Expansion of the porphyrin π-system: Stepwise annelation of porphyrin β,β′-pyrrolic faces leading to trisquinoxalinoporphyrin

Article abstract of DOI:10.1039/b901338e

Lateral extension of the porphyrin π-electron system by ring annelation of β,β′-pyrrolic faces is reported. Three separate syntheses of trisquinoxalinoporphyrin 1, differing in the sequence in which pyrrolic rings are elaborated, are reported. The most ef

Full text of DOI:10.1039/b901338e

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Expansion of the porphyrin p-system: stepwise annelation of porphyrin
b,b0-pyrrolic faces leading to trisquinoxalinoporphyrinw
Tony Khoury and Maxwell J. Crossley*
Received (in Montpellier, France) 21st January 2009, Accepted 26th January 2009
First published as an Advance Article on the web 25th February 2009
DOI: 10.1039/b901338e
Lateral extension of the porphyrin p-electron system by ring annelation of b,b0-pyrrolic faces is
reported. Three separate syntheses of trisquinoxalinoporphyrin 1, differing in the sequence in
which pyrrolic rings are elaborated, are reported. The most efficient pathway converts readily
accessible zinc(II) corner bisquinoxalinoporphyrin 7 into 1 in five steps in 47% yield overall.
Routes to 1 are also established from linear bisquinoxalinoporphyrin 8 and quinoxalinoporphyrin
10. The ring annelation process involves a nitration, reduction, photooxidation sequence to
1
establish a-dione functionality that is reacted with 1,2-diaminobenzene. The H NMR spectrum
of 1 reveals that it exists predominantly as a single trans-tautomer in which the two inner
hydrogens reside on the nitrogens of the unsubstituted pyrrolic ring and its opposite
quinoxalino-fused pyrrolic ring. Each of the synthetic routes established in this study could have
use in elaboration of more complex oligoporphyrin arrays.
trisquinoxalinoporphyrin 1 and tetrakisquinoxalinoporphyrin
2 starting from a porphyrin-2,3,7,8-tetraone.4
Introduction
Porphyrinoid macrocycles appear in many naturally occurring
redox systems and they have many functional properties that
make them attractive for use in emerging technologies. The
redox and photoactive functions performed by porphyrins in
nature establish the paradigm for molecular electronics and
show that porphyrins may be useful components of rationally
designed molecular electronic devices and new artificial light-
harvesting systems.
Porphyrins are essentially planar macrocycles with exten-
sive p-systems.1 In addition, a porphyrin ring has a diameter
of B1 nm and so is well-suited as a building block for the
construction of devices 5–10 nm in size, thought necessary in
first generation ‘molecular electronics’.2 For new materials
and molecular electronic circuit applications, it is desirable
to have multiple-connector building blocks. The porphyrin
periphery with its four pyrrolic rings arranged on a square
matrix has a geometry that allows construction of molecular
arrays based on a square grid motif. Up to four connections
can be made through p-system annelation of each of the
pyrrolic rings. Additionally, expansion of the p-system of the
porphyrin offers a means to modulate the redox and photo-
physical properties of the macrocycle.3–10 This is also the case
with related phthalocyanines and porphyrazines.6,11,12
Recently, we presented an efficient synthetic protocol for
stepwise elaboration of the pyrrolic faces of a porphyrin.
This strategy was demonstrated by synthetic routes to
School of Chemistry, The University of Sydney, NSW 2006,
Australia. E-mail: m.crossley@chem.usyd.edu.au;
Fax: +61 2 93513329; Tel: +61 2 93512751
w Electronic supplementary information (ESI) available: Variable-
temperature NMR spectra of trisquinoxalinoporphyrin 1, NOESY
spectra of 7,18-dinitroporphyrin 24a and full details of infrared
Herein we explore three other synthetic sequences to tris-
spectra of all new compounds are given. See DOI: 10.1039/b901338e
quinoxalinoporphyrin 1 by further elaboration of corner
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Scheme 1 Three pathways to the trisquinoxalinoporphyrin 1 and to more elaborated oligoporphyrin systems when the fused quinoxalino groups
are replaced by tetraazaanthracene-bridged porphyrin units.
bisquinoxalinoporphyrin 7, linear bisquinoxalinoporphyrin 8
and quinoxalinoporphyrin 10 (Scheme 1), compounds that
have been prepared from the parent porphyrin 3 in earlier
studies.13,14 These compounds can also be regarded as model
systems for terminal (compound 10) and interior components
(compounds 7 and 8) of extended oligomeric porphyrins,
where fused quinoxalines are replaced by tetraazaanthracene-
bridged porphyrin units.
6 and a mixture of zinc(II) 7-amino and 8-aminoporphyrin-
2,3-diones.15 The latter compounds were smoothly photo-
oxidised to corner zinc(II) porphyrin-2,3,7,8-tetraone13,15 5,
which upon reaction with 1,2-diaminobenzene afforded the
corner zinc(II) bisquinoxalinoporphyrin 7. The overall yield of
7 for the seven steps from 3 was 40%.13 Treatment of tetraone
6 with 1,2-diaminobenzene and then Zn(OAc)2ꢁ2H2O gave
linear zinc(II) bisquinoxalinoporphyrin 8 in 18% from 3.13
Copper(II) quinoxalinoporphyrin 10 was prepared in 65%
overall yield by nitration of 4 to give the corresponding
2-nitroporphyrin, followed by demetallation and reduction
to 2-aminoporphyrin, and photooxidation to the 2,3-dione16 9,
which was reacted with 1,2-diaminobenzene and remetallated.14,17
Results and discussion
The synthetic strategy undertaken in this work was to
further functionalise metallated quinoxalinoporphyrin and
bisquinoxalinoporphyrins that were obtained from 5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)porphyrin 3 via its copper(II)
chelate 4 (Scheme 1).
Synthesis of trisquinoxalinoporphyrin 1 from metallated corner
bisquinoxalinoporphyrins 7 and 12 (Pathway 1)
The starting materials for the sequences were prepared by
reported methods.4,13–15 Thus dinitration of porphyrin 4
followed by demetallation and reduction to a mixture of
diaminoporphyrins, photooxidation and partial metallation
with zinc(II) afforded free-base porphyrin-2,3,12,13-tetraone
The first pathway (Scheme 2) requires functionalisation of the
C-ring (equivalent to the D-ring by symmetry) of a corner
bisquinoxalinoporphyrin. For nitration at
a porphyrin
b-pyrrolic position the use of copper(II) chelates is usually
preferred because of the high selectivity of the reaction but in
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Scheme 2 Pathway 1, Reagents and conditions: (i) NO2 in light petroleum, CH2H2; (ii) HCl, CH2Cl2; (iii) SnCl2ꢁ2H2O in HCl–Et2O; (iv) O2,
hn and 1,2-diaminobenzene in CH2Cl2.
more p-expanded porphyrins, as in this case, the zinc(II) chelate
porphyrin 7 was readily available in fewer steps than the
copper(II) chelate it was used directly.
can also be used.4,18 As the corner zinc(II) bisquinoxalino-
Nitration of zinc chelate 7 afforded an inseparable mixture
of zinc(II) 12- and 13-nitro-bisquinoxalinoporphyrins 11 in
83% yield (Scheme 2). Demetallation of 11 and chromato-
graphy of the product afforded the free-base corner 13-nitro-
bisquinoxalinoporphyrin 14a in 26% yield and the corner
12-nitro-bisquinoxalinoporphyrin 14b in 63% yield. Analogous
reactions (with almost equivalent yields) occur on the corres-
ponding corner zinc(II) 5,10,15,20-tetraphenyl-bisquinoxalino-
porphyrin, and X-ray crystal structure analysis of the analogue
of compound 14a confirms the assignment of the structure.
Buttressing by the quinoxaline groups makes the 12-position
sterically more accessible than the 13-position; this effect is
discussed further below.
As both isomers, 14a and 14b, afford the same a-dione 16,
batches of the mixture were used in the subsequent steps.
Free-base corner 12- and 13-nitro-bisquinoxalinoporphyrins
14 were reduced to afford the corresponding corner 12- and
13-amino-bisquinoxalinopophyrins 15. The aminoporphyrins
15 have significant double bond character across the C12–C13
bond and were smoothly photooxidised in the presence of
1,2-diaminobenzene for five hours to give 1 in 64% yield
presumably by way of corner bisquinoxalinoporphyrin-
12,13-dione 16 (Scheme 2). Indeed, the corner bisquinoxalino-
porphyrin-12,13-dione 16 was isolated in 32% yield when
the sequence was carried out without the addition of
1,2-diaminobenzene. Singlet oxygen is the oxidant and the
porphyrin is able to directly catalyse its formation. The lower
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yield of isolated dione 16 is attributed to its instability
under the photooxidation conditions and to the formation of
undesirable side products. We have previously reported the
formation of porphyrin-lactone and a macrocyclic anhydride
upon further oxidation of 5,10,15,20-tetraphenylporphyrin-
2,3-dione.19 Clearly, trapping the dione 16 as it is formed by
reaction with 1,2-diaminobenzene is beneficial. The overall
yield of 1 by pathway 1 was 47% over four steps.
The 1H NMR spectrum of 1 showed clearly the C2v
symmetry of the molecule and indicated that its tautomeric
equilibrium is skewed to almost completely favour the trans-
tautomer in which the two inner hydrogens reside on the
nitrogens of the unsubstituted pyrrolic ring and its opposite
quinoxalino-fused pyrrolic ring (as drawn in Scheme 1). This is
shown by appearance of the resonances of the inner NH
hydrogens as two one-proton broad singlets at ꢂ0.44 and
ꢂ0.36 ppm and a single resonance for the b-pyrrolic protons
(variable-temperature NMR spectra of 1 are given in the
4
ESIw). By decreasing the temperature to 230 K, J coupling
(J = 1.8 Hz) was detected between the b-pyrrolic protons and
the more downfield of the inner NH resonances of 1. Irradia-
tion of this resonance collapsed the resonance of the b-pyrrolic
protons to a sharp singlet.
In the preferred tautomer of trisquinoxalinoporphyrin 1, the
b,b0-pyrrolic positions of rings that are protonated on the
inner nitrogens form part of the 18-atom 18-p-electron
aromatic delocalisation pathway. The non-protonated
A- and C-rings both have a fused quinoxaline which is able
to have a greater share of the electron density across the
b,b0-pyrrolic positions.
The corner copper(II) bisquinoxalinoporphyrin 12 was also
used as a primary precursor, and it has been found that upon
nitration, the corner copper(II) 12- and 13-nitro-bisquinoxalino-
porphyrins 13 were obtained in 97% yield (Scheme 2).
Demetallations of compounds 13 were successfully achieved
by stirring them in a refluxing mixture of dichloromethane,
concentrated sulfuric acid and trifluoroacetic acid for three
days. Chromatography of the products gave corner 13- and
12-nitro-bisquinoxalinoporphryins, 14a and 14b, in 16% and
52% yield, respectively. Again, the 12-nitro isomer pre-
dominated. The overall yield of nitro-bisquinoxalinoporphyrins
14 using copper chelate 6 is comparable to that obtained from
the zinc chelate 7, despite the harsher demetallation conditions
required.
Pathway 1 (Scheme 2) is a very efficient route for preparing
trisquinoxalinoporphyrin 1 in good overall yield that should
be easy to scale-up to afford 1 in gram quantities.
Synthesis of trisquinoxalinoporphyrin 1 from the zinc(II) linear
bisquinoxalinoporphyrin 8 (Pathway 2)
Scheme 3 Pathway 2, Reagents and conditions: (i) NO2 in light
petroleum, CH2H2; (ii) HCl, CH2Cl2; (iii) SnCl2ꢁ2H2O in HCl–Et2O;
(iv) O2, hn and 1,2-diaminobenzene in CH2Cl2.
The second pathway requires functionalisation of the B-ring of
a linear bisquinoxalinoporphyrin. Isomers will not arise in this
pathway because of the symmetry of the starting material in
which all four b-pyrrolic positions that are available for
reaction are equivalent. Reactions on two metallated linear
bisquinoxalinoporphyrins 8 and 17 were investigated. Nitra-
tion of the linear zinc(II) bisquinoxalinoporphyrin 8 afforded
the linear zinc(II) 7-nitro-bisquinoxalinoporphyrin 18 in 74%
yield (Scheme 3). Acidic demetallation of 18 gave the linear
7-nitro-bisquinoxalinoporphyrin 20 in 93% yield.
Reduction of 20 afforded the linear 7-amino-bisquinoxalino-
porphyrin 21, which was photooxidised in the presence
of 1,2-diaminobenzene for five hours to afford 1 in 20%
yield.
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Photooxidation is the problematic step. Compound 21 is
4
predominately the tautomer shown (evinced by J couplings
Synthesis of trisquinoxalinoporphyrin 1 from the copper(II)
quinoxalinoporphyrin 10 (Pathway 3)
between the inner NHs and the b-pyrrolic groups) and thus the
C7–C8 bond has substantial aromatic character as it is part of
the 18-atom 18-p-electron aromatic delocalisation pathway.
Photooxidation of aminoporphyrins involving singlet oxygen
occurs much more readily and in better yield when the amino
group is attached to an isolated double bond on the porphyrin
periphery rather than to one involved in the aromatic
delocalisation pathway. Despite these difficulties, linear
7-amino-bisquinoxalinoporphyrin 21 is an important building
block in its own right and has been used to create chiral
cavities and dendrimers as will be reported separately.
The linear bisquinoxalinoporphyrin-7,8-dione 22 is an inter-
mediate in the conversion of aminoporphyrin 21 into 1 (Scheme 3)
and was also made independently and reacted with 1,2-diamino-
benzene to give 1 (see Scheme 4). The overall yield of 1 from
zinc(II) linear bisquinoxalinoporphyrin 8 by pathway 2 was 14%.
Use of the copper(II) chelates in this sequence failed. Nitra-
tion of linear copper(II) bisquinoxalinoporphyrin 17 afforded
the linear copper(II) nitro-bisquinoxalinoporphyrin 19 in 92%
yield but it could not be demetallated even with TFA–sulfuric
acid mixtures (Scheme 3).
In order to synthesise trisquinoxalinoporphyrin
1 it is
necessary to elaborate two pyrrolic rings of a quinoxalino-
porphyrin. This was achieved by nitration of copper(II)
quinoxalinoporphyrin 10 using nitrogen dioxide to give a
mixture of the copper(II) dinitroquinoxalinoporphyrins 23 in
87% yield (Scheme 4). The mixture of dinitro-quinoxalino-
porphyrins 23 was demetallated by stirring with concentrated
sulfuric acid for 15 min to afford free-base dinitroquinoxalino-
porphyrins 24 in 97% yield. Examination of the 1H NMR
spectrum of the regioisomers 24 showed no resonance patterns
that would indicate dinitration of the same pyrrolic ring. This
observation is in accord with studies of the dinitration of
copper(II) 5,10,15,20-tetraphenylporphyrin in which all the
possible isomers except the 2,3-dinitroporphyrin were
obtained.20 Hence all the dinitroquinoxalinoporphyrin iso-
mers formed will lead to trisquinoxalinoporphyrin 1 and the
mixture was carried forward.
The dinitroquinoxalinoporphyrins 24 were stirred with tin(II)
chloride dihydrate to give the diamino-quinoxalinoporphyrins
25, which were photooxidised to an inseparable mixture of
Scheme 4 Pathway 3, Reagents and conditions: (i) NO2 in light petroleum, CH2H2; (ii) H2SO4, CH2Cl2; (iii) SnCl2ꢁ2H2O in HCl–Et2O; (iv) O2, hn,
CH2Cl2; (v) 1,2-diaminobenzene, CH2Cl2.
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7- and 8-aminoquinoxalinoporphyrin-12,13-diones 26 and
quinoxalinoporphyrin-7,8,17,18-tetraone 27 (Scheme 1).
The mixture of aminoporphyrin-dione 26 and porphyrin-
tetraone 27 was condensed with 1,2-diaminobenzene to give
the linear 7-amino-bisquinoxalinoporphyrin 21 in 6% yield
and the trisquinoxalinoporphyrin 1 in 10% yield. This product
has arisen from annelation of the B- and D-rings of 10
(as labelled in Scheme 2). The residual amino-bisquinoxalino-
porphyrin 26 could also be converted into 1. Compound 26
was subjected to prolonged photooxidation to afford the
bisquinoxalinoporphyrin-dione 22 in 23% yield; products of
over-oxidation were also observed, a consequence of the dione
22 being more susceptible to oxidation than the starting
amino-bisquinoxalinoporphyrin 26. It is probable that the
photooxidation reaction would have gone better on the corres-
ponding zinc(II) chelate of 26 which has increased bond order
of the C7–C8 bond which would allow a shorter reaction time,
thereby reducing the possibility of over-oxidation.15,19 The
dione 22 was reacted with 1,2-diaminobenzene to give 1 in
77% yield. This product has arisen from annelation of the
B- and C-rings of 10.
The formation of intermediates 26 and 27 has direct analogy
to the results obtained by photooxidation of a mixture of
free-base 2,x-diamino-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
porphyrins which gives the corresponding 7- and 8-amino-
porphyrin-2,3-diones and the porphyrin-2,3,12,13-tetraone 6.15
Dione units shift the tautomeric equilibrium of free-base
porphyrins to greatly favour the trans-tautomer in which
the inner hydrogens do not reside on the nitrogen of the
a-diketopyrrolic ring. This also imposes double bond character
on the b,b0-pyrrolic bond opposite it and aromatic character
to the b,b0-pyrrolic bond in adjacent pyrrolic rings. An amino
group situated on a double bond is photooxidised much more
Fig. 1 Through-space connectivity of H(8)–Ho–H(12) seen in partial
NOESY spectra of 7,18-dinitroporphyrin 24a.
The amount of the 7,18-dinitroquinoxalinoporphyrin 24a
obtained is about three times more than expected on statistical
grounds alone. Previously, mono-nitration of 9 gave 7-nitro 4
12-nitro 4 8-nitro in the ratio 5 : 3 : 1.5, largely the result of
the 7-position being more accessible for nitration due to the
quinoxalino group restricting rotation of the 5- and 20-aryl
groups and buttressing these aryls into a more orthogonal
arrangement to the porphyrin plane on a time average than the
10- and 15-aryl groups.18 The formation of 7,18-dinitro-
quinoxalinoporphyrin 24a in moderate yield in this work can
reasonably be accounted for as being due to the same effect.
readily than one situated on an aromatic bond.15,17,21–23
A
fused quinoxalino group also shifts the position of tautomeric
equilibrium (to a lesser extent) in the same way18 but is greatly
out-competed by a dione unit when they are in competition in
adjacent pyrrolic rings. The formation of intermediates 26 and
27 can be readily understood as arising from the initial
influence of the quinoxalino group and then the dominance
of the first formed dione (or precursor keto-imine) in controlling
bond order and subsequent reactivity at the second amino site.
The overall yield of 1 from 10 following Pathway 3 was 9%
in five steps. This sequence showed that 1 can be synthesised
from the copper(II) quinoxalinoporphyrin 10 by functionalisa-
tion of two additional pyrrolic rings through nitration and
eventual conversion of each to an a-diketopyrrolic ring.
Careful column chromatography of a batch of the regio-
isomers 24 over silica (1 : 3 dichloromethane–light petroleum
over 48 hours) allowed isolation of 1 part 7,18-dinitro-
quinoxalinoporphyrin 24a from 4 parts of other dinitro-
quinoxalinoporphyrin regioisomers.
Conclusions
Three different routes are used to prepare trisquinoxalino-
porphyrin 1 by further functionalisation and annelation of
pre-formed porphyrins. Starting from corner zinc(II) bis-
quinoxalinoporphyrin 7 or linear zinc(II) bisquinoxalino-
porphyrin 8, functionalisation of only one additional ring
was required. Corner zinc(II) bisquinoxalinoporphyrin 7 is
converted into 1 in 47% overall yield over four steps
(Scheme 2); corner copper(II) bisquinoxalinoporphyrin
12 was also converted to 1 by this route. Linear zinc(II)
bisquinoxalinoporphyrin 8 is converted into 1 in 14% overall
yield over four steps (Scheme 3). Functionalisation of two
rings is required to convert copper(II) quinoxalinoporphyrin
The C2v symmetry of dinitroporphyrin 24a was apparent in
its 1H NMR spectrum and the substitution pattern was
confirmed by NOESY studies which showed a through space
connectivity between H(8) (dH 8.89), the Ho of the aryl at the
10-position (dH 8.02) and H(12) (dH 8.66) (Fig. 1 and ESIw).
A NOESY interaction is also seen between the b-pyrrolic
protons and one of the two tert-butyl signals.
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10 into 1 and this was achieved in 9% over five steps
(Scheme 4). Each synthetic route established in this work
could have use in elaboration of more complex oligoporphyrin
arrays.
and 8.87 (ABq, J 4.8 Hz, b-pyrrolic H), 8.98 (s, b-pyrrolic H),
9.10 (s, b-pyrrolic H); m/z (ESI) 1374.9 ([M+H]+ requires
1374.7).
The major determinate of yield was the ease with which
photooxidation steps in each sequence proceeded and this was
related to bond order effects. As with simpler aminoporphyrin
systems photooxidation proceeds best when there is substan-
tial double bond character on the bond to be oxidised. In a
free-base compound when the bond to be oxidised has essen-
tially aromatic character the bond order can be increased by
conversion to a metalloporphyrin derivative.22 The amino-
porphyrins all acted as singlet oxygen sensitisers and addition of
rose bengal was not required for porphyrin-dione formation.
Studies underway in our laboratories show that free-base
trisquinoxalinoporphyrin 1 and metallated derivatives have
second harmonic properties in non-linear optical experiments
and they show important incoherent photon up-conversion by
triplet–triplet annihilation. These studies will be reported
elsewhere.
{12- and 13-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:7,8-b00]porphyrinato}copper(II) 13. {5,10,
15,20-Tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrinato}copper(II)13 12 (206 mg, 0.155 mmol) was dis-
solved in CH2Cl2 (125 ml) and treated with a solution of
nitrogen dioxide in light petroleum (1 M), added portion-wise
with stirring until nitration was complete. The crude mix-
ture was purified by column chromatography over silica
(CH2Cl2–light petroleum 1 : 2). The front running band
was collected to give a mixture of {12- and 13-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrinato}copper(II) 13 (207 mg, 97%) as a green micro-
crystalline solid, mp 4 300 1C. An analytically pure sample
was obtained by recrystallisation (CH2Cl2–MeOH); (Found: C,
75.77; H, 6.99; N, 8.75. C88H59CuN9O2 + CH3OH requires C,
76.01; H, 7.10; N, 8.96%); (HR-ESI-FT/ICR found: [M + H]+
1373.6887. C88H95CuN9O2 requires 1373.6918); nmax(CHCl3)/cmꢂ1
3017s, 2964s, 2904m, 1527m (NO2), 1363s (NO2); lmax(CHCl3)/nm
309sh (log e 4.57), 342 (4.68), 389sh (4.56), 421 (4.81),
459sh (4.88), 482 (5.08), 585 (4.28), 629 (4.13); m/z (ESI)
1373.9 ([M + H]+ requires 1373.7).
In addition, the methodology developed for the synthesis of
1 establishes protocols that will be of use in the construction
of T-junction molecular assemblies, grids and compounds of
possible application in molecular electronics and photonics. Syn-
thesis of such compounds is also underway in our laboratories.
12- and 13-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:7,8-b00]porphyrins 14b and 14a
Experimental
General procedures
Method 1: demetallation of zinc(II) corner 12- and 13-nitro-
bisquinoxalinoporphyrin 11. A solution of {12- and 13-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:
7,8-b00]porphyrinato}zinc(II) 11 (610 mg, 0.443 mmol) in
CH2Cl2 (140 ml) was stirred with hydrochloric acid (140 ml,
8 M) for 20 min, then poured onto ice (200 g). When the ice
melted the organic phase was separated, washed with water
(200 ml), sodium carbonate solution (10%, 2 ꢃ 250 ml) and
water (200 ml), dried over anhydrous sodium sulfate, filtered
and the filtrate evaporated to dryness. The crude mixture
was purified by chromatography over silica (CH2Cl2–light
petroleum 1 : 2). The front running green band was collected
and the solvent was removed to give 13-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrin 14a (150 mg, 26%) as a green microcrystalline solid,
mp 4 300 1C. An analytically pure sample was obtained by
recrystallisation (CH2Cl2–MeOH); (Found: C, 77.48; H, 7.43;
N, 9.23. C88H97N9O2 + 3CH3OH requires C, 77.58; H, 7.80;
N, 8.95%); (HR-ESI-FT/ICR found: [M + H]+ 1312.7854.
C88H98N9O2 requires 1312.7838); nmax(CHCl3)/cmꢂ1 3325w
(NH), 3021s, 3008w, 2964s, 2928m, 1507m (NO2), 1362s
(NO2); lmax(CHCl3)/nm 311sh (loge 4.37), 344 (4.56), 389sh
(4.54), 421 (4.72), 457sh (4.83), 482 (5.03), 562 (4.00), 610
(4.09), 629 (4.09), 689 (3.89); dH(400 MHz; CDCl3) ꢂ0.51
(2 H, br s, inner NH), 1.44 (18 H, s, t-butyl H), 1.49 (36 H, s,
t-butyl H), 1.53 (18 H, s, t-butyl H), 7.74–7.79 (4 H, m,
quinoxaline H, aryl H), 7.82–7.84 (1 H, m, quinoxaline H),
7.87–7.98 (12 H, m, quinoxaline H, Ho, Hp), 8.01 (1 H, t,
J 1.8 Hz, Hp), 8.07 (2 H, d, J 1.7 Hz, Ho), 8.74 and 8.79 (2 H,
ABq, J 4.8 Hz, b-pyrrolic H), 8.92 (1 H, s, b-pyrrolic H); m/z
(ESI) 1312.9 ([M + H]+ requires 1312.8).
General procedures were the same as those described
elsewhere.18
Synthesis of trisquinoxalinoporphyrin 1 from metallated
corner bisquinoxalinopophyrin (Pathway 1, Scheme 2)
{12- and 13-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:7,8-b00]porphyrinato}zinc(II) 11. {5,10,15,
20-Tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrinato}zinc(II)13 7 (0.822 g, 0.618 mmol) was dissolved in
CH2Cl2 (750 ml) and treated with a solution of nitrogen dioxide
in light petroleum (1 M), added portion-wise with stirring
until the nitration was complete by TLC analysis. The crude
mixture was purified by column chromatography over silica
(CH2Cl2–light petroleum 3 : 2). The front running green band
was collected to give a mixture of {12- and 13-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrinato}zinc(II) 11 (0.725 g, 83%) as a black shiny
microcrystalline solid, mp 4 300 1C. An analytically pure
sample was obtained by recrystallisation (CH2Cl2–MeOH);
(Found: C, 73.28; H, 6.96; N, 8.57. C88H95N9O2Zn + CH2Cl2
requires C, 73.16; H, 6.69; N, 8.63%); (HR-ESI-FT/ICR found:
[M + H]+ 1374.7070. C88H96N9O2Zn requires 1374.6973);
n
max(CHCl3)/cmꢂ1 3022s, 2963s, 1523m (NO2), 1363s (NO2);
lmax(CHCl3)/nm 343 (log e 4.62), 401sh (4.65), 424 (4.83),
465 (4.88), 491 (5.12), 555sh (3.82), 599 (4.34), 639 (3.99);
dH(400 MHz; CDCl3) 1.45 (s, t-butyl H), 1.47 (s, t-butyl H),
1.482 (s, t-butyl H), 1.483 (s, t-butyl H), 1.522 (s, t-butyl H),
1.523 (s, t-butyl H), 7.76 (t, J 1.8 Hz, Hp), 7.78–7.94
(m, quinoxaline H, Ho, Hp), 8.01 (d, J 1.8 Hz, Ho), 8.02–8.03
(m, Ho, Hp), 8.78 and 8.829 (ABq, J 4.7 Hz, b-pyrrolic H), 8.832
ꢀc
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The second green band was collected and the solvent
removed to give 12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:7,8-b00]porphyrin 14b (366 mg,
63%) as a green microcrystalline solid, mp 4 300 1C. An
analytically pure sample was obtained by recrystallisation
(CH2Cl2–MeOH); (Found: C, 78.59; H, 7.43; N, 9.40.
C88H97N9O2 + 2CH3OH requires C, 78.51; H, 7.69; N,
9.16%); (HR-ESI-FT/ICR found: [M + H]+ 1312.7845.
C88H98N9O2 requires 1312.7838); nmax(CHCl3)/cmꢂ1 3326w
(NH), 3026s, 3014w, 2864s, 1524w (NO2), 1363m (NO2);
collected to give 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
trisquinoxalino[2,3-b0:7,8-b00:12,13-b0 00]porphyrin 1 (0.398 g,
64%) as a green microcrystalline solid, mp 4 300 1C. An
analytically pure sample was obtained by recrystallisation
(CHCl3–MeOH); (Found: C, 81.42; H, 7.48; N, 9.93.
C94H100N10 + CH3OH requires C, 81.39; H, 7.48; N,
9.99%); (ESI-HRMS found: [M
+
H]+ 1369.816.
C94H101N10 requires 1369.821); nmax(CHCl3)/cmꢂ1 3346w
(NH), 2962s, 2926s, 2856s, 1595s, 1576w, 1558w, 1545w,
1516w, 1506w, 1495w, 1487w, 1475m, 1466m, 1431w, 1393w,
1362s, 1352m, 1300m, 1248m, 1236m, 1204w, 1190w, 1173w,
1153m, 1136w, 1111s; lmax(CHCl3)/nm 307sh (loge 4.36), 345
(4.59), 390sh (4.71), 421 (4.87), 466 (4.83), 492 (4.94), 537sh
(3.98), 576 (4.15), 608 (4.18), 629sh (4.00), 638 (4.01), 687
(3.30); dH(400 MHz; CDCl3; 300 K) ꢂ0.44 (1 H, br s, inner
NH), ꢂ0.36 (1 H, br s, inner NH), 1.46 (36 H, s, t-butyl H),
1.49 (36 H, s, t-butyl H), 7.71–7.75 (4 H, m, quinoxaline H),
7.77–7.80 (2 H, m, quinoxaline H), 7.82–7.85 (2 H, m,
quinoxaline H), 7.87–7.89 (2 H, m, quinoxaline H), 7.89
(4 H, d, J 1.6 Hz, Ho), 7.92 (2 H, t, J 1.7 Hz, Hp), 7.94 (4 H,
d, J 1.6 Hz, Ho), 7.95–7.99 (2 H, m, quinoxaline H), 8.02 (2 H,
t, J 1.7 Hz, Ho), 8.76 (2 H, s, b-pyrrolic H); dH(400 MHz;
CDCl3; 230 K) ꢂ0.59 (1 H, s, inner NH), ꢂ0.52 (1 H, br s,
inner NH), 1.40 (36 H, s, t-butyl H), 1.45 (36 H, s, t-butyl H),
7.76–7.80 (8 H, m, quinoxaline H), 7.88–7.95 (16 H, m,
quinoxaline H, Ho, Hp), 8.82 (2 H, d, J 1.6 Hz, b-pyrrolic H);
m/z (ESI) 1369.9 ([M + H]+ requires 1369.8).
l
max(CHCl3)/nm 314sh (log e 4.46), 342 (4.57), 385sh (4.56),
421 (4.75), 455sh (4.89), 477 (5.06), 560 (4.10), 599 (4.14), 626
(4.07), 682 (3.77); dH(400 MHz; CDCl3) ꢂ0.29 (2 H, br s, inner
NH), 1.45 (18 H, s, t-butyl H), 1.48 (36 H, s, t-butyl H), 1.54
(18 H, s, t-butyl H), 7.74–7.78 (3 H, m, quinoxaline H, Hp),
7.82–7.88 (5 H, m, quinoxaline H, aryl H), 7.89 (2 H, d,
J 1.8 Hz, Ho), 7.91–7.94 (5 H, m, quinoxaline H, Ho, Hp), 7.98
(2 H, d, J 1.7 Hz, Ho), 8.01 (1 H, t, J 1.8 Hz, Hp), 8.03 (2 H, d,
J 1.9 Hz, Hp), 8.68 and 8.70 (2 H, ABq, J 4.8 Hz, b-pyrrolic
H), 8.78 (1 H, s, b-pyrrolic H); m/z (ESI) 1312.9 ([M + H]+
requires 1312.8).
Method 2: demetallation of copper(II) corner 12- and
13-nitro-bisquinoxalinoporphyrin 13. A solution of {12- and
13-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino-
[2,3-b0:7,8-b00]porphyrinato}copper(II) 13 (180 mg, 0.131 mmol)
in CH2Cl2 (90 ml) was stirred and heated at 100 1C with
trifluoroacetic acid (2 ml) and concentrated sulfuric acid (98%,
4.4 ml) for 3 days, then poured onto ice (50 g). When the ice
melted the organic phase was separated, washed with water
(200 ml), sodium carbonate solution (10%, 2 ꢃ 200 ml), water
(200 ml), dried over anhydrous sodium sulfate, filtered and the
filtrate evaporated to dryness. The crude mixture was purified
by chromatography over silica (CH2Cl2–light petroleum; 1 : 2)
to give two fractions. The first fraction gave 13-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]-
porphyrin 14a (28.0 mg, 16%) as a green microcrystalline
solid, mp 4 300 1C, which co-chromatographed with an
authentic sample prepared by method 1. The second fraction
gave 12-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bis-
quinoxalino[2,3-b0:7,8-b00]porphyrin 14b (90.0 mg, 52%) as a
green microcrystalline solid, mp 4 300 1C, which co-chromato-
graphed with an authentic sample prepared by method 1.
12,13-Dioxo-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bis-
quinoxalino[2,3-b0:7,8-b00]porphyrin 16. The above reactions
were repeated on 12- and 13-nitro-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]porphyrin 14
(48.4 mg, 0.0369 mmol) but without addition of 1,2-diamino-
benzene. The solvent was removed under vacuum and the
crude mixture was purified by column chromatography over
silica (CH2Cl2–light petroleum 2 : 3). The front running
orange band was collected and the solvent removed to
give 12,13-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:7,8-b00]porphyrin 16 (15.2 mg, 32%) as
a black microcrystalline solid, mp 4 300 1C; (ESI-HRMS
found: [M + H]+ 1297.772. C88H97N8O2 requires 1297.773);
n
max(CHCl3)/cmꢂ1 3354w (NH), 2964s, 2903m, 2866m, 1724s
(CO), 1595m; lmax(CHCl3)/nm 352sh (loge 4.68), 404 (4.97),
464 (4.85), 530sh (4.47), 589sh (4.12), 684 (3.66), 710 (3.60),
760 (3.59); dH(400 MHz; CDCl3) 0.15 (1 H, br s, inner NH),
0.19 (1 H, br s, inner NH), 1.43 (18 H, s, t-butyl H), 1.44 (18 H,
s, t-butyl H), 1.47 (18 H, s, t-butyl H), 1.48 (18 H, s, t-butyl H),
7.65 (2 H, d, J 1.8 Hz, Ho), 7.70 (2 H, d, J 1.8 Hz, Ho),
7.71–7.93 (15 H, m, quinoxaline H, Ho, Hp), 8.00 (1 H, t,
J 1.8 Hz, Hp), 8.33 and 8.55 (2 H, d of ABq, J 4.7, JNH 1.9 Hz,
b-pyrrolic H); m/z (ESI) 1296.9 (M+ requires 1296.8).
5,10,15,20-Tetrakis(3,5-di-tert-butylphenyl)trisquinoxalino-
[2,3-b0:7,8-b00:12,13-b00 0]porphyrin 1. A solution of crude
12- and 13-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:7,8-b00]porphyrin 14 (0.593 g, 0.451 mmol)
in a HCl–ether mixture (4 M, 40 ml) was stirred with tin(II)
chloride dihydrate (0.441 g, 1.95 mmol) in the dark for 2 h.
Work-up as before gave 12- and 13-amino-5,10,15,20-tetra-
kis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:7,8-b00]porphyrin
15. The mixture was dissolved in CH2Cl2 (2 L) and
photooxidised in the presence of 1,2-diaminobenzene (0.218 g,
Synthesis of trisquinoxalinoporphyrin 1 from metallated
linear bisquinoxalinoporphyrin (Pathway 2, Scheme 3)
2.02 mmol) for
5 h. Mass spectroscopy showed the
presence of 12,13-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:7,8-b00]porphyrin 16 as an inter-
mediate. The solvent was removed under vacuum and the
crude mixture purified by column chromatography over silica
(CH2Cl2–light petroleum 1 : 3). The first dark green band was
{7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquin-
oxalino[2,3-b0:12,13-b00]porphyrinato}zinc(II) 18. {5,10,15,20-
Tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,13-b00]-
porphyrinato}zinc(II)13
8 (60.0 mg, 0.0451 mmol) was
dissolved in CH2Cl2 (500 ml) and nitrated. The crude mixture
ꢀc
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was purified by column chromatography over silica
(CH2Cl2–light petroleum 3 : 2). The front running band was
collected and the solvent was removed to give 7-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-
b0:12,13-b00]porphyrinato}zinc(II) 18 (46.0 mg, 74%) as a green
shiny microcrystalline solid, mp 4 300 1C. An analytically
pure sample was obtained by recrystallisation (CHCl3–MeOH);
(Found: C, 74.30; H, 6.98; N, 8.74. C88H95N9O2Zn + 1/2CHCl3
requires C, 74.03; H, 6.70; N, 8.78%); (HR-ESI-FT/ICR
found: [M]+ 1373.6931. C88H95N9O2Zn requires 1373.6890);
petroleum 1 : 3). The first dark green band was collected and
the solvent was removed to give 5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)trisquinoxalino[2,3-b0:7,8-b00:12,13-b0 00]porphyrin
1 (7.0 mg, 20%) as a green microcrystalline solid, mp 4 300 1C,
which co-chromatographed with an authentic sample
reported above.
Synthesis of {7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:12,13-b00]porphyrinato}copper(II) 19.
{5,10,15,20-Tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino-
[2,3-b0:12,13-b00]porphyrinato}copper(II)13 17 (100 mg, 0.0752 mmol)
was dissolved in CH2Cl2 (300 ml) and nitrated. The crude
mixture was purified by column chromatography over silica
(CHCl3–light petroleum 1 : 2). The front running band was
collected to give {7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:12,13-b00]porphyrinato}copper(II)
19 (95.0 mg, 92%) as a green shiny microcrystalline solid,
mp 4 300 1C. An analytically pure sample was obtained by
recrystallisation (CHCl3–MeOH); (Found: C, 75.85; H, 6.88;
N, 9.06. C88H95CuN9O2 + CH3OH requires C, 76.01; H, 7.10;
N, 8.96%); (HR-ESI-FT/ICR found: [M + H]+ 1373.7017.
n
max(CHCl3)/cmꢂ1 2964s, 2903m, 2866m, 1526m (NO2), 1362s
(NO2); lmax(CHCl3)/nm 349 (loge 4.64), 403sh (4.73), 465
(5.30), 559 (3.88), 608 (3.93), 642sh (4.32); 659 (4.62) nm;
dH(400 MHz; CDCl3) 1.489 (18 H, s, t-butyl H), 1.493 (18 H, s,
t-butyl H), 1.498 (18 H, s, t-butyl H), 1.501 (18 H,
s, t-butyl H), 7.78–7.97 (20 H, m, quinoxaline H, Ho, Hp),
9.07–9.09 (2 H, m, tight ABq, b-pyrrolic H), 9.27 (1 H, s,
b-pyrrolic H); m/z (ESI) (m/z): 1374.7 ([M
requires 1374.7).
+
H]+
7-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino-
[2,3-b0:12,13-b00]porphyrin 20. A solution of {7-nitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,13-b00]-
porphyrinato}zinc(II) 18 (46.0 mg, 0.0334 mmol) in CH2Cl2
(20 ml) was stirred with hydrochloric acid (20 ml, 8 M) for
20 min. After work-up the crude mixture was purified by
chromatography over silica (CH2Cl2–light petroleum 1 : 1).
The front running green band was collected and evaporated
to give 7-nitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-
bisquinoxalino[2,3-b0:12,13-b00]porphyrin 20 (41.0 mg, 93%)
as a green microcrystalline solid, mp 4 300 1C. An analytically
pure sample was obtained by recrystallisation (CHCl3–MeOH);
(Found: C, 79.08; H, 7.47; N, 9.52. C88H97N9O2 + CH3OH
requires C, 79.49; H, 7.57; N, 9.37%); (HR-ESI-FT/ICR
C88H96CuN9O2 requires 1373.6983);
2964s, 2903m, 2866m, 1522w (NO2), 1362s (NO2);
max(CHCl3)/nm 349 (loge 4.70), 398sh (4.67), 461 (5.25),
n
max(CHCl3)/cmꢂ1
l
550 (3.90), 626 (4.21), 660 (4.47) nm; m/z (ESI) 1373.8
([M + H]+ requires 1373.7).
Synthesis of trisquinoxalinoporphyrin 1 from the copper(II)
quinoxalinoporphyrin 3 (Scheme 4, Pathway 3)
{Dinitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b0]porphyrinato}copper(II) isomers 23. {5,10,15,20-Tetrakis(3,
5-di-tert-butylphenyl)quinoxalino[2,3-b0]porphyrinato}copper(II)14
10 (1.61 g, 1.31 mmol) was dissolved in CH2Cl2 (300 ml) and
nitrated as above. The reaction was followed by TLC analysis
which showed the initial formation of nitro-5,10,15,20-tetrakis-
(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]porphyrinato}copper(II).
When none of the mononitro adducts remained, the solution was
evaporated to dryness and the resultant product was subjected to
chromatography over silica (CH2Cl2–light petroleum 1 : 2). The
major band yielded {dinitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b0]porphyrinato}copper(II) isomers 23
(1.50 g, 87%) as a shiny purple microcrystalline solid (recrystallisa-
tion from CH2Cl2–MeOH), mp 4 300 1C; (Found: C, 74.2; H, 7.2;
N, 8.6. C82H92CuN8O4 + CH3OH requires C, 73.9; H, 7.2;
N, 8.3%); (HR-ESI-FT/ICR found: [M + H]+ 1316.6660.
C82H93CuN8O4 requires 1316.6615); nmax(CHCl3)/cmꢂ1 2985s,
2905s, 2868s, 1530s (NO2), 1363s (NO2); lmax (CHCl3)/nm 344
(log e 4.50), 385sh (4.43), 457 (5.09), 574 (4.08), 535sh (3.83), 623
(4.13); m/z (ESI) 1316.9 ([M + H]+ requires 1316.7).
found: [M
+
H]+ 1312.7785. C88H98N9O2 requires
1312.7833); nmax(CHCl3)/cmꢂ1 3369w (NH), 2964s, 2905m,
1533m (NO2), 1364m (NO2); lmax(CHCl3)/nm 354 (loge 4.65),
423sh (4.93), 449 (5.37), 536 (4.21), 577 (4.05), 620 (4.05); 675
(3.99); dH(400 MHz; CDCl3) ꢂ1.97 (1 H, d, J 1.8 Hz, inner
NH), ꢂ1.92 (1 H, br s, inner NH), 1.48 (18 H, s, t-butyl H),
1.49 (36 H, s, t-butyl H), 1.50 (18 H, s, t-butyl H), 7.72–7.83
(8 H, m, quinoxaline H), 7.90 (1 H, t, J 1.8 Hz, Hp), 7.93–7.97
(7 H, m, Ho, Hp), 7.98 (2 H, d, J 1.8 Hz, Ho), 7.99 (2 H, d,
J 1.8 Hz, Ho), 9.02 and 9.04 (2 H, d of ABq, J 4.9, JNH 1.8 Hz,
b-pyrrolic H), 9.17 (1 H, d, J 2.5 Hz, b-pyrrolic H); m/z (ESI)
1312.8 ([M + H]+ requires 1312.8).
5,10,15,20-Tetrakis(3,5-di-tert-butylphenyl)trisquinoxalino
[2,3-b0:7,8-b00:12,13-b00 0]porphyrin 1. A solution of 7-nitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:
12,13-b00]porphyrin 20 (34.0 mg, 0.0259 mmol) in a HCl–ether
mixture (4 M, 10 ml) was stirred with tin(II) chloride dihydrate
(26.0 mg, 0.115 mmol) in the dark for 1.5 h. After work-up
Dinitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b0]porphyrin isomers 24. A solution of {dinitro-5,10,15,
20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]porphyrinato}-
copper(II) isomers 23 (1.50 g, 1.14 mmol) in CH2Cl2 (50 ml)
was stirred with concentrated sulfuric acid (98%, 6.5 ml) for
15 min. After work-up the crude mixture was passed through
a plug of silica (CH2Cl2–light petroleum 1 : 1) to afford
dinitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b0]porphyrin isomers 24 (1.39 g, 97%) as a green
the
7-amino-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bis-
quinoxalino[2,3-b0:12,13-b00]porphyrin 21 was obtained, which
was then dissolved in CH2Cl2 (0.5 L) and photooxidised in the
presence of 1,2-diaminobenzene (25.0 mg, 0.231 mmol) for
5 h. The solvent was removed and the crude mixture was
purified by column chromatography over silica (CH2Cl2–light
ꢀc
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1084 | New J. Chem., 2009, 33, 1076–1086

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microcrystalline solid (recrystallisation from a CH2Cl2–MeOH
solution), mp 4 300 1C; (Found: C, 77.65; H, 7.7; N, 8.9.
C82H94N8O4 + CH3OH requires C, 77.4; H, 7.7; N, 8.7%).
(HR-ESI-FT/ICR found: [M + H]+ 1255.7462. C82H95N8O4
requires 1255.7471). nmax(CHCl3)/cmꢂ1 3369w (NH), 3006s,
3000s, 2965s, 2868m, 1533m (NO2), 1363s (NO2);
21 (90 mg, 6%) as a brown microcrystalline solid, mp 4 300 1C.
An analytically pure sample was obtained by recrystallisation
(CHCl3–MeOH);
(HR-ESI-FT/ICR
found:
[M+H]+
1282.8047. C88H100N9 requires 1282.8098); nmax(CHCl3)/cmꢂ1
3492w (NH2), 3376w (NH), 3024m, 2960s, 2927s, 2871s, 1609w,
1594m, 1549m, 1463s, 1361m; lmax(CHCl3)/nm 349 (loge 4.54),
408 (4.96), 464 (5.17), 546 (4.22), 587 (3.82), 619 (4.03),
677 (4.26); dH(400 MHz; CDCl3) ꢂ2.77 (1 H, d, J 2.0 Hz, inner
NH), ꢂ2.02 (1 H, s, inner NH), 1.48 (18 H, s, t-butyl H), 1.49
(54 H, s, t-butyl H), 4.81 (2 H, br s, amine H), 7.70–7.75 (5 H, m,
quinoxaline H), 7.78–7.84 (3 H, m, quinoxaline H), 7.92 (1 H, t,
J 1.8 Hz, Hp), 7.93–7.98 (8 H, m, Ho, Hp), 8.01 (1 H, t, J 1.8 Hz,
Hp), 8.02 (2 H, d, J 1.7 Hz, Hp), 8.06 (1 H, d, J 2.4 Hz, b-pyrrolic
H), 8.96 (1 H, dd, A of ABq, J 4.8, JNH 1.8 Hz, b-pyrrolic H)
and 9.00 (1 H, dd, B of ABq, J 4.8, JNH 1.8 Hz, b-pyrrolic H);
l
max(CHCl3)/nm 347 (loge 4.46), 394sh (4.48), 457 (5.11),
550 (4.01), 609 (3.99), 692 (3.72); dH(400 MHz; CDCl3)
ꢂ2.14 (s, inner NH), ꢂ2.03 (s, inner NH), ꢂ1.96 (s, inner
NH), ꢂ1.94 (s, inner NH), ꢂ1.88 (s, inner NH), ꢂ1.80 (s, inner
NH), ꢂ1.24 (s, inner NH), 1.47–1.50 (m, t-butyl H), 1.52–1.55
(m, t-butyl H), 7.75–8.07 (m, quinoxaline H, Ho, Hp), 8.10
(t, J 2.0 Hz, Hp), 8.12 (d, J 1.8 Hz, Ho), 8.62–9.17 (m, b-pyrrolic H);
m/z (ESI) 1255.8 ([M + H]+ requires 1255.7).
Isolation of 7,18-dinitro-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)quinoxalino[2,3-b0]porphyrin 24a. Dinitro-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]porphyrin
isomers 24 (1.39 g, 1.107 mmol) were further fractionated by
chromatography over silica (CH2Cl2–light petroleum 1 : 3) to
give two fractions. The first fraction was an inseparable
mixture of the 7,12-, 7,13-, 7,17-, 8,12-, 8,13- and 8,17-dinitro-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]-
porphyrin 24b (1.14 g, 79%). The second fraction gave
7,18-dinitro-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino-
[2,3-b0]porphyrin 24a (0.250 g, 21%) as a green microcrystal-
line solid, mp 4 300 1C. An analytically pure sample was
obtained by recrystallisation (CH2Cl2–MeOH); (HR-ESI-FT/
ICR found: [M + H]+ 1255.7433. C82H95N8O4 requires
1255.7471); nmax(CHCl3)/cmꢂ1 3323w (NH), 3016s, 2965s,
2905m, 1526m (NO2), 1363s (NO2); lmax(CHCl3)/nm 352
(loge 4.34), 451 (5.03), 562sh (3.79), 604 (3.90), 695 (3.79),
726sh (3.74); dH(400 MHz; CDCl3) ꢂ0.95 (2 H, br s, inner
NH), 1.48 (36 H, s, t-butyl H), 1.54 (36 H, s, t-butyl H),
7.78–7.83 (4 H, m, quinoxaline H), 7.84 (2 H, t, J 1.7 Hz, Hp),
7.87 (2 H, t, J 1.7 Hz, Hp), 8.01 (4 H, d, J 1.7 Hz, Ho),
8.02 (4 H, d, J 1.8 Hz, Ho), 8.66 (2 H, s, b-pyrrolic H), 8.89
(2 H, s, b-pyrrolic H); m/z (ESI) 1255.8 ([M + H]+ requires
1255.7).
m/z (ESI) 1282.9 ([M +
H]+ requires 1282.8); (m/z)
(MALDI-TOF) 1282.7 ([M + H]+ requires 1282.8).
The second green band was collected to give 5,10,
15,20-tetrakis(3,5-di-tert-butylphenyl)trisquinoxalino[2,3-b0:
7,8-b00:12,13-b0 0 0]porphyrin 1 (150 mg, 10%) as a green micro-
crystalline solid, mp 4 300 1C, which co-chromatographed
with an authentic sample prepared previously.
Synthesis of 7,8-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:12,13-b00]chlorin 22. The 7-amino-5,
10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,
13-b00]porphyrin 21 (17.0 mg, 0.0133 mmol), isolated in the
previous procedure, was dissolved in CH2Cl2 (500 ml) and
subjected to further photoirradiation for 4 h. The reaction
was monitored by TLC analysis, and when no starting material
remained the solvent was removed under vacuum and the
residue was purified by chromatography over silica
(CHCl3–light petroleum 1 : 1). The major red brown band
was collected and evaporated to yield 7,8-dioxo-5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,13-b00]-
chlorin 22 (4.0 mg, 23%) as a black microcrystalline solid, mp
4 300 1C. An analytically pure sample was obtained by
recrystallisation (CH2Cl2–acetonitrile); (ESI-HRMS found:
[M+H]+ 1297.774. C88H97N8O2 requires 1297.773);
n
max(CHCl3)/cmꢂ1 3400w (NH), 3024s, 3017s, 3012w, 3004w,
5,10,15,20-Tetrakis(3,5-di-tert-butylphenyl)trisquinoxalino-
[2,3-b0:7,8-b00:12,13-b0 0 0]porphyrin 1. A solution of dinitro-5,10,
15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]porphyrins
24 (1.38 g, 1.10 mmol) in a HCl–ether mixture (4 M, 150 ml) was
stirred with tin(II) chloride dihydrate (2.5 g, 11.1 mmol) in the
dark for 3 h. Work-up of the reaction mixture afforded diamino-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b0]-
porphyrin isomers 25. The mixture 25 was dissolved in CH2Cl2
(2 L) and photooxidised for 2 h. The residue afforded an
inseparable mixture of amino-quinoxalinoporphyrin-dione 26
[m/z (MALDI-TOF) 1211.3 ([M + H]+ requires 1210.8)]
and quinoxalinoporphyrin-tetraone 27 [m/z (MALDI-TOF)
1226.2 ([M + H]+ requires 1225.7)]. The reaction products
and 1,2-diaminobenzene (810 mg, 7.49 mmol) in CH2Cl2 (60 ml)
were stirred for 20 min. The solvent was removed and the crude
mixture was purified by column chromatography over silica
(CHCl3–light petroleum 1 : 1). The front running brown band
was collected and gave a linear 7-amino-5,10,15,20-tetrakis-
(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,13-b00]porphyrin
2961s, 2929s, 2858m, 1725s (CO), 1598s; lmax(CHCl3)/nm 348
((loge 4.45), 405 (4.59), 454sh (4.48), 495sh (4.23), 532 (4.22),
620 (3.59), 677 (3.72), 767 (3.47); dH(400 MHz; CDCl3) 1.37
(36 H, s, t-butyl H), 1.41 (36 H, s, t-butyl H), 4,49 (2 H, br s, inner
NH), 7.43 (4 H, d, J 1.7 Hz, Ho), 7.55–7.58 (4 H, m, quinoxaline
H), 7.60–7.66 (8 H, m, quinoxaline H, Ho), 7.75 (2 H, t,
J 1.7 Hz, Hp), 7.79 (2 H, t, J 1.8 Hz, Hp), 7.81 (2 H, s,
b-pyrrolic H); m/z (ESI) 1297.7 ([M+H]+ requires 1297.8).
Conversion of 7,8-dioxo-5,10,15,20-tetrakis(3,5-di-tert-butyl-
phenyl)bisquinoxalino[2,3-b0:12,13-b00]chlorin 22 to 1. 7,8-Dioxo-
5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b0:12,
13-b00]porphyrin 22 (11.0 mg, 8.48 mmol) and 1,2-diamino-
benzene (43.0 mg, 0.397 mmol) in CH2Cl2 (10 ml) were stirred
at room temperature for 1 min. The solvent was removed under
vacuum and the crude mixture was passed through a plug of
silica (CH2Cl2–light petroleum 1 : 1). The front running green
band was collected and evaporated to dryness to give 5,10,
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1076–1086 | 1085

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15,20-tetrakis(3,5-di-tert-butylphenyl)trisquinoxalino[2,3-b0:
7,8-b00:12,13-b00 0]porphyrin
(9.0 mg, 77%) as green
9 M.-C. Yoon, R. Misra, Z. S. Yoon, K. S. Kim, J. M. Lim,
T. K. Chandrashekar and D. Kim, J. Phys. Chem. B, 2008, 112,
6900–6905.
10 Y. Inokuma, N. Ono, H. Uno, D. Y. Kim, S. B. Noh, D. Kim and
A. Osuka, Chem. Commun., 2005, 3782–3784.
1
a
microcrystalline solid, mp 4 300 1C, which co-chromato-
graphed with an authentic sample prepared in the previous
procedure.
11 E. H. Gacho, H. Imai, R. Tsunashima, T. Naito, T. Inabe and
N. Kobayashi, Inorg. Chem., 2006, 45, 4170–4176.
12 P. A. Stuzhin and C. Ercolani, in The Porphyrin Handbook,
ed. K. M. Kadish, K. M. Smith and R. Guilard, Academic Press,
San Diego, CA, 2003, vol. 15, pp. 263–364.
Acknowledgements
13 W. E, K. M. Kadish, P. J. Sintic, T. Khoury, L. J. Govenlock,
Z. Ou, J. Shao, K. Ohkubo, J. R. Reimers, S. Fukuzumi and
M. J. Crossley, J. Phys. Chem. A, 2008, 112, 556–570.
14 M. J. Crossley, P. J. Sintic, R. Walton and J. R. Reimers, Org.
Biomol. Chem., 2003, 1, 2777–2787.
This research was funded by an Australian Research Council
Discovery Grant (A29906559) to M.J.C. We thank The
University of Sydney for a Henry Bertie and Florence Mabel
Gritton Research Scholarship to T.K.
15 M. J. Crossley, L. J. Govenlock and J. K. Prashar, J. Chem. Soc.,
Chem. Commun., 1995, 2379–2380.
16 M. J. Crossley and P. L. Burn, J. Chem. Soc., Chem. Commun.,
1991, 1569–1571.
References
17 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.
18 M. J. Crossley, C. S. Sheehan, T. Khoury, J. R. Reimers and
P. J. Sintic, New J. Chem., 2008, 32, 340–352.
1 D. Dolphin, The Porphyrins, Academic Press, New York,
1979.
2 J. R. Reimers, N. S. Hush and M. J. Crossley, J. Porphyrins
phthalocyanines, 2002, 6, 795–805.
3 N. K. S. Davis, M. Pawlicki and H. L. Anderson, Org. Lett., 2008,
10, 3945–3947.
19 M. J. Crossley and L. G. King, J. Chem. Soc., Chem. Commun.,
1984, 920–922.
4 T. Khoury and M. J. Crossley, Chem. Commun., 2007, 4851–4853.
5 K. Nakai, K. Kurotobi, A. Osuka, M. Uchiyama and
N. Kobayashi, J. Inorg. Biochem., 2008, 102, 466–471.
´
6 Y. Rio, S. Rodrıguez-Morgade and T. Torres, Org. Biomol. Chem.,
2008, 6, 1877–1894.
7 P. J. Sintic, W. E, Z. Ou, J. Shao, J. A. McDonald, Z.-L. Cai,
K. M. Kadish, M. J. Crossley and J. R. Reimers, Phys. Chem.
Chem. Phys., 2008, 10, 268–280.
20 M. M. Catalano, M. J. Crossley, M. M. Harding and L. G. King,
J. Chem. Soc., Chem. Commun., 1984, 1535–1536.
21 K. M. Kadish, W. E, P. J. Sintic, Z. Ou, J. Shao, K. Ohkubo,
S. Fukuzumi, L. J. Govenlock, J. A. McDonald, A. C. Try,
Z.-L. Cai, J. R. Reimers and M. J. Crossley, J. Phys. Chem. B,
2007, 111, 8762–8774.
22 M. J. Crossley, M. M. Harding and S. Sternhell, J. Am. Chem.
Soc., 1992, 114, 3266–3272.
8 M. Tao, X. Zhou, J. Ma, D. Liu and J. Xing, Dyes Pigm., 2007, 75,
408–412.
23 M. J. Crossley, P. L. Burn, S. S. Chew, F. B. Cuttance and
I. A. Newsom, J. Chem. Soc., Chem. Commun., 1991, 1564–1566.
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1086 | New J. Chem., 2009, 33, 1076–1086