A new phthalocyanine-ferrocene conjugated dyad

Article abstract of DOI:10.1016/S0022-328X(01)00906-8

The synthesis and optical properties of a new phthalocyanine-ferrocene conjugated dyad are reported. Using a Pd(0)-catalysed cross-coupling reaction, an unsymmetrical substituted metallophthalocyanine linked to a ferrocene subunit by an arylene-alkynylene spacer has been prepared. The electronic properties of this linearly π-conjugated compound and related ones were investigated by UV-visible spectroscopy.

Full text of DOI:10.1016/S0022-328X(01)00906-8

Journal of Organometallic Chemistry 637–639 (2001) 751–756
www.elsevier.com/locate/jorganchem
Note
A new phthalocyanine–ferrocene conjugated dyad
Ana Gonz a´ lez-Cabello, Purificaci o´ n V a´ zquez *, Tom a´ s Torres *
Departamento de Qu ´ı mica Org a´ nica (C-I), Uni6ersidad Aut o´ noma de Madrid, Cantoblanco, 28049 Madrid, Spain
Received 27 December 2000; received in revised form 16 March 2001; accepted 20 March 2001
Abstract
The synthesis and optical properties of a new phthalocyanine–ferrocene conjugated dyad are reported. Using a Pd(0)-catalysed
cross-coupling reaction, an unsymmetrical substituted metallophthalocyanine linked to a ferrocene subunit by an arylene–
alkynylene spacer has been prepared. The electronic properties of this linearly p-conjugated compound and related ones were
investigated by UV–visible spectroscopy. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Phthalocyanines; Ferrocene; Arylene–alkynylene; Pd(0)-catalysed cross-coupling
1
. Introduction
It is well known, that polyacetylene spacers operate
as effective bridges for conducting electronic charge
between redox active terminal units. Furthermore, it is
possible to modulate the electronic coupling properties
of such systems by introducing polycyclic hydrocar-
bons, as phenyl rings, along the wire between the two
terminal units [6]. These linkers fulfil important requi-
sites such as rigidity, linearity and synthetic versatility.
Following our interest in exploiting electronic and
photonic interactions between individual subunits in
multicomponent systems [7], we report herein the syn-
thesis and optical properties of a new phthalocyanine–
ferrocene conjugate consisting of an unsymmetrical
substituted metallophthalocyanine linked to a ferrocene
subunit by an arylene–alkynylene spacer.
Phthalocyanines (Pcs) have been an area of increas-
ing research for several years, due to their applicability
in a variety of fields, such as liquid crystals, semicon-
ductors, non-linear optics and electron transfer, among
others [1]. Pcs are compounds of special interest for
their unique redox [2] and photophysical properties. On
the other hand, it is well known that ferrocene exhibits
chemical stability and well defined electrochemical
properties, and therefore it has been widely used in the
construction of multicomponent systems [3].
Taking into account the particular electronic charac-
teristics of phthalocyanines, ferrocene-bridge–phthalo-
cyanine dyads combining two redox active centres
should be an excellent model for studying intramolecu-
lar electron transfer processes.
Until now, only a few examples of covalently linked
phthalocyanine–ferrocene systems have been reported
[4,5], and most of them are not conjugated systems.
Recently [5], we have reported on phthalocyanine–fer-
rocene dyads and triads in which both subunits are
bound together through ethenyl spacers.
*
Corresponding authors. Tel.: +34-91-397-4705; fax: +34-91-
397-3966.
E-mail addresses: purificacion.vazquez@uam.es (P. V a´ zquez),
tomas.torres@uam.es (T. Torres).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00906-8

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A. Gonz a´ lez-Cabello et al. / Journal of Organometallic Chemistry 637–639 (2001) 751–756
To the best of our knowledge this is the first phthalo-
trum of 4 a new signal appears at 3.3 ppm
cyanine–ferrocene dyad in which the active centres are
corresponding to the proton of the terminal ethynyl
connected by a polyalkynyl spacer [8].
group.
The synthesis of the metallophthalocyanine–fer-
rocene system 1 has been carried out following a
modified Sonogashira procedure. The reaction between
phthalocyanine 4 and iodoferrocene 5 using a catalyst
formed by tris(dibenzylidenacetone)dippalladium(0)
[Pd (dba) ] and triphenylarsine (AsPh ) in a freshly
2
. Results and discussion
Phthalocyaninato zinc(II)-ferrocene dyad (1) has
been prepared from ethynyl-Pc (2), previously described
by us [9], in a three-step sequence (Scheme 1).
2
3
3
distilled and deaerated diisopropyl amine afforded com-
Thus (tri-tert-butyl-ethynylphthalocyaninato) zinc(II)
pound 1 in moderate yield.
(
2) [9] (mixture of isomers) was reacted with 4-
Although in the present case a copper-free palladium
catalyst was used to perform the cross-coupling, in
order to minimize the homocoupling reaction of the
phthalocyanine 4, compound 6 was always detected
under the employed conditions. The isolation of fer-
trimethylsilylethynyliodobenzene [10] using Sono-
gashira conditions [PdCl (PPh ) , CuI] employing
triethyl amine as base and affording the corresponding
2
3 2
1
cross-coupling compound 3 in good yield. The H-
NMR spectrum of this compound shows one singlet at
l 0.4 ppm for the trimethysilyl group and a large
number of signals for the tert-butyl groups, pointing
out the mixture of regioisomers that constitute com-
pound 3.
rocene–metallophthalocyaninato dyad 1 from the
reaction mixture was carried out by column
chromatography. In this process compound 6 could
1
also be isolated. In the H-NMR spectrum of 1, it is
possible to assign the signals corresponding to the
ferrocene subunit, namely two multiplets centred at l
4.2 and 4.6 ppm for the substituted cyclopentadienyl
ring and a broad singlet at l 4.4 ppm for the unsubsti-
tuted one.
The trimethylsilyl group of compound 3 could be
quantitatively removed by treatment with tetrabutyl
ammonium fluoride in tetrahydrofurane solution af-
1
fording the terminal alkyne 4. In the H-NMR spec-
Scheme 1.

A. Gonz a´ lez-Cabello et al. / Journal of Organometallic Chemistry 637–639 (2001) 751–756
753
The UV–visible spectra of compounds 1, 2, 4 and 6
are depicted in Fig. 1. The position of the Soret band
B band) in compounds 1 and 4 is quite similar to that
of the parent ethynyl-phthalocianinato 2. However,
while the ethynyl-Pc 2 shows only a Q band at 684 nm,
as is usual in metallated Pcs, compound 1 exhibits a
split Q band (680 and 692 nm) somewhat shifted to the
red. However, there are no remarkable differences be-
tween the UV–visible spectra of compounds 1 and 4,
thus indicating that the splitting is a consequence of the
increasing conjugation of the Pc-system and not of an
electronic coupling between the Pc and the ferrocene
subunits. Taking into account this fact and references
in the literature [4,5], it is possible to suggest that the
ferrocenyl group is electronically independent in com-
pound 1.
The UV–visible spectrum of the homocoupling com-
pound 6 also shows a split Q-band, as well as a
broadening and red-shifting of this absorption with
regard to compound 2. This effect has been observed in
(
−
5
mol dm−3) (—), 2 (2.9×10−5 mol dm−3) (···), 4 (3.7×10−5 mol dm−3) (- - -), and 6
Fig. 1. Electronic spectra in CHCl of 1 (1.4×10
3
−
5
−3
(8.6×10
mol dm ) (—).

754
A. Gonz a´ lez-Cabello et al. / Journal of Organometallic Chemistry 637–639 (2001) 751–756
Scheme 2.
other conjugated systems previously described by our
group and it has been explained as the result of the
extended conjugation of the system [9,11]. The close
resemblance between the UV–visible spectra of 1 and 6,
the latter having a higher conjugation degree, suggests a
saturation of the optical properties in the series. This
effect had been already observed in related di-
ethynylethene bisphthalocyaninato complexes [12].
Attempts to prepare triad 7 (Scheme 2) by reaction of
diiodoferrocene (8) with two molar equivalents of
phthalocyaninato 4 led to the monosubstituted com-
pound 9 in moderate yield (Pd (dba) –AsPh , room
4. Experimental
Infrared spectra were recorded on a Perkin–Elmer
spectrophotometer. The H-NMR spectra were ob-
1
tained on a Bruker AC300. UV–visible spectra were
recorded on a Perkin–Elmer Lambda 6 spectrometer
using chloroform as solvent. The mass spectra were
determined on a VG AutoSpec spectrometer. Elemental
analyses were performed on a Perkin–Elmer 2400 CHN
elemental analyser.
Reactions were performed under an atmosphere of
dry nitrogen. Solvents were distilled prior to use from
an appropiate drying agent. Chromatographic purifica-
tion were performed on silica gel columns (Merck,
230–400 mesh) and aluminium oxide neutral (70–230
mesh) with the indicated eluents. 4-trimethylsi-
lylethynyliodobenzene [10], 1,1%-diiodoferrocene [13]
and (tri-tert-butyl-ethynylphthalocyaninato)zinc(II) (2)
[9] were prepared according to literature procedures.
All tetrasubstituted phthalocyanines synthesized were
obtained as a mixture of 2,9,16,24-, 2,10,16,24-,
2
3
3
temperature, 12 h, 48%) together with an important
amount of unreacted diiododerivative 8 and compound
6. The second cross-coupling reaction on the ferrocene
seems to be more difficult, thus facilitating the forma-
tion of the dimer 6. By performing the reaction under
stronger reaction conditions (Pd (dba) –AsPh , 36 h rt
2
3
3
and then 12 h 50 °C) compound 7 could be detected in
the reaction mixture by mass spectrometry but the
synthetic method is revealed to be inadequate.
2
,9,17,24-, and 2,9,16,24-regioisomers.
3. Conclusions
4.1. 1-Iodoferrocene
A novel type of linearly p-conjugated molecular
This compound was synthesized using a modified
literature procedure [14]. Ferrocene (0.5 g, 2.68 mmol)
was stirred for 30 min in 2.5 ml of dry tetrahydrofurane
and 2.5 ml of dry hexane under argon at rt and then
cooled to 0 °C. A 1.5 ml volume of a 1.5 M solution of
BuLi in pentane (2.23 mmol) was added dropwise
during 30 min. The mixture was stirred another 90 min
at this temperature and then was cooled to −78 °C
dyad, in which a Pc chromophore is linked to a fer-
rocene moiety by an arylene–alkynylene spacer has
been prepared. UV–visible investigations did not reveal
a significant interaction between the Pc and the metal-
locene. Electrochemical studies are now underway in
order to detect potential electronic interactions between
the two electroactive subunits.
t

A. Gonz a´ lez-Cabello et al. / Journal of Organometallic Chemistry 637–639 (2001) 751–756
755
+
(
dry ice/acetone bath). To this cooled solution was
rapidly added a solution containing 1.06 g of iodine
4.17 mmol) dissolved in 20 ml of dry diethyl ether
(m-NBA) m/z (%) 870 (100) [(M+H) ]. Anal. Calc.
for C H N Zn·3H O: C, 70.16; H, 5.45; N, 12.12.
Found: C, 70.60; H, 5.34, N, 11.75%.
54
44
8
2
(
during 15 min. After the resulting mixture was stirred
at −78 °C for 1 h, it was allowed to warm slowly to
rt, at which point 10 ml of water was added, and the
solution stirred for additional 15 min. The mixture was
extracted with CH Cl (3×25 ml), washed with water,
4.4. Tri-tert-butyl-2-ethynyl-[4-( ferrocenylethynyl)
phenyl]phthalocyaninatozinc(II) (1)
1-Iodoferrocene (80 mg, 0.25 mmol) was stirred in
freshly distilled and deaerated diisopropylamine in the
2
2
and brine and dried over MgSO . The product was
4
purified by column chromatography in aluminium ox-
ide using n-hexane as eluent. Yield 42%, orange
presence of Pd (dba)3 (20 mg) and AsPh3 (50 mg).
2
Compound 4 (110 mg, 0.125 mmol) was then added
and the mixture was stirred under argon atmosphere at
90 °C for 10 h. The green solution was evaporated to
dryness, extracted with dichloromethane, and washed
with water. The compound was purified by column
chromatography (silica gel toluene–isopropyl alcohol
40:1). Yield 27% (35 mg), dark green powder. M.p.
needles. M.p. 45 °C. [lit. 44–45 °C].
1
H-NMR (CDCl ): l 4.1 (t, 2H), 4.2 (s, 5 H), 4.4 (t,
3
2H).
4
2
.2. Tri-tert-butyl-{ethynyl-2-phenyl-[4-ethynyl-
-(trimethylsilyl)]}phthalocyaninatozinc(II) (3)
\
250 °C.
1
t
A mixture of (tri-tert-butylethynylphthalocyaninato)
H-NMR (CDCl ): l 1.3–1.8 (m, 27 H, Bu), 4.18
3
zinc(II) (2) (114 mg, 0.12 mmol) and 4-trimethylsi-
lylethynyliodobenzene (39 mg, 0.12 mmol) was stirred
under argon at 40 °C for 10 h, in freshly distilled and
deaerated Et N in the presence of [Pd(PPh ) Cl ] (18
(m, 2H, FcH), 4.35 (s broad, 5H, FcH), 4.61 (m, 2H,
FcH), 7.6–8.9 (m, 16H, ArH). UV–visible (CHCl )
3
3
−1
−1
umax (log m dm mol cm ) 351 (4.66), 616 (4.17), 680
(4.81), 692 (4.87). IR (KBr) w 2923, 2212 (CꢀC), 1635
Anal. Calc. for
C H N ZnFe·3H O: C, 69.35; H, 5.27; N, 10.11.
3
3 2
2
−
1
mg, 10%) and CuI (5 mg). The solution obtained was
evaporated to dryness. The residue was extracted with
CH Cl and washed with water. The product was
(CꢁN), 1088, 802 cm
.
64
52
8
2
Found: C, 69.56; H, 5.67, N, 10.45%.
2
2
purified by chromatography (silica gel, toluene–isopro-
pyl alcohol 100:1). Yield 76%, dark-blue powder. M.p.
4.5. Bis-[(tri-tert-butylphthalocyaninato)zinc(II)]-
1,4-bis-[phenyl-(4-ethynyl)]butadiyne (6)
\
250 °C.
1
H-NMR (CDCl ): l 0.4 [s, 9H, Si(CH ) ], 1.4–1.6
3
3 3
t
(
(
m, 27 H, Bu), 7.3–8.2 (m, 16H, ArH). UV–visible
From the chromatographic separation performed
above before isolation of compound 1, product 6 was
eluted. Yield 19% (20 mg), dark green powder. M.p.\
250 °C.
3
−1
−1
CHCl ) u
(log m dm mol
cm ) 290 (4.92), 350
3
max
(
2
5.05), 615 (4.62), 679 (5.25), 692 (5.32). IR (KBr) w
−
1
954, 2153 (CꢀC), 1612 (CꢁN), 1087, 862, 834 cm
.
+
+
1
t
FAB -MS (m-NBA) m/z (%) 941 (100) [(M+H) ].
Anal. Calc. for C H N SiZn·2H O: C, 69.53; H, 5.68;
H-NMR (CDCl ): l 1.4–1.9 (m, 54H, Bu), 6.7–9.4
3
3
(m, 32H, ArH). UV–visible (CHCl ) u (log m dm
5
7
52
8
2
3
max
−
1
−1
N, 10.73. Found: C, 69.96; H, 5.77, N, 11.45%.
mol
cm ) 351 (4.3), 679 (4.1), 694 (4.2). IR (KBr) w
−
1
2
955, 2205 (CꢀC), 1615 (CꢁN), 1046, 830, 741 cm
;
4.3. Tri-tert-butyl-[ethynyl-2-phenyl-(4-ethynyl)]
HRMS-MALDI-TOF (dithranol) calc. for C108H86-
N Zn 1734.580 (exact), found 1734.583.
phthalocyaninatozinc(II) (4)
16
2
An equimolecular amount of tetrabutyl ammonium
fluoride in tetrahydrofuran solution (1 M) was added
dropwise to a stirred solution of compound 3 (0.09
mmol) dissolved in anhydrous tetrahydrofurane during
Acknowledgements
This work was supported by CICYT and Comunidad
de Madrid (Spain) through grants MAT-99-0180 and
07N/0020/98, respectively.
10 min. After 15 min the solvent was removed and the
residue was extracted with toluene. After drying the
organic layer with sodium sulphate and evaporating the
solvent, the product was purified by chromatography
on silica gel using CH Cl as eluent. Yield 99%, dark-
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1
t
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