A cyclic porphyrin tetramer linked by azo and butadiyne bridges

Article abstract of DOI:10.1002/ejoc.201000388

A soluble cyclic porphyrin oligomer (CPO) consisting of four 5,10-diarylporphyrins linked by alternating azo and butadiyne bridges has been synthesised via an aminated dinickel(II) butadiyne dimer. This is the first cyclic tetramer that combines both azo and butadiyne bridges and extends the azoporphyrin family, which comprises only a very few examples. The electronic absorption spectrum of the tetramer is more similar to spectra of azoporphyrins than to those of butadiyne-linked dimers or tetramer, exhibiting a twocomponent Soret band with a splitting of 4190 cm^-1 and a strongly red-shifted Q band maximum, at 735 nm.

Full text of DOI:10.1002/ejoc.201000388

FULL PAPER
DOI: 10.1002/ejoc.201000388
A Cyclic Porphyrin Tetramer Linked by Azo and Butadiyne Bridges
[a]
[a]
[a]
ˇ ´
Bruno Basic, John C. McMurtrie, and Dennis P. Arnold*
Keywords: Porphyrinoids / Porphyrins / Azo compounds
A soluble cyclic porphyrin oligomer (CPO) consisting of four
5,10-diarylporphyrins linked by alternating azo and buta-
diyne bridges has been synthesised via an aminated di-
nickel(II) butadiyne dimer. This is the first cyclic tetramer
that combines both azo and butadiyne bridges and extends
the azoporphyrin family, which comprises only a very few
examples. The electronic absorption spectrum of the tetra-
mer is more similar to spectra of azoporphyrins than to those
of butadiyne-linked dimers or tetramer, exhibiting a two-
component Soret band with a splitting of 4190 cm–1 and a
strongly red-shifted Q band maximum at 735 nm.
Introduction
would provide the optimum degree of interporphyrin conju-
Porphyrins play an important role in several biological gation and be a good bridge for facilitating electronic com-
systems including oxygen transport, photosynthesis, and munication between the porphyrins in the ground state.[29]
enzymes. Their capacity to absorb visible light, facilitate The azo bridge provides a short distance between the por-
oxidation and reduction, and act as energy- and electron- phyrin rings and a conjugated linker with little steric hin-
transfer agents, in particular when several are held closely drance.
together, is of particular interest to chemists who seek to
mimic Nature and to make and use these compounds in azoporphyrin dimers from 5,10,15-triphenyl- and 5,15-di-
order to synthesise novel advanced materials.
arylporphyrinylamines.[46] More recently a 5,10-diaryl-sub-
We reported the copper-promoted synthesis of the first
Elucidation of the crystal structure of the light-harvest- stituted porphyrin (“corner porphyrin”) has also been
ing antenna complex LH2 of Rhodopseudomonas acido- linked to give an azo dimer.[47] Chen and co-workers re-
phila[1–3] has brought about efforts to synthesise a range of ported the synthesis using iron(III) mediated coupling, of
cyclic porphyrin oligomers (CPOs) with the aim of studying the dizinc azoporphyrin derived from 5,10,15-triphenylpor-
excitation energy transfer (EET) and creating analogues of phyrin.[48] Inspired by previous work in the field[5–7,49] our
natural light-harvesting antennae. Since the pioneering research aims towards the synthesis of new cyclic azo-linked
work of Sanders and Anderson,[4] several CPOs in which tetramers, for example 1, that utilises alternating azo and
the individual porphyrin rings are connected by covalent butadiyne bridges (Figure 1).
bonds have been reported.[5–10] CPOs have also been investi-
gated in other fields such as host-guest chemistry and single
molecule photochemistry.[7] We are interested in covalently
linked arrays in which the bridging units are fully conju-
gated with the porphyrin π-system, including CPOs. Since
the first conjugated diporphyrin system, a butadiyne-linked
dimer,[11] was synthesised, many other porphyrin systems
that offer strong electronic communication through their
conjugated linkers have been investigated. The butadiyne
and other linkers have been studied extensively, with numer-
ous papers reporting interesting results with potential in
various fields,[7,10,12–36] including recently two-photon ab-
sorption[31,34,37–44] and two-photon photodynamic ther-
apy.[14,15,41,45] Anderson suggested that an azo linkage
[a] Chemistry, Faculty of Science and Technology, Queensland
University of Technology,
G. P. O. Box 2434, Brisbane 4001, Australia
Fax: +61-7-3864-1804
E-mail: d.arnold@qut.edu.au
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201000388.
Figure 1. Azo/butadiyne-linked Ni-cyclic porphyrin tetramer 1.
Eur. J. Org. Chem. 2010, 4381–4392
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B. Basˇic´, J. C. McMurtrie, D. P. Arnold
FULL PAPER
Previously we sought to synthesise compound 2, a cyclic loss of the dimer.[47] The unsubstituted azo-linked dimer 5
porphyrin tetramer that is linked by azo bridges alone (Fig- was also considered as a starting material for compound 1
ure 2). The intended synthetic route was supposed to use provided that it could be brominated and then furnished
an aminated dinickel(II) azo dimer 3 that would have been with (trimethylsilyl)acetylene groups (Figure 3). We found
obtained from a nitrated precursor (4). Though the unsub- that the bromination of the dimer proved unreliable so that
stituted dinickel(II) azo-linked dimer 5 was synthesised, compound 7 could not be obtained from compound 8.[47]
compound 4 could not be made reliably.[47] Attempts to Here we present an alternative methodology that led to the
make compound 2 from compound 4 failed, resulting in the successful synthesis of tetramer 1 (Scheme 1).
Figure 2. Proposed retrosynthesis of compound 2.
Figure 3. Proposed retrosynthesis of compound 1.
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A Cyclic Porphyrin Tetramer
Scheme 1. Synthesis of the azo/butadiyne-linked cyclic porphyrin tetramer 1: (i) 0.75 equiv. I2, 1.5 equiv. AgNO2, DCM/MeCN; (ii)
1.5 equiv. NBS, CHCl3/pyridine; (iii) 20 equiv. HCCSiMe3, 80 mol-% AsPh3, 20 mol-% Pd2(dba)3, TEA 45 °C; (iv) Ni(acac)2, toluene
120 °C; (v) 6 equiv. Cu(OAc)2·H2O, pyridine 80 °C; (vi) 10% Pd on C, 8 equiv. NaBH4, DCM/MeOH; (vii) 0.5 equiv. Cu(OAc)2·H2O,
2 equiv. pyridine, toluene 80 °C. Ar = 3,5-di-tert-butylphenyl.
Results and Discussion
The general instability of the azo bridge suggested to us
that compound 1 would have to be synthesised by establish-
ing a butadiyne-linked dimer first. In order to avoid the
possible pitfalls of nitrating the unsubstituted meso posi-
tions of the dinickel(II) butadiyne-linked corner porphyrin
dimer 9 (Figure 4), we decided that the monomer from
which a dimer is to be synthesised should already be ni-
trated (16 in Scheme 1).
Figure 4. Structure of compound 9.
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The unsubstituted corner porphyrin monomer (10) was the bromination of 14 and the subsequent introduction of
nitrated using the AgNO2/I2 method[47,50,51] yielding com- the acetylene group to give 16 took slightly less time with a
pound 11 in a 93% recrystallised yield. From here several slightly greater overall yield.
synthetic routes were explored (Scheme 1). The first route
It is interesting to note that the synthesis of dimer 17
involved brominating the nitrated free-base corner por- involved a one-pot desilylation/dimerisation reaction using
phyrin (11) to yield compound 12 which was converted into copper(II) acetate in pyridine in which there was no need
the free-base porphyrin 13 via a copperless method.[52] Me- to isolate the intermediate compound with a deprotected
tallation of 13 gave compound 16 that was then self-coupled acetylene group prior to coupling. This was observed in ear-
using the Cu(OAc)2 method[46] to give the nitrated di- lier work done by the Arnold group involving porphyrins
nickel(II) butadiyne-linked dimer 17 in a 97% yield and with acetylene linkers,[53] and by others working in different
50% recrystallised yield. The non-recrystallised material fields.[54–59] We find it to be a very convenient and high-
was used to obtain the aminated dinickel(II) butadiyne- yielding method.
linked dimer 18. Although there were some concerns that
Our attempts to create a zinc analogue of tetramer 1 have
the butadiyne link might be lost, the NaBH4 method used so far been unsuccessful, however, Zn analogues of com-
for the reduction of the nitro group did not affect the buta- pounds 17 and 18 have been made (Scheme 2). Initially,
diyne bridge. Dimer 18 was synthesised in an 83% yield. porphyrin 21 was made from compound 20, which in turn
However, due to its high solubility in common organic sol- was obtained by brominating compound 19. However, the
vents, only a 10% recrystallised yield was obtained. Here, yields were low and so porphyrin 13 was used as the precur-
too, the non-recrystallised product proved to be substan- sor to synthesise porphyrin 21 in a 91% yield. The com-
tially pure by NMR spectroscopy and was used in the sub- pound was very soluble in common organic solvents and
sequent copper(II) catalysed self-coupling step that yielded the first crop recovered after recrystallization amounted to
the azo/butadiyne-linked tetramer 1. It is remarkable that only a 9% yield. Therefore the non-recrystallised product
the tetramer was obtained reproducibly in 44% recrystal- was self-coupled to give dimer 22. The nitro groups were
lised yield in this double coupling reaction. No other prod- reduced giving the aminated dizinc(II) butadiyne-linked di-
ucts, including linear oligomers, were identified. Dark in- mer 23. While the syntheses of 22 and 23 were achieved in
tractable matter was left at the top of the chromatography 95% and 80% yield, respectively, the self-coupling step of
column. The other synthetic routes in Scheme 1 differ in the aminated dimer 23 resulted in the loss of the starting
the order in which metallation, bromination and alk- material in favour of non-porphyrinic material. The inabil-
ynylation take place. The yields and the reaction times do ity to synthesise the Zn4 azo/butadiyne-linked cyclic por-
not differ much, however, we found that the route involving phyrin tetramer also meant that a free base analogue was
Scheme 2. Synthesis of butadiyne-linked Zn corner porphyrin dimers: (i) 1.5 equiv. NBS, CHCl3/pyridine; (ii) 20 equiv. HCCSiMe3,
80 mol-% AsPh3, 20 mol-% Pd2(dba)3, TEA 45 °C; (iii) Zn(OAc)2, chloroform 60 °C; (iv) 6 equiv. Cu(OAc)2·H2O, pyridine 80 °C; (v)
10% Pd on C, 6 equiv. NaBH4, DCM/MeOH. Ar = 3,5-di-tert-butylphenyl.
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A Cyclic Porphyrin Tetramer
out of reach. Currently, it stands that the synthesis of the Figure 5. The mass spectrogram gave [M + H]+ at m/z
zinc tetramer will have to follow a different path from that 3114.16. This supported the notion that compound 1 was
established for the nickel tetramer 1.
indeed prepared as m/z calculated for [M + H]+ of the cyclic
Although nitrated monomers were selected as the precur- tetramer, C200H201N20Ni4, requires 3114.38.
sors for the tetramer (1), the unsubstituted butadiyne-linked
Ni corner porphyrin dimer 9 could have been used as well.
As stated above we chose to synthesise dimer 17 from a
monomer rather than risk losing the butadiyne bridge dur-
ing nitration. However, 10,10Ј-unsubstituted butadiyne di-
mer 9 was synthesised in order to compare the effect of the
substituent groups on the spectra of butadiyne-linked di-
mers (Scheme 3). The synthesis itself was challenging as it
required the monobrominated corner porphyrin 24. Mono-
bromination of the porphyrin meso positions can be frus-
trating for two main reasons. Firstly, it is difficult to ensure
that only one meso position will be brominated. Secondly,
the monobromoporphyrin and dibromoporphyrin are hard,
though not impossible, to separate.
After chromatographic purification, compound 24 was
Figure 5. Obtained (line) and predicted (bar) MS data for the azo/
butadiyne-linked Ni cyclic porphyrin tetramer (1).
metallated with nickel giving 25 in a quantitative yield that
was converted into 26 by substituting the bromine with the
protected alkynyl group. Previous reactions of this type pro-
ceeded well using the copperless method. In this instance
the reaction did not proceed. It was necessary to use cop-
per(I) iodide as coupling reagent for the target compound
to be achieved. Compound 26 was then self-coupled to give
dimer 9 in a 76% recrystallised yield. Further modification
of this compound was not pursued at this time. The com-
pound should be seen as a potential substrate for the inves-
tigation of reactions involving the unsubstituted meso posi-
tions.
The 1H NMR spectrum of tetramer 1 shows eight β-pro-
ton peaks (Table 1, Figure S1). This is due to the lack of
symmetry within the individual porphyrin units. Though
Table 1. Chemical shifts of the porphyrin hydrogen atoms
(Figure 6) for the butadiyne-linked dimers and the cyclic porphyrin
tetramer.
Com-
2-H
3-H 7-H 8-H
12-H 13-H 17-H 18-H
pound
1
8.97 10.14 10.59 10.29 9.55 8.84 8.64 8.66
8.95 9.70 9.80 9.36 9.17 8.88 8.76 8.74
8.62 9.43 9.41 9.02 8.86 8.50 8.49 8.41
9.06 9.92 10.05 9.48 9.26 8.97 8.85 8.82
8.66 9.61 9.62 9.20 8.99 8.55 8.54 8.46
1
The tetramer 1 was characterised by H NMR, UV/Vis,
17
18
22
23
MALDI-TOF mass and Raman spectroscopy. The mass
spectrum of the molecular ion region corresponded with
the theoretical isotopic pattern for [M + H]+ as shown in
Scheme 3. Synthesis of the unsubstituted butadiyne-linked dimer 9: (i) 1 equiv. NBS, CHCl3/pyridine 0 °C; (ii) Ni(acac)2, toluene 120 °C;
(iii) 20 equiv. HCCSiMe3, 80 mol-% CuI, 10 mol-% Pd2(PPh3)2Cl2, TEA 45 °C; (iv) 6 equiv. Cu(OAc)2·H2O, pyridine 80 °C. Ar = 3,5-di-
tert-butylphenyl.
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B. Basˇic´, J. C. McMurtrie, D. P. Arnold
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the four monomers are chemically equivalent their own each. The nitrated butadiyne-linked Ni dimer 17 has an
symmetry resembles that of a monomer with two different even smaller splitting of 810 cm–1 while the Q-band has red-
substituent groups. Thus, the eight peripheral protons are shifted by 10 nm. The aminated Ni dimer 18 does not show
all chemically different. The peaks of the protons flanking a clear splitting of the Soret band, however, the Q-band has
the azo and butadiyne linkers are shifted significantly shifted significantly to 705 nm.
downfield due to the electron-withdrawing effect of those
groups. The signal of the 7-H is further downfield than for
any other nickel(II) porphyrin in our experience.
Table 2. Summary of absorption spectroscopy data for the buta-
diyne-linked dimers.
Compound
M
Substituents
λmax Q /nm Splitting /cm–1
The 1H NMR spectra of the butadiyne-linked com-
pounds 17, 18, 22 and 23 also show eight β peaks that are a
result of asymmetry of the porphyrin macrocycles (Table 1).
Figure 6 shows the numbering of the β-protons. The peaks
of dimers 17 and 22 are shifted further downfield than the
peaks of dimers 18 and 23 due to the electron-withdrawing
properties of the nitro groups and the electron-donating
properties of the amino groups.
5[47]
9
17
18
22
23
Ni H, H
Ni H, H
Ni NO2, NO2
Ni NH2, NH2
Zn NO2, NO2
Zn NH2, NH2
738
619
629
705
660
755
4340
1000
810
n/a
1190
n/a
The nitrated butadiyne-linked Zn dimer 22 displays a So-
ret band splitting of 1190 cm–1 and the Q-band at 660 nm.
The aminated zinc dimer 23 does not have a clear splitting
of the Soret band, which is similar to its nickel analogue.
However, the Q-band is red-shifted to 755 nm, which is
50 nm more than compound 18. Taking the splitting in the
Soret band as an indication of good ground state electronic
communication, the spectroscopic data suggest that the azo
bridge caters for a better electronic communication than the
butadiyne linker.
The absorption spectrum of the azo/butadiyne-linked cy-
clic tetramer (1) shows features that are more characteristic
of the azo-linked systems than butadiyne-linked systems
(Figure 8). There is a significant splitting of the Soret band
amounting to 4190 cm–1 and the very broad Q-band is at
735 nm. Although the Soret splitting is not as large as for
the azo-linked nickel corner porphyrin dimer 5, it is much
bigger than the splittings of the butadiyne-linked dimers.
Furthermore, when compared to the absorption spectra
Figure 6. Proton position assignments for butadiyne dimers and
the tetramer.
The electronic absorption spectra of the synthesised buta-
diyne-linked dimers (Figure 7) exhibit the general features of the butadiyne-linked tetramer (27)[6] and diphenylethyne-
of similar dimers. The Q-bands are broad and red-shifted linked tetramer 28,[5] the spectrum of compound 1 indicates
and more intense relative to the Soret bands when com- a much better electronic communication throughout the
pared with monomers. It should be noted that the Soret system (Figure 9, Table 3). Neither the spectrum of com-
band splittings are much smaller than the splittings ob- pound 27 nor that of 28 shows a splitting of the Soret band.
served for the azo-linked nickel corner porphyrin dimer The electronic communication for compound 28 is de-
(Table 2). Compound 9 is a butadiyne-linked analogue of creased because the porphyrin rings are not in the same
azoporphyrin 5. Its Q-band is found at 619 nm while the plane with respect to the diphenylethyne linkers and this
Soret band shows two splittings of approximately 1000 cm–1 hinders the π-overlap. Compound 27 does not show Soret
Figure 7. Comparison of the absorption spectra of butadiyne-linked dimers 17 (dotted), 18 (bold), 22 (dashed), and 23 (solid) in CH2Cl2.
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A Cyclic Porphyrin Tetramer
Figure 8. Comparison of the absorption spectra of tetramer 1 (bold), azo-linked dimer 5 (solid),[47] and butadiyne-linked dimer 9 (dashed)
in CH2Cl2.
Figure 9. Butadiyne-linked tetramer 27[6] and diphenylethyne-linked tetramer 28.[5]
band splitting, however, the intensity of its Q-band normal- four-coordinate to a high spin six-coordinate state. This is
ized per chromophore was increased compared with that of significant as the Ni–N bond length of the four-coordinate
the parent monomer.[6] Conversely, the intensity of the So- nickel porphyrin is shorter than that of the six-coordinate
ret band was decreased. This phenomenon confirms that nickel compounds.[60–63] The shorter bond length between
the degeneracy of the a1u and a2u orbitals of the porphyrins the nickel and the nitrogen atoms translates into puckering
is significantly lifted and that a new π-electronic system in of the macrocycle.[64] It is not as flat as a free base por-
the tetramer is formed..[18]
phyrin for example. Because the six-coordinate nickel com-
pounds have longer Ni–N bond lengths the macrocycle is
not as puckered. This allows for a much better π-overlap
and an increase in the overall conjugation of the system.
Further evidence of the six-coordinate state of nickel when
in pyridine comes from 1H NMR analysis. The proton spec-
trum of the compound could not be obtained in deuterated
pyridine as the six-coordinate nickel(II) is paramagnetic.
Similar results were obtained for the first azoporphyrin.[65]
It is worth noting that the relatively broad range of ab-
sorption displayed by the tetramer might be applicable to
organic photonics and electronics. The large π-conjugation
and photochemical and thermal stability, makes porphyrin
derivatives attractive as possible materials for photonic and
electronic applications. The fact that porphyrin derivatives
are part of light harvesting and photo-induced electron
transfer systems in the photosynthetic apparatus of plants
suggests that porphyrins could be used as photosensitisers
in dye-sensitized solar cells.[13,66–69] However, individual
porphyrin units exhibit relatively narrow absorption bands
Table 3. Absorption spectroscopy data for the cyclic porphyrin
tetramers.
Compound
M
λmax Soret /nm λmax Q /nm Splitting /cm–1
1[a]
Ni
Ni
Ni
Ni
Zn
427 and 520
428 and 521
429 and 523
503
735
737
737
659
591
4190
4170
4190
n/a
1[b]
1[c]
27[b][6]
28[c][5]
430
n/a
[a] In DCM. [b] In chloroform. [c] In toluene.
The Q-band of compound 28 is at 591 nm in toluene and
at 659 nm for compound 27 in chloroform. The absorption
spectra of compound 1 in both chloroform and toluene
have the Q-band located at 737 nm. The spectrum of tetra-
mer 1 also shows a large red-shift when the UV/Vis spec-
trum is recorded in pyridine solution (Figure 10). The Q-
band has a shift of more than 100 nm as it moves from 735
to 852 nm. The difference in the spectra could be explained
as a result of the nickel core atoms changing from low spin
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Figure 10. Absorption spectra of 1 in DCM (solid) and pyridine (bold).
tive column chromatography, Merck silica gel (230–400 mesh) was
used. The 1H NMR spectra were measured on a Bruker Avance
instrument operating at 400 MHz. All samples were prepared in
deuterated chloroform. The chemical shifts are reported in ppm
and referenced against the residual CHCl3 peak at δ = 7.26 ppm.
The coupling constants are given in Hz. 13C NMR spectra were
not recorded, as these spectra for porphyrins do not add materially
to structure confirmation when 1H spectra can be fully assigned by
the use of two-dimensional techniques. The UV/Vis spectra were
recorded in dichloromethane (DCM) on a Varian Cary 50 instru-
ment. Liquid Secondary Ion (LSI) and Electrospray Ionisation
(ESI) mass spectra were recorded at the Organic Mass Spectrome-
try Facility, University of Tasmania, Hobart. LSIMS data were ob-
tained on a Kratos ISQ double focusing magnetic sector mass spec-
trometer using a direct insertion probe and fitted with an LSIMS
ion source, using 10 kV cesium ions as the primary beam, and m-
nitrobenzyl alcohol as the liquid matrix. ESI spectra were obtained
on a Thermo Electron LTQ Orbitrap mass spectrometer. Samples
were dissolved in dichloromethane and then diluted 1:100 in meth-
anol before being infused into the mass spectrometer at a flow rate
of 50 µL/min. A voltage of 4500 V was applied at the tip. Matrix-
assisted laser desorption/ionisation (MALDI) spectra were ob-
tained at The University of Queensland, Brisbane. Analysis was
performed with an Applied Biosystems Voyager-DE STR BioSpec-
trometry workstation. The instrument was operated in positive po-
larity in reflectron mode for analysis. The samples were spotted on
a stainless steel sample plate using sinapinic acid as the matrix and
allowed to air-dry. Data from 100 laser shots (337 nm laser) were
collected, signal-averaged, and processed with the instrument man-
ufacturer’s Data Explorer software. Isotopic modelling was calcu-
lated by MassLynx V3.5 software by Micromass Limited and on-
line using Isotopident on the Expert Protein Analysis System (Ex-
PASY) server. The IR spectra were collected using a Nicolet 870
Nexus Fourier transform infrared (FTIR) system equipped with an
attenuated total internal reflectance (ATR) accessory with a single
bounce diamond cell. The Raman spectra were collected on a Reni-
shaw Spectroscope 1000 coupled to an Olympus microscope using
a helium/neon 633 nm laser with power of 0.2 mW at the sample.
which results in low power conversion efficiencies when
porphyrin-containing polymers are used as active layers in
organic solar cells.[68,70] Thus, a polymer incorporating
larger porphyrinic arrays such as that found in compound
1 might exhibit a greater efficiency.
Conclusions
In summary, by synthesising the azo/butadiyne-linked Ni
cyclic porphyrin tetramer we have extended both the fami-
lies of azo- and butadiyne-linked porphyrin compounds. We
have demonstrated that the butadiyne linker is much more
robust than the azo linker. Previously we have found that
the unsubstituted meso positions of the azo-linked por-
phyrin dimer are not amenable to further modification
without incurring the loss of the bridge. Here we have dem-
onstrated that the remaining meso positions of the por-
phyrin dimers linked by a butadiyne bridge can be further
modified to facilitate the synthesis of a new CPO that has
both the butadiyne and azo bridges. The three-dimensional
geometry of the tetramer is presently unknown, although
we have determined the X-ray crystal structures of three
nickel(II) dimers containing azo linkers.[46,47] The presence
of the NiII ion causes out-of-plane deformation of the
macrocycles, leading to a ruffled geometry for the rings,[64]
and an overall shallow sigmoidal shape for the dimers. The
tetramer, therefore, is expected to assume the shape of a
gently undulating sheet.
Finally, we have concluded that the coordinated metal
plays an important role when it comes to linking porphyrin
moieties by azo bridges. Further investigation is required to
explain the fact that nickel corner porphyrins with an
amino group can be linked using copper catalysis, while the
analogous zinc compounds cannot.
5-Bromo-15,20-bis(3,5-di-tert-butylphenyl)-10-nitroporphyrin (12):
Porphyrin 11 (56 mg, 7.65ϫ10–5 mol) was dissolved in 10 cm3 of
chloroform. To this N-bromosuccinimide (NBS) (27 mg, 2 equiv.,
1.53ϫ10–4 mol) and pyridine (123 µL, 20 equiv., 1.53ϫ10–3 mol)
were added. The solution was heated at reflux for 5 h. The reaction
did not go to completion. The solvent was removed and the residue
purified by column chromatography using DCM/hexane/triethyl-
amine (TEA) (100:100:1) as eluent. Two red fractions were isolated.
The first was the target compound; yield 69% (43 mg). The second
Experimental Section
General Procedures: All chemicals used were of Analytical Reagent
grade and were purchased from Sigma–Aldrich. 5,10-Diarylpor-
phyrin 10, nitro derivative 11 and its nickel(II) complex 14 and
zinc(II) complex 19 were prepared as described.[47,71,72] Solvents
were evaporated under reduced pressure at 40 °C. Analytical TLC
was performed using Merck Silica Gel 60 F254 plates. For prepara-
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A Cyclic Porphyrin Tetramer
was the starting material. The product was recrystallised from
DCM/methanol; yield 61% (38 mg). The product was contami-
nated with an unidentified porphyrin impurity. H NMR: δ = 9.74
[M]+ requires 865.2501). The reaction was repeated successfully on
a 160 mg scale and the alternative route was repeated successfully
on an 80 mg scale giving the same percentage yields.
1
(d, J = 5.0 Hz, 1 H, 7-H), 9.62 (d, J = 5.0 Hz, 1 H, 3-H), 9.34 (d,
J = 5.0 Hz, 1 H, 8-H), 9.26 (d, J = 5.0 Hz, 1 H, 12-H), 8.98 (d, J
= 5.0 Hz, 1 H, 13-H), 8.92 (d, J = 5.0 Hz, 1 H, 2-H), 8.85 (d, J =
5.0 Hz, 1 H, 18-H), 8.82 (d, J = 5.0 Hz, 1 H, 17-H), 8.03 (d, J =
1.8 Hz, 2 H, o-Haryl), 8.02 (d, J = 1.8 Hz, 2 H, o-Haryl), 7.86 (m, J
= 1.8 Hz, 2 H, p-Haryl), 1.56 (s, 18 H, tBu-H), 1.55 (s, 18 H, tBu-
H), –2.56 (br. s, 2 H, inner NH) ppm. IR: υ(NO2 asym) 1515 s,
υ(NO2 sym) 1364 s cm–1. UV/Vis λmax/nm (ε/103 mol–1 dm3 cm–1):
425 (183), 523 (11.9), 563 (7.39), 594 (5.75), 653 (3.43). MS (LSI):
m/z: (LSI) 810.3399 (C48H53BrN5O2 [M + H]+ requires 810.3383).
The reaction was repeated successfully on a 160 mg scale giving the
same percentage yield.
15,20-Bis(3,5-di-tert-butylphenyl)-5-[2-(trimethylsilyl)ethynyl]-
10-nitroporphyrinatonickel(II) (16): Porphyrin 15 (30 mg,
3.45ϫ10–5 mol) was dissolved in TEA (15 cm3) in a Schlenk flask
under argon. To this (trimethylsilyl)acetylene (97 µL, 20 equiv.,
6.90ϫ10–4 mol), Pd2(dba)3 (6 mg, 20 mol-%, 6.90ϫ10–6 mol), and
AsPh3 (8.5 mg, 80 mol-%, 2.76ϫ10–5 mol) were added. The solu-
tion was stirred at 45 °C for 2 h. The solvent was removed and the
residue purified by column chromatography using DCM/hexane
(1:2) as eluent. A single red compound was isolated; yield 98%
(30 mg). It was recrystallised from DCM/methanol; yield 42%
(13 mg). The product was a dark red powder. Alternatively, com-
pound 13 (8.5 mg, 1.02ϫ10–5 mol) was dissolved in 2 cm3 of tolu-
ene. To this Ni(acac)2 (8.5 mg, 3.30ϫ10–5 mol) was added. The
solution was heated at reflux for 2 h. The solvent was removed
and the residue purified by column chromatography using DCM/
hexane (1:2) as eluent. A single red compound was isolated; yield
99% (9 mg). It was recrystallised from DCM/methanol; yield 65%
(6 mg). The product was a dark red powder. 1H NMR: δ = 9.60
(d, J = 5.0 Hz, 1 H, 7-H), 9.48 (d, J = 5.0 Hz, 1 H, 3-H), 9.27 (d,
J = 5.0 Hz, 1 H, 8-H), 9.15 (d, J = 5.0 Hz, 1 H, 12-H), 8.86 (d, J
= 5.0 Hz, 1 H, 13-H), 8.83 (d, J = 5.0 Hz, 1 H, 2-H), 8.73 (d, J =
5.0 Hz, 1 H, 18-H), 8.71 (d, J = 5.0 Hz, 1 H, 17-H), 7.83 (d, J =
1.8 Hz, 2 H, o-Haryl), 7.82 (d, J = 1.8 Hz, 2 H, o-Haryl), 7.78 (m, J
= 1.8 Hz, 2 H, p-Haryl), 1.50 (s, 18 H, tBu-H), 1.49 (s, 18 H, tBu-
15,20-Bis(3,5-di-tert-butylphenyl)-5-[2-(trimethylsilyl)ethynyl]-10-
nitroporphyrin (13): Compound 12 (20 mg, 2.46ϫ10–5 mol) was
dissolved in TEA (15 cm3) in a Schlenk flask under argon. To
this (trimethylsilyl)acetylene (70 µL, 20 equiv., 4.92ϫ10–4 mol),
Pd2(dba)3 (5 mg, 20 mol-%, 4.92ϫ10–6 mol), and AsPh3 (6 mg,
80 mol-%, 1.96ϫ10–5 mol) were added. The solution was stirred at
45 °C for 4 h. The solvent was removed and the residue purified by
column chromatography using DCM/hexane/TEA (100:200:1) as
eluent. A single red compound was isolated; yield 100% (20 mg).
It was recrystallised from DCM/methanol; yield 24% (5 mg). The
product was contaminated with an unidentified porphyrin impu-
rity. 1H NMR: δ = 9.77 (d, J = 4.8 Hz, 1 H, 7-H), 9.63 (d, J =
4.9 Hz, 1 H, 3-H), 9.36 (d, J = 4.8 Hz, 1 H, 8-H), 9.24 (d, J =
4.9 Hz, 1 H, 12-H), 8.95 (d, J = 4.9 Hz, 1 H, 13-H), 8.92 (d, J =
4.9 Hz, 1 H, 2-H), 8.83 (d, J = 4.7 Hz, 1 H, 18-H), 8.80 (d, J =
4.7 Hz, 1 H, 17-H), 8.03 (d, J = 2.0 Hz, 2 H, o-Haryl), 8.01 (d, J =
2.0 Hz, 2 H, o-Haryl), 7.85 (m, J = 2.0 Hz, 2 H, p-Haryl), 1.55 (s, 18
H, tBu-H), 1.54 (s, 18 H, tBu-H), 0.65 (s, 9 H, CH3 silyl-H), –2.25
H), 0.58 (s, 9 H, SiCH3-H) ppm. IR: υ(CC) 2151 w cm–1
,
υ(NO2 asym) 1509 s cm–1, υ(NO2 sym) 1349 s cm–1. UV/Vis: λmax/nm
(ε/103 mol–1 dm3 cm–1) 431 (144), 545 (12.2). MS (ESI): m/z:
884.3870 (C43H60N5NiO2Si [M + H]+ requires 884.3870). The reac-
tion was repeated successfully on a 170 mg scale giving the same
percentage yield.
(br. s, 2 H, inner NH) ppm. IR: υ(CC) 2166 m cm–1, υ(NO2 asym
)
1516 m cm–1, υ(NO2 sym) 1364 s cm–1. UV/Vis: λmax/nm (ε/
103 mol–1 dm3 cm–1) 434 (191), 535 (12.3), 570 (9.89), 605 (5.78),
664 (2.31). MS (ESI): m/z: 827.4586 (C53H61N5O2Si, [M]+ requires
827.4595). The reaction was repeated successfully on a 180 mg scale
giving the same percentage yield.
1,4-Bis[15,20-bis(3,5-di-tert-butylphenyl)-10-nitroporphyr-
inatonickel(II)-5-yl]butadiyne (17): Compound 16 (30 mg, 3.39ϫ
10–5 mol) was dissolved in pyridine (18 cm3). To this copper(II)
acetate (40 mg, 6 equiv., 2.03ϫ10–4 mol) was added and the solu-
tion was stirred at 80 °C. The starting material was consumed after
19 h. The reaction mixture was poured into 2  HCl (50 cm3) and
extracted with DCM. The organic layer was washed with 2  HCl
(50 cm3) and water (50 cm3) before being dried with anhydrous po-
tassium carbonate. The organic layer was decanted and the solvent
evaporated; yield 97% (26 mg). It was recrystallised from DCM/
methanol; yield 50% (14 mg). The product was a dark red/brown
5-Bromo-15,20-bis(3,5-di-tert-butylphenyl)-10-nitroporphyrinato-
nickel(II) (15): Compound 14 (54 mg, 6.84 ϫ10–5 mol) was dis-
solved in 5 cm3 of chloroform. To this NBS (18 mg, 1.5 equiv.,
1.03ϫ10–14 mol) and pyridine (8 µL, 1.5 equiv., 1.03ϫ10–4 mol)
were added. The solution was heated at reflux for 1 h. The solvent
was removed and the residue purified by column chromatography
using DCM/hexane (1:1) as eluent. A single red compound was
isolated; yield 97% (58 mg). It was recrystallised from DCM/meth-
anol; yield 66% (39 mg). The product was a dark red powder. Al-
ternatively, compound 12 (44 mg, 5.42ϫ10–5 mol) was dissolved in
minimum amount of toluene. To this Ni(acac)2 (44 mg,
1.71ϫ10–4 mol) was added. The solution was heated at reflux for
3 h. The solvent was removed and the residue purified by column
chromatography using DCM/hexane (1:2) as eluent. A single red
compound was isolated; yield 89% (42 mg). It was recrystallised
from DCM/methanol; yield 60% (28 mg). The product was a dark
1
powder. H NMR: δ = 9.80 (d, J = 5.0 Hz, 2 H, 7,7Ј-H), 9.70 (d,
J = 4.8 Hz, 2 H, 3,3Ј-H), 9.36 (d, J = 5.0 Hz, 2 H, 8,8Ј-H), 9.17
(d, J = 4.8 Hz, 2 H, 12,12Ј-H), 8.95 (d, J = 4.8 Hz, 2 H, 2,2Ј-H),
8.88 (d, J = 4.8 Hz, 2 H, 13,13Ј-H), 8.76 (d, J = 5.0 Hz, 2 H, 17,17Ј-
H), 8.74 (d, J = 5.0 Hz, 2 H, 18,18Ј-H), 7.88 (br. s, 4 H, o-Haryl),
7.84 (br. s, 4 H, o-Haryl), 7.80 (br. s, 2 H, p-Haryl), 7.78 (br. s, 2 H,
p-Haryl), 1.52 (s, 36 H, tBu-H), 1.50 (s, 36 H, tBu-H) ppm. IR:
υ(CC) 2171 w cm–1, υ(NO2 asym) 1508 m cm–1, υ(NO2 sym) 1342 s
cm–1. Raman: υ(CC) 2190 s cm–1, υ(CC) 1369 m cm–1. UV/Vis:
λmax/nm (ε/103 mol–1 dm3 cm–1) 461 (140), 479 (140), 559 (29.4), 629
(31.1). MS (ESI): m/z: 1621.6781, (C1 0 0 H1 0 1 N1 0 NiO4
[M + H]+ requires 1621.6714). The reaction was repeated success-
fully on a 100 mg scale giving the same percentage yield.
1
red powder. H NMR: δ = 9.57 (d, J = 5.1 Hz, 1 H, 7-H), 9.46 (d,
J = 5.0 Hz, 1 H, 3-H), 9.26 (d, J = 5.1 Hz, 1 H, 8-H), 9.18 (d, J =
5.2 Hz, 1 H, 12-H), 8.86 (d, J = 5.2 Hz, 1 H, 13-H), 8.81 (d, J =
5.0 Hz, 1 H, 2-H), 8.75 (d, J = 5.0 Hz, 1 H, 18-H), 8.72 (d, J = 1,4-Bis[10-amino-15,20-bis(3,5-di-tert-butylphenyl)porphyrinato-
5.0 Hz, 1 H, 17-H), 7.81 (br. s, 4 H, o-Haryl), 7.77 (br. s, 2 H, p-
nickel(II)-5-yl]butadiyne (18): Dimer 17 (10 mg, 6.10ϫ10–6 mol)
Haryl), 1.50 (s, 36 H, tBu-H) ppm. IR: υ(NO2 asym) 1513 s cm–1, was dissolved in DCM/methanol (4 cm3/4 cm3) that was bubbled
υ(NO2 sym) 1336 s cm–1. UV/Vis: λmax/nm (ε/103 mol–1 dm3 cm–1
423 (121), 538 (14.7). MS (LSI): m/z: 865.2507 (C48H50BrN5NiO2
)
with argon for 10 min. Argon atmosphere was maintained and then
10% palladium on carbon (3 mg) was added followed by addition
Eur. J. Org. Chem. 2010, 4381–4392
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4389

B. Basˇic´, J. C. McMurtrie, D. P. Arnold
FULL PAPER
of sodium borohydride (2 mg, 8 equiv., 4.88ϫ10–5 mol). The start-
ing material was consumed after 45 min. The solvent was evapo-
rated and the residue filtered through a cotton wool plug after dis-
solving in DCM. The DCM solution was washed with water and
the product extracted. The solvent was removed; yield 83% (8 mg).
It was recrystallised from DCM/methanol; yield 10% (1 mg). The
product was a dark green/purple sticky powder. 1H NMR: δ = 9.43
(d, J = 4.8 Hz, 2 H, 3,3Ј-H), 9.41 (d, J = 4.8 Hz, 2 H, 7,7Ј-H), 9.02
(d, J = 4.8 Hz, 2 H, 8,8Ј-H), 8.86 (d, J = 4.6 Hz, 2 H, 12,12Ј-H),
8.62 (d, J = 4.8 Hz, 2 H, 2,2Ј-H), 8.50 (d, J = 4.6 Hz, 2 H, 13,13Ј-
H), 8.49 (d, J = 4.6 Hz, 2 H, 17,17Ј-H), 8.41 (d, J = 4.6 Hz, 2 H,
18,18Ј-H), 7.81 (d, J = 1.8 Hz, 4 H, o-Haryl), 7.79 (d, J = 1.8 Hz, 4
15,20-Bis(3,5-di-tert-butylphenyl)-5-[2-(trimethylsilyl)ethynyl]-10-ni-
troporphyrinatozinc(II) (21): Porphyrin 20 (107 mg, 1.29ϫ10–5 mol)
was dissolved in 10 cm3 of chloroform and stirred. To this Zn-
(OAc)2 (107 mg, 4.87ϫ10–4 mol) in 2 cm3 of methanol was added.
The mixture was refluxed at 60 °C. After 30 min the starting mate-
rial was consumed. The solution was washed with water and the
product was extracted with DCM. The solvent was evaporated and
the product was dark purple/green; yield 91 % (105 mg). It was
recrystallised from DCM/methanol yielding a few shiny purple
crystals; yield 9% (10 mg). The product was contaminated with an
unidentified porphyrin impurity. 1H NMR (CDCl3 with [D5]-
pyridine): δ = 9.77 (d, J = 4.7 Hz, 1 H, 7-H), 9.64 (d, J = 4.8 Hz,
H, o-Haryl), 7.70 (m, J = 1.8 Hz, 4 H, p-Haryl), 5.77 (br. s, 4 H, 1 H, 3-H), 9.36 (d, J = 4.7 Hz, 1 H, 8-H), 9.24 (d, J = 4.8 Hz, 1
NH2), 1.49 (s, 36 H, tBu-H), 1.48 (s, 36 H, tBu-H) ppm. IR: υ(NH2) H, 12-H), 8.94 (d, J = 4.8 Hz, 1 H, 13-H), 8.92 (d, J = 4.8 Hz, 1
3378 m, υ(CC) 2128 w cm–1, υ(NH2) 1228 m cm–1. Raman: υ(CC) H, 2-H), 8.82 (d, J = 4.8 Hz, 1 H, 18-H), 8.79 (d, J = 4.8 Hz, 1 H,
2182 s cm– 1 , υ(CC) 1370 m cm– 1 . UV/Vis: λm a x /nm (ε/
17-H), 7.98 (d, J = 1.8 Hz, 2 H, o-Haryl), 7.96 (d, J = 1.8 Hz, 2 H,
o-Haryl), 7.80 (m, J = 1.8 Hz, 2 H, p-Haryl), 1.53 (s, 18 H, tBu-H),
103 mol–1 dm3 cm–1) 424 sh (106), 444 (124), 469 sh (65.5), 554
(8.02), 705 (33.5). MS (ESI): m/z: 1561.7233 (C100H105N10Ni2 [M 1.52 (s, 18 H, tBu-H), 0.63 (s, 9 H, CH3 silyl-H) ppm. IR: υ(CC)
+ H]+ requires 1561.7231). The reaction was repeated successfully
on a 30 mg scale giving the same percentage yield.
2145 w cm–1, υ(NO2 asym) 1500 s cm–1, υ(NO2 sym) 1330 s cm–1. UV/
Vis: λmax/nm (ε/103 mol–1 dm3 cm–1) 435 (195), 565 (13.0). MS
(LSI): m/z: 890.3783 (C53H60N5NiZnO2 [M + H]+ requires
890.3808).
Azo/Butadiyne Ni Tetramer (1): Compound 18 (29 mg,
1.84 ϫ 10–5 mol) was dissolved in toluene (18.4 cm3) creating a
0.001  solution. To this copper(II) acetate (1.8 mg, 0.5 equiv.,
9.20ϫ10–6 mol) was added followed by pyridine (3 µL, 2 equiv.,
3.68ϫ10–5 mol). The solution was stirred at 80 °C for 20 h. The
solvent was removed and the residue washed with water and ex-
tracted with DCM. The solvent was removed and the residue puri-
fied by column chromatography using DCM/hexane (1:1) as eluent.
A single wine-red compound was isolated; yield 55% (16 mg). The
compound was recrystallised from DCM/methanol as dark purple
1,4-Bis[15,20-bis(3,5-di-tert-butylphenyl)-10-nitroporphyrinato-
zinc(II)-5-yl]butadiyne (22): Compound 21 (30 mg, 3.36ϫ10–5 mol)
was dissolved in pyridine (20 cm3). To this copper(II) acetate
(40 mg, 6 equiv., 2.02ϫ10–4 mol) was added and the solution was
stirred at 80 °C. The starting material was consumed after 24 h.
The solvent was removed and the residue extracted with DCM after
being washed with water (2ϫ15 cm3). The solvent was evaporated
and the residue purified by column chromatography using DCM/
hexane/pyridine (200:200:1); yield 95% (26 mg). It was recrystal-
lised from DCM/methanol; yield 58% (16 mg). The product was a
1
crystals; yield 44% (13 mg). H NMR: δ = 10.59 (d, J = 4.8 Hz, 4
H, 7,7Ј,7ЈЈ,7ЈЈЈ-H), 10.29 (d, J = 4.8 Hz, 4 H, 8,8Ј,8ЈЈ,8ЈЈЈ-H), 10.14
(d, J = 5.0 Hz, 4 H, 3,3Ј,3ЈЈ,3ЈЈЈ-H), 9.55 (d, J = 4.8 Hz, 4 H, dark purple/green powder. 1H NMR: δ = 10.05 (d, J = 4.7 Hz, 2
12,12Ј,12ЈЈ,12ЈЈЈ-H), 8.97 (d, J = 4.8 Hz, 4 H, 2,2Ј,2ЈЈ,2ЈЈЈ-H), 8.84 H, 7,7Ј-H), 9.92 (d, J = 4.5 Hz, 2 H, 3,3Ј-H), 9.48 (d, J = 4.7 Hz,
(d, J = 4.8 Hz, 4 H, 13,13Ј,13ЈЈ,13ЈЈЈ-H), 8.66 (d, J = 4.9 Hz, 4 H, 2 H, 8,8Ј-H), 9.26 (d, J = 4.8 Hz, 2 H, 12,12Ј-H), 9.06 (d, J =
18,18Ј,18ЈЈ,18ЈЈЈ-H), 8.64 (d, J = 4.9 Hz, 4 H, 17,17Ј,17ЈЈ,17ЈЈЈ-H), 4.5 Hz, 2 H, 2,2Ј-H), 8.97 (d, J = 4.8 Hz, 2 H, 13,13Ј-H), 8.85 (d,
7.91 (d, J = 1.7 Hz, 8 H o-Haryl), 7.90 (d, J = 1.7 Hz, 8 H, o-Haryl),
7.77 (d, J = 1.7 Hz, 8 H, o-Haryl), 1.53 (s, 72 H, tBu-H), 1.52 (s, 72
J = 4.6 Hz, 2 H, 17,17Ј-H), 8.82 (d, J = 4.6 Hz, 2 H, 18,18Ј-H),
8.05 (d, J = 2.0 Hz, 4 H, o-Haryl), 8.00 (d, J = 2.0 Hz, 4 H, o-Haryl),
H, tBu-H) ppm. UV/Vis: λmax/nm, (ε/103 –1 cm–1) 427 (174), 520 7.84 (t, J = 2.0 Hz, 2 H, p-Haryl), 7.82 (t, J = 2.0 Hz, 2 H, p-Haryl),
(235), 735 (76.7). Raman: υ(CC) 2178 s cm–1, υ(CC) 1350 s cm–1. 1.57 (s, 36 H, tBu-H), 1.57 (s, 36 H, tBu-H) ppm. IR: υ(CC) 2187 w
UV/Vis in toluene: λmax/nm (ε/103 mol–1 dm3 cm–1) 441 (169), 527
(268), 761 (79.0), 852 (87.2). MS (MALDI-TOF): m/z: 3114.16
(C200H201N20Ni4 [M + H]+ requires 3114.38).
cm–1, υ(NO2 asym) 1500 m cm–1, υ(NO2 sym) 1333 s cm–1. Raman:
υ(CC) 2187 s cm–1, υ(CC) 1352 m cm–1. UV/Vis: λmax/nm (ε/
103 mol–1 dm3 cm–1) 463 (141), 490 (156), 578 (19.1), 660 (40.1). MS
(MALDI-TOF): m/z: 1632.58 (C100H101N10ZnO4 [M + H]+ re-
quires 1632.65). The reaction was repeated successfully on a 60 mg
scale giving the same percentage yield.
5-Bromo-15,20-bis(3,5-di-tert-butylphenyl)-10-nitroporphyrinato-
zinc(II) (20): Compound 19 (195 mg, 2.23 ϫ10–4 mol) was dis-
solved in 10 cm3 of chloroform. To this NBS (60 mg, 1.5 equiv.,
3.35ϫ10–14 mol) and pyridine (27 µL, 1.5 equiv., 3.35ϫ10–4 mol) 1,4-Bis[10-amino-15,20-bis(3,5-di-tert-butylphenyl)porphyrinato-
were added. The solution was heated at reflux for 30 min. The sol-
vent was removed and the residue purified by column chromatog-
raphy using DCM/hexane/pyridine (100:100:1) as eluent. A single
green/purple compound was isolated; yield 85% (166 mg). It was
recrystallised from DCM/methanol; yield 74% (145 mg). The prod-
uct was a dark purple powder that was contaminated with an un-
identified porphyrin impurity. 1H NMR (CDCl3 with [D5]pyridine):
δ = 9.79 (d, J = 4.7 Hz, 1 H, 7-H), 9.67 (d, J = 4.8 Hz, 1 H, 3-H),
9.37 (d, J = 4.7 Hz, 1 H, 8-H), 9.28 (d, J = 4.9 Hz, 1 H, 12-H),
8.97 (d, J = 4.9 Hz, 1 H, 13-H), 8.93 (d, J = 4.8 Hz, 1 H, 2-H),
8.85 (d, J = 4.5 Hz, 1 H, 18-H), 8.81 (d, J = 4.5 Hz, 1 H, 17-H),
zinc(II)-5-yl]butadiyne (23): Dimer 22 (66 mg, 4.03ϫ10–5 mol) was
dissolved in DCM/methanol (25 cm3/25 cm3) that was bubbled with
argon for 10 min. Argon atmosphere was maintained and then 10%
palladium on carbon (21 mg) was added followed by addition of
sodium borohydride (9.1 mg, 6 equiv., 2.42ϫ10–5 mol). The start-
ing material was consumed after 40 min. The solvent was evapo-
rated and the residue filtered through a cotton wool plug after dis-
solving in DCM. The DCM solution was washed with water and
the product extracted. The solvent was removed yielding small pur-
1
ple crystals; yield 80% (51 mg). H NMR: δ = 9.62 (d, J = 4.6 Hz,
2 H, 7,7Ј-H), 9.61 (d, J = 4.6 Hz, 2 H, 3,3Ј-H), 9.20 (d, J = 4.6 Hz,
7.99 (br. s, 2 H, o-Haryl), 7.97 (br. s, 2 H, o-Haryl), 7.81 (br. s, 2 H, p- 2 H, 8,8Ј-H), 8.99 (d, J = 4.6 Hz, 2 H, 12,12Ј-H), 8.66 (d, J =
Haryl), 1.54 (br. s, 36 H, tBu-H) ppm. IR: υ(NO2 asym) 1515 s cm–1,
υ(NO2 sym) 1329 m cm–1. UV/Vis: λmax/nm (ε/103 mol–1 dm3 cm–1)
427 (235), 556 (17.1), 601 (7.10). MS (MALDI-TOF): m/z: 870.88
(C48H50BrN5O2Zn [M]+ requires 871.24).
4.6 Hz, 2 H, 2,2Ј-H), 8.55 (d, J = 4.6 Hz, 2 H, 13,13Ј-H), 8.54 (d,
J = 5.0 Hz, 2 H, 17,17Ј-H), 8.46 (d, J = 5.0 Hz, 2 H, 18,18Ј-H),
7.95 (t, J = 1.6 Hz, 8 H, o-Haryl), 7.74 (t, J = 1.6 Hz, 2 H, p-Haryl),
7.72 (t, J = 1.6 Hz, 2 H, p-Haryl), 6.38 (br. s, 4 H, NH2), 1.53 (s, 36
4390
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 4381–4392

A Cyclic Porphyrin Tetramer
H, tBu-H), 1.52 (s, 36 H, tBu-H) ppm. IR: υ(NH2) 3395b, υ(CC)
86% (24 mg). 1H NMR: δ = 9.79 (s, 1 H, 20-H), 9.65 (d, J = 4.6 Hz,
1 H, 3-H), 9.58 (d, J = 5.0 Hz, 1 H, 7-H), 9.19 (d, J = 4.6 Hz, 1
H, 2-H), 9.09 (d, J = 4.8 Hz, 1 H, 18-H), 8.90 (d, J = 4.8 Hz, 1 H,
17-H), 8.88 (d, J = 5.0 Hz, 1 H, 8-H), 8.80 (d, J = 4.6 Hz, 1 H, 12-
H), 8.78 (d, J = 4.6 Hz, 1 H, 13-H), 7.88 (m, J = 2.0 Hz, 4 H, o-
Haryl), 7.76 (t, J = 2.0 Hz, 2 H, p-Haryl), 1.50 (s, 36 H, tBu-H), 0.60
(s, 9 H, CH3 silyl-H) ppm. UV/Vis: λmax/nm (ε/103 mol–1 dm3 cm–1)
420 (253), 535 (16.8), 567 (9.26). MS (ESI): m/z: 839.4004,
(C53H61N4NiSi [M + H]+ requires 839.4019).
2125 w cm–1, υ(NH2) 1217 s cm–1. Raman: υ(CC) 2174 m cm–1
,
υ(CC) 1350 m cm–1. UV/Vis: λmax/nm (ε/103 mol–1 dm3 cm–1) 427
(142), 442 (96.2), 687 (16.2), 755 (22.2). MS (MALDI-TOF): m/z:
1572.59 (C100H105N10Ni2 [M + H]+ requires 1572.70).
Attempted Synthesis of Azo/Butadiyne Zn Tetramer: Compound 23
(27 mg, 1.72ϫ10–5 mol) was dissolved in toluene (17.2 cm3) creat-
ing a 0.001  solution. To this copper(II) acetate (1.7 mg,
0.5 equiv., 8.51ϫ10–6 mol) was added followed by pyridine (5.6 µL,
4 equiv., 6.88ϫ10–5 mol). The solution was stirred at 80 °C. The
starting material was consumed within 1 h. The solvent was re-
moved and the residue washed with water and extracted with
DCM. The tetramer was not formed. The main products were non-
1,4-Bis[10,15-bis(3,5-di-tert-butylphenyl)porphyrinatonickel(II)-5-yl-
]butadiyne (9): Compound 26 (20 mg, 2.38 ϫ10–5 mol) was dis-
solved in pyridine (12 cm3). To this solution, copper(II) acetate
(29 mg, 6 equiv., 1.43ϫ10–4 mol) was added and the solution was
stirred at 80 °C. The starting material was consumed after 21 h.
The reaction mixture was poured into 2  HCl (25 cm3) and ex-
tracted with DCM. The organic layer was washed with 2  HCl
(25 cm3) and water (25 cm3) before being dried with anhydrous po-
tassium carbonate. The organic layer was decanted and the solvent
evaporated; yield 93% (17 mg). It was recrystallised from DCM/
methanol; yield 76% (14 mg). The product was a dark green pow-
1
porphyrinic compounds as shown by H NMR spectroscopy.
5-Bromo-10,15-bis(3,5-di-tert-butylphenyl)porphyrin (24): Porphyrin
10 (58 mg, 8.44ϫ10–5 mol) was dissolved in 10 cm3 of chloroform
and stirred in an ice bath. To this pyridine (68 µL, 8.44ϫ10–4 mol)
was added followed by NBS (15 mg, 1 equiv., 8.44ϫ10–5 mol). Af-
ter 30 min the reaction was stopped and solvent removed. Product
was purified by column chromatography using DCM/hexane/TEA
(200:200:1) as eluent. Three red fractions were collected. The first
was the dibrominated porphyrin; yield 15%. The second was the
target compound; yield 80%. The third was starting material; yield
5%. The target compound was recrystallised from DCM/methanol.
The product was a red/purple powder; yield 78 % (51 mg). 1H
NMR: δ = 10.12 (s, 1 H, 20-H), 9.77 (d, J = 4.9 Hz, 1 H, 3-H),
9.70 (d, J = 4.9 Hz, 1 H, 7-H), 9.37 (d, J = 4.9 Hz, 1 H, 2-H), 9.31
(d, J = 4.5 Hz, 1 H, 18-H), 9.05 (d, J = 4.5 Hz, 1 H, 17-H), 8.99
(d, J = 4.9 Hz, 1 H, 8-H), 8.94 (d, J = 4.8 Hz, 1 H, 13-H), 8.91 (d,
J = 4.8 Hz, 1 H, 12-H), 8.09 (d, J = 2.0 Hz, 2 H, o-Haryl), 8.08 (d,
J = 2.0 Hz, 2 H, o-Haryl), 7.85 (m, J = 2.0 Hz, 2 H, p-Haryl), 1.57
(s, 18 H, tBu-H), 1.56 (s, 18 H, tBu-H), –2.91 (br. s, 2 H, inner
NH) ppm. UV/Vis: λmax/nm (ε/103 mol–1 dm3 cm–1) 416 (406), 513
(17.1), 547 (8.03), 587 (5.26), 643 (3.80). MS (LSI): m/z: 764.3487
(C48H53BrN4 [M]+ requires 764.3454).
1
der. H NMR: δ = 9.89 (d, J = 4.8 Hz, 2 H, 3,3Ј-H), 9.83 (s, 2 H,
20,20Ј-H), 9.82 (d, J = 4.8 Hz, 2 H, 7,7Ј-H), 9.29 (d, J = 4.8 Hz, 2
H, 2,2Ј-H), 9.11 (d, J = 4.8 Hz, 2 H, 18,18Ј-H), 9.00 (d, J = 4.8 Hz,
2 H, 8,8Ј-H), 8.92 (d, J = 4.8 Hz, 2 H, 17,17Ј-H), 8.82 (d, J =
5.1 Hz, 2 H, 12,12Ј-H), 8.80 (d, J = 5.1 Hz, 2 H, 13,13Ј-H), 7.93
(d, J = 2.0 Hz, 4 H, o-Haryl), 7.90 (d, J = 2.0 Hz, 4 H, o-Haryl),
7.78 (t, J = 2.0 Hz, 2 H, p-Haryl), 7.76 (t, J = 2.0 Hz, 2 H, p-Haryl),
1.53 (s, 36 H, tBu-H), 1.51 (s, 36 H, tBu-H) ppm. Raman: υ(CC)
2194 s cm– 1 , υ( CC ) 1 36 8 s cm– 1 . U V/ Vi s: λm a x /nm ( ε/
103 mol–1 dm3 cm–1) 425 (136), 444 (143), 467 (157), 545 (24.1), 619
(42.8). MS (ESI): m/z: 1531.7058, (C100H103N8Ni2 [M + H]+ re-
quires 1531.7013).
Supporting Information (see also the footnote on the first page of
1
this article): H NMR spectra of all new compounds (Figures S1–
S15).
5-Bromo-10,15-bis(3,5-di-tert-butylphenyl)porphyrinatonickel(II)
(25): Porphyrin 24 (50 mg, 6.52ϫ10–5 mol) was dissolved in 10 cm3
of toluene and stirred. To this Ni(acac)2 (50 mg, 1.95ϫ10–4 mol)
was added. The mixture was refluxed for 2 h after which the start-
ing material was consumed. The product was purified by column
chromatography using DCM/hexane (1:1) as eluent. A single red
fraction was collected. The solvent was evaporated and the product
was recrystallised from DCM/methanol to give red/purple crystals;
Acknowledgments
We thank the Australian Research Council for financial support
through Discovery Grant DP0663774 and Prof. K.-i. Sugiura for
collaboration on the corner porphyrin synthesis. B. B. thanks the
Queensland University of Technology for post-graduate scholar-
ships.
1
yield 100% (53 mg). H NMR: δ = 9.74 (s, 1 H, 20-H), 9.65 (d, J
= 4.8 Hz, 1 H, 3-H), 9.58 (d, J = 5.0 Hz, 1 H, 7-H), 9.18 (d, J =
4.8 Hz, 1 H, 2-H), 9.10 (d, J = 4.6 Hz, 1 H, 18-H), 8.91 (d, J =
4.6 Hz, 1 H, 17-H), 8.88 (d, J = 5.0 Hz, 1 H, 8-H), 8.82 (d, J =
4.9 Hz, 1 H, 13-H), 8.80 (d, J = 4.9 Hz, 1 H, 12-H), 7.88 (d, J =
2.0 Hz, 2 H, o-Haryl), 7.86 (d, J = 2.0 Hz, 2 H, o-Haryl), 7.75 (t, J
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Received: March 22, 2010
Published Online: May 27, 2010
4392
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