An unprecedented dimerization of 1,2,3-butatriene catalyzed by palladium complexes

Article abstract of DOI:10.1246/cl.2004.1466

Dehydrogenative dimerization of (Z)-1,4-bis(trimethylsilyl)-l,2,3- butatriene was catalyzed by Pd complexes in the presence of allyl halides to give predominantly an acyclic conjugated enyne, while addition of methylaluminoxane (MAO) instead of allyl hali

Full text of DOI:10.1246/cl.2004.1466

1
466
Chemistry Letters Vol.33, No.11 (2004)
An Unprecedented Dimerization of 1,2,3-Butatriene Catalyzed by Palladium Complexes
ꢀ
y
y
y
y
Noriyuki Suzuki, Hidekazu Tezuka, Yoshiyuki Fukuda, Hajime Yoshida, Masakazu Iwasaki,
#
y
y
Masahiko Saburi, Meguru Tezuka, Teiji Chihara, and Yasuo Wakatsuki
RIKEN, Wako, Saitama 351-0198
Department of Applied Chemistry, Faculty of Engineering, Saitama Institute of Technology, Okabe, Saitama 369-0293
y
(Received August 20, 2004; CL-040987)
Dehydrogenative dimerization of (Z)-1,4-bis(trimethylsil-
mide, to our surprise, a conjugated acyclic enyne 2 was predom-
inantly obtained accompanied by a small amount (typically 3–
5%) of 3, 4, and 5 (Figure 1). Although the reaction has not been
optimized yet, the yield amounted to 44% (isol.) when it was
conducted in THF at 120 C for 19 h. The starting material 1 dis-
appeared at this stage.
yl)-1,2,3-butatriene was catalyzed by Pd complexes in the pres-
ence of allyl halides to give predominantly an acyclic conjugated
enyne, while addition of methylaluminoxane (MAO) instead of
allyl halides produced an unprecedented dimer that has an alkyn-
yl-substituted cyclopentadienyl structure.
ꢁ
Selected bond lengths (Å)
and angles (deg):
1
,2,3-Butatrienes, which are examples of cumulative unsat-
Si1*
Si2
urated hydrocarbons, have attracted organometallic chemists be-
cause of their varying reactivities towards transition-metal com-
C1-C2
C2-C3
C3-C3*
C3-C4
1.194(3)
1.450(3)
1.505(4)
1.339(3)
C4
C3
C1*
1
C2*
C3*
C4*
plexes. For example, we recently reported that 1,4-disubstitut-
2
C2
C1
Si1-C1-C2 177.6(3)
C1-C2-C3 178.0(3)
C2-C3-C3* 115.8(3)
C2-C3-C4 120.4(2)
C3*-C3-C4 123.7(3)
Si2-C4-C3 127.5(2)
2
ed-1,2,3-butatrienes form ꢀ -ꢁ-complexes with Rh, while they
form a 1-metallacyclopent-3-yne compound with a zirconocene
Si1
Si2*
3
unit. There have also been some examples of transition metal-
catalyzed reactions in which 1,2,3-butatrienes are involved. Iyo-
da reported Ni-catalyzed cyclodimerization and cyclotrimeriza-
Figure 2. Molecular structure of 2. Drawn with 50% probabil-
ity. Hydrogen atoms are in part omitted for clarity.
4
tion of 1,2,3-butatrienes that give radialene compounds. Rh-cat-
2
,5
alyzed hydrosilation of butatriene has also been reported.
However, transition metal-catalyzed C–C bond formation reac-
tions of 1,2,3-butatrienes are still rare.
The dimer 2 was fully characterized by NMR and mass
spectrometry, and its structure was confirmed by X-ray analysis
(Figure 2). Besides allyl bromide, allyl chloride (Y. 38%) and
methallyl chloride (Y. 34%) were also effective. Benzyl bromide
gave 2 in 14% yield, but the formation of numerous by-products
was observed. Employing normal alkenes such as 1-hexene, in
place of allyl halides, resulted in a low yield and selectivity.
It is to be emphasized that the reaction is dehydrogenative
dimerization of butatriene. Pd-catalyzed dimerization of 1,3-
diynes producing (E)-1,2-divinyl-1,2-diethynylethene has been
8
One of the authors recently reported the efficient synthesis
of (Z)-1,4-bis(trimethylsilyl)-1,2,3-butatriene (1) using a Ru cat-
6
alyst. Because a trimethylsilyl group can be transformed into
various functional groups, compound 1 is potentially useful.
Thus, the development of carbon–carbon bond forming reaction
using 1 is intriguing. Herein we wish to describe the unprece-
dented dimerization reactions of 1 catalyzed by palladium com-
plexes.7
9
reported, in which the products lose no hydrogens overall.
5
mol% Pd(PPh3)4
X
Me3Si
SiMe3
There must be a compound that accepts hydrogen atoms in this
reaction system. Allyl bromide decreased with an increase of 2.
The formation of propyl bromide, however, was not observed by
GC. Taking account of the moderate yield of 2 and the formation
of 4, a proportion of 1 might accept hydrogen atoms. The low
yield of 4 may be rationalized by the formation of polymeric
products. GPC analysis showed that the reaction mixture con-
tained polymers whose molecular weight was in 800–4200
(Mw) range.
Me3Si
H
SiMe3
H
C
C
C
C
in THF
Me3Si
Me3Si
SiMe3
1
120 °C, 3-19 h
2
SiMe3
SiMe3
SiMe3
Me3Si
Me3Si
3
4
5
Although details of the reaction pathway are still vague, a
plausible mechanism is as follows: the formation of palladacy-
Figure 1. Dehydrogenative dimerization of 1 catalyzed by Pd
in the presence of allyl halides and the minor products.
1
0
cle and subsequent double ꢂ-hydrogen elimination results in
liberation of 2 (Scheme 1). The role of allyl bromide is still a
puzzle. Since a small amount of propylene was detected by
GC (ca. 1–3%), it might at first form a ꢁ-allylpalladium species.
Indeed, using [(ꢁ-allyl)PdCl]2 as a catalyst produced 2 in 20%
yield although the selectivity was not excellent. When catalytic
amount (0.1 equiv.) of allyl bromide was used, 2 was obtained in
8% yield. In the presence of CuCl2, 2 was not obtained at all. Ad-
dition of NEt3 retarded the reaction. The reaction from 3, which
The reaction of 1 and a catalytic amount of Pd(PPh3)4 in a
THF solution, with no additives, gave a mixture of unidentified
products, although the starting material was consumed. Judging
from gas chromatogram (GC) and mass spectrum, it is likely that
some of the products consisted of dimeric compounds of 1, albeit
in low yields.
Therefore, we investigated the effect of additives. When a
reaction was carried out in the presence of one equiv of allyl bro-
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.11 (2004)
1467
is an isomer of 1, under the same conditions did not give 2. Thus,
the possibility that 1 initially isomerized to 3 and was then in-
volved in the reaction to give 2 is ruled out. It is noteworthy that
using allyl esters instead of allyl halide predominantly gave the
allylated product 5 in ca. 30% yield. The reaction using (Z)-
(or ꢂ-Si elimination–reinsertion) occurs, and intramolecular car-
bopalladation on the alkenyl silane results in a five-membered
ring. An example of the 1,2-shift of silicon and a transition metal
around a double bond has been reported, although it would be
uncommon. The butatriene with tert-butyl groups, (Z)-2,2,7,7-
tetramethylocta-3,4,5-triene, did not give cyclopentadienyl com-
pounds under the same conditions.
1
2
2,2,7,7-tetramethylocta-3,4,5-triene, [(Z)-t-Bu-CH=C=C=CH-
t-Bu], under the same conditions gave a mixture of products
6b
in low yields. GC-MS analysis showed that a few of the products
þ
Both dimeric products 2 and 6 have ꢁ-conjugated enyne
structures, and are of interest as building blocks for electronic
and optical materials as well as ligands for organometallics.
had M ¼ 328 (164 ꢂ 2), and no dehydrogenated dimers were
found.
6
1
Pd0
The authors thank Dr. M. Nishiura (RIKEN) for X-ray dif-
fraction studies. This work was financially supported by Yamada
Science Foundation, the Ministry of Education, Culture, Sports,
Science, and Technology of Japan (Grant-in-Aid for Scientific
Research, C: No. 15550059), and SORST program of Japan
Science and Technology (JST).
H
Me3Si
SiMe3
SiMe3
Pd
Pd
Me3Si
Me3Si
H2] + Pd0
[
Me3Si
H
H
SiMe3
SiMe3
References and Notes
Present address: Department of Chemistry, College of Humanities
and Sciences, Nihon University, Sakurajosui, Setagaya-ku, Tokyo
2
#
SiMe3
Me Si
SiMe3
3
Me3Si
Me3Si
Pd
1
56-8550, Japan. E-mail: waky@chs.nihon-u.ac.jp
Pd
H
1
For example, see a) A. Nakamura, P.-J. Kim, and N. Hagihara, J.
Organomet. Chem., 3, 7 (1965). b) D. Bright and O. S. Mills, J. Chem.
Soc. A, 1966, 594. c) U. Schubert and J. Gr o¨ nen, Organometallics, 6,
2459 (1987). d) A. Maercker and A. Groos, Angew. Chem., Int. Ed.
Engl., 35, 210 (1996). e) L. Stehling and G. Wilke, Angew. Chem.,
Int. Ed. Engl., 27, 571 (1988).
SiMe3
Me3Si
H
SiMe3
SiMe3
MAO
SiMe3
Me3Si
Me3Si
SiMe3
Me3Si
2
3
N. Suzuki, Y. Fukuda, C.-E. Kim, H. Takahara, M. Iwasaki, M. Saburi,
M. Nishiura, and Y. Wakatsuki, Chem. Lett., 32, 16 (2003).
a) N. Suzuki, M. Nishiura, and Y. Wakatsuki, Science, 295, 660
SiMe3
Pd
SiMe3
Pd
H
Me3Si
(
2002). b) N. Suzuki, N. Aihara, H. Takahara, T. Watanabe, M.
Me3Si
Me3Si
Iwasaki, M. Saburi, D. Hashizume, and T. Chihara, J. Am. Chem.
Soc., 126, 60 (2004).
Al
SiMe3
4
a) M. Iyoda, S. Tanaka, M. Nose, and M. Oda, J. Chem. Soc., Chem.
Commun., 1983, 1058. b) M. Iyoda, S. Tanaka, H. Otani, M. Nose,
and M. Oda, J. Am. Chem. Soc., 110, 8494 (1988). c) M. Iyoda, Y.
Kuwatani, M. Oda, Y. Kai, N. Kaneshisa, and N. Kasai, Angew. Chem.,
Int. Ed. Engl., 29, 1062 (1990).
Pd
H Al
Scheme 1. Plausible mechanism for dimerization of 1.
5
6
T. Kusumoto and T. Hiyama, Bull. Chem. Soc. Jpn., 63, 3103 (1990).
a) Y. Wakatsuki, H. Yamazaki, N. Kumegawa, and P. S. Johar,
Bull. Chem. Soc. Jpn., 66, 987 (1993). b) Y. Wakatsuki, H. Yamazaki,
N. Kumegwa, T. Satoh, and J. Y. Satoh, J. Am. Chem. Soc., 113, 9604
8
SiMe3
1
mol% Pd(PPh3)4
Me3Si
7
Me3Si
H
SiMe3
H
5
1
2
1
eq MAO
4
3
C
C C C
in toluene
(
1991).
1
70 °C, 20 h
Me3Si
SiMe3
6
7
8
For examples of Pd-catalyzed reactions of allenes, a) M. Arisawa,
T. Sugihara, and M. Yamaguchi, Chem. Commun., 1998, 2615.
b) R. Zimmer, C. U. Dinesh, E. Nandanan, and F. A. Khan, Chem.
Rev., 100, 3067 (2000). References therein.
6
: 60% (33% isol.)
Figure 3. Pd-catalyzed dimerization of 1 in the presence of
MAO.
1
2. H NMR (CDCl3): ꢃ 0.14 (s, 18H), 0.15 (s, 18H), 6.69 (s, 2H).
1
3
C NMR (CDCl3): ꢃ ꢃ1:23, ꢃ0:24, 101.79, 102.34, 136.49, 141.27.
The result above prompted us to study further the possibility
of dimerization reaction of 1. Methylaluminoxane (MAO) is
well known as an activator in olefin polymerization. It reacts
with catalyst precursors to form and stabilize cationic species
in the reaction system. When 1 was reacted in the presence of
catalytic amount of Pd(PPh3)4 and MAO that contained one
equiv of Al atoms, the cyclopentadienyl compound 6 was pre-
dominantly obtained in moderate yield (60%, Figure 3). The
HRMS Calcd for C20H38Si4 390.2051, Found 390.2057. Crystal Data:
C20H38Si4, Mr ¼ 390:86, triclinic, a ¼ 6:212ð1Þ, b ¼ 10:747ð3Þ, c ¼
1:430ð3Þ Aꢀ , ꢄ ¼ 109:947ð4Þ, ꢂ ¼ 97:206ð5Þ, ꢅ ¼ 99:890ð4Þ , V ¼
ꢁ
1
6
92:6ð3Þ Aꢀ , P1 (# 2), Z ¼ 1, R1 ¼ 0:055, wR ¼ 0:133, GOF ¼ 0:90.
3
ꢁ
The crystallographic data have been deposited (CCDC 242990).
D. H. Camacho, S. Saito, and Y. Yamamoto, J. Am. Chem. Soc., 124,
924 (2002).
9
10 Although it seems sterically crowded, it may be possible taking
account of the formation of a Rh-(Z)-1 complex. See Ref. 2.
11 6. H NMR (CDCl3): ꢃ 0.00 (s, 9H), 0.02 (s, 9H), 0.18 (s, 18H), 2.15 (d,
1
1
13
29
structure of 6 was fully characterized by H, C and Si NMR,
1
J ¼ 13 Hz, 1H, CH2), 2.19 (d, J ¼ 13 Hz, 1H, CH2), 3.41 (br, 1H, CH),
1
HMQC, and HMBC. All of the C–Si bonds were confirmed by
13
6
.57 (br, 1H, CH). C NMR (CDCl3): ꢃ ꢃ1:94, 0.34, 0.38, 0.50, 20.93
1
CSi CH 2 CSi CH
29
13
1
the Si satellites observed in C NMR. It is surprising that 6 has
a Me3Si group at the 2-position instead of the 1-position. The re-
action path of this dimerization is thus more puzzling. One pos-
sible route is proposed in Scheme 1. After a ꢂ-hydrogen elimi-
nation from the palladacycle, MAO reacts with Pd–H to form
cationic species. The 1,2-shift of silicon and palladium atoms
( J ¼ 47 Hz, J ¼ 119:3 Hz, CH ), 56.10 ( J ¼ 34 Hz, J
¼
1
2
135:8 Hz, CH), 99.92 (q, JCSi ¼ 87 Hz), 104.88 (q, JCSi ¼ 17 Hz),
2
9
1
19.84 (q), 145.45 (q), 146.08 (CH), 154.92 (q). Si NMR (C6D6): ꢃ
ꢃ19:0, ꢃ10:0, 3.5, 5.0. HRMS Calcd. for C20H40Si4 392.2207, Found
92.2212.
3
1
2
Z. Xi, R. Fischer, R. Hara, W. Sun, Y. Obora, N. Suzuki, K. Nakajima,
and T. Takahashi, J. Am. Chem. Soc., 119, 12842 (1997).
Published on the web (Advance View) October 16, 2004; DOI 10.1246/cl.2004.1466