Selective dimerization of aryl-substituted terminal alkynes on bis(indenyl)zirconocene derivatives

Article abstract of DOI:10.1246/cl.2011.1443

Dimerization of aryl-substituted terminal alkynes on indenyl zirconium complexes occurred in a selective way. 1,4-Aryl-1,3-diene derivatives were formed exclusively after hydrolysis. It is in sharp contrast to the reaction on [Cp₂Zr] complexes.

Full text of DOI:10.1246/cl.2011.1443

doi:10.1246/cl.2011.1443
Published on the web December 5, 2011
1443
Selective Dimerization of Aryl-substituted Terminal Alkynes
on Bis(indenyl)zirconocene Derivatives
Shenyong Ren,1,2,3 Takashi Seki,4 David Necas,1,2,3 Hiroyuki Shimizu,5 Kiyohiko Nakajima,6
Ken-ichiro Kanno,1,2,3 Zhiying Song,1,2,3 and Tamotsu Takahashi*1,2,3
1Catalysis Research Center, Hokkaido University, Kita-ku, Sapporo, Hokkaido 001-0021
2Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-0812
3SORST, Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo 102-0075
4JX Nippon Oil & Energy Corporation, Naka-ku, Yokohama, Kanagawa 231-0815
5Japan Polyethylene Corporation, Kawasaki-ku, Kawasaki, Kanagawa 210-0865
6Department of Chemistry, Aichi University of Education, Igaya, Kariya, Aichi 448-8542
(Received July 11, 2011; CL-110587; E-mail: tamotsu@cat.hokudai.ac.jp)
Dimerization of aryl-substituted terminal alkynes on indenyl
zirconium complexes occurred in a selective way. 1,4-Aryl-1,3-
diene derivatives were formed exclusively after hydrolysis. It is
in sharp contrast to the reaction on [Cp2Zr] complexes.
However, when we used [(Ind)3ZrH] (9) for dimerization of
phenylacetylene, we found that ¡,¡¤-metallacyclopentadiene
with indenyl ligand 10 was selectively formed. In addition,
[(Ind)2Zr(CO)2] (11) also showed the same selectivity for the
dimerization of phenylacetylene.
Zirconium indenyl complex, [(Ind)3ZrH] (9) was prepared
by the reaction of [(Ind)2ZrBu2] and an excess of indene as
shown in eq 3.
Dimerization of aryl-substituted terminal alkynes 1 on low
valent transition metal to metallacyclopentadienes is attractive
since these metallacycles can be converted into various
functionalized 1,3-dienes or substituted arenes.1 However,
formally there are three possible regioisomers 2 (¡,¡-diaryl),
3 (¡,¢-diaryl), and 4 (¢,¢-diaryl) as shown in eq 1, because of
the orientations of two terminal alkynes for combining on the
metal. And in most cases the ¡,¢-diaryl isomer 3 was the major
one,1a,1c,1j,1k to avoid the steric problems. Therefore, the ¢,¢-
diaryl isomer 4 and ¡,¡-diaryl isomer 2 are relatively rare. Only
one example has been shown for the selective dimerization of
phenyl acetylene to ¡,¡¤-metallacyclopentadiene 2, in the case
of titanium using pyridinediamide ligand with 2,6-dimethyl-
phenyl substituents on the imide nitrogen.1c
2 n-BuLi
excess indene
[(Ind)2ZrBu2]
ð3Þ
[(Ind)2ZrCl2]
[(Ind)3ZrH]
9
The complex 9 was prepared as pale-yellow powder in 64%
yield. The structure of 9 was determined by X-ray analysis and
its structure is shown in Figure 1.5 Three indenyl ligands
coordinate to zirconium in an ©3 fashion.6 One hydride ligand
was found on the Zr metal center.
In order to confirm the bonding mode of indenyl ligand, we
compared the bond distances between zirconium and indenyl
ligands. All of the distances between zirconium and C(1), C(2),
C(3), C(10), C(11), C(12), C(19), C(20), C(21), are in the range
from 2.48 to 2.60 ¡. On the other hand, the Zr-C distances of
Zr-C(4), Zr-C(9), Zr-C(13), Zr-C(18), Zr-C(22), and Zr-C(27)
are relatively longer and ranged from 2.78 to 2.83 ¡. This clearly
shows that all of the three indenyl ligands are best described as
©3 ligands.6
Three regioisomers
Ar
Ar
Ar
Ar
MLn
+
2
+
LnM
ð1Þ
Ar
LnM
LnM
Ar
Ar
2
1H NMR of compound 9 showed one doublet peak at
5.79 ppm and one triplet peak at 2.03 ppm assignable to two
protons of C(1) and C(3), and one proton of C(2), respec-
tively, of 5-membered ring in indenyl ligands. One singlet
peak was observed at 2.95 ppm assignable to H attached to
zirconium.
1
3
4
We then tested the dimerization of phenylacetylene using
simple zirconocene complexes. Our study was started from
conveniently generated Negishi reagent [Cp2ZrBu2].2,3 In this
example, phenylacetylene coupled with [Cp2Zr] (in situ generated
from [Cp2ZrBu2]) to form zirconacyclopentadiene. Protonolysis of
the reaction mixture gave three products 5-7 as shown in eq 2.
Ph
Ph
Ph
Ph
+
Ph
Ph
C(25)
C(26)
1) [Cp2ZrBu2]
2) H+
+
Ph
+
ð2Þ
2 Ph
Ph
Ph
7a 43%
C(27)
C(22)
C(24)
C(23)
Ph
5a 32%
C(19)
1a
6a trace
8a 0%
H(1)
C(3)
C(4)
C(2)
Product 5a was generated from the ¡,¡-diaryl isomer in
Zr
C(20)
32% yield. And both 6a and 7a were formed from the ¡,¢-diaryl
isomer in the combined yield of 43%. There was no related
product from the ¢,¢-diaryl isomer. Recently, Szymoniak
reported similar result in a [Cp2ZrCl2]/Ln system.4 A mixture
of 1,4- and 1,3-diphenylbutadiene in a ratio of 2.5 to 1 was
obtained. This clearly shows that dimerization of phenylacety-
lene on the [Cp2Zr] system is not selective.
C(5)
C(6)
C(21)
C(1)
C(14)
C(13)
C(9)
C(12)
C(11)
C(15)
C(8)
C(18)
C(7)
C(10)
C(16)
C(17)
Figure 1. Molecular structure of hydridotris(indenyl)zirconium (9).
© 2011 The Chemical Society of Japan www.csj.jp/journals/chem-lett/
Chem. Lett. 2011, 40, 1443-1444

1444
Table 1. Selective formation of 1,4-diarylbutadiene 5a-5e
NMR yield of 5/%
Entry Aryl-C¸CH Product
by complex 9 by complex 11
1
2
3
4
5
1a
1b
1c
1d
1e
5a
5b
5c
5d
5e
68
77
38
49
55
77
60
51
83
75
Figure 2. Molecular structure of dimerization product 10e of thienyl-
acetylene on hydridotris(indenyl)zirconium (9).
Dimerization reaction of phenylacetylene using complex 9
was then carried out. Phenylacetylene reacted with the complex
9 in THF at room temperature to give zirconacyclopentadiene
10a in 98% yield.7 It is interesting to report that hydrolysis of
the reaction mixture gave 1,4-diphenyl-1,3-diene 5a exclusively
in 68% yield. No formation of other isomer related compounds
such as 6, 7, and 8 was observed.
This unusual selective dimerization of coupling reaction
was also observed for other aryl-substituted terminal alkynes
such as p-tolylacetylene, ( p-bromophenyl)acetylene, (p-methoxy-
phenyl)acetylene, and 3-thienylacetylene. In all cases, only 1,4-
diaryl-1,3-dienes 5b-5e were obtained in 77, 38, 49, and 55%
yields, respectively, after hydrolysis. Results are shown in
Table 1.
It is not clear but we believe the selectivity comes from
the interaction of aryl groups with indenyl ligand. Therefore
5a-5e were selectively formed. It is important to note that
[(Ind)2ZrBu2] did not show similar selectivity. [(Ind)2ZrBu2] is
not stable in the solution. Other complexes such as [(Ind)3ZrH]
and [(Ind)2Zr(CO)2] are stable in the solution. It is the major
difference between [(Ind)2ZrBu2] and the other two complexes,
9 and 11.9
This paper is in celebration of the 2010 Nobel Prize
awarded to Professors Richard F. Heck, Akira Suzuki, and
Ei-ichi Negishi.
Ar
Ar
H+
References and Notes
1
[(Ind) ZrH]
9
3
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Ar
2
ð4Þ
(Ind)2Zr
1a: Ar = Ph
1b:
1c:
1d:
1e:
Tol
Ar
Ar
p-BrC6H4
p-MeC6H4
3-thienyl
10a-e
5a-e
In the case of 3-thienylacetylene, the corresponding zirco-
nacyclopentadiene 10e was isolated as crystals. Its structure
was determined by X-ray analysis. The structure is shown in
Figure 2. It clearly shows that two 3-thienyl groups are at the
¡,¡¤-positions of zirconacyclopentadiene moiety.
According to the structure of 10e, there is no interaction was
observed between 3-thienyl group and indenyl ligand in the
crystal structure.
CO
[(Ind)2Zr(CO)2]
[(Ind)3ZrH]
90%
9
11
Ar
Ar
2
3
E. Negishi, S. J. Holmes, J. M. Tour, J. A. Miller, F. E. Cederbaum, D. R.
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H+
11
ð5Þ
Ar
2
(Ind)2Zr
Ar
Ar
In order to make clear the effect of the “[(Ind)2Zr]” system
for the selectivity, we used [(Ind)2Zr(CO)2] (11).8
4
5
6
C. Denhez, S. Médégan, F. Hélion, J.-L. Namy, J.-L. Vasse, J.
Szymoniak, Org. Lett. 2006, 8, 2945.
Complex [(Ind)2Zr(CO)2] (11) was prepared by the reaction
of complex 9 with CO in 90% yields which was higher than the
known method.8 By the reaction of 11 with phenylacetylene at
room temperature in THF for 12 h, 5a was exclusively obtained
in 77% yield after hydrolysis of the reaction mixture. In the case
of other aryl-substituted alkynes, comparable results were
obtained which are shown in Table 1. Both [(Ind)3ZrH] (9)
and [(Ind)2Zr(CO)2] (11) gave similar results and 1,4-diaryl-
dienes 5a-5e were exclusively obtained. The formation of the
other regioisomers or related products was not observed in these
all examples.
For crystal structure of [(Ind)3ZrCl] see: C. Schmid, H. G. Alt, W. Milius,
J. Organomet. Chem. 1997, 544, 139.
For ©3 coordination mode of indenyl ligand on metals, for reviews see:
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D. Zargarian, Coord. Chem. Rev. 2002, 233-234, 157. c) J. M. O’Connor,
C. P. Casey, Chem. Rev. 1987, 87, 307.
7
Coupling reactions of internal alkynes with bis[1,3-bis(trimethylsilyl)-
indenyl]zirconium complex: C. A. Bradley, I. Keresztes, E. Lobkovsky,
V. G. Young, P. J. Chirik, J. Am. Chem. Soc. 2004, 126, 16937.
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8
9
Supporting Information is available electronically on the CSJ-Journal
Web site, http://www.csj.jp/journals/chem-lett/index.html.
Chem. Lett. 2011, 40, 1443-1444
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/