P. G. Steel, C. W. T. Teasdale / Tetrahedron Letters 45 (2004) 8977–8980
Table 1. Suzuki and Heck reactions carried out using polymer supported catalyst 7
8979
Ph
CO2tBu
7 (1 mol% Pd)
MeO
7 (1 mol% Pd)
K2CO3, DMA,165ºC
B(OH)2
Ph
Ph-X
CO2tBu
Et3N, DMA, 165ºC
Ph-X
OMe
Entry
X
Recyclesa
Yieldb
Entry
X
Recyclesa
Yieldb
1
2
3
4
5
Br
Br
I
1c
4c
57
55
95
95
95
6
7
8
I
I
I
1c
8c
>14d
87
82
83
1c
I
5c
>14d
I
a Recycles before >5% drop in isolated yield.
b Yield of purified product after chromatography.
c Reactions carried out in air.
d Reactions carried out under Ar.
Peris, E.;Mata, J.;Faller, J. W.;Crabtree, R. H.
Organometallics 2002, 21, 700–706.
O
O
4. Recently and concurrent with this work Peris et al. have
demonstrated the immobilisation of 1 on various clays and
the application of this combination as a supported catalyst
for Heck and Sonagashira reactions. (a) Mas-Marza, E.;
Segarra, A. M.;Claver, C.;Peris, E.;Fernandez, E.
Tetrahedron Lett. 2003, 44, 6595–6599;(b) Poyatos, M.;
Marquez, F.;Peris, E.;Claver, C.;Fernandez, E. NewJ.
Chem. 2003, 27, 425–431.
5. (a) Dijkstra, H. P.;Slagt, M. Q.;McDonald, A.;Kruithof,
C. A.;Kreiter, R.;Mills, A. M.;Lutz, M.;Spek, A. L.;
Klopper, W.;van Klink, G. P. M.;van Koten, G. Eur. J.
Inorg. Chem. 2003, 22, 830–838;(b) van de Kuil, L. A.;
Grove, D. M.;Gossage, R. A.;Zwikker, J. W.;Jennes-
kens, L. W.;Drenth, W.;van Koten, G. Organometallics
1997, 16, 4985–4994.
I
8
In conclusion, these pincer CNC systems provide very
effective ligands for supported catalysis showing
enhanced stability and functioning at low loading levels
of catalyst.10 Limitations do exist in the lower activity of
aryl bromides and the (related) need for high activation
temperatures. We suspect that these are due to the very
high ligand binding in the precatalyst system and the
difference in rate determining step between aryl iodides
and bromides. More active equi-stable supported cata-
lyst systems that address these issues are being deve-
loped in our laboratory and results will be reported in
due course.
6. Complete coupling of phenyl iodide with 4-meth-
oxyphenylboronic required 36h at 165ꢁC. In contrast
the unfunctionalised complex promoted this transform-
ation in <24h at the same temperature. Conversions after
1h 1 66%, 4ax 58%;4h 1 81%, 4ax 70%;24h 1 100%, 4ax
94%;36h 4ax 100%.
7. Krchnak, V.;Vagner, J.;Lebl, M. Int. J. Pept. Prot. Res.
1988, 32, 415–416.
Acknowledgements
8. The reactions for Suzuki coupling studies were typically
conducted as follows: catalyst 7 (50mg, ꢁ1mol%), K2CO3
(270mg, 1.95mmol), boronic acid (1.50mmol), aryl halide
(1.31mmol), diethylene glycol dibutyl ether (323lL,
1.31mmol, GC standard), dry DMA (10mL) and a
magnetic stirrer were added to a RadleyÕs Carouselꢂ
parallel synthesis reaction tube. The reaction mixture was
degassed by bubbling argon through the reaction tube
contents for 30min prior to use. The tube was then sealed
with a Teflon screw cap and heated to 165ꢁC for 48h.
After cooling to room temperature the reaction contents
were filtered and the supported resin washed with DCM
(3 · 10mL). For GC analysis the filtrate was made up to
50mL in a standard volumetric flask with DCM and a
small aliquot taken for GC analysis of the reaction. For an
isolated yield the organic filtrate was extracted with water
(3 · 20mL) and dried with MgSO4. The mixture was
filtered and the solvent removed in vacuo and the product
purified by flash column chromatography. The catalyst
was washed further with THF/water (1:1, 3 · 10mL) and
diethyl ether (3 · 10mL) and dried in vacuo for further
use. All products were characterised by comparison with
We thank the EPSRC for financial support of this work
(C.W.T.T.);Dr. A. M. Kenwright for assistance with
NMR experiments, Dr. M. Jones for mass spectra and
Dr. C. Ottley for the ICP-MS analysis.
References and notes
1. (a) Cornils, B.;Herrmann, W. A. J. Catal. 2003, 216, 23–
31;(b) McNamara, C. A.;Dixon, M. J.;Bradley, M.
Chem. Rev. 2002, 102, 3275–3299;(c) de Miguel, Y. R.;
Brule, E.;Margue, R. G. J. Chem. Soc., Perkin Trans. 1
2001, 3085–3094;(d) Clapham, B.;Reger, T. S.;Janda, K.
D. Tetrahedron 2001, 57, 4637–4662.
2. (a) Herrmann, W. A.;Ofele, K.;Von Preysing, D.;
Schneider, S. K. J. Organomet. Chem. 2003, 687, 229–
248;(b) Herrmann, W. A. Angew. Chem., Int. Ed. 2002,
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3. (a) Peris, E.;Loch, J. A.;Mata, J.;Crabtree, R. H. Chem.
Commun. 2001, 22, 201–202;(b) Loch, J. A.;Albrecht, M.;