Preparation of N-bridged diiron phthalocyanines bearing bulky or small electron-withdrawing substituents

Article abstract of DOI:10.1142/S1088424610002069

The synthesis of novel μ-nitrido diiron phthalocyanine with electron-withdrawing substituents is reported: μ-nitrido tetra- methylsulfonylphthalocyanine (13), μ-nitrido tetra- ethylsulfonylphthalocyanine (14), μ-nitrido tetra- adamantylsulfonylphthalocyan

Full text of DOI:10.1142/S1088424610002069

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 324–334
DOI: 10.1142/S1088424610002069
Published at http://www.worldscinet.com/jpp/
Preparation of N-bridged diiron phthalocyanines bearing
bulky or small electron-withdrawing substituents
Ümit İşcia,b, Fabienne Dumoulina◊, Vefa Ahsen*a,c◊ and Alexander B. Sorokin*b◊
a Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, Turkey
b Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON) UMR 5256, CNRS-Université
Lyon 1, 2, av. A. Einstein, 69626 Villeurbanne Cedex, France
c TUBITAK-Marmara Research Center, Materials Institute, P.O. Box 21, Gebze 41470, Turkey
Received 1 September 2009
Accepted 16 October 2009
ABSTRACT: The synthesis of novel µ-nitrido diiron phthalocyanine with electron-withdrawing
substituents is reported: µ-nitrido tetra-methylsulfonylphthalocyanine (13), µ-nitrido tetra-ethylsulfonyl-
phthalocyanine (14), µ-nitrido tetra-adamantylsulfonylphthalocyanine (15), µ-nitrido tetra-cyclohexyl-
sulfonylphthalocyanine (16). These complexes were characterized by ESI-MS, UV-vis, FT-IR and EPR
techniques. The state of these complexes depends on the size of the substituents. Complexes 13 and 14
-
bearing small methylsulfonyl and ethylsulfonyl substituents are cationic (PcFeIVNFeIVPc)+N3 complexes
while complexes 15 and 16 with bulkier adamantylsulfonyl and cyclohexylsulfonyl substituents are
formally neutral PcFeIIINFeIVPc complexes which can be represented as PcFe(+3.5)NFe(+3.5)Pc.
KEYWORDS: µ-nitrido dimer, diiron, alkylsulfonyl substituents, catalysis.
study of µ-nitrido diiron macrocyclic complexes with
Fe-N-Fe unit and their application in oxidation cataly-
INTRODUCTION
Transition metal complexes of phthalocyanines are
sis [11]. µ-nitrido diiron tetra-tert-butylphthalocyanine
widely investigated owing to their interesting properties
showed remarkable catalytic properties including mild
in many areas such as photosensitizers [1, 2], catalysts
oxidation of methane [11a] and benzene [11b]. Prepara-
[1, 3], electrocatalysts [1, 4], sensors [1, 5], nonlinear
tion of µ-nitrido diiron phthalocyanines with electron-
optical devices [1, 6] and different fields of materials sci-
withdrawing SO2R substituents resulted in FeIIINFeIV
ence [1, 7]. These versatile compounds are readily acces-
(R = t-Bu) and FeIVNFeIV (R = n-hexyl) complexes show-
sible and their properties can be tuned by changing the
ing a promising catalytic activity in the oxidation of alky-
metal ion as well as by introducing appropriate substitu-
laromatic compounds [12]. Thus, binuclear N-bridged
ents at the periphery of phthalocyanine ligand. Iron phtha-
iron phthalocyanine complexes emerge as a novel class of
locyanine complexes exhibit good catalytic properties in
oxidation catalysts with interesting catalytic properties.
oxidation [8, 9]. Significantly, the µ-oxo dimer form of
Although a number of N-bridged binuclear complexes on
iron tetrasulfophthalocyanine supported on silica sup-
phthalocyanine [13] and porphyrin [14] platforms as well
ports showed better catalytic properties than monomeric
as mixed ligand systems [15] have been described, they
one in oxidation of different substrates [10]. In the search
often contain unsubstituted macrocyclic ligands. Because
for the stable binuclear structures some of us started the
of that, these µ-nitrido binuclear complexes exhibit only
limited solubility in common organic solvents, pre-
venting their investigation and application in cataly-
š
SPP full member in good standing
sis. Introduction of the substituents on the periphery of
phthalocyanine ligand should provide better solubility.
In addition, one can influence the catalytic properties by
*Correspondence to: Alexander B. Sorokin, email: alexander.
sorokin@ircelyon.univ-lyon1.fr, fax: +33 472-445-399 and
Vefa Ahsen, email: ahsen@gyte.edu.tr, fax: +90 262-605-3101
Copyright © 2010 World Scientific Publishing Company

PREPARATION OF N-BRIDGED DIIRON PHTHALOCYANINES
325
the appropriate choice of the nature of the substituents
(electron-donating vs. electron-withdrawing). Besides
the catalytic properties, there are a number of other inter-
esting aspects associated with the synthesis and charac-
terization of µ-nitrido complexes of general formula (Pc)
M–N-M(Pc), (Pc)M–N-M(P) and (Pc)M–N-M′(P) (P =
porphyrinato anion, M and M′ are transition metal ions):
(i) reaction mechanisms of formation of formally mixed
valence MIII-N-MIV or MIII-N-M′IV species; (ii) extensive
electronic charge redistribution and magnetic coupling
occurring for the two metal ions operated by the bridg-
ing N atom along the linearly arranged M–N-M moiety;
and (iii) high oxidation state for the Fe atoms (>3) and
easy access to stable materials containing iron in a high-
valent state, i.e. Fe(IV) [16, 17]. Consequently, demand
for the preparation of novel µ-nitrido diiron complexes
with modified properties is high. Herein, we publish the
preparation and characterization of four novel µ-nitrido
diiron phthalocyanines with SO2R electron-withdrawing
substituents of different size: small groups (methyl and
ethyl) and bulky substituents (cyclohexyl and adaman-
tyl). These µ-nitrido diiron phthalocyanine complexes
were characterized by ESI-MS as well as UV-vis, FT-IR
and EPR techniques.
water. After drying in vacuum at 50 °C, the crude product
was recrystallized from ethanol. Yield: 1.2 g (60%), mp
166 °C. Anal. calcd. for C9H6N2O2S: C, 52.42; H, 2.93;
N, 13.58; S, 15.55%. Found: C, 52.20; H, 2.84; N, 13.29;
1
S, 15.70. H NMR (500 MHz, CDCl3): δ, ppm 3.1 (s,
3H), 8.1 (d, 1H), 8.3 (d, 1H), 8.4 (s, 1H). 13C NMR (500
MHz, CDCl3): δ, ppm 145.6, 134.9, 132.6, 132.1, 120.8,
117.8, 114.2, 114.0, 44.5. IR (KBr): ν, cm-1 3100, 3026,
2938, 2236, 1591, 1388, 1325, 1152, 965, 764, 645, 534.
ESI-MS: m/z 207.31 [M + H]+.
Preparation of 1,2-dicyano-4-ethylsulfonylbenzene
(4). 1,2-dicyano-4-ethylsulfonylbenzene (4) was synthe-
sized and purified as described above for 3. The amounts
of the reagents employed were 4-nitrophthalonitrile
(1.73 g, 0.01 mol), sodium ethanesulfinate (1.28 g, 0.01
mol), and dried DMSO (50 mL). Yield: 1.4 g (62%), mp
130 °C. Anal. calcd. for C10H8N2O2S: C, 54.53; H, 3.66;
N, 12.72; S, 14.56%. Found: C, 54.12; H, 3.72; N, 12.90;
S, 14.12. 1H NMR (500 MHz, CDCl3): δ, ppm 1.3 (t, 3H),
3.2 (q, 3H), 8.0 (d, 1H), 8.2 (d, 1H), 8.3 (s, 1H). 13C NMR
(500 MHz, CDCl3): δ, ppm 144.2, 134.7, 132.8, 132.6,
120.6, 117.8, 114.3, 114.1, 50.6, 7.2. IR (KBr): ν, cm-1
3103, 3077, 2943, 2239, 1591, 1387, 1314, 1133, 1051,
849, 738, 654, 497. ESI-MS: m/z 221.22 [M + H]+.
Preparation of 1,2-dicyano-4-adamantylthioben-
zene (5) [19c]. 4-nitrophthalonitrile (2.5 g, 14.5 mmol)
and adamantanethiol (2.5 g, 14.6 mmol) were dissolved
in anhydrous DMSO (10 mL) under argon atmosphere.
After stirring for 15 min at room temperature, dry and
finely powdered potassium carbonate (6 g, 43.5 mmol)
was added portion-wise over 15 min with efficient stir-
ring. The reaction mixture was stirred under argon at
room temperature for 24 h. Then, the mixture was poured
into 200 mL of ice-water. The resulting solid was col-
lected by filtration and washed with water. After drying
in vacuum at 50 °C, the crude product was recrystallized
from ethanol.Yield: 3.3 g (81%), mp 144 °C. Anal. calcd.
for C18H18N2S: C, 73.43; H, 6.16; N, 9.51; S, 10.89%.
EXPERIMENTAL
General
All solvents were dried before use as described in ref-
erence 18. X-band (9.5 GHz) EPR spectra were recorded
at 77 K on a Bruker ESP 300E spectrometer using
a standard rectangular (TE102) EPR cavity (Bruker
ER4102ST). Microwave power of 1.6 mW and modu-
lation amplitude 1 G were used. Infrared spectra (IR)
were recorded on a Bio-Rad FTS 175C FTIR spectro-
photometer. UV-visible absorption spectra were obtained
using a Shimadzu 2001 UV Pc spectrophotometer. Mass
spectra were measured on a Bruker microTOF spectrom-
eter equipped with electronspray ionization (ESI) source
and on a MALDI (Matrix Assisted Laser Desorption
Ionization) Bruker Microflex LT using 2,5-dihydroxy-
benzoic acid as the matrix. 1H and 13C NMR spectra were
recorded in deuterated chloroform (CDCl3) on a Varian
500 MHz spectrometer. Sodium methanesulfinate and
sodium ethanesulfinate were prepared according to lit-
erature protocol [19a].
1
Found: C, 73.10; H, 6.30; N, 9.45; S, 10.70. H NMR
(500 MHz, CDCl3): δ, ppm 1.6–2.2 (m, 15H), 7.7 (d, 1H),
7.8 (d, 1H), 7.9 (s, 1H). 13C NMR (500 MHz, CDCl3):
δ, ppm 141.2, 141.0, 140.1, 133.2, 115.9, 115.4, 115.3,
115.2, 50.1, 44.1, 36.2, 30.1. IR (KBr): ν, cm-1 2914,
2881, 2848, 2232, 1580, 1474, 1339, 1103, 1036, 843,
684, 526. ESI-MS: m/z 317.25 [M + Na]+.
Preparation of 1,2-dicyano-4-cyclohexylthioben-
zene (6). 1,2-dicyano-4-cyclohexylthiobenzene (6) was
synthesized and purified as described above for 5. The
amounts of the reagents employed were: 4-nitrophthalo-
nitrile (2.5 g, 14.5 mmol), cyclohexylthiol (1.7 g, 14.6
mmol), potassium carbonate (6 g, 43.5 mmol) and dried
DMSO (10 mL). Yield: 2.6 g (75%), mp 93 °C. Anal.
calcd. for C14H14N2S: C, 69.39; H, 5.82; N, 11.56; S,
13.23%. Found: C, 68.90; H, 5.76; N, 11.89; S, 13.33.
1H NMR (500 MHz, CDCl3): δ, ppm 1.2–2.2 (m, 10H),
3.3 (m, 1H), 7.5(d, 1H), 7.6 (s, 1H), 7.7 (d, 1H). 13C
NMR (500 MHz, CDCl3): δ, ppm 140.7, 130.3, 130.1,
Synthesis
Preparation of 1,2-dicyano-4-methylsulfonylben-
zene (3) [19b]. A mixture of 1.73 g (0.01 mol) of
4-nitrophthalonitrile and 1.02 g (0.01 mol) sodium meth-
anesulfinate in 50 mL of dimethyl sulfoxide (DMSO) was
stirred for 24 h under argon atmosphere at 80 °C. Then,
the mixture was poured into 500 mL of ice water. The
resulting solid was collected by filtration and washed with
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 325–334

326
Ü. ISCI ET AL.
,
130.0, 117.8, 115.8, 115.6, 111.1, 45.6, 32.8, 25.8, 25.6.
IR (KBr): ν, cm-1 2860, 2236, 1578, 1470, 1343, 1102,
1090, 837, 760, 524. ESI-MS: m/z 265.18 [M + Na]+.
Preparation of 1,2-dicyano-4-adamantylsulfonyl-
benzene (7). To a solution of 1,2-dicyano-4-ad-
amantylthiobenzene (3 g, 10 mmol) in dry CH2Cl2 (50 mL)
cooled at 0 °C was slowly added m-chloroperbenzoic acid
(17.2 g, 100 mmol) in CH2Cl2 (500 mL). The mixture
was warmed to room temperature and vigorously stirred
at this temperature overnight (12 h). A saturated sodium
sulfite solution was then added, and the organic phase
was extracted with CH2Cl2 (3 × 50 mL) and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the solid was recrystallized from ethanol to give
2.6 g (79%) of 1,2-dicyano-4-adamantylsulfonylbenzene
as a white solid. mp 266 °C. Anal. calcd. for C18H18N2O2S:
C, 66.23; H, 5.56; N, 8.58; S, 9.82%. Found: C, 66.11; H,
dry o-dichlorobenzene-DMF (2 mL), FeCl2 (2.2 mmol).
Yield: 995 mg (62%). Anal. calcd. for C40H32FeN8O8S4:
C, 51.28; H, 3.44; N, 11.96; S, 13.69%. Found: C, 51.08;
H, 3.37; N, 11.18; S, 12.94. UV-vis (CHCl3): λmax, nm
(log ε) 670 (5.1), 606 (4.2), 336 (4.6). IR (KBr): ν, cm-1
2938, 1605, 1455, 1402, 1306, 1143, 1046, 838, 724, 582,
533. MALDI-MS: m/z 936.21 [M]+; calcd. for C40H32Fe-
N8O8S4: 936.06.
Preparation of tetra-(adamantylsulfonyl)phtha-
locyaninatoiron(II) (11). Tetra-(adamantylsulfonyl)
phthalocyaninatoiron(II) (11) was synthesized and puri-
fied as described above for 9. The amounts of the reagents
employed were: 1,2-dicyano-4-adamantylsulfonylben-
zene (4) (1 g, 3.06 mmol), dry o-dichlorobenzene-DMF
(3 mL), FeCl2 (1.02 mmol). Yield: 495 mg (47%). Anal.
calcd. for C72H72FeN8O8S4: C, 63.52; H, 5.33; N, 8.23; S,
9.42%. Found: C, 63.21; H, 5.67; N, 8.16; S, 9.88. UV-vis
(CHCl3): λmax, nm (log ε) 683 (4.8), 336 (4.5). IR (KBr):
ν, cm-1 2925, 2848, 1602, 1513, 1404, 1300, 1140, 1090,
1037, 970, 826, 750, 704, 580, 554. MALDI-MS: m/z
1361.54 [M + H]+; calcd. for C72H72FeN8O8S4: 1360.37.
Preparation of tetra-(cyclohexylsulfonyl)phtha-
locyaninatoiron(II) (12). Tetra-(cyclohexylsulfonyl)
phthalocyaninatoiron(II) (12) was synthesized and puri-
fied as described above for 9. The amounts of the reagents
employed were: 1,2-dicyano-4-cyclohexylsulfonylben-
zene (4) (1 g, 3.65 mmol), dry o-dichlorobenzene-DMF
(3 mL), FeCl2 (1.12 mmol). Yield: 420 mg (40%). Anal.
calcd. for C56H56FeN8O8S4: C, 58.32; H, 4.89; N, 9.72; S,
11.12%. Found: C, 58.06; H, 4.37; N, 9.95; S, 10.88. UV-
vis (CHCl3): λmax, nm (log ε) 681 (4.7), 326 (4.3). IR (KBr):
ν, cm-1 2938, 2856, 1605, 1449, 1402, 1306, 1145, 1102,
1050, 1002, 889, 824, 758, 683, 591, 548. MALDI-MS:
m/z 1152.77 [M]+; calcd. for C56H56FeN8O8S4: 1152.25.
µ-nitrido-bis[tetra-(methylsulfonyl)phthalocya-
ninatoiron] (13). 9 (170 mg, 0.19 mmol) and sodium
azide (1.1 g) were suspended in α-chloronaphthalene
(70 mL) under argon. The mixture was heated for 24 h
at 190 °C under intensive stirring. The reaction mixture
was cooled and resulting dark blue solution was filtered.
The dark blue solid was washed with water and ethanol.
The solution was chromatographed on Al2O3 (neutral)
with CH2Cl2 to remove impurities. Then, 13 was collected
using CH2Cl2:EtOH (1:1) as eluent. Evaporation of solvent
afforded pure 13 as a dark blue powder. Yield: 100 mg
(59%). IR (KBr): ν, cm-1 928 (Fe=N-Fe). UV-vis (CHCl3):
1
5.14; N, 8.09; S, 9.64. H NMR (500 MHz; CDCl3): δ,
ppm 1.4–2.2 (m, 15H), 8.0 (d, 1H), 8.1 (d, 1H), 8.2 (s, 1H).
13C NMR (500 MHz; CDCl3): δ, ppm 140.8, 135.3, 134.9,
134.0, 120.4, 117.0, 114.4, 114.3, 62.5, 35.6, 35.1, 28.2.
IR (KBr): ν, cm-1 3100, 3033, 2910, 2860, 2232, 1591,
1455, 1390, 1301, 1284, 1185, 1141, 1040, 856, 628,
560. ESI-MS: m/z 325.20 [M - H]+.
Preparation of 1,2-dicyano-4-cyclohexylsulfonyl-
benzene (8). 1,2-dicyano-4-cyclohexylthiobenzene (8)
was synthesized and purified as described above for 7.
The amounts of the reagents employed were 1,2-dicyano-
4-cyclohexylthiobenzene (3 g, 12 mmol), m-chloroper-
benzoic acid (20.6 g, 120 mmol) and dry CH2Cl2 (550
mL). Yield: 73% (2.4 g), mp 161 °C. Anal. calcd. for
C14H14N2O2S: C, 61.29; H, 5.14; N, 10.21; S, 11.69%.
1
Found: C, 61.08; H, 5.70; N, 10.88; S, 11.20. H NMR
(CDCl3): δ, ppm 1.0–2.1 (m, 10H), 2.9 (m, 1H), 8.0 (d,
1H), 8.2 (d, 1H), 8.3 (s, 1H). 13C NMR (CDCl3): δ, ppm
142.8, 134.2, 133.7, 133.3, 120.3, 117.2, 114.0, 113.9,
63.7, 25.3, 24.8, 24.7. IR (KBr): ν, cm-1 3073, 3036,
2856, 2237, 1590, 1456, 1313, 1112, 1109, 847, 766,
542, 525. ESI-MS: m/z 313.18 [M + K]+.
Preparation of tetra-(methylsulfonyl)phthalocya-
ninatoiron(II) (9). 3 (1 g, 4.8 mmol) was heated at 130 °C
in a mixture of dry o-dichlorobenzene-DMF (3:1) under
argon for 8 h in the presence of FeCl2 (1.5 mmol). The sol-
vent was removed under reduced pressure. The blue solid
was extracted with CH2Cl2. 9 was isolated by chromatog-
raphy on silica gel using a mixture of CH2Cl2-EtOH (10:1).
Yield: 250 mg, (24%). Anal. calcd. for C36H24FeN8O8S4: C,
49.09; H, 2.75; N, 12.72; S, 14.56%. Found: C, 49.28; H,
2.70; N, 12.98; S, 14.20. UV-vis (CHCl3): λmax, nm (log ε)
665 (4.7), 327 (4.6). IR (KBr): ν, cm-1 2926, 1599, 1404,
1300, 1146, 1047, 834, 720, 578, 530. MALDI-MS: m/z
880.14 [M]+; calcd. for C36H24FeN8O8S4: 880.12.
λmax, nm (log ε) 654 (4.3), 319 (4.5). ESI-MS: m/z 1797.04
[M + Na]+; calcd. for C72H48Fe2N17O16S8Na: 1796.98.
µ-nitrido-bis[tetra-(ethylsulfonyl)phthalocyan-
inatoiron] (14). µ-nitrido-bis [tetra-(ethylsulfonyl)phthalo-
cyaninatoiron] (14) was synthesized and purified as described
above for 13. The amounts of the reagents employed were:
tetra-(ethylsulfonyl)phthalocyaninatoiron(II) (10) (170 mg,
0.18 mmol), α-chloronaphthalene, NaN3 (1.1 g). Yield: 110
mg(64%). IR(KBr):ν, cm-1 930(Fe=N-Fe). UV-vis(CHCl3):
Preparation of tetra-(ethylsulfonyl) phthalocyani-
natoiron(II) (10). Tetra-(ethylsulfonyl)phthalo-cyanina-
toiron(II) (10) was synthesized and purified as described
above for 9. The amounts of the reagents employed were:
1,2-dicyano-4-ethylsulfonylbenzene(4)(1.5g,6.8mmol),
λ
max, nm (log ε) 652 (4.3), 319 (4.5). ESI-MS: m/z 1909.36
[M + Na]+; calcd. for C80H64Fe2N17O16S8Na: 1909.11.
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 326–334

PREPARATION OF N-BRIDGED DIIRON PHTHALOCYANINES
327
µ-nitrido-bis[tetra-(adamantylsulfonyl)phthalocy-
aninatoiron] (15). 11 (200 mg, 0.147 mmol) and sodium
azide (1.5 g) were suspended in xylenes (70 mL) under
argon. The mixture was heated for 24 h at 150 °C under
intensive stirring. The reaction mixture was cooled and
resulting dark blue solution was separated from insoluble
material by filtration. The solution was chromatographed
on Al2O3 (neutral) with CH2Cl2 to remove impurities.
Then, 15 was collected using CH2Cl2:EtOH (100:1) mix-
ture as eluent. Evaporation of solvent afforded pure 15
as a dark blue powder. Yield: 100 mg (50%). IR (KBr):
ν, cm-1 930 (Fe=N-Fe). UV-vis (CHCl3): λmax, nm (log ε)
639 (5.09), 319 (4.2). ESI-MS: m/z 2760.03 [M + Na]+;
calcd. for C144H144Fe2N17O16S8Na: 2759.74.
µ-nitrido-bis[tetra-(cyclohexylsulfonyl)phthalocya-
ninatoiron] (16). 12 (100 mg, 0.086 mmol) and sodium
azide (1.5 g) were suspended in dry dimethylsulfoxide
(70 mL) under argon. The mixture was heated for 24 h at
170 °C under intensive stirring. The reaction mixture was
cooled and resulting dark blue solution was separated from
insoluble material by filtration. The solution was chro-
matographed on Al2O3 (neutral) with CH2Cl2 to remove
impurities. Then, 16 was collected using CH2Cl2:EtOH
(100:1) mixture as eluent. Evaporation of solvent afforded
pure 16 as a dark blue powder. Yield: 48 mg (48%). IR
(KBr): ν, cm-1 931 (Fe=N-Fe). UV-vis (CHCl3): λmax, nm
(log ε) 634 (4.3), 319 (4.5). ESI-MS: m/z 2341.43 [M +
Na]+; calcd. for C112H112Fe2N17O16S8Na: 2341.48.
Reduction of µ-nitrido dimers 13 and 14.
[FePc(SO2methyl)4]2N (13) or [FePc(SO2ethyl)4]2N
(14) (25 mg) was dissolved in CH2Cl2 and hydrazine
(1 mL) was added. This mixture
was then filtered and the solution was chromatographed on
Al2O3 (neutral) with CH2Cl2:EtOH (100:1) mixture. The
product was recovered by evaporation of the solvent.
RESULTS AND DISCUSSION
Synthesis and characterization of the monomers
The synthesis of alkylsulfonyl phthalonitriles is com-
monly carried out by oxidation of alkylthio-substituted
phthalonitrile with oxidant such as m-chloroperbenzoic
acid (m-CPBA) or hydrogen peroxide (H2O2) [20]. How-
ever, methyl and ethyl sulfonyl phthalonitriles are diffi-
cult to prepare from corresponding thiols because of their
gaseous state. To overcome this problem, we used sodium
methanesulfinate and sodium ethanesulfinate to obtain
alkylsulfonyl phthalonitriles directly, thus avoiding an
oxidation step (Scheme 1). Sodium alkylsulfinate salts can
easily be prepared from corresponding RSO2Cl by trea-
ment with Na2SO3 in high 92% yield [19]. This approach
afforded methyl (3) and ethyl (4) sulfonyl-substituted
phthalonitriles with 60 and 62% yield, respectively.
ESI-MS spectra indicated the formation of 3 and 4.
IR spectra of 3 and 4 show the typical CϵN stretch-
ing vibration at 2236 and 2239 cm-1. O=S=O vibrations
around 1130 and 1320 cm-1 confirmed the alkylsulfonyl
substitution. The intense peaks at 1152 and 1325 cm-1 (3)
and at 1133 and 1314 cm-1 (4) were assigned to O=S=O
stretching vibrations of alkylsulfonyl group.
Phthalonitriles 7 and 8 were synthesized in two steps
(Scheme 2).
Na2SO3
was constantly stirred for 2 h under
argon. After evaporation of all the
components, the crude product was
RSO2Cl
RSO2Na
NaHCO3
R = CH3 (1)
dissolved in CH2Cl2 and the solu-
R = CH2CH3 (2)
tion was chromatographed on Al2O3
(neutral) with CH2Cl2:EtOH (100:1)
mixture. The product was recovered
by evaporation of the solvent.
CN
CN
CN
CN
DMSO
K2CO3
+
RSO2Na
Oxidation of µ-nitrido dimers 15
and 16. [FePc (SO2adamantyl)4]2N (15)
or [FePc(SO2cyclohexyl)4]2N (16) (25
mg) was dissolved in CH2Cl2 and 1.0 g
of oxidant (H5PV2Mo10O40) was added.
This mixture was constantly stirred for
2 h under argon. The reaction mixture
RSO2
NO2
R = CH3 (1)
R = CH2CH3 (2)
R = CH3 (3)
R = CH2CH3 (4)
Scheme 1. Synthesis of alkylsulfonyl-substituted phthalonitriles using sodium
akylsulfinate salts
CN
CN
CN
CN
CN
RSH
m-CPBA
CH2Cl2
O
CN
K2CO3
DMSO
NO2
R
S
S
R
O
(5)
R =
(7)
R =
R =
(8)
(6)
R =
Scheme 2. Synthesis of alkylsulfonyl-substituted phthalonitriles from alkylthio phthalonitriles
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 327–334

328
Ü. ISCI ET AL.
,
RO2S
X
SO2R
N
N
RO2S
N
N
N
Fe
N
N
N
SO2R
N
RO2S
RO2S
N
CN
CN
N
FeCl2
NaN3
N
N
RO2S
SO2R
SO2R
Fe
N
O
N
N
N
DMF: o-DCB
RO2S
N
S
N
N
R
SO2R
N
N
O
Fe
N
N
N
SO2R
-
R = CH3 (3)
R = CH3 (9)
R = CH3 (13), X = N3
-
R = CH2CH3 (10)
R = CH2CH3 (14), X = N3
R = CH2CH3 (4)
(11)
(12)
(15)
no X
R =
(7)
R =
R =
(8)
R =
R =
R =
(16) no X
Scheme 3. Synthesis of alkylsulfonyl-substituted µ-nitrido diiron phthalocyanines
Thetreatmentof4-nitrophthalonitrilewithcorrespond-
iron phthalocyanines clearly indicates the presence of
sulfonyl function (O=S=O). The intense peaks at 1159
and 1310 cm-1 (9), at 1145 and 1305 cm-1 (10), at 1150
and 1300 cm-1 (11) and at 1146 and 1305 cm-1 (12) were
assigned to the O=S=O stretching vibrations of alkylsul-
fonyl group. The peaks at 2925 and 2860 cm-1 (9), at 2938
and 2878 cm-1 (10), at 2908 and 2849 cm-1 (11) and at
2934 and 2860 cm-1 (12) were assigned to C-H stretching
vibrations. The observation of C-H stretching vibrations
in the range of 2940–2850 cm-1 and O=S=O vibrations
around 1160 and 1300 cm-1 confirmed the retention of
alkylsulfonyl substituents in phthalocyanines 9, 10, 11
and 12. MALDI-MS spectra showed expected molecular
peaks of 9, 10, 11 and 12. [M]+ peak was observed at
m/z = 880 for 9, at m/z = 936 for 10 and [M + H]+ peak was
observed at m/z = 1361 for 11, [M]+ peak was observed
at m/z = 1152 for 12.
ing thiols and K2CO3 in DMSO afforded the thioethers 5
and 6 with 81% and 75% yield, respectively. Their oxida-
tion with m-chloroperbenzoic acid in CH2Cl2 gave alkyl-
sulfonyl phthalonitriles 7 and 8 in good yields, 79% and
73%, respectively. The IR spectra of 5, 6, 7 and 8 show
the typical CϵN stretching vibration at 2232, 2236, 2232
and 2237 cm-1. 1H NMR spectra of alkylsulfonylphthalo-
nitrilesaredifferentfromthoseofalkylthiophthalonitriles.
While the aromatic protons of alkylthiophthalonitriles
appear at 7.5–7.8 ppm, the aromatic protons of alkylsul-
fonylphthalonitriles shifted at 8.0–8.3 ppm, reflecting the
increase of electron-withdrawing character of substitu-
ents upon oxidation to SO2R.
The syntheses of iron phthalocyanines 9, 10, 11 and
12 were achieved by treating the corresponding phthalo-
nitriles (3, 4, 7 and 8) with FeCl2 in the o-dichlorobenzene-
DMF (3:1) mixture at reflux temperature (Scheme 3).
The o-dichlorobenzene-DMF mixture was used for
these preparations since dimethylaminoethanol could not
be used because of the decomposition of the alkylsul-
fonylphthalonitriles under the reaction conditions [20].
The sharp peak of CϵN vibrations in the IR spectra of
phthalonitriles 3, 4, 7 and 8 at 2236, 2239, 2233 and 2237
cm-1, respectively, disappeared after conversion into iron
phthalocyanines. After purification by column chroma-
tography alkylsulfonyl-substituted iron phthalocyanines
were characterized by UV-vis, IR and MS techniques.
UV-vis spectra showed expected Q and B phthalocyanine
bands. Interestingly, Q band maxima of methyl (9), ethyl
(10), cyclohexyl (12) and adamantyl (11) substituted
phthalocyanines were observed at 665, 670, 681 and
683 nm, respectively. The reason for this red shift of Q
band with increase of bulkiness of substituents is not yet
clear. The IR spectra of all the alkylsulfonyl-substituted
Synthesis and characterization of the µ-nitrido dimers
µ-nitrido diiron phthalocyanines are usually prepared by
treatment of monomeric iron complex with NaN3 at high
temperature in chloronaphthalene [15]. These complexes
can also be prepared using xylene as solvent [11, 12]. The
choice of solvent depends on the solubility of monomer
precursor. µ-nitrido dimeric complexes 13 and 14 were
obtained by treatment of 9 and 10 with NaN3 in refluxing
α-chloronaphthalene with yields of 59% and 64%, respec-
tively. Complex 15 was prepared by treatment of 11 with
NaN3 in refluxing xylene in 50% yield. Since the mono-
meric complex 12 was not soluble in xylene, the µ-nitrido
dimer 16 was prepared in refluxing DMSO in 48% yield.
The successful preparation of 13, 14, 15 and 16 was
evidenced by ESI-MS analyses, FT-IR, UV-vis and EPR
methods.
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PREPARATION OF N-BRIDGED DIIRON PHTHALOCYANINES
329
Fig. 1. Molecular peak cluster of 15 in ESI-MS spectrum (a) and simulated molecular peak cluster for 15, C144H144Fe2N17O16S8Na (b)
The ESI-MS spectra of the four µ-nitrido complexes
exhibit unique molecular peaks corresponding to the
expected values of the molecular ion with sodium: m/z =
1797.04 [M + Na]+ for 13, m/z = 1911.36 [M + Na]+ for
14, m/z = 2760.03 [M + Na]+ for 15 and m/z = 2341.43
[M + Na]+ for 16. The isotopic patterns fit the theoritical
ones (see the spectrum of the adamantyl derivative (15)
on Fig. 1), confirming the proposed structures.
The IR spectrum of unsubstituted µ-nitrido diiron
phthalocyanine (PcFe)2N exhibit characteristic absorp-
tions due to the anti-symmetric Fe-N=Fe stretching
vibration at 915 cm-1 [13a]. This Fe-N=Fe vibration
is red-shifted to about 930 cm-1 for substituted deriva-
tives, similar to the previously described tert-butyl, tert-
butylsulfonyl and hexylsulfonyl substituted derivatives
(signals respectively shifted to 938 cm-1 [11], 931 and
929 cm-1 [12]). Accordingly, the Fe-N-Fe anti-symmetric
stretching vibrations in the IR spectra of 13, 14, 15 and
16 are clearly seen at 928, 930, 930 and 931 cm-1, respec-
tively (Fig. 2).
The four prepared µ-nitrido complexes 13, 14, 15 and
16 can be divided into two groups depending on the size
of their substituents: 13 and 14 bear small substituents
(methyl and ethyl), whereas 15 and 16 have bulky substit-
uents (adamantyl and cyclohexyl groups, respectively).
The two dimers with small substituents (13 and 14) have
nearly identical IR spectra (Fig. 2A,B), demonstrating
that both their oxidation state and their geometry are
similar. In contrast, despite their same oxidation state, the
IR spectra of the two dimers bearing bulky substituents
(15 and 16) are different (Fig. 2C,D). This is probably
due to a different geometric arrangement modifying the
recorded vibrations, the steric hindrance of an adamantyl
group being more important than the one of a cyclohexyl
group, thus imposing maybe more rigid structures even if
adamantyl and cyclohexyl substituents can both be con-
sidered as being bulky.
The IR spectra of 13 and 14 having small substituents
(Me and Et) showed a strong signal at 2030 and 2034
cm-1,respectively, assigned to N3- vibration (Fig. 3) while
the signal in this range was absent in the spectra of 15 and
16 with bulky substituents. These data suggest the pres-
ence of an azide anion needed to compensate a positive
charge of 13 and 14. Thus, 13 and 14 can be tentatively
-
assigned as (PcFeIVNFeIVPc)+N3 complexes. The absence
of N3- signal in IR spectra of 15 and 16 suggests that 15
and 16 are neutral: this is consistent with PcFeIIINFeIVPc
structure. In addition, the complexes bearing small sub-
stituents exhibit peaks of strong intensity around 960
cm-1 that are not observable on the spectra of 15 and 16.
This may be due to the different oxidation state of the
complexes.
The solid-state EPR spectra of the four N-bridged dim-
ers were recorded at 77 K. [FePc(SO2methyl)4]2N (13) and
[FePc(SO2ethyl)4]2N (14) show no EPR signals confirm-
ing Fe(IV)Fe(IV) formulation. [FePc(SO2adamantyl)4]2N
(15) and [FePc(SO2cyclohexyl)4]2N (16) dimers show
a typically axially symmetry spectrum (g = 2.101, g =
2.109), consistent with a low-spin complex having an A1
ground state (Fig. 4).These parameters are similar to those
observed for non-substituted nitrido-dimers of Fe(III)
octaphenyltetraazaporphine and appear to be indicative
of extensive delocalization over the two iron centers. The
absence of nitrogen hyperfine structure in EPR spectrum
is in accordance with Fe+3.5–N-3–Fe+3.5 formalism [14c].
µ-nitrido bridged species exhibit an exceptional inertness
and stability because of the delocalization of an unpaired
electron. Data obtained by other spectroscopic methods
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 329–334

330
Ü. ISCI ET AL.
,
Fig. 2. IR spectra of [FePc(SO2methyl)4]2N (13) (A), [FePc(SO2ethyl)4]2N (14) (B), [FePc(SO2adamantyl)4]2N (15) (C) and
[FePc(SO2cyclohexyl)4]2N (16) (D)
Fig. 3. Expansion of IR spectra of 13 [FePc(SO2methyl)4]2N (A) and 14 [FePc(SO2ethyl)4]2N (B)
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 330–334

PREPARATION OF N-BRIDGED DIIRON PHTHALOCYANINES
331
Table 1. Q band values of phthalocyanine monomer, neutral
and oxidized cationic dimers
Q band values (λ, nm)
Substituent
Monomer
methyl ethyl
adamantyl
683
cyclohexyl
681
665
—
670
—
Neutral dimer
639
634
Oxidized
654
652
651
649
cationic dimer
are also in agreement with formulation of 15 with ada-
mantylsulfonyl and 16 with cyclohexylsulfonyl substit-
uents as neutral FeIIIFeIV N-bridged dimer and 13 with
methylsulfonyl and 14 with ethylsulfonyl as cationic
-
FeIVFeIV complex containing N3 for compensation of
charge. The presence of N3- in 13 and 14 were evidenced
by the presence of 2034 and 2030 cm-1 strong signal in
IR spectrum.
Fig. 4. X band 77 K EPR spectrum of [FePc(SO2adamantyl)4]2N
dimer (15)
Fig. 5. UV-vis spectra of 13 (dash line) and reduced 13 (solid line) (A), 14 (dash line) and reduced 14 (solid line) (B), 15 (solid
line) and oxidized 15 (dash line) (C), 16 (solid line) and oxidized 16 (dash line) (D). Oxidation and reduction experiments were
performed using H5PV2Mo10O40 and hydrazine, respectively, in CH2Cl2 under argon as described in the Experimental section
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 331–334

332
Ü. ISCI ET AL.
,
Phthalocyanine systems exhibit two strong absorption
bands in electronic absorption spectra. The positions of
Soret band (near 340 nm) and of intense Q band (between
600 and 700 nm due to π−π* ligand transition) of phthal-
ocyanine complexes are affected by electronic interaction
between ligands as well as by the state of central atom,
axial ligation and peripheral substitution [21, 22]. The
UV-vis spectra of 13, 14, 15 and 16 have been recorded:
the strong π−π interaction between two phthalocyanine
moieties in dimers results in a blue shift as compared
with monomer complexes: from 665 nm to 654 nm for
9/13, from 670 nm to 652 nm for 10/14, from 683 nm to
639 nm for 11/15 and from 681 nm to 634 nm for 12/16,
respectively (Table 1).
thus influencing the ground oxidation state. In order to
get insight further spectroscopic and theoretical stud-
ies are necessary. X-ray structural determination would
be especially useful, but in the case of tetra-substituted
phthalocyanines this is highly challenging because of the
presence of four positional isomers. It is worth noting
that an N-bridged diiron tetra-substituted phthalocya-
nine contains ten positional isomers. Taking into account
the remarkable catalytic properties of this kind of com-
plexes [11, 12], potential applications of these N-bridged
diiron complexes as catalysts in oxidation will be studied
further.
Acknowledgements
Q bands of oxidized 13 and 14 (FeIVFeIV state) are red-
shifted compared to those of neutral 15 and 16 (FeIIIFeIV
state). This difference can be explained by the differ-
ence in the oxidation state of iron: it has been previously
described that unsubstituted neutral (FePc)2N can easily
be oxidized to cationic (FePc)2N+ complex, resulting in a
red shift of Q band from 626 nm to 634 nm in pyridine
[13a].
This work was partly supported by grant ANR-08-
BLAN-0183-01 from Agence Nationale de la Recher-
che (ANR, France). Umit Isci thanks the French
Embassy in Ankara for PhD fellowship. Mr. Ilker Un and
Mr. Bünyamin Cosut are acknowledged for NMR,
MALDI and LC-ESI-MS analyses. We are grateful to Dr.
P. Afanasiev and Dr. E.V. Kudrik for the fruitful discus-
sions and assistance in EPR measurements.
Thus, 15 and 16, obtained as PcFeIVNFeIIIPc neutral
form, were oxidized by H5PV2Mo10O40 to PcFeIVN-
FeIVPc+. In turn, 13 and 14, synthesized as PcFeIVN-
FeIVPc+ cationic oxidized form, were reduced by
hydrazine. Figure 5 shows the UV-vis spectra of the
dimers in their two oxidation states. These experiments
indicate interconversion between FeIIIFeIV and FeIVFeIV
states and confirm formulations of 13, 14, 15, 16 based
on IR and EPR data.
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