11102 J. Am. Chem. Soc., Vol. 121, No. 48, 1999
Buchmeiser and Wurst
on a Merrifield polymer using a permanently “renewable”
triazene-linker. Generally speaking, the most striking advantages
of heterogeneous catalytic systems is their easy removal from
the reaction mixture which, in case of sufficient stability, allows
their reuse as well as the formation of catalyst and ligand-free
products. Besides a lack of knowledge about the exact chemical
structure of a heterogeneous catalytic system, a major drawback
in the synthesis of stable heterogeneous palladium(II) systems
is often related to the rather low durability of the corresponding
complexes. Generally, the high temperatures which are required
to promote the coupling reaction lead to the fast formation of
palladium black. In general, such heterogeneous coupling
reactions are characterized by low to moderate TONs (e5000)
and low to moderate yields in the case where aryl chlorides are
used.22,24,26 Consequently, to obtain acceptable yields, compa-
rably large amounts of palladium(II) (usually 0.5-3 mol %)
are required. The problem of temperature-induced catalyst
degradadion may somehow be reduced if microwave28 or high
pressure29 are used to promote the corresponding coupling
reaction. While phosphine-based ligands possess excellent
bindung properties for palladium(II) and allow the preparation
of highly active systems,30 they are easily transformed into the
corresponding phosphine oxides. This reaction results in a slow
but permanent release of palladium (catalyst bleeding) which
significantly aggrevates their industrial use. To circumvent this
problem, more stable catalytic systems have been elaborated
for homogeneous catalysis.31-33 Phosphapalladacyles,34-40 which
may also be used in nonaqueous ionic solvents,41 and more
recently an aza-analogue were reported32 to be a highly active
Heck-type catalysts. Finally, homoleptic chelating N-hetero-
cyclic carbene complexes17,42-45 have to be mentioned. Other
cyclic, chelating N- and P-based ligands31,46 such as dipyridyl,
phenantroline, etc. are well-known in homogeneous catalysis47,48
as they form stable complexes with a large variety of metal
ions. Nevertheless, due to the nonselectivity of binding, the
catalytically active metal ion is often replaced by traces of other
matel ions present in technical grade chemicals such as iron,
copper, nickel, etc., leading to a fast deterioration of the catalyst.
In this contribution, the use of a palladium-selective ligand, its
heterogenization by ring-opening metathesis polymerization
(ROMP), and the synthesis of the catalysts as well as some
applications are presented.49
Results and Discussion
Preparation of the Heterogeneous Catalyst. Standard
procedures for the preparation of polymer-supported ligands
usually entail the surface modification of commercially available
polymer supports, e.g. polystyrene-divinylbenzene (PS-DVB)
or chloromethylated PS-DVB (Merrifield polymer). Neverthe-
less, this synthetic route is characterized by some disadvantages.
To achieve a maximum derivatization capacity (usually ex-
pressed in mmol of functional group/g of resin) porous materials
with high surface areas have to be chosen. As a major part of
the specific surface area (σ) results from internal pores, large
amounts of the desired ligand are located at the interior of the
particle. This leads to a diffusion-controlled reaction during
catalysis which usually significantly reduces the overall reaction
rate constant.15 Another critical point lies in the usually
employed divergent synthetic approach for surface derivatiza-
tions. The synthetic protocol often consists of at least two to
three steps. Due to the heterogeneous character of such
transformations, each step may not be accomplished in a
quantitative way. In contrast to homogeneous reactions, the
resulting “byproducts” are not removed. This leads to a situation,
where a significant amount of the initial functionality is not
transformed into the desired ligand. Poor definitions in terms
of chemical structure and problems of catalyst poisoning are
often the consequence.
(25) Djakovitch, L.; Heise, H.; Ko¨hler, K. J. Organomet. Chem. 1999,
584, 16-26.
(26) Mehnert, C. P.; Ying, J. Y. Chem. Commun. 1997, 2215-2216.
(27) Bra¨se, S.; Enders, D.; Ko¨bberling, J.; Avemaria, F. Angew. Chem.
1998, 110, 3614-3616.
Ring-opening metathesis polymerization (ROMP) has been
demonstrated to present a powerful tool in the preparation of
functionalized polymer supports.49-64 Even complex function-
alities may be introduced with high reproducibility and without
(28) Larhed, M.; Hallberg, A. J. Org. Chem. 1996, 61, 9582-9584.
(29) Voigt, K.; Schick, U.; Meyer, F. E.; de Meijere, A. Synlett 1994,
189-190.
(30) van Strijdonck, G. P. F.; Boele, M. D. K.; Kamer, P. C. J.; de Vries,
J. G.; van Leeuwen, P. W. N. M. Eur. J. Inorg. Chem. 1999, 1073-1096.
(31) Shaw, B. L.; Perera, S. D. Chem. Commun. 1998, 1863-1864.
(32) Ohff, M.; Ohff, A.; Milstein, D. Chem. Commun. 1999, 357-358.
(33) Crisp, G. T.; Gebauer, M. G. Tetrahedron 1996, 52, 12465-12474.
(34) Herrmann, W. A.; Reisinger, C. P.; O¨ fele, K.; Broâmer, C.; Beller,
M.; Fischer, H. J. Mol. Catal. A Chem. 1996, 108, 51-56.
(35) Beller, M.; Fischer, H.; Herrmann, W. A.; O¨ fele, K.; Broâmer, C.
Angew. Chem. 1995, 107, 1992-1993.
(47) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994, 33,
497-526.
(48) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satho, T.; Fujii,
H. Science 1998, 280, 560-564.
(49) Buchmeiser, M. R. Austrian Patent Application A 344/99 020399.
(50) Ambrose, D.; Fritz, J. S.; Buchmeiser, M. R.; Atzl, N.; Bonn, G.
K. J. Chromatogr. A 1997, 786, 259-268.
(51) Buchmeiser, M. R.; Atzl, N.; Bonn, G. K. International Patent
Application AT404 099 (181296), PCT /AT97/00278.
(52) Buchmeiser, M. R.; Sinner, F.; Tessadri, R.; Bonn, G. K. Austrian
Patent Application AT 405 056 (010497).
(36) Beller, M.; Riermeier, T. H. Tetrahedron Lett. 1996, 37, 6535-
6538.
(37) Herrmann, W. A.; Broâmer, C.; O¨ fele, K.; Reisinger, C.-P.;
Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem. 1995, 107, 1989-
1992.
(53) Buchmeiser, M. R.; Tessadri, R. Austrian Patent Application A 1132/
97 (020797).
(54) Buchmeiser, M. R.; Atzl, N.; Bonn, G. K. J. Am. Chem. Soc. 1997,
119, 9166-9174.
(38) Herrmann, W. A.; Broâmer, C.; Reisinger, C.-P.; Riermeier, T. H.;
O¨ fele, K.; Beller, M. Chem. Eur. J. 1997, 3, 1357-1364.
(39) Islam, S. M.; Palti, B. K.; Mukherjee, D. K. J. Mol. Catal. A 1997,
124, 5-20.
(55) Eder, K.; Buchmeiser, M. R.; Bonn, G. K. J. Chromatogr. A 1998,
810, 43-52.
(56) Seeber, G.; Buchmeiser, M. R.; Bonn, G. K.; Bertsch, T. J.
Chromatogr. A 1998, 809, 121-129.
(40) Herrmann, W. A.; Bo¨hm, V. P. W.; Reisinger, C.-P. J. Organomet.
Chem. 1999, 576, 23-41.
(57) Buchmeiser, M. R.; Tessadri, R.; Seeber, G.; Bonn, G. K. Anal.
Chem. 1998, 70, 2130-2136.
(41) Herrmann, W. A.; Bo¨hm, V. P. W. J. Organomet. Chem. 1999,
572, 141-145.
(58) Buchmeiser, M. R.; Bonn, G. K. Am. Lab. 1998, 11, 16-19.
(59) Huber, C. G.; Buchmeiser, M. R. Anal. Chem. 1998, 70, 5288-
5295.
(42) Herrmann, W. A.; Elison, M.; Fischer, J.; Ko¨cher, C.; Artus, G. R.
J. Chem. Eur. J. 1996, 2, 772-780.
(43) Herrmann, W. A.; Schwarz, J.; Gardiner, M. G.; Spiegler, M. J.
Organomet. Chem. 1999, 575, 80-86.
(60) Sinner, F.; Buchmeiser, M. R.; Tessadri, R.; Mupa, M.; Wurst, K.;
Bonn, G. K. J. Am. Chem. Soc. 1998, 120, 2790-2797.
(61) Buchmeiser, M. R.; Sinner, F. M. Austrian Patent Application A
604/99 070499.
(62) Buchmeiser, M. R.; Sinner, F.; Mupa, M.; Wurst, K. Macromol-
ecules. In press.
(44) Herrmann, W. A.; Elison, M.; Fischer, J.; Ko¨cher, C.; Artus, G. R.
J. Angew. Chem. 1995, 107, 2602-2605.
(45) Herrmann, W. A.; Reisinger, C.-P.; Spiegler, M. J. Organomet.
Chem. 1998, 557, 93-96.
(46) Rau, T.; Shoukry, M.; van Eldik, R. Inorg. Chem. 1997, 36, 1454-
1463.
(63) Seeber, G.; Brunner, P.; Buchmeiser, M. R.; Bonn, G. K. J.
Chromatogr. A 1999, 848, 193-202.