W(O-2,6-C6H3X2)2Cl4/Bu4Sn as metathesis catalyst of 1-alkenes

Article abstract of DOI:10.1016/S1381-1169(98)00120-4

Tungsten compounds with aryloxo ligands, i.e., W(O-2,6-C₆H₃X₂)₂Cl₄ (X = Cl, Ph) and Bu₄Sn, were investigated as catalytic systems for the metathesis of 1-alkenes of varying carbon lenghts. The catalytic system was activated at 85°C for 20 min prior to use. Optimum metathesis activity with 1-alkenes was observed at 85°C and a Sn/W molar ratio = 3. The W(O-2,6-C₆H₃X₂)₂Cl₄/Bu₄Sn catalytic system is very active for the metathesis of 1-alkenes with a carbon chain length of about six to eight and it favours a more polar solvent such as chlorobenzene.

Full text of DOI:10.1016/S1381-1169(98)00120-4

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Journal of Molecular Catalysis A: Chemical 133 1998 167–173
ž
/
W O-2,6-C6 H3 X2 2Cl4rBu4Sn as metathesis catalyst of
1-alkenes
)
C. van Schalkwyk, H.C.M. Vosloo , J.A.K. du Plessis
SASOL Centre for Separation Technology, Potchefstroomse UniÕersiteit Õir Christelike Hoer Onderwys, Potchefstroom 2520, South Africa
¨
Received 17 October 1997; accepted 16 March 1998
Abstract
Ž
.
Ž
.
Tungsten compounds with aryloxo ligands, i.e., W O-2,6-C6H3X2 2Cl4 XsCl, Ph and Bu4Sn, were investigated as
catalytic systems for the metathesis of 1-alkenes of varying carbon lenghts. The catalytic system was activated at 858C for 20
min prior to use. Optimum metathesis activity with 1-alkenes was observed at 858C and a SnrW molar ratios3. The
Ž
.
W O-2,6-C6H3X2 2Cl4rBu4Sn catalytic system is very active for the metathesis of 1-alkenes with a carbon chain length of
about six to eight and it favours a more polar solvent such as chlorobenzene. q 1998 Elsevier Science B.V. All rights
reserved.
Ž
.
Keywords: Alkene metathesis; 1-Alkenes; Tungsten VI oxaryl derivatives; Solvent polarity
1. Introduction
ity of the electronic and steric properties of the
various aryloxide ligands, it is possible to con-
trol the activity and sometimes the stereoselec-
Over the years, many homogeneous catalytic
systems were developed for the metathesis of
w
x
tivity of the metathesis reaction 3,4 . If the
electron-withdrawing properties of the aryloxo
ligand are increased, an increase in the metathe-
Ž
.
1-alkenes. Tungsten VI aryloxide complexes of
Ž
.
Ž
the type W OAr Cl6yn OArsphenoxide or
substituted phenoxide in particular are effective
n
.
w x
sis activity is observed 4 . Another factor influ-
alkene metathesis catalysts that could easily be
synthesized from WCl6 and phenol derivatives
encing the metathesis reaction is the position of
the substituent on the aryloxide ligands. Com-
plexes with substituents on positions 2 and 6 of
the aryloxide ligands were found to be the more
active catalysts for the metathesis of 1-alkenes
w
x
1–3 .
Trans-W OAr Cl2 in combination with
Ž
.
4
EtAlCl2 or Et3Al2Cl3 are active catalytic sys-
w x
tems for the metathesis of alkenes 2 . Quignard
w x
1 .
w
x
Ž
.
et al. 1,3 reported that W OAr Cl4 with
2
Ž
.
Ž
In this study, W O-2,6-C6H3X2 2Cl4 Xs
Ž
EtAlCl2 or R4M Rsmethyl or butyl; MsSn
or Pb are also active catalytic systems for the
.
Cl, Ph with Bu4Sn were investigated as cat-
.
alytic system for the metathesis of 1-alkenes
with different carbon chain lengths. Various
parameters, i.e., SnrW molar ratio, reaction
temperature, solvent, type of aryloxide ligand
alkene metathesis reaction. Due to the versatil-
)
Corresponding author.
1381-1169r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
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.
PII S1381-1169 98 00120-4

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)
168
C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
Ž
.
and the chain length of the terminal alkenes,
were varied.
gen. The W O-2,6-C6H3Cl2 2Cl4 complex was
Ž
recrystallized with ethanol and the W O-2,6-
C6H3Ph2 2Cl4 complex was washed with hex-
.
ane. Yields of 79% black microcrystals and
80% dark-green microcrystals were obtained for
the Cl and Ph derivatives, respectively. Both
complexes are air-stable, but because they are
known to slowly decompose and deactivate with
2. Experimental
2.1. Reagents
Ž
2.1.1. Tungsten compounds
continued exposure to air detected by a colour
Ž
.
Ž
.
.
The W O-2,6-C6H3X2 2Cl4 XsCl, Ph
change to grey , the complexes were stored
w x
catalyst was synthesized using WCl6 and the
under nitrogen 5 .
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.
appropriate phenol. The WCl6 Merck was pu-
rified by sublimation and stored under nitrogen
2.3. Catalytic reactions
w
x
4–6 . The phenolic compounds, 2,6-dichloro-
phenol and 2,6-diphenylphenol Aldrich , were
used as obtained from the supplier.
Ž
.
All catalytic reactions were carried out under
nitrogen using standard techniques, and all addi-
tions of liquids were made using gas-tight sy-
ringes.
The tungsten precatalyst 5=10 mol was
placed in a minireactor filled with nitrogen.
2.1.2. Cocatalyst
Ž
.
The Bu4Sn Aldrich was used as obtained
from the supplier.
y
5
Ž
.
This was followed by the addition of the sol-
2.1.3. SolÕents
Chlorobenzene Merck , benzene Holpro ,
carbon tetrachloride Saarchem , octane and
3
Ž
.
Ž
vent, chlorobenzene 2.5 cm , and Bu4Sn 1.5
Ž
.
Ž
.
4
= 10y mol . The catalyst mixture was then
.
Ž
.
Ž
heated to 858C. After 20 min, the alkene 2.5=
Ž
.
hexane Merck were distilled from P2O5 and
10y mol was added to the mixture and the
3
.
stored under a nitrogen atmosphere.
reaction mixture was stirred until equilibrium
3
Ž
.
was reached. An excess amount ca. 0.5 cm of
water was added to terminate the catalytic reac-
2.1.4. Substrates
The alkenes, 1-pentene, 1-hexene, 1-heptene,
1-octene and 1-decene Aldrich , were degassed
and stored under a nitrogen atmosphere.
Ž
tion followed by 1,2-dichlorobenzene internal
Ž
.
Ž
.
.
standard for GC gas chromatography analyses .
These reaction conditions were used through-
out, unless otherwise indicated.
(
)
2.2. Synthesis of W O-2,6-C6 H3 X2 2Cl4
2.4. Analysis
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.
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.
W O-2,6-C6H3X2 2Cl4 XsCl, Ph was
synthesized using the method of Quignard et al.
w
x
Reaction mixtures were analysed with a Carlo
Erba HRGC 5300 gas chromatograph equipped
5,6 :
CCl4
WCl6 qHO-2,6-C6H3X2 re™flux
Ž
with an Alltech SE-30 capillary column 30
.
m=0.32 mm=0.25 mm and flame ionization
W O-2,6-C H X Cl4 q2HCl
Ž
.
6
3
2
2
Ž
.
detector FID . The following instrumental con-
ditions were used: inlet temperature of 300 8C,
injection volume of 0.2 ml, oven programmed
from 70–2508C at 108C miny1, N2 carrier gas
y
3
Ž
A solution of HO-2,6-C6H3X2 5=10
.
3
Ž
.
mol in CCl4 20 cm was added to a solution
of WCl6 2.5=10
The mixture was stirred under reflux for 4 h.
The complex was filtered and dried under nitro-
y
3
3
Ž
. Ž .
mol in CCl4 20 cm .
with a flow rate of 2 cm3 miny at 208C and
1
FID temperature of 3508C.

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C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
169
The internal standard method was used to
calculate the % mol 1-alkene and metathesis
products formed.
3.2. Influence of cocatalystrW molar ratio
Various cocatalysts are known to activate the
Ž
.
w
x
W O-2,6-C6 H 3 X 2 2Cl4 precatalyst 1,3 .
Bu4Sn was the cocatalyst of choice because it
was economical, safe to handle and gave better
3. Results and discussion
w x
reproducibility of results in previous studies 4 .
The results of the reactions of different alkenes
3.1. Reaction products
Ž
.
with the W O-2,6-C6H3Cl2 2Cl4rBu4Sn cat-
alytic system at different SnrW molar ratios are
given in Fig. 1.
Ž
.
Ž
The W O-2,6-C6H3X2 2Cl4rBu4Sn Xs
.
Ph, Cl catalytic systems show a high activity
and selectivity towards the metathesis of termi-
nal and internal alkenes. Gas chromatographic
analyses of the reaction mixtures indicated the
formation of primary and secondary metathesis
products. All the secondary metathesis products
have a carbon chain length longer than the
substrate and shorter than the high molecular
In all cases, an increase in primary metathesis
product yield was observed with an increase in
the SnrW molar ratio. A maximum yield of
primary metathesis products is obtained at
SnrW molar ratios of 2 to 5 and the yields
generally decrease at higher SnrW molar ratios.
Ž
A similar trend was observed for the W O-2,6-
w x
mass primary metathesis product 4
.
C6H3Ph2 2Cl4rBu4Sn catalytic system, al-
though the decrease in yields at higher molar
2CH CH CH5CH2 |CH2 5CH2
3Ž
.
2
n
Ž
.
ratios is more gradual Fig. 2 .
qCH CH CH5CH CH CH3
3Ž
.
Ž
.
2
2
n
n
with ns2, 3, 4, 5 or 7.
An unknown product, not related to any
metathesis product, was also observed in small
3.3. Influence of reaction temperature
Ž
.
w x
w x
yields -5% . Although no isomerisation was
observed during the metathesis reaction, the ap-
pearance of the secondary metathesis products
Quignard et al. 1 and Vosloo et al. 4
indicated that a reaction temperature of 858C is
essential for optimum activity of the tungsten
aryloxide precatalysts. The effect of the reaction
w x
is proof that isomerisation also took place 4 .
Ž
.
Ž
Fig. 1. Influence of the SnrW molar ratio on the metathesis activity of the W O-2,6-C6 H3Cl2 2Cl4rBu4Sn catalytic system temperature
. Ž
.
Ž
.
Ž
.
Ž .
s858C; times2 h . v 1-Decene; l 1-Octene; B 1-Hexene; ' 1-Pentene.

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170
C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
Ž
.
Ž
Fig. 2. Influence of the SnrW molar ratio on the metathesis activity of the W O-2,6-C6 H3Ph2 2Cl4rBu4Sn catalytic system temperature
. Ž
.
Ž
.
Ž
.
Ž .
s858C; times2 h . v 1-Decene; l 1-Octene; B 1-Hexene; ' 1-Pentene.
temperature on the catalytic activity of the
3.4. Influence of solÕents
Ž
.
W O-2,6-C6H3Ph2 2Cl4rBu4Sn catalytic sys-
tem towards the different alkenes was also in-
vestigated. The results are shown in Fig. 3.
A very low yield of primary metathesis prod-
Ž
Different solvents 1-octene, hexane, octane,
.
benzene and chlorobenzene were investigated
to optimise the reaction conditions for the W O-
Ž
Ž
.
ucts was observed in the presence of the W O-
2,6-C6H3Ph2 2Cl4rBu4Sn catalytic system.
.
2,6-C6 H3Ph2 2Cl4rBu4Sn catalytic system
The influence of solvents on the metathesis of
1-octene was investigated and the results are
shown in Fig. 4.
from 0 to 408C for all the alkenes. A drastic
increase in primary metathesis products is ob-
served from 60 to 808C. A maximum yield of
primary metathesis products is obtained at 858C
and the yields decrease at higher temperatures.
1-Hexene gives the highest yield of primary
metathesis products at 858C and 1-octene the
lowest.
In both hexane and octane, low yields of
Ž
.
primary ca. 8% in each case and secondary
Ž
.
20 and 13%, respectively metathesis products
are observed. Similar low yields are obtained if
1-octene is used as solvent and substrate. In
benzene, very little primary metathesis products
Ž
.
Fig. 3. Influence of the reaction temperature on the primary metathesis products of the W O-2,6-C6 H3Ph2 2Cl4rBu4Sn catalytic system
Ž
. Ž
.
Ž
.
Ž
.
Ž .
SnrW molar ratios3; times2 h . v 1-Decene; l 1-Octene; B 1-Hexene; ' 1-Pentene.

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C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
171
Ž
.
Fig. 4. Influence of various solvents on the products formed in the presence of the W O-2,6-C6 H3Ph2 2Cl4rBu4Sn catalytic system
Ž
.
SnrW molar ratios3; times2 h .
is observed, while 22% secondary metathesis
products are formed. Only in chlorobenzene
equilibrium is reached with 50% primary
metathesis products being formed.
From these results it seems as if polarity
plays a major role in determining the activity
and selectivity of the catalytic system. To deter-
mine if solvent polarity do indeed play a role,
mixtures of varying composition of chloroben-
steady decrease until the solvent mixture con-
tains 50% of hexane. This is followed by a
dramatic decrease if the amount of hexane con-
tent is increased further. The primary metathesis
reaction is almost terminated at hexane contents
greater than 70%. This strengthens the observa-
tion that the catalytic system is more active in a
polar medium.
Ž
.
zene and hexane were used as solvent Fig. 5 .
With an increase in hexane content of the
solvent mixture a gradual increase in secondary
metathesis products is observed from 8 to 20%.
Initially, the primary metathesis products show
3.5. Influence of 1-alkenes with different carbon
chain lengths
If the influence of the carbon chain length of
the alkene on the metathesis activity of the
Ž
.
Fig. 5. Influence of hexanerchlorobenzene solvent mixtures on the metathesis activity of the W O-2,6-C6 H3Ph2 2Cl4 catalytic system with
Ž
. Ž
.
Ž
.
Ž .
1-hexene temperatures858C; SnrW molar ratios3; times2 h . B PMP; l SMP; v unknown products.

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)
172
C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
Ž
.
Fig. 6. Influence of different carbon chain length alkenes on the metathesis activity of the W O-2,6-C6 H3 X2 2Cl4rBu4Sn catalytic system
Ž
. Ž
.
Ž .
SnrW molar ratios3; times2 h . B XsCl; l XsPh.
Ž
.
. Ž
C6H3X2 2Cl4rBu4Sn catalytic system Xs
W O-2,6-C6H3X2 2Cl4rBu4Sn catalytic sys-
Ž
.
.
tem XsPh, Cl is investigated, the results
shown in Fig. 6 are obtained.
Ph, Cl can be obtained by the double alkylation
w x
of the tungsten atom 3 .
It is evident from these results that both the
catalytic systems are the most active for alkenes
with carbon chain lengths ranging from C6 to
Double bond isomerisation was not observed
directly but the presence of secondary metathe-
sis products is an indication of double-bond
Ž
C8. In this region, the W O-2,6-C6 H 3
w x
.
migration taking place 4 . The extent of the
Cl2 2Cl4rBu4Sn catalytic system gives a higher
yield of primary metathesis products than the
secondary metathesis reactions is rather limited
and because no isomerisation products are ob-
served, it can be concluded that the formation of
the metal carbene is favoured.
phenyl-substituted derivative.
It seems as if it is necessary for the catalyst
to have an electrophilic metal centre in order to
be an active metathesis catalyst.
In addition to its role in forming the metal
carbene, the cocatalyst, Bu4Sn, may also play a
role to enhance the electrophilic character of the
4. Conclusions
Ž
.
It is clear that the W O-2,6-C6H3X2 2Cl4
Ž
.
complexes XsPh, Cl , in the presence of
Bu4Sn, have a high activity for the metathesis
of the C6 to C8 1-alkenes and a higher selectiv-
ity for primary metathesis products. The opti-
w
x
metal centre 12,13 . The increased electrophilic
character can be further stabilised by a polar
solvent, which may explain the higher metathe-
sis activity observed when a polar solvent is
used.
Ž
m um conditions for the W O -2,6-
.
Ž
C6H3X2 2Cl4rBu4Sn catalytic system Xs
.
Ph, Cl can be summarised as follows:
Ž .
Ž .
a SnrW molar ratios between 2 and 5;
b Reaction temperatures between 60 and
908C; and
Ž .
Acknowledgements
c A polar solvent such as chlorobenzene.
The mechanism for metathesis requires a
w
x
metal carbene as active species 7–11 . The
The financial assistance of the SASOL Cen-
tre for Separation Technology and the Founda-
Ž
m etal carbene for the W O -2,6-

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C. Õan Schalkwyk et al.rJournal of Molecular Catalysis A: Chemical 133 1998 167–173
173
w x
5
F. Quignard, M. Leconte, J. Basset, L. Hsu, J.J. Alexander,
Ž
tion for Research Development THRIP Pro-
Ž
.
S.G. Shore, Inorg. Chem. 26 1987 4272.
.
gramme is gratefully acknowledged.
w x
6
Ž
.
H. Funk, W.Z. Baumann, Anorg. Allg. Chem. 231 1973
264.
w x
7
K.J. Ivin, J.C. Mol, Olefin Metathesis and Metathesis Poly-
merization, Academic Press, London, 1997.
w x
Ž .
8
w x
9
T.A. Manuel, J. Org. Chem. 27 1962 3941.
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