Synthesis, characterization and electrochemistry of succinyloxyl-bridged metal-free and transition metal porphyrin dimers

Article abstract of DOI:10.1080/15533170600962505

Novel metal-free and Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mn(III) porphyrin dimers bridged by meso-succinyloxyl were prepared in high yields. The new compounds were characterized by elemental analysis, ¹H NMR, MS, IR and UV-vis spectroscopy

Full text of DOI:10.1080/15533170600962505

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 36:673–679, 2006
Copyright # 2006 Taylor & Francis Group, LLC
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1080/15533170600962505
Synthesis, Characterization and Electrochemistry
of Succinyloxyl-Bridged Metal-Free and Transition Metal
Porphyrin Dimers
Xiuli Cheng, Ying Li, Yuhua Shi, and Tongshun Shi
College of Chemistry, Jilin University, Changchun, P.R. China
and magnetic energy with implications in biological functions.
Novel metal-free and Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Different substituents introduced onto the porphyrin core could
Mn(III) porphyrin dimers bridged by meso-succinyloxyl were
prepared in high yields. The new compounds were characterized
change its redox potentials and result in different ability in epox-
idations. It is also noteworthy that porphyrins and their coordi-
by elemental analysis, 1H NMR, MS, IR and UV-vis spectroscopy.
Molar conductance data indicate that the monomeric complexes
of Fe(III) and Mn(III) have 1 : 1 electrolytic behavior; the
nation compounds have been used as specific nuclear magnetic
shift reagents,[6,7] nonlinear optical material,[8,9] simulation
dimeric complexes of Fe(III) and Mn(III) have 1 : 2 electrolytic materials for the photosynthesis system,[10] molecular imprint-
behavior, while the others show no electrolytic behavior. Mean-
while, the electrochemistry properties of the dimers were
ing,[11] and molecular apparatus.[12] Therefore, it is very important
to study the correlation of their structure, reaction and function.
analyzed and compared with their corresponding monomeric por-
phyrins. The order of the first reduction potentials is observed
Porphyrin dimer linked by a covalent bond such as dihalide
or dicarboxylic acid with two monohydroxyTPPs (TPP ¼
as the porphyrin free-base < Ni21 ꢀ Cu21 < Zn21, and that of
the first oxidation potentials is entirely contradictory. The electro- tetraphenylporphyrin) or monoamino TPPs is one of the most
familiar systems for their simple and classical synthesis
chemical results also indicate that the dimeric porphyrins show
two-electron redox behavior.
method.[13–19] In addition, these porphyrin dimers usually
have better catalytic activities and bigger molar extinction
Keywords porphyrin,
dimer,
synthesis,
metal
complex,
coefficients than their monomeric analogues. However, to
this day, the porphyrin dimers linked to two monohydrox-
yTPPs by succinic acid have not been reported. In this
paper, a meso-succinyloxyl bridged porphyrin dimer and its
Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mn(III) transition metal
complexes (Scheme 1) are synthesized first, and that, their
reduction and oxidation processes are analyzed by cyclic
voltammetry and compared with their corresponding
monomers. Our investigations will provide credible exper-
imental surpport to study their properties, including catalytic
activities of the metalloporphyrin complexes.
electrochemistry
INTRODUCTION
Procedures for the synthesis and functionalization of mono-
meric porphyrin molecules have received considerable attention
for a number of years. Thus far, almost any porphyrin can be
obtained using available methodology.[1] Many research groups
have now moved toward the design and development and
applications of porphyrin multipolymers and porphyrin ana-
logues.[2–12] Synthesis of bis-porphyrins and porphyrin oligo-
mers, coupled with their photophysical and photochemical
properties have evolved to be an important endeavor because por-
phyrins play important roles in transferring and saving electrical
EXPERIMENTAL
Materials
Pyrrole (Alderich Chemical Company Inc., USA) was
freshly distilled prior to use. N, N0-dimethylformamide(DMF)
was distilled according to the literature method before use.[20]
Tetrabutylammonium perchlorate (TBAP) was used as an elec-
trolyte for electrochemical studies was synthesized according
to the reported procedures.[21] All other solvents and chemicals
were of analytical reagent grade quality purchased commer-
cially and used as received (Tiantai Fine Chemical Company
Inc.). Neutral alumina (200–300 mesh, activated at 1208C
Received 18 June 2006; accepted 6 July 2006.
We thank the National Natural Science Foundation of China
(59783001) for financial support of this work.
Address correspondence to Tongshun Shi, College of Chemistry,
Jilin University, Jiefang Road 2519, Changchun 130023,
P.R. China. E-mail: cxl@email.jlu.edu.cn
673

674
X. CHENG ET AL.
SCH. 1. Syntheses of the free-base and metal porphyrin.
þ
23
23
.
.
for 5 h then deactivated with 5% water) was used for column Ag /Ag (0.01 mol dm AgNO3 þ 0.1 mol dm TBAP in
chromatography. Where solvent mixtures were used, the CH3CN) reference electrode. The reference electrode was separ-
proportions were given by volume.
ated from the bulk of the solution by a fritted glass bridge filled
with the solvent/supporting electrolyte mixture. High-purity
grade Ar was used to deoxygenate the DMF solutions for 10
minutes before each experiment. For cyclic voltammetry
Measurements
23
studies, concentrations were of the order of 1023 mol dm
.
Elemental analyses were performed by a Perkin-Elmer
240C auto elementary analyzer. Ultraviolet-visible spectra
were recorded on a Schimadzu UV-365 spectrophotometer
with chloroform as solvent. Concentrations of the compounds
.
Synthesis
were of the order of 1025 mol dm23. Infrared spectra (KBr
.
5-(4-hydroxylphenyl)-10,15,20-triphenylporphyrin (H2HPT
pellets) were recorded by a Nicolet FTIR-5PC spectropho- PP, HP ¼ hydroxylphenyl, TPP ¼ triphenylporphyrin). The
1
tometer in the region 4000–400 cm21. H nuclear magnetic synthesis of the H2P was based on Alder’s method, which
resonance (NMR, 400 MHz) spectra were obtained in CDCl3 involves the condensation under reflux of stoichiometric
solutions using
a Varian Unity-400NMR spectrometer; amounts of pyrrole and appropriate aldehydes in propionic
chemical shifts were given in ppm versus tetramethylsilane acid.[22] Mixture of 4-hydroxybenzaldehyde (0.02 mmol) and
(TMS) and were referenced against residual solvents signals. of benzaldehyde (0.06 mmol) was added to 250 ml hot propio-
Mass spectra (FBA) were obtained using a VG-Quattro mass nic acid at ca. 1258C (Scheme 1). Pyrrole (0.08 mmol) was
23
spectrometer. Molar conductances of 1023 mol dm DMF added gradually to the hot solution, which was then allowed to
.
solution at 258 were measured on a DDX-11A conductometer. reflux for 30 min. The resulting reaction mixture was condensed
Reactions were monitored by thin layer chromatography. Thin to about 70 ml by vacuum, then cooled to the room temperature;
layer chromatography was performed on glass micro-plates 70 ml ethanol was then added and kept overnight at room temp-
coated with silica gel G.
Cyclic voltammetry was carried out with a CHI600A cessively with ethanol, air-dried, dissolved in a minimal amount
Electrochemical Workstation. three-electrode system of chloroform and purified on a neural alumina column
erature. The purple crude product was filtered off, washed suc-
A
was used that consisted of a platinum button working (10 ꢀ 2 cm). The first purple band containing tetraphenylpor-
electrode, a platinum wire counterelectrode and a homemade phyrin (H2TPP) was eluted with chloroform. The second

PORPHYRIN DIMERS BRIDGED BY SUCCINYLOXYL
675
purple band was eluted with chloroform/ethanol (50:1 v/v), elemental analyses for these porphyrins are close to the calcu-
then concentrated and recrystallized from CHCl3/CH3OH to lated values. Comparisons of the data of molar conductance
give the pure free-base H2HPTPP 890 mg. Yield: 4.2%.
with the reference,[24] the ligands and their complexes of
Zn(II), Co(II), Ni(II), Cu(II) show non-electrolytic behavior;
the monomeric complexes of Mn(III) and Fe(III) are 1:1 elec-
trolytic compounds, while their dimeric complexes, are 1:2
electrolytic compounds.
The Succinyloxyl-Bridged Dimeric Porphyrin (H4-
dimer). In the preparation of the mixture of H2HPTPP
(0.9 mmol) and anhydrous aluminum chloride (60 mg) was
stirred in chloroform (60 mL) at room temperature. Succinyl
chloride (0.45 mmol) was slowly dropped into the mixture,
and then the system was kept stirring for 10 h. The deposit
was removed and the solution was washed with saturated
KHCO3 aqueous solutions and distilled water, then dried
over anhydrous Na2SO4 and concentrated. The product was
purified by means of chromatography on neutral alumina
(30 ꢀ 1.5 cm) with chloroform as the eluent. The porphyrin
dimer ligand was obtained in about 96% yield.
UV-Vis and Infrared Spectra
The spectral features of the ligands and their complexes
are summarized in Table 2. Two porphyrin free bases both
have one band in the uv region, and four Q bands awithin
the visible region and were assigned to p ! pꢁ (a2m ! egꢁ)
and p ! pꢁ (a1m ! egꢁ) of the p orbital of the porphyrin
macrocycle, respectively.[25] They are slightly shifted with
respect to the tetraphenylporphyrin (420, 516, 550, 591, and
648 nm).[26] The relative intensities of these bands is as
follows: 420 ꢂ 515 . 550 . 590 . 650 nm, this is similar
to the findings in H2TPP.[27] As compared with the mono-
meric porphyrins, the absorption values of the dimeric por-
phyrins remained unchanged except that the molar
extinction coefficients exhibit an overall increase.
As compared with the porphyrin free-bases, the number of
absorption bands of the complexes decreases which is the
important characteristic of metalloporphyrin.[28] These spec-
troscopic findings may be attributed to the improvement in
the overall molecular symmetry (D2h ! D4h). It is also
important to note that as the cleavage of the molecular
orbital decreases, the degeneracy increases when the metal
ion is coordinated with the porphyrin ligand.[29] On the
other hand, the molar extinction coefficients of M2-dimer
are obviously higher than thaose of their corresponding
Metalloporphyrins (MHPTPP and M2-Dimer). The tran-
sition metal ions were incorporated according to the standard
method.[23] For example, Co2-dimer was prepared as follows:
.
H4-dimer (63 mg) and CoCl2 6H2O (0.3 g) was stirred in
30 ml DMF, the mixture was refluxed and the reaction was
monitored by thin layer chromatography. The solution was
then cooled, extracted by water and chloroform several
times, and dried over anhydrous Na2SO4. Solvent was
removed and the residue was separated by chromatography
on a column packed with neutral alumina with chloroform as
an eluent. The solvent was removed to get the product at
58 mg, yield 88%. Other complexes were also prepared by
the method described as above. The yields were all above 85%.
RESULTS AND DISCUSSION
Elemental Analyses and Molar Conductance
The elemental analyses for carbon, hydrogen, nitrogen, M-P. Within the MTPP series of compounds, the soret
empirical formulae, formula weights, and molar conductance bands of Mn(III)TPPCl, Mn(II)TPP, Fe(III)TPPCl and
values of the complexes are given in Table 1. The results of Fe(II)TPP were found at 480, 440, 412 and 423 nm,
TABLE 1
Elemental analyses and molar conductance values of the complexes
Elemental analyses (%)a
Molar conduc-
tance (Ohm21
cm21 mol21 b
)
Empirical formula
and formula weight
Compounds
C
H
N
H2HPTPP
H4-dimer
C44H30N4O, 631.7
C92H62N8O4, 1343.62
82.58 (82.79) 4.70 (4.79) 8.95 (8.88)
82.69 (82.84) 4.80 (4.65) 8.30 (8.34)
77.00 (77.23) 4.01 (4.09) 7.75 (7.83)
78.81 (79.02) 4.10 (4.18) 8.13 (8.01)
78.96 (79.03) 4.18 (4.18) 7.92 (8.01)
78.55 (78.76) 4.10 (4.17) 8.12 (7.99)
78.55 (78.65) 4.14 (4.16) 8.05 (7.98)
4.2
4.8
(FeCl)2-dimer
Co2-dimer
Ni2-dimer
Cu2-dimer
Zn2-dimer
Fe2C92H58N8O4Cl2, 1522.13
Co2C92H58N8O4, 1457.39
Ni2C92H58N8O4, 1456.90
Cu2C92H58N8O4, 1466.62
Zn2C92H58N8O4, 1470.31
149.2 (70.2)
9.5 (8.6)
5.2 (4.7)
7.4 (6.9)
5.1 (4.8)
171.0 (76.2)
(MnCl)2-dimer Mn2C92H58N8O4Cl2, 1520.31 77.10 (77.28) 4.04 (4.09) 7.90 (7.84)
aTheoretical values are given in parentheses.
bMolar conductance values of the corresponding monomer complexes (M-P) are given in the parentheses.

676
X. CHENG ET AL.
TABLE 2
UV-Vis spectra of the ligands and complexes
Maximum absorption peaks (lmax nm)(lg1)
Compounds
Soret band
Q band
550 (3.81)
H2HPTPP
H4-dimer
420 (5.01)
420 (5.90)
410 (5.23)
415 (5.54)
410 (5.23)
410 (5.64)
415 (5.18)
415 (5.50)
420 (5.90)
420 (5.90)
420 (5.90)
425 (5.90)
475 (4.94)
480 (5.45)
515 (4.04)
515 (4.48)
570 (4.11)
570 (4.60)
530 (4.00)
530 (4.43)
530 (4.08)
530 (4.36)
540 (4.28)
540 (4.54)
550 (4.41)
550 (4.60)
525 (3.81)
530 (4.25)
590 (3.53)
590 (4.00)
650 (3.45)
650 (3.45)
550 (4.15)
615 (4.04)
615 (4.58)
FeHPTPPCl
(FeCl)2-dimer
CoHPTPP
Co2-dimer
NiHPTPP
Ni2-dimer
CuHPTPP
Cu2-dimer
ZnHPTPP
Zn2-dimer
MnHPTPPCl
(MnCl)2-dimer
595 (3.64)
595 (4.04)
580 (4.00)
580 (4.46)
620 (4.00)
620 (4.48)
respectively. The Soret bands of Mn-P, Mn2-dimer, Fe-P and bending vibration bands are absent in both MHPTPP and
Fe2-dimer were found at 475, 480, 410 and 415 nm, respect- M2-dimer, since the hydrogen atoms are replaced by the
ively, indicating that Mn and Fe are trivalent.
metal ion to form M-N bond. A strong band appears at about
The important band frequencies and assignments of IR 1004 cm21 due to the deformation of the porphyrin ring by
spectra for the ligands and the dimeric complexes as presented the interaction of M-N bonding.[31] These spectroscopic data
in Table 3. The medium intensity absorption peak of H2HPTPP also indicate that the two macrocycles in the dimeric com-
at 3521 cm21 assigned to the O-H stretching vibration disap- plexes (M2-dimer) were both occupied by the metal ions.
pears in the dimers. The bands at 3316 and 966 cm21 in the One medium intensity absorption band at about 1762 cm21
free-base porphyrins, are due to the N-H stretching and assigned to the C55O stretching vibration appears, synchro-
bending vibration of the macrocycle. The N-H stretching and nously two medium intensity absorption bands assigned to
TABLE 3
Infrared spectra of complexes and liganda (cm21
)
Compounds
nO-H
nN-H
nCH2
nC¼O
dC-H
nC-N
nC-O-C
pP
dN-H
H2HTPP
H4-dimer
3521 m
3316 m
1441 w 1349 w
998 w
998 w
1004 s
1004 s
1004 s
1004 s
1006 s
1006 s
1004 s
1004 s
1002 s
1002 s
1010 s
1006 s
966 s
966 s
3316 m 2923 m 1762 m 1442 w 1352 w
1441 w 1339 w
1198 m
1205 m
1203 m
1201 m
1203 m
1205 m
1203 m
FeHPTPPCl
(FeCl)2-dimer
CoHPTPP
Co2-dimer
NiHPTPP
3533 m
3562 m
3563 m
3500 m
3533 m
3496 m
2924 m 1764 m 1440 w 1338 w
1441 w 1350 w
2925 m 1765 m 1440 w 1350 w
1441 w 1351 w
Ni2-dimer
CuHPTPP
Cu2-dimer
ZnHPTPP
Zn2-dimer
MnHPTPPCl
(MnCl)2-dimer
2924 m 1763 m 1441 w 1351 w
1440 w 1346 w
2925 m 1761 m 1442 w 1346 w
1440 w 1340 w
2924 m 1764 m 1440 w 1340 w
1443 w 1342 w
2923 m 1763 m 1443 w 1342 w
aStrong: s; medium: m; weak: w.

PORPHYRIN DIMERS BRIDGED BY SUCCINYLOXYL
677
the C-O-C stretching vibration at about 1204 cm21 and the
CH2 stretching vibration at 2923 cm21 are also seen in the
spectra. These data confirm the presence of meso-succinyloxyl
groups.
1H NMR Spectra
1
The H NMR chemical shift values in CHCl3 (d, ppm) for
H4-dimer are at 22.77 (4H, s, pyrrole-NH), 3.36(4H, t,
CH2), 7.25(4H, d, 3,5-PhO), 7.74(18H, m, 3,4,5-Ph),
8.20(12H, d, 2,6-Ph), 8.58(4H, d, 2,6-PhO), 8.84(16H, d,
bH). As compared with the chemical shift values for
H2HPTPP,[32] the signal at 10.11(1H, OH) disappears, with a
new signal appearing at 3.36 (4H, CH2). These data indicate
that the succinyloxyl (-OOCCH2CH2COO-) group is present
within the overall molecular structure. Additionally, the
signal at 22.77 (4H, pyrrole-NH) disappears, since the
hydrogen atom in the N-H bond is replaced by the transition
metal ion. This also suggests that the two porphyrin cores in
the dimeric complexes are both occupied by the metal ion.
Other peaks of the dimer complexes are broadened compared
with those of the corresponding monomeric complexes. The
above specral findings confirm the formation of all the new
porphyrin analogues.
FIG. 1. Cyclic voltammograms of H2HPTPP and H4-dimer.
literature.[33–39] The cyclic voltammograms of the two porphyrin
free-bases and their zinc complexes in DMF containing
0.1 mol dm21 TBAP are presented in Figure 1 and Figure 2.
.
As compared to the redox potentials of dimeric porphyrins
with those of the monomeric porphyrins, the values of the
former are shifteted toward positive potentials. This may be
attributed to the formation of succinyloxyl bridge attached to
tetraphenylporphyrins. The electron-donating (hydroxyl)
group would have decreased the electron density of the
p-ring system and the energy of both the HOMO and the
LUMO, which makes them harder to oxidize and easier to
reduce than the corresponding monomeric species.
ELECTROCHEMISTRY
The electrochemical properties of the porphyrins were studied
by cyclic voltammetry. The redox potentials for all the com-
pounds are summarized in Table 4, and the assignments as to
the site of electron transfer are based on both the analysis of
the electrochemical data in this paper and the data in the
TABLE 4
Half-wave potentials calculated in cyclic voltammetry studies E1/2/V (vs. Agþ/Ag)
Central metal ion Ring reduction
Ring oxidation
(1st)
Compounds
MIII/MII
MII/MI
1st
2nd
H2HPTPP
H4-dimer
0.65a
0.75a
0.49a
0.60a
0.64a
0.77a
0.60a
0.65a
0.57a
0.66a
0.44a
0.48 (0.51a)
0.75a
0.65a
21.50
21.46
21.48
21.43
21.64
21.60
21.60
21.56
21.59
21.56
21.77
21.72
21.73
21.72
21.95
21.91
21.85
22.14
FeHPTPPCl
(FeCl)2-dimer
CoHPTPP
Co2-dimer
NiHPTPP
20.58
20.57
0.03a
21.23
21.22
0.04a
22.17
22.14
22.11
22.08
22.18
22.11
22.04
22.19
Ni2-dimer
CuHPTPP
Cu2-dimer
ZnHPTPP
Zn2-dimer
MnHPTPPCl
(MnCl)2-dimer
20.62
20.60
aValue given is Epa, at 120 mV/s.

678
X. CHENG ET AL.
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