Synthesis of triazole-bridged unsymmetrical porphyrin dyads and porphyrin-ferrocene conjugates

Article abstract of DOI:10.1002/ejoc.200901070

A simple method has been used to synthesize four porphyrin azides with cores such as N₄, N₃S, N₂SO and N ₂S₂ in 6090% yields by treating the corresponding aminoporphyrms with tert-butyl nitrite (tBuON

Full text of DOI:10.1002/ejoc.200901070

FULL PAPER
DOI: 10.1002/ejoc.200901070
Synthesis of Triazole-Bridged Unsymmetrical Porphyrin Dyads and
Porphyrin–Ferrocene Conjugates
Vijayendra S. Shetti[a] and Mangalampalli Ravikanth*[a]
Keywords: Click chemistry / Energy transfer / Electron transfer / Azides / Sandwich complexes / Porphyrinoids
A simple method has been used to synthesize four porphyrin
azides with cores such as N4, N3S, N2SO and N2S2 in 60–
90% yields by treating the corresponding aminoporphyrins
with tert-butyl nitrite (tBuONO) and azidotrimethylsilane
(TMSN3) in THF/CH3CN under mild reaction conditions. The
hitherto unknown aminoporphyrins with heteroatom cores
were synthesized from their corresponding nitroporphyrins
by standard SnCl2/HCl reduction. The azidoporphyrins were
and the best yields of triazole-bridged dyads and conjugates
were obtained with CuI/DIPEA in THF/CH3CN at room tem-
perature for overnight. The unsymmetrical porphyrin dyads
and porphyrin–ferrocene conjugates were characterized by
various spectroscopic and electrochemical techniques. In un-
symmetrical porphyrin dyads, the NMR, absorption and elec-
trochemical studies indicate a weak interaction between the
two porphyrin sub-units. However, preliminary photophysi-
used to synthesize six triazole-bridged unsymmetrical por- cal studies support an efficient singlet-singlet energy transfer
phyrin dyads containing two different types of porphyrin
sub-units as well as five triazole-bridged porphyrin–ferro-
cene conjugates under CuI-catalyzed “click” reaction condi-
tions. Various CuI-catalyzed reaction conditions were studied
from one porphyrin unit to another in five unsymmetrical dy-
ads reported here. In porphyrin–ferrocene conjugates, the
fluorescence of porphyrin was quenched significantly due to
photo-induced electron transfer from ferrocene to porphyrin.
derivative of the bis-porphyrin (I) by coupling the NiII de-
rivative of β-azidotetrarylporphyrin with the NiII derivative
of meso-ethynyldiphenylporphyrin in DMF in the presence
of CuSO4·5H2O/ascorbic acid at 50 °C. Odobel and co-
workers[4b] explored various CuI-catalyzed conditions to
synthesize triazole-bridged metalloporphyrin dyads (II) and
found that copper carbene [N,NЈ-bis(2,4,6-trimethylphenyl)-
4,5-dihydroimadazol-2-ylidene]CuBr in the solvent mixture
THF/water (3:1) was the better catalyst to afford triazole-
bridged dyads. We recently reported[4c] on the first synthesis
of a triazole-bridged unsymmetrical porphyrin dyad (III)
under click reaction conditions by reacting 21,23-dithiapor-
phyrin (N2S2 core) containing an alkyne functional group
and a normal porphyrin (N4 core) containing an azide func-
tional group in the presence of sodium ascorbate and
CuSO4 in a water/acetone mixture at 80 °C for four days.
Except for the above-mentioned communications, to the
best of our knowledge there are no reports available on tri-
azole-bridged porphyrin dyads. We have been involved in
the synthesis of unsymmetrical dyads[5] containing two dif-
ferent porphyrin sub-units such as porphyrin and hetero-
porphyrin connected by various linkers with an aim to
identify the best unsymmetrical porphyrin dyads showing
maximum singlet–singlet energy transfer for various molec-
ular electronic applications. During our studies, we realized
that the bridging group connecting two different porphyrins
plays an important role in energy transfer at singlet state.
For example, the diphenylethyne-bridged porphyrin dyad
containing N4 and N2S2 porphyrin sub-units exhibited inef-
Introduction
Sharpless and co-workers[1] discovery of copper(I)-cata-
lyzed variant of Huisgen’s 1,3-diploar cycloaddition of
azides and alkynes to afford 1,4-disubstituted 1,2,3-triazoles
under mild conditions, popularly known as “click chemis-
try” has resulted in explosive growth of research articles
and reviews[2] describing the wealth of applications of this
practical and sensible approach in various research fields
including bioconjugation, materials science and drug dis-
covery. The advantages of CuI-catalyzed “1,3-dipolar”
cycloaddition reactions are: (1) to afford the 1,4-regio-
isomer exclusively with minimum work-up and purification,
(2) to increase the reaction rate, (3) to eliminate the need
for elevated temperatures and (4) favourable reaction condi-
tions for variety of functional groups. Although the CuI-
catalyzed cycloaddition reaction is versatile and extensively
used, reports on the applications of this methodology to
porphyrin chemistry is still in their infancy. There are some
reports on triazole-appended porphyrin systems[3] but re-
ports on triazole-bridged porphyrin dyads[4] and other con-
jugates synthesized under CuI-catalyzed cycloaddition reac-
tions are very scarce (Figure 1). Chen and co-workers[4a] re-
ported the synthesis of a β-meso-1,2,3-triazole-linked NiII
[a] Department of Chemistry, Indian Institute of Technology,
Bombay, Powai, Mumbai 400076, India
E-mail: ravikanth@chem.iitb.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901070.
494
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
ficient energy transfer from the N4 porphyrin sub-unit to jugates 7–11 support a weak interaction between the sub-
the N2S2 porphyrin sub-unit.[4c] However, in triazole- units. The fluorescence studies indicate low fluorescence
bridged porphyrin dyads containing N4 and N2S2 porphyrin yields for porphyrin–ferrocene conjugates 7–11 because of
sub-units III, an efficient energy transfer from the N4 por- photo-induced electron transfer from ferrocene to por-
phyrin sub-unit to the N2S2 porphyrin sub-unit was ob- phyrin and efficient singlet–singlet energy transfer from the
served.[4c] This result inspired us to synthesize more exam- porphyrin sub-unit to another in most of the triazole-
ples of triazole-bridged unsymmetrical porphyrin dyads bridged porphyrin dyads 1–6 reported here.
containing two different porphyrin sub-units. In this paper,
we present our detailed account on the synthesis of the di-
phenyl-1,2,3-triazole-bridged unsymmetrical porphyrin dy-
ads 1–6 containing two different porphyrin sub-units such
as N4/ZnN4–N3S, N4/ZnN4–N2S2, ZnN4–N2SO, N3S–N2S2
units (Figure 2) as well as 1,2,3-triazole-bridged porphyrin–
ferrocene conjugates 7–11 (Figure 3) with N4, N3S, N2S2
and N2SO cores under click reaction conditions. To synthe-
size the dyads and conjugates, we required the unknown
meso-(azidophenyl)porphyrin building blocks with hetero-
atom-substituted porphyrin cores, which were synthesized
from the corresponding aminoporphyrins by applying Mo-
ses reaction conditions[6] reported recently, and the amino-
porphyrins were, in turn, synthesized from nitroporphyrins
under standard SnCl2/HCl conditions.[7] The NMR, ab-
sorption and electrochemical studies carried out on unsym-
metrical porphyrin dyads 1–6 and porphyrin–ferrocene con-
Figure 2. Various triazole-bridged unsymmetrical dyads synthe-
sized in the present work.
Figure 3. Various triazole-bridged porphyrin–ferrocene conjugates
synthesized in the present work.
Results and Discussion
Mono meso-(p-Nitrophenyl)porphyrin Building Blocks with
N4 (12), N3S (15), N2S2 (17) and N2SO (19) Cores
The mono meso-(nitrophenyl)porphyrin building blocks
with different cores 12, 15, 17 and 19 were prepared by
following various approaches as outlined below. The mono
meso-(p-nitrophenyl)porphyrin with N4 core 12 was synthe-
sized by mixed condensation[8] of one equivalent of p-ni-
trobenzaldehyde with three equivalents of p-tolualdehyde
and four equivalents of pyrrole under Lindsey’s porphyrin
forming conditions[9] and afforded compound 12 in 10%
yield (Scheme 1). The mono-meso-(p-nitrophenyl)por-
phyrins with N3S (15), N2S2 (17) and N2SO (19) cores were
synthesized as presented in Scheme 1. The unsymmetrical
thiophenediol[10] 14 was prepared in 48% yield by treating
Figure 1. Triazole-bridged porphyrin dyads described in the litera-
ture.
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2-(p-tolylhydroxymethyl)thiophene (13) with two equiva- with one equivalent of 16-oxatripyrrin[11] 18 under the same
lents of nBuLi followed by 1.2 equiv. of 4-nitrobenzalde- mild porphyrin-forming conditions. The porphyrins 12, 15,
hyde in THF at 0 °C. The 21-thiaporphyrin containing a p- 17 and 19 were characterized by mass, NMR, absorption
nitrophenyl group in the meso-position 15 was prepared in and fluorescence spectroscopic techniques. The molecular
8% yield by condensing one equivalent of diol 14 with two ion peak in mass spectra confirmed the identities of all four
equivalents of p-tolualdehyde and three equivalents of pyr- porphyrins. The 1H NMR spectra showed characteristic sig-
role under mild acid-catalyzed porphyrin-forming condi- nals expected for porphyrins 12, 15, 17 and 19. The larger
tions.[9] The 21,23-dithiaporphyrin containing
a p-ni- number of signals observed for pyrrole and thiophene pro-
trophenyl group in meso-position 17 was synthesized in tons for porphyrins 12, 15, 17 and 19 indicate the unsym-
10% yield by condensing one equivalent of diol 14 with one metric nature of these porphyrins. The absorption spectra
equivalent of 16-thiatripyrrin[11] 16 in CH2Cl2 under mild of porphyrins 12, 15, 17 and 19 showed four Q-bands and
acid-catalyzed conditions. The porphyrin 19 with N2SO one Soret band and peak positions were matching closely
core containing meso-nitrophenyl group was synthesized with their corresponding meso-tetratolylporphyrin ana-
similarly in 8% yield by condensing one equivalent of 14 logues.[12]
Scheme 1. Synthesis of meso-(p-nitrophenyl)porphyrins with N4, N3S, N2S2, N2SO cores.
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
Scheme 2. Synthesis of meso-(p-aminophenyl)- and meso-(p-azidophenyl)porphyrins with N4, N3S, N2S2, N2SO cores.
Mono meso-(p-Aminophenyl)porphyrin Building Blocks with ylsilane (TMSN3) under mild reaction conditions. We em-
N4 20, N3S 21, N2S2 22 and N2SO 23 Cores
ployed Moses conditions to prepare meso-(azidophenyl)-
porphyrins 24–27 in 60–90% yields by reacting meso-
(aminophenyl)porphyrin with 1.5 equiv. of tBuONO fol-
lowed by 1.2 equiv. of TMSN3 in CH3CN/THF (Scheme 2).
Although the yields are in the same range as those obtained
with standard NaN3 method, we found that the reaction
is simple, easy to handle and equally efficient to prepare
azidoporphyrins in decent yields. The meso-(azidophenyl)-
porphyrins 24–27 were confirmed by ES-MS mass which
The mono meso-(p-aminophenyl)porphyrins with various
porphyrin cores 20–23 were synthesized by reducing the ni-
tro group of corresponding mono-meso(p-nitrophenyl)por-
phyrins 12, 15, 17 and 19, respectively, with SnCl2 in the
presence of concd. aqueous HCl[7] (Scheme 2). Column
chromatographic purification on silica afforded meso-(p-
aminophenyl)porphyrins 20–23 in 75–85% yields. The
meso-(aminophenyl)porphyrins 20–23 were confirmed by
molecular ion peak in mass spectra and elemental analysis
which was matching with the exact composition of amino
1
showed either M+ or (M – N2)+ peak. In H NMR, the
absence of signal at δ = 4.00 ppm corresponding to the
amino group confirmed the transformation of the amino
group to an azido group. The absorption spectra of meso-
(azidophenyl)porphyrins 24–27 showed four Q-bands and
one Soret band and peak positions are almost matching
with those of meso-(nitrophenyl)- and meso-(aminophenyl)-
porphyrins.
1
porphyrins. In H NMR spectra of aminoporphyrins 20–
23, a broad signal around 4.0 ppm indicated the presence
of amino group. The absorption spectra of aminopor-
phyrins 20–23 showed four Q-bands and one strong Soret
band with peak maxima were almost matching with those
of nitroporphyrins.
Triazole-Bridged Unsymmetrical Porphyrin Dyads 1–6
Mono meso-(p-Azidophenyl)porphyrin Building Blocks with
N4 (24), N3S (25), N2S2 (26) and N2SO (27) Cores
To synthesize triazole-bridged click porphyrin dyads, we
need an access to meso-(ethynylphenyl)porphyrin building
The meso-(azidophenyl)porphyrins were prepared earlier blocks along with meso-(azidophenyl)porphyrin building
by Odobel and others[4a,4b] from the corresponding amines blocks. The mono meso-(4-ethynylphenyl)porphyrin build-
via their diazonium salts. Although this method works ef- ing blocks such as 28 (N4 core), 29 (ZnN4) and 30 (N3S
ficiently, NaN3 is toxic and explosive and needs to be han- core) were synthesized by following the reported pro-
dled carefully. Moses and co-workers[6] recently reported cedures.[5b,13] Using meso-(azidophenyl)porphyrin and
the synthesis of aromatic azides from their corresponding meso-(ethynylphenyl)porphyrin building blocks, we carried
amines using stable, less hazardous and non-explosive rea- out a series of 1,3-dipolar cycloaddition reactions under
gents such as tert-butyl nitrite (tBuONO) and azidotrimeth- various reaction conditions to synthesize triazole-bridged
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porphyrin dyads 1–6. Initially, we attempted to synthesize not form. Further we modified the reaction conditions and
the free-base porphyrin dyad 4 by click reaction conditions reacted 25 and 29 in toluene in the presence of Diisopro-
used by us earlier[4c] for preparation of N4–N2S2 porphyrin pylethylamine (DIPEA) and CuSO4·5H2O/sodium ascorb-
dyad III (Figure 1) by reacting 24 and 28 in the presence ate at room temperature for 7 d. We noticed the formation
of sodium ascorbate and CuSO4 in a water/acetone mix- of dyad 1 in very trace amount after three days but no
ture at 80 °C for four days. However, we noticed that the improvement in dyad 1 formation even after seven days.
N4 porphyrin 28 was metallated by copper under these re- The first success in the synthesis of dyad 1 came when we
action conditions which was not observed while preparing used Odobel’s reaction conditions[4b] by reacting 25 and
porphyrin dyad III. Odobel and co-workers[4b] also ob- 29 in THF/H2O (1:5) in the presence of Cu[P(OEt)3]I
served copper insertion problem during their investi- at 50 °C for 12 h. The reaction worked smoothly
gations for the preparation of dyad II. Hence, to optimize and afforded dyad 1 in 45% yield. Since the catalyst
the conditions, we carried out series of trial reactions using Cu[P(OEt)3]I[14] is not readily available, we then modified
ZnII-metallated N4 ethynylporphyrin 29 with N3S azido- the conditions further by reacting 25 and 29 in THF/
porphyrin 25 under various reaction conditions. The por- CH3CN (1:1) in the presence of CuI/DIPEA at room tem-
phyrins 25 and 29 were reacted under same click reaction perature for 12 h. After simple work-up and flash column
conditions used for dyad III but the expected dyad 1 did chromatographic purification on basic alumina, the dyad
Scheme 3. Synthesis of triazole-bridged unsymmetrical porphyrin dyads and porphyrin–ferrocene conjugates.
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
1 was obtained as purple solid in 50% yield. The dyad 2 Absorption, Electrochemical and Fluorescence Properties of
was prepared by reacting 26 and 29 and dyad 3 was pre- Dyads 1–6
pared by reacting 27 and 29 under similar click reaction
conditions used for dyad 1 and afforded in 46–48% yields
The absorption spectra of dyads 1–6 along with meso-
(Scheme 3). The free-base dyads 4 and 5 were prepared by (azidophenyl)porphyrin monomers 24–27 were recorded in
demetallation of dyads 1 and 2, respectively, in CH2Cl2 in dichloromethane and data are presented in Table 1. The
the presence of small amount of TFA at room tempera- comparison of absorption spectra of dyad 5 along with its
ture. The free-base porphyrin dyad 6 was prepared under corresponding porphyrin monomers 26 and 28 is shown in
same conditions by reacting 26 and 30 in THF/CH3CN in Figure 4. According to Figure 4 the absorption spectra of
the presence of CuI/DIPEA at room temperature for 12 h. the dyads show the absorption bands corresponding to both
The N3S porphyrins are known to form metal complexes the constituted porphyrin monomers. For instance, the dyad
which require harsh reaction conditions[12,15] and N2S2 1 containing ZnN4 and N3S porphyrin sub-units showed
porphyrins generally do not form metal complexes al- 515, 549, 587, 615 and 677 nm in Q-band region and
though one report on Ru(II) complex of N2S2 porphyrin 422 nm with a shoulder at 430 nm in Soret band region.
is available in literature.[16] Thus, to synthesize the triazole- In this dyad, the bands at 515, 615, 677 and 430 nm were
bridged free base porphyrin dyads containing two different exclusively due to N3S porphyrin sub-unit and the bands at
types of heteroporphyrin sub-units such as compound 6, 549, 587 and 422 nm are majorly due to ZnN4 porphyrin
the reaction conditions developed for the synthesis of sub-unit. Similarly in all other dyads, the absorption bands
compounds 1–3 are applicable. However, the dyads con- corresponding to both the porphyrin sub-units are present.
taining free base N4 porphyrin and heteroporphyrin sub- The comparison of absorption spectra of dyads 1–6 with
units can be obtained only through demetallation of the those of their corresponding porphyrin monomers indicate
corresponding metallated N4-heteroporphyrin dyads.
that the absorption bands of dyads are sum of the absorp-
The dyads 1–6 were characterized by mass, NMR, ab- tion bands of their corresponding porphyrin monomers
sorption, electrochemical and fluorescence techniques. The with negligible shifts in their peak maxima supporting a
dyads 1–6 showed a peak corresponding to the loss of N2 very weak interaction among the two porphyrin sub-units
1
in the MALDI-TOF spectra. The H NMR resonances of in dyads 1–6.
dyads 1–6 were assigned on the basis of spectra observed
The redox chemistry of the triazole-bridged porphyrin
for the corresponding porphyrin monomers taken indepen- dyads containing two different macrocycles 1–6 along with
dently. For example, in dyad 1, the signals of the two β- their meso-(azidophenyl)porphyrin monomers 24–27 was
thiophene protons appeared as sets of two doublets at δ = followed by cyclic voltammetry at a scan rate of 50 mV/s
9.79 and 9.84 ppm; the eight β-pyrrole protons of the ZnN4 and differential pulse voltammetry (DPV) using tetrabu-
porphyrin sub-unit gave rise to three sets of signals in the tylammonium perchlorate as supporting electrolyte (0.1 )
8.8–9.1 ppm region; the signals of the six β-pyrrole protons in dichloromethane. The representative reduction waves of
of N3S porphyrin sub-unit appeared at δ = 8.71–8.74; the dyads 1 and 5 are presented in Figure 5. In general dyads
triazole signal appeared as singlet at δ = 8.79 and the inner 1–6 showed two or three oxidations and three or four re-
NH signal appeared as singlet at δ = –2.65 ppm. Similarly ductions and peak potentials were assigned on the basis of
the dyads 2 and 3 also showed similar features and signals their corresponding meso-(azidophenyl)porphyrin mono-
were assigned by comparing them with their corresponding mers. For instance the dyad 1 containing ZnN4 and N3S
porphyrin monomers. A comparison of chemical shifts of porphyrin sub-units showed three oxidations at 0.77, 1.07
various protons of the dyads 1–3 with those of their corre- and 1.47 V and three reductions at –1.02, –1.35 and –1.55 V.
sponding individual monomer units indicate only minor The first oxidation at 0.77 V was due to oxidation of ZnN4
differences suggesting that the two porphyrin sub-units in porphyrin sub-unit because it is easier to oxidize as com-
dyads 1–3 interact very weakly. The dyads 4 and 5 which pared to free base N3S porphyrin. The oxidation at 1.47 V
were prepared by demetallation of the corresponding dyads was assigned to the oxidation of N3S porphyrin sub-unit
1 and 2 showed similar 1H NMR spectral features like their and oxidation at 1.07 V was due to oxidation of both ZnN4
corresponding metallated dyads and exhibited an additional and N3S porphyrin sub-units. Similarly, the first reduction
signal at –2.70 ppm corresponding to two inner NH signals at –1.02 V was due to reduction of N3S porphyrin sub-unit;
of N4 porphyrin sub-unit. The free-base dyad 6 containing the last reduction at –1.55 V was due to reduction of ZnN4
a N3S and N2S2 porphyrin sub-units showed the combined porphyrin sub-unit and reduction at –1.35 V was due to re-
1H NMR spectral features of its corresponding N3S and duction of both ZnN4 and N3S porphyrin sub-units. Simi-
N2S2 porphyrin monomers with negligible changes in their larly, the other dyads also exhibited oxidation and re-
chemical shifts compared to its constituted porphyrin duction waves, and the peak potentials were in the same
monomers supporting that the two porphyrin sub-units in- range of their corresponding porphyrin monomers
1
teract very weakly and retain most of their HNMR spec- (Table 1). Thus, the electrochemical studies also indicated
tral features. Thus, 1H NMR studies indicate that porphyrin that the two porphyrin sub-units in dyads 1–6 interact very
sub-units in triazole-bridged porphyrin dyads 1–6 interact weakly.
1
very weakly and retain most of their individual H NMR
The steady state and time-resolved fluorescence studies
spectral features.
of dyads 1–6 along with their appropriate reference com-
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Table 1. Absorption and electrochemical data of click dyads 1–6 along with the (azidophenyl)porphyrin monomers 24–27 recorded in
dichloromethane.
Compound Soret band λ [nm] (logε)
Q bands λ [nm] (logε)
Potential (V) vs. SCE
Oxidation
Reduction
24
420 (6.02)
516 (4.56)
591 (3.99)
548 (4.05)
515 (4.57)
618 (3.54)
515 (4.38)
634 (2.98)
513 (4.20)
645 (3.07)
515 (4.43)
587 (3.89)
677 (3.76)
515 (4.39)
589 (3.73)
697 (3.71)
512 (4.31)
588 (3.72)
710 (3.62)
515 (4.40)
591 (3.65)
515 (4.23)
590 (3.36)
697 (3.37)
515 (4.30)
621 (3.30)
695 (3.51)
552 (4.29)
1.00
1.40
–1.18
–1.54
647 (3.96)
588 (3.53)
551 (4.11)
678 (3.91)
550 (3.95)
698 (3.70)
546 (3.67)
711 (3.65)
549 (4.52)
615 (3.61)
Zn24
25
421 (5.36)
430 (5.79)
0.78
1.08
1.06
–1.26
–1.03
–1.56
–1.38
1.43
1.53
1.42
1.47
26
27
1
437 (5.46)
433 (5.05)
422 (5.86)
1.14
1.07
1.07
–0.93
–0.95
–1.26
–1.18
–1.55
430 (sh)
0.77
0.77
0.78
–1.02
–0.83
–0.92
–1.35
2
3
422 (5.69)
422 (5.71)
437 (5.50)
550 (4.39)
633 (3.34)
1.06
1.08
1.31
–1.19
–1.14
–1.52
–1.58
548 (4.34)
644 (3.07)
4
5
421 (5.55)
420 (5.30)
429 (sh)
551 (4.10)
614 (3.50)
551 (3.91)
647 (3.37)
1.07
1.05
1.45
1.12
–1.03
–1.17
–1.12
–1.34
–1.51
–1.48
436 (5.14)
1.38 –0.82
6
435 (5.35)
550 (3.98)
680 (3.50)
1.08
1.40
1.59 –0.89
–1.02
–1.33
Figure 5. Reduction waves of click dyads (a) 1 and (b) 5 recorded
in dichloromethane with TBAP as supporting electrolyte (scan rate:
50 mV/s).
Figure 4. Q-band absorption spectra of 5 (solid line), 28 (dotted
line) and 26 (dashed line) recorded in dichloromethane. The inset
shows their corresponding Soret band absorption spectra.
phyrin sub-unit. However, when the 1:1 mixture of its corre-
pounds were recorded in dichloromethane at room tem- sponding monomers was recorded at 550 nm, the emission
perature and the data is presented in Table 2. In dyads 1–3, was exclusively observed for the ZnN4 porphyrin sub-unit.
the ZnN4 porphyrin sub-unit acts as energy donor and ab- Furthermore, the excitation spectrum of the dyad 1 re-
sorbs strongly at 550 nm; N3S, N2S2 and N2SO porphyrin corded at 750 nm matched closely with the absorption spec-
sub-units respectively acts as energy acceptors and do not trum. These results indicate that there is an efficient energy
absorb strongly at 550 nm. A comparison of steady state transfer in singlet state from the ZnN4 porphyrin sub-unit
emission spectra of ZnN4–N3S dyad 1 along with its 1:1 to the N3S porphyrin sub-unit. Similarly, in the case of dyad
mixture of corresponding porphyrin monomers 25 and 29 2, upon excitation at 550 nm, the emission from the ZnN4
recorded at 550 nm is shown in part a of Figure 6. Inspec- porphyrin sub-unit is quenched significantly and a strong
tion of this reveals that on excitation of dyad at 550 nm emission is observed for the N2S2 porphyrin sub-unit, which
where the ZnN4 porphyrin sub-unit absorbs strongly, the supports an efficient energy transfer from the ZnN4 por-
emission from ZnN4 porphyrin emission is quenched by phyrin sub-unit to the N2S2 porphyrin sub-unit in dyad 2.
87% and a strong emission is observed from the N3S por- Interestingly, in the case of dyad 3 containing ZnN4 and
500
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
Table 2. Emission data of click dyads 1–6 along with the (azidophenyl)porphyrin monomers 24–27 recorded in dichloromethane.
Compound
Φdonor
% Quenching
τdonor [ps]
Energy transfer efficiency
24
Zn24
25
26
27
1
0.084
0.036
0.016
0.0073
0.013
0.0046
0.0036
0.01
–
–
–
–
–
87
90
73
97
98
–
8140
1590
1590
1240
1030
150
190
990
230
280
–
–
–
–
–
90
88
37
97
97
–
2
3
4
0.0028
0.0014
0.0005
5
6
290
N2SO porphyrin sub-units, the energy transfer is not ef- emission was noted from the N2S2 porphyrin sub-unit, in
ficient from the ZnN4 porphyrin to the N2SO porphyrin this case it is difficult to calculate the magnitude of emission
sub-unit. This requires further investigation.
of N3S porphyrin sub-unit quenched because the emission
bands of both N3S and N2S2 porphyrin sub-units overlap
with each other significantly. However, the fact that the
emission was noted mainly from N2S2 porphyrin sub-unit,
we conclude that the energy transfer is possible from the
N3S porphyrin sub-unit to the N2S2 porphyrin sub-unit in
dyad 6.
The time-resolved fluorescence studies carried out on dy-
ads 1–6 also support the assumption of an efficient energy
transfer from one porphyrin sub-unit to the other in dyads
1–6. The dyads were excited at 406 nm and monitored at
two different wavelengths corresponding to the emission
peak maxima of donor porphyrin sub-unit and acceptor
porphyrin sub-unit. The fluorescence decays of dyads 1–6
monitored at acceptor heteroporphyrin sub-unit was fitted
to single exponential and the lifetime τ was closely matched
with the corresponding porphyrin monomer. The fluores-
cence decays of dyads 1–6 monitored at emission peak max-
ima of donor porphyrin sub-unit were fitted to two ex-
ponential with a dominant contribution from one compo-
nent. For instance the fluorescence decay of dyad 1 was
fitted to two exponential decay with lifetime of 150 ps
(90%) as the major component and decay with lifetime of
1.2 ns (10%) as the minor component. The minor compo-
nent with life time of 1.2 ns was attributed to the mono-
meric porphyrin impurity present in the dyad 1 and the
major component decay with 150 ps is the quenched life-
time of donor ZnN4 porphyrin sub-unit due to singlet–sing-
let energy transfer from the donor ZnN4 porphyrin sub-unit
to the acceptor N3S porphyrin sub-unit. In other dyads 2–
5, similar observations were made and the shorter major
component decay was attributed to energy transfer from
donor porphyrin sub-unit to acceptor porphyrin sub-unit
(Table 2).
Figure 6. Comparison of emission spectra of click dyads (thick line)
(a) 1 and (b) 5 along with 1:1 mixture of corresponding monomers
(dashed line) recorded in dichloromethane at λex = 550 and 410 nm,
respectively.
The steady-state fluorescence spectra of the free-base
porphyrin dyads 4 and 5 were recorded at 420 nm where
the N4 porphyrin sub-unit absorbs strongly. As is clear from
Figure 6 (b) shown for dyad 5, on excitation at 420 nm, the
emission from the N4 porphyrin sub-unit was quenched by
98% and the strong emission was noted mainly from N2S2
porphyrin sub-unit. Similar observation was made for dyad
4 also, where the N4 porphyrin sub-unit was quenched by
97% and a strong emission was noted for the N3S por-
phyrin sub-unit. These results support an efficient energy
transfer in the singlet state from the N4 porphyrin sub-unit
to the heteroporphyrin sub-unit in dyads 4 and 5. The fluo-
Triazole-Bridged Porphyrin–Ferrocene Conjugates 7–11
The meso-(azidophenyl)porphyrin building blocks 24–27
rescence spectrum of free-base dyad 6 containing N3S and were used further to synthesize triazole-bridged porphyrin–
N2S2 porphyrin sub-units was recorded at 425 nm where ferrocene conjugates 7–11. Linking ferrocene moieties to
N3S porphyrin sub-unit absorbs relatively strongly com- porphyrin is of interest because the ferrocene, according to
pared to the N2S2 porphyrin sub-unit. Although the major thermodynamic considerations, is able to reduce porphyrin
Eur. J. Org. Chem. 2010, 494–508
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501

V. S. Shetti, M. Ravikanth
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hence porphyrin–ferrocene hybrid molecules can be used in phyrinic protons which may be arising from the dynamic
various photochemical devices, including donor-acceptor processes such as rotational isomerism taking place in solu-
molecules that mimic the initial stages in the photosynthetic tion at room temperature.[18] In general the chemical shift
process at the molecular level.[17] Herein we describe the patterns of all conjugates were almost matching with those
utility of meso-(azidophenyl)porphyrin building blocks for of corresponding meso-(azidophenyl)porphyrins supporting
the synthesis of triazole-bridged porphyrin–ferrocene con- weak interaction between porphyrin and ferrocenyl sub-
jugates under similar click reaction condition used above units.
for the synthesis of unsymmetrical porphyrin dyads. In a
The absorption spectra of conjugates 7–11 were recorded
typical reaction, one equivalent of meso-(azidophenyl)por- in dichloromethane. The absorption peak maxima of conju-
phyrin building block was treated with one equivalent of gates are exactly matching with their corresponding meso-
ethynyl ferrocene in THF/CH3CN in the presence of CuI/ (azidophenyl)porphyrin monomers with slight alterations in
DIPEA at room temperature for 12 h (Scheme 3). TLC their extinction coefficients supporting a weak interaction
analysis showed three spots corresponding to the small between porphyrin and ferrocene sub-units (Table 3). The
amounts of unreacted starting materials as first two spots electrochemical properties of porphyrin–ferrocene conju-
followed by the major polar spot corresponding to the re- gates 7–11 were followed by cyclic voltammetry at scan rate
quired porphyrin–ferrocene conjugates. Column chromato- of 50 mV/s using tetrabutylammonium perchlorate as sup-
graphic purification on silica gel afforded pure porphyrin– porting electrolyte in dichloromethane. In general, as men-
ferrocene conjuagates 7–11 in 48–52% yield. The por- tioned above, the porphyrins exhibit two oxidation and two
phyrin–ferrocene conjugate 8 was obtained in quantitative reduction waves corresponding to the formation of mono,
yield by demetallation of 7 by treating it with TFA in dications and mono, dianions of porphyrin ring respec-
CH2Cl2 for 1 h followed by column chromatographic purifi- tively.[19] The absolute E1/2 values depend on the nature of
cation. The porphyrin–ferrocene conjugates 7–11 were the porphyrin. In porphyrin–ferrocene conjugates, an ad-
highly soluble in all common organic solvents and charac- ditional redox couple corresponding to the oxidation of fer-
terized by mass, NMR, absorption, electrochemical and rocene ring is also expected. A comparison of oxidation and
fluorescence techniques.
reduction waves of meso-(azidophenyl)porphyrin 25 and
The molecular ion peak in ES-MS mass spectra con- azidoporphyrin–ferrocene conjugate 9 is shown in Figure 7
firmed the identity of all porphyrin–ferrocene conjugates 7– and the data is presented in Table 3. The ethynyl ferrocene
11. It is clear that the conjugate 9 exhibits similar NMR shows a reversible oxidation couple at 0.65 V.[17] In triazole-
features like meso-(azidophenyl)porphyrin monomer 25 ex- bridged porphyrin–ferrocene conjugates 7–11, the reversible
cept for a few changes. The 2, 6-protons of meso-phenyl oxidation couple was noted in 0.53–0.57 V region. Thus, in
group which is connected to the triazole ring was shifted conjugates 7–11, the ferrocene group is easier to oxidize
downfield by about 1 ppm; a characteristic singlet at which can be rationalized as follows. In porphyrin–ferro-
8.2 ppm for the triazole proton and three signals in 4.2– cene conjugate, the meso-phenyl groups are orthogonal to
5.1 ppm region for nine ferrocene proton signals. In the re- the porphyrin plane thus preventing the electron density
maining conjugates, apart from the above-mentioned distribution between porphyrin and ferrocene groups re-
changes, we also noticed the presence of minor sets of ad- sulting in easier oxidation of ferrocene ring compared to
ditional signals for ferrocenyl as well as for selected por- ethynyl ferrocene. The oxidation and reduction potentials of
Table 3. Absorption and electrochemical data of porphyrin–ferrocene click conjugates 7–11 recorded in dichloromethane.
Compound
Soret band
Q-bands
Potential [V] vs. SCE
Oxidation
λ [nm] (logε)
λ [nm] (logε)
Reduction
I
I
II
III
II
7
8
421 (5.81)
419 (5.84)
548 (4.39)
587 (3.65)
516 (5.84)
551 (4.15)
591 (3.84)
647 (3.76)
515 (4.34)
550 (3.87)
617 (3.28)
677 (3.66)
515 (4.50)
549 (4.04)
634 (3.02)
697 (3.79)
513 (4.24)
544 (3.62)
645 (2.67)
711 (3.61)
0.57
0.79
1.10
–1.50
–1.70
0.57
0.53
0.56
0.57
1.03
1.08
1.47
–1.17
–1.49
–1.36
–1.20
–1.18
9
430 (5.47)
437 (5.57)
433 (5.13)
–1.04
–0.89
–0.93
10
11
1.13
502
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
Table 4. Emission data of porphyrin–ferrocene click conjugates 7–11 recorded in dichloromethane.
Compound
λem [nm]
Φf
τf [ns]
krad [106 s–1]
knr [108 s–1]
7
600
653
686
709
718
648
0.029
0.032
0.0091
0.0040
0.0065
1.11
4.35
1.11
1.16
0.81
26.12
7.35
8.19
3.44
8.02
8.74
2.22
8.92
8.58
12.26
8
9
10
11
porphyrin ring did not show any shifts compared to meso-
(azidophenyl)porphyrins further supporting a weak interac-
tion between ferrocene and porphyrin sub-units in por-
phyrin–ferrocene conjugates 7–11. The fluorescence proper-
ties of porphyrin–ferrocene conjugates 7–11 were studied by
both steady state and time-resolved fluorescence techniques.
The comparison of steady state fluorescence spectra of por-
phyrin–ferrocene conjugate 9 with meso-(azidophenyl)por-
phyrin 25 is shown in Figure 8 and the data are tabulated
in Table 4. Inspection of Figure 8 and Table 4 indicates that
the emission peak maxima of porphyrin in porphyrin–ferro-
cene conjugates is almost identical with the emission peak
maxima of the corresponding monomeric porphyrin. How-
ever, the quantum yields of porphyrin in porphyrin–ferro-
cene conjugates are decreased compared to the correspond-
ing monomeric porphyrins. The singlet state lifetime for
porphyrin–ferrocene conjugates was measured by single-
photon counting technique. All conjugates were excited at
406 nm and were detected at the emission peak maxima of
the porphyrin in porphyrin–ferrocene conjugates. The fluo-
rescence decays of porphyrin–ferrocene conjugates 7–11
were fitted to single exponential decay functions. The sing-
let state lifetime τ, rate of radiative decay kr and rate of
nonradiative decay knr presented in Table 4 reveal the fol-
lowing as compared to their corresponding reference meso-
(azidophenyl)porphyrin monomers: (1) the singlet state life-
time τ of porphyrin in porphyrin–ferrocene conjugates 7–
11 is decreased. (2) The rates of radiative decay kr is de-
creased and non-radiative decay knr is increased for por-
phyrin in porphyrin–ferrocene conjugates 7–11. All these
results suggest that the fluorescence of porphyrin in por-
phyrin–ferrocene conjugates is significantly quenched which
is attributed tentatively to electron transfer from ferrocene
to singlet excited state of porphyrin.
Figure 8. Comparison of emission spectra of 25 (solid line) and 9
(dotted line) recorded in dichloromethane. The concentration used
was 2 ϫ10–6 .
Conclusions
Three new mono-nitroporphyrins with N3S, N2S2 and
N2SO cores were synthesized by condensing an unsymmet-
rical thiophenediol with p-tolualdehyde/pyrrole, 16-thia-
tripyrrin and 16-oxatripyrrin, respectively, under mild por-
phyrin-forming conditions. The mono-aminoporphyrins
were synthesized from corresponding mono-nitropor-
phyrins under standard SnCl2/HCl conditions. The mono-
azidoporphyrins were synthesized by adopting a simple ap-
proach of treating mono-aminoporphyrins with tert-butyl
nitrite/azidotrimethylsilane at room temperature. The
mono-azidoporphyrins have been used to synthesize a series
of triazole-bridged unsymmetrical porphyrin dyads con-
taining two different porphyrin sub-units and triazole-
bridged porphyrin–ferrocene conjugates under “click reac-
tion” conditions. Under various CuI-catalyzed click reac-
tion conditions employed, the best yields were obtained
when we used CuI/DIPEA (0.1:1) in THF/CH3CN at room
temperature for overnight. The ground state properties of
dyads and conjugates indicate a weak interaction between
the two sub-units. A preliminary photophysical studies sup-
port an efficient energy transfer from one porphyrin sub-
unit to another in unsymmetrical porphyrin dyads and elec-
tron-transfer from ferrocene to porphyrin in porphyrin–fer-
rocene conjugates. Presently, we are exploring the click reac-
tion approach developed in this paper to synthesize more
elaborate assemblies.
Experimental Section
Chemicals: All general chemicals and solvents were procured from
S.D. Fine chemicals, India. Column chromatography was per-
formed using silica gel and basic alumina obtained from Sisco Re-
Figure 7. Cyclic voltammogram of (a) 25 and (b) 9 recorded in
dichloromethane with TBAP as supporting electrolyte (scan rate:
50 mV/s).
Eur. J. Org. Chem. 2010, 494–508
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503

V. S. Shetti, M. Ravikanth
FULL PAPER
search Laboratories, India. tert-butyl nitrite and Azidotrimethylsil-
ane were purchased from Aldrich. Tetrabutylammonium per-
chlorate was purchased from Fluka and used without further puri-
fications.
12.2 mmol) and nBuLi (7.70 mL of 1.6  solution in hexane,
12.2 mmol) were added to a solution of 2-(p-tolylhydroxymethyl)-
thiophene (13) (1 g, 4.9 mmol) in diethyl ether (30 mL) and stirred
at 0 °C for 1 h. An ice cold solution of 4-nitrobenzaldehyde (0.9 g,
5.8 mmol) in THF was added and stirring was continued for an
additional 1 h. Saturated aqueous NH4Cl solution was added to
the reaction mixture and was extracted with diethyl ether
(3ϫ50 mL). The organic layers were combined, washed with satu-
rated brine and dried with sodium sulfate. The crude product was
concentrated in vacuo and purified by silica gel column chromatog-
raphy using petroleum ether/ethyl acetate (72:28) to afford the diol
14 as white solid in 47% yield (800 mg); m.p. 125 °C. 1H NMR
(400 MHz, CDCl3): δ = 2.34 (s, 3 H, tolyl), 2.43 (br. s, 1 H, OH),
2.65 (br. s, 1 H, OH), 5.92 (s, 1 H, CHOH), 6.06 (s, 1 H, CHOH),
6.70 (d, J = 3.3 Hz, 1 H, thiophene), 6.75 (d, J = 3.3 Hz, 1 H,
thiophene), 7.16 (d, J = 7.9 Hz, 2 H, Ar), 7.29 (d, J = 8.2 Hz, 2 H,
Ar), 7.60 (d, J = 9.1 Hz, 2 H, Ar), 8.19 (d, J = 8.8 Hz, 2 H, Ar)
ppm. 13C NMR (100 MHz, CDCl3): δ = 21.3, 71.6, 72.6, 110.2
123.9, 124.5, 125.3, 126.3, 127.1, 129.5, 138.2, 139.9, 146.4, 149.7,
1
Instrumentation: H NMR spectra were recorded with Varian 300
and 400 MHz instruments using tetramethylsilane (TMS) as an in-
ternal standard. 13C NMR spectra were recorded on Varian spec-
trometer operating at 100.6 MHz. All NMR measurements were
carried out at room temperature in deuteriochloroform (CDCl3).
Absorption and steady state fluorescence spectra were obtained
with Perkin–Elmer Lambda-35 and PC1 Photon Counting Spectro-
fluorometer manufactured by ISS USA, respectively. The fluores-
cence quantum yields (Φf) were estimated from the emission and
absorption spectra by comparative method.[20] The time-resolved
fluorescence decay measurements[21] were carried out at magic an-
gle using a picosecond diode laser based time correlated single pho-
ton counting (TCSPC) fluorescence spectrometer from IBH, UK.
The energy transfer efficiencies for dyads 1–5 were calculated from
the lifetime data of dyads and their corresponding appropriate
monomers.[20] The radiative and non-radiative rate constants, kr
and knr were calculated by the following equations:
149.8 ppm. ES MS: m/z (%)
C19H17NO4S (355.41): calcd. C 64.21, H 4.82, N 3.94, S 9.02; found
C 64.25, H 4.75, N 3.95, S 9.05.
= 338.07 (100) [M –
OH]+.
ΣK = 1/τf
kr = Φfk
(1)
(2)
(3)
5-(4-Nitrophenyl)-10,15,20-tri(p-tolyl)-21-thiaporphyrin (15): Sam-
ples of 14 (0.5 g, 1.4 mmol), p-tolualdehyde (0.33 mL, 2.8 mmol)
and pyrrole (0.29 mL, 4.2 mmol), were dissolved in dichlorometh-
ane (300 mL) degassed with nitrogen and stirred for 10 min. The
condensation was initiated by adding BF3·OEt2 (0.4 mL of 2.5 
solution) while stirring the reaction mixture at room temperature
for 1 h under nitrogen atmosphere. DDQ (0.32 g, 1.4 mmol) was
then added and the reaction mixture was stirred in air for ad-
ditional 1 h. The crude compound containing mixture of por-
phyrins was subjected to silica gel column chromatography using
petroleum ether/dichloromethane (60:40) which afforded monothia
nitro porphyrin 15 in 8% yield (80 mg); m.p. Ͼ300 °C. 1H NMR
(400 MHz, CDCl3): δ = –2.68 (s, 2 H, NH), 2.70 (s, 9 H, CH3),
7.52 (d, J = 7.6 Hz, 4 H, Ar), 7.62 (d, J = 7.9 Hz, 2 H, Ar), 8.06
(d, J = 7.9 Hz, 4 H, Ar), 8.12 (d, J = 7.9 Hz, 2 H, Ar), 8.40 (d, J
= 8.5 Hz, 2 H, Ar), 8.56 (d, J = 4.2 Hz, 1 H, β-pyrrole), 8.62 (d, J
= 4.2 Hz, 1 H, β-pyrrole) 8.65–8.68 (m, 4 H, Ar) 8.96 (m, 2 H, β-
pyrrole) 9.60 (d, J = 5.1 Hz, 1 H, β-thiophene) 9.78 (d, J = 5.1 Hz,
1 H, β-thiophene) ppm. 13C NMR (100 MHz, CDCl3): δ = 22.0,
123.1, 125.01125.5, 127.9, 128.9, 129.6, 129.8, 132.5, 132.8, 133.4,
133.7, 134.7, 134.9, 135.2, 135.5, 136.3, 136.7, 138.2, 138.3, 139.8,
139.9, 140.0, 147.2, 147.3, 148.2, 148.6, 155.2, 156.7, 158.4 ppm.
ES MS: m/z (%) = 718.85 (100) [M]+. C47H34N4O2S (718.86): calcd.
C 78.53, H 4.77, N 7.79, S 4.46; found C 78.60, H 4.70, N 7.83, S
4.48. UV/Vis [in dichloromethane, λmax/nm (logε)]: 431 (5.48), 516
(4.36), 553 (3.97), 617 (3.57), 676 (3.73).
knr = k – kr
ES-MS spectra were recorded with a Q-Tof Micromass spectrome-
ter. MALDI-TOF spectra were obtained from Axima-CFR manu-
factured by Kratos Analyticals. Cyclic voltammetric (CV) and
differential pulse voltammetric (DPV) studies were carried out with
BAS electrochemical system utilizing the three electrode configura-
tion consisting of a glassy carbon (working electrode), platinum
wire (auxiliary electrode) and saturated calomel (reference elec-
trode) electrodes in dry dichloromethane using 0.1  tetrabutylam-
monium perchlorate as supporting electrolyte.
5-(4-Nitrophenyl)-10,15,20-tri(p-tolyl)porphyrin (12): Samples of p-
tolualdehyde (1.19 g, 1.17 mL, 9.9 mmol), 4-nitrobenzaldehyde
(0.5 g, 3.3 mmol) and pyrrole (0.87 g, 0.91 mL, 13.2 mmol) were
dissolved in dichloromethane (300 mL) and purged with nitrogen
whilst stirring for 10 min. The condensation was initiated by adding
catalytic amount of BF3·OEt2 (0.4 mL of 2.5  solution) and stir-
ring was continued for 1 h under nitrogen atmosphere at room tem-
perature. 2,3-Dichloro-5,6-dicyano-benzoquinone (DDQ) (0.75 g,
3.3 mmol) was then added and the reaction mixture was stirred in
air for additional 1 h. The solvent was removed under reduced pres-
sure and the crude compound was subjected to silica gel column
chromatography. The desired compound was moved as purple band
with petroleum ether/dichloromethane (60:40) and the solvent was
removed on rotary evaporator to afford pure nitro porphyrin in
5-(4-Nitrophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (17): A
solution of 14 (0.5 g, 1.4 mmol) and 5,10-bis(p-tolyl)-15,17-dihy-
dro-16-thiatripyrrane (0.6 g, 1.4 mmol) in dichloromethane
(300 mL) was degassed with nitrogen whilst stirring for 10 min.
BF3·OEt2 (0.4 mL of 2.5  solution) was added to initiate the con-
densation and the reaction mixture was stirred at room temperature
for 1 h under nitrogen atmosphere. DDQ (0.32 g, 1.4 mmol) was
added and the reaction mixture was stirred in air for additional
1 h. The solvent was removed under reduced pressure and the tlc
analysis of crude compound showed the formation of desired com-
pound as sole product. The crude compound was subjected to silica
gel column chromatography using petroleum ether/dichlorometh-
ane (60:40) to obtain the pure mononitrodithiaporphyrin 17 in 10%
yield (103 mg); m.p. Ͼ300 °C. 1H NMR (400 MHz, CDCl3): δ =
2.70 (s, 9 H, CH3), 7.61 (d, J = 7.6 Hz, 6 H, Ar), 8.10–8.13 (m, 6
1
10% yield (232 mg); m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3):
δ = –2.77 (s, 2 H, NH), 2.70 (s, 9 H, CH3), 7.55 (d, J = 7.7 Hz, 6
H, Ar), 8.08 (d, J = 7.7 Hz, 6 H, Ar), 8.37 (d, J = 8.2 Hz, 2 H,
Ar), 8.61 (d, J = 8.7 Hz, 2 H, Ar), 8.70 (d, J = 5.0 Hz, 2 H, β-
pyrrole), 8.80 (s, 4 H, β-pyrrole), 8.89 (d, J = 4.5 Hz, 2 H, β-pyr-
role) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.2, 116.5, 120.8,
121.3, 121.8, 127.0, 128.2, 134.0, 134.8, 135.3, 137.7, 139.2, 147.8,
149.5 ppm. ES MS: m/z (%) = 702.33 (100) [M]+. C47H35N5O2
(701.81): calcd. C 80.43, H 5.03, N 9.98; found C 80.50, H 4.98, N
10.01. UV/Vis [in dichloromethane, λmax/nm (logε)]: 420 (5.57), 516
(4.23), 553 (3.98), 591 (3.74), 647 (3.67).
2-[Hydroxy(4-nitrophenyl)methyl]-5-[hydroxy(p-tolyl)methyl]thio-
phene (14): N,N,NЈ,NЈ-Tetramethyl ethylenediamine (1.9 mL,
504
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Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
H, Ar), 8.37 (d, J = 8.8 Hz, 2 H, Ar), 8.54 (d, J = 4.5 Hz, 1 H, β-
pyrrole), 8.64–8.69 (m, 4 H, β-pyrrole + Ar), 8.72 (d, J = 4.5 Hz,
1 H, β-pyrrole) 9.52 (d, J = 5.1 Hz, 1 H, β-thiophene), 9.72 (d, J
= 4.5 Hz, 3 H, β-thiophene) ppm. 13C NMR (100 MHz, CDCl3):
δ = 21.6, 122.7, 128.4, 130.0, 133.5, 134.1, 134.3, 134.7, 134.8,
134.9, 135.0, 135.2, 135.4, 135.8, 136.0, 136.2, 138.1, 138.2, 138.3,
147.1, 147.6, 147.9, 148.2, 148.3, 148.6, 148.6, 155.3, 156.7, 156.8,
157.0 ppm. ES MS: m/z (%) = 736.2 (100) [M]+. C47H33N3O2S2
(735.91): calcd. C 76.71, H 4.52, N 5.71, S 8.71; found C 76.61, H
4.57, N 5.77, S 8.75. UV/Vis [in dichloromethane, λmax/nm (logε)]:
438 (5.65), 516 (4.66), 551 (4.28), 634 (3.68), 698 (4.03).
Ar), 8.60 (d, J = 4.5 Hz, 2 H, β-pyrrole), 8.68 (d, J = 4.5 Hz, 1 H,
β-pyrrole) 8.73 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.92 (m, 2 H, β-
pyrrole), 9.74 (d, J = 5.1 Hz, 1 H, β-thiophene), 9.80 (d, J = 5.1 Hz,
1 H, β-thiophene) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.6,
110.1, 114.4, 123.5, 123.8, 127.4, 128.4, 128.8, 128.9, 131.3, 131.5,
132.1, 133.1, 134.2, 134.5, 135.4, 137.6, 138.4, 139.1, 139.8, 146.3,
147.4, 154.5, 154.6, 157.4, 157.9 ppm. ES MS: m/z (%) = 688.80
(100) [M]+. C47H36N4S (688.88): calcd. C 81.94, H 5.27, N 8.13, S
4.65; found C 81.97, H 5.25, N 8.20, S 4.55. UV/Vis [in dichloro-
methane, λmax/nm (logε)]: 433 (5.72), 517 (4.62), 555 (4.36), 621
(3.82), 682 (4.14).
5-(4-Aminophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (22):
Yield 75%; m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = 2.70
5-(4-Nitrophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin (19):
The samples of 14 (0.5 g, 1.4 mmol) and 5,10-bis(p-tolyl)-16-oxa-
15,17-dihydrotripyrrane (18) were condensed in dichloromethane
(300 mL) in the presence of catalytic amount of BF3·OEt2 (0.4 mL
of 2.5  solution) for 1 h under nitrogen atmosphere followed by
oxidation with DDQ at room temperature in air and gave a crude
product which was subjected to silica gel column chromatography
using dichloromethane/methanol (98:2) to afford 19 in 8% yield
1
(s, 9 H, CH3), 4.04 (broad s, 2 H, NH2), 7.10 (d, J = 8.2 Hz, 2 H,
Ar), 7.60 (d, J = 7.6 Hz, 6 H, Ar), 8.03 (d, J = 4.5 Hz, 2 H, β-
pyrrole), 8.12 (d, J = 7.9 Hz, 6 H, Ar), 8.62–8.68 (m, 3 H, Ar + β-
pyrrole), 8.73 (d, J = 4.5 Hz, 1 H, β-pyrrole), 9.67–9.72 (m, 3 H, β-
thiophene), 9.74 (d, J = 4.8 Hz, 1 H, β-thiophene) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.6, 114.3, 128.3, 131.7, 133.8, 134.0,
134.3, 134.4, 134.5, 134.6, 134.8, 135.3, 135.4, 135.6, 135.7, 137.8,
138.6, 146.5, 147.7, 148.1, 148.2, 156.4, 156.5, 156.6, 156.9 ppm.
ES MS: m/z (%) = 706.4 (100) [M]+. C47H35N3S2 (705.93): calcd.
C 79.97, H 5.00, N 5.95, S 9.08; found C 79.95, H 5.05, N 5.92, S
9.10. UV/Vis [in dichloromethane, λmax/nm (logε)]: 440 (5.58), 518
(4.56), 555 (4.30), 637 (3.52), 703 (4.04).
1
(81 mg); m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = 2.70 (s,
9 H, CH3), 7.54 (d, J = 7.6 Hz, 4 H, Ar), 7.61 (d, J = 7.6 Hz, 2 H,
Ar), 8.02–8.06 (m, 4 H, Ar), 8.10 (d, J = 8.0 Hz, 2 H, Ar), 8.37–
8.47 (m, 5 H, β-pyrrole + Ar), 8.55 (d, J = 4.3 Hz, 1 H, β-pyrrole),
8.66 (d, J = 8.7 Hz, 2 H, Ar), 9.20 (s, 2 H, β-furan), 9.56 (d, J =
5.1 Hz, 1 H, β-thiophene), 9.74 (d, J = 5.1 Hz, 1 H, β-thiophene)
ppm. 13C NMR (100 MHz, CDCl3): δ = 21.4, 21.5, 121.2, 121.7,
127.5, 127.6, 129.8, 130.1, 132.4, 133.6, 133.9, 134.1, 134.2, 134.7,
135.8, 136.5, 136.9, 137.5, 137.8, 138.0, 139.3, 139.4, 147.6, 150.1,
150.6, 155.4, 155.6, 156.6, 156.9, 157.8, 159.5 ppm. ES MS: m/z
(%) = 720.21 (100) [M]+. C47H33N3O3S (719.85): calcd. C 78.42, H
4.62, N 5.84, S 4.45; found C 78.47, H 4.58, N 5.77, S 4.53. UV/
Vis [in dichloromethane, λmax/nm (logε)]: 432 (5.48), 513 (4.58), 546
(4.06), 644 (3.44), 710 (3.99).
5-(4-Aminophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin
1
(23): Yield 75%; m.p. Ͼ300 °C H NMR (400 MHz, CDCl3): δ =
2.69 (s, 9 H, CH3), 3.62 (br. s, 2 H, NH2), 7.12 (d, J = 8.5 Hz, 2
H, Ar), 7.52 (d, J = 7.6 Hz, 4 H, Ar), 7.60 (d, J = 7.6 Hz, 2 H,
Ar), 8.02–8.05 (m, 6 H, Ar), 8.11 (d, J = 7.9 Hz, 2 H, Ar), 8.37–
8.38 (m, 2 H, β-pyrrole), 8.53 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.58
(d, J = 4.5 Hz, 1 H, β-pyrrole), 9.13 (s, 2 H, β-furan), 9.68 (d, J =
5.1 Hz, 1 H, β-thiophene), 9.74 (d, J = 5.1 Hz, 1 H, β-thiophene)
ppm. 13C NMR (100 MHz, CDCl3): δ = 21.4, 21.5, 114.2, 120.1,
120.4, 127.5, 128.2, 129.3, 129.5, 131.0, 133.4, 133.5, 133.8, 134.1,
134.3, 134.6, 134.9, 135.1, 135.7, 135.9, 137.5, 137.7, 137.9, 139.7,
146.3, 150.8, 151.0, 155.1, 155.4, 156.3, 156.5, 158.7, 159.1 ppm.
MALDI-TOF: m/z (%) = 690.4 (100) [M]+. C47H35N3OS (689.87):
calcd. C 81.83, H 5.11, N 6.09, S 4.65; found C 81.85, H 5.09, N
6.15, S 4.60. UV/Vis [in dichloromethane, λmax/nm (logε)]: 435
(5.50), 515 (4.62), 551 (4.24), 648 (3.54), 716 (4.16).
General Synthesis of meso-(Aminophenyl)porphyrins 20–23: To a
solution of nitroporphyrin in CHCl3/HOAc (1:2) was added a solu-
tion of SnCl2·2H2O (4 equiv.) in concd. aqueous HCl. The mixture
was vigorously stirred in a preheated oil bath (65–70 °C) for
30 min, refluxed overnight and neutralized with ammonia solution
(25%) to pH 8–9. Chloroform (50 mL) was added, and the mixture
was stirred for 1 h. The organic phase was separated, and the water
phase was extracted with CHCl3 (2ϫ50 mL). The combined or-
ganic layer was washed once with dilute ammonia solution, three
times with water, dried with anhydrous Na2SO4 and then concen-
trated to dryness. The residue was purified by silica gel column
chromatography using petroleum ether/dichloromethane to get
pure meso-(aminophenyl)porphyrin in 75–84% yield.
General Synthesis of meso-(Azidophenyl)porphyrins 24–27: Sample
of meso-(aminophenyl)porphyrin was dissolved in CH3CN /THF
(1:1) in a 25 mL round-bottomed flask and cooled to 0 °C in an
ice bath. To this stirred mixture was added tBuONO (1.5 equiv.)
followed by TMSN3 (1.2 equiv.) slowly. The resulting solution was
stirred at room temperature for 1 h. The reaction mixture was con-
centrated under vacuum and the crude product was purified by
silica gel chromatography using petroleum ether/dichloromethane
to afford pure meso-(azidophenyl)porphyrin in 60–90% yield.
5-(4-Aminophenyl)-10,15,20-tri(p-tolyl)porphyrin (20): Yield 84%;
m.p. Ͼ300 °C. 1H NMR (400 MHz, CDCl3): δ = –2.76 (s, 2 H,
NH), 2.70 (s, 9 H, CH3), 3.98 (broad, 2 H, NH2), 7.05 (d, J =
8.2 Hz, 2 H, Ar), 7.54 (d, J = 8.2 Hz, 6 H, Ar), 7.98 (d, J = 8.2 Hz,
2 H, Ar), 8.09 (d, J = 8.2 Hz, 6 H, Ar), 8.84 (s, 6 H, β-pyrrole),
8.91 (d, J = 4.5 Hz, 2 H, β-pyrrole) ppm. 13C NMR (100 MHz,
CDCl3): δ = 21.7, 113.6, 120.1, 127.5, 134.7, 135.8, 137.4, 139.5,
146.1 ppm. ES MS: m/z (%) = 672.38 (100) [M]+. C47H37N5
(671.83): calcd. C 84.02, H 5.55, N 10.42; found C 84.10, H 5.60,
N 10.32. UV/Vis [in dichloromethane, λmax/nm (logε)]: 421 (5.64),
517 (4.24), 555 (4.06), 593 (3.76), 647 (3.77).
5-(4-Azidophenyl)-10,15,20-tri(p-tolyl)porphyrin (24): Yield 90%;
m.p. Ͼ300 °C. 1H NMR (400 MHz, CDCl3): δ = –2.78 (s, 2 H,
NH), 2.70 (s, 9 H, CH3), 7.41 (d, J = 8.2 Hz, 2 H, Ar), 7.55 (d, J
= 7.9 Hz, 6 H, Ar), 8.07 (d, J = 7.9 Hz, 6 H, Ar), 8.19 (d, J =
8.2 Hz, 2 H, Ar), 8.80 (d, J = 4.5 Hz, 2 H, β-pyrrole), 8.86 (m, 6
H, β-pyrrole) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.7, 117.5,
120.4, 120.6, 127.6, 131.5, 134.7, 135.8, 137.5, 139.2, 139.3,
139.9 ppm. ES MS: m/z (%) = 698.41 (100) [M]+. C47H35N7
(697.83): calcd. C 80.89, H 5.06, N 14.05; found C 80.95, H 5.09,
N 14.12.
5-(4-Aminophenyl)-10,15,20-tri(p-tolyl)-21-thiaporphyrin (21): Yield
1
75%; m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = –2.66 (s, 2
H, NH), 2.70 (s, 9 H, CH3), 4.02 (broad s, 2 H, NH2), 7.11 (d, J
= 8.2 Hz, 2 H, Ar), 7.53 (d, J = 7.9 Hz, 4 H, Ar), 7.61 (d, J =
7.9 Hz, 2 H, Ar), 8.03–8.08 (m, 6 H, Ar), 8.13 (d, J = 7.9 Hz, 2 H,
5-(4-Azidophenyl)-10,15,20-tri(p-tolyl)-21-thiaporphyrin (25): Yield
1
80%; m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = –2.68 (s, 2
Eur. J. Org. Chem. 2010, 494–508
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
505

V. S. Shetti, M. Ravikanth
FULL PAPER
H, NH), 2.71 (s, 9 H, CH3), 7.49 (d, J = 8.5 Hz, 2 H, Ar), 7.55 (d,
J = 7.9 Hz, 4 H, Ar), 7.63 (d, J = 7.6 Hz, 2 H, Ar), 8.08 (d, J =
7.6 Hz, 4 H, Ar), 8.12 (d, J = 7.6 Hz, 2H Ar), 8.24 (d, J = 7.6 Hz,
5.1 Hz, 1 H, β-thiophene), 9.84 (d, J = 5.1 Hz, 1 H, β-thiophene)
ppm. MALDI-TOF: m/z (%)
C96H68N10SZn (1456.46): calcd. C 79.02, H 4.70, N 9.60, S 2.20;
found C 79.05, H 4.68, N 9.62, S 2.17.
= 1428.6 (100) [M –
28]+.
1
2 H, Ar), 8.62–8.69 (m, 3 H, β-pyrrole), 8.69 (d, J = 4.5 Hz, H β-
pyrrole), 8.95 (m, 2 H, β-pyrrole), 9.70 (d, J = 5.1 Hz, 1 H, β-
thiophene), 9.77 (d, J = 5.1 Hz, 1 H, β-thiophene) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.6, 118.4, 118.7, 124.1, 127.5, 128.4,
129.0, 131.8, 132.7, 133.2, 133.8, 134.3, 134.5, 135.5, 135.6, 135.8,
137.7, 138.0, 139.3, 139.6, 140.1, 147.2, 154.6, 157.2, 157.7 ppm.
ES MS: m/z (%) = 685.38 (100) [M – 28]+. C47H34N6S (714.88):
calcd. C 78.96, H 4.79, N 11.76, S 4.49; found C 78.90, H 4.85, N
11.80, S 4.53.
ZnN4–N2S2 Porphyrin Click Dyad (2): Yield 48%; m.p. Ͼ300 °C.
1H NMR (400 MHz, CDCl3): δ = 2.72 (s, 18 H, CH3), 7.57 (d, J
= 7.3 Hz, 6 H, Ar), 7.65 (d, J = 7.3 Hz, 6 H, Ar), 8.10–8.16 (m, 12
H, Ar), 8.39–8.42 (m, 6 H, Ar), 8.49 (d, J = 8.2 Hz, 2 H, Ar), 8.71
(s, 2 H, β-pyrrole), 8.73 (d, J = 3.9 Hz, 1 H, β-pyrrole), 8.76 (d, J
= 3.9 Hz, 1 H, β-pyrrole), 8.79 (s, 1 H, triazole), 8.96 (s, 4 H, β-
pyrrole), 9.01 (d, J = 4.5 Hz, 2 H, β-pyrrole), 9.03 (d, J = 4.5 Hz,
2 H, β-pyrrole), 9.73–9.77 (m, 4 H, β-thiophene) ppm. MALDI-
5-(4-Azidophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (26): TOF: m/z (%) = 1446.8 (100) [M – 28]+. C96H67N9S2Zn (1473.43):
1
Yield 80%; m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = 2.71
(s, 9 H, CH3), 7.48 (d, J = 8.5 Hz, 2 H, Ar), 7.62 (d, J = 8.2 Hz, 6
H, Ar), 8.13 (d, J = 7.9 Hz, 6 H, Ar), 8.23 (d, J = 8.5 Hz, 2 H,
Ar), 8.64 (d, J = 4.2 Hz, 1 H, β-pyrrole), 8.69–8.71 (m, 3 H, β-
pyrrole), 9.63 (d, J = 5.1 Hz, 1 H, β-thiophene), 9.70–9.71 (m, 3
H, β-thiophene) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.6,
118.3, 128.3, 132.5, 134.1, 134.3, 134.5, 134.6, 134.7, 134.8, 134.9,
135.5, 135.6, 135.7, 137.9, 138.2, 138.4, 140.3, 147.8, 147.9, 148.1,
156.3, 156.6, 156.7 ppm. ES MS: m/z (%) = 732.18 (100) [M]+.
C47H33N5S2 (731.93): calcd. C 77.13, H 4.54, N 9.57, S 8.76; found
C 77.16, H 4.51, N 9.60, S 8.70.
calcd. C 78.11, H 4.57, N 8.54, S 4.35; found C 78.14, H 4.54, N
8.52, S 4.37.
ZnN4–N2SO Porphyrin Click Dyad 3: Yield 46%; m.p. Ͼ300 °C.
1H NMR (400 MHz, CDCl3): δ = 2.72 (s, 18 H, CH3), 7.57 (m, 10
H, Ar), 7.63 (d, J = 8.2 Hz, 2 H, Ar), 8.01 (d, J = 8.2 Hz, 1 H,
Ar), 8.05–8.15 (m, 12 H, Ar), 8.25 (d, J = 7.6 Hz, 1 H, Ar), 8.37
(d, J = 8.2 Hz, 2 H, Ar), 8.41 (d, J = 8.8 Hz, 2 H, Ar), 8.43 (d, J
= 4.5 Hz, 1 H, β-pyrrole), 8.48 (d, J = 8.5 Hz, 2 H, Ar), 8.49 (d, J
= 4.5 Hz, 1 H, β-pyrrole), 8.57 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.61
(d, J = 4.5 Hz, 1 H, β-pyrrole), 8.78 (s, 1 H, triazole), 8.94–9.08
(m, 8 H, β-pyrrole), 9.21 (s, 2 H, β-furan), 9.74 (d, J = 5.1 Hz, 1
H, β-thiophene), 9.79 (d, J = 5.1 Hz, 1 H, β-thiophene) ppm.
MALDI-TOF: m/z (%) = 1429.25 (100) [M – 28]+. C96H67N9OSZn
(1457.45): calcd. C 78.97, H 4.63, N 8.63, S 2.21; found C 78.95,
H 4.65, N 8.65, S 2.19.
5-(4-Azidophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin
1
(27): Yield 60%; m.p. Ͼ300 °C. H NMR (400 MHz, CDCl3): δ =
2.70 (s, 9 H, CH3), 7.48 (d, J = 8.2 Hz 2 H, Ar), 7.54 (d, J = 8.2 Hz,
4 H, Ar), 7.61 (d, J = 7.6 Hz, 2 H, Ar), 8.04 (d, J = 7.9 Hz, 4 H,
Ar), 8.10 (d, J = 7.9 Hz, 2 H, Ar), 8.21 (d, J = 8.5 Hz, 2 H, Ar),
8.41 (m, 2 H, β-pyrrole), 8.50 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.55
(d, J = 4.5 Hz, 1 H, β-pyrrole), 9.18 (s, 2 H, β-furan), 9.64 (d, J =
5.1 Hz, 1 H, β-thiophene), 9.72 (d, J = 4.8 Hz, 1 H, β-thiophene)
ppm. 13C NMR (100 MHz, CDCl3): δ = 21.7, 118.4, 121.1, 127.7,
128.5, 129.9, 133.2, 133.7, 134.3, 134.5, 134.8, 135.5, 135.7, 136.4,
136.5, 137.9, 138.1, 139.8, 140.2, 150.9, 155.6, 156.8, 158.8,
159.3 ppm. MALDI-TOF: m/z (%) = 686.8 (100) [M – 28]+.
C47H33N5OS (715.86): calcd. C 78.86, H 4.65, N 9.78, S 4.48; found
C 78.90, H 4.60, N 9.83, S 4.40.
Demetallated dyads 4 and 5 can be obtained by treating dichloro-
methane solution of zinc dyads 1 and 2 (10 mg in 10 mL of dichlo-
romethane) with minute amount of trifluoroacetic acid (0.1 mL) at
room temperature followed by neutralization with triethylamine.
The resulting compound was passed through a small plug of basic
alumina to get pure demetallated dyads in quantitative yields.
N4-N3S Porphyrin Click Dyad 4: M.p. Ͼ300 °C. 1H NMR
(400 MHz, CDCl3): δ = –2.73 (s, 2 H, NH), –2.65 (s, 1 H, NH),
2.72 (s, 18 H, CH3), 7.57 (d, J = 7.6 Hz, 10 H, Ar), 7.65 (d, J =
7.9 Hz, 2 H, Ar), 8.08–8.13 (m, 12 H, Ar), 8.16 (d, J = 7.9 Hz, 2
H, Ar), 8.32–8.42 (m, 6 H, Ar), 8.48 (m, 2 H, β-pyrrole), 8.64 (d,
J = 4.5 Hz, 1 H, β-pyrrole), 8.69–8.79 (m, 4 H, triazole + β-pyr-
role), 8.86–8.98 (m, 8 H, β-pyrrole), 9.79 (d, J = 5.1 Hz, 1 H, β-
thiophene), 9.84 (d, J = 5.1 Hz, 1 H, β-thiophene) ppm. MALDI-
TOF: m/z (%) = 1366.65 (100) [M – 28]+. C96H70N10S (1394.55):
calcd. C 82.61, H 5.06, N 10.03, S 2.30; found C 82.60, H 5.08, N
10.04, S 2.28.
General Synthesis of Click Porphyrin Dyads 1–6 and Porphyrin–
Ferrocene Click Conjugates 7–11: Samples of one equivalent of
meso-(azidophenyl)porphyrin and one equivalent of ethynylferro-
cene or ethynylporphyrin were dissolved in 1:1 mixture of THF/
CH3CN under nitrogen atmosphere with stirring at room tempera-
ture. To this 1 equiv. of diisopropylethylamine (DIPEA) was added
followed by the addition of CuI (0.1 equiv.) and continued stirring
for 12 h. Progress of the reaction was monitored by periodic tlc
analysis. The solvent was removed under reduced pressure and the
crude mixture was subjected to basic alumina flash column
chromatography. The small amounts of unreacted precursors were
removed with dichloromethane and the desired fraction of the click
porphyrin dyad/ferrocene conjugate was eluted with 1–2% meth-
anol in dichloromethane and the resulting compound was recrys-
tallised from dichloromethane/hexane to give the desired products
as brownish red solid in 46–52% yields.
N4-N2S2 Porphyrin Click Dyad 5: M.p. Ͼ300 °C. 1H NMR
(400 MHz, CDCl3): δ = –2.73 (s, 2 H, NH), 2.72 (s, 18 H, CH3),
7.57 (d, J = 7.3 Hz, 6 H, Ar), 7.65 (d, J = 7.3 Hz, 6 H, Ar), 8.10–
8.17 (m, 12 H, Ar), 8.36–8.44 (m, 6 H, Ar), 8.49 (d, J = 8.2 Hz, 2
H, Ar), 8.70–8.79 (m, 5 H, triazole + β-pyrrole), 8.88 (s, 4 H, β-
pyrrole), 8.92 (d, J = 4.5 Hz, 2 H, β-pyrrole), 8.96 (d, J = 4.5 Hz,
2 H, β-pyrrole), 9.71–9.74 (m, 3 H, β-thiophene), 9.79 (d, J =
5.1 Hz, 1 H, β-thiophene) ppm. MALDI-TOF: m/z (%) = 1383.61
(100) [M – 28]+. C96H69N9S2 (1411.51): calcd. C 81.62, H 4.92, N
8.92, S 4.54; found C 81.64, H 4.91, N 8.93, S 4.52.
ZnN4–N3S Porphyrin Click Dyad (1): Yield 50%; m.p. Ͼ300 °C. 1H
NMR (400 MHz, CDCl3): δ = –2.65 (s, 1 H, NH), 2.72 (s, 18 H,
CH3), 7.52–7.58 (m, 12 H, Ar), 7.65 (d, J = 7.9 Hz, 2 H, Ar), 8.08–
8.18 (m, 14 H, Ar), 8.38–8.44 (m, 4 H, Ar + β-pyrrole), 8.51 (d, J
N3S-N2S2 Porphyrin Click Dyad 6: Yield 46%; m.p. Ͼ300 °C. 1H
NMR (400 MHz, CDCl3): δ = –2.64 (s, 1 H, NH), 2.72 (s, 18 H,
= 8.5 Hz, 2 H, Ar), 8.64 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.71–8.72 CH3), 7.52–7.58 (m, 4 H, Ar), 7.64 (d, J = 7.9 Hz, 10 H, Ar), 8.06–
(m, 2 H, β-pyrrole), 8.74 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.79 (s, 1 8.18 (m, 12 H, Ar), 8.38–8.52 (m, 6 H, Ar), 8.63 (d, J = 4.5 Hz, 1
H, triazole), 8.97–9.03 (m, 4 H, β-pyrrole), 9.02 (d, J = 4.5 Hz, 2
H, β-pyrrole), 9.06 (d, J = 4.5 Hz, 2 H, β-pyrrole), 9.79 (d, J =
H, β-pyrrole), 8.68 (d, J = 4.2 Hz, 1 H, β-pyrrole), 8.71–8.73 (m, 4
H, β-pyrrole), 8.74 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.78 (s, 1 H,
506
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Eur. J. Org. Chem. 2010, 494–508

Porphyrin Dyads and Porphyrin–Ferrocene Conjugates
triazole), 8.80 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.94–8.98 (m, 2 H,
β-pyrrole), 9.72–9.86 (m, 6 H, β-thiophene) ppm. MALDI-TOF:
m/z (%) = 1399.87 (100) [M – 28]+. C96H68N8S3 (1428.47): calcd.
C 80.64, H 4.79, N 7.84, S 6.73; found C 80.66, H 4.77, N 7.85, S
6.72.
8.19 (s, 1 H, triazole), 8.24 (d, J = 8.5 Hz, 2 H, Ar), 8.39–8.49 (m,
4 H, 2β-pyrrole + 2Ar), 8.54–8.60 (m, 2 H, β-pyrrole), 9.19 (s, 2
H, β-furan), 9.68 (d, J = 4.8 Hz, 1 H, β-thiophene), 9.75 (d, J =
5.1 Hz, 1 H, β-thiophene) ppm. 13C NMR (100 MHz, CDCl3): δ =
21.7, 67.1, 67.6, 69.1, 69.9, 116.9, 119.5, 121.4, 125.6, 127.8, 128.5,
129.9, 131.6, 133.1, 133.7, 134.5, 135.0, 135.5, 135.7, 136.8, 137.8,
138.1, 139.7, 141.4, 148.2, 150.9, 155.6, 156.8, 159.4 ppm. ES MS:
m/z (%) = 925.72 (100) [M]+. C59H43FeN5OS (925.92): calcd. C
76.53, H 4.68, N 7.56, S 3.46; found C 76.55, H 4.67, N 7.55, S
3.46.
1
ZnN4-Ferrocene Click Conjugate 7: Yield 50%; m.p. Ͼ300 °C. H
NMR (400 MHz, CDCl3): δ = 2.72 (s, 9 H, CH3), 4.27 (s, 5 H,
ferrocene), 4.45 (t, J = 1.8 Hz, 2 H, ferrocene), 5.22 (t, J = 1.8 Hz,
2 H, ferrocene), 7.56 (d, J = 6.7 Hz, 6 H, Ar), 7.97 (d, J = 8.5 Hz,
1 H, Ar), 8.09–8.12 (m, 6 H, Ar), 8.19 (d, J = 8.5 Hz, 1 H, Ar),
8.21 (s, 1 H, triazole), 8.40 (d, J = 8.5 Hz, 1 H, Ar), 8.42 (d, J =
8.5 Hz, 1 H, Ar), 8.94–9.05 (m, 8 H, β-pyrrole) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.9, 52.3, 52.9, 53.6, 67.1, 68.0, 69.6, 70.0,
110.1, 118.7, 121.6, 121.8, 123.9, 124.2, 124.9, 127.2, 127.7, 128.3,
131.3, 132.2, 132.7, 134.2, 134.8, 135.0, 136.4, 137.3, 139.9, 145.2,
149.8, 150.5, 150.7 ppm. ES MS: m/z (%) = 971.53 (100) [M]+.
C59H43FeN7Zn (971.27): calcd. C 72.96, H 4.46, N 10.09; found C
72.98, H 4.47, N 10.06.
Supporting Information (see also the footnote on the first page of
this article): NMR and mass spectra of selected compounds.
Acknowledgments
M. R. thanks the Council of Scientific and Industrial Research
(CSIR) and Department of Science and Technology (DST) for fin-
ancial support and V. S. thanks the CSIR for a fellowship.
N4-Ferrocene Click Conjugate 8: M.p. Ͼ300 °C. 1H NMR
(400 MHz, CDCl3): δ = –2.76 (s, 1 H, NH), 2.71 (s, 9 H, CH3),
4.27 (s, 5 H, ferrocene), 4.45 (t, J = 1.8 Hz, 2 H, ferrocene), 5.21
(t, J = 1.8 Hz, 2 H, ferrocene), 7.56 (d, J = 6.4 Hz, 6 H, Ar), 7.97
(d, J = 8.2 Hz, 2 H, Ar), 8.09–8.11 (m, 6 H, Ar), 8.20 (s, 1 H,
triazole), 8.42 (d, J = 8.2 Hz, 2 H, Ar), 8.87–8.94 (m, 8 H, β-pyr-
role) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.7, 67.0, 67.6, 69.2,
69.8, 100.3, 120.6, 124.4, 124.8, 127.6, 134.7, 135.3, 137.6, 139.2,
[1] H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. Int.
Ed. 2001, 40, 2004–2021.
[2] a) V. D. Bock, H. Hiemstra, J. H. van Maarseveen, Eur. J. Org.
Chem. 2006, 51–68; b) J. E. Moses, A. D. Moorhouse, Chem.
Soc. Rev. 2007, 36, 1249–1262; c) M. Meldal, C. W. Tornoe,
Chem. Rev. 2008, 108, 2952–3015.
[3] a) C. Maeda, S. Yamaguchi, C. Ikeda, H. Shinokubo, A.
Osuka, Org. Lett. 2008, 10, 549–552; b) F. C. Santos, A. C.
Cunha, M. B. V. de Souza, A. C. Tome, M. G. P. M. S. Neves,
V. F. Ferreira, J. A. S. Cavaleiro, Tetrahedron Lett. 2008, 49,
7268–7270; c) Y. Ikawa, H. Harada, M. Toganoh, H. Furuta,
Bioorg. Med. Chem. Lett. 2009, 19, 2448–2452.
[4] a) D.-M. Shen, C. Liu, Q.-Y. Chen, Eur. J. Org. Chem. 2007,
1419–1422; b) M. Severac, L. L. Pleux, A. Scarpaci, E. Blart,
F. Odobel, Tetrahedron Lett. 2007, 48, 6518–6522; c) S. Pun-
idha, J. Sinha, A. Kumar, M. Ravikanth, J. Org. Chem. 2008,
73, 323–326.
[5] a) I. Gupta, M. Ravikanth, J. Org. Chem. 2004, 69, 6796–6811;
b) S. Punidha, N. Agarwal, M. Ravikanth, Eur. J. Org. Chem.
2005, 2500–2517; c) S. Punidha, N. Agarwal, I. Gupta, M. Ra-
vikanth, Eur. J. Org. Chem. 2007, 1168–1175; d) S. Rai, M.
Ravikanth, Tetrahedron 2007, 63, 2455–2465.
[6] B. Karine, A. D. Moorhouse, J. E. Moses, Org. Lett. 2007, 9,
1809–1811.
[7] X. Liu, J. Liu, K. Jin, X. Yang, Q. Peng, L. Sun, Tetrahedron
2005, 61, 5655–5662.
[8] S. Shanmugathasan, C. Edwards, R. W. Boyle, Tetrahedron
2000, 56, 1025–1046.
144.5, 158.2 ppm. ES MS: m/z (%)
=
908.14 (100) [M]+.
C59H45FeN7 (907.88): calcd. C 78.05, H 5.00, N 10.80; found C
78.03, H 5.02, N 10.80.
N3S-Ferrocene Click Conjugate 9: Yield 52%; m.p. Ͼ300 °C. 1H
NMR (400 MHz, CDCl3): δ = –2.68 (s, 1 H, NH), 2.71 (s, 9 H,
CH3), 4.20 (s, 5 H, ferrocene), 4.41 (s, 2 H, ferrocene), 4.91 (s, 2 H,
ferrocene), 7.56 (d, J = 7.9 Hz, 4 H, Ar), 7.63 (d, J = 7.6 Hz, 2 H,
Ar), 8.08 (d, J = 7.9 Hz, 4 H, Ar), 8.14 (d, J = 7.9 Hz, 2 H, Ar),
8.20 (s, 1 H, triazole), 8.25 (d, J = 8.5 Hz, 2 H, Ar), 8.43 (d, J =
8.5 Hz, 2 H, Ar), 8.62 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.66–8.72
(m, 3 H, β-pyrrole), 8.96 (m, 2 H, β-pyrrole), 9.72 (d, J = 5.1 Hz,
1 H, β-thiophene), 9.80 (d, J = 5.1 Hz, 1 H, β-thiophene) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 21.7, 67.0, 69.1, 69.8, 116.9, 119.5,
121.4, 124.3, 126.0, 127.5, 128.5, 129.1, 129.2, 132.0, 132.6, 133.3,
133.6, 134.3, 134.5, 134.8, 135.4, 135.8, 136.0, 136.9, 137.8, 138.1,
139.3, 139.5, 141.7, 144.8, 145.7, 147.1, 148.0, 148.2, 153.7, 154.7,
157.0, 157.8 ppm. ES MS: m/z (%)
=
925.14 (100) [M]+.
C59H44FeN6S (924.93): calcd. C 76.61, H 4.79, N 9.09, S 3.47;
found C 76.62, H 4.80, N 9.08, S 3.46.
[9] J. S. Lindsey, I. C. Schreiman, H. C. Hsu, P. C. Kearney, A. M.
Marguerettaz, J. Org. Chem. 1987, 52, 827–836.
[10] S. Punidha, M. Ravikanth, Synlett 2005, 14, 2199–2203.
[11] P. Y. Heo, C. H. Lee, Bull. Korean Chem. Soc. 1996, 17, 515–
520.
[12] L. Latos-Grazynski, Core-Modified Heteroanalogues of Por-
phyrins and Metalloporphyrins, in: The Porphyrin Handbook
(Eds.: K. M. Kadish, K. M Smith, R. Guilard), Academic
Press, New York, 2000; vol. 2, p. 361–416.
1
N2S2-Ferrocene Click Conjugate 10: Yield 51%; m.p. Ͼ300 °C. H
NMR (400 MHz, CDCl3): δ = 2.71 (s, 9 H, CH3), 4.27 (s, 5 H,
ferrocene), 4.45 (t, J = 1.8 Hz, 2 H, ferrocene), 5.22 (t, J = 1.8 Hz,
2 H, ferrocene), 7.63 (d, J = 7.6 Hz, 6 H, Ar), 8.03 (d, J = 8.2 Hz,
1 H Ar), 8.13 (d, J = 7.6 Hz, 6 H, Ar), 8.19 (s, 1 H, triazole), 8.24
(d, J = 8.2 Hz, 1 H, Ar), 8.40–8.45 (m, 2 H, Ar), 8.67–8.78 (m, 4
H, β-pyrrole), 9.65–9.78 (m, 4 H, β-thiophene) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.7, 67.6, 69.8, 69.9, 119.4, 125.5, 128.4,
134.4, 134.7, 134.9, 135.4, 135.9, 136.8, 138.0, 138.4, 147.8, 148.1,
[13] R. S. Loewe, R. K. Lammi, J. R. Diers, C. Kirmaier, D. F. Bo-
cian, D. Holten, J. S. Lindsey, J. Mater. Chem. 2002, 12, 1530–
1552.
148.3, 156.7 ppm. ES MS: m/z (%)
=
941.81 (100) [M]+.
C59H43FeN5S2 (941.98): calcd. C 75.23, H 4.60, N 7.43, S 6.81;
found C 75.24, H 4.61, N 7.41, S 6.81.
[14] N. F. Langille, T. F. Jamison, Org. Lett. 2006, 8, 3761–3764.
[15] I. Gupta, M. Ravikanth, Coord. Chem. Rev. 2006, 250, 468–
518.
[16] C.-H. Hung, C.-K. Ou, G.-H. Lee, S.-M. Peng, Inorg. Chem.
2001, 40, 6845–6847.
[17] a) P. D. W. Boyd, A. K. Burrell, W. M. Campbell, P. A. Cocks,
K. C. Gordon, G. B. Jameson, D. L. Officer, Z. Zhao, Chem.
Commun. 1999, 637–638; b) D. T. Gryko, F. Zhao, A. A. Yas-
N2SO-Ferrocene Click Conjugate 11: Yield 48%; m.p. Ͼ300 °C. 1H
NMR (400 MHz, CDCl3): δ = 2.70 (s, 9 H, CH3), 4.20 (s, 5 H,
ferrocene), 4.41 (t, J = 1.8 Hz, 2 H, ferrocene), 4.90 (t, J = 1.8 Hz,
2 H, ferrocene), 7.55 (d, J = 7.6 Hz, 4 H, Ar), 7.62 (d, J = 7.6 Hz,
2 H, Ar), 8.05 (d, J = 7.6 Hz, 4 H, Ar), 8.10–8.13 (m, 2 H, Ar),
Eur. J. Org. Chem. 2010, 494–508
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
507

V. S. Shetti, M. Ravikanth
FULL PAPER
seri, K. M. Roth, D. F. Bocian, W. G. Kuhr, J. S. Lindsey, J.
Org. Chem. 2000, 65, 7356–7362; c) S. Rai, G. Gayatri, G. N.
Sastry, M. Ravikanth, Chem. Phys. Lett. 2008, 467, 179–185.
[18] B. Koszarna, H. Butenschön, D. T. Gryko, Org. Biomol. Chem.
2005, 3, 2640–2645.
[19] K. M. Kadish, E. Caemelbecke, J. Solid State Electrochem.
2003, 7, 254–258.
[20] I. Gupta, M. Ravikanth, Inorg. Chim. Acta 2007, 360, 1731–
1742.
[21] D. Kumaresan, A. Datta, M. Ravikanth, Chem. Phys. Lett.
2004, 395, 87–91.
Received: September 21, 2009
Published Online: December 10, 2009
508
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 494–508