Synthesis of the desired monomer commences with
formation of acid chloride 68 followed by condensation with
11-bromo-1-undecanol to provide bromoester 7 in 95% yield.
Hydroxy functionalized pincer ligand 8, synthesized as
previously reported,5a was coupled to the C11 spacer to form
the nonmetalated SCS ligand 9 in 80% yield (Scheme 2).
Scheme 1. Tandem Catalysis and Self-Assembly
Scheme 2. Ligand Synthesis
Palladation of 9 was carried out by ligand exchange of
[Pd(CH3CN)4](BF4)29 to form the cyclopalladated monomer
10 in quantitative yield. Further ligand exchange of the
resultant cationic Pd-BF4 complex to form the neutral Pd-
Cl complex required stirring with brine to provide 10 in 80%
isolated yield.10 Monomer 10 was polymerized using 11 at
45 °C in chloroform to yield polymer 1 (Scheme 3).11
pincer complexes at every repeat unit, resulting in the highest
catalyst loading of all pincer-ligand based polymeric Heck
catalysts. Norbornene was chosen as the polymerizable unit
to provide a well-controlled route to polymers via ring-
opening metathesis polymerization.6 A flexible C11 alkyl
chain was introduced between the backbone and the terminal
palladated SCS pincer ligand to decouple the side-chain from
the polymer backbone and to increase solubility.7
Scheme 3. Metalation and Polymerization
(4) (a) Bergbreiter, D. E.; Osburn, P. L.; Yun-Shan, L. J. Am. Chem.
Soc. 1999, 121, 9531-9538. (b) Bergbreiter, D. E.; Osburn, P. L.; Frels, J.
D. J. Am. Chem. Soc. 2001, 123, 11105-11106. (c) Ohff, M.; Ohff, A.;
van der Boom, M. E.; Milstein, D. J. Am. Chem. Soc. 1997, 119, 11687-
11688. (d) Morales-Morales, D.; Lee, D. W.; Wang, Z.; Jensen, C. M.
Organometallics 2001, 20, 1144-1147. (e) Morales-Morales, D.; Grause,
C.; Kasaoka, K.; Redon, R.; Cramer, R. E.; Jensen, C. M. Inorg. Chim.
Acta 2000, 958-963. (f) Morales-Morales, D.; Redon, R.; Yung, C.; Jensen,
C. Chem. Commun. 2000, 1619-1620. (g) Miyazaki, F.; Yamaguchi, K.;
Shibasaki, M. Tetrahedron Lett. 1999, 40, 7379-7383. (h) Peris, E.; Loch,
J. A.; Mata, J.; Crabtree, R. H. Chem. Commun. 2001, 201-202. (i) Tulloch,
A. A. D.; Danopoulos, A. A.; Tizzard, G. J.; Coles, S. J.; Hursthouse, M.
B.; Hay-Motherwell, R. S.; Motherwell, W. B. Chem. Commun. 2001,
1270-1271.
(5) (a) Huck, W. T. S.; van Veggel, F. C. J. M.; Kropman, B. L.; Blank,
D. H. A.; Keim, E. G.; Smithers, M. M. A.; Reinhoudt, D. N. J. Am. Chem.
Soc. 1995, 117, 8293-8294. (b) van Manen, H.-J.; Nakashima, K.; Shinkai,
S.; Kooijman, H.; Spek, A. L.; van Veggel, F. C. J. M.; Reinhoudt, D. N.
Eur. J. Inorg. Chem. 2000, 2533-2540. (c) Huck, W. T. S.; van Veggel,
F. C. J. M.; Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1996, 35, 1213-
1215. (d) Huck, W. T. S.; Hulst, R.; Timmerman, P.; van Veggel, F. C. J.
M.; Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1997, 36, 1006-1008.
(e) Albrecht, M.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten, G.
Chem. Eur. J. 2000, 6, 1431-1445. (f) Loeb, S. J.; Shimizu, G. K. H. J.
Chem. Soc., Chem Commun. 1993, 1395-1397. (g) Beletskaya, I. P.;
Chuchurjukin, A. V.; Dijkstra, H. P.; Van Klink, G. P. M.; Van Koten, G.
Tetrahedron Lett. 2000, 41, 1075-1079.
To provide insights into the catalytic activity of 1, Heck
coupling experiments between 2 and various alkene acceptors
(7) (a) Portugall, M.; Ringsdorf, H.; Wendorff, J. H. Makromol. Chem.
1978, 179, 273-276. (b) Finkelmann, H.; Happ, M.; Potrugall, M.;
Ringsdorf, H. Makromol. Chem. 1978, 179, 2541-2544.
(8) Jacobine, A. F.; Glaser, D. M.; Nakos, S. T. Polym. Mater. Sci. Eng.
1989, 60, 211-216.
(9) This complex was synthesized as previously reported; see: Lai, T.-
W.; Sen, A. J. Am. Chem. Soc. 1981, 103, 4627-4629.
(10) All compounds have been characterized by 1H NMR and 13C NMR
spectroscopy, mass spectrometry, and elemental analysis.
(6) (a) Fu¨rstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012-3043. (b)
Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29.
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Org. Lett., Vol. 4, No. 5, 2002