A simple synthesis of pyridine-tethered porphyrins

Article abstract of DOI:10.1016/S0040-4039(00)01110-2

Zinc porphyrin 4, in which a pyridine ligand is tethered to the 3-position of a meso-phenyl substituent via a nine-atom spacer, has been synthesised and is found to exist as the intramolecularly bound complex in solution. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01110-2

Tetrahedron Letters 41 (2000) 6655±6656
A simple synthesis of pyridine-tethered porphyrins
Andrew N. Cammidge* and Karen M. Lifsey
School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Received 26 May 2000; accepted 29 June 2000
Abstract
Zinc porphyrin 4, in which a pyridine ligand is tethered to the 3-position of a meso-phenyl substituent via
a nine-atom spacer, has been synthesised and is found to exist as the intramolecularly bound complex in
solution. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: porphyrins; pyridines.
Metalloporphyrins which bear tethered ligands capable of reversible binding to the central metal
1
ion are potentially important as synthetic mimics of biological catalysts (such as cytochromes) and
as sensors. With the latter application in mind, we sought a straightforward synthesis of pyridine-
tethered porphyrins which could be easily adapted to in¯uence the intramolecular binding. A few
examples of such tethered porphyrins are known.1 However, a simple molecular model indicated
that novel porphyrin 4, in which a pyridine is attached to the 3-position of a meso-phenyl group
via a nine-atom spacer, would form a relatively strain-free intramolecular complex. More
importantly, it was envisaged that 4 could be easily synthesised by a general procedure and
modi®cation would allow access to a range of derivatives.
,2
Porphyrin 4 was synthesised as shown in Scheme 1. Sodium was dissolved in 1,6-hexane diol
and the alkoxide solution treated with 4-picolyl chloride. The resulting alcohol 1 was coverted to
the chloride 2, using thionyl chloride, and used to alkylate mono-hydroxy porphyrin 3 (made by a
3
statistical condensation of pyrrole with benzaldehyde and 3-hydroxybenzaldehyde ). Metallation
4
4
with zinc acetate a€orded tethered porphyrin 4. Monomethoxy porphyrin 5 was also prepared
by methylation and metallation of 3.
The absorption spectrum of model porphyrin 5 undergoes changes typical for zinc porphyrins5
(
lmax=419 nm in CH Cl , l =428 nm when fully complexed with pyridine in CH Cl2
2
2
max
2
(pK=3.8)). The absorption spectrum for 4 is essentially identical to that of the 5:pyridine com-
plex. The spectrum is not concentration dependent, implying that 4 exists as the intramolecularly
*
Corresponding author. E-mail: a.cammidge@uea.ac.uk
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01110-2

6656
Scheme 1. Reagents and conditions: (i) HO(CH
acid, re¯ux 30 min (5%); (iv) K CO , TBAI, MEK, re¯ux 12 h (92%); (v) zinc acetate, DMF (93%); (vi) K
CH ) SO , TBAI, MEK, re¯ux 12 h (74%); (vii) zinc acetate, DMF (91%)
2
)
6
ONa/HO(CH
2
)
6
OH (74%); (ii) SOCl
2
, CH
2
Cl
2
(54%); (iii) propionic
2
3
2
CO
3
,
(
3
2
4
1
complexed species. This deduction is supported by the H NMR spectrum of 4, which shows the
pyridine hydrogens shielded by the porphyrin ring current.4
The use of this and related derivatives for sensor applications and catalysis is currently being
explored.
Acknowledgements
We thank the EPSRC for support (K.M.L.) and the EPSRC Mass Spectrometry Service Centre
at Swansea for accurate mass measurements.
References
1
2
3
4
. D'Souza, F.; Hsieh, Y.-Y.; Deviprasad, G. R. Inorg. Chem. 1996, 35, 5747±5749 and references therein.
. Takahashi, K.; Terashima, T.; Komura, T.; Imanaga, H. Bull. Chem. Soc. Jpn. 1989, 62, 3069±3074.
. Maiya, G. B.; Krishnan, V. J. Phys. Chem. 1985, 89, 5225±5235.
ꢀ
. Selected characterisation data. Compound 4: m.p. 197±200 C; ꢀ
H
(300 MHz, CDCl
J 6.3 Hz, pyridine-H2,6), 2.92 (2H, t, J 5.6 Hz), 3.49 (2H, s), 3.87 (2H, t, J 7.6 Hz), 5.48 (2H, d, J 6.3 Hz, pyridine-
3
) 1.4±1.8 (8H, m), 2.40 (2H, d,
H
3,5), 7.23 (1H, m), 7.55±7.75 (11H, m), 8.12±8.28 (7H, m), 8.8±8.9 (8H, m); acc. mass (FAB) found 884.3036
ꢀ
(
M+H), C56
H
46
5
N O
2
Zn=884.2943. Compound 5: m.p. >290 C; ꢀ
H
(300 MHz, CDCl
3
) 3.98 (3H, s), 7.33 (1H, dd,
J 8.2 Hz, 2.6 Hz), 7.64 (1H, t, J 7.4 Hz), 7.72±7.84 (11H, m), 8.20±8.26 (6H, m), 8.94±9.02 (8H, m); acc. mass
FAB) found 707.1812 (M+H), C45 OZn=707.1789.
. Whitten, D. G.; Lopp, I. G.; Wildes, P. D. J. Am. Chem. Soc. 1968, 90, 7196±7200.
(
31 4
H N
5