P NMR Studies of Catalytic Intermediates in Triphenylphosphine

The Corporate Research Science Laboratories, P.O. Box 45, Linden, ... JOHN C. REISCH — The Intermediates Technology Division of Exxon Chemical...
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P NMR Studies of Catalytic Intermediates in Triphenylphosphine Rhodium Complex Hydroformylation Systems A L E X I S A . O S W A L D , J O S E P H S. M E R O L A , and E D M U N D J . M O Z E L E S K I — The Corporate Research Science Laboratories, P.O. Box 45, Linden, NJ 07036

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R O D N E Y V. K A S T R U P — The Analytical and Information Division of Exxon Research and Engineering Company, P.O. Box 121, Linden, NJ 07036 J O H N C . R E I S C H — The Intermediates Technology Division of Exxon Chemical Company, P.O. Box 241, Baton Rouge, LA 70821

Phosphorus-31 NMR was found to be a powerful tool in studies correlating the structure of triphenylphosphine rhodium complexes with their behavior as catalysts (1,2). In a previous study (2), the rate of dissociation of the tris(triphenylphosphine) rhodium carbonyl hydride (Formula I, in Figure 1, i.e., tris-TPP complex) low temperature, low pressure hydroformylation catalyst, dis­ covered by Wilkinson (3), was determined in the presence of excess TPP in aromatic solvents at varying temperatures. The dissociation product, i.e., bis-(triphenylphosphine) rhodium carbonyl hydride (II), was proposed (2) as a key catalytic inter­ mediate in the selective terminal hydroformylation of n-1-olefins as outlined by the catalyst cycle of Figure 1 using commercial TPP complex plus excess TPP catalyst systems (4,5,6). In the pre­ sent work, further catalytic intermediates and their equilibria were studied (Figure 1). These studies were carried out primarily at low temperatures using a JEOL FX900 spectrometer, under varying partial pressures of reactant gases, particularly H2 and CO mix­ tures, in NMR pressure tubes. Chemical shifts were calculated with reference to a 1M solution of aqueous H3PO4. For most of the present studies, the tris-TPP complex was generated from dicarbonyl acetylacetonato rhodium (III, Acac com­ plex) and TPP by low pressure hydrogénation via the scheme shown in Figure 1. The first step of this sequence is known (3). The complete conversion to the tris-TPP complex under ambient conditions was developed as a facile and quantitative, preparative method during the course of the present work. The Acac complex was usually added to provide a 1% mixture in an appropriate solution of TPP in a previously nitrogenated, stirred, 9 to 1 volume mixture of toiuene and perdeuterobenzene. One of the CO 1igands was immediately displaced by TPP as indi­ cated by the instant gas evolution. After removing the CO in vacuum, the resulting solutions of the intermediate (IV) were hydrogenated to obtain the tri s-TPP complex. The 2,4-pentanedione by-product did not compete in the presence of excess TPP and Hz for coordinating the rhodium. 0097-6156/81/0171-0503$05.00/0 © 1981 American Chemical Society Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

PHOSPHORUS

504

CHEMISTRY

+H (-CH CH CHO) 2

3

3

2

2

j CH =CH.

Acoc"Rh(Ph P)CO 3

2

[(Ph P) Rh(CO)CH CH ]

(Ph P) Rh(CO)H 3

3

3

.CO

VIII

(Ph P) Rh(CO)

[(Ph P) Rh(CO)H" 3

3

2

2

IV

COCH CH 2

TH =CH

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CO RCHOI I H

+

Acac~Rh (CO)

2

3

IX

2

(Hi P) Rh(CO) H

0

3

0

2

2

I I III

*! [(Ph P) Rh(CO)] 3

2

[Ph PRh(CO) ] 3

3

2

VI

VII Figure

1.

Catalytic

intermediates and their relationship to the proposed cycle of selective terminal hydroformylation.

2,a

catalytic

(Ph P) Rh(CO)H 3

3

Ph P 3

P/Rh = 9 Ph PO

2 Atm. H

3

9

Ph P 3

2,b

(Ph P) Rh(CO)H 3

3

(Ph P) Rh(CO) H „^ P/Rh = 9 Ph PO 2 Atm. H /CO JL 3

ΓΤΊ

2

2

3

2

P/Rh = 6 2 Atm. H /CO 2

I ι ι ι ι 1ι ι ι ι I 40 30

t, » , , 1 20

10

0

-10

C H E M I C A L S H I F T , ppm Figure 2,

The effect of H and H?/ COon 1% toluene solutions TPP as shown by Ρ NMR at -90° C. 2

of Acac

Rh(CO) plus

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Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

2

2

104.

OSWALD E T A L .

NMR

Studies of Catalytic

Intermediates

505

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In the second f i g u r e ( 2 a ) , a 31 ρ NMR spectrum at -90° o f such a tris-TPP complex i s shown i n the presence o f 6 moles free TPP per mole complex under about 2 Atm hydrogen pressure a f t e r equi1ibration. In a s e r i e s o f experiments s i m i l a r mixtures c o n t a i n ­ ing d i f f e r e n t r a t i o s o f the s t a r t i n g Acac complex and TPP, were placed under about 2 Atm pressure o f a 1 to 1 mixture o f Hz and CO, and equi1ibra ted by mechanical shaking. The NMR spectra were then determined at - 9 0 ° . At P/Rh r a t i o s o f 9 and 6, the t r i s TPP complex was the dominant species (Figure 2 , b and c ) . At a P/Rh r a t i o o f 3 . 3 , these species became minor components. In another s e r i e s o f experiments, a 1% s o l u t i o n o f the t r i s TPP complex, ( I ) , plus excess TPP to provide a P/Rh r a t i o o f 9, was placed under H2 and then 13co p r e s s u r e . The r e s u l t s were similar. They are i l l u s t r a t e d by Figure 3. When 2 Atm o f H2 was fol lowed by 2 Atm CO, the mixture contained predominantly the presumed dicarbonyl hydride (Figure 1 , V and Figure 3 , a ) . The use o f a high r a t i o o f H2 to CO (2 Atm to 0.3 Atm), r e s u l t e d mainly i n the tris-TPP complex (Figure 3 , b ) . On the other hand, 0.3 Atm CO alone r e s u l t e d mainly i n an u n i d e n t i f i e d complex, p r e ­ sumably a t r i c a r b o n y l dimer (Figure 1, VI and Figure 3 , c ) . A p p a r e n t l y , the p a r t i a l pressures o f not only the CO but o f the Hz as well have a major e f f e c t on the e q u i l i b r i a between the di f f e r e n t complex speci e s . When a 1 % n-valeraldehyde s o l u t i o n o f the Acac complex ( I I I ) , plus varying amounts o f TPP, were pressured to 2 Atm with a 1 to 1 mixture o f H2/C0, the i n i t i a l complex e q u i l i b r i a were about the same as those p r e v i o u s l y found i n the aromatic sol vent. As i s shown by Figure 4, when the P/Rh r a t i o was 1 5 , the dominant Rh compound at 35°C was the tris-TPP complex ( I ) . At a P/Rh r a t i o o f 6, the presumed dicarbonyl hydride (V) was the major complex. When the P/Rh r a t i o was only 3 . 3 , major amounts o f the rhodium were i n the form o f f a s t exchanging more h i g h l y carbonylated species. However, i t was found that i n aldehyde s o l u t i o n the t r i s TPP complex i s l a r g e l y converted to a presumed dimer (VII) when stored f o r 16 hours (Figure 5,a). It appears that the same dimer i s a l s o formed q u a n t i t i v e l y from the Acac complex under N2 at room temperature (Fi gure 5 , b ) . These r e a c t i o n s could be reversed to provide the tris-TPP upon p r e s s u r i n g the s o l u t i o n by 2 Atm Hz (Figure 5 , c ) . In Figure 1, the observed reactions are i n d i c a t e d i n the context o f a proposed c a t a l y t i c scheme f o r terminal hydroformy­ lation. The r e a c t i o n pathway i n v o l v i n g the a l k y l phosphine i n t e r ­ mediate (VIII) i s the most l i k e l y . O v e r a l l , the r e s u l t s o f the NMR studies provide c o n s i s t e n t explanations f o r the process p a r a ­ meters o f s e l e c t i v e h y d r o f o r m y l a t i o n , p a r t i c u l a r l y o f the low pressure continuous product f l a s h o f f process (.5,6.). It was shown t h a t , i n c o n t r a s t to p r i o r i n d i c a t i o n s (3_) » the tris-phosphine complex (I) i s a remarkably s t a b l e and favored species i n the presence o f excess phosphine and H 2 . This complex (I) i s postu­ l a t e d to have a key r o l e i n the r e v e r s i b l e generation and

Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

506

PHOSPHORUS CHEMISTRY

3,a

Ph P 3

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(Ph P) Rh(CO)H ^p(Ph P) Rh(CO) H 3

3

3

2

2

Ph PO

2 Atm. Ho

3

2 Atm. ^ C 0 1

X

t I i I I I I I I 1 I

40

30

20

10

0

-10

C H E M I C A L SHIFT, ppm Figure

3.

u

I3

The effect of H / CO and CO on /% toluene solutions Rh(CO)H, plus TPP as shown by Ρ NMR at -60° C. 2

of

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Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

(Ph P) 3

3

OSWALD E T AL.

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104.

NMR

Studies of Catalytic

ι . . . . 1 . . . . . . . . .

40

30

1»»» •

20

10

Intermediates

507

I . . ι • ι • ι ι ι1

0

-10

C H E M I C A L SHIFT, ppm Figure 4.

The effect of H I CO on 1% valeraldehyde solutions of AcacRhfCO) 2 plus TPP as shown by Ρ NMR at -35° C. 2

31

Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

PHOSPHORUS

508

v

Λ

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CHEMISTRY

5,a

[(Ph P) Rh(CO) 3

2

2

]

Ph P 3

UU 5,b Ph P 3

(Ph P) Rh(CO)H 3

3

5,c Ph P 3

KJ

40

l i t

k i i k.

30

20

• •·••• I

10

0

-10

C H E M I C A L SHIFT, ppm Figure 5. Complexes derived in 1% aldehyde solutions (a) from (Ph ) Rh(CO)H, (b)from A cacRh(CO) plus 3 TPP, and (c)from A cacRh(CO); 3 TP Ρ under 2 atm. H as shown in /% i-butyraldehyde solution by Ρ NMR at -6QP C. J

3

2

:

31

Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

104.

OSWALD E T AL.

NMR

Studies of Catalytic

Intermediates

509

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s t a b i l i z a t i o n o f the r e a c t i v e , key c a t a l y t i c trans-bis-phosphine complex intermediate, II.

Literature Cited: 1. Tolman, C. A., Meakin, P. Ζ., Lindner, D. L., Jesson, J. P., J. Amer. Chem. Soc., 1974, 96, 2762. 2. Advances in Chemistry, Editors Alyea, E. C., and Meek, D. W., American Chemical Society, 1981, 196, 78, paper of"31PNMR Studies of Equilibria and Ligand Exchange in Triphenylphos­ phine Rhodium Complex and Related Chelated Bis-Phosphine Rhodium Complex Hydroformylation Catalyst Systems," by Kastrup, R. V., Merola, J . S., and Oswald, A. A., in press. 3. Bonati, F., and Wilkinson, G., J . Chem. Soc. Α., 1964, 3159; Yagupsky, G., Brown, C. Κ., and Wilkinson, G., J. Chem. Soc. A, 1968, 2660 and Chem. Commun., 1969, 1244; Evans, D., D., Osborn, J . Α., Wilkinson, G., J. Chem. Soc. A, 1968, 3133; Yagupsky, Μ., Brown, C. Κ., Yagupsky, G., and Wilkinson, G., J . Chem. Soc. A, 1 970, 941; Yagupsky, G., Brown, C. Κ., Wilkinson, G., J. Chem. Soc. A, 1979, 1392; Brown, C. Κ., Wilkinson, G., J. Chem. Soc. A, 1970, 2753. 4. Pruett, R. L . , Smith, J . Α., J. Org. Chem., 1969, 34, 327. 5. Advances in Organometallic Chemistry, Editors: Stone, F. G. Α., West, R., Academic Press, Inc., 1979, 17, 1. Chapter on Hydroformylation by Pruett, R. L. 6. New Synthesis with Carbon Monoxide, Editor Falbe, J., Springer-Verlag, Berlin-Heidelberg-New York, 1980, 1, Chapter on Hydroformylation, Oxo Synthesis Roelen Reaction by Cornils, B. RECEIVED

July 7, 1981.

Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.