31P NMR Studies of Catalytic Intermediates in Triphenylphosphine

104 31

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

Downloaded by UNIV OF LEEDS on May 18, 2016 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch104

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


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

31

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


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


506

PHOSPHORUS CHEMISTRY

3,a

Ph P 3


(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

31


(Ph P) 3

3

OSWALD E T AL.


104.

NMR


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


PHOSPHORUS

508

v

Λ


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


104.

OSWALD E T AL.

NMR


Intermediates

509


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.


31P NMR Studies of Catalytic Intermediates in Triphenylphosphine

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