutions and some suggestions as to t h e i r p o s s i b l e nature are given. A c r y l i c and crotonic acids are hydrogenated c a t a l y t i c a l l y v i a the ruthenium(II) ir-complexes. Crotonaldehyde and c r o t o n i t r i l e complexes of chlororuthenate(II) are not hydrogenated but undergo hydration and/or polymerization. K i n e t i c data f o r the hydrogenation of the organic acids f i t a w e l l established mechanism. The fa c t o r s which influence r e a c t i o n rates i n the hydrogenation steps are thoroughly discussed. / - i i i -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v i LIST OF FIGURES v i i i ABBREVIATIONS x i ACKNOWLEDGEMENT x i i i CHAPTER I. INTRODUCTION 1 A. Aim of Work 1 B. Homogeneous Catalysis 2 C. Homogeneous Catalysis by Ruthenium Complexes 3 1. Hydrogenation of Inorganic Substrates 3 2. Polymerization of Olefins and Acetylenes 3 3. Acetylene and Olefin Hydration 5 4. Carbonylation and Decarbonylation Reactions ... 6 D. Olefin Hydrogenation 7 1. Systems Involving Ru(II) Complexes in Aqueous Media 7 2. Systems Involving Ru(II) and Ru(I) Complexes in Dimethylacetamide 9 3. Systems Involving Ru(II)-Phosphine Complexes .. 11 4. Systems Involving Other Ru Complexes 16 CHAPTER II. APPARATUS, MATERIALS AND EXPERIMENTAL PROCEDURE 18 A. Materials 18 - i v -Page B. Procedure and Apparatus for the Measurement of the Uptake of Hydrogen Gas 20 C. Procedure for Measurement of Complexation Rates ... 23 D. Procedure for Measurement of Formation Constants... 26 CHAPTER III. THE Ru(IV)-Ti(III) REACTION 27 CHAPTER IV. THE RUTHENIUM(II)-MALEIC ACID SYSTEM 33 A. Complex Formation 33 1. Stoichiometry 33 2. Kinetics 33 3. Discussion 39 CHAPTER V. THE RUTHENIUM(II)-ACRYLIC ACID SYSTEM 56 A. Complex Formation 56 1. Stoichiometry 56 2. Kinetics 59 3. Discussion 62 B. Hydrogenation of Acrylic Acid 70 1. Kinetics 7 0 2. Discussion 73 CHAPTER VI. THE RUTHENIUM(II)-CROTONIC ACID SYSTEM 77 A. Complex Formation 77 1. Stoichiometry 7 7 2. Kinetics 8 1 3. Discussion 87 - v -Page B. Hydrogenation of Crotonic Acid 89 CHAPTER VII. REACTIONS OF RUTHENIUM(II) WITH CROTONALDEHYDE, CROTONITRILE, VINYL HALIDES, AND DIACETONE ACRYLAMIDE.. 95 A. Crotonaldehyde Experiments 95 B. Crotonitrile Experiments 96 1. Hydrogenation Attempts 96 2. Complexation Experiments 96 C. Vinyl Chloride and Vinyl Fluoride Experiments 97 D. Diacetone Acrylamide Experiments 97 CHAPTER VIII. GENERAL DISCUSSION 101 A. Formation of the Ruthenium(II)-Olefin Complexes ... 101 B. Additional Comments on the Solutions of Chlororuthenate(II) 113 C. Catalytic Hydrogenation 114 REFERENCES 121 / - v i -LIST OF TABLES Table The complexation of chlororuthenate(II) by maleic acid I. Kinetic data. Effect of variation of maleic acid concentration on the rate constants k' and k' c II Kinetic data. Effect of variation of ruthenium, acid, and chloride concentrations on the rate constant k'. III Derived rate constants from the corrected data IV Derived rate constants from the uncorrected data ... V Arrhenius activation parameters for the rate constant k l VI Effect of varying chloride concentration on the i n i t i a l absorbance of Ru(II)-olefin solutions The ruthenium(II)-acrylic acid system V i i Kinetic data for the complexation of chlororuthenate-(II) by acrylic acid VIII Derived rate constants for the complexation IX Kinetic data for the hydrogenation of the complex .. The ruthenium(II)-crotonic acid sytem X Kinetic data for the complexation of chlororuthenate-(II) by crotonic acid XI Derived rate constants for the complexation XII Kinetic data for the hydrogenation of the complex .. / The complexation of chlororuthenate(II) by crotonitrile XIII Kinetic data at 60° - v i i -Table Page General discussion XIV Summary of the kinetic data for a series of complexa-tions between chlororuthenate(II) and various substrates 102 XV Summary of kinetic data for the Ru(II)-catalyzed hydrogenation of various olefins 115 - v i i i -LIST OF FIGURES Figure Page 1 Absorption spectrum of "(NH 4) 2Ru(H 20)C± 5" i n 3 M HC1 19 2 Apparatus for constant pressure gas-uptake measure-ments 21 3 Apparatus for the kinetic study of the chloro-ruthenate(II)-maleic acid reaction 25 4 Absorption spectrum of Ru(II) i n 3 M HC1 28 5 Variation with time of the absorbance at 680 mp of a Ru(II) solution 29 6 Absorbance at 680 mp of a Ru(II) solution thermo-statted at alternate temperatures of 60 and 80° .... 31 The complexation of chlororuthenate(II) by maleic acid 7 Effect of the presence and absence of maleic acid on the absorbance, at 680 mp, of Ru(II) solutions 35 8 First-order rate plots 36 9 Plots of k' vs. [M.A.] 40 c 10 Typical plot of 1/k^ vs. 1/[M.A.] 41 11 Typical plot of [M.A.]/k^ vs. [M.A.] 41 12 Arrhenius plot of kn (k. from intercepts of 1/k' l c l c c vs. 1/[M.A.] plots) 46 13 Arrhenius plot of k^ c (k^ c from slopes of [M.A.]/k^ _ vs. [M.A.] plots) 46 14 Arrhenius plot of k^ (k^ from intercepts of 1/k' vs. 1/[M.A.]) 48 15 Arrhenius plot of k^ (k^ from slopes of [M.A.]/k' vs. [M.A. ]) 48 16 Effect of Li C l on spectra of Ru(II) in 2 M HC1 50 17 Effect of chloride concentration on the i n i t i a l absorbance of Ru(II)-formic acid solutions 52 - ix -18 Effect of chloride on the Ru(II)-formic acid reaction rate . 54 The ruthenium(II)-acrylic acid system 19 Variation with time of the absorbance at 680 my of Ru(II)-acrylic acid solutions 57 20 Beer's law plot for chlororuthenate(II) solutions i n 3 M HC1 60 21 "Equilibrium absorbance" of Ru(II)-acrylic acid solutions versus acrylic acid concentration 61 22 Plot of (T L + A/e M) vs. e^/A 61 23 Typical plot of absorbance at 680 mu versus time for the Ru(II)-acrylic acid complexation 64 24 Typical plots of log A vs. time 64 25 Plots of k'1 vs. [A.A.] 65 26 Plot of log(k_ 1[L ]/k 2)vs. 1/Temperature 67 27 Arrhenius plot of k^ 69 28 Typical rate plots for the hydrogenation of acrylic acid 71 29 Dependence of the rate of R^-gas uptake on £ ^ u * * ] ; T j o t a ; L 7^ 30 Arrhenius plot of k^» rate constant for the hydrogenation of acrylic acid 75 The ruthenium(II)-crotonic acid system 31 Variation with time of the absorbance at 680 my of Ru(II)-crotonic acid solutions 78 32 "Equilibrium absorbance" of Ru(II)-crotonic acid solutions versus crotonic acid concentration 79 33 Plot of (T L + A/e M) vs. (e^/A) 80 34 Typical plots of log A vs. time 83 35 Plots of k' vs. [C.A.] 84 - x -F i g u r e Page 36 P l o t s of k' and k' v s . [C.A.] at 33° 85 c 37 P l o t of 1/k' vs. 1/[C.A.] at 50.9 and 60.7° 85 38 P l o t s of 1/k' and 1/k' v s . 1/[C.A.] at 33° 86 c 39 Arrhenius p l o t of \c 90 40 T y p i c a l p l o t s of the Ru(II) c a t a l y z e d hydrogenation of c r o t o n i c a c i d 91 41 Arrhenius p l o t of k^ f o r the hydrogenation of c r o t o n i c a c i d 94 42 A b s o r p t i o n spectrum of the r u t h e n i u m ( I I ) -99 c r o t o n i t r i l e complex - x i -ABBREVIATIONS The following l i s t of abbreviations, most of which are commonly adopted i n chemical research literature, w i l l be employed in this thesis. A l l temperatures are i n °C unless specifically denoted °K." A. absorbance A.A. acrylic acid acac acetylacetonate atm. atmosphere bipy 2,2'-bipyridyl C. A. crotonic acid D. A.A. diacetone acrylamide D.M.A. dimethylacetamide e.s.r. electron spin resonance Et ethyl hr. hour i . r . infrared K formation (equilibrium) constant k rate constant L ligand * L expelled ligand M metal atom or moles/litre M.A. maleic acid / Me methyl mu millimicrons (nanometers) - x i i -n.m.r. n u c l e a r magnetic resonance Ph phenyl PPh^ t r i p h e n y l phosphine R a l k y l s. seconds T temperature or t o t a l u.v. u l t r a v i o l e t v i s . v i s i b l e V.P.C. vapor phase chromatography f AH enthalpy of a c t i v a t i o n + AS entropy of a c t i v a t i o n e molar e x t i n c t i o n c o e f f i c i e n t / / • - x i i i -ACKNOWLEDGEMENT I am g r a t e f u l f o r the guidance and the encouragement I received from Dr. B.R. James throughout the course of t h i s work. I would also l i k e to thank Mr. Larry Markham f o r assistance with the text. - 1 -/CHAPTER I INTRODUCTION A. Aim of Work Studies on chlororuthenate(II) i n aqueous acid solution showed that such species could form complexes with olefins and subsequently catalyze the hydrogenation of these olefins, provided that the double bond had a carboxylic acid group adjacent to i t . ^ A later study showed that fluoro olefins could also be complexed, and that the fluoro 2 groups could also activate the double bond. However, the product i n this latter case turned out to be one of hydration rather than hydrogenation. This thesis i s concerned with some of the questions that arose from such studies, namely: 1. Complex formation What is the mechanism by which the olefin complexes are formed, and what factors affect the complexation? 2. Hydrogenation a) Could electron-withdrawing substituents other than the carboxylic acid group activate the double bond for hydrogenation? b) What i s the correlation between the rates of hydrogenation and the s t a b i l i t i e s of the Ru(II)-olefin complexes? - 2 -B. Homogeneous Catalysis Over the last decade an enormous amount of data has been collected and published on transition metal complexes as catalysts in homogeneous systems. A few of the many reactions which make use of these catalysts are: 1. Hydroformylation of olefins catalyzed by cobalt or rhodium complexes (oxo reaction).^'^ \ / t £=C + H_ + CO — > CH-C-CO / \ 2 •A 2. Hydrogenation of olefins. Complexes of many transition metals (including a l l of the Group VIII metals) have now been found to act as hydrogenation catalysts, some showing high selectivity for specific o l e f i n s . ^ 3 3. Oxidation of olefins to ketones, aldehydes and vinyl esters by palladium chloride (Wacker process). 4. Polymerization of olefins catalyzed by mixtures of non-transition metal organometallics with transition metal compounds (Ziegler-Natta > 6 catalysts). 5. Hydration of acetylenes to aldehydes catalyzed by certain 7 8 metal ions, e.g. Hg(II), Ru(III). A number of works reviewing the f i e l d , or parts thereof, have appeared. Ones which have in part a bias towards hydrogenation include 9 10-12 13 14 15 those written by Bond, Halpern, James, ' Frankel and Dutton, Vol'pin and Kolomnikov,and B i r d . ^ The subject has also been among the 18 19 themes of recent meetings of professional societies. ' - 3 -C. Homogeneous Catalysis by Ruthenium Complexes In line with the overall trend noted above, the chemistry of ruthenium complexes has undergone f a i r l y intensive investigation. The introduction to this thesis w i l l now consider homogeneous catalysis by these complexes, and i n Section D, i n somewhat more detail, the particular reaction of homogeneous hydrogenation of olefins. Reactions catalyzed by these ruthenium complexes are too numerous to describe 14 here, but have been reviewed by James. Some of them, chosen so as to i l l u s t r a t e the scope of the f i e l d , are: 1. Hydrogenation of Inorganic Substrates. In aqueous HC1 solutions, Ru(III) chloride is a catalyst for the reduction by hydrogen of Fe(III) to Fe(II), and of Ru(IV) to 20 Ru(III). Mechanistic studies revealed that H 2 was s p l i t heterolytically: R u 1 1 1 + H 2 ^ RuIi:iH~ + H + R u m H - + 2 F e n i R u 1 1 1 + 2Fe 1 1 + H + Similarly, i n dimethylacetamide (DMA), R u C l ^ catalyzes the reduction of Fe(III) to F e ( I I ) , 2 1 of Ru(IV) stepwise to Ru(III), Ru(II) 22 and Ru(I), and of 0 2 to H20. 2-In aqueous HC1 solution, Ru(CO)Cl,. is reduced autocatalytically 23 by H 2 to a Ru(II) chlorocarbonyl. 2. Polymerization of Olefins and Acetylenes a) Ru01g catalyzes the polymerization of hept-l-yne and phenylacetylene to dimers and trimers in the presence of hydridic - 4 -24 reducing agents such as LiAlH^, BH^ or ^^f, b) In ethanol or methanol, R u C l g hydrate catalyzes the dimerization of ethylene to butenes, of butadiene to 2,4,6-octatriene, of methyl acrylate to dimethyl 2-hexenedioate, and the addition of ethylene to methyl acrylate to give methyl esters of linear mono-25 unsaturated acids. c) Complexes of Ru(II) and Ru(III) catalyze polymerization of acr y l o n i t r i l e i n ethanol. With RuCl 3 under H 2 (15-40 atm.) at 150°C, cis and trans-1,4-dicyano-l-butenes were obtained along with propionitrile 26-29 and small amounts of adiponitrile. RuCl 0(C-_H- Q), dichloro-(dodeca-2,6,10-triene-l,12-diyl)ruthenium(IV), and Ru(acac).j gave similar results. From unsuccessful attempts to achieve this dimerization with other Ru(II) and Ru(III) complexes with 29 30 different ligands, ' i t appeared that coordination of two or more molecules of acry l o n i t r i l e to the catalyst were necessary for dimerization to occur. The dimerization took place at lower pressure when 29 -N-methylpyrrolidine or SnCl^ with bifunctional amines and/or 31 bifunctional alcohols was added. d) Polymerization of cyclobutenes i n 1^0 or alcohol to / 32 33 polybutadienes has been achieved with RuCl^ ' A Ziegler-type mechanism was indicated. Ru-Cl + HC—CH — > Ru-CH=CH-CH=CH. + HC1 I I 2 CH2-CH2 - 5 -R -Ru-I R I -Ru I -Ru-C^ 1 R = growing polymer chain. 1 can then complex to other monoenes, and add them to the growing chain The terminal chains had methyl and al l e n e end groups. This was believed to come about v i a hydride s h i f t s w i t h i n the chain,and from the chain to a new monomer u n i t : 34 Ru-CH=CH-CH2-CH2-R + HC = CH \ I H 2C CH 2 Ru-CH=CH-CH2-CH3 + CH2=C=CH-CH2-R 3. Acetylene and O l e f i n Hydration a) Ru(III) c h l o r i d e i n aqueous acid s o l u t i o n has been found to catalyze the hydration of acetylene to acetaldehyde, methylacetylene to acetone, and phenyl p r o p i o l i c acid to acetophenone and C0 2 ( v i a spontaneous decarboxylation of the B-keto acid) 35 0Hr —Ru-CH III CH OH -k-m 1 CH 0H-. -> -Ru. I CH ill CH +H C 2H 2 -Ru- + "CH =CH(OH)" <P-I ^ -^Ru-CH=CH(OH) (CH3CHO) - 6 -Chlororuthenate(II) also catalyzes the hydration, but with a rapid f a l l - o f f i n rate due to the buildup of less reactive Ru(II) carbonyl species. The Ru(II) carbonyls are also formed i n the Ru(III) 23 system, but more slowly. b) Fluoroethylenes complex with chlororuthenate(II) i n acid solutions, and are catalytically hydrated: vinyl fluoride to acetaldehyde, 2 and 1,1-di-fluoroethylene to acetic acid. 4. Carbonylation and Decarbonylation Reactions. a) Alcohols and aldehydes are decarbonylated by chloro(diethyl-36—38 phenylphosphine)Ru(II) complexes to give alkanes and olefins. b) R u C l - j o r R u2(C0)g i n diglyme catalyzes production of alkane diols from dienes and formaldehyde at 140° under 700 atm. of C0 2 and H 2 (2:1). 3 9 c) [Ru(C0)^] 3 catalyzes carbonylation of acetylenes to hydroquinone i n tetrahydrofuran or dioxane at 200° (120 atm. CO, 10 u v. 40 atm. H 2). 2C 2H 2 + 2C0 + H 2 — ^ H O - Q - O H or 2C 2H 2 + 3C0 + H20 — > H0-^_/- OH + C0 2 This has also been accomplished with RuCl^ i n H20, alcohol or dioxane, 41 and with Ru2(C0)g i n methanol. d) Catalytic carbonylation of amines to give N-formyl products 42 has been recently reported using Ru complexes. - 7 -D. Olefin Hydrogenation 1. Systems Involving Ru(II) Complexes in Aqueous Media; a) Halpern and James f i r s t used a ruthenium complex, chloro-ruthenate(II), to hydrogenate olefins, i n 1960. Maleic, fumaric and acrylic acids were a l l successfully hydrogenated at 65-90° and 1 atm. 1.43 44 1^2 i n aqueous 3 M HC1. On subsequent investigation with ethylene, i t appeared that the reactions might proceed through an i n i t i a l S N1 dissociation of the chlororuthenate, followed by a complexation with the o l e f i n . The olefin complex would then react with hydrogen to form a hydride, which would subsequently rearrange to yield the product and regenerate the catalyst species 2. RuCl 2" n — ^ RuCl 3 -? + C l " (1.1) n =^ n-1 k - l 1 2 RuCl 3 -? + ole f i n — ^ » RuCl ,(olefin) (1.2) n-1 n-1 RuCl .(olefin) + H_ —^> RuCl , + saturated product (1.3) n-1 / n-I Scheme 1 The olefin complexation reactions (1.1) and (1.2) yield the rate law - d [ R u n ] T * k.k 9[Ru I 3 :] T[olefin] - = - i - s i (1.4) d t k ^ f d - ] + k 2 [olefin] * II where T = total concentration of Ru . - 8 -while the rate law for the hydrogenation step (once the olefin complex i s f u l l y formed) i s -d[H ] (1.5) The kinetic data available were consistent with these rate laws. Exchange experiments"'' indicated that reaction (1.3) proceeded via Scheme 2. Ethylene, propylene, and 5-norbornene-2,3-dicarboxylic anhydride H + X (fast) " S +H' K ,* _ R u _ + ^ _ c v -Ru. 7 R u - C / •C—H \ Scheme 2 a l l complexed, but could not be hydrogenated. Acrylamide did complex 45 and was hydrogenated, while the complexes formed with vinyl fluoride 2 and 1,1-difluoroethylene were catalytically hydrated. It therefore appeared that two conditions for hydrogenation were (i) a substituent on the double bond of the right "electron withdrawing power", and ( i i ) the absence of a competing reaction. One unsolved problem was that, regardless of what subsequent reaction took place, the value of k^ i n reaction (1.1) should be independent of the olefin used. However, this was not found to be the case when systems which varied only i n 2 44 46. the type of olefin were compared. ' ' - 9 -b) RuCl^ has been reported to catalyze reduction of dienes ( i n c l u d i n g butadiene) to monoenes i n 3 M NaCl under 5 atm. at room 47 temperature. In 3 M HC1, however, the hydrogenation of butadiene was not observed, as hydration and/or polymerization of the o l e f i n occurred i n the absence of ruthenium.* c) A c i d s o l u t i o n s of t e t r a c h l o r o ( b i p y r i d y l ) r u t h e n a t e ( I I ) , 2-RuCl^(bipy) , catalyze maleic a c i d (MA) hydrogenation at 80°C and 48 1 atm. U^. Gas uptake measurements showed i n i t i a l a u t o c a t a l y s i s , which d i f f e r s from the chlororuthenate systems, and then a l i n e a r rate of r e a c t i o n . Scheme 3 was proposed to account f o r t h i s . [ R u C l 4 ( b i P y ) ] 2- + MA K, [RuCl 3(bipy)(MA)] + C l " 2- MA. [RuCl 3H(bipy)] I + | ( H + + Cl") * 2- - 2 [ R u C l 3 H ( b i P y ) ] z + s u c c i n i c a c i d [RuCl 2H(bipy) (MA)] + C l [ R u C l 2 ( b i p y ) ( a l k y l ) ] Scheme 3 2. Systems Involving Ru(II) and Ru(I) Complexes i n Dimethylacetamide. Solutions of RuCl 3 >3H 20 i n dimethylacetamide (DMA) were reported to react with H 2 to produce Ru(II), and then Ru(I), i n successive steps 49 - 10 -The Ru(II) solutions did catalyze hydrogenation of ethylene at 80° and 1 atm. BL^A^H^, but the system was complex due to the further reduction of the metal. Ru(I) also catalyzed olefin hydrogenation via reactions (1.6)-(1.8), Ru^ 2RU1 (1.6) k T 1 TTT Ru 1 .+ H 2 Ru L L K 2 (k 1 > k ) (1.7) ^-1 k III 2 I Ru H 2 + olef i n > Ru + saturated product (1.8) giving the rate law -d[H 2] _ k^K'[H 2] [olefin] [Ru 1]^/ 2 dt ~~ k _ i + k 2[olefin] 1/2 where K' = (K/2) . From deuterium tracer studies, the path of 22 reaction (1.8) was found to be as shown i n Scheme 4. D R CHR-CHDR H R R / * \£> H CHR-CD2R Z J E 7 i CHDR-CHDR + / . RU / / Ru D CH2R-CD2R + / Scheme 4 - 11 -Addition of CO to the DMA solutions of Ru(I) andRu(II) resulted i n formation of Ru^CO) and Ru I(C0) 2 > and RuI]"(CO) and Ru i : C(CO) 2, respectively. Activity of the catalysts decreased as the number of CO ligands i n the Ru coordination sphere increased. 3. Systems Involving Ru(II)-Phosphine Complexes. In the presence of PPh„, the solutions of RuClo.3EL0 in DMA were r 3 3 2 found to be effective catalysts for the H 2 reduction of maleic and 22 50 fumaric acids. ' The active species was found to be RuHClCPPh^)^ (Ru(I) was not produced). The reaction mechanism reported was: K l RuClH(PPh.)_ — ^ RuClH(PPh,)_ + PPh, (1.9) K RuClH(PPh 3) 2 + olefin ^ — ^ RuCl(PPh 3) 2(alkyl) (1-10) RuCl(PPh ) 0 ( a l k y l ) + H — R u C l H ( P P h ) + saturated (1.11) 6 1 1 J Z product These reactions yield the rate law -d[H 9] kK.tRu 1 1] [o l e f i n ] [ H ] . ±_ = £ i ± (I l O " ) dt 1 + K 2[olefin] + [PPh 3]/K 1 v ' ' where [PPh3] = free concentration of PPh 3 = t P P h 3 ] T - 2[Ru I ] C] T. The kinetic data agreed completely with this law. Prior to the work in DMA, other groups had used hydrogenated solutions of RuCl 2(PPh 3)^ and RuCl2(PPh 3 ) 3 in different solvents to catalyze olefin and acetylene reduction. Again the active species was reported to be RuHCl(PPh 3) 3 < Wilkinson's group reported such reduction - 12 -at 25° and 1 atm. * n ethanol-benzene, and found the catalyst to be the most active yet discovered for the hydrogenation of alk-l-enes. The hydrogenation of n-heptene in benzene catalyzed by the RuC^CPPh^)^ complex was slow, but i n benzene-ethanol i t was rapid after an i n i t i a l 52 53 induction period. ' Alkenes of the type RCH=CH2 were rapidly reduced in benzene using the hydride complex, but internal,cyclic and substituted alk-l-enes were reduced only very slowly. Acetylene 51 53 reduction, i n contrast to the early report, was not effective. A number of factors limited detailed kinetic studies of the hydride complex in benzene; however, the reaction appeared to be zero- to first-order i n alkene concentration, and was inhibited by PPh^. The suggested mechanism was based on that indicated for a comparable rhodium complex, R h H ( C O ) ( P P h ^ ) a n d I s shown in equations (1.9)-(1.11). Complexes of the form RuH(OCOR)(PPh^)^ have also been studied.^ They are less active than the chlorides, but like them show high selectivity for alk-l-enes. The reaction with the trifluoroacetate complex appears to be first-order in both and catalyst up to the sol u b i l i t y limit of the catalyst, and this i s consistent with the mechanism of reactions (1.9)-(1.11) i f the i n i t i a l dissociation of the complex is complete at the concentrations used. The rate law is similar to that given i n equation (1.12), but without the [PPh^J/K^ term in the denominator. According to this law, the plot of (rate) * vs. / [olefin] should give a straight line with a positive y intercept, and such a plot was presented for the trifluoroacetate system, although the rate has been stated to be linearly dependent on [olefin]. The - 13 -values of (obtained from the k i n e t i c data) f o r both the carboxylato 53 and c h l o r i d e c a t a l y s t systems i n d i c a t e that s i g n i f i c a n t amounts of a l k y l should be present, but no evidence f o r a l k y l species was obtained under the hydrogenation conditions. However, i n deuterated chloroform a r e v e r s i b l e r e a c t i o n at high , pressure of C^H^ (35 atm.) was A A- ' . . 53,55 in d i c a t e d by n.m.r.: (Ph,P) LRuH + C.H, — * (Ph_)P LRu(C 0H_) 3 n 2 4 * c — 3 n 2 5 (L « C l " or CF 3C0 2") N.m.r and molecular weight determination evidence were i n disagreement f o r the CF 3C0 2~ system i n that the n.m.r. spectrum of RuH(CF 3C0 2) ( P P h ^ showed a hydride quartet, suggesting l i t t l e d i s s o c i a t i o n , while the molecular weight determination i n d i c a t e d extensive dissociation."'"' However, the DMA studies on the RuHCl(PPh 3) 3 system mentioned 22 50 previously strongly support bhe mechanism. ' The solutions of the c a t a l y s t i n both DMA and benzene were v i o l e t - r e d , i n colour. Introduction of ethylene to the DMA s o l u t i o n s (1 atm. pressure, room temperature) turned them brown, while a d d i t i o n of s u f f i c i e n t maleic a c i d turned them yellow. Bath o l e f i n s could be subsequently hydrogenated. Intro-duction of ethylene to the benzene solutions caused no colour change 53 u n t i l ethylene pressure was increased to 35 atm. The report d i d not sta t e whether or not ethylene was hydrogenated. This perhaps i n d i c a t e s that the hydride complex d i s s o c i a t e s l e s s (reaction (1.9)) i n benzene. Alk-l-ynes,gave brown solutions i n benzene but were not hydrogenated. - 14 -Reaction (1.10) i s believed to proceed v i a a four-centre t r a n s i t i o n 22 53 55 st a t e , as i n Scheme 2. ' * S t e f i c i n terference by the PPh^ groups could cause low hydrogenation rates with non-terminal alkenes. Reaction (1.11) i s believed to occur v i a Scheme 5. PPh_ C-CH 3 / \ \ \ Ru C l PPh, PPh, \ H Ru C l PPh. Hp—CH Scheme 5 PPh, H H \ \ ; i v Ru PPh Z c i c-c-i C-C-H\ \ PPh, H PPh s i IV Ru . C l H / I Oxidative-addition of to the square planar a l k y l complex i s thought to be r a t e - c o n t r o l l i n g , although the reductive e l i m i n a t i o n of alkane v i a reactions 2 and 3 could be the slow step. An a l t e r n a t i v e mechanism i n v o l v i n g d i r e c t hydrogenolysis of the Ru-C bond i n the 52 a l k y l cannot be completely ruled out e i t h e r . - 15 -Systems studied similar to the ones just mentioned include the following: (i) Ru^^Cl^ and PPh^ i n methanol or benzene. Hydrogenation of olefins and acetylenes^ and 3-oxo-l,4-diene steroids"*^ has been reported. The steroid hydrogenation i s the f i r s t reported using a Ru catalyst. l,4-Androstadiene-3,17-dione(I) was reduced selectively to 4-androstene-3,7-dione(II). Androstane-3,17-dione(III) was also produced, and appeared to be formed from (I) simultaneously with (II). The percentage of (II) in the product increased notably as the pressure of H 2 was increased. ( i i ) The bridged complex [(PPh 3) 3RuCl 3Ru(PPh 3) 3] i n benzene-58 methanol hydrogenates oct-l-ene. RuHCl(PPh 3) 3 i s presumably the c a t a l y s t i n systems (i) and ( i i ) . ( i i i ) R u C l 2 L 3 (L = t e r t i a r y phosphine or arsine) with L i A l H ^ i n a number of solvents has s e l e c t i v e l y reduced o l e f i n / a c e t y l e n e mixtures.^ 9'^^ The hydride was not required when using R u C l 2 ( P P h 3 ) 3 or R u C l 2 ( A s E t 2 P h ) 3 . (iv) H 2Ru(Ph 2PCH 3) 4, H2Ru(CO) (Ph 2PCH 3) 3, RuClH(CO) ( P P h ^ , and R u C l 2 ( P h 3 P ) 3 have been used to reduce keto, formyl and n i t r i l e groups, as w e l l as non-aromatic carbon-carbon double and t r i p l e bonds.^ Optimum conditions employ 10-100 atm. H 2 at 20-130° i n hydrocarbon, ether or al c o h o l systems. (v) Protonation of Ru 2(C0 2Me)^Cl i n HBF^-MeOH gives a blue 62 s o l u t i o n which turns red when ch l o r i d e i s removed. On addi t i o n of - 16 -PPh^, e i t h e r the blue or red solutions catalyze reduction of alk-l-enes, dienes and acetylenes. Other Ru-phosphine complexes have been prepared, e.g. RuCl 2(RCN) 2~ ( P P h 3 ) 2 , 6 3 [ P ( O P h ) 3 ] A R u C l H , 6 4 , 6 5 and ( C H ^ N t R u C l ^ P P h ^ ] , 6 6 but l i t t l e data are a v a i l a b l e as yet on t h e i r c a t a l y t i c a c t i v i t y . 4. Systems Involving Other Ru Complexes. a) A Z i e g l e r system using a Ru(III) complex.6'' R u * * * ( a c a c ) / A l ( i - b u t y l ) 3 has been used to hydrogenate oct-l-ene (40°, 3.5 atm. H,,) . The mechanism given i s : R_A1 + MX — > R.A1X + RMX . (1.13) J n 2 n-1 RMX , + H_ — > RH + HMX , (1.14) n—1 / n—1 HMX . + o l e f i n — > (alkyl)-MX . (1.15) n-1 n-1 (alkyl)-MX + H 2 — > ^ n - l + P r o d u c t d-16) Instead of (1.16), (1.17) and (1.18) may occur. (alkyl)-MX . + HMX , > product + (1.17) n-I n-1 0 an - l ) 2 (MX ,) " + H„ — > 2 HMX , (1.18) n-1 2 2 n-1 - 17 -b) Dimethylformamide (DMF) and DMA solutions of RuCl^ 68 hydrogenate dicyclopentadiene to the f u l l y saturated hydrocarbon. Details were given for DMF only (25°, 1 atm. R^). Ru(II) was believed to be i n the f i n a l green solution. c) Trans-Ru(CO) 3(PPh 3) 2 h a s been reported unreactive with up to 150°. When irradiated at 365 my i t forms an unstable photoproduct which can hydrogenate cyclohexene.^ A further report, however, has indicated that RuH 2(C0) 2(PPh 3) 2 i s formed from Ru(C0) 3(PPh 3) 2 at 130° and 120 atm. H 2. 7 0 d) R U 3 ( C O ) ^ Q ( N O ) 2 isomerizes hex-l-ene at ambient temperatures and A atm. H2; n-hexane was a by-product.7^" / / - 18 -CHAPTER II APPARATUS, MATERIALS AND EXPERIMENTAL PROCEDURE A. Mater i a l s The blue chlororuthenate(II) solutions used i n these experiments were made by reducing "(NH^RuO^O^l,!' i n aqueous 3 M HC1 s o l u t i o n with T i C l 3 . The ruthenium s a l t was obtained from Johnson Matthey Co. I t i s IV designated a Ru(III) s a l t , but i s probably ( N H ^ R u (0H)C1 5. I t s 72 73 spectrum i n 3 M HC1 (Figure 1) i s l i k e that reported f o r Ru(IV), ' and unlike that of R u ( I I I ) . 7 4 , 7 5 T i C l ^ was obtained from Alpha Inorganics Inc. I t was dispensed from aqueous 3 M HC1 stock solutions which were stored under nitrogen. These solutions were standardized spectrophotometrically using Hartmann and Schlafer's value of 5 f o r the molar e x t i n c t i o n c o e f f i c i e n t at X = 510 mp.76 These solutions were p e r i o d i c a l l y standardized, as max r J they were very oxygen-sensitive, and the T i ( I I I ) concentration would f a l l over a period of time with normal handling. 3 M HC1 solutions were obtained by d i l u t i n g the concentrated acid from three sources! - 1 9 -6 u <o o c o 12000 8000 h 4000 Figure 1. 300 ZTuO Wavelength, my Absorption spectrum of "(NH^,) 2Ru(H 20)Cl 5", 10~ 4 M i n 3.0 M HC1. - 20 -(a) B.D.H. standard ampoules. (b) C P . grade from The Nichols Co. (c) Concentrated Standard HC1 sol u t i o n s from Fischer S c i e n t i f i c Co. Maleic a c i d used was B.D.H. reagent grade. I t was r e c r y s t a l l i z e d from water and dr i e d i n vacuum p r i o r to d i s s o l v i n g i n 3 M HC1. Stock solutions of crotonic acid i n 3 M HC1 were made using the B.D.H. reagent grade a c i d as supplied. A c r y l i c a c i d ( s t a b i l i z e d with 2 . - m e t n o x y P n e n ° l ) w a s that supplied by Eastman Organic Chemicals. I t was dispensed neat from the b o t t l e . The nitrogen used was a p r e p u r i f i e d grade supplied i n cy l i n d e r s by Canadian L i q u i d A i r Co. P r e p u r i f i e d hydrogen was obtained from Matheson of Canada Ltd. The hydrogen was passed through a Deoxo c a t a l y t i c p u r i f i e r (Engelhard Industries Inc.) to remove any 0^ traces before use. A l l other chemicals used were of reagent grade and d i s t i l l e d water was used i n a l l experiments. B. Procedure and Apparatus f o r the Measurement of the Uptake of  Hydrogen Gas. The rate at which a s o l u t i o n of a p a r t i c u l a r Ru complex could absorb hydrogen gas was measured by following the uptake of H 2 i n a constant pressure apparatus (Figure 2). In a t y p i c a l experiment, the desired amounts of Ru(IV) and o l e f i n / s o l u t i o n s were added to f l a s k A and frozen at l i q u i d nitrogen temperature. The T i C l g s o l u t i o n and required amount of 3 M HC1 were then added. The f l a s k was connected to the apparatus v i a a glass s p i r a l arrangement at Figure 2. Apparatus f or constant pressure gas-uptake measurements. - 22 -B, and the s o l u t i o n was then degassed by a l t e r n a t e f r e e z i n g and pumping under vacuum with taps C and D open, and thawing with C closed. A pressure of (<1 atm.) was then admitted to the f l a s k above the froz e n s o l u t i o n , and with C closed the f l a s k was t r a n s f e r r e d to the o i l bath E, and the connecting s p i r a l j o i n e d to the apparatus at F. The apparatus up to tap C was then evacuated and f i l l e d with to a pressure approximately a l i t t l e greater than i n the heated f l a s k . C was then opened, and the pressure adjusted to that desired f o r the experiment. Taps G and H and the Edward's high vacuum needle valve (J) were closed, and the experiment was i n i t i a t e d by s t a r t i n g the shaker arm K. The c l o s i r i g of tap G trapped a volume of gas at the known pressure of the r e a c t i o n i n arm r . Uptake of gas, or e v o l u t i o n when i t occurred, was i n d i c a t e d by a change i n the o i l l e v e l s s^ and s^. Admittance of more gas through J to the gas burette (arms L and M) restored the o r i g i n a l pressure i n the f l a s k , as i n d i c a t e d by the o i l l e v e l s , s,returning to t h e i r o r i g i n a l p o s i t i o n s . The uptake of was measured by following with a t r a v e l l i n g telescope the r i s e i n mercury i n the tube M, whose radius was known. The concentration of i n the s o l u t i o n at any p a r t i c u l a r pressure was c a l c u l a t e d from the s o l u b i l i t y data of Wiebe and Gaddy, 7 7 c o r r e c t i n g f o r the e f f e c t of H C l . ' 7 7 a ' 7 ^ Pressure i n the apparatus p r i o r to the s t a r t of an experiment was measured with the manometer N. The glass s p i r a l arrangement was found to be an e f f e c t i v e way of keeping a shaking f l a s k connected to the r e s t of the apparatus without i n t r o d u c i n g undue s t r a i n i n the system. - 23 -The reaction flasks were indented to aid dissolution of a n d the shaking rate was kept high enough to prevent diffusion control i n the reaction. The reaction flask, i n an experiment, was thermostated in a four l i t r e beaker f i l l e d with silicone o i l . The beaker was insulated on the sides with polystyrene foam, and enclosed i n a wooden box* The beaker's top was protected with styrofoam. The capillary o i l manometer 0 and the gas burette were housed i n a water bath at 25°C. Temperature control i n both o i l and water baths was effected by means of 25 watt elongated light bulbs connected via Merc to Merc relay control circuits to Jumo thermo regulators. Both baths were continually stirred, and temperature variation was no more than + 0.05°C. The o i l i n the capillary manometer was n-butyl phthalate, which has negligible vapor pressure at 25°C. The vacuum pump used was a Duo-Seal Vacuum Pump supplied by Welch Scientific Co. The shaker bar was driven by a Welch variable speed electric motor. Both stirrers and the shaker were connected to Powerstats (voltage regulators) supplied by the Superior Electric Co. C. Procedure for Measurement of Complexation Rates Rates of the complexation between blue chlororuthenate(II) and ole f i n i c species were measured spectrophotometrically by following the absorbance of chlororuthenate(II) at 680 my (e = 737 + 5% in 3 M HC1). The yellow olefin complexes absorb negligibly at this wavelength, and Ti(III) also absorbs insignificantly. - 24 -The procedure i n general was to make up a solution, omitting one reagent, i n an optical c e l l (3 cc volume) f i t t e d with a serum cap, and then to deoxygenate the solution with which had been previously bubbled through a 3 M HC1 tower. The c e l l , and also the last reagent i f i t s volume so merited i t , were then brought to the desired reaction temperature. Reaction was then i n i t i a t e d by adding the last reagent to the c e l l via a syringe. Kinetic runs and a l l spectra but one were measured on a Perkin-Elmer 202 u.v.-vis. spectrophotometer. The spectrum of Ru(IV) i n 3 M HC1 was taken on a Cary 14 recording spectrophotometer. A Haake constant temperature circulator model FSe connected to a Perkin-Elmer Controlled Temperature C e l l Mount was used to control the temperatures of the complexation experiments . Much use was made of a P.E. accessory time drive recording drum in order to obtain charts of absorbance versus time during the kinetic runs. The drum could be revolved at different rates of speed by different drive motors while the instrument stayed on a fixed wavelength. In early experiments on the Ru(II)-maleic acid system a somewhat different method was used. A 60 ml volume of a Ru(IV)-olefin solution was made up i n a 3-necked vessel (see Figure 3) . The solution was thermostated in an o i l bath and degassed with nitrogen. Ti(III) was then injected. During the course of the reaction, samples were withdrawn via ^-flushed syringes and injected into N^-flushed optical cells f i t t e d with serum caps. The cells were then quenched in ice-water and the absorbance at 680 my was then measured. The results were in reasonable agreement with those obtained via the continuous recording 00 X \S \V\;V\ serum cap extension clamp • v v v rubber tubing ZZZZ glass tubing ice-water bath screw clamp hypodermic needle C 0 0 \ ro 4 main gas flow \ \ \ s V v \ y \ \ v \ \ s \ \, .\ \ \ \ \ \ to nitrogen cyli n d e r Figure 3. Apparatus f o r the k i n e t i c study of the chlororuthenate(II)-maleic acid reaction. - 26 -technique. The instrument used was a single beam Beckman D.U. spectro-photometer. D. Procedure for Measurement of Formation Constants The procedure for measuring the formation constant for the reaction RuCl , + olefin — R u C l , (olefin) n-1 K — n-1 was the following: -3 -2 Reaction solutions (total volume 6 cc) 10 M i n Ru(IV) and 10 M in Ti(III) were made up i n Bausch and Lomb Spectronic 20 cuvettes f i t t e d with serum caps. The cuvettes were thermostated at 50°C; olefin was added after the development of the blue Ru(II) colour (see Chapter III). The absorbance at 680 mp was measured from time to time in a Bausch and Lomb Spectronic 20 spectrophotometer, using the infrared lamp and f i l t e r , over a period of several hours. Olefin concentration was -4 -2 varied over a series of solutions between 10 to 10 M. Optical cells and a continuous recording spectrophotometer were not used primarily because metal was precipitated during the later stages of the reaction (see Chapter III). - 27 -CHAPTER III THE Ru(IV)-Ti(III) REACTION This chapter presents some qualitative observations which were made on the reaction between Ru(IV) and T i ( I I I ) : Ru(IV) + 2Ti(III) —=- Ru(II ) + 2Ti(IV) This reaction produces a blue colour i n 3 M HC1, with a peak at 680 my 79 80 characteristic of chlororuthenate (II) ' (see Figure 4). It was found that at high temperatures (60-80°) and under ^ atmosphere there was an i n i t i a l , almost instantaneous development of the blue colour. The rate of increase of the absorbance at 680 my then f e l l off u n t i l a period was reached where the absorbance held steady (Figure 5). It took approximately 15 min. to reach the steady period at 60°, and somewhat less time at 80°. The absorbance then decreased u n t i l eventually metal was precipitated. Solutions held at 35° showed a slow increase in colour intensity, even after being followed for relatively long periods ('v 2 hr.). On standing at room temperature for periods longer than a day, these solutions eventually lost their colour and precipitated metal. - 28 -I i . J : U 300 500 700 900 Wavelength, mn ure 4. Absorption spectrum of Ru(II) i n 3.0 M HC1. - 30 -In one experiment a solution was heated alternately at 80° and 35°. After the f i r s t 80° heating period, the absorbance increased when the temperature was held at 35°, and decreased when the solution was heated to 80°. Similar results were obtained when the alternate temperatures were 60° and 80° except that during the 60° periods, absorbance reached a maximum and then started a slow decline (Figure 6). Some preliminary studies on the blue solutions formed when Ru(IV) was reacted with T i ( I I I ) , and when Ru(III) was reacted with T i ( I I I ) , gave some indication that Ru(III) i s produced as the blue colour fades; however, more work i s required here. Disproportionation of Ru(II) to metal and Ru(III) may possibly be occurring. Equilibrium shifts between the different species, (e.g. 3— 2— RuCl 5(H 20) , RuCl^ ) which are collectively known as chlororuthenate (II) (RuCl 2 n) could also be involved. These species have not been n 35 81 characterized yet, but are known to exist i n aqueous HC1 solutions. ' 2-The blue colour i s believed to be due to a four-coordinate RuCl. 4 species. In solutions i n which L i C l was i n i t i a l l y present, the process of development and decay of absorbance at 680 my (60°) occurred more rapidly the higher the concentration of L i C l . In solutions 2 M i n HC1 and 2 M i n L i C l , there was insufficient time to observe the build-up and steady periods, and only the f a l l - o f f period was noted. This indicates that the possible disproportionation of Ru(II) i s taking place through higher rather than lower chloro species. In complexation experiments, the rate of decrease of absorbance at 680 my due to complexation of Ru(II) by olefin was often at least a s o l u t i o n at 60° net change i n absorbance between 60° heating periods due to the s o l u t i o n being placed i n an 80° bath. extrapolated l i n e . (Solution was at 60° but absorbance recorder did not immediately function.) \ ? _L 2000 4000 6000 8000 Time a f t e r a d d i t i o n of T i ( I I I ) , seconds 10000 Figure 6. Absorbance at 680 my of a Ru(II) s o l u t i o n thermosatted at alt e r n a t e temperatures of TV - 1 TTT - 9 60 and 80°. ([Ru 1± l t l a l = 10 M; [ I i 1 ] = 10 M; [HC1] - 3 M). - 32 -factor of ten greater than the rates of the absorbance changes due to the "Ru(IV)-Ti(III)" reaction. Thus, i t was not always necessary to correct the complexation rate data for the latter reaction. However, this latter point had to be checked whenever reaction conditions (substrate, temperature and concentration) were changed. - 33 -CHAPTER IV THE RUTHENIUM(II) - MALEIC ACID SYSTEM A. Complex Formation 1. Stoichiometry The reaction between ruthenium(II) chlorides and maleic acid (M.A.) i n aqueous HC1 had been observed earlier, and i t s stoichiometry established spectrophotometrically.* The f i n a l product in solution was found to be a 1:1 Ru(II)-olefin complex, abbreviated Ru**(M.A.), -3 -1 with a formation constant K of 5 x 10 M at 25°, where R m [RuTI(M.A.)] [RuI][][M.A.] The nature of this complex as regards structure and other coordinated ligands (such as chloride, water) was not determined. 44 On comparison with a similarly formed 1:1 ethylene complex, the maleic acid complex was considered to involve the olefinic ligand ir-bonded through the double bond.* 2. Kinetics HC1 solutions of Ru(IV) (from (NH^)2Ru(0H)Cl5) and M.A. instantly turned the blue colour of Ru(II) on addition of Ti(III) . At temperatures - 34 -of 30° or greater, the blue colour then faded as the excess olefin complexed the Ru(II). Simultaneously, the absorbance at 680 my decreased (Figure 7, curve i i ) . The f i n a l colour of the solutions was yellow. The kinetic data were gathered prior to the discovery (presented in the last chapter) that on mixing Ru(IV) and Ti(III) there i s a further slow increase i n the absorbance at 680 my after the fast increase which occurs when the reagents are i n i t i a l l y mixed (Figure 7, curve i ) . Since, in these experiments, Ti(III) was the last reagent added, the observed decrease in absorbance was the net result of two opposing processes -the complexation, and the reaction(s) responsible for the slow build-up i n curve i of Figure 7. The rate of the "slow build-up" was not negligible compared to the rate of complexation. The loss of absorbance due solely to the ol e f i n complexing (Acorrected = Ac) was therefore found by a point-by -point subtraction of the slow increase, in absorbance at a given temperature, when olefin was not present, from the absorbance observed with olefin present. The net result for a particular run i s shown i n curve i i i of Figure 7. Plots of log Ac versus time gave f a i r l y good straight lines (Figure 8), showing that the rate was pseudo-first-order i n Ru(II) at the concentrations used. From the slope of these plots, rate constants k c' were computed. These rate constants were obtained over a series of ole f i n concentrations and a temperature range of 30-60°.for solutions • / i n which Ti(III) was i n 10-fold excess, and M.A. in 10-fold or greater excess over Ru(II). The complete kinetic data are summarized in Table I and II. - 35 -i o oo vO J-1 t d <D o o CO < 400 300 1200 Time, sec. Figure 7. V a r i a t i o n with time of absorbance at 680 rruof Ru(II) solutions at 45°C. Absorbances were measured d i r e c t l y a f t e r i n j e c t i o n of T i ( I I I ) i n t o a Ru(IV) s o l u t i o n . (10~ 3 M Ru(II), 10~ 2 M T i ( I I I ) , 3 M HC1). i ) s o l u t i o n with no maleic a c i d present i i ) s o l u t i o n with 0.1 M R.A. i n i t i a l l y present i i i ) A c~net absorbance f o r the R u ( I I ) - o l e f i n complexation (absorbance at x = absorbance at y - o p t i c a l density corresponding to length z ) . - 36 -I I L_ 0 500 1000 Time, Figure 8. F i r s t - o r d e r rate p l o t s f o r rea c t i o n . ([Ru 1*]. . . = • " i n i t i a l a) [M.A.] = 0.015 M; 45° b) [M.A.] = 70.025 M; 55° i I 1500 2000 seconds the Ru(II)-maleic a c i d 10~ 3 M; HC1 = 3 M). TABLE I . K i n e t i c data f o r the complexation of c h l o r o r u t h e n a t e ( I I ) by maleic a c i d . E f f e c t of v a r i a t i o n a I I -3 of [M.A.] on the pseudo f i r s t - o r d e r r a t e constants k' and k^ ([Ru I n i t i a l = ^ [ T i 1 1 1 ] = 0.015 M; [HC1] = 3 M). Temperature, [M.A.] x 10 , M °C 1.5 1.9 2.5 5.0 10 k' k' c -k' ( a l l r a t e constants - s.^ k' k' k» c c. x 10 4) k' k' c k' k» c 30 0.425 0.71 0.455 0.70 0.58 0.88 1.20 1.75 2.0 2.3 35 0.86 1.7 0.93 1.8 1.1 2.0 1.65 2.8 2.1 3.5 40 1.5 2.4 1.9 3.2 2.2 3.5 3.5 5.8 7.3 b 9.5 45 3.0 4.1 3.7 4.7 4.1 5.6 6.3 8.65 15 18 50 5.2 7.3 6.0 8.2 6.3 9.6 12 15 21 25 55 8.9 d 11 14 12 18.5 23 30 40 55 60 20 c 26 20 26 21 28 39 43 71 82 Average r e p r o d u c i b i l i t y of constants was + 5% Average of 3 runs Average of 2 runs Time s c a l e s of l o g A vs. time and of the c o r r e c t i o n s could not be matched a c c u r a t e l y . TABLE I I . K i n e t i c data f o r the complexation of chlororuthenate(II) by maleic a c i d . E f f e c t of v a r i a t i o n of [Ru**], [H +] and [Cl ] on the pseudo f i r s t - o r d e r rate constants k' and k'. TTT c ( [ T i ] = 0.015 M where [HC1] = 3 M, and 0.01 M where [HC1] = 2 M). Temperature, °C [Ru 1 1] x 10 3, M [M.A.] x 10 2, M [HC1], M [ L i C l ] , M k' ( x l 0 A ) , s ? 1 0.5 5 3 0 3 1.0 5 3 0 3 1.0 5 3 0 39 1.0 5 3 1.01 38 1.0 5 3 2.38 38 1.0 5 3 3.64 35 1.0 1.5 3 0 20 1.0 1.5 2 0 18 1.0 1.5 2 0.5 20 23 1.0 1.5 2 1.0 23 1.0 1.5 2 1.5 23 1.0 1.5 2 2.0 22 1.0 1.5 2 2.5 20 - 39 -P l o t s of k c' vs. [M.A.] were curved, showing a f a l l - o f f i n rate as M.A. concentration was increased (Figure 9). The system therefore appeared s i m i l a r to the Ru(II)-ethylene (see Section D l , Chapter I). P l o t s of l / k c ' vs. l/[M.A.] gave s t r a i g h t l i n e s with p o s i t i v e i n t e r c e p t s , as i n the ethylene system (Figure 10). However, i n contrast to the ethylene system, no inverse dependence of the rate constant on c h l o r i d e was found. The method of obtaining the corrected curves for the o l e f i n complexa-t i o n (curve i i i - Figure 7) assumes that the r e a c t i o n responsible f o r the slow increase of absorbance, when o l e f i n i s absent, i s independent of the decrease of the concentration of Ru(II) due to complexation. I f t h i s i s not the case, then point curve i i i shows a f a s t e r decrease of absorbance due to o l e f i n complexation than i s a c t u a l l y the case, and the true value (k^) of the pseudo rate constant cannot be determined. However, k ' w i l l give an upper l i m i t f o r t h i s rate constant. A lower c l i m i t can be obtained by assuming that the slow increase (curve i -Figure 7) has a n e g l i g i b l e e f f e c t on the o v e r a l l measured decrease; p l o t t i n g the log of the uncorrected absorbance of curve i i versus time gives the lower l i m i t , the uncorrected rate constant k'. The uncorrected data analyse s i m i l a r l y to the corrected data (e.g., p l o t s of log A vs. time are l i n e a r , k' vs. [M.A.] curves f a l l - o f f at higher [M.A.], e t c . ) . 3. Discussion The f a l l - o f f of the p l o t s of k' (or k^ _) vs. [M.A.],at high [M.A.] and the s t r a i g h t l i n e p l o t s of 1/k' (or 1/k^) vs. 1/[M.A.] with p o s i t i v e intercepts, (Fig.10) suggest a mechanism of the "Ru(II)-ethylene c l a s s " , - AO -- 41 -0.0 Figure 10. 20 40 1/[M.A.], M' -1 60 II, T y p i c a l p l o t of 1/k' vs. 1/[M.A.] ([Ru L , , , c i n i t i a l 3 M HC1; 50°). 80 10~ 3 M; 10 [M.A.] x 10 , M Figure 11. T y p i c a l p l o t of [M.A.]/k' vs. [M.A.] ( [ R u 1 1 ] , . . , = 10~ 3 M; c i n i t i a l 3 M HC1; 50°). - 42 -namely a p r i o r d i s s o c i a t i o n of the chlororuthenate complex followed by a complexation with the maleic a c i d : II 1 II * Ru L — ^ Ru L , + L n ^ — n-1 lr I I 2 I I Ru L , + M.A. — ^ > Ru L .. (M.A.) n-1 n-1 where L = l i g a n d . This mechanism gives the rate law -dtRu11] _ WVJCM.AQ] dt ~ dt ^ k , [M.A.][Ru l : EL ] 1 / n k.-jL*] + kjM.A.] (4.1) * II When [M.A.] and [L ] are i n large excess over [Ru ], and therefore constant during a re a c t i o n , equation 4.1 reduces to -dtRu 1 1] = k ' t R u 1 1 ! ] , . n k.k»[M.A.] with k' = 1 1 ^ (4.2) k_ x [ L ] + k 2[M.A.] Since the corrected and uncorrected data analyze s i m i l a r l y , a s i m i l a r expression can be w r i t t e n f o r the corrected rate constant k. k 0 [M.A.] k i l c 2c 1 C k _ i c t L * ] + k 2 c[M.A.] - 43 -This mechanism accounts f o r the observed f i r s t - o r d e r dependence on ruthenium; the blue colour of the solutions i s a t t r i b u t e d to the Ru**L n species, the concentration of which i s taken to be equal to the t o t a l Ru(II) concentration ([Ru**]^). Equation 4.2 gives k [L*] 1 / k ' = 1 / k l + k'k^M.A.] <4'3> From the p l o t s of 1/k1 vs. 1/M.A.] at d i f f e r e n t temperatures, values of k^ were obtained from the i n t e r c e p t s , and values of (k ^ [L J/k-jk^) from the slopes (Table I I I ) . On m u l t i p l y i n g equation 4.3 by [M.A.], one obtains [M.A.] m [M.A.] k - l [ L ] ( . k' k*j + k ^ ( 4 , 4 ) [M.A.] A p l o t of - L r - i — v s . [M.A. ] thus incorporates k.. i n t o the slope and k_ 1[L*] k 1 — r — r i n t o the i n t e r c e p t , and values for these constants were also K 1 K 2 obtained from such p l o t s (Figure 11). Also, i n i t i a l slopes of the p l o t s of k' vs. [M.A.] (where * k l k 2 k_^[L ] >> k 2[M.A.]) have values of —— [ j*] • a n d these r a t i o s were al s o c a l c u l a t e d . The complete set of derived rate constants for the corrected data i s summarized i n Table I I I ; the uncorrected data are given i n Table IV. The sets of data are considered reasonably consistent. Plots of log k^ c vs. 1/T are given i n Figures 12 and 13 f o r the two sets of k^ c values i n Table I I I . Plots of log k^ (from uncorrected TABLE III. Derived rate constants for the Ru(II)-maleic acid complexation (from the corrected data - with rate TT — 1 TTT _ 0 constants Ic/). ([Ru ] ± n l t l a l - 10 M; [T± ] = 1.5 x 10 M; [HC1] - 3 M). Temp. °C lc "intercept" i n 4 _ 1 xlO ,s. lc "slope" xlO ,s. k l c [ L * ] / k 2 c f xl0 2,M k l c [ L * ] / k 2 c 8 xl0 2,M k _ l c [ L * ] / k l c k 2 c C " i n i t i a l slope" M s. k - l c [ L * ] / k l c k 2 c d "slope" M s. k _ l c [ L * ] / k l c k 2 c e "intercept" M s. 30 5.1 4.6 10.9 9.75 252 212 204 35 5.3 4.6 3.6 3.2 53 68 64 40 15.5 22 8.1 11.4 46 52 56 45 * 25 36 8.05 11.6 28 32 35 50 36 40 6.2 7.0 18 17 18.5 55 135 127 16.2 15.2 11 12 12 60 100 123 5.15 6.3 6,1 5.15 5.8 4> a b c d from the intercept of 1/k^ vs. 1/-[M.A.] plots from the slope of [M.A.]/k^ vs. [M.A.] plots from the i n i t i a l slope of k^ vs. [M.A.] plots from the slope of 1/k^ vs. 1/[M.A.] plots k - l c [ L ^ / k 2 c = k - l c [ L * ] / k l c k 2 c d X k l { f) k^ from column a) g) k^ from column b) from the intercept of [M.A.]/k^ vs. [M.A.] plots TABLE IV. Derived r a t e constants f o r the Ru(I I ) - m a l e i c a c i d complexation (from the uncorrected data - w i t h TT -*} i n -2 r a t e constants k ' ) . ([Ru J l n l t ± a l - 10 M; [ T i ] = 1.5 x 10 M; [HC1] = 3 M). Temp. k a  k l k b * f k _ x [ L ] / k 2 r k ^ t L * ] / ^ 8 k ^ f L * ] / ^ 0 k _ 1 [ L * ] / k 1 k 2 d k _ 1 [ L * ] / k 1 k 2 e °C " i n t e r c e p t " , 4 -1 "sl o p e " 4 -1 2 2 " i n i t i a l s l o p e " " s l o p e " " i n t e r c e p t " xlO ,s. xlO ,s. xlO ,M xlO ,M M s. M s. M s. 30 3.2 7.2 10.5 23.5 . 288 328 365 35 2.9 2.95 3.8 3.8 135 130 134 40 13 21 12.1 19.0 95 91 100 45 22 47 9.5 20.7 64 44 53 i 50 33 49 8.1 12.0 25 24.5 30 £ 55 85 114 13.3 18.0 18 16 17 60 131 146 10.3 12.7 9.2 7.85 8.55 b c d from the i n t e r c e p t of 1/k' vs. 1/[M.A.] p l o t s from the slope of [M.A.]/k' vs. [M.A.] p l o t s from the i n i t i a l slope of k' v s . [M.A.] p l o t s from the slope of 1/k' v s . 1/[M.A.] p l o t s from the i n t e r c e p t of [M.A.]/k' vs. [M.A.] p l o t s k_^[L*]/k2 = k ^ I l / V k ^ x k x ff) k^ from column a) g) k^ from column b) - 46 --3.5 -3.0 " .r+-2.5 60 o -2.0 -3.10 3.20 103/T, °K _ 1 3.30 Figure 12. Arrhenius p l o t of k^ c f o r Ru(II)-maleic acid system. (k^ c from inter c e p t s of 1/k^ vs. 1/[M.A.] p l o t s ) . Figure 13. Arrhenius p l o t of k^ c for Ru(II)-maleic a c i d system (k. from slopes of [M.A.]/k' vs. [M.A.] p l o t s ) , l c c - 47 -k') vs.. 1/T are given in Figures 14 and 15. Arrhenius parameters, obtained from a least mean squares analysis of these plots, are given in Table V. 44 2 In the corresponding systems using ethylene, fluoroethylene, 45 * and acrylamide, the expelled ligand L was thought to be chloride. An inverse dependence of k' on [Cl ] was noted i n a l l these systems, i n qualitative agreement with equations such as 4.1, but a quantitative analysis was precluded for a number of reasons: a) variation in ionic strength over the chloride concentration range (3-6 M), b) uncertainties in the solu b i l i t y of ethylene during these variable conditions, and c) changes i n the equilibrium distribution of chloro complexes over the chloride concentration range used. The maleic acid system showed no significant variation i n rate with added chloride up to 6.6 M at 3 M HC1, or up to 4.5 M at 2 M HC1; these experiments were carried out at less than limiting maleic acid * concentrations, so that the inverse effect of L should have been observable. These rate data thus suggest that the leaving ligand i s not chloride, although again the limitations noted above make i t d i f f i c u l t to draw any definite conclusions. In the experiments at 2 M HC1, spectra of the blue solutions were taken prior to addition of olefin, and i t was noted that the maximum absorbances of these spectra decreased i n value as the L i C l concentration was increased (Figure 16), while the position of the peak appeared to / shift slightly toward longer wavelength . 81 2+ Adamson noted that the vis i b l e absorption band of Ru(H„0) moved - 48 --3.5 0 / 0 -3.0 r-t At 00 o -2.5 -°/ -2.0 0/ 1 1 r r 3.00 3.10 3.20 3.30 10 3/T, °K~ 1 Figure 14. Arrhenius p l o t of k n f o r Ru(II)-maleic a c i d system. (k^ from i n t e r c e p t s of 1/k' vs. 1/[M.A.] p l o t s . -3.5 - 0 0 -3.0 -Log -2.5 -2.0 0 / 1 x a / Oy 1 / D /o 1 3.00 3.10 3.20 3.30 10 3/T, °K 1 Figure 15. Arrhenius p l o t of k^ f o r Ru(II)-maleic acid system. (k from slopes of [M.A.]/k' vs. [M.A.] p l o t s . - 49 -TABLE V. Arrhenius activation parameters for rate constant of the Ru(II)-maleic acid complexation. Parameter Corrected data Uncorrected data ki ki l c 1 "intercept "slope , "intercept "slope method"3 method" method"3 method,,b AH+ ' 23 + 2 23 + 2 29 + 2 25 + 4 kcal/mole A t , t ' 1 + 7 3 + 7 12 + 6 8 + 13 cal/mole deg The plot of log k^ (or log k-^ ) vs. 1/T used k^ ( k^ c) values obtained from plots of l/k» (1/kJ.) vs. 1/[M.A.]. The log plot used k- (k. ) values from the slopes of [M.A.]/k' ± l c ([M.A.]/k^) vs. [M.A.] plots. - 50 -0.2 CM I O C ca 3 I O co C o o CO o cu o e « .f i H o co 0.4 " 0.6 0.8 " 1.0 -1.2 ' 1.4 350 Figure 16. 450 650 550 Wavelength, my E f f e c t of L i C l on spectra of chlororuthenate(II) i n 2 M HC1. 750 [ L i C l ] 0.0 1.0 2.0 2.5 Time spectrum was taken a f t e r a d d i t i o n of T i ( I I I ) @ 900 sec. @ 700 sec. @ 400 sec. not recorded, probably < 400 sec. The blue colour of the solutions was allowed to develop u n t i l i t reached maximum i n t e n s i t y , except f o r solutions with [ L i C l ] > 2 M. With [ L i C l ] > 2 M, "build-up" of the colour was too rapid to be observed and the spectra of these solutions was taken as soon as p o s s i b l e . - 51 -towards longer wavelengths and varied i n intensity as the degree of chloride ion complexing was increased by addition of hydrochloric acid. He also presented observations and results of chromatographic, electrochemical and other spectrochemical experiments as evidence that a series of interconvertible ruthenium(II) chloro complexes, 82 analogous to the ruthenium(III) series, exists i n hydrochloric acid. 35 Kemp noted that the i n i t i a l absorbance of formic acid solutions of Ru(II) (3 M i n HC1) varied with chloride concentration (Figure 17), dropping sharply over the range 3 to 6 M Cl . Similar effects were noted with other olefin systems i n the course of this investigation (Table VI). The formic acid system was found to be similar to the ethylene system, and a similar equation to 4.4 was derived: [HCOOH] = k - l ^ L ^ [HCOOH] k 1 k ^ k1 Assuming L to be chloride, Kemp expected that at constant [HCOOH] a linear dependence of [HCOOH]/k' on [Cl~] would be obtained. At low [Cl ] this was the case, but at higher [Cl ] (between 4 and 5 M) the curves departed from linearity (Figure 18). Similar departures had been previously observed i n the Ru(II)-ethylene reaction. Although k' of the maleic acid system did not significantly decrease i n 3 M HC1 solution as the added L i C l concentration was varied from 0 to 3.6 M, there are undoubtedly more than one Ru(II) species present at this acid concentration; also, i t appears that over this range of Cl (3 to 6 M), a shift i n equilibria between the species i s quite likely. - 52 -- 53 -TABLE VI. Effect of varying C l " concentration on the i n i t i a l absorbance of Ru(II) solutions in a series of Ru(II)-olefin systems. ([Ru 1 1]. . . , = 10~3 M; 60°). i n i t i a l Olefin i n 1 1 1 ] [HC1] [LiCl] [olefin] Absorbance x 102, M M M x 10 2 M at 680 my maleic 1.5 3.0 0 5 0.62 a c i d a 1.5 3.0 3.64 5 0.43 acrylic 1.0 2.0 0 1.5 0.89C a c i d b A 1.0 2.0 2.0 1.5 0.73d croto- , 1.0 2.0 0 1.5 0.92C n i t r i l e A 1.0 2.0 2.0 1.5 0.84d a Olefin was present when Ti(III) was added to Ru(IV). Absorbances given are those f i r s t recorded. Olefin was absent when Ti(III) was added. Build-up of blue colour to this maximum absorbance was observed. Slow decay of blue colour from this i n i t i a l absorbance was observed. / - 54 -- 55 -Therefore, at higher c h l o r i d e , production of a Ru(II) species more ac t i v e f o r complexation with maleic a c i d could be masking i n h i b i t i o n by — * C l . A l t e r n a t i v e l y of course, L could be water; then no inverse chloride e f f e c t would be a n t i c i p a t e d . This matter w i l l be discussed further i n a more general discussion of the mechanism of these o l e f i n complexation reactions (Chapter VI I I ) . r - 56 -CHAPTER V THE RUTHENIUM(II)-ACRYLIC ACID SYSTEM A. Complex Formation 1. Stoichiometry Blue s o l u t i o n s of Ru(II) i n 3 M HC1 with a c r y l i c a c i d present i n 10-fold excess faded, and eventually turned yellow-red, i n d i c a t i n g complexation. The re a c t i o n occurred at conveniently measurable rates at temperatures > 35°. The r e a c t i o n stoichiometry was determined by measuring the absorbances of a s e r i e s of s o l u t i o n s i n which the -3 [Ru(II)] was constant at 10 M; the a c r y l i c a c i d , ([A.A.]), was varied -4 -3 over the range 10 to 10 M. The absorbance at 680 my of a Ru(IV) s o l u t i o n at 50° i n t o which T i ( I I I ) was i n j e c t e d , was followed u n t i l i t had increased to a constant value. The a c r y l i c acid was then added and the absorbance followed f o r several hours. T y p i c a l p l o t s are shown i n Figure 19. A slow decrease i n absorbance occurred (portion i of curve a, Figure 19), followed by a very slow decrease (portion i i ) and the eventual appearance of metal i n the s o l u t i o n . The l a t t e r behavior corresponded to that observed f o r solutions i n which o l e f i n was not added. Por t i o n i i of each curve was therefore extrapolated back to f i n d the f i n a l e q uilibrium absorbance, f o r the complexation reaction, that would have been reached i f the slower " n o n - o l e f i n i c " r e a c t i o n had not been occurring. 0.0 a) [A.A.] = 4 x I O - 4 M b) [A.A.] = 8 x 10 M 200 400 600 Time, minutes 800 1000 1200 Fi g u r e 19. Decrease i n absorbance at 680 mp of 10 M Ru(II) s o l u t i o n s a f t e r a d d i t i o n of a c r y l i c a c i d (10 P o r t i o n i i of each curve i s e x t r a p o l a t e d back t o give the " e q u i l i b r i u m absorbance" to I O - 3 M). ( [ T i 1 1 1 ] = 10" 2 M; [HC1]'- 3 M) - 58 -Now i t can be shown that for a 1:1 complex, the following relationships hold: Ru(II) + CH„CHCO„H RuI3:(CHoCHC0oH) (5.1) [Ru I ]-(C 3H 40 2)] [ R u 1 1 ] ! ^ ^ ] T M - [M] [M](TL-TM+[M]) (5.2) where T„ and T_ = total metal and olefin used M L [M] = metal concentration at equilibrium A " EBTM [M] - T-^- (5.3) M B where A = f i n a l equilibrium absorbance e., = extinction coefficient of the metal M e_ = extinction coefficient of the complex. On substitution of equation 5.3 into 5.1, one obtains: A EBTM TM 1 1 eM" eB / For a system in which complex and ligand do not absorb at the chosen wavelength, z = 0 and a - 59 -A ^MeM 1 M To determine e^, the absorbances at 680 my of a series of Ru(IV) -3 -3 solutions varying in concentration from 0.6 x 10 to 3 x 10 M, with Ti(III) added in 10-fold or greater excess were measured at room temperature. There was some variation i n the time at which measurements were taken after the addition of Ti( I I I ) . For the solutions of lower concentrations (up to 1.8 x 10 M), the absorbances were steady before a period of 600 seconds had passed. For the solutions of higher -3 concentrations, (2.4 and 3 x 10 M) absorbances were s t i l l slowly increasing after 1000 seconds, so these absorbances were measured then. The absorbance follows Beer's law at the concentrations used in the kinetic experiments, the plot of A vs. concentration possibly deviating -3 from linearity at concentrations above 1.8 x 10 M Ru (Figure 20). From the slope of A vs. [Ru], the value of E m was found to be 737 + 5%. Values reported by some other workers are: 1050 + 15%,^ 750, 720,1 and 780. 3 5 Figure 22 shows the plot of (T + ^—) vs. (refer to Equation L EM A 5.5) for the Ru(II)-acrylic acid system. The linear plot shows the 4 -1 complex to be 1:1, with K equal to 4 x 10 M 2. Kinetics The kinetics of the complexation were studied in a similar manner to those of the maleic acid system. The procedure differed in that the olefin rather than Ti(III) was the last reagent to be added to the - 60 -u * u L O T T 2.0 3.0 [Ru ] x 10 , M Figure 20. P l o t of absorbance at 680 my vs. ruthenium concentration f o r s olutions of chlororuthenate(II) i n 3 M HC1 ( [ T i 1 1 1 ] = 3 x 10" 2 M). - 61 -i o CO VO CD o c co •o u o CO [A.A.], x 10 Figure 21. E f f e c t of varying a c r y l i c a c i d concentration on the "equilibrium absorbance" of solutions of Ru(II) and a c r y l i c a c i d ( [ R u 1 1 ] = 10~ 3 M; [ T i 1 1 1 ] = 10~ 2 M; [HC1] = 3 M). - 62 -r e a c t i o n s o l u t i o n s . This l a s t a d d i t i o n was performed only a f t e r the absorbance at 680 my appeared steady. The p l o t s of log A versus time were then l e f t uncorrected. This was the case f o r a l l experiments except f o r the two slowest runs at the lowest concentrations of a c r y l i c a c i d and the lowest temperature. In these l a t t e r two cases, the slow "non-o l e f i n i c " increase occurred over a r e l a t i v e l y long time period (> 1.5 hr. at 35°), and t h i s and the decrease i n absorbance due to complexation were of a s i m i l a r magnitude. These l a t t e r two cases were corrected as f o r the maleic acid runs. The rate data are displayed i n Table VII. A t y p i c a l p l o t showing the loss of absorbance due to complexation i s presented i n Figure 23. P l o t s of l o g A vs. time are presented i n Figure 24. P l o t s of k' vs. [A.A.] displayed the f a l l - o f f i n r a t e at higher [A.A.] (Figure 25) except f o r the p l o t at 35°, the lowest temperature, which was l i n e a r . P l o t s of 1/k' vs. 1/[A.A.] were l i n e a r with p o s i t i v e i n t e r c e p t s except again f o r the 35° p l o t , which passed through the o r i g i n . The r e a c t i o n rate, as i n the maleic a c i d system, was found to be f i r s t - o r d e r i n Ru(II) and e s s e n t i a l l y independent of C l . 3. Discussion It can be seen on examination of equation 4.2 that, at temperatures •JL*] » k 2 [ * and concentrations where k .[L ] >> k„[olefin], the equation reduces to k . k _ [ o l e f i n ] k' = 1 1 ^ (5.6) k _ x [ L ] A p l o t of 1/k' vs. 1/[A.A.] i n t h i s case w i l l therefore have the slope - 63 -TABLE VII. Kinetic data for the complexation of chlororuthenate(II) by acrylic acid ( [ T i 1 1 1 ] = 10~2 M). Temp. [Ru 1 1] [HC1] [LiCl] [A.A.] k' °C xlO 3, M M M M 2 -xlO ,s. 35.8 1.0 3.0 0 0.05 0.032 1.0 3.0 0 0.091 0.060 1.0 3.0 0 0.50 0.33 1.0 3.0 0 1.10 0.61 1.0 3.0 0 1.60 1.05 1.0 3.0 0 2.20 1.35 40.85 1.0 3.0 0 1.10 1.21 1.0 3.0 0 1.40 1.46 1.0 3.0 0 1.70 1.75 1.0 3.0 0 2.20 2.10 1.0 3.0 0 3.00 2.68 46.2 1.0 3.0 0 0.20 0.51 1.0 3.0 0 0.50 1.18 1.0 3.0 0 0.80 1.71 1.0 3.0 0 1.10 2.18 1.0 3.0 0 1.40 2.80 1.0 3.0 0 1.70 3.18 52.0 1.0 3.0 0 0.45 1.96 1.0 3.0 0 0.70 2.75 1.0 3.0 0 0.81 3.36 1.0 3.0 0 1.10 3.83 60.3 1.0 3.0 0 0.05 0.88 1.0 3.0 0 0.10 1.62 1.0 3.0 0 0.16 2.70 1.0 3.0 0 0.22 3.22 1.0 3.0 0 0.30 3.82 1.0 3.0 0 0.45 4.87 60 1.0 2.0 0 0.015 0.304 1.0 2.0 2 0.015 0.375 1.0 3.0 0 0.107 1.45 0.5 3.0 0 0.107 1.80 1.0 3.0 0 0.10 1.62 k' 2 C -1 xlO ,s. 0.048a 0.072 k' values used in data analysis. - 64 -0.6 > cu CJ c CO u o CO 0.4 0.2 I 100 -L 1 400 200 300 Time, sec. Figure 23. T y p i c a l p l o t of absorbance at 680 my versus time f o r the II -3 R u ( I I ) - a c r y l i c a c i d complexation ([Ru ] = 10 M; TTT —0 [A.A.] = 0.2 M; [ T i ] = 10 M; [HC1] = 3 M; 46°). -0.2 -0.4 oo o -0.6 -0.8 a) 0.2 M [A.A.]; 46° b) 1.4 M [A.A.]; 41° ^ \ a \ b \° 1 0 100 Time,sec. 200 II Figure 24. T y p i c a l p l o t s of log A vs. time f o r the Ru - a c r y l i c a c i d complexation [HC1] = 3 M) II -3 III -2 ([Ru ] = 10 M; [ T i ] = 10 M; - 65 --3 ITT -9 10 M; [Ti •"-] = 10 M; [HC1] = 3 M, - 66 -* k ^[L J/k^c^, and a zero intercept; k^ cannot be determined from such a plot. The k^ value at 35° was therefore determined by calculating the * * ratios k ^[L l/k^ from the values of k ^[L ]/k^k2 at the higher * temperatures, where the values of k^ were known. A plot of log(k ^[L l/k^) vs. 1/T (Figure 26) was then extrapolated to 35°, and the value of k ^[L ]/k2 so obtained was divided by k ^[L J/k^^ computed from the slope of the 35° plot. The data were checked by plotting [A.A.]/k' vs. [A.A.], The results * from these plots (k^ from the slopes and k ^[L J/k^c^ from the intercepts) are displayed i n Table VIII together with the data from the 1/k' vs. 1/[A.A.] plots. The plots of [A.A.]/k' vs. [A.A.] showed a greater point scatter than the plots of 1/k1 vs. 1/[A.A.]. However, the data are i n reasonable agreement except for the k^ values at 52°. Arrhenius parameters for k^ were obtained using the "intercept" values. The plot of log k^ vs. 1/T i s shown in Figure 27. AH^ was 2.3 kcal/mole and AS was -56 cal/mole deg. The least mean squares analysis of the plot gave the variation i n Arrhenius parameters (from standard deviations) as + 0.4 kcal/mole for AH and +1.5 cal/mole deg. for AS . These were thought to be not r e a l i s t i c . A graphical analysis, performed by considering the uncertainty in the k^ values and taking "limiting slopes" over the log k^ ranges, gave the variations as + 1.5 cal/mole for AH and +4.5 cal/mole deg for AS . The k^ "slope values" do not increase regularly with temperature, and could not be used for a determination of Arrhenius parameters; the values, however, presumably indicate a quite small activation energy. - 67 -/ TABLE V I I I . Derived r a t e constants f o r the R u ( I I ) - a c r y l i c a c i d complexation. ([Ru ] = 10~ M; [ T i 1 1 1 ] = 10~ 2 M; [HC1] = 3 M). Temperature °C k 3  k l " i n t e r c e p t " in2 _ 1 x 10 ,s. "s l o p e " i n2 -1 x 10 ,s. k ^ t L * ] / ^ 0 "slope" M s. k _ 1 [ L * ] / k 1 k 2 d " i n t e r c e p t " M s. k _ 1 [ L * ] / k 2 e M 35.8 10.0 8 10.6 159 15.95 f 40.85 10.0 10.5 80.5 80.9 8.05 46.2 10.3 9.45 39.4 37.0 4.06 • 52.0 12.1 8.5 19.1 19.7 2.30 60.3 13.9 11.1 5.26 5.18 0.73 k 1 from i n t e r c e p t of 1/k' vs. 1/[A.A.] p l o t s . k^ from slope of [A.A.]/k' vs. [A.A.] p l o t s . c from the slope of 1/k1 vs. 1/[A.A.] p l o t s . ^ from the i n t e r c e p t of [A.A.]/k' vs. [A.A.] p l o t s . 6 k _ 1 [ L * ] / k 2 = k j * x k ^ l L * ] / ^ 0 f * e x t r a p o l a t e d from p l o t s of l o g (k_^[L ]/k 2) v s . 1/T. 8 ^ = k ^ / k ^ t L * ] 0 x k ^ f L * ] / ^ . - 69 --0.8 -o.7 r 3.00 3.10 10 3/T, ° K _ 1 3.20 3.30 Figure 27. Arrhenius p l o t of k 1 f o r the complexation of chloro-ruthenate(II) by a c r y l i c a c i d i n 3 M HC1. / - 70 -B. Hydrogenation of A c r y l i c A cid 1. K i n e t i c s Solutions of the R u ( I I ) - a c r y l i c aci d complex were found to absorb gas. The rate of hydrogen uptake was thus measured with the gas-uptake apparatus, according to the procedure ou t l i n e d i n Chapter I I . The k i n e t i c measurements were taken while o l e f i n concentration was high enough so that complexing of the ruthenium(II) was e s s e n t i a l l y complete, with the rate thus being independent of the o l e f i n concentration. The i n i t i a l colour of the s o l u t i o n s , at the reagent concentration used, was dark amber. The f i n a l colour was green. Metal was eventually p r e c i p i t a t e d a f t e r the green colour formed. The uptake of hydrogen was p l o t t e d against time, and good l i n e a r p l o t s were obtained (Figure 28) f o r the i n i t i a l part of the experiments. The p l o t s f e l l away from l i n e a r i t y as the o l e f i n substrate was used up. This corresponded to the disappearance of the amber colour. Experiments were performed i n which Ru(II) concentration, H 2 concentration, and temperature were v a r i e d . The rate data are displayed i n Table IX. In s i m i l a r systems with maleic and fumaric a c i d s 1 45 and acrylamide, the rate of gas uptake was found to be f i r s t - o r d e r i n both hydrogen and Ru(II) g i v i n g a rate law of form -d[H ] d t = k 3 [ H 2 ] [ R u ( I I ) ] T (5.7) ./ where [Ru(II)]^, = t o t a l concentration of ruthenium. The same type of dependence i s found i n these studies f o r the a c r y l i c a c i d system, although the p l o t of rate of gas uptake vs. [Ru(II)] might - 71 -0 1000 2000 3000 Time, s . Figure 28. T y p i c a l rate p l o t s f o r the Ru(II) catalyzed hydrogenation of a c r y l i c acid i n 3 M HC1. ( [ R u 1 1 ] = 1.27 x 10~ 2 M; [A.A.] = 0.10 M). 70°, [ T i ] = 0.13 M; H pressure = 563 mm of Hg TTT 60°, [ Ti ] = 0.12 M; H. pressure = 634 mm of Hg. - 72 -TABLE IX. Effect of variation of the Ru(II) concentration,hydrogen pressure, and temperature on the hydrogenation of acrylic acid i n 3 M HC1. ([A.A.] = l O - 1 M; [ T i 1 1 1 ] = 1.2 or 1.3 x 10 _ 1 M ) . Temp. [Ru I : L] T H 2 [H2] Rate of H 2 k 3 °C pressure, uptake x l 0 2 , M mm of Hg x l 0 4 , M x l 0 5 , M s."1 M " ^ ? 1 60 0.158 634 4.93 0.080 1.02 0.317 634 4.93 0.294 1.88 0.633 634 4.93 0.574 1.84 1.27 634 4.93 1.06 1.70 1.27 634 4.93 1.11 1.78 2.82 634 4.93 2.24 1.61 3.14 634 4.93 1.39 0.90a 0.639 303 2.36 0.288 1.93 50 1.26 684 5.36 0.465 0.688 65 1.27 602 4.67 1.68 2.83 70 1.27 563 4.39 2.21 3.96 75 1.27 516 4.06 2.95 5.72 80 1.28 457 3.64 3.69 7.92 The plot of gas uptake vs. time f e l l from linearity at the beginning of this experiment. - 73 -deviate slightly from linearity (Figure 29). The Arrhenius activation parameters for were determined to be AH = 17.9 + 0.6 kcal/mole and AS = -3.5 + 2 cal/mole deg from a least mean squares analysis of the plot of Figure 30. 2. Discussion The hydrogenation of the Ru(II)-acrylic acid complex appears to f a l l into the same general class of reactions as the previously reported 1 45 hydrogenations of maleic and fumaric acids and acrylamide. The mechanism i s depicted below: H H \ ' - R u - l l ' I C / \ H C02H _ H H + H 2 '/ F, (slow) + C 3 H 4 ° 2 (fast) H fl '/ \ / —Ru— + .C C— H '\ /\ \ H C02H H H C02H „ H H / R u- . ll / \ H C02H 1/ —Ru —C -1 H C—H C0„H ^H Scheme 6 Rapid formation of the Ru(II)-olefin complex occurs. The complex then picks up hydrogen in the rate-determining slow step, the hydrogen being s p l i t heterolytically. The hydride ion then migrates via a four-centre - 74 -- 76 -t r a n s i t i o n s t a t e to a carbon of the double bond, while the other carbon forms a o-bond to the metal. The a l k y l complex then picks up a proton and forms the saturated product molecule, while the metal i s l i b e r a t e d and then complexed again to continue the process. Studies on the maleic and fumaric a c i d systems^" with and D^O revealed that a d d i t i o n of hydrogen to the o l e f i n was s t e r e o s p e c i f i c a l l y c i s ; and also that the hydrogen o r i g i n a t e d from the solvent, i n d i c a t i n g that the metal-hydride complex A undergoes a f a s t hydrogen exchange with the solvent. - 77 -CHAPTER VI THE RUTHENIUM(II)-CROTONIC ACID SYSTEM Inve s t i g a t i o n s of the Ru(II)-crotonic a c i d system were c a r r i e d out i n the same manner as the studies on the a c r y l i c a c i d and maleic a c i d systems. The data analyzed s i m i l a r l y i n a l l these systems, and hence the method of a n a l y s i s i s not presented again i n t h i s chapter. The r e s u l t s , rate constants, and derived rate constants are presented. A l l symbols used (e.g., f o r rate constant of complexation derived from corrected data) are analogous to those used i n the maleic and a c r y l i c a c i d systems. Dif f e r e n c e s i n observations and r e s u l t s , where they e x i s t , are noted. A. Complex Formation 1. Stoichiometry The absorbance of a s e r i e s of s o l u t i o n s i n which the [Ru(II)] was -3 -A held at 10 M and the c r o t o n i c a c i d , ([C.A.]),was v a r i e d from 2 x 10 -3 to 2.8 x 10 M, was measured as a f u n c t i o n of time. The decay of abosrbance f o r two runs i s shown i n Figure 31. As with the a c r y l i c acid system, the f i n a l e q u i l i b r i u m absorbance, A, was found by ex t r a p o l a t i n g back the slower " n o n - o l e f i n i c " decrease i n absorbance to zero time. The formation constant, K, for Ru** + C.A. — ^ Ru**(C.A.) was then A eM found from the p l o t (Figure 33) of (T T + — ) vs. — ( r e f e r to equations - 78 -0.2 a) [C.A.] = 8 x 10 -4 b) [C.A.] = 2.2 x 10 M -3 M -e- -e-43- -e-0.0 J_ 100 200 300 Time, minutes Figure 31. Decrease i n absorbance at 680 mp of 10 after addition of crotonic acid ( T i 1 1 1 3 M). 400 -3 500 M Ru(II) solutions = 10~ 2 M; [HC1] = 0.0 12 _ L _ 18 _JL_ 24 30 [C.A.] x 10 , M Figure 32. E f f e c t of varying crotonic a c i d concentration on the "eq u i l i b r i u m absorbance" of solutions of Ru(II) and crotonic a c i d ( [ R u 1 1 ] = 10~ 3 M; [ T i 1 1 1 ] = 10~ 2 M; [HC1] = 3 M). - 81 -5.2 and 5.5), and was found to be 1 x 10 M . This i s an order of magnitude less than the formation constant found for acrylic acid (K«* 4 3 x 10 ), but i s of the same order as the constants previously found for 1 45 fumaric and maleic acids and acrylamide. 2. Kinetics The familiar yellow-brown olefin complexes formed at measurable rates between 33 and 60° when olefin, i n at least 10-fold excess over Ru(II), was added to the blue Ru(II) solutions. The plots of log A (A at 680 my) versus time again gave good straight lines, k' values were obtained for a series of olefin concentrations at four temperatures. As i n the acrylic acid system, at the lowest temperature, 33°, the rate of the "non-olefinic" increase i n absorbance was not negligible compared to the complexation rates; therefore k^ values were computed for the experiments at this temperature. At the three higher temperatures, 40-60°, k' vs. [C.A.] f e l l off with increasing olefin, and the plots of 1/k* vs. 1/[C.A.] were straight lines with positive intercepts. At 33°, k' vs. [C.A.] also appeared to f a l l off with increasing [C.A.], and the c plot of 1/k^ vs. 1/[C.A.] also had a positive intercept. However, the plot of k 1 vs. [C.A.] at 33° was a straight line, and the "inverse plot", 1/k' vs. 1/[C.A.] had a zero intercept. The rate data are displayed i n Table X. Figures 34, 35, 36, 37, and 38 show, respectively: typical plots of log A vs. time, plots of k* vs. [C.A.] (50 and 60°), k' and k' vs. [C.A.] at 33°, the plots of c 1/k' vs. 1/[C.A.] at 50 and 60°, and the plots of 1/k^ , and 1/k' vs. 1/[C.A.] at 33°. - 82 -TABLE X. Kinetic data for the complexation of chlororuthenate(II) by crotonic acid ([Ru 1 1] . = 10~ 3 M; i n i t i a l III -7 [Ti ] = 10 M; [HC1] = 3.0 M). • Temperature [C.A.] k' °C x 10, M x 10^,s. * 4C -1 x 10 , s. 33.0 0.50 2.16 2.92 0.67 2.89 3.93 1.00 4.93 5.23 1.30 5.29 6.17 40.65 0.50 6.45 0.67 8.15 1.00 11.85 1.30 14.3 50.9 0.67 29.9 1.00 41.4 1.30 52.8 1.60 59.9 60.7 0.50 80.8 0.67 93.8 1.00 146 1.30 168 1.30 173 1.57 181 - 83 --0.2 -0.4 -oo o -0.6 -0.8 500 Figure 34. T y p i c a l f i r s t order rate p l o t s f o r the Ru(II)-crotonic a c i d complexation ( [ R « I I ] i n i t l a l = 1 0 ~ 3 M5 [ T i 1 1 1 ] = 1 0 ~ 2 M ? [HC1] = 3 M). a) [C.A.] = 0.13 M; 41° b) [C.A.] = 0.157 M; 61° - 84 -Figure 35. E f f e c t on the rate constant, k', of varying crotonic acid II -3 TTT -? concentration ([Ru ] = 10 M; [ T i ] = 10 M; [HC1] = ' 3 M). - 85 -Figure 36. V a r i a t i o n , with crotonic a c i d concentration,of the r a t e -TT -T , TTT -2 constants k' and k^ at 33° ([Ru x ] = 10 M; [ T i iJ-] = 10 M; [HC1] = 3 M). 3.0 -O- 50.9° - O 60.7° CO . 2.0 CN • -1 o i-H * 1.0 0.0 i i 0 4 8 12 16 1/[C.A.], M _ 1 Figure 37. Plots of 1/k' versus 1/[C.A.] at 50.9 and 60.7° ( [ R u 1 1 ] = 10~ 3 M; [ T i 1 1 1 ] = 10" 2 M; [HC1] - 3 M). - 86 -5.0 / / - 87 -3. Discussion Derived rate data from the plots of 1/k' vs. 1/[C.A.], and from the plots of [C.A.]/k' vs. [C.A.] are displayed in Table XI. From the data, the value of k, at 33° cannot be determined with l c any certainty. The plot of k^ vs. [C.A.] appears to curve, and the plot of 1/k^ , vs. 1/tC.A.] yields a value of k^ c from the intercept of 2 x -3 -1 10 s . The plot of [C.A.]/k^ vs. [C.A.] at 33° yields the same value. was found from the uncorrected data by a process similar to that used i n the acrylic acid system; the plot of log(k ^[L J/k^vs. 1/T was extended back from the higher temperatures to find the value of k_ 1[L ]/k 2 at 33°. This was then divided by the values of k_ 1[L l / k ^ at 33° obtained from a) the slope of the plot of 1/k' vs. 1/[C.A.] at this temperature, and b) the average of the values of [C.A.]/k' (referring to Equation 5.6, when k_ 1[L ] » k 2 [olefin], [C.A.]/k' = k 1 [olefin]/k^k^ constant). This process was performed three times, with three sets of k_^[L ]/k 2 values (Table x i ) . One set was computed from the "slope" plots ([C.A.]/k' vs. [C.A.] at 40-60°); the other two were "mixed" sets obtained * by multiplying the values k_^[L ]/k^k2 (obtained from the slopes of the 1/k' vs. 1/[C.A.] plots) by the values k^ (obtained from the slopes of the [C.A.]/k' vs. [C.A.] plots), and by multiplying the similar values of k_^[L ]/k.jk2 (obtained from the intercepts of the [C.A.]/k' vs. [C.A.] plots) by the values of k^ (obtained from the intercepts of the 1/k' vs. 1/[C.A.] plots). A l l the values of k^ obtained by this process were in -3 -1 the range 3-4 x 10 s , a value greater than k^ , whereas i t was expected that k^ c should be greater. The d i f f i c u l t y appears to be that for the lower temperatures, 33° and 40°, the experiments were run over II TABLE XI. Derived rate constants for the Ru(II)-crotonic acid complexation ([Ru ] IIT -? [Ti ] =10 M; [HC1] = 3 M). i n i t i a l 10- 3 M; Temp. k_ 1[L*]/k 1k 2 c k_ 1[L*]/k 1k 2 d k ^ f L * ] / ^ 6 k ^ f L * ] / ^ k_ 1[L*]/k 2 k ^ l L * ] / ^ °C "intercept" "slope" "slope" "intercept" (column a x column c) (column b x column c) (column a x column d) (column b x column d) x 10 ,s. in3 _ 1 xlO ,s. M s. M 8. xlO.M xl0,M xl0,M xl0,M 33 2.0f 1.9£ 141f 139.5f 6.73J 8.64j 4-58 4-5g 183g 186g 9.11j 3-4h 3-4h 230h 228h 40.65 9.5 6.2 75.5 70 7.19 4.67 6.65 4.31 , 50.9 17 22 18 19 3.06 3.93 3.24 00 4.16 0 0 i 60.7 58 41 5.55 5.0 3.22 2.26 2.92 2.05 from intercept of 1/k' vs. 1/[C.A.] from slope of [C.A.]/k' vs. [C.A.] C from slope of 1/k' vs. 1/[C.A.] d from intercept of [C.A.]/k' vs. [C.A.] 6 k_ 1[L*]/k 2 = k_ 1[L*]/k 1k 2 c x k ^ ^ Values from corrected data at 33° assuming k' vs. [C.A.] plot was curved. 8 Values from corrected data assuming k' vs. [C.A.] plot was a straight line. Values from uncorrected data at 33°. J Extrapolated from plot of log(k_ 1[L ]/k2) vs. 1/T. * * k ,[L ]/kjk 2 at 33 was also obtained from the - l l i n i t i a l slopes of k' (and k^) vs. [C.A.]. Values were 235 and 158 for the uncorrected and the corrected data, respectively. - 89 -an olefin range where k' vs. [C.A.] had not started to, or was only just starting to curve. If one assumes that 1/k' vs. 1/[C.A.] does not curve, then k. c l c must be found by the same process as k^. The values obtained for k^ c -3 -1 by this method were in the range 4-5 x 10 s Extending the rate studies into a range of higher C.A. concentration was prevented due to the sol u b i l i t y limits of the olefin. The Arrhenius plot using the k^ "slope" values (from plots of -3 -1 [C.A.]/k' vs. [C.A.]) at 40-60°, and a value of 3 x 10 s for ^ at 33°, i s shown in Figure 39. The plot yields activation parameters of 4. 4. AH = 20 kcal/mole and AS = -6 cal/mole deg. When a graphical analysis was performed on the plot, allowing for the inaccuracy in -3 -1 the values of log k 0^ at 33° was given a range of 2-5 x 10 s ), the determination was found to be satisfactory. Variations were + 2 cal/mole for AH^ and + 7 cal/mole deg. for AS^. A similar analysis on the log k^ values from the intercept plots gave the t t results 18.5 + 2 cal/mole for AH and -9.5 + 8 cal/mole deg for AS . B. Hydrogenation of Crotonic Acid Amber solutions of the Ru(II)-crotonic acid complex took up hydrogen at measurable rates between 45 and 75°. Ru(II) was present in -2 concentrations of 1.27 or 0.63 x 10 M, and a l l other reagents were present in concentrations at least 10-fold greater than this. Uptake of hydrogen was linear with respect to time (Figure 40) except for the two experiments at 69.5° in which uptake was i n i t i a l l y linear, but then slowly f e l l off. One of these experiments was followed through to - 90 -- 91 -1.5 CN 1.0 cu JO u o co ,o a) S3 0.5 0 1000 2000 3000 Time, s. Figure 40. T y p i c a l p l o t s of the Ru(II) catalyzed hydrogenation of crotonic a c i d i n 3 M HC1 ( [ R u 1 1 ] = 0.633 M; [C.A.] = 0.133 M; [ T i 1 1 1 ] = 0.13 M). , pressure = 638 mm of Hg , H 2 pressure = 702 mm of Hg - 92 -the appearance of metal. The colour of the solution was amber when metal f i r s t appeared; no green colour was observed prior to this appearance i n contrast to observations i n the acrylic acid system. Two experiments were performed at different E^ concentrations at 64.5°, and another two were run at different concentrations of Ru(II) at 65.9°. The results showed uptake to be essentially first-order i n these reagents, olefin being in 10-fold excess over Ru(II). The rate law i s again -d[H ] d t = k 3[Ru(II)] T[H 2] indicating a similar mechanism for hydrogenation of the Ru(II)-C.A. complex as with the other Ru(II)-olefin complexes. The rate data are displayed i n Table XII. The Arrhenius activation parameters for k^ were found to be AH+ = 9.8 + 0.3 kcal/mole and AS + = -38 + 1 cal/mole deg. The Arrhenius plot i s given i n Figure 41. - 93 -TABLE XII. Effect of variation of the Ru(II) concentration, hydrogen pressure, and temperature on the hydrogenation of crotonic acid i n 3 M HC1 ([C.A.] = 1.3 x IO - 1 M; [ T i 1 1 1 ] = 1.3 x I f f 1 M) Temp. [Ru ] T H 2 [H2] Rate of H 2 uptake k 3 °C xl0 2,M Pressure, 4 x l Q 5 -1 -1-1 mm of Hg 69.5 1.27 565 4.41 1.28 2.29 0.633 565 4.41 0.658 2.36 64.5 0.633 605 4.70 0.542 1.82 0.633 611 4.75 0.541 1.80 0.633 304 2.36 0.301 2.02 59.5 0.633 638 4.96 0.483 1.54 44.5 0.633 702 5.56 0.256 0.728 74.5 0.633 522 4.11 0.819 3.15 - 94 -of c r o t o n i c acid in.3 M HC1. - 95 -CHAPTER VII REACTIONS OF RUTHENIUM(II) WITH CROTONALDEHYDE, CROTONITRILE, VINYL HALIDES, AND DIACETONE ACRYLAMIDE Various other experiments were performed i n the course of determining which other o l e f i n s could be hydrogenated i n 3 M HC1 using Ru(II) as c a t a l y s t . S p e c i f i c a l l y , i t was desired to f i n d o l e f i n s i n which the double bond was ac t i v a t e d by groups other than carboxylic a c i d . These other experiments f a i l e d i n t h e i r main purpose. Some o l e f i n s were found which would complex with Ru(II), but the complexes could not be hydrogenated under the r e a c t i o n conditions used. Observations and r e s u l t s from these experiments are presented below. A. Crotonaldehyde Experiments Crotonaldehyde, i n 10-fold excess over ruthenium, was added to a re a c t i o n mixture of Ru(IV) and T i ( I I I ) i n 3 M HC1; the rea c t i o n f l a s k at 55° was connected to the gas uptake apparatus. The s o l u t i o n turned yellow-brown under a ^-atmosphere, but no s i g n i f i c a n t uptake of H was noted. At the end of,the experiment, an o i l y yellow p r e c i p i t a t e / formed. I t was soluble i n e t h y l a l c o h o l and s l i g h t l y soluble i n eth y l ether. The experiment was repeated at 80° under with a blank s o l u t i o n (no Ru present). The s o l u t i o n turned from c l e a r to pale yellow - 96 -and a small amount of yellow-brown p r e c i p i t a t e eventually formed. A second experiment under with Ru present y i e l d e d about twice as much p r e c i p i t a t e i n the same time period. In a d d i t i o n , the stock s o l u t i o n of 0.4 M crotonaldehyde i n 3 M HC1 turned from c l e a r to brown on standing f o r two months at room temperatures, and eventually y i e l d e d a dark yellow-brown p r e c i p i t a t e . I t appears that hydration and/or polymerization of crotonaldehyde occurs i n 3 M HC1, and that t h i s process i s speeded up i f Ru(II) i s present. B. C r o t o n i t r i l e Experiments 1. Hydrogenation Attempts C r o t o n i t r i l e formed a yellow-brown complex with Ru(II). The r e a c t i o n f l a s k was coupled to the gas uptake apparatus under a E^-atmosphere and heated to 80°. Both the o i l l e v e l s and mercury l e v e l s of the apparatus moved so as to i n d i c a t e gas evolution and then uptake a l t e r n a t e l y . A f t e r 1 hour, condensation was noted on the glass tubes above the o i l l e v e l s and as cloudy o i l droplets i n the neck of the r e a c t i o n f l a s k . The complex colour was weaker, and the c r o t o n i t r i l e smell was s t i l l strong when the r e a c t i o n f l a s k was disconnected from the gas uptake apparatus. The behavior of the o i l l e v e l s and the condensa-t i o n suggest that hydration and/or polymerization of c r o t o n i t r i l e was occurring. 2. Complexation Experiments The complexing of Ru(II) by c r o t o n i t r i l e at 60° was followed spectrophotometrically at 680 my for three d i f f e r e n t sets of reaction - 97 -conditions. The r e s u l t s are l i s t e d i n Table XIII. Again there was no inverse c h l o r i d e dependence of rate noted, k', i n f a c t , was greater when L i C l was present i n the r e a c t i o n s o l u t i o n . The spectrum of the f i n a l product was s i m i l a r to the spectra of the other ruthenium(II)-o l e f i n complexes (Figure 42). C. V i n y l Chloride and V i n y l F l u o r i d e Experiments V i n y l c h l o r i d e polymerized i n the gas uptake apparatus over the o i l and mercury l e v e l s without being exposed to ruthenium. V i n y l bromide did not appear to be polymerizing p r i o r to exposure to Ru(II). On exposure, however, polymerization i n the apparatus was noted. This continued a f t e r the access to Ru(II) was cut o f f . D. Diacetone Acrylamide Experiments Solutions containing diacetone acrylamide, (D.A.A.), 0 H CH, q II I I 3 II CH =CH-C-N-C CH— C-CH, 2. | 2. 5 CH 3 and Ru(II) turned from blue to yellow-brown, i n d i c a t i n g complex formation had occurred. On exposure to ^ -atmosphere, gas uptake was observed and measured. The rates at two temperatures were very s i m i l a r to those obtained under the same conditions using a c r y l i c a c i d as substrate; the uptake rate at 80° f o r D.A.A. was 3.50 x 10 ~* M/sec, and f o r a c r y l i c a c i d was 3.69 M/sec, while at 60° the rate was 1.29 x 10 M/sec f o r D.A.A. and 1.08 x 10 ^  M/sec (average of 2 runs) f o r a c r y l i c a c i d . The f i n a l s o l u t i o n from one of the D.A. experiments was extracted - 98 -TABLE X I I I . K i n e t i c data f o r the complexation of c h l o r o r u t h e n a t e ( I I ) by c r o t o n i t r i l e at 60°. E f f e c t of v a r i a t i o n of [C 4H 5N] and [ C l " ] . ( [ R u 1 1 ] ^ ^ ^ = 10~ 3 M; [ T i 1 1 1 ] = 10~ 2 M). [C^H N] [HC1] [ L i C l ] k' x l 0 2 , M M M x l 0 3 , s ? 3.0 2 0 6.66 1.5 2 0 3.54 1.5 2 2 4.85 - 99 -1500r - 100 -with ether and analyzed by V.P.C., but no discernible peaks were obtained. A larger quantity of reaction solution containing Ru(II), Ti(III) and D.A.A. was heated at 60° for two hours under N2> This solution yielded an acrylic acid peak when subjected to V.P.C. analysis. Hydrolysis of the substituted amide therefore appears to have taken place in 3 M HC1 appreciably faster than any hydrogenation (and/or complexation). / / - 101 -CHAPTER VIII GENERAL DISCUSSION A. Formation of the Ruthenium(II)-01efin Complexes The k i n e t i c s of formation of the ruthenium(II) complexes with maleic a c i d , a c r y l i c a c i d , and crotonic a c i d , which were described i n t h i s t h e s i s , have been analyzed i n terms of the mechanism below. k RuL — ^ RuL , + L (8.1) n "q-— n-1 -1 k 2 RuL . + o l e f i n — ^ > RuL . ( o l e f i n ) (8.2) n-1 n-1 The o v e r a l l Ru: o l e f i n stoichiometry i s 1:1. The rate law i s -drRu 1 1] m k l k 2 [ R u I l L n ] C ° l e f l n ] d t k ^ t o l e f i n ] + k 2 [ L * ] (8.3) This mechanism has been invoked by previous workers f o r the formation 44 2 25 of s i m i l a r Ru(II) complexes with ethylene, fluoroethylenes ' and 45 acrylamide; and also f o r the re a c t i o n of ruthenium(II) chlorides 46 7 with formic a c i d . Table XIV summarizes a l l the data i n c l u d -ing those obtained i n the present t h e s i s . Table XIV. Summary of k i n e t i c data f o r a s e r i e s of complexations between chlororuthenate(II) and various substrates. Substrate Inverse c h l o r i d e dependence k x 103, -1 sec AH+, kcal/mole AS+, cal/mole deg * k2 -1 ^ D e r i v a t i o n Reference of constants 1,1-difluoroethylene yes 0.3 ^29 ^+13 3.3 -x 103 a 2,45 fluoroethylene yes ^13.0 ^28 — *1.4 x 10 3 b 2,45 maleic a c i d no 10.0 23 + 2 1 + 7 / 19.4\8 c present 12.3 2 3 + 2 3 + 7 \to 16.9/ d work 13.1 29 + 2 12 + 6 ( 7 - 8 f e 14.6 25 + 4 8 + 13 \to 9.7/ f a c r y l i c a c i d no 139 111 2.3 + 1.5 -56 + 4.5 1.378 e f present work c r o t o n i t r i l e no 6.66b 35h present work cro t o n i c a c i d — 58 18.5 + 2 -9.5 + 8 ( 3'1)" e present 41 20 + 2 -6 + 7 \to 4.9/ f ; work acrylamide yes 17 17 -12 1.59 e 45 ethylene yes 3.4 23 - 4 3.6 x 102 e 44 formic a c i d yes 1.0 23.5 - 5 33.0 f 46 o NJ (k measured i n 3 M HC1 at 6 0°e x c e p t f o r acrylamide i n 3 M HC1 at 45° and c r o t o n i t r i l e i n 2 M HC1 at 6 0 ° ) . a b c l i m i t i n g rate of k' v s . [ o l e f i n ] at high [ o l e f i n ] . highest measured rate at 6 0 ° . from p l o t s of 1/k1 v s . d ' e f c 1/[M.A.]. from p l o t s of [M.A.]/k* vs. [M.A.]. from p l o t s of 1/k' v s . 1 / [ o l e f i n ] . from p l o t s of [substrate]/k' v s . [ s u b s t r a t e ] . s "mixed"derivations. k^k.j/k^tL ] (from i n i t i a l slope of k' v s . [substrate]) x f a s t e s t measured rate - value very approximate. - 103 -The ethylene data were the f i r s t to be reported, followed by those f o r the formic a c i d system. Both systems showed an inverse c h l o r i d e dependence and thus i t was thought that the rate constant k^ r e f e r r e d to d i s s o c i a t i o n of c h l o r i d e from RuCl . The k, values f o r the two n 1 systems should therefore have been independent of o l e f i n . They d i f f e r e d 46 by a f a c t o r of ca. three, and i t was stated that t h i s d i f f e r e n c e seemed l a r g e r than that which would be expected due to experimental v a r i a t i o n . The systems with the fluoroethylenes and acrylamide were studied subsequently and inverse c h l o r i d e dependences were again noted. The estimated k^ values d i f f e r e d by a f a c t o r of ca. 40 and were both greater and l e s s than those of the ethylene and formic a c i d systems. The apparent discrepancies were a t t r i b u t e d to the f a c t that the nature of the Ru**Cl species was uncertain. The c h l o r i d e concentration n r a f f e c t s the d i s t r i b u t i o n of chlororuthenate(II) species present (see Figures 16 and 17 on pp. 50, 52 ), and there i s undoubtedly a mixture of such complexes present i n i t i a l l y . The peak of the blue s o l u t i o n s at about 680 mp has been a t t r i b u t e d 2— 79 81 to a RuCl^ species with unspecified coordination. Adamson has presented evidence f o r the existence i n HC1 solutions of i n t e r -c o n v e r t i b l e , hexaccordinate, Ru* ICl (H o0)5 n ^ complexes. The n z o-n higher spin complexes appeared quite l a b i l e and magnetic evidence suggested the possible existence of an e q u i l i b r i u m between low-spin / 3-octahedral complexes, such as RuCl^R^O) , and a high-spin four-2-coordinate species (possibly tetrahedral) such as RuCl^ . S u b s t i t u t i o n reactions of tetrahedral t r a n s i t i o n metal complexes have been l i t t l e . .. ,83 studied. - 104 -The i n t e r p r e t a t i o n of the c h l o r i d e dependence i s thus a d i f f i c u l t matter. The new data presented i n t h i s thesis f o r the maleic, a c r y l i c and cr o t o n i c a c i d systems extend even furt h e r the' range of reported values. The a c r y l i c a c i d system, with i t s r e l a t i v e l y f a s t rates and very low a c t i v a t i o n energy, i s very d i f f e r e n t indeed from the other systems. The maleic and a c r y l i c a c i d systems showed no s i g n i f i c a n t inverse c h l o r i d e e f f e c t on the measured rates, and thus k^ was interpreted * as r e f e r r i n g to d i s s o c i a t i o n of a l i g a n d , L , an i o n or molecule other than c h l o r i d e . 2 I t was suggested that the much slower complexing rates (compared to rates f o r the other systems) with difluoroethylene might be a t t r i b u t e d to the formation of a complex with two carbon-metal o bonds 84 rather than the usual ir bonded complex, and that loss of two chloride ligands might be necessary f o r r e a c t i o n . The k i n e t i c s and mechanism of formation of such a bonded complexes with f l u o r o o l e f i n s , do not appear to have been reported. The new data obtained, however, show that the fluoroethylenes are not p a r t i c u l a r exceptions to a u n i f i e d d i s s o c i a t i v e mechanism. Thus i t i s concluded that the a n a l y s i s of the k i n e t i c data for a l l the systems reported i n Table XIV, i s severely l i m i t e d by the uncertainty of the composition of the i n i t i a l ruthenium complexes present i n s o l u t i o n ; and the e q u i l i b r i a between the various chloro-ruthenate(II) species w i l l have to be elucidated before a more meaningful comparison of the k^ values (and c h l o r i d e dependencies) can be made. C l e a r l y , such e q u i l i b r i a could be w r i t t e n over p a r t i c u l a r c h l o r i d e ranges as, f o r example; - 105 -R u C l 4 ( H 2 0 ) 2 2- + C l R u C U C H - O ) 3-RuCl Further e q u i l i b r i a with t r i c h l o r o and hexachloro species might be involved; these e q u i l i b r i a might be f a s t or slow compared with t h e i r subsequent r e a c t i v i t y towards o l e f i n . I t would appear that d i f f e r e n t o l e f i n s tend to i n t e r a c t with d i f f e r e n t species i n s o l u t i o n , and indeed one p a r t i c u l a r o l e f i n could react i n i t i a l l y with more than one ruthenium c h l o r i d e . An inverse c h l o r i d e dependence could r e s u l t , f o r example, from e i t h e r a slow p r e d i s s o c i a t i o n r e a c t i o n ( r e a c t i o n 8.1), or replacement of some ac t i v e t e t r a h e d r a l species by a l e s s a c t i v e pentachloro complex. Within a s e r i e s of octahedral complexes, l a b i l i t y u s ually increases with 85 increasing number of chloride ligands on the metal atom. Independence of c h l o r i d e could i n d i c a t e p r e d i s s o c i a t i o n o f , f o r example, a water liga n d . The d i s s o c i a t i o n mechanism invoked hinges almost e n t i r e l y on the observed k i n e t i c dependence on the o l e f i n concentration. Another mechanism which gives r i s e to k i n e t i c s of the same form i s shown i n Scheme 7. Ru II + o l e f i n Ru ( o l e f i n ) (+L ) product X Scheme 7 - 106 -This involves formation of a product X i n a slow step following a rapid preequilibrium, the rate law i s - d f R u 1 1 ^ ] k K t R u ] T o t a l [ o l e f i n ] d t [L*] + K f o l e f i n ] (I f no l i g a n d d i s s o c i a t e s i n the i n i t i a l e q u i l i b r i u m step then the denominator of the r i g h t hand term i s 1 + K [ o l e f i n ] ) . An inverse dependence on c h l o r i d e can r e s u l t i f the rapid o l e f i n coordination involves loss of c h l o r i d e from the i n i t i a l ruthenium species. Such a mechanism implies that at high o l e f i n (zero order i n o l e f i n ) the Ru**(olefin) complex i s f u l l y formed. To account for the spectrophotometric data, then, the o l e f i n complex would have to have e s s e n t i a l l y the same v i s i b l e spectrum as the s t a r t i n g Ru** complex. 44 This seems improbable. Also, f o r the ethylene system (at conditions approaching zero order i n o l e f i n ) the k i n e t i c s were followed by gas uptake, and no preequilibrium was observed. Further evidence against the mechanism i s the f a c t that equilibrium constants f o r the o l e f i n complexation are measured by varying the o l e f i n at concentrations close to that of the t o t a l ruthenium concentration. The mechanism implies that, even at these lower o l e f i n concentrations, the blue colour w i l l fade completely when the r a t i o of the o l e f i n concentration to the concentration of ruthenium i s greater than 1. This was not observed. There i s also the problem of the nature of the Ru**(olefin) decomposition product X with t h i s mechanism. In summary, there i s no evidence at a l l f o r a preequilibrium reaction - 107 -with o l e f i n at the conditions of the k i n e t i c measurements. Since the experimental work f o r t h i s thesis was completed, two other reports have appeared which furt h e r add to the f a c t o r s that must be considered while pondering upon the nature of the species present i n the blue ruthenium c h l o r i d e s o l u t i o n s . 86 Rose and Wilkinson have i s o l a t e d the polynuclear species I I 2-Ru,. C1^2 from methanol, and a species of approximately the same composition from aqueous s o l u t i o n s . The species was thought to be present i n s o l u t i o n i n dimethylformamide, methanol and H 20; and was formed by Pt black/H 2 reduction of RuCl 3,3H 20. The evidence f o r the existence of the species (e.s.r. and elemental analysis) seemed convincing, although there i s d i f f i c u l t y i n accounting f o r the paramagnetism of the complex, which shows about 1 unpaired e l e c t r o n per 5 ruthenium atoms. I f the polynuclear species e x i s t s i n the 3 M HC1 solutions used i n the present work, then the slow p r e d i s s o c i a t i o n step could involve formation of a monomeric species, f o r example: 2- (+ x C l ) 5Ru C l n RuCl n + o l e f i n f a s t •> Ru ( o l e f i n ) The observed o l e f i n dependence would be consistent with t h i s , but a more complex dependence on ruthenium should be observed under c e r t a i n conditions. At high o l e f i n ( l i m i t i n g ) concentration, the k back re a c t i o n i s n e g l i g i b l e , the rate law can become - 108 --mn11] m k , 2-dt k l l K U 5 L i 1 2 J and the reaction i s f i r s t order i n total ruthenium. The estimated values (multiplied by 5) would then refer to slow dissociation of the cluster species. Again, however, values should be independent 2-of the ol e f i n used i f the Ru^Cl^ species was the sole reacting species. At lower olefin concentration, the limiting rate law becomes -d[Ru I T] _ (\ V/5 , f_ „ 2-,l/5 r , . dt " k 2 [ R u 5 C 1 1 2 1 lolefxn], and a fractional dependence on total ruthenium would be expected. At particular intermediate olefin concentrations, a dependence on ruthenium somewhere between one-fifth and f i r s t order should be observed. However, a l l the individual kinetic runs at low to high olefin concentrations, that were described i n this thesis, yielded good, first-order, log absorbance versus time plots. Also, similar pseudo first-order rate constants were obtained with ruthenium-maleic acid experiments run at different i n i t i a l ruthenium concentrations, at ole f i n concentrations between the limiting conditions (Table II). Thus the present kinetic data do not indicate the presence of any kinetically significant polynuclear ruthenium(II) complexes i n 3 M HC1. 87 Mercer and Dumas have isolated the Ru(II)-Ru(III) mixed valence ( 2 \ j cations Ru 0Cl 0. (n = 0, 1, 2) from the blue solutions i n dilute I j+n ^ HC1 (up to 0.2 M), and these workers consider that such species are 88 present i n the solutions. Since this report appeared, Plackett in this - 109 -laboratory has carried out studies to find i f ruthenium(III) is present i n the 3 M HC1 solutions. These and other, studies described below give no evidence for the presence of Ru(III) under the experimental conditions used to study the complexation and hydrogenation of olefins. 23 Previous work on the reaction of carbon monoxide with HC1 solutions of ruthenium(III) (prepared via H 2 reduction of solutions of the "(NH 4) 2Ru(H 20)Cl 5" salt) had established reaction 8.4. R u 1 1 1 + CO > Ru I i : t(C0) (8.4) The monocarbonyl, which was isolated as (NH4)2Ru(CO)Cl^, has also been 89 prepared by other methods. Acid solutions of this complex react with 23 hydrogen according to reaction 8.5. Ru I i : C(C0) + 1/2H2 > RuI]:(C0) + H + (8.5) This Ru(II) monocarbonyl was isolated as (NH4)2Ru(C0) ( H ^ C l ^ . It has 89 also been synthesized by other methods. Now the blue solutions, 3 M in HC1, also reacted with CO i n a 1:1 stoichiometry (measured in a gas burette - Figure 2) to form the 23 same Ru(II) monocarbonyl. The v i s i b l e absorption spectra of the Ru(II) monocarbonyls, prepared by both methods, were identical and were unlike the spectrum of the Ru(III) monocarbonyl. This seemed inconsistent with the acid blue solutions containing any ruthenium(III). The absorption peaks of the Ru(III) carbonyl are much stronger (e *\» 6500 at 245 my and 3300 at 450 my) - 110 -than those of the Ru(II) carbonyl ( e ^ 425 at 325 my and 300 at 375 my), and consequently even a small amount of Ru(III) i n the blue s o l u t i o n would have caused the spectrum of the monocarbonyl product to d i f f e r from that of the product made by H 2 reduction. However, CO can reduce the ions of platinum metals with the 90 formation of lower valence carbonyls and CO^; as, f o r example: I I I H 2 ° I + Rh + 3C0 -=-> Rh (C0) 2 + C0 2 + 2H (8.6) Thus i t i s p o s s i b l e that Ru(II) monocarbonyl was produced from Ru(III) The reduction step i t s e l f involves no net absorption or evolution of gas: I I I H 2 ° I + Rh + CO — - — > Rh + 2H + C0 2 (8.7) Thus, i f the blue s o l u t i o n contained some Ru(III) species, any reduction of them to Ru(II), as i n re a c t i o n 8.7, would not have been d i r e c t l y observable by the gas burette studies; r e a c t i o n 8.8 with Mercer and Dumas' species giving apparent 1:1 stoichiometry (a net of 4 molecules of gas i s taken up per 4 atoms of ruthenium). H 0 2 [ R u I I I - R u 1 1 ] + 5C0 - 2—> 4Ru I : t(C0) + C0 2 + 2H + (8.8) However, i f the CO a d d i t i o n i s performed i n the presence of soda-lime, which absorbs C0 2 > i t i s t h e o r e t i c a l l y p o s s i b l e to t e l l i f Ru(III) i s present; a net number of 5 molecules of gas would be taken 88 up per 4 ruthenium atoms g i v i n g a stoichiometry of 1.25:1. Plackett - I l l -has repeated the CO absorption studies On the blue solutions in the presence of such a trap. The stoichiometries obtained were somewhat inconclusive as i t was not possible to determine the actual end point of the CO addition due to interference from the slower second stage of the reaction (in which bicarbonyl i s formed). However, the uptakes appeared to be similar, slightly more gas being taken up without the soda lime trap than with i t , which would argue against the presence of any significant amounts of Ru(III) i n the fresh blue solutions. Furthermore, gas samples were withdrawn from the reaction vessel and subjected to mass spectrometric and gas chromatographic analyses. No CO^ peaks were obtained. 86 91 92 Other workers ' ' have reported the production of Ru(III) from aqueous Ru(II) solutions under certain conditions. 86 Wilkinson and Rose have shown that i n the ethylene system ca. 5% of ruthenium is present as Ru(III) after the blue solutions have 91 reacted with ethylene. Rechnitz and Catherino have reported that Ru(III) is formed in the blue solutions by water oxidation of Ru(II) in 0.03 to 0.3 M acid; they followed the Ru(III) production by loss of 92 the blue colour at 690 my. Grube and Nann stated that i n HC1 solutions weaker than 2 M i n acid, bivalent ruthenium i s not stable: 3Ru 2 + > Ru° + 2Ru 3 + (8.9) They further stated that in 2 M HC1, Ru(II) is "relatively" stable. As noted i n Chapter III, the blue colour in 3 M HC1 eventually does fade,with eventual production of metal, and Ru(III) may be produced. - 112 -Pr o v i s i o n f o r the fading had to be allowed f o r i n measurement of the formation constants (Chapters V and VI)^as complexing took place extremely slowly at the concentrations of o l e f i n employed. There do not appear to be any reports i n the l i t e r a t u r e of the production of Ru(III) i n the blue solutions of Ru(II) when hydrochloric acid strength i s greater than 2 M, but i t may w e l l be that production of Ru(III) species does occur i n the blue 3 M HC1 sol u t i o n s used i n t h i s work. Whether or not these species are there i n any s i g n i f i c a n t amounts or there at a l l would seem to be dependent on both conditions and time, a f t e r formation of the blue colour, when the ruthenium s o l u t i o n s are examined. A l l k i n e t i c complexations i n t h i s present work were run under conditions when the absorbance at 680 my was increasing or steady, and therefore when Ru(III) would presumably not yet be forming i n s o l u t i o n . The excess T i ( I I I ) used i n the solutions should, of course, reduce Ru(III) back to Ru(II). However, i t was found that the Ru(III) reduction i s much slower than that of Ru(IV). The slow fading of the blue colour may therefore r e f l e c t a competition between oxidation or disproportionation of Ru(II) to Ru(III), and reduction of Ru(III) by T i ( I I I ) with the scales tipped i n favor of the former. 93 Wilkinson and Rose have c a r r i e d out electrophoresis experiments on the blue s o l u t i o n s . They concluded that c a t i o n i c species as 87 postulated by Mercer and Dumas were not i n f a c t present; but again, i f Ru* 1 1 cations are being produced very slowly, experimental r e s u l t s of t h i s nature would depend very much on conditions and the time, a f t e r i n i t i a l formation of the blue colour, at which the i n v e s t i g a t i o n was c a r r i e d out. - 113 -In summary, no evidence was obtained f o r the existence of any Ru(III) complexes i n the blue solutions used i n t h i s work, at the times and under the conditions at which complexation experiments were c a r r i e d out. C l e a r l y the k i n e t i c data obtained are u s e f u l i n terms of a study of c a t a l y t i c properties (hydrogenation, hydration) of the o l e f i n complexes once they are formed; but, f o r the reasons stated e a r l i e r , a d e t a i l e d analysis i s severely l i m i t e d . B. A d d i t i o n a l Comments on the Solutions of Chlororuthenate(II). 91 Rechnitz and Catherino suggested the production of Ru(III)in the chlororuthenate(II) solutions was caused by h y d r o l y t i c attack on Ru** (0.03 to 0.3 M HC1). R u 1 1 + H 20 > OH" + R u 1 1 1 + 1/2H2 (8.10) They detected the production of hydrogen and t h e i r postulated mechanism involved formation of hydrated electrons: H Q + R u 1 1 H 90-+ R u 1 1 1 (8.11) — 4- f aef H 20 + H > H + H 20 (8.12) Basolo and Pearson, however,concluded that r e a c t i o n 8.11 was most 92 improbable for t h i s system. Grube and Nann reported that the e l e c t r o l y t i c reduction of ruthenium(III) i n hydrochloric a c i d proceeded to the - 114 -divalent state i n concentrated a c i d ; b u t , i n d i l u t e acid,metal resulted, and t h i s was thought to be due to disproportionation of ruthenium(I). 95 Dwyer et a l . , although recognizing that solutions of ruthenium(II) do disproportionate i n d i l u t e a c i d , disputed the existence of ruthenium(I) i n aqueous s o l u t i o n . I t seems from the l i t e r a t u r e reports that the s t a b i l i t y of Ru(II) solutions does tend to increase as s o l u t i o n a c i d i t y increases,and thus some kind of h y d r o l y t i c attack may be taking place; t h i s s t a b i l i t y trend i s i n contrast with the known o x i d i z i n g capacity of water, which increases with increasing a c i d i t y . F i n a l l y , the slow buildup of blue colour i n the R u ^ - T i 1 1 1 reaction may be due to a ruthenium(IV) dimer which i s reduced le s s e a s i l y than most of the i n i t i a l ruthenium(IV)^1,96,97 C. C a t a l y t i c Hydrogenation A c r y l i c and crotonic acids were c a t a l y t i c a l l y reduced by hydrogen i n the chlororuthenate(II) s o l u t i o n s . The mechanisms were not studied i n any d e t a i l but the systems follow c l o s e l y , k i n e t i c a l l y and spectrophotometrically, the well-studied maleic a c i d system 1 (Chapter IV). The rate-determining step of the mechanisms i s thought to be reaction of the 1:1 R u 1 1 ( o l e f i n ) complex with H^ to give a monohydride species, H R u I 1 ( o l e f i n ) . Subsequent reactions involve i n s e r t i o n of o l e f i n into the Ru-H bond to give the a l k y l , and protonation of the a l k y l to give the saturated product and regenerate the c a t a l y s t (Scheme 6,p.73). The values of the rate constants at 80° and the a c t i v a t i o n parameters are summarized i n Table XV together with the determined formation constants of the o l e f i n complexes. Table XV. Summary of kinetic data for the Ru(II)-catalyzed hydrogenation of various olefins. Olefin k at 80° M s AH+, kcal/mole AS+, cal/mole deg K -2 -1 x 10 ,M Reference acrylic acid 7.92 17.9 + 0.6 -3.5 + 2 ^400b present work crotonic acid 3.74a 9.8 + 0.3 -38 + 1 ^10 b present work maleic acid 2.3 14 -17 ^50 C 1 fumaric acid 3.6 17 - 8 ^20 C 1 acrylamide 7.2 10 -26 ^60 45 ethylene o d <50 44 5-norbornene-2,3-dicarboxylic anhydride o e 2 C 1 propylene o d 1 value obtained via extrapolation of Arrhenius plot. (Highest temperature for raw data was 75°). c d measured at 50°. measured at 25°. olefin complexed, metal precipitated slowly, complex catalyzed D„-H„0 exchange. - 116 -The r e l a t i v e l y small d i f f e r e n c e s i n the hydrogenation rates and (except f o r a c r y l i c acid) i n the formation constants do not show any obvious general trends. The a c r y l i c a c i d system e x h i b i t s the l a r g e s t formation constant and f a s t e s t hydrogenation rates, while the ethylene complex i s not hydrogenated and i t s formation constant i s r e l a t i v e l y 44 small ( c e r t a i n l y l e s s than that of maleic acid ). However, i t i s not c l e a r i f these e f f e c t s are s i g n i f i c a n t ; the r e l a t i v e weakness of the ethylene complex i s probably not the major f a c t o r governing i t s non-hydrogenation. While the complex has to be s u f f i c i e n t l y stable to be formed at the o l e f i n concentrations employed f o r the hydrogenation (so that the o l e f i n may be a c t i v a t e d ) , the a c t u a l value of the s t a b i l i t y constant may not be too c r i t i c a l - at l e a s t f o r these ruthenium systems, since both the ethylene complex and other complexes (5-norbornene-2,3-2 98 d i c a r b o x y l i c anhydride) which were not hydrogenated ' were completely formed under the hydrogenation conditions. The non-hydrogenation was r a t i o n a l i z e d * i n terms of a subsequent hydride t r a n s f e r step (k of Scheme 8) not competing e f f e c t i v e l y with p a reverse protonation step (k_ ) k H + + H R u 1 1 ( o l e f i n ) Ru ( o l e f i n ) + H a 2 ^ k -a Ru-alkyl Scheme 8 The complete rate law, for the chlororuthenate(II) systems, with t h i s scheme i s - 117 -d[H ] k [H +] 1 -k B+k H >.tH +] (8.13) and v a r i a t i o n i n the measured rate constants (k=rate/[H^][Ru^,]) f o r d i f f e r e n t o l e f i n s can a r i s e from v a r i a t i o n s i n k , k and k Q . Unfortunately, a ' -a 3 3 ' nothing i s known about the second term i n the bracket, i . e . the r e l a t i v e values of k. and k , and i t would be hard to discover much g -a about i t f o r the following reasons: a) V a r i a t i o n of hydroch l o r i c a c i d strength a f f e c t s the d i s t r i b u t i o n of the chlororuthenate complexes. b) Ruthenium(II) i s unstable i n water at low a c i d i t i e s . c) No i n e r t anion has been found that could s u b s t i t u t e f o r ch l o r i d e i n these systems and keep both d i s t r i b u t i o n of the complexes and i o n i c strength c o n s t a n t . 2 ' 4 4 Now, since both k^ and k_^ can vary f o r d i f f e r e n t o l e f i n s , the c o n t r i b u t i o n from the term i n brackets can t h e o r e t i c a l l y go from e s s e n t i a l l y zero (k >> k„) to unity (k„ >> k ). The f a c t that only - c x g $ -a J o l e f i n s with electron-withdrawing substituents are hydrogenated has been a t t r i b u t e d 1 to the promotion of the hydride trans f e r process: -^Ru" II 3> -Ru^HC CH 0 (8.14) and i t i s p o s s i b l e that f o r these systems, k >> k , g i v i n g a r e a l 3 -a hydrogenation rate with the measured rate constant r e f e r r i n g to k^ (ref e r to equation 8.13). The hydrogenation rate constants f o r the - 118 -o l e f i n systems studied vary by only a f a c t o r of four (Table XV), although more s i g n i f i c a n t v a r i a t i o n s are noted i n the a c t i v a t i o n parameters; these v a r i a t i o n s would then r e f l e c t d i f f e r e n c e s i n the r e a c t i o n path f o r the net h y d r i d i c s u b s t i t u t i o n . Ethylene has no electron-withdrawing groups to promote the k 3 r e a c t i o n ; so that f o r t h i s o l e f i n k >> k and the bracket term i s -a 3 zero, g i v i n g zero hydrogenation rate. C l e a r l y , both s t e r i c and e l e c t r o n i c f a c t o r s could influence the subsequent hydride t r a n s f e r process (reaction 8.14) and, since formation constants f o r a s e r i e s of o l e f i n complexes w i l l also depend on these f a c t o r s , i n d i r e c t c o r r e l a t i o n between the hydrogenation rates and the s t a b i l i t y constants may e x i s t . Unfortunately, such s t e r i c and e l e c t r o n i c f a c t o r s i n o l e f i n complexes are not w e l l understood generally. The e f f e c t of the nature of the o l e f i n on the k step must also be a an important f a c t o r . This step could involve a "hydride" d i r e c t •v '.85 s u b s t i t u t i o n : TT ^ TT ^ + Cl-Ru 1 | — H - R u — 1 | + H C l ~ (8.15) C C 99 100 or r e a c t i o n v i a o x i d a t i v e - a d d i t i o n to give a dihydride: ' C C C Cl-Ru*- 1| + H — > H R u - 1 | — > HRu" || + H +C1~ C 1 C C Oxidative-addition i s promoted by increase of electron density at the metal centre."^* The a c t i v a t e d o l e f i n s with electron-withdrawing groups are u n l i k e l y to favour such r e a c t i o n , but they may promote hydride . - 119 -s u b s t i t u t i o n (8.15) v i a a S N2 mechanism. In summary, considering the multistep nature of the c a t a l y t i c hydrogenation r e a c t i o n , i t i s not at a l l c l e a r what trends may be a n t i c i p a t e d between s t a b i l i t i e s of the m e t a l - o l e f i n complexes f o r systems of t h i s type and the r e a c t i v i t i e s of the complexes towards hydrogen. Systematic studies of the kind i n t h i s present work are necessary to e l u c i d a t e the f a c t o r s involved. Evidence f o r h e t e r o l y t i c 103 s p l i t t i n g of hydrogen has been obtained by Halpern's group by c a r r y i n g out studies on a s e r i e s of copper and s i l v e r complexes using ligands of varying b a s i c i t y . These workers were able to c o r r e l a t e r e a c t i v i t y with b a s i c i t y e f f e c t s of the coordinated ligands f o r the hydride s u b s t i t u t i o n reactions. I t would be of considerable i n t e r e s t to carry out s i m i l a r studies with the ruthenium(II) system using, for example, d i f f e r e n t halides and other anions. However, there i s again the complication that very l i t t l e i s known about the general chemistry of such complexes. 104 Markham i n t h i s laboratory has studied the hydrogenation of a v a r i e t y of o l e f i n i c substrates using the hydridophosphine c a t a l y s t HRuCl(PPh 3)2« The mechanism (reactions 1.9-1.11) f o r these hydrogenations i s quite d i f f e r e n t from that of the chlororuthenate(II) systems, and the rate-determining step involves o x i d a t i v e - a d d i t i o n of H 2 to a Ru(II) a l k y l species. An extremely i n t e r e s t i n g r e s u l t i s that o l e f i n s with electronegative substituents (e.g., acrylamide) are much l e s s / e f f e c t i v e l y hydrogenated than simple terminal o l e f i n s such as ethylene, hex-l-ene, etc., since the "electronegative o l e f i n s " tend to i n h i b i t - 120 -the o x i d a t i v e - a d d i t i o n step. 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