Oligomerization of phenylferrocenylacetylene under the action of WCl 6

Article abstract of DOI:10.1016/j.jorganchem.2012.02.013

Phenylferrocenylacetylene was found to be capable of oligomerizing in the presence of WCl₆ (130 °C, 24 h) to afford short polyenes (with about 5 monomer units in the macromolecule) in up to ～30% yield. The polyenes synthesized are promising rea

Full text of DOI:10.1016/j.jorganchem.2012.02.013

Journal of Organometallic Chemistry 706-707 (2012) 124e127
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Oligomerization of phenylferrocenylacetylene under the action of WCl6
Inna V. Tatarinova, Ol’ga A. Tarasova, Marina V. Markova, Lyudmila V. Morozova, Al’bina I. Mikhaleva,
*
Boris A. Trofimov
A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of Russian Academy of Sciences, 1 Favorsky St., 664033 Irkutsk, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Phenylferrocenylacetylene was found to be capable of oligomerizing in the presence of WCl6 (130 ꢀC,
24 h) to afford short polyenes (with about 5 monomer units in the macromolecule) in up to w30% yield.
The polyenes synthesized are promising reactive macromonomers and building blocks for high-tech
materials.
Article history:
Received 15 November 2011
Received in revised form
31 January 2012
Accepted 3 February 2012
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Phenylferrocenylacetylene
Oligomerization
Wolfram hexachloride
Electroconductivity
Paramagnetism
1. Introduction
obtain polyenes with pendant ferrocene substituents was poly-
merization or oligomerization of ferrocenylacetylenes [5].
The last decades have witnessed an immense research interest
in ferrocene-containing polymers and oligomers due to the quest
for novel high-tech materials including those employed in living
systems and processes of transmission and storage of information
[1,2]. For example, ferrocene-containing pyrrole was polymerized
with glucoxidaze on the electrode surface to study the charge
transfer from the enzyme to electrode [3]. As mediators between
oxidases and electrode, ferrocene-containing polysiloxanes were
used. Electrochemical properties of ferrocene-containing oligomers
of polyethylene oxides were studied. The structure of these oligo-
mers was close to that of natural compound, glycerol oligoethers,
where a ferrocene moiety was bonded with the main chain by the
sulfide bridge [3]. It is known that the incorporation of the ferro-
cene fragment into diverse polymeric architectures imparts them
valuable redox, electric, magnetic, preceramic, catalytic and optical
properties [2,4].
Numerous applications of such an approach were summarized in
reviews and monographs [5]. However, it was reported [5] that
many early attempts to polymerize ethynylferrocene produced
poorly characterized oligomers [6,7]. Only decades later [8], the
Schrock metathesis catalyst, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)
[OCMe(CF3)2]2, has been employed in ethynylferrocene polymeri-
zation to furnish well soluble polyene polymers with up 50 double
bonds. Polymerization of N-(4-propynyloxy)-2-aza- [3]-ferroceno-
phane, catalyzed by the Rh(I) complex, produced polyenes with
pendant ferrocenophane [9]. The polymerization of diphenylace-
tylenes containing the ferrocenyl group in para- or meta-positions
was accomplished in the presence of catalytic system TaCl5-n-
Bu4Sn [10]. Recently [11], dipolar second-order nonlinear optical
chromophores containing ferrocene donor entity and 3-
dicyanomethylidene-1-indanone acceptor group bridged by the
polyene chain of different length were synthesized.
Synthesis of polyenes bearing pendant ferrocene substituents is
one of the priority areas in this research. The insertion of ferrocene
units into the polyene backbone attracts a special attention owing
to the electronic donating ability, reversible of redox chemistry,
peculiar steric properties and ready functionalization of these
fragments [5]. As followed from the review, the most logical way to
The above short literature excursus clearly shows that the
polymerization of acetylenes with ferrocene-containing substitu-
ents meets with success only in the case of application of sophis-
ticated, inaccessible and expensive metal-complex catalysts.
The present work deals with the development of a facile and
convenient method for the synthesis of polyene oligomers con-
taining pendant ferrocene and benzene substituents via the oligo-
merization of phenylferrocenylacetylene (1) in the presence of
cheaper and available catalyst WCl6. Novelty and challenge of this
research was that, unlike most known examples related to terminal
* Corresponding author. Fax: þ7 3952 419346.
E-mail address: boris_trofimov@irioch.irk.ru (B.A. Trofimov).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.013

I.V. Tatarinova et al. / Journal of Organometallic Chemistry 706-707 (2012) 124e127
125
ferrocenylacetylenes, here, an internal acetylene, namely ferroce-
nylacetylene bearing phenyl substituent at the acetylenic carbon,
was subjected to oligomerization. Polymerization of such acety-
lenes is known to be substantially hampered due to steric
hindrances toward the growth of polymer chain imposed by the
phenyl substituents. It is not occasionally that the polymers of
internal acetylenes with ferrocene substituents are virtually
unknown, the only exception being likely the above-cited work
[11]. Meanwhile, the introduction of extra benzene substituent into
every unit of the polyene increases conjugation degree and ability
of the polyconjugated chain to electron transfer. Besides, this
creates additional opportunities for chemical modification of the
oligomer through the reactions of the benzene ring.
When reproducing the protocols [12e15], at the first three steps
we frustrated to reach the yields of the target compounds indicated
in the above-cited works (Scheme 1). Only at the last step the yield
of the target product (relative to the original protocol) was
augmented noticeably due to the increase of the reaction duration.
2.2. Oligomerization of phenylferrocenylacetylene (1)
Oligomerization of phenylferrocenylacetylene (1) was carried
out in the presence of WCl6 (Scheme 2). The catalytic system
WCl6ePh4Sn, commonly employed for the polymerization of
diverse acetylenic monomers [16], was used for the comparison.
The efficacy of radical initiation by dinitrile of azoisobutyric acid
(AIBN) and UV-irradiation was also checked. The oligomerization
conditions and oligomers yields are shown in Table 1.
2. Results and discussion
Under these conditions the oligomers of phenylferroceny-
lacetylene 2 were obtained in up to 29% overall yield. The oligomers
consisted of soluble (chlorobenzene, nitrobenzene, chloroform,
tetrahydrofuran) and insoluble (in some cases) fractions. Molecular
weight of soluble oligomer prepared by WCl6 catalysis (130 ꢀS, 24 h,
Table 1) was 1700 that corresponded to five elementary units.
The reactivity of disubstituted acetylenes in the WCl6 or
WCl6ePh4Sn-catalyzed polymerization is known to be many-fold
lower (by 4e5 times) than that of the terminal acetylenes [16]. In
2.1. Synthesis of phenylferrocenylacetylene (1)
The starting monomer (phenylferrocenylacetylene)
1 was
synthesized by the method representing a combination of the
following four steps: (1) the synthesis of copper phenylacetylenide
[12], (2) synthesis of chloromercuroferrocene [13], (3) syntheis of
iodoferrocene [14] and (4) non-catalytic cross-coupling of the latter
with copper phenylacetylenide [15] (Scheme 1).
NH OH
CuI/
EtOH-H2O, 20 oC, 15 min
4
1.
Cu
60% (77% [12])
HgCl
Hg(CH3COO)
LiCl (EtOH-H2O)
Hg(CH3COO)2
Fe
Fe
2.
Fe
o
MeOH-C H ,
20 C, 22 h
6
6
refluxing, 1 h
42% (73% [13])
.
I
2I2
HgCl
I
Na2S2O3
n
-Xylene
I2 /
115-120 oC
Fe
Fe
3.
Fe
54% (64% [14])
I
Pyridine
refluxing, 10 h
4.
+
Cu
Fe
Fe
93% (84% [15])
Scheme 1. Synthesis of phenylferrocenylacetylene.

126
I.V. Tatarinova et al. / Journal of Organometallic Chemistry 706-707 (2012) 124e127
The study of thermal oxidative destruction of
a sample
(obtained with 4.6 wt % WCl6, 130 ꢀS, 24 h, Table 1) of oligomers 2
demonstrated that it lost 10 wt % of weight upon heating up to
250 ꢀS. Further heating (up to 400 ꢀS) resulted in 50 wt % weight
loss. The DTA curve showed one exothermic peak at 275 ꢀS
WCl6
n
(D
T ¼ 118 ꢀS). Total destruction of the oligomer occurred at 540 ꢀS.
Fe
1
Fe
2
3. Conclusion
In conclusion, for the first time, WCl6 was shown to be active for
the oligomerization of internal ferrocenylacetylenes to afford short
polyenes with pendant ferrocene and benzene substituents in
moderate yields. Such polyenes are promising reactive macro-
monomers and building blocks for the design of high-tech polymer
materials including those possessing improved redox, electric,
magnetic, preceramic, catalytic and optical properties.
n = 5 (for soluble oligomer obtained in the presence of
WCl6 (130 oC, 24 h))
Scheme 2. Polymerization of phenylferrocenylacetylene.
our case, the observed low proneness of phenylferrocenylacetylene
to polymerization is in good agreement with these literature data.
The comparison of oligomer yields obtained in the presence of
WCl6 and the system WCl6ePh4Sn (Table 1) show that these cata-
lysts possess almost similar reactivity.
Radical initiation of phenylferrocenylacetylene polymerization
(AIBN, UV-irradiation or both) afforded the oligomers in negligible
yields (not exceeding 5%), the final products being completely
insoluble (Table 1).
4. Experimental
4.1. Materials
Solvents (chlorobenzene, toluene, n-hexane) were purified
according to the literature protocols [17]. AIBN was recrystallized
twice from ethanol (m.p. 102 ꢀS).
Phenylferrocenylacetylene (1) was synthesized by the proce-
dures [12e15]. Before polymerization, monomeric phenyl-
ferrocenylacetylene (1) was purified by recrystallization from
ethanol, constants of the monomer corresponded to literature data
[15], purity of the monomer was controlled by IR, NMR and
chromatomass-spectrometry techniques.
According to the IR spectroscopy data, oligomers 2 have polyene
main chain with pendant ferrocenyl and phenyl substituents
(Scheme 2).
The spectra of the oligomers contained no absorption bands of
the C^C bond (in the monomer, these bands were observed at
2208 and 2223 cmꢁ1). Bands of other groups and bonds were
significantly broadened that was typical for oligomers. The
absorption bands of the ferrocene skeleton and benzene ring
remained at 1685e1780 cmꢁ1 and 693e700, 756e765, 1600,
1630e1638, 3057e3065 cmꢁ1, respectively. The absorption bands
4.2. Physical measurements
IR spectra of phenylferrocenylacetylene (1) and oligomers 2
were registered in the region 400e4000 cmꢁ1 with a FT IR Spec-
trometer Vertex-70 instrument as KBr pellets. NMR spectra were
recorded at room temperature on a Bruker DPX 400 (400.13 MHz
for 1H and 100.6 MHz for 13S) using SDCl3 solvent and HMDS as the
internal standard.
The electrical conductivity of oligomers 2 was measured with an
E6-13A teraohmmeter. The studied samples were prepared as
pellets by molding under a pressure of 700 kg cmꢁ2. The oligomers
were doped with iodine using diffusion technique from gas phase
for 24 h.
The ESR spectra were measured with an ELEXSYS E580 Bruker
spectrometer in CW or pulse mode at room temperature. The
concentration of paramagnetic centers was calculated by the
method of double integration using the calibrated diphenylpy-
crylhydrazyl as standard.
of the S]S bond appeared in the region 1640e1650 cmꢁ1
.
Electroconductivity and paramagnetism of the soluble fraction
of oligomers 2 were measured and its thermal stability was
evaluated.
As expected, oligomers 2 showed semi-conducting properties
(
s
¼ 1.0 10ꢁ9 S cmꢁ1). Doping of the oligomers with iodine increased
their electroconductivity by 3 orders (
s
¼ 1.0 10ꢁ6 S cmꢁ1).
Oligomers 2 were paramagnetic. In their ESR spectra, a singlet
on the background of very broad line of Fe3þ (N ¼ 6.7 1017 spin gꢁ1
ΔH ¼ 9.2 G; g ¼ 2.0029) was registered.
;
Table 1
Oligomerization conditions and yield of oligophenylferrocenylacetylene.
The mass spectra (electron impact, 70 eV) were recorded on
a Shimadzu GCMS-QP5050A instrument. The microanalyses were
performed on a Flash EA 1112 Series elemental analyzer.
The thermogravimetric analysis (TGA) of oligomers 2 was per-
formed on a Q-1500D derivatograph (MOM, Hungary), maximal
temperature 700 ꢀS, at heating rate of 5 ꢀC minꢁ1; the sensitivity
for DTA was 1/10.
Oligomerization of phenylferrocenylacetylene under UV-
irradiation was performed in a quartz ampoule using a 222 W Hg
lamp.
Catalyst (wt %)a or Solvent
initiator (wt %)a or
initiation
Monomer
concentration,
wt %
T, ꢀS Time, h Yieldb, %
WCl6, 4.6
No solvent
No solvent
100
100
130
130
90
64
24
24
24
24
24
48
48
48
29 (15c)
15 (15c)
14 (4c)
11 (11c)
12 (9c)
6 (6c)
Chlorobenzene 30
Chlorobenzene 10
90
80
WCl6-Ph4Sn, 14
Benzene
Benzene
Benzene
Benzene
Benzene
30
10
35
35
35
80
90
85
85
AIBN, 4.0
AIBN þ UV, 2.0
UV
4 (0c)
5 (0c)
5 (0c)
To evaluate the molecular weight of oligomers 2 size exclusion
chromatography (SEC) in THF (0.2% solution) was conducted at an
elution rate of 1.1 mL minꢁ1 using Waters gel columns: 250, 500,
and 1000Å at 25 ꢀS.
a
Relative to monomer.
Overall yield of oligomer.
Yield of soluble fraction.
b
c

I.V. Tatarinova et al. / Journal of Organometallic Chemistry 706-707 (2012) 124e127
127
4.3. Synthesis
brown powders, infusible on heating up to 350 ꢀS, insoluble in n-
hexane, ethanol, acetone, acetonitrile. Anal. Calc. for C18H14Fe
(286.16): C, 75.55; H, 4.93; Fe, 19.52. Found for soluble fraction: S,
74.97; H, 5.08; Fe, 19.10.
4.3.1. Phenylferrocenylacetylene
M.p. 126-128 ꢀS. IR (KBr, cmꢁ1): 3097 w, 3064 w, 3023 w,
2922 m, 2851 w, 2223 and 2208 (nC^C), 1955 w, 1885 w,1767e1644
(w, ferrocene skeleton), 1596 w, 1570 w, 1492 m, 1439 m, 1408 w,
1386 w, 1350 w, 1331 w, 1292 w, 1275 w, 1254 w, 1204 m, 1165 w,
1154 w, 1102 m, 1069 m, 1051 w, 1024 m, 999 m, 922 m, 864 w,
822 s, 813 m, 785 w, 693 s, 669 w, 544 m, 515 m, 496 s, 483 s, 468 m.
Acknowledgements
The authors express their gratitude to Yu. A. Myachin and Dr. T.I.
Vakulskaya for the measurements performed.
1H NMR (CDCl3):
d 7.47 (m, 2H, Ho), 7.29 (m, 3H, Hm,p), 4.48 (t, 2H,
3Ja ¼ 1.9 Hz, Ha), 4.22 (s, 5H, C5H5), 4.21 (t, 2H, 3Jb ¼ 1.9 Hz, Hb).
,
b
,a
13C NMR (CDCl3):
d 131.37 (Co),128.25 (Cm), 127.62 (Cp),123.92 (Ci of
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4.3.2. Oligomerization of phenylferrocenylacetylene (typical
procedure)
Phenylferrocenylacetylene (8.78 g, 30.68 mmol) and WCl6
(0.404 g, 1.02 mmol) was placed in an ampoule blown with argon.
The ampoule was sealed and thermostated at 130 ꢀS for 24 h. The
reaction mixture was dissolved in benzene (20 ml), the insoluble
fraction was separated from soluble one by filtration. The insoluble
fraction was washed with benzene. The soluble fraction was
precipitated in n-hexane (100 ml) and washed with the precipitator
(3 ꢂ 50 ml). Both fractions were dried in vacuum (1 Hg mm) until
the constant weight to give 2.55 g of oligophenylferrocenylacety-
lene in 29% overall yield. The yield of soluble fraction was 15%
(1.32 g). Both fractions of oligophenylferrocenylacetylene are dark-
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