Copolymerization of acetylene with ethylene in the presence of dibenzenetitanium(0)

Article abstract of DOI:10.1023/A:1016080716618

The interaction between acetylene and dibenzenetitanium(0) at a room temperature results in the acetylene polymerization and its reduction to ethylene, ethane, and methane at the expense of H atoms of the acetylene molecule. The catalytically active speci

Full text of DOI:10.1023/A:1016080716618

Russian Chemical Bulletin, International Edition, Vol. 51, No. 5, pp. 817—819, May, 2002
817
Copolymerization of acetylene with ethylene in the presence
of dibenzenetitanium(0)
E. F. Kvashina,ꢀ G. N. Petrova, G. P. Belov, O. S. Roshchupkina, and O. N. Efimov
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (096) 517 8910. Eꢀmail: kaplunov@icp.ac.ru
The interaction between acetylene and dibenzenetitanium(0) at a room temperature
results in the acetylene polymerization and its reduction to ethylene, ethane, and methane at
the expense of H atoms of the acetylene molecule. The catalytically active species capable of
copolymerizing acetylene with ethylene that are formed during the reaction or are added into
the system originate from the interaction of dibenzenetitanium(0) with acetylene.
Key words: dibenzenetitanium(0), acetylene, ethylene, reduction, copolymerization, oxiꢀ
dative addition.
We have shown earlier1 that Ti0 bisꢀarene complexes
do not react with alkenes but acetylene readily polymerꢀ
izes in the presence of these complexes. Polyacetylene
formed can be used for the production of lithium accuꢀ
mulators.2 The interaction of acetylene and ethylene with
dibenzenetitanium(0) at a room temperature was studied
in this work.
ing solution is decolorized, and a polymer is precipiꢀ
tated. The products of the reaction between dibenzeneꢀ
titanium and acetylene are presented in Table 1. When
an excess of acetylene interacts with the titanium comꢀ
plex (С2H2 : Ti = 85 : 1), a violet polyacetylene film is
formed on the walls of the reaction vessel. When the
С2H2 : Ti ratio was decreased to 8 : 1, only traces of the
polyacetylene film were found. The major reaction prodꢀ
uct is distinctly different in appearance. This is a black
round lump of ∼1 mm diameter. In this case (see Table 1,
run 2), the ethylene content in the gas phase decreases.
This loss of ethylene can be due to its polymerization.
Experiment with a mixture of ethylene and acetylene
confirmed this suggestion (see Table 1, run 3). Even
traces of the polyacetylene film were not found after
run 3, and the main reaction product represented black
spherical particles 3—4 mm in diameter. These particles
are formed during stirring the liquid phase because of
adhesion of small particles initially precipitated from the
solution. The yield of the solid product increased by
100 times compared to the previous run. This fact conꢀ
firms the participation of ethylene in polymerization.
Earlier1 we showed that the Ti0 complex does not
react with ethylene. Hence, the active species responꢀ
sible for the catalysis of ethylene polymerization arise
from the interaction of the Ti0 complex with acetylene.
It is known that the С≡С and С—Н bonds in the acetyꢀ
lene molecule can be broken in the presence of transiꢀ
tion metal complexes. The insertion of a transition metal
atom at the С≡С bond produces carbyne compounds,
which can further transform into methane.4,5 The cleavꢀ
age of the С—Н bond in the acetylene molecule by
transition metal complexes is usually accompanied by
Experimental
The Ti0 bisꢀarene complex, dibenzenetitanium, was preꢀ
pared by coꢀcondensation of the Ti atoms vaporized in a high
vacuum with a solid benzene matrix cooled with liquid nitroꢀ
gen.1,3 After defrosting, the benzene solution of dibenzeneꢀ
titanium was introduced into a cell combined with a vacuum
circular setup, and acetylene was passed through the cell at
∼20 °C. The gas phase was periodically sampled for GLC analysis
on a Biokhromꢀ3 chromatograph (flameꢀionization detector,
0.4×300 cm column packed with Al2O3). The ESR spectra
were recorded on an SE/X 2544 radiospectrometer (Radiopan,
Poznan). The IR spectra of the samples were obtained on a
Specord IRꢀ75 spectrophotometer in the KBr pellets. The DSC
thermograms of the polymer melting and crystallization were
obtained on a DSMꢀ2М instrument at the 16 °C min–1 rate of
heating/cooling. The polymer weighed samples were 5—7 mg.
Results and Discussion
The Ti0 bisꢀarene complexes are diamagnetic comꢀ
pounds,3 which are very sensitive to oxygen and highly
soluble in benzene and toluene. Their solutions are redꢀ
coloured (λmax = 505 nm). During the interaction of the
Ti0 complex with acetylene, gaseous reaction products
(methane, ethane, and ethylene) are evolved, the startꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 754—756, May, 2002.
1066ꢀ5285/02/5105ꢀ817 $27.00 © 2002 Plenum Publishing Corporation

818
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 5, May, 2002
Kvashina et al.
Table 1. Products of interaction between dibenzenetitanium(0) and acetylene
a
Run
С0
V/mL
pb/Torr
(Ti : C2H2)c
t/min
Yield of the reaction products/mol
Polymer
/mol mL–1
CH4
C2H4
C2H6
Type
Yield
/g per 1 g Ti
1
2
2•10–5
2•10–5
6
8
450 (1 : 85)
50 (1 : 8)
55
21
80
0.26•10–7
1•10–6 0.33•10–7
1.9•10–7
Violet film
Traces of violet film
and black sperical lump
in 24 h
16
0.1
0.25•10–7 2.5•10–6
0.49•10–7 0.5•10–6 0.44•10–6
3
2.6•10–5
3
200 (1 : 150)
1440
(24 h)d
—
—
—
Black spherical particle
40
a Concentration of the initial solution.
b Acetylene initial pressure.
c Molar ratio.
d Ethylene initial pressure was 400 Torr.
the oxidative addition of both fragments formed to the
metal atom.6 One can suggest that Ti0 in our system is
oxidized through a similar reaction to form ethynylhydrido
complex, which interacts with acetylene to form ethylꢀ
ene, whereas the reaction with ethylene leads to ethane.
These transformations can occur in the same transition
complex due to the cleavage of the Тi—H bonds in the
ethynylhydrido complex and the Н atom transfer to the
acetylene molecule to form the С—Н bond of alkene.7
Acetylene itself rather than a solvent (benzene) is a source
of hydrogen when methane, ethylene, and ethane are
formed from acetylene. Experiment with deuterated
material unlike the known powdery polyethylene and
acetylene—ethylene blockꢀcopolymer, which are formed
in the presence of the Zigler catalysts.10 To recognize
the ethylene—acetylene copolymer, the polymeric prodꢀ
uct was extracted with xylene on a Soxhlet apparatus. If
a mixture of two polymers, polyacetylene and polyethylꢀ
ene, was produced by the reaction, the latter could be
dissolved in boiling xylene. However, pure polyethylene
was not found in this experiment. Therefore, one can
suggest that the polymer obtained is a copolymer of ethylꢀ
ene and acetylene. Nevertheless, a comparison of the
DSC thermograms for two polymers synthesized with
the use of dibenzenetitanium and in the VOCl3—Al(Bui)3
catalytic system gives evidence of an essential difference
between these polymeric products. It has been reliably
proved for the latter catalyst11 that the polymeric prodꢀ
ucts are ethylene—acetylene blockꢀcopolymers and polyꢀ
acetylene blocks in a copolymer chain have different
lengths. Depending on the content of the polyacetylene
blocks, the color of the copolymers formed changes from
lightꢀblue to darkꢀblue and even black similarly to that
of polymers synthesized by us. A typical thermogram of
the ethylene—acetylene blockꢀcopolymer is shown in
Fig. 1 (curve 2), where two peaks are clearly seen: the
endothermic peak of melting of the polyethylene blocks
(m.p. 120—130 °С depending on the content of the polyꢀ
acetylene blocks) and the exotermic peak (at T > 200 °С)
caused by oxidation of the conjugated double bonds in
the polyacetylene blocks with the air oxygen that is present
in a calorimetric cell. The DSC pattern for the polymer
synthesized by us differs substantially. First, a broad peak
is seen in the 80—100 °С range. Second, a peak for polyꢀ
ethylene melting is shifted to a higher temperature reꢀ
gion, and this corresponds to the ethylene homopolyꢀ
mer. Third, the exothermic peak typical of the known
ethylene—acetylene blockꢀcopolymers is absent. These
data confirm the fact of ethylene polymerization in the
system, but the polymer obtained cannot be unambiguꢀ
acetylene of the isotope composition С2D2 : С2Н2
=
70 : 30 at a 10ꢀfold excess of acetylene to titanium and
the initial pressure of 200 Torr confirms this suggestion.
The absorption bands at 2145 and 2200 cm–1 of the
stretching vibrations of the СD2 group of deuteriumpolyꢀ
ethylene8 are seen in the IR spectrum of the black polyꢀ
mer product. Hence, the reduction of deuteroacetylene
to deuteroethylene in this system occurs at the expence
of the H atoms of acetylene.
Acetylene dehydrogenation seems to be accompaꢀ
nied by the formation of carbyneꢀlike lowꢀvalent titaꢀ
nium compounds (possibly linear polymers).7 This is conꢀ
firmed indirectly by a black color of the polymer product
obtained.
According to the ESR spectroscopic data, the initial
diamagnetic Ti0 complex transforms into a paramagnetic
compound upon the interaction of dibenzenetitanium
with acetylene. The ESR spectrum of the paramagnetic
compound is a singlet with the gꢀfactor of 1.993. One
can suggest that the active sites of polymerization arising
in the system are the molecules of a TiI compound. A
similar assumption on the TiI participation in the reacꢀ
tion center of ethylene polymerization has been reported
earlier.9
The black polymeric product (see Table 1, run 3) is
not dissolved in boiling decalin and represents an elastic

Copolymerization of acetylene and ethylene
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 5, May, 2002
819
Q
Hence, we showed for the first time that acetylene is
reduced to methane, ethane, and ethylene upon the inꢀ
teraction of dibenzenetitanium(0) with acetylene and
acetylene is the source of the H atoms. The copolymerꢀ
ization of acetylene with ethylene was first found, and
this reaction is catalyzed by the singleꢀcomponent sysꢀ
tem containing dibenzenetitanium(0) as the starting
complex.
122
133
2
1
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110
150
190
230
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Received June 27, 2001;
in revised form January 22, 2002