Organometallics 1995, 14, 1770-1775
1770
Homogeneous Multimetallic Catalysts. 1lo1 Carbonylation of Aryl Iodides with HSiEt3 Catalyzed by Pd-Co Bimetallic Systems Yoshihiko Misumi, Youichi Ishii, and Masanobu Hidai" Department of Chemistry and Biotechnology, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Received November 28, 1994@ The PdCl~(PPh3)~-Ru3(C0)~2 or PdC12(PPh3)2-C02(C0)8 bimetallic catalyst has been found to be effective for carbonylation of aryl iodides and HSiEt3 to give benzyl silyl ether a s the major product, although neither PdC12(PPh3)2, Ru3(C0)12, nor C O ~ ( C Oalone )~ had any appreciable catalytic activity. Addition of NEt3 to the Pd-Co mixed-metal-catalyzed carbonylation reaction remarkably changed the selectivity of t h e products, and 1,2-diaryl1,2-disiloxyethane was obtained as the major product. Studies on the hydrosilylation of 4-TolCHO with HSiEt3 under CO revealed t h a t the formation of benzyl silyl ether in the former reaction may proceed through the formylation of aryl iodide followed by hydrosilylation of the resulting aldehyde. In contrast, the aldehyde was not included a s a n intermediate in the formation of 1,2-diaryl-1,a-disiloxyethane in the latter reaction. An aroylcobalt complex ArCOCo(CO)3(PPhs)was suggested a s a n intermediate for t h e 1,2-diaryl-l,2-disiloxyethane production based on the following observations: (1)the aroylcobalt complex ArCOCo(CO)3(PPh3) can be produced from aryl iodide, [Co(CO)J, and PPh3 with a Pd(0) catalyst; (2) hydrosilylation of the aroylcobalt complex ArCOCo(CO)a(PPhs)under 50 a t m of CO pressure a s the major product. The detailed mechanisms are produced 1,2-diary1-1,2-disiloxyethane proposed for the catalytic carbonylations of aryl iodides with HSiEt3 by using the bimetallic catalysts.
Introduction Homogeneous bimetallic or multimetallic catalysis has recently attracted much attention for its unique or enhanced catalytic activity and selectivitye2 In spite of a considerable number of bimetallic catalyst systems having been developed and used in a variety of synthetic reactions, the reaction mechanism or the origin of the synergism has been elucidated in only limited examples. We have continuously focused our attention on bimetallic catalysts with the intention of developing novel and effective catalytic systems and already reported several bimetallic catalysts including the Co2(CO)s-RuCl3 system for homologation of methan01,~the Coz(CO)8-Ru3(CO)12 system for hydroformylation of olefin^,^ and the PdC12(PPh3)2-Ru3(C0)12 system for formylation of aryl iodides and vinyl iodides (eq 1).l In these carbonylation reactions with CO/H2, the bimetallic catalysts exhibited much higher activity than the corresponding single-metal catalysts. We proposed that the synergistic effects can be explained by the dinuclear reductive elimination reactions between acylcobalt o r acylpalladium intermediates and hydridoru@
Abstract published in Advance ACS Abstracts, March 15, 1995.
(1)Part 10: Misumi, Y.; Ishii, Y.; Hidai, M. J . Mol. Catal. 1993,
78,1. (2) ( a ) Braunstein, P.; Rose, J. In Stereochemistry of Organometallic and Znorganic Compounds;Bernal, I., Ed.; Elsevier: Amsterdam, 1989; Vol. 3, pp 3-138. (b)Roberts, D. A.; Geoffroy, G. L. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 6, pp 763-877. ( 3 ) Hidai, M.; Orisaku, M.; Ue, M.; Koyasu, Y.; Kodama, T.; Uchida, Y. Organometallics 1983,2, 292. (4)( a ) Hidai, M.; Fukuoka, A,; Koyasu, Y.; Uchida, Y. J . Mol. Catal. 1986,35,29. (b) Hidai, M.; Matsuzaka, H. Polyhedron 1988,7,2369. (c) Ishii, Y.; Sato, M.; Matsuzaka, H.; Hidai, M. J . Mol. Catal. 1989, 5 4 , L13.
Art + CO + H2 + NE13
PdC12(PPh&
thenium species to give the corresponding aldehyde^.',^-^ Very recently, a related bimetallic mechanism was proposed for the remarkable rate enhancement in the hydroformylation of 1-alkenes catalyzed by a dinuclear rhodium complex.6 On the other hand, catalytic carbonylation with CO/ HSiR3 instead of CO/H2 has been noted as a useful tool for organic ~ y n t h e s e s .Considering ~ the formal similarity in the reactivities toward organometallic compounds between dihydrogen and hydrosilanes,8 we have embarked on the investigation into catalytic carbonylation of aryl iodides (ArI) with CO/HSiEt3 by using bimetallic catalyst systems. This has led us to the finding that Pd-Co and Pd-Ru mixed-metal catalysts were specifically effective for formation of M H O (11,ArCHzOSiEts (21, and (ArCHOSiEt& (3) (1-3a; Ar = 4-Tol; 1-3b, (5) Koyasu, Y.; Fukuoka, A,; Uchida, Y.; Hidai, M. Chem. Lett. 1985, 1083. (6) Broussard, M. E.; J u m a , B.; Train, S. G.; Peng, W.-J.; Laneman, S. A,; Stanley, G. G. Science 1993,260,1784. ( 7 ) ( a ) Murai, S.; Sonoda, N. Angew. Chem., Int. Ed. Engl. 1979, 18,837. ( b ) Matsuda, I.; Ogiso, A,; Sato, S.; Izumi, Y. J . A m . Chem. Soc. 1989,111,2332. (c) Ojima, I.; Ingallina, P.; Donovan, R. J.;Clos, N. Organometallics 1991,10, 38. (d) Doyle, M. P.; Shanklin, M.S. Organometallics 1994,13,1081. (e) Zhou, J-Q.;Alper. H. Organometallics 1994,13,1586. (f)Ojima, I.; Tsai, C-Y. J . Am. Chem. Soc. 1994, 116,3643. (81Tilley, T. D. In The Chemistry of Organic Silicon Compounds; Patai, S . , Rappoport, Z., Eds.; John Wiley & Sones: Chichester, U.K., 1989; pp 1417-1419.
0276-733319512314-1770$09.00/0 . 0 1995 American Chemical Society ~
~
~
~
*
RU3(CO)12 ArCHO + HNEt31 (1) 1
Homogeneous Multimetallic Catalysts
Organometallics, Vol. 14,No. 4, 1995 1771
Table 1. Carbonylation of 4-To11 Catalyzed by Palladium and/or Various Metal Carbonyl@ ~
amt of NEtl convl' entrv
I 2 3 4 5 6 7 8 9 10
cat.
tmmol)
PdCI?(PPh3)? PdCl?(PPh,)? Ru~(CO)I? RudC0)12 Coz(C0)x Co?(CO)x PdCl~(PPh~)?-Ru3(CO)l~ PdCI?(PPh3)?-Rui(CO)l? PdCIz(PPhi)?-Cor(CO)x PdClz(PPh3)?-Coz(CO)x
3 3 3 3 3
Table 2. Carbonylation of ArI Catalyzed by PdCIz(PPh3)z and/or Co2(C0)gu
yield (%)I'
(9%)
la 2a 3a EtlSiI'
10 4 5 0 4 5 79 64 85 70
3 0 2 2 0 0 0 1 0 0 0 0 0 0 0 0 0 0 10 40 4 17 10 3 0 76 0 2 6 57
9 2
80 30
Reaction conditions: 4-To11 (2.5 mmol). HSiEt3 (7.5 mmol), metal complex (0.05 mmol as metal atom), CbHh (5 mL), CO (50 atm), 80 "C, 3 h. Determined by GLC analysis. Determined as Et3SiOEt.
Ar = Ph; 1-3c, Ar = 4-MeOCsH4; 1-3d, Ar = 4-FCsHd In this paper we wish to describe the scope of these reactions and elucidate the bimetallic mechanisms.
Results and Discussion Catalytic Carbonylation of Aryl Iodides with CO/HSiEts. Table 1shows the results of the carbonylation reaction of 4-To11 with CO/HSiEt3 catalyzed by PdC12(PPh3)2 and/or some metal carbonyl complexes a t 80 "C. None of the complexes showed any more than a marginal catalytic activity for this reaction by itself. Thus, when PdC12(PPh3)2 was employed as the catalyst, the total yield of the carbonylation products was only 5% (entry 1). No more than 1%of the carbonylation products were detected in the reactions using Cr(CO)s, Mo(CO)s, W(CO)6, Mnz(C0h0, Fe(C015, RudCO)12, and Co2(CO)~.The catalytic activities of mixed-metal catalysts PdCl2(PPh&-Cr(C0)6, -Mo(CO)s, -w(co)6,-Mn2(CO)lo, and -Fe(C0I5 were also poor and almost equal to or less than that of PdC12(PPh3)2. In sharp contrast, when R u s ( C O ) ~or~ COZ(CO)S was used in combination with PdC12(PPh3)2, 4-To11 was effectively carbonylated to give 4-TolCHO (la), 4-methylbenzyl triethylsilyl ether (2a), and 1,2-bis(4-tolyl)-1,2-bis(triethylsiloxy)ethane (3a),where 2a was the major product (entries 7 and 9). These results clearly show that the synergistic effect between palladium and ruthenium or cobalt enabled the carbonylation reaction of 4-To11 with C01 HSiEt3. These reactions with COMSiEt3 do not require the addition of a base, which is indispensable for the formylation reaction of ArI with CO/H2 in order to quench the HI formed, and the formation of EtsSiI was observed in this case. Interestingly, the addition of NEt3 to the Pd-Co bimetallic system dramatically changed the distribution of the carbonylation products, where 3a became the major product (57%yield a t 70% conversion, entry 10). A similar change was not observed in the Pd-Ru-catalyzed reaction (entry 8). The diastereomer ratio of 3a was almost 1 : l in every case. It should be pointed out that dimeric 1,2-diol derivatives were first obtained from the catalytic carbonylation of aryl iodides with COhydrosilane by using the Pd-Co bimetallic system in the presence of NEt3. The EtsSiI formed in the Pd-Co-catalyzed reaction was determined by GLC analysis after being converted into EtsSiOEt by treatment with N E t a t O H . It was found that the yield of Et3SiI was almost equal to that
I 2 3 4
4-To1
5 6 7 8
Ph
Pd co Pd-Co Pd-Co
1 4 85 70
0
Pd
2
5
co 3
3 62 67 3
3
1 4 83 80
0
3
1 6 54 54
3
Pd-Co Pd-Co
9 IO II 12
4-CH30ChH4
13 14 15 16
4-FCbH4
Pd co Pd-Co Pd-Co Pd co Pd-Co Pd-Co
3 0 0 2 0 3 I 0
0 0 76 6
2 0 0 57
0 0 61 4
0 0 0 52
0
0 0 0 57
0
0 0 0 28
3
0 0 0
3 81 2 7
5 I 3
0 38 0
'I Reaction conditions are the same as shown in Table I except ArI (2.5 mmol) was used instead of 4-TolI. I' Determined by GLC analysis.
of 2a in the reaction without NEt3, while in the presence of NEt3 it was about half that of 3a. On the basis of these observations, the carbonylation reactions are considered to follow eq 2 or 3, depending upon the absence or the presence of NEt3, respectively. PdC12(PPh3)2
Arl + CO + PHSiEt3
*
COP(Cole Ar 7 OSiEt3
+ EtgSiI (2)
2
2Arl+ 2 C O + 3HSIEt3 + NE13
EQSIO
OSiEt3
PdCIp(PPh&
c
co2(co)8
+ Et3SiI + HNEt3l (3)
3
Table 2 summarizes the results of carbonylation reactions of some ArI with CO/HSiEt3 by using PdC12(PPh& and/or COz(C0)8 catalysts. Similarly to the reaction of 4-To11with COMiSiEt3, benzyl silyl ether (2) or 1,2-diaryl-1,2-disiloxyethane (3) was selectively obtained from the carbonylation of ArI, although the reaction rate exhibited a dependency on the Ar group of the substrate. The carbonylation reaction of ArI with CO/HSiEt3 by the Pd-Co mixed catalyst is especially interesting in the point that a specific combination of two catalytically ineffective complexes displays a remarkable synergistic effect, and the distribution of the products is completely changed upon the addition of NEt3. We have therefore investigated the reaction mechanism of this Pd-Cocatalyzed reaction t o elucidate the origin of the synergism. Reaction of Tolualdehyde with Triethylsilane under CO Pressure. Two possible reaction mechanisms may be considered for the above mentioned carbonylation of aryl iodide with CO/HSiEt3. One includes the formylation of aryl iodide to form the
Misumi et al.
1772 Organometallics, Vol. 14, No. 4, 1995 Table 3. Reaction of 4-TolCHO with HSiEt3 Catalyzed by Palladium and/or Cobalt under Various Conditions"
1
0. I 50 50 50 50
3 4
5 6 7 8 9 10
17
5 0.1
Pd-Co
I
100 50 50 50 50
I2 14 15' 16
0. I
3 3
co
11
13
2 98 5 30
Pd
2
50 50 50 50 50
3 3
0.1
100 100
0.1
100 5 4
0. I
7 0.1
100 100
6 5
3
3
0.1
0 71 0 9 0 O
0 4 1 20 0 0
100 99 21 29
0 1 14 16
0 0 I 96 88 0 0
0 0 O 3 5 0 0
Reaction conditions: 4-TolCHO (2.5 mmol), HSiEti (7.5 mmol), metal complex (0.05 mmol as metal atom). ChHh ( 5 mL), 80 "C, 3 h. Determined by GLC analysis. MelSiI (0.I mmol).
corresponding aldehyde as the intermediate and the following hydrosilylation or silylation to give the silyl ethers 2 or 3. In the other mechanism, silyl ethers are directly formed from aryl iodide on organometallic species, not via the free aldehyde. In fact, the hydrosilylation of 1 to give 2 is well-known to be catalyzed by a variety of metal complexe~,~ while NiC12-Et2S1° and COZ(CO)S'~ are effective for the silylation of 1 to form 3, although the latter reactions require much higher temperatures (120-140 "C) than the present bimetallic carbonylation (80 "C). Therefore, we have examined the reaction of l a with HSiEt3 under the catalytic carbonylation conditions in order to obtain information about the reaction mechanism. The results are summarized in Table 3. When CO was not pressurized, PdC12(PPh& was an effective hydrosilylation catalyst for l a in the presence of a catalytic amount of 4-To11 (entry 2). However, under CO pressure (50 atm), the activity of palladium was strongly suppressed. Only when the reaction was conducted in the presence of 4-To11 without NEt3 were 2a and 3a obtained in low yields without selectivity (entry 4). As is well-known, C02(C0)~showed a very high activity for the hydrosilylation of l a to give 2a when CO was not pressurized (entries 7 and 8). Again under CO pressure, the selectivity of the cobalt catalyst was lost (entries 9 and 10). Surprisingly, when the palladium and cobalt catalysts were used together in the presence of tolyl iodide without NEt3, the hydrosilylation of the aldehyde proceeded smoothly to give 2a (entry 14). An addition of a catalytic amount of Me3SiI instead of tolyl iodide was also effective (entry 15). I t is of great interest that the use of the mixed-metal catalyst cancels the negative effect of the CO pressure toward the catalysis. A cooperative effect of the two metal species obviously seems t o play a critical role in the selective formation of 2a under CO pressure. As is ~~~
(9) Ojima, I. In The Chemistry oforganic Silicon Compounds;Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: Chichester, U.K., 1989; pp 1499-1501. (10)Frainnet, E.; Bourhis, R.; Simonin, F.; Moulines, F. J . Organomet. Chem. 1976, 105, 17. (111 Murai, S. Private communication.
seen in entries 14 and 15, this Pd-Co-catalyzed hydrosilylation requires aryl or silyl iodide as a cocatalyst. Because ArI can be easily converted into carbonylation products and EtsSiI by the reaction of eq 2, the latter might act as the true cocatalyst. However, we must await further investigations to elucidate the role of the iodide cocatalyst and the detailed mechanism of the bimetallic catalysis. On the basis of these observations, it may be concluded that aldehyde 1 is a highly probable intermediate for the catalytic carbonylation of ArI to form 2 (eq 2). It should also be mentioned that the Pd-Co mixed system was not effective for the hydrosilylation of l a in the presence of NEt3. In this case, the conversion of l a was very low regardless of the addition of tolyl iodide and neither 2a nor 3a was obtained (entries 16 and 17). This fact cleanly indicates that 1 cannot be the intermediate for the carbonylation of ArI to form 3 (eq 3). Mechanism for the Catalytic Formation of 2 from Aryl Iodides and CO/HSiEts. As described above, we suppose that the carbonylation in the absence of NEt3 (eq 2) proceeds via the aldehyde intermediate. Scheme 1depicts the proposed total mechanism for this reaction. ArI is first taken into the catalytic cycle by the oxidative addition to a Pd(0) species, and the following CO insertion leads to the formation of an aroylpalladium complex ArCOPdI(PPh3)2.12 On the other hand, the reaction of C02(CO)8 with HSiEt3 is supposed to give a hydridosilylcobalt complex H(SiEts)Co(CO)sas the primary product.13 Since neither single-metal catalyst, PdC12(PPh& nor COZ(CO)S, is effective for the carbonylation of ArI with CO/HSiEt3, the bimetallic reaction between the aroylpalladium and hydridocobalt complexes should be included in the catalysis. As is referred to in the Introduction, we have previously found that the reaction of an aroylpalladium complex with certain hydridometal species yields the corresponding aldehyde, which constitutes the key step in the bimetallic formylation of ArI with COA32.l In the present carbonylation with COA3SiEt3, a similar dinuclear reductive elimination between the aroylpalladium complex and a hydridocobalt species such as H(SiEt3)Co(CO)s is assumed to produce the aldehyde ArCHO. An equimolar amount of EtsSiI should also be formed at this stage, and the Pd(0) and Co(0) species are regenerated. Further reaction of the aldehyde and HSiEt3 by the Pd-CO mixedmetal catalyst selectively produces 2 under the catalytic conditions. It is noteworthy that both the formylation of ArI giving ArCHO and the hydrosilylation of ArCHO forming 2 are catalyzed by the Pd-Co bimetallic catalyst. When NEt3 is added to the reaction system, H(SiEt3)CO(CO)~ is converted into the carbonylcobaltate anion [CO(CO)J.~~ This prevents the aroylpalladium complex from undergoing the dinuclear reductive elimination with the hydridocobalt; therefore the aldehyde formation is suppressed in the presence of NEt3. The results shown in Tables 1 and 2 are in agreement with these discussions and the formation of 3 should be attributed to a completely different mechanism. (12)Kudo, K.; Hidai, M.; Uchida, Y. J . Organomet. Chem. 1971,33, 393. (13)Sisak, A.;Ungvary, F.; Marko, L. Organometallics 1986,5, 1019.
Homogeneous Multimetallic Catalysts
Organometallics, Vol. 14,No.4,1995 1773 Scheme 1
co Ar PdIL2
ArCOPdILp
Arl
A r 7OSIEt3
Pd-Co-Arl (or Et3SlI) -v ArCHO 1
2
HSiEt3
+
1t2 C02(CO)8
Et3SII
''
co
HSIEt3
(L = PPh3 or CO)
Hydrosilylation of Aroylcobalt Complexes under CO Pressure. Very recently, we have reported that a Pd(0) complex catalyzes the formation of aroylcobalt complexes ArCOCo(CO)a(PPha)from ArI, [Co(C0)41-, and PPh3.14 Because [Co(CO)41- is generated from C O Z ( C O or ) ~Coz(C0)6(PPh3)2 ~~ and a hydrosilanel CO under basic conditions (vide infra), it is reasonable to assume that ArCOCo(CO)s(PPhs)is formed during the bimetallic carbonylation in the presence of NEt3 (eq 3). Therefore, we have examined the hydrosilylation of the aroylcobalt complexes under the catalytic carbonylation conditions. Some studies were already reported on the reactions of acylmetal complexes with hydr0si1anes.l~Cutler et al. reported that MeCOCo(CO)s(PPhs)reacts with HSiEt3 smoothly to give EtOSiEts and Et3SiCo(C0)3(PPh3) under a nitrogen atmosphere at room temperature, while the addition of CO or RCHO completely inhibits this reaction.16 They also reported similar reactions of acylmanganese c0mp1exes.l~ However, reactivities of acyl complexes toward HSiR3 under CO pressure have not been investigated so far, and furthermore the coupling of an acyl ligand leading to the formation of 1,2-disiloxyethanes has never been observed. The results of reactions between some aroylcobalt complexes and HSiEt3 are tabulated in Table 4. The aroylcobalt complex 4-TolCOCo(C0)3(PPh3)reacted with 3 equiv of HSiEt3 at room temperature under a nitrogen atmosphere to give a mixture of 2a (44%)and 3a (18%) (entry 1). The result was different from that of the reaction between MeCOCo(CO)s(PPhs)and HSiEt3 in that an appreciable amount of 3a was obtained, although 2a was still the major product. Under an atmospheric pressure of CO, l a was formed in addition to 2a and 3a, but the reaction was not selective. In contrast, the reaction under 50 atm of CO did not proceed a t room temperature. When the reaction was performed at 80 "C under 50 atm of CO, a dimeric silyl (14) Misumi, Y.; Ishii, Y.; Hidai, M. Chem. Lett. 1994, 695. (15) (a) Wegmen, R. W. Organometallics 1986,5, 707. (b) KovPcs, I.; Sisak, A.; Ungvary, F.; Marko, M.Organometallics 1988,7,1025. (16) Gregg, B. T.; Cutler, A. R. Organometallics 1992,11, 4276. (17)Gregg, B. T.; Hanna, P. K.; Crawford, E. J.; Cutler, A. R. J. A m . Chem. SOC.1991,113,384.
Table 4. Reactions of A ~ C O C O ( C O ) ~ - ~ ( P and P ~HSiEt3O ~)~ amtof
amtof
(mmol)
(mmol)
c ~ ~ ( c oN E)~ A~ entry
I' 2' 3 4 5 6 7d 8 9 10
Ar 4-TO1
n
1
I 1 1 1 1 0 Ph I 4-MeOC6H4 I 4-FC6H4 1
3 0.025 0.025
3 3 3 3 3
CO pressure (atm)
0 1 50 50 50 50 50 50 50 50
yield ( % ) h 1 2 3 1' 41 1 0 6 4 41 15 I1 15
44 31 20 1 11 3 10 3 9 4
18 21 68 67 71 76 2 60 36 46
[ I Reaction conditions: A~COCO(CO)~-,,(PP~A),, (0.5 mmol), HSiEtl (1.5 mmol), CbHb ( 5 mL, except for entry 7). 80 "C (except for entries 1 and 2). 3 h. Determined by GLC analysis. At room temperature. C6H6 (3 mL), hexane (2 mL).
ether 3a was obtained as the major product (entry 3, eq 4). Addition of NEt3 further suppressed the formation
Ar
) - C O ( C O ) ~ ( P P ~+ ~ )HSiEt3 0
-
of 2a and the selectivity of 3a became quite high (entry 4). Use of a catalytic amount of C02(CO)8was also found
effective for inhibiting the formation of 2a (entries 5 and 6). Similarly, other aroylcobalt complexes reacted with HSiEts to form 3 as the major products (entries 8-10). In contrast, the hydrosilylation of 4-TolCOCo(C0)4did not give 3a selectively (entry 7). From these results, it is clear that ArCOCo(CO)a(PPhdis a highly probable intermediate for the catalytic formation of 3 in the carbonylation of ArI with CO/HSiEts in the presence of NEt3. Extensive studies have been done concerning catalyzedls and uncatalyzed17 reactions of acyl complexes with hydrosilanes to give siloxyalkyl complexes. Treatment of silyl complexes with aromatic aldehydes also
Misumi et al.
1774 Organometallics, Vol. 14,No.4,1995 Scheme 2
co ArPdlL2
ArCOPdlL2
Ar I
PdL2
PPh3
(L = PPh3 or CO) forms siloxyalkyl complexes such a s Mn(C015(CHPhOSiEts), which in turn undergo thermolysis to give 1,2-disiloxyethanesvia the homolytic fission of the metal-siloxyalkyl bond followed by radical c0up1ing.l~ Therefore, it may be considered that the reaction of eq 4 proceeds through the formation of the siloxybenzylcobalt complex ArCH(OSiEt3)Co(CO)3(PPh3),the subsequent homolytic fission of the Co-C bond to liberate the siloxybenzyl radical (OSiEts)ArCH, and the coupling of the radical to form 3. Obviously, the aryl group favors this process by stabilizing the siloxyalkyl radical. Mechanism for the Catalytic Formation of 3. The reaction mechanism for the catalytic formation of 3 is proposed in Scheme 2. In this mechanism, ArI first reacts with a Pd(0) species through oxidative addition, and the aryl or aroyl group is then transferred from the palladium to the cobalt center by the reaction of ArPdIL2 or ArCOPdILz (L = PPh3 or CO) with [Co(CO)41- to give the aroyl complex ArCOCo(CO)s(PPhs). The anion [Co(CO)41may be formed by the reaction of Coz(CO)8or Coz(COI6(PPh& with HSiEt3 and NEt3. I t was actually confirmed by the IR spectrum that the reaction of C02(CO)6(PPh3)2 with HSiEts and NEt3 under CO pressure forms [Co(CO)4]-. I t was also confirmed that anion complex [Co(CO)3(PPh3)1- reacts with 1 atm of CO to form [Co(CO)4]-. Hydrosilylation of the aroyl complex gives the siloxybenzyl complex ArCH(OSiEts)Co(C0)3(PPh3), which leads to the formation of 3 via the coupling of the siloxybenzyl radical formed by the homolytic cleavage of the Co-C bond, concurrent with regeneration of (18)( a ) Hanna, P.K.; Gregg, B. T.; Cutler, A. R. Organometallics 1991,10,31. (b) Crawford, E.J.; Hanna, P. K.; Cutler, A. R. J . A m . Chem. SOC.1989,111,6891.(c)Akita, M.;Mitani, 0.; Moro-oka, Y. J . Chem. SOC.,Chem. Commun. 1989,527. (19)Gladysz, J. A.Acc. Chem. Res. 1984,17, 326.
Coz(CO)e(PPh3)2. EtsSiI may be formed from [Et3SiNEt3]+ and I-. This mechanism is in full agreement with the stoichiometry shown in eq 3. Finally, it should be emphasized that this provides a rare example in which the organic group transfer from one metal center to another has been revealed to function as a key step in the actual homogeneous catalytic reaction. The bimetallic systems seem to have the potential to enable the unique reactions which are inaccessible through single-metal catalysts.
Conclusions By using a new bimetallic catalyst composed of PdC12(PPh3)z and C02(CO)8, we have developed the novel carbonylation reaction of ArI with COMSiEt3. The reaction products were strongly affected by the addition of NEt3. In the reaction without NEt3, we proposed the reaction mechanism including the dinuclear reductive elimination between an aroylpalladium complex and a hydridocobalt species to give aldehyde 1 as an initial product, which is further transformed to 2 by the bimetallic catalyst. In contrast, in the reaction with NEt3, the aryl or aroyl group transfer from the palladium center to the cobalt has been shown to be an important step, which leads to the formation of 3. These mechanistic studies, we believe, not only demonstrate new possibilities of bimetallic catalysis but also provide a guiding principle in designing bimetallic catalysts.
Experimental Section General Procedure. All catalytic reactions including carbonylation of aryl iodides and hydrosilylation of aldehydes were performed in a 50 mL stainless-steel autoclave. Reactions of aroylcobalt complexes and hydrosilanes under 50 atm of CO were also performed by using the same autoclave, while
Homogeneous Multimetallic Catalysts
Organometallics, Vol. 14,No. 4, 1995 1775
those under 1 atm of Nz or CO were carried out in a 20 mL Hydrosilylation of 4-TolCHO under CO Pressure. In Schlenk tube. Benzene was freshly distilled from sodium a typical run, 4-TolCHO (0.300 g, 2.5 mmol), HSiEt3 (0.872 g, benzophenone prior to use. Reagents including NEt3, PhI, 7.5 mmol), PdClz(PPh3)~(0.035 g, 0.05 mmol), Coz(C0)~ (0.0086 EtOH, HSiEt3, and 4-TolCHO were also dried and distilled g, 0.025 mmol), and benzene (5 mL) as a solvent were charged prior to use. Complexes PdCl~(PPh3)2,~~ A ~ C O C O ( C O ) ~ ( P P ~ ~in ) , ~an ~ autoclave under nitrogen. The autoclave was imC O Z ( C O ) ~ ( P P ~and ~ ) ZNa[Co(C0)3(PPh3)Iz1 ,~~ were prepared mediately pressurized to 50 atm with CO at room temperature according to the literature method. Other organic reagents and heated to 80 "C in an oil bath. The reaction was allowed and metal carbonyls were used as received. t o proceed at this temperature for 3 h with magnetic stirring. Quantitative GLC analyses were carried out on a Shimadzu After the reaction, the autoclave was rapidly cooled to room GC-14A instrument equipped with a flame ionization detector temperature, and the pressure was slowly released. Tetradeand a 25 m x 0.25 mm fused-silica capillary column CBP 1or cane (ca. 0.5 g) was added to the reaction mixture as an CBP 10. 'H and I3C NMR spectra were measured on a JEOL internal standard. The liquid phase was analyzed by GLC, GMN-270 spectrometer. MS and HRMS were recorded on a which indicated that all the 4-TolCHO was consumed, and 2a JEOL JMS-AX505H mass spectrometer. IR spectra were and 3a were formed in 96% and 3% yields, respectively. recorded with a Shimadzu FTIR-8100M spectrometer by using Hydrosilylation of ArCOCo(CO)s(PPhs). For entry 1or a NaCl cell. Elemental analysis was performed with a Perkin2 in Table 4, HSiEt3 (0.174 g, 1.5 mmol) was added to a Elmer 240011 CHN Analyzer. benzene solution (5 mL) of 4-TolCOCo(C0)3(PPh3)(0.262 g, 0.5 Catalytic Carbonylation of Aryl Iodides with HSiEt3. mmol) and tetradecane (ca. 0.05 g) as an internal standard, In a typical run, 4-To11 (0.545 g, 2.5 mmol), HSiEt3 (0.872 g, and the resulting mixture was stirred under Nz or CO, respectively. After 3 h, the liquid phase was analyzed by GLC. 7.5 mmol), PdClz(PPh3)~(0.035 g, 0.05 mmol), Coz(C0)s(0.0086 g, 0.025 mmol), and benzene (5 mL) as a solvent were charged For entries 3-6 and 8-10, ArCOCo(CO)3(PPh3)(0.262 g, in an autoclave under nitrogen. The autoclave was pressurized 0.5 mmol), HSiEt3 (0.174 g, 1.5 mmol), and benzene (5 mL) to 50 atm with CO at room temperature, and heated to 80 "C were charged in an autoclave under nitrogen. For entries 5 in an oil bath. The reaction was allowed to proceed at this and 6, CO~(CO)S (0.086 g, 0.025 mmol) was charged in addition. For entry 7,4-TolCOCo(C0)4in hexane (2 mL) prepared from temperature for 3 h with magnetic stirring. After the reaction, the autoclave was rapidly cooled to room temperature, and the 4-TolCOCl (0.078 g, 0.5 mmol) and K[CO(CO)~] (0.5 mmol) in pressure was slowly released. Then NEt3 (3 mmol) and EtOH THF (1 mL) and ether (4 mLIz2was charged in an autoclave under nitrogen, and benzene (3 mL), HSiEt3 (0.174 g, 1.5 (3 mmol) were added with stirring under nitrogen to quench Et3SiI formed during the carbonylation. Tetradecane (ca. 0.5 mmol), and NEt3 (0.303 g, 3 mmol) were added. The autoclave g) was added to the reaction mixture as an internal standard, was pressured to 50 atm with CO at room temperature, and and the liquid phase was analyzed by GLC, which showed that heated to 80 "C in an oil bath with stirring. After 3 h, the autoclave was cooled and the pressure was released. Then the conversion of 4-To11 and the yields of 2a and Et3SiI were 85%, 76%, and 80%, respectively. A similar reaction in the tetradecane (ca. 0.05 g) was added as an internal standard, presence of NEt3 (0.303 g, 3 mmol) afforded a mixture of la and the liquid phase was analyzed by GLC. In the case of entry 5 in Table 4, the formation of Coz(C0)6(PPh3)2(0.101 g, (2%),2a (6%),3a (57%),and Et3SiI (30%) at 70% conversion of 4-TolI. Compounds 2a-d and 3a-d were fully identified 50%)was confirmed by the IR spectrum (1958 cm-I, CHC13).23 by 'H NMR'O and MS or HRMS after purification by silica-gel Conversion of Co2(CO)6(PPh3)2into [Co(CO)d-. COZ(C0)6(PPh3)2 (0.020 g, 0.025 mmol), HSiEt3 (0.029 g, 0.25 column chromatography and bulb-to-bulb distillation. The mmol), NEt3 (0.303 g, 3 mmol), and THF (5 mL) as a solvent spectral data for newly synthesized compounds 2d and 3d are as follows. were charged in a n auctoclave under nitrogen. The autoclave was immediately pressurized to 50 atm with CO at room 4-FC6H4CH20SiEt3(2d). Colorless oil. 'H NMR (CDC13): 6 0.64 (9, J = 7.8 Hz, 6 HI, 0.97 (t, J = 7.8 Hz, 9 HI, 4.69 (s, temperature and heated t o 80 "C in an oil bath. The reaction 2 H), 7.01 (pseudo-t, J = 8.8 Hz, 2 HI, 7.29 (dd, J = 8.3 and was allowed to proceed a t this temperature for 3 h with magnetic stirring. After the reaction, the autoclave was 5.6 Hz, 2 H). I3C NMR (CDC13): 6 4.5, 6.7, 64.1, 115.0 (d, 'JFC = 22 Hz), 127.8 (d, 3 J ~ = c 7 Hz), 137.0 (d, 4 J ~ = c 4 Hz), 161.9 rapidly cooled to room temperature, and the pressure was slowly released. The IR spectrum of the resulting mixture =C 244 Hz). HRMS calcd for C13H210FSi: 240.1346. (d, ~ J F Found: 240.1352. showed an absorption at 1887 cm-' which is assignable to (4-FC&CHOSiEt& (3d). Colorless oil (mixture of dia[Co(C0)41-. A THF solution of Na[Co(CO)3(PPh3)](0.05 mol dm-3) was stereomers). 'H NMR (CDC13): 6 0.20-0.30, 0.45-0.54 (m, 12 H each), 0.68 (t, J = 7.8 Hz, 18 H) 0.87 (t,J = 7.8 Hz, 18 allowed t o react with 1atm of CO. In the IR spectrum of the H), 4.45, 4.71 (s, 2 H each), 6.77-6.99 (m, 12 H), 7.25 (dd, J = resulting solution, absorptions a t 1931, 1856, and 1811 cm-' due to [Co(C0)3(PPh3)]- remarkably decreased and a strong 8.6 and 5.6 Hz, 4 H). 13C NMR (CDC13): 6 4.5, 4.8, 6.5, 6.7, 78.2, 79.1, 113.7 (d, 'JFC= 22 Hz), 114.2 (d, 'JFC= 21 Hz), absorption at 1888 cm-l assignable to [Co(CO)41-was observed. 128.91 (d, 3 J ~=c 7 Hz), 128.96 (d, 3 J ~ = c 9 Hz), 136.6 (d, 4 J ~ c Supplementary Material Available: lH and 13C NMR = 2 Hz), 138.7 (d, 4 J ~ = c 4 Hz), 162.0 (d, 'JFC = 246 Hz), 162.2 spectra for 2d and 3d (4 pages). Ordering information is given (d, 'JFC= 245 Hz). Anal. Calcd for C~,&&FZS~~:C, 65.23; on any current masthead page. H, 8.42. Found: C, 65.14; H, 8.59. (20) Trost, B. M.; Verhoeven, T. R. In Comprehensiue Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 8, p 801. (21) Tso, C. C.; Cutler, A. R. Polyhedron 1993, 12, 149.
OM9409074 (22) Heck, R. F.; Breslow, D. J.Am. Chem. SOC.1962,84, 2499. (23) Manning, A. R. J . Chem. SOC.A 1968, 1135.
