Ferrocenylanthracene polymers: The direct synthesis using "Lawesson's Reagent"

Article abstract of DOI:10.1016/S1387-7003(03)00059-5

A method for polymerizing ferrocenylanthraquinone compounds was investigated, using a methodology developed originally for the polymerization of 9,10-anthracenedithiols. This procedure uses an in situ reaction of "Lawesson's Reagent" (p-methoxyphenylthion

Full text of DOI:10.1016/S1387-7003(03)00059-5

Inorganic Chemistry Communications 6 (2003) 639–642
www.elsevier.com/locate/inoche
Ferrocenylanthracene polymers: the direct synthesis using
‘‘LawessonÕs Reagent’’
*
Ian R. Butler , Alfonso G. Caballero, Glenn A. Kelly
Department of Chemistry, University of Wales, Bangor, Bangor, Gwynedd LL57 2UW, UK
Received 11 February 2003; accepted 22 February 2003
Abstract
A method for polymerizing ferrocenylanthraquinone compounds was investigated, using a methodology developed originally for
the polymerization of 9,10-anthracenedithiols. This procedure uses an in situ reaction of ‘‘LawessonÕs Reagent’’ (p-meth-
oxyphenylthionophosphine sulphide dimer), with anthraquinone allowing polymerization to proceed across the 9- and 10-positions
of the ferrocenylanthraquinones resulting in polymers with pendant ferrocene groups on the polymer backbone. Monomers used for
these reactions were anthraquinone (literature comparison), 2-ferrocenylanthraquinone and 2,6-diferrocenylanthraquinone.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Anthraquinone; Ferrocene; Ferrocenylanthraquinone; ‘‘LawessonÕs Reagent’’; Polymers
1. Introduction
we report the synthesis and characterization of these two
compounds prior to their polymerization with ‘‘Lawes-
sonÕs Reagent’’ or p-methoxyphenylthionophosphine
sulphide dimer (see Fig. 1).
Polymers with ferrocene side groups are of significant
interest as potential electrode mediators and as materials
for the inclusion into electronic devices [1–3]. The use of
anthracene as a backbone would provide an excellent
conjugated polymer with well-defined rigid structures
[4]. Materials containing anthracene are of particular
interest because of their potential electroluminescent
properties [5]. This work is a continuation of our long-
standing interest in the area of ferrocenylanthracene
chemistry [6]. The starting materials for the polymeri-
zation experiments were anthraquinone, 2-ferro-
cenylanthraquinone and 2,6-diferrocenylanthraquinone.
The synthesis of 1-ferrocenylanthraquinone was first
reported by Roberts [7] in 1990 from the reaction of the
commercially available 1-diazoniumanthraquinone (Al-
drich Fast Red AL Salt) and ferrocene. A one-pot syn-
thesis of a mixture of 2-ferrocenylanthraquinone and
2,6-diferrocenylanthraquinone has recently been re-
ported by Coudret and Launay [8], but these com-
pounds were not isolated or characterized. In this paper
This reagent is well known to polymerize diketones
such as anthraquinone [9], as it an oxygen scavenger
replacing the oxygen with sulphur. It is a convenient
thiation reagent for ketones, amides, esters and S-
substituted thioesters [10]. In the case of anthraquinone
it is long-established that the thioketone is unstable and
thus forms a polymer with persulphide bridges. This
polymer, anthracene polydisulphide, has also been re-
ported to undergo reduction with sodium borohydride
to give anthracene 9,10-dithiol which has in turn been
used as a monomer in the reaction with 9,10-diethy-
nylanthracene to give conjugated acetylene polymers
with anthracene backbones [11].
2. Experimental
2.1. Preparation of 2-ferrocenylanthraquinone, method 1
Using a standard literature procedure [10], concen-
trated HCl (7 ml) was added to 2-aminoanthraquinone
(2.73 g, 0.0125 mol) at 30 °C. Then a solution of sodium
* Corresponding author. Tel.: +44-0-12-48-382-390; fax: +44-0-12-
48-370-528.
E-mail address: chs026@bangor.ac.uk (I.R. Butler).
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00059-5

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I.R. Butler et al. / Inorganic Chemistry Communications 6 (2003) 639–642
zonium sulphate salt. Excess of ferrocene (35 g,
0.188 mol) was dissolved under nitrogen atmosphere in
200 ml of dichloromethane in another flask. To this
ferrocene solution was added the dried diazonium
salt and the mixture was stirred for 2 h. The prod-
uct formation was followed by TLC; the product
appears as a violet spot. The final solution was evapo-
rated and the residue was columned on a chromato-
graphic silica gel column. The final product was eluted
with 100% ether as a violet powder. Yield 43.7 g (36%).
Fig. 1.
nitrite (0.87 g, 0.0125 mol) in distilled water (5 ml) was
added dropwise while stirring. The temperature was
then raised to 50 °C. A solution of warm distilled water
(80 ml) was then added and the mixture was filtered
while hot. The unreacted solid was washed with warm
distilled water. To the warm filtrate, NaCl (24 g) was
added and the mixture was stirred for 10 min and then
left to cool. The yellow precipitate was then filtered,
washed with saturated NaCl solution and dried in air.
Yield: 1.40 g. The yellow product was used directly in
the next step without characterization.
To the previously formed 2-anthraquinone diazo-
nium chloride (1.40 g, 0.0052 mol) in dry CH2Cl2 (50
ml), ferrocene (2.90 g, 0.015 mol) in dry CH2Cl2 (50 ml)
was added dropwise while stirring. The mixture was
then stirred overnight at room temperature. The mixture
was then filtered, the filtrate concentrated under vacuum
and suspended in toluene. The suspension was loaded
onto a column of silica gel and the product eluted with
petrol (40/60 °C) and diethyl ether (1:1).
2.3. Preparation of 2-ferrocenylanthraquinone, method 3
1-Ferroceneboronic acid (0.25 g, 1:0 ꢀ 10ꢁ3 mol) and
2-bromoanthraquinone (0.35 g, 1:2 ꢀ 10ꢁ3 mol) were
dissolved in a solution of dry DMF (30 ml) and potas-
sium carbonate (0.20 g). Tetrakis(triphenylphosphine)
palladium (0) (0.05 mol%) was then added under N2 gas.
The mixture was then heated to reflux for 20 min under
N2 gas (after 2 min the solution changed from dark
orange to violet). After cooling to room temperature,
the mixture was stirred for two days. The product was
purified by column chromatography using neutral alu-
mina and diethyl ether and petroleum ether (40/60 °C)
as eluting solvent. The product was found to be identi-
cal to 1-ferrocenyl-2-anthraquinone. Yield 0.39 g (91%)
dH (250 MHz, CDCl3): 4.06(s, 5CH), 4.48(s, 2CH),
4.84(s, 2CH), 7.39–8.42(m, 7ArH).
Yield 0.44 g (22%). Appearance – blue/black crystals,
mp 174 °C (uncorr.) dH (CDCl3): 4.04(s, 5H), 4.46(t,
J ¼ 1:8 Hz, 2H), 4.82(t, J ¼ 1:8 Hz, 2H), 7.79(m, 3H),
8.19(d, J ¼ 8 Hz, 1H), 8.30(m, 3H). dC(62.9 MHz,
CDCl3): 67.23(2C, cyclopentadienyl b), 70.20(5C, cy-
clopentadienyl, unsubstituted), 70.58(2C, cyclopenta-
dienyl a), 82.12(C, cyclopentadienyl ipso), 123.70,
127.17, 127.20, 127.63, 130.78, 133.50, 133.56, 133.61,
133.81, 134.12, 147.58, 156.33, 182.75(CO), 183.5(CO).
MS (EI) m=e (rel. int.): 392 Mþ. (100%), 213(15%),
196(12%), 121(32%). Elemental analysis (FeC24H16O2);
calc. %: C 73.47, H 4.08, found %: C 73.79, H 4.05. This
compound has been also characterized by single crys-
tal X-ray diffraction, the results of which will be pre-
sented in a general synthetic manuscript with the
crystallographic structures of a range of ferrocenyl
anthraquinones.
2.4. Preparation of 2,6-diferrocenylanthraquinone
To a solution of nitrosyl sulphuric acid (2.5 g) in
sulphuric acid (15 ml, 78%), 2,6-diaminoanthraquinone
(1.18 g, 0.005 mol) was added with vigorous stirring.
After stirring for 2 h, the mixture was filtered and flu-
oroboric acid (25 ml, 50%) was then added to the fil-
trate. A white precipitate was then formed which was
isolated by filtration, washed with water and dried in air.
The 2,6-anthraquinone tetrazonium boron tetrafluoride
salt was then used directly in the next step without
characterization.
To the crude 2,6-anthraquinone tetrazonium salt in
dichloromethane (50 ml), ferrocene was added (2.5 g,
0.01 mol) while stirring. The mixture was then stirred
overnight at room temperature. The mixture was then
filtered, the solvents were evaporated under vacuum and
the product was purified by flash chromatography
(solvents: 20% diethyl ether/dichloromethane). Yield
0.60 g (21%). Appearance blue/black solid. dH (250
MHz, CDCl3): 4.09(s, 10CH), 4.51(s, 4CH), 4.88(s,
4CH), 7.85(m, 2ArH), 8.30(m, 4ArH). MS (EI) m=e (rel.
int.): 576 Mþ (30%), 392 (100%), 379 (55%), 363 (18%),
215 (20%).
2.2. Preparation of 2-ferrocenylanthraquinone, method 2
2-Aminoanthraquinone (60 g, 0.269 mol, 1 equiv.)
was dissolved in 100 ml of concentrated sulphuric acid
under nitrogen atmosphere. To the well stirred solution,
nitrosyl sulphuric acid (37.57 g, 0.300 mol, 1.1 equiv.)
was added slowly and the mixture was allowed to react
for 15 min. Afterwards, the reaction mixture was slowly
added to an ice/water bath. The precipitate was filtered,
washed with 200 ml of water and air dried as the dia-
Accurate mass: calc. 576.047507, found 576.049562.
Elemental anal.: calcd; C, 70.83%, H, 4.16, found
67.94%, 4.25.

I.R. Butler et al. / Inorganic Chemistry Communications 6 (2003) 639–642
641
2.5. Formation of polymers from 2,6-diferrocenylanthr-
aquinone
phuric acid, using standard conditions [13], followed by
reaction with ferrocene gave the product in 36% yield.
Again although the reaction yields are significantly
better the reaction workup and product isolation pro-
cedure was tedious. An improved procedure involved
the catalytic ‘‘Suzuki’’ coupling reaction of 1-ferrocen-
eboronic acid [14] and 2-bromoanthraquinone (from
the ‘‘Sandmeyer’’ reaction of 2-diazoniumanthraqui-
none and copper(II) bromide) using tetrakis(triphenyl-
phosphine) palladium (0) as catalyst using standard
conditions [15], giving the product in 91% yield (see
Scheme 2).
To a stirred solution of ‘‘LawessonÕs Reagent’’ (0.30
g, 7 ꢀ 10ꢁ4 mol) in boiling chlorobenzene (30 ml), 2,6-
diferrocenylanthraquinone (0.20 g, 3 ꢀ 10ꢁ4) was added
in hot chlorobenzene (50 ml). The mixture was then
heated to reflux for 1.5 h. The mixture was then allowed
to cool and the brown solid was filtered. Yield 125 mg
(67%). Petroleum ether(40/60 °C) was added to the
mother liquor to give a further crop of brown crystals.
Yield 25 mg (14%). Overall yield – 81%.
dH(250 MHz, CDCl3): 4.03(br. s, 10CH), 4.36(br. s,
4CH), 4.78(br. s, 4CH), 7.69(br. s, 3ArH), 8.31(br. s,
3ArH).
An attempt was first made to synthesize 2,6-difer-
rocenylanthraquinone from the tetrazonium chloride
salt, but the yield from this procedure was very low (1%)
due to the relative instability of this particular salt.
Therefore our starting materials were finally synthesized
by converting the tetrazonium chloride salt of the an-
thraquinone into tetrazonium tetrafluoroborate [13].
2,6-Diaminoanthraquinone is first reacted with nitrosyl
sulphuric acid in concentrated sulphuric acid to create
the tetrazonium salt with bisulphate as the counter ion.
The mixture is then reacted immediately with tetraflu-
oroboric acid to give the more stable tetrazonium tet-
rafluoroboric salt (see Scheme 3).
A similar reaction of 2-ferrocenylanthraquinone un-
der identical experimental conditions gave a deep green/
black polymer which was characterized by solid state
NMR as follows. 13C (125.77 MHz) d: 33.38, 56.26,
73.30 with underlying ca. 70.00–82.00, broad reso-
nances, 90.2, 118.31, 133.23, 163.29, 174.63, 204.61. The
deep red polymer which was prepared from LawessonÕs
Reagent and unsubstituted anthraquinone using the
literature methodology was similarly characterized 13C
(125.77 MHz) d: (43.14, 51.43, 85.62, 127.56, 134.42,
169.30, 176.14, 210.57, 217.36, 252.76).
This more stable salt was then reacted with an excess
of ferrocene in dichloromethane to give 2,6-difer-
rocenylanthraquinone in improved yields (21%) (see
Scheme 4).
3. Results and discussion
This dark blue black solid was characterized by
NMR and mass spectrometry and exhibited a clean
The ferrocenylanthraquinone monomer compounds
were all synthesized from cheap and commercially
available aminoanthraquinone starting materials. Sev-
eral procedures were initially used to form the precursor,
2-ferrocenylanthraquinone, beginning with diazotiza-
tion of 2-aminoanthraquinone using a mixture of so-
dium nitrite and hydrochloric acid [12]. The diazonium
chloride salt was then reacted with an excess of ferro-
cene in dichloromethane, giving a dark blue solid in 22%
yield (see Scheme 1).
Scheme 2.
The poor yields prompted the use of an alternative
diazotization procedure using nitrosyl sulphuric acid as
the active reagent. Thus diazotization with nitrosyl sul-
Scheme 3.
Scheme 1.
Scheme 4.

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I.R. Butler et al. / Inorganic Chemistry Communications 6 (2003) 639–642
ca. 33 and 56 ppm. This was consistent with the results
obtained of a control polymer prepared from only an-
thraquinone and LawessonÕs Reagent which showed
similar resonances at ca. 43 and 51 ppm.
4. Conclusions
Scheme 5.
The synthesis of ferrocene containing polysulphide
polymers of anthracene have been obtained for the first
time. These materials will now be used as precursors for
material science applications.
parent ion at m=e 576. The main by-product of the re-
action was 2-ferrocenylanthraquinone. The NMR
spectra were as anticipated with the ferrocenyl reso-
nances observed at 4:09d (unsubstituted rings), 4:51d
and 4:88d.
Acknowledgements
3.1. Polymerization of 2,6-diferrocenylanthraquinone
and 2-ferrocenylanthraquinone
We gratefully acknowledge the EPSRC and ESF for
the funding of our students. We also thank both Mr.
Glyn Connolly for the NMR service at the University of
Wales, Bangor and the staff at the University of Wales,
Swansea for the Mass Spectrometry.
Once the 2,6-diferrocenylanthraquinone and 2-ferro-
cenylanthraquinones had been isolated, the next exper-
iments carried out were to see if the carbonyl groups on
the 9- and 10-positions on the anthraquinone could be
polymerized forming a polymer with pendant ferrocenyl
units. When these diferrocenyl compound was added to
a hot solution of ‘‘LawessonÕs Reagent’’ [16] (two
equivalents) in chlorobenzene in each case a green/black
to dark brown polymer material resulted after the mix-
tures were heated to reflux for 1.5 h (see Scheme 5).
The products were isolated as solids which slowly
precipitated from the solution on cooling in 45%
(monoferrocenyl) and 81% (diferrocenyl) yield. More
soluble oligomeric fractions of these polymers were
characterized by 1H NMR in deuterated chloroform.
The spectra in each case exhibited very broad reso-
nances, typical of polymeric material, in the region of
between d4:03 and 4.78 ppm indicating the presence of
the cyclopentadienyl protons. Broad resonances in
the region of d7:69 and 8.31 ppm again were a charac-
teristic of the aromatic environments of the anthracenyl
protons.
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anthraquinone and 2-ferrocenylanthraquinone were also
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