Synthesis and Electrochemistry of Ferrocenylphthalocyanines

Article abstract of DOI:10.1021/om990208x

A series of phthalocyanines containing 4, 8, and 16 2-ferrocenylethoxy moieties on the periphery have been prepared and spectroscopically characterized. The UV-vis spectrum of the tetraferrocenyl phthalocyanine 4 shows an unusual long-wavelength band at ca. 760 nm in nonpolar solvents. When the spectral changes of this compound and its analogue [1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato]zinc(II) (12) are studied in different solvents and at various concentrations, along with their fluorescence spectra, it can be concluded that this band is not likely due to a slipped cofacial dimer as reported previously. Compound 4 is not emissive, which can be explained by the efficient quenching due to electron transfer from ferrocene to the excited phthalocyanine. The value of ΔG° for this photoinduced electron transfer has been estimated to be -0.48 eV. Electrochemical studies of these phthalocyanine-ferrocene conjugates by cyclic voltammetry have revealed that all the ferrocenyl redox centers attached to the macrocyclic core are electrochemically independent and undergo an oxidation at the same potential.

Full text of DOI:10.1021/om990208x

3528
Organometallics 1999, 18, 3528-3533
Syn th esis a n d Electr och em istr y of
F er r ocen ylp h th a locya n in es
Ka-Wo Poon, Yan Yan, Xi-you Li, and Dennis K. P. Ng*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong, People’s Republic of China
Received March 25, 1999
A series of phthalocyanines containing 4, 8, and 16 2-ferrocenylethoxy moieties on the
periphery have been prepared and spectroscopically characterized. The UV-vis spectrum
of the tetraferrocenyl phthalocyanine 4 shows an unusual long-wavelength band at ca. 760
nm in nonpolar solvents. When the spectral changes of this compound and its analogue
[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato]zinc(II) (12) are studied in different solvents
and at various concentrations, along with their fluorescence spectra, it can be concluded
that this band is not likely due to a slipped cofacial dimer as reported previously. Compound
4 is not emissive, which can be explained by the efficient quenching due to electron transfer
from ferrocene to the excited phthalocyanine. The value of ∆G° for this photoinduced electron
transfer has been estimated to be -0.48 eV. Electrochemical studies of these phthalocyanine-
ferrocene conjugates by cyclic voltammetry have revealed that all the ferrocenyl redox centers
attached to the macrocyclic core are electrochemically independent and undergo an oxidation
at the same potential.
In tr od u ction
together,4-7 porphyrins are of special interest because
of their biological relevance and unique redox and
photophysical properties.3,8,9 Porphyrins with up to four
ferrocenyl substituents have been reported, some of
which are also capable of sensing anionic guest species.9
Phthalocyanines are porphyrin analogues exhibiting
intriguing but distinct physicochemical properties.10 It
is therefore worthwhile to investigate the related
phthalocyanine-ferrocene conjugates, only a few ex-
amples of which have been reported so far, with a
maximum number of four ferrocenyl units in a macro-
cycle.11,12 We have recently extended this series of
In the past few years, there has been a growing
interest in molecular systems containing multiple redox-
active centers.1-3 These molecules can act as potential
candidates for multielectron redox catalysts2 and serve
as models for the studies of light-initiated intramolecu-
lar electron transfer that may shed light on complex but
practically useful processes such as solar energy conver-
sion and artificial photosynthesis.1a,3 Ferrocene, owing
to its chemical stability and well-defined electrochem-
istry, has been widely used in the construction of such
multicomponent systems. Among the various frame-
works that link the redox-active ferrocenyl units
(6) For systems containing diferrocenyl units linked with polyenes
or poly(vinylene)phenylenes, see for example: (a) Ribou, A.-C.; Launay,
J .-P.; Sachtleben, M. L.; Li, H.; Spangler, C. W. Inorg. Chem. 1996,
35, 3735. (b) Hradsky, A.; Bildstein, B.; Schuler, N.; Schottenberger,
H.; J aitner, P.; Ongania, K.-H.; Wurst, K.; Launay, J .-P. Organome-
tallics 1997, 16, 392.
(7) For systems containing multi-ferrocenyl units linked with other
moieties, see for example: (a) Fillaut, J .-L.; Linares, J .; Astruc, D.
Angew. Chem., Int. Ed. Engl. 1994, 33, 2460. (b) Fillaut, J .-L.; Astruc,
D. New J . Chem. 1996, 20, 945. (c) Deschenaux, R.; Monnet, F.;
Serrano, E.; Turpin, F.; Levelut, A.-M. Helv. Chim. Acta 1998, 81, 2072.
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3079. (b) Hisatome, M.; Takano, S.; Yamakawa, K. Tetrahedron Lett.
1985, 26, 2347. (c) Beer, P. D.; Kurek, S. S. J . Organomet. Chem. 1987,
336, C17. (d) Kadish, K. M.; Xu, Q. Y.; Barbe, J .-M. Inorg. Chem. 1987,
26, 2565. (e) Xu, Q. Y.; Barbe, J .-M.; Kadish, K. M. Inorg. Chem. 1988,
27, 2373. (f) Maiya, G. B.; Barbe, J .-M.; Kadish, K. M. Inorg. Chem.
1989, 28, 2524. (g) Loim, N. M.; Abramova, N. V.; Sokolov, V. I.
Mendeleev Commun. 1996, 46. (h) Burrell, A. K.; Campbell, W.; Officer,
D. L. Tetrahedron Lett. 1997, 38, 1249.
(9) (a) Beer, P. D.; Drew, M. G. B.; Hesek, D.; J agessar, R. J . Chem.
Soc., Chem. Commun. 1995, 1187. (b) Beer, P. D.; Drew, M. G. B.;
J agessar, R. J . Chem. Soc., Dalton Trans. 1997, 881.
(10) Phthalocyanines-Properties and Applications; Leznoff, C. C.,
Lever, A. B. P., Eds.; VCH: New York, 1989; Vol. 1; 1993; Vol. 2; 1993;
Vol. 3; 1996; Vol. 4.
(11) (a) J in, Z.; Nolan, K.; McArthur, C. R.; Lever, A. B. P.; Leznoff,
C. C. J . Organomet. Chem. 1994, 468, 205. (b) Cook, M. J .; Cooke, G.;
J afari-Fini, A. J . Chem. Soc., Chem. Commun. 1995, 1715. (c) Dabak,
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Sanchez, J . L.; Frampton, C. S. Inorg. Chem. 1998, 37, 411. (e)
Gonza´lez, A.; Va´zquez, P.; Torres, T. Tetrahedron Lett. 1999, 40, 3263.
(1) (a) Chow, H.-F.; Mong, T. K.-K.; Nongrum, M. F.; Wan, C.-W.
Tetrahedron 1998, 54, 8543 and references therein. (b) Uno, M.;
Dixneuf, P. H. Angew. Chem., Int. Ed. Engl. 1998, 37, 1714.
(2) (a) Steiger, B.; Anson, F. C. Inorg. Chem. 1994, 33, 5767. (b) Bard,
A. J . Nature 1995, 374, 13.
(3) (a) Schmidt, E. S.; Calderwood, T. S.; Bruice, T. C. Inorg. Chem.
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366, C6. (c) Wagner, R. W.; Brown, P. A.; J ohnson, T. E.; Lindsey, J .
S. J . Chem. Soc., Chem. Commun. 1991, 1463. (d) Giasson, R.; Lee, E.
J .; Zhao, X.; Wrighton, M. S. J . Phys. Chem. 1993, 97, 2596 and
references therein. (e) Uosaki, K.; Kondo, T.; Zhang, X.-Q.; Yanagida,
M. J . Am. Chem. Soc. 1997, 119, 8367. (f) Thornton, N. B.; Wojtowicz,
H.; Netzel, T.; Dixon, D. W. J . Phys. Chem. B 1998, 102, 2101.
(4) For systems containing multi-ferrocenyl units linked with poly-
mers, see for example: (a) Casado, C. M.; Mora´n, M.; Losada, J .;
Cuadrado, I. Inorg. Chem. 1995, 34, 1668. (b) Manners, I. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1602. (c) Watson, K. J .; Zhu, J .; Nguyen,
S. T.; Mirkin, C. A. J . Am. Chem. Soc. 1999, 121, 462.
(5) For systems containing multi-ferrocenyl units linked with den-
drimers, see for example: (a) Cuadrado, I.; Mora´n, M.; Casado, C. M.;
Alonso, B.; Lobete, F.; Garc´ıa, B.; Ibisate, M.; Losada, J . Organome-
tallics 1996, 15, 5278. (b) Deschenaux, R.; Serrano, E.; Levelut, A.-M.
Chem. Commun. 1997, 1577. (c) Vale´rio, C.; Fillaut, J .-L.; Ruiz, J .;
Guittard, J .; Blais, J .-C.; Astruc, D. J . Am. Chem. Soc. 1997, 119, 2588.
(d) Castro, R.; Cuadrado, I.; Alonso, B.; Casado, C. M.; Mora´n, M.;
Kaifer, A. E. J . Am. Chem. Soc. 1997, 119, 5760 and references therein.
(e) Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.; Losada, J .;
Belsky, V. J . Am. Chem. Soc. 1997, 119, 7613. (f) Ko¨llner, C.; Pugin,
B.; Togni, A. J . Am. Chem. Soc. 1998, 120, 10274.
10.1021/om990208x CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/30/1999

Ferrocenylphthalocyanines
Organometallics, Vol. 18, No. 17, 1999 3529
1
yellow microcrystals (0.24 g, 27%; mp 163-166 °C). H NMR
complexes by preparing phthalocyanines connected on
the periphery to 4, 8, and 16 ferrocenyl moieties with
oxyethylene linkers. The synthesis and the spectroscopic
and electrochemical properties of these novel macro-
cycles are reported herein.
(CD3SOCD3): δ 7.84 (dd, J ) 7.5, 8.4 Hz, 1 H, Ar H), 7.66 (d,
J ) 8.4 Hz, 1 H, Ar H), 7.64 (d, J ) 7.5 Hz, 1 H, Ar H), 4.32
(t, J ) 6.6 Hz, 2 H, OCH2), 4.23 (t, J ) 1.8 Hz, 2 H, Fc), 4.15
(s, 5 H, Fc), 4.08 (t, J ) 1.8 Hz, 2 H, Fc), 2.80 (t, J ) 6.6 Hz,
2 H, FcCH2). 13C{1H} NMR: δ 161.3, 134.4, 125.0, 117.0, 116.6,
115.3, 113.1, 104.9, 83.8, 70.6, 69.3, 69.0, 68.2, 29.6. IR (KBr):
v 2227 m cm-1 (CtΝ). HRMS (LSI): m/z calcd for C20H1656Fe-
Exp er im en ta l Section
N2O (M+) 356.0612, found 356.0607. Anal. Calcd for C20H16
-
Gen er a l P r oced u r e. Reactions were performed under an
atmosphere of nitrogen. Tetrahydrofuran (THF) was distilled
from sodium benzophenone ketyl. n-Pentanol, n-hexanol, and
n-octanol were distilled from sodium prior to use. N,N-
Dimethylformamide (DMF) was predried over barium oxide
and distilled under reduced pressure. Chromatographic puri-
fications were performed on silica gel columns (Macherey-
Nagel, 70-230 mesh) with the indicated eluents unless
otherwise stated. Hexanes used in chromatography was
distilled from anhydrous CaCl2. The electrolyte [Bu4N][ClO4]
was recrystallized from dry acetone three times prior to use.
All other reagents and solvents were of reagent grade and were
used as received. 2-Ferrocenylethanol (1)13 and 2-ferrocenyl-
ethyl p-toluenesulfonate (5)14 were prepared according to
literature procedures.
FeN2O: C, 67.44; H, 4.53; N, 7.86. Found: C, 67.45; H, 4.54;
N, 7.81.
[Tetr a k is(2-fer r ocen yleth oxy)p h th a locya n in a to]zin c-
(II) (4). A mixture of 3 (100 mg, 0.28 mmol) and Zn(OAc)2‚
2H2O (22 mg, 0.10 mmol) in n-hexanol (3 mL) was heated to
90 °C; then 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (0.01 mL,
0.07 mmol) was added. The mixture was stirred at 150 °C for
16 h; then the volatiles were removed under reduced pressure.
The resulting deep green residue was subjected to chroma-
tography using CHCl3 as eluent to give 4 as a green solid (80
mg, 77%). 1H NMR: δ 8.38-8.98 (m, 4 H, Ar H), 7.66-8.08
(m, 4 H, Ar H), 7.00-7.64 (m, 4 H, Ar H), 4.54-4.92 (m, 8 H,
OCH2), 4.02-4.38 (m, 36 H, Fc), 2.86-3.50 (m, 8 H, FcCH2).
UV-vis (THF) [λmax, nm (log ꢀ)]: 316 (5.41), 347 (5.35), 629
(5.29), 664 (sh), 698 (5.94). MS (MALDI-TOF): an isotopic
1
Melting points were uncorrected. H and 13C NMR spectra
cluster peaking at m/z 1490.2 (M+). Anal. Calcd for C80H64
-
were recorded on a Bruker DPX 300 spectrometer (1H, 300
MHz; 13C, 75.4 MHz) in CDCl3 unless otherwise stated. Spectra
were referenced internally using the residual solvent (1H:
CDCl3, δ 7.26; CD3SOCD3, δ 2.50; C6D6, δ 7.15) or solvent
(13C: CDCl3, δ 77.0) resonances relative to SiMe4. IR spectra
were measured on a Nicolet Magna 550 FT-IR spectrometer
as KBr pellets. UV-vis and fluorescence spectra were taken
on a Hitachi U-3300 spectrophotometer and a Hitachi F-4500
spectrofluorometer, respectively. Liquid secondary-ion (LSI)
mass spectra were recorded on a Bruker APEX 47e Fourier
transform ion cyclotron resonance (FTICR) mass spectrometer
with a 3-nitrobenzyl alcohol matrix. Matrix-assisted laser
desorption/ionization time-of-flight (MALDI-TOF) spectra were
obtained on a Bruker bench TOF mass spectrometer equipped
with a standard UV-laser desorption source, using R-cyano-
4-hydroxycinnamic acid as matrix. Elemental analyses were
performed by the Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences.
Electrochemical measurements were carried out on a BAS
CV-50W voltammetric analyzer. The cell contained inlets for
a platinum-sphere working electrode, a platinum-plate counter
electrode, and a Ag-AgNO3 (0.1 mol dm-3 in MeCN) reference
electrode, which was connected to the solution by a Luggin
capillary whose tip was placed close to the working electrode.15
Typically, a 0.1 mol dm-3 solution of [Bu4N][ClO4] in DMF
(unless otherwise stated) containing 1.0 mmol dm-3 of sample
was purged with nitrogen for 20 min; then the voltammograms
were recorded at ambient temperature. Potentials were ref-
erenced to the Ag-Ag+ couple in MeCN.
Fe4N8O4Zn: C, 64.48; H, 4.33; N, 7.52. Found: C, 65.28; H,
4.63; N, 7.32.
3,6-Bis(2-fer r ocen yleth oxy)p h th a lon itr ile (7). A mix-
ture of 2,3-dicyanohydroquinone (6; 200 mg, 1.25 mmol) and
K2CO3 (700 mg, 5.07 mmol) in DMF (4 mL) was stirred at room
temperature for 15 min. Then 2-ferrocenylethyl p-toluene-
sulfonate (5; 1.0 g, 2.60 mmol) was added and the mixture was
stirred at 90 °C for 2 days. The resulting dark brown solution
was poured into H2O (100 mL) and then extracted with CHCl3
(3 × 50 mL). The combined extracts were dried with anhydrous
Na2SO4 and evaporated in vacuo. The residue was purified by
column chromatography using CHCl3/hexanes (4:1) as eluent
to obtain 7 as a yellow solid (400 mg, 55%; mp 198-200 °C).
1H NMR: δ 7.04 (s, 2 H, Ar H), 4.21 (s, 4 H, Fc), 4.14 (s, 10 H,
Fc), 4.11 (s, 4 H, Fc), 4.08 (t, J ) 6.3 Hz, 4 H, OCH2), 2.87 (t,
J ) 6.3 Hz, 4 H, FcCH2). 13C{1H} NMR: δ 155.0, 118.2, 113.1,
105.3, 83.5, 70.8, 68.9, 68.6, 67.8, 29.7. IR (KBr): v 2227 m
cm-1 (CtΝ). HRMS (LSI): m/z calcd for C32H2856Fe2N2O2 (M+)
584.0849, found 584.0856. Anal. Calcd for C32H28Fe2N2O2: C,
65.78; H, 4.83; N, 4.79. Found: C, 65.18; H, 4.67; N, 4.72.16
[1,4,8,11,15,18,22,25-Octa k is(2-fer r ocen yleth oxy)p h th -
a locya n in a to]zin c(II) (8). A mixture of 7 (100 mg, 0.17
mmol) and Zn(OAc)2‚2H2O (22 mg, 0.10 mmol) in n-pentanol
(3 mL) was heated to 90 °C, then DBU (0.01 mL, 0.07 mmol)
was added. The mixture was stirred at 150 °C overnight and
then poured into a mixture of methanol and water (1:1, 50
mL). The precipitate formed was filtered off and chromato-
graphed on a basic alumina column using CHCl3/THF (5:1)
1
as eluent to give 8 as a green powder (54 mg, 53%). H NMR
3-(2-F er r ocen yleth oxy)p h th a lon itr ile (3). A mixture of
2-ferrocenylethanol (1; 1.15 g, 5.0 mmol), 3-nitrophthalonitrile
(2; 0.43 g, 2.5 mmol), and K2CO3 (0.69 g, 5.0 mmol) in DMF (3
mL) was stirred at room temperature for 21 h. The volatiles
were then removed under reduced pressure, giving a brown
residue which was subjected to chromatography using THF/
hexanes (1:4) as eluent. Compound 3 was isolated as orange-
(C6D6): δ 7.48 (br s, 8 H, Ar H), 5.04 (br s, 16 H, OCH2), 4.29
(s, 16 H, Fc), 4.07 (s, 40 H, Fc), 3.92 (s, 16 H, Fc), 3.27 (br s,
16 H, FcCH2). UV-vis (THF) [λmax, nm (log ꢀ)]: 327 (5.15),
661 (5.04), 736 (5.72). MS (MALDI-TOF): an isotopic cluster
peaking at m/z 2404.6 (M+). Anal. Calcd for C128H112Fe8N8O8-
Zn: C, 63.99; H, 4.70; N, 4.66. Found: C, 62.66; H, 4.71; N,
4.45.16
(12) A few ferrocene-containing porphyrazines have also been
reported: (a) Baumann, T. F.; Sibert, J . W.; Olmstead, M. M.; Barrett,
A. G. M.; Hoffman, B. M. J . Am. Chem. Soc. 1994, 116, 2639. (b)
Baumann, T. F.; Nasir, M. S.; Sibert, J . W.; White, A. J . P.; Olmstead,
M. M.; Williams, D. J .; Barrett, A. G. M.; Hoffman, B. M. J . Am. Chem.
Soc. 1996, 118, 10479.
(13) Rinehart, K. L., J r.; Curby, R. J ., J r.; Sokol, P. E. J . Am. Chem.
Soc. 1957, 79, 3420.
(14) Lee, C. C.; Chen, S.-C.; Sutherland, R. G. Can. J . Chem. 1975,
53, 232.
Tetr akis(2-fer r ocen yleth oxy)ph th alon itr ile (10). A mix-
ture of 1 (1.38 g, 6.0 mmol), tetrafluorophthalonitrile (9; 0.10
(16) The experimental carbon contents for 7 and 8 were marginal.
Attempts to further purify these compounds by column chromatogra-
phy and obtain better analytical data, unfortunately, were unsuccess-
ful. The unsatisfactory data for 8 could be related to the fact that
phthalocyanines are notoriously difficult to combust (see: Hu, M.;
Brasseur, N.; Yildiz, S. Z.; van Lier, J . E.; Leznoff, C. C. J . Med. Chem.
1998, 41, 1789). The compounds were deemed to be pure by chromato-
graphic and spectroscopic analyses.
(15) Sawyer, D. T.; Sobkowiak, A.; Roberts, J . L., J r. Electrochem-
istry for Chemists, 2nd ed.; Wiley: New York, 1995; Chapter 6.

3530 Organometallics, Vol. 18, No. 17, 1999
Poon et al.
Sch em e 1
Sch em e 2
g, 0.5 mmol), and K2CO3 (0.83 g, 6.0 mmol) in DMF (5 mL)
was stirred at 100 °C for 24 h and then poured into water (50
mL). The mixture was extracted with CHCl3 (3 × 30 mL), and
the combined extracts were dried over anhydrous Na2SO4 and
rotary evaporated. The crude product was purified by column
chromatography with toluene as eluent to afford a yellow solid
(265 mg, 51%, mp 139-141 °C). 1H NMR: δ 4.0-4.3 (m, 44
H, Fc & OCH2), 2.76 (br s, 4 H, FcCH2), 2.67 (br s, 4 H, FcCH2).
13C{1H} NMR: δ 152.7, 150.7, 113.1, 104.5, 84.3, 83.8, 75.7,
74.9, 69.3, 69.2, 68.7, 68.2, 67.8, 30.5, 30.4. IR (KBr): v 2231
m cm-1 (CtΝ). MS (LSI): an isotopic cluster peaking at m/z
1040.14 (M+). Anal. Calcd for C56H52Fe4N2O4: C, 64.65; H, 5.04;
N, 2.69. Found: C, 64.54; H, 5.06; N, 2.72.
the characteristic pattern for metal-free phthalocya-
nines (λmax (CHCl3): 320, 356, 629, 663, 695, 730 nm).
Its 1H NMR spectrum recorded in CDCl3, however,
exhibited complex multiplets for the phthalocyanine
ring protons, indicating that a mixture of isomers was
produced. It is worth noting that, under similar reac-
tion conditions, a single isomer could be obtained
for phthalocyanines containing substituents such as
t
-OCH2C6H4nBu, -OCH2 Bu, -OMe, and -OCHEt2 at
the 1,8,15,22-positions.17,18 It appears that the steric as
well as the electronic nature of the substituent is crucial
in the formation of a single isomer in the cyclization of
3-substituted phthalonitriles.17b,19
The octaferrocenylphthalocyanine 8 was prepared by
the route shown in Scheme 2. Reaction of the tosylate
5 with 2,3-dicyanohydroquinone (6) in the presence of
K2CO3 afforded the dinitrile 7 in moderate yield. Upon
treatment with zinc acetate and DBU, this compound
was converted to 8, which could only be purified by
chromatography on basic alumina columns; the com-
pound was unstable and turned yellow in silica gel
columns.
The tetraferrocenyl dinitrile 10 was prepared using
tetrafluorophthalonitrile (9) and 1 as the starting
materials (Scheme 3).20 Substitution occurred in the
presence of K2CO3, giving 10 in moderate yield. At-
tempts to prepare the corresponding zinc phthalocya-
nine using the above procedure were not successful. The
metal-free hexadecakis(2-ferrocenylethoxy)phthalocya-
nine (11), however, could be prepared using lithium in
n-octanol followed by acid treatment. The reaction
temperature was critical in the preparation of 11 and
should be controlled at ca. 120-130 °C. Higher reaction
Hexa d eca k is(2-fer r ocen yleth oxy)p h th a locya n in e (11).
Lithium (10 mg, 1.44 mmol) was suspended in n-octanol (3
mL). The suspension was stirred at 150 °C until the solution
became clear. The homogeneous solution was cooled to 90 °C,
and then dinitrile 10 (100 mg, 0.10 mmol) was added. The
temperature was increased to 120 °C, at which point the
mixture was stirred for 4 h. Glacial acetic acid (3 mL) was
then added, and the mixture was kept at this temperature for
15 min before being poured into a mixture of methanol and
water (1:1, 50 mL). The precipitate formed was filtered off and
chromatographed with CHCl3/THF (10:1) as eluent to give 11
1
as a green powder (15 mg, 15%). H NMR: δ 5.08 (br s, 16 H,
OCH2), 4.58 (br s, 16 H, OCH2), 4.35 (br s, 16 H, Fc), 4.08-
4.23 (m, 96 H, Fc), 3.98 (br s, 32 H, Fc), 3.18 (br s, 16 H,
FcCH2), 3.08 (br s, 16 H, FcCH2). UV-vis (THF) [λmax, nm (log
ꢀ)]: 323 (5.21), 349 (5.16), 386 (5.13), 669 (5.01), 692 (5.04),
732 (sh), 756 (5.62). MS (MALDI-TOF): an isotopic cluster
peaking at m/z 4168.6 (M+). Anal. Calcd for C224H210
-
Fe16N8O16: C, 64.62; H, 5.08; N, 2.69. Found: C, 64.31; H, 5.21;
N, 2.66.
Resu lts a n d Discu ssion
Treatment of 2-ferrocenylethanol (1) with 3-nitro-
phthalonitrile (2) under alkaline conditions gave the
dinitrile 3, which underwent typical cyclization to afford
the tetrasubstituted phthalocyanine 4 as a mixture of
constitutional isomers, as revealed by 1H NMR spec-
troscopy (Scheme 1). In an attempt to prepare a single
1,8,15,22-tetrasubstituted isomer, 3 was treated with
lithium in n-octanol at lower temperature (70 °C).17
After acidification with acetic acid, a deep green solid
was obtained, the UV-vis spectrum of which showed
(17) (a) Leznoff, C. C.; Hu, M.; McArthur, C. R.; Qin, Y.; van Lier,
J . E. Can. J . Chem. 1994, 72, 1990. (b) Leznoff, C. C.; Hu, M.; Nolan,
K. J . M. Chem. Commun. 1996, 1245.
(18) (a) Kasuga, K.; Kawashima, M.; Asano, K.; Sugimori, T.; Abe,
K.; Kikkawa, T.; Fujiwara, T. Chem. Lett. 1996, 867. (b) Kasuga, K.;
Asano, K.; Lin, L.; Sugimori, T.; Handa, M.; Abe, K.; Kikkawa, T.;
Fujiwara, T. Bull. Chem. Soc. J pn. 1997, 70, 1859.
(19) Rager, C.; Schmid, G.; Hanack, M. Chem. Eur. J . 1999, 5, 280.
(20) Eberhardt, W.; Hanack, M. Synthesis 1997, 95.

Ferrocenylphthalocyanines
Sch em e 3
Organometallics, Vol. 18, No. 17, 1999 3531
length band was tentatively attributed to a slipped face-
to-face dimer.18b To reveal the origin of this band, the
concentration dependency of the absorption spectra of
4 and 12 was studied. For both compounds in toluene
or CH2Cl2, the intensity of the “monomer” band at ca.
700 nm decreased while that of the “dimer” band at ca.
760 nm increased with decreasing concentration of
phthalocyanines (from 1 × 10-5 to 2 × 10-7 mol dm-3).
Compound 12 showed fluorescence emission at 714 nm
in CH2Cl2 upon excitation at 630 nm; no emission was
observed at a wavelength longer than 760 nm, indicat-
ing that the species absorbing at 760 nm was not
fluorescent. The spectral changes of a CH2Cl2 solution
of 12 after ultrasonic treatment were also examined.
The “dimer” band became more intense, while the
“monomer” band together with the fluorescence at 714
nm was significantly weakened. All the observations
suggested that the longer wavelength absorption may
not be due to a cofacial dimer which is expected to be
dominant in higher concentrations as in the cases of
zinc(II)21 and aluminum(III)22 complexes of tetrasul-
fonatophthalocyanine in MeCN/H2O and aqueous alco-
hol, respectively, which were also assumed to adopt a
dimeric structure with a face-to-face slipped or tilted
conformation. The dimer of the former zinc(II) complex
was also found to be emissive, which again contradicts
our results.21 Thus, the exact nature of this band
remains to be explored.
The electrochemical properties of all the ferrocenyl
phthalonitriles and phthalocyanines were investigated
by cyclic voltammetry, and the data are collected in
Table 1. The voltammograms of the dinitriles 3, 7, and
10 in DMF showed two couples at ca. 0.0 and -2.0 V
assignable to the ferrocene (oxidation to ferrocenium
cation) and dicyanobenzene (reduction to the corre-
sponding radical anion) moieties, respectively. By com-
parison of the reduction potentials of benzonitrile (-2.32
V vs SCE or -2.63 V vs Ag-Ag+ in MeCN),23,24 phtha-
lonitrile, and these compounds (Table 1), it is clear that
the electron-withdrawing cyano group greatly facilitates
the addition of electrons to the π system while the
electron-donating 2-ferrocenylethoxy group makes the
reduction more difficult. On the basis of the separation
between the anodic and cathodic potentials (∆E) and
the plots of peak current vs square root of the scan rate,
which showed deviation from a straight line at higher
scan rates, all these couples were regarded as quasi-
reversible, except the phthalonitrile reduction of 10,
which was basically irreversible. Addition of ferrocene
to the solution of 10 only increased the cathodic and
anodic current without significantly shifting or splitting
the potential. This indicated that the ferrocenyl units
in 10 are electrochemically very similar to free fer-
rocene. The voltammogram of ferrocene was also re-
corded under identical conditions. The peak currents for
the ferrocene-ferrocenium couple were much lower
F igu r e 1. UV-vis spectra of 4 in THF, DMF, diethyl
ether, toluene, CHCl3, or CH2Cl2.
temperatures would lead to the formation of black
mixtures with no indication of the presence of 11.
All the new compounds were characterized by elemen-
tal analyses and various spectroscopic methods. The
UV-vis spectra of 4 are peculiar and worth mentioning.
As shown in Figure 1, the spectra of 4 are solvent-
dependent. In THF, DMF, and diethyl ether solutions,
the spectra show a typical Q-band at 695-701 nm along
with broad signals at 316-379 nm due to the phthalo-
cyanine (B band) and ferrocene. In less polar solvents
such as toluene, CHCl3, and CH2Cl2, the Q-band is
broadened and slightly shifted to the red (707-718 nm),
and an additional band emerges at 752-758 nm.
Similar phenomena were observed previously for the
Mg(II) and Zn(II) (12) complexes of 1,8,15,22-tetrakis-
(3-pentyloxy)phthalocyanine, and the longest wave-
(21) Kaneko, Y.; Arai, T.; Tokumaru, K.; Matsunaga, D.; Sakuragi,
H. Chem. Lett. 1996, 345.
(22) Yoon, M.; Cheon, Y.; Kim, D. Photochem. Photobiol. 1993, 58,
31.
(23) Bartak, D. E.; Houser, K. J .; Rudy, B. C.; Hawley, M. D. J . Am.
Chem. Soc. 1972, 94, 7526.
(24) The potential of Ag-Ag+ in MeCN was taken as +0.31 V vs
the saturated calomel electrode (SCE), as determined for this system
previously using ferrocene as an internal standard (see: Wong, Y.-L.;
Ma, J .-F.; Law, W.-F.; Yan, Y.; Wong, W.- T.; Zhang, Z.-Y.; Mak, T. C.
W.; Ng, D. K. P. Eur. J . Inorg. Chem. 1999, 313).

3532 Organometallics, Vol. 18, No. 17, 1999
Ta ble 1. Electr och em ica l Da ta for P h th a lon itr iles a n d P h th a locya n in esa
Poon et al.
ferrocene
phthalonitrile/phthalocyanine
compd
E
1/2(ox)
∆Eb
|ip,a/ip,c
|
E1/2(ox1)
∆Eb
|ip,a/ip,c
|
E1/2(red1)
∆Eb
|ip,a/ip,c
|
E1/2(red2)
∆Eb
|ip,a/ip,c|
phthalonitrile
3
7
10
4c
8d
11e
-1988
-2008
-2013
-2078
-1306
-1348
-1209
91
93
70
154
72
53
0.95
0.89
0.91
0.53
1.12
0.80
0.59
43
20
63
44
43
79
79
70
76
72
93
1.02
1.02
0.97
1.01
1.01
0.37
288
215
342f
56
57
0.54
0.66
-1784
-1788
-1493
104
89
138
0.63
0.78
0.93
226
106
a
Recorded with [Bu4N][ClO4] as electrolyte in DMF (0.1 mol dm-3) at ambient temperature with a scan rate of 100 mV s-1 unless
otherwise stated. Potentials are expressed in mV vs Ag-Ag+ in MeCN. ∆E ) |Ep,c - Ep,a|. E1/2(red3) for phthalocyanine appeared at
b
c
-1982 mV with ∆E ) 111 mV. The scan rate was 20 mV s-1. E1/2(ox2) for phthalocyanine appeared at 490 mV with ∆E ) 43 mV. e In
d
f
CH2Cl2. Ep,c(ox2) and Ep,c(red3) for phthalocyanine appeared at 610 and -1852 mV, respectively. Ep,c
.
F igu r e 2. Cyclic voltammogram of 4 in DMF containing
0.1 mol dm-3 [Bu4N][ClO4] at a scan rate of 100 mV s-1
.
F igu r e 4. Cyclic voltammogram of 11 in CH2Cl2 contain-
ing 0.1 mol dm-3 [Bu4N][ClO4] at a scan rate of 100 mV
s-1. An enlarged figure is shown in the inset.
cyanines are very similar and fall in the normal region
(1.5-1.7 V) reported for other phthalocyanines.25 As
shown in Figures 2-4, a remarkable trend is the
increase of relative peak currents of the ferrocene couple
with respect to either one of the phthalocyanine couples
as the number of ferrocenyl units increased from 4 to 8
to 16 in a molecule. A sharp cathodic stripping peak was
observed for the ferrocene couple of 11 with a peak
current ratio |ip,a/ip,c| much smaller than unity (0.37).
This waveform suggested that adsorption of the oxidized
product onto the electrode may occur, which was also
seen for some ferrocene-containing dendrimers.5a,e Ad-
dition of a small amount of MeCN (1:5 v/v in relation to
CH2Cl2) reduced the peak-to-peak separation (∆E) of the
ferrocene couple to 126 mV. This, however, could not
solve the problem of adsorption (|ip,a/ip,c| ) 0.25), and
the other redox couples for phthalocyanine turned to be
even weaker. The voltammogram of 11 in THF gave a
higher peak current ratio (|ip,a/ip,c| ) 0.57) for the
ferrocene couple, showing that this solvent can better
dissolve the oxidized product and relieve the adsorption.
The couple, however, became less reversible, as shown
by the large peak-to-peak separation (420 mV). In all
cases, no splitting of the ferrocene couple was observed.
Such splitting again was not seen in the differential
pulse voltammograms of all these ferrocenylphthalo-
cyanines recorded under the same conditions. It appears
that all the ferrocenyl moieties attached to these
phthalocyanines behave independently and are oxidized
at the same potential.
F igu r e 3. Cyclic voltammogram of 8 in DMF containing
0.1 mol dm-3 [Bu4N][ClO4] at a scan rate of 20 mV s-1
.
than those of 10 at the same concentration, showing
that 10 may undergo a multielectron redox process.
All the voltammograms of phthalocyanines 4 (Figure
2), 8 (Figure 3), and 11 (Figure 4) showed a quasi-
reversible oxidation attributed to the ferrocenyl units
together with one to two quasi-reversible oxidations and
up to three quasi-reversible reductions due to the
phthalocyanine π system (Table 1).25 As 11 was not
soluble in DMF, the voltammogram was recorded in
CH2Cl2. The potential difference between the first
oxidation and reduction couples for phthalocyanines is
related to the energy gap between their highest occupied
and the lowest unoccupied molecular orbitals (HOMO
and LUMO). The values for these ferrocenylphthalo-
(25) Lever, A. B. P.; Milaeva, E. R.; Speier, G. In Phthalocyanines:
Properties and Applications; Leznoff, C. C., Lever, A. B. P., Eds.;
VCH: New York, 1993; Vol. 3, pp 1-69.
The electronic interaction between the ferrocenyl
units and the macrocyclic core in these ferrocenylphtha-

Ferrocenylphthalocyanines
Organometallics, Vol. 18, No. 17, 1999 3533
locyanines also seemed to be insignificant at the ground
state. This was based on the observation that the
absorption spectrum of 12 mixed with 4 equiv of
ferrocene was almost identical with that of 4 in CHCl3.
The ferrocenyl moieties, however, were very efficient in
quenching the excited state of 4, for which no fluores-
cence was observed. We attributed this quenching to a
photoinduced electron transfer (PET) in which ferrocene
behaves as an electron donor. The overall free energy
change for this PET was determined by the Rehm-
Weller equation:26
was determined to be -0.48 eV, showing that this PET
is a thermodynamically favorable process. The alterna-
tive quenching pathway by energy transfer from the
phthalocyanine’s S1 state to ferrocene is excluded be-
cause of its endothermic nature (the S1 state of ferrocene
at 2.46 eV).28 The estimated value of ∆G° for this system
is of the same order with and lies between those of
octamethylporphyrins linked with a ferrocenyl group at
a meso position (ca. -0.1 eV)3d and the ferrocenylpor-
phyrin containing three cationic pyridinum moieties at
the meso positions (-0.66 eV).3f
To conclude, we have prepared and characterized
three novel phthalocyanines with 4, 8, and 16 ferrocenyl
units. The redox-active ferrocenyl groups appear to be
independent, undergoing an electrochemical oxidation
at the same potential and a rapid electron transfer to
the excited phthalocyanine core.
∆G° ) e[E1/2(D•+/D) - E1/2(A/A•-)] - ∆E(0,0) - wp
where e is the charge on the electron, E1/2 is the half-
wave reduction for potential for either the donor (D•+
/
D) or acceptor (A/A•-) couples in volts, ∆E(0,0) is the
relevant singlet state energy, and wp is a Coulombic
interaction term between the oxidized donor and re-
duced acceptor. For polar solvents with a high dielectric
constant, this term is usually small (<0.1 eV) and is
neglected here.3f On the basis of the electrochemical
data for 4 (Table 1) and the value of ∆E(0,0) for
(phthalocyaninato)zinc(II) (1.83 eV),27 the value of ∆G°
Ack n ow led gm en t. We thank Prof. D. Chan’s group
for measuring the MALDI-TOF spectra and the Hong
Kong Research Grants Council and The Chinese Uni-
versity of Hong Kong for financial support.
OM990208X
(27) Kavarnos, G. J . Fundamentals of Photoinduced Electron Trans-
fer; VCH: New York, 1993; p 43.
(28) Sohn, Y. S.; Hendrickson, D. N.; Gray, H. B. J . Am. Chem. Soc.
1971, 93, 3603.
(26) Rehm, D.; Weller, A. Isr. J . Chem. 1970, 8, 259.