Molecularly defined palladium(0) monophosphine complexes as catalysts for efficient cross-coupling of aryl chlorides and phenylboronic acid

Article abstract of DOI:10.1039/b006791l

Various 1,6-diene palladium(0) monophosphine complexes have been prepared from tmedaPd(CH₃)₂, PR₃, and the corresponding 1,6-diene. These molecularly defined Pd complexes catalyzed the Suzuki coupling of aryl chlorides wit

Full text of DOI:10.1039/b006791l

Molecularly defined palladium(0) monophosphine complexes as catalysts for
1
efficient cross-coupling of aryl chlorides and phenylboronic acid
Mario G o´ mez Andreu, Alexander Zapf and Matthias Beller*
Institut f u¨ r Organische Katalyseforschung an der Universit a¨ t Rostock e.V., Buchbinderstr. 5-6, 18055 Rostock,
Germany
Received (in Liverpool, UK) 16th August 2000, Accepted 30th August 2000
First published as an Advance Article on the web
Various 1,6-diene palladium(0) monophosphine complexes
have been prepared from tmedaPd(CH , PR , and the
(Ph
3, (Cy
were obtained by suspending (tmeda)Pd(CH
230 °C in the corresponding 1,6-diene. After gently warming
the mixtures, elimination of ethane occurred and the desired
products were isolated by filtration, washed with cold pentane
and dried under vacuum.
3
P)Pd(C
6
H
10O) 1, (Cy
3
P)Pd(dvds) 2, (Cy
3
P)Pd(C
)Pd(C
6
H
10NH)
3
)
2
3
3
P)Pd(C
6
H10O) 4, and (o-biphenyl)PCy
2
6
H10O) 5
17
corresponding 1,6-diene. These molecularly defined Pd
complexes catalyzed the Suzuki coupling of aryl chlorides
3
)
2
3
and PR at
with phenylboronic acid more efficiently than traditional
II
Pd –PR
3
pre-catalysts.
The cross-coupling reaction of aryl halides and arylboronic
acids (Suzuki reaction) is the most versatile and important
method for the synthesis of substituted biaryls. This class of
A preliminary screening of optimal reaction conditions for
the Suzuki coupling of an activated aryl chloride (2-chloro-
benzonitrile) with phenylboronic acid in the presence of
different palladium catalysts revealed that the coupling pro-
ceeds smoothly using THF as the solvent in the presence of a
mixture of potassium triphosphate and potassium fluoride as
base. In order to compare appropriately the efficiency of the
different defined catalysts with each other and with in situ
catalysts, we performed catalyst tests at low palladium
concentration (0.05 mol% Pd). It is important to note that there
are relatively few examples of Suzuki cross-couplings of aryl
2
compounds constitute important building blocks for the synthe-
sis of biologically active substances, e.g. pharmaceuticals such
as the sartan family of drugs for high blood pressure and
3
herbicides. Additionally, biaryls have found application as
4
chiral ligands for catalysis and in materials science, e.g. liquid
5
crystals. Suzuki cross-coupling reactions of aryl bromides and
iodides have been extensively studied in organic synthesis.
Apart from further expanding the scope of this reaction, current
interest focuses on the use of economically more attractive aryl
chlorides as substrates for this reaction. Notable advances in the
8
c,18
chlorides known that proceed at such low catalyst loading.
As shown in Table 1 the cross-coupling reactions of a variety of
aryl chlorides with phenylboronic acid proceed in the presence
of 1,6-diene stabilized monophosphine in varying yields
depending on the catalyst.
6
cross-coupling reactions of aryl chlorides with arylboronic
7
acids have been described recently by the groups of G. Fu, S.
8
9
10
11
Buchwald, S. A. Guram, S. Nolan, and W. A. Herrmann as
well as by our group.12 In general, important improvements in
this area have been made possible by the use of in situ ‘Pd’–L
3 6
Complex 1 (PPh Pd(C H10O)) was shown to be inactive
towards all the substrates, although at higher concentrations (0.5
mol% Pd) with the activated 2-chlorobenzonitrile a limited
cross-coupling reaction could be observed (32%). 1,6-Diene
palladium(0) complexes with the more basic ligand tricyclohex-
ylphosphine 2–4 show good conversion with 2-chlorobenzoni-
trile, chlorobenzene and 4-chlorotoluene (67–96%). Best results
were achieved with the 1,6-diene complex containing ‘Buch-
II
catalysts consisting of a Pd source and sterically hindered
basic ligands such as dialkylarylphosphines, tri-tert-butylphos-
phine, adamantylphosphines or N-heterocyclic carbenes. It is
generally agreed that these in situ catalysts are reduced under
reaction conditions13 to afford coordinatively unsaturated
3 2
complexes such as 16e PdL , 14e PdL , and 12e PdL, which
may constitute the ‘real’ catalysts. The importance of coor-
2 6
wald’s ligand’ [5 (o-biphenyl)PCy Pd(C H10O)]. With only
0
dinatively unsaturated Pd species as ‘true catalysts’ in various
0.05 mol% of this catalyst good to excellent yields of biaryls
were obtained from activated (2-chlorobenzonitrile: 97%), non-
activated (4-chlorotoluene: 82%; chlorobenzene: 87%) and
deactivated (4-chloroanisole: 72%) aryl chlorides. The general
trend of catalyst activity is in good agreement with previously
reported investigations on the corresponding in situ systems.
However, there are some notable features of the new catalysts:
1. 1,6-Diene palladium(0) monophosphine complexes are
cross-coupling reactions has been demonstrated.14
In order to avoid side-reactions which may parallel the pre-
formation of the ‘real’ catalyst and which often lead to loss of
catalyst activity, it is desirable to use defined Pd mono-
phosphine complexes as catalysts. To the best of our knowledge
0
there is no report about the use of defined Pd mono- or
11
diphosphine complexes and only one report applying a
0
defined Pd dicarbene species as catalyst in the Suzuki cross-
significantly more reactive than mixtures of Pd(OAc)
2
or
coupling reaction. Recently, we introduced triphenylphosphine
palladium(0) diallyl ether as a stable and active catalyst for
Pd (dba) and phosphines (Table 2). Hence, the obtained
2
3
15
telomerization of butadiene and methanol. In this paper we
0
3
describe the use of 1,6-diene stabilized Pd –PR complexes as
efficient catalysts for the Suzuki cross-coupling of aryl
chlorides.
Based on the work of P o¨ rschke16 et al., who developed a
0
highly effective route for the synthesis of 1,6-diene Pd
0
complexes, we synthesized various monophosphine Pd species
as shown in Scheme 1. As phosphine ligands triphenylphos-
phine, tricyclohexylphosphine, and the so-called ‘Buchwald-
ligand’ o-biphenyldicyclohexylphosphine were employed. In
order to investigate the influence of the 1,6-diene part on the
0
formation of the L–Pd fragment we decided also to prepare the
monotricyclohexylphosphine palladium complex with diallyl
ether, diallyl amine and tetramethyldivinyl disiloxane.
Scheme 1 1,6-Diene complexes of palladium(0).
DOI: 10.1039/b006791l
Chem. Commun., 2000, 2475–2476
2475
This journal is © The Royal Society of Chemistry 2000

Table 1 Reactions of aryl chlorides with phenylboronic acid in the presence
of various Pd complexes
ligand as shown by an increase of product yields in the series:
0
a
(
o-biphenyl)PCy
2 6 3 6
Pd(C H10O) 5 > (Cy P)Pd(C H10O) 4 9
(
Ph P)Pd(C 10O) 1. 3. The effectiveness of the studied
3
6
H
complexes 2–4 is directly related to their ability to liberate the
0
diene part and to generate the corresponding 12e [L–Pd ]
species. Previously, it has been shown that an increasing
acceptor strength of the 1,6-diene moiety results in an
increasing stability of the 1,6-diene complex.16 In agreement
with these studies we observe an decrease in reactivity in the
order 4 > 3 > 2.
In summary, we have shown that 1,6-diene palladium(0)
monophosphine complexes are extremely efficient catalysts for
Suzuki cross-coupling reactions of various aryl chlorides. By
variations of both the diene and the phosphine part of the
complex the catalytic properties of the complexes can be tuned.
It is clearly shown that these defined monophosphine catalysts
are superior to generally applied mixtures of Pd-pre-catalysts
and phosphines. Thus, this class of catalysts offers promising
features for a number of other important palladium-catalyzed
coupling reactions.
2
This work is funded by DMC . We thank Dr O. Briel and Dr
2
Karch (DMC ) for helpful discussions and Dr M. Hateley
(IfOK) for help with this manuscript.
Notes and references
1
Part 19 in the series ‘Palladium-catalyzed Synthesis of Fine chemicals’;
for part 18 see A. Ehrentraut, A. Zapf and M. Beller, Synlett, in press.
N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457; H. Geissler, in
Transition Metals for Organic Synthesis, Vol. 1, ed. M. Beller and C.
Bolm, Wiley-VCH, Weinheim, 1998; A. Suzuki, in Metal-catalyzed
Cross-coupling Reactions, eds. F. Diederich and P. J. Stang, Wiley-
VCH, Weinheim, 1997; A. Suzuki, J. Organomet. Chem., 1999, 576,
2
1
47.
3
4
H. H. Szmant, Organic building blocks of the chemical industry, John
Wiley & Sons, New York, 1989.
A. S. Parsons, J. M. Garcia and V. Snieckus, Tetrahedron Lett., 1994,
3
1
5, 7537; D. W. Old, J. P. Wolfe and S. L. Buchwald, J. Am. Chem. Soc.,
998, 120, 9722.
5
6
E. Poetsch, Kontakte, 1988, 15.
H. Gr o¨ ger, J. Prak. Chem., 2000, 342(4), 334; R. St u¨ rmer, Angew.
Chem., 1999, 111, 3509; Angew. Chem., Int. Ed., 1999, 38, 3307; T. H.
Riermeier, A. Zapf and M. Beller, Top. Catal., 1997, 4, 301; V. V.
Grushin and H. Alper, Chem. Rev., 1994, 94, 1047.
Scheme 2 Suzuki cross-coupling reactions of aryl chlorides with phenyl-
boronic acid.
Table 2 Reactions of aryl chlorides with phenylboronic acid in the presence
7 A. F. Littke and G. C. Fu, Angew. Chem., 1998, 110, 3586; Angew.
Chem., Int. Ed., 1998, 38, 3387; A. F. Littke, C. Dai and G. C. Fu, J. Am.
Chem. Soc., 2000, 122, 4020.
0
a
of various Pd catalysts
8
(a) J. P. Wolfe and S. L. Buchwald, Angew. Chem., 1999, 111, 2570;
Angew. Chem., Int. Ed., 1999, 39, 2413; (b) R. A. Singer and S. L.
Buchwald, Tetrahedron Lett., 1999, 40, 1095; (c) J. P. Wolfe, R. A.
Singer, B. H. Yang and S. L. Buchwald, J. Am. Chem. Soc., 1999, 121,
9
550.
9
X. Bei, T. Crevier, A. S. Guram, B.Jandeleit, T. S. Powers, H. W.
Turner, T. Uno and W. H. Weinberg, Tetrahedron Lett., 1999, 40,
3
855.
0 C. Zhang, J. Huang, M. L. Trudell and S. P. Nolan, J. Org. Chem., 1999,
4, 3804.
1 V. P. W. B o¨ hm, C. W. K. Gst o¨ ttmayr, T. Weskamp and W. A.
Herrmann, J. Organomet. Chem., 2000, 595, 186.
1
1
1
6
2 M. Beller, H. Fischer, W. A. Herrmann and C. Broßmer, Angew. Chem.,
1
1
995, 107, 1992; A. Zapf and M. Beller, Chem. Eur. J., 2000, 6,
830.
1
3 C. Amatore and A. Jutand, Acc. Chem. Res., 2000, 33, 314.
1
4 F. Paul, J. Patt and J. F. Hartwig, J. Am. Chem. Soc., 1994, 116, 5969;
J. F. Hartwig and F. Paul, J. Am. Chem. Soc., 1995, 117, 5373; P. W.
Jolly, Angew. Chem., 1985, 97, 279; Angew. Chem., Int. Ed. Engl., 1985,
2
4, 283.
1
1
5 F. Vollm u¨ ller, J. Krause, S. Klein, W. M a¨ gerlein and M. Beller, Eur. J.
Inorg. Chem., 2000, in press.
6 J. Krause, K.-J. Haack, G. Cestaric, R. Goddard and K.-R. P o¨ rschke,
Chem. Commun., 1998, 129; J. Krause, G. Cestaric, K.-J. Haack, K.
Seevogel, W. Strom and K.-R. P o¨ rschke, J. Am. Chem. Soc., 1999, 121,
9
807.
catalyst turnover numbers are amongst the highest yet reported
for the Suzuki reaction of non-activated aryl chlorides. 2. The
catalyst properties are mainly determined by the phosphine
1
7 H. Nakazawa, F. Ozawa and A. Yamamoto, Organometallics, 1983, 2,
241.
18 A. Zapf, A. Ehrentraut and M. Beller, Angew. Chem., in press.
2476
Chem. Commun., 2000, 2475–2476