SnIV porphyrin scaffolds for axially bonded multiporphyrin arrays: Synthesis and structure elucidation by NMR studies

Article abstract of DOI:10.1002/chem.201304344

A simple, one-step, supramolecular strategy was adopted to synthesize Sn^IV-porphyrin-based axially bonded triads and higher oligomers by using meso-pyridyl Sn^IV porphyrin, meso-hydroxyphenyl-21,23- dithiaporphyrin, and Ru^II porphyrin as building blocks and employing complementary and non-interfering Sn^IV-O and Ru^II...N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. ¹H, ¹H-¹H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn^IV-porphyrin-based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady-state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn^IV porphyrin to the axial 21,23-dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru ^II porphyrin unit(s), which quench the fluorescence of the Sn ^IV porphyrin and 21,23-dithiaporphyrin units. Supramolecular arrays consisting of up to seven porphyrin units (see figure) were prepared on the basis of Sn^IV porphyrins by stepwise and one-pot synthetic strategies and their structures elucidated by detailed NMR spectroscopic studies.

Full text of DOI:10.1002/chem.201304344

DOI: 10.1002/chem.201304344
Full Paper
&
Porphyrins
SnIV Porphyrin Scaffolds for Axially Bonded Multiporphyrin
Arrays: Synthesis and Structure Elucidation by NMR Studies
Avanish Dvivedi, Yogita Pareek, and Mangalampalli Ravikanth*[a]
Abstract: A simple, one-step, supramolecular strategy was
adopted to synthesize SnIV-porphyrin-based axially bonded
triads and higher oligomers by using meso-pyridyl SnIV por-
phyrin, meso-hydroxyphenyl-21,23-dithiaporphyrin, and RuII
porphyrin as building blocks and employing complementary
and non-interfering SnIVÀO and RuII···N interactions. The mul-
tiporphyrin arrays are stable and robust and were purified
by column chromatography. 1H, 1H–1H COSY and NOESY
NMR spectroscopic studies were used to unequivocally
deduce the molecular structures of SnIV-porphyrin-based
triads and higher oligomers. Absorption and electrochemical
studies indicated weak interaction among the different por-
phyrin units in triads and higher oligomers, in support of the
supramolecular nature of the arrays. Steady-state fluores-
cence studies on triads indicated the possibility of energy
transfer in the singlet state from the basal SnIV porphyrin to
the axial 21,23-dithiaporphyrin. However, the higher oligo-
mers were weakly fluorescent due to the presence of heavy
RuII porphyrin unit(s), which quench the fluorescence of the
SnIV porphyrin and 21,23-dithiaporphyrin units.
were treated with RuII porphyrins to construct dyad to pentad
based on RuII–pyridyl N interactions, and their photophysical
properties were investigated.[20–24] In continuation of our stud-
ies on SnIV-porphyrin-based multiporphyrin arrays, herein we
used meso-pyridyl SnIV porphyrins containing one to four
meso-pyridyl groups as scaffolds to construct multiporphyrin
arrays such as tetrad 1, pentad 2, hexad 3 and heptad 4. In
SnIV-porphyrin-based arrays 1–4, the 21,23-dithiaporphyrins are
used as axial ligands that are connected to the SnIV center
through SnIV–O interactions, and the RuII porphyrins as periph-
eral ligands that are connected to meso-pyridyl group(s) of SnIV
porphyrin through RuII···N interactions. Multiporphyrin arrays
1–4 were synthesized by a two- or one-step approach. In the
two-step approach, we first synthesized triads 5–8 by treating
one equivalent of SnIV porphyrins 9–12 with two equivalents
of 21,23-dithiaporphyrin 13; in the second step, triads 5–8
were treated with a stoichiometric amount of RuTPP(CO)(EtOH)
(14) to afford multiporphyrin arrays 1–4. In the one-step ap-
proach, the three porphyrin building blocks, that is, SnIV por-
phyrins 9–12, 13 and 14, reacted in stoichiometric ratio to
afford multiporphyrin arrays 1–4. We found that the one-step
approach was more convenient and beneficial than the two-
step approach. Multiporphyrin arrays 1–4 are robust and
stable under the conditions of column-chromatographic purifi-
cation. Generally, SnIV-porphyrin-based multiporphyrin arrays
reported in the literature[8] were not purified by column chro-
matography and were generated in NMR tubes for structure
elucidation. Although our arrays were not sufficiently stable to
obtain molecular-ion peaks under mass-spectrometric condi-
tions, the molecular structures of triads 5–8 and higher oligo-
mers 1–4 were unequivocally elucidated by 1D and 2D NMR
studies. The spectral, electrochemical and photophysical prop-
erties of these multiporphyrin arrays are also described.
Introduction
Tin(IV) porphyrins are ideal scaffolds for the construction of ax-
ially bonded multiporphyrin arrays because of their unique
characteristic features, such as strong affinity toward oxygen-
donor ligands.[1] This oxygen affinity of SnIV in combination
with the affinity of RuII, ZnII and RhIII for nitrogen has been
used by Sanders et al., Maiya et al. and others for the construc-
tion of novel multiporphyrin supramolecular structures.[2–14]
Most of the axially bonded SnIV-porphyrin-based porphyrin
arrays reported in the literature contain only tetrapyrrolic por-
phyrins/metalloporphyrins as axial ligands, but limited reports
are available on SnIV-porphyrin-based multiporphyrin arrays in
which other porphyrinoids, such as modified porphyrins and
expanded porphyrins, have been used as axial ligands. We re-
cently reported triads[15] containing thiaporphyrins as axial li-
gands and tetrads[16] containing expanded core-modified por-
phyrins as axial ligands. Recently, we also reviewed the synthe-
sis and properties of SnIV-porphyrin-based multiporphyrin as-
semblies reported till now to emphasize their importance for
various applications and also to encourage more research on
novel SnIV-porphyrin-based arrays.[17] It is well established that
meso-pyridyl porphyrins are ideal building blocks for the con-
struction of noncovalent multiporphyrin arrays.[18,19] For exam-
ple, porphyrins containing one to four meso-pyridyl groups
[a] A. Dvivedi, Y. Pareek, Prof. M. Ravikanth
Department of Chemistry
Indian Institute of Technology Bombay
Powai, Mumbai 400 076 (India)
E-mail: ravikanth@chem.iitb.ac.in
Supporting information (MS data, NMR data and absorption and emission
spectra for all compounds) for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304344.
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Results and Discussion
were synthesized by treating SnIV porphyrins 9–12 with 13 in
1:2 ratio in refluxing benzene for 12–24 h (Scheme 1). Accord-
ing to our experience, such reactions cannot be monitored by
TLC analysis on silica gel or by absorption spectroscopy, since
the axially bonded triads are generally unstable on silica, and
absorption spectroscopy always shows the features of both
constituent porphyrin monomers. The crude compounds were
purified by column chromatography on alumina with CH2Cl2/
1–5% acetone as eluent and recrystallized from CH2Cl2/hexane
to afford pure triads 5–8 in 55–65% yield. The MALDI-TOF
mass spectra of triads 5–8 showed peaks corresponding to
MÀ(O-dithiaporphyrin), which are characteristic of such axially
bonded triads.[1] We carried out detailed 1D and 2D NMR stud-
ies on triads 5–8 to deduce their molecular structures. The
1H NMR spectra of triad 7 and its corresponding monomers 11
The required SnIV derivatives of 5-(4-pyridyl)10,15,20-tris(p-ani-
syl)porphyrin (9), 5,15-bis(4-pyridyl)-10,20-bis(p-anisyl)porphyrin
(10), 5,10,15-tris(4-pyridyl)-20-(p-anisyl)porphyrin (11) and
5,10,15,20-tetrakis(4-pyridyl)porphyrin (12) were prepared by
treating the appropriate meso-pyridyl porphyrins with
SnCl2·2H2O under standard reaction conditions.[25] The other re-
quired porphyrin building blocks, 5-(4-hydroxyphenyl)-
10,15,20-triphenyl-21,23-dithiaporphyrin (13) and RuTPP(CO)-
(EtOH) (14) were prepared by following the reported proce-
dures.[15]
Synthesis of and NMR studies on triads 5–8
To prepare the SnIV-porphyrin-based arrays 1–4, we first at-
tempted to synthesize the appropriate triads 5–8. Triads 1–4
1
and 13 are compared in Figure 1a, and a partial H–1H COSY
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of 8.67–8.70 ppm. In triad 7, the
axial
dithiaporphyrin
unit
showed three sets of signals at
9.62 (type a), 9.54 (type a’) and
9.37 ppm (type a’’) for four b-
thiophene protons and three
sets of signals at 8.63 (type b),
8.49 (type c) and 8.03 ppm
(type c’) for four b-pyrrole pro-
tons. In triad 7, the thiophene
protons of type a and pyrrole
protons of type b of the axial
21,23-dithiaporphyrin
unit,
which are remote from the cen-
tral SnIV porphyrin unit, ap-
peared in the most downfield
region, whereas the type a’ and
a’’ protons of thiophene and
type c and c’ protons of pyrrole,
which face towards the basal
SnIV porphyrin, appeared in an
upfield region due to the ring-current effect of the SnIV por-
phyrin. The meso-aryl protons of both basal SnIV porphyrin and
axial 21,23-dithiaporphyrin units in triad 7 also experienced
slight upfield or downfield shifts. For example, the 2,6-protons
of the meso-pyridyl group, which appeared in the region of
9.10–9.17 ppm in 11, were shifted upfield in triad 7 and ap-
peared in the region of 8.97–8.99 ppm, whereas the 3,5-pro-
tons of the meso-pyridyl group, which appeared at 8.28 ppm
in 11, were shifted slightly downfield and appeared in the
region of 8.34–8.37 ppm in triad 7. However, the most promi-
nent ring-current effects were observed for phenoxyl groups
of the 21,23-dithiaporphyrin units that were bound to the SnIV
center in triad 7. In monomeric 21,23-dithiaporphyrin 13, the
2,6- and 3,5-protons of the hydroxyphenyl group appeared as
two doublets at 7.28 and 8.12 ppm, respectively. In triad 7,
these protons are affected by both the inherent deshielding
effect of the axial 21,23-dithiaporphyrin unit and the shielding
effect of the basal SnIV porphyrin unit and appear at 2.43 ppm
and 6.66 ppm, respectively, as revealed by the proton-connec-
Scheme 1. Synthesis of triad 5.
spectrum of triad 7 is shown in Figure 1b. The protons were
assigned on the basis of the resonance position, integrated in-
1
tivity pattern in the H–1H COSY spectrum shown in Figure 1b.
1
tensity and proton-to-proton connectivity revealed in the H–
The other triads 5, 6 and 8 also showed similar NMR features,
and the protons were identified by 1D and 2D NMR spectros-
copy. Thus, NMR spectroscopy is very useful technique to con-
firm the formation of triads 5–8.
1H COSY spectra to elucidate the structures of triads 5–8. Fig-
ure 1a reveals that certain protons of the basal SnIV porphyrin
and axial 21,23-dithiaporphyrin in triad 7 experienced shifts be-
cause of the ring-current effect of the adjacent porphyrins and
appeared in different regions than in corresponding monomer-
ic SnIV porphyrin 11 and 21,23-dithiaporphyrin 13. The SnIV por-
phyrin monomer 11 showed two sets of signals for eight b-
pyrrole protons: a doublet at 9.27 ppm corresponding to two
protons and a multiplet in the 9.10–9.17 ppm region corre-
sponding to six protons. In triad 7, these protons of the SnIV
porphyrin unit experienced shifts and appeared as a doublet
at 8.95 ppm and a multiplet in the 9.40–9.42 ppm region, re-
spectively. Similarly, 21,23-dithiaporphyrin 13 showed one set
of signals for four b-thiophene protons in the region of 9.67–
9.72 ppm and one set for four b-pyrrole protons in the region
Synthesis of and NMR studies on multiporphyrin arrays 1–4
We attempted to synthesize the desired multiporphyrin arrays
1–4 by stepwise and one-pot synthetic approaches
(Scheme 2). In the stepwise approach, tetrad 1 was synthesized
by treating one equivalent of triad 5 with one equivalent of
RuTTP(CO)(EtOH) (14) in CHCl3 at room temperature with stir-
ring for two days, followed by column chromatography on
basic alumina, which afforded pure tetrad 1 as a purple solid
in 60% yield. We also synthesized tetrad 1 in a one-step reac-
tion by treating one equivalent of SnIV porphyrin 9 with two
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equivalents of 21,23-dithiaporphyrin building block
13 and one equivalent of 14 in benzene at reflux for
24 h to afford pure tetrad 1 in 60% yield. Although
both approaches yielded the desired tetrad 1 in
decent yield, we used the one-step approach to syn-
thesize the other multiporphyrin arrays 2–4, because
it was economically beneficial compared to the two-
step approach. Thus, treatment of one equivalent of
SnIV porphyrins 10–12 with two equivalents of 13
and one equivalent of 14 in refluxing benzene for 2–
7 d followed by chromatographic purification on an
alumina column and recrystallization afforded multi-
porphyrin arrays 2–4 as dark purple solids in 60–70%
yield.
The 1H NMR, COSY, and NOESY spectra of tetrad
1 are presented in Figure 2, and the relevant data for
multiporphyrin arrays 1–4 and their corresponding
triads 5–8 are presented in Table 1. We attempted to
identify all resonances of the three porphyrin sub-
units in arrays 1–4 that experienced porphyrin ring-
current effects and were shifted upfield or downfield
on the basis of the resonance position, integrated in-
1
tensity data and coupling constants in H NMR spec-
tra as well as the proton-to-proton connectivity infor-
mation revealed in the COSY and NOESY spectra. The
formation of tetrad 1 to heptad 4 was clearly evident
in the large upfield shifts observed for meso-phen-
oxyl group of the axial 21,23-dithiaporphyrin unit,
which coordinated to the SnIV
porphyrin through SnIVÀO inter-
action, and the meso-pyridyl pro-
tons of the SnIV porphyrin, which
coordinated to the RuII porphy-
rin through RuII···N interactions.
For example, in monomeric
21,23-dithiaporphyrin 13, the
2,6- and 3,5-protons of the
meso-hydroxyphenyl group ap-
peared as two sets of doublets
at 7.28 and 8.12 ppm, respec-
tively. However, as mentioned
for triads 5–8, on coordination
of 21,23-dithiaporphyrin 13 to
the SnIV porphyrin through
a meso-phenoxyl group, the 2,6-
and 3,5-protons of the meso-
phenoxyl group experienced up-
field shifts and appeared at
about 2.44 and about 6.66 ppm,
respectively, due to the strong
ring-current effect of the SnIV
porphyrin. Furthermore, in arrays
1–4, on coordination of the RuII
porphyrin to the meso-pyridyl N
atoms of the basal SnIV porphy-
rin unit, the 2,6 and 3,5-protons
Figure 1. a) 1H NMR spectra of triad 7 (i) and its corresponding monomers 11 (ii) and 13
1
(iii). b) Partial H–1H COSY spectrum of 7 showing the connectivity between 2,6- and 3,5-
aryl protons.
Scheme 2. Synthesis of tetrad 1 by stepwise (method 1) and one pot (method 2) synthetic approaches.
of the meso-phenoxyl group ex-
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significant shifts observed for 2,6- and 3,5-pyridyl protons and
2,6- and 3,5-phenoxyl protons because of ring-current effects,
the pyrrole protons of the basal SnIV porphyrin and pyrrole/
thiophene protons of the axial 21,23-dithiaporphyrin also expe-
rienced ring-current effects and appeared at downfield/upfield
positions in arrays 1–4. The detailed proton assignments for
arrays 1–4 were carried out by means of 1D and 2D NMR stud-
ies, and the analytical approach is exemplified here for tetrad
1.
In tetrad 1, we took the meso-anisyl OCH3 protons of the
SnIV porphyrin into consideration and followed their NOE corre-
lations. The OCH3 protons of meso-anisyl group of the SnIV por-
phyrin appeared as two singlets at 3.78 and 3.81 ppm, which
were assigned as type n and m, respectively, on the basis of in-
tensity and number of protons. Both type m and type n OCH3
protons showed nuclear Overhauser effects (NOEs) with a mul-
tiplet observed in the 7.01–7.04 ppm region, which we recog-
nized as type i aryl protons. The multiplet in the 7.01–
7.04 ppm (type i) region showed cross-peak correlation with
a resonance in the 8.06–8.10 ppm region corresponding to
two protons and a resonance in the 8.15–8.17 ppm region cor-
responding to four protons, which we identified as type i’’ and
type i’ meso-aryl protons, respectively, of the SnIV porphyrin.
The type i’ protons in the 8.15–8.17 ppm region showed NOE
correlation with a doublet at 9.04 ppm and doublet at
9.26 ppm, which were identified as type f and type e pyrrole
protons, respectively, of the SnIV porphyrin. The type f protons
at 9.04 ppm showed cross-peak correlation in the COSY spec-
trum with a multiplet resonance in the 7.84–7.87 ppm region,
which in turn showed NOE correlation with a doublet reso-
nance at 6.38 ppm corresponding to 3,5-pyridyl protons. Thus,
the multiplet resonance in the 7.84–7.87 ppm region was as-
signed to type g protons of the SnIV porphyrin. Similarly, the
resonance at 9.30 ppm was identified as type d pyrrole protons
of the SnIV porphyrin, since it showed NOE correlation with
a type i’’ resonance multiplet in the 8.06–8.10 ppm region and
also showed cross-peak correlation with type e protons at
9.26 ppm in the COSY spectrum. The axial 21,23-dithiaporphy-
rin protons were also identified on the basis of their location,
coupling constants and correlations in COSY and NOESY spec-
tra. The type a and type b protons of the axial 21,23-dithiapor-
phyrin unit, which are remote from the ring-current effect of
SnIV porphyrin, appeared as singlets at 9.62 and 8.63 ppm re-
spectively.
1
Figure 2. a) 1H NMR spectrum of tetrad 1, b) partial H–1H COSY spectrum of
tetrad 1, and c) partial H–1H NOESY spectrum of tetrad 1 recorded in CDCl3.
1
perienced slight upfield shifts compared to triads 5–8, but the
largest upfield shifts were observed for the 2,6- and 3,5-pro-
tons of the meso-pyridyl group due to the strong ring-current
effect of the RuII porphyrin on the meso-pyridyl protons of the
SnIV porphyrin. In triads 5–8, the 2,6-protons of the meso-pyrid-
yl protons, which appeared at about 8.95 ppm, were shifted
upfield in the corresponding arrays 1–4 and appeared in the
range of 1.75 to 2.06 ppm. Similarly, the meso-pyridyl 3,5-pro-
tons, which appeared at about 8.35 ppm in triads 5–8, were
shifted upfield and appeared in the region of 5.73 to 6.38 ppm
in arrays 1–4. These protons were clearly identified by cross-
peak analysis of the H–1H COSY spectrum. In addition to clear
1
Table 1. 1H NMR data of selected protons for oligomers 1–4 and their corresponding triads 5–8 recorded in CDCl3.
Compound
2,6-Ar
2,6-py
3,5-Ar
3,5-py
SnP type i
N2S2P type c’
N2S2P type c
N2S2P type a’’
N2S2P type a’
5
6
7
8
1
2
3
4
2.46 (d)
2.45 (d)
2.43 (d)
2.41 (d)
2.10 (d)
1.63 (d)
1.23 (d)
0.85 (d)
8.95 (d)
8.93 (d)
8.99 (m)
8.96 (d)
2.06 (d)
1.97 (d)
1.89 (d)
1.75 (d)
6.64 (d)
6.66 (d)
6.66 (d)
6.68 (d)
6.42 (d)
6.12 (d)
5.96 (d)
5.68 (d)
8.31–8.36 (m)
8.35 (d)
8.34–8.37 (m)
8.36 (d)
6.38 (d)
6.24 (d)
7.17–7.22 (m)
7.19 (d)
7.18 (d)
8.03 (d)
8.04 (d)
8.03 (d)
8.04 (d)
7.84–7.87 (m)
7.60–7.65 (m)
7.37–7.45 (m)
7.01 (d)
8.45 (d)
8.47 (d)
8.49 (d)
8.51 (d)
8.39 (d)
8.35 (d)
8.32–8.34 (m)
8.35–8.36 (m)
9.31 (d)
9.02 (d)
9.37 (d)
7.78–7.81 (m)
8.86 (d)
8.59–8.70 (m)
8.32–8.34 (m)
7.87–7.92 (m)
9.47 (d)
9.43 (d)
9.54 (d)
8.16–8.23 (m)
9.34 (d)
9.23 (d)
9.13 (d)
8.97 (d)
7.01–7.04 (m)
6.83 (d)
7.53 (d)
5.93 (d)
5.73 (d)
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The 3,5-protons of the meso-phenoxyl group, which ap-
peared at 6.42 ppm, showed NOE correlation with a multiplet
resonance in the 7.84–7.87 ppm region and also with a doublet
resonance at 8.86 ppm, which were recognized as type c’ and
type a’’ protons of the 21,23-dithiaporphyrin unit. The resonan-
ces at 8.39 ppm and 9.34 ppm were due to type c and type a’
protons, respectively, as these resonances showed cross-peak
21,23-dithiaporphyrin unit in tetrad 1, which appeared as
a multiplet resonance in the 7.84–7.87 ppm region, experi-
enced an upfield shift with increasing number of RuTPP(CO)
units and appeared at 7.01 ppm in heptad 4. Similarly, the thio-
phene protons of type a’’ appearing at 8.86 ppm in tetrad
1 were shifted upfield and appeared as multiplet in the 7.87–
7.92 ppm region in heptad 4. Thus, NMR studies revealed that
the protons of the basal SnIV porphyrin and axial 21,23-dithia-
porphyrin units in tetrad 1 to heptad 4 were sensitive to the
number of RuTPP(CO) units and experienced upfield shifts with
increasing number of RuTPP(CO) units.
1
correlations with type c’ and type a’’ resonances in the H–1H
COSY spectrum. The eight pyrrole protons (type h) of the
RuTPP unit in tetrad 1 appeared as a singlet at 8.69 ppm and
showed a slight downfield shift compared to its corresponding
1
1
monomer 14. Thus, H NMR, H–1H COSY, and NOESY NMR are
very useful to identify all relevant resonances of the three por-
phyrin units in tetrad 1 that were shifted due to ring-current
effects of porphyrin units. A similar approach was used to char-
acterize pentad 2, hexad 3 and heptad 4. However, the chemi-
cal shifts of certain protons of the basal SnIV porphyrin unit
and axial 21,23-dithiaporphyrin units, as well as the connector
protons of the meso-aryl and meso-pyridyl groups, experienced
upfield shifts as the number of RuTPP(CO) units increased from
one in tetrad 1 to four in heptad 4. A comparison of the
1H NMR spectra of tetrad 1, pentad 2, hexad 3 and heptad 4 is
presented in Figure 3, and the relevant data along with those
Absorption, electrochemical and photophysical properties of
triads 5–8 and higher oligomers 1–4
The absorption spectra of triads 5–8 and higher oligomers 1–4
were recorded in CH2Cl2, and the data are tabulated in Table 2.
The absorption spectra of triad 7 and its corresponding higher
oligomer, hexad 3, are shown in Figure 4a. The absorption
spectra of triads 5–8 showed features corresponding to the
monomers, and the spectra appear to be almost superimposi-
tions of those of the corresponding monomers with slight
shifts in their peak maxima. For example, triad 7 showed two
Soret bands at 426 and 437 and five Q bands at 516, 557, 600,
629 and 700 nm. The bands at 426 and 600 nm are due to the
SnIV porphyrin, those at 437, 516, 629 and 700 nm are due to
the 21,23-dithiaporphyrin unit and that at 557 nm is due to
both porphyrin units. The other triads 5, 6 and 8 also showed
similar features, and this indicates that the SnIV porphyrin and
21,23-dithiaporphyrin units interact weakly and retain their
characteristic absorption features in triads. The absorption
spectra of higher oligomers 1–4 showed the additional absorp-
tion features of the RuIITPP unit in addition to those of the SnIV
porphyrin and 21,23-dithiaporphyrin units (Figure 4b). The ab-
sorption spectrum of hexad 3 (Figure 4b) shows an additional
band at 412 nm in the Soret region corresponding to the
Figure 3. 1H NMR spectra of tetrad 1 (i), pentad 2 (ii), hexad 3 (iii), and
heptad 4 (iv).
of their corresponding triads are
Table 2. Absorption data for triads 5–8 and higher oligomers 1–4.
tabulated in Table 1. It is clearly
evident from Figure 3 and the
data in Table 1 that the bridging
2,6-aryl and 2,6-pyridyl protons,
which appeared as two close
doublets at 2.10 and 2.06 ppm
in tetrad 1, are well separated in
heptad 4 and appear at 0.85 and
1.75 ppm, respectively. Similarly
the 3,5-aryl and 3,5-pyridyl pro-
tons also experienced upfield
Compound
Soret bands l [nm] (lge)
Q bands l [nm] (lge)
5
6
7
8
1
2
3
4
434 (5.32)
435 (5.93)
517 (3.99)
517 (4.66)
516 (4.88)
515 (4.79)
518 (4.88)
523 (4.91)
522 (5.07)
529 (5.11)
559 (3.85)
606 (3.57)
604 (4.04)
600 (4.27)
595 (3.80)
609 (4.35)
607 (4.26)
603 (4.30)
598 (4.22)
634 (3.23)
702 (3.44)
700 (4.07)
700 (4.29)
699 (4.13)
701 (4.19)
700 (4.12)
700 (4.28)
701 (4.23)
558 (4.49)
557 (4.75)
554 (4.57)
559 (4.68)
561 (4.69)
558 (4.83)
557 (4.83)
634 (3.72)
629 (4.07)
632 (3.69)
426 (5.80), 437 (5.99)
423 (5.85), 437 (5.95)
414 (5.97), 435 (6.13)
412 (6.02), 433 (5.90)
411 (6.17), 435 (5.98)
410 (6.19), 438 (5.88)
shifts on going from tetrad 1 to heptad 4, but the magnitude
of the upfield shifts was smaller and the signals were less well
separated compared to the 2,6-aryl and 2,6-pyridyl protons. In
addition to connector protons, the other protons of the SnIV
porphyrin and N2S2 porphyrin were also shifted upfield with in-
creasing number of RuTPP(CO) units on going from tetrad 1 to
heptad 4. For example, the type c’ pyrrole protons of the
RuIITPP unit along with bands corresponding to the other two
porphyrin units. However, the Q bands of the RuTPP unit in
hexad 3 merged with those of the other two porphyrin units.
The other higher oligomers 1, 2 and 4 also showed similar
overlapping absorption features of all three constituent mono-
mers with slight shifts in their absorption peak maxima. Thus,
the absorption study on triads and higher oligomers indicated
&
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Figure 5. Reduction waves of cyclic voltammograms of triad 7 (i) and corre-
sponding higher oligomer hexad 3 (ii) recorded in dichloromethane contain-
ing 0.1m TBAP as supporting electrolyte (scan rate 50 mVsÀ1).
showed one or two oxidation and two reduction peaks, which
were not very well defined, and the peak potentials were as-
signed on the basis of their corresponding constituent mono-
mers. For instance, triad 7 containing SnIV porphyrin and 21,23-
dithiaporphyrin showed two oxidation peaks at 1.06 and
1.54 V and three reduction peaks at À0.72, À1.25 and À1.38 V.
The oxidation peak at 1.06 V is exclusively due to the 21,23-di-
thiaporphyrin, which is easier to oxidize, whereas that at 1.54 V
is due to the SnIV porphyrin, which is difficult to oxidize. The
first reduction peak at À0.72 is exclusively due to the SnIV por-
phyrin, and the other two reduction peaks at À1.25 and
À1.38 V are due to both SnIV porphyrin and 21,23-dithiapor-
phyrin units. In higher oligomers such as 3, we observed an
extra oxidation peak at 0.90 V and an extra reduction peak at
À1.56 V corresponding to the RuII porphyrin unit. All other
triads and higher oligomers exhibited similar redox features
(Table 3). Thus, the electrochemical studies indicated that the
porphyrin units in triads 5–8 and higher oligomers 1–4 interact
weakly and retain their characteristic features without major al-
terations in their properties.
Figure 4. Comparison of the Q bands and Soret bands (inset) in the absorp-
tion spectra of a) triad 6 (dotted line) and hexad 3 (solid line) and b) tetrad
1 (dotted line), pentad 2 (dash line), hexad 3 (dash-dotted line) and heptad
4 (solid line) recorded in CH2Cl2.
that the constituent monomers retain their absorption features
in the arrays, which thus act as supramolecular arrays.
The redox properties of triads 5–8, higher oligomers 1–4
and their corresponding monomers were investigated by cyclic
voltammetry at a scan rate of 50 mVsÀ1 with tetrabutylammo-
nium perchlorate as supporting electrolyte in dichloromethane
(Table 3). The representative reduction waves of triad 7 and
hexad 3 are shown in Figure 5. In general, the triads 5–8
The steady-state fluorescence properties of triads 5–8 and
higher oligomers 1–4 were studied in CH2Cl2 at an excitation
wavelength of 550 nm, where the SnIV porphyrin unit absorbs
strongly. In all these systems, the SnIV porphyrin acts
as energy donor and the axial dithiaporphyrin unit
acts as energy acceptor, but the RuII porphyrin in
Table 3. Redox data for triads 5–8 and higher oligomers 1–4.
higher oligomers 1–4 quenches the fluorescence of
both the SnIV porphyrin and axial dithiaporphyrin
Compound
Potential [V vs. SCE]^
Reduction
Oxidation
units. The fluorescence spectra of triads 5 and 8 re-
corded at 550 nm are shown in Figure 6a and the rel-
9
10
11
12
13
14
5
1
6
2
7
–
–
–
–
–
0.87
–
0.88
–
0.90
–
0.90
–
–
–
–
–
1.18
–
1.10
1.06
1.08
1.04
1.06
1.03
1.05
1.05
1.46
1.52
1.54
–
À0.90
À0.82
À0.72
À0.52
À0.96
–
À0.86
À0.84
À0.81
À0.81
À0.72
À0.70
À0.63
À0.52
À1.30
–
–
–
–
–
–
–
–
–
–
À1.23
À1.15
À0.92
À1.24
–
evant data are tabulated in Table 4. In triads, on exci-
tation at 515 nm, where the axial dithiaporphyrin
unit absorbs strongly, fluorescence from the 21,23-di-
–
–
thiaporphyrin unit was observed at 700 nm with
1.43
1.43
1.41
1.47
1.43
1.54
1.48
–
À1.59
À1.28
À1.28
À1.26
À1.27
À1.25
À1.24
À1.24
À1.23
À1.39
À1.39
À1.38
À1.36
À1.38
À1.34
À1.35
À1.30
–
a quantum yield lower than that of corresponding
À1.59
monomer 13. On the other hand, in triads 5–8, on
–
excitation at 550 nm, where the SnIV porphyrin unit
absorbs relatively strongly, emission from the SnIV
porphyrin unit was quenched by 90–99% and strong
emission was observed from the 21,23-dithiaporphy-
rin unit at 700 nm with a quantum yield of 0.0029.
À1.58
–
À1.56
–
3
8
4
0.91
–
À1.55
Chem. Eur. J. 2014, 20, 1 – 11
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ing of both SnIV porphyrin and 21,23-dithiaporphyrin units in-
creased with increasing number of RuII porphyrin units in
higher oligomers 1–4. This is attributed to strong spin–orbit
coupling induced by the RuII porphyrin units. Thus, the fluores-
cence studies indicated possible energy transfer from basal
SnIV porphyrin to axial 21,23-dithiaporphyrin in triads 5–8 and
strong quenching of fluorescence of both SnIV porphyrin and
21,23-dithiaporphyrin in tetrad 1 to heptad 4 due to the pres-
ence of RuII porphyrins, which induces strong spin–orbit cou-
pling.
Conclusion
We have prepared a series of SnIV-porphyrin-based triads and
higher oligomers under simple reaction conditions using an
axial-bonding approach. A 21,23-dithiaporphyrin was used as
axial coordinating unit that coordinated to the SnIV center
through SnÀO interaction to generate triads. The higher oligo-
mers, that is, tetrad, pentad, hexad and heptad, were synthe-
sized by coordinating RuII porphyrin to the meso-pyridyl
groups of the SnIV porphyrin unit of triads through Sn···pyridyl
N interaction. The formation of triads and higher oligomers
was established by extensive 1D and 2D NMR studies. Absorp-
tion and electrochemical studies indicated that the porphyrin
units in triads and higher oligomers interact weakly, retain
their independent features and thus act as supramolecular
arrays. Steady-state fluorescence studies indicated possible
energy transfer from the SnIV porphyrin unit to the axial dithia-
porphyrin unit in triads and the quenching of fluorescence of
both SnIV porphyrin and axial dithiaporphyrin units in higher
oligomers due to the presence of the RuII porphyrin, which in-
duces strong spin–orbit coupling. We hope that the availability
of more such axially bonded arrays containing different types
of macrocycles will help to build materials for future applica-
tions.
Figure 6. Comparison of the emission spectra of a) triad 5 (dotted line) and
triad 8 (solid line) and b) tetrad 1 (solid line), pentad 2 (dashed line), hexad
3 (dash-dotted line) and heptad 4 (dotted line) recorded at an excitation
wavelength of 550 nm in CH2Cl2.
Table 4. Quantum yields F and degrees of quenching Q of triads 5–8
and higher oligomers 1–4 excited at 550 nm.
Compound
FSnP
FN
2 S2
Q(SnP) [%]
Q(N2S2P) [%]
P
5
6
7
8
1
2
3
4
0.00297
0.0028
0.0025
0.0021
0.00071
<10À5
<10À5
<10À5
0.0030
0.0029
0.0026
0.0022
0.00080
0.00042
0.00026
0.00013
90
91
92
93
97
99
99
100
–
–
–
–
89
94
96
98
Experimental Section
General procedure for synthesis of triads 5–8
Triads 5–8 were synthesized by reaction of SnIV porphyrins 9–12
with 21,23-dithiaporphyrin 13 in 1:2 ratio in refluxing dry benzene
for 12–24 h under nitrogen atmosphere. The solvent was evaporat-
ed under reduced pressure and resulting residue was purified by
column chromatography on basic alumina. The desired product
was eluted with dichloromethane/acetone (1–5%) and recrystal-
lized from dichloromethane/hexane to afford triads 5–8 in 55–65%
yield.
The excitation spectrum recorded at 720 nm showed features
of both porphyrin units. A 1:2 mixture of the corresponding
SnIV porphyrin and 21,23-dithiaporphyrin monomers showed
emission mainly from the SnIV porphyrin upon excitation at
550 nm. All of these observations indicated that the energy
was transferred in the singlet state from the SnIV porphyrin
unit to the axial 21,23-dithiaporphyrin in triads 5–8. In higher
oligomers 1–4, because of the presence of the RuII porphyrin,
significant quenching of the singlet excited states of both SnIV
porphyrin and 21,23-dithiaporphyrin units resulted in weak
fluorescence. Fluorescence spectra of higher oligomers 1–4 re-
corded at an excitation wavelength of 550 nm are shown in
Figure 6b, and the relevant data are included in Table 4. Fig-
ure 6b and Table 4 clearly show that the fluorescence quench-
1
Triad 5: Yield 60%; m.p. >3008C. H NMR (400 MHz; CDCl3; Me4Si):
d=2.46 (d, J=8.0 Hz, 4H, 2,6-phenoxyl Ar), 3.88 (s, 3H, OCH3
type n), 3.90 (s, 6H, OCH3 type m), 6.64 (d, J=8.1 Hz, 4H, 3,5-phe-
noxyl Ar), 7.17–7.22 (m, 6H, meta-anisyl Ar, SnP type i), 7.79 (brs,
16H, Ar), 8.03 (d, J=4.68 Hz, 2H, b-pyrrole N2S2 unit type c’), 8.18–
8.26 (m, 12H, Ar), 8.31–8.36 (m, 2H, 3,5-pyridyl+6H, ortho-anisyl Ar
SnP type i’+2H, Ar), 8.45 (d, J=4.6 Hz, 2H, b-pyrrole N2S2 unit
type c), 8.63 (s, 4H, b-pyrrole N2S2 unit type b), 8.95 (d, J=4.7 Hz,
2H, 2,6-pyridyl), 9.05 (d, J=4.8 Hz, 4H, b-pyrrole SnP unit type g
and type f), 9.31 (d, J=5.0 Hz, 2H, b-thiophene N2S2 unit type a’’),
9.44 (s, 4H, b-pyrrole SnP unit type e and type d), 9.47 (d, J=
&
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4.7 Hz, 2H, b-thiophene N2S2 unit type a’), 9.62 ppm (s, 4H, b-thio-
phene N2S2 unit type a); UV/Vis (CH2Cl2): lmax/nm (lg(e/
molÀ1 dm3 cmÀ1)): 434 (5.32), 517 (3.99), 559 (3.85), 606 (3.57), 634
(sh, 3.23), 702 (3.44); MALDI-TOF MS: m/z calcd: 2149.4 [M+];
found: 1485.2 [M+ÀC44H28N2OS2] or [M+À21,23-dithiaporphyrin
unit].
crystallized from dichloromethane/hexane to afford pure 1–4 as
dark purple solids in 60–70% yield.
Stepwise synthetic approach: Compounds 1, 2, 3 and 4 were also
synthesized by treating their corresponding triads 5, 6, 7 and 8
with one, two, three and four equivalents of RuTPP(CO)EtOH (14),
respectively, in chloroform at room temperature in air for 2–4 d.
The solvent was evaporated under reduced pressure and residue
was subjected to column chromatography on basic alumina. The
desired product was eluted with dichloromethane and recrystal-
lized from dichloromethane/hexane to afford compounds 1–4 in
55–66% yield.
1
Triad 6: Yield 65%; m.p. >3008C. H NMR (400 MHz; CDCl3; Me4Si):
d=2.45 (d, J=8.2 Hz, 4H, 2,6-phenoxyl Ar), 3.90 (s, 6H, OCH3 SnP
unit), 6.66 (d, J=8.3 Hz, 4H, 3,5-phenoxyl Ar), 7.19 (d, J=8.5 Hz,
4H, ortho-anisyl Ar SnP unit type i), 7.52–7.55 (m, 4H, Ar), 7.71–7.74
(m, 4H, Ar), 7.79 (brs, 12H, Ar), 8.04 (d, J=4.5 Hz, 2H, b-pyrrole
N2S2 unit type c’), 8.17–8.19 (m, 10H, Ar), 8.32 (d, J=8.5 Hz, 4H,
meta-anisyl Ar SnP unit type i’), 8.35 (d, J=5.8 Hz, 4H, 3,5-pyridyl),
8.47 (d, J=4.5 Hz, 2H, b-pyrrole N2S2 unit type c), 8.63 (s, 4H, b-
pyrrole N2S2 unit type b), 8.93 (d, J=5.7 Hz, 4H, 2,6-pyridyl), 9.02
(d, J=5.1 Hz, 2H, b-thiophene N2S2 unit type a’’), 9.34 (d, J=4.8 Hz,
4H, b-pyrrole SnP unit type g), 9.43 (d, J=5.0 Hz, 2H, b-thiophene
N2S2 unit type a’), 9.51 (d, J=4.9 Hz, 4H, b-pyrrole, SnP unit type f),
9.62 ppm (s, 4H, b-thiophene N2S2 unit type a); UV/Vis (CH2Cl2):
lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 435 (5.93), 517 (4.66), 558 (4.49),
604 (4.04), 634 (sh, 3.72), 700 (4.07); MALDI-TOF MS: m/z calcd:
2120.4 [M+]; found: 1456.3 [M+ÀC44H28N2OS2] or [M+À21,23-ditha-
porphyrin unit].
1
Tetrad 1: Yield 60%; H NMR (400 MHz; CDCl3; Me4Si): d=2.06 (d,
J=6.5 Hz, 2H, 2,6-pyridyl), 2.10 (d, J=8.3 Hz, 4H, 2,6 phenoxyl Ar)
3.78 (s, 3H, OCH3 SnP unit type n), 3.81 (s, 6H, OCH3 SnP unit
type m), 6.38 (d, J=6.0 Hz, 2H, 3,5 pyridyl), 6.42 (d, J=8.3 Hz, 4H,
3,5 phenoxyl Ar), 7.01–7.04 (m, 6H, meta-anisyl Ar SnP type i),
7.40–7.43 (m, 4H, Ar), 7.56–7.60 (m, 4H, Ar), 7.68–7.72 (m, 6H, Ar),
7.78 (brs, 18H, Ar), 7.84–7.87 (m, 2H, b-pyrrole SnP unit type g+
2H, b-pyrrole N2S2 unit type c’), 8.06–8.10 (m, 2H, ortho-anisyl Ar
SnP unit type i’’+4H, Ar), 8.15–8.17 (m, 4H, ortho-anisyl Ar SnP
unit type i’+4H, Ar), 8.21–8.23 (m, 6H, Ar), 8.27 (d, J=7.4 Hz, 4H,
Ar), 8.39 (d, J=4.4 Hz, 2H, b-pyrrole N2S2 unit type c), 8.63 (s, 4H,
b-pyrrole N2S2 unit type b), 8.69 (s, 8H, b-pyrrole RuTPP uint
type h), 8.86 (d, J=5.1 Hz, 2H, b-thiophene N2S2 unit type a’’), 9.04
(d, J=5.1 Hz, 2H, b-pyrrole SnP unit type f), 9.26 (d, J=5.0 Hz, 2H,
b-pyrrole SnP unit type e), 9.30 ( d, J=5.0 Hz, 2H, b-pyrrole SnP
unit type d), 9.34 (d, J=5.1 Hz, 2H, b-thiophene N2S2 unit type a’),
9.62 ppm (s, 4H, b-thiophene N2S2 unit type a); UV/Vis (CH2Cl2):
lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 414 (5.97), 435 (6.13), 518 (4.88),
559 (4.68), 609 (4.35), 701 (4.19); MALDI-TOF MS: m/z: calcd:
2891.6 [M+]; found: 1485.2 [M+ÀC44H28N2OS2ÀC45H28N4ORu].
1
Triad 7: Yield 55%; m.p. >3008C. H NMR (400 MHz; CDCl3; Me4Si):
d=2.43 (d, J=8.3 Hz, 4H, 2,6-phenoxyl Ar), 3.89 (s, 3H, OCH3), 6.66
(d, J=8.4 Hz, 4H, 3,5-phenoxyl Ar), 7.18 (d, J=8.6 Hz, 2H, meta-
anisyl Ar SnP unit type i), 7.52–7.80 (m, 16H, Ar), 8.03 (d, J=4.5 Hz,
2H, b-pyrrole N2S2 unit type c’), 8.17–8.22 (m, 14H, Ar), 8.31 (d, J=
8.6 Hz, 2H, ortho-anisyl Ar SnP unit type i’), 8.34- 8.37 (m, 6H, 3,5-
pyridyl), 8.49(d, J=4.4 Hz, 2H, b-pyrrole N2S2 unit type c), 8.63 (s,
4H, b-pyrrole N2S2 unit type b), 8.95 (d, J=5.8 Hz, 2H, b-pyrrole
SnP unit type d), 8.97–8.99 (m, 6H, 2,6-pyridyl), 9.37 (d, J=4.9 Hz,
2H, b-thiophene N2S2 unit type a’’), 9.40–9.42 (m, 6H, b-pyrrole SnP
unit types g, f and e), 9.54 (d, J=4.8 Hz, 2H, b-thiophene N2S2 unit
type a’), 9.62 ppm (s, 4H, b-thiophene N2S2 unit type a); UV/Vis
(CH2Cl2): lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 425 (5.80), 437 (5.99), 516
(4.88), 557 (4.75), 600 (sh, 4.27), 629 (sh, 4.07), 700 (4.29); MALDI-
TOF MS: m/z calcd: 2091.4 [M+]; found: 1428.3 [M+ÀC44H27N2OS2]
or [M+À21,23-dithaporphyrin unit].
1
Pentad 2: Yield 70%; H NMR (400 MHz; CDCl3; Me4Si): d=1.63 (d,
J=8.2 Hz, 4H, 2,6 phenoxyl Ar), 1.97 (d, J=6.8 Hz, 4H, 2,6-pyridyl),
3.69 (s, 6H, OCH3), 6.12 (d, J=8.2 Hz, 4H, 3,5 phenoxyl Ar), 6.24 (d,
J=5.6 Hz, 4H, 3,5-pyridyl), 6.83 (d, J=8.4 Hz, 4H, meta-anisyl Ar,
SnP unit type i), 7.22–7.24 (m, 4H, Ar), 7.44–7.48 (m, 8H, Ar,) 7.60–
7.65 (m, 2H, b-pyrrole N2S2 unit type c’+8H, Ar), 7.69–7.83 (m, 4H,
ortho-anisyl Ar, SnP unit type i’+4H, b-pyrrole SnP unit type g+
22H, Ar), 7.95 (d, J=7.5 Hz, 6H, Ar), 8.12–8.16 (m, 8H, Ar), 8.19 (d,
J=7.5 Hz, 8H, Ar), 8.23–8.26 (m, 6H, Ar), 8.35 (d, J=4.4 Hz, 2H, b-
pyrrole N2S2 unit type c), 8.59–8.70 (m, 4H, b-pyrrole N2S2 unit
type b+2H, b-thiophene N2S2 unit type a’’+16H, b-pyrrole RuTPP
unit type h), 8.89 (d, J=4.9 Hz, 4H, b-pyrrole SnP unit type f), 9.23
(d, J=5.0 Hz, 2H, b-thiophene N2S2 unit type a’), 9.65 ppm (s, satel-
lite, J=13.1 Hz, 4H, b-thiophene N2S2 unit type a); UV/Vis (CH2Cl2):
lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 412 (6.02), 433 (5.90), 523 (4.91),
561 (4.69), 607 (4.26), 700 (4.12); MALDI-TOF MS: m/z: calcd:
3604.7 [M+]; found: 1456.4 [M+ÀC44H28N2OS2ÀC90H56N8O2Ru2].
1
Triad 8: Yield 58%; m.p. >3008C. H NMR (400 MHz; CDCl3; Me4Si):
d=2.41 (d, J=8.4 Hz, 4H, 2,6-phenoxyl Ar), 6.68 (d, J=8.4 Hz, 4H,
3,5 phenoxyl Ar), 7.78–7.81 (m, 2H, b-thiophene N2S2 unit type a’’+
18H, Ar), 8.04 (d, J=4.5 Hz, 2H, b-pyrrole N2S2 unit type c’), 8.16–
8.23 (m, 2H, b-thiophene N2S2 unit type a’+12H, Ar), 8.36 (d, J=
5.9 Hz, 8H, 3,5-pyridyl), 8.51 (d, J=4.5 Hz, 2H, b-pyrrole N2S2 unit
type c), 8.63 (s, 4H, b-pyrrole N2S2 unit type b), 8.96 (d, J=5.9 Hz,
8H, 2,6-pyridyl), 9.44 (satellite, 8H, b-pyrrole SnP unit type g),
9.63 ppm (s, 4H, b-thiophene N2S2 unit type a); UV/Vis (CH2Cl2):
lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 423 (5.85), 437 (5.95), 515 (4.79),
554 (4.57), 595 (sh, 3.80), 632 (sh, 3.69), 699 (4.13); MALDI-TOF MS:
m/z calcd 2062.4 [M+]; found: 1398.3 [M+ÀC44H28N2OS2] or [M+
À21,23-dithaporphyrin unit].
1
Hexad 3: Yield 62%; H NMR (400 MHz; CDCl3; Me4Si): d=1.23 (d,
J=8.3 Hz, 4H, 2,6-phenoxyl Ar), 1.87–1.89 (m, 6H, 2,6-pyridyl), 3.50
(s, 3H, OCH3), 5.93 (d, J=6.5 Hz, 2H, 3,5-pyridyl), 5.96 (d, J=8.3 Hz,
4H, 3,5-phenoxyl Ar), 6.01 (d, J=6.8 Hz, 4H, 3,5-pyridyl), 6.57 (d,
J=8.6 Hz, 2H, meta-anisyl Ar, SnP unit type i), 7.09–7.12 (m, 8H,
Ar), 7.28–7.32 (m, 4H, Ar), 7.37–7.45 (m, 2H, b-pyrrole N2S2 unit
type c’+12H, Ar), 7.53 (d, J=8.5 Hz, 2H, ortho-anisyl Ar SnP unit
type i’), 7.58–7.65 (m, 6H, b-pyrrole SnP unit types g, f, and e+8H,
Ar), 7.74–7.78 (m, 12H, Ar), 7.84–7.85 (m, 20H, Ar), 7.94 (d, J=
7.7 Hz, 4H, Ar), 8.06–8.09 (m, 4H, Ar), 8.11–8.13 (m, 4H, Ar), 8.17 (d,
J=7.6 Hz, 6H, Ar), 8.25–8.29 (m, 8H, Ar), 8.32–8.34 (m, 2H, b-pyr-
role N2S2 unit type c+2H, b-thiophene N2S2 unit type a’’), 8.56 (brs,
14H, b-pyrrole RuTPP unit type h’), 8.63 (d, J=4.5 Hz, 4H, b-pyrrole
N2S2 unit type b), 8.68 (brs, 10H, b-pyrrole RuTPP unit type h), 8.76
(d, J=5.0 Hz, 2H, b-pyrrole SnP unit type d), 9.13 (d, J=5.0 Hz, 2H,
General procedure for synthesis of multiporphyrin arrays
from tetrad 1 to heptad 4
One-pot synthetic approach: Compounds 1–4 were synthesized
by heating one equivalent of 9, 10, 11 and 12 and two equivalents
of 13 with one, two, three and four equivalents of 14, respectively,
in benzene under nitrogen atmosphere for 1–7 d. The crude com-
pounds were purified by column chromatography on basic alumi-
na and the fast-moving desired band was collected with dichloro-
methane/petroleum ether (90/10%). The resulting solids were re-
Chem. Eur. J. 2014, 20, 1 – 11
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b-thiophene N2S2 unit type a’), 9.68 ppm (satellite, J=12.92 Hz, 4H,
b-thiophene N2S2 unit type a); UV/Vis (CH2Cl2): lmax/nm (lg(e/
molÀ1 dm3 cmÀ1)): 411 (6.17), 435 (5.98), 522 (5.07), 558 (4.83), 603
(4.30), 700 (4.28).
1
Heptad 4: Yield 65%; H NMR (400 MHz; CDCl3; Me4Si): d=0.85 (d,
J=8.4 Hz, 4H, 2,6 phenoxyl Ar), 1.75 (d, J=6.5 Hz, 8H, 2,6-pyridyl),
5.68 (d, J=8.4 Hz, 4H, 3,5 phenoxyl Ar), 5.73 (d, J=6.6 Hz, 8H, 3,5-
pyridyl), 6.85–6.89 (m, 16H, Ar), 7.01 (d, J=4.4 Hz, 2H, b-pyrrole
N2S2 unit type c’), 7.36–7.40 (m, 18H, Ar), 7.63–7.69 (m, 32H, Ar),
7.72–7.75 (m, 8H, Ar), 7.87–7.92 (m, 2H, b-thiophene N2S2 unit
type a’’+2H, b-pyrrole N2S2 unit type b’+10H, Ar), 7.99–8.01 (m,
4H, Ar), 8.09–8.11 (m, 4H, Ar), 8.15 (d, J=7.6 Hz, 18H, Ar), 8.35–
8.36 (m, 2H, b-pyrrole N2S2 unit type b+2H, b-pyrrole N2S2 unit
type c), 8.52 (s, 32H, b-pyrrole RuTPP unit type h), 8.66 (d, J=
4.5 Hz, 4H, b-pyrrole SnP unit type g), 8.74 (d, J=4.6 Hz, 4H, b-pyr-
role SnP unit type f), 8.97 ppm (d, J=5.0 Hz, 2H, b-thiophene N2S2
unit type a’), 9.78 ppm (s, 4H, b-thiophene N2S2 unit type a); UV/Vis
(CH2Cl2): lmax/nm (lg(e/molÀ1 dm3 cmÀ1)): 410 (6.19), 438 (5.88), 529
(5.11), 557 (4.83), 598 (sh, 4.22), 701 (4.23).
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Acknowledgements
M.R. thanks Department of Science and Technology (DST) for
financial support. A.D. and Y.P. thank Council of Scientific and
Industrial Research (CSIR) for senior research fellowship.
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Keywords: multiporphyrin arrays · multicomponent reactions ·
porphyrinoids · supramolecular chemistry · tin
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Received: November 6, 2013
Revised: December 16, 2013
Published online on && &&, 0000
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FULL PAPER
Supramolecular arrays consisting of up
to seven porphyrin units (see figure)
were prepared on the basis of SnIV por-
phyrins by stepwise and one-pot syn-
thetic strategies and their structures elu-
cidated by detailed NMR spectroscopic
studies.
&
Porphyrins
A. Dvivedi, Y. Pareek, M. Ravikanth*
&& – &&
SnIV Porphyrin Scaffolds for Axially
Bonded Multiporphyrin Arrays:
Synthesis and Structure Elucidation by
NMR Studies
Chem. Eur. J. 2014, 20, 1 – 11
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ