Phosphorus-nitrogen compounds Part 17: The synthesis, spectral and electrochemical investigations of porphyrinophosphazenes

Article abstract of DOI:10.1142/S1088424610001945

The reactions of unsymmetrical porphyrins (1 and 2) with Ni(OAc) ₂· 4H₂O in boiling DMF produce porphyrin complexes (3 and 4). From the reactions of free porphyrin ligands 1 and 2 with hexachlorocyclotriphosphazatriene, N₃P₃Cl₆, the new free porphyrino-phosphazene derivatives (5 and 6) are obtained. On the other hand, the reactions of N₃P₃Cl₆ with porphyrin complexes (3 and 4) afford the new porphyrino-phosphazene complexes (7 and 8). In the literature there are a few examples of the porphyrino- phosphazene architectures. The structural investigations of all the compounds have been made by elemental analyses, MS, FTIR, ¹H NMR, ³¹P NMR and UV-visible techniques. The cyclic voltammograms (CVs) are examined in acetonitrile (MeCN) containing 0.1 M tetrabutylammonium- tetrafluoroborate (TBATFB) to investigate the surface attachment properties at the glassy carbon electrode (GCE) and the influence of the presence of metal cations in the porphyrin ring.

Full text of DOI:10.1142/S1088424610001945

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 227–234
DOI: 10.1142/S1088424610001945
Published at http://www.worldscinet.com/jpp/
Phosphorus-nitrogen compounds. Part 17. The synthesis,
spectral and electrochemical investigations of porphyrino-
phosphazenes
Gamze Egemena, Mustafa Hayvalıa◊, Zeynel Kılıç*a, A. Osman Solaka and
Zafer Üstündağb
a Department of Chemistry, Ankara University, Tandoğan 06100, Ankara, Turkey
b Department of Chemistry, Dumlupınar University, Kütahya, Turkey
Received 14 April 2009
Accepted 30 May 2009
ABSTRACT: The reactions of unsymmetrical porphyrins (1 and 2) with Ni(OAc)2·4H2O in boiling
DMF produce porphyrin complexes (3 and 4). From the reactions of free porphyrin ligands 1 and 2
with hexachlorocyclotriphosphazatriene, N3P3Cl6, the new free porphyrino-phosphazene derivatives
(5 and 6) are obtained. On the other hand, the reactions of N3P3Cl6 with porphyrin complexes (3 and 4)
afford the new porphyrino-phosphazene complexes (7 and 8). In the literature there are a few examples
of the porphyrino-phosphazene architectures. The structural investigations of all the compounds have
been made by elemental analyses, MS, FTIR, 1H NMR, 31P NMR and UV-visible techniques. The cyclic
voltammograms (CVs) are examined in acetonitrile (MeCN) containing 0.1 M tetrabutylammonium-
tetrafluoroborate (TBATFB) to investigate the surface attachment properties at the glassy carbon electrode
(GCE) and the influence of the presence of metal cations in the porphyrin ring.
KEYWORDS: porphyrino-phosphazenes, synthesis, Ni(II) complexes, spectroscopy, electrochemistry.
sustainable source [9]. Compared to other organic dyes,
INTRODUCTION
some metalloporphyrins have advantages in the photo-
Porphyrins with extended chromophores are being
induced hydrogen evolution systems with polymer solid
investigated for applications that range from material sci-
[10, 11].
ence to medicine [1, 2]. In some cases, ring fusion results
Phosphazene chemistry has experienced rapid growth
in highly red-shifted chromophores that could have value
and is a major part of the inorganic non-metallic field
in photodynamic therapy [3–5]. It is known that por-
[12, 13]. The six-membered cyclotriazaphosphazene,
phyrin as a photosensitizer can localize on tumor cells
N3P3Cl6, is the most investigated phosphorus-nitrogen
and photo-trigger to produce singlet oxygen to cleave
compound. N3P3Cl6 has been used in the preparation of
DNA and eventually damage the tumor cells [6]. Differ-
new phosphazene derivatives with different side groups
ent structural units are being utilized to act as bridging
[14]. Recently, chiral functional groups have been intro-
units in the production of nanoscale systems, including
duced onto the cyclic ring to form single diastromers [15].
molecular wires and arrays [7, 8]. Porphyrins are also
Reactions of chlorophosphazenes with many mono-, di-,
used in different fields of research, including solar energy
and polyfunctional reagents can lead to the formation
conversion catalysis, and photocatalytic water splitting
of a great variety of products. A review concerning the
is a challenging reaction to supply hydrogen from a
reactions of chlorophosphazenes has been published
[16]. Cyclophosphazene derivatives have found industrial
applications in the production of lubricants [17], optical
š
SPP full member in good standing
materials [18], inflammable textile polyphosphazene
fibers, advanced elastomers with different organic and
*Correspondence to: Zeynel Kılıç, email: zkilic@science.
ankara.edu.tr, tel: +90 312–2126720, fax: +90 312–2232395
Copyright © 2010 World Scientific Publishing Company

228
G. EGEMEN ET AL.
CH3
CH3
HN
N
N
N
N
(i)
OH
OH
H3C
Ni
H3C
N
NH
N
R
R
R = H
(1)
(3)
R = H
R = OMe (2)
R = OMe (4)
CH3
CH3
(ii)
(iii)
CH3
CH3
Cl
Cl
N
Cl
Cl
N
N
N
P
P
Cl
N
N
P
P
Cl
P
N
N
N
P
HN
N
O
R
H3C
Cl
Ni
N
O
H3C
Cl
Cl
NH
N
Cl
R
(5)
R = OMe (6)
R = H
R = H
(7)
(8)
CH3
R = OMe
CH3
Scheme 1.The synthesis of porphyrino-phosphazene ligands and their Ni(II) complexes. Reagents and conditions. (i) Ni(OAc)2·4H2O,
DMF, reflux. (ii) N3P3Cl6, NaH, THF, -10 °C. (iii) N3P3Cl6, NaH, THF, -10 °C
inorganic side groups [19, 20], and rechargeable lithium
batteries [21, 22] and multidimensional use as biomedi-
cal materials including synthetic bones [23, 24], selective
anti-cancer and anti-bacterial reagents [25].
Aldrich Chemical Co. (USA). NaH with 60% paraffin
was used after it was washed with heptane and then
filtered. Melting points were measured on a Gallenkamp
apparatus using a capillary tube. 1H and 31P NMR spectra
were recorded on a Bruker DPX FT-NMR (400 MHz)
spectrometer (SiMe4 as internal and 85% H3PO4 as external
standards). FTIR spectra were recorded on a Mattson
1000 FTIR spectrometer in KBr discs and were reported
in cm-1 units. UV-visible spectra were measured using
UNICAM UV2–100 series spectrometer. Microanalyses
were carried out by the microanalytical service of
TUBITAK (Turkey). Electrospray ionization (ESI) mass
spectrometric analyses were performed on the Agilent
1100 MSD spectrometer. Thin-layer chromatography
(TLC) was performed on Merck DC Alufolien Kiesegel
60 B254 sheets. Column chromatography was performed
on Merck Kiesegel 60 (230–400 mesh ATSM) silica
gel. Electrochemical experiments were performed using
a Gamry Reference 600 workstation (Gamry, USA)
equipped with C3 cell stand (BAS, USA). Before
electrochemical experiments, solutions were purged with
pure argon gas (99.999%) for at least 10 minutes and
an argon atmosphere was maintained over the solution
during experiments. Working electrode was a glassy
carbon disk (BAS) and the counter electrode was a Pt
wire. The reference electrode was a Ag+/Ag (0.01 M)
used in MeCN.
Interestingly, to date, there is only one report on
cyclic-phosphazenes appended with six substited por-
phyrin rings in order to study physical and chemical
properties [26]. In addition, there is also one report on
a porphyrin appended with four cyclo-triphosphazene
rings [27]. This paper reports (i) the synthesis of two new
porphyrino-phosphazene ligands (5 and 6) and their com-
plexes of Ni(II) (7 and 8) (Scheme 1), (ii) the structures of
the free-ligands and their complexes determined by ele-
mental analyses, mass spectrometry (MS), Fourier trans-
form infrared spectroscopy (FTIR), 1H and 31P NMR, and
UV-visible data, and (iii) cyclic voltammetric studies that
have been performed to evaluate the redox potentials.
EXPERIMENTAL
General
The reaction solvents were dried and distilled by
standard methods before use. The reagents were of
commercial grade and used without further purification.
Hexachlorocyclotriphosphazatriene was purchased from
Copyright © 2010 World Scientific Publishing Company
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SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL INVESTIGATIONS OF PORPHYRINO-PHOSPHAZENES
229
Synthesis
3508 (O-H), 3050;3019 (C-H arom.), 2918;2848 (C-H
aliph.), 1602 (C=N), 1508 (C=C), 1276 (C-O), 961
5,10,15-tris(4-methylphenyl)-20-(4-hydroxyphenyl)
porphyrin (1) [28, 29] and 5,10,15-tris(4-methylphenyl)-
20-(4-hydroxyphenyl)porphyrinatonickel(II) (3) [30]
were prepared according to methods reported in the lit-
erature. Elemental analyses, mass spectrometry, ESI-MS,
FTIR and H NMR data of these compounds have been
given for purity and comparison purposes. 31P NMR
(CDCl3), H NMR (CDCl3) and UV-vis (CHCl3) data
of all the compounds are listed in Tables 1, 2 and 3,
respectively.
(C-N), 796 (β-pyrrole C-H). MS (ESI) : m/z (%) 730 ([M
+ H]+, 100).
5,10,15-tris(4-methylphenyl)-20-(3-methoxy-4-
hydroxyphenyl)porphyrinatonickel(II) [THMPNi], (4).
A solution of 2 (0.10 g, 0.15 mmol) in DMF (25 mL) was
heated and Ni(OAc)2·4H2O (0.20 g, 0.75 mmol) was slowly
added to this. The mixture was refluxed for 1 h and then
cooled. The solvent was evaporated and the solid residue
was washed with water to remove the remaining Ni(OAc)2.
The residue was filtered, dried, and subjected to column
chromatography with dichloromethane. Claret red powder
was obtained and was crystallized from dichloromethane/
n-hexane (1:1). Yield: 108 mg (95%), mp > 300 °C, Rf =
0.71 (CH2Cl2). Anal. calcd. for C48H36N4O2Ni: C, 75.91;
H, 4.78; N, 7.38%. Found: C, 76.68; H, 4.56; N, 7.16%.
IR (KBr): ν, cm-1 3510 (O-H), 3051;3017 (C-H arom.),
2916;2853 (C-H aliph.), 1598 (C=N), 1504 (C=C), 1256
(C-O), 951 (C-N), 797 (β-pyrrole C-H). MS (ESI): m/z
(%) 759 ([M + H]+, 100).
2,4,4,6,6-pentachloro-2-[5,10,15-tris(4-methy-
lphenyl)-porphyrin-20-(4-phenoxy)]-cyclo-2λ5,
4λ5,6λ5-triphosphaza-1,3,5-triene [TPPP], (5) and
2,4,4,6,6-pentachloro-2-[5,10,15-tris(4-methyl-
phenyl)-porphyrin-20-(3-methoxy-4-phenoxy)]-
cyclo-2λ5,4λ5,6λ5-triphosphaza-1,3,5-triene [TPMPP],
(6). To a solution of 1 (0.10 g, 0.15 mmol) in dry THF
(20 mL) was added NaH (60% suspension in paraffin
oil) (6.0 mg, 0.15 mmol) and the mixture was stirred at
room temperature. The red colour of the mixture was
changed to green, indicating porphyrin had turned to its
Na salt form. A stirred solution of N3P3Cl6 (0.05 g, 0.15
mmol) in THF (5 mL) was added and the mixture was
stirred at -10 °C for over 1 h. The green colour of the
mixture changed to red, indicating that reaction was
complete. The solvent was evaporated completely and
the residue was subjected to column chromatography
first with n-heptane and then toluene. Purple powder
of compound 5 was obtained and was crystallized
from toluene. The same procedure was used for the
synthesis of porphyrino-phosphazene ligand (6) from
free porphyrin ligand (2). Yield [TPPP], (5): 103 mg
(70%), mp > 300 °C, Rf = 0.77 (CH2Cl2). Anal. calcd.
for C47H35N7OP3Cl5: C, 57.37; H, 3.59; N, 9.96%.
Found: C, 58.21; H, 2.96; N, 10.14%. IR (KBr): ν,
cm-1 3317 (N-H), 3053;3024 (C-H arom.), 2920;2851
(C-H aliph.), 1600 (C=N), 1203 (P=N), 1007 (C-N),
798 (β-pyrrole C-H), 590;527 (P-Cl). MS (ESI): m/z
(based on 35Cl, %) 982 ([M + H]+, 10). Yield [TPMPP],
(6): 114 mg (75%), mp > 300 °C, Rf = 0.73 (CH2Cl2).
Anal. calcd. for C48H37N7O2P3Cl5: C, 56.85; H, 3.68;
N, 9.67%. Found: C, 57.76; H, 3.37; N, 10.01%. IR
(KBr): ν, cm-1 3311 (N-H), 3065;3019 (C-H arom.),
2916;2859 (C-H aliph.), 1592 (C=N), 1207 (P=N), 966
(C-N), 798 (β-pyrrole C-H), 598;523 (P-Cl). MS (ESI):
m/z (based on 35Cl, %) 1012 ([M + H]+, 1).
1
5,10,15-tris(4-methylphenyl)-20-(4-hydroxyphe-
nyl)porphyrin [THP], (1). Yield: 335 mg (3%), mp >
300 °C, Rf = 0.57 (CH2Cl2). Anal. calcd. for C47H36N4O:
C, 83.90; H, 5.39; N, 8.33%. Found: C, 84.12; H, 5.21;
N, 8.22%. IR (KBr): ν, cm-1 3503 (O-H), 3313 (N-H),
3052;3021 (C-H arom.), 2921;2842 (C-H aliph.), 1608
(C=N), 1510 (C=C), 1280 (C-O), 966 (C-N), 796
(β-pyrrole C-H). MS (ESI): m/z (%) 673 ([M]+, 100).
5,10,15-tris(4-methylphenyl)-20-(3-methoxy-4-
hydroxyphenyl)porphyrin [THMP], (2). 4-hydroxy-
3-methoxy benzaldehyde (2.30 g, 15.1 mmol) was
dissolved in 500 mL of propionic acid and 4-methyl-
benzaldehyde (5.30 mL, 45.2 mmol) was added to this.
The mixture was heated to 120 °C with vigorous stirring,
and then freshly distilled pyrrole (4.18 mL, 60.2 mmol)
was added dropwise. The resulting mixture was refluxed
for 4 h. Then, the mixture was allowed to cool and was
left overnight at room temperature. The separated solid
was removed by filtration. The filtrate was washed with
hot water to remove the remaining propionic acid and
other undesired polymeric tars. Solid lumps obtained
thereby were dried and purified by column chromatogra-
phy with dichloromethane. Purple powder was obtained
and was crystallized from dichloromethane/n-hexane (1:1).
Yield: 320 mg (3%), mp > 300 °C, Rf = 0.54 (CH2Cl2).
Anal. calcd. for C48H38N4O2: C, 82.03; H, 5.45; N,
7.97%. Found: C, 81.72; H, 5.33; N, 7.61%. IR (KBr): ν,
cm-1 3504 (O-H), 3311 (N-H), 3061;3019 (C-H arom.),
2914;2849 (C-H aliph.), 1598 (C=N), 1508 (C=C), 1261
(C-O), 966 (C-N), 796 (β-pyrrole C-H). MS (ESI) : m/z
(%) 703 ([M + H]+, 100).
5,10,15-tris(4-methylphenyl)-20-(4-hydroxy-
phenyl)porphyrinatonickel(II) [THPNi], (3). Yield:
105 mg (96%), mp > 300 °C, Rf = 0.72 (CH2Cl2). Anal.
calcd. for C47H34N4ONi: C, 77.38; H, 4.70; N, 7.68%.
Found: C, 77.53; H, 4.39; N, 7.41%. IR (KBr): ν, cm-1
Table 1. 31P NMR spectral data (CDCl3) of 5–8 (δ in ppm,
J in Hz)
Compound
Spin system
AX2
δPOCl
δPCl
2JPP
2
5
PA 13.33 PX 20.77
59.5
6
7
8
AX2
AX2
AX2
PA 14.27 PX 22.16
PA 13.12 PX 22.49
PA 14.25 PX 21.60
60.5
60.2
60.7
Copyright © 2010 World Scientific Publishing Company
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230
G. EGEMEN ET AL.
1
Table 2. H NMR spectral data (CDCl3) of 1–8 (δ in ppm, J in Hz, br: broad, s: singlet, d: doublet, dd: doublet-doublet,
m: multiplet)
H2
H3
H1
O
O
CH3
Hb
Hb
Ha
CH3
Ha
O
H2
H2
H1
H1
NH
Ar-CH3
Ar-O-CH3
Ar-OH
Ar-H1
Ar-H2
Ar-H3
Ar-Ha
Ar-Hb
CH (β-pyrr.)
1
2
-2.73
(s, 2H)
2.73
(s, 9H)
—
5.02
(br, 1H)
7.19
8.08
—
7.73
8.12
8.95
(m, 8H)
(d, 2H)
(d, 2H)
(d, 6H)
(d, 6H)
3JHH 8.4
3JHH 8.4
3JHH 7.7
3JHH 7.7
-2.70
(s, 2H)
2.75
(s, 9H)
4.05
(s, 3H)
6.04
(br, 1H)
7.30
(d, H)
3JHH 8.1
7.79
7.73
(d, H)
4JHH 2.0
7.59
8.13
8.94
(m, 8H)
(dd, 2H)
3JHH 8.1
4JHH 2.0
(d, 6H)
(d, 6H)
3JHH 7.5
3JHH 7.5
3
4
5
6
7
8
—
—
2.71
(s, 9H)
—
5.05
(br, 1H)
7.18
7.93
—
7.62
7.98
8.77 (m, 4H)
8.80 (d, 2H)
3JHH 4.7
(dd, H)
3JHH 8.2
4JHH 2.1
(dd, H)
3JHH 8.2
4JHH 2.1
(d, 6H)
(d, 6H)
3JHH 7.8
3JHH 7.8
8.86 (d, 2H)
3JHH 4.7
2.70
(s, 9H)
4.02
(s, 3H)
6.06
(br, 1H)
7.28
(d, H)
3JHH 8.0
7.61
7.50
(d, H)
4JHH 2.0
7.52
7.93
8.79 (m, 4H)
8.80 (d, 2H)
3JHH 4.9
(dd, H)
3JHH 8.0
4JHH 2.0
(d, 6H)
(d, 6H)
3JHH 7.6
3JHH 7.6
8.83 (d, 2H)
3JHH 4.9
-2.74
(s, 2H)
2.74
(s, 9H)
—
—
—
—
—
7.71
8.29
—
7.60
8.13
8.80 (d, 2H)
3JHH 4.7
8.91 (m, 4H)
8.95 (d, 2H)
3JHH 4.7
(dd, 2H) (dd, 2H)
(d, 6H)
(d, 6H)
3JHH 8.5
4JHH 2.1
3JHH 8.5
4JHH 2.0
3JHH 7.7
3JHH 7.7
-2.74
(s, 2H)
2.74
(s, 9H)
4.01
(s, 3H)
7.69
(d, H)
3JHH 8.5
7.84
7.88
(d, H)
4JHH 2.1
7.59
8.13
8.84 (d, 2H)
3JHH 4.8
8.90 (m, 4H)
8.93 (d, 2H)
3JHH 4.8
(dd, H)
3JHH 8.5
4JHH 2.1
(d, 6H)
(d, 6H)
3JHH 7.5
3JHH 7.5
—
—
2.75
(s, 9H)
—
7.68
8.08
—
7.51
7.92
8.68 (d, 2H)
3JHH 4.9
8.79 (m, 4H)
8.81 (d, 2H)
3JHH 4.9
(dd, 2H) (dd, 2H)
(d, 6H)
(d, 6H)
3JHH 8.5
4JHH 2.1
3JHH 8.5
4JHH 2.1
3JHH 7.6
3JHH 7.6
2.77
(s, 9H)
3.99
(s, 3H)
7.58
(d, H)
3JHH 7.9
7.62
7.66
(d, H)
4JHH 2.3
7.50
7.91
8.73 (d, 2H)
3JHH 4.9
8.79 (m, 4H)
8.81 (d, 2H)
3JHH 4.9
(dd, H)
3JHH 7.9
4JHH 2.3
(d, 6H)
(d, 6H)
3JHH 7.8
3JHH 7.8
2,4,4,6,6-pentachloro-2-[5,10,15-tris(4-methy-
tris(4-methylphenyl)-porphyrinatonickel(II)-20-(3-
methoxy-4-phenoxy)]-cyclo-2λ5,4λ5,6λ5-triphosphaza-
1,3,5-triene [TPMPPNi], (8). To a solution of 3 (0.10 g,
0.13 mmol) in dry THF (20 mL) was added NaH (60%
lphenyl)-porphyrinatonickel(II)-20-(4-phenoxy)]-
cyclo-2λ5,4λ5,6λ5-triphosphaza-1,3,5-triene
[TPPPNi], (7) and 2,4,4,6,6-pentachloro-2-[5,10,15-
Copyright © 2010 World Scientific Publishing Company
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SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL INVESTIGATIONS OF PORPHYRINO-PHOSPHAZENES
231
Table 3. UV-vis (in CHCl3) data of 1–8
Compound
Colour
λ
max, nm (ε × 10 4 M-1.cm-1)
Soret band
Q bands
1
2
3
4
5
6
7
8
purple
purple
418 (130.0)
420 (87.0)
416 (94.0)
416 (92.7)
418 (110.4)
420 (130.3)
416 (75.0)
416 (46.5)
518 (4.7)
518 (4.7)
528 (6.6)
528 (6.6)
516 (3.6)
514 (4.6)
528 (4.3)
528 (2.5)
552 (2.2)
552 (3.2)
—
594 (0.8)
594 (2.4)
—
650 (0.8)
648 (2.4)
—
claret red
claret red
purple
—
—
—
552 (1.5)
552 (2.0)
—
594 (0.7)
592 (0.1)
—
650 (1.3)
648 (0.8)
—
purple
claret red
claret red
—
—
—
suspension in paraffin oil) (5.2 mg, 0.13 mmol) and the
mixture was stirred at room temperature. A stirred solu-
tion of N3P3Cl6 (0.05 mg, 0.13 mmol) in THF (5 mL) was
added and the mixture was stirred at -10 °C for over 4h.
The solvent was evaporated completely and the resi-
due was subjected to column chromatography first with
n-heptane and then toluene. Claret red powder of com-
pound 7 was obtained and was crystallized from toluene.
The same procedure was used for the synthesis of porphy-
rino-phosphazene complex (8) from porphyrin complex
(4). Yield [TPPPNi], (7): 110 mg (71%), mp > 300 °C,
Rf = 0.93 (CH2Cl2). Anal. calcd. for C47H33N7OP3Cl5Ni:
C, 54.24; H, 3.20; N, 9.42%. Found: C, 54.39; H, 3.43;
N, 9.29%. IR (KBr): ν, cm-1 3060;3022 (C-H arom.),
2922;2852 (C-H aliph.), 1602 (C=N), 1211 (P=N),
1004 (C-N), 796 (β-pyrrole C-H), 596;525 (P-Cl). MS
(ESI): m/z (based on 35Cl, %) 1038 ([M + H]+, 0.3). Yield
[TPMPPNi], (8): 117 mg (73%), mp > 300 °C, Rf = 0.86
(CH2Cl2). Anal. calcd. for C48H35N7O2P3Cl5Ni: C, 53.84;
H, 3.29; N, 9.16%. Found: C, 54.31; H, 3.07; N, 8.82%.
IR (KBr): ν, cm-1 3055;3020 (C-H arom.), 2920;2855
(C-H aliph.), 1596 (C=N), 1211 (P=N), 970 (C-N), 798
(β-pyrrole C-H), 604;527 (P-Cl). MS (ESI): m/z (based
on 35Cl, %) 1068 ([M + H]+, 1).
phosphazene ligands, 5 and 6. The crude products after
evaporating the solvent in the reduced pressure were
purified by column chromatography on silica gel. The
synthetic and analytical data of the new compounds 5–8
are given in the experimental part. Elemental analyses,
FTIR, ESI-MS, UV-vis, 31P and 1H NMR data are
consistent with the proposed structures. The MS spectra
of the compounds show molecular ion [M]+ (for 1) and
protonated molecular ion [M+H]+ (for 2–8) peaks.
IR spectra
The FTIR spectra of all the compounds exhibit two
weak intensity absorption bands at 3065–3051 cm-1 and
3024–3017 cm-1. These are attributed to the asymmetric
and symmetric stretching vibrations of the aromatic C-H
bonds. All the porphyrino-phosphazene derivatives dis-
play the intense characteristic bands between 1211–1203
cm-1 and 1007–966 cm-1 corresponding to the νP=N of the
phosphazene skeleton and νC-N of the porphyrin ring,
respectively. The compounds (1, 2, 3 and 4) and (1, 2,
5 and 6) exhibit absorption bands for νO-H and νN-H in the
range of 3510–3503 cm-1 and 3317–3311 cm-1, respec-
tively. The characteristic stretching bands for νO-H dis-
appear in the FTIR spectra of porphyrino-phosphazene
derivatives and their complexes (5–8); νN-H stretching
bands disappear in the spectra of all the nickel(II) com-
plexes (3, 4, 7 and 8).
RESULTS AND DISCUSSION
Synthesis
31P and 1H NMR spectra
Preparation of the new porphyrinato-phosphazene-
Ni(II) complexes (7 and 8) was accomplished in a two-
step process (Scheme 1). The first pathway (i) involves
the complexation of 1 and 2 with Ni(OAc)2 in boiling
DMF to afford the corresponding complexes, 3 and 4. The
second pathway (ii) involves the condensation reactions
of 3 and 4 with N3P3Cl6 in dry THF at -10 °C to produce
new porphyrinato-phosphazene-Ni(II) complexes (7 and
8), respectively. On the other hand, the other synthetic
route (iii) involves the condensation reactions of 1 and 2
with N3P3Cl6 in dry THF at -10 °C to give free porphyrino-
The 1H-decoupled 31P NMR data of all the porphyrino-
phosphazene derivatives are listed in Table 1. The spin
systems are interpreted as simple AX2 from the 31P NMR
spectra. Chemical shifts and coupling constants of free
porphyrino-phosphazene ligands (5 and 6) and their
nickel(II) complexes (7 and 8) are very near each other;
the average values are 13.74 ppm for δPOCl, 21.76 ppm for
δPCl and 60.3 Hz for 2JPP.
I2n all of the new porphyrino-phosphazene ligands
1
and their complexes, the H NMR signals have been
assigned on the basis of chemical shifts, multiplicities,
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232
G. EGEMEN ET AL.
and coupling constants (Table 2). The NH protons of 1,
2, 5 and 6 resonate as singlet. The average value is -2.72
ppm. These NH peaks disappear in the spectra of the por-
phyrinato complexes (3, 4, 7 and 8). In addition, broad
OH peaks at 6.06–5.02 ppm for (1–4) disappear in the
spectra of the porphyrino-phosphazene ligands (5 and 6)
and their complexes (7 and 8).
changes occur in the free ligands conjugated π-electronic
systems. In other words, the phosphazene ring does not
affect the porphyrin π-conjugated systems, as is observed
in the electrochemical behavior below.
Electrochemistry
derivatives
of
porphyrino-phosphazene
The anodic oxidation of tetraphenylporphyrins in
either free ligand or metalloform leads to the polymer-
ized insoluble thin films on the glassy carbon electrode in
MeCN (containing 0.1 M TBATFB). Figure 3(a) shows
the consecutive voltammograms of 2,4,4,6,6-pentachloro
-2-[5,10,15-tris(4-methylphenyl)-porphyrin-20-(4-
phenoxy)]-cyclo-2λ5,4λ5,6λ5-triphosphaza-1,3,5-triene
(5) (TPPP) as a representative ligand bearing phospha-
zene ring. The first two irreversible peaks are related to
the oxidation of porphyrin ring, forming first π-cation
radical (P1) and then the oxidation of π-cation to dica-
tion in solution (P2) [33, 34].
To aid understanding of the influence of the presence
of metal within the porphyrin ring, the electrochemistry of
TPPPNi (7) was also investigated. The striking influence
of the presence of nickel(II) in the porphyrin ring is the
inhibition of P1 and P2 peaks corresponding to the forma-
tion of π-cation [TPPP]+· and dication of the free ligand
([TPPP2+]), respectively (Fig. 3(a)). The third oxidation
peak (P3) around +2.2 V is common in both voltammo-
grams of free ligand and metalloporpyrin. This indicates
that the third peak is related to the oxidation of pheriph-
eral phenyl groups rather than the central porphyrin ring,
forming cation radicals, [TPPP2+]+· and [TPPPNi]+·, for
free ligand and nickel(II) complex, respectively. Another
common aspect of both voltammograms is the suppres-
sion of the wave in the successive scans after the first one,
due to the formation of electroinactive film at the GC sur-
face. The suppression of the oxidation wave in the suc-
cessive scans is a well-known behavior of electroinactive
films gradually formed on the conductive substrates [35].
It should be emphasized that electrochemical deposition is
not observed when the potential scan is performed in the
anodic potential range between 0 V and +0.7 V as well as
between 0V ad +1.3V, as is shown in the insets of Fig. 3(a).
This suggest that covalent bond is not formed until the gen-
eration of [TPPP2+]+· and [TPPPNi]+· radicals that attack
the graphitic structure of the glassy carbon surface.
UV-vis spectra
Figures 1 and 2 depict UV-vis spectra of all the com-
pounds. The UV-vis spectral data are summarized in Table 3.
The well-known Soret bands are observed at ca. 418 nm,
common for all porphyrin derivatives [31]. Of the four
less-intensive Q bands at about 517, 551, 592 and 648 nm
which are observed in the electronic spectra of the free
ligands (1, 2, 5 and 6), the last three bands disappear in the
spectra of the complexes (3, 4, 7 and 8). In addition, the
β-bands characteristic of metalloporphyrins are observed
at 528 nm for the Ni(II) complexes (3, 4, 7 and 8) [32]. It
is noteworthy to point out that the UV-vis absorptions of
the free ligands are mainly attributable to the porphyrin
skeleton. However, one can conclude that no significant
Fig. 1. The UV-visible spectra of 1 (∆), 3 (○), 5 (▼) and 7 (●)
This behavior at GC seems contrary to that reported
in the literature for a free porphyrin base molecule and
metalloporphyrin at the Pt surface [33]. When reaching
the P3 peak potential, peripheral phenyl groups of por-
phyrin are oxidized, leading to the formation of polymer
in solution and deposition to the Pt electrodes. In the case
of GC surface, a covalent bond is formed by the attack
of the cation radicals of ligand and the complex with the
graphitic structure of the GC surface. Although the elec-
trodeposited porphyrin polymer is electroactive on the Pt,
covalently bonded porphyrin film is not at the GC surface.
Fig. 2. The UV-visible spectra of 2 (∆), 4 (○), 6 (▼) and 8 (●)
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SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL INVESTIGATIONS OF PORPHYRINO-PHOSPHAZENES
233
the oxydation of the central porphyrin ring, and that the
phosphazene derivative does not influence the oxydation
mechanism. The solubility of porphyrino-phosphazene
ligands (5 and 6) and their complexes (7 and 8) in com-
mon organic solvents are much higher than the porphy-
rin ligands (1 and 2) and their complexes (3 and 4). In
the future, many new porphyrino-phosphazenes may be
obtained from the chloride replacement reactions of the
compounds 5–8 with organic substituents, such as pri-
mary and secondary amines, diamines, amino alcohols
and diols.
Acknowledgements
The authors acknowledge Ankara University Research
Fund (Grant 20050705107) for financial support.
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