Chemistry Letters Vol.34, No.3 (2005)
287
Table 2. Hydroformylation of linear olefins catalyzed by den-
drimer-Rh complexesa
Ph
CN
CO Et
CHO
+
(i),(ii)
CN
CO Et
CN
Ph
Ph
base sites
2
Ph
b
b
2
Entry
Olefins
Ligand Time /h Conv. /% Select. /%
(B : L)
CO Et
2
90 % yield
Scheme 1. One-pot reaction using the dendritic nanoreactor.
Reaction conditions:styrene 0.5 mmol, ethyl cyanoacetate 0.75
mmol, [RhCl(cod)]2 0.0025 mmol, 1a 0.005 mmol, 3 0.015
mmol, THF 2 mL, CO 5 atm, H2 5 atm. (i) 40 ꢁC, 9 h. (ii)
60 ꢁC, 24 h.
73
79
96
19
25 : 75
26 : 74
26 : 74
1a
1b
1
1
1
2
(3)
(4)
5
3
1b
4
1
c
NEt
26 : 74
4
3
49
63
98
9
26 : 74
26 : 74
27 : 73
25 : 75
1a
1b
1
1
4
1
5
6
7
chains favors hydroformylation of higher olefins. The specific
nanoenvironment created by the dense amino groups inside the
dendrimers can act not only as a promoter and anchor of the ac-
tive Rh species but also as a base catalyst, promoting one-pot
three reactions within the dendrimers.
7
1b
c
NEt
8
3
45
60
31 : 69
28 : 72
28 : 72
26 : 74
9
10
11
1a
1b
1
1
(5)
15
This work was supported by a Grant-in-Aid for Scientific
Research from JSPS. We thank the center of excellence
(21COE) program ‘Creation of Integrated Ecochemistry’ of
Osaka University.
96
14
1b
4
1
c
NEt
12
3
f
e
e
e
d
1.0
3 + 5
44/43
14/26
27/28
1a
1b
13
6
5
f
d
1.9
14
References and Notes
f
c,d
1
2
For a book on dendrimers, see: ‘‘Dendrimers and Other
´
Dendritic Polymers,’’ ed. by J. M. J. Frechet and D. A. Tomalia,
Wiley & Sons, New York (2001).
For recent reviews on dendritic catalysts, see: a) D. Astruc and
F. Chardac, Chem. Rev., 101, 2991 (2001). b) R. van Heerbeek,
P. C. J. Kamer, P. W. N. M. van Leeuwen, and J. N. H. Reek,
Chem. Rev., 102, 3717 (2002).
NEt
12
1.0
15
3
aReaction conditions: substrate 1 mmol, [RhCl(cod)]2 0.0025
mmol, 2 0.015 mmol, THF 2 mL, CO 5 atm, H2 5 atm, 60 ꢁC.
bDetermined by GC. NEt3 0.07 mmol. 1-Octene 0.5 mmol,
c
d
1-octadecene 0.5 mmol, 40 ꢁC. Conversions of olefins (3/5).
e
fRatio of conversions of 3 to 5.
3
4
a) J. F. G. A. Jansen, E. M. M. de Brabander-van den Berg,
and E. W. Meijer, Science, 266, 1226 (1994). b) S. Hech and
sponding aldehydes were formed as main products (B/L ¼
25=75) in high yield with traces of isomerization products
(Entries 1 and 2). On the other hand, for the higher olefins of
1-decene and 1-octadecene, the dendritic nanoreactor using 1b
showed higher catalytic activity than 1a (Entries 5, 6, 9, and
10). The above phenomenon was not observed when using tri-
ethylamine instead of the dendrimers (Entries 4, 8, and 12). Re-
gioselectivity of the products was almost constant among dendri-
mers 1a, 1b and NEt3. Intermolecular competitive hydroformy-
lations between 1-octene and 1-octadecene were carried out with
the dendrimers 1a and 1b at 40 ꢁC. Notably, the relative reaction
rate of 1-octene over 1-octadecene increased by a factor of 1.9
using dendrimer 1b. The congested surface alkyl groups on the
dendrimer 1b might have stronger affinity for 1-octadecene than
1-octene giving preferential penetration of 1-octadecene into the
dendrimer.
´
J. M. J. Frechet, Angew. Chem., Int. Ed., 40, 74 (2001).
For several examples of dendrimer-encapsulated metal catalysts,
see: Ru complex a) Q.-H. Fan, Y.-M. Chen, X.-M. Chen, D.-Z.
Jiang, F. Xi, and A. S. C. Chan, Chem. Commun., 2000, 789.
Pd complex b) M. Ooe, M. Murata, T. Mizugaki, K. Ebitani,
and K. Kaneda, J. Am. Chem. Soc., 126, 1604 (2004). Pd
nanoparticles c) Y. Niu, L. K. Yeung, and R. M. Crooks, J.
Am. Chem. Soc., 123, 6840 (2001). d) M. Ooe, M. Murata, T.
Mizugaki, K. Ebitani, and K. Kaneda, Nano Lett., 2, 999 (2002).
A. P. H. J. Schenning, C. Elissen-Romn, J. W. Weener,
M. W. P. L. Baars, S. J. van der Gaast, and E. W. Meijer,
J. Am. Chem. Soc., 120, 8199 (1998).
Immobilization of metal complexes on dendrimers by electro-
static interactions, see: a) U. Boas, A. J. Karlsson, B. F. M.
de Waal, and E. W. Meijer, J. Org. Chem., 66, 2136 (2001). b)
R. van de Coevering, M. Kuil, R. J. M. K. Gebink, and
G. van Koten, Chem. Commun., 2002, 1636.
5
6
The internal amino groups within the dendrimer acted as a
base catalyst for the Knovenagel condensation. For example,
the reaction between benzaldehyde and ethyl cyanoacetate using
dendrimer 1 afforded (E)-ethyl 2-cyanocinnamate in 99% yield.
The combined action of the active Rh species and the base sites
of the dendritic catalyst could be applied to a one-pot synthesis
(Scheme 1). Treatment of styrene and methyl cyanoacetate
under the hydroformylation conditions afforded directly ethyl
2-cyano-4-phenylpentanoate, a valuable intermediate of glutari-
mide, in 90% yield.11 The Rh complex and tertiary amino groups
within the dendrimer participate in three sequential reactions:
hydroformylation, the Knoevenagel condensation, and hydroge-
nation.12
7
8
E. Monflier, H. Bricout, F. Hapiot, S. Tilley, A. Aghmiz, and
´
C. D. Frohling and C. W. Kohlpaintner, in ‘‘Applied
Homogeneous Catalysts with Organometallic Compounds,’’ ed.
by B. Cornils and W. A. Herrmann, Wiley-VCH, Weinheim
(1996), p 27.
Recent example of hydroformylation catalyzed by self-
assembled Rh complex, see: V. F. Slagt, P. C. J. Kamer,
P. W. N. M. van Leeuwen, and J. N. H. Reek, J. Am. Chem.
Soc., 126, 1526 (2004).
A. M. Masdeu-Bulto, Adv. Synth. Catal., 346, 435 (2004).
9
10 Formation of Rh hydride species is facilitated in the presence of
amine: see, P. S. Hallman, D. Evans, J. A. Osborn, and G.
Wilkinson, J. Chem. Soc., Chem. Commun., 1967, 305.
11 R. R. Goehring, T. D. Greenwood, G. C. Nwokogu, J. S. Pisipati,
T. G. Rogers, and J. F. Wolfe, J. Med. Chem., 33, 926 (1990).
12 Use of NEt3 instead of 1a could also promote the sequencial
reactions to give the corresponding product in almost the same
yield.
In summary, we report the encapsulation of Rh complexes
within surface alkylated PPI dendrimers through ionic interac-
tions. The congested surface of dendrimers with long alkyl
Published on the web (Advance View) January 29, 2005; DOI 10.1246/cl.2005.286