Hydroformylation of olefins catalysed by (1,5-cyclooctadiene) salicylaldoximatorhodium under atmospheric pressure

JOURNALOF

MOLECULAR CATALYSIS E LS EV I ER

Journal of Molecular Catalysis 88 (1994) 277-286

,

Hydroformylation of olefins catalyzed by ( 1,5cyclooctadiene) salicylaldoximatorhodium under atmospheric pressure Wanzhi Chen, Yun Xu, Shijian Liao

*

Dalian Institute of Chemical Physics, Chinese Academy of Scwnces, Dalian 116023, People's Repubhc of China

(Received May 13, 1993; accepted November 2, 1993)

Abstract Hydroformylation of vinylarenes, alkenes and cyclic olefins has been mvestigated usmg (1,5cyclooctadiene) salicylaldoximatorhodium ( Rh (SOX) (COD)) as catalyst precursor at 0.1 MPa and 60°C in toluene. It has been found that the anionic salicylaldoximatochelate ligand plays an important role in determining the hydroformylation activity under mild conditions. The reaction rate and regioselectivity also depend on the phosphine or phosphite ligands added. The combination of Rh(SOX) (COD) with diphosphine ligands is the more active in the hydroformylation of vinylarenes, but those with monophosphine ligands are favoured in the hydroformylation of alkenes. The use of diphosphine increases the formation of branched aldehydes both in the hydroformylation of vinylarenes and alkenes. Increasing the phosphine concentration results in a decrease of the catalytic activity, but the regioselectivity almost keeps constant in all cases. Key words: hydroformylauon;olefins, phosphlne ligands; rhodium, salicylaldoxlmatoligand

1. Introduction The homogeneous hydroformylation of olefins has attracted much interest, especially in terms of its synthetic utility, as well as the studies probing the mechanism of this valuable process [ 1]. Much of the recent effort has been focused on the use of rhodium complexes as catalysts (usually containing phosphine ligands), since some rhodium complexes exhibit high activity [ 2 - 6 ] as compared to other transition metal catalysts. However, in many cases the regioselectivity is not very high, The development of a catalyst for the regioselective * Corresponding author; fax. ( + 86-411 )3632426. 0304-5102/94/$07.00 © 1994 Elsevier Science B V. All rights reserved SSDl0304-5 102(93) E0288-R

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IV Chert et al. / Journal t)f Molecuhw Cataly 9is 88 t 1994) 2 7 ~ 2 8 6

hydroformylation of vinylarenes to 2-arylpropanals under mild conditions would be of significance, since these aldehydes can be used in the preparation of perfumes and nonsteroidal anti-inflammatory agents [ 7]. Extensive research has been directed to this field, yet none of the existing catalysts are fully satisfactory. We previously described the hydroformylation of styrene catalyzed by Rh(I) complexes containing different chelate ligands having N and O as donating atoms [8-10]. In this paper, we report the catalytic performance of R h ( S O X ) ( COD ) in the hydroformylation of vinylarenes, linear and cyclic olefins under atmospheric pressure.

-...~=CH..~,,~ OH

2. Experimental

All reactions were performed under an inert atmosphere of nitrogen or argon. Inert gases were dried and deoxygenated by successive passing through columns packed with copper and 5,~ molecular sieve respectively. Styrene, p-methylstyrene and E,E,Z-1,5,9-cyclododecatriene were dried with molecular sieves and distilled under reduced pressure just before use. Toluene was refluxed and distilled from sodium-benzophenone under inert gas. Acenaphthylene was recrystallized from absolute alcohol. R h ( S O X ) ( C O D ) was synthesized from [ R h ( C O D ) C I ] 2 (prepared by the method described in the literature [ 11 ] ) and the salt of salicylaldoxime in tetrahydrofuran at room temperature. Sodium salicylaldoxlmate ( 0.159 g, 1.0 mmol) was added to a stirred solution of [ R h ( C O D ) C I ] 2 (0.246 g, 0.5 mmol) in tetrahydrofuran (20 ml). This mixture was stirred continuously for 24 h. The precipitate was removed by filtrauon. The volume of filtrate was reduced to ca. 5 ml by evacuation and cooled to 0°C to give an orange powder which was filtered off, dried in vacuo at room temperature: yield 88%. Analysis. Found: C, 51.57; H, 5.17; N, 3.32. Calcd: C, 51.87: H, 5.16: N, 4.03. IR: ~,(C=C) 1460 cm I (s), 1435 cm 1 (s): u ( C = N ) 1590 cm-~. More detailed information will be published elsewhere together with the synthesis of other rhodium complexes. All hydroformylation reactions were conducted in jacketed glass bottles under an oxygenfree atmosphere of CO and H2 ( 1: 1) at a constant pressure of 0.1 MPa. The reactor was evacuated, filled with carbon monoxide and hydrogen, then R h ( S O X ) ( C O D ) and the appropriate phosphine or phosphite ligands in toluene were injected successively. The mixture was stirred for 20 min and the reaction was started by injection of olefins into the reactor through a self-sealing silicon rubber cap. The temperature was regulated with circulating water and a thermostat. The reaction rate was monitored by a constant-pressure gas burette connected to the reactor. The products were analyzed by gas chromatography with a 2 m OV-101 column.

279

W. Chen et al. / Journal of Molecular Catalysis 88 (1994) 277-286 3. R e s u l t s a n d d i s c u s s i o n

3.1. H y d r o f o r m y l a t i o n o f sO, rene

In the hydroformylation of styrene, 2-phenylpropanal and 3-phenylpropanal were produced, without hydrogenation products of the aldehydes and the starting olefins.

,(~J=

+ C0 + H2

=

~/~ICHO

+ (~I~CHO

The Rh complex alone shows no catalytic activity in the hydroformylation of styrene at 60°C and 0.1 MPa pressure. The effects of ligands such as triphenyl phosphite, bis (diphenylphosphino) methane (dppm), 1,2-bis (diphenylphosphino) ethane (dppe) and 1,3-bis(diphenylphosphino)propane (dppp) were examined. As shown in Table 1, the combination of R h ( S O X ) (COD) with dppm is inactive in the hydroformylation of styrene. Fairly rapid hydroformylation rates can be achieved using R h ( S O X ) (COD) in the presence of dppp, dppe and P (OPh) 3 under mild conditions. Rh ( SOX ) ( COD ) in combination with dppp is the best catalyst system with which an optimum reaction rate (turnover frequency) of 0.89 m i n - ~can be obtained. This activity is almost 7 times higher than that of P(OPh) 3. The regioselectivity of these catalyst systems is of the same magnitude as those reported by others [2,12]. Both combinations with dppe and dppp lead to a 2-phenylpropanal selectivity over 93%. The use of phosphite ligand which is a good electron acceptor allows the formation of 3-phenylpropanal in 60,2% selectivity. Obviously, this result demonstrates that the regioselectivity strongly depends on the electron donating ability of the phosphorous ligands. Table 1 Hydroformylanonof styrene~ Phosphlne or phosphtte

P/Rh

TOP I mm- L)

TO~

Regloselectivlty (%) 2-phenylpropanal

3-phenylpropanal

39.8

60.2

P(OPh)3

2

0 13

43

dppm

2

0

0

dppe

2 5 10

0.74 0.25 0.11

267 90 39

96.0 97.4 96 3

4.0 2.6 3.7

dppp

1 2 5 !0

0.55 0.89 0 79 0.46

74 194 213 178

93.8 95.4 94.5 96.0

62 4.6 5.5 4.0

a 0 1 MPa. 60°C, toluene8 ml, styrene 2 ml. reactionrime 7 h, Rh(SOX) (COD) 2.0 x 10 5 mol. t, Initialturnoverfrequencydefinedas moles of styreneconvertedper mole of Rh per min. Turnoverdefinedas mole of styreneconverted per mole of Rh withinthe reaction time.

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w. Chen et al / Journal of Molecular Catalysls 88 (1994) 277-286

The influence of P / R h ratio was investigated since it is an important factor in the hydroformylation of olefins. M a x i m u m catalyst activity can be obtained at a ratio of P / Rh --- 2, and catalyst deactivation with time is also observed at a lower P / R h ratio. Increasing the P / R h ratio results in a decrease of initial catalyst activity, but the catalyst activity can persist for a longer period. Therefore, a small excess of phosphine ligand is essential for the hydroformylation of styrene. The regioselectivity is essentially insensitive to the P / R h ratio as demonstrated in Table 1. Although there are some small variations, the selectivity to the branched aldehyde is quite similar in all cases (93.8-97.4% branched). This result is unusual since it is known that the P / R H ratio controls the behaviour of hydroformylation reaction and that an excess of phosphine ligand favours the formation of the linear aldehyde at the expense o f reaction rate [ 1 ]. The behaviour of Rh ( S O X ) ( C O D ) - d i p h o s p h i n e system is somewhat similar to that of the Rh-triphenylphosphole system [ 13] which was thought to be the first example for which reaction rate and selectivity are not affected by the P / R h ratio. The effect of catalyst concentration on the reaction rate and regioselectivity of styrene hydroformylation was studied using the R h ( S O X ) ( C O D ) ~ l p p p system as catalyst (see Figs. 1 and 2). Unexpectedly, the regioselectivity to 2-phenylpropanal decreases sharply with the increase of catalyst concentration. The regioselectivity of over 96% to 2-phenylpropanal can be obtained at a concentration of 1.0 mM, compared with only 75% at a

600

-3

/-,00

N 2oo ~

0

1

2

4. 6 TIME (h)

8

9

Fig. I. Effect of catalyst concentrauon on styrene hydroformylation.Reaction conditions: 0. l MPa, 60°C, toluene 8 ml, styrene 2 ml, dppp/Rh(SOX)(COD) = 1 Catalyst concentration: (1) 1.0x 10-3 M. (2) 2.0x 10-3 M, (3) 4.0x 10 3 M.

W. Chen et al. / Journal of Molecular Catalysis 88 (1994) 277-286

281

100

*6

50

or"

...-------02

CONCENTRATION(10-3 M)

Fig. 2. Effect of catalyst concentration on the regloselectivlty of styrene hydroformylation. Reaction conditions are the same as those m Fig. 1. ( 1) 2-phenylpropanal, (2) 3-phenylpropanal

concentration of 6.0 mM, i.e., a higher catalyst concentration induces more linear aldehyde, 3-phenylpropanal.

3.2. Hydroformylation of p-methylso'rene

Table 2 shows the results with p-methylstyrene as substrate, which is hydroformylated to 2- (p-methylphenyl) propanal and 3- ( p-methylphenyl ) propanal similarly to styrene.

- ~

+ CO + H2

=

_~CHO

+ ~ C H O

The catalyst activity is lower than that of styrene. The highest activity in this case too is obtained using the diphosphine ligand. A TOF up to 0.45 min-~ is achieved with R h ( S O X ) (COD)--dppe system. Diphosphine ligands also induce the highest regioselectivity in branched aldehyde (over 95%). PPh 3 is a useful ligand in the p-methylstyrene hydroformylation, since it gives fairly good regioselectivity. Using P(OPh)3 ligand gives rise to the linear aldehyde, 3-(p-methylphenyl)propanal, as the major product (62% selectivity). The catalyst activity usually decreases on increasing the P / R h ratio. PPh3 is an exception. In this case, a higher P / R h ratio favours the reaction rate and leads to a better regioselectivity.

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W. Chen et al. /Journal of Molecular Catalysts 88 (19941 277-286

Table 2 Hydroformylauon of p-methylstyrene a Phosphine or phosphtte

(ram

P/Rh

TOF

TO

Regloselectv,'lt~ ( % )

') ISO b

ll"

P( OPh ) 3

2 5

0.10 0

28 0

37 5 -

62.5

PPh3

2 5

0.03 0 10

10 43

74 7 87.5

25 3 12.5

dppe

2 5

0.45 0. I I

10 48

95 7 97 5

4.3 25

dppp

2 5

0.37 0.29

19 76

95 6 96 0

4.4 40

" Reaction con&uons are the same as those m Table I b iso = 2-(p-methylphenyl) propanal. • n = 3- (p-methylphenyl) propanal.

3.3. Hydroformylation o f acenaphthylene

The h y d r o f o r m y l a t i o n o f acenaphthylene to a c e n a p h t h e n e - l - c a r b o x a l d e h y d e is o f considerable potential use as an efficient route to a c e n a p h t h e n e - l - c a r b o x y l i c acid by the oxidation of the aldehyde. It is k n o w n that a c e n a p h t h e n e - l - c a r b o x y l i c acid is a plant-growth controlling substance. The reaction has been briefly reported, which occurred under pressure using [ R h ( C O ) , C 1 ] 2 - P P h 3 ( I0 MPa, 100°C) [ 14] and P t - S n catalyst systems (22 M P a ) [15]. +

CO

÷

H2

~-

~CHO

The results listed in Table 3 show that the hydroformylation of acenaphthylene can proceed successfully under 0.1 M P a pressure using R h ( S O X ) ( C O D ) as catalyst. The h y d r o f o r m y l a t i o n reaction affords acenaphthene- 1-carboxaldehyde as the only product, but the reaction rate is l o w e r than that o f styrene due to the conjugate system of acenaphthylene. Nevertheless, up to 40 moles of the aldehyde per mole Rh can be obtained within 10 h under atmospheric pressure.

3.4. Hydroformylation o f indene and I 2-diphenvlethvlene

U n d e r mild conditions, indene and 1,2-diphenylethylene cannot be h y d r o f o r m y l a t e d to their c o r r e s p o n d i n g aldehydes using these catalyst systems.

W. Chen et al / Jout~lal of Molecular Catalysts 88 (1994) 277-286

283

Table 3 Hydroformylationof acenaphthylene~ Phosphine

P/Rh

Temperatu~ (°C)

TO

Selectivity (~)

PPh3

5

75

27

100

dppe

2 5 5

60 60 75

40 23 22

100 100 100

dppp

2 5

75 60

40 15

100 100

0.1 MPa, toluene 10 ml, acenaphthylene 0 38 g, reaction time 10 h, Rh(SOX)(COD) 2.0 × 10 5 tool.

Table 4 Hydroformylatton of ternunal olefins~ Olefin

Llgand

TOF (ram -~ )

TO

Regloselecuvlty ( % ) a

iso

1-hexene

PPh~ dppe

0.96 0.36

267 131

83.9 45.3

16.1 54.7

1-octene

PPh~ dppe

0.28 0.1 I

I 12 36

84.6 54 5

15.4 45.5

0 1 MPa, 60°C, toluene 9 ml, olefin I ml, P/Rh = 5, reaction time 10 h, Rh(SOX) (COD) 2.0 × 10-5 tool

3.5. Hydroformylation of linear aliphatic alkenes R-CH=CH 2 ÷

CO *

H2

-

R/~/CHO

÷ R"~CHO

Rh (SOX) ( COD ) is also a useful catalyst precursor for terminal aliphatic olefins. Hydroformylation of two olefins with different chain-length and the effect of mono- and diphosphine ligands on the reaction was studied under atmospheric pressure. The results are summarized in Table 4. It can be seen from Table 4, the hydroformylation of alkenes takes place readily to give linear and branched aldehydes. The catalytic systems involving PPh3 are usually more active than that of the complexes with diphosphine ligands. This result is just opposite to that in the hydroformylation of vinylarenes under the same conditions. PPh3 induces high regioselectivity to linear aldehyde, i.e., linear aldehyde is the isomer prevailing when the monophosphine ligand is employed as cocatalyst. In contrast with styrene hydroformylation, the n/iso ratio is nearly one by using diphosphine as ligand. Comparing the results of vinylarene and alkene hydroformylation, it can be concluded that monodentate ligand promotes the formation of the linear aldehyde whereas the bidentate ligand favours the formation of the branched aldehyde using Rh(SOX) (COD) as catalyst. Therefore, we can get either branched or linear products with a good regioselectivity through the choice of phosphine ligands.

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W. Chen et al. / Journal of Molecular Catalysis 88 (1994) 277-286

3.6. Hydroformylation of E, E,Z- 1,5, 9-cyclododecatriene

Few reports [ 16] have been devoted to the hydroformylation of E,E,Z-l,5,9-cyclododecatriene, and usually high temperatures and pressures are needed. The Rh ( SOX ) ( COD ) dppe system is so active that this cyclic olefin can be hydroformylated to its corresponding aldehyde under mild conditions. The kinetic curve referring to the reaction is reported in Fig. 3. Up to 30 moles of aldehyde per mole rhodium can be obtained within 10 h at a ratio of dppp/Rh = 1. The G C - M S analysis shows that only monoaldehyde was obtained. However, whether the hydroformylation took place at a trans double bond or cis double bond was not determined. The above results show that the Rh (SOX) ( COD ) complex containing an anionic chelate ligand having N and O as donating atoms is a very effective hydroformylation catalyst in the presence of phosphine ligands even under atmospheric pressure. Its catalytic efficiency compares favourably with those of the [ R h ( C O ) 2C1] 2 and [ Rh (COD) CI ] 2 systems which are inactive under the same reaction conditions, although their catalytic properties are known under elevated pressures and temperatures. Therefore, the activity of the R h ( S O X ) (COD) complex can be attributed to the chelate effect of the salicylaldoximato ligand bound to rhodium atom. According to the present observations, the nature of the Rh-diphosphine system is still not clear. However, the experimental results suggest that the R h ( S O X ) fragment is maintained even in the presence of excess donor ligands. Attempts to clarify the nature of the catalytically active species and the mechanism of the reaction are in progress.

30

20 O

~

10

0

2

~ 6 TIME{h)

8

10

Fig. 3, Hydroformylatlonof E,E,Z-1,5,9-cyclododecatnene.Reaction condmons. 0.1 MPa, 60°C, toluene 9 ml, cyclododecamene I ml, Rh(SOX) ( COD ) 2.0 × 10-5 mol, dppe/Rh(SOX) (COD) = 1.

W. Chen et al. / Journal of Molecular Catalysis 88 (1994) 277-286

285

Acknowledgement We thank the National Natural Science Foundation of China, the Science Foundation of Chinese Academy of Sciences and the Laboratory of Organometallic Chemisty, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences for financial support.

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