A new synthesis of porphyrins: Via a putative trans-manganese(iv)-dihydroxide intermediate

Article abstract of DOI:10.1039/c9dt03573g

A new method for the synthesis of meso-substituted porphyrins was developed. In this two-step methodology, the first step involves the condensation of pyrroles/dipyrromethanes with aldehydes in a water-methanol mixture under acidic conditions. The second step involves manganese induced cyclization followed by oxidation via PhIO/O₂. This methodology has been useful for the synthesis of a wide range of trans-A₂B₂ porphyrins and also symmetric porphyrins in moderate to good yields. A detailed investigation of the manganese induced cyclization reaction has allowed us to characterize a Mn-porphyrinogen complex. A series of analytical and spectroscopic techniques and DFT calculations have led us to the conclusion that the putative intermediate species are trans-manganese(iv)-dihydroxide complexes. EPR and magnetic susceptibility measurements helped us to assign the oxidation state of the manganese complexes in their native state. The assumption of trans-manganese(iv)-dihydroxide as the true intermediate for this porphyrin synthesis has been authenticated via in situ UV-Vis experiments. This new methodology is certainly different from other previously reported methodologies in many aspects and most importantly these reactions can be easily performed on a gram scale for the synthesis of porphyrins.

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A new synthesis of porphyrin via a putative trans-manganese(IV)-
dihydroxide intermediate
Sruti Mondal, Kasturi Sahu, Bratati Patra, Subhrakant Jena, Himansu S. Biswal,* and Sanjib Kar*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A new method for the synthesis of meso-substituted porphyrins was developed. In two-step methodology,
the first step involves the condensation of pyrrole/ dipyrromethane with aldehyde in water-methanol
10 mixture in acidic conditions. The second step employs a manganese induced cyclization followed by
oxidation via PhIO/O2. This methodology has been useful for the synthesis of wide range of trans-A2B2
porphyrin and also symmetric porphyrins in moderate to good yields. A detailed investigation of the
manganese induced cyclization reaction has allowed us to characterize a Mn- porphyrinogen complex. A
series of analytical, spectroscopic techniques and DFT calculations has led us to the conclusion that these
15 putative intermediate species are trans-Manganese(IV)-dihydroxide complexes. EPR and magnetic
susceptibility measurements helped us to assign the oxidation state of the manganese complexes in the
native state. The question of trans-Manganese(IV)-dihydroxide as the true intermediates for these
porphyrin synthesis has been authenticated via in-situ UV-Vis experiments. This new methodology is
certainly different from previously reported other methodologies in many aspects and most importantly,
20 these reactions can be easily performed in the gram scale synthesis of porphyrins.
Introduction
oxidation of porphyrinogen to porphyrin by using a quinone
based oxidant (Scheme 1). One of the important porphyrin based
analogue is the trans-A2B2-porphyrins, which has versatile
45 applications in many areas. 8
Metalloporphyrins are a very important class of molecules
having key role in various biological relevant processes. 1 Few of
25 the important biological processes where the metalloporphyrins
are relevant includes photosynthesis, transport and storage of
R2
2
dioxygen and various other electron transfer reactions. Thus
Previous works
there is a constant strive to synthesize newer varieties of
porphyrin scaffold in order to mimic the naturally occurring
30 metalloporphyrins.3 The synthetic approach to synthesize
artificial porphyrin derivatives are a major field of attraction since
1930s. Hans Fisher is the pioneer in the synthesis of porphyrin
derivatives.4 Rothemund et al. have synthesized the tetraphenyl
porphyrin via a direct condensation reaction of pyrrole and
35 aldehyde in presence of pyridine in a sealed tube at around
R1
R2
N
NH
N
NH
NH
(i) TFA/BF3-etherate etc,
CH2Cl2
HN
(ii) DDQ/Chloranil
R1
R1
CHO
R2
R2
Present work
R1
R2
N
NH
N
NH
NH
(i) H2O, CH3OH, HCl
5
(ii) DMF, Mn(OAc)2
(iii) CH2Cl2, Air/PhIO
HN
220°C. A milder version has been reported by Adler et al.
R1
R1
CHO
Aldehydes and pyrroles condense in presence of propionic acid at
141°C in presence of air. 6 Lindsey developed the two-step one
flask methodology in mild conditions and with satisfactory
40 yields. 7 First step is an acid catalysed condensation reaction and
formation of porphyrinogen, and the second step involves the
R2
Scheme 1. Synthetic application of meso-substituted trans-A2B2-
50 Porphyrins.
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OMe
NC
CHO
25
It is clearly observed from the above discussions that the choice
of reagents in porphyrin synthesis owing to mild conditions with
wide substrate scope are still rather small in number. Herein, an
attempt has been made to decipher a new synthetic strategy for
the facile synthesis of a series of meso−substituted porphyrins in
mild conditions. First step of the synthesis involves the
condensation of aldehyde and pyrrole/dipyrromethane in acidic
condition (Scheme 1). Second step involves the manganese
templated ring formation reaction. Finally on oxidation via
NH
NH
MeO
HN
N
CN
NC
N
NH
5
OMe
2
20
NH
NH
CHO
10 PhIO/air resulted the formation of meso-substituted porphyrins in
good/moderate yields. This strategy has been extended for the
synthesis of meso-substituted trans−A2B2-porphyrins and
symmetric A4 −porphyrins. In order to understand the role of
manganese in the ring formation reaction, we have isolated and
15 characterized a representative Mn−porphyrinogen complex as a
HN
N
N
NH
3
CHO
19
NH
NH
putative reaction intermediate.
A
combined analytical,
MeO
electrochemical, spectroscopic techniques, and DFT studies are
presented to conform the structure of this putative reactive
intermediate (Mn−porphyrinogen complex) and to unravel the
20 role of this reaction intermediate in porphyrin synthesis.
N
NH
N
OMe
MeO
HN
4
Results and discussion
CHO
18
15
NH
NH
NC
Synthesis and Characterization
HN
N
N
CN
NC
In order to establish the general nature of the synthetic strategy
(Table 1), we have explored the scope of this newly designed
25 porphyrin synthesis by synthesizing
NH
5
F
F
F
OMe
Table 1. Scope of the synthesis of meso-substituted trans-A2B2-
NH
NH
F
CHO
MeO
Porphyrins.
F
F
F
F
F
F
F
R2
HN
N
F
F
N
NH
F
F
R1
R2
N
NH
N
NH
NH
(i) H2O, CH3OH, HCl
(ii) DMF, Mn(OAc)2
(iii) CH2Cl2, Air/PhIO
HN
OMe
6
R1
R1
CHO
F
F
F
F
CN
R2
15
NH
NH
F
CHO
NC
30
F
F
F
F
F
F
F
F
DPM/
Aldehyde
Porphyrin
Yield (%)
HN
N
F
F
N
NH
Pyrrole
CN
7
F
F
F
F
28
NH
NH
CHO
F
CHO
13
N
H
F
F
F
F
F
F
F
F
HN
N
N
F
NH
N
F
N
NH
HN
1
8
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OMe
MeO
CHO
10
N
H
F
F
F
F
F
N
NH
N
NH
NH
OMe
MeO
NC
HN
NH HN
NHHN
H2O, CH3OH
HCl
CN
NC
F
F
F
F
dipyrromethane
aldehyde
OMe
9
F
DMF (dry),
Mn(OAc)2
CHO
F
F
F
F
F
F
F
F
a series of porphyrin derivatives bearing both electron donating
as well as electron withdrawing functional groups at the
porphyrin periphery. Under the optimized reaction conditions, the
respective aldehyde and the corresponding dipyrromethane were
dissolved in a (2:1) CH3OH and water mixture. After treatment
with aqueous HCl, the reaction mixture was kept on stirring for
approx. 2 hours at room temperature. The extracted product was
F
F
NH
N
OH
CH2Cl2
HN
N
IV
CN
Mn
CN
NC
NC
H
5
N
Air / PhIO
N
OH
N
NH
F
F
F
F
F
F
F
F
F
F
7
7-Mn
45
10 dissolved in dry DMF and anhydrous Mn(OAc)2 was added to it
and was stirred for another one hour. It is worthwhile to mention
here that while using the Mn(OAc)2-tetrahydrate as a metal
source, tetrapyrromethanes as the precursor ligand and followed
by workup mostly in the non-chlorinated solvents, Kumar et al.
15 have obtained the Mn(III) corroles. 9 The compound obtained on
drying was dissolved in CH2Cl2 and was kept for stirring
overnight with silica-gel. The crude product was purified over
silica gel chromatography and resulted the formation of pure
trans-A2B2-Porphyrins in good yields (Figs S3-S11, see ESI† and
20 Table 1). Iodosyl benzene is the effective oxidizing agent for this
transformation. However, in half of these cases, aerial oxidation
is sufficient enough to lead the desired conversion to occur. The
same reaction was successful across a broad range of dry solvents
like dichloromethane, methanol, acetonitrile, toluene and THF.
25 However, we have observed that DMF is the most suitable
solvent for this purpose.
Fig. 1 Proposed mechanism.
The EPR spectrum (Fig. 2) which is observed in CH3OH-
50 C2H5OH glass at 100K displays a sextet (g ~ 2.003) originating
from the hyperfine coupling of the unpaired electron with 55Mn
nucleus (55Mn, 100%, I =5/2). An approximate A-value of 95 G,
D-value of 180 G and E-value of 20 G were determined from
simulations of the experimental data and these values are within
55 the ranges of the reported values of other Mn-complexes.10 This
conforms the paramagnetic nature of the Mn-complex, 7-Mn.
In order to understand the reaction mechanism better,
we have isolated a green colour reaction intermediate by using
column chromatography. We assume that these compounds may
30 be the true intermediates as they deliver the porphyrin derivatives
upon oxidation (Fig. 1). Unfortunately, these intermediate
compounds are not sufficiently stable and thus, we were unable to
get single crystals of these species. However, we have
characterized a representative derivative (7-Mn) thoroughly by
35 using various techniques like CHN analysis, ESI-MS analysis,
conductivity measurements, UV-Vis, FT-IR, ESR and magnetic
susceptibility measurements (Figs S1-S2 and Table S1; see
Fig. 2
Experimental X-band EPR spectrum (black) of 7-Mn at
100 K in CH3OH-C2H5OH glass in a flat cell and the
simulated spectrum (red)
60
From the variable temperature magnetic susceptibility
measurements (300K to 2K) (Fig. 3), we have observed that the
65 room temperature magnetic moment is 3.71 at 300K. 11 Fig. 3
shows plot of the eff versus temperature (T) for
polycrystalline sample of 7-Mn. A satisfactory fit, displayed in
Fig. 3, was obtained with J12 = −51 cm-1, g1= 1.980, g2 = 2.000
ESI†).
The composition of this compound (7-Mn) was
confirmed by using CHN analysis and also by ESI-MS analysis.
40 From the conductivity measurements, the compound, 7-Mn
shows no conductivity in acetonitrile solution. This clearly
indicates that there is no dissociable counter ions in the
compound (7-Mn).
a
a
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and  = −3.36 K. Fitting of the magnetic data indicates the 45 1.57−1.72 Å. The Mn··∙N(pyrrolic NH) (Mn··∙N2 and Mn··∙N4)
presence of both Mn(IV) and porphyrinogen radical. An
antiferromagnetic interaction exists between the Mn(IV) ion (SMn=3/2)
and the porphyrinogen radical (Srad = 1/2).
bond distances in 7-Mn are 2.50 and 2.60 Å respectively. These
values are outside the typical range of Mn−N bond distances.
However, the Mn··∙N(pyridine) bond distances in
a
5
Mn(III)−peroxo intermediate has been reported to be as high as
13d
50 2.49 Å.
However, the Mn··∙N(pyrrolic N) (Mn··∙N1 and
Mn··∙N3) bond distances are usual and matches nicely with the
earlier reports of similar bond distances. 13
4.0
TD-DFT Calculations
3.5
Exp
The DFT calculated UV-Vis and FT-IR spectra corroborate
55 well with the experimentally obtained spectra (Fig. 5, Fig. 6 and
Table S2-S5; see ESI†). The experimentally obtained UVVis
spectrum of the 7-Mn in its native state is in fully consistent with
the calculated values (Table S4). For example, 7-Mn displays
intense band in the visible spectrum at 416, 470, and 621 nm
60 (Table S1), the TD-DFT computed values for these transitions are
at 432 nm (SOMO-3 to LUMO), 472nm (SOMO-2 to LUMO),
and 620 nm (SOMO-11 to LUMO). The origin of the bands at
416, 470, and 621 nm attributed to the LMCT, LMCT, and ILCT
transitions, respectively (Fig. 7). While reducing the compound
65 by using LiAlH4 in DCM solution, the band at 416 nm is red
shifted to 432 nm and other bands at the visible region loses their
intensity significantly (Fig. S12; see ESI†). As shown in Fig. 6,
not only UV-Vis. spectra,
Sim
3.0
2.5
J
12
2.0
MnIV
R
1.5
1.0
0
50 100 150 200 250 300
T/K
Fig. 3 Plot of the effective magnetic moment vs. temperature
(From 2 to 300 K) for the complex 7-Mn.
10 The cyclic voltammogram (Fig. S2; see ESI†) of 7-Mn in CH3CN
reveals a reversible couple at 0.48 V and a quasi-reversible
couple at -0.73 V vs Fc/Fc+. While comparing with analogous
Mn(IV) complexes, we have assigned the couple at 0.48 V as
1.0
0.8
0.6
0.4
0.2
0.0
Mn(IV)/Mn(III) couple and at −0.73 V as Mn(III)/Mn(II) couple.
12
15
To support the experimental observation and to get better
insight about the structural parameters, DFT calculations were
carried out on 7-Mn as a representative example (Fig. 4 and
Table S2-S5; see ESI†). The bond lengths and angles which of
DFT optimized structures match reasonably well with the
20 previously reported other Mn(IV) hydroxide complexes. In the
optimized structure (Fig. 4), the two Mn−OH bond distances are
1.86 and 1.87 Å respectively. These distances fall in the ranges of
300
400
500
600
700
800
Wavelength (nm)
70
previously reported and well characterized
complexes.
L
MnIV(OH)
Fig. 5
UV-Vis spectra of 7-Mn: Experimental UV-Vis absorption
13a
spectrum (──) and TDDFT (TD-B97D/6-31G*)-based absorption
spectrum (──) (Lorentzian broadening with FWHM ~ 25 nm).
25
30
35
1.0
0.8
0.6
0.4
0.2
0.0
500
1000
1500
2000
2500
3000
3500
IR Frequency (cm-1)
40 Fig. 4 DFT optimized structure of 7-Mn
75
Fig. 6
IR spectrum of 7-Mn: Experimentally recorded FT-IR
spectrum (──) and IR spectrum (──) obtained from DFT (B97-D/6-
31G*) computation (scaling factor; 0.90, Lorentzian broadening
with FWHM ~ 25 cm-1).
For these complexes, the Mn−OH bond distances are in the range
of 1.79-1.88 Å. These values are significantly longer than related
13
MnIV=O complexes, which is reported to be in the range of
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but also the experimental IR spectra of 7-Mn can be reproduced 25 excess iodosyl benzene and it yields the trans-A2B2-Porphyrins
with reasonable accuracy by DFT calculation. Some of the
significant and distinguishable IR stretching and bending
frequencies of 7-Mn are listed in Table S5. In-situ UV-Vis
experiments (Fig. 8) supports that the Mn-complex, 7-Mn
instantly. Iodosyl benzene is the effective oxidizing agent which
can convert the Mn(IV)- porphyrinogen derivatives to the
corresponding trans-A2B2-Porphyrins. However, in half of these
cases, aerial oxidation is sufficient enough to lead the desired
30 conversion to occur. Conversion of Mn(IV)- porphyrinogen
derivatives to the trans-A2B2-Porphyrins occur very fast in the
time scale. Literature reports suggest that the Mn(IV)-OH
intermediate14 (7-Mn) is a potent H-atom abstractor and has the
ability to carry out the H-atom abstraction reaction efficiently
35 (Scheme 2), it is even more potent than its analogous Mn=O
species. 14 The resultant Mn(II) porphyrin (Scheme 2) is unstable
at the experimental condition and thus demetalates easily.2c
5
*
*
*
H
NH
N
OH
DMF (dry),
Mn(OAc)2
NH
N
N
NH
HN
H
Sol
H
O2
IV
*
II
Mn
*
*
Mn
*
*
*
H
H
N
NH HN
N
H
OH
N
Sol
dipyrromethane
aldehyde
*
*
*
7-Mn
*
*
H
H
H
NH
N
OH
NH
O
N
H
NH
O2/ PhIO
N
OH
H
Fig. 7 Calculated single occupied molecular orbitals (SOMO),
H
IV
HAT
HAT
*
Mn
OH
*
*
II
Mn
O
*
*
III
Mn
O
H
N
H
10 lowest unoccupied molecular orbital (LUMO) and the
corresponding orbital energies of 7-Mn.
N
H
N
N
N
N
H
H
H
H
H
H
H
*
*
*
*
*
*
H
H
H
NH
N
H
N
NH
N
O
N
NH
O
N
- Mn(H2O)6
HAT
HAT
*
II
*
*
Mn
O
III
*
*
Mn
OH
*
H
HN
H
N
N
N
H
H
H
*
40
Scheme 2
Probable mechanism for the conversion of Mn(IV)-
porphyrinogen derivatives to the porphyrins via hydrogen
abstraction (HAT=hydrogen abstraction).
45
Based on these observations, we can conclude that the
metal has performed a dual role in the present case. Firstly, it acts
as
a chelating agent and brings the aldehyde and the
Fig. 8
Electronic absorption spectrum of a) 7-Mn in CH2Cl2
corresponding tetrapyrromethanes in a planar conformation and
leads to the macrocycle formation and secondly, it provides the
15 solution. After this excess of PhIO was added to this solution; b)
Recorded from the crude reaction mixture after 3 mins, c) crude
reaction mixture after 6 mins, d) crude reaction mixture after 9
mins, e) crude reaction mixture after 12 mins, f) crude reaction
mixture after 15 mins, g) reaction mixture after 20 mins (passed
20 through a silica gel filter to remove the residual Mn salt and excess
PhIO, and h) Pure 7 in CH2Cl2 solution.
50 redox equivalents for the reaction. Oxidative macro-cyclization
mediated by metal salts have been reported extensively in the
literature. 15 However, it was limited mostly to the cyclization of
a,c-biladienes.16 One major drawback is that one needs to
demetallate the porphyrin derivatives and also the substrate scope
55 is very narrow.17
is the intermediate for the desired transformation to occur. For
this purpose, the isolated Mn-complex, 7-Mn, is treated with
Conclusions
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In summary, we have developed an efficient, milder (occurs at
using
julX
programme
developed
by
Dr.
E.
RT), cheap (while using aerial oxygen), and environment benign 55 Bill, Max-Planck Institute, Muelheim an der Ruhr, Germany.
methodology for the facile synthesis of Porphyrin (including
trans-A2B2-Porphyrin) derivatives. Most interestingly, these
reactions can be easily scaled up and can be useful for the gram
scale synthesis of porphyrins. Negligible to no scrambling (for
Cyclic voltammetry measurements were carried out using a CH
Instruments model CHI1120A electrochemistry system.
glassycarbon working electrode, a platinum wire as an auxiliary
A
5
electrode and a saturated calomel reference electrode (SCE) were
trans-A2B2-Porphyrin) is observed in almost all of these cases. In 60 used in a threeelectrode configuration. Tetrabutyl ammonium
half of these representative synthesis, excess iodosylbenezene is
used as an oxidizing agent and in the rest examples, air is used as
10 an oxidizing agent. Excess iodosylbenezene is obviously more
expensive than the traditionally used oxidizing agent like DDQ.
perchlorate (TBAP) was the supporting electrolyte (0.1M) and
the concentration of the solution was 103M with respect to the
complex. The half wave potential E0298 was set equal to 0.5(Epa
+
Epc), where Epa and Epc are anodic and cathodic cyclic
However in the traditional synthetic routes, using DDQ as 65 voltammetric peak potentials, respectively. The scan rate used
oxidizing agent, a large excess of chlorinated solvents was used
as reaction medium. In the present cases, we can limit the use of
15 chlorinated solvents in the reaction medium. Thus the
commercial feasibility of this new method may arise while
was 100 mV s1.The solution electrical conductivity was checked
using a CON 700 Conductivity/ºC/ºF Bench Meter. EPR spectra
at X-band frequency (ca. 9.5 GHz) were obtained with a Bruker
EMX (ER 073) System. The EPR spectra were simulated on a
performing these reactions in the large scale and using air as an 70 home written program using C language and used a third order
oxidizing agent. In-situ UV-vis experiments supports that the
trans-Mn(IV)-dihydroxide is the putative intermediate for the
20 desired transformation to occur. To support the experimental
observation and to get better insight about the structural
perturbation treatment.
Computational Method
The geometry optimization was carried out at the density-
functional theory (DFT) level using the B97 functional with
parameters, DFT calculations were carried out on 7-Mn as a 75 dispersion correction as implemented in the Turbomole program.
representative example. The DFT calculated UV-Vis and FT-IR
spectra corroborate well with the experimentally obtained spectra.
25 The role of the trans-Mn(IV)-dihydroxide putative intermediate
has been appreciated as potent H-atom abstractor which
ultimately leads to the generation of free base porphyrins.
19-22 The resolution of the identity (RI) approximation as well as
23
the multipole-accelerated RI (MARIJ) approximation
were
employed to speed up calculation. The 6-31G(d) basis set was
used for hydrogen, carbon, nitrogen, oxygen and fluorine and def-
80 TZVP basis et was used for manganese. The harmonic vibrational
frequencies of 7-Mn were calculated numerically at the same
level of theory. The time dependent DFT calculations were also
performed at same level of theory and basis sets with Gaussian-
09 software. 24
Experimental section
30 Materials
85
The precursor’s pyrrole, Manganese(II) acetate (98%) and
aldehydes were purchased from Aldrich, USA. Other chemicals
were of reagent grade. Hexane and CH2Cl2 were distilled from
KOH and CaH2 respectively. For spectroscopy studies, HPLC
35 grade solvents were used. 5-phenyldipyrromethane, 5-(4-
Syntheses
Synthesis of trans-A2B2-porphyrins, 1-7
90 The trans-A2B2-porphyrins (1−7) were prepared by following a
methoxyphenyl)dipyrromethane,
and
5-(4-
general procedure. Hence, only one representative case is
cyanophenyl)dipyrromethane were prepared by following an
earlier literature report. 18
discussed below. 0.100
g
(0.4 mmol) of 5-(4-
cyanophenyl)dipyrromethane and 49.3 L (0.4 mmol) of
2,3,4,5,6-Pentafluorobenzaldehyde were dissolved in 50mL
95 MeOH and 25 mL water (2:1) mixture. Subsequently, 5 mL of
aqueous HCl (36%) was added to it. The reaction mixture was
kept on stirring for 2 hours at room temperature. The crude
product was washed and extracted several times with chloroform
and water and dried over anhydrous Na2SO4. The solvent was
100 evaporated to dryness. The extracted product was dissolved in dry
DMF and 0.173 g (1 mmol) of Manganese(II) acetate was added
to it. The mixture was stirred for another one hour at RT. The
dark colored product was evaporated to dryness. The crude
product was dissolved in minimum dichloromethane and excess
105 PhIO was added to it and it was stirred at room temperature in
presence of air and the rate of the reaction was monitored through
thin layer chromatography (1, 2, 6, and 7). The reaction generally
yields the desired product in 10-15 minutes. The reaction mixture
was immediately purged through a previously packed silica gel
40 Characterization
UVVis spectral studies were performed on a PerkinElmer
LAMBDA-750 spectrophotometer. The elemental analyses were
carried out with a PerkinElmer 240C elemental analyzer. FTIR
spectra were recorded on a PerkinElmer spectrophotometer with
45 samples prepared as KBr pellets. The NMR measurements were
carried out using a Bruker 400 and 700 MHz NMR spectrometer.
Chemical shifts are expressed in parts per million (ppm) relative
to residual chloroform ( = 7.26). Electrospray mass spectra were
recorded on a Bruker Micro TOF─QII mass spectrometer.
50 The magnetic susceptibility of the samples were measured by
using a superconducting quantum interference device (SQUID)
manufactured by Quantum Design, USA. Simulations of the
experimentally obtained magnetic measurements were performed
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(100-200 mesh) column. The final product was eluted using pure
DCM as eluent. In half of these cases, the desired product is
formed without addition of any external oxidant, like PhIO and
the aerial oxygen is sufficient enough to perform the reaction (3,
4, and 5).
and extracted several times with chloroform and water and dried
over anhydrous Na2SO4. The solvent was evaporated to dryness.
The extracted product was dissolved in dry DMF and 3.175 g
(18.35 mmol) of Manganese(II) acetate was added to it. The
55 mixture was stirred for another one hour at RT. The dark colored
product was evaporated to dryness. The crude product was
dissolved in minimum dichloromethane and excess PhIO was
added to it and it was stirred at room temperature in presence of
air and the rate of the reaction was monitored through thin layer
5
Synthesis
of
5,15-Bis(4-cyanophenyl)-10,20-
diphenylporphyrin, 5
4.2 g (17 mmol) of 5-(4-cyanophenyl)dipyrromethane and 1.8
10 mL (17 mmol) of benzaldehyde were dissolved in 1L MeOH and 60 chromatography. The reaction generally yields the desired
500 mL water (2:1) mixture with subsequent addition of 50 mL
of aqueous HCl. The reaction mixture was kept on stirring for 2
hours at room temperature. The crude product was washed and
extracted several times with chloroform and water and dried over
product in 10-15 minutes. The reaction mixture was immediately
purged through a previously packed silica gel (100-200 mesh)
column. The final product was eluted using DCM-hexane (1:1)
mixture as eluent.
15 anhydrous Na2SO4. The solvent was evaporated to dryness. The 65 Synthesis of Mn(IV)- porphyrinogen derivative, 7-Mn
extracted product was dissolved in 100ml dry DMF and 7.3 g
(42.5 mmol) of Manganese(II) acetate was added to it. The
mixture was stirred for another one hour at RT. The dark
coloured product was evaporated to dryness. The crude product
0.100 g (0.4 mmol) of 5-(4-cyanophenyl)dipyrromethane and
49.3 L (0.4 mmol) of 2,3,4,5,6-Pentafluorobenzaldehyde was
dissolved in 50mL MeOH and 25 mL water (2:1) mixture.
Subsequently, 5 mL of aqueous HCl (36%) was added to it. The
20 was dissolved in minimum dichloromethane and was stirred 70 reaction mixture was kept on stirring for 2 hours at room
overnight at room temperature in presence of air. The reaction
mixture was purged through a silica gel (100-200 mesh) column.
Synthesis of 5,10,15,20-Tetraphenylporphyrin, 8
temperature. The crude product was washed and extracted several
times with chloroform and water and dried over anhydrous
Na2SO4. The solvent was evaporated to dryness. The extracted
product was dissolved in dry DMF and 0.173 g (1 mmol) of
6.8 mL (0.098 mol) of pyrrole and 10 ml (0.098 mol)
25 of benzaldehyde was dissolved in 2 L MeOH and 1 L water (2:1) 75 Manganese(II) acetate was added to it. The mixture was stirred
mixture. Subsequently, 100 mL of aqueous HCl (36%) was added
to it. The reaction mixture was kept on stirring for 2 hours at
room temperature. The crude product was washed and extracted
several times with chloroform and water and dried over
for another one hour at RT. The dark colored product was
evaporated to dryness. The reaction mixture was purged through
a silica gel (100-200 mesh) column. The final green color product
was eluted using DCM-hexane (2:3) mixture as eluent.
30 anhydrous Na2SO4. The solvent was evaporated to dryness. The 80 For 5,15-Bis(pentafluorophenyl)-10,20-diphenylporphyrin, 1
extracted product was dissolved in 200ml dry DMF and 30 g
(0.173 mol) of Manganese(II) acetate was added to it. The
mixture was stirred for another one hour at RT. The dark colored
product was evaporated to dryness. The crude product was
Yield: 28% (49 mg). Anal. Calcd (found) for C44H20F10N4 (1): C,
66.50 (66.67); H, 2.54 (2.32); N, 7.05 (7.16). 1H NMR (400 MHz,
Chloroform-d) δ 8.95 (d, J = 4.9 Hz, 4H), 8.80 (d, J = 4.9 Hz,
4H), 8.22 (d, J = 6.9 Hz, 4H), 7.79 (q, J = 7.9, 7.1 Hz, 6H), -2.84
35 dissolved in minimum dichloromethane and excess PhIO was 85 (br s, 2 H). Other analytical data are consistent with the
added to it and it was stirred at room temperature in presence of
air and the rate of the reaction was monitored through thin layer
chromatography. The reaction generally yields the desired
product in 30 minutes. The reaction mixture was immediately
previously reported authentic compounds. 25
For
5,15-Bis(4-cyanophenyl)-10,20-bis(4-
methoxyphenyl)porphyrin, 2
Yield: 25% (35 mg). Anal. Calcd (found) for C48H32N6O2 (2): C,
1
40 purged through a previously packed silica gel (100-200 mesh) 90 79.54 (79.66); H, 4.45 (4.36); N, 11.59 (11.64). H NMR (400
column. The final product was eluted using DCM-hexane (1:1)
mixture as eluent.
MHz, Chloroform-d) δ 8.92 (m, 4H), 8.74 (m, 4H), 8.35 (m, 4H),
8.12 (m, 4H), 8.08 (m, 4H), 7.32 (m, 4H), 4.11 (s, 6H), -2.80 (br
s, 2H). Other analytical data are consistent with the previously
reported authentic compounds. 26
Synthesis of 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin,
9
45
95 For 5,15-Dimesityl-10,20-diphenylporphyrin, 3
0.5 mL (7.34 mmol) of pyrrole and 1.0 gm (7.34 mmol) of 4-
methoxybenzaldehyde was dissolved in 300 mL MeOH and 150
mL water (2:1) mixture. Subsequently, 30 mL of aqueous HCl
(36%) was added to it. The reaction mixture was kept on stirring
Yield: 20% (31 mg). Anal. Calcd (found) for C50H42N4 (3): C,
85.93 (85.86); H, 6.06 (6.11); N, 8.02 (8.15). 1H NMR (400 MHz,
Chloroform-d) δ 8.78 (m, 4H), 8.69 (m, 4H), 8.23 (m, 4H), 7.75
(m, 6H), 7.28 (s, 4H), 2.63 (s, 6H), 1.84 (s, 12H), -2.62 (br s, 2H).
50 for 2 hours at room temperature. The crude product was washed
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Other analytical data are consistent with the previously reported
authentic compounds.
Acknowledgements
27
Financial support received from the Department of Atomic
Energy, (India) is gratefully acknowledged. Authors thankfully
60 acknowledge NISER-Bhubaneswar for providing infrastructure
and instrumental supports. The authors gratefully acknowledge
the financial support provided by SERB (Science & Engineering
Research Board), India to carry out this research work. We would
like to acknowledge Dr. Chandan Mukherjee (IIT Guwahati) for
65 the fitting of the magnetic data. We would also like to
acknowledge Dr. Vinayak Rane (BARC) for the fitting of the
EPR data.
For 5,15-Bis(4-methoxyphenyl)-10,20-diphenylporphyrin, 4
Yield: 19% (24 mg). Anal. Calcd (found) for C46H34N4O2 (4): C,
81.88 (81.78); H, 5.08 (5.17); N, 8.30 (8.39). 1H NMR (400 MHz,
Chloroform-d) δ 8.91 – 8.81 (m, 8H), 8.23 – 8.21 (m, 4H), 8.13
(d, J = 8.2 Hz, 4H), 7.76 (td, J = 8.2, 7.5, 5.3 Hz, 6H), 7.29 (d, J
= 8.3 Hz, 4H), 4.10 (s, 6H), -2.76 (s, 2H). Other analytical data
5
are consistent with the previously reported authentic compounds.
28
10
For 5,15-Bis(4-cyanophenyl)-10,20-diphenylporphyrin, 5
Yield: 18% (1g). Anal. Calcd (found) for C46H28N6 (5): C, 83.11
1
Notes and references
(83.10); H, 4.25 (4.33); N, 12.64 (12.77). H NMR (400 MHz,
Chloroform-d) δ 8.90 (d, J = 4.8 Hz, 4H), 8.74 (d, J = 4.9 Hz,
School of Chemical Sciences, National Institute of Science Education and
70 Research (NISER), Bhubaneswar – 751005, India, and Homi Bhabha
National Institute, Training School Complex, Anushakti Nagar, Mumbai,
400 094, India,
15 4H), 8.34 (d, J = 7.8 Hz, 4H), 8.25 – 8.17 (m, 4H), 8.08 (d, J =
7.8 Hz, 4H), 7.85 – 7.73 (m, 6H), -2.82 (s, 2H). Other analytical
data are consistent with the previously reported authentic
29
compounds.
E-mail: sanjib@niser.ac.in; himansu@niser.ac.in.
For5,15-Bis(4-methoxyphenyl)-10,20-
20 bis(pentafluorophenyl)porphyrin, 6
75 † Electronic Supplementary Information (ESI) available: NMR spectrum
of 1-9. ESI-MS spectrum of 7-Mn. Composition and energies of selected
molecular orbitals of 7-Mn. TD-DFT calculated electronic transitions for
7-Mn. These data can be obtained free of charge via
Yield: 15% (25 mg). Anal. Calcd (found) for C46H24F10N4O2 (6):
C, 64.64 (64.75); H, 2.83 (2.65); N, 6.56 (6.45). 1H NMR (400
MHz, Chloroform-d) δ 8.98 (d, J = 4.9 Hz, 4H), 8.80 (d, J = 4.8
Hz, 4H), 8.23 – 8.01 (m, 4H), 7.34 – 7.28 (m, 4H), 4.11 (s, 6H), -
25 2.80 (s, 2H). Other analytical data are consistent with the
previously reported authentic compounds. 24
www.ccdc.cam.ac.uk/data_request/cif. See DOI: 10.1039/b000000x/
80
1.
2.
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Applications to Chemistry, Physics, Materials Science,
Engineering, Biology and Medicine, Vol. 1, World Scientific,
2010.
For5,15-bis(4-cyanophenyl)-10,20-
bis(pentafluorophenyl)porphyrin, 7
85
90
Yield: 15% (25 mg). Anal. Calcd (found) for C46H18F10N6 (7): C,
30 65.41 (65.54); H, 2.15 (2.32); N, 9.95 (9.86). 1H NMR (400 MHz,
Chloroform-d) δ 8.86 (s, 8H), 8.35 (d, J = 7.7 Hz, 4H), 8.11 (d, J
= 7.7 Hz, 4H), -2.89 (s, 2H). Other analytical data are consistent
with the previously reported authentic compounds. 30
For 5,10,15,20-Tetraphenylporphin, 8
35 Yield: 13% (1.9 g). Anal. Calcd (found) for C44H30N4 (8): C,
85.97 (85.83); H, 4.92 (5.01); N, 9.11 (9.16). 1H NMR (400
MHz, Chloroform-d) δ 8.85 (s, 8H), 8.23 (m, 8H), 7.77 (m, 12H),
-2.77 (s, 2H). Other analytical data are consistent with the
95 3.
(a) B. Meunier, Chem. Rev. 1992, 92, 1411-1456; (b) K. M.
Smith, Porphyrins and metalloporphyrins, Vol. 9, Elsevier
Amsterdam, 1975; (c) E. B. Fleischer, Acc. Chem. Res. 1970,
3, 105-112; (d) A. Nakano, A. Osuka, I. Yamazaki, T.
Yamazaki and Y. Nishimura, Angew. Chem. Int. Ed. 1998, 37,
3023-3027; (e) A. Osuka, N. Mataga and T. Okada, Pure Appl.
Chem. 1997, 69, 797-802; (f) H. Furuta, T. Asano and T.
Ogawa, J. Am. Chem. Soc. 1994, 116, 767-768; (g) J. L.
Sessler and A. K. Burrell, in Macrocycles, Springer, 1992, pp.
177-273; (h) C. M. Lemon, P. J. Brothers and B. Boitrel,
Dalton Trans. 2011, 40, 6591-6609; (i) W. Sinha, M. G.
Sommer, N. Deibel, F. Ehret, B. Sarkar and S. Kar, Chem.
Eur. J. 2014, 20, 15920-15932; (j) W. Sinha, M. G. Sommer,
N. Deibel, F. Ehret, M. Bauer, B. Sarkar and S. Kar, Angew.
Chem., Int. Ed., 2015, 54, 13769-13774; (k) W. Sinha, M. G.
Sommer, L. Hettmanczyk, B. Patra, V.Filippou, B. Sarkar and
S. Kar, Chem. - Eur. J., 2017, 23, 2396-2404; (l) B. Patra, S.
Sobottka, W. Sinha, B. Sarkar and S. Kar, Chem. - Eur. J.,
2017, 23, 13858-13863; (m) A. Garai, S. Sobottka, R.
Schepper, W. Sinha, M. Bauer, B. Sarkar and S. Kar, Chem. -
Eur. J., 2018, 24, 12613-12622; (n) B. Patra, S. Sobottka, S.
Mondal, B. Sarkar and S. Kar, Chem. Commun., 2018, 54,
9945-9948; (o) R. Padilla, H. L. Buckley, A. L. Ward and J.
Arnold, Chem. Commun., 2014, 50, 2922-2924; (p) C. P. Gros,
F. Brisach, A. Meristoudi, E. Espinosa, R. Guilard and P. D.
Harvey, Inorg. Chem., 2007, 46, 125-135; (q) A. L. Ward, H.
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31
previously reported authentic compounds.
100
40 For 5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin, 9
Yield: 10% (140 mg). Anal. Calcd (found) for C48H38N4O4 (9): C,
78.45 (78.51); H, 5.21 (5.32); N, 7.62 (7.77). 1H NMR (400
MHz, Chloroform-d) δ 8.86 (s, 8H), 8.14 (m, 8H), 7.30 (m, 8H),
4.10 (s, 12H), -2.75 (s, 2H). Other analytical data are consistent
45 with the previously reported authentic compounds. 32
105
110
115
120
For Mn(IV)- porphyrinogen derivative, 7-Mn
Anal. Calcd (found) for C46H24F10MnN6O2 (7-Mn): C, 58.92
(58.81); H, 2.58 (2.67); N, 8.96 (8.85). max/nm (/M1cm1) in
dichloromethane: 416 (10860), 470 (7970), 576 (4020), 621
50 (7140). The electrospray mass spectrum in acetonitrile showed
peaks centred at m/z = 920.1210 correspond to [7-Mn−OH]+
(920.1149 calcd for C46H23F10MnN6O).
Conflicts of interest
55 There are no conflicts of interest to declare.
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DOI: 10.1039/C9DT03573G
Table of Contents
An efficient, milder (occurs at RT), scalable, and environment benign methodology for the facile
synthesis of Porphyrin derivatives without using quinone based oxidants has been developed.