Fluoroacrylate-bound fluorous-phase soluble hydrogenation catalysts

Article abstract of DOI:10.1021/ol991352h

(GRAPHS PRESENTED) Fluoroacrylate polymer-bound hydrogenation catalysts are described. N-Acryloxysuccinimide-containing fluoroacrylate polymers were converted into phosphine ligands and subsequently into analogues of Wilkinson's catalyst by amidation of N-acryloxysuccinimide active ester residues and Rh exchange. The resulting catalysts have excellent activity and can be reused following fluorous biphasic liquid/liquid separation and extraction.

Full text of DOI:10.1021/ol991352h

ORGANIC
LETTERS
2
000
Vol. 2, No. 3
93-395
Fluoroacrylate-Bound Fluorous-Phase
Soluble Hydrogenation Catalysts
3
David E. Bergbreiter,* Justine G. Franchina, and Brenda L. Case
Department of Chemistry, Texas A&M UniVersity, P.O. Box 30012,
College Station, Texas 77842-3012
bergbreiter@tamu.edu
Received December 15, 1999
ABSTRACT
Fluoroacrylate polymer-bound hydrogenation catalysts are described. N-Acryloxysuccinimide-containing fluoroacrylate polymers were converted
into phosphine ligands and subsequently into analogues of Wilkinson’s catalyst by amidation of N-acryloxysuccinimide active ester residues
and Rh exchange. The resulting catalysts have excellent activity and can be reused following fluorous biphasic liquid/liquid separation and
extraction.
Fluorous biphasic chemistry is now well established. Since
acryloxysuccinimide (NASI, 2). This monomer is available
commercially from DuPont. The product fluoroacrylate
1
Horvath’s original report in 1994, it has become a useful
strategy in both synthesis and catalysis.2 Typically, fluo-
-8
(8) (a) van Vliet, M. C. A.; Arends, I. W. C. E.; Sheldon, R. A. Chem.
rous-phase solubility (and separations) in such chemistry is
Commun. 1999, 263-4. (b) Keim, W.; Vogt, M.; Wasserscheid, P.;
Driessen-Holscher, B. J. Mol. Catal. A: Chem. 1999, 139, 171-5. (c) Sinou,
D.; Pozzi, G.; Hope, E. G.; Stuart, A. M. Tetrahedron Lett. 1999, 40, 849-
9
the result of attachment of a so-called “Teflon pony-tail”
onto a catalyst, reagent, or substrate. Given the success in
changing solubility of catalysts, reagents, and substrates
generally with soluble polymers10-14 and the availability of
fluorinated monomers, we reasoned that soluble fluorinated
supports could be used as a general sort of macromolecular
8
1
52. (d) Nishikido, J.; Nakajima, H.; Saeki, T.; Ishii, A.; Mikami, K. Synlett
998, 1347-8. (e) Koch, D.; Leitner, W. J. Am. Chem. Soc. 1998, 120,
13398-13404. (f) A. Juliette, J. J. J.; Rutherford, D.; Horv a´ th, I. T.; Gladysz,
J. A. J. Am. Chem. Soc. 1999, 121, 2696-2704. (g) Horv a´ th, I. T.; Kiss,
G.; Cook, R. A.; Bond J. E.; Stevens, P. A.; Rabai, J.; Mozeleski, E. J. J.
Am. Chem. Soc. 1998, 120, 3133-43. (h) Guillevic, M. A.; Rocaboy, C.;
Arif, A. M.; Horv a´ th, I. T.; Gladysz, J. A. Organometallics 1998, 17, 707-
“
Teflon pony-tail”. The hydrogenation catalysts described
7
4
17. (i) Li, C. B.; Nolan, S. P.; Horv a´ th, I. T. Organometallics 1998, 17,
52-6. (j) Herrera, V.; de Rege, P. J. F.; Horv a´ th, I. T.; Le Husebo, T.;
below supported on a fluorous-phase soluble fluoropolymer
demonstrate this idea.
Hughes, R. P. Inorg. Chem. Commun. 1998, 1, 197-9. (k) Hughes, R. P.;
Zheng, X. M.; Morse, C. A.; Curnow, O. J.; Lomprey, J. R.; Rheingold, A.
L.; Yap, G. P. A. Organometallics 1998, 17, 457-465. (l) Hope, E. G.;
Kemmitt, R. D. W.; Paige, d. R.; Stuart, A. M. J. Fluorine Chem. 1999,
The fluoroacrylate polymers used in this work were
prepared using the fluoroacrylate monomer 1 and N-
99, 197-200. (m) Richter, B.; Deelman, B. J.; van Koten, G. J. Mol. Catal.
A: Chem. 1999, 145, 317-21. (n) Endres, A.; Maas, G. Tetrahedron Lett.
1999, 40, 6365-8. (o) Moineau, J.; Pozzi, G.; Quici, S.; Sinou, D.
Tetrahedron Lett. 1999, 40, 7683-6. (p) Kling, R.; Sinou, D.; Pozzi, G.;
Choplin, A.; Quignard, F.; Busch, S.; Kainz, S.; Koch, D.; Leitner, W.
Tetrahedron Lett. 1998, 39, 9439-9442
(9) Gladysz, J. A. Science (Washington, D.C.) 1994, 266, 55-6.
(10) Bergbreiter, D. E. Catal. Today 1998, 42, 389-97.
(11) Harwig, C. W.; Gravert, D. J.; Janda, K. D. Chemtracts 1999, 12,
1-26.
(12) Bergbreiter, D. E.; Case, B. L.; Liu, Y. S.; Caraway, J. W.
Macromolecules 1998, 31, 6053-6062.
(
(
(
(
1) Horv a´ th I. T. Acc. Chem. Res. 1998, 31, 641-50.
2) Curran, D. P. Angew. Chem. Int. Ed. 1998, 37, 1174-1196.
3) Horv a´ th, I. T. Acc. Chem. Res. 1998, 31, 641-50.
4) de Wolf, E.; van Koten, G. Deelman, B.-J. Chem. Soc. ReV. 1999,
2
8, 37-41.
(
5) Barthel-Roas, L. P.; Gladysz, J. A. Coord. Chem. ReV. 1999, 192,
5
87-605.
(
6) Curran, D. P. Med. Chem. ReV. 1999, 19, 432-438.
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0.1021/ol991352h CCC: $19.00 © 2000 American Chemical Society
1
Published on Web 01/20/2000

1
polymer 3 was prepared by a free radical polymerization
AIBN as initiator, 48 h) in benzotrifluoride as solvent at
complete, the two layers were easily separated. H NMR and
31
(
P NMR spectroscopy were used to characterize the product.
The H NMR spectrum showed the loss of the NASI
1
100 °C (Scheme 1). The product fluoroacrylate copolymer
methylene peak at δ 2.9 and the presence of aromatic peaks
31
between δ 7.2 and 7.8, from the diphenylphosphine. The P
NMR spectrum showed a peak at δ -16, for the product
polymer, and a small peak at δ 35, for phosphine oxide. The
amount of oxidized phosphine ligand varied but typically
was <10%. The complete conversion of the NASI group to
amide was also confirmed by comparing the integral for the
aromatic protons of the phosphine ligand to the integral for
Scheme 1
the fluoroacrylate -OCH - group at δ 4.5, which showed the
2
expected 10 mol % loading of phosphine.
The rhodium catalyst 5 was prepared by the reaction of
the phosphine-containing polymer 4 with µ-dichlorotetra-
1
2
ethylene dirhodium ([RhCl(CH
2 2 2 2
CH ) ] ). The resulting
was isolated by precipitation using methanol and was
fluorous-phase soluble polymer-bound rhodium catalysts
1
31
characterized using IR and H NMR spectroscopy and
formed in these reactions were found by P NMR spectros-
copy to have a single broad signal centered at δ 32.8. This
broad signal is presumably a result of phosphine-rhodium
exchange and sequence and stereochemical heterogeneities
in the polymer structure and is typical of broad signals seen
15
elemental analysis. When the fluoroacrylate monomer and
NASI were present in a 12:1 feed ratio, the product polymer
contained ca. 10 mol % of NASI. NMR analysis showed
2
broad peaks due to the -OCH - peak of the fluoroacrylate at
12,18
δ 4.5 and a peak at δ 2.9 corresponding to the two
methylenes of the NASI group in a ratio of 5:1, respectively.
In a prior report,16 we have shown that a reactive ester-
containing fluoropolymer such as 1 could be derivatized by
reaction with an amine-containing dye. We were able to
similarly attach diphenylphosphinopropylamine to 3 (Scheme
with other soluble polymer-bound catalysts.
The 3:1 ratio
of P:Rh in the product polymer was confirmed by elemental
analysis (a 3.3:1 ratio was found). Other fluoroacrylate
polymers, 6 and 7, and similar Rh(I) catalysts, 8 and 9, were
also prepared using chemistry analogous to that used to
prepare 5 (Figure 1).
17
2
). In this reaction, 3 was dissolved in FC-77 and allowed
Scheme 2
Figure 1.
to react with an equivalent amount of diphenylphosphino-
propylamine dissolved in THF. The two phases were stirred
rapidly to form a white emulsion. When the reaction was
Studies of rates and turnover numbers with these Rh(I)
catalysts show that these fluorous-phase soluble polymer-
bound hydrogenation catalysts are comparable to traditional
hydrogenation catalysts. For example, the reported rate for
hydrogenation of 1-octene in p-xylene at 100 ( 2 °C with
(
(
(
13) Gravert, D. J.; Janda, K. D. Chem. ReV. 1997, 97, 489-509.
14) Geckeler, K. E. AdV. Polym. Sci. 1995, 121, 31-79.
15) Analytical data and representative experimental procedures for
polymers 3, 4, and 5 are available as Supporting Information.
(16) Bergbreiter, D. E.; Franchina, J. G. Chem. Commun. 1997, 1531-
2
.
(
17) FC-77 is a mixture of perfluorinated octanes available from the 3M
(18) Bergbreiter, D. E.; Chandran, R. S. J. Am. Chem. Soc. 1987, 109,
174-179.
Co., cf. Zhu, D. W. Macromolecules 1996, 29, 2813-17.
394
Org. Lett., Vol. 2, No. 3, 2000

Wilkinson’s catalyst is 190 mmol of H
the reported rate for hydrogenation of cyclohexene in
benzene with Wilkinson’s catalyst is 75 mmol of H /mmol
of Rh/h at 25 °C. In comparison, rates for the hydrogenation
of 1-octene, cyclohexene, and bicyclo[2.2.1]hept-2-ene with
the fluorous polymer-bound catalyst 5 were 203, 78, and 65
2
/mmol of Rh/h while
activity. In studying catalyst reuse, hydrogenations were
carried out using a Parr apparatus at 30 psi. In a typical
recycling experiment, a mixture of 5 mL of THF, containing
2 mmol of an alkene, and 5 mL of FC-77 containing a
polymer-bound catalyst such as 5 was added to a Parr reactor
2
18
2 2
under N . Flushing the reactor with H and shaking then
mmol of H
2
/mmol of Rh/h at 25 °C on the basis of the
formed an emulsion, and hydrogenation commenced. When
the hydrogenation was complete, the upper layer was
removed and the lower layer was washed twice with fresh
THF. Then a new upper layer containing another portion of
the initial alkene (or another alkene) was added to the lower
layer, the apparatus was flushed with hydrogen, and then
the reaction was restarted.
In summary, fluoracrylates are useful supports for fluo-
rous-phase soluble polymers whose activity and turnover
numbers are comparable or superior to those of other
fluorinated catalysts. Such polymers should also be a viable
way to prepare other polymer-supported reagents and
substrates that will be fluorous-phase soluble. Such product
polymer-supported species can easily be separated from
organic solutions but retain excellent reactivity as judged
by the catalytic activity described above.
measured Rh loading of 0.013 mmol of Rh/g of polymer.
These rates are comparable or better than those reported by
us for other polymer-supported hydrogenation catalysts. In
prior work, we reported that the hydrogenation rate for
1
-octene at 100 °C with a polyethylene-bound Rh(I) catalyst
was 99 mmol of H /mmol of Rh/h, that the rate of
hydrogenation of this same alkene with a polystyrene-bound
catalyst was ca. 5 mmol of H /mmol of Rh/h, and that the
rate of hydrogenation of 1-octene with an amphoteric
polymer-supported catalyst in CH CN at 25 °C was 14 mmol
/mmol of Rh/h.1 Rates measured with other similar
2
2
3
8,19
of H
2
fluorous polymer-bound Rh(I) catalysts were comparable.
For example, 8 and 9 hydrogenated 1-octene, cyclohexene,
and bicyclo[2.2.1]hept-2-ene with rates or 44, 17, 14 and
15, 20, and 56 mmol of H
2
/mmol of Rh/h, respectively.
These soluble fluorous polymer-bound catalysts can be
Acknowledgment. Support of this work by the National
Science Foundation (CHE-9707710) and the Robert A.
Welch Foundation is gratefully acknowledged. Dr. S. J. Getty
of DuPont and Drs. N. L. Franchina and D. W. Zhu of 3M
are acknowledged for supplying us with the necessary
monomers and fluorocarbon solvents.
recycled several times. The only limitation we have found
is the necessity of a strict inert atmosphere to prevent
oxidation of the phosphine ligands. This recycling employed
simple liquid/liquid-phase separation. In a typical procedure,
turnover numbers measured for the fluorous polymer catalyst
5
through seven cycles were 21 700 mmol of alkene
hydrogenated/mmol of Rh. Similar recyclability was seen
for catalyst 8 through 10 use/reuse cycles (670 mmol of
alkene hydrogenated/mmol of Rh/cycle, respectively). The
catalysts could be recycled and reused without a loss in
Supporting Information Available: Experimental pro-
cedures for the formation of the copolymers 3, 5, and 6 along
with spectra data, molecular weight data, and elemental
analyses. This material is available free of charge via the
Internet at http:pubs.acs.org.
(19) Bergbreiter, D. E.; Liu, Y.-S. Tetrahedron Lett. 1997, 38, 7843-
7
846.
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