Synthesis of mono meso-pyridyl 21,23-dithiaporphyrins and unsymmetrical non-covalent porphyrin dimers

Article abstract of DOI:10.1016/j.tet.2004.07.011

A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single

Full text of DOI:10.1016/j.tet.2004.07.011

Tetrahedron 60 (2004) 8437–8444
Synthesis of mono meso-pyridyl 21,23-dithiaporphyrins and
unsymmetrical non-covalent porphyrin dimers
*
Sokkalingam Punidha and Mangalampalli Ravikanth
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400076, India
Received 23 February 2004; revised 11 June 2004; accepted 1 July 2004
Abstract—A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The
method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single
products in 8–11% yield. Two of the three mono meso-pyridyl N2S2 porphyrins were used to synthesize non-covalent unsymmetrical
porphyrin dimers containing one N2S2 and one N4 porphyrin cores.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
meso positions in a cis fashion and used them to construct
covalently linked energy donor appended systems.6 We also
prepared cis-pyridyl porphyrin building blocks with N3S
and N3O porphyrin cores and synthesized non-covalent
unsymmetrical trimers containing one N3S and two N4
porphyrin cores.7 The porphyrins with one functional group
are more desirable and available synthetic reports in the
literature are useful only to synthesize mono-functionalized
N3S and N3O porphyrins.8 To the best of our knowledge,
there are no reports available on mono-functionalized
21,23-dithiaporphyrins (N2S2 core). In this paper, we report
the synthesis of three N2S2 porphyrins with one pyridyl
group at the meso position (Chart 1) and its use to further
construct two novel unsymmetrical non-covalent dimers
having two different porphyrin cores. These are the first
examples of non-covalent porphyrin dimers with N2S2 and
N4 porphyrin cores.
Porphyrins and metalloporphyrins provide an advantageous
class of building blocks for the construction of large multi-
component architectures because of their relatively facile
synthesis, stability and diversity of properties. Several
synthetic strategies are employed for the assembly of
multiporphyrin systems. A wide variety of porphyrin arrays
of ever-increasing size have been constructed by the
traditional methodology of covalently linking porphyrins.1
More recently, the incorporation of porphyrins into
porphyrin assemblies via non-covalent interactions has
proven to be an attractive method for array formation.2 By
controlling the choice of materials, the supramolecular
structure of the array can be engineered. To a large extent,
the majority of the self-assembling porphyrin arrays are
based on metal–ligand interactions and meso-pyridyl
porphyrins play a key role in this kind of array. There are
several reports available on non-covalent porphyrin assem-
blies connected via pyridyl groups which are mostly
concerned with normal porphyrin (N4 core) systems.3 The
core-modified porphyrins with cores such as N3S, N3O,
N2S2, N2O2, N2SO exhibit unique chemistry and different
properties from N4 porphyrin systems.4 Core-modified
porphyrins with functional groups such as iodophenyl,
ethynyl phenyl, pyridyl etc at meso positions are suitable
building blocks to synthesize unsymmetrical porphyrin
arrays.5 We recently prepared heteroporphyrins building
blocks having two iodophenyl and ethynyl phenyl groups at
Keywords: meso-Pyridyl porphyrins; Core-modified porphyrins; Non-
covalent; Unsymmetrical array.
* Corresponding author. Fax: C91-22-576-7152;
e-mail: ravikanth@chem.litb.ac.in
Chart 1. Mono meso-pyridyl 21,23-dithiaporphyrins.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.07.011

8438
S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
Scheme 1. General synthetic scheme of unsymmetrical diols 4–6 and unsymmetrical tripyrrin 7.
2. Results and discussion
column chromatography. Since the unsymmetrical diols
have two chiral centres, the TLC analysis showed the
presence of an additional minor spot close to the major diol
spot, which might be due to its diastereomer. However, we
collected the major spot and used it for porphyrin reactions.
Because the chirality is lost on porphyrin formation, no
attempts were made to characterize the minor spot. The
diols 4 and 5 were obtained in 40% yields and diol 6 was
afforded as semi-solid in 45% yield. The unsymmetric
nature of diols was clearly evident in their 1H NMR spectra.
The thiophene and CH protons which appear as singlets in
the symmetrical diol9 appeared as multiplets in diols 4–6
due to unsymmetrical substitution.
2.1. Unsymmetrical thiophene diols 4–6 and
unsymmetrical tripyrrin 7
To synthesize mono meso-pyridyl 21,23-dithiaporphyrins,
the unknown key precursors such as unsymmetrical
thiophene diols and unsymmetrical 16-thiatripyrrins were
required. The unsymmetrical thiophene diols 4–6 were
synthesized in two steps starting with thiophene (Scheme 1).
The desired thiophene mono-ol, 2-(p-tolylhydroxymethyl)
thiophene8b was prepared by treating thiophene with
1 equiv. of n-BuLi followed by addition of 1.2 equiv. of
p-tolualdehyde in THF at 0 8C. The TLC analysis of the
crude mixture indicated the formation of desired mono-ol
along with symmetrical diol and unreacted aldehyde. The
mono-ol was separated from the mixture by column
chromatography and afforded mono-ol in 65% yield. The
thiophene mono-ol was then treated with 2 equiv. of n-BuLi
followed by addition of pyridine 2- or 3- or 4-carboxalde-
hyde in THF at 0 8C. After work-up, the crude mixture
containing the desired unsymmetrical diol along with some
unreacted mono-ol and aldehyde was subjected to silica gel
The unsymmetrical 16-thiatripyrrin 7 was prepared by
treating 1 equiv. of unsymmetrical diol 6 with 40 equiv. of
pyrrole in CH2Cl2 in the presence of a catalytic amount of
BF3$OEt2 (Scheme 1). The excess pyrrole was removed
under vacuum and the TLC analysis showed only one major
spot along with polymeric material at the bottom of the TLC
plate. The crude compound was subjected to silica gel
column chromatography and afforded 7 in 40% yield. The
unsymmetric nature of 7 was clearly established by the
Scheme 2. Two general synthetic schemes for the preparation of mono meso-pyridyl 21,23-dithiaporphyrins 1–3.

S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
8439
TLC analysis after the first column indicated the formation
of the desired compound as the sole product. The crude
compounds were subjected to second silica gel column
chromatography using CH2Cl2 and the pure porphyrins were
afforded as purple solidsin 8–11% yields. Alternately porphyrin
3 was also prepared using unsymmetrical 16-thiatripyrrin 7.
One equivalent of unsymmetrical 16-thiatripyrrin 7 was
condensed with 1 equiv. of symmetrical thiophene diol
(2,5-(p-tolylhydroxymethyl) thiophene)9 in propionic acid
at refluxing temperature for 2 h (Method B). The crude
compound obtained after usual work-up was purified by
column chromatography and afforded 3 in 6% yield. Thus
by following the method B, the porphyrin 3 was afforded in
much lower yield than method A. Hence the synthesis of
porphyrins 1 and 2 were not attempted using method B.
However, both the methods are clean and the desired
compounds were obtained as the single product. No
scrambling was observed in these reactions.
The porphyrins 1–3 were characterized by 1H and 13C NMR
spectroscopy, mass spectrometry, elemental analysis, infra-
1
red and absorption spectroscopies. The H NMR spectrum
of porphyrin 3 is presented in Figure 1(top) and the data of
selected protons are presented in Table 1. In the H NMR
1
spectra, the thiophene and pyrrole protons of 1–3 appeared
as two or three signals unlike S2TPP4 in which they appear
as singlets. This is due to the unsymmetric substitution of
porphyrins 1–3. The presence of strong m/z peak at 692
confirmed the product. The absorption spectra of 1–3
showed four Q-bands (Fig. 2) and one Soret band and the
extinction coefficients were almost comparable to that of
S2TPP (Table 2).
Figure 1. 1H NMR spectra of 3 (top) and dimer 9 (bottom) recorded in
CDCl3.
2.3. Non-covalent unsymmetrical dimers 8 and 9
splitting of thiophene and CH signals in the 1H NMR spectra
which appears as a singlet in symmetrical 16-thiatripyrrin.10
The MC ion peak in the mass spectrum also confirmed the
product.
Porphyrins with pyridyl groups at meso positions are ideal
building blocks to synthesize non-covalent porphyrin
arrays.2,3 Since the heteroporphyrins with pyridyl groups
at meso-positions are very few,7,11 the chemistry remained
unexplored. In general, meso-pyridyl N4 porphyrins form
non-covalent porphyrin arrays by co-ordinating with
different metalloporphyrins (MZZn, Mg, Ru, Rh etc.).
However, our earlier study7 with cis-pyridyl heteroporphyr-
ins with N3S cores showed that the N3S porphyrins prefers
to form non-covalent trimers with RuTPP(CO)(EtOH) but
not with ZnTPP. Furthermore, cis-pyridyl N3O porphyrins
did not form non-covalent arrays with any metallopor-
phyrin. Thus, the chemistry of meso-pyridyl heteropor-
phyrins are core dependent and quite different from N4
porphyrins.
2.2. Mono meso-pyridyl 21,23-dithiaporphyrins 1–3
To synthesize 21,23-dithiaporphyrins 1–3 with one 2- or
3- or 4-pyridyl functional group at the meso position (Chart 1),
we followed any one of the two methods (Method A and B)
shown in Scheme 2. Porphyrins 1–3 were synthesized by
condensing 1 equiv. of unsymmetric thiophene diols 4–6,
respectively with 1 equiv. of the symmetrical 16-thiatri-
pyrrin (5,10-ditolyl-16-thia-15,17-dihydrotripyrrin)10 in
propionic acid at refluxing temperature for 2 h (Method
A). The propionic acid was removed under vacuum and
washed thoroughly with slight warm water and dried in an
oven at 100 8C. The crude black compounds of 1–3 were
passed through silica gel column eluting with CH2Cl2/
2%CH3OH to remove the non-porphyrinic materials. The
The mono meso-pyridyl N2S2 porphyrins 1–3 were explored
to construct non-covalent unsymmetrical dimers containing
one N2S2 and one N4 porphyrin cores. To synthesize
unsymmetrical dimer 8, we treated 1 equiv. of 2 with
1
Table 1. H NMR Spectroscopy chemical shifts (d in ppm) of selected protons in CDCl3
Porphyrin
b-Pyrrole
b-Thiophene
2,6-Pyridyl
3,5/3,4-Pyridyl
2
8
3
9
8.61(d), 8.69(s), 8.75(d)
9.58(d), 9.71(s), 9.73(d)
9.06(bs), 9.50(bs)
1.90(d), 2.22(s)
9.07(bs)
7.80(m), 8.55(d)
6.98(t), 7.38(d)
8.19(m)
6.84(d), 8.16(d), 8.64(d)
8.60(d), 8.69(s), 8.73(d)
7.08(d), 7.92(d), 8.50(d), 8.58 (d)
8.30(d), 9.38(d), 9.58(d), 9.62(d)
9.57(d), 9.73(m)
8.06(d), 9.21(d), 9.47(d), 9.50(d)
1.92(d)
6.00(d)

8440
S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
Figure 2. Q-bands and Soret band (inset a) absorption spectra of 3 (solid line) and 9 (dotted line). The inset b shows the absorption spectra of dimer 9 (dotted
line) and 1:1 mixture of 3 and RuTPP(CO)(EtOH) (dashed line). All were recorded in toluene and the concentrations used were: Soret band, 5!10K6 M; and
Q-bands, 5!10K5 M.
1 equiv. of RuTPP(CO)(EtOH) in toluene at refluxing
temperature for 12 h (Scheme 3). As the reaction pro-
gressed, the colour of the reaction mixture changed from
bright red to brownish red. The reaction progress was
monitored with TLC and the reaction was stopped after
complete disappearance of 2 as judged by TLC. The solvent
was removed under vacuum and the crude compound was
subjected to silica gel column chromatography using
petroleum ether/dichloromethane (80:20). The fast moving
unreacted RuTPP(CO)(EtOH) was removed and the desired
dimer 8 was then collected with petroleum ether/dichloro-
methane (60:40) as a purple solid in 40% yield. Similarly,
treating the porphyrin 3 with RuTPP(CO)(EtOH) under
same conditions gave the dimer 9 in 56% yield (Scheme 3).
Interestingly, porphyrin 1 did not form any dimer which
may be due to steric hindrance. Furthermore, porphyrins
1–3 when treated with ZnTPP under different reaction
conditions also did not form a dimer. The dimers 8 and 9
were highly soluble in most organic solvents and charac-
terized by NMR spectroscopy, mass spectrometry, ele-
mental analysis, infrared and Uv–visible spectroscopy. The
1H NMR spectrum of dimer 9 comparing with monomer 3
shown in Figure 1 clearly demonstrated the formation of
dimer. The signals of dimers 8 and 9 were composed of the
parts of RuTPP and N2S2 porphyrin 2 and 3 respectively.
The pyrrole and phenyl protons of the RuTPP part of dimers
8 or 9 appeared at almost the same chemical shifts of
starting monomer RuTPP(CO)(EtOH). It is well-known that
the porphyrin ring current changes the chemical shifts of the
protons located near the porphyrin plane. The protons of
mono pyridyl N2S2 porphyrin were shifted upfield from its
parent porphyrin because of the RuTPP ring current. The
pyrrole and thiophene protons of N2S2 porphyrin unit of
dimers 8 and 9 were shifted upfield compared to their
corresponding monomers 2 and 3, respectively (Fig. 1 and
Table 1). However, the maximum upfield shifts were
observed for the 2,6- and 3,4-/3,5-pyridyl protons of the
N2S2 porphyrin unit implying the coordination of pyridyl
Table 2. Absorption data of mono meso-pyridyl 21,123-dithiaporphyrins recorded in toluene
Porphyrin
Soret band l (nm) (3!10K4
)
Absorption Q-bands l (nm) (3!10K3
)
IV
III
II
I
1
2
3
8
437 (28.5)
437 (13.1)
437 (37.5)
438 (136.5)
412 (204.3)
437 (128.6)
413 (67.1)
515 (28.4)
515 (13.4)
515 (32.2)
520 (19.3)
531 (sh)
549 (8.2)
549 (5.0)
549 (9.6)
552 (9.9)
567 (sh)
548 (7.7)
634 (2.2)
634 (1.4)
634 (2.4)
635 (1.7)
697 (4.8)
697 (2.5)
697 (5.6)
698 (3.1)
1:1 Mixture of 2 and
RuTPP(CO)(EtOH)
516 (15.5)
633 (2.4)
697 (3.3)
9
437 (204.2)
412 (292.9)
437 (217.1)
411 (66.3)
519 (28.1)
531 (sh)
515 (26.8)
550 (sh)
567 (sh)
548 (8.8)
634 (2.1)
633 (2.5)
697 (4.1)
697 (5.1)
1:1 Mixture of 3 and
RuTPP(CO)(EtOH)

S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
8441
Scheme 3. Synthetic scheme for the preparation of non-covalent unsymmetrical dimer 8 and 9.
group with central ruthenium ions. The large upfield shifts
of 2,6-pyridyl protons compared with 3,4-/3,5-pyridyl
protons indicate that these protons experienced large ring
current effect of RuTPP because of their proximity to the
RuTPP core. The elemental analysis and mass data were in
agreement with dimer formation. IR measurements showed
the n(CO) stretch at 1943 cmK1. The absorption spectra
of dimers 8 and 9 were compared with 1:1 mixture of
RuTPP(CO)(EtOH) and 2 and 3, respectively. The absorp-
tion spectra indicated that the dimers exhibited bands
corresponding to both the units whereas, 1:1 mixture
showed bands corresponds mainly to the mono-pyridyl
N2S2 porphyrin unit. Furthermore, in the dimer 8 or 9, the
extinction coefficient of the Soret band of RuTPP unit was
three times to that of the RuTPP unit of a 1:1 mixture,
supporting the co-ordination of the pyridyl group of N2S2
porphyrin to the central ruthenium ion of the Ru(TPP)(CO)
(Table 2).
unsymmetrical covalent dimers using the methodology
reported in this paper.
4. Experimental
4.1. General
1H and 13C NMR spectra were recorded using a Varian
400 MHz instrument using tetramethylsilane as an internal
standard. Absorption and fluorescence spectra were
obtained with Perkin–Elmer Lambda-35 and Lambda-55
instruments, respectively. The IR spectra were recorded
with a Nicolet Impact-400 FT-IR spectrometer and the
ES MS mass spectra were recorded with a Q-Tof micro
(YA-105) mass spectrometer. Toluene, THF and diethyl-
ether were obtained from S.D. Fine chemicals, India, and
were dried by standard procedures before use. All general
chemicals were obtained from Qualigens, India. p-Tolualde-
hyde, thiophene, pyrrole, pyridine carboxaldehydes were
obtained from Lancaster. Column chromatography was
performed using 60–120 mesh silica obtained from Sisco
Research Laboratories, India.
3. Conclusions
In summary, we synthesized mono meso-pyridyl 21,23-
dithiaporphyrins using readily available precursors. The
porphyrins were obtained as single products in good yields
by following any one of the two methods mentioned in this
paper. The mono-meso-pyridyl porphyris were used to
construct the non-covalent unsymmetrical porphyrin dimers
containing N4 and N2S2 porphyrin units. We are presently
exploring the synthesis of other mono-functionalized
21,23-dithiaporphyrin building blocks for the synthesis of
4.1.1. 2-(2-Pyridylhydroxymethyl)-5-(p-tolylhydroxy-
methyl) thiophene (4). A distilled diethylether (30 mL)
was taken in a dry 250 mL three necked round-bottomed
flask equipped with a rubber septum, gas inlet and gas outlet
tube and a positive pressure of N2 was maintained. A mono-
ol (2-(p-tolylyhydroxymethyl) thiophene) (1 g, 4.90 mmol)
followed by n-BuLi (6.1 mL of ca. 15% solution in hexane)
were added to it at 0 8C and stirring was continued for 1 h.

8442
S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
Then the ice-cold solution of 2-pyridine carboxaldehyde
(0.93 mL, 9.79 mmol) in dry THF (20 mL) was added to the
stirred solution. The reaction mixture was stirred at 0 8C for
15 min and then brought to room temperature. The reaction
was quenched by adding an ice-cold NH4Cl solution
(50 mL, ca. 1 M). The organic layer was washed with
water and brine solution and dried over anhydrous Na2SO4.
The solvent was removed on a rotary evaporator under
reduced pressure to afford the crude compound. TLC
analysis showed three major spots corresponding to the
unreacted 2-pyridine carboxaldehyde, unreacted mono-ol
and the desired diol 4. In addition to the major spot of diol,
we have also noted one minor spot just above the major diol
spot, which was not characterized. The aldehyde, the mono-
ol and the minor unidentified fractions were removed by
silica gel column chromatography (1–3% CH3OH/CH2Cl2)
and the major diol fraction 4 was collected (609 mg, 40%)
with 4% CH3OH/CH2Cl2 as a white solid, mp 121–122 8C;
[Found: C, 69.19; H, 5.20; N, 4.32; S, 10.11. C18H17NO2S
requires C, 69.43; H, 5.50; N, 4.50; S, 10.30%]; Rf (4%
CH3OH/CH2Cl2) 0.51; nmax (KBr) 3457, 3357, 3059, 2871,
1488, 1437, 1054, 806, 760, 692 cmK1; dH (400 MHz,
CDCl3) 8.52–8.55 (1H, bs, pyridyl), 7.66 (1H, t, JZ7.5 Hz,
pyridyl), 7.28 (2H, d, JZ8.1 Hz, o-tolyl), 7.20–7.22 (2H, m,
pyridyl), 7.13 (2H, d, JZ8.1 Hz, m-tolyl), 6.83 (1H, d, JZ
4.4 Hz, thiophene), 6.70 (1H, d, JZ4.4 Hz, thiophene), 5.91
(2H, s, CHOH), 2.32 (3H, s, Me); dC (400 MHz, CDCl3)
148.2, 147.6, 140.2, 137.8, 137.6, 129.3, 126.4, 126.3,
125.0, 124.5, 123.1, 121.6, 72.5, 70.9, 21.3; ES MS 312 (8
MHC), 295 (12), 294 (100), 175 (10), 119 (18%).
white semi-solid, mp 125–126 8C; [Found: C, 69.28; H,
5.41; N, 4.30; S, 10.18. C18H17NO2S requires C, 69.43; H,
5.50; N, 4.50; S, 10.30%]; Rf (4% CH3OH/CH2Cl2) 0.47;
nmax (KBr) 3457, 3350, 3050, 3022, 2872, 1484, 1438, 1050,
806, 760, 692 cmK1; dH (400 MHz, CDCl3) 8.18 (2H, d, JZ
8.8 Hz, pyridyl), 7.21–7.25 (4H, m, tolyl), 7.06 (2H, d, JZ
8.8 Hz, pyridyl), 6.62 (1H, d, JZ5.2 Hz, thiophene), 6.59
(1H, d, JZ5.2 Hz, thiophene), 5.82 (2H, s, CHOH), 2.27
(3H, s, Me); dC (400 MHz, CDCl3) 148.6, 146.4, 146.2,
140.7, 137.4, 129.4, 126.3, 124.7, 124.3, 123.1, 121.4, 71.9,
70.4, 21.1; m/z (ES MS) 312 (5 MHC), 294 (100), 194
(32%).
4.1.4. 5-(4-Pyridyl)-10-(p-tolyl)15,17-dihydro-16-thiatri-
pyrrin (7). A mixture of 6 (500 mg, 1.61 mmol) and pyrrole
(4.5 mL, 64.3 mmol) were degassed by bubbling with N2 for
10 min. BF3$OEt2 (202 mL, 1.61 mmol) was added and the
reaction mixture was stirred for 30 min at room temperature.
The solution was diluted with CH2Cl2 (100 mL), then
washed with 0.1 M NaOH, followed by water. The organic
layer was dried over anhydrous Na2SO4. The solvent was
removed under reduced pressure and the unreacted pyrrole
was removed by vacuum distillation at room temperature.
TLC analysis of the crude mixture showed no other product
formation except small amounts of polymeric material at the
origin. The resulting dark yellow viscous liquid was purified
by column chromatography (silica gel 60–120 mesh, ethyl
acetate/petroleum ether (50:50) to afford tripyrrin 7
(263 mg, 40%) as an orange oily liquid; [Found: C, 76.44;
H, 5.46; N, 10.10; S, 7.70. C26H23N3S requires C, 76.24; H,
5.66; N, 10.26; S, 7.83%]; Rf (50% ethyl acetate/petroleum
ether) 0.49; nmax (KBr) 3403, 3290, 3091, 2968, 2864, 1615,
1602, 1462, 1072, 861, 762, 741 cmK1; dH (400 MHz,
CDCl3) 8.40 (2H, d, JZ8.0 Hz, pyridyl), 8.30 (2H, bs, NH),
7.60 (2H, d, JZ8.0 Hz, pyridyl) 7.09–7.11 (4H, m, tolyl),
6.71–6.73 (4H, m, pyrrole), 6.54–6.56 (2H, m, pyrrole),
6.05 (1H, s, thiophene), 5.84 (1H, s, thiophene), 5.81 (1H, s,
CH), 5.46 (1H, s, CH), 2.27 (3H, s, Me); dC (400 MHz,
CDCl3) 150.2, 147.7, 145.9, 137.3, 136.7, 133.3, 128.3,
128.2, 125.3, 122.9, 122.4, 121.3, 117.2, 108.2, 107.3, 45.7,
36.9, 21.1; m/z (ESMS) 409 (100 MKHC), 394 (40), 252
(8), 237 (15), 239 (10), 169 (12%).
4.1.2. 2-(3-Pyridylhydroxymethyl)-5-(p-tolylhydroxy-
methyl) thiophene (5). To a three-necked 250 mL round-
bottomed flask containing mono-ol (1 g, 4.90 mmol) in
ether (30 mL), was added n-BuLi (6.1 mL of a 15% solution
in hexane) under the same experimental conditions as
mentioned above. 3-Pyridine carboxaldehyde (0.93 mL,
9.67 mmol) in dry THF (20 mL) was added slowly to the
reaction mixture followed by workup and chromatography
to afford the desired diol 5 (624 mg, 41%) as a white solid,
mp 120–122 8C; [Found: C, 69.12; H, 5.25; N, 4.37; S,
10.20. C18H17NO2S requires C, 69.43; H, 5.50; N, 4.50; S,
10.30%]; Rf (4% CH3OH/CH2Cl2) 0.48; nmax (KBr) 3440,
3352, 3050, 3020, 2868, 1600, 1481, 1432, 809, 761,
692 cmK1; dH (400 MHz, CDCl3) 8.23 (1H, bs, pyridyl),
8.16–8.18 (1H, m, pyridyl), 7.58–7.60 (1H, m, pyridyl),
7.21 (2H, d, JZ8.2 Hz, o-tolyl), 7.04–7.06 (1H, m, pyridyl),
7.01 (2H, d, JZ8.2 Hz, m-tolyl), 6.52 (1H, d, JZ4.4 Hz,
thiophene), 6.49 (1H, d, JZ4.4 Hz, thiophene), 5.76 (2H, s,
CHOH), 2.24 (3H, s, Me); dC (400 MHz, CDCl3) 149.6,
147.9, 147.2, 144.7, 137.5, 134.9, 129.1, 128.3, 124.7,
124.3, 123.7, 123.5, 71.9, 69.7, 21.3; m/z (ES MS) 312 (8
MHC), 294 (100), 219 (12), 174 (15), 119 (10), 102 (17%).
4.1.5. 5-(2-Pyridyl)-10,15,20-tris(p-tolyl)-21,23-dithia-
porphyrin (1). A solution of 4 (367 mg, 1.18 mmol) and
symmetrical 16-thiatripyrrin (5,10-ditolyl-16-thia-15,17-
dihydrotripyrrin) (500 mg, 1.18 mmol) in 125 mL of
propionic acid was refluxed for 3 h. The progress of the
reaction was checked by absorption spectroscopy, which
showed bands characteristic of the desired porphyrin. The
excess propionic acid was removed under vacuum and the
resultant black solid was washed several times with warm
water and dried in an oven at 100 8C. The crude product was
then purified by silica gel column chromatography using
CH3OH/CH2Cl2 (2:98) as eluent, to afford the desired
porphyrin 1 (67 mg, 8.2%) as a purple solid, mpO300 8C;
[Found: C, 80.03; H, 4.95; N, 6.24; S, 9.44. C46H33N3S2
requires C, 79.82; H, 4.92; N, 6.07; S, 9.25%]; Rf (2%
CH3OH/CH2Cl2) 0.44; nmax (KBr) 2929, 2864, 1456, 976,
794; dH (400 MHz, CDCl3) 9.70–9.73 (4H, m, b-thiophene),
9.20–9.22 (1H, bs, pyridyl), 8.69–8.71 (4H, m, b-pyrrole),
8.27–8.29 (2H, m, pyridyl), 8.12–8.14 (6H, m, o-tolyl),
7.71–7.73 (1H, m, pyridyl), 7.60–7.62 (6H, m, m-tolyl),
4.1.3. 2-(4-Pyridylhydroxymethyl)-5-(p-tolylhydroxy-
methyl) thiophene (6). The diol 6 was prepared following
the same method given for diols 4 and 5 by adding n-BuLi
(6.1 mL of a 15% solution in hexane) to mono-ol (1 g,
4.90 mmol) in diethylether (30 mL) followed by ice cold
solution of 4-pyridine carboxaldehyde (0.93 mL,
9.79 mmol) in dry THF (20 mL). Purification of the crude
product by silica gel column chromatography (4% CH3OH/
CH2Cl2) gave the desired diol 6 (685 mg, 45%) as an off-

S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
8443
2.70 (9H, s, Me); dC (400 MHz, CDCl3) 156.8, 149.5, 148.4,
147.9, 147.6, 138.4, 137.9, 136.2, 135.7, 135.0, 134.8,
134.5, 131.2, 130.3, 129.5, 128.3, 128.0, 122.6, 21.6; m/z
(ES MS) 692 (100% MC).
silica gel column chromatography using petroleum ether/
dichloromethane (60:40) as solvent and afforded dimer 8
(17 mg, 40%) as a purple solid, mpO300 8C; [Found: C,
76.30; H, 4.50; N, 6.70; S, 4.50. C46H33N3S2 requires C,
76.36; H, 4.29; N, 6.84; S, 4.47%]; Rf (60% pet ether/
dichloromethane) 0.48; nmax (KBr) 2930, 2858, 1943, 1443,
1358, 1267, 1177, 1021, 800, 755; dH (400 MHz, CDCl3)
9.62 (1H, d, JZ4.8 Hz, b-thiophene), 9.58 (1H, d, JZ
4.8 Hz, b-thiophene), 9.38 (1H, d, JZ4.8 Hz, b-thiophene),
8.77 (8H, s, b-pyrrole of TPP), 8.64 (1H, d, JZ5.0 Hz,
b-pyrrole of 2), 8.54 (4H, d, JZ8 Hz, o0-Ph of TPP), 8.50
(4H, d, JZ8 Hz, o0-Ph of TPP), 8.30 (1H, d, JZ4.8 Hz,
b-thiophene), 8.14 (2H, d, JZ5.2 Hz, b-pyrrole of 2), 7.58–
7.64 (14H, m, o-tolyl of 2Cm-Ph of TPP), 7.42–7.50 (10H,
m, m-tolyl of 2Cp0-Ph of TPP), 7.38 (1H, d, JZ4.4 Hz,
4-pyridyl), 6.98 (1H, t, JZ2.0, 4.4 Hz, 3-pyridyl), 6.84
(1H, d, JZ5.0 Hz, b-pyrrole of 2), 2.65 (9H, s, Me), 2.22
(1H, s, 6-pyridyl), 1.90 (1H, d, JZ2.0 Hz, 2-pyridyl); dC
(400 MHz, CDCl3) 157.2, 156.0, 153.4, 152.0, 150.9, 148.5,
147.9, 147.6, 146.3, 146.1, 145.8, 144.5, 143.9, 142.7,
141.5, 139.2, 138.0, 136.7, 135.7, 134.6, 134.1, 132.5,
131.6, 128.9, 128.4, 125.3, 123.6, 120.3, 22.8, 21.6; m/z (ES
MS) 1435 (15 MC), 741 (40), 713 (10), 692 (100%).
4.1.6. 5-(3-Pyridyl)-10,15,20-tris(p-tolyl)-21,23-dithia-
porphyrin (2). Condensation of 5 (367 mg, 1.18 mmol)
with symmetrical 16-thiatripyrrin (500 mg, 1.18 mmol) in
propionic acid (125 mL) using similar reaction and
purification methods as mentioned for 1, gave the desired
porphyrin 2 (86 mg, 10.5%) as a purple solid, mpO300 8C;
[Found: C, 79.64; H, 4.77; N, 6.20; S, 9.11. C46H33N3S2
requires C, 79.82; H, 4.92; N, 6.07; S, 9.25%]; Rf (2%
CH3OH/CH2Cl2) 0.46; nmax (KBr) 2926, 2860, 1450,
982, 794; dH (400 MHz, CDCl3) 9.73 (1H, d, JZ5.1 Hz,
b-thiophene), 9.71 (2H, s, b-thiophene), 9.58 (1H, d, JZ
5.1 Hz, b-thiophene), 9.50 (1H, bs, pyridyl), 9.06 (1H, bs,
pyridyl), 8.74–8.76 (1H, d, JZ4.5 Hz, b-pyrrole), 8.69 (2H,
s, b-pyrrole), 8.61 (1H, d, JZ4.5 Hz, b-pyrrole), 8.55 (1H,
d, JZ7.5 Hz, pyridyl), 8.13–8.15 (6H, m, o-tolyl), 7.79–
7.81 (1H, m, pyridyl), 7.60–7.62 (6H, m, m-tolyl), 2.70 (9H,
s, Me); dC (400 MHz, CDCl3) 156.7, 153.3, 149.1, 148.4,
148.1, 147.9, 147.7, 141.2, 140.1, 136.1, 135.9, 135.3,
134.8, 134.3, 133.7, 128.9, 128.3, 128.0, 122.8, 21.6; m/z
(ES MS) 692 (100% MC).
4.1.9. Unsymmetrical non-covalent dimer (9). Compound
3 (20 mg, 0.0289 mmol) was treated with RuTPP(CO)
(EtOH) (23 mg, 0.0289 mmol) in toluene under the same
reaction condition as for 8 to yield the dimer 9 (23 mg, 56%)
as a purple solid, mpO300 8C; nmax (KBr) 1943 (CO); dH
(400 MHz, CDCl3) 9.50 (1H, d, JZ4.8 Hz, b-thiophene),
9.47 (1H, d, JZ4.8 Hz, b-thiophene), 9.21 (1H, d, JZ
4.8 Hz, b-thiophene), 8.66 (8H, s, b-pyrrole of TPP), 8.58
(1H, d, JZ5.2 Hz, b-pyrrole of 3), 8.50 (1H, d, JZ5.2 Hz,
b-pyrrole of 3), 8.20–8.30 (4H, m, o1-ph of TPP), 8.10–8.18
(4H, m, o1-phl of TPP), 8.06 (1H, d, JZ4.8 Hz, b-thiophene),
7.92 (1H, d, JZ5.2 Hz, b-pyrrole of 3), 7.84 (4H, t, JZ
7.6 Hz, p-ph of TPP), 7.58–7.70 (m, ml-ph of TPPCo-tolyl
of 3), 7.43–7.47 (6H, m, m-tolyl of 3), 7.08 (1H, d, JZ
5.2 Hz, b-pyrrole of 3), 6.00 (2H, d, JZ2.4 Hz, 3,5-pyridyl),
2.61 (6H, s, Me), 2.26 (3H, s, Me), 1.92 (2H, d, JZ2.4 Hz,
2,6-pyridyl); dC (400 MHz, CDCl3) 157.0, 156.6, 153.4,
152.2, 150.9, 149.8, 148.5, 147.6, 156.9, 146.3, 145.8,
143.9, 142.7, 141.5, 139.7, 139.2, 138.0, 136.1, 135.8,
134.1, 132.6, 132.1, 131.1, 129.0, 128.4, 126.3, 123.0,
119.3, 22.8, 21.6; m/z (ES MS) 1435 (17 MC), 713 (10), 692
(100%).
4.1.7. 5-(4-Pyridyl)-10,15,20-tris(p-tolyl)-21,23-dithia-
porphyrin (3). Condensation of 6 (367 mg, 1.18 mmol)
with symmetrical 16-thiatripyrrin (500 mg, 1.18 mmol) in
propionic acid (125 mL) using similar reaction and
purification methods as mentioned for 1, gave the desired
porphyrin 3 (90 mg, 11%) as a purple solid. The compound
3 was also prepared by following method B. Condensation
of 2,5-bis (p-tolylhydroxymethyl) thiophene (200 mg,
0.617 mmol) with 5-(4-pyridyl)-10-(p-tolyl)-15,17-dihydro-
16-thiatripyrrin 7 (253 mg, 0.617 mmol) in propionic acid
followed by chromatography gave 3 (26 mg, 6.1%) as a
purple solid, mpO300 8C; [Found: C, 79.71; H, 4.77; N,
6.28; S, 9.10. C46H33N3S2 requires C, 79.82; H, 4.92; N,
6.07; S, 9.25%]; Rf (2% CH3OH/CH2Cl2) 0.50; nmax (KBr)
2930, 2860, 1455, 982, 798; dH (400 MHz, CDCl3)
9.72–9.74 (3H, m, b-thiophene), 9.57 (1H, d, JZ5.2 Hz,
b-thiophene), 9.07 (2H, bs, pyridyl), 8.73 (1H, d, JZ4.8 Hz,
b-pyrrole), 8.69 (2H, s, b-pyrrole), 8.60 (1H, d, JZ4.8 Hz,
b-pyrrole), 8.18–8.19 (2H, m, pyridyl), 8.12–8.14 (6H, m,
o-tolyl), 7.61–7.63 (6H, m, m-tolyl), 2.69 (9H, s, Me); dC
(400 MHz, CDCl3) 157.0, 156.6, 155.1, 150.9, 149.8, 148.7,
148.5, 147.6, 146.9, 138.0, 136.1, 135.7, 135.1, 134.9,
134.7, 133.6, 129.5, 128.3, 21.6; m/z (ES MS) 692 (100%
MC).
Acknowledgements
This research was supported by Department of Atomic
Energy (No. 2001/37/21/BRNS/797) and Council of
Scientific and Industrial Research, Govt. of India, New
Delhi. Mass spectra were obtained at Department of
Chemistry, IIT-Bombay.
4.1.8. Unsymmetrical non-covalent dimer (8). The
dithiaporphyrin building block, 2 (20 mg, 0.0289 mmol)
was dissolved in 30 mL of toluene in a two necked 100 mL
round-bottomed flask and was purged with N2 for 10 min.
RuTPP(CO)(EtOH) (23 mg, 0.0289 mmol) was then added
and the solution was refluxed with stirring overnight. The
reaction was monitored with TLC and absorption spectro-
scopy. The TLC analysis after 12 h showed complete
consumption of 2, and absorption spectroscopy showed
characteristic splittings and shifts in soret and in Q-bands.
The heating was stopped and the solvent was removed under
reduced pressure. The crude compound was purified by
References and notes
1. Choi, M.-Y.; Yamazaki, T.; Yamazaki, I.; Aida, T. Angew.
Chem. Int. Ed. 2004, 43, 150–158 and references cited therein.

8444
S. Punidha, M. Ravikanth / Tetrahedron 60 (2004) 8437–8444
2. (a) Wojaczynski, J.; Latos-Grazynski, L. Coord. Chem. Rev.
2000, 204, 113–171. (b) Imamura, T.; Fukushima, K. Coord.
Chem. Rev. 2000, 198, 133–156.
R. K.; Forsyth, T. P.; Jaquinod, L.; Gerzevske, K. R.; Nurco,
D. J.; Senge, M. O.; Lioccia, S.; Boschi, T.; Smith, K. M.
J. Am. Chem. Soc. 1996, 118, 3869. (g) Kadish, K. M.; Guo,
N.; Camelbecke, E. V.; Froiio, A.; Paolesse, R.; Monti, D.;
Taglitesta, P.; Boschi, T.; Prodi, L.; Bolletta, F.; Zaccheroni,
N. Inorg. Chem. 1998, 37, 2358.
3. (a) Funatsu, K.; Imamura, T.; Ichimura, A.; Sasaki, Y.
J. Chem. Soc., Chem. Commun. 1988, 960–961. (b) Funatsu,
K.; Kimura, A.; Imamura, T.; Sasaki, Y. Chem. Lett. 1995,
765–766. (c) Alessio, E.; Macchi, M.; Heath, S.; Marzilli, L. G.
J. Chem. Soc., Chem. Commun. 1996, 1411–1412. (d) Kariya,
N.; Imamura, T.; Sasaki, Y. Inorg. Chem. 1997, 36, 833–839.
(e) Kariya, N.; Imamura, T.; Sasaki, Y. Inorg. Chem. 1998, 37,
4986–4995. (f) Kumar, R. V.; Balasubramanian, S.; Goldberg,
I. Inorg. Chem. 1998, 37, 541–542. (g) Sharma, C. V. K.;
Broker, G. A.; Huddleston, J. W.; Baldwin, J. W.; Metzger,
R. M.; Rogers, R. D. J. Am. Chem. Soc. 1999, 121, 1114–1117.
4. Latos-Grazynski, L.; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; The Porphyrin Handbook; Vol. 2. Academic: New York;
2000. p. 361–416.
6. (a) Kumaresan, D.; Agarwal, N.; Ravikanth, M. J. Chem. Soc.,
Perkin Trans. 1 2001, 1644–1648. (b) Kumaresan, D.; Gupta,
I.; Ravikanth, M. Tetrahedron Lett. 2001, 42, 8547–8550.
(c) Kumaresan, D.; Agarwal, N.; Gupta, I.; Ravikanth, M.
Tetrahedron 2002, 58, 5347–5356.
7. Santra, S.; Kumaresan, D.; Agarwal, N.; Ravikanth, M.
Tetrahedron 2003, 59, 2353–2362.
8. (a) Cho, W.-S.; Kim, H.-J.; Littler, B. J.; Miller, M. A.; Lee,
C.-H.; Lindsey, J. S. J. Org. Chem. 1999, 64, 7890–7901.
(b) Gupta, I.; Agarwal, N.; Ravikanth, M. Eur. J. Org.
Chem. 2004, 1693–1697.
5. (a) Paolesse, R.; Taglitesta, P.; Boschi, T. Tetrahedron Lett.
1996, 37, 2637. (b) Pandey, R. K.; Forsyth, T. P.; Gerzevske,
K. R.; Lin, J. J.; Smith, K. M. Tetrahedron Lett. 1992, 33,
5315. (c) Gust, D.; Moore, T. A.; Moore, A. L.; Krasnovsky,
A. A.; Liddell, P. A.; Nicodem, D.; Degraziano, J. M.;
Kerrigan, P.; Makings, L. R.; Pessiki, P. J. J. Am. Chem. Soc.
1993, 115, 5684. (d) Bonfantini, E. E.; Officer, D. L.
Tetrahedron Lett. 1993, 34, 8531. (e) Arnold, D. P.; Nischinsk,
L. J. Tetrahedron Lett. 1993, 34, 693. (f) Paolesse, R.; Pandey,
9. Ulman, A.; Manassen J. Chem. Soc., Perkin Trans. 1 1979,
1066–1069.
10. (a) Sridevi, B.; Narayanan, S. J.; Srinivasan, A.; Reddy,
M. V.; Chandrashekar, T. K. J. Porphyrins Phthalocyanines
1998, 2, 69–78. (b) Heo, P.-Y.; Lee, C.-H. Bull. Korean Chem.
Soc. 1996, 17, 515–520.
11. (a) Kumaresan, D.; Santra, S.; Ravikanth, M. SynLett 2001,
1635–1637. (b) Berlicka, A.; Pacholska, E.; Latos-Grazynski,
L. J. Porphyrins Phthalocyanines 2003, 7, 8–16.