F g a stone, robert west (eds ) advances in organometallic chemistry, vol 17 catalysis and organic syntheses academic press (1979)

57 I INTRODUCTION Hydroformylation is the general term applied to the reaction of an olefin with carbon monoxide and hydrogen to form an aldehyde.. The reaction is first order in olefi

Catalysis and Organic Syntheses

VOLUME 17

1979

ACADEMIC PRESS New York San Francisco - London

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Contents

LIST OF CONTRIBUTORS

PREFACE I I1 111 IV V VI VII VIII IX I I 1 I11 IV V Hydroformy lation ROY L PRUETT Introduction

Commercial Utilization

Reaction Mechanism

Secondary Products and Reactions Substrates

Catalyst Separation and Recycle

Heterogeneous Catalysts

Catalysts Other than Cobalt and Rhodium Commercial Technology Trends

References

.

.

.

.

.

.

.

.

The Fischer-Tropsch Reaction CHRISTOPHER MASTERS Introduction

Fischer-Tropsch Related Organometallic Chemistry

Possible Mechanisms for the Fischer-Tropsch Reaction

New Technology

Summary

References

ix xi i 2 3 10 15 46 47 53 57 57 61 66 86 96 99 100 Selectivity Control in Nickel-Catalyzed Olefin Oligomerization B BOGDANOVIC I Introduction 105

I1 Methods of Preparation and Some Features of Nickel Catalysts Active for the Oligomerization of Olefins and Related Reactions 107 I I 1 Formation and Probable Structure of the Catalytically Active Species 114

IV Examples of Selectivity Control 119

References 137

Palladium-Catalyzed Reactions of Butadiene and Isoprene JIRO TSUJI I Comparison of Nickel- and Palladium-Catalyzed Reactions of Butadiene 141

I1

111

IV

V

VI

VII

VIII

IX

X

XI

Catalytic Species

Dimerization of Butadiene

Telomerization of Butadiene

Dimerization and Telomerization of Isoprene

Cyclization Reactions

Reactions of Carbon Dioxide

Cooligomerization of Butadiene with Olefins

Oxidative Reactions of Butadiene with Pd*+ Salts

Other Reactions

Application of the Telomerization of Butadiene to Natural Product Synthesis

References

146 148 151 168 176 178 179 181 182 182 189 Synthetic Applications of Organonickel Complexes in Organic GIAN PAOLO CHIUSOLI and GIUSEPPE SALERNO Chemistry I Introduction 195

I1 Carbon-Carbon Bond Formation 198

I11 Formation of Bonds Other Than Carbon-Carbon 234

References 243

Mechanistic Pathways in the Catalytic Carbonylation of Methanol by Rhodium and Iridium Complexes DENIS FORSTER I Introduction 255

I1 The Carbonylation of Methanol Catalyzed by Rhodium Complexes in Solution 257

111 Supported Rhodium Carbonylation Catalysts for Methanol Carbonylation 262

IV Iridium-Catalyzed Methanol Carbonylation 264

References 267

Catalytic Codimerization of Ethylene and Butadiene AARON C L SU I Introduction 269

I1 The Rhodium Catalyst System 271

I11 Ni-Based Catalyst System 291

IV Co and Fe Catalyst System 309

V Pd-Based Catalyst System 315

References 3 16

Contents vi i

Hydrogenation Reactions Catalyzed by Transition Metal

Complexes BRIAN R JAMES

I

I 1

111

IV

V

VI

VII

VIII

IX

X

XI

XI1

Introduction

Recent Studies of Catalyst Systems Discovered prior to 1971 Asymmetric Hydrogenation

Supported Transition Metal Complexes as Catalysts

Membrane Systems Phase-Transfer Catalysts Molten Salt Systems Transition Metal Clusters Including Dimers

Hydrogenation of Aromatic Hydrocarbons

Photocatalysis

Hydrogenase Systems

Hydrogen Transfer from Solvents

Miscellaneous New Catalysts

Summary

References

319 321 338 361 367 368 376 378 380 381 383 388 3 9 0 Homogeneous Catalysis of Hydrosilation by Transition Metals JOHN L SPEIER I Introduction 407

I1 Chloroplatinic Acid as a Homogeneous Catalyst 409

111 Homogeneous Catalysis with Metals Other Than Platinum 428

IV Effects of the Structure of the M a ne . 434

V Studies with Conjugated Dienes 441

VI Hydrosilation of Acetylenes 443

References 445

Olefin Metathesis N CALDERON J P LAWRENCE and E A OFSTEAD I Introduction 449

I1 Origins of Carbene-Metal Complexes 451

111 Cyclopropanation 459

I V Stereochemical Aspects of the Olefin Metathesis Reaction 468

V Metathesis of Substrates Bearing Polar Groups 482

VI Conclusion 489

References 489

SUBJECT IN D E X . 493

CUM UL A T I VE LIST OF CONTRIBUTORS 507

C U M U L A T I V E LIST OF TITLES 509

List of Contributors

Numbers in parentheses indicate the pages on which the authors’ contributions begin

B B O G D A N O V I ~ (103, Max-Planck-Institut f i r Kohlenforschung,

N CALDERON (449), The Goodyear Tire and Rubber Company, Research

G I A N PAOLO CHIUSOLI (195), Zstituto di Chimica Organica

Mulheim a d Ruhr, West Germany

Division, Akron, Ohio 44316

dell’ Universita, Via d’Azeglio 85, Parma, Italy

Company, St Louis, Missouri 63166

Columbia, Vancouver, British Columbia, Canada

Division, Akron, Ohio 44316

DENIS FORSTER (255), Corporate Research Laboratories, Monsanto

BRIAN R JAMES (319), Department of Chemistry, University of British

J P LAWRENCE (449), The Goodyear Tire &Rubber Company, Research

CHRISTOPHER MASTERS* (6 1), KoninklijkelShell-Laboratorium, Shell Re-

E A OFSTEAD (449), The Goodyear Tire and Rubber Company, Re- search B.V., Amsterdam, The Netherlands

search Division, Akron, Ohio 44316

ROY L PRUETT ( l ) , Chemicals and Plastics Division, Union Carbide

GIUSEPPE SALERNO (195), Istituto di Chimica Organica dell’ Universita,

JOHN L SPEIER (407), Dow Corning Corporation, Midland, Michigan

AARON C L Su (269), Elastomer Chemicals Department, Pioneering

Division, Experimental Station, E I du Pont de Nemours and Com- pany, Wilmington, Delaware 19898

JIRO TSUJI (141), Tokyo Institute of Technology, Meguro, Tokyo,

Japan 152

Corporation, South Charleston, West Virginia

Via d’Azeglio 85, Parma, Italy

*Resent address: Shell Chemicals U K Ltd., Shell-Mex House, Strand, London, Eng- land WCZR ODX

Preface

This volume of Advances in Organometallic Chemistry is concerned

exclusively with the involvement of metal compounds in catalysis and organic synthesis We have collected together ten chapters on these topics so as to provide in one volume a survey of the growing importance

of organometallics in industrial processes and laboratory syntheses It is impossible to provide complete coverage of the subject within the con- fines of a single volume of necessarily limited length Nevertheless, we believe that our contributors have presented ample evidence of what many regard as the most significant growth area of organometallic chem- istry and one of vast technological importance

Several articles on these topics have appeared in earlier volumes For

the convenience of readers they are listed here In addition, articles on Ziegler-Natta catalysis and on organolithium compounds in diene poly- merization are planned for the next volume of this serial publication

The Olefin Metathesis Reaction

T J Katz, Vol 16, p 283-317

Supported Transition Metal Complexes as Catalysts

F R Hartley and P N Vezey, Vol 15, p 189-234

Activation of Alkanes by Transition Metal Compounds

D E Webster, Vol 15, p 147-188

Palladium-Catalyzed Organic Reactions

P M Henry, Vol 13, p 363-452

Organozinc Compounds in Synthesis

J Furukawa and N Kawabata, VoI 12, p 83-134

Boranes in Organic Chemistry

Recent Advances in Organothallium Chemistry

r-Allylnickel Intermediates in Organic Synthesis

Catalysis by Cobalt Carbonyls

Olefin Oxidation with Palladium(I1) Catalyst in Solution

H C Brown, Vol 11, p 1-20

A McKiUip and E C Taylor, Vol 1 1 , p 147-206

P Heimbach, P W Jolly, and G Wilke, Vol 8, p 29-86

A J Chalk and J F Harrod, Vol 6, p 119-170

A Aguild, Vol 5 p 321-352

F G A STONE

ROBERT WEST

I

I I

111

IV

v

VI

VII

VIII

IX

Hydro formylation

ROY L PRUETT

Chemicals and Plastics Division Union Carbide Corporation South Charleston, West Virginia

Introduction

Commercial Utilization

Reaction Mechanism

Secondary Products and Reactions

A Isomer Problems

B Alcohol Formation

C Alkane Formation

D Ketone Formation

E Olefin Isomerization

F Other Secondary Reactions

Substrates

A Acyclic Olefins

B Cyclic Olefins

C a$-Unsaturated Aldehydes, Ketones, and D Unsaturated Ethers and Alkenyl Esters E Conjugated Dienes

Catalyst Separation and Recycle

Heterogeneous Catalysts

Catalysts Other Than Cobalt and Rhodium Commercial Technology Trends

References

.

.

Esters 1

2

3

. 10

. 10

12

. 12

13

13

. 14

15

. 15

32

33

_ _ 42

. 44

. 46

. 47

53

. 57

. 57

I INTRODUCTION

Hydroformylation is the general term applied to the reaction of an olefin with carbon monoxide and hydrogen to form an aldehyde Because unsaturated hydrocarbons, especially C,-C, olefins, are important build- ing blocks in the petrochemical industry, and because oxygenated prod- ucts such as alcohols or acids are industrially important chemicals, the hydroformylation reaction has been the subject of intensive investigation

At the present time, about 8-10 billion pounds of aldehydes or derivatives

thereof are produced annually by hydroformylation of an olefin substrate, with butyraldehyde from propylene being the largest single primary prod-

1

Copyright 0 1979 by Academic Press, Inc

uct at a volume of about 6 billion pounds per year The process is the most important industrial synthesis which uses metal carbonyl catalysts

(I)

The hydroformylation reaction was discovered by Otto Roelen in 1938 (2, 3) while investigating the influence of olefins on the Fischer-Tropsch reaction (I 1 Particularly in commercial publications, it has been termed the “0x0” reaction; the more proper term, “hydroformylation,” was proposed by Adkins ( 4 )

The reaction does not proceed in the absence of catalysts As the contemporary Fischer-Tropsch catalysts were heterogeneous, the first hydroformylation catalyst was a solid (66% silica, 30% cobalt, 2% tho- rium oxide, and 2% magnesium oxide) Only later was the conclusion

reached and proved ( 5 ) that the actual catalytic species is homogeneous

The hydroformylation reaction has been the subject of excellent re- views (for example 1 , 6-8); therefore, the object of this particular treatise

is not to provide comprehensive coverage of all aspects The basic chem- istry is presented, along with recent developments of interest as reported

in the literature, although not in chronological order Stereochemical studies (6) are included only when pertinent to another point under consideration Carbonylations or hydrocarboxylation reactions which produce ketones, esters, acids, esters, or amides are not included (1 )

Also not included is the so-called “Reppe” synthesis, which is repre-

sented by Eq ( 1 )

( 1 )

RCH = CH, + 3C‘O + 2H,O + RCH,CH,CH,OH + 2C0,

II COMMERCIAL UTILIZATION

The primary product of hydroformylation, as it is usually practiced, consists of aldehydes with one more carbon atom than the olefin sub- strate

atives are alcohols, formed either by direct hydrogenation [Eq ( 3 ) ] , or

by an aldol condensation followed by hydrogenation [Eq (4)]

applications The major alcohol formed through the aldol sequence is 2-

ethylhexanol, again derived from propylene [Eq (4), R = CH,CH,-1 This alcohol is esterified with phthalic anhydride to form dioctyl phthalate (DOP), the utility of which is for plasticizing polyvinyl chloride resins

Processes have been described (9, 10) which combine the hydroformyl-

ation, aldol, and hydrogenation steps into a single process; however, these have not gained widespread industrial usage at this time Alcohols

of higher chain length, principally C,,-C,, , are utilized as detergents Other derivatives formed from the aldehydes are acids and amines,

produced by oxidation and reductive amination, respectively [Eqs (51,

111 REACTION MECHANISM

After it was recognized that the hydroformylation reaction is catalyzed

by a soluble species, HCo(CO), was proposed as the catalyst ( 1 1 ) Sub-

sequent proposals regarding the mechanism were made by Wender et a l

(12), and Natta et al (13, 14) made some important observations con- cerning the kinetics of the reaction The first-order dependence on hy- drogen pressure is balanced by an inverse first-order dependence on carbon monoxide partial pressure Therefore, the reaction rate is nearly independent of total pressure The reaction is first order in olefin and first order in cobalt at higher carbon monoxide partial pressures

Another important line of investigation concerned the ‘ ‘carbonyl in- sertion” reaction, which was best defined in manganese chemistry (15,

1 6 ) and extended to acylcobalt tetracarbonyls by Heck and Breslow The

“insertion” may be through three-membered ring formation or by nu- cleophilic attack of an alkyl group on a coordinated CO group

The mechanism offered by Heck and Breslow (17, 18) has been the

one most accepted as representing the probable reaction course This is

This scheme is shown with ethylene as the olefin substrate If the olefin

is substituted, i.e., RCH-LH,, the possibility exists for the formation

of the isomers RCH,CH,CO(CO)~ or RCH(CH,)Co(CO), in Eq (8) These isomers, which result from the insertion of olefin into the Co-H bond, then produce the isomeric aldehydes RCH,CH,CHO and RCH(CH,)CHO The understanding of the factors which determine these pathways and control the desired product, has been the motivation for much study For rhodium carbonyls, the reaction follows a similar pathway except for the complication of equilibria involving the presumed intermediate [HRh(CO),] (19) A similar equilibrium was postulated at an early date

by Natta et al (14) in order to explain the half-order dependence on

But for the less reactive cyclic olefin, the expression became, with RhJCO),, as the catalyst,

hydrogenation of the acyl intermediate (3) to aldehyde and HRh(CO),

(1) The Rh,(CO),, which was added as catalyst was transformed after a short induction period, the I-heptene reacted rapidly, and the acyl deriv- ative, not Rh,(C0)12, was seen in high-pressure infrared spectra (19, 20)

In the case of cyclohexene, no change was noted in the initial spectrum

of Rh,(CO),, at temperatures below 100°C and not too long reaction times This agrees with the kinetic data in that the reaction of the olefin with HRh(CO), is the rate-limiting step with this less reactive olefin, and that the HRh(CO), is in equilibrium with Rh,(CO),, At higher tempera- tures and/or longer reaction times, Rh,(CO)la was seen in the infrared spectrum and the reaction was slower The thermodynamically favored cluster under these conditions is Rh,(CO),, , and the equilibrium would

be less favorable for formation of HRh(CO),

Most hydroformylation investigations reported since 1960 have in- volved trialkyl or triarylphosphine complexes of cobalt and, more re- cently, of rhodium Infrared studies of phosphine complex catalysts under reaction conditions as well as simple metal carbonyl systems have pro- vided substantial information about the postulated mechanisms Spectra

of a cobalt I-octene system at 250 atm pressure and 150°C (21) contained absorptions characteristic for the acyl intermediate C,H,,COCo(CO), (2103 and 2002 cm-') and CO,(CO), The amount of acyl species present under these steady-state conditions increased with a change in the CO/

H, ratio in the order 3/1 > 1/1 > 1/3 This suggests that for this system

under these conditions, hydrogenolysis of the acyl cobalt species is a rate-determining step

However, when a less active olefin (e.g., diisobutylene or cyclohexene)

or a liganded system (Bu,P/Co = 2/1,80 atm CO/H2, 19OOC) was used, the hydrido species, e.g., HCo(CO),PBu, , predominated throughout the re- action The author concluded that in slower systems, initial interaction

of the olefin with the hydrido species HCo(CO),L could be the rate- determining step These results are complementary to those discussed

(vide supra) for the rhodium carbonyl catalysis

It should be noted that these results with the cobalt carbonyl phosphine catalysts may not apply over a wide range of conditions At milder conditions of lower temperature and low catalyst concentration, the con- version of Co,(CO), to HCo(CO),PR, is only partially completed, even with up to 5/1 ratios of P/Co (22)

In a different type of investigation, the individual steps of the hydro- formylation of ethylene by HIr(CO),[P(iso-C,H,),] were characterized

by high-pressure infrared studies (23) This particular catalyst was chosen because of its relative stability The series of spectra in Figs 1-3 show the changes that occurred on treating HIr(CO),(P-i-Pr,) with 200 psi of

ethylene at 50°C (Fig I), and on treating the resultant C2H,COIr(C0),)(P-

FIG 2 Infrared spectral changes during the reaction of C2H,Ir(CO),P-i-Pr3 and carbon

monoxide in heptane Reprinted with permission from J Organornetal Chem 94, 303

(1975) Copyright by Elsevier Sequoia S A

For the phosphine-substituted cobalt carbonyl hydroformylations, it is probable that the mechanism follows the pathway of Heck and Breslow (17, 18), although the possibility of an associative mechanism has been raised (7) The increased stability of the HCo(CO),PR, complexes toward

loss of CO was cited.as being suggestive of a nondissociative pathway The studies of Wilkinson et a l during the late 1960’s (24-27) concerning

TABLE I INFRARED SPECTRA OF IRIDIUM COMPLEXES (23) HIr(CO)3(P-i-Pr3) CZH5Ir(CO),(P-i-Pr3) CZH5COIr(CO)3(P-i-Pr3)

This selection was substantiated by the observation (29) that, if

HRh(CO)(PPh,), and HRh(CO),(PPh,), are present together in solution, only the latter reacts with ethylene at 25°C and 1 atm, as shown by NMR spectra

By inspection of Figs 4 and 5 it can be seen that the associative

formylation of olefins (24-27)

for the rhodium-triphenylphosphine-catalyzed hydro-

0 0

C H Z C H ~ R

I

co ph3P'l,/,,,l

IV SECONDARY PRODUCTS AND REACTIONS

A Isomer Problems

The principal product of the hydroformylation which is most desired

in industrial applications is a linear aldehyde The unmodified, cobalt- catalyzed processes produce a mixture of linear and branched aldehydes, the latter being mostly an a-methyl isomer For the largest single appli- cation-propylene to butyraldehydes-the product composition has an isomer ratio (ratio of percent linear to percent branched) of (2.54.0)/1 The isobutyraldehyde cannot be used to make 2-ethylhexanol, and iso-

Hydroformylation 11

butanol has less industrial value than n-butanol Consequently, isomer control of the hydroformylation is of tremendous economic importance and has been the motivating force behind detailed investigations of the mechanism, reaction parameters, and ligand effects

For unmodified cobalt reactions, the most influential parameter is car- bon monoxide partial pressure This effect is demonstrated in Table 11

(See also Section V,A, 1 .) Hydrogen pressure had a smaller effect (30)

Large discrepancies exist in the literature concerning the effect of tem- perature At first, temperature was concluded to have a large effect on the product isomer composition (31) Later work (32) showed that the very high reaction rates obtained at high temperatures required vigorous mixing to ensure against depletion of reactant gases in the liquid phase

If depletion occurred, a condition of artificially low PCo resulted and low isomer ratios were obtained Under conditions of sufficient agitation, temperature had an insignificant effect on isomer ratio

The relative value of n-butyraldehyde and isobutyraldehyde is well exemplified by the recent disclosure (33) of a process for decomposing unwanted isobutyraldehyde back to the elements of propylene, carbon monoxide, and hydrogen for recycling to make more n-butyraldehyde

TABLE I1 EFFECT O F CARBON MONOXIDE PARTIAL PRESSURE ON

ISOMERIC DISTRIBUTION O F T H E HYDROFORMYLATION

PRODUCTS OF OLEFINS (30)a

90 1.7

93

2

150

1.6 4.4

1 1 3.7

1 1 2.4 1.3 4.5 1.3 3.1 1.4 8.1 Solvent, benzene or toluene; PHI, 80 atm; catalyst,

Temperature 100°C

Temperature 110°C

Temperature 116°C

C%(CO)*

between 32 and 210 atm, is inversely proportional to the square of the

partial pressure The full kinetic expression for alcohol formation is expressed by Eq (17)

d[RoH1 - k[RICHO][Co][PH,][P COY

An alternate pathway for the hydrogenation has been suggested by Aldridge and Jonassen (35):

to produce all alcohols or all aldehydes (Section V,A)

C Alkane Formation

Interception of the reaction sequence at the alkylcobalt carbonyl stage before “ carbonyl insertion,” and hydrogenation of this intermediate,

produces an alkane This undesired side reaction is only minor (1-3%) in

cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins Ethylben- zene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (38)

Hydroformy lation 13

a$-Unsaturated aldehydes and ketones are mainly hydrogenated to the corresponding saturated compounds (39) In the main, conjugated dienes have yielded practically only monoaldehydes with cobalt catalysts

(40)

D Ketone formation

Ketones are formed under conditions of low total pressure and high

olefin concentration Bertrand et a l (41) pictured the formation as out- lined in Eqs (20) and (21) Ketone formation is most pronounced with ethylene (least hindered olefin), and diethyl ketone has been obtained in

190°C) (30) Complete isomerization was observed by Asinger and Berg (43) in the hydroformylation of 1-dodecene a t 150"-200"C The different results obtained by varying the partial pressure of carbon monoxide have been explained by postulating the presence of two catalytic species hav- ing different C O K o ratios, with the one having the lower ratio (more coordinatively unsaturated) being responsible for the isomerization Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride However, it has been shown that aldehydes may be found with formyl groups attached to

a carbon atom other than the two of the double bond even under "non-

isomerizing" conditions Piacenti and co-workers (44, 45) studied the hydroformylation of [ l-'T]propylene and of o-deuterated a-olefins Even for a-olefins with chain lengths up to C,, the formyl group was attached

to all possible carbon atoms in the product mixture However, in the deuterated experiments, deuterium was present only on carbons 2, 3,

and o of the resulting aldehydes These results were explained by pro-

posing that the isomerization of a rr-olefin cobalt carbonyl occurs without elimination of free olefin before aldehyde formation

CD,C H,C H,C I HC H,CH , + C D,CH,CH,CHZC HCH,

CHO

F Other Secondary Reactions

As a result of the temperatures involved, particularly in cobalt reac- tions, aldol condensations of the aldehydes can occur The aldol product can dehydrate and then be hydrogenated [Eq (22)l:

OH

I

2CH,CH,CH,CHO -+ CH,CH,CH,CHCHCHO

I CH,CH,

The dimer aldol (6) can then react further to form trimers (7, 8) either

by acetal formation, Eq (23), or by Tischenko reaction, Eq (24)

A small amount of formate esters (4%) is formed in the cobalt hydro-

formylation cycle ( 4 6 ) The amount is undetectable in the rhodium-cata-

lyzed reaction

V SUBSTRATES

A Acyclic Olefins

1 Unmodified Metal Carbonyl Catalysts

The reaction rates of various types of olefins follow much the same pattern with both cobalt- and rhodium-catalyzed systems Wender and co-workers (47) classified the nonfunctional substrates as straight-chain terminal, internal, branched terminal, branched internal, and cyclic ole- fins The results they obtained are given in Table 111

Some significant observations can be made from these results Straight- chain terminal olefins are the most reactive Little if any difference exists

between 2- and 3-internal, linear olefins Branching is important only if

present at one or more of the olefinic carbon atoms: reaction becomes more difficult as branching increases Cyclic olefins react in an irregular fashion, but all are less reactive than terminal, linear olefins

68.3 66.2 66.8 65.6 64.4 63.0

21.3

18.1 19.3 20.0 18.8 64.3 1.32 4.19 4.26 2.2 16.2 4.87 2.29 1.35 6.23 22.4 25.7 10.8 4.7 5.82

Olefin, 0.5 mole; 65 ml methylcyclohexane; 2.8 g (8.2 x

mole) Co,(CO),; 110°C; CO/H, 1/1; 233 atm Table reprinted

with permission from J Am Chem SOC 78, 5101 (1956)

Copyright by the American Chemical Society

Similar results were obtained by Heil and Marko (48) for an unmodified rhodium system (see Table IV)

The inclusion of styrene in Table IV is noteworthy Styrene hydrofor-

mylates easily with rhodium catalyst to give a mixture of 2- and 3-phen-

ylpropionaldehyde in good yield ( 1 ) This is in contrast to the results reported for the cobalt system, in which hydrogenation to ethylbenzene was the principal reaction

Hydroformylation 17 TABLE IV

HYDROFORMYLATION OF VARlOUS OLEFINS,

2-Methyl- I-pentene 2-Methyl-2-pentene

trans-4-Methyl-2-pentene 2.4.4-TrirnethyI-2-pentene

2,3-Dimethyl-2-butene

I24 55.8

50 1 40.5 34.4 40.2 41.9 25.7 14.7 29.7 3.0 0.7

(I Reaction conditions: 0.5 mole olefinfliter; toluene solvent; 5.3 x lo-* rnrnole Rh,(CO),,/liter; 7 5 T : 130

atrn COIH,

Branching at an olefinic carbon atom inhibited the reaction markedly, the most dramatic case being that of 2,3-dimethyl-2-butene It should be noted that the product in this case is nearly exclusively 3,4-dimethylpen- taldehyde for either cobalt or rhodium catalysis ( 1 ) Thus, a general rule that products containing a formyl group attached to a quaternary carbon atom are not formed (49) remains valid Hydroformylation proceeds only after isomerization has occurred

Because of the extreme industrial importance of simple hydrocarbons such as propylene in hydroformylation, the reaction of a-olefins has been studied in much detail As noted before, the formyl group can be attached

to either of the carbon atoms which constitute the original double bond For olefins of greater than C , chain length, the formyl group may, under

certain conditions, also be attached to a carbon atom which was originally saturated But for propylene only two isomers are possible, as shown in

possible, both cobalt and rhodium hydroformylations have been studied with product composition as the goal

For cobalt as catalyst, variations in reaction parameters have been studied as a means of controlling the product composition (or isomer ratio) Thus, variations in isomer ratio from 1 : to about 4 : 1 were observed under widely differing conditions of temperature, catalyst con- centration, partial pressure of hydrogen, and partial pressure of carbon monoxide

The most influential parameter in cobalt-catalyzed hydroformylation

was found to be carbon monoxide partial pressure Piacenti et af (30)

showed this to be influential for both a- and internal olefins Results are

detailed in Tables V and VI The percent of n-aldehyde rose rapidly as the carbon monoxide partial pressure was increased up to 30-40 atm C O ;

further increase had little effect 1-Pentene clearly gave a higher per- centage of straight-chain aldehyde than 2-pentene, but the difference was insignificant in the lower P c o experiments

The hydrogen partial pressure has a small but reproducible effect on the hydroformylation product composition The direction of the change

found was the same as for carbon monoxide partial pressures: the

higher PH2 experiments gave higher percentages of n-aldehyde

Conflicting results have been reported for the effects of catalyst con- centration in the cobalt-catalyzed reaction In early work, Hughes and

Kirshenbaum (31) reported that these parameters were very influential in

determining product composition; high temperatures and high catalyst concentrations resulted in products containing decreased amounts of the

TABLE V HYDROFORMYLATION O F P R O P Y L E N E A T V A R I O U S co P A R T I A L

PRESSURES" (30) Carbonyl equiv./olefin Straight-chain

70.0

58.2 50.4 44.5 47.5

61.7 65.7 72.6 75.5 79.8 81.1 81.3 81.4

~~~ ~

Reaction conditions: Propylene, 5 g; CO,(CO)~, 0.05 g; benzene,

27 g; PH, 80 atm; temperature, 80°C

Hydroformylation 19 TABLE VI

35.6

28 I

25.4 23.0 21.1 19.2 19.2 19.2 19.2

8.6

5 4

5.3 5.2

5 I

5 I

5.0 5.0 5.0

a Reaction conditons: Pentene, 5 g; Co,(CO),, 0.05

g ; benzene, 27 g; PHz, 80 atm; temperature, 80°C

A = % n-hexanal of total aldehydes formed: B and

C = % 2-methylpentanal and 2-ethylbutanal respec-

tively

linear isomer However, later work suggests that these results may have been artifacts caused by high reaction rates Both high temperatures and high catalyst concentration increase the rate of aldehyde formation and probably caused a depletion in dissolved carbon monoxide This would have the same apparent effect as a lower partial pressure of carbon

monoxide Pino et a l (32) showed that the rate of agitation, which

simulated varying degrees of transport of carbon monoxide from the gas phase to the liquid phase, caused a variation in n-hexanal content (from pentene) of 68.5-78.6% They also found that, provided the reaction rate was controlled by varying the concentration of olefin and of catalyst, the product composition varied only slightly as a function of either temper- ature or catalyst concentration Results found are tabulated in Tables VII and VIII

TABLE VII

PROPYLENE" (32) EFFECT OF TEMPERATURE ON PRODUCT COMPOSITION IN THE HYDROFORMYLATION OF

Temperature Pco g C,Hd100 g g Co,(CO)$IOO g Straight-chain

2(n-C4H,),P] Under the same conditions except at a temperature of 190°C, the n-hexanol was 84% of the hexyl alcohol produced

In addition to the increased proportion of linear product, other differ- ences from the unmodified cobalt-catalyzed reaction may be noted The

TABLE VIII EFFECT OF CATALYST CONCENTRATION ON PRODUCT

COMPOSITION I N THE HYDROFORMYLATION OF PROPYLENE

CONDUCTED IN THE PRESENCE OF ETHYL ORTHOFORMATE"

orthoformate, 90 g; PHs, 80 atm; Pco 230 atm; temperature,

110°C

Hydroformy lation 21

pressure of 500 psi is significantly less than that employed in processes using CO,(CO)~ [or HCo(CO),] as catalyst Without stabilizing ligands, high partial pressures of carbon monoxide are necessary to maintain the stability of cobalt hydrocarbonyl and prevent decomposition to cobalt metal; the pressure required increases logarithmically as the reaction temperature is increased (53) However, it is recognized that phosphines are stronger a-donors and poorer r-acceptors than carbon monoxide Thus, in Co,(CO),(PR,), or HCo(CO),PR, , the remaining carbon mon- oxide ligands are more strongly bound to the cobalt atom because the metal tends to transfer the increased electron density back to the ligand

tion of I-pentene The products consisted of hexyl aldehydes and hexyl alcohols in the ratios of 95:s and 30:70, respectively In a negative aspect of the reaction, they observed 23% hydrogenation of alkene to alkane at a reaction temperature of 195°C with the phosphine-modified catalyst Tucci (54) reported less alkane formation (4-5%) under more

favorable reaction conditions ( 160°C, H,/CO 1.2, 1 h o u r reaction time) The selectivity to straight-chain product as well as the rate of reaction were found to be greater for the more basic phosphines ( 5 2 , 55), as shown

much greater rates of reaction than the substituted complex; Tucci (57)

found a reaction rate ratio of 175 at 120°C Thus, if an equilibrium exists

with small amounts of uncomplexed catalyst being present, the effect of this small amount will be magnified and the rate and product composition

will reflect uncomplexed cobalt catalysis

(27)

O X 0 condlUons HCo(CO),L

HCo(CO), + CO z= HCo(CO),

If ligand dissociation is important, and if it is more extensive when L

= PPh, than when L = PR,, then the PPh,-Co catalysts system should

be very sensitive to changes in ligand concentration This was found to

be the case (55), as shown in Fig 6

Another significant and positive characteristic of phosphine-modified cobalt systems is that a high proportion of linear products can be obtained

from internal olefins, with only a small sacrifice in reaction rates (58), as

shown in Table X

Tucci (5#), studying mainly terminal olefins, cited two reasons for the high selectivity for linear products in the phosphine-modified cobalt ca- talysts: (a) stereoselective addition of the hydride species to the olefinic double bond, and (b) inhibition of olefin isomerization However, the results obtained with internal olefins as substrate tended to discount the likelihood of the second reason, and it is generally accepted that selective anti-Markovnikov addition arising from steric hindrance is the principal cause for linear products from nonfunctional olefins

-1.8 -1.9

-2.5

P/Co RATIO FIG 6 Concentration effects of various organophosphines on hydroformylation rates Reprinted with permission from Znd E n g Chem., Prod Res Dev 9,516 (1970) Copyright

by the American Chemical Society

Hydroformylation 23

TABLE X COMPARISON OF HYDROFORMYLATION OF I-HEXENE A N D 2-HEXENE" (58)

' I Reaction of 30.5 ml of olefin in 75 ml of benzene solvent at 400 psi total pressure, H,/

CO = 2 Catalyst charge 1.28 g Co,(CO), and 2.56 g Bu,P Reaction run overnight (about

17 hours) Table reprinted with permission from Ind E n g Chern Prod R e s D e v 7, 226 (1968) Copyright by the American Chemical Society

M O M normal products x 100/mol% normal plus mol% branched products

H,/CO = I , only 87% conversion of the I-hexene occurred overnight, also incomplete

1.Time to consume 4 of the total gas reacted during the run

hydrogenation of the RCHO product to RCH,OH

Further progress in providing linear aldehydes from olefinic substrates has been provided by modified rhodium catalysts Without modifiers, the product from the hydroformylation has very low normal : is0 isomer ra- tios; I-octene gave only 31% of the linear isomers in one example (28)

In an early investigation (28, 59, 6 0 ) , critical combinations of several

reaction parameters were discovered to produce unusually high yields of the linear isomer The parameters included low partial pressure of carbon monoxide, high concentration of phosphite or aryl phosphine ligands, and low total gas pressure The catalyst was a soluble complex of rhod- ium, formed in situ from rhodium metal in many cases Isomer ratios of

10: 1 to 30: I were obtained by appropriate selection of these reaction

parameters Losses to alkane were minimal, even with Pco a s low a s 10

psi Tables XI-XIV illustrate the effects of these various reaction param-

eters on the product composition

These effects of the reaction parameters were interpreted in terms of

a catalyst equilibrium series, a s shown in Eq (28)

c 0

HRh(CO),(PR,) + HRh(CO)Z(PR,)z '0 HRh(CO)(PR,), ( 2 8 )

High ligand concentrations and/or low partial pressures of carbon mon- oxide cause a predominance of species substituted by more than one phosphorus ligand These species containing multiple ligands present a greater sterically hindered environment for the olefin substrate and favor

the linear product (24) Trialkylphosphines, the more basic ligands of the

TABLE XI

HYDROFORMYLATION OF I-OCTENE AT VARIOUS

TOTAL PRESSURES~ (28)

~~

Reaction time % Aldehyde which

Octene, 112 g; 5% Rh/C, 15 g; triphenyl phosphite,

15 g; toluene, 200 ml; temperature, 90°C; 1/1 H,/CO

Table reprinted with permission from J Org Chem

34, 327 (1%9) Copyright by the American Chemical

Society

series studied, probably do not participate in multiple substitution be- cause of the increased electron density imposed by the ligand without

effective back-bonding ability to remove the density Likewise, the o-

substituted triaryl phosphites were less effective It was concluded that these were too sterically crowded to permit multisubstituted catalyst species

Wilkinson and co-workers studied in detail the beneficial effects of

triarylphosphine modification of rhodium carbonyls (24, 25, 27, 61) In

TABLE XI1

HYDROFORMYLATION OF I-OCTENE WITH VARYING CONCENTRATIONS OF LIGAND" (28)

% Aldehyde which Reaction time is P(OC,H,X (g) (min) straight-chain

Octene, 112 g; 5% Rh/C, 15 g; toluene, 200 ml; tem-

perature, 90°C; 80-100 psi of 1/1 HdCO

In the absence of ligand, the reaction would not pro- ceed at the cited conditions of temperature and pressure;

slightly more severe conditions were required Table re-

printed with permission from J Org Chem 34, 327

Copyright by the American Chemical Society

Hydroformylation 25

T A B L E XI11

RATIOS" (5'9)

HYDROFORMYLATION OF 1 - O C T E N E WITH VARIOUS Hz/CO

Reaction % Aldehyde which H,/CO Ratio RhiC (g) time (min) is straight-chain

'I Octene, 112 g ; 5% RhlC 10-15 g; toluene, 200 ml; triphenyl

phosphite, 15 g; temperature 90°C; pressure, 80-100 psi

addition to affording improved isomer ratios, the reaction proceeded under conditions of temperature which were much milder than those effective with cobalt or even phosphine-modified cobalt catalysts The halide complex RhCl(CO)(PPh,), was effective as a catalyst at tempera- tures >60°C and pressures of CO/H, > 20 atm ( 2 4 ) However, with such

halide complexes an inhibition period was always observed which could

be eliminated by addition of a base such as triethylamine This suggested that the amine was acting a s a hydrogen halide acceptor to form a catalytically active hydride species by hydrogenolysis The resulting HRh(CO)(PPh,), was highly active a s a catalyst, effective even at 25°C and 1 atm From I-alkenes, approximately 95% of the straight-chain aldehyde was produced

a Octene, I12 g ; toluene, 200 ml: 5% RWC, 10 g; R,P 0.05 mole;

pressure, 80-100 psi l i l H,/CO Table reprinted with permission from

J O r g Chem 34, 327 (1969) Copyright by the American Chemical

Society

Information published from several sources about 1970 presented de- tails on both the halide-containing RhCI(CO)(PPh,),- and the hydride- containing HRh(CO)(PPh,),-catalyzed reactions Brown and Wilkinson (25) reported the relative rates of gas uptake for a number of different olefinic substrates, including both a- and internal olefins These relative rates are listed in Table XV 1-Alkenes and nonconjugated dienes such

as 1,Shexadiene reacted rapidly, whereas internal olefins such as 2- pentene or 2-heptene reacted more slowly by a factor of about 25 It

should also be noted that substitution on the 2 carbon of 1-alkene ( 2 -

methyl- 1-pentene) drastically lowered the rate of reaction Steric consid- erations are very important in phosphine-modified rhodium catalysis

In the same study, Brown and Wilkinson reported on the effects of excess phosphine, including an increase in the ratio of straight branched- chain products and also a decrease in the rate of the competing hydro- genation and isomerization reactions The total rate of reaction was also

decreased with excess phosphine, but not to an excessive degree over the range studied The above conclusions were applicable to 1 : 1 mixtures

of hydrogen and carbon monoxide A ratio of 2/1 HJCO resulted in higher reaction rates and higher isomer ratios, and it also dramatically increased the undesirable hydrogenation and isomerization reactions Some quantitative data for these trends are given in Table XVI

Catalytic runs were carried out at higher pressures (400 psi) and tem-

TABLE XV RELATIVE RATES OF HYDROFORMYLATION OF UNSATURATED

I-Heptene I-Dodecene Vinyl acetate Cyclooctene Ethyl vinyl ether 2-Pentenes cis-2-Heptene dl-Limonene 2-Methyl- I-pentene

3.50 3.18 0.75 0.26 0.20 0.15 0.12 0.10 0.06

(I Catalyst, HRh(CO)(PPh,),, 2.5 mm; solvent, benzene, olefin concen- tration 1.0 M; temperature, 25°C; pressure, 500 mm of 1/1 H.JCO Table reprinted with permission from J Chem Soc A, p 2753 (1970) Copyright

by the Chemical Society

Rate measured as gas uptake in ml min-I 1 : 1 : 1 Mixtures of alkene, hydrogen, and carbon monoxide at 600 mm total pressure gave uptakes for ethylene and propylene of 4.55 and 1.60 ml min-I, respectively

Hydroformy lation 27

TABLE XVI REACTION PRODUCTS FROM THE HYDROFORMYLATION OF I-HEXENE" (25)

Hydrogenation and Moles excess Temperature n-Aldehyde isomerization products

PPh, ("C) H2/C0 (% of total) (%)

2s

40 2s

I atm HJCO

peratures of 25", 45", and 65"C, with no excess phosphine, and a gas ratio

of 1/1 H,/CO Low isomer ratios of ( 2 - 4 ) : 1 were obtained When the gas ratio was 2/1, the isomer ratio was still low and the competing hydrogen- ation and isomerization reactions were serious However, conducting the reaction with a 100-fold molar excess of triphenylphosphine gave a

slightly higher isomer ratio ( 5 6 ) and decreased the competing reactions

to a combined 4-5% In an "ultimate" reaction conducted in molten triphenylphosphine under 400 psi, high rates were obtained, as well as isomer ratios up to 16: 1, but the competing hydrogenation accounted for

7-2S% of the product composition

Another study in 1970 (62) reported a HRh(CO)(PPh,),-catalyzed re-

action at 500 psi and 107°C It was found that a s a general rule, propylene

gave an isomer ratio of about 2 : 1, whereas higher a-olefins gave ratios

of about 3 : 1 Under these general conditions conversions and selectivi- ties to aldehyde were excellent, as noted in Table XVII [see also ( 6 3 ) ]

The rate of hydroformylation was found to vary in a nonlinear fashion

as a function of triphenylphosphine concentration A maximum in rate

was noted at a triphenylphosphine/HRh(CO)(PPh,), weight ratio of ( S -

10) : 1 , as illustrated in Fig 7 A maximum in selectivity to linear aldehyde

was noted at about a 5 : 1 ratio, and no significant further increase was noted up to a 50: I ratio of triphenylphosphine to rhodium complex

In these studies it was also reported that butyraldehyde isomer ratios

were increased by lowering the partial pressure of carbon monoxide, but that this decrease in Pco caused a dramatic and parallel increase in

propane formation It was concluded that propane was formed in lieu of isobutyraldehyde at low Pco This effect is illustrated in Fig 8

Craddock et al (64) studied the hydroformylation of a-olefins (princi-