Spectra and stabilities of α-substituted phthalocyaninatoirons

Article abstract of DOI:10.1016/j.molcata.2006.02.069

Three aryloxy (alkoxy) α-substituted phthalocyaninatoirons (FePcs) were prepared and their UV-vis spectra in air or by adding of peroxide showed a new band at the red side of the Q band which can be assigned to a complexes of phthalocyaninatoirons with oxygen or peroxide. The appearance of this band related to the instability of these FePcs so their decomposition was also studied, by the benzoylperoxide oxidation.

Full text of DOI:10.1016/j.molcata.2006.02.069

Journal of Molecular Catalysis A: Chemical 253 (2006) 25–29
Spectra and stabilities of ␣-substituted phthalocyaninatoirons
Liang Yanga,b, Mei-Jin Lina,b, Xiao-Li Zhua,b, Xiu-Zhi Xua,b, Jun-Dong Wanga,b,∗
a College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350002, PR China
b State Key Laboratory of Structural Chemistry, Fujian Institute of research on the Structure of Matter, Fuzhou 350002, PR China
Received 9 February 2006; accepted 28 February 2006
Available online 18 April 2006
Abstract
Three aryloxy (alkoxy) ␣-substituted phthalocyaninatoirons (FePcs) were prepared and their UV–vis spectra in air or by adding of peroxide
showed a new band at the red side of the Q band which can be assigned to a complexes of phthalocyaninatoirons with oxygen or peroxide. The
appearance of this band related to the instability of these FePcs so their decomposition was also studied, by the benzoylperoxide oxidation.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Synthesis; Spectroscopy; Stability; Phthalocyaninatoirons
trimethyl-3ꢀ-pentoxy)phthalonitrile] were synthesized as
described in literature [6]. All other reagents and solvents
were of reagent grade and used without further purifica-
tion. All synthetic reactions were performed under nitrogen
atmosphere.
1. Introduction
Phthalocyanines, especially those containing redox-active
central metal ions such as phthalocyaninatoirons, are excellent
catalysts of oxidative desulfurisation of hydrocarbons [1]. In
recent years, these compounds have also been examined as bio-
logically simulated oxidative metalloenzymes [2]. Generally,
unsubstituted phthalocyanines have poor solubility and a high
tendency of aggregation in solvents [3], which considerably lim-
its the scope of the investigations. Substituents such as alkyl and
alkoxyl groups have often been introduced to the periphery of the
phthalocyanine macrocycle to improve their solubility. But the
stability decreasing of substituted phthalocyanines in the oxidiz-
ing media has also been found, even under very mild conditions
[4]. A few investigations on the stability of phthalocyanines
have been reported to date [4,5]. Here we report some exper-
imental results of the decompositions of three aryloxy (alkoxy)
␣-substituted phthalocyaninatoirons with benzoylperoxide oxi-
dation, and related changes of their spectra.
2.2. Measurements
The infrared spectra were recorded in the range of
400–4000 cm−1 by use of a Perkin–Elmer FT-IR spectropho-
tometer. Elemental analyses were carried out on a Vario EL
III elemental analyses instrument. And UV–vis spectra were
recorded on PE-Lambda9 UV–vis spectrophotometer using
1 cm path length cuvettes at room temperature.
2.3. General process of the synthesis of lithium and
metal-free phthalocyanines 1a–1c
2. Experimental
Compounds 1a–1c were obtained by the procedure similar
to the literature [7]. Under nitrogen atmosphere, 40 mmol of
phthalonirile and 40 mmol of Li were heated at 120 ◦C for 4 h in
10 mL of n-pentanol. After cooling down to room temperature,
10 mL of methanol and 5 mL of hydrochloric acid were added
with vigorous stirring for 10 min. The residue was immediately
passed through a silica gel column (using CHCl3 as eluant),
and the obtained green eluate was evaporated, to give desired
compounds.
2.1. Materials
The substituted phthalonitriles [3-phenoxyphthalonitrile,
3-(2ꢀ,4ꢀ-ditertbutylphenoxy)phthalonitrile, and 3-(2ꢀ,2ꢀ,4ꢀ-
∗
Corresponding author. Tel.: +86 591 87893457; fax: +86 591 83709114.
E-mail address: wangjd@fzu.edu.cn (J.-D. Wang).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.02.069

26
L. Yang et al. / Journal of Molecular Catalysis A: Chemical 253 (2006) 25–29
2.9. Tetrakis(2ꢀ,4ꢀ-ditertbutylphenoxy)
2.4. Tetrakis(2,2,4-tirmethyl-3-pentoxy)phthalocyanine
(1a)
phthalocyaninatoiron (2b)
Yield: 0.932 g (9.1%). C64H82N8O4 (1023.43): calc., C,
74.82; H, 8.07; N, 10.91; found, C, 74.82; H, 8.04; N, 10.78;
mass: m/z: 1023 (M+); IR (KBr): 1585.1 (νC C), 1480.7 cm−1
(νC N), 1241.1, 1108.8 cm−1 (νAr O C), 2955.6, 2868.9 cm−1
Yield: 0.594 g (95.4%). C88H96N8O4Fe (1384.69): calc., C,
76.28; H, 6.98; N, 8.09; found, C, 76.32; H, 6.90; N, 8.42;
mass: m/z: 1384 (M+); IR (KBr): 1585.8, 1481.2 cm−1 (νC N),
1384, 1082.0 cm−1 (νAr O Ar), 1585.8 cm−1 (νC C), 2953.7,
2849.1 cm−1 (νCH ), 741.01 (νM–N).
(νCH ).
3
3
2.5. Tetrakis(2ꢀ,4ꢀ-ditertbutylphenoxy)phthalocyanine (1b)
2.10. Tetrakisphenoxyphthalocyaniatoiron (2c)
Yield: 0.402 g (95.5%). C56H32N8O4Fe (936.19): calc., C,
71.80; H, 3.44; N, 11.96; found, C, 72.22; H, 4.30; N, 11.61;
mass: m/z: 936 (M+); IR (KBr): 1581.9 (νC C), 1488.9 cm−1
(νC N), 1246.2, 1205.7 cm−1 (νAr O Ar), 748.76 (νM–N).
Yield: 2.31 g (17.4%). C88H98N8O4 (1330.7): calc., C, 79.36;
H, 7.42; N, 8.41; found, C, 79.51; H, 7.60; N, 7.77; mass: m/z:
1032.0 (M+); IR (KBr): 1585.8 (νC C), 1484.9 cm−1 (νC N),
1250.9, 1086.1 cm−1 (νAr O Ar), 2958.8, 2867.9 cm−1 (νCH ).
3
3. Results and discussion
2.6. Tetrakisphenoxyphthalocyaniatolithium (1c)
3.1. Synthesis of substituted phthalocyaninatoirons
Yield: 2.24 g (25.5%). C56H33N8O4Li (888.28): calc., C,
75.76; H, 3.36; N, 12.62; found, C, 75.22; H, 3.59; N, 12.22;
mass: m/z: 889.4 (M+); IR (KBr): 1582.6 (νC C), 1488.8 cm−1
(νC N), 1245.9, 1180.5 cm−1 (νAr O Ar).
As shown in the Scheme 1, instead of commonly used
method of condensation of precursor and metal salt, the
title phthalocyaninatoirons are synthesized from correspond-
ing metal-free phthalocyanines so as to simplify the pro-
cess of purification because of the easy decomposition of
these substituted phthalocyanines, even though the yields of
metal-free phthalocyanines were lower. Another result was
that with smaller substituents, the protonation of LiPc by
acid was uneasy and resulted with a half protonated LiHPc,
as 1c, which was used in the next reaction without further
treatment.
2.7. General process of the synthesis of
phthalocyaninatoiron 2a–2c
Compounds 2a–2c were obtained by the procedure similar
to the literature [8]. Under nitrogen atmosphere, 0.45 mmol of
precursors 1a–2c and 7.9 mmol of FeCl3 were heated at 115 ◦C
for 2 h in 10 mL of pyridine. The reaction mixture was imme-
diately passed through a short alumina column (20:1, v/v of
toluene:pyridine as eluant) to remove unreacted metal salt. Then
the obtained green eluate was evaporated to give desired com-
pounds.
3.2. The UV–vis spectroscopy studies of substituted
phthalocyaninatoirons in atmosphere
The alkoxy complex 2a showed a typical Q0–0 and Soret
bands of Pc ring at 683, 618 and 347 nm in pyridine at atmo-
sphere, but in the toluene, a new band (753 nm, named as L
bands) was found at the longer wavelength side of the Q band,
anditsintensitiesincreaseaccompaniedby theintensitydecreas-
ing of the Q band, while standing the solution at room tempera-
ture in air, as shown in Fig. 1. This L bands were also observed
in acetone and acetonitrile solutions, but not observed in polar
solvents, DMF, dimethyl sulfoxide, and pyridine. In case of 2b
2.8. Tetrakis(2,2,4-tirmethyl-3-pentoxy)-
phthalocyaninatoiron (2a)
Yield: 0.34 g (70%). C64H80N8O4Fe (1080.57): calc., C,
71.09; H, 7.46; N, 10.36; found, C, 70.80; H, 7.38; N, 9.40;
mass: m/z: 1080 (M+); IR (KBr): 1587.4, 1485.6 cm−1 (νC N),
1244.3, 1114.7 cm−1 (νAr O C), 1587.4 cm−1 (νC C), 2956.1,
2869.9 cm−1 (νCH ), 742.47 (νM–N).
3
Scheme 1. Reagents and conditions: (i) pentanol, Li, 120 ◦C, 4 h, and then con. HCl; (ii) FeCl3, DMF, 150 ◦C, 4 h.

L. Yang et al. / Journal of Molecular Catalysis A: Chemical 253 (2006) 25–29
27
Fig. 1. Electronic absorption spectral changes of the toluene solution containing
compound 2a with time ([2a]0 = l × 10−5 mol L−1), and the inset is the correc-
tion between ln(A) and time.
Fig. 2. Absorption spectra of 2a (l × 10−5 mol L−1) in toluene (solid line), pyri-
dine (dashed line) and toluene containing 0.1 mol L−1 phenol (dot line).
and 2c, the L bands also appeared but with weak intensities than
that of 2a.
pound 2a. Recently, Kobayashi and co-workers reported that
one phthalocyaninatoiron substituted with eight phenyl groups
at ␣ position shows absorption bands that may be assigned to
metal-to-ligand charge transfer (MLCT) transitions, in the near-
IR region beyond the Q band in pyridine, due to lowering of
molecular symmetry from D4h to D2d [8]. But for compound
2a, this MLCT band was not found in pyridine. In addition, the
oxidation of the pc ring also gives rise to a new band at the
longer wavelength side of the Q band. But in this case, a rel-
atively strong band should be accompanied in the wavelength
range from 500 to 600 nm [13]. However, such a band was not
observed for the present complex. In Fig. 2, we can also find a
band at 785 nm for the protonated 2a by phenol in toluene, so the
L bands at 753 nm cannot also be assigned to the protonation.
IncheckingtheoriginofthisLband, wefoundthatthisLband
disappeared immediately after adding a small amount of acid,
such as acetic acid or phenol, or decreased by adding of pyridine
to the solution. These facts led to a conjecture that the L band at
753 nm was related to the center Fe and meso-nitrogen atoms.
Another clue was that a peak was found out in the mass spec-
tra for one pyridine coordination and an additional small group
For the origin of this L band, we checked if it is whatever
reported. It is known that the Q bands of MPcs are shifted
to the longer wavelength region by formation of the slipped
face-to-face dimmer [9]. And the red shift of the Q bands was
also reported for the zeolite encapsulated MPcs, of which pc
rings are considered to be distorted so as to reside in the narrow
cavities of the zeolite. Furthermore, it is also reported that the
electronic absorption of ␮-oxo dimmeric PcFe complex in non-
coordinating solvents, the Q and B bands always bathochromic
shift. However, these reasons could not give us some acces-
sible explain for the L band. The structure of PcCo with the
same substituents as compound 2a showed that their ring skele-
ton maintained the planar conformation and the distance of the
˚
two neighboring rings is 7.5 A [10]. And the bond distance of
˚
Fe O Fe is 3.42 A in ␮-oxo PcFe dimmer [11]. These results
ruled out the possibility of the slipped face-to-face dimmer, ring
distortion or ␮-oxo PcFe dimmer as the L bands origin. It can be
further confirmed by the fact that the vibrations of Fe O Fe at
852 and 824 cm−1 [12] were not found in the IR spectra of com-
Scheme 2. The schematic diagram of the complexes of title compounds with oxygen and oxidants in some solvents.

28
L. Yang et al. / Journal of Molecular Catalysis A: Chemical 253 (2006) 25–29
with mass 32. Also considered a model reported by Kaliya et al.
for PcFe catalysts interact with oxidants (dioxygen, peroxides,
hydroperoxides and peracids) [14], as shown in Scheme 2A, we
surmised a model for the origin of this L band as showed in
Scheme 2B, in which electrons of O1 and O2 are attracted to Fe
atom and the O2 atom with somewhat lacking of electron inter-
act with meso-nitrogen atoms. And the coordinated pyridine at
one side of the center Fe could enhance the coordination of the
O2 on the other side, as well known for the analog porphyrins. In
these complexes, the O2 ligand can be replaced by the stronger
coordinate pyridine at Fe and stronger protonate H at meso N, so
the L band can be disappeared by acid or decreased by pyridine.
No appearance of the L bands in analogous metal-free, Zn, Co,
Cu, Pd derivatives [15] or the PcFe with small bulk substituents
[16] is perhaps mainly attributed to their weak coordination abil-
ities of center atoms or short distances of two neighboring Pc
rings.
Fig. 3. The absorption spectra of 2a (1 × 10−5 mol L−1) in toluene (solid line)
and in toluene containing BPO (5 × 10−3 mol L−1) (dash line, after 26 min).
In order to further prove out our assumption, the benzoyl
peroxide (BPO) was added to the toluene solution of compound
2a. As expected, there was a new band at 746 nm that was also
found (Fig. 3).
The decomposition of title compounds by the oxidation of
BPO was relatively fast where the effect of air was ignored.
The decomposition with BPO in toluene or pyridine is shown in
Fig. 4. It was found that the order of their decomposition rate is
2a > 2b > 2c and in good agreement with the order of their max-
imum absorption wavelengths. As foregoing mentioned model,
the key step is to form the intermediate as shown in Scheme 2.
Firstly, the donor substituents at ␣ position lead to some increase
of the electronic densities of meso-nitrogen atom and the rise of
C N bond length, and the corresponding red shift of the Q band
indicated the level of this effect. So the introduction of the donor
substituents at ␣ position will increase the electron of meso N
atom what is beneficial for the forming of intermediate, and the
3.3. The decomposition by benzoylperoxide oxidation
It was observed that when this L band appeared, the sub-
stituted FePcs slowly decomposed, as shown in Fig. 1. The
decomposition also occurred when protonated by adding acid
but not by adding pyridine. When standing the sample solution
in air, the decomposition rate was not clearly recorded because
the air diffusion into the sample was difficult to be controlled.
Fig. 4. Electronic absorption spectral changes of the toluene solution containing compound 2a and BPO with time ([2a]0 = l × 10−5 mol L−1
,
)
[BPO]0 = 5 × l0−3 mol L−1) (a); the correction between 1/A and time in toluene/BPO solution (b) where [2a–2c]0 = l × 10−5 mol L−1, [BPO]0 = 5 × l0−3 mol L−1
and in pyridine/BPO solution (c) where [2a–2c]0 = l × 10−5 mol L−1, [BPO]0 = 0.1 mol L−1).

L. Yang et al. / Journal of Molecular Catalysis A: Chemical 253 (2006) 25–29
29
C N bond lengthen also lowed the stability of Pc. Secondly, and
References
perhaps more importantly, the bulk of the substituents affect the
easy of interaction between the PcFe and oxidant. Finally, the
fact that the decomposition in the pyridine needs a high concen-
tration of oxidant may suggest the coordination of the solvent
to the axial position compete with the coordination of oxidant
to the Fe ion.
The decomposition reaction order was 2, extracted from the
maximabsorptionoftheoriginalQband, indicatedtheformation
of intermediate from Pc and oxidant is a second-order reaction
and the L band is a “new Q band” of the intermediate. Where
the decomposition in air was a first-order reaction belongs to the
constant O2 concentration in solution come by the diffusion of
O2 from air. As a band of intermediate, the strength of L band
was hold constant within the decomposition and disappeared
slowly at last when the most of phthalocyanine decomposed. In
addition, the decomposition of BPO itself in this condition is
very slow [17].
[1] (a) K.M. Kadish, K.M. Smith, R. Guilard (Eds.), The Porphyrin Hand-
book, vol. 19, Academic Press, New York, 2003;
(b) C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines, Properties and
Applications, vols. I–IV, VCH, New York, 1989–1996;
(c) A.L. Thomas, Phthalocyanine Research and Applications, CRC Press,
Boston, 1990.
[2] (a) M. Sono, M.P. Roach, E.D. Coulter, J.H. Dawson, Chem. Rev. 96
(1996) 2841;
(b) S. Ferguson-Miller, G.T. Babcock, Chem. Rev. 96 (1996) 2889;
(c) V.N. Nemykin, I.N. Tert’yakova, S.V. Volkov, V.D. Li, N.G.
Mekhryakova, O.L. Kaliya, E.A. Luk’yanets, Russ. Chem. Rev. 69 (4)
(2000) 325.
[3] A.W. Snow, in: K.M. Kadish, K.M. Smith, R. Guilard (Eds.), The
Porphyrin Handbook, vol. 17, Academic Press, New York, 2003, pp.
130–176 (Chapter 109).
[4] N. d’Alessandro, L. Tonucci, M. Bressan, L.K. Dragani, A. Morvillo,
Eur. J. Inorg. Chem. (2003) 1807–1814.
[5] (a) N. Grootboom, T. Nyokong, J. Mol. Catal. A. 179 (2002) 113–123;
(b) W. Pasiuk-Bronikowska, M. Krajewska, I. Flis-Kabluska, Ployhedron
18 (1998) 561–569.
[6] W. Xie, H. Xu, C. Gan, Z. Pan, T. Yan, B. Peng, Chin. J. Chem. Phys.
16 (6) (2003) 491–498.
4. Conclusion
[7] K. Kasuga, M. Kawashima, K. Asano, T. Sugimori, K. Abe, T. Kikkawa,
T. Fujiwara, Chem. Lett. (1996) 867–868.
[8] T. Fukuda, S. Homma, N. Kobayashi, Chem. Commun. (2003)
1574–1575.
[9] K. Kasuga, N. Matsuura, K. Inoue, M. Handa, T. Sugimori, K. Isa, M.
Nakata, Chem. Lett. 31 (3) (2002) 352–353.
[10] J.D. Wang, J.L. Huang, X.Z. Xu, J.W. Cai, N.S. Chen, Chinese J. Struct.
Chem. 5 (2004) 516–519.
[11] M.J. Lin, J.D. Wang, N.S. Chen, J.L. Huang, Inorg. Chem. Commun. 8
(2005) 900–902.
[12] V.N. Nemykin, I.N. Tert’yakova, S.V. Volkov, V.D. Li, N.G.
Mekhryakova, O.L. Kaliya, E.A. Luk’yanets, Russ. Chem. Rev. 69 (4)
(2002) 325–346.
The formation of the complexes of phthalocyaninatoirons
with oxygen and oxidant BPO leads to a new band
(named as L band) at the longer wavelength side of Q
band. This L band belongs to an oxygen or peroxidant-
coordinated intermediate which leads to the decomposition
of the phthalocyaninatoirons. The donor substituents at ␣
position can enhance the decomposition so as to reduce the
chemical stability of phthalocyaninatoirons, and the steric
congestion of substituent further enhances the decomposi-
tion.
[13] E.A. Ough, M.J. Stillman, Inorg. Chem. 34 (1995) 4317–4325.
[14] O.L. Kaliya, E.A. Lukyanets, G.N. Vorozhtsov, J. Porphyrins Phthalo-
cyanines 3 (1999) 592–610.
Acknowledgements
[15] M.J. Lin, Master’s Degree Thesis, University of Fuzhou, 2003.
[16] G. Schmid, E. Witke, U. Schlick, S. Knecht, M. Hanack, J. Mater. Chem.
5 (6) (1995) 855–859.
This work was supported by Science Foundation of Fujian
Province (E0310007), and Science and Technology Developing
Foundation of Fuzhou University (2004-XQ-10).
[17] W.E. Cass, J. Am. Chem. Soc. 68 (10) (1946) 1976–1982.