Synthesis of 5,10,15,20-meso-unsubstituted and
5,10,15,20-meso-substituted-21,23-ditellura/
diselena core-modified porphyrinogens: oxidation
and detection of mercury(II)†
Sohail Ahmad, Kumar Karitkey Yadav, Sarangthem Joychandra Singh
and S. M. S. Chauhan
*
Tellurium and selenium incorporated 5,10,15,20-meso-unsubstituted-21,23-ditellura/diselena core-
modified porphyrinogens (N
2
Te
2
and N
2
Se
2
), 5,10,15,20-meso-unsubstituted-21-tellura/selena core-
modified porphyrinogens (N
3
Te and N
3
Se) and fully substituted meso-carbons porphyrinogens
(N
2
Te
2
, N
2
Se
2
and higher analogs) are synthesized by 3 + 1 condensation of tellurophene/
selenophene dipyrranes and their corresponding diols in the presence of BF
3
–etharate or BF
3
–
methanol. The meso-unsubstituted and substituted porphyrinogens were oxidized with chloranil/0.1%
aqueous FeCl
3
in CHCl
3
at room temperature to obtain the corresponding porphines and porphyrins
which are further reduced to corresponding chlorin and bacteriochlorin, whereas the fully meso-
substituted porphyrinogens were found to be good ligands for Hg
2+
. The structures of the products
were characterized by IR,
1
H,
13
C,
125
Te,
77
Se NMR, CHN analysis, mass spectrometry and single-
crystal XRD.
Introduction
Porphyrinogens (calixpyrroles) are a class of tetrapyrrolic mac-
rocycles composed of four pyrrole rings linked through the
meso-positions by carbon atoms. The b- and meso-positions in
porphyrinogens are reactive positions at which suitable
substituents can be introduced to tune the properties of the
porphyrinogens for specic applications. Fully meso-substituted
porphyrinogens are stable and have been used in anion
binding,
1
detection of various explosive
1f
and self-assembly,
1
while meso-unsubstituted porphyrinogens have remained
unexplored due to unstability and complexity in synthesis.
2
Meso-unsubstituted porphyrinogens are highly desirable
synthetic precursors for the construction of meso-unsubstituted
porphines
3,4
and other complex systems with special physical
and chemical properties.
3b,5
Porphines/porphyrins of porphyri-
nogens are used as a starting material for various newer
porphyrins.
5
These are further utilized for the synthesis of
longer-wavelength absorbing
5c–e
and uorescing molecules such
as chlorins, bacteriochlorins and purpurins which are poten-
tially used as uorescence imaging or phototherapeutic
agents.
5f–i
A wide variety of porphyrinogens with donor atoms (O, S, N
and P) containing nonpyrrolic arene units,
6–9
have been
designed and synthesized to modify the binding ability of the
porphyrinogens. The 5,10,15,20-meso-octamethyl-21,23-dithia-
porphyrinogen (N
2
S
2
) and 5,10,15,20-meso-octamethyl-21-thia-
porphyrinogen (N
3
S) ligands containing nitrogen–sulfur donor
atoms are highly selective complexing agents towards heavy
transition metal ions (Hg
II
, Cd
II
and Ag
I
).
10
Therefore, a similar
development is anticipated for the porphyrinogen with heavier
chalcogen donor atoms such as selenium and tellurium, due to
their ‘soness’ and better sigma-donor capacity as compared to
the lighter group 16 congeners.
11
The synthesis of selenium and
tellurium 21- and 21,23-core-modied porphyrins,
12,3b
in which
one or more heteroatoms replace some of the four nitrogen
atoms, has been already reported with altered core sizes, metal
ion binding properties,
12
reactivity
12
and redox potentials.
12
Herein we report the synthesis of novel meso-unsubstituted
Te/Se core-modied porphyrinogens and meso-substituted Te/
Se core-modied porphyrinogens via acid catalyzed 3 + 1
condensation of corresponding tellurophene/selenophene
dipyrranes and diols. The meso-unsubstituted porphyrinogens
are further oxidized to their corresponding porphyrins and
porphines, whereas the meso-substituted porphyrinogens were
utilized for the complexation of Hg
2+
.
Bio-organic Research Laboratory, Department of Chemistry, University of Delhi,
Delhi-110 007, India. E-mail: smschauhan@chemistry.du.ac.in; Fax: +91-11-
27666845; Tel: +91-11-27666845; +91-9871969266
† Electronic supplementary information (ESI) available:
1
H and
13
C NMR spectra
of all new compounds.
125
Te and
77
Se NMR spectra of all porphyrinogens. UV-Vis
spectra of porphyrinogens in the presence of Hg
2+
.
125
Te,
77
Se NMR of 5g and 5h in
the presence of Hg
2+
. CCDC 932049. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c3ra46491a
Cite this: RSC Adv. , 2014, 4, 3171
Received 8th November 2013
Accepted 2nd December 2013
DOI: 10.1039/c3ra46491a
www.rsc.org/advances
This journal is © The Royal Society of Chemistry 2014 RSC Adv., 2014, 4, 3171–3180 | 3171
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