Homogeneous multimetallic catalysts

Journal of Molecular Catalysis, 54 (1989)

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Homogeneous Multimetallic Catalysts Part 9.* Hydroformylation of Norbomene by Cobalt-Ruthenium Bimetallic Catalyst YOUICHI ISHII, MASANOBU SATO, HIROYUKI MATSUZAKA and MASANOBU HIDAI** Department of Synthetic Chemistry, Faculty Hongo, Bunkyo-ku, Tokyo 113 (Japan)

of Engineering,

The University

of Tokyo,

(Received February 22, 1989; accepted June 20,1989)

Recently homogeneous multimetallic catalysts have been attracting much interest, since they are expected to show unique catalytic activities and selectivities which cannot be achieved by a single metal catalyst [ 1 - 31. We have been interested in the characteristic catalysis and cluster chemistry of cobalt-ruthenium bimetallic systems [4 - 61. In the course of our research work on carbonylation reactions by these systems, we have recently found that the cobalt-catalyzed hydroformylation of olefms is remarkably accelerated by addition of RuJCO) 12, which has essentially no catalytic hydroformylation activity by itself [7]. From the point of view of elucidating the cobalt-ruthenium bimetallic synergistic effect, stoichiometric reactions of acylcobalt complexes with various metal hydrides seem to be informative. In fact, it has been revealed that the dinuclear reductive elimination of an aldehyde from an acylcobalt complex and HRu(CO), is much faster than that with HCo(CO), [8,9]. This fact suggests that also in the catalytic hydroformylation by the cobalt-ruthenium bimetallic catalyst, a ruthenium hydride species participates in the step of hydrogenolysis of an acylcobalt intermediate. However, these stoichiometric reactions were conducted under ambient conditions, and no direct information was obtained on the reaction under catalytic hydroformylation conditions (at cu. 100 “C and under high CO and Hz pressures). In order to obtain further information on the mechanism of the cobalt-ruthenium bimetallic synergistic effect, hydroformylation of norbomene by a cobalt-ruthenium mixed catalyst was examined. Norbomene is known to insert easily into an acyl-metal bond [lo, 111, and th&efore in the hydroformylation of norbomene, competition between the hydrogenolysis and norbomene *For Part 8, see [6]. **Author to whom correspondence should be addressed. @ Elsevier Sequoia/Printed in The Netherlands

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insertion of an acyl complex intermediate may be expected. Here we wish to briefly describe some of the results. A typical procedure for hydroformylation is as follows: a 100 ml autoclave was charged with norbomene (1.88 g, 20 mmol), Co2(CO)s (0.034 g, 0.1 mmol), Ru~(CO)~~ (0 - 0.43 g, 0 - 0.66 mmol), and benzene as a solvent (20 ml) under a nitrogen atmosphere, and CO (40 kg cmm2) and H2 (40 kg cme2) were introduced. The reactor was rapidly heated (within 20 min) to 90 “C and the reaction was allowed to proceed at that temperature for 4 h with agitation. After the reaction, the autoclave was rapidly cooled to room temperature and the pressure was released. Then the reaction mixture was quickly treated with an excess of NaBH4, since it proved suitable to determine 2-norbomanecarbaldehyde (l), the hydroformylation product, as 2-norbomanemethanol (2) due to the instability of (1). After NaBHe reduction, the reaction products were analyzed by GC, isolated by silica gel column chromatography, and identified by IR, ‘H NMR and MS spectra. Results obtained are listed in Table 1. Products detected by GC after NaBHe reduction were (2) and la&ones (3) and (4) (Scheme 1). (4) was confirmed to be a secondary product by the NaBH, reduction of (3). In the hydroformylation by Co2(CO)s alone, yield of aldehyde (1) was low, and la&one (3) was the major product. In contrast, addition of Ru3(C0)i2, which is essentially catalytically inactive in the hydroformylation of norbomene, remarkably promoted the yield of (2), causing it to be the major product, while the selectivities of (3) and (4) were decreased. At the same time acceleration of the CO/H, uptake was observed, as shown in Fig. 1. The higher Ru/Co ratio resulted in a higher selectivity in the hydroformylation. A similar change in product distribution was also observed when TABLE 1 Hydroformylation Run

1 2s 3 4 5

of norbornene by CO~(CO)~-RU~(CO)~~~

Catalyst Co :Ru

Conv.b (%)

YieldC (%)

Selectivity (%)’

(2)d

(3F

(4)e

(2)

(3) + (4)

l:o 0:l 1:l 1:5 1:lO

41 3 83 93 99

9 0.8 29 38 55

19 tr 21 12 15

1 0 4 3 tr

21 35 41 55

49 30 16 15

aReaction conditions: see text. bNorbornene consumed/norbornene charged. CBased on the norbornene charged. Norbomane and high-boiling products co-oligomers of norbornene and CO) were also formed, but not determined. dGC yield. Qolated yield. fYield/norbornene consumed. sRus(CO)r2: 0.2 mmol.

(probably

LlS

0

co2GOhl I

0

+

CO/H*

CHO

o?

0 (1)

(31

NaBH, + (3) -0

+

0 Gi?

CHpOH

0

(4)

(21

Scheme 1. Pres we drop

( ks/cm*t

Ru CO

Co:Ru = 1:1

Co:Ru = 1:5 Co:Ru = 1:lO

1

2

3

4

Time (h)

1. Time-dependence curve of the pressure drop in the hydroformylation bornene with Co/Ru catalysts. Reaction conditions: see text. Fig.

of nor-

PPhs was added to the reaction system, although PPhs favored hydroformylation regardless of the presence of RUDER and caused a decrease in the rate of the reaction, thus requiring a higher reaction temperature. For example, (2) was obtained in 29% and 51% by the hydroformylation with Co2(CO)s-PPh, and (Co:P = 1:3) CO~(CO)~-RU~(CO)~~-PP~, (Co:Ru:P = 1:1:3),.respectively, at 110 “C for 20 h. The major path of the hydroformylation of an olefin by Co2(CO)s is considered to include alkylcobalt formation by olefin insertion into a cobalt hydride (or by the caged geminate radical pair process [ 13 - 16]), acylcobalt formation by CO insertion, and hydrogenolysis of the intermediary acylcobalt forming an aldehyde [123. In contrast, carbonylation of norbomene is reported to give la&one (3) by a facile insertion of norbomene into an acyl-metal bond and subsequent CO insertion aud

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cyclization. Therefore in the cobalt-catalyzed hydroformylation of norbornene, addition of Hz and insertion of norbornene to the 2-norbomylcarbonylcobalt complex compete, and this probably decreases the selectivity of aldehyde formation. This is also supported by the fact that incorporation of the sterically bulky PPh, ligand favored the hydroformylation in comparison to the formation of (3) due to retardation of norbomene insertion. In the hydroformylation of cyclohexene by the CO~(CO)~-RU,(CO)~, catalyst, no mixed metal cluster formation was observed by IR [53. Although participation of a trace amount of mixed metal clusters cannot be excluded at this stage, the cluster catalysis seems to be of small importance. Therefore the result that addition of RUDER, which has essentially no carbonylation activity, increased the selectivity of hydroformylation indicates that ruthenium favors the hydrogenolysis of the acylcobalt; this is reasonably explained by considering a ruthenium hydride species as a hydrogenolysis reagent of the acylcobalt, as depicted in Scheme 2. That is,

,

(1) D-W H2

:f

Scheme 2.

a ruthenium hydride species generated from RUDER, which smoothly causes dinuclear reductive elimination with an acylcobalt, promotes the formation of aldehyde (1) from 2norbomylcarbonylcobalt complex (5). As a result, the rate of hydrogenolysis of (5) was increased to give (1) as the major product in comparison to the norbomene insertion. If the rate-determining step of the present carbonylation is the hydrogenolysis of (5), the mechanism stated above also explains the rate enhancement by the addition of RQCO) 12. However, the rate-determining step in the hydroformylation of an internal olefin is reported to be initial interaction between the olefin and HCO(CO)~ [ 17,181, and if the alkylcobalt formation from norbomene and HCO(CO)~ is the slow step, the rate enhancement is not explicable by the ruthenium hydride-promoted aldehyde formation. In such a case, ruthenium should also be involved in the initial activation of norbomene, and to make these points clear, further study including kinetic measurements is needed.

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In conclusion, by using norbomene as an olefin, it was revealed that in the hydroformylation by the cobalt-ruthenium mixed metal catalyst, ruthenium participates, at least in the hydrogenolysis step of the acylcobalt, to affect the product distribution. Further investigation on the mechanism of the cobalt-ruthenium synergistic effect is now in progress. References 1 P. Braunstein and J. Rose, in I. BernaI (ed.), Stereochemistry of Organometallic and Inorganic Compounds, Vol. 3, Elsevier, Amsterdam, 1988. 2 D. A. Roberts and G. L. Geoffroy, in G. Wilkinson, F. G. A. Stone and E. W. Abel (eds.), Comprehensive Organometallic Chemistry, Pergamon, Oxford, 1982, Vol. 6, pp. 763 - 877. 3 M. Hidai, Yuki Gosei Kagaku Kyokaishi, 43 (1985) 941. 4 M. Hidai and H. Matsuzaka, Polyhedron, 7 (1988) 2369. 5 H. Matsuzaka, A. Fukuoka, Y. Koyasu, M. Ue, M. Orisaku and M. Hidai, Nippon Kagaku Kaishi, (1988) 705. 6 H. Matsuzaka, T. Kodama, Y. Uchida and M. Hidai, Organometallics, 7 (1988) 1608. 7 M. Hidai, A. Fukuoka, Y. Koyasu and Y. Uchida, J. Mol. Catal., 35 (1986) 29. 8 Y. Koyasu, A. Fukuoka, Y. Uchida and M. Hidai, Chem. Lett., (1985) 1083. 9 M. Tanaka, T. Sakakura, T. Hayashi and T. Kobayashi, Chem. Lett., (1986) 39. 10 P. Hong and H. Yamazaki, Abstract, 32nd Symp. Organometall. Chem., Osaka, Japan, 1985, p, 160. 11 Fr. Pat. 1352 841 (1964) to Rhone-Poulenc S.A. 12 P. Pino, F. Piacenti and M. Bianchi, in I. Wender and P. Pino (eds.), Organic Syntheses via Metal Carbonyls, Wiley, New York, 1977, Vol. 2, pp. 43 - 135. 13 T. E. NaIesnik and M. Grchin, Organometallics, 1 (1982) 222. 14 T. E. Naiesnik, J. H. Freudenberger and M. Grchin, J. Mol. Catal., 16 (1982) 43. 15 J. A. Roth, P. Wiseman and L. Ruszsla, J. Organometall. Chem., 240 (1983) 271. 16 F. UngvSry and L. Mark&J. Organometall. Chem., 249 (1983) 411. 17 R. Whyman, J. Organometall. Chem., 81 (1974) 97, 18 M. F. Mirbach, J. Organometall. Chem., 265 (1984) 205.