Gas phase hydroformylation of propene catalyzed by a polymer bound rhodium(I) complex

Journal of Mok?cuhr Catalysis, 80 (1993) 365-375 Elsevier Science Publishers B.V., Amsterdam

365

MO75

Gas phase hydroformylation of propene catalyzed by a polymer bound rhodium (I) complex

Bernd Heinrich*, Yuying Chen and Jes Hjortkjaer Institut for Kemiteknik, Polyteknisk Lcereanstalt, DTH, bygn. 229,280O Lyngby (Denmark); tel. (+45)45931222-2950, fax. (+45)42882258

(Received July 31,1992; accepted December 22,1992)

Abstract

The continuous gas phase hydroformylation of propene is catalyzed by a cationic rhodium carbonyl complex co-ordinatively bound to a copolymer of 2-vinylpyridine and methyl acrylate crosslinked with 5 mol% ethene diacrylate. The counter ion had a strong effect on both activity and deactivation. At 403 K and 1100 kPa total pressure (C,: CO : Hz = 2.4: 2.2 : 1.0) the total initial rate was 8.5 X 10e7 mol/ (s gRh) with tetraphenylborate as counter ion. The regioselectivity was close to 1. The catalyst rapidly lost about 50% of its initial activity. Deactivation was accompanied by benzene formation, indicating a reaction of the tetraphenylborate counter ion with traces of water. As benzene formation diminished, deactivation slowed down. A catalyst with chloride as charge balancing ligand was less active and needed activation at higher temperatures than the tetraphenylborate complex. Only slow deactivation was observed with this catalyst.

Key words: counter ion effect; deactivation; hydroformylation; polymer bound; propene; rhodium

Introduction

Hydroformylation of propene homogeneously catalyzed by rhodium complexes is an example of the successful application of soluble transition metal complexes in industrial catalysis [ 11.

Nevertheless, many attempts have been made during the past three dec- ades to support soluble transition metal catalysts on solids. The main goal is to combine the easy recovery of solid catalysts with the high activity and se- lectivity of soluble complexes. Organic polymers have been widely used as support materials [ 21.

Preparation of a polymer supported catalyst usually involves ligand exchange reactions between the soluble complex and functional groups in the polymer matrix. Often, poly (styrene-divinylbenzene ) copolymers functionalized with phosphines have been used as supports, especially for rhodium based hydroformylation catalysts [ 3,4]. Tertiary phosphine functionalities in the

*Corresponding author.

0304-5102/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved.

366 B. Heinrich et al. /J. Mol. Catal. 80 (1993) 365-375

polymer matrix provide the highest possible analogy with the homogeneous catalyst HRh (CO) ( PPh,)3 [ 51. The catalysts are air sensitive due to the formation of phosphine oxide from the tertiary phosphine ligands and oxygen impurities in the feed [ 61. Therefore, it is of interest to examine polymer bound catalysts containing ligands other than phosphine.

Catalysts in which rhodium is bound through pyridine or other amine groups within the polymer support are active in hydroformylation reactions and are less air sensitive than phosphine based catalysts [ 7,8].

Here we present results on the gas phase hydroformylation of propene using a poly (2-vinylpyridine-methyl acrylate ) copolymer crosslinked with ethene diacrylate as the catalyst support to which the rhodium is bound through pyridine and probably carboxylic ligands [ 91.

Our studies on the liquid phase carbonylation of methanol with this type of catalyst revealed some deactivation due to metal leaching from the support into the product stream [lo]. The loss of precious metal from the support is the major problem with “heterogenized” transition metal complexes in liquid phase reactions, but in gas phase reactions metal loss is unlikely to occur. Therefore, the gas phase hydroformylation of propene was chosen to monitor the activity of the catalyst, because in this reaction both reactants and products remain in the gas phase, when the experimental examination is performed as described below (see Experimental).

Two different catalysts were used for propene hydroformylation: A zwit- terionic rhodium complex with tetraphenylborate as the counter ion and a chloride complex. The former is the most active catalyst, but regioselectivities (R = rate of n-butanal formation (r,,)/rate of rY.so-butanal formation ( rko) ) were between 1 and 2 for both of them. During the hydroformylation experiments with the rhodium (1)tetraphenylborate catalyst an unexpected product was detected which turned out to be benzene. The obvious source for the benzene formed are the phenyl groups of the tetraphenylborate counter ion which probably reacts with water. The deactivation of the tetraphenylborate containing catalyst may be related to the benzene formation.

Experimental

Catalyst preparation The crosslinked copolymer support was synthesized from 2-vinylpyridine

(25 mol%), methyl acrylate (70 mol%) and ethene diacrylate (5 mol%) as previously described [ 9,101. Tetracarbonyldichlorodirhodium (synthesized by McCleverty’s method [ 111) reacted with copolymer beads (250-500 pm in diameter) in methanol at room temperature for about 17 h. Then a solution of tetraphenylboron sodium (Aldrich, 99.5 + % ) in water was added in most cases to exchange chloride with tetraphenylborate. The N/Rh-ratio in the catalysts

B. Heinrich et al. 1 J. Mol. Catal. 80 (1993) 365-375 367

was between 14 and 30 mol/mol, corresponding to 0.18-0.09 mmol rhodium in 1 g of catalyst.

The yellow catalyst beads were filtered off the methanol/water mixture, washed successively with water and methanol, dried and stored in a desiccator at low pressure. One catalyst sample was dried in a vacuum oven at 313 K for 4 days.

Preparation of reactant mixtures Propene (Alfax, 99%), carbon monoxide (Dansk Ilt, 99% or Linde,

99.97% ) and hydrogen (Dansk Ilt, > 99% as determined by GC) were all transferred from their respective cylinders into one empty cylinder, using the pressure in the cylinders of the pure gasses as the driving force. The pressure drop in the carbon monoxide and hydrogen cylinders was used as a rough estimate of the amount of gas transferred to the blend cylinder thus allowing approxi- mate control of blend composition.

All valves and tubes were flushed with the pure gasses, before filling of the blend cylinders was started to avoid entrance of larger amounts of air. In some cases, the reactants were dried by passing them over molecular sieves (Molsi 5A) before mixing.

The gas mixtures were analyzed as described below.

Analysis The rhodium content of the catalysts was determined by atomic absorp-

tion spectrometry (Perkin Elmer 2100). A known amount of catalyst was re- fluxed in concentrated hydrochloric acid for four hours. From the resulting orange liquid a known volume was withdrawn and diluted with water. The absorption of this sample at 343.5 nm was determined and compared with the absorptions of a series of standards prepared from tetracarbonyldichlorodirhodium and 0.1 M hydrochloric acid. The measured rhodium content was close to the theoretical content calculated from the amount of tetracarbonyldichlorodirhodium and copolymer used for the catalyst preparation.

The infrared spectra of fresh and used catalysts were recorded on a Perkin Elmer 1760X FTIR spectrophotometer. Potassium bromide discs were made from 5 mg of catalyst and 200 mg of potassium bromide. The composition of the reactant mixture was determined by GC (Hewlett Packard 5790A) with a Porapak Q column (length 1.8 m, 0.3 cm i.d.) and thermal conductivity detection. Helium was used as carrier gas and pure propene and carbon monoxide as standards. Samples were injected with a 0.5 ml sample loop and peak areas evaluated by a Hewlett Packard 3390A integrator. The hydrogen content of the blends was calculated as 100% - %carbon monoxide - %propene. Small amounts of nitrogen, oxygen, propane and argon (total < 1% ) were also present in the reactant mixtures as determined by GC (Perkin Elmer 8500) with a 25 m, 0.53 mm id. fused silica PLOT column (mol-sieve 5A, Chrompack) and thermal conductivity detection. Hydrogen was used as carrier gas.


The amounts of n-butanal, iso-butanal and benzene in the product stream from the reactor were quantified by GC (Shimadzu GCS-A) with a SCOT Sqa- lan column (length 50 m, 0.53 mm i.d., Perkin Elmer) using flame ionization detection and nitrogen carrier gas at 308 K oven temperature. Samples from the reactor were injected into the column with a 1.27 ml sample loop and a splitter valve (split ratio approx. 1: 15).

Peak areas were determined by a Hewlett Packard 3390A integrator. Cal- ibration curves were made by injecting known amounts of liquid benzene (Ald- rich, 99.9% ), iso- or n-butanal (Merck, > 99% ) into volumetric flasks flushed with nitrogen and sealed with rubber septa. After the liquid had evaporated, samples were withdrawn with gas tight syringes and injected into the column.

The benzene formed during the experiments was identified by GC-MS (VG-TRIO 2).

Reactor system Figure 1 shows the reactor system used for the gas phase hydroformylation

of propene. In the stainless steel reactor (5, Fig. 1 ), diameter 0.7 cm, was placed 0.5-

1.5 g (1.5-4.5 ml) catalyst depending on the experiment. Flow rates of between 0.02 and 1 ml/s were adjusted with a fine metering valve (6, Fig. 1) and measured either with a soap bubble flow meter and a stopwatch or a digital soap bubble flow meter (Chrompack). In a typical experiment with 1 g (3 ml) of catalyst at 373 K and 600 kPa and a 0.2 ml/s flow rate measured at 295 K and 100 kPa, the gas hourly space velocity was 240 h-’ (295 K, 100 kPa) and the corresponding space time was 71 s (373 K, 600 kPa).

A thermostated oil bath (4, Fig. 1) was used to control reaction tempera-

Fig. 1. Reactor system. ( 1) Gas bottle containing hydrogen, carbon monoxide and propene. (2 )

Reduction valve. (3) Precision reduction valve. (4) Thermostatted oil bath. (5) Stainless steel

reactor. (6) Fine metering valve. (7) Sample loop. (8) GC. (9) Bubble flask. (10) Soap bubble

flow meter.

B. Heinrich et al. /J. Mol. Catal. 80 (1993) 365-375 369

tures between 373 and 413 K. Total pressure in the reactor was regulated with a precision reduction valve (Matheson or Union Carbide; 3, Fig. 1) between 600 and 1100 kPa. After reduction to atmospheric pressure, the product gas was analyzed after intervals of typically 15 min by injection of gas samples into the GC with a 1.27 ml sample loop (7, Fig. 1). The bubble flask (9, Fig. 1) gave a visual impression of the gas flow.

During all the hydroformylation experiments conversion was kept low (less than 1% of the limiting reactant). This allowed calculation of the rates for n- and iso-butanal formation as F [ aldehyde] / Wn,,, where F is the flow rate in ml/s from the reactor, [aldehyde] is the concentration of n- or iso-butanal (mol/ml) in the product stream and IV, is the weight of rhodium in the reactor.

Results

Catalyst activity and stability Shortly after immersing the reactor in the heated oil bath, n- and iso-

butanal were detected in the product stream. No other oxo-products were found and no hydrogenation activity was observed. Propane, however, was present in small amounts in the reactant blends, as it is an impurity in the propene used.

Figure 2 shows the hydroformylation activity at 403 K and 1100 kPa ( C&H6 : CO : H2 = 2.4 : 2.2 : 1.0) as a function of time for a catalyst containing 1.9% rhodium by weight (Cat.1, Table 1). A rapid decrease in activity during the first few hours is evident from Fig. 2. After that, the activity decreases more slowly. The experiment was stopped after 10 days. At that time, about 7% of the initial catalyst activity was retained. Also from Fig. 2 it can be seen that the regioselectivity is about 1 at the beginning of the experiment, increasing slightly towards the end to about 1.3. A similar deactivation pattern was observed during other experiments, summarized in Table 1. Catalyst 3, Table 1, containing 0.9 wt.% rhodium had an initial activity (ri = r, + rise) of 35 X 10m8 mol/ (s gRh). After 2.4 h the measured total rate (r) was 21 x 1Om8 mol/ (s gRh) implying a decrease in rate of about 17% of the initial activity per hour. After 24 h the final rate (rf) was 6x 10-s mol/ (s gRh), indicating a much slower deactivation (3.3% per hour of the activity after 2.4 h) following the rapid deactivation in the beginning of the run.

Results for catalyst 2, Table 1, at 373 K and 393 K indicate that the fast deactivation during the first hours of each run was even faster at higher temperatures.

The N/Rh ratio had no significant effect on catalyst activity or lifetime (Table 1 ), but only the region of large ligand excess was investigated.

Catalyst 4, Table 1, behaved differently from the other catalysts. At 600 kPa ( C3H6 : CO : Hz = 2 : 1: 1) and 403 K this catalyst only produced traces of aldehydes. As the temperature was raised to 413 K, the activity increased with


I I I I I I I I 1

50 100 150 200

Time / (hours)

Fig. 2. Rate of n-butanal (Cl) and iso-butanal (m) formation as a function of time. T=403 K, P,,=llOOkPa (C,:CO:H,=2.4:2.2:1.0),1gofcatalyst,1.9wt.%Rh.

TABLE 1

Initial total hydroformylation rates ( ri), rates after short reaction time (r), relative to ri, and final rates ( rf) relative to r for various poly (2-vinylpyridine methacrylate ) bound rhodium complexes

Cat. N/Rh mmol Rh Pmt C,:CO:H, T 10s ri r/Tic rJrc (mol/mol) g cat (kPa) (K) mol

0 s gRh

1” 14 0.18 1100 2.4:2.2:1.0 403 85 0.80 (4) 0.09 (241) 2 18 0.15 600 1.0:1.3:1.1 373 25 0.40 (4) 0.66 (84) 2 18 0.15 600 1.0:1.3:1.1 393 50 0.36 (2) 0.28 (20) 3 30 0.09 1100 1.0:1.2:1.1 373 35 0.60 (2.4) 0.29 (24) 4b 30 0.09 600 2.O:l.O:l.O 413 7 5.10 (8) 0.99 (26)

“Catalyst dried in a vacuum oven. See also Figs. 2 and 3. bCateIyst not treated with NaBPh,. ‘Hours on stream.

time, to 35.5~ 10F8 mol/(s gRh) (R=O.S) after 8 h and was 35.1~ lOma mol/ (s gRh) (R= 1.1) after 26 hours at 413 K. Cooling to 403 K again resulted in a steady total rate at this temperature of 19.5 X 10M8 mol/(s gRh) (R= 1.3). Activation of the catalyst at 413 K was thus necessary.

From the above results at 403 and 413 K an activation energy of about 80 kJ/mol for propene hydroformylation was estimated, since the deactivation between the rate measurements at the two temperatures, to a good approxi-

B. Heinrich et al. j J. Mol. Catal. 80 (1993) 365-375 371

mation, can be neglected in this case. Since the regioselectivity decreases with temperature, the activation energy for iso-butanal formation is considerably higher than for n-butanal formation, being approximately 93 and 71 kJ/mol respectively.

Benzene formation During most of the hydroformylation experiments considerable amounts

of an unknown compound were detected. This turned out to be benzene, the obvious source for which is the tetraphenylborate counter ion to the cationic rhodium complex. BPh, is probably coordinated to rhodium through one of the phenyl groups [ 12,131.

The following reaction can, in principle, occur at the rhodium complex:

B(CcH5)4 +xH,O+B(C,H,),_,( (OH), +xC,H, .

Figure 3 shows the amount of benzene formed per second as a function of time for the hydroformylation experiment shown in Fig. 2. Benzene formation was substantial during the first hours of the run, then it gradually stopped. Similar behaviour was shown by all catalysts which had been treated with sodium tetraphenylborate. The area under the curve in Fig. 3 is an estimate of the total amount of benzene formed. An area corresponding to 3.6 x 10m4 mol was found (by square counting) for Fig. 3. Since 1.85 x 10m4 mol rhodium were present in the reactor, about 2 moles of benzene per mol rhodium were formed during

1 2 3 4

Time / (hours)

Fig. 3. Amount of benzene formed per second as a function of time. Conditions as stated for Fig. 2.


the first 4 h of the experiment. Benzene formation proceeded more rapidly at higher temperatures. Benzene was also formed, when nitrogen was passed through the reactor containing 1 g fresh catalyst (1.52% Rh) at 600 kPa and 373 K.

After pretreating the catalyst with nitrogen for 103 h at the same pressure and temperature (about 3 mol benzene per mol rhodium were formed during this period), propene hydroformylation started, as the feed was switched to a reactant mixture (C&H,: CO : Hz = 2.3 : 1.2 : 1.0)) still at 600 kPa and 373 K. The reaction rate increased to 17x 10M8 mol/ (s gRh) (R= 1.5) after 7 h. Then the rate slowly decreased so that 33 h after the maximum rate had been reached, the rate was 12~10~~ mol/(s gRh) (Rz1.7).

After reaction, the weight of the used catalyst was 0.90 g, indicating a weight loss of about 10%.

Infrared spectroscopy measurements Catalyst + NaBPh, The IR spectrum of fresh catalyst (1.9 wt.% Rh) treated with sodium

tetraphenylborate showed 4 peaks of about equal intensities in the carbonyl stretching region, at 2105,2085,2043 and 2012 cm-l, respectively.

Possible catalyst structures are shown in Fig. 4. The peaks at 2012 and 2085 cm-’ are probably due to complex 1, Fig. 4, where X= Cl [ 141. The re- maining two peaks may represent the same complex, but with X = BPh,. After use of the catalyst in the hydroformylation reaction, the spectrum partly changes. The peaks at 2043 and 2105 cm-’ disappear and two new peaks are seen at 1988 and 2064 cm-‘. The other two peaks remain unchanged. This indicates that structural changes take place around the complexes originally holding the tetraphenylborate counter ion as the latter is transformed by the action of water. For example, structures 2 and 3, Fig. 4, may form as the bulky phenyl groups are removed from the counter ion. The formation of the pro- posed bidentately bound complexes could explain the shift of the carbonyl stretchings to lower frequencies. In the spectral region from 400-800 cm-’ a band at 468 cm-’ and a weak band at 523 cm-’ are seen. These are probably Rh-N- and Rh-0 stretching vibrations, confirming that structures like those in Fig. 4 are actually formed.

Bands at 613,706 and 734 cm-’ related to the aromatic rings in the tetra-

[Rh (CO), ]+ X- Rh

Fig. 4. Possible catalyst structures. X= Cl or BPh,.

B. Heinrich et al. /J. Mol. Catal. 80 (1993) 365-375 373

phenylborate counter ion all lose intensity upon use of the catalyst, while the Rh-N- and Rh-0 bands are practically unchanged.

Catalyst-NaBPh, The catalyst which had not been treated with sodium tetraphenylborate

contained only 0.9 wt.% rhodium. Therefore, only weak carbonyl stretching bands appear in the IR spectrum of the fresh catalyst at 1989 and 1955 cm-‘. Shoulders are observed at about 2090 and 2020 cm-l representing complex 1, Fig.4, with X= Cl. Upon use of the catalyst, two low intensity bands are seen at about 2000 and 2049 cm-l. The spectra obtained are, however, relatively poor due to the low rhodium loading, so that care should be taken in the inter- pretation of the observed changes.

The regions from 800 to 400 cm-’ were practically unchanged in the spectra of fresh and used catalyst, with bands at 467 and 523 cm-’ as for the tetraphenylborate containing catalyst. The bands at 734,706 and 613 cm-l present in the spectra of the tetraphenylborate containing catalyst were not found.

Discussion

The maximum propene hydroformylation rate of about 8~ lop7 mol/ (s gRh ) (Fig. 2 ) observed with the polymer bound rhodium complex catalyst here described, is ten times lower than the rates achieved in liquid phase with rhodium complexes attached to phosphine functionalized poly (styrene divinylbenzene) at 373 K and 1450 kPa [ 151. At 403 K and 101 kPa a rate of 2.9 x 10e7 mol/ (s gRh) was observed for the gas phase hydroformylation of propene with a catalyst containing rhodium coordinated to phosphine on polystyrene-coated silica gel [ 161. Using the kinetic parameters as given previously [ 161, a rate of 7 x lop6 mol/ (s gRh) can be estimated for this catalyst at the same conditions as those in Fig. 2.

The comparatively lower rates achieved with our catalyst may partly be explained by the differences in ligand environment around the rhodium. In our catalyst the rhodium is bound to the support through bonds to N and/or 0. These interactions are expected to be weaker than bonds to tertiary phosphines which through both good electron donation and n-acidity promote the electronic transitions going on during the catalytic cycles for alkene hydroformylation [ 51. Another reason for the observed lower rates could be diffusion limitations, leaving some of the catalytic sites inaccessible to reactants. The activation energy found for the hydroformylation of propene with catalyst 4, Table 1, of 80 kJ/mol is, however, too high to describe diffusion processes, suggesting the differences in activity between our catalysts and the phosphine bonded catalysts [ 15,161 to be chemical in origin.

The counter ion had a marked effect on both activity and stability of our catalyst. Complexes holding the tetraphenylborate counter ion were the most


active hydroformylation catalysts. They also rapidly lost activity. This deactivation was accompanied by the release of benzene indicating that a reaction involving coordinated tetraphenylborate and traces of water was responsible for both deactivation and benzene formation. This means that a catalytically poorer complex results from the counter ion transformation. The source of water could be either the gas flowing through the catalyst bed and/or incomplete drying of the catalyst. Attempts to provide a totally water free reaction environment seemingly failed, unless the suggested reaction, accounting for benzene formation, is incorrect. Since benzene was also formed when nitrogen was passed through the catalyst bed (see Benzene formation), another plausi- ble reaction between hydrogen and the tetraphenylborate ions can be excluded.

From the IR spectra of fresh and used catalysts respectively, it is clear that the exchange of chloride with tetraphenylborate was incomplete, and the concentration of phenyl groups diminished upon use of the catalyst. The rapid deactivation observed as the formation of benzene proceeded could be a con- sequence of bidentate coordination of the polymeric ligand, leading to coordi- natively more saturated and catalytically poorer complexes.

The IR spectra of the catalyst containing only chloride species only show the expected CO stretching frequencies of complex 1 (2085 and 2012 cm-‘), Fig. 4, as shoulders while two other bands of low intensity are present at lower frequencies. Due to the low rhodium loading in this particular catalyst and the resulting poor spectra, it seems unjustified to carry the discussion of catalyst structure too far on these grounds. Probably, as with the tetraphenylborate containing catalyst, several complex structures are present in the polymer.

The activation at elevated temperature necessary to achieve measurably high rates with this catalyst reflects the need for some rearrangement of complexes inside the pores of the polymer support. This rearrangement is not necessary with the tetraphenylborate containing catalysts, suggesting it to be of a chemical rather than a physical nature.

The pretreated catalyst, in which part of the phenyl groups were removed from the counter ion prior to catalysis, also deactivated slowly, like the chloride containing catalyst. This suggests that the presence of reactants during the period when benzene is formed, accelerates deactivation.

Recent studies on the homogeneous hydroformylation of olefins with Rh(cod) ($-PhBPh,) (cod=cyclooctadiene) did not reveal any benzene formation [ 171, and the same is true for the reductive carbonylation of olefins with the same catalyst in solution [ 181.

The slow deactivation seen with all the catalysts examined here could be due to the reduction of rhodium (I) to metal, because the colour of the catalyst particles changed from yellow to brown-grey upon use in the hydroformylation reaction. However, no further investigations regarding this point were made.

B. Heinrich et al. /J. Mol. Catal. 80 (1993) 365-375

References

315

1

2

3

4

5 6

7 8 9

10 11 12 13 14 15 16 17 18

B. Cornils, in J. Falbe (ed.), New Syntheses with Carbon Monoxide, Springer Verlag, Hei- delberg, 1980), p. 1. C.U. Pittman, Jr., in G. Wilkinson, F.G.A. Stone and E.W. Abel (eds.), Comprehensive Or- ganometallic Chemistry, vol. 8, Pergamon, Oxford, 1982, p. 553. W.O. Haag and D.D. Whitehurst, in J.W. Hightower (ed.), Catalysis, Proc. Znt. Congr. 5th, Miami Beach, FL, August 1972, vol. 1, North-Holland, New York, 1973, p. 465. N.L. Holy, in L.H. Pignolet (ed.), Homogeneous Catalysis with Metal Phosphine Complexes, Plenum, New York, 1983, p. 443. D. Evans, J.A. Osborn and G. Wilkinson, J. Chem. Sot. (A), (1968) 3133. K.G. Allum, R.D. Hancock, I.V. Howell, R.C. Pitkethly and P.J. Robinson, J. Catal., 43

(1976) 322. US Pat., 4178312 to J.T. Carlock, Conoco Inc. D.L. Hunter, SE. Moore, R.A. Dubois and P. Garrou, Appl. Catal., 19 (1985) 275. G. Yuan, Y. Chen and R. Chen, Chin. J. Pol. Sci., 7 (1989) 219. J. Hjortkjmr, Y. Chen and B. Heinrich, Appl. Catal., 67 (1991) 269. J.A. McCleverty and G. Wilkinson, Znorg. Synth., 8 (1966) 211. M.J. Nolte, G. Gafner and L.M. Haines, Chem. Commun., 23 (1969) 1406. P. Albano, M. Aresta and M. Manassero, Znorg. Chem., 19 (1980) 1069. D. Rollman, Znorg. Chim. Acta, 6 (1972) 137. KS. Ro and S.I. Woo, J. Mol. Catal., 61 (1990) 27. H. Arai, J. Catal., 51 (1978) 135. I. Amer and H. Alper, J. Am. Chem. Sot., 112 (1990) 3674. J.-Q. Zhou and H. Alper, J. Chem. Sot., Chem. Commun., 4 (1991) 233.

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Gas phase hydroformylation of propene catalyzed by a polymer bound rhodium(I) complex