Synthesis of 21-oxoporphyrin building blocks and energy donor appended systems

Article abstract of DOI:10.1016/S0040-4039(01)01837-8

A series of 21-oxoporphyrin building blocks bearing iodo- and ethynyl functional groups were synthesized and characterized. A boron-dipyrrin unit appended 21-oxoporphyrin was constructed using the building blocks, under mild palladium coupling conditions

Full text of DOI:10.1016/S0040-4039(01)01837-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 8547–8550
Synthesis of 21-oxoporphyrin building blocks and energy donor
appended systems
D. Kumaresan, Iti Gupta and M. Ravikanth*
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400 076, India
Received 4 July 2001; accepted 28 September 2001
Abstract—A series of 21-oxoporphyrin building blocks bearing iodo- and ethynyl functional groups were synthesized and
characterized. A boron–dipyrrin unit appended 21-oxoporphyrin was constructed using the building blocks under mild palladium
coupling conditions which exhibited efficient energy transfer from boron–dipyrrin to 21-oxoporphyrin. © 2001 Published by
Elsevier Science Ltd.
Core modification of the porphyrin ring by introducing
thiophene, furan, selenophene and tellurophene in place
of pyrrole led to novel hetero-substituted porphyrins
which exhibit interesting properties in terms of both
aromatic character and their ability to stabilize metals
In this paper, we report the synthesis and characteriza-
tion of a series of 21-oxoporphyrin building blocks
bearing iodo- and ethynyl functional groups and their
application towards the construction of energy donor
appended 21-oxoporphyrin systems.
1
in unusual oxidation states. However, the chemistry of
core-modified porphyrins is not very well developed
and the main emphasis of reports which are available
on core-modified systems are on insertion and stabiliza-
The 21-oxoporphyrin building blocks bearing iodo- and
ethynyl functional groups are synthesized as outlined in
Scheme 1. The double alkylation of the dianion of
furan with benzaldehyde afforded the 2,5-bis(phenyl
2
tion of metals in unusual oxidation states. Reports on
3b
oxoporphyrins are scarce even though they exhibit
interesting physico-chemical and electrochemical prop-
hydroxymethyl)furan. The condensation of 1 equiv. of
2,5-bis(phenyl hydroxymethyl) furan with 2 equiv. of
meta or para-iodobenzaldehyde and 3 equiv. of pyrrole
in the presence of BF ·OEt in CH Cl gave a mixture
3
erties. Recently, we have been exploring core modified
porphyrin chemistry and we prepared an unsymmetrical
3
2
2
2
4
porphyrin pentamer containing a dithiaporphyrin
of three porphyrins. The crude porphyrin mixture con-
taining three porphyrins was subjected to column chro-
matography and the desired porphyrin building block 1
or 2 was eluted second with CH Cl /2%CH OH, in 12%
(
N S ) core as the central unit with four peripheral
2 2
normal porphyrin (N ) units, and observed energy
4
transfer from peripheral normal porphyrins to a central
dithiaporphyrin core. We have also reported the syn-
thesis of different types of b-substituted thiapor-
2
2
3
yield. Similarly, the condensation of 1 equiv. of 2,5-
bis(phenyl hydroxymethyl)furan with 2 equiv. of meta
or para-trimethylsilylethynyl benzaldehyde followed by
5
phyrins.
*
0
Corresponding author.
040-4039/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0040-4039(01)01837-8

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D. Kumaresan et al. / Tetrahedron Letters 42 (2001) 8547–8550
Scheme 1. Synthetic scheme for the preparation of 7.
1
Figure 1. H NMR spectrum of 7 recorded in CDCl . (*) indicates solvent impurity. The absorption spectrum of 7 is shown in
3
inset (a). The emission spectra of 7 (solid line) and 1:2 mixture of 4 and BDPY (dashed line) recorded in toluene is shown in inset
(
b).

D. Kumaresan et al. / Tetrahedron Letters 42 (2001) 8547–8550
8549
column chromatography yielded porphyrin building
Acknowledgements
blocks 3 or 5, respectively, in 13% yield. The deprotec-
tion of the trimethylsilyl group by treating 3 or 5 with
K CO in THF–methanol (3:1) gave 4 or 6, respec-
Financial assistance from the Council of Scientific and
Industrial Research and the Department of Atomic
Energy (No. 2001/37/21/BRNS/797), Government of
India to M.R. is gratefully acknowledged.
2
3
tively, in 90% yield. All the porphyrin building blocks
1
were characterized by H NMR, FAB mass and
6
absorption and emission spectroscopies. The building
blocks with iodo- and ethynyl functional groups are
7
ideal to construct light harvesting systems. Thus, the
coupling of 4 with N,N-difluoroboryl-1,9-dimethyl-5-(4-
iodophenyl)dipyrrin (BDPY-I) in toluene/triethylamine
at 35°C in the presence of Pd (dba) and AsPh fol-
References
1. Ravikanth, M.; Chandrashekar, T. K. Struct. Bonding
2
3
3
1
995, 82, 105 and references cited therein.
lowed by column chromatography on silica gel using
8
1
2
. (a) Latos-Grazynski, L.; Lisowski, J.; Olmstead, M. M.;
Balch, A. L. Inorg. Chem. 1989, 28, 1183; (b) Latos-
Grazynski, L.; Lisowski, J.; Olmstead, M. M.; Balch, A. L.
Inorg. Chem. 1989, 28, 3328; (c) Chmielewski, P.;
Grzeszczuk, M.; Latos-Grazynski, L.; Lisowski, J. Inorg.
Chem. 1989, 28, 3546; (d) Latos-Grazynski, L.; Pacholska,
E.; Chmielewski, P. J.; Olmstead, M. M.; Balch, A. L.
Inorg. Chem. 1996, 35, 566; (e) Latos-Grazynski, L.;
Pacholska, E.; Chmielewski, P. J.; Olmstead, M. M.;
Balch, A. L. Angew. Chem., Int. Ed. Engl. 1995, 34, 2252;
CH Cl /15% ethyl acetate gave 7 in 17% yield. The H
2
2
NMR spectrum of 7 is shown in Fig. 1. The furan
protons appeared as a singlet at 9.22 ppm and the three
pyrrole rings of the porphyrin appeared as three sepa-
rate signals indicating the low symmetric nature of the
porphyrin ring. The two pyrrole rings of the BDPY
group gave multiplets at 6.35 and 6.70 ppm, respec-
tively. The FAB mass spectrum showed a molecular ion
peak at 1251 confirming the product. The absorption
spectrum of 7 recorded in CH Cl is shown as an inset
2
2
(
f) Pandian, R. P.; Chandrashekar, T. K. J. Chem. Soc.,
Dalton Trans. 1993, 119.
(
a) in Fig. 1. It showed three Q-bands and one Soret
band. The band at 515 nm, which is mainly due to
BDPY units, is very strong compared to the other two
Q-bands, which are due to the porphyrin ring. The
fluorescence spectra of 7 along with a 1:2 mixture of 4
and BDPY in toluene at an excitation wavelength of
3
. (a) Latos-Grazynski, L.; Olmstead, M. M.; Balch, A. L.
Chem. Eur. J. 1997, 3, 268; (b) Gross, Z.; Saltsman, I.;
Pandian, R. P.; Barzilay, C. M. Tetrahedron Lett. 1997, 38,
383; (c) Sridevi, B.; Narayanan, S. J.; Srinivasan, A.;
Chandrashekar, T. K. J. Chem. Soc., Dalton Trans. 1998,
979; (d) Sridevi, B.; Narayanan, S. J.; Srinivasan, A.;
2
485 nm are presented in Fig. 1 inset (b). As seen from
1
Fig. 1, the mixture of 4 and BDPY recorded at an
excitation wavelength of 485 nm showed emission
mainly due to BDPY, since at this wavelength the
BDPY unit absorbs strongly. When the mixture was
excited at 420 nm, where 4 is the strong absorber,
emission mainly due to 4 was observed. However, in
the case of 7, strong emission was observed due to the
porphyrin unit irrespective of the excitation wave-
length. On excitation of 7 at 485 nm where BDPY
absorbs strongly, the emission was mainly due to the
porphyrin unit (Fig. 1). The emission quantum yield of
the BDPY unit in 7 (0.019) was reduced 10 times from
the free BDPY unit (0.19), whereas the quantum yield
of the porphyrin unit was slightly increased. These
results suggest that there is an efficient energy transfer
from the BDPY unit to the 21-oxoporphyrin unit in 7.
Recently we reported the BDPY appended 21,23-dithia-
porphyrin system in which we failed to observe energy
Reddy, M. V.; Chandrashekar, T. K. J. Porphyrins
Phthalocyanines 1998, 2, 69.
. (a) Ravikanth, M. Tetrahedron Lett. 2000, 41, 3709; (b)
Kumaresan, D.; Agarwal, N.; Ravikanth, M. J. Chem.
Soc., Perkin Trans. 1 2001, 1644.
4
5
6
. Ravikanth, M. Chem. Lett. 2000, 480.
. Spectral data for selected compounds: 1: H NMR
1
(
CDCl , l in ppm) 7.58 (t, 2H, Ar), 7.89 (m, 6H, Ar),
3
8.20–8.39 (m, 8H, Ar), 8.65 (s, 2H, Ar), 8.85 (s, 2H,
b-pyrrole), 9.07 (m, 4H, b-pyrrole), 9.64 (s, 2H, b-furan).
FAB-MS C H N OI calcd av. mass 867.5, obsd m/z
44
27
3
2
868. Anal. calcd: C, 60.9; H, 3.13; N, 4.84. Found: C, 61.1,
H, 3.42; N, 4.58. UV–vis (umax, nm) 421 (119667), 507
(
(
14750), 538 (3434), 613 (2205), 674 (2241). Fluorescence
1
uex=515 nm, in toluene) 677, 745 (ƒ=0.0062). 3:
H
NMR (CDCl , l in ppm) 0.39 (s, 18H, CH ), 7.68 (t, 2H,
3
3
Ar), 7.79 (m, 6H, Ar), 7.89 (d, 2H, Ar), 8.10 (d, 2H, Ar),
8
8
.19 (d, 4H, Ar), 8.31 (s, 2H, Ar), 8.57 (m, 4H, b-pyrrole),
9
transfer from BDPY to 21,23-dithiaporphyrin. Thus,
.85 (s, 2H, b-pyrrole), 9.20 (s, 2H, b-furan). FAB-MS
by changing the heteroatom from sulfur to oxygen in
the porphyrin core, the energy transfer dynamics were
altered. A detailed photophysical study is needed to
understand these observations.
+
C H N Si O calcd av. mass, 808.1, obsd m/z 808 (M ).
54
45
3
2
Anal. calcd: C, 80.1; H, 5.61; N, 5.19. Found: C, 79.3, H,
.90; N, 5.42. UV–vis (umax, nm) 423 (128567), 444
46728), 507 (18110), 538 (3687), 612 (2601), 673 (2753).
5
(
Fluorescence (u =515 nm, in toluene) 677, 745 (ƒ=
ex
1
In conclusion, we have synthesized 21-oxoporphyrin
building blocks containing iodo- and ethynyl functional
groups. We have also shown the use of porphyrin
building blocks in the construction of energy donor
appended systems. The building blocks reported in this
paper are useful for the synthesis of unsymmetrical
porphyrin arrays containing 21-oxoporphyrin and nor-
0.037). 4: H NMR (CDCl , l in ppm) 3.20 (s, 2H, CCH),
3
7.75 (m, 8H, Ar), 7.91 (m, 2H, Ar), 8.18 (m, 6H, Ar), 8.32
(s, 2H, Ar), 8.57 (m, 4H, b-pyrrole), 8.86 (m, 2H, b-
pyrrole), 9.20 (s, 2H, b-furan). FAB-MS C H N O calcd
48
29
3
av. mass, 663.7, obsd m/z 664. Anal. calcd: C, 86.8; H,
4.40; N, 6.35. Found: C, 85.9, H, 4.39; N, 6.18. UV–vis
(umax, nm) 421 (171856), 443 (33833), 507 (16747), 538
mal porphyrin (N ) units and such studies are presently
under investigation in our laboratory.
(4930), 612 (2716), 674 (2456). Fluorescence (u =485 nm,
in toluene) 677, 745 (ƒ=0.037).
4
ex

8
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D. Kumaresan et al. / Tetrahedron Letters 42 (2001) 8547–8550
7
8
. Ravikanth, M.; Strachan, J. P.; Li, F.; Lindsey, J. S.
130.3, 130.5, 131. 5, 134.4, 137.49, 142.0, 157.9. FAB-MS
Tetrahedron 1998, 37, 2358.
C H N OB F calcd av. mass 1252.2, obsd m/z 1251.
82
55
7
2 4
1
. Data for compound 7: H NMR (CDCl , l in ppm) 1.25
Anal. calcd: C, 78.6; H, 4.42; N, 7.86. Found: C, 77.8, H,
4.35; N, 7.78. UV–vis (umax, nm) 425 (180539), 443
(34207), 515 (150228), 611 (3896), 673 (3895). Fluorescence
3
(
s, 12H, CH ), 6.35 (m, 4H, BDPY pyrrole), 6.70 (m, 4H,
3
BDPY pyrrole), 7.48 (m, 4H, Ar), 7.67 (m, 4H, Ar), 7.78
m, 8H, Ar), 7.99 (m, 2H, Ar), 8.21 (m, 6H, Ar), 8.42 (s,
(
(u =485 nm, in toluene) 542, 678, 746 nm (ƒBDPY=0.019,
ex
2
9
H, Ar), 8.65 (d, 2H, b-pyrrole), 8.93 (s, 2H, b-pyrrole),
ƒporphyrin=0.038).
9. Ravikanth, M.; Agarwal, N.; Kumaresan, D. Chem. Lett.
2000, 836.
13
.22 (s, 2H, b-furan). C NMR (77.1 MHz, CDCl , l in
3
ppm) 15.02, 29.79, 119.66, 121.6, 125.1, 127.1, 128.4,