Symmetrical tetra-β″-sulfoleno-meso-aryl-porphyrins-synthesis, spectroscopy and structural characterization

Article abstract of DOI:10.1142/S1088424613501204

We report here the preparation (in one-pot) of a tetra-β″- sulfoleno-meso-aryl-porphyrin in about 80% yield by using an optimized modification of Lindsey's variant of the Adler-Longo approach. The Zn(II)-, Cu(II)- and Ni(II)-complexes of the symmetrical p

Full text of DOI:10.1142/S1088424613501204

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 115–122
DOI: 10.1142/S1088424613501204
Published at http://www.worldscinet.com/jpp/
Symmetrical tetra-b″-sulfoleno-meso-aryl-porphyrins —
synthesis, spectroscopy and structural characterization
Srinivas Banalaa†, Klaus Wurstb and Bernhard Kräutler*a◊
a Institute of Organic Chemistry, b Institute of General, Inorganic and Theoretical Chemistry,
University of Innsbruck, Innrain 80/82, Innsbruck, Austria
Dedicated to Professor Aslan Tsivadze on the occasion of his 70th birthday
Received 14 August 2013
Accepted 31 October 2013
ABSTRACT: We report here the preparation (in “one-pot”) of a tetra-b″-sulfoleno-meso-aryl-porphyrin
in about 80% yield by using an optimized modification of Lindsey’s variant of the Adler–Longo
approach. The Zn(II)-, Cu(II)- and Ni(II)-complexes of the symmetrical porphyrin were prepared and
characterized spectroscopically. Crystal structures of the fluorescent Zn(II)- and of the non-fluorescent
Ni(II)-tetra-b″-sulfoleno-meso-aryl-porphyrinates showed the highly substituted porphyrin ligands to
be nearly perfectly planar. The Zn(II)-complex of this porphyrin has been used as a thermal precursor
of a reactive diene, and — formally — of lateral and diagonal bis-dienes, of a tris-diene and of a tetra-
diene, which all underwent [4+2]-cycloaddition reactions in situ with a range of dienophiles. Thus,
the tetra-b″-sulfoleno-meso-aryl-porphyrin and its metal complexes represent reactive building blocks,
“programmed” for the syntheses of symmetrical and highly functionalized porphyrins.
KEYWORDS: crystal structure, metalloporphyrins, nickel, salt effect, synthesis, zinc.
which were expected to undergo efficient [4+2]-
cycloaddition reactions [5]. Towards this goal, the
b″-sulfoleno-pyrrole 2 [6–10] was used as pyrrol moiety,
which reacted with 3,5-di-tert-butyl-benzaldehyde (7) to
furnish, after oxidation, the tetra-b″-sulfoleno-meso-aryl-
porphyrin 1 in 44% yield [5]. Incorporation of a Zn(II)-ion
occurred readily and nearly quantitatively to provide the
Zn(II)-tetra-b″-sulfoleno-meso-aryl-porphyrinate 1-Zn
[5]. The potential diene-reactivity of the Zn-complex
1-Zn could easily be set free by heating at 140°C and
by (four fold) thermal extrusion of sulfur dioxide [5, 11].
To date, the symmetrical complex 1-Zn was used for the
preparation of mono-and bisfullereno-Zn(II)-porphyrins
[5], of tris- and tetra-fullereno-Zn(II)-porphyrins [11], of
blackened Zn(II)-porphyrins [12], of an unsymmetrical
porphyrin-chlorin spiro-dimer [13] and of a hexafullereno-
diporphyrin [14] (see Fig. 1). Thus, the Zn-porphyrin
1-Zn was applied as a versatile reactive building block,
allowing the construction of more complex covalent
assemblies by porphyrin-LEGO® [14]. In a related
approach, tris-meso-aryl-tetra-b″-sulfoleno-corroles were
INTRODUCTION
Synthetic porphyrins are fascinating heterocyclic
compounds, inspired by the ubiquitous “pigments of
life” [1]. The characteristic and extensively p-conjugated
chromophore of the porphyrins, their capacity for
coordination of the transition metal ions, and their rigid
molecular structures give these macrocyclic tetrapyrroles
a unique capacity for unusual photochemistry, for redox-
processes for catalysis and for being building-blocks in
supramolecular structures having a wealth of interesting
chemical properties [2–4].
The tetra-b″-sulfoleno-meso-aryl-porphyrin 1 and its
metal complexes 1-M were designed as masked dienes,
◊SPP full member in good standing
*Correspondence to: Bernhard Kräutler, email: bernhard.
kraeutler@uibk.ac.at, tel: +43 512-50757701, fax: +43 512-
50757799
†Currentaddress:InstituteofChemistryTC2,TechnicalUniversity
of Berlin, Strasse des 17. Juni 124, Berlin D-10623, Germany
Copyright © 2014 World Scientific Publishing Company

116
S. BANALA ET AL.
O
O
Ar
O
O
S
S
O2S
O2S
O2S
N
N
N
N
dieno
phile
Zn
Ar
Zn
+
Ar
O2S
S
S
O
Ar
O
(excess)
O
O
Zn
O2S
O2S
O2S
Zn
Zn
Zn
O2S
O
O
dieno
phile
e.g.
, C60
=
Fig. 1. Tetra-b″-sulfoleno-meso-aryl-porphyrin is a symmetrical, reactive building-block. The zinc(II)-complex 1-Zn was used in
(multiple) model [4+2]-cycloaddition reactions with dienophiles, e.g. with C60-fullerene and with 1,4-benzoquinone, to furnish a
range of mono-, bis-, tris- and tetra-cycloadducts
prepared and used to synthesize a difullereno-corrole with
excellent regioselectivity [15]. In view of the relevance
of the pyrrole 2 and the porphyrin 1 as the main building
blocks in porphyrin-LEGO® approaches [14], it was our
interest to improve the yields for their preparation, as well
as to explore transition metal complexes closely related to
the Zn-complex 1-Zn, as is reported here.
of the substituted pyrrole 5 was removed efficiently by
hydrogenolysis, which was carried out in the presence
of triethylamine, and providing the white crystalline
triethyl ammonium salt 6 in 92% yield. Acid mediated
decarboxylation of the pyrrole 2-carboxylic acid 6 in
a thoroughly degassed mixture of acetic acid-trifluoro
acetic acid (5:1, v/v) at 100°C (4.5 h heating to reflux
under argon) followed by work-up and chromatographic
purification gave the b″-sulfoleno-pyrrole 2 [7] in
71% yield (Scheme 1, see Experimental section). The
sulfoleno-pyrrole 2 could be recrystallized from solutions
in MeOH. Good quality crystals were obtained this way,
suitable for X-ray structure analysis [10].
RESULTS AND DISCUSSION
b″-Sulfoleno-pyrrole (2) was synthesized in
a
multi-step sequence via benzyl-b″-sulfoleno-pyrrole
2-carboxylate 5 [9] from benzyl-2-isocyanoacetate
(3) and the a,b-unsaturated bissulfone 4, based on
the so called “(3+2)-pyrrole approach” and using an
established protocol [7–9] (Scheme 1): The benzyl group
Having in hand an improved method for the pre-
paration of the pyrrole 2, the stage was now set for the
condensation of 2 and 3,5-di-tert-butylbenzaldehyde (7),
followed by oxidation to give the porphyrin 1. Originally,
Copyright © 2014 World Scientific Publishing Company
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SYMMETRICAL TETRA-b″-SULFOLENO-MESO-ARYL-PORPHYRINS
117
O
O
O
O
O
O
C-
O
O
S
S
S
S
N+
(a)
(b)
(c)
+
O
O
O
S
O
OBn
O
Ph
N
N
N
H
+HNEt3
O-
H
H
OBn
4
6
3
5
2
Scheme 1. Synthesis of sulfoleno pyrrole: (a) KOtBu, THF, -20°C, 17 h, 67%. (b) H2 (1 atm.), 10% Pd/C, MeOH, NEt3 at rt/36 h,
92%; (c) CF3COOH, CH3COOH (1:5), 100°C, 4.5 h, 71%
O
O
S
O
O
O
O
O
O
O
O
S
S
S
S
N
H
NH
N
N
N
N
N
N
2
(a)
(b)
M
+
or (c)
HN
H
O
S
S
S
S
O
O
O
O
O
O
O
O
7
1-M M = Zn, Ni, Cu
1
Scheme 2. Synthesis of tetrasulfolenoporphyrin 1 and of the complexes 1-Zn, 1-Cu and 1-Ni. (a) 0.25 equiv. (C16H33)(CH3)3N+Cl−,
.
CH2Cl2, CH3CH(OEt)3, BF3 OEt2, 24 h, rt (79%); (b) Zn(OAc)2·2H2O, DMF 40 min, 100°C (90%) or Ni(OAc)2·4H2O, DMF, 2.5 h,
100°C (91%); (c) Cu(OAc)2·H2O, CH2Cl2/MeOH (10:1), 2 h reflux (99%)
the tetrasulfoleno-porphyrin 1 was prepared (in 44%
yield) in a BF3·OEt2 catalyzed tetramerization of pyrrole 2
and aldehyde 7, followed by in-situ chloranil oxidation [5]
(Scheme 2). The Adler–Longo type porphyrin synthesis
reaction proceeds via the reversible condensation of aryl
aldehyde and pyrrole to provide a porphyrinogen, as
investigated by Lindsey and coworkers [16]. This group
also reported a beneficial effect of specific salt additives,
resulting in an improvement of the yield of the acid
catalyzed condensation for the peparation of tetraaryl
porphyrins [17]. In their preparations, organic-soluble
R4N+Cl- and R4P+X- salts (X = Cl, BPh4, R = alkyl, aryl
and mixed) were used to obtain up to 2-fold increase
of yields. Although influencing factors remained less
clear, optimization with Bu3BzlNCl and with a variety
of aldehydes was reported. Thus, in our work, attention
concentrated on hexadecyl trimethyl ammonium chloride.
Indeed, addition of C16H33(CH3)3NCl improved the yield
best (Table 1, entry 5), and this effect was then explored
further to find improved reaction conditions. Keeping
the C16H33(CH3)3NCl concentration constant at 0.2 eq.,
increasing amounts of BF3·OEt2 from 0.8 eq. to 6 eq. lead
to gradually improved yields (Table 1, entries 5 to 8).
Further optimization indicated that 6 eq. of BF3·OEt2 with
0.25 eq. of [C16H33(CH3)3NCl], in 10 mM concentration
(in each reactant), condensation for 24 h and chloranil
oxidation gave the porphyrin in yields of around 80–90%
(Table 1, entries 8 and 9). Under the same conditions, but
without the addition of the quaternary ammonium salt, the
reaction gave 51% of porphyrin (Table 1, entry 10). To get
good yields of the porphyrin 1, sulfoleno-pyrrole 2 and
3,5-di-tert-butyl-benzaldehyde (7) were recrystallized
from MeOH and EtOH respectively, and dried on high
vacuum, before their use in the tetramerization reaction.
Crystalline sulfoleno-pyrrole 2 (50.4 mg, 0.321 mmol),
recrystallized 3,5-di-(tert-butyl) benzaldehyde (7, 1.2 eq.)
and C16H33(CH3)3NCl (0.25 eq.) were dissolved in abs.
CH2Cl2 (conc. = ca 10 mM), and triethyl orthoacetate (1.7
eq.) was added. BF3·OEt2 (6 eq.) was added to the mixture,
which was stirred for 24 h at room temperature under
argon and under protection from light. Then chloranil (1.4
eq.) was added and the mixture was heated to reflux for
1.5 h. Work up gave crude porphyrin 1 in up to 90% yield
(see Experimental section). Pure porphyrin 1 was obtained
by silica gel chromatography and precipitation in CH2Cl2-
MeOH. The precipitate was washed with diethyl ether and
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 117–122

118
S. BANALA ET AL.
Table 1. Optimization experiments for the synthesis of the
tetra-b″-sulfoleno porphyrin 1a
addition, 1 was further characterized by fluorescence-
1
spectroscopy (see Fig. 2), as well as H,1H-homo- and
1H,13C-hetero-nuclear NMR-spectra (13C NMR: see
Supporting information).
.
Entry
Salt (eq. vs. 2)
BF3 OEt2; time
Yield, %b
1
2
None
0.8; 24 h
0.8; 11 h
0.8; 12 h
0.8; 12 h
0.8; 24 h
1.6; 24 h
3; 24 h
47
Having the porphyrin 1 in hand, Cu(II)-, Zn(II)- and
Ni(II)- ions were inserted by using Cu(II)-acetate in
CH2Cl2-MeOH solution (by heating at reflux) or, with
Zn(II)-andNi(II)-acetates,inDMFat100°C.Thereaction
progress was followed with UV-vis-spectroscopy and by
TLC. UV-vis spectra of metalloporphyrins 1-Ni, 1-Cu,
1-Zn had characteristic strong Soret and weak Q-band
absorption bands (see Figs 2 and 3, and Experimental
section).
Bu4NBr; 0.2
C19H42NCl; 0.2
C19H42NCl; 1.0
C19H42NCl; 0.2
C19H42NCl; 0.2
C19H42NCl; 0.2
C19H42NCl; 0.2
C19H42NCl; 0.25
None
39.4
50
3
4
5c
33.3
50
6
37
7
58
8
6; 24 h
82
The Zn(II)-porphyrin 1-Zn has been prepared and
characterized earlier [5]. X-ray diffraction quality
crystals of 1-Zn were obtained here by diffusing hexane
into a solution of CH2Cl2. The crystal structure of 1-Zn
(Fig. 4) showed a practically planar porphyrin core, and
meso-aryl groups that were nearly perpendicular (87°
dihedral angle) to the porphyrin plane. The lengths of the
equatorial bonds (e.g. Zn-N =
9
6; 24 h
90
10
6; 24 h
51
aStandard initial concentrations of pyrrole 2 and aldehyde: 10 mM;
bcalculated from UV-vis-spectra with e420nm = 380200 M-1.cm-1;
cinitial concentrations of pyrrole 2 and aldehyde: 1.6 mM.
2.08 Å) were in standard range
of Zn-N distances in porphyrins
(2.05–2.08 Å) [18]. The Ca−
Cb bonds were 1.345 Å long,
indicating partial double bond
character of an aromatic nature,
and were shortened, compared to
the sulfoleno-pyrrol (1.421Å).
The methylene-SO2 groups were
slightly bent from the porphyrin
plane. The zinc-ion was penta-
Fig. 2. UV-vis- and fluorescence spectra of 1 and the zinc-complex 1-Zn. Left. Overlay
of UV-vis-spectra normalized to a common intensity maximum of the “Soret” band; right.
Fluorescence spectra of solutions of 1 (excitation at 516 nm) and of 1-Zn (excitation at
554 nm) in CH2Cl2 and recorded at room temperature
coordinate due to axial coordi-
nation of one water molecule,
with a Zn–O bond distance
of 2.09 Å. The Zn atom was
situated at 0.303 Å above the
porphyrine core, increasing the
four N–Zn–O angles to 98.7°. Two of the N–Zn–N angles
amounted to 162.5°, and four to 88.7°, respectively.
The copper complex 1-Cu was prepared by heating
1 with Cu(II)-acetate in 10:1 of CH2Cl2-MeOH at 60°C
for 2 h and isolation (in 99% yield) by precipitation
in CH2Cl2-MeOH. The UV-vis-spectrum of the non-
fluorescent Cu(II)porphyrin
1 showed Soret and
1
Q-bands at 418 and 539.5 nm, respectively. A H NMR
characterization was not performed for the paramagnetic
CuII porphyrin 1-Cu. However mass spectrometry
confirmed the stoichiometric metal incorporation.
The pseudo-molecular ion [M + H]+ occurred at m/z =
1484.7, corresponding to the molecular formula
C84H100N4O8S4Cu (m/z calcd. = 1483.6). The base-peak
at m/z = 1227.9 indiacted efficient loss of 4 SO2 groups.
Fragments due to loss of a Cu-ion were not found in the
spectrum of 1-Cu (some loss of the Cu-ion in a FAB-
mass spectrometric study of metallo-prophyrins has been
reported) [19]. Crystals, grown by diffusing n-heptane
Fig. 3. UV-vis-spectra of non-fluorescent 1-Cu and of 1-Ni (in
CH2Cl2, room temperature; overlay of the two spectra normalized
to a common intensity maximum of the “Soret” band)
dried under HV at 50°C for 15h to give a sample of 89.8 mg
(78.7% yield) of the porphyrin 1 as a microcrystalline
sample. The strongly fluorescent porphyrin 1 was identi-
1
fied by its UV-vis-, mass- and H NMR-spectra [5]. In
Copyright © 2014 World Scientific Publishing Company
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SYMMETRICAL TETRA-b″-SULFOLENO-MESO-ARYL-PORPHYRINS
119
O
O
O
O
S
S
N
N
N
N
Zn
S
S
O
O
O
O
Fig. 4. Structural formula and crystal structure of 1-Zn (which crystallized as a mono-aqua-complex)
into a CH2Cl2 solution of 1-Cu, did not have the quality
needed for an X-ray structure determination.
EXPERIMENTAL
The Ni(II)-insertion was completed in 2.5 h when
Ni(OAc)2 and 1 were heated in DMF at 100°C. The
General
Ni(II)-tetrasulfoleno-porphyrinate 1-Ni was obtained
in 91% yield, after recrystallization. The UV-vis-
absorption spectrum of the Ni(II)poprhyrin 1-Ni showed
a strong Soret band at 418 nm, and a Q-band at 530 nm,
as is typical of Ni(II)-porphyrins [20]. A solution of
1-Ni in CH2Cl2 was non-fluorescent, as expected. Its
MS-spectrum indicated a pseudomolecular ion [M + H]+
at m/z = 1479.4, and a base-peak at m/z = 1223.6 ([M –
4SO2 + H]+). The 1H NMR-spectrum of the diamagnetic
complex 1-Ni showed the spectrum of a D4h symmetric
compound, with signal positions and shapes similar to
that of 1-Zn. The small shift differences may be due
largely to the smaller ionic radii of Ni(II)- than Zn(II)-
ions and correspondingly shorter equatorial bond lengths
in 1-Ni (see below).
3-Sulfolene, potassium tert-butanolate (KOtBu) were
from Fluka and were used as received. Dichloromethane
(CH2Cl2), ethyl acetate (EtOAc), petrol ether 40–60 (PE),
methanol (MeOH), tetrahydrofurane (THF), acetic acid
(HOAc), trifluoroacetic acid (TFA) were from ACROS
and were distilled before use. For synthesis, solvents
were dried (CH2Cl2 over P2O5, THF over Na). Glassware
for all reactions was oven dried at 110 °C and cooled
under HV, and purged with nitrogen flow prior to use.
Column chromatography (CC): Fluka silica gel 60 (230–
400 mesh). High vacuum (HV): ca. 0.05 mbar.
Spectroscopy: UV-vis: Hitachi U-3000, lmax (log e)
in nm. Fluorescence: Varian Cary Eclipse, lEx and lEm
1
in nm. H and 13C NMR: Brucker 300, Varian 500 unity
(300 K); chemical shifts (d) in ppm, with d(CHCl3) =
7.26 ppm, d(13CHCl3) = 76.3 ppm, d(CHD2OD) = 3.31
ppm, d(13CD3OD) = 49.0 ppm. FAB-MS: Finnigan
MAT-95, positive ion mode, glycerine matrix; m/z (rel.
intensity %).
The 1-Ni porphyrin was crystallized by slow diffusion
of n-hexane into CH2Cl2 solution, and X-ray quality
crystals were obtained. X-ray structure showed (Fig. 5)
a planar porphyrin core, with an ideal square planar
coordination of the Ni atom (four N–Ni–N angles of
90° and two of 180°). The Ni–N bonds were 1.975 Å
long, i.e. in the range of standard Ni–N bond lengths
in nickel porphyrins (1.942–2.002 Å) [18]. The Ca−Cb
bond lengths were 1.343 Å, i.e. similar to those in 1-Zn.
The meso-aryl groups were nearly perpendicular to the
porphyrin plane (dihedral angles of 87° and 89°). The
Synthesis
Triethylammoniumsulfolenopyrrole-2-carboxylate
6. A two neck round bottomed flask equipped with
magnetic stirring bar and a three way adapter, was
charged 10 g of benzyl pyrrole-2-carboxylate (5) (34.33
mmol, 1 equiv.) and 250 mL of MeOH. A suspension of 5
was obtained, which was purged with argon, whereupon
4.75 mL (34.3 mmol, 1 equiv.) triethylamine were added
.
CH2–SO2 groups were tilted by 14.3° from the porphyrin
plane. These latter structural properties were similar to
those of the Zn(II)-porphyrin 1-Zn.
Copyright © 2014 World Scientific Publishing Company
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S. BANALA ET AL.
O
O
O
O
S
S
N
N
N
Ni
N
S
S
O
O
O
O
Fig. 5. Structural formula and crystal structure of 1-Ni
under argon. Then 1 g of 10% Pd/C (0.94 mmol, 0.27
equiv.) was added under argon. The mixture was vented
with argon, followed by bubbling-in hydrogen for 3 min.
The reaction was stirred at room temperature first under
one atmosphere of hydrogen (15 h), followed by further
reaction under a balloon filled with hydrogen (for 33 h
additional). Then the reaction was stopped, the mixture
was diluted with 250 mL of MeOH, filtered through cellite
and washed with 100 mL of acetone. The solvents were
removed under reduced pressure and a yellow powder
was obtained. The dry powder was then dissolved in
300 mL of CH2Cl2 and 5 mL of triethylamine, the solution
was filtered, to remove insoluble material. Solvents were
removed under reduced pressure and the residual yellow
powder was first washed with diethyl ether, and dried on
HV overnight to give 9.5 g (91.6%) of microcrystalline
colorless pyrrole 6. 300 MHz 1H NMR (CDCl3): d, ppm
1.28 (t, J = 7.4 Hz, 9H, N–CH2–CH3), 3.04 (q, J = 7.4 Hz,
6H, N–CH2–CH3), 4.16 (s, 2H, CH2–SO2), 4.40 (s, 2H,
CH2–SO2), 6.67 (br s, 1H, CHpy), 9.71 (br s, 1H, NH).
b″-Sulfoleno-pyrrole 2. An oven dry argon-flushed 1
L round-bottomed flask, equipped with an intense cooler,
was charged under argon with 2 g of triethylammonium
sulfolenopyrrole-2-carboxylate (6, 6.62 mmol), 240 mL
of HOAc and 50 mL of trifluoro acetic acid (0.74 mol,
200 eq.). The solution was degassed by sonication and
venting with argon for 5 min, and the flask was kept under
argon filled balloon. The reaction flask was immersed in
a pre-heated oil bath at 100°C and heated to reflux for
4.5 h, where upon it turned red. The flask was removed
from the oil bath and the hot solution was poured into a 2
L beaker containing 1 kg of ice kept in an ice-bath. Then
485 mL of 10 M NaOH were added in small amounts and
with intense stirring to the ice-cooled reaction mixture,
followed by Na2CO3 powder (in small amounts) until
the pH reached ca. 9. The mixture was extracted with
EtOAc (5 × 200 mL), and the collected organic extracts
were washed with water (200 mL), and brine (100 mL).
The pooled solution was dried over MgSO4, filtered
and the solvents were removed under reduced pressure
to obtain brown mixture which was purified by column
chromatography (15 × 2.5 cm). The product 2 was eluted
with 3–5% of EtOAc in CH2Cl2. The collected product
fractions were evaporated to dryness under reduced
pressure to obtain a light yellow powder. This was washed
with 2–3 mL of ether and the coloured solution was
removed and discarded. The white crystalline product 2
was transferred to a small vial, dried on HV at 50°C for
overnight to give 720.1 mg (70%). For crystallization, a
saturated methanolic solution of 2 was left to evaporate
slowly at room temperature. TLC: EtOAc/CH2Cl2, 1:9;
Rf = 0.4, mp 220°C (dec., Lit. 235°C dec. [6]). 300 MHz
1H NMR (CD3OD): d, ppm 4.18 (s, 4H, H2C(31)), 6.75
(br s, 2H, HC(2)).
Tetra-b″-sulfoleno-porphyrin 1. An oven dry argon-
flushed round-bottomed flask was charged with 50.4 mg
(0.321 mmol) of sulfoleno pyrrole (2), 81.1 mg (0.371
mmol, 1.18 equiv.) of 3,5-di-tert-butyl-benzaldehyde
and 25 mg (0.0784 mmol, 0.25 equiv.) of hexadecyl
trimethyl ammonium chloride. The mixture was dried
under HV for 3 h at 25°C, and under argon 35 mL of abs
CH2Cl2 were added (concentration in each reactant is ca.
10 mM). The obtained colorless solution was flushed with
argon for 5 min, and, while stirring, 100 mL (88.9 mg,
Copyright © 2014 World Scientific Publishing Company
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SYMMETRICAL TETRA-b″-SULFOLENO-MESO-ARYL-PORPHYRINS
121
0.548 mmol, 1.7 equiv.) of triethyl orthoacetate were
Rf = 0.2. UV-vis (CH2Cl2, c = 3.83 × 10-5 M): lmax, nm
(log e) 590 (3.92), 549.5 (4.41), 424 (5.85), 402 (4.73),
326 br (4.25). Fluorescence (CH2Cl2, c = 1.104 × 10-5
M): lEx, nm 554 (O.D. = 0.25); lEm, nm (a.u.) 650 (129),
601 (70.6). 300 MHz 1H NMR (CDCl3): d, ppm 1.50 (s,
added, followed by stirring for 10 min at 25°C. To the
solution 500 mL of BF3·OEt2 (48% solution in Et2O, 287.9
mg, 1.99 mmol, 6 equiv.) was added through the septum
and continued to stir at room temperature for 24 h under
protection from light. To the obtained dark rose coloured
solution, 110 mg of chloranil (0.441 mmol, 1.4 equiv.)
was added under argon and the reaction mixture was
heated to reflux for 1.5 h. The cold solution was poured
in sat.NaHCO3 (50 mL) and the products were extracted
with CH2Cl2 (5 × 50 mL). The collected brown organic
phases were washed with sat. NaCl solution (60 mL) and
filtered through a plug of dried cotton. The product was
purified by column chromatography (20 × 2.5 cm) with a
CH2Cl2-PE gradient. The product eluted with 3:2 CH2Cl2/
PE (v/v). The reddish product containing fractions were
combined and the solvents were removed under reduced
pressure. The dry residue was re-dissolved in CH2Cl2 (ca.
10 mL) and precipitated with excess of PE (ca. 40 mL).
The microcrystalline precipitate was washed with diethyl
ether and dried under HV at 50°C for 15 h to give 89.8 mg
(78.7%) of the porphyrin 1. TLC: (red fluorescent spot
under 365 nm UV light) CH2Cl2/PE, 8:2; Rf = 0.35, mp
132–135°C (dec.). UV-vis (CH2Cl2, c = 3.93 × 10-5 M):
t-
72H, Bu531), 4.18 (s, 16H, H2C21), 7.81 (d, J = 1.8 Hz,
8H, HC52), 7.96 (t, J = 1.8 Hz, 4H, HC54). FAB-MS (pos.
ion, C84H100N4O8S4Zn, calcd. 1484.57): m/z (%) 1491.3
(5), 1490.3 (10), 1489.3 (16), 1488.3 (21), 1487.3 (24),
1486.3 (24), 1485.3 (22, [M + H]+), 1484.3 (19, [M]+),
1424.4 (4), 1423.4 (5), 1422.4 (5), 1421.4 (4, [M – SO2 +
H]+), 1296.5 (6), 1295.5 (9), 1294.5 (10), 1293.5 (11,
[M – 3SO2 + H]+), 1292.5 (10, [M – 3SO2]+), 1291.4
(9), 1246.5 (17), 1245.5 (20), 1244.5 (21), 1243.5 (15),
1242.5 (16), 1233.5 (41), 1232.5 (62), 1231.5 (69), 1230.5
(95), 1229.5 (100, [M – 4SO2 + H]+), 1228.5 (94, [M –
4SO2]+), 1227.5 (37), 1226.5 (30), 1217.5 (16), 1216.5
(21), 1215.5 (24), 1214.5 (26), 1213.5 (25), 1212.5 (20).
X-ray structure analysis, crystal data and structure
refinement: for crystallization, a layer of n-hexane was
added on top of a solution of ca. 2 mg of 1-Zn in CH2Cl2
(3 mL), and the sample was stored at room temperature
over few days (for crystallography, see Supporting
information).
lmax, nm (log e) 648.0 (3.68), 592.0 (3.80), 547 (3.71),
Cu(II)-tetra-b″-sulfoleno-porphyrinate (1-Cu). A
dry and argon flushed round-bottomed flask charged with
24.7 mg (17.3 mmol) of sulfoleno porphyrin 1 and 35 mg
(171 mmol, 10 equiv.) of Cu(OAc)2·H2O. The mixture
was evacuated under HV for 1 h and under argon 15 mL
of abs CH2Cl2 and 1.5 mL of abs MeOH (10:1, v/v)
were added. The resulting brown solution was heated to
reflux in a pre-heated oil bath at 60°C under argon. The
reaction progress was followed by TLC, (17:3 CH2Cl2/
PE; red non-fluorescent product spot slightly ahead of
the spot of 1-2H) and UV-vis spectra. After 2 h, 1-2H
was completely consumed and the flask was removed
from the oil bath and allowed to cool down. The mixture
was washed with water (30 mL) and extracted in CH2Cl2
(4 × 25 mL). The collected organic extracts were dried
over Na2SO4, filtered and the solvents were evaporated
under reduced pressure. The dry residue was re-dissolved
in CH2Cl2 (4–5 mL) and precipitated with excess of PE
(20 mL). The precipitate was dried under HV at 50°C for
15 h to give 26.1 mg (99%) of the Cu(II)-tetrasulfoleno-
porphyrinate 1-Cu. TLC: CH2Cl2/PE, 8.5:1.5; Rf = 0.45.
UV-vis (CH2Cl2, c = 1.764 × 10-5 M): lmax, nm (log e)
539.5 (4.44), 418 (5.76), 397 sh (4.61), 323 br (4.16).
FAB-MS (pos. ion, C84H100N4O8S4Cu, calcd. 1483.57):
m/z (%) 1486.7 (29), 1485.7 (33), 1484.7 (34, [M + H]+),
1422.8 (6), 1421.6 (8), 1420.7 (10, [M – SO2 + H]+),
1419.7 (6), 1260.8 (28), 1259.8 (33), 1258.8 (38), 1257.8
(33), 1244.9 (25), 1243.9 (28), 1241.8 (28), 1231.8 (30),
1230.7 (56), 1229.8 (61), 1228.9 (86, [M – 4 SO2 + H]+),
1227.9 (100, [M – 4 SO2]+), 1226.8 (43), 1225.9 (38).
Tetrasulfoleno Ni(II) porphyrin (1-Ni). A dry
and argon flushed round-bottomed flask charged with
55 mg (38.6 µmol) of sulfoleno porphyrin 1, 205 mg
514.5 (4.37), 480.5 (3.66), 420 (5.58), 380 sh (4.54), 270
(4.40). Fluorescence (in CH2Cl2, c = 7.58 × 10-6 M): lEx,
nm 516 (O.D. = 0.2); lEm, nm (a.u) 656.8 (250.1), 722
1
(126.1). 300 MHz H NMR (CDCl3): d, ppm -3.08 (br s,
2H), 1.51 (s, 72H), 4.15 (br s, 16H), 7.83 (d, J = 1.7 Hz,
8H), 7.96 (t, J = 1.7 Hz, 4H). 75 MHz 13C NMR (CDCl3):
see Table S1, Supporting information. FAB-MS (positive
ion, C84H102N4O8S4: calcd. 1422.66): m/z (%) 1425.6 (10),
1424.6 (20), 1423.6 (36, [M + H]+), 1422.6 (12, M+),
1360.7 (10), 1359.7 (12, [M – SO2 + H]+), 1296.8 (8),
1295.8 (6, [M – 2SO2 + H]+), 1232.8 (5), 1231.8 (5, [M
– 3SO2 + H]+), 1169.8 (18), 1168.8 (52), 1167.8 (90, [M –
4SO2 + H]+), 1166.8 (100, [M – 4SO2]+), 1165.8 (70).
Zn(II)-tetra-b″-sulfoleno-porphyrinate (1-Zn). A
dry argon flushed flask equipped with reflux condenser
was charged with 50 mg (35.11 µmol) of tetrasulfoleno
porphyrin 1, 160 mg (728.93 mmol, 20.76 equiv.) of
Zn(OAc)2·2H2O and 25 mL of DMF. The resulting brown
solution was flushed with argon and stirred at 100°C
under argon, reaction progress was followed with TLC
(17:3 CH2Cl2/PE) and UV-vis-spectra. After 40 min no
starting material was left and the flask was removed from
the oil bath. The cooled reaction mixture was washed
with water (100 mL), extracted the product with EtOAc
(4 × 40 mL). The collective organic extractions were
filtered through a plug of dried cotton and solvents were
removed under reduced pressure. The dry crude product
was re-dissolved in minimum amount of CH2Cl2, and the
porphyrin 1-Zn was precipitated with excess of PE (~1:5
v/v). The precipitate was dried under HV at 50°C for
15 h to yield 47 mg (90%) of Zn(II)-tetra-b″-sulfoleno-
porphyrinate (1-Zn). TLC: (CH2Cl2/MeOH, 10/0.05)
Copyright © 2014 World Scientific Publishing Company
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122
S. BANALA ET AL.
of (824 µmol, 21 equiv.) Ni(OAc)2·4H2O and 16 mL of
dimethyl formamide (DMF). The resulting solution was
purged with argon, stirred in a pre-heated oil bath at
100°C under argon. The reaction progress was followed
with TLC, and UV-vis spectra. After 2.5 h, complete
conversion of 1 was observed, and the flask was removed
from the oil bath. The cold reaction mixture was washed
with water (100 mL) and the porphyrin was extracted into
EtOAc (4 × 40 mL). The collected organic phases dried
on Na2SO4, filtered and the solvent was removed under
reduced pressure. The red dry product was re-dissolved
in CH2Cl2 (6 mL), added PE 40–60 (35 mL) and placed
in 4°C refrigerator to give micro-crystals overnight,
which were dried under HV at 50°C for 15 h. In this
way, 52.2 mg (91.3%) of tetrasulfoleno Ni(II)-porphyrin
(1-Ni) were obtained. TLC: CH2Cl2/PE, 8.5:1.5; Rf = 0.3.
UV-vis (CH2Cl2, c = 4.255 × 10-5 M): lmax, nm (log e) 562
(3.45), 530 (4.30), 418 (5.42), 300 br (4.17), 240 (4.40).
1H NMR (300 MHz, CDCl3): d, ppm 1.47 (s, 72H), 4.06
(br s, 16H), 7.67 (d, J = 1.7 Hz, 8H), 7.89 (t, J = 1.8 Hz,
4H). 75 MHz 13C NMR (CDCl3): seeTable S2, Supporting
information. FAB-MS (pos. ion, C84H100N4O8S4Ni, calcd.
1478.58): m/z (%) 1483.5 (12), 1482.5 (18), 1481.5 (32),
1480.4 (26), 1479.4 (22, [M + H]+), 1478.4 (20, [M]+),
1419.5 (8), 1418.5 (14), 1417.5 (18), 1416.5 (19), 1415.5
(29, [M – SO2 + H]+), 1227.6 (20), 1226.6 (42), 1225.6
(68), 1224.6 (92), 1223.6 (100, [M – 4SO2 + H]+), 1222.6
(94), 1221.6 (60), 1220.6 (50).
the Cambridge Crystallographic Data Centre (CCDC)
under numbers CCDC-950012 and 950013. Copies
can be obtained on request, free of charge, via www.
ccdc.cam.ac.uk/data_request/cif or from the Cambridge
Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223-336-033 or
email: deposit@ccdc.cam.ac.uk).
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CONCLUSION
The here reported improved synthesis of the b″-tetra-
sulfolenopyrrol 1 made use of the beneficial effect of
added detergent salts on the pyrrole tetramerization to
porphyrinogens [16]. The versatile porphyrinoid building
block 1 was obtained in a remarkable yield of up to
80–90%, pavingthewaytofurtherstudiesofthechemistry
of this type of reactive porphyrins. The synthesis of
several transition metal complexes of 1 is described here.
The functionalizable tetrasulfoleno porphyrins, obtained
from 1, are valuable basic units in up to four sequential
cycloaddition reactions, as investigated in recent studies
with the Zn(II)-complex 1-Zn [5, 11, 12, 14].
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Sanders JKM. J. Am. Chem. Soc. 1990; 112:
6507–6514.
Supporting information
Supplementary material is available free of charge
via the Internet at http://www.worldscinet.com/jpp/jpp.
shtml.
Crystallographic data for structures 1-Ni and 1-Zn
(excluding structure factors) have been deposited at
20. Buchler JW. In The Porphyrins, Vol. I, Dolphin D.
(Ed.)Academic Press: NewYork, 1978; pp 389–474.
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J. Porphyrins Phthalocyanines 2014; 18: 122–122