A new synthetic approach to porphyrin-α-diones and a -2,3,12,13-tetraone: Building blocks for laterally conjugated porphyrin arrays

Article abstract of DOI:10.1039/b007389j

We report the first use of the Dess-Martin periodinane (DMP) for the oxidation of an arylamine to an α-dione. The methodology is illustrated by the preparation of free-base and metal chelated porphyrin-α-diones in up to 52% yield by oxidation of 2-aminoporphyrins with the DMP. We also found that DMP could be used to oxidise a 2,3-diaminoporphyrin to a porphyrin-α-dione in good yield with other free-base diaminoporphyrin isomers forming a trans-porphyrintetraone in 20% yield.

Full text of DOI:10.1039/b007389j

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A new synthetic approach to porphyrin-ꢀ-diones and a -2,3,12,13-
tetraone: building blocks for laterally conjugated porphyrin arrays
Vinich Promarak and Paul L. Burn*
1
The Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford,
UK OX1 3QY
Received (in Cambridge, UK) 12th September 2000, Accepted 31st October 2000
First published as an Advance Article on the web 11th December 2000
We report the first use of the Dess–Martin periodinane (DMP) for the oxidation of an arylamine to an α-dione.
The methodology is illustrated by the preparation of free-base and metal chelated porphyrin-α-diones in up to
52% yield by oxidation of 2-aminoporphyrins with the DMP. We also found that DMP could be used to oxidise
a 2,3-diaminoporphyrin to a porphyrin-α-dione in good yield with other free-base diaminoporphyrin isomers
forming a trans-porphyrintetraone in 20% yield.
comparison with the DMP oxidation of 2-hydroxyporphyrins
to porphyrin-α-diones we chose copper, zinc and free-base
Introduction
The development of synthetic porphyrin arrays has attracted
much interest because of the important role porphyrins play
in electron transfer processes in biological systems. Utilisation
of these properties could lead to the development of new
classes of organic materials for molecular wires,1–3 photovoltaic
devices4–8 and non-linear optics.6,9–11 Recently many types of
porphyrin arrays have been reported where the porphyrin
rings are covalently linked through either their meso-
positions3,4,7–10,12–14 or β-pyrrolic positions.1,15–25 Of the porphy-
rin arrays linked through the β-pyrrolic positions most have
involved condensation reactions of porphyrin-α-diones17,21–25 or
tetraones1,15 with benzene-1,2,4,5-tetraamine. The traditional
route to porphyrin-α-diones involved photo-oxidation of a 2-
amino-5,10,15,20-tetraphenylporphyrin followed by hydrolysis
of the resultant keto-imino chlorin.26 This approach was later
extended and a mixture of diamino-5,10,15,20-tetrakis(3Ј,5Ј-di-
tert-butylphenyl)porphyrins were photo-oxidised to form two
different tetraones, the trans-2,3,12,13-tetraone and cis-2,3,7,8-
tetraone.15 Free-base and metallo 2-hydroxy-5,10,15,20-tetra-
phenylporphyrins have also been oxidised to porphyrin-α-
diones.27 However, the most facile method so far reported
for preparation of porphyrin-α-diones is the oxidation of
2-hydroxyporphyrins with the Dess–Martin periodinane
(DMP).28 DMP was successfully used for the preparation
of porphyrin-α-diones from free-base and metal chelated
2-hydroxy-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)por-
phyrins.28 In the case of the free-base 2-hydroxyporphyrin, the
reaction mechanism for the DMP oxidation was considered to
be similar to the oxidation of 1,3-dicarbonyls to tricarbonyls,
where the oxidation was assumed to occur through the enol
form of the dicarbonyl.29 However, there was no evidence in the
case of the copper and zinc 2-hydroxyporphyrins for significant
keto–enol tautomerism, suggesting that DMP could oxidise
“phenols” under mild conditions. In contrast to the 2-hydroxy-
tetra-meso-phenylporphyrins the corresponding 2-aminopor-
2-aminoporphyrins as our substrates.
Results and discussion
5,10,15,20-Tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyrin
was
chosen for this study as the 3,5-di-tert-butylphenyl meso-
substituents provide good solubility to the porphyrin. The
synthetic pathways followed for the preparation of the
porphyrin-α-diones and porphyrintetraone are illustrated in
Scheme 1. To form the critical aminoporphyrin intermediates
we followed literature procedures.15,26 Chelation of copper into
free-base porphyrin 1 was achieved in a quantitative yield
by treatment with cupric acetate monohydrate in a dichloro-
methane–methanol mixture heated at reflux. After the second
step, the nitration, the pathways for formation of the porphyrin-
α-diones and porphyrintetraone diverged. For the preparation
of the porphyrin-α-diones, copper porphyrin 2 was mono-
nitrated with a solution of nitrogen dioxide in light petroleum
with the reaction followed closely by thin-layer chromato-
graphy. Under these conditions the mono-nitrated copper
2-nitroporphyrin 3 could be isolated in 96% yield.
For the preparation of the porphyrin-α-diones 9, 10, and 11,
the free-base and metal chelated 2-amino porphyrins were pre-
pared from 3 in the following manner. For the preparation of
the free-base 2-aminoporphyrin (6), porphyrin 3 was demetal-
lated with concentrated sulfuric acid in dichloromethane to
give the free-base 2-nitroporphyrin 4 in quantitative yield. 4 was
then reduced with a mixture of tin() chloride dihydrate and
concentrated hydrochloric acid in dichloromethane to give the
crude 2-aminoporphyrin 6. The free-base 2-aminoporphyrin is
very susceptible to photo-oxidation26,31 and although 1H NMR
and infrared spectra could be obtained they often contained
signals that corresponded to the free-base porphyrin-α-dione 9.
Critically the infrared spectrum showed that there was no nitro
group remaining after the reduction. Although we did not
isolate 6 in a pure form before the DMP oxidation, thin-layer
chromatography clearly showed that there was no porphyrin-
α-dione present. The copper- and zinc-chelated 2-amino-
porphyrins 7 and 8 were prepared in a slightly different manner
from 6. For the zinc derivative, the free-base 2-nitroporphyrin
4 was metallated with zinc acetate dihydrate in a dichloro-
methane–methanol mixture heated at reflux.31 Under these
1
phyrins do not show an imine tautomeric form by H NMR.30
We therefore considered that if porphyrin “phenols” could be
oxidised by DMP then the corresponding porphyrin “anilines”
might also be susceptible to DMP oxidation to a porphyrin-α-
dione. In this paper, we report a new method for the prepar-
ation of porphyrin-α-diones from 2-aminoporphyrins and
2,3-diaminoporphyrins, and the extension of this methodology
to the synthesis of free-base porphyrin-2,3,12,13-tetraone. For
14
J. Chem. Soc., Perkin Trans. 1, 2001, 14–20
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b007389j

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Scheme 1 Reagents and conditions: i, Cu(OAc)2ؒH2O, CH2Cl2, MeOH, reflux, 1 h; ii, NO2 in light petroleum, CH2Cl2, rt; iii, conc. H2SO4, CH2Cl2,
rt; iv, Zn(OAc)2ؒ2H2O, CH2Cl2, MeOH, reflux, 1.5 h; v, SnCl2ؒ2H2O, conc. HCl, CH2Cl2, in the dark, rt, 2–4 d; vi, NaBH4, 10% Pd–C, CH2Cl2–
MeOH (4:1), rt, 1 h; vii, DMP, CH2Cl2, rt, in the dark, then aqueous HCl.
conditions zinc 2-nitroporphyrin 5 was isolated in 95% yield.
Reduction of 5 was achieved with sodium borohydride in
the presence of 10% palladium on activated carbon in a
dichloromethane–methanol mixture (4:1) to give the zinc-
chelated 2-aminoporphyrin 8 in ≈96% yield.31 As in the case of
6 we did not isolate 8 in a pure form after chromatography.
not purify the 2-aminoporphyrins, 6–8, before the oxidation
step.
The oxidations of 6–8 were all carried out in a similar
manner. In each case DMP was added to a solution of the
2-aminoporphyrin and the mixture was stirred at room temper-
ature in the dark. The progress of the reaction was monitored
by thin-layer chromatography and when it was judged that
the starting material had been consumed dilute hydrochloric
acid (for 6 and 7) or water (for 8) was added. The aqueous
treatment was included to hydrolyse any imine intermediates
that may have formed during the oxidation as in the case of the
photo-oxidation of 2-aminoporphyrins.
Therefore, the two-step procedure developed involved the
reduction of the 2-nitroporphyrin to the amine and subsequent
oxidation with DMP. Under these conditions 4 was converted
to the free-base porphyrin-α-dione 9 in a 52% overall yield for
the two steps. Moreover, the DMP oxidation of the in situ
formed copper 2-aminoporphyrin 7 and zinc 2-aminoporphyrin
8 gave the corresponding copper porphyrin-α-dione 10 and zinc
porphyrin-α-dione 11 in yields of 37 and 20% respectively for
the two steps. The oxidation of the copper 2-aminoporphyrin
was significantly slower and required more oxidant than those
of the other two 2-aminoporphyrins, 6 and 8. We believe the
lower yields of copper and zinc porphyrin-α-diones are due to
competition between the oxidation of the 2-aminoporphyrin
and the porphyrin-α-dione formed in the reaction mixture. In
the case of the copper 2-aminoporphyrin 7 the sluggish nature
1
However, H NMR and infrared spectroscopy clearly showed
that 8 had been formed. In fact, it was interesting to note
that, although 8 was susceptible to photo-oxidation31 on silica,
the 1H NMR and infrared spectra both had little of the
porphyrin-α-dione present in the samples suggesting that the
zinc derivative was more photochemically stable than the
free-base compound. Again the infrared spectrum showed
the absence of any remaining nitro groups. The copper 2-nitro-
porphyrin 3 was reduced to form the corresponding copper
2-aminoporphyrin in an 89% yield. Unlike the free-base and
zinc-chelated 2-aminoporphyrin derivatives we were able to
isolate the copper 2-aminoporphyrin 7 as a single compound by
chromatography over silica. The infrared spectrum of 7 clearly
showed the presence of the amine group and the absence of
absorptions from the nitro moiety. The susceptibility of 6–8
to photo-oxidation follows the same trend we observed with
the photo-oxidation of the 2-hydroxyporphyrins. For the
2-hydroxyporphyrins the copper derivative was also the most
resilient to oxidation with the free-base being the least.28 Never-
theless, to ensure that the formation of the porphyrin-α-diones
in this study was only due to the treatment with DMP we did
J. Chem. Soc., Perkin Trans. 1, 2001, 14–20
15

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of the oxidation leaves the formed porphyrin-α-dione in contact
with the oxidant for a longer period of time and it is well known
that the α-dione can undergo further oxidative degradations.26
For the zinc 2-aminoporphyrin it may be that the amine group
and formed α-dione have similar rates of oxidation. It is
interesting to note that in the study on the oxidation of
2-hydroxyporphyrins with DMP the zinc derivative also gave
the lowest yield.28
“cis” as well as the “trans” porphyrintetraones. To test this the
oxidations of 16 and 17 were carried out by the addition of
DMP to the reaction mixture until thin-layer chromatography
indicated that no starting material remained. However, in both
cases many compounds were found to be present by thin-layer
chromatography and after aqueous acid work-up and separ-
ation by column chromatography over silica no compounds
that corresponded to porphyrintetraones were obtained.
We next investigated the oxidation reaction of diamino-
porphyrins 15, 16, and 17 with DMP to give the tetraones 18,
19, and 20 respectively. Copper 2-nitroporphyrin 3 was further
nitrated with nitrogen dioxide under the same conditions used
for the mono-nitration. The six possible copper dinitropor-
phyrin 12 isomers, in contrast to the five reported in the liter-
ature,15 were isolated in a total yield of 77%. The copper
dinitroporphyrin isomers could not be easily separated by
column or centrifugal thin-layer chromatography over silica. As
a consequence the mixture of copper dinitroporphyrins was
then demetallated with concentrated sulfuric acid in dichloro-
methane to give 13 in a quantative yield, as a mixture of free-
base dinitroporphyrins. The free-base dinitroporphyrin isomers
could also not be easily separated to give the individual isomers.
To study the formation of the free-base and metal-chelated
porphyrintetraones the diaminoporphyrins were synthesised
following the procedures used for the 2-aminoporphyrins. The
free-base diaminoporphyrins 15 were formed in ≈97% yield by
reduction of 13 with stannous chloride dihydrate and hydro-
chloric acid. The infrared spectrum of 15 clearly showed
absorptions at 3485 and 3391 cmϪ1 corresponding to the amine
groups and no absorptions due to the nitro and carbonyl
groups were observed. To form 17, 13 was first metallated with
zinc acetate dihydrate in a dichloromethane–methanol mixture
heated at reflux to give the zinc dinitroporphyrins 14 in 98%
yield. The copper, 12, and zinc, 14, were then reduced with
sodium borohydride in the presence of 10% palladium on
activated carbon to the corresponding diaminoporphyrins 16
and 17. Again the complete reduction of both nitro groups was
confirmed by infrared spectroscopy. There were no absorptions
due to the nitro groups or indeed carbonyls and the absorptions
due to the amine moieties were clearly observed. In addition,
the 1H NMR of the crude 17, although complicated, was
consistent with the structures. Also, as in the case of the copper
2-aminoporphyrin it was possible to isolate the copper di-
aminoporphyrins by chromatography over silica. Nevertheless,
for all three diaminoporphyrin derivatives the DMP oxidation
was carried out immediately after the reduction to avoid any
photo-oxidation.
As the oxidations of the metallated 2-aminoporphyrins were
sluggish and low yielding we thought that the absence of the
desired porphyrintetraones might be due to over oxidation of
the α-diones formed in the reaction. To investigate this we
carried out the oxidation of 17 with DMP in the usual manner
but stopped the reaction before all the starting material had
been consumed. We chose the zinc derivative rather than the
copper so that the products could be more easily identified.
After work-up and purification over silica gel starting material
17, 9%, zinc porphyrin-α-dione 11, 3%, and a mixture of
aminoporphyrin-α-diones 21,15 32%, were isolated. This result
As in the case of the 2-aminoporphyrins the oxidations were
carried out by the addition of aliquots of DMP and the reac-
tion stopped when thin-layer chromatography indicated that
no starting material remained. For the free-base diaminopor-
phyrins 15 we found that the “trans” porphyrin-2,3,12,13-
tetraone 18 was formed in a yield of 20%. As only two of the six
isomers can lead to the “trans” porphyrintetraone the yield of
20% corresponds to a conversion of 60% assuming that all the
dinitro isomers are formed in equal amounts. The product was
easily separated by column chromatography over silica gel and
1H NMR was identical, except that the NH protons were found
at Ϫ1.80 rather than Ϫ1.32, to that reported in the literature.15
The yield of 18 is similar to that achieved by the photo-
oxidation of free-base diaminoporphyrins. Interestingly, as in
the case of the photo-oxidation of the free-base diamino-
porphyrins the “cis” porphyrintetraone was not isolated. We
believe that DMP might not have the right oxidation potential
to oxidise the free-base diaminoporphyrins which lead to the
non-aromatic “cis” porphyrin-2,3,17,18-tetraone. In the case of
the photo-oxidation experiments the “cis” porphyrin-2,3,17,18-
tetraone was obtained by photo-oxidising intermediary zinc
aminoporphyrin-α-diones.15 We therefore wondered whether
the metal-chelated diaminoporphyrins would give rise to the
suggests that there is competing oxidation of the starting
material and intermediate α-diones. Perhaps the most surpris-
ing result from this experiment was that zinc porphyrin-α-dione
11 was isolated as this could only come from the 2,3-diamino-
porphyrin 23. To confirm this we reduced the zinc 2,3-di-
nitroporphyrin 2232 to 23 and oxidised 23 with DMP using
16
J. Chem. Soc., Perkin Trans. 1, 2001, 14–20

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the standard method. Under these conditions 11 was isolated in
an excellent yield of 78% for the two steps. We believe that this
is the first example of an “ortho” diamine being oxidised to an
α-dione using DMP.
[2-Nitro-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyr-
inato]copper(II) 3
A solution of nitrogen dioxide in light petroleum (0.69 M, in
total 20.5 cm3) was added in small aliquots to a solution of 2
(4.00 g, 3.55 mmol) in dichloromethane (200 cm3). The reaction
was followed by thin-layer chromatography (dichloromethane–
light petroleum; 1:4). When no starting material was observed,
the mixture was immediately passed through a plug of silica gel
using dichloromethane as eluent. The solvent was completely
removed to give a purple residue which was then purified by
column chromatography over silica using a dichloromethane–
light petroleum mixture (1:4) as eluent. The main fraction was
collected and the solvent completely removed to give 3 as a
purple solid (3.96 g, 96%) which had identical infrared and
UV–visible spectra to those reported in the literature;33
mp > 296 ЊC; νmax(KBr disc)/cmϪ1 1527 (NO2); λmax(CHCl3)/nm
(log (ε/dm3 molϪ1 cmϪ1)) 426 (5.35), 549 (4.21), and 591 (4.01).
Conclusion
We have found that DMP can be utilised to oxidise aminopor-
phyrins to porphyrin-α-diones. We have utilised this new
method for the preparation of free-base and metallated
porphyrin-α-diones from 2-aminoporphyrins and in one case
a 2,3-diaminoporphyrin. Finally, DMP has also been used to
form the free-base “trans” porphyrin-2,3,12,13-tetraone. Oxid-
ations using DMP have an advantage over the photo-oxidation
route to similar compounds in that it can be carried out on
larger scales more easily. However, for the formation of the
simple porphyrin-α-dione, oxidation of a 2-hydroxyporphyrin
with the DMP is still the preferred method.
2-Nitro-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyrin 4
Experimental
A solution of 3 (100 mg, 0.08 mmol) in dichloromethane (10
cm3) was treated with concentrated sulfuric acid (0.5 cm3). The
reaction mixture was stirred at room temperature for 8 min and
then it was poured into an ice–water mixture (20 cm3). The
aqueous layer was separated and extracted with dichlorometh-
ane (3 × 20 cm3). The combined organic layers were washed
with water (20 cm3), sodium bicarbonate solution (5%, 20 cm3),
water (20 cm3), dried over anhydrous sodium sulfate, filtered,
and the solvent completely removed leaving a purple residue.
The residue was recrystallised from a dichloromethane–
methanol mixture to give 4 as a purple solid (94 mg, 100%)
which had identical 1H NMR, infrared and UV–visible spectra
to those reported in the literature;33 νmax(KBr disc)/cmϪ1 3329
(NH) and 1530 (NO2); δH(200 MHz; CDCl3) Ϫ2.55 (2 H, br s,
NH), 1.54 (72 H, tert-butyl H), 7.77–7.84 (4 H, m, C(4Ј)), 8.07–
8.11 (8 H, m, C(2Ј)H and C(6Ј)H), 8.79 (2 H, β-pyrrolic H),
8.96 (3 H, β-pyrrolic H), and 9.07–9.12 (2 H, β-pyrrolic H);
λmax(CHCl3)/nm (log (ε/dm3 molϪ1 cmϪ1)) 430 (5.33), 530 (4.20),
564 (3.69), 607 (3.58), and 666 (3.99).
1H NMR spectra were recorded on either Bruker AM-400 (400
MHz), Bruker AM-500 (500 MHz) or Varian Gemini 200 (200
MHz) spectrometers. Chemical shifts (δ) are reported relative to
the residual solvent peak in parts per million (ppm). Infrared
spectra were recorded on a Perkin-Elmer Paragon 1000 infrared
spectrometer as KBr disks. UV–visible spectra were measured
in spectrophotometric grade chloroform on a Perkin-Elmer
Lambda 14P UV–visible spectrometer. Melting points were
recorded on a Gallenkamp melting point instrument and are
uncorrected. Laser desorption ionization (LDI) mass spectra
were measured on a Micromass Tofspec 2E spectrometer with
samples directly applied onto the MALDI target. MALDI were
measured on a Micromass Tofspec 2E spectrometer using a
dithranol (1,8,9-trihydroxyanthracene) matrix in reflectron
(high resolution) mode. Fast atom bombardment (FAB) mass
spectra were recorded on a VG Autospec Spectrometer. Due to
a combination of metal chelation, molecular size, and different
degrees of protonation the molecular weights observed by mass
spectroscopy generally appeared as a complex isotopic cluster
above the parent ion. We have quoted the mass for the mono-
isotopic species for each compound. Microanalyses were
performed by Elemental Microanalysis Ltd, Devon, UK. All
solvents for recrystallisation were distilled before use. Light
petroleum ether refers to the fraction of boiling point 60–80 ЊC
and it was routinely distilled before use. Merck AR grade
methanol was used. Analytical thin-layer chromatography
(TLC) was performed with Merck aluminium plates coated
with silica gel 60 F254. Column chromatography was carried
out using either the flash chromatography technique or gravity
feed chromatography, with ICN silica gel 32-63 mesh, 60 Å.
Centrifugal thin-layer chromatography was carried out using a
Harrison Model 7924T Chromatotron. Where solvent mixtures
are used, the proportions are given by volume. DMP was
purchased from Lancaster, UK and used as obtained.
2,3-Dioxo-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)chlorin 9
Tin() chloride dihydrate (185 mg, 0.821 mmol) and concen-
trated hydrochloric acid (0.5 cm3) were added to a solution of 4
(91 mg, 0.082 mmol) in dichloromethane (4 cm3). The reaction
mixture was stirred under nitrogen atmosphere at room tem-
perature in the dark. The reaction was monitored by thin-layer
chromatography (dichloromethane–light petroleum 1:4). After
stirring for 3 days, dichloromethane (20 cm3) and water (20 cm3)
were added. The organic layer was separated, washed with
water (30 cm3), sodium bicarbonate solution (5%, 30 cm3),
water (30 cm3), dried over anhydrous sodium sulfate, filtered,
and the solvent completely removed to yield a brown–purple
solid of 6 (≈87 mg, ≈99%); νmax(KBr disc)/cmϪ1 3486 (NH2), 3392
(NH2), and 3310 (NH). DMP (36 mg, 0.08 mmol) was added to
a solution of 6 (≈87 mg, ≈0.08 mmol) in dichloromethane (10
cm3). The reaction mixture was stirred at room temperature in
the dark for 45 min at which point thin-layer chromatography
(dichloromethane–light petroleum 2:3) showed that no 6
remained. Hydrochloric acid (1 M, 30 cm3) was added and the
reaction mixture was stirred for a further 20 min. The organic
layer was separated, washed with water (2 × 100 cm3), dried
over anhydrous sodium sulfate, filtered, and the solvent com-
pletely removed. The residue was purified by column chrom-
atography over silica gel using a dichloromethane–light
petroleum mixture (2:3) as eluent to give 9 (46 mg, 52%) which
had identical 1H NMR28 and infrared33 spectra to those
reported in the literature; νmax(KBr disc)/cmϪ1 3354 (NH), 1738
[5,10,15,20-Tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyrinato]-
copper(II) 2
A mixture of 1 (6.00 g, 5.64 mmol), copper() acetate mono-
hydrate (2.00 g, 10.0 mol), dichloromethane (300 cm3), and
methanol (90 cm3) was heated at reflux for 1.5 h. The reaction
mixture was allowed to cool and the solvent removed. The
residue was passed through a plug of silica using dichloro-
methane as eluent. The main fraction was collected and the
solvent completely removed to give a red purple solid of 2 (6.34
g, 100%) which had similar infrared and UV–visible spectra to
those reported in the literature;33 mp > 296 ЊC; λmax(CHCl3)/nm
(log (ε/dm3 molϪ1 cmϪ1)) 419 (5.69), 505sh (3.59), 541 (4.30),
577 (3.57), and 618 (3.18).
(C᎐O), and 1727 (C᎐O).
᎐
᎐
J. Chem. Soc., Perkin Trans. 1, 2001, 14–20
17

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[2-Amino-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyr-
inato]copper(II) 7
8.09 (2 H, d, J4Ј,2Ј = J4Ј,6Ј = 2 Hz, C(2Ј)H and C(6Ј)H), 8.11 (2 H,
d, J4Ј,2Ј = J4Ј,6Ј = 2 Hz, C(2Ј)H and C(6Ј)H), 8.17 (4 H, m, C(2Ј)H
and C(6Ј)H), 8.74 (1 H, 1/2ABq, JA,B = 4.5 Hz, β-pyrrolic H),
8.92 (1 H, 1/2Abq, JA,B = 4.5 Hz, β-pyrrolic H), and 8.99–9.06
(4 H, m, β-pyrrolic H). DMP (26 mg, 0.06 mmol) was added to
a solution of 8 (≈69 mg, ≈0.06 mmol) in dichloromethane
(13 cm3). The mixture was stirred at room temperature in
the dark for 2 h at which point thin-layer chromatography
(dichloromethane–light petroleum 2:3) showed that no 8
remained. Water (50 cm3) was added and the reaction mixture
was stirred for a further 40 min. The organic layer was separ-
ated, dried over anhydrous sodium sulfate, filtered, and the
solvent completely removed. The residue was purified by col-
umn chromatography over silica gel using a dichloromethane–
light petroleum mixture (2:3–1:1) as eluent to give 11 (14 mg,
20%) which had identical 1H NMR,28 infrared and UV–
visible33 spectra to those reported in the literature; νmax(KBr
10% Palladium on activated carbon (45 mg) was added to a
solution of 3 (64 mg, 0.054 mmol) in a dichloromethane–
methanol mixture (4:1) (12 cm3) and the mixture was degassed
with nitrogen. Sodium borohydride (52 mg, 1.75 mmol) was
added in small portions over a 6 min period. The reaction
mixture was stirred at room temperature under a nitrogen
atmosphere in the dark for 1 h and then evaporated to dryness.
The residue was passed through a plug of silica using dichloro-
methane as eluent. The solvent was completely removed to give
a red–purple residue. For analysis the residue was purified by
column chromatography over silica using a dichloromethane
and light petroleum mixture (1:4) as eluent. Care was taken to
avoid photo-oxidation by keeping the silica column sub-
stantially in the dark. The main fraction was collected and the
solvent completely removed. The residue was recrystallised
from a dichloromethane–methanol mixture to give 7 as a purple
solid (55 mg, 89%); mp > 296 ЊC; νmax(KBr disc)/cmϪ1 3486
(NH2) and 3392 (NH2); λmax(CHCl3)/nm (log (ε/dm3 molϪ1
cmϪ1)) 423 (5.51), 544 (4.24), and 595 (3.79); m/z (LDI) 1138.8
disc)/cmϪ1 1727 (C᎐O); λmax(CHCl3)/nm (log (ε/dm3 molϪ1
᎐
cmϪ1)) 410 (5.13), 489 (4.35), 633 (3.73), and 720 (3.78).
Method 2. 10% Palladium on activated carbon (27 mg) was
added to a solution of the 2,3-dinitro-5,10,15,20-tetrakis(3Ј,5Ј-
di-tert-butylphenyl)porphyrinatozinc() 23 (15 mg, 0.012 mmol)
in a dichloromethane–methanol mixture (4:1) (4 cm3) and the
reaction mixture was degassed with nitrogen. Sodium boro-
hydride (24 mg, 0.616 mmol) was added. The reaction mixture
was stirred at room temperature under nitrogen in the dark for
1 h. The solvent was removed and the residue was passed
through a plug of silica using dichloromethane as eluent. The
main fraction was collected and the solvent completely removed
to give a red–purple residue of 22 (≈14 mg, ≈98%). DMP (11 mg,
0.025 mmol) was added to a stirred solution of 22 (14 mg, 0.012
mmol) in dichloromethane (3 cm3). The reaction mixture was
stirred at room temperature in the dark for 25 min. The mixture
was passed through a plug of silica using dichloromethane as
the eluent. After removal of the solvent, the residue was puri-
fied by column chromatography over silica using a dichloro-
methane and light petroleum mixture (2:3) as eluent to give
11 (11 mg, 78%) which co-chromatographed with and had an
identical 1H NMR to an authentic sample.
(Mϩ ); C76H93N5Cu requires 1138.7.
᝽
[2,3-Dioxo-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)chlor-
inato]copper(II) 10
10% Palladium on activated carbon (121 mg) was added to a
solution of 3 (164 mg, 0.140 mmol) in a dichloromethane–
methanol mixture (4:1) (30 cm3) and the reaction mixture was
degassed with nitrogen. Sodium borohydride (132 mg, 3.49
mmol) was added in small portions over a 10 min period. The
reaction mixture was stirred at room temperature under a
nitrogen atmosphere in the dark for 1 h and then evaporated to
dryness. The residue was passed through a plug of silica using
dichloromethane as eluent. The main fraction was collected and
the solvent completely removed to give a red–purple residue of
7 (≈155 mg, ≈98%). DMP (58 mg, 0.14 mmol) was added to a
solution of 7 (≈155 mg, ≈0.136 mmol) in dichloromethane (25
cm3). The reaction mixture was stirred at room temperature in
the dark for 5 h. DMP (25 mg, 0.058 mmol) was added and
stirred for a further 11 h. Hydrochloric acid (1 M, 30 cm3) was
added and the mixture was stirred for a further 45 min. The
organic layer was separated, washed with water (2 × 50 cm3),
sodium bicarbonate solution (5%, 50 cm3), water (50 cm3),
dried over anhydrous sodium sulfate, filtered, and the solvent
completely removed. The residue was purified by column
chromatography over silica gel using a dichloromethane–light
petroleum mixture (2:3–1:1) as eluent to give 10 (58 mg, 37%)
which had identical infrared28 and UV–visible spectra33 to
those reported in the literature; λmax(CHCl3)/nm (log (ε/dm3
molϪ1 cmϪ1)) 414 (4.85), 486 (4.22), 544 (3.55), 632 (3.76), and
708 (3.62).
[Dinitro-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyr-
inato]copper(II)s 12
A solution of nitrogen dioxide in light petroleum (0.51 M, in
total 8 cm3) was added in small aliquots to a solution of 3 (1.80
g, 1.54 mmol) in dichloromethane (100 cm3). The reaction was
followed by thin-layer chromatography (dichloromethane–light
petroleum 1:4). When no starting material was observed, the
mixture was immediately passed through a plug of silica gel
using dichloromethane as eluent. The solvent was completely
removed to give a purple residue which was then purified by
column chromatography over silica using a dichloromethane–
light petroleum mixture (1:4) as eluent. Six possible isomers of
the copper-dinitroporphyrins were collected. The solvent was
completely removed to give 1215 as a mixture of six isomers
as a red–purple solid (1.44 g, 77%). A sample for analysis was
recrystallised from a dichloromethane–methanol mixture;
mp > 296 ЊC (Found: C, 74.5; H, 7.55; N, 6.85. C76H90CuN6O4
requires C, 75.1; H, 7.5; N, 6.9%); νmax(KBr disc)/cmϪ1
1531 (NO2); λmax(CHCl3)/nm (log (ε/dm3 molϪ1 cmϪ1)) 438
[2,3-Dioxo-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)chlor-
inato]zinc(II) 11
Method 1. 10% Palladium on activated carbon (49 mg) was
added to a solution of 5 (72 mg, 0.06 mmol) in a
dichloromethane–methanol mixture (4:1) (14 cm3) and the
reaction mixture was degassed with nitrogen. Sodium boro-
hydride (58 mg, 1.5 mmol) was added in small portions over an
8 min period. The reaction mixture was stirred at room tem-
perature under a nitrogen atmosphere in the dark for 1 h and
then evaporated to dryness. The residue was passed through a
plug of silica using dichloromethane as eluent. The main
fraction was collected and the solvent was completely removed
to give a red–purple solid 8 (≈69 mg, ≈98%); νmax(KBr disc)/cmϪ1
3486 (NH2) and 3392 (NH2); δH(200 MHz; CDCl3) 1.57–1.59
(72 H, tert-butyl H), 4.53 (br s, NH2), 7.82–7.85 (3 H, m, C(4Ј)),
7.91 (1 H, dd, J2Ј,4Ј = J6Ј,4Ј = 2 Hz, C(4Ј)H), 7.95 (1 H, s, C(3)H),
ϩ
ؒ
(5.19), 559 (4.08), and 601 (4.03); m/z (MALDI) 1213.8 (M );
C76H90N6O4Cu requires 1213.6.
Dinitro-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyrins
13
A solution of 12 (1.74 mg, 1.431 mmol) in dichloromethane
(150 cm3) was treated with concentrated sulfuric acid (2 cm3).
The reaction mixture was stirred at room temperature for 10
min and then poured into an ice–water mixture (100 cm3). The
18
J. Chem. Soc., Perkin Trans. 1, 2001, 14–20

View Article Online
aqueous layer was separated and extracted with dichlorometh-
ane (3 × 100 cm3). The combined organic layers were washed
with water (100 cm3), sodium bicarbonate solution (5%, 100
cm3), water (100 cm3), dried over anhydrous sodium sulfate,
filtered, and the solvent completely removed leaving a purple
residue. The residue was purified by column chromatography
on silica gel using a dichloromethane–light petroleum (1:4)
mixture as eluent to give 13 as a purple solid (1.65 mg, 100%);
mp > 296 ЊC (Found: C, 78.7; H, 8.39; N, 7.1. C76H92N6O4
requires C, 79.1; H, 8.0; N, 7.3%); νmax(KBr disc)/cmϪ1 3341
(NH), 3316 (NH), and 1532 (NO2), 1477, 1363, 1294, 1248,
1207, 1157, 918, and 802; λmax(CHCl3)/nm (log (ε/dm3 molϪ1
cmϪ1)) 442 (5.32), 539 (4.13), 583 (3.96), 618sh (3.76), and 683
(4.04); δH(500 MHz; CDCl3) Ϫ2.48 to Ϫ2.40 and Ϫ2.18 to
Ϫ2.09 (6 H, NH), 1.50–1.56 (72 H, tert-butyl H), 7.80–7.88
(4 H, m, C(4Ј)H), 8.00–8.14 (8 H, m, C(2Ј)H and C(6Ј)H), and
[Diamino-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyr-
inato]copper(II)s 16
10% Palladium on activated carbon (93 mg) was added to a
solution of 12 (57 mg, 0.05 mmol) in a dichloromethane–
methanol mixture (4:1) (12 cmϪ3) and the reaction mixture was
degassed with nitrogen. Sodium borohydride (89 mg, 2.3 mmol)
was added in small aliquots over a 10 min period. The reaction
mixture was stirred at room temperature under nitrogen in the
dark for 1 h and then evaporated to dryness. The residue was
passed through a plug of silica using dichloromethane as elu-
ent. The main fraction was collected and the solvent completely
removed to give a purple residue. The residue was purified by
column chromatography in the dark using a dichloromethane–
light petroleum (2:3) mixture as eluent. Care was taken to avoid
photo-oxidation by keeping the silica column substantially in
the dark. The main fraction was collected and the solvent
completely removed. The residue was recrystallised from a
dichloromethane–methanol mixture to give a purple solid of 16
(40 mg, 74%); mp > 296 ЊC (Found: C, 78.6; H, 8.2; N, 7.15.
C76H94CuN6 requires C, 79.0; H, 8.0; N, 7.3%); νmax(KBr disc)/
cmϪ1 3484 (NH2) and 3390 (NH2); λmax(CHCl3)/nm (log (ε/dm3
molϪ1 cmϪ1)) 427 (5.18), 544 (4.08), 552sh (4.06), and 600 (3.77);
8.77–9.11 (6 H, m, β-pyrrolic H); m/z (MALDI) 1153.1 (Mϩ
)
᝽
and 1154.1 (MHϩ); C76H93N6O4 requires 1153.7.
[Dinitro-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyr-
inato]zinc(II)s 14
A mixture of 13 (175 mg, 0.151 mmol), zinc() acetate dihy-
drate (67 mg, 0.30 mmol), dichloromethane (30 cmϪ3), and
methanol (8 cmϪ3) was heated at reflux for 1 h. The reaction
mixture was allowed to cool and the solvent removed. The
residue was passed through a plug of silica using dichloro-
methane as eluent and the main fraction was collected and
the solvent completely removed. The residue was purified by
column chromatography over silica using a dichloromethane–
light petroleum mixture (1:4–1:1) as eluent to give 14 as a
purple solid (181 mg, 98%); mp > 296 ЊC; νmax(KBr disc)/cmϪ1
1525 (NO2); λmax(CHCl3)/nm (log (ε/dm3 molϪ1 cmϪ1)) 441
(5.30), 527sh (3.61), 566 (4.14), and 611 (4.06); δH(400 MHz;
CDCl3) 1.53–1.55 (72 H, t-butyl H), 7.78–7.86 (4 H, C(4Ј)H),
7.94–8.05 (8 H, C(2Ј)H and C(6Ј)H), 8.87–9.01 (4 H, β-pyrrolic
H), and 9.16–9.21 (2 H, β-pyrrolic H); m/z (MALDI) 1214.8
ϩ
ؒ
m/z (LDI) 1153.9 (M ); C76H94N6Cu requires 1153.7.
Attempted preparation of [2,3,12,13-tetraoxo-5,10,15,20-
tetrakis(3Ј,5Ј-di-tert-butylphenyl)porphyrinato]zinc(II) 20
10% Palladium on activated carbon (360 mg) was added to a
solution of 14 (190 mg, 0.156 mmol) in a dichloromethane–
methanol mixture (4:1) (40 cm3) and the reaction mixture was
degassed with nitrogen. Sodium borohydride (295 mg, 7.80
mmol) was added in small portions over a 15 min period. The
reaction mixture was stirred at room temperature under nitro-
gen in the dark for 1 h. The solvent was removed and the
residue was passed through a plug of silica using dichloro-
methane as eluent. The main fraction was collected and the
solvent completely removed to give a purple solid of 17 (≈170
mg, ≈94%); mp > 296 ЊC; νmax(KBr disc)/cmϪ1 3485 (NH2),
3392 (NH2); δH(400 MHz; CDCl3) 1.54–1.56 (72 H, tert-butyl
H), 4.39 (2 H, br s, NH2), 7.27–7.81 (14 H, phenyl H and
β-pyrrolic H), and 8.57–8.97 (4 H, β-pyrrolic H). DMP (62 mg,
0.15 mmol) was added in small aliquots to a stirred solution of
17 (≈170 mg, ≈0.146 mmol) in dichloromethane (25 cm3) at
room temperature in the dark. The reaction mixture was stirred
for 30 min and then water (50 cm3) was added. The reaction
mixture was stirred for a further 40 min. The organic layer
was separated, dried over anhydrous sodium sulfate, filtered,
and the solvent completely removed. After purification by
column chromatography over silica using a dichloromethane–
light petroleum mixture (2:3) as eluent, three main bands
were isolated. Starting material (17) (15 mg, 9%), 11 (5 mg,
3%) (a sample of which co-chromatographed with and had an
identical 1H NMR to an authentic compound), and 2115
(55 mg, 32%); νmax(KBr disc)/cmϪ1 3482 (NH2), 3395 (NH2),
(Mϩ ); C76H90N6O4Zn requires 1214.6.
᝽
2,3,12,13-Tetraoxo-5,10,15,20-tetrakis(3Ј,5Ј-di-tert-butyl-
phenyl)porphyrin 18
Tin() chloride dihydrate (0.19 g, 0.84 mmol) and concentrated
hydrochloric acid (0.5 cm3) were added to a solution of 13 (139
mg, 0.120 mmol) in dichloromethane (4 cm3). The reaction
mixture was stirred under a nitrogen atmosphere at room tem-
perature in the dark. The progress of the reaction was moni-
tored by thin-layer chromatography (dichloromethane–light
petroleum 1:4). After stirring for 4 days, dichloromethane (30
cm3) and water (30 cm3) were added. The organic layer was
separated, washed with water (30 cm3), sodium bicarbonate
solution (5%, 30 cm3), water (30 cm3), dried over anhydrous
sodium sulfate, filtered and the solvent completely removed to
yield a brown–purple solid. The crude product was recrystal-
lised from a dichloromethane–methanol mixture to give 15 as a
brown–purple solid (≈127 mg, ≈97%); νmax(KBr disc)/cmϪ1 3485
(NH2), 3392 (NH2), and 3321 (NH). DMP (98 mg, 0.23 mmol)
was added to a solution of 15 (≈127 mg, ≈0.116 mmol) in
dichloromethane (15 cm3). The reaction mixture was stirred at
room temperature in the dark for 35 min at which point thin-
layer chromatography (dichloromethane–light petroleum 2:3)
showed that no 15 remained. Hydrochloric acid (1 M, 10 cm3)
was added and the mixture was stirred for a further 30 min. The
organic layer was separated, washed with water (3 × 50 cm3),
dried over anhydrous sodium sulfate, filtered and the solvent
completely removed. The residue was purified by column
chromatography over silica gel using a dichloromethane–light
petroleum (2:3) mixture as eluent to give 18 (25 mg, 20%). The
ϩ
ϩ
ؒ
and 1726 (C᎐O); m/z (FAB) 1170.7 (M ) and 1171.7 (MH );
᎐
C76H92N5O2Zn requires 1170.7.
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J. Chem. Soc., Perkin Trans. 1, 2001, 14–20