A novel and efficient method for double bond isomerization

Article abstract of DOI:10.1016/S0022-328X(03)00392-9

Isomerization of α-alkenes is carried out in the presence of a catalytic amount of palladium (II) chloride and triethylsilane at room temperature. This novel and efficient method affords high yields in the absence of solvent for double bond isomerization of alkenes.

Full text of DOI:10.1016/S0022-328X(03)00392-9

Journal of Organometallic Chemistry 678 (2003) 1Á4
/
www.elsevier.com/locate/jorganchem
Short communication
A novel and efficient method for double bond isomerization
a,
Maryam Mirza-Aghayan *, Rabah Boukherroub , Mohammad Bolourtchian ,
b
a
a
Maryam Hoseini , Kourosh Tabar-Hydar
a
a
Chemistry and Chemical Engineering Research Center of IRAN (CCERCI), P.O. Box 14335-186, Tehran, Iran
b
Physique de la Mati e` re Condens e´ e, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau, France
Received 31 August 2002; received in revised form 24 March 2003; accepted 24 March 2003
Abstract
Isomerization of a-alkenes is carried out in the presence of a catalytic amount of palladium (II) chloride and triethylsilane at room
temperature. This novel and efficient method affords high yields in the absence of solvent for double bond isomerization of alkenes.
#
2003 Elsevier Science B.V. All rights reserved.
Keywords: Isomerization; a-Alkenes; Palladium (II) chloride; Triethylsilane
1
. Introduction
tions of silicon hydrides with palladium dichloride have
already been reported for the reduction of Schiff-bases
[7] and the preparation of halosilanes [8]. More recently,
Double bond shift is one of the major industrial
processes in the context of petrochemical oil-refining
steps and follows the thermodynamic driving forces.
Selective olefin isomerization under mild conditions is
therefore a goal that merits increased attention of the
organometallic chemists. Diverse processes for olefin
isomerization continue to be topics of widespread
interest [1,2]. p-Coordination of transition metals such
as rhodium and nickel facilitates the attainment of the
thermodynamic equilibrium under mild conditions.
In some cases, however, the double bond isomeriza-
tion is an undesirable reaction. When the transition
metal complex induces catalytically both a reaction at
the double bond and its isomerization, the kinetics and
the product distribution are affected and thus the
selectivity of the reaction.
palladium dichloride (PdCl ) was used as a catalyst for
2
the conversion of organic halides to the corresponding
alkanes by triethylsilane [9]. Moreover, the versatile
behavior of the PdCl /R SiH system was demonstrated
2
3
in a wide variety of transformations: conversion of
alcohols to the corresponding silyl ethers, halides and
alkanes [10].
This letter investigates the reactivity of the system
in the presence of a-olefins. We will report
SiH/PdCl system as an extremely efficient
Et
the use of Et
SiH/PdCl
3
2
3
2
method for the isomerization of a-olefins in the absence
of solvent under mild conditions.
2. Results and discussion
Silicon hydrides have met successful applications in
substitution, reduction and addition processes [3Á5].
/
At earlier stage of our work, we have investigated the
Most of these reactions are catalyzed by transition metal
complexes. The combination of organosilicon reagents
and palladium (Pd) complexes provides additional
examples of the versatility of organosilanes as useful
precursors in organic chemistry [6]. Synthetic applica-
efficiency of Ph SiH/PdCl system for the carbonÁ
/
3
2
carbon double bond isomerization. In a typical experi-
ment, addition of palladium dichloride (20 mol.%) to a
stirred mixture of 1-alkene (0.2 g, one equivalent) and
triphenylsilane (0.5 equivalent) in 10 ml of dry hexane at
room temperature under an argon atmosphere gave only
1
0% conversion of 1-alkene to 2- and 3-alkenes. This
*
Corresponding author. Tel.: ꢀ
03-7185.
E-mail address: m.mirzaaghayan@ccerci.ac.ir (M. Mirza-Aghayan).
/
98-21-803-6144/6145; fax: ꢀ98-21-
/
result is somehow deceptive because of the low conver-
sion yield. In the next step, we have used triethylsilane
8
0
022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00392-9

2
M. Mirza-Aghayan et al. / Journal of Organometallic Chemistry 678 (2003) 1Á4
/
Et SiH/PdCl (0.5 equivalent/10%) for 7 h at room
3
2
temperature gave a ratio of the different isomers (25/52/
6/7%) in 68%. The reaction time and palladium
1
chloride concentration have also an influence on the
product distribution. The reaction of one equivalent of
Scheme 1.
1
3
-dodecene with Et SiH/PdCl (one equivalent/20%) for
3 2
days at room temperature yielded 5/79/10/6% of the
instead of triphenylsilane without any solvent. As
previously, to a stirred mixture of 1-alkene and triethyl-
silane was added a catalytic amount of palladium
dichloride at room temperature. GC/MS analysis shows
different isomers.
Good conversions and yields were obtained when one
equivalent of 1-alkene was reacted with one equivalent
of Et SiH in the presence of 10% PdCl for 6 h at room
3
2
the formation of isomers 2-alkene and 3-alkene (cis Á
/
temperature. The results are summarized in the Table 2.
In the next step, we have tested the efficiency of the
trans mixtures) accompanied with the corresponding
alkane. The isomerization of a-olefins is outlined in
Scheme 1.
CÄ/C double bond isomerization over the hydrosilyla-
tion reaction. In this purpose, we have studied the
reaction of styrene with Et SiH/PdCl under the same
conditions. After 17 h reaction at room temperature,
We have tried different experimental conditions in
order to optimize the conversion of 1-alkene to its
isomers 2- and 3-alkenes. In the first set of experiments,
we have carried out the reaction of one equivalent of 1-
alkene in the presence of Et SiH/PdCl (0.2 equivalent/
3
2
1
GC/MS and H-NMR analysis showed only the forma-
tion of ethylbenzene (51%) resulting from hydrogen
3
2
addition to the CÄC double bond (Scheme 2). There was
no detectable products arising from addition of Et SiH
/
1
0%). We have found that the conversion and the
3
reaction yields are still low. The results are summarized
in Table 1.
For example, the reaction of one equivalent of 1-
across the CÄ
/
C double bond or dehydrogenative silyla-
tion as previously observed for cationic Pd (II) com-
plexes [11].
dodecene with Et SiH/PdCl (0.2 equivalent/10%) for 17
3
2
The efficiency and the experimental simplicity of the
present method are very appreciated in comparison with
the methods previously employed for the isomerization
h at room temperature led to a low conversion. The
resulting ratio of 1-dodecene/2-dodecene/3-dodecene/
dodecane was 48/31/18/3%. Comparable results were
obtained with 1-tetradecene, 1-hexadecene and 1-octa-
diene. Increasing the amount of Et SiH in the reaction
3
mixture (Et SiH/PdCl ꢁ0.5 equivalent/10%) increases
the conversion yield. Reaction of 1-tetradecene with
/
3
2
Scheme 2.
Table 1
3 2
Isomerization of 1-alkenes in the presence of Et SiH/PdCl : 0.2 equivalent/10% after 17 h at room temperature
a
b
b
a
Entry
1-Alkene
%
2-Alkene
%
3-Alkene
%
n-Alkane
%
Yield %
1
1
1
1
-Dodecene
48
50
61
62
31
28
27
24
18
18
10
11
3
4
2
3
49
46
37
35
-Tetradecene
-Hexadecene
-Octadecene
a
Determined by GC/Ms analysis.
Determined by GC/Ms analysis for cis and trans mixtures.
b
Table 2
3 2
Isomerization of neat 1-alkenes using Et SiH/PdCl : 1/10% after 6 h at room temperature
a
b
b
a
n-Alkane %
Entry
1-Alkene
%
2-Alkene
%
3-Alkene
%
Yield %
1
1
1
1
1
1
-Octene
-Decene
8
16
13
21
3
65
50
56
50
71
66
12
26
27
18
3
15
8
77
76
83
68
74
73
-Dodecene
-Tetradecene
-Hexadecene
-Octadecene
4
11
23
17
10
7
a
Determined by GC/Ms analysis.
Determined by GC/Ms analysis for cis and trans mixtures.
b

M. Mirza-Aghayan et al. / Journal of Organometallic Chemistry 678 (2003) 1Á
/
4
3
bond or from hydrosilylation reaction even for longer
reaction times.
In conclusion, we have shown that the Et SiH/PdCl
Scheme 3.
3
2
system is very efficient for the carbonÁ
isomerization. The reaction is simple and easy to carry
out. The migration of the carbonÁcarbon double bond
is self-limited and no hydrosilylation reaction takes
place during the isomerization process. It should be
noted that the absence of solvent in these reactions is
beneficial from an environmental point of view. Further
investigations using the same catalyst for other chemical
transformations are currently in progress.
/
carbon double
of 1-alkenes. For example, the isomerization process
that involves contacting olefins with a titanium catalyst
on alumina in the presence of water [2f] takes place at
/
3
00Á570 8C, whereas with Et SiH/PdCl the migration
/
3
2
occurs at room temperature in the absence of solvents.
Birdwhistell et al. have reported the isomerization of 1-
heptene in the presence of Ni[P(OEt) ] . This reaction is
3
4
initiated by adding H SO to an ether solution of 1-
2
4
heptene and Ni[P(OEt)3]4 at 0 8C [12]. Ni[P(OEt)3]4,
however, is not very stable. It decomposes upon
exposure to air and requires special care during its
transfer and manipulation.
3. Experimental
In earlier studies by some among us on the reduction
of alkyl bromides and iodides with Et SiH/PdCl , we
have observed the formation of small amounts of
All manipulations were carried under an argon atmo-
3
2
sphere. Hexane was distilled over sodium and stored
under argon. The reported yields are based on GC/Ms
analysis using a FISON GC 8000 series TRIO 1000 gas
chromatography equipped with a column capillary CP
Et SiCl and molecular hydrogen along with triethylsilyl
3
bromide and triethylsilyl iodide, respectively. This result
allowed us to suggest the formation of metallic Pd
according to the reaction pathway below (Scheme 3)
Sil.5 CB, 60 Mꢂ0.25 mm i.d.
/
[
8b,10].
We believe that the reaction mechanism is a stepwise
process. In the first step, metallic Pd was generated by
3.1. General procedure for isomerization of the a-olefins
To a solution of 1-alkene (0.2 g, one equivalent) and
triethylsilane (one equivalent) was added a catalytic
amount of palladium (II) chloride (10 mol.%) at room
temperature under an argon atmosphere. The resulting
mixture was stirred for indicated time at room tempera-
ture (see Table 1) and then 10 ml of hexane was added to
the solution. The residue was filtered over silica gel (to
remove the palladium salts) and the filtrate was evapo-
rated. The crude product was analyzed by GC/MS.
the reduction of palladium dichloride with Et SiH
3
(
Scheme 3). This Pd (0) serves as active entity in the
catalyzed isomerization reaction and accounts for the
formation of the corresponding alkane. The second step
consists on the formation of a palladium complex by an
oxidative addition of Et SiH to the metallic palladium
3
followed by a reductive elimination with a 1,2-hydride
shift to produce the first isomerization [8b,13]. The
second migration of the carbonÁcarbon double bond
/
takes place in a similar manner (Scheme 4). The
hydrogenation product results from addition of mole-
References
cular hydrogen (generated from the reaction of Et SiH
3
[
[
[
1] (a) D. Evans, J. Osborn, G. Wilkinson, J. Chem. Soc. (Lond.) A
(1968) 3133;
(b) C.P. Casey, C.R. Cyr, J. Am. Chem. Soc. 95 (1973) 2248;
with PdCl ) to the double bond, catalyzed by Pd (0) [14].
2
Surprisingly, there was no formation of other products
resulting from additional isomerization of the double
(
(
(
c) D.E. Bergbreiter, G.L. Parson, J. Organomet. Chem. 208
1981) 47;
d) M. Akita, H. Yasuda, K. Nagasuna, A. Nakamura, Bull.
Chem. Soc. Jpn 56 (1983) 554;
e) H. Waskamatsu, M. Nishida, N. Adachi, M. Mori, J. Org.
Chem. 65 (2000) 3966.
(
2] (a) U.S. patent 5,043,523, 1991;
(
(
(
(
(
(
(
(
b) U.S. patent 4,367,362, 1983;
c) W.O. patent 0,164,608, 2001;
d) U.S. patent 5,396,015, 1995;
e) U.S. patent 5,198,597, 1993;
f) Eur. Patent 588,680, 1994;
g) Span. ES 2,018,110, 1991;
h) Span. ES 2,010,123, 1989;
i) F.R. patent 2,657,605, 1991.
3] (a) C. Chatgilialoglu, Acc. Chem. Res. 25 (1992) 188;
b) C. Chatgilialoglu, Chem. Rev. 95 (1995) 1229 (and references
cited therein).
(
Scheme 4.

4
M. Mirza-Aghayan et al. / Journal of Organometallic Chemistry 678 (2003) 1Á4
/
[
[
4] W.P. Weber, Silicon Reagents for Organic Synthesis, Springer,
Berlin, 1983.
[9] R. Boukherroub, C. Chatgilialoglu, G. Manuel, Organometallics
15 (1996) 1508.
[10] C. Ferreri, C. Costantino, C. Chatgilialoglu, R. Boukherroub, G.
5] I. Ojima, in: S. Patai, Z. Rappoport (Eds.), The Chemistry of
Organosilicon Compounds (Chapter 15), Wiley, Chichester, 1980,
Manuel, J. Organomet. Chem. 554 (1998) 135Á137.
/
pp. 1479Á
/
1526.
[11] A.M. LaPointe, F.C. Rix, M. Brookhart, J. Am. Chem. Soc. 119
(1997) 906.
[
6] J. Tsuji, Palladium Reagents and Catalysts Innovation in Organic
Synthesis, Wiley, Chichester, 1995.
[12] K.R. Birdwhistell, J. Lanza, J. Chem. Educ. 74 (1997)
579.
[
[
7] I. Ojima, T. Kogure, Y. Nagai, Tetrahedron Lett. (1973) 2475.
8] (a) J.D. Citron, J.E. Lyons, L.H. Sommer, J. Org. Chem. 34
[13] B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis
with Organometallic Compounds, Wiley, 2000.
[14] M. Mirza-Aghayan, R. Boukherroub, M. Bolourtchian, M.
Hosseini, Tetrahedron Lett. vol. 44/24 (2003) 4579.
(
(
1969) 638;
b) A. Kunai, T. Sakurai, E. Toyoda, M. Ishikawa, Y. Yama-
moto, Organometallics 13 (1994) 3233.