Hydroformylation reactions using recyclable rhodium-complexed dendrimers on silica [4]

Full text of DOI:10.1021/ja993196f

956
J. Am. Chem. Soc. 2000, 122, 956-957
Table 1. Hydroformylation of Styrene with
Rh-PPh2-PAMAM-SiO2 Catalystsa
Hydroformylation Reactions Using Recyclable
Rhodium-Complexed Dendrimers on Silica
temp conversionc selectivityd
entry
catalyst
cycleb (°C)
(%)
B:L ratio
S. Christine Bourque and Howard Alper*
1e
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
11a(C2-G3)
11a(C2-G3)
11b(C4-G3)
11b(C4-G3)
11b(C4-G3)
11b(C4-G3)
11c(C6-G3)
11c(C6-G3)
11c(C6-G3)
11c(C6-G3)
11d(C12-G3)
11d(C12-G3)
11d(C12-G3)
11d(C12
12a(C2-G4)
12a(C2-G4)
12b(C4-G4)
12b(C4-G4)
12b(C4-G4)
12b(C4-G4)
12c(C6-G4)
12c(C6-G4)
12c(C6-G4)
12c(C6-G4)
12d(C12-G4)
12d(C12-G4)
12d(C12-G4)
12d(C12-G4)
1
2
1
2
3
4
1
2
3
4
1
2
3
4
1
2
1
2
3
4
1
2
3
4
1
2
3
4
75
75
65
65
65
65
65
65
65
65
65
65
65
65
75
75
65
65
65
65
65
65
65
65
65
65
65
65
99
5
99
90
65
6
8:1
ndf
9:1
7:1
7:1
Department of Chemistry, UniVersity of Ottawa
10 Marie Curie, Ottawa, Ontario, Canada K1N 6N5
Leo E. Manzer
nd
99
92
84
80
99
99
88
76
99
12
99
90
63
13
99
99
99
90
99
99
99
99
10:1
12:1
13:1
11:1
8:1
11:1
12:1
10:1
8:1
DuPont Central Research & DeVelopment
Experimental Station, Wilmington, Delaware 19880-0262
Prabhat Arya
Steacie Institute of Molecular Sciences, NRC,
Ottawa, Ontario, Canada K1A 0R6
ReceiVed September 3, 1999
nd
10:1
12:1
11:1
12:1
8:1
In recent years, considerable attention has been directed toward
the attachment of homogeneous catalysts to insoluble supports
in an attempt to combine the practical advantages of a hetero-
geneous catalyst with the efficiency of a homogeneous system.1
Heterogenization allows for easy separation of the reaction
products from the catalyst, which opens up the possibility of
recycling, while homogenization offers excellent specificity and
high catalytic activity. Typically, immobilization of a catalyst on
a solid support results in a significant decrease in the activity of
the catalyst.1a,b
9:1
12:1
11:1
12:1
7:1
9:1
9:1
Dendrimers, a relatively new class of compounds introduced
about 20 years ago, have already found numerous applications2
including metal complexation2d and occasional use as catalysts.3
Previously we reported that a silica-supported polyamidoamine
dendrimer ligand for rhodium (Rh-PPh2-PAMAM-SiO2) is a
highly active and regioselective catalyst for the hydroformylation4
of aryl olefins and vinyl esters.5 However, the third- and fourth-
generation catalysts displayed low activity compared to the lower
generations. This was believed to be due to incomplete phospho-
nation reactions arising from steric crowding and ultimately
a 10.0 mmol of styrene, 10 mL of CH2Cl2, 22 h, 1000 psi of a 1:1
ratio of CO:H2, 25 mg of catalyst. b Catalyst was recovered by
microporous filtration after the first cycle, washed with CH2Cl2, and
1
reused in the next cycle. c Determined by H NMR and GC. d Deter-
1
mined by H NMR. e 2.0 mmol of styrene. f Not determined.
resulting in the threshold of dendrimer growth being reached.6 It
was perceived that extending the chain length of each generation
would relieve the steric crowding and allow for increased catalyst
loading at higher generations. To extend the chain length, the
ethylenediamine linker was substituted by 1,4-diaminobutane, 1,6-
diaminohexane, and 1,12-diaminododecane. The lengthening of
the monomeric unit of the dendrimer should decrease the
congestion at the surface. This can easily be observed by
comparing the theoretical amine content (Table 1 in the Support-
ing Information) for the various chain lengths and generations.
For example, the C12 G-4 (1.84 mmol of NH2/g of SiO2)
dendrimer has approximately half the amine content of the C2
G-4 (3.55 mmol NH2/g SiO2) dendrimer.
Polyamidoamino (PAMAM) dendrimers up to generation 4 (1-
4) were constructed on the surface of aminopropylsilica employing
a standard divergent growth strategy.7,8 The isolation of the
dendrimers under construction proved to be extremely time-
consuming, as the filters generally became clogged with precipi-
tated diamine. In the case of the diaminedodecane linkers,
filtration and washing took up to 3 days. Figures 1-3 (see
Supporting Information for Figures 2 and 3) show the gradual
(1) (a) Annis, D. A.; Jacobsen, E. N. J. Am. Chem. Soc. 1999, 121, 707-
714. (b) Shuttleworth, S. J.; Allin, M.; Sharma, P. K. Synthesis 1997, 1217-
1239. (c) Nozaki, K.; Itoi, Y.; Shibahara, F.; Shirakawa, E.; Ohta, T.; Takaya,
H.; Hiyama, T. J. Am. Chem. Soc. 1998, 120, 4051-4052. (d) Chen, J.; Alper,
H. J. Am. Chem. Soc. 1997, 119, 893-895. (e) Nait Ajjou, A.; Alper H. J.
Am. Chem. Soc. 1998, 120, 1466-1468.
(2) (a) Matthews, O. A.; Shipway, A. N.; Stoddart, J. F. Prog. Polym. Sci.
1998, 23, 1-56. (b) Frechet, J. M. J.; Hawker, C. J.; Gitsov, I.; Leon, J. W.
Pure Appl. Chem. 1996, 10, 1399-1425. (c) Ardin, N.; Astruc, D. Bull. Soc.
Chim. Fr. 1995, 132, 875-909. (d) Caminade, A. M.; Laurent, R.; Chaudret,
B.; Majoal, J. P. Coord. Chem. ReV. 1998, 178-180, 793-821. (e) Bianchini,
C.; Burnaby, D. G.; Evans, J.; Fredani, P.; Meli, A.; Oberhauser, W.; Psaro,
R.; Sordelli, L.; Vizza, F. J. Am. Chem. Soc. 1999, 121, 5961-5971.
(3) (a) Knapen, J. W. J.; van der Made, A. W.; de Wilde, J. C.; van
Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 372, 659-663. (b) Reetz, M. T.; Lohmer, G.; Schwickardi, R. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1526-1529. (c) Reetz, M. T. Topics Catal.
1997, 4, 187-200.
(4) (a) Ungvary, F. Coord. Chem. ReV. 1999, 188, 263-296. (b) Ungvary,
F. Coord. Chem. ReV. 1997, 167, 233-260. (c) Dickson, R. S. Homogeneous
Catalysis with Compounds of Rhodium and Iridium; D. Reidel: Boston, 1985;
Chapter 4. (d) Herrmann, W. A.; Cornils, B. Angew. Chem., Int. Ed. Engl.
1997, 36, 1048-1067.
(5) Bourque, S. C.; Maltais, F.; Xiao, W.-J., Tardif, O.; Alper, H.; Arya,
P.; Manzer, L. E. J. Am. Chem. Soc. 1999, 121, 3035-3038.
(6) A communication, which was received following submission of the
manuscript, concerns the synthesis of phosphine-functionalized carbosilane
dendrimers (G0-G2) and the use of their palladium complexes for allylic
alkylation. The authors note that, “The dendrimer with seventy-two phosphine
groups could not be prepared, probably because of surface congestion.” See:
de Groot, D.; Eggeling, E. B.; de Wilde, J. C.; Kooijman, H.; van Haaren, R.
J.; van der Made, A. W.; Spek, A. L.; Voget, D.; Reek, J. N. H.; Kanier, P.
C. J.; van Leeuwen, P. W. N. M. J. Chem. Soc., Chem. Commun. 1999, 1623-
1624.
(7) (a) Tomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin,
S.; Roeck, J.; Ryder, J.; Smith, P. Polym. J. 1995, 17, 117-132. (b) Tomalia,
D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.;
Ryder, J.; Smith, P. Macromolecules 1986, 19, 2466-2468. (c) Tomalia, D.
A.; Hall, M.; Hedstrand, D. J. Am. Chem. Soc. 1987, 109, 1061-1063. (d)
Tomalia, D. A.; Berry, V.; Hall, M.; Hedstrand, D. Macromolecules 1987,
20, 1164-1167. (e) Tsubokawa, N.; Ichioka, H.; Satoh, T.; Hayashi, S.; Fujiki,
K. React. Funct. Polym. 1998, 37, 75-82.
(8) See Supporting Information for procedure, Figure 2, and the hydro-
formylation results of vinyl acetate.
10.1021/ja993196f CCC: $19.00 © 2000 American Chemical Society
Published on Web 01/19/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 5, 2000 957
Figure 1. Proposed structures of the third generation C2, C4, and C6 Rh-PPh2-PAMAM-SiO2 dendrimers, displaying the gradual decongestion of
the terminal groups as the diamine linker increases.
decongestion of the terminal groups on the third- and fourth-
generation dendrimers as the diamine linker increases from 2 to
12 carbons.
7-10 and 21-24). However, there is not a significant activity
difference between the 6- and 12-carbon dendrimers.
After the hydroformylation reaction, the product solution is
orange or yellow. There is evidently a slow leaching of rhodium
from the silica. Soxhlet extraction does not remove this excess
rhodium. Pressurizing the catalyst in dichloromethane with
hydrogen gas (1000 psi) does not promote the leaching of the
catalyst from the solid support; however, pressurizing the catalyst
with either carbon monoxide or mixtures of carbon monoxide
and hydrogen (1000 psi total pressure) does promote the leaching
of rhodium. Preleaching of the catalyst was attempted by
pressurizing the catalyst in dichloromethane with carbon monoxide
and rinsing away the leached rhodium for several cycles until no
rhodium was observed to leach from the silica. However, addition
of substrate to the preleached catalyst in dichloromethane
promotes further leaching of rhodium under hydroformylation
conditions.
The dendrimers on silica were phosphonated prior to com-
plexation with rhodium.3b,5,8 Each terminal amine was phospho-
nated by reaction with diphenylphosphinomethanol, prepared in
situ from paraformaldehyde and diphenylphosphine. The phos-
phonated dendrimers (5-8) on silica were easily complexed to
chloro(dicarbonyl)rhodium(I) dimer in distilled and degassed
hexanes at 40 °C for 12 h under argon to give G-1(9a-9d),
G-2(10a-10d), G-3(11a-11d), and G-4(12a-12d) complexes.
The hydroformylation of styrene and vinyl acetate was
examined using a 1:1 carbon monoxide and hydrogen gas mixture
(total pressure ) 1000 psi) in dichloromethane (eq 1).8 The
hydroformylation results for styrene are summarized in Table 1,
and the results obtained for vinyl acetate are provided in Table 2
of the Supporting Information.
In conclusion, this investigation demonstrates the importance
of the length of the spacer chain on the activity and recyclability
of the dendrimer rhodium complex.
Acknowledgment. We are grateful to DuPont Canada and to the
NSERC/ NRC Research Partnership Program for support of this research.
S.C.B. is also grateful to the Ontario Ministry of Energy, Science and
Technology for an OGSST scholarship.
The hydroformylation of either styrene or vinyl acetate proceeds
in up to quantitative yields, and in fine regioselectivity. These
silica-supported catalysts are easily recovered by microporous
filtration using a 0.45-µm membrane filter and are reusable for
at least three more cycles. Generally, as the chain length is
increased from 2 (Table 1 , entries 1, 2, 15, and 16) to 4 carbons
(Table 1, entries 3-6 and 17-20), the catalytic activity and
recyclablity increases dramatically as shown. There is another
increase of activity going from 4 to 6 carbons (Table 1, entries
Supporting Information Available: General procedures, the pro-
posed structures of the third- (C12) fourth-generation Rh-PPh2-
PAMAM-SiO2 dendrimers, and the hydroformylation results of vinyl
acetate with Rh-PPh2-PAMAM-SiO2 catalysts (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JA993196F