Palladium-catalyzed arylation of cyclopentadienes

Article abstract of DOI:10.1002/1521-3765(20000915)6:18<3426::AID-CHEM3426>3.0.CO;2-B

Cyclopentadiene and metallocenes, typically zirconocene dichloride, are suitable substrates for multiple arylations with aryl bromides in palladium-catalyzed reactions. Thus, various aryl bromides bearing either an electron-donating or an electron-withdrawing substituent can react with these substrates to afford the corresponding 1,2,3,4,5-pentaaryl-1,3-cyclopentadienes in a single preparative step. Derivatives of cyclopentadiene, including di- and trisubstituted cyclopentadienes, and indene are arylated in a similar fashion.

Full text of DOI:10.1002/1521-3765(20000915)6:18<3426::AID-CHEM3426>3.0.CO;2-B

FULL PAPER
Palladium-Catalyzed Arylation of Cyclopentadienes
Gerald Dyker,*[a] Jörg Heiermann,[a] Masahiro Miura,*[b] Jun-Ichi Inoh,[b]
Sommai Pivsa-Art,[b] Tetsuya Satoh,[b] and Masakatsu Nomura[b]
Abstract: Cyclopentadiene and metallocenes, typically zirconocene dichloride, are
suitable substrates for multiple arylations with aryl bromides in palladium-catalyzed
reactions. Thus, various aryl bromides bearing either an electron-donating or an
electron-withdrawing substituent can react with these substrates to afford the
corresponding 1,2,3,4,5-pentaaryl-1,3-cyclopentadienes in a single preparative step.
Derivatives of cyclopentadiene, including di- and trisubstituted cyclopentadienes, and
indene are arylated in a similar fashion.
Keywords: domino reactions ´ ex-
tended p-systems ´ palladium catal-
ysis ´ rotamers
Furthermore, cyclopentadiene and its derivatives, including
di- and trisubstituted cyclopentadienes, and indene have been
found to be capable of undergoing similar multiple arylations
under the appropriate conditions. The details of these novel
reactions are summarized herein.
Introduction
Suitable building blocks are fundamentally important for the
construction of nano-sized electronic and optoelectronic
devices.[1, 2] Functionalized porphyrins, for instance, are
among the most frequently incorporated elements of such
devices, since they are easily accessible in one- or two-step
procedures and, even more important, they offer interesting
features that can be triggered by the central metal ion of the
complex.[3] In this respect, we became interested in the
synthesis of arylated cyclopentadienes, especially the penta-
arylcyclopentadienes (6); they, too, are extended p-systems
with remarkable optoelectronic properties, for instance,
electroluminescence,[4] they can form complexes with tran-
sition metals,[5] and it has been shown that their complexes can
be used for reversible switching.[6]
A multitude of potential applications arises from these
fascinating properties. However, reported methods for the
preparation of pentaarylcyclopentadienes (6) are limited to
multistep procedures,[7] which are somewhat tedious and, in
general, less suitable for sterically demanding aryl groups.
Recently, we discovered an unprecedented palladium-cata-
lyzed domino reaction[8] that starts with metallocenes and
excess arylbromides (2, X ˆ Br) to ultimately form penta-
arylcyclopentadienes (6) in a single preparative step.[9, 10]
Results and Discussion
When the reaction of a number of metallocenes (Cp2M; M ˆ
Fe, Co, Ni, TiCl2, and ZrCl2) (0.5mmol) with bromobenzene
(2a) was examined in the presence of palladium acetate
(0.125mmol), triphenylphosphine (0.5mmol) and cesium
carbonate (6 mmol) at 1308C for 6 h, 1,2,3,4,5-pentaphenyl-
1,3-cyclopentadiene (6a) was produced, the yield being
dependent on the central metal; the best result, 70% yield
of 6a, was achieved when zirconocene dichloride (1) was used
(Scheme 1 and Table 1, entry 1). Titanocene dichloride and
Cl
Zr
Cl
Ar
X
1
3
2
Pd cat.
Pd cat.
[a] G. Dyker, J. Heiermann
Fb 6, Organic/Organometallic Chemistry
Gerhard-Mercator-Universität Duisburg, Lotharstrasse 1
47048 Duisburg (Germany)
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
+
Fax : (‡49)203-3794192
+
Ar
Ar
Ar
E-mail: dyker@uni-duisburg.de
Ar
[b] M. Miura, J.-I. Inoh, S. Pivsa-Art, T. Satoh, M. Nomura
Department of Applied Chemistry, Faculty of Engineering
Osaka University, Suita, Osaka 565-0871 (Japan)
Fax : (‡81)6-6879-7362
4
5
6
Scheme 1. Multiple palladium-catalyzed arylation of cyclopentadiene
E-mail: miura@ap.chem.eng.osaka-u.ac.jp
units; Arˆ aryl, X ˆ Br, Cl.
3426
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3426 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 18

3426±3433
Table 1. Arylation of zirconocene dichloride (1).
Entry
Compound 2
[Pd(OAc)2]
[mmol] [mmol]
PR3
Cs2CO3 solvent
[mmol] [mmol]
t
T
[8C]
Yield of products [%][a]
R, X
R
[h]
4
5
6
1
2
3
4
phenyl, Br (2a)
phenyl, Br (2a)
phenyl, Br (2a)
4-methylphenyl, Br (2b)
6
3
6
6
6
6
6
6
6
6
6
6
6
6
6
6
7
6
6
6
0.125phenyl
0.0125phenyl
0.125
0.125
0.0125
0.1253-methylphenyl
0.125
0.125
0.125phenyl
06.5
0.1
DMF
6
0.56
0.56
0.056
DMF
0.56
0.56
DMF
DMF
0.56
0.56
0.56
0.56
0.56
0.56
0.1
6
130
20
±
±
70
9
±
DMF
130 21
±
77
78
tBu
tBu
tBu
DMF
DMF
DMF
3
1
20
130
130
130
±
±
±
54-methylphenyl, Br (
6
7
8
9
10
11
12
13
14
154-
16
17
18
19
20
2b)
±
±
60
3-methylphenyl, Br (2c)
3-methylphenyl, Br (2c)
2,5-dimethylphenyl, Br (2d)
2,5-dimethylphenyl, Br (2d)
3,4-dimethylphenyl, Br (2e)
3,4-dimethylphenyl, Br (2e)
3,5-dimethylphenyl, Br (2 f)
4-tBuphenyl, Br (2g)
4-methoxyphenyl, Br (2h)
n-butoxyphenyl, Br (2i)
4-n-octyloxyphenyl, Br (2j)
4-carboethoxyphenyl, Br (2k)
4-fluorophenyl, Br, (2l)
4-fluorophenyl, Br, (2l)
1-naphthyl, Br (2n)
06.5
06.5
6
130
±
±
±
±
±
±8
±
70
±
±
70
5
±
±
±
tBu
tBu
DMF
DMF
24
14
DMF
DMF
DMF
DMF
DMF
DMF
1
22
130
130
80
31
[b]
130
130
±
±
0.1253,4-dimethylphenyl 06.5
0.125
0.125
0.125
0.125
0.125
0.125
0.05
0.1254-fluorophenyl
0.125
0.125
tBu
tBu
tBu
tBu
tBu
tBu
tBu
3
1
23
1310.5
18
4
130
130
130
±
130
130
46
85
78
5
±
±
3
±
45
0
±
±
140
±
±
±
±
±
±
38
±
±
5
63
1522
6
DMF
130
06.5
DMF
0.56
0.56
24
DMF
DMF
±
tBu
tBu
1
21
130
130
60
48
[a] Isolated yield based on the amount of cyclopentadiene moiety (1 mmol ˆ 100%). [b] Contaminated with C5H(Ph)(2,5-Me2C6H3)4 (8%).
nickelocene also afforded >60% yields of 6a, while cobalto-
cene and especially ferrocene proved rather unreactive (yields
of 23% and <1%, respectively). Evidently, the metallocenes
should fragment during the stepwise arylation; 1,2,4-triphen-
yl-1,3-cyclopentadiene (4a) (21%) and 1,2,3,4-tetraphenyl-
1,3-cyclopentadiene (5a) (9%) were isolated as intermediary
products (Table 1, entry 2) from the reaction of 1 with reduced
amounts of 2a (3 mmol) and palladium acetate
(0.0125mmol). It is noted that cesium carbonate proved far
superior than potassium carbonate; the use of potassium
carbonate led to the increased formation of biphenyl as an
Ullmann-type coupling product,[11] the yield of 6a was <10%,
even with zirconocene dichloride.
The phosphine ligands are also crucial for the success of the
domino reaction when substituted bromobenzenes were used.
Triphenylphosphine caused the contamination of phenyl
groups in the products.[12] The scrambling of aryl moieties
would be avoided with the use of triarylphosphines that have
the same aryl groups as the starting aryl bromide. This was
confirmed in reactions in which 3-methyl-, 3,4-dimethyl-, and
4-fluorobromobenzenes, (2c, 2e and 2l, respectively,) were
used (Table 1, entries 6, 10, and 18, respectively), the expected
products 6c, 6e, and 6l were obtained. This problem was
overcome in a more general manner with the use of the
relatively more basic and sterically hindered tri-tert-butyl-
phosphine.[13, 14] Furthermore, it was found in several exam-
ples that this phosphine can enhance the domino reaction
considerably; the reaction of metallocene 1 with 4-bromo-
toluene (2b), for instance, was completed within one hour to
give penta(4-methylphenyl)cyclopentadiene (6b) in an iso-
lated yield of 78% (Table 1, entry 4). Remarkably, the
amount of palladium catalyst under optimized conditions
can be reduced to 0.25mol% per transferred aryl group to
achieve an acceptable isolated yield (60%), as in the case of
6b (Table 1, entry 5). However, with a relatively bulky
bromide, such as 2,5-dimethylbromobenzene (2d), triphenyl-
phosphine afforded a considerably better yield of product 6d
(70%, Table 1, entry 8) as compared with tri-tert-butylphos-
phine (31%, Table 1, entry 7), even under consideration that
an impurity of approximately 8% of the corresponding
tetra(2,5-dimethylphenyl)phenylcyclopentadiene was indicat-
ed by mass spectrometry of the crude product; the purity
fortunately became 98% (73% recovery) after a single
recrystallization from methanol/benzene. Both electron-rich
aryl bromides, such as 4-bromoanisole (2h), and electron-
poor aryl bromides, such as ethyl 4-bromobenzoate (2k),
reacted with 1 to give the corresponding pentaarylcyclopen-
tadienes 6h and 6k. Derivatives with long side chains, such as
6j, are of possible interest as building blocks for organo-
metallic liquid crystals.[7d]
The formation of the ortho-substituted and thus very
sterically-crowded
penta(2,5-dimethylphenyl)cyclopenta-
diene (6d) deserves special attention. Compound 6d was
found to consist of at least six rotamers at room temperature;
1
its H NMR spectrum in CDCl3 showed six methine proton
peaks (three major signals at d ˆ 5.10, 5.29 and 5.46 and three
minor signals at d ˆ 4.85, 5.07 and 5.25; Figure 1a) and more
than 20 methyl peaks. This spectrum resembles the spectrum
Figure 1. Methine proton peaks in 1H NMR spectrum of compounds a) 6d
and b) 6e in CDCl3 at room temperature.
Chem. Eur. J. 2000, 6, No. 18
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3427 $ 17.50+.50/0
3427

G. Dyker et al.
FULL PAPER
previously reported for tetra(2-
methylphenyl)cyclopentadie-
none at the low temperature of
À438C.[14] The peaks in the
1H NMR spectrum of 6d in
[D6]DMSO were still sharp,
even at 1008C, thus reflecting
its crowded nature, while at
1508C they were completely
broadened (Figure 2). It was
somewhat surprising that pen-
ta(3,4-dimethylphenyl)cyclo-
pentadiene (6e) also consists of
several rotamers as indicated
by the methine peaks (Fig-
ure 1b), whereas penta(3-meth-
ylphenyl)cyclopentadiene (6c)
showed a single methine peak,
as did its penta(4-methylphen-
yl) isomer 6b. The tempera-
ture-dependent spectrum of 6e
was similar to that of 6d. This
phenomenon may arise from
the restricted movement of
two adjacent methyl groups
which make the rotation of the
phenyl rings in 6e difficult.
15h, again indicating the stepwise character of the arylation
process. In the case of the relatively more hindered bromide,
2,6-dimethylbromobenzene (2o), the arylation is terminated
at the stage of triarylcyclopentadiene 4o. The presented
arylation reactions in o-xylene were found to be much slower
compared with those in DMF. Thus, when reduced amounts of
aryl bromides 2b and 2l and o-xylene as the solvent were
applied at 1208C (Table 2, entries 5and 13), tetra(4-methyl-
phenyl)- and tetra(4-fluorophenyl)cyclopentadienes (5b and
5l, respectively) were obtained as the major products. The
coupling reaction of 2-chlorobromobenzene (2m) proved that
aryl bromides are more reactive than aryl chlorides, as was
expected (Table 2, entry 14). However, under more rigorous
reaction conditions 4-chlorotoluene (2b') led to an excellent
result (Table 2, entry 2).
4-Bromophenol, 4-bromobenzonitrile, and 4-bromobenzal-
dehyde could not be used for the arylation of cyclopentadiene.
This problem was solved by using an acetal as the protecting
group. Thus, pentaacetal 8a was obtained in 56% yield
starting from dioxolane 7a (Scheme 2). The synthesis of
pentaketone 9b (R ˆ CH3) was achieved in a one-pot
procedure, including deketalization. The pentacarbonyl com-
pounds 9 could be valuable building blocks for the construc-
tion of extended p systems by multiple condensation reac-
tions. For instance, the fivefold condensation of 9a with p-
toluidine proceeds almost quantitatively to give the corre-
sponding pentakisimine. Since its final purification by column
chromatography or by crystallization proved difficult, the full
characterization was performed on the reduction product 10.
The fact that stoichiometric metalation of the cyclopenta-
diene unit is not a prerequisite significantly enhances the
scope of the domino arylation; substituted and annulated
cyclopentadienes now belong to the group of suitable starting
materials. We tested the application of 1,2,4-triaryl-1,3-cyclo-
pentadienes (11) to synthesize pentaarylcyclopentadienes 12
with a defined substitution pattern (Scheme 3). The arylation
of di-1,4-(4-chlorophenyl)-1,3-cyclopentadiene (13) also led to
Figure 2. Temperature-depend-
ence of 1H NMR spectrum of
compound 6d in [D6]DMSO.
It was quite interesting to find that cyclopentadiene (3)
itself is equally suited for the multiple arylation process as
metallocene 1 when the reaction is carried out in a screw-cap
tube to prevent the loss of volatile substrate (Table 2). The
yields achieved are similar or better than those obtained when
1 was used.
A comparison of entries 7 and 8 of Table 2 (34 h and 19 h
reaction time, respectively) reveals that the arylation process
is rather slow in the case of the bulky bromide 2d; evidently
the major part of the 62% yield of 6d is formed in the last
Table 2. Arylation of cyclopentadiene (3).
Entry
Compound 2
[Pd(OAc)2]
[mmol] [mmol]
PR3
Cs2CO3 solvent
t
T
Yield of products [%][a]
R, X
R
[mmol] [mmol]
[h] [8C]
4
5
6
[b]
1
2
3
4
4-methylphenyl, Br (2b)
4-methylphenyl, Cl (2b)
4-methylphenyl, Cl (2b)
4-methylphenyl, Cl (2b)
6
10
10
6
4
6
6
6
6
6
6
6
4
6
6
4
6
6
0.025
0.05
0.025
0.025
0.025
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.075
0.05
0.05
0.05
0.05
tBu 0.156
tBu 0.12
tBu 0.06
tBu 0.06
tBu 0.06
tBu 0.156
tBu 0.12
tBu 0.12
tBu 0.12
tBu 0.12
tBu 0.1
tBu 0.12
tBu 0.12
tBu 0.6
tBu 0.12
tBu 0.12
tBu 0.12
tBu 0.12
DMF
11450
DMF
o-xylene 24
o-xylene 24
o-xylene 24
±
72
±
87
6
6
6
4
160
140
140
120
±
140
140
140
140
140
140
120
140
140
140
140
140
±
±
±
±
87
45
60
11
46
±
32
54-methylphenyl, Cl (
6
7
8
9
10
11
12
13
14
2b)
10
3-methylphenyl, Br (2c)
2,5-dimethylphenyl, Br (2d)
2,5-dimethylphenyl, Br (2d)
4-methoxyphenyl, Br (2h)
4-n-butoxyphenyl, Br (2i)
4-carboethoxyphenyl, Br (2k)
4-fluorophenyl, Br (2l)
DMF
18
DMF
140
34
19
6
24
41
6
6
42
24
±
77
6
6
6
6
6
6
4
6
6
4
6
6
±
±
±
±
±
±
±
±
±
±
52
±
62
15
61
61
30
82
9
17
58
±
DMF
DMF
DMF
DMF
DMF
o-xylene
DMF
DMF
±
24
±
48
18
±
4-fluorophenyl, Br (2l)
2-chlorophenyl, Br (2m)
151-naphthyl, Br (
2n)
[c]
16
17
18
1-naphthyl, Br (2n)
2,6-dimethylphenyl, Br (2o)
4'-pentyl-biphenyl-1-yl, Br (2p)
o-xylene 24
DMF
DMF
46
54
±
±
±
±
24
24
±
72
[a] Isolated yield based on the amount of cyclopentadiene (3) used. [b] Maximum yield achieved; range of yields for this reaction achieved in several
laboratories in Germany and Japan was always between 70 and 87%. [c] Tetranaphthylcyclopentadiene 5n was formed in about 15% yield, but was not fully
characterized.
3428
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3428 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 18

Arylation of Cyclopentadienes
3426±3433
O
R
O
O
O
O
R
O
R
R'
+
+ 3
Br
Br
a
R
7 (6 equiv)
7a: R = H
7b: R = CH3
O
R
11a (R = H)
11b (R = OCH3)
2q (R' = Cl)
7a (R' = 1,3-dioxolane-2-yl)
O
O
O
R
O
b
Pd cat.
R
R
O
O
O
R
R'
8a (56%)
R = H
R
O
O
R
R
c
O
R
R'
9a (71%)
9b (68% over
two steps)
12a (R = H, R' = Cl, 61%)
12b (R = OCH3, R' = Cl, 55%)
12c (R = OCH3, R' = 1,3-dioxolane-2-yl, 49%)
H3C
CH3
Scheme 3. Twofold arylation of triarylcyclopentadienes 11. Reaction
conditions for 12a: 2.5equiv aryl bromide, 2.5mol% [Pd(OAc) 2],
12 Mol% P(tBu)3, Cs2CO3, DMF, 1208C, 24 h; for 12b and 12c: 2 ± 3 equiv
aryl bromide, 2.5mol% [Pd(OAc) 2], 10 mol% P(tBu)3, Cs2CO3, DMF,
1408C, 20 ± 68 h. Yields are given for the mixture of three double-bond
isomers.
NH
NH
H
N
CH3
H3C
+
HN
CH3
Br
CH3
Cl
Cl
HN
2f
13
Pd cat.
10 (43%)
CH3
Scheme 2. Pentacarbonyl compounds and their derivatization. Reaction
conditions a) 5mol% [Pd(OAc) 2], 12 mol% P(tBu)3, Cs2CO3, DMF,
1408C, 21 h; b) p-TosOH, acetone, reflux; c) 1) p-toluidine, benzene, p-
TosOH, Dean-Stark trap; 2) LiAlH4.
H3C CH3
H3C
CH3
the formation of pentaarylcyclopentadiene 12d (Scheme 4).
In each case, a yield of approximately 50% or more of a
mixture of double bond isomers was obtained. It is anticipated
that all double bond isomers of each of the pentaarylcyclo-
pentadienes 12 should give the same organometallic complex
after metalation.
Cl
Cl
H3C
CH3
Under the applied reaction conditions, indene (14) was
found to undergo threefold arylation exclusively at the 1- and
3-positions to give the 1:3 products 15 (Scheme 5and Table 3,
entries 1 ± 4). This observation is important for the mecha-
nistic interpretation of the domino reaction and implies that
12d (60%)
Scheme 4. Threefold arylation of diarylcyclopentadiene 13. Reaction
conditions: 3.6 equiv aryl bromide, 2.5mol% [Pd(OAc) 2], 12 mol%
P(tBu)3, Cs2CO3 DMF, 1208C, 24 h; the yield is for the mixture of three
double-bond isomers.
À
the successive C C bond formation takes place by the
reaction of an aryl palladium halide with indenyl anions,
presumably their cesium salts, at the 1- and 3-positions, which
have the highest electron density. Arylation by carbopallada-
tion is less likely to be involved, since stoichiometric reactions
of this kind in indenes are known to give arylation products at
the 2-position,[16] and a catalytic Heck-type reaction under
Chem. Eur. J. 2000, 6, No. 18
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3429 $ 17.50+.50/0
3429

G. Dyker et al.
FULL PAPER
Table 3. Arylation of indenes 15 and 17.
Entry
Indeneq
Compound 2
[Pd(OAc)2]
[mmol] [mmol]
PR3
Cs2CO3 Solvent
t
T
Product Yield [%][a]
R, X
R
[mmol] [mmol]
[h] [8C]
1
2
3
4
5
14
14
14
14
16
phenyl, Br (2a)
4-methylphenyl, Br (2b)
4-methoxyphenyl, Br (2 f)
3,5-dimethylphenyl, Br (2n) 3.6
4-methylphenyl, Br (2b) 2.50.025
3.6
3.6
3.6
0.025
0.025
0.025
0.025
tBu 0.06
tBu 0.06
tBu 0.06
tBu 0.06
tBu 0.06
3.6
3.6
3.6
3.6
DMF
DMF
DMF
DMF
6
3
6
1
5140
140
140
140
15a
15b
15 f
15n
17b
81
80
45
72
58
2.5DMF
140
[a] Isolated yield based on the amount of indene.
sterically crowded pentaarylcyclopentadienes. While the
method which uses cyclopentadiene itself without the use of
a stoichiometric amount of a metal is more economical than
that with metallocenes, the latter has some advantages,
however; metallocenes are commercially available, so that
predistillation of dicyclopentadiene is not required, and the
reaction can be carried out using a standard flask. We will
further investigate synthetic applications of multiple-arylated
cyclopentadienes, such as the electropolymerization of chlo-
rosubstituted derivatives of 12 and the polymerization by
McMurry reaction of the dicarboxaldehyde derived from 12c,
in order to develop a route to a new type of conducting
polymer.
Ar
Ar
X
2
Pd cat.
Ar
Ar
15
14
Ar
X
Ar
2
Ph
Ph
Pd cat.
Ar
17
16
Scheme 5. Double palladium-catalyzed arylation of indenes 14 and 16;
Arˆ aryl, X ˆ Br, Ph ˆ phenyl.
Experimental Section
somewhat different conditions was reported to start with the
arylation at the 2-position.[17] For the multiple arylation of
cyclopentadiene (3) there is a possibility that a Heck-type
mechanism partially contributes to the reaction sequence.
However, since intermolecular Heck arylation of tri- and
tetrasubstituted alkenes is generally slow, the third to fifth
arylations of cyclopentadiene (3) would preferably occur by
coupling with the corresponding cyclopentadienyl anions.
Note that the pKa value of cyclopentadiene in dimethylsulf-
oxide at 258C (18.0) is known to be smaller than that of indene
(20.1),[18] hence, it should be relatively more susceptible
toward reaction with the base. Therefore, even the first
arylation could occur on the cyclopentadienyl anion. It may
be reasonable to consider that the first arylation involves
transmetalation when metallocenes are used.[19] The ineffi-
ciency of ferrocene may be attributed to the fact that it is an
18-electron complex with substantial stability. In turn, the
formal 16- and 20-electron complexes, zirconocene dichloride
and nickelocene, are considered to be reactive, as was
experimentally observed. In the reaction of 2-phenylindene
(16) with 2b, we observed a twofold arylation, again at the 1-
and 3-positions (Scheme 5and Table 3, entry 5); due to steric
hindrance, the third arylation is inhibited. This agrees with the
lack of hexaarylated products in the reaction of zirconocene
dichloride (1) and cyclopentadiene (3).
General: Melting points are uncorrected. 1H NMR spectra (300 or
500 MHz) were recorded in CDCl3 with TMS as the internal standard
unless otherwise noted. 13C NMR spectra (75or 125MHz) were measured
with CDCl3 as the solvent and as the internal standard (d ˆ 77.05). MS data
were obtained by EI; all samples were measured at 70 eVand 2958C unless
otherwise stated. Substituted cyclopentadienes 11a,[20] 11b,[21] and 13[22]
were prepared according to or in analogy to published procedures.
General procedure for palladium-catalyzed cross-coupling reactions of aryl
halides (2) with zirconocene dichloride (1) or with cyclopentadiene (3): A
mixture of zirconocene dichloride (1, 146 mg,500 mmol) or of cyclopenta-
diene (3, 66 mg, 1.0 mmol) and aryl halide (2, 6.00 mmol), cesium
carbonate (1.96 g, 6.00 mmol), palladium acetate (12.5± 125 mmol), di-
methyl formamide, (10 mL) and an appropriate phosphine ligand (50 ±
150 mmol) was heated under argon in a screw-cap tube for 1 ± 72 h at
120 ± 1608C (see below and also Tables 1 and 2; further remarks:
1. sensitive phosphine ligands such as tri-tert-butylphosphine are added
after the solvent; 2. the oil bath is preheated to the reaction temperature
before the tube is inserted; 3. for the reaction with 1, a two-necked flask
with a balloon that is filled with nitrogen may also be used, which gives
essentially the same results as when a sealed tube is used). After cooling to
room temperature, CH2Cl2 (50 mL) and p-toluene sulfonic acid (12 mmol)
were added while stirring. After 10 min the mixture was filtered through
silica gel (5g) with CH 2Cl2 (25mL) as eluent. The solvent was removed in
vacuo at 508C and 15mbar, the residue dried in vacuo at 50 8C and 0.5mbar
and separated by flash chromatography on silica gel.
1,2,3,4-Tetrakis-(4-carboethoxyphenyl)-cyclopentadiene (5k) and 1,2,3,4,5-
pentakis-(4-carboethoxyphenyl)-cyclopentadiene (6k) from cyclopenta-
diene (3): 4-Bromobenzoic acid ethyl ester (2k) (1.37 g, 6.00 mmol) was
coupled with cyclopentadiene (3) according to the general procedure; for
detailed reaction conditions see Table 2, entry 11 (for comparison: data of
the corresponding synthesis from zirconocene dichloride is given in Table 1,
entry 15). Thin-layer chromatography of the crude product: Rf ˆ 0.49
(biphenyl-4,4'-dicarboxylic acid diethyl ester), 0.29 (5k), 0.22 (6k) (petro-
leum ether/ethyl acetate 3:1, silica gel). Separation of the products by flash
chromatography (petroleum ether/ethyl acetate 3:1, silica gel) yielded
three fractions.
In summary, we have shown that various cyclopentadienes
as well as metallocenes can be multiply arylated by a single
reaction with aryl halides in a palladium catalyzed reaction.
This novel synthetic method represents an efficient and
straightforward alternative to classical methods, thus opening
up opportunities for the construction of even extremely
3430
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3430 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 18

Arylation of Cyclopentadienes
3426±3433
‡
First fraction: Biphenyl-4,4'-dicarboxylic acid diethyl ester (159 mg, 18%)
as colorless crystals with m.p. 2208C; its NMR spectroscopic data matched
published data.[23]
(m, 1H), 6.62 ± 7.24 (m, 15H); MS: m/z (%): 586 [M] ; elemental analysis
calcd (%) for C45H46 (586.86): C 92.10, H 7.90; found C 91.98, H 8.01.
1,2,3,4,5-Penta(3,5-dimethylphenyl)-1,3-cyclopentadiene (6 f): M.p. 213 ±
2148C; 1H NMR: d ˆ 2.05(s, 12H), 2.12 (s, 12H), 2.18 (s, 6H), 4.98 (s,
1H), 6.61 ± 6.82 (m, 15H); 13C NMR: d ˆ 21.17, 21.26, 21.36, 61.54, 126.33,
126.86, 127.61, 127.87, 127.92, 135.72, 136.39, 136.51, 136.61, 137.26, 138.62,
144.28, 145.57; MS: m/z (%): 586 [M] ; elemental analysis calcd (%) for
C45H46 (586.86): C 92.10, H 7.90; found C 92.20, H 7.86.
Second fraction: Tetraarylcyclopentadiene 5k (152 mg, 24%) as a yellow
solid: m.p. 203 ± 2088C; IR (film): nÄ ˆ 2981 (m), 2935(w), 2905(w), 1718
(s), 1604 (s), 1563 (w), 1511 (w), 1463 (w), 1445 (w), 1405 (m), 1367 (s), 1309
(s, sh), 1273 (s), 1206 (m), 1180 (s), 1109 (s), 1020 (s), 890 (w), 865(m), 850
(m), 771 (s), 747 (m), 704 cmÀ1 (m); UV/Vis (acetonitrile): lmax (lg e) ˆ 370
‡
1
(4.35), 284 (4.42), 254 (4.44, sh), 230 nm (4.50); H NMR: d ˆ 1.36 (t, J ˆ
1,2,3,4,5-Penta(4-t-butylphenyl)-1,3-cyclopentadiene (6g): M.p. 243 ±
2458C; 1H NMR: d ˆ 1.19 (s, 18H), 1.23 (s, 9H), 1.25(s, 18H), 5.05(s,
1H), 6.89 ± 7.18 (m, 20H); 13C NMR: d ˆ 31.33, 31.46, 34.42, 34.50, 61.31,
124.27, 124.32, 125.16, 127.79, 128.07, 129.45, 132.84, 133.73, 135.73, 143.89,
7.2 Hz, 6H), 1.38 (t, J ˆ 7.2 Hz, 6H), 4.12 (s, 1H, C5H), 4.35(ªquintetº,
ªJº ˆ 7.5Hz, 8H), 7.03 (d, J ˆ 8.6 Hz, 4H), 7.21 (d, J ˆ 8.7 Hz, 4H), 7.86
(ªdº, ªJº ˆ 8.6 Hz, 8H); 13C NMR: d ˆ 14.31 (q), 14.32 (q), 45.90 (t, C5H),
60.94, 61.05(all t), 127.68 (d), 128.74, 129.41 (all s), 129.62, 129.70 (all d),
139.86, 140.40, 141.11, 145.08 (all s), 166.26, 166.31 (all s, CO), one d is
‡
144.84, 148.33, 148.50, 148.87; MS: m/z (%): 726 [M] ; elemental analysis
calcd (%) for C55H66 (727.12): C 90.85, H 9.15; found C 90.58, H 9.12.
‡
‡
superimposed; MS: m/z (%): 659 (45) [M‡1] , 658 (100) [M] , 57 (10), 44
(55), 41 (10); elemental analysis calcd (%) for C41H38O8 (658.7): C 74.76, H
5.81; found C 74.62, H 5.79.
1,2,3,4,5-Penta(4-methoxyphenyl)-1,3-cyclopentadiene (6h): M.p. 193 ±
1
1948C; H NMR: d ˆ 3.68 (s, 6H), 3.71 (s, 3H), 3.75(s, 6H), 4.89 (s, 1H),
6.56 ± 6.58 (m, 4H), 6.67 ± 6.71 (m, 6H), 6.88 ± 6.92 (m, 8H), 7.08 ± 7.10 (m,
2H); 13C NMR: d ˆ 55.00, 55.04, 55.06, 61.68, 113.00, 113.19, 113.80, 128.71,
128.76, 129.18, 129.88, 130.56, 131.14, 142.06, 144.87, 157.50, 157.67, 157.84;
Third fraction: Pentaarylcyclopentadiene 6k (233 mg, 30%) as a yellow
solid with m.p. 1608C (Lit.: m.p. 1608C)[7d]; IR (film): nÄ ˆ 2981 (w), 2938
(w), 2904 (w), 2873 (w), 1719 (s), 1606 (m), 1463 (w), 1445(w), 1404 (w),
‡
MS: m/z (%): 596 [M] ; elemental analysis calcd (%) for C40H36O5
1367 (m), 1308 (w), 1278 (s), 1178 (m), 1107 (s), 1021 (m), 860 (w), 775(w),
(596.72): C 80.51, H 6.08; found C 80.28, H 6.07.
À1
749 (w), 735(w), 706 cm
(w); UV/Vis (acetonitrile): lmax (lg e) ˆ 361
1,2,3,4,5-Penta(4-butoxyphenyl)-1,3-cyclopentadiene (6i): M.p. 83 ± 848C;
1H NMR: d ˆ 0.91 ± 0.98 (m, 15H), 1.37 ± 1.52 (m, 10H), 1.64 ± 1.77 (m,
10H), 3.80 ± 3.90 (m, 10H), 4.86 (s, 1H), 6.54 ± 7.07 (m, 20H); 13C NMR:
d ˆ 14.01, 14.08, 19.40, 19.44, 31.50, 31.56, 61.64, 67.40, 67.51, 96.06, 96.37,
96.70, 113.50, 113.74, 114.34, 128.60, 128.70, 129.17, 129.87, 130.48, 131.14,
142.04, 144.82, 157.09, 157.25, 157.41; MS: m/z (%): 806 [M] ; elemental
analysis calcd (%) for C55H66O5 (807.12): C 81.85, H 8.24; found C 81.48, H
8.26.
(4.34), 275(4.54), 239 nm (4.77); 1H NMR: d ˆ 1.30 (m, 6H), 1.34 (m, 3H),
1.35(t, J ˆ 7.0 Hz, 6H), 4.30 (m, 4H), 4.33 (m, 2H), 4.35(q, J ˆ 7.0 Hz, 4H),
5.25 (s, 1H, C5H), 6.99 (d, J ˆ 8.7 Hz, 4H), 7.09 (d, J ˆ 8.6 Hz, 4H), 7.26 (d,
J ˆ 8.1 Hz, 2H), 7.72 (d, J ˆ 8.7 Hz, 4H), 7.85(d, J ˆ 8.5Hz, 4H), 7.88 (d,
J ˆ 8.4 Hz, 2H); 13C NMR: d ˆ 14.24 (q), 14.27 (q), 60.86 (t), 60.97 (t), 61.04
(t), 62.63 (d, C5H), 128.24, 128.72, 129.28 (all d), 129.53, 129.83, 130.26,
128.93, 129.51, 139.03, 139.55, 141.89, 144.65, 147.21, 166.08, 166.18 (all s),
‡
‡
three q and one t are superimposed; MS: m/z (%): 807 (55.1) [M‡1] , 806
1,2,3,4,5-Penta(4-octyloxyphenyl)-1,3-cyclopentadiene (6j): viscous oil;
1H NMR: d ˆ 0.85± 0.90 (m, 15H), 1.23 ± 1.43 (m, 50H), 1.65± 1.78 (m,
10H), 3.79 ± 3.89 (m, 10H), 4.86 (s, 1H), 6.53 ± 7.07 (m, 20H); MS: m/z (%):
‡
(100) [M] , 660 (10), 351 (12), 323 (12), 177 (11), 44 (36); elemental analysis
calcd (%) for C50H46O10 (806.9): C 74.43, H 5.78; found C 74.32, H 5.75.
1,2,4-Tri(4-methylphenyl)-1,3-cyclopentadiene (4b): M.p. 151 ± 1548C;
1H NMR: d ˆ 2.31 (s, 3H), 2.35(s, 3H), 2.36 (s, 3H), 3.88 (s, 2H), 6.32 (s,
1H), 6.96 (s, 1H), 7.03 (d, J ˆ 8.1 Hz, 2H), 7.12 ± 7.30 (m, 8H), 7.46 (d, J ˆ
8.1 Hz, 2H); 13C NMR: d ˆ 21.32, 21.36, 21.42, 45.03, 124.63, 127.41, 128.09,
128.79, 128.98, 129.18, 131.01, 132.98, 134.04, 134.21, 135.86, 136.37, 136.50,
‡
1086 [M] ; elemental analysis calcd (%) for C75H106O5 (1087.66): C 82.82, H
9.82; found C 82.39, H 9.86.
1,2,3,4-Tetra(4-fluorophenyl)-1,3-cyclopentadiene (5l): M.p. 208 ± 2098C;
1H NMR: d ˆ 3.94 (s, 2H), 6.85± 6.91 (m, 10H), 7.11 ± 7.14 (m, 4H);
13C NMR: d ˆ 46.06, 115.10 (d, J ˆ 24.2 Hz), 115.23 (d, J ˆ 21.2 Hz), 129.19
(d, J ˆ 7.8 Hz), 131.24 (d, J ˆ 7.8 Hz), 131.84, 132.04, 138.79, 142.67, 161.30
‡
138.15, 141.14, 144.34; MS: m/z (%): 336 [M] ; elemental analysis calcd
(%) for C26H24 (336.47): C 92.81, H 7.19; found C 92.58, H 7.19.
‡
(d, J ˆ 246.7 Hz), 162.57 (d, J ˆ 245.7 Hz); MS: m/z (%): 442 [M] ;
1,2,3,4-Tetra(4-methylphenyl)-1,3-cyclopentadiene (5b): M.p. 179 ± 1808C;
1H NMR: d ˆ 2.27 (s, 6H), 2.28 (s, 6H), 3.94 (s, 2H), 6.85(d, J ˆ 8.1 Hz,
4H), 6.95(d, J ˆ 7.8 Hz, 4H), 6.97 (d, J ˆ 8.1 Hz, 4H), 7.08 (d, J ˆ 8.1 Hz,
4H); 13C NMR: d ˆ 21.27, 21.43, 45.87, 127.49, 128.56, 128.64, 129.56, 133.65,
elemental analysis calcd (%) for C29H16F4 (440.43): C 78.72, H 4.10; found C
78.72, H 4.16.
1,2,3,4,5-Penta(4-fluorophenyl)-1,3-cyclopentadiene (6l): M.p. 186 ±
1878C; 1H NMR: d ˆ 4.90 (s, 1H), 6.73 ± 6.77 (m, 4H), 6.84 ± 6.95(m,
14H), 7.07 ± 7.10 (m, 2H); 13C NMR: d ˆ 62.12, 114.97 (d, J ˆ 22.4 Hz),
115.22 (d, J ˆ 22.1 Hz), 115.77 (d, J ˆ 21.5Hz), 129.73 (d, J ˆ 7.4 Hz), 130.50
(d, J ˆ 8.3 Hz), 131.32, 131.35, 131.63 (d, J ˆ 8.3 Hz), 132.96, 142.55, 145.62,
161.56 (d, J ˆ 247.3 Hz), 161.63 (d, J ˆ 244.3 Hz), 161.84 (d, J ˆ 247.3 Hz);
‡
133.77, 135.63, 135.78, 138.89, 143.77; MS: m/z (%): 426 [M] ; elemental
analysis calcd (%) for C33H30 (426.60): C 92.91, H 7.09; found C 92.74, H
6.98.
1,2,3,4,5-Penta(4-methylphenyl)-1,3-cyclopentadiene (6b): M.p. 2508C;
1H NMR: d ˆ 2.17 (s, 6H), 2.20 (s, 3H), 2.26 (s, 6H), 4.97 (s, 1H), 6.81 ±
6.95(m, 18H), 7.07 (d, J ˆ 7.8 Hz, 2H); 13C NMR: d ˆ 21.26, 21.42, 61.97,
128.10, 128.20, 128.36, 128.63, 129.02, 129.81, 133.05, 133.35, 135.25, 135.34,
‡
MS: m/z (%): 536 [M] ; elemental analysis calcd (%) for C35H21F5 (536.54):
C 78.35, H 3.94; found C 78.13, H 3.95.
1,2,4-Tri(1-naphthyl)-1,3-cyclopentadiene
(4n):
M.p.
213 ± 2148C;
‡
135.38, 135.69, 143.24, 145.70; MS: m/z (%): 516 [M] ; elemental analysis
1H NMR: d ˆ 4.27 (s, 2H), 7.13 ± 7.91 (m, 19H), 7.98 (d, J ˆ 8.5Hz, 1H),
calcd (%) for C40H36 (516.72): C 92.98, H 7.02; found C 92.56, H 7.04.
‡
8.24 ± 8.26 (m, 1H), 8.54 ± 8.56 (m, 1H); MS: m/z (%): 444 [M] ; elemental
1,2,3,4,5-Penta(3-methylphenyl)-1,3-cyclopentadiene (6c): M.p. 163 ±
analysis calcd (%) for C35H24 (444.57): C 94.56, H 5.44; found C 94.04, H
5.48.
1
1648C; H NMR: d ˆ 2.08 (s, 6H), 2.15(s, 6H), 2.23 (s, 3H), 5.02 (s, 1H),
6.77 ± 6.93 (m, 15H), 6.99 ± 7.04 (m, 5H); 13C NMR: d ˆ 21.29, 21.37, 21.48,
62.19, 125.43, 126.10, 126.87, 127.14, 127.17, 127.19, 127.38, 127.52, 128.20,
129.27, 129.73, 130.80, 135.79, 136.32, 136.75, 137.00, 137.70, 138.32, 144.09,
1,2,3,4,5-Penta(1-naphthyl)-1,3-cyclopentadiene (6n, mixture of rotamers):
1
M.p. 248 ± 2508C; H NMR: d ˆ 4.25± 4.63 (m, 1H), 6.78 ± 8.23 (m, 35H);
‡
MS: m/z (%): 696 [M] ; elemental analysis calcd (%) for C55H36 (696.89): C
‡
146.08; MS: m/z (%): 516 [M] ; elemental analysis calcd (%) for C40H36
94.69, H 5.21; found C 94.18, H 5.26.
(516.72): C 92.98, H 7.02; found C 92.94, H 7.10.
1,2,4-Tri(2,6-dimethylphenyl)-1,3-cyclopentadiene (4o): M.p. 182 ± 1838C;
1H NMR: d ˆ 2.15(s, 6H), 2.16 (s, 6H), 2.30 (s, 6H), 3.58 (s, 2H), 6.32 (s,
1H), 6.94 ± 7.15(m, 9H); 13C NMR: d ˆ 20.89, 21.08, 21.29, 48.35, 126.56,
126.60, 126.77, 127.04, 127.54, 134.93, 136.16, 136.31, 136.33, 136.53, 137.62,
1,2,3,4-Tetra(2,5-dimethylphenyl)-1,3-cyclopentadiene (5d, mixture of ro-
tamers): M.p. 73 ± 748C; 1H NMR: d ˆ 1.77 ± 2.20 (m, 24H), 3.63 ± 4.03 (m,
‡
2H), 6.61 ± 6.97 (m, 12H); MS: m/z (%): 482 [M] ; elemental analysis calcd
(%) for C37H38 (482.71): C 92.07, H 7.93; found C 91.77, H 7.85.
‡
141.01, 141.63, 144.51; MS: m/z (%): 378 [M] ; elemental analysis calcd (%)
1,2,3,4,5-Penta(2,5-dimethylphenyl)-1,3-cyclopentadiene (6d, mixture of
for C29H30 (378.56): C 92.01, H 7.99; found C 91.98, H 7.84.
rotamers): M.p. 194 ± 1968C; 1H NMR: d ˆ 1.72 ± 2.46 (m, 30H), 4.86 ± 5.45
1,2,3,4,5-Penta(4'-n-pentyl-1-biphenyl-4-yl)-1,3-cyclopentadiene (6p): M.p.
133 ± 1358C; 1H NMR: d ˆ 0.86 ± 0.89 (m, 15H), 1.31 ± 1.32 (m, 20H), 1.61 ±
1.62 (m, 10H), 2.62 (m, 10H), 5.20 (s, 1H), 7.10 ± 7.51 (m, 40H); MS: m/z
‡
(m, 1H), 6.46 ± 7.10 (m, 15H); MS: m/z (%): 586 [M] ; elemental analysis
calcd (%) for C45H46 (586.86): C 92.10, H 7.90; found C 91.92, H 7.97.
‡
1,2,3,4,5-Penta(3,4-dimethylphenyl)-1,3-cyclopentadiene (6e, mixture of
rotamers): M.p. 168 ± 1708C; 1H NMR: d ˆ 1.97 ± 2.22 (m, 30H), 4.97 ± 5.10
(%): 1176 [M] ; elemental analysis calcd (%) for C90H96 (1176.74): C 91.78,
H 8.22; found C 91.72, H 8.13.
Chem. Eur. J. 2000, 6, No. 18
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3431 $ 17.50+.50/0
3431

G. Dyker et al.
FULL PAPER
1,2,3,4,5-Penta(4-(1,3-dioxolan-2-yl)phenyl)-1,3-cyclopentadiene (8a): Di-
oxolane 7a (1.38 g, 6.00 mmol, 6 equiv) was coupled with cyclopentadiene
(3) according to the general procedure; for detailed reaction conditions see
Scheme 2. Thin-layer chromatography of the crude product: Rf ˆ 0.69, 0.54,
0.27 (8a), 0.01 (petroleum ether/ethyl acetate 1:2, silica gel). Separation of
the products by flash chromatography (petroleum ether/ethyl acetate 1:2,
silica gel) gave 450 mg (56%) of 8a as yellow solid with m.p. 248 ± 2508C;
IR (film): nÄ ˆ 3036 (w), 2952 (w), 2883 (s), 1611 (w), 1512 (w), 1471 (w),
1418 (m), 1387 (s), 1307 (w), 1283 (w), 1220 (m), 1185(w), 1083 (s), 1020 (s),
980 (s), 943 (s), 831 (s), 760 (w), 717 (w), 667 (w), 584 cmÀ1 (w); UV/Vis
(acetonitrile): lmax (lg e) ˆ 341 (4.17), 269 (4.35, sh), 246 nm (4.43);
1H NMR: d ˆ 3.93 ± 4.11(m, 20H), 5.06 (s, 1H, C5H), 5.63 (s, 2H), 5.68 (s,
1H), 5.70 (s, 2H), 6.92 (ªdº, ªJº ˆ 8.4 Hz, 4H), 6.99 (ªdº, ªJº ˆ 8.4 Hz,
4H), 7.12 (ªdº, ªJº ˆ 8.3 Hz, 4H), 7.17 (ªdº, ªJº ˆ 8.3 Hz, 2H), 7.23 (ªdº,
ªJº ˆ 8.1 Hz, 4H), 7.26 (ªdº, ªJº ˆ 8.1 Hz, 2H); 13C NMR: d ˆ 62.46(d,
C5H), 65.16, 65.22, 65.24 (all t), 103.53, 103.57, 103.68 (all d), 126.00, 126.28,
126.83, 128.42, 128.98, 130.06 (all d), 135.69, 136.12, 136.36, 136.62, 138.55,
143.81, 146.66 (all s), one s is superimposed; MS (70 eV, 3058C): m/z (%):
3H), 2.36 (s , 6H), 7.20 ± 6.95(m, 28H), 7.35(ªdº, ª Jº ˆ 8.2 Hz, 2H), 7.59
(ªdº, ªJº ˆ 8.55, 4H), 7.76 ± 7.72 (m, 6H), 8.30 (s, 2H), 8.35 (s, 1H,), 8.40 (s,
2H); 13C NMR: d ˆ 21.01 (q), 21.04 (q), 62.65(d), 120.79, 120.84, 128.43,
128.68, 128.86, 129.33, 129.39, 129.74, 129.78, 130.47 (all d), 134.85, 135.29,
135.33, 135.76, 135.80, 135.89, 137.96, 138.45, 140.80, 144.75, 147.23, 149.38,
149.42, 149.47 (all s), 158.88, 159.09, 159.13 (all d), one q and two d are
superimposed.
Since the final purification of the pentakisimine by column chromatog-
raphy or by crystallization proved difficult, the full characterization was
performed on the reduction product 10. Therefore, a solution of crude
pentakisimine in dry THF (5mL) was added dropwise at room temper-
ature to a solution of LiAlH4 (228 mg, 6.00 mmol)in dry THF(5mL). After
stirring for 2 h the reaction mixture was hydrolyzed with a saturated
aqueous solution of ammonium chloride(50 mL) and washed with brine
(50 mL). The combined water layers were extracted three times with ethyl
acetate(30 mL), the combined organic extracts were then filtered through
celite (2 g), and the solvent was removed in vacuo. Thin-layer chromatog-
raphy: Rf ˆ 0.46, 0.40 (10), 0.30, 0.13, 0.00 (hexanes/ethyl acetate 2:1, silica
gel). The fraction with Rf ˆ 0.40 was isolated by flash chromatography to
yield pentakisamine 10 (45mg, 43%) as a yellow solid. M.p. 93 ± 96 8C; IR
(film): nÄ ˆ 3413 (s, br, -NH), 3018 (s), 2917 (s), 2862 (s), 1616 (s), 1522 (s),
1466 (m), 1406 (m), 1321 (s), 1301 (m), 1249 (m), 1182 (w), 1126 (w), 1019
(w), 807 cmÀ1 (m); UV/Vis (acetonitrile): lmax (lg e) ˆ 346 (4.18), 306 (4.33,
sh), 251 nm (4.94); 1H NMR: d ˆ 2.21 and 2.22 (both s, overall 15H), 3.76 (s,
br, 5H), 4.11 (s, 4H), 4.14 (s, 2H), 4.21 (s, 4H), 5.04 (s, 1H), 6.50 (ªddº,
ªJº ˆ 15.3, 8.5 Hz, 10H), 7.00 ± 6.91 (m, 22H), 7.11 (ªdº, ªJº ˆ 8.3 Hz, 4H),
7.14 (ªdº, ªJº ˆ 2.7 Hz, 4H); 13C NMR: d ˆ 20.41 (q), 20.43 (q), 48.37, 48.50,
48.55 (all t), 61.99 (d), 112.93, 113.00, 113.11 (all d), 126.70 (s), 126.76 (s),
127.00, 127.15, 127.99, 128.58, 129.07, 129.70, 129.72, 130.27 (all d), 134.62,
135.06, 137.12, 137.54, 137.67, 138.01, 143.86, 145.97, 146.00, 146.03, 146.10
(all s), one q, one d and one s are superimposed; MS (70 eV, 3508C): m/z
‡
‡
‡
808 (18) [M‡2] , 807 (57) [M ‡ 1] , 806 (100) [M] , 762 (18), 734 (12);
elemental analysis calcd (%) for C50H46O10 (806.9): C 74.43, H 5.75; found
C 74.54, H 5.78.
1,2,3,4,5-Penta(4-formylphenyl)-1,3-cyclopentadiene (9a): Compound 8a
(485mg, 0.60 mmol) and p-toluene sulfonic acid monohydrate (43.0 mg,
0.23 mmol) were dissolved in wet acetone (75mL), and the mixture was
refluxed for 20 h. The solvent was partially removed in vacuo to a final
mixture volume of approximately 20 mL (508C and 400 mbar). Thin-layer
chromatography: Rf ˆ 0.43 (9a), 0.29, 0.00(petroleum ether/ethyl acetate
1:2, silica gel). Compound 9a was isolated by flash chromatography
(petroleum ether/ethyl acetate 1:2, silica gel) as a yellow foam (320 mg,
91%) with m.p. 1158C after drying in vacuo at 758C at 0.2 mbar; IR (film):
nÄ ˆ 3047 (w), 2971 (w), 2829 (w), 2735(w), 1701 (s), 1601 (s), 1565(m), 1509
(w), 1413 (w), 1388 (w), 1361 (w), 1306 (m), 1285(w), 1210 (s), 1170 (s),
1127 (w), 1104 (w), 1079 (w), 1015(w), 846 (s), 752 (w), 736 (w), 710 (w),
513 cmÀ1 (w); UV/Vis (acetonitrile): lmax (lg e) ˆ 374 (4.22), 291 (4.38, sh),
256 (4.66), 198 nm (4.93); 1H NMR: d ˆ 5.35 (s, 1H, C5H), 7.11 (ªdº, ªJº ˆ
8.3 Hz, 4H), 7.21 (ªdº, ªJº ˆ 8.1 Hz, 4H), 7.39 (ªdº, ªJº ˆ 8.1 Hz, 2H), 7.60
(ªdº, ªJº ˆ 8.3 Hz, 4H), 7.73 (ªdº, ªJº ˆ 8.3 Hz, 4H), 7.76 (ªdº, ªJº ˆ
‡
(%): 1041(1.9) [M] , 936 (2.7), 827 (11), 723 (25), 618 (21), 515 (10), 361
(16), 106 (100); elemental analysis calcd (%) for C75H71N5 (1042.4): C 86.42,
H 6.87, N 6.72; found C 86.37, H 6.85, N 6.63.
Palladium-catalyzed cross-coupling reactions of aryl halides (2) with
substituted or annelated cyclopentadienes; typical example: 1-(4-anisyl)-
2,5-di(4-chlorophenyl)-3,4-diphenylcyclopentadiene (12b): A mixture of
1-(4-anisyl)-3,4-diphenylcyclopentadiene (11b, synthesized by an analo-
gous procedure to that in ref. [21], 649 mg, 2.00 mmol), 4-chlorobromo-
benzene (2q) (575 mg,3.00 mmol), Cs2CO3 (2.61 g, 8.00 mmol), [Pd(OAc)2]
(11 mg, 50 mmol), and tri-tert-butylphosphine(39.1 mg, 200 mmol) in DMF
(10 mL) was heated under argon in a screw-cap tube for 68 h at 1408C.
After cooling to room temperature CH2Cl2 (30 mL) was added and the
mixture was filtered through silica gel (5g) with CH 2Cl2 (50 mL) as eluent.
The solvent was evaporated at 508C and 15mbar, the residue was
subsequently dried in vacuo at 508C and 0.5mbar and finally separated
by flash chromatography on silica gel. Thin-layer chromatography: Rf ˆ
0.51 (4,4'-dichlorobiphenyl), 0.31 ± 0.29 (silica, petroleum ether/ethyl
acetate 25:1). The fraction with Rf ˆ 0.31 ± 0.29 was isolated to give 12b
(533 mg, 49%, mixture of three double bond isomers) as a yellow solid.
M.p. 90 ± 958C; IR (KBr): nÄ ˆ 3060 (w), 2952 (w), 1606 (w), 1508 (s), 1487
(s), 1289 (w), 1249 (s), 1177 (m), 1091 (m), 1032 (w), 1014 (w), 830 (m),
698 cmÀ1 (s); UV/Vis (acetonitrile): lmax (lg e) ˆ 344 (4.08), 277 (4.24, sh),
8.2 Hz, 2H), 9.85(s, 2H), 9.90 (s, 1H), 9.95(s, 2H);
13C NMR: d ˆ
62.85(d, C5H), 128.86, 129.34, 129.60, 129.80, 130.46, 130.61 (all d),
135.05, 135.54, 135.72, 140.17, 140.71, 143.14, 145.06, 147.63 (all s), 191.34
(s), 191.50 (s), one d is superimposed; MS (70 eV, 3258C): m/z (%) ˆ 588
‡
‡
‡
(11) [M‡2] , 587 (44) [M‡1] , 586 (100) [M] , 762 (18), 734 (12); HRMS:
calcd for C40H26O5 586.17803; found: 586.17980.
1,2,3,4,5-Penta(4-acetylphenyl)-1,3-cyclopentadiene (9b): Dioxolane 7b
(1.46 g, 6.00 mmol) was coupled with cyclopentadiene (3) according to
the general procedure; for detailed reaction conditions see Scheme 2. After
acidic workup the reaction directly led to the unprotected pentaarylketone
9b. Thin-layer chromatography of the crude product: Rf ˆ 0.83, 0.67, 0.36
(9b), 0.17, 0.06 (petroleum ether/ethyl acetate 1:2, silica gel). The products
were separated by flash chromatography (petroleum ether/ethyl acetate
1:2, silica gel). Biphenyl and unreacted dioxolane 7b were found only in
marginal amounts as these compounds were removed during the drying of
the product mixture in vacuo. The fraction with Rf ˆ 0.36 was isolated by
flash chromatography to yield pentaarylcyclopentadiene 9b as a yellow
solid (449 mg, 68%) after drying in vacuo at 1008C at 0.5mbar, its NMR
spectroscopic data matched published data.[7d] 1H NMR: d ˆ 2.47 (s, 6H),
2.51 (s, 3H) 2.55 (s, 6H), 5.31 (s, 1H, C5H), 7.04 (ªdº, ªJº ˆ 8.6 Hz, 4H), 7.14
(ªdº, ªJº ˆ 8.6 Hz, 4H), 7.31 (ªdº, ªJº ˆ 8.5Hz, 2H), 7.65 (ªdº, ª Jº ˆ
8.6 Hz, 4H), 7.79 (ªdº, ªJº ˆ 8.5Hz, 4H), 7.81 (ªdº, ª Jº ˆ 8.5Hz, 2H);
13C NMR: d ˆ 26.38(q), 26.40 (q), 26.48 (q), 62.42 (d, C5H), 128.11, 128.33,
128.38, 128.86, 129.09, 129.99 (all d), 135.47, 136.02, 136.14, 139.11, 139.71,
142.08, 144.74, 147.27 (all s), 197.31 (s), 197.49 (s), one s is superimposed.
1
250 (4.37, sh), 226 nm (4.47, sh); H NMR: d ˆ 3.69, 3.72 and 3.76 (s, 3H,
OCH3), 4.94, 4.98 and 5.00 (s, 1H, C5H), 6.60 ± 6.70 (m, 2H), 6.84 ± 7.16 (m,
‡
‡
20H); MS (70 eV; 2508C); m/z (%): 548 (19) [M‡4] , 547 (33) [M‡3] , 5 46
‡
‡
‡
(78) [M‡2] , 545 (51) [M‡1] , 544 (100) [M] ; elemental analysis calcd
(%) for C36H26Cl2O (545.5): C 79.26, H 4.80; found C 79.18, H 4.75.
2,5-Di(4-chlorophenyl)-1,3,4-triphenyl-1,3-cyclopentadiene (12a, mixture
of double bond isomers): M.p. 104 ± 1088C; 1H NMR: d ˆ 4.99 ± 5.04
‡
(m, 1H), 6.86 ± 7.19 (m, 23H); MS: m/z (%): 514, 516 [M] ; elemental
analysis calcd (%) for C35H24Cl2 (515.48): C 81.55, H 4.69; found C 81.35,
H 4.76.
1,2,3,4,5-Penta(4-(N-4-methylphenyl)aminomethylphenyl)-1,3-cyclopenta-
diene (10): A mixture of pentaaldehyde 9a (58 mg, 0.10 mmol), p-toluidine
(161 mg, 1.50 mmol) and p-TosOH monohydrate (5.0 mg, 30 mmol) in dry
benzene (20 mL) was refluxed for 15h with a Dean-Stark trap. After
filtration through celite (2 g) with dry dichloromethane (30 mL) as eluent
the solvent was removed in vacuo. The residue was treated at 1008C and
0.3 mbar to remove excess p-toluidine by sublimation. The remaining crude
product, an orange-red solid (110 mg), was identified by NMR spectros-
copy as slightly impure pentakisimine; 1H NMR: d ˆ 2.33 (s , 6H), 2.34 (s ,
1-(4-Anisyl)-2,5-di(4-(1,3-dioxolan-2-yl)phenyl)-3,4-diphenylcyclopenta-
diene (12c, mixture of double bond isomers): M.p. 80 ± 838C; 1H NMR:
d ˆ 3.66, 3.70 and 3.73 (s, 3H, OCH3), 3.95± 4.11 (m, 8H, O-C H2CH2-O),
5.02, 5.05 and 5.08 (s, 1H, C5H), 5.62, 5.66 and 5.70 (s, 1H, O-CH-O), 6.56 ±
6.65(m, 2H, o-Ansiyl-H), 7.29 ± 6.85(m, 20H); MS: m/z (%): 622 (11), 621
‡
‡
(46) [M‡1] , 620 (100) [M] ; elemental analysis calcd (%) for C42H36O5
(620.74): C 81.27, H 5.85; found C 81.19 H 5.92.
3432
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3432 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 18

Arylation of Cyclopentadienes
3426±3433
1,4-Di(4-chlorophenyl)-2,3,5-tri(3,5-dimethylphenyl)-1,3-cyclopentadiene
(12d, mixture of double bond isomers): M.p. 172 ± 1758C; 1H NMR: d ˆ
1.90 ± 2.24 (m, 18H), 4.99 ± 5.02 (m, 1H), 6.50 ± 7.27 (m, 17H); MS: m/z
Chem. 1995, 34, 1288 ± 1291; d) S. Barry, A. Kucht, H. Kucht, M. D.
Rausch, J. Organomet. Chem. 1995, 489, 195± 199; e) I. Kuksis, M. C.
Baird, Organometallics 1996, 15, 4755 ± 4762; f) D. J. Hammack,
M. M. Dillard, M. P. Castellani, A. L. Rheingold, A. L. Rieger, P. H.
‡
(%): 589, 600 [M] ; elemental analysis calcd (%) for C41H36Cl2 (599.64): C
Â
82.12, H 6.05; found C 82.00, H 6.47.
Rieger, Organometallics 1996, 15, 4791 ± 4797; g) I. Kuksis, I. Kovacs,
1,1,3-Triphenylindene (15a): M.p. 134 ± 1358C (Lit.: 132 ± 1348C[24]);
1H NMR: d ˆ 6.82 (s, 1H), 7.20 ± 7.32 (m, 13H), 7.35± 7.46 (m, 3H), 7.56
(d, J ˆ 7.3 Hz, 1H), 7.64 (d, J ˆ 7.1 Hz, 2H); 13C NMR: d ˆ 65.62, 121.22,
125.57, 125.71, 126.55, 126.82, 127.61, 127.72, 128.17, 128.42, 135.12, 141.47,
M. C. Baird, K. F. Preston, Organometallics 1996, 15, 4991 ± 5002;
h) C. Janiak, R. Weimann, F. Görlitz, Organometallics 1997, 16, 4933 ±
4936.
[6] A. M. Bond, R. Colton, D. A. Fiedler, L. D. Field, D. Leslie, T. He,
P. A. Humphery, C. M. Lindall, F. Marken, A. F. Masters, H.
Schumann, K. Suehring, V. Tedesco, Organometallics 1997, 16,
2787 ± 2797.
[7] a) W. Broser, P. Siegle, H. Kurreck, Chem. Ber. 1968, 101, 69 ± 83;
b) L. D. Field, K. M. Ho, C. M. Lindall, A. F. Masters, A. G. Webb,
Aust. J. Chem. 1990, 43, 281 ± 291; c) T. R. Jack, C. J. May, J. Powell, J.
Am. Chem. Soc. 1977, 99, 4707 ± 4716; d) H. Schumann, H. Kucht, A.
Kucht, Z. Naturforsch. B 1992, 47, 1281 ± 1289; e) R. H. Lowack,
K. P. C. Vollhardt, J. Organomet. Chem. 1994, 476, 25± 32.
[8] L. F. Tietze, U. Beifuss, Angew. Chem. 1993, 105, 137 ± 170; Angew.
Chem. Int. Ed. Engl. 1993, 32, 131 ± 163.
‡
142.28, 143.54, 150.94; MS: m/z (%): 344 [M] .
1,1,3-Tri(4-methylphenyl)indene (15b): M.p. 63 ± 648C; 1H NMR: d ˆ 2.30
(s, 6H), 2.40 (s, 3H), 6.75(s, 1H), 7.04 (d, J ˆ 8.1 Hz, 4H), 7.17 (d, J ˆ
8.1 Hz, 4H), 7.20 ± 7.29 (m, 4H), 7.37 (d, J ˆ 7.3 Hz, 1H), 7.52 ± 7.54 (m, 3H);
13C NMR: d ˆ 21.13, 21.43, 64.88, 121.13, 125.37, 125.55, 126.62, 127.48,
127.59, 128.81, 129.05, 132.33, 135.98, 137.40, 140.72, 141.23, 141.78, 142.39,
‡
151.33; MS: m/z (%): 386 [M] ; elemental analysis calcd (%) for C30H26
(386.53): C 93.22, H 6.78; found C 92.83, H 6.81.
1,1,3-Tri(4-methoxyphenyl)indene (15 f): M.p. 708C; 1H NMR: d ˆ 3.75(s,
6H), 3.85 (s, 3H), 6.71 (s, 1H), 6.75± 6.79 (m, 4H), 6.95± 6.99 (m, 2H),
7.18 ± 7.37 (m, 8H), 7.52 ± 7.59 (m, 3H); 13C NMR: d ˆ 55.22, 55.35, 64.07,
113.64, 113.99, 121.23, 125.44, 125.68, 126.77, 127.92, 128.84, 128.91, 136.01,
[9] M. Miura, S. Pivsa-Art, G. Dyker, J. Heiermann, T. Satoh, M. Nomura,
Chem. Commun. 1998, 1889 ± 1890.
‡
141.06, 141.31, 142.56, 151.87, 158.33, 159.36; MS: m/z (%): 434 [M] ;
[10] For
a related reaction of iodocyclopentadienyl complexes with
elemental analysis calcd (%) for C30H26O3 (434.53): C82.92, H 6.03; found
C 82.82, H 6.01.
tributyl(cyclopentadienyl)stannane to give a mixture of 1,2,4,5- and
1,1,2,4-substituted cyclopentadienes, see: R. Boese, G. Bräunlich, J.-P.
Gottenland, J.-T. Hwang, C. Troll, K. P. C. Vollhardt, Angew. Chem.
1996, 108, 1100 ± 1102; Angew. Chem.,Int. Ed. Engl. 1996, 35, 995±
998.
1,1,3-Tri(3,5-dimethylphenyl)indene (15n): M.p. 145± 146 8C; 1H NMR:
d ˆ 2.22 (s, 12H), 2.37 (s, 6H), 6.76 (s, 1H), 6.85± 6.87 (m, 5H), 7.01 (s, 1H),
7.20 ± 7.31 (m, 4H), 7.39 (d, J ˆ 7.3 Hz, 1H), 7.55 (d, J ˆ 7.6 Hz, 1H);
13C NMR: d ˆ 21.51, 21.60, 65.37, 121.15, 125.39, 125.50, 125.56, 126.52,
128.18, 129.29, 135.19, 137.38, 137.87, 141.70, 141.83, 142.41, 143.65, 151.11;
[11] G. Dyker, J. Org. Chem. 1993, 58, 234 ± 238.
[12] W. A. Herrmann, C. Brossmer, C.-P. Reisinger, T. H. Riermeier, K.
Öffele, M. Beller, Chem. Eur. J. 1997, 3, 1357 ± 1364, and references
cited therein.
‡
MS: m/z (%): 428 [M] ; elemental analysis calcd (%) for C33H32 (428.61): C
92.47, H 7.53, found C 92.22, H 7.53.
1,3-Di(4-methylphenyl)-2-phenylindene (17b): M.p. 146 ± 1478C; 1H NMR:
d ˆ 2.23 (s, 3H), 2.40 (s, 3H), 5.06 (s, 1H), 6.97 ± 7.08 (m, 7H), 7.11 ± 7.16 (m,
3H), 7.20 ± 7.31 (m, 7H); 13C NMR: d ˆ 21.23, 21.53, 57.64, 120.34, 123.67,
125.44, 126.38, 126.60, 127.63, 127.85, 129.15, 129.21, 129.24, 132.39, 135.57,
135.83, 136.54, 136.86, 140.42, 144.88, 145.12, 148.18; MS: m/z (%): 372
[13] For a review on sterically hindered phosphines, see: V. V. Grushin, H.
Alper, Chem. Rev. 1994, 94, 1047 ± 1062, and references cited therein.
[14] The use of tert-butylphosphine in other palladium-catalyzed reactions
of aryl bromides and chlorides: amination a) M. Nishiyama, T.
Yamamoto, Y. Koie, Tetrahedron Lett. 1998, 39, 617 ± 620; b) T.
Yamamoto, M. Nishiyama, Y. Koie, Tetrahedron Lett. 1998, 39, 2367 ±
2370; Suzuki coupling: c) A. F. Littke, G. C. Fu., Angew. Chem. 1998,
110, 3586 ± 3587; Angew. Chem. Int. Ed. Engl., 1998, 37, 3387 ± 3388;
Heck reaction: d) A. F. Littke, G. C. Fu., J. Org. Chem. 1999, 64, 10 ±
11; aryloxylation: e) G. Mann, C. Incarvito, A. L. Rheingold, J. F.
Hartwig, J. Am. Chem. Soc. 1999, 121, 3224 ± 3225.
‡
[M] ; elemental analysis calcd (%) for C29H24 (372.50): C 93.51, H 6.49;
found C 93.43, H 6.39.
Acknowledgement
[15] R. Willem, A. Jans, C. Hoogzand, M. Gielen, G. V. Binst, H.
Pepermans, J. Am. Chem. Soc. 1985, 107, 28 ± 32.
Financial support by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie as well as a generous donation of palladium
acetate by the Degussa AG are gratefully acknowledged. A part of this
work was also supported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, Sports, and Culture of Japan.
[16] a) H. Horino, M. Arai, N. Inoue, Bull. Chem. Soc. Jpn. 1974, 47, 1683 ±
1686; b) R. F. Heck, J. Am. Chem. Soc. 1968, 90, 5518 ± 5526.
[17] a) O. Reiser, M. Weber, A. de Meijere, Angew. Chem. 1989, 101,
1071 ± 1072; Angew. Chem. Int. Ed. Engl. 1989, 28, 1037 ± 1038; b) M.
Weber, Ph.D. Dissertation, Hamburg, 1992.
[18] F. G. Bordwell, Acc. Chem. Res. 1988, 21, 456 ± 463.
[19] For exchange of cyclopentadienyl ligands, see: Comprehensive
Organometallic Chemistry, Vol. 8 (Eds.: G. Wilkinson, F. G. A. Stone,
E. W. Abel), Pergamon, Oxford, 1982, p. 1048.
[20] K. Sekiguchi, A. Sera, Y. Otsuki, K. Maruyama, Bull. Chem. Soc. Jpn.
1975, 48, 4090 ± 4094.
[1] M. S. Vollmer, F. Würthner, F. Effenberger, P. Emele, D. U. Meyer, T.
Stümpfig, H. Port, H. C. Wolf, Chem. Eur. J. 1998, 4, 260 ± 269, and
references cited therein.
[2] ª Chemistry for the 21st Centuryº in Molecular Electronics (Eds.: J.
Jortner, M. Ratner), Blackwell Science, Oxford, 1997.
[3] Expanded,Contracted and Isomeric Porphyrins (Eds.: J. L. Sessler,
S. J. Weghorn), Elsevier, 1997, .
[21] B. H. Freeman, J. M. F. Gagan, D. Lloyd, Tetrahedron 1973, 29, 4307 ±
4312.
[4] a) C. Adachi, T. Tsuji, S. Saito, Appl. Phys. Lett. 1990, 56, 799 ± 801;
b) Y. Ohmori, Y. Hironaka, M. Yoshida, N. Tada, A. Fujii, K. Yoshino,
Synth. Metal 1997, 85, 1241 ± 1242.
[22] S. S. Hirsch, W. J. Bailey, J. Org. Chem. 1978, 43, 4090 ± 4094.
[23] A. Jutand, A. Mosleh, J. Org. Chem. 1997, 62, 261 ± 274.
[24] C. F. Koelsch, P. R. Johnson, J. Am. Chem. Soc. 1943, 65, 567 ± 573.
[5] a) C. Janiak, H. Schumann, Adv. Organomet. Chem. 1991, 33, 291 ±
393; b) J. Okuda, Topics Curr. Chem. 1991, 160, 97 ± 145; c) D. Matt,
M. Huhn, M. Bonnet, I. Tkatchenko, U. Englert, W. Kläui, Inorg.
Received: January 14, 2000 [F2239]
Chem. Eur. J. 2000, 6, No. 18
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0618-3433 $ 17.50+.50/0
3433