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J. Am. Chem. Soc. 1998, 120, 10274-10275
One of us has previously developed the synthesis of the
Josiphos derivative (R)-(S)-1 as a precursor for the immobilization
of such ferrocenyl ligand on a variety of supports.6 In the present
work (R)-(S)-1 was chosen as starting material because it fulfills
two important criteria. First, the necessary functional group, a
primary amine, is well suited for the construction of dendritic
structures using amide connectivities, and is placed at a remote
position from the phosphine fragments. This minimizes the steric
interactions that could alter the delicate conformational properties
of the chelate ring of the catalyst. Second, the chain length of
the tether appears to be sufficient to ensure conformational
flexibility at the periphery of the dendrimer.
Dendrimers Containing Chiral Ferrocenyl
Diphosphine Ligands for Asymmetric Catalysis
Christoph Ko¨llner,†,‡ Benoˆıt Pugin,*,§ and Antonio Togni*,‡
Laboratory of Inorganic Chemistry
Swiss Federal Institute of Technology
ETH-Zentrum, CH-8092 Zu¨rich, Switzerland
NoVartis SerVices AG, Catalysis and Synthesis SerVices
P.O. Box, CH-4002 Basel, Switzerland
ReceiVed April 6, 1998
Thus, a slight excess of (R)-(S)-1 cleanly reacts with benzene-
1,3,5-tricarboxylic acid trichloride (2)7 and adamantane-1,3,5,7-
tetracarboxylic acid tetrachloride (3),8 affording the first generation
dendrimers 4 and 5, respectively, in good yields after chromato-
graphic purification.9 With a view to preparing dendrimers of
the second generation, intermediate 7 was obtained, after depro-
tection, from the reaction of (R)-(S)-1 with 5-(tert-butyldimeth-
ylsiloxy)isophthaloyl dichloride (6),10 in 92% yield (Scheme 1).
Hence, macromolecules 8 and 9 (Chart 1), containing six and
eight ferrocenyl units, respectively, were prepared in excellent
yields when building block 7 was reacted with the acid chlorides
2 and 3. For the efficient formation of the ester connections the
addition of catalytic amounts of 4-(pyrrolidino)pyridine was
necessary.9
The preparation and characterization of dendrimers containing
transition-metal-complex fragments has received considerable
attention in recent years,1 and the aspect of chirality in dendritic
architectures2 has been recognized as a multifaceted problem most
recently.3 However, the application of chiral organometallic
dendrimers in asymmetric catalysis is a field still very much in
its infancy.4 Because of the proven efficacy of chiral ferrocenyl
ligands in a number of asymmetric catalytic reactions,5 we set
up a study aimed at incorporating such ligands into dendritic
structures. Thus, well-defined, high-molecular multicenter cata-
lysts offer a potential solution to the notorious problem of catalyst
recovery, by virtue of, e.g., nanofiltration or precipitation. We
report herein the preparation of dendritic ligands containing up
to eight ferrocenyl diphosphines, as well as first selected
applications in hydrogenation reactions.
All new multiple ferrocenyl ligands display relatively simple
NMR characteristics and are monodisperse.9 As one would
expect, in the 31P NMR spectra of compounds 4, 5, 7, 8, and 9
only one pair of doublets is observed, with the typical long range
4JPP coupling constant of ca. 34 to 37 Hz. This indicates the
equivalence of the ferrocenyl units. The larger dendrimers 8 and
* To whom correspondence should be addressed at the following: e-mail:
† Part of the planned Ph.D. thesis of C.K. at ETH-Zu¨rich.
‡ ETH-Zentrum.
§ Catalysis and Synthesis Services.
1
9 show broad signals in the H NMR 300 MHz spectra at room
(1) For general reviews on dendrimers, see: (a) Newkome, G. R.;
Moorefield, C. N.; Vo¨gtle, F. Dendritic Molecules: Concepts, Syntheses and
PerspectiVes; VCH: Weinheim, 1996. (b) Tomalia, D. A.; Naylor, A. M.;
Goddard, W. A., III Angew. Chem. 1990, 102, 119; Angew. Chem., Int. Ed.
Engl. 1990, 29, 138. (c) Tomalia, D. A. Aldrichim. Acta 1993, 26, 91. (d)
Tomalia, D. A.; Durst, H. D. Top. Curr. Chem. 1993, 165, 193. (e) Issberner,
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(g) Ardoin, N.; Astruc, D. Bull. Soc. Chim. Fr. 1995, 132, 875. For recent
reports concerning metal-containing dendrimers, see: (h) Balzani, V.; Cam-
pagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi, M. Acc. Chem. Res. 1998,
31, 26. (i) Achar, S.; Immoos, C. E.; Hill, M. G.; Catalano, V. J. Inorg. Chem.
1997, 36, 2314. (j) Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.;
Losada, J.; Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613. (k) Castro, R.;
Cuadrado, I.; Alonso, B.; Casado, C. M.; Mora`n, M.; Kaifer, A. E. J. Am.
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1996, 15, 5278. (m) Vale´rio, C.; Fillaut, J.-L.; Ruiz, J.; Guittard, J.; Blais,
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R. J. Angew. Chem. 1994, 106, 895; Angew. Chem., Int. Ed. Engl. 1994, 33,
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Soc. 1996, 118, 5708. (p) Huck, W. T. S.; van Veggel, F. C. J. M. v.;
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temperature, possibly indicating slow conformational equilibria
in the sterically rather crowded inner core of the dendrimers.
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obtained when corresponding DMSO-d6 solutions are measured
at 80 and 120 °C, respectively. The new high-molecular-weight
compounds were also characterized by MALDI-TOF mass
spectrometry.11 Molecular peaks at m/z values in very good
agreement with the calculated ones, as well as in-source
fragmentation11c patterns very similar to those of the “monomeric”
(5) For reviews, see: (a) Togni, A. Angew. Chem. 1996, 108, 1581; Angew.
Chem., Int. Ed. Engl. 1996, 35, 1475. (b) Togni, A. In Organic Synthesis Via
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Soc. 1996, 118, 1031. For industrial-scale applications, see: (g) Spindler, F.;
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of Organic Reactions; Malz, R. E., Jr., Ed.; Chem. Ind. Vol. 68; Dekker:
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1996, 125, 276188z). (b) Pugin, B. (Novartis Ltd.), PCT Int. Appl. WO 96
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Int. Appl. WO 97 02,232 (Chem. Abstr. 1997, 126, 185879e).
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P. K.; Lapierre, J.-M.; Greiveldinger, G.; Seebach, D. HelV. Chim. Acta 1997,
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(4) See, e.g.: (a) Seebach, D.; Marti, R. E.; Hintermann, T. HelV. Chim.
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(9) For experimental details, see the Supporting Information.
(10) Miller, T. M.; Kwock, E. W.; Neenan, T. X. Macromolecules 1992,
25, 3143.
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see, e.g.: (a) Hummelen, J. C.; van Dongen, J. L. J.; Meijer, E. W. Chem.
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Moore, J. S. J. Am. Soc. Mass Spectrom. 1994, 5, 731. (c) For a discussion
of in-source fragmentations in MALDI MS, see: Reiber, D. C.; Grover, T.
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S0002-7863(98)01137-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/19/1998