Construction of building blocks for extended porphyrin arrays by nitration of porphyrin-2,3-diones and quinoxalino[2,3-b]porphyrins

Article abstract of DOI:10.1039/b712643c

Nitration of metal(II) porphyrin-2,3-diones 3-5 and quinoxalino[2,3-b] porphyrins 13-15 with nitrogen dioxide gave a mixture of β-pyrrolic functionalised nitro-porphyrin isomers in relative abundance of 7-nitro- > 12-nitro- > 8-nitro. The large selectivity for reaction at the 7-position over the adjacent 8-position (>5 to 1 in the diones 3-5 and about 3 to 1 in the quinoxalinoporphyrins 13-15) is especially striking. This selectivity results mainly from electronic effects and is consistent with a mechanism involving a porphyrin π-cation radical intermediate. A key step incorporated into the isomer separation sequence was to make use of the different chromatographic polarity of metalated compounds compared to unmetalated compounds coupled with the observation that introduction of a nitro group to the 7-position of free-base porphyrin-dione greatly increases its rate of metalation while introduction of the nitro group at the 12-position greatly decreases its rate of metalation, relative to the unsubstituted parent. Thus demetalation of zinc(ii) nitro-porphyrin-dione isomers, which are difficult to separate, allows for highly selective remetalation of the 7-isomer and its very easy separation from the unmetalated 12-nitro-porphyrin-dione. These nitrated compounds are useful building blocks for more elaborate systems. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b712643c

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Construction of building blocks for extended porphyrin arrays by
nitration of porphyrin-2,3-diones and quinoxalino[2,3-b]porphyrinsw
Maxwell J. Crossley,* Craig S. Sheehan, Tony Khoury, Jeffery R. Reimers and
Paul J. Sintic
Received (in Montpellier, France) 16th August 2007, Accepted 15th October 2007
First published as an Advance Article on the web 25th October 2007
DOI: 10.1039/b712643c
Nitration of metal(II) porphyrin-2,3-diones 3–5 and quinoxalino[2,3-b]porphyrins 13–15 with
nitrogen dioxide gave a mixture of b-pyrrolic functionalised nitro-porphyrin isomers in relative
abundance of 7-nitro- 4 12-nitro- 4 8-nitro. The large selectivity for reaction at the 7-position
over the adjacent 8-position (45 to 1 in the diones 3–5 and about 3 to 1 in the
quinoxalinoporphyrins 13–15) is especially striking. This selectivity results mainly from electronic
effects and is consistent with a mechanism involving a porphyrin p-cation radical intermediate.
A key step incorporated into the isomer separation sequence was to make use of the different
chromatographic polarity of metalated compounds compared to unmetalated compounds coupled
with the observation that introduction of a nitro group to the 7-position of free-base porphyrin-
dione greatly increases its rate of metalation while introduction of the nitro group at the
12-position greatly decreases its rate of metalation, relative to the unsubstituted parent. Thus
demetalation of zinc(II) nitro-porphyrin-dione isomers, which are difficult to separate, allows for
highly selective remetalation of the 7-isomer and its very easy separation from the unmetalated
12-nitro-porphyrin-dione. These nitrated compounds are useful building blocks for more
elaborate systems.
while bends can be introduced where the porphyrin-2,3,7,8-
tetraones are incorporated into the framework.25–27
Introduction
Nitro groups are a very useful functionality to incorporate
into porphyrin systems,1–7 especially when positioned at the b-
Selective incorporation of a nitro group into porphyrin-2,3-
dione building blocks would provide a functionality that can
pyrrolic periphery.8–16 A range of transformations have been
be converted into a considerable range of other functionalised
developed, some of which are summarised in Scheme 1, that
extended systems, as well as allowing substituents to act as
allow for the introduction of functional groups that are
handles for attachment to external redox centres and which
otherwise very difficult to access.10,15–21 The porphyrin-2,3-
might be used modulate properties.28–30 A porphyrin macro-
dione 1 (M = 2H) is of particular use in condensation
cycle that contains both nitro and a-dione functionality would
also be useful building blocks for controlled stepwise-synthesis
of unsymmetrical oligoporphyrins.31
reactions17 while the quinoxalinoporphyrin 2 (M = 2H) serves
as a model for the development of chemistry on laterally
extended oligoporphyrin systems.22
Nitro-quinoxalinoporphyrins are envisaged as building
Porphyrin-2,3-diones 1 have been used as building blocks
for the synthesis of laterally-bridged bis-porphyrins.23 For
blocks for exploration of synthetic routes to porphyrin
systems with two, three, and even all four pyrrolic rings
annulated.26 Nitrations of quinoxalino[2,3-b]porphyrins 2
more elaborate systems such as laterally-bridged oligopor-
phyrins, porphyrin-2,3,12,13- and -2,3,7,8-tetraones porphyr-
would also be a good model for the determination and control
ins have been prepared and used in analogous reactions; these
of the likely outcome of nitration of more elaborated laterally-
tetraones being accessed from isomeric mixtures of dinitro-
bridged oligoporphyrin systems. Control of the site of
porphyrins.24 Linear ‘pseudo one-dimensional molecular
nitration of extended systems will be crucial for development
wires’ are accessible from the porphyrin-2,3,12,13-tetraones
of architectures based on a square-grid motif leading to two-
dimensional arrays.
For such nitrated porphyrin-dione and quinoxalino-por-
School of Chemistry, The University of Sydney, NSW 2006,
Australia. E-mail: m.crossley@chem.usyd.edu.au;
Tel: +61 2 9351 2751
w Electronic supplementary information (ESI) available: List of NOE
enhancements for 7- and 12-nitro-porphyrin-diones 6a and 6c and 7-
and 12-nitro-quinoxalinoporphyrins 10a and 10c. The partial 1H
NMR spectrum (400 MHz) of zinc(II) 7-nitro-quinoxalinoporphyrin
10a in CDCl3 with additional signals of lower intensity belonging to
the zinc(II) 8-nitro-quinoxalinoporphyrin 10b is also given. See DOI:
10.1039/b712643c
phyrin building blocks to be especially useful, methodology
needed to be developed which would allow them to be
obtained as pure compounds rather than isomeric mixtures.
To date, only the nitration of copper(II) 2-methyl-5,10,15,20-
tetraphenylporphyrin and two copper(II) 2-nitro-5,10,15,20-
tetraarylporphyrins has been reported and in each case the
selectivity was low and only with considerable effort were
small amounts of pure compounds, sufficient for individual
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Scheme 1 Some transformations involving ring annulations and ring modifications deriving from 2-nitroporphyrins (Ar = 3,5-di-tert-
butylphenyl).
characterisation, obtained from the isomeric mixture of
products.9
30 min when zinc(II) chelation was found to have occurred
exclusively to the 7- and 8-nitro-porphyrin-2,3-diones isomers.
The resultant mixture was readily separated by chromatogra-
phy to give zinc(II) 7-nitro-porphyrin-dione 6a in 70% yield
and free-base 12-nitro-porphyrin-dione 16c (Scheme 3). The
regiochemistry of the isomers was assigned by means of 1H
NMR decoupling and NOE experiments (see ESIw). Trace
quantities of the 8-nitro-porphyrin-dione isomer 6b were
identified by 1H NMR and TLC in latter dilute fractions
during the fractionated collection of the band containing 6a
and could not be separated.
In this paper we explore the directive effects of the dione and
fused quinoxaline groups on nitration of the porphyrin nu-
cleus, we examine the influence of the co-ordinated metal ion
on the reactions, and we develop a demetalation-selective
remetalation strategy for relatively easy separation of some
of the nitro-porphyrin-a-diones. A rationalisation on the
relative abundance of the regioisomers that arise from nitra-
tion is also presented.
The large difference in metalation rates for free-base
nitro-porphyrin-dione regioisomers 16a and 16c was readily
observed by metalation of the separated isomers. The reaction
of free-base 7-nitro-porphyrin-dione 16a with 1.1 equiv. of
zinc(II) acetate at 25 1C was complete after 20 min (Scheme 3).
By contrast, the reaction of free-base 12-nitro isomer 16c with
zinc(II) acetate under similar conditions had gone to comple-
tion after stirring for 68 h. Metalation of 16c with excess
zinc(II) acetate in the dichloromethane–methanol mixture
heated at reflux reduced the reaction time to 8 h. The reaction
of the non-nitrated analogue, free-base porphyrin-dione 1,
with 1.1 equiv. of zinc(II) acetate at 25 1C was complete after
26 h to give zinc(II) porphyrin-dione 3. Thus, introduction of a
nitro group to the 7-position of free-base porphyrin-dione
increases the rate of metalation while introduction of the nitro
group at the 12-position decreases the rate of metalation
relative to the unsubstituted parent.
Results and discussion
Scheme 2 summarises nitration and ring annulation of zinc(II),
copper(II) and palladium(II) 5,10,15,20-tetrakis(3,5-di-tert-bu-
tylphenyl)porphyrin-2,3-diones 3–5, prepared by direct meta-
lation of free-base porphyrin-dione 1, and nitration of the
corresponding quinoxalino[2,3-b]porphyrins 13–15, prepared
by similar metalation of the free-base quinoxalinoporphyrin 2.
Nitration of metal(II) porphyrin-2,3-diones
Zinc(II) porphyrin-dione 332 was treated with aliquots of a
solution of nitrogen dioxide in light petroleum until TLC
analysis showed that none of the starting material remained.
A mixture of zinc(II) nitro-porphyrin-diones 6a–c was ob-
tained in 80% yield. The remainder of the product was much
more polar and consistent with porphyrin ring-cleaved com-
pounds; such ring-cleaved compounds are the major product
of nitration of simpler zinc(II) 5,10,15,20-tetraarylporphyrins
and are the result of initial nitration at a meso-position rather
than at a b-pyrrolic position.
The mixture of zinc(II) nitro-porphyrin-diones 6a–c was
observed as a single band by TLC analysis and could not be
separated by column chromatography. It was found, however,
that upon demetalation with hydrochloric acid and subse-
quent selective remetalation, achieved by stirring the mixture
of free-base regioisomers with zinc(II) acetate at room tem-
perature, zinc(II) chelation of free-base 7- and 8-nitro-porphyr-
in-diones 16a and 16b proceeded at a faster rate than free-base
12-nitro-porphyrin-dione 16c. Reaction conditions were opti-
mised to 0.75 equiv. of zinc(II) acetate and a reaction time of
The titration endpoint of the nitration of copper(II) and
palladium(II) porphyrin-2,3-dione complexes 4 and 5,32 was
determined by treating an aliquot from the reaction mixture
with 1,2-benzenediamine 9 and examining this mixture by
TLC analysis for the presence of the corresponding metallated
quinoxalinoporphyrin22 since the metalloporphyrin-diones co-
eluted with nitration products. In each macrocycle nitration
will be directed towards the b-pyrrolic periphery9,33 to give
three possible nitro-porphyrin-dione regioisomers: the 7-nitro-
porphyrin-dione 6–8a, the 8-nitro-porphyrin-dione 6–8b, and
the 12-nitro-porphyrin-dione 6–8c (Scheme 2).
Selective remetalation could not be applied to the copper(II)
or palladium(II) nitro-porphyrin-diones as they co-elute with
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Scheme 2 Reagents and conditions: i, NO2–light petroleum, CH2Cl2; ii, 1,2-benzenediamine, CH2Cl2, 1 h (Ar = 3,5-But2C6H3).
the free-base isomers 16a and 16c. In contrast to the mixture of
zinc(II) isomers, copper(II) and palladium(II) nitro-porphyrin-
dione regioisomers could be separated by chromatography.
The copper(II) 7-nitro-porphyrin-dione 7a and copper(II) 12-
nitro-porphyrin-dione 7c were isolated in yields of 42 and
28%, respectively, with the 8-nitro isomer 7b not being
isolated or detected. In a similar fashion palladium(II) 12-nitro
and 8-nitro isomers 8c and 8b were isolated in combined yield
of 43% (in a ratio of 3 : 1, respectively, determined by 1H
NMR), and the 7-nitro isomer 8a was isolated in 49% yield
(Scheme 2). The differing ratios of isomeric abundance for
these two complexes, best demonstrated by the greater pro-
portion in which the 8-nitro isomer is formed with the
palladium(II) chelate, clearly indicate that the complexed metal
ion influences nitration patterns. It should also be noted that
the regiochemistry of the copper(II) and palladium(II) chelates
was determined by condensation of the nitro-porphyrin-dione
adduct with 1,2-benzenediamine 9 followed by comparison of
the resultant nitro-quinoxalinoporphyrin with authentic sam-
ples of known regiochemistry (as described in the following
section). This further condensation reaction was required as
the copper(II) nitro-porphyrin-dione isomers are paramagnetic
The copper(II) and palladium(II) regioisomers were also
prepared by demetalation of zinc(II) nitro-porphyrin-dione
isomers 6a–c followed by remetalation with the appropriate
metal(II) ion (Scheme 3). This approach allowed for the large
scale purification of the copper(II) chelates. In the case of the
palladium(II) isomers the metalation proceeded only after the
reaction solvent was changed from acetic acid–chloroform to
acetic acid–toluene, which allowed the solution to reflux at a
higher temperature and improve solubility of the porphyrin
(Scheme 3). Additionally, trace quantities of the metallated 8-
nitro isomer were obtained as an inseparable mixture with the
palladium(II) 12-nitro isomer 8c.
Preparation of separated nitro-quinoxalinoporphyrin isomers
Preparation of pure nitro-quinoxalinoporphyrin regioisomers
was important for the assignment of the regiochemistry of the
products obtained by nitration of quinoxalinoporphyrins
15–17 and metal(II) porphyrin-diones 3–5.
Zinc(II) nitro-porphyrin-dione isomers 6a–c were reacted
with 1,2-benzenediamine 9 and the resultant mixture of
isomers separated by chromatography to give zinc(II)
7-nitro-quinoxalinoporphyrin 10a in 65% yield and zinc(II)
12-nitro-quinoxalinoporphyrin 10c in 23% yield (Scheme 2).
1
and could not be demetallated, while the H NMR spectrum
of the palladium(II) isomers was complex.
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Scheme 3 Reagents and conditions: i, HCl (7 mol dmÀ3), Et2O; ii, Zn(OAc)2 Á 2H2O (0.8 equiv.), CH2Cl2–CH3OH, stir, r.t., 30 min;
iii, Zn(OAc)2 Á 2H2O, CH2Cl2–MeOH, heat, 8 h; iv, Cu(OAc)2 Á H2O, CH2Cl2–MeOH, heat, 90 min; v, PdCl2, NaOAc, AcOH–C7H8, heat,
5 min (Ar = 3,5-But2C6H3).
The regiochemistry of the isomers was assigned by means of
1H NMR decoupling and NOE experiments (see ESIw). The
1H NMR spectrum of zinc(II) 7-nitro-quinoxalinoporphyrin
10a also contained extra peaks which are due to the presence
of the zinc(II) 8-nitro-quinoxalinoporphyrin 10b; a singlet and
an AB-quartet were observed along with additional peaks of
undetermined multiplicity amongst the tight AB-quartet of
10a. The ratio of 10a to 10b was 7 : 1 as determined by
1H NMR analysis, in particular, by integration of the signals
(d 9.13 for 10a and d 9.27 for 10b) of the protons next to the
nitro group (see ESI,w Fig. S1). This ratio was used to
determine the proportion of 8-nitro-porphyrin-dione 6b
produced during the nitration of 3.
Nitration of metal(II) quinoxalinoporphyrins
The zinc(II), copper(II) and palladium(II) quinoxalinoporphy-
rins 13–15 used in this study were prepared using published
procedures.22 Each of the metal(II) quinoxalinoporphyrins was
nitrated by treatment with aliquots of a solution of nitrogen
dioxide in light petroleum until TLC analysis showed that
none of the starting quinoxalinoporphyrin remained to give
the corresponding metal(II) nitro-quinoxalinoporphyrins
10–12 (Scheme 2).
Nitration of zinc(II) quinoxalinoporphyrin 13 gave a mix-
ture of zinc(II) 7-nitro-quinoxalinoporphyrin 10a and zinc(II)
8-nitro-quinoxalinoporphyrin 10b in 40% yield, and zinc(II)
12-nitro-quinoxalinoporphyrin 10c in 13% yield. The ratio of
By contrast, the regioisomers of copper(II) nitro-quinoxali-
noporphyrins 11a–c and palladium(II) nitro-quinoxalinopor-
phyrins 12a–c co-eluted and could not be prepared from a
mixture of the corresponding nitro-porphyrin-dione isomers.
Therefore demetalation of zinc(II) nitro-porphyrin-diones 6a–c
followed by separation of resultant free-base derivates
(through zinc(II) remetalation) and condensation with
1,2-benzenediamine 9 was used to prepare these adducts
(Scheme 4). As the zinc(II) 7-nitro-quinoxalinoporphyrin 10a
used in this experiment contained trace quantities of the
8-nitro isomer 10b, small amounts of the 8-nitro isomer were
also observed in the 1H NMR spectra of free-base 7-nitro-
quinoxalinoporphyrin 17a and the corresponding palla-
1
10a to 10b, determined by H NMR analysis, was 3.4 : 1.
Nitration of copper(II) quinoxalinoporphyrin 14 gave an
inseparable mixture of copper(II) nitro-quinoxalinoporphyrin
regioisomers 11a–c in 92% yield. In order to determine the
ratio of nitro-quinoxalinoporphyrin isomers produced by this
nitration, the mixture of 11a–c was demetallated with sulfuric
acid–trifluoroacetic acid followed by zinc(II) chelation to give
1
separable isomers of which H NMR spectra can be obtained
(Scheme 4). Zinc(II) 7-nitro-quinoxalinoporphyrin 10a and
zinc(II) 8-nitro-quinoxalinoporphyrin 10b were afforded in
61% yield, and zinc(II) 12-nitro-quinoxalinoporphyrin 10c in
26%. The ratio of 10a to 10b was found to be 3.5 : 1.0 by
1H NMR analysis.
1
dium(II) complex 12a. The H NMR of these trace quantities
Nitration of palladium(II) quinoxalinoporphyrin 15 also
showed the formation of a single more polar band by TLC
analysis. A mixture of palladium(II) nitro-quinoxalinopor-
phyrin isomers 12a–c was obtained in 82% yield (Scheme 2).
of zinc(II) and palladium(II) 8-nitro isomers were of use when
assigning the regiochemical outcomes from the nitration of
quinoxalinoporphyrins 13–15 as it enabled the yield of each
isomer to be quantified.
It should also be noted that 1H NMR analysis of the
resultant mixture of free-base nitro-quinoxalinoporphyrins
produced from the condensation and subsequent demetalation
of the copper(II) nitro-porphyrin-diones 7a–c failed to detect
the presence of the 8-nitro isomer.
1
The H NMR spectrum of the mixture of isomers had three
singlets at d 9.01, 9.05 and 9.18 which, by comparison with
the H NMR spectra of authentic samples of the individual
1
isomers, are due to the b-pyrrolic proton adjacent to the
nitro group of palladium(II) 7-nitro isomer 12a, palladium(II)
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Scheme 4 Reagents and conditions: (A), i, HCl (7 mol dmÀ3), Et2O; ii, Cu(OAc)2 Á H2O, CH2Cl2–CH3OH, heat, 75 min; iii, PdCl2, NaOAc,
AcOH–CHCl3, heat, 18 h; (B), iv, H2SO4–CF3CO2H, CH2Cl2 (Ar = 3,5-But2C6H3).
12-nitro isomer 12c, and palladium(II) 8-nitro-quinoxalinopor-
phyrin 12b, respectively. By measuring the area under these
resonances, the ratio of 12a to 12b to 12c was 1.9 : 1.0 : 1.5.
porphyrin-dione 3, palladium(II) porphyrin-dione 5, zinc(II)
quinoxalinoporphyrin 13, and palladium(II) quinoxalinopor-
phyrin 15 were undertaken (Fig. 1). In these experiments
enhancements of protons at the 8- and 12-positions were
investigated as they are likely to have the same relaxation
mechanism as these protons are both adjacent to the same
meso-aryl group. The 8- and 12-b-pyrrolic positions of zinc(II)
porphyrin-dione 3 showed a similar enhancement of 2.3 and
2.2%, respectively. For palladium(II) porphyrin-dione 7, a
similar enhancement was observed for the 8- and 12-positions
(2.0 and 2.0%). This indicated that the 8-position was not
sterically hindered relative to the 12-position. Similar NOE
experiments on the quinoxalinoporphyrins 13 and 15 showed
that the 8-position was less hindered than the 12-position
(1.6 and 1.9% for 13 and 1.7 and 2.1% for 15).
Rationalisation of the isomeric abundance of nitro-porphyrin-a-
diones and nitro-quinoxalinoporphyrins
The relative abundance of the nitro-porphyrin-dione regio-
isomers produced by the nitration of the porphyrin-diones 3–5
was 7 nitro- 4 12 nitro- 4 8 nitro-porphyrin-dione. The same
trend was observed for the nitration of quinoxalinoporphyrins
13–15. A summary of the percentage abundance of each
isolated isomer is displayed in Table 1.
If the regiochemistry of the nitration was statistical, the
isomers would be formed in equal amounts. This is clearly not
the case. To investigate whether the relative abundance of the
isomers was caused by steric hindrance of the b-pyrrolic
carbons by the meso-aryl groups NOE experiments on zinc(II)
The trends observed in the enhancements of the b-pyrrolic
protons when the ortho-protons of the meso-aryl groups are
saturated do not explain the preference for nitration at the
Table 1 The regioisomer abundancea obtained from the nitration of respective metalloporphyrins is compared to calculated spin-density ratios
for the cation radicals evaluated for the three reaction sites
Observed product (%)a
Calculated cation-radical relative spin densities (%)
Porphyrin starting material
7-Nitro (a)
8-Nitro (b)
12-Nitro (c)
7-Nitro (a)
8-Nitro (b)
12-Nitro (c)
3 Zn
4 Cu
5 Pd
13 Zn
14 Cu
15 Pd
a
64
60
54
59
51
42
10
—
12
17
16
23
26
40
34
24
29
35
52
14
34
45
47
21
19
34
34
39
29
32
Percentage abundance of nitro regioisomers was calculated from isolated yields of the direct nitration product (for 4), demetalation and
subsequent remetalation with zinc(II) (for 14) or its condensation derivative (for 3). In all cases integration of 1H NMR signals was used to
determine distribution of the 7- and 8-isomers. For 4, condensation with 9 followed by demetalation and then 1H NMR analysis, failed to reveal
the presence of the 8-isomer.
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52 : 14 : 34). These results imply the participation of the
porphyrin HOMO orbital in the highest-energy transition
state involved in the nitration mechanism. These results are
consistent with a mechanism involving porphyrin p-cation
radical intermediate.9,14
Conclusions
Metallated nitro-porphyrin-diones 6–8 were prepared by the
treatment of the corresponding metalloporphyrin-diones 3–5
with nitrogen dioxide and in each case a mixture of regio-
isomers was produced with the relative abundance being
7-nitro- 4 12-nitro- 4 8-nitro-porphyrin-dione. Separation
of these isomers exploited various demetalation-remetalation
strategies. Most effective was that of zinc(II) chelation where it
was shown that the rate of zinc(II) metalation was much slower
for the 12-nitro isomer, thereby affording the facile separation
of valuable difunctionalised building blocks.
In a similar fashion nitro-quinoxalinoporphyrins 10–12
were prepared by nitration with the same trend in relative
abundance observed. Authentic samples of nitro-quinoxalino-
porphyrin regioisomers were also prepared by condensation of
respective nitro-porphyrin-diones with 1,2-benzenediamine 9.
These products assisted in determining regioisomer abundance
whilst demonstrating the ability of these compounds to be
further functionalised.
Fig. 1 Enhancement of each b-pyrrolic proton in 3 and 13 due to
saturation of the ortho-protons on the meso-aryl groups.
The relative abundance of nitro-porphyrin-2,3-diones and
nitro-quinoxalinoporphyrins isomers was investigated by
means of NOE experiments. It was found that the regioselec-
tivity of the nitration was determined by steric factors at the 7
b-pyrrolic position but that electronic factors are also playing
a role at other b-pyrrolic positions. These abundances were
found to correlate with the small amount of the porphyrin
HOMO orbital that is delocalized onto the reactive site of the
porphyrin, implying the participation of this orbital in the
highest-energy transition state accessed by the nitration
process.
12-position over the 8-position that was observed for the
nitration of porphyrin-2,3-diones 3–5 and quinoxalinopor-
phyrins 13–15. Thus the relative abundance of these isomers
is not due to steric factors. The relatively higher yield of the 7-
nitro isomer can be rationalised by either the quinoxaline
group or a-diketone functionality restricting the rotation of
the neighbouring aryl group, which would decrease the steric
effect at the 7-position and thereby allow easier access for
nitration. However, this explanation cannot solely account for
the observed isomer distribution as the relative amounts of
regioisomers is clearly dependent on metal(II) chelation.
Electronic factors appear to play an important role in
regioisomer distribution. A relevant indicator is the extent to
which the three sites of attachment participate in the highest-
occupied molecular orbital (HOMO) of the reactant porphyr-
ins. While typically the porphyrin HOMO is only slightly
delocalised onto the reactive b carbons,22 such delocalisation
may indeed play a critical role in the reaction mechanism, say
by facilitating attack on the starting material or a reaction
intermediary. To access this effect, calculations of the spin
densities of the cation radicals of the zinc(II) and palladium(II)
starting materials were performed, and the relative participa-
tions at the 7-, 8- and 12- positions of the reactant porphyrins
are compared to the experimental product distribution shown
in Table 1. The palladium(II) quinoxalinoporphyrin 15 is
observed to differentiate least between products (with ratios
of 42 : 23 : 35 for the 7-, 8- and 12-products, respectively, a
result which is directly paralleled by the spin densities (45 : 23 :
34, respectively). Similarly, the zinc(II) porphyrin-dione reac-
tant 3 produces the greatest differentiation for the compared
compounds (with observed ratios of 70 : 10 : 20), as is also
predicted based upon the calculated spin densities (ratios of
As well as the transformations arising from initial reduction
of the nitro group shown in Scheme 1, methodologies have
been developed previously for a range of nucleophilic ipso- and
cine-substitution reactions on metallo-2-nitroporphyrins lead-
ing to introduction of many other functional groups in addi-
tion to or by displacement the nitro group.1,33–39 The
compounds prepared in this work thus offer access to a
considerable range of compounds with modulated properties.
In addition, nitro-porphyrin-2,3-diones are of interest in their
own right for determining the degree of synergy between the
groups as a function of the position of substitution. The dione
unit of porphyrin-2,3-diones has been found to exhibit inde-
pendent redox character to the macrocycle,32 and strongly
influences the position of inner periphery tautomerisation in
free-base porphyrins.32,40 The nitro group should work in
concert with the dione when the groups are on opposite rings
but compete against it when they are on adjacent rings on the
porphyrin periphery. Studies of these properties are underway.
The nitro-porphyrin-2,3-diones prepared in this work have
proved to be very valuable building blocks for the synthesis of
asymmetric extended arrays of porphyrins and of compounds
with in-built electronic bias for use as molecular rectifiers. The
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nitro-quinoxalinoporphyrins have been very useful in explora-
tion of synthetic routes to extended porphyrin systems in
which two, three and four pyrrolic rings have been annulated.
These studies will be reported soon.
[2,3-Dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
chlorinato]zinc(II) 6a and 2,3-dioxo-12-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorin 16c. A mixture of [7-, 8-
and 12-nitro-2,3-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)chlorinato]zinc(II) 6a–c (1.07 g, 0.891 mmol) was dis-
solved in ether (60 cm3) and shaken with aqueous hydrochloric
acid (7 mol dmÀ3; 60 cm3) for 5 min. The organic phase was
washed with water (60 cm3), aqueous sodium carbonate (5%;
60 cm3) and brine (60 cm3), dried over anhydrous sodium
sulfate, and filtered. The filtrate was evaporated to dryness and
the residue dissolved in dichloromethane (60 cm3). Zinc(II)
acetate dihydrate (155 mg, 0.707 mmol) and methanol (6 cm3)
were added and the mixture stirred in the dark for 30 min and
evaporated to dryness without heating. The residue was
purified by dry-column flash chromatography over silica (di-
chloromethane–light petroleum, 1 : 2 changing to dichloro-
methane–light petroleum, 2 : 1 after the major brown band
had been collected).
Experimental
General procedures
Melting points were recorded on a Reichert melting point
stage and are uncorrected. Microanalyses were performed at
the Micro-analytical Unit, The University of New South
Wales. Infra-red spectra were recorded on a Perkin-Elmer
Model 1600 FT-IR spectrophotometer in the stated solvents.
Ultraviolet-visible spectra were routinely recorded on a Hita-
chi 150-20 spectrophotometer in chloroform that was deaci-
dified by filtration through an alumina column. 1H NMR
spectra were recorded on either a Bruker AC-200 (200 MHz),
a Bruker DPX-400 (400 MHz), or a Bruker AMX600 (600
MHz) spectrometer as stated. Deuteriochloroform was used as
the solvent with tetramethylsilane (TMS) as an internal stan-
dard. Signals are recorded in terms of chemical shift (in ppm),
multiplicity, coupling constants (in Hz) and assignment, in
that order. The following abbreviations for multiplicity are
used: s, singlet; d, doublet; dd, doublet of doublets; t, triplet;
tt, triplet of triplets; m, multiplet; br, broad; ABq, AB quartet.
Matrix assisted laser desorption ionisation time of flight
(MALDI-TOF) mass spectra were recorded on a VG TofSpec
spectrometer. Mass spectra were obtained as an envelope of
the isotope peaks of the molecular ion. The mass correspond-
ing to the envelope’s maxima is reported and was compared
with the maxima of a simulated spectrum. Column chromato-
graphy was routinely carried out using the gravity feed column
technique on Merck silica gel Type 9385 (230–400 mesh).
Analytical thin layer chromatography (TLC) analyses were
performed on Merck silica gel 60 F254 precoated sheets
(0.2 mm). All solvents used were routinely distilled prior to
use, unless otherwise stated. Light petroleum refers to the
fraction of bp 60–80 1C. Ether refers to diethyl ether and was
distilled over crushed calcium chloride and stored over sodium
wire. Ethanol-free chloroform was obtained by distillation
from calcium chloride and passage through alumina. Merck
AR grade methanol was used. Where solvent mixtures were
used, the proportions are given by volume.
The major brown band was collected and evaporated to
dryness to give 2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorin 16c (277 mg, 27%) as a purple amor-
phous powder, mp 4300 1C (Found: C, 80.0; H, 8.3; N, 5.9.
C76H91N5O4 requires C, 80.2; H, 8.1; N, 6.15%);
n
max(CHCl3)/cmÀ1 3372 (NH), 2965, 2904, 2868, 1736, 1728
(CO), 1592, 1523 (NO2), 1509, 1477, 1462, 1426, 1394, 1364,
1348 (NO2), 1293, 1265, 1248, 1085, 1071, 1029, 1009, 923,
908, 884 and 854; lmax(CHCl3)/nm 265 (log e 4.15), 374 (4.61),
421 (5.10), 483 (4.46), 529 sh (4.14) and 625 (3.83); dH(400
MHz; CDCl3) À1.80 (1 H, br s, inner NH), À1.77 (1 H, br s,
inner NH), 1.46–1.48 (36 H, m, tert-butyl H), 1.50 (18 H, s,
tert-butyl H), 1.51 (18 H, s, tert-butyl H), 7.69–7.72 (4 H, m,
aryl Ho), 7.75–7.77 (3 H, m, aryl Hp), 7.82 (1 H, t, J 1.8, aryl
Hp), 7.96 (2 H, d, J 1.8, aryl Ho), 7.99 (2 H, d, J 1.8, aryl Ho),
8.58 (2 H, dd, 3J 4.9 and 4J 1.7, b-pyrrolic H), 8.77 (1 H, dd, 3J
5.0 and 4J 1.8, b-pyrrolic H) and 8.85–8.87 (2 H, m, 13-H and
b-pyrrolic H); m/z (MALDI-TOF) 1139 (M + H requires
1139).
The major green band was collected and evaporated to
dryness to give [2,3-dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorinato]zinc(II) 6a (751 mg, 70%) as a
green amorphous powder, mp 4300 1C (Found: C, 74.5; H,
7.2; N, 5.3. C76H89N5O4Zn + 0.25 CH2Cl2 requires C, 74.9;
H, 7.4; N, 5.7%); nmax(CHCl3)/cmÀ1 2965, 2905, 2868, 1727
(CO), 1592, 1523 (NO2), 1498, 1477, 1465, 1427, 1394, 1364,
1332 (NO2), 1291, 1248, 1176, 1115, 1069, 1014, 999, 936, 916,
900, 882, 854, 828 and 802; lmax(CHCl3)/nm 314 sh (log e
4.24), 418 (5.05), 484 (4.32) and 652br (3.98); dH(400 MHz;
CDCl3) 1.44 (18 H, s, tert-butyl H), 1.45 (18 H, s, tert-butyl
H), 1.48 (36 H, s, tert-butyl H), 7.59–7.61 (4 H, m, aryl Ho),
7.66 (1 H, t, J 1.8, aryl Hp), 7.70 (1 H, t, J 1.8, aryl Hp), 7.75 (1
H, t, J 1.8, aryl Hp), 7.76 (1 H, t, J 1.8, aryl Hp), 7.86 (2 H, d, J
1.8, aryl Ho), 7.87 (2 H, d, J 1.8, aryl Ho), 8.31 (1 H, d, J 4.8, b-
pyrrolic H), 8.47 and 8.48 (2 H, ABq, J 4.7, b-pyrrolic H), 8.56
(1 H, d, J 4.8, b-pyrrolic H) and 8.76 (1 H, s, 8-H); m/z (CI)
1202 (M + H + 2, 100%) and 1200 (M + H, 31).
Syntheses
Nitration of [2,3-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)chlorinato]zinc(II) 3. A solution of [2,3-dioxo-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]zinc(II) 3 (2.73
g, 2.36 mmol) in dichloromethane (160 cm3) was treated with
an aliquot of nitrogen dioxide in light petroleum (0.1 mol
dmÀ3; 0.04 equiv.) every 5 min until TLC analysis showed that
none of the starting material remained. The crude product was
purified by chromatography over silica (dichlorometha-
ne–light petroleum; 3 : 2) and the major brown–green band
collected and evaporated to dryness to give a mixture of
zinc(II) nitro-porphyrin-2,3-diones 6a–c (2.27 g, 80%) as an
inseparable mixture which co-eluted and had a 1H NMR
spectrum which was a composite of authentic samples.
Trace quantities of [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorinato]zinc(II) 6b were ob-
tained in mixture with 6a in latter fractions obtained from
the second band. This mixture was inseparable by column
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chromatography and 1H NMR analysis indicated that it
accounted for less than 5% of nitrated products.
[2,3-Dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
chlorinato]copper(II) 7a and [2,3-dioxo-12-nitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)chlorinato]copper(II) 7c
Method 1. A solution of [2,3-dioxo-5,10,15,20-tetrakis
[2,3-Dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
chlorinato]zinc(II) 6c. 2,3-Dioxo-12-nitro-5,10,15,20-tetrakis
(3,5-di-tert-butylphenyl)chlorin 16c (219 mg, 0.192 mmol)
and excess zinc(II) acetate dihydrate (135 mg, 0.613 mmol)
was dissolved in dichloromethane–methanol (10 : 1; 20 cm3)
and the mixture heated at reflux for 8 h (or stirred at 25 1C for
68 h). The crude product was purified by flash chromatogra-
phy over silica (dichloromethane–light petroleum, 1 : 1) and
the major brown band collected and evaporated to dryness to
give [2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)chlorinato]zinc(II) 6c (230 mg, 99%) as a purple amor-
phous powder, mp 4300 1C (Found: C, 73.95; H, 7.5; N, 5.3.
C76H89N5O4Zn + 0.5 CH2Cl2 requires C, 73.8; H, 7.3; N,
5.6%); nmax(CHCl3)/cmÀ1 2965, 2904, 2868, 1729 (CO), 1593,
1524 (NO2), 1506, 1477, 1427, 1394, 1364, 1341 (NO2), 1293,
1248, 1166, 1139, 1093, 1028, 1008, 936, 900, 880, 863 and 832;
(3,5-di-tert-butylphenyl)chlorinato]copper(II)
4
(202 mg,
0.175 mmol) in dichloromethane (12 cm3) was treated with
an aliquot of nitrogen dioxide in light petroleum (0.1 mol
dmÀ3; 0.04 equiv.) every 5 min until TLC analysis showed that
none of the starting material remained. The endpoint of the
nitration was determined by shaking an aliquot of the reaction
mixture with 1,2-benzenediamine 9 and examining the deriva-
tives for the presence of copper(II) quinoxalinoporphyrin 14 by
TLC analysis. The crude product was purified by chromato-
graphy over silica (dichloromethane–light petroleum, 1 : 3).
The major brown band was collected and evaporated to
dryness to give [2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorinato]copper(II) 7c (58 mg, 28%) as a
brown amorphous powder, mp 4300 1C (from dichloro-
methane–acetonitrile) (Found: C, 75.8; H, 7.3; N, 5.6.
C76H89CuN5O4 requires C, 76.1; H, 7.5; N, 5.8%);
lmax(CHCl3)/nm 321 sh (log e 4.31), 371 (4.50), 423 (4.96), 486
n
(NO2), 1509, 1477, 1427, 1394, 1364, 1344, 1295, 1265, 1248,
max(CHCl3)/cmÀ1 2965, 2905, 2869, 1726 (CO), 1593, 1528
(4.43), 518 sh (4.25), 573 sh (3.74), 621 (3.75) and 645–860 br
(3.70); dH(400 MHz; CDCl3) 1.44 (36 H, s, tert-butyl H), 1.47
(18 H, s, tert-butyl H), 1.48 (18 H, s, tert-butyl H), 7.59 (4 H,
d, J 1.6, aryl Ho), 7.69–7.71 (3 H, m, aryl Hp), 7.75 (1 H, t,
J 1.6, aryl Hp), 7.84 (2 H, d, J 1.6, aryl Ho), 7.85 (2 H, d, J 1.6,
aryl Ho), 8.25–8.28 (2 H, m, 7- and 18-H), 8.50 (1 H, d, J 4.7,
17-H), 8.59 (1 H, d, J 4.8, 8-H) and 8.70 (1 H, s, 13-H); m/z
(CI) 1200 (M + H, 100%).
1168, 1099, 1072, 1052, 1032, 1010, 936, 900, 880, 865 and 832;
l
max(CHCl3)/nm 370sh (log e 4.50), 419 (4.95), 486 (4.37), 510
(4.26), 659sh (3.71) and 710 (3.76); m/z (MALDI-TOF) 1200
(M + H requires 1200).
The major green band was collected and evaporated to
dryness to give [2,3-dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorinato]copper(II) 7a (89 mg, 42%) as a
green amorphous powder, mp 4300 1C (from dichlorometha-
ne–acetonitrile) (Found: C, 75.7; H, 7.4; N, 5.5. C76H89Cu-
N5O4 requires C, 76.1; H, 7.5; N, 5.8%); nmax(CHCl3)/cmÀ1
2965, 2905, 2868, 1727 (CO), 1593, 1527 (NO2), 1477, 1427,
1394, 1364, 1334, 1294, 1248, 1178, 1119, 1074, 1015, 1002,
936, 916, 900, 856 and 828; lmax(CHCl3)/nm 418 (log e 4.98),
477sh (4.29), 653 (3.91) and 707 (3.92); m/z (MALDI-TOF)
1201 (M + H requires 1200).
2,3-Dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
chlorin 16a. [2,3-Dioxo-7-nitro-5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)chlorinato]zinc(II) 6a (303 mg, 0.252 mmol) was
dissolved in ether (25 cm3) and shaken with aqueous hydro-
chloric acid (7 mol dmÀ3; 25 cm3) for 5 min. The organic phase
was separated and washed with water (25 cm3), aqueous
sodium carbonate (5%; 25 cm3) and brine (25 cm3), dried
over anhydrous sodium sulfate, and filtered. The filtrate was
evaporated to dryness and the residue purified by chromato-
graphy over silica (Type 9385, dichloromethane–light petro-
leum, 1 : 2). The major green band was collected and
evaporated to dryness to give 2,3-dioxo-7-nitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)chlorin 16a (286 mg, 99%) as
a purple amorphous powder, mp 4300 1C (Found: C, 79.8; H,
8.25; N, 5.8. C76H91N5O4 requires C, 80.2; H, 8.1; N, 6.15%);
Method 2. A mixture of [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorinato]zinc(II) 6a, [2,3-dioxo-8-
nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]zinc
(II) 6b and [2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)chlorinato]zinc(II) 6c (2.2 : 1) (1.03 g, 0.86 mmol)
was dissolved in ether (60 cm3) and shaken with hydrochloric
acid (7 mol dmÀ3, 60 cm3) for 5 min. The organic phase was
separated and washed with water (60 cm3), aqueous sodium
carbonate (5%; 60 cm3) and brine (60 cm3), dried over
anhydrous sodium sulfate and filtered. The filtrate was
evaporated to dryness and the residue dissolved in a dichloro-
methane–methanol mixture (10 : 1; 60 cm3). Copper(II) acetate
monohydrate (526 mg, 2.64 mmol) was added and the mixture
heated at reflux for 90 min. The crude product was purified by
chromatography over silica (column diameter: 40 mm,
packing height: 350 mm, maximum loading: 500 mg, dichlor-
omethane–light petroleum, 1 : 3).
n
max(CHCl3)/cmÀ1 3346 (NH), 2965, 2904, 2868, 1732 (CO),
1592, 1534 (NO2), 1476, 1426, 1394, 1364, 1344 (NO2), 1279,
1248, 1214, 1206, 1151, 1121, 1106, 1068, 999, 992, 983, 920,
900, 882 and 846; lmax(CHCl3)/nm 265 (log e 4.15), 414 (5.09),
475sh (4.35), 615 (3.92) and 683 sh (3.78); dH(400 MHz;
CDCl3) À1.66 to À1.26 (2 H, br m, inner NH), 1.46 (18 H,
s, tert-butyl H), 1.47 (18 H, s, tert-butyl H), 1.50 (18 H, s, tert-
butyl H), 1.51 (18 H, s, tert-butyl H), 7.69–7.72 (5 H, m, aryl
Ho,p), 7.76 (1 H, t, J 1.8, aryl Hp), 7.78 (1 H, t, J 1.8, aryl Hp),
7.81 (1 H, t, J 1.8, aryl Hp), 7.94 (2 H, d, J 1.8, aryl Ho), 7.95 (2
H, d, J 1.8, aryl Ho), 8.52 and 8.53 (2 H, ABq, J 4.7, b-pyrrolic
H), 8.58 (1 H, d, J 5.0, b-pyrrolic H), 8.74 (1 H, d,
J 5.0, b-pyrrolic H) and 8.88 (1 H, s, 8-H); m/z (CI) 1138
(M + H, 100%).
The major brown band was collected and evaporated to
dryness to give [2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorinato]copper(II) 7c (281 mg, 27%) as a
brown amorphous powder. The major green band was
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collected and evaporated to dryness to give [2,3-dioxo-7-nitro-5,
10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]copper(II)
7a (600 mg, 58%) as a green amorphous powder. The 8-nitro
isomer 7b was not detected.
CDCl3) 1.43 (18 H, s, tert-butyl H), 1.44 (18 H, s, tert-butyl
H), 1.47 (18 H, s, tert-butyl H), 1.48 (18 H, s, tert-butyl H),
7.56-7.58 (4 H, m, aryl Ho), 7.66 (1 H, t, J 1.7, aryl Hp), 7.70 (1
H, t, J 1.8, aryl Hp), 7.75 (1 H, t, J 1.7, aryl Hp), 7.77 (1 H, t,
J 1.7, aryl Hp), 7.82–7.84 (4 H, m, aryl Ho), 8.25 (1 H, d, J 5.0,
b-pyrrolic H), 8.45–8.48 (3 H, m, b-pyrrolic H) and 8.68 (1 H,
s, b-pyrrolic H); m/z (MALDI-TOF) 1242 (M + H requires
1243).
[2,3-Dioxo-7-, 8- and 12-nitro-5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)chlorinato]palladium(II) 8a–c
Method 1. A solution of [2,3-dioxo-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)chlorinato]palladium(II) 5 (1.01 g, 0.846
mmol) in dichloromethane (55 cm3) was treated with an
aliquot of nitrogen dioxide in light petroleum (0.1 mol
dmÀ3; 0.04 equiv.) every 5 min until TLC analysis showed
that none of the starting material remained. The endpoint of
the nitration was determined by shaking an aliquot of the
reaction mixture with 1,2-benzenediamine 9 and examining the
derivatives for the presence of palladium(II) quinoxalinopor-
phyrin by TLC analysis. The crude product was purified by
chromatography over silica (dichloromethane–light petro-
leum, 1 : 3).
Method 2. A mixture of [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorinato]zinc(II) 6a, [2,3-dioxo-8-
nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]-
zinc(II) 6b and [2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)chlorinato]zinc(II) 6c (36.0 mg, 0.030 mmol)
was dissolved in dichloromethane (30 cm3) and shaken with
hydrochloric acid (7 mol dmÀ3, 30 cm3) for 2 min. The organic
layer was washed with water (100 cm3), sodium carbonate
solution (10%, 2 Â 100 cm3), water (2 Â 100 cm3), dried over
anhydrous sodium sulfate and filtered. The filtrate was evapo-
rated to dryness and the residue dissolved in a toluene–glacial
acetic acid mixture (1 : 1; 24 cm3). Palladium(II) chloride (43.0
mg, 0.243 mmol) and sodium acetate (62.0 mg, 0.756 mmol)
were added and the mixture was heated at reflux for 5 min.
Dichloromethane (40 cm3) was added and the organic phase
separated, washed with water (100 cm3), sodium carbonate
solution (10%, 2 Â 100 cm3), water (2 Â 100 cm3), dried over
anhydrous sodium sulfate, filtered and evaporated to dryness.
The crude mixture was purified by chromatography over silica
(dichloromethane–light petroleum, 1 : 3). The first running
green band was collected and the solvent was removed to give
[2,3-dioxo-12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
chlorinato]palladium(II) 8c (major) and [2,3-dioxo-8-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]palla-
dium(II) 8b (20 : 1) (12.2 mg, 33%) as a green microcrystalline
solid. The second major green band was collected and the
solvent removed to afford [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorinato]palladium(II) 8a (19.5
mg, 52%) as a green microcrystalline solid.
The first major green band was collected and evaporated to
dryness to give a mixture of [2,3-dioxo-12-nitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)chlorinato]palladium(II)
8c
and [2,3-dioxo-8-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)chlorinato]palladium(II) 8b (3 : 1) (453 mg, 43%) as a
green amorphous powder, mp 4300 1C (from dichlorometha-
ne–methanol) (Found: C, 73.2; H, 7.35; N, 5.4. C76H89N5O4Pd
requires C, 73.4; H, 7.2; N, 5.6%); nmax(CHCl3)/cmÀ1 2965,
2905, 2869, 1727 (CO), 1593, 1529 (NO2), 1514, 1477, 1427,
1394, 1364, 1347, 1299, 1276, 1248, 1168, 1104, 1077, 1060,
1038, 1018, 972, 952, 940, 900, 880, 868 and 834; lmax(CHCl3)/
nm 271 (log e 4.38), 363 (4.43), 413 (5.00), 478 (4.39), 507
(4.24), 639sh (3.78) and 674 (3.80); dH(600 MHz; CDCl3)
Palladium(II) 12-nitro-porphyrin-2,3-dione 8c: 1.436 (18 H, s,
tert-butyl H), 1.440 (18 H, s, tert-butyl H), 1.46 (18 H, s, tert-
butyl H), 1.48 (18 H, s, tert-butyl H), 7.55–7.57 (4 H, m, aryl
Ho), 7.69–7.71 (3 H, m, aryl Hp), 7.77 (1 H, t, J 1.8, aryl Hp),
7.80 (2 H, d, J 1.8, aryl Ho), 7.82 (2 H, d, J 1.7, aryl Ho), 8.17 (1
H, d, J 5.0, b-pyrrolic H), 8.20 (1 H, d, J 5.0, b-pyrrolic H),
8.39 (1 H, d, J 5.0, b-pyrrolic H), 8.51 (1 H, d, J 5.0, b-pyrrolic
H) and 8.73 (1 H, s, b-pyrrolic H). Palladium(II) 8-nitro-
porphyrin-2,3-dione 8b: 1.44 (18 H, s, tert-butyl H), 1.45 (18
H, s, tert-butyl H), 1.47 (18 H, s, tert-butyl H), 1.48 (18 H, s,
tert-butyl H), 7.56 (2 H, d, J 1.8, aryl Ho), 7.57 (2 H, d, J 1.7,
aryl Ho), 7.71-7.73 (3 H, m, aryl Hp), 7.76 (1 H, t, J 1.8, aryl
Hp), 7.82 (2 H, d, J 1.8, aryl Ho), 7.84 (2 H, d, J 1.8, aryl Ho),
8.26 (1 H, d, J 5.0, b-pyrrolic H), 8.47–8.50 (2 H, m, b-pyrrolic
H), 8.51 (1 H, s, b-pyrrolic H) and 8.56 (1 H, d, J 5.0, b-
pyrrolic H); m/z (MALDI-TOF) 1241 (M + H requires 1243).
The second major green band was collected and evaporated
to dryness to give [2,3-dioxo-7-nitro-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)chlorinato]palladium(II) 8a (512 mg,
49%) as a green amorphous powder, mp 4300 1C (from
dichloromethane–methanol) (Found: C, 73.3; H, 7.45; N,
5.4. C76H89N5O4Pd requires C, 73.4; H, 7.2; N, 5.6%);
[7-, 8- and 12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)
quinoxalino[2,3-b]porphyrinato]zinc(II) 10a–c
Method 1. A solution of [5,10,15,20-tetrakis(3,5-di-tert-bu-
tylphenyl)quinoxalino[2,3-b]porphyrinato]zinc(II) 13 (201 mg,
0.163 mmol) in dichloromethane (10 cm3) was treated with an
aliquot of nitrogen dioxide in light petroleum (0.1 mol dmÀ3
;
0.04 equiv.) every 5 min until TLC analysis showed that none
of the starting material remained. The crude product was
purified by chromatography over silica (dichloromethane–
light petroleum, 2 : 5). The first major band was collected
and evaporated to dryness to give a mixture of [7-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
porphyrinato]zinc(II) 10a and [8-nitro-5,10,15,20-tetrakis-
(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]porphyrinato]zinc(II)
10b (17 : 5) (83 mg, 40%) as a purple amorphous powder. The
second major band was collected and evaporated to dryness to
give [12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-qui-
noxalino[2,3-b]porphyrinato]zinc(II) 10c (27 mg, 13%) as a
purple amorphous powder.
n
max(CHCl3)/cmÀ1 2965, 2904, 2869, 1729 (CO), 1593, 1530
(NO2), 1477, 1447, 1427, 1394, 1364, 1350, 1337, 1320, 1299,
1274, 1248, 1182, 1140, 1124, 1078, 1012, 940, 918, 900, 882,
860 and 828; lmax(CHCl3)/nm 269 (log e 4.39), 410 (5.02), 475
(4.28), 512sh (3.77), 625 (3.94) and 669 (3.92); dH(400 MHz;
ꢀc
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Method 2. A mixture of [7-, 8- and 12-nitro-2,3-dioxo-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]zinc(II) 6a–c
(628 mg, 0.523 mmol) and 1,2-benzenediamine 9 (243 mg, 2.24
mmol) was dissolved in dichloromethane (9 cm3) and stirred in
the dark for 2 h. The mixture was evaporated to dryness and
the residue purified by chromatography over silica (dichlor-
omethane–light petroleum, 1 : 2). The first major band gave
7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b]porphyrinato]zinc(II) 10a (436 mg, 65%) as a purple
amorphous powder, mp 4300 1C (from dichlorometha-
ne–methanol) (Found: C, 77.1; H, 7.5; N, 7.5. C82H93N7
O2Zn requires C, 77.3; H, 7.4; N, 7.7%); nmax(CHCl3)/cmÀ1
2965, 2904, 2868, 1593, 1522 (NO2), 1476, 1425, 1393, 1363,
1334, 1297, 1282, 1248, 1185, 1165, 1120, 1106, 1072, 1002,
943, 908 and 856; lmax(CHCl3)/nm 339 (log e 4.40), 449 (5.12),
541 (3.81), 576 (4.02), 623 (4.26) and 780 (3.07); dH(400 MHz;
CDCl3) 1.47 (18 H, s, tert-butyl H), 1.48 (18 H, s, tert-butyl
H), 1.52 (18 H, s, tert-butyl H), 1.53 (18 H, s, tert-butyl H),
7.77–7.87 (6 H, m, quinoxalino H and aryl Hp), 7.90 (1 H, t,
J 1.4, aryl Hp), 7.92–7.95 (5 H, m, aryl Ho,p), 8.02 (2 H, d, J
1.6, aryl Ho), 8.05 (2 H, d, J 1.9, aryl Ho), 8.83 and 8.85 (2 H,
ABq, J 4.7, b-pyrrolic H), 8.95 and 9.00 (2 H, AX, J 4.7,
b-pyrrolic H) and 9.13 (1 H, s, b-pyrrolic H); m/z (CI) 1272 (M
+ H, 100%). The sample also contained approximately 13%
of [8-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinox-
alino[2,3-b]porphyrinato]zinc(II) 10b. dH(400 MHz; CDCl3,
b-pyrrolic region) 8.82–8.87 (multiplicity unknown), 8.92
and 9.01 (AX, J 4.7) and 9.27 (s).
dichloromethane–methanol) (Found: C, 77.1; H, 7.6; N, 7.4.
C82H93CuN7O2 requires C, 77.4; H, 7.4; N, 7.7%);
n
max(CHCl3)/cmÀ1 2965, 2904, 2868, 1593, 1526 (NO2),
1495, 1476, 1426, 1393, 1363, 1338 (NO2), 1294, 1288, 1248,
1168, 1124, 1110, 1076, 1006, 943, 922, 900, 883, 858, 823, 806
and 795; lmax(CHCl3)/nm 287 (log e 4.40), 336 (4.50), 444
(5.24), 529 (3.90), 565 (4.07) and 612 (4.35); m/z (MALDI-
TOF) 1273 (M + H requires 1273).
Method 2. A solution of [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)porphyrinato]copper(II) 7a (102
mg, 0.085 mmol) and 1,2-benzenediamine 9 (18.5 mg, 0.171
mmol) in dichloromethane (6 cm3) was stirred at room tem-
perature for 30 min. The mixture was evaporated to dryness
and the residue purified by chromatography over silica
(dichloromethane–light petroleum, 1 : 3). The major green
band was collected and evaporated to dryness to give [7-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]copper(II) 11a (102 mg, 95%) as a purple
amorphous powder.
[12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinox-
alino[2,3-b]porphyrinato]copper(II) 11c
Method 1. 12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphe-
nyl)quinoxalino[2,3-b]porphyrin 17c (61.0 mg, 0.050 mmol)
and copper(II) acetate monohydrate (32.2 mg, 0.161 mmol)
were dissolved in a dichloromethane–methanol solution (10 :
1, 4 cm3) and the mixture heated at reflux for 60 min. The
solvent was evaporated to dryness and the residue purified by
chromatography over silica (dichloromethane–light petro-
leum, 1 : 2). The major brown band collected and evaporated
to dryness to give [12-nitro-5,10,15,20-tetrakis(3,5-di-tert-bu-
tylphenyl)quinoxalino[2,3-b]porphyrinato]copper(II) 11c (60
mg, 94%) as a purple amorphous powder, mp 4300 1C (from
dichloromethane–methanol) (Found: C, 77.2; H, 7.6; N, 7.4.
C82H93CuN7O2 requires C, 77.4; H, 7.4; N, 7.7%);
The second major band gave [12-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]por-
phyrinato]zinc(II) 10c (156 mg, 23%) as a purple amorphous
powder, mp 4300 1C (from dichloromethane–methanol)
(Found: C, 76.95; H, 7.4; N, 7.3. C82H93N7O2Zn requires C,
77.3; H, 7.4; N, 7.7%); nmax(CHCl3)/cmÀ1 2965, 2904, 2888,
1728, 1649, 1593, 1525, 1502, 1477, 1424, 1364, 1314, 1248,
1176, 1110, 1068, 1015, 944, 900, 863 and 830; lmax(CHCl3)/
nm 338 (log e 4.46), 455 (5.01), 540 (3.84), 581 (4.26), 614 (4.01)
and 650 (2.99); dH(400 MHz; CDCl3) 1.48 (36 H, s, tert-butyl
H), 1.51 (18 H, s, tert-butyl H), 1.52 (18 H, s, tert-butyl H),
7.76 (1 H, t, J 1.6, aryl Hp), 7.78–7.82 (3 H, m, quinoxalino H
and aryl Hp), 7.85–7.90 (2 H, m, quinoxalino H), 7.91-7.93
(6 H, m, aryl Ho,p), 8.01 (2 H, d, J 1.6, aryl Ho), 8.02 (2 H, d,
J 2.1, aryl Ho), 8.89 and 8.96 (2 H, AX, J 4.7, b-pyrrolic H),
8.96 and 8.98 (2 H, ABq, J 4.7, b-pyrrolic H) and 9.08 (1 H, s,
b-pyrrolic H); m/z (CI) 1272 (M + H, 100%).
n
max(CHCl3)/cmÀ1 2964, 2904, 2869, 1593, 1514 (NO2),
1477, 1427, 1393, 1364, 1345, 1298, 1248, 1230, 1182, 1166,
1113, 1072, 1043, 1012, 945, 899, 881 and 866; lmax(CHCl3)/
nm 306 (log e 4.36), 340 (4.46), 420sh (4.77), 462 (5.06), 526
(3.86), 565 (4.26) and 598sh (3.91); m/z (MALDI-TOF) 1273
(M + H requires 1273).
Method 2. A solution of [2,3-dioxo-12-nitro-5,10,15,20-tet-
rakis(3,5-di-tert-butylphenyl)porphyrinato]copper(II) 7c (103
mg, 0.085 mmol) and 1,2-benzenediamine 9 (20.4 mg, 0.189
mmol) in dichloromethane (6 cm3) was stirred at room tem-
perature for 30 min. The mixture was evaporated to dryness
and the residue purified by chromatography over silica (di-
chloromethane–light petroleum, 1 : 2). The major brown band
was collected and evaporated to dryness to give [12-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]copper(II) 11c (107 mg, 98%) as a purple
amorphous powder.
[7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino
[2,3-b]porphyrinato]copper(II) 11a
Method 1. 7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphe-
nyl)quinoxalino[2,3-b]porphyrin 17a (61.6 mg, 0.051 mmol)
and copper(II) acetate monohydrate (32.1 mg, 0.161 mmol)
were dissolved in a dichloromethane–methanol solution (10 :
1; 4 cm3) and the mixture heated at reflux for 60 min. The
solvent was evaporated to dryness and the residue purified by
chromatography over silica (dichloromethane–light petro-
leum, 1 : 2). The major green band collected and evaporated
to dryness to give [7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b]porphyrinato]copper(II) 11a (59 mg,
91%) as a purple amorphous powder, mp 4300 1C (from
Nitration of [5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)qui-
noxalino[2,3-b]porphyrinato]copper(II) 14.
A
solution of
[5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]copper(II) 14 (352 mg, 0.287 mmol) in dichlo-
romethane (20 cm3) was treated with an aliquot of nitrogen
ꢀc
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New J. Chem., 2008, 32, 340–352 | 349

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dioxide in light petroleum (0.1 mol dmÀ3; 0.04 equiv.) every 5
min until TLC analysis showed that none of the starting
material remained. The crude product was purified by chro-
matography over silica (dichloromethane–light petroleum, 1 :
4). The major band was collected and evaporated to dryness to
give a mixture of copper(II) nitro-quinoxalino[2,3-b]porphyrin
regioisomers 11a–c (334 mg, 92%). nmax(CHCl3)/cmÀ1 1526
(NO2) and 1344 (NO2); m/z (MALDI-TOF) 1272 (M + H
requires 1273).
leum, 1 : 2). The major brown band collected and evaporated
to dryness to give 7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b]porphyrin 17a (52 mg, 89%) as a
purple amorphous powder.
12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxa-
lino[2,3-b]porphyrin 17c
Method 1. [12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b]porphyrinato]zinc(II) 10a (221 mg,
0.174 mmol) was dissolved in ether (30 cm3) and shaken with
aqueous hydrochloric acid (7 mol dmÀ3; 30 cm3) for 5 min.
The organic phase was separated and shaken with aqueous
hydrochloric acid (7 mol dmÀ3; 25 cm3) for 5 min. The organic
phase was separated and washed with aqueous sodium carbo-
nate (5%; 25 cm3) and brine (25 cm3), dried over anhydrous
sodium sulfate, and filtered. The filtrate was evaporated to
dryness and the residue purified by chromatography over silica
(dichloromethane–light petroleum, 1 : 2). The major brown
band was collected and evaporated to dryness to give 12-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrin 17c (186 mg, 88%) as a purple amorphous
powder, mp 4300 1C (from dichloromethane-methanol)
(Found: C, 81.0; H, 8.1; N, 7.9. C82H95N7O2 requires C,
81.35; H, 7.9; N, 8.1%); nmax(CHCl3)/cmÀ1 3520, 3412, 3363
(NH), 2964, 2905, 2866, 1681, 1593, 1556, 1507, 1477, 1427,
1394, 1363, 1348 (NO2), 1294, 1247, 1168, 1135, 1097, 1032,
1097, 1032, 1011, 1000, 908, 883 and 855; lmax(CHCl3)/nm 302
(log e 4.35), 341 (4.48), 393sh (4.59), 453 (5.22), 542 (4.21), 604
(3.89) and 666 (3.64); dH(400 MHz; CDCl3) À2.30 (2 H, br s,
inner NH), 1.48–1.49 (36 H, m, tert-butyl H), 1.53–1.55 (36 H,
m, tert-butyl H), 7.72–7.77 (2 H, m, quinoxalino H), 7.78 (1 H,
t, J 1.8, aryl Hp), 7.79–7.84 (3 H, m, quinoxalino H and aryl
Hp), 7.92–7.94 (2 H, m, aryl Hp), 7.94–7.96 (4 H, m, aryl Ho),
8.07 (2 H, d, J 1.8, aryl Ho), 8.10 (2 H, d, J 1.8, aryl Ho), 8.94
7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino
[2,3-b]porphyrin 17a
Method 1. [7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphe-
nyl)quinoxalino[2,3-b]porphyrinato]zinc(II) 10a (496 mg, 0.390
mmol) was dissolved in ether (25 cm3) and shaken with
aqueous hydrochloric acid (7 mol dmÀ3; 25 cm3) for 10 min.
The organic phase was separated and shaken with aqueous
hydrochloric acid (7 mol dmÀ3; 25 cm3) for 5 min. The organic
phase was separated and washed with aqueous sodium carbo-
nate (5%; 25 cm3) and brine (25 cm3), dried over anhydrous
sodium sulfate, and filtered. The filtrate was evaporated to
dryness and the residue purified by dry-flash chromatography
over silica (dichloromethane–light petroleum, 1 : 2). The major
brown band was collected and evaporated to dryness to give 7-
nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxali-
no[2,3-b]porphyrin 17a (454 mg, 96%) as a purple amorphous
powder, mp 4300 1C (from dichloromethane-methanol)
(Found: C, 81.7; H, 7.8; N, 7.85. C82H95N7O2 requires C,
81.35; H, 7.9; N, 8.1%); nmax(CHCl3)/cmÀ1 3336 (NH), 2965,
2868, 1593, 1532 (NO2), 1476, 1427, 1394, 1363, 1346 (NO2),
1281, 1248, 1166, 1120, 1105, 999, 909, 883 and 851;
lmax(CHCl3)/nm 296 (log e 4.33), 359 (4.49), 441 (5.24), 533
(4.12), 571 (4.06), 605 (4.02), 662 (3.37) and 752 (3.12); dH(400
MHz; CDCl3) À2.00 (2 H, br s, inner NH), 1.47 (18 H, s, tert-
butyl H), 1.48 (18 H, s, tert-butyl H), 1.53 (36 H, s, tert-butyl
H), 7.70–7.79 (4 H, m, quinoxalino H), 7.80 (1 H, t, J 1.8, aryl
Hp), 7.83 (1 H, t, J 1.8, aryl Hp), 7.89 (1 H, t, J 1.8, aryl Hp),
7.93 (1 H, t, J 1.8, aryl Hp), 7.95–7.98 (4 H, m, aryl Ho),
8.03–8.06 (4 H, m, aryl Ho), 8.67 and 8.69 (2 H, ABq, b-
pyrrolic H), 8.92 (1 H, d, J 5.0, b-pyrrolic H), 9.01 (1 H, d,
J 5.0, b-pyrrolic H) and 9.07 (1 H, s, 8-H); m/z (MALDI-TOF)
1210 (M + H requires 1211). The sample also contained
approximately 11% of 8-nitro-5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)quinoxalino[2,3-b]porphyrin 17b. dH(400 MHz;
CDCl3, b-pyrrolic H region) 8.75 (d, J 4.7) and 9.24 (s).
3
4
(1 H, dd, J 5.0 and J 1.6, b-pyrrolic H), 8.99–9.03 (3 H, m,
3
4
b-pyrrolic H) and 9.05 (1 H, dd, J 5.0 and J 1.6, b-pyrrolic
H); m/z (MALDI-TOF) 1211 (M + H requires 1211).
Method 2. [12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b]porphyrinato]copper(II) 11c (60.6
mg, 0.048 mmol) was demetallated using trifluoroacetic acid
and concentrated sulfuric acid following the procedure
described previously in this section to give 12-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
porphyrin 17c (54 mg, 93%).
[7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxa-
lino[2,3-b]porphyrinato]palladium(II) 12a
Method 2. [7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphe-
nyl)quinoxalino[2,3-b]porphyrinato]copper(II) 11a (60.6 mg,
0.048 mmol) was moistened with trifluoroacetic acid (1.5
cm3). Concentrated sulfuric acid (18 mol dmÀ3; 0.20 cm3)
was added and the mixture stirred for 15 min, then poured
onto ice (10 g). Ether (10 cm3) was added and the organic
phase washed with water (3 Â 10 cm3). Water (10 cm3) was
added to the organic phase and sodium carbonate added to the
two phase system with vigorous stirring until no more gas was
produced. The organic phase was washed with water (10 cm3),
brine (10 cm3), dried over anhydrous sodium sulfate and
filtered. The filtrate was evaporated to dryness and purified
by chromatography over silica (dichloromethane–light petro-
Method 1. A solution of 7-nitro-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)quinoxalino[2,3-b]porphyrin 17a (221 mg,
0.182 mmol), sodium acetate (32.5 mg, 0.396 mmol) and
palladium(II) chloride (128 mg, 0.721 mmol) in an acetic
acid–chloroform mixture (2 : 1; 60 cm3) was heated at reflux
for 18 h. Ether (40 cm3) was then added and the organic phase
washed with water (4 Â 40 cm3), sodium carbonate solution
(5%, 40 cm3), brine (40 cm3), dried over anhydrous sodium
sulfate, filtered and evaporated to dryness. The residue was
purified by dry-flash chromatography over silica (dichloro-
methane–light petroleum, 1 : 2) and the major red band
collected and evaporated to dryness to give [7-nitro-
ꢀc
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350 | New J. Chem., 2008, 32, 340–352

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5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]palladium(II) 12a (235 mg, 98%) as a red
amorphous powder, mp 4300 1C (from dichlorometha-
ne–methanol) (Found: C, 75.2; H, 7.0; N, 7.15. C82H93N7O2Pd
requires C, 74.9; H, 7.1; N, 7.5%); nmax(CHCl3)/cmÀ1 2965,
2904, 2868, 1594, 1527 (NO2), 1477, 1394, 1364, 1342 (NO2),
1299, 1248, 1170, 1113, 1079, 1017, 948, 909 and 862;
(1 H, d, J 5.0, b-pyrrolic H), 8.83 (1 H, d, J 5.0, b-pyrrolic H),
8.84 (2 H, ABq, b-pyrrolic H) and 9.05 (1 H, s, 13-H); m/z
(MALDI-TOF) 1314 (M + H requires 1315).
[8-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxa-
lino[2,3-b]porphyrinato]palladium(II) 12b and [12-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]porphyrina-
to]palladium(II) 12c. A solution of a mixture of [2,3-dioxo-
12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)chlorinato]
palladium(II) 8c and [2,3-dioxo-8-nitro-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)chlorinato]palladium(II) 8b (3 : 1) (61.4
mg, 0.049 mmol) and 1,2-benzenediamine 9 (10.8 mg, 0.100
mmol) was stirred at room temperature for 30 min. The
mixture was evaporated to dryness and the residue purified
by chromatography over silica (dichloromethane–light petro-
leum, 1 : 2). The major red band was collected and evaporated
lmax(CHCl3)/nm 346 (log e 4.54), 407 sh (4.80), 442 (5.22),
514 (3.93), 547 (4.10) and 592 (4.44); dH(400 MHz; CDCl3)
1.45 (18 H, s, tert-butyl H), 1.46 (18 H, s, tert-butyl H),
1.50–1.51 (36 H, m, tert-butyl H), 7.74–7.81 (6 H, m, quinox-
alino H and aryl Hp), 7.87-7.90 (5 H, m, aryl Ho,p), 7.91 (1 H, t,
J 1.8, aryl Hp), 7.97 (2 H, d, J 1.8, aryl Ho), 7.99 (2 H, d, J 1.8,
aryl Ho), 8.74 and 8.76 (2 H, ABq, J 5.0, b-pyrrolic H), 8.80 (1
H, d, J 5.0, b-pyrrolic H), 8.88 (1 H, d, J 5.0, b-pyrrolic H) and
9.01 (1 H, s, 8-H); m/z (MALDI-TOF) 1314 (M + H requires
1315). The sample also contained approximately 9% of
[8-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b]porphyrinato]palladium(II) 12b. dH(400 MHz, CDCl3,
b-pyrrolic H region) 8.84 (d, J 5.0), 8.89 (d, J 5.1) and 9.18 (s).
to dryness to give
a mixture of [12-nitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]porphyrinato]
palladium(II) 12c and [8-nitro-5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)quinoxalino[2,3-b]porphyrinato]palladium(II) 12b
(3 : 1) (63 mg, 97%) as a red amorphous powder which had a
1
composite H NMR spectrum of authentic samples.
Method 2. A solution of [2,3-dioxo-7-nitro-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)chlorinato]palladium(II) 8a (60.4
mg, 0.049 mmol) and 1,2-benzenediamine 9 (20.8 mg, 0.192
mmol) was stirred at room temperature for 30 min. The
mixture was evaporated to dryness and the residue purified
by chromatography over silica (dichloromethane–light petro-
leum, 1 : 2). The major red band was collected and evaporated
to dryness to give [7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
Nitration of [5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quin-
oxalino[2,3-b]porphyrinato]palladium(II) 15.
A solution of
[5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]palladium(II) 15 (202 mg, 0.159 mmol) in
dichloromethane (15 cm3) was treated with an aliquot of nitro-
gen dioxide in light petroleum (0.1 mol dmÀ3; 0.04 equiv.) every
5 min until TLC analysis showed that none of the starting
material remained. The crude product was purified by chroma-
tography over silica (dichloromethane–light petroleum, 1 : 4)
and the major red band collected and evaporated to dryness to
give a mixture of [7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino-[2,3-b]porphyrinato]palladium(II) 12a, [8-ni-
tro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]
porphyrinato]palladium(II) 12b and [12-nitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]porphyrinato]
palladium(II) 12c (169 mg, 82%). The ratio of the palladium(II)
nitro-quinoxalino[2,3-b]porphyrin isomers, 12a : 12b : 12c, was
found to be 1.9 : 1 : 1.5 by integration of the resonances due to
protons adjacent to the nitro group.
phenyl)quinoxalino[2,3-b]porphyrinato]palladium(II)
12a
(58 mg, 90%) as a red amorphous powder.
[12-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino
[2,3-b]porphyrinato]palladium(II) 12c. A solution of 12-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrin 17c (130 mg, 0.107 mmol), sodium acetate (55.1
mg, 0.672 mmol) and palladium(II) chloride (53.4 mg, 0.301
mmol) in an acetic acid–chloroform mixture (2 : 1; 36 cm3) was
heated at reflux for 18 h. Ether (40 cm3) was then added and
the organic phase washed with water (4 Â 40 cm3), sodium
carbonate solution (5%, 40 cm3), brine (40 cm3), dried over
anhydrous sodium sulfate, filtered and evaporated to dryness.
The residue was purified by chromatography over silica (di-
chloromethane–light petroleum, 1 : 2) and the major red band
collected and evaporated to dryness to give [12-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b]-
b]porphyrinato]palladium(II) 12c (132 mg, 94%) as a red
amorphous powder, mp 4300 1C (from dichlorometha-
ne–methanol) (Found: C, 74.8; H, 7.2; N, 7.2. C82H93N7O2Pd
requires C, 74.9; H, 7.1; N, 7.5%); nmax(CHCl3)/cmÀ1 2965,
2904, 2868, 1594, 1529 (NO2), 1515, 1477, 1428, 1394, 1363,
1349 (NO2), 1300, 1248, 1228, 1185, 1168, 1117, 1077, 1052,
1021, 958, 900 and 868; lmax(CHCl3)/nm 302 (log e 4.44), 346
(4.53), 411sh (4.73), 439sh (4.99), 457 (5.13), 509 (3.86), 547
(4.40) and 578 (4.01); dH(400 MHz; CDCl3) 1.46–1.47 (36 H,
m, tert-butyl H), 1.51 (18 H, s, tert-butyl H), 1.52 (18 H, s, tert-
butyl H), 7.75 (1 H, t, J 1.8, aryl Hp), 7.76–7.84 (5 H, m,
quinoxalino H and aryl Hp), 7.85–7.88 (4 H, m, aryl Ho),
7.90–7.92 (2 H, m, aryl Hp), 7.97–8.00 (4 H, m, aryl Ho), 8.73
Spin-density calculation
The spin-density calculations wer performed using the Gaus-
sian-03 package.41 The B3LYP density-functional42 was used
in conjunction with the SDD43 basis set for Zn and Pd as well
as the 6-31G* basis set44 for C, H, N, and O. All calculations
were performed at optimized gas-phase geometries of the
cations of molecules without aryl meso substituents.
Acknowledgements
This research was funded by an Australian Research Council
grant to M. J. C. and J. R. R. We thank the Australian
Government and The University of Sydney for post-graduate
research scholarships to C. S. S. and T. K. We thank the
Australian Partnership on Advanced Computing (APAC) for
the provision of computing resources.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008
New J. Chem., 2008, 32, 340–352 | 351

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26 T. X. Lu, J. R. Reimers, M. J. Crossley and N. S. Hush, J. Phys.
Chem., 1994, 98, 11878–11884.
References
1 L. Jaquinod, in The Porphyrin Handbook, ed. K. M. Kadish, K. M.
Smith and R. Guilard, Academic Press, San Diego, CA, 2000, vol.
1, pp. 201–237.
2 M. G. H. Vicente, in The Porphyrin Handbook, eds. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, San Diego, 2000,
vol. 1, pp. 149–199.
27 J. R. Reimers, N. S. Hush and M. J. Crossley, J. Porphyrins
Phthalocyanines, 2002, 6, 795–805.
28 M. J. Crossley, P. L. Burn, S. J. Langford and J. K. Prashar,
J. Chem. Soc., Chem. Commun., 1995, 1921–1923.
29 K. M. Kadish, W. E. P. J. Sintic, Z. Ou, J. Shao, K. Ohkubo, S.
Fukuzumi, L. J. Govenlock, J. A. McDonald, J. A. Try, Z.-L. Cai,
J. R. Reimers and M. J. Crossley, J. Phys. Chem. B, 2007, 111,
8762–8774.
3 R. Beavington and P. L. Burn, J. Chem. Soc., Perkin Trans. 1,
1999, 583–592.
4 S. M. LeCours, H.-W. Guan, S. G. DiMagno, C. H. Wang and M.
J. Therien, J. Am. Chem. Soc., 1996, 118, 1497–1503.
5 T. E. O. Screen, I. M. Blake, L. H. Rees, W. Clegg, S. J. Borwick
and H. L. Anderson, J. Chem. Soc., Perkin Trans. 1, 2002,
320–329.
6 T.-G. Zhang, Y. Zhao, I. Asselberghs, A. Persoons, K. Clays and
M. J. Therien, J. Am. Chem. Soc., 2005, 127, 9710–9720.
7 T.-G. Zhang, Y. Zhao, K. Song, I. Asselberghs, A. Persoons, K.
Clays and M. J. Therien, Inorg. Chem., 2006, 45, 9703–9712.
8 J. E. Baldwin, M. J. Crossley and J. DeBernardis, Tetrahedron,
1982, 38, 685–692.
30 J. R. Reimers, T. X. Lu, M. J. Crossley and N. S. Hush,
Nanotechnology, 1996, 7, 424–429.
31 M. J. Crossley, P. J. Sintic, J. A. Hutchison and K. P. Ghiggino,
Org. Biomol. Chem., 2005, 3, 852–865.
32 K. M. Kadish, W. E. R. Zhan, T. Khoury, L. J. Govenlock, J. K.
Prashar, P. J. Sintic, K. Ohkubo, S. Fukuzumi and M. J. Crossley,
J. Am. Chem. Soc., 2007, 129, 6576–6588.
33 M. J. Crossley, L. G. King, I. A. Newsom and C. S. Sheehan,
J. Chem. Soc., Perkin Trans. 1, 1996, 2675–2684.
34 M. J. Crossley, P. L. Burn, S. J. Langford, S. M. Pyke and A. G.
Stark, J. Chem. Soc., Chem. Commun., 1991, 1567–1568.
35 M. J. Crossley, J. J. Gosper and M. G. Wilson, J. Chem. Soc.,
Chem. Commun., 1985, 1798–1799.
36 M. J. Crossley and L. G. King, J. Org. Chem., 1993, 58,
4370–4375.
9 M. M. Catalano, M. J. Crossley, M. M. Harding and L. G. King,
J. Chem. Soc., Chem. Commun., 1984, 1535–1536.
10 L. Jaquinod, C. Gros, M. M. Olmstead, M. Antolovich and K. M.
Smith, Chem. Commun., 1996, 1475–1476.
11 L. Jaquinod, R. G. Khoury, K. M. Shea and K. M. Smith,
Tetrahedron, 1999, 55, 13151–13158.
37 M. J. Crossley and L. G. King, J. Chem. Soc., Perkin Trans. 1,
1996, 1251–1260.
12 L. Jiao, B. H. Courtney, F. R. Fronczek and K. M. Smith,
Tetrahedron Lett., 2006, 47, 501–504.
38 M. J. Crossley, L. G. King and S. M. Pyke, Tetrahedron, 1987, 43,
4569–4577.
13 L. Jiao, E. Hao, F. R. Fronczek, M. G. H. Vicente and K. M.
Smith, Chem. Commun., 2006, 3900–3902.
39 M. J. Crossley, L. G. King and J. L. Simpson, J. Chem. Soc.,
Perkin Trans. 1, 1997, 3087–3096.
14 O. Siri, L. Jaquinod and K. M. Smith, Tetrahedron Lett., 2000, 41,
3583–3587.
40 M. J. Crossley, L. D. Field, M. M. Harding and S. Sternhell,
J. Am. Chem. Soc., 1987, 109, 2335–2341.
15 H. J. H. Wang, L. Jaquinod, D. J. Nurco, M. G. H. Vicente and K.
M. Smith, Chem. Commun., 2001, 2646–2647.
16 H. J. H. Wang, L. Jaquinod, M. M. Olmstead, M. G. H. Vicente,
K. M. Kadish, Z. Ou and K. M. Smith, Inorg. Chem., 2007, 46,
2898–2913.
17 M. J. Crossley and P. L. Burn, J. Chem. Soc., Chem. Commun.,
1987, 39–40.
18 M. J. Crossley, T. W. Hambley and L. G. King, Bull. Soc. Chim.
Fr., 1996, 133, 735–742.
19 M. J. Crossley, T. W. Hambley, L. G. Mackay, A. C. Try and R.
Walton, Chem. Commun., 1996, 1077–1079.
20 M. J. Crossley and L. G. King, J. Chem. Soc., Chem. Commun.,
1984, 920–922.
21 M. J. Crossley and J. A. McDonald, J. Chem. Soc., Perkin Trans.
1, 1999, 2429–2431.
22 M. J. Crossley, P. J. Sintic, R. Walton and J. R. Reimers, Org.
Biomol. Chem., 2003, 1, 2777–2787.
41 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven, K. N.
Kudin, J. C. Burant, J. M. Millam, I. S. S. J. Tomasi, V. Barone, B.
Mennuci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M.
Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J.
Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. A. Ayala, K.
Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G.
Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J.
V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. G. Johnson, W.
Chen, M. W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN 03,
(revision B02), Gaussian Inc., Pittsburgh, PA, 2003.
42 A. D. Becke, J. Chem. Phys., 1993, 93, 5648.
23 M. J. Crossley and P. L. Burn, J. Chem. Soc., Chem. Commun.,
1991, 1569–1571.
24 M. J. Crossley, L. J. Govenlock and J. K. Prashar, J. Chem. Soc.,
Chem. Commun., 1995, 2379–2380.
43 D. Andrae, U. Haußermann, M. Dolg, H. Stoll and H. Preuß,
Theor. Chim. Acta, 1990, 77, 123.
25 N. S. Hush, J. R. Reimers, L. E. J. Hall and L. A. M. J. Crossley,
Ann. N. Y. Acad. Sci., 1998, 852, 1–21.
44 W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys., 1972,
56, 2257.
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352 | New J. Chem., 2008, 32, 340–352