Making conjugated connections to porphyrins: A comparison of alkyne, alkene, imine and azo links

Article abstract of DOI:10.1039/b109915a

A series of porphyrins 5-9 has been prepared, in which an aryl substituent is linked to the porphyrin via azo, imine, alkene and alkyne bridges. The strength of aryl-porphyrin electronic coupling in these systems was evaluated from the red shift and intensification of the Q band absorption and emission spectra, and from the incremental red shift on changing from the phenyl to a 4-nitrophenyl substituent. The azo link provides the strongest electronic communication between the porphyrin and the benzene ring. The crystal structures of azo compounds 5a and 5c show that the porphyrin and benzene rings are almost coplanar, whereas imine 7a and alkene 8a are significantly twisted in the solid state. Imine and alkyne linked porphyrin dimers 18 and 23 were also synthesized; the alkyne-linked dimer is much more conjugated than its imine-linked analogue.

Full text of DOI:10.1039/b109915a

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Making conjugated connections to porphyrins: a comparison of
alkyne, alkene, imine and azo links
Thomas E. O. Screen,a Iain M. Blake,a Leigh H. Rees,b William Clegg,c Simon J. Borwickb
and Harry L. Anderson*a
1
a Department of Chemistry, University of Oxford, Dyson Perrins Laboratory,
South Parks Road, Oxford, UK OX1 3QY. E-mail: harry.anderson@chem.ox.ac.uk
b Department of Chemistry, University of Oxford, Chemical Crystallography Laboratory,
9 Parks Road, Oxford, UK OX1 3PD
c Department of Chemistry, University of Newcastle, Newcastle upon Tyne, UK NE1 7RU
Received (in Cambridge, UK) 30th October 2001, Accepted 12th December 2001
First published as an Advance Article on the web 10th January 2002
A series of porphyrins 5–9 has been prepared, in which an aryl substituent is linked to the porphyrin via azo,
imine, alkene and alkyne bridges. The strength of aryl–porphyrin electronic coupling in these systems was evaluated
from the red shift and intensification of the Q band absorption and emission spectra, and from the incremental
red shift on changing from the phenyl to a 4-nitrophenyl substituent. The azo link provides the strongest electronic
communication between the porphyrin and the benzene ring. The crystal structures of azo compounds 5a and 5c
show that the porphyrin and benzene rings are almost coplanar, whereas imine 7a and alkene 8a are significantly
twisted in the solid state. Imine and alkyne linked porphyrin dimers 18 and 23 were also synthesized; the alkyne-
linked dimer is much more conjugated than its imine-linked analogue.
example stilbene 2 exhibits more red-shifted absorption
Introduction
maxima and larger 2nd and 3rd order NLO coefficients than its
Porphyrin-based electronic materials continue to attract atten-
tolan (diphenylacetylene) analogue 3.14 This is attributed to
tion because of their unusual electro-optical and nonlinear
poor sp1–sp2 π-overlap, due to the energy mismatch between the
optical (NLO) behaviour.1 Work by several research teams has
p-orbitals on sp1 and sp2 carbon atoms.15 Alkyne-links achieve
led to the conclusion that acetylenic meso-substituents provide
the most efficient way of making conjugated connections to
higher conjugation in porphyrin-based materials because they
allow planar π-overlap whereas aryl or alkene-links twist out of
porphyrin π-systems. For example, Therien and coworkers
conjugation, due to steric interactions with the β-pyrrole sub-
have shown that donor–acceptor aryl-ethynyl porphyrins such
stituents. Changing the atom attached at the porphyrin meso
position to nitrogen should also remove this steric clash. An azo
substituent is iso-electronic with an alkene, and almost as slim
as an alkyne, which suggests that it may be interesting to
as 1 have much higher second order NLO coefficients than
analogous meso-aryl porphyrins,2,3 while we have shown that
the strong inter-porphyrin conjugation in butadiyne-linked
porphyrin oligomers results in exceptional third order NLO
explore the chemistry of meso azo-linked porphyrins. Azo-
behaviour.4,5 meso-Tetraalkynylporphyrins are also remarkable
linked porphyrins such as 4 have also been predicted to have
for their sharp red-shifted absorption spectra6–9 and strong
strong NLO behaviour,16 but the synthesis of compounds of
optical limiting in the visible region.10
this type has not been reported.
Imines are generally easier to prepare than azo compounds,
and an imine link might be expected to have properties inter-
mediate between an azo and an alkene. However it has long
been known that whereas E-stilbenes and E-azobenzenes are
The pre-eminence of alkyne links in this area contrasts
with the emerging design principles in the wider field of con-
jugated organic materials, where alkene links generally provide
stronger electronic communication than alkynes.11–13 For
roughly planar, E-benzalanilines (Ar–N᎐CH–Ph) are twisted.
The N-aryl ring is at an angle of about 50Њ to the plane of the
᎐
N᎐CH–Ph group, as revealed in the solid state by X-ray crystal-
᎐
lography,17 in the gas phase by electron diffraction18 and in
320
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b109915a

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t
᎐
Scheme 1 Ar = 3,5-Bu 2C6H3; a: Y = H; b: Y = NO2; c: Y = C᎐CSiMe3.
᎐
solution by CNDO/S CI (complete neglect of differential over-
Results and discussion
lap configuration interaction) simulation of UV spectra.19 This
nonplanarity results in weaker conjugation in imine-linked
systems.20 We set out to explore this effect in meso imine-linked
porphyrins.
Synthesis
Porphyrin azo dyes 5a–c were prepared by treating zinc por-
phyrin 10 with aryldiazonium tetrafluoroborates 11a–c22 in
THF at room temperature (Scheme 1). The reaction is fastest
with the most electrophilic 4-nitrophenyl diazonium salt 11b.
The dioxo-porphyrin 12 was also isolated as a by-product from
all three reactions, while the desired product was isolated in
23–27% yield. No disubstituted products were formed, even
when using a large excess of the diazonium salt, due to the
strongly electron-withdrawing effect of the azo substituent.
Many types of aromatic electrophilic substitution have been
reported with porphyrins,23 but as far as we are aware there have
been no previous reports of azo coupling. An alternative route
to porphyrin azo dyes would be to react a porphyrin diazonium
salt with an electron-rich aromatic unit. There is only one pre-
vious report of the synthesis of a porphyrin meso-diazonium
salt, and this was used for Sandmeyer halogenation rather than
azo-coupling.24 We prepared a meso-aminoporphyrin 13 via
nitration of 10 (Scheme 1) but all attempts at making the
diazonium salt from this, and its subsequent reaction with
porphyrin 10 to give dimer 14, were unsuccessful.
Here we present a survey of meso-substituted porphyrins
with alkyne, alkene, imine and azo links. To the best of our
knowledge, this is the first synthesis of meso-azo-arylpor-
phyrins such as 5a–c. There is only one previous report21 of
meso-imine-arylporphyrins such as 6a,b and 7a,b, and these
previous imines had β-pyrrolic alkyl substituents, making
them much less conjugated. We have also prepared meso-
ethene-arylporphyrins 8a,b and meso-ethynyl-arylporphyrins
9a,b for comparison. Here we also compare the properties of
imine-linked and acetylene-linked porphyrin dimers.
Imine linked porphyrin-aryl compounds 6a and 6b were
prepared in 68% and 49% yields by condensing aminopor-
phyrin 13 with benzaldehydes 15a and 15b (Scheme 1). Com-
pound 13 was refluxed over 4 Å molecular sieves in the presence
of an excess of benzaldehyde and Amberlyst 15 macroreticular
ion-exchange resin as catalyst. With 6b, difficult removal of
excess unreacted 4-nitrobenzaldehyde reduced the yield. For the
isomeric imines 7a and 7b, formylporphyrin 16 was prepared
via Vilsmeier formylation of 10, then reaction with anilines 17a
and 17b to give 7a and 7b in 78% and 85% yields (Scheme 2).
Imine linked porphyrin dimer 18 was prepared under analogous
conditions from formylporphyrin 16 and aminoporphyrin 13.
The strength of porphyrin–aryl conjugation was assessed
by comparing the absorption and emission spectra of these
compounds, and by crystallographic and computational
analysis of their geometries.
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329
321

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Scheme 2 Ar = 3,5-But2C6H3; a: Y = H; b: Y = NO2.
Scheme 3 Ar = 3,5-But2C6H3; a: Y = H; b: Y = NO2.
This gave 18 in 32% yield. The disappointing yield of dimer
may be due to degradation of the aminoporphyrin during the
long reaction time.
The ethene linked meso-arylporphyrins 8a and 8b were
formed by Wittig reaction between 16 and phosphonium salts
A porphyrin–aryl connection which provides efficient electronic
communication will lead to a large change of the porphyrin
electronic spectra due to conjugation into the benzene ring.
Selected absorption spectra are shown in Fig. 1. Conjugation
between the porphyrin and the aryl substituent is manifested in
three ways: (i) change in positions of absorption and emission
maxima relative to unsubstituted porphyrin 10; (ii) change in
positions of absorption maxima on incorporation of the nitro
group; (iii) change in the oscillator strength of absorptions,
since the addition of conjugated connections to the meso
positions of porphyrins generally intensifies the Q band by
increasing the a1u/a2u orbital separation.1c
(i) Both the Q and B bands of all the porphyrin derivatives
show a large red shift relative to the core porphyrin 10. Azo
compounds 5a–c display by far the largest shifts, and in 5b
the Soret band is widely split (Fig. 1a), indicating strong
conjugation with the aryl substituent and suggesting this link
provides the best electronic overlap. There is little difference
between the absorption spectra of compounds 6–9. In general,
the red shift increases in the order: alkene 8 < imine 6 ≈ imine
7 < acetylene 9 < azo 5, a trend which may be explained by
decreasing steric bulk of the porphyrin-to-benzene bridge.
(ii) The para-nitro group gives an additional red shift in all
cases. The magnitude of this change should give an indication
of the extent of communication between the porphyrin and the
19a and 19b (Scheme 2). meso CH᎐CH–Ar porphyrins have
᎐
previously been prepared as intermediates to ethane linked
photosynthetic models by Nishitani et al.,25 and in low yield
from pyrrole and cinnamaldehyde by Czuchajowski et al.,26
but neither investigation addressed the extent of conjugation
across the ethene link. meso-Ethynylporphyrins 9a and 9b
were prepared using Heck–Sonogashira coupling between
meso-bromoporphyrin 20 and the arylacetylenes 21a and
21b (Scheme 3).27 Acetylene linked porphyrin dimer 23 was
synthesised via coupling of trimethylsilylacetylene to 20,
deprotection and a second Pd-catalysed reaction of this with
another equivalent of 20 (Scheme 3). Dimer 23 was isolated in
70% yield. Therien and coworkers have previously reported the
synthesis of the phenyl (rather than the 3,5-di-tert-butylphenyl)
analogue of this dimer.28
Electronic absorption and emission spectra
The electronic spectra of compounds 5–10 are summarised in
Table 1. Data for porphyrin dimers 18 and 23 are also included.
322
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329

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Table 1 Summary of electronic spectra and torsional parameters for porphyrins 5–10, 18 and 23a
Compound
–X1X2–
–Y
λmaxB/nm
λmaxQ/nm
fB
fQ
λem/nm
Φf
θAB/Њ
θBC/Њ
θAC/Њ
5a
5b
5c
6a
6b
7a
7b
8a
8b
9a
9b
10
18
23
N᎐N
H
457
415, 485
469
432
425
438
447
435
434
439
452
418
427, 443
415, 481
655
692
672
616
642
623
634
614
628
623
637
586
663
710
1.74
1.71
1.52
0.98
1.39
1.34
0.98
1.27
1.36
1.33
2.16
1.22
1.18
1.62
0.20
0.31
0.22
0.11
0.12
0.11
0.13
0.11
0.09
0.12
0.24
0.06
0.15
0.25
640
645
638
627
665
640
664
628
0.001
0.0004
0.0009
0.004
0.002
0.015
0.022
0.101
0.003
0.175
0.017
0.100
0.004
0.070
9.7 (0.3)
(0.4)
5.9 (0.2)
(0.2)
5.0 (0.1)
(7.4)
(10.9)
24.7 (1.4)
(0.8)
14.7 (20.2)
(19.6)
—
—
—
(52.9)
—
4.6 (0.5)
(0.6)
22.2 (0.4)
(29.4)
(29.4)
60.7 (39.0)
(39.6)
44.7 (37.9)
(38.5)
(<0.1)
(<0.1)
—
(36.1)
(0.4)
᎐
N᎐N
NO2
᎐
᎐
N᎐N
C᎐CTMS
26.1 (0.3)
(22.1)
(19.0)
36.3 (40.2)
(40.1)
41.6 (57.8)
(57.8)
—
—
—
(16.8)
—
᎐
᎐
N᎐CH
H
᎐
N᎐CH
NO2
H
NO2
H
NO2
H
NO2
—
᎐
CH᎐N
᎐
CH᎐N
᎐
CH᎐CH
᎐
CH᎐CH
650
᎐
C᎐C
C᎐C
᎐
627, 681
628, 682
594, 646
624
᎐
᎐
᎐
H
N᎐CH
—
—
᎐
᎐
C᎐C
730
᎐
a λmaxB, λmaxQ, fB, fQ, λem and Φf are the absorption maxima, oscillator strengths, emission maxima and fluorescence quantum yield in CH2Cl2–1%
pyridine. λmaxB, λmaxQ, fB and fQ refer to the porphyrin B and Q bands; in cases with several Q band maxima, the longest wavelength peak is listed here.
Oscillator strengths in dimers 18 and 23 are per porphyrin macrocycle. θAB, θBC and θAC are the interplane angles as defined in Fig. 2 from X-ray
crystallographic analysis (and from MM2 molecular mechanics calculations).
aryl substituent. Replacement of a hydrogen by a nitro group in
the azo-linked system gives the largest Q band shift of 37 nm,
comparing 5a and 5b (Fig. 1a and Table 1), which is about twice
that for compounds 6–9, reinforcing our conclusion that
the azo link provides exceptionally efficient conjugation. The
presence of a nitro group, or a nitrogen in the link, leads to a
large reduction in fluorescence quantum yield ΦF, the only
exceptions being imines 7a and 7b, where the nitro compound is
more fluorescent. Perhaps here the addition of the nitro group
favours interaction of the imine nitrogen with the benzene ring,
reducing electronic communication with, and quenching of, the
porphyrin.
(iii) The increase in the Q band oscillator strength fQ relative
to that of 10 indicates the effectiveness of conjugation between
the porphyrin and benzene.† Again, an increase in oscillator
strength on addition of the para-nitro group would also testify
to good electronic communication across the conjugated
system. There is a general increase in Soret and Q-band
oscillator strengths relative to unsubstituted porphyrin 10
(Table 1). The effect is largest in para-nitro phenylacetylene 9b
and azo compounds 5a–c. The intensification of the Q-band in
the azo compounds again reveals the strong conjugation
between porphyrin and benzene ring.
assessed by X-ray crystallography and by molecular mechanics
modelling using the MM2 force field. Crystallographic data for
5a, 5c, 7a and 8a are summarised in Table 2. We were unable to
grow satisfactory crystals of the remaining compounds.
The planarity was evaluated by measuring angles between
the mean planes of the porphyrin core and C–X–X–C bridge,
θAB and between the planes of the C–X–X–C link and the
benzene ring, θBC, as illustrated in Fig. 2. In addition, the angle
between the porphyrin ring and benzene ring, θAC, was also
measured. Note that θAC is not always the sum or difference of
θAB
θBC, because these are dihedral angles between least-
squares planes; although the major contribution to θAB and θBC
is torsion about the bond between pairs of rings, other minor
tilting factors are also included. These torsional parameters are
listed in Table 1, from X-ray crystallography, where available,
and from molecular mechanics.
The acetylene linked systems are calculated to be essentially
planar (θAC = 0), but the barrier to rotation is probably small.
The crystal structures of several meso-arylethynylporphyrins
have been reported.7,29–31 These structures have θAC values in the
range 3.5–60Њ (mean 30.4Њ for all 9 observations), showing that
the electronic preference for planarity is easily compromised by
crystal packing interactions.
The absorption spectra of porphyrin dimers 18 and 23 are
compared with those of their monomer analogues in Fig. 1b
and 1c respectively. The acetylene linked dimer 23 shows a large
red-shift, intensification of the Q band oscillator strength and
a splitting of the Soret compared to meso-phenylethynyl
porphyrin 9a (Fig. 1c), which indicates that there is strong
conjugation between the porphyrin rings. Imine dimer 18 has
an absorption spectrum which is similar to the meso-aryl imine
porphyrins 6a and 7a (Fig. 1b). This can be explained by the
twisting of the N-porphyrin ring in a similar manner to that
seen in N-benzalanilines, limiting the conjugation between the
porphyrins. However, as for 6b, the long tail to the absorption
to longer wavelengths, and the increase in Q band oscillator
strength, suggest that some of the dimer exists in a planar more
conjugated conformation.
The calculated structures of all three azo compounds also
show very small deviations from planarity of less than 0.5Њ. The
X-ray structure of azo compound 5a (Fig. 3) shows an almost
planar geometry across the azo bond (θAB = 9.7Њ; θBC = 5.9Њ),
whereas that of 5c is more twisted (θAB = 26.1Њ; θBC = 5.0Њ).
These values are significantly larger than those predicted by
our modelling, but agree well with values of 5–15Њ found for
E-azobenzene.32 The planarity of these azoporphyrins is
consistent with a high degree of conjugation.
For alkene linked porphyrin 8a, modelling predicts θAB
=
57.8Њ and θBC = 20.2Њ. The X-ray structure of 8a (Fig. 3)
indicates that molecular mechanics exaggerates the distortion,
as in the crystal θAB = 41.6Њ and θBC = 14.7Њ. The shortest H–H
contacts (Fig. 4) are HA–HB (2.32 Å) and HB–C (2.15 Å); both
these contacts are close to the sum of the van der Waals
radii‡ so are likely to contribute towards the nonplanarity. The
other H–H distances HD–HE (2.73 Å) and HE–HF (2.44 Å) are
significantly longer.
Our molecular mechanics calculations gave least realistic
geometries for the imines, where electronic effects due to the
interaction of the imine nitrogen with the aromatic system are
important, as well as steric effects. MM2 calculations predict
imines 7a,b to have θAB = 40.1Њ and θBC ≈ 0, which seems
Crystal structures and molecular mechanics calculations
Electronic conjugation requires efficient orbital overlap, and
is maximised if the π-system is planar. The planarity of the
meso-arylporphyrins 5–9 and porphyrin dimers 18 and 23 was
† Oscillator strength, f, was calculated using the equation:
f = 4.319 × 10Ϫ9 A/n
where A is the integrated absorption band (plotted as ε / cmϪ1), and n
is the solvent refractive index (1.42 for CH2Cl2).
‡ Using van der Waals radii of H = 1.10 Å, C = 1.77 Å, N = 1.64 Å from
Ref. 44.
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329
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Fig. 3 X-Ray structure of 5a and the pyridine complexes of 5c, 7a and
8a (50% probability ellipsoids, H atoms and solvent molecules omitted
for clarity).
Fig. 1 Absorption spectra in CH2Cl2–1% pyridine of a) 5a (plain), 5b
(bold) and 10 (dashed); b) 6a (plain), 7a (dashed) and 18 (bold); c) 9a
(plain) and 23 (bold).
Fig. 4 Short intramolecular H–H contacts in porphyrins 6–9.
HB (2.23 Å) and HB–HC (2.07 Å), which are again within van
der Waals contact. The HB–HC distance in imine 7a is shorter
than that in alkene 8a, despite the greater θBC in the imine, due
to the shorter length of the C᎐N bond (1.25 Å) in 7a compared
᎐
with the C᎐C bond (1.34 Å) in 8a. This short C᎐N bond
᎐
᎐
increases the steric congestion and nonplanarity. The discrep-
ancy between predicted and observed structures casts doubt on
the calculated geometry of imines 6a, 6b and 18, although the
nonplanarity of these systems is not necessarily the same in the
solid state (as determined experimentally by crystallography) as
in isolated molecules (as deduced from molecular mechanics
calculations), because intermolecular interactions are ignored
in the calculations and may have a significant effect in the solid
state.
Fig. 2 Definition of torsional angles θAB and θBC
.
unlikely given the large distortions of the N-phenyl ring in benz-
alanilines. The X-ray structure of 7a (Fig. 3) shows θAB = 36.3Њ
and θBC = 24.7Њ. As in 8a, the shortest H–H distances are HA–
324
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Table 2 Crystallographic data for compounds 5a, 5c, 7a and 8a§
5a
5c
7a
8a
Formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
C54H56N6Znؒ0.75C5H12
908.53
C59H64N6SiZnؒC5H5NؒC5H12 C55H57N5Znؒ1.5C5H5Nؒ0.5C5H12 C56H58N4ZnؒC5H5NؒCHCl3
1101.91
Triclinic
P1
13.3930(7)
13.4790(5)
17.9480(9)
95.685(3)
95.402(2)
104.110(3)
3103.3
1008.15
Orthorhombic
P212121
15.0697(8)
19.5369(10)
20.9405(11)
90
90
90
6165.2(6)
4
1050.97
Monoclinic
P21/c
15.839(3)
19.805(5)
18.687(4)
90
111.46(1)
90
5455.6(5)
4
Triclinic
¯
¯
P1
12.780(8)
14.281(7)
14.546(8)
97.162(6)
97.805(6)
103.870(6)
2519.2(2)
2
α/deg
β/deg
γ/deg
V/Å3
Z
2
T /K
150
150
23098
150
39754
150
24767
Reflections measured 9336
Unique reflections
R1
Rw2
9336 (Rint = 0.00)
0.0870
0.2092
11907 (Rmerge = 0.048)
16470 (Rint = 0.05)
11180 (Rint = 0.03)
0.0592
0.0869
0.0579
0.0659
0.2115
0.0692
The calculated structure for imine dimer 18 has twists
between the imine bond atoms and the N-porphyrin ring, θAB
and the C-porphyrin ring, θBC, of 16.8Њ and 52.9Њ respectively.
With an even greater value of θAB expected in the actual
structure, it is not surprising that the absorption spectrum of 18
shows only weak conjugation.
obtained on a VG Autospec from a 3-nitrobenzyl alcohol
matrix in Oxford or by the EPSRC service at Swansea.
MALDI-TOF mass spectra were recorded on a Micromass Tof
Spec 2E mass spectrometer from anthracene-1,8,9-triol matrix.
Only molecular ions and major peaks are reported. IR spectra
were recorded in KBr discs using a Perkin Elmer Paragon 1000
spectrophotometer. None of the solids reported here melt
below 350 ЊC. Molecular modelling calculations were run on
Oxford Molecular Cache software version 4.1, and minimised
using molecular mechanics employing a conjugate gradient
optimisation method with the augmented MM2 force field to a
convergence of 1 × 10Ϫ5 kcal molϪ1.
Aryldiazonium tetrafluoroborates 11a–c were prepared
according to the general procedure of Doyle and Bryker.22 5,15-
Bis(3Ј,5Ј-di-tert-butylphenyl)porphyrin (H210) was prepared
using the method for synthesising the bis-phenyl analogue
reported by Therien and co-workers.34 [5,15-Bis(3Ј,5Ј-di-tert-
butylphenyl)porphyrinato]copper() (Cu10), [5,15-bis(3Ј,5Ј-di-
tert-butylphenyl)-10-(formyl)porphyrinato]copper() (Cu16),
[5,15-bis(3Ј,5Ј-di-tert-butylphenyl)-10-(formyl)porphyrin]
(H216) and [5,15-bis(3Ј,5Ј-di-tert-butylphenyl)-10-(formyl)-
porphyrinato]zinc() (16) were prepared according to the route
reported by Susumu et al.35 4-Trimethylsilylethynylphenyl-
diazonium tetrafluoroborate 11c was kindly provided by
Dr Sally Anderson.36
,
Conclusions
Analysis of the electronic spectra of porphyrin–aryl com-
pounds 5–9 shows that the azo-link allows most efficient
π-overlap between the porphyrin and the aryl moiety. This is
manifested by strong red shifts in the absorption bands relative
to the other porphyrins, a large increase in oscillator strength of
the Q band and a further red shift and intensification of the Q
band on addition of a nitro group comparing compounds
5a and 5b. The X-ray crystal structure of azo compounds 5a
and 5c show that the azo link is almost coplanar with the
porphyrin macrocycle, supporting the spectral evidence for
strong electronic communication.
Alkene and imine links do not provide as good conjugation
as the azo bridge. The crystal structures of imine linked por-
phyrin 7a and alkene linked 8a both show a large twist across
the bridging unit, explaining the reduced conjugation observed
for these compounds. For 8a this can be explained on steric
grounds and the structure is predicted with reasonable accuracy
by a simple molecular mechanics model. However, additional
distortions are found in imine 7a, perhaps due to interactions
between the nitrogen lone pair and the adjacent benzene ring
which are not adequately reproduced by the MM2 force field.
Acetylene linked porphyrin dimer 23 shows strong com-
munication between the porphyrin rings. The nonplanarity
expected in imine linked porphyrin dimer 18, due to steric and
electronic factors, is evident in its absorption spectrum, which
shows very limited conjugation. The results reported here
indicate that azo-linked porphyrin oligomers such as 14 should
be even more conjugated than their alkyne-linked analogues,
but viable routes to these azo-linked systems have yet to be
discovered.
X-Ray crystallographic data collection and processing§
Crystals of 5a were grown by vapour diffusion of pentane into
a solution of the porphyrin in CHCl3. Crystals of 5c were
grown by vapour diffusion of pentanes into a solution of the
porphyrin in CH2Cl2 containing pyridine. Crystals of 8a were
grown by vapour diffusion of methanol into a solution of the
porphyrin in CHCl3 containing pyridine. Data for 5a, 5c and
8a were collected using an Enraf-Nonius DIP2000 Image
Plate Diffractometer with graphite monochromated Mo-Kα
radiation (λ = 0.7107 Å). Structure 5a was solved using the
program SIR-9237 and refined using full-matrix least-squares
on all F0 data [SHELXL-93].38 Structure 5c was solved using
2
SIR-92 on all 11907 reflections with I > 5σ(I ), but refined (by
full matrix least squares against F [CRYSTALS]39 using only
6181 reflections with I > 7σ(I ). This gave more than 10 observ-
ations per variable and compensated for the unrealistically
low estimate of σ produced by the DIP2000 diffractometer.
Structure 8a was solved using SIR-92 and refined using
full-matrix least-squares on all F data [CRYSTALS]. All
non-hydrogen atoms were refined anisotropically and hydrogen
Experimental
UV measurements were carried out using a Perkin Elmer
Lambda 14P spectrophotometer. Fluorescence measurements
were carried out on a Fluoro-Max 2 spectrofluorimeter, and
fluorescence quantum yields were measured relative to tetra-
phenylporphyrin in benzene (ΦF = 0.11).33 1H and 13C NMR
spectra were obtained using Bruker AM-200, 400 or 500 MHz
instruments using deacidified deuterochloroform; coupling
constants J are quoted in Hertz. FAB mass spectra were
§ CCDC reference numbers 173279–173282 for 5a, 5c, 7a and 8a
respectively. See http://www.rsc.org/suppdata/p1/b1/b109915a/ for crys-
tallographic files in .cif or other electronic format.
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329
325

View Article Online
atoms were included in calculated positions with isotropic
displacement parameters. Crystals of 5a were found to contain
one pentane molecule per porphyrin, disordered over two
positions, with a total occupancy of 75%. 5c crystallised with
one pyridine coordinated to the porphyrin and one disordered
pentane molecule. 8a crystallised with one coordinated pyridine
and one chloroform molecule in the asymmetric unit.
in methanol (100 cm3) and the reaction stirred at room temper-
ature for 2 h. After this time, the mixture was passed through a
short silica plug and the solvents removed. The residue was
chromatographed on silica eluting with CH2Cl2–60–80 petrol-
eum ether (1 : 1) and crystallised from chloroform by layered
addition of 30–40 petroleum ether to yield the pure product as
green crystals (52 mg, 27%). λmax(CH2Cl2)/nm 418 (log ε 4.98),
463 (5.20), 646 (4.58); δH(500 MHz; CDCl3, d5-pyridine) 10.16
(1 H, s, meso H ), 9.90 (2 H, d, J 4.7, βH), 9.33 (2 H, d, J 4.5,
βH), 9.15 (2 H, d, J 4.7, βH), 9.08 (2 H, d, J 4.5, βH), 8.41 (2 H,
d, J 8.3, p-NO2 phenyl H ), 8.15 (4 H, d, J 1.7, But aryl H), 7.89
(2 H, t, J 1.7, But aryl H), 7.86 (2 H, d, J 8.3, p-NO2 phenyl H ),
1.62 (36 H, s, But H ), 0.39 (9 H, s, TMS); δC(125 MHz; CDCl3,
d5-pyridine) 153.9, 151.5, 150.4, 149.5, 149.0, 147.1, 141.6,
134.0, 133.3, 132.9, 132.2, 130.6, 130.0, 129.6, 125.5, 124.5,
123.0, 121.3, 108.9, 105.3, 97.3, 35.3, 32.0, 0.3; m/z (FAB) 951
(Mϩ, C59H64N6SiZn requires 950.7).
Crystals of 7a were grown by vapour diffusion of pentane
into a solution of the porphyrin in CHCl3 containing pyridine.
Data were collected using a Bruker SMART 1K CCD diffract-
ometer using synchrotron X-rays (λ = 0.6883 Å) at Daresbury
SRS Station 9.8, solved by direct methods and refined using
2
full-matrix least-squares on all F0 data [SHELXTL].40 The
crystals contained one pyridine coordinated to the zinc and one
disordered pyridine at 50% occupancy, as well as a disordered
pentane at 50% occupancy. The coordinated pyridine and
the imine bridge are both two-fold disordered, and were
successfully resolved and modelled.
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(nitro)porphyrinato]-
zinc(II)
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-phenylazoporphyrinato]-
zinc(II) 5a
The most successful conditions for meso-mononitration were
similar to those reported by Cowan and Sanders.41 Free base
porphyrin H210 (0.607 g, 0.88 mmol) was added to a vigorously
stirred mixture of conc. HNO3 (60 cm3) and acetic acid (60 cm3)
at 0 ЊC. The mixture was stirred for 7 h, maintaining the tem-
perature at 0–4 ЊC, after which time the reaction mixture was
poured into iced water. The porphyrin product was extracted
with CH2Cl2, washed with water, and the organic layer evapor-
ated to dryness to give crude 5,15-bis(3Ј,5Ј-di-tert-butylphenyl)-
10-(nitro)porphyrin. λmax(CH2Cl2)/nm 416 (log ε 5.56), 514
(4.36), 552 (3.91), 585 (3.96), 642 (3.62); νmax(KBr)/cmϪ1 1525
(NO2), 1363 (NO2); δH(250 MHz; CDCl3) 10.37 (1 H, s, meso
H ), 9.40 (2 H, d, J 4.7, βH), 9.37 (2 H, d, J 5.0, βH), 9.13 (2 H,
d, J 5.0, βH), 9.08 (2 H, d, J 4.7, βH), 8.12 (2 H, d, J 1.8, aryl
H ), 7.90 (2 H, t, J 1.8, aryl H ), 1.60 (36 H, s, But H ), Ϫ2.84
(2 H, s, NH ); m/z (MALDI-TOF) 732.1 (Mϩ, C48H53N5O2
requires 731.97).
All the product from the nitration was dissolved in CHCl3
(100 cm3) and Zn(OAc)2ؒ2H2O (0.970 g, 4.42 mmol) in meth-
anol (10 cm3) was added. The solution was stirred at room
temperature for 30 min. The reaction mixture was passed
through a silica plug to remove excess zinc residues, then
purified by column chromatography (silica, 12 : 1 : 0.5 60–80
petroleum ether–EtOAc–pyridine). The product was eluted as a
dark purple solution and recrystallised from CHCl3–methanol
to yield [5,15-bis(3Ј,5Ј-di-tert-butylphenyl)-10-(nitro)porphyr-
inato]zinc() (0.551 g, 78% over two steps). λmax(CH2Cl2–1%
pyridine)/nm 318 (log ε 4.25), 427 (5.21), 561 (4.06), 611 (3.80);
νmax(KBr)/cmϪ1 1513 (NO2), 1328 (NO2); δH(500 MHz; CDCl3,
d5-pyridine) 10.19 (1 H, s, meso H ), 9.33 (2 H, d, J 4.7, βH),
9.28 (2 H, d, J 4.4, βH), 9.04 (2 H, d, J 4.7, βH), 8.98 (2 H, d,
J 4.4, βH), 8.00 (4 H, d, J 1.8, aryl H ), 7.80 (2 H, t, J 1.8, aryl
H ), 1.51 (36 H, s, But H ); δC(125 MHz; CDCl3, d5-pyridine)
151.8, 150.7, 149.4, 148.7, 144.7, 141.5, 134.5, 132.8, 132.5,
129.9, 129.2, 128.2, 124.2, 121.1, 109.8, 35.1, 31.8; m/z (FAB)
795 (Mϩ, C48H51N5O2Zn requires 795.34).
Zinc porphyrin 10 (75 mg, 0.10 mmol) was dissolved in THF
(75 cm3) and phenyldiazonium tetrafluoroborate 11a (192 mg,
1.0 mmol) was added as a solution in methanol (50 cm3). The
reaction was stirred at room temperature for 15 h. The reaction
mixture was then passed through a short silica plug and the
solvents removed. The residue was chromatographed on silica
eluting with 1 : 1 CH2Cl2–60–80 petroleum ether and crystal-
lised from CH2Cl2 by layered addition of 1% H2O–methanol to
yield 5a as green crystals (20 mg, 23%): λmax(CH2Cl2–1%
pyridine)/nm 457 (log ε 5.22), 602 (4.07), 655 (4.57); νmax(KBr)/
cmϪ1 1594 (N᎐N); δ (500 MHz; CDCl , d -pyridine) 10.05
(1 H, s, meso H ), 9.84 (2 H, d, J 4.7, βH), 9.21 (2 H, d, J 4.4,
βH), 9.01 (2 H, d, J 4.7, βH), 8.93 (2 H, d, J 4.4, βH), 8.48 (2 H,
d, J 7.7, phenyl H ), 8.04 (4 H, d, J 1.8, But aryl H ), 7.79 (2 H, t,
J 1.8, But aryl H ), 7.70 (2 H, t, J 7.7, phenyl H ), 7.56 (1 H, t,
J 7.7, phenyl H ), 1.53 (36 H, s, But H ); δC(125 MHz; CDCl3,
d5-pyridine) 154.8, 151.3, 150.2, 149.2, 148.6, 147.4, 142.1,
133.7, 132.3, 131.8, 130.22, 130.20, 130.0, 129.4, 129.1, 124.2,
122.9, 120.8, 108.9, 35.1, 31.9; m/z (FAB) 854 (Mϩ, C54H56N6Zn
requires 854.46).
᎐
H
3
5
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(4-nitrophenyl)azopor-
phyrinato]zinc(II) 5b
Porphyrin 10 (50 mg, 0.067 mmol) was dissolved in THF (60
cm3) and the solution cooled to 0 ЊC. 4-Nitrophenyldiazonium
tetrafluoroborate 11b (80 mg, 0.333 mmol) was then added as a
solution in methanol (40 cm3) and the reaction stirred for 1 h.
On completion, the solvents were removed and the residue
chromatographed on silica eluting with CH2Cl2. Crystallisation
from CHCl3 by layered addition of 30–40 petroleum ether
yielded the pure product as green crystals (14 mg, 23%):
λmax(CH2Cl2–1% pyridine)/nm 415 (5.02), 485 (5.05), 692 (4.71);
νmax(KBr)/cmϪ1 1592 (N᎐N), 1520 (NO ), 1334 (NO ); δ (500
᎐
2
2
H
MHz; CDCl3, d5-pyridine) 10.12 (1 H, s, meso H ), 9.92 (2 H, d,
J 4.7, βH), 9.26 (2 H, d, J 4.4, βH), 9.06 (2 H, d, J 4.7, βH), 8.95
(2 H, d, J 4.4, βH), 8.54 (2 H, d, J 8.8, phenyl H ), 8.47 (2 H, d,
J 8.8, phenyl H ), 8.09 (4 H, d, J 1.8, But aryl H ), 7.85 (2 H, d,
J 1.8, But aryl H ), 1.57 (36 H, s, But H ); δC(125 MHz; CDCl3,
d5-pyridine) 157.6, 152.2, 150.2, 149.2, 148.9, 147.6, 141.7,
134.5, 132.3, 132.2, 130.5, 129.9, 128.1, 126.1, 125.3, 125.2,
122.9, 121.2, 111.5, 35.2, 32.0; m/z (FAB) 899 (Mϩ, C54H55-
N7O2Zn requires 899.45).
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(amino)porphyrinato]-
zinc(II) 13
Reduction of the nitro group to obtain the amine was
performed using the successful procedure reported by both
Baldwin and co-workers,42 and Arnold’s group.43 [5,15-
Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(nitro)porphyrinato]zinc()
(0.480 g, 0.604 mmol) was dissolved in CH2Cl2 (200 cm3) and
methanol (200 cm3) and 10% Pd on carbon (320 mg) was added.
The mixture was degassed and NaBH4 (0.571 g, 15.5 mmol)
added in portions over 20 min. Stirring was continued for 1.5 h
at room temperature. The Pd/carbon was then filtered off, the
filtrate washed with water and the organic phase evaporated to
[5,15-Bis(3,5-di-tert-butylphenyl)-10-(4-trimethylsilylethynyl-
phenyl)azoporphyrinato]zinc(II) 5c
Compound 10 (150 mg, 0.20 mmol) was dissolved in THF (150
cm3) and 4-trimethylsilylethynylphenyldiazonium tetrafluoro-
borate 11c (288 mg, 1.0 mmol) was then added as a solution
326
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329

View Article Online
dryness. Pure 13 was obtained by recrystallisation from
CH2Cl2–methanol (0.385 g, 83%). λmax(CH2Cl2–1% pyridine)/
nm 306 (log ε 4.17), 353 (4.08), 432 (5.28), 542 (3.98), 646 (4.09);
νmax(KBr)/cmϪ1 3389 (NH2); δH(500 MHz; CDCl3, d5-pyridine)
9.22 (1 H, s, meso H ), 9.05 (2 H, d, J 4.2, βH), 8.81 (2 H, d,
J 4.2, βH), 8.68 (2 H, d, J 4.2, βH), 8.55 (2 H, d, J 4.2, βH), 7.91
(4 H, d, J 1.7, aryl H ), 7.71 (2 H, d, J 1.7, aryl H ), 3.91 (2 H, s,
NH2), 1.50 (36 H, s, But H ); δC(125 MHz; CDCl3, d5-pyridine)
153.0, 149.1, 148.5 (2C), 142.3, 139.6, 133.5, 133.4, 130.5, 129.6,
129.4, 122.6, 121.5, 120.5, 99.9, 35.1, 31.9; m/z (FAB) 765 (Mϩ,
C48H53N5Zn requires 765.36).
βH), 8.12 (4 H, s, But aryl H ), 7.85 (2 H, s, But aryl H ), 7.54
(2 H, m, phenyl H ), 7.36 (3 H, m, phenyl H ), 1.55 (36 H, s, But
H ); δC(125 MHz; CDCl3, d5-pyridine) 165.4, 153.6, 151.3,
150.4, 150.0, 149.3, 148.7, 142.2, 133.7, 132.5, 132.0, 130.1,
129.4, 129.1, 125.8, 123.1, 121.2, 120.9, 110.5, 108.4, 35.3, 32.0;
m/z (MALDI-TOF) 853.4 (Mϩ, C55H57N5Zn requires 853.47).
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(4-nitrophenylimino-
methyl)porphyrinato]zinc(II) 7b
Toluene (12 cm3) was added to 16 (0.099 g, 0.13 mmol),
4-nitroaniline 17b (0.351 g, 2.54 mmol) and Amberlyst 15 (30
mg) under argon and the mixture heated to reflux for 3 h over a
Soxhlet apparatus containing 4 Å molecular sieves. The solids
were then filtered off and the product recrystallised from
CH2Cl2–methanol to obtain 7b (0.097 g, 85%). Found: C, 73.55:
H, 6.55: N, 9.85. C55H56N6O2Zn requires C, 73.52: H, 6.28: N,
9.35%; λmax(CH2Cl2–1% pyridine)/nm 447 (log ε 5.16), 574
(3.85), 634 (4.16); λem(CH2Cl2–1% pyridine)/nm 667 (λex 445
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(phenylmethylidene
amino)porphyrinato]zinc(II) 6a
Toluene (15 cm3) and benzaldehyde 15a (0.26 cm3, 2.56 mmol)
were added to aminoporphyrin 13 (0.073 g, 0.085 mmol) and
Amberlyst 15 (30 mg) under argon and the mixture heated
to reflux for 3 h over a Soxhlet apparatus containing 4 Å
molecular sieves. The solids were filtered off and the product
chromatographed in 10 : 1 : 0.1 60–80 petroleum ether–EtOAc–
pyridine. Recrystallisation from CHCl3–methanol yielded the
pure product, 6a (0.049 g, 68%). λmax(CH2Cl2–1% pyridine)/nm
nm); νmax(KBr)/cmϪ1 1577 (C᎐N), 1521 (NO ), 1338 (NO );
᎐
2
2
δ (500 MHz; CDCl , d -pyridine) 11.06 (1 H, br s, N᎐CH ),
᎐
H
3
5
10.16 (1 H, s, meso H ), 9.97 (2 H, d, J 5.0, βH), 9.29 (2 H, d,
J 5.0, βH), 9.07 (2 H, d, J 5.0, βH), 8.97 (2 H, d, J 5.0, βH), 8.45
(2 H, d, J 5.0, phenyl H ), 8.06 (4 H, s, But aryl H ), 7.82 (2 H, s,
But aryl H ), 7.71 (2 H, d, J 5.0, phenyl H ), 1.56 (36 H, s, But
H ); δC(125 MHz; CDCl3, d5-pyridine) 167.1, 159.5, 151.7,
151.6, 149.9, 149.2, 148.8, 145.3, 142.0, 134.3, 132.5, 132.2,
130.1, 129.0, 125.6, 124.1, 121.8, 121.1, 109.9, 109.0, 35.2,
32.0; m/z (MALDI-TOF) 898.5 (Mϩ, C55H56N6O2Zn requires
898.47).
432 (log ε 5.47), 571 (4.14), 616 (4.33); νmax(KBr)/cmϪ1 1591 (C᎐
᎐
N); δH(500 MHz; CDCl3, d5-pyridine) 9.95 (1 H, s, meso H ),
9.37 (2 H, d, J 4.5, βH), 9.25 (2 H, d, J 4.5, βH), 9.04 (2 H, d,
J 4.5, βH), 9.01 (1 H, s, N᎐CH ), 8.98 (2 H, d, J 4.5, βH), 8.41
᎐
(2 H, d, J 7.0, phenyl H ), 8.10 (4 H, d, J 2.0, But aryl H ), 7.81
(2 H, t, J 2.0, But aryl H ), 7.43 (3 H, m, phenyl H ), 1.65–1.55
(36 H, s, But H ); δC(125 MHz; CDCl3, d5-pyridine) 168.3, 150.7,
150.3, 150.1, 148.5, 143.4, 142.5, 137.1, 134.1, 133.0, 131.9,
131.6, 131.2, 130.3, 129.6, 129.3, 128.1, 121.9, 120.6, 104.0,
35.2, 32.0; m/z (MALDI-TOF) 853.8 (Mϩ, C55H57N5Zn
requires 853.47).
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(phenylethenyl)porphyr-
inato]zinc(II) 8a
Benzyl triphenylphosphonium bromide 19a (0.454 g, 1.28 cm3)
and NaOMe (0.069 g, 1.28 mmol) were dissolved in DMF (10
cm3) under argon. The solution was stirred for 30 min and then
warmed to 50 ЊC. 16 (0.100 g, 0.13 mmol) was added dropwise
as a solution in DMF (10 cm3) and the reaction mixture heated
at 85 ЊC for 45 min. Column chromatography on silica (1 : 1 60–
80 petroleum ether–CH2Cl2) followed by recrystallisation from
CH2Cl2–methanol yielded 8a (0.069 g, 63%) as purple crystals.
λmax(CH2Cl2–1% pyridine)/nm 435 (log ε 5.52), 568 (4.21),
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(4-nitrophenylmethyl-
ideneamino)porphyrinato]zinc(II) 6b
Toluene (15 cm3) was added to 13 (0.075 g, 0.098 mmol),
4-nitrobenzaldehyde 15b (0.442 g, 2.93 mmol) and Amberlyst
15 (approx. 30 mg) under argon and the mixture heated
to reflux for 1.5 h over a Soxhlet apparatus containing 4 Å
molecular sieves. The solids were filtered off and the product
chromatographed in 10 : 1 : 0.1 60–80 petroleum ether–EtOAc–
pyridine. Recrystallisation from CH2Cl2–methanol yielded the
pure product, 6b (0.043 g, 49%). λmax(CH2Cl2–1% pyridine)/nm
425 (log ε 5.40), 572 (4.06), 618 (4.17), 642 (4.16); νmax(KBr)/
614 (4.22); νmax(KBr)/cmϪ1 1591 (C᎐C); δ (500 MHz; CDCl ,
᎐
H
3
d -pyridine) 10.07 (1 H, s, meso H ), 9.84 (1 H, d, J 16, C᎐CH ),
᎐
5
9.61 (2 H, d, J 4.5, βH), 9.29 (2 H, d, J 4.5, βH), 9.04 (2 H, d,
J 3.5, βH), 9.03 (2 H, d, J 3.5, βH), 8.10 (4 H, d, J 2.0, But aryl
H ), 7.96 (2 H, d, J 7.5, phenyl H ), 7.81 (2 H, t, J 2, But aryl H ),
7.57 (2 H, t, J 7.5, phenyl H ), 7.43 (1 H, t, J 7.5, phenyl H ), 7.41
(1 H, d, J 16, C᎐CH ), 1.60–1.50 (36 H, m, But H ); δ (125 MHz;
cmϪ1 1592 (C᎐N), 1524 (NO ), 1342 (NO ); δ (500 MHz;
᎐
2
2
H
CDCl3, d5-pyridine) 10.04 (1 H, s, meso H ), 9.36 (2 H, d, J 4.3,
βH), 9.29 (2 H, d, J 4.2, βH), 9.09 (2 H, d, J 4.2, βH), 9.06 (2 H,
᎐
C
d, J 4.3, βH), 8.90 (1 H, s, N᎐CH ), 8.40 (4 H, two s, phenyl H ),
CDCl3, d5-pyridine) 150.4, 150.2, 149.9, 149.2, 148.5, 142.0,
138.7, 132.2, 131.4, 131.1, 130.3, 129.8, 129.2, 128.0, 127.0,
121.9, 120.7, 117.3, 105.5, 35.3, 32.0; m/z (MALDI-TOF) 852.6
(Mϩ, C56H58N4Zn requires 852.47).
᎐
8.15 (4 H, s, But aryl H ), 7.87 (2 H, s, But aryl H ), 1.75–1.50 (36
H, s, But H ); δC(125 MHz; CDCl3, d5-pyridine) 165.7, 150.3,
150.1, 149.2, 148.4, 145.1, 143.1, 142.1, 141.7, 132.9, 131.8,
131.3, 130.0, 129.5, 127.7, 124.2, 122.5, 122.1, 120.6, 104.8,
35.0, 31.8; m/z (MALDI-TOF) 898.8 (Mϩ, C55H56N6O2Zn
requires 898.47).
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(4-nitrophenylethenyl)-
porphyrinato]zinc(II) 8b
4-Nitrobenzyl triphenylphosphonium bromide 19b (0.512 g,
1.28 mmol) and NaOMe (0.069 g, 1.28 mmol) were dissolved in
DMF (10 cm3) under argon and the solution stirred for 30 min
then warmed to 50 ЊC. 16 (0.100 g, 0.13 mmol) was added
dropwise as a solution in DMF (10 cm3) and the reaction
mixture heated at 85 ЊC for 15 h. Column chromatography on
silica (1 : 1 60–80 petroleum ether–CH2Cl2) followed by
recrystallisation from CH2Cl2–methanol yielded 8b (0.064 g,
56%). Found: C, 74.44: H, 6.86: N, 8.07. C56H57N5O2Zn
requires C, 74.60: H, 6.49: N, 7.91%; λmax(CH2Cl2–1%
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(phenyliminomethyl)por-
phyrinato]zinc(II) 7a
Toluene (12 cm3) and aniline 17a (0.56 cm3, 6.36 mmol) were
added to formylporphyrin 16 (0.099 g, 0.13 mmol) and Amber-
lyst 15 (approx. 30 mg) under argon and the mixture heated
to reflux for 4 h over a Soxhlet apparatus containing 4 Å
molecular sieves. The solids were then filtered off and the
product recrystallised from CH2Cl2–methanol to obtain 7a
(0.085 g, 78%). λmax(CH2Cl2–1% pyridine)/nm 438 (log ε 5.52),
570 (4.16), 622 (4.18); λem(CH2Cl2–1% pyridine)/nm 640 (λex 437
pyridine)/nm 434 (log
λem(CH2Cl2–1% pyridine)/nm 652 (λex 435 nm); νmax(KBr)/cmϪ1
1591 (C᎐C), 1517 (NO ), 1339 (NO ); δ (500 MHz; CDCl ,
ε 5.18), 570 (4.10), 628 (4.24);
nm); νmax(KBr)/cmϪ1 1590 (C᎐N); δH(500 MHz; CDCl3,
᎐
d -pyridine) 10.90 (1 H, br s, N᎐CH ), 10.13 (1 H, s, meso H ),
᎐
᎐
5
2
2
H
3
9.66 (2 H, br s, βH), 9.31 (2 H, d, J 4.5, βH), 9.03 (4 H, d, J 4.0,
d -pyridine) 10.11 (1 H, s, meso H ), 9.95 (1 H, d, J 16, C᎐CH ),
᎐
5
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329
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9.55 (2 H, d, J 4.5, βH), 9.31 (2 H, d, J 4.5, βH), 9.06 (2 H, d,
J 4.5, βH), 9.05 (2 H, d, J 4.5, βH), 8.37 (2 H, d, J 8.0, phenyl
H ), 8.11 (4 H, d, J 2.0, But aryl H ), 7.98 (2 H, t, J 8.0, phenyl
0.0482 mmol) was dissolved in dry toluene (10 cm3) and pyr-
idine (0.3 cm3) and the solution also degassed. Phenylacetylene
21a (0.011 cm3, 0.0964 mmol) was added to the porphyrin solu-
tion and the active catalyst solution transferred via cannula to
this mixture. The reaction was heated to 80 ЊC and stirred under
inert atmosphere for 2 h. On completion, the mixture was
washed with water (2 × 20 cm3) and the organic phase evapor-
ated to dryness. The residue was chromatographed on silica
eluting with 2 : 1 60–80 petroleum ether–CH2Cl2 and 9a was
then obtained as a green solid by crystallisation from CHCl3 by
layered addition of 30–40 petroleum ether (29 mg, 71%).
λmax(CH2Cl2–1% pyridine)/nm 439 (log ε 5.61), 574 (4.20), 623
H ), 7.86 (2 H, t, J 2, But aryl H ), 7.43 (1 H, d, J 16, C᎐CH ),
᎐
1.65–1.55 (36 H, s, But H ); δH(125 MHz; CDCl3, d5-pyridine)
150.8, 150.4, 150.0, 149.1, 148.8, 147.2, 144.7, 142.5, 139.1,
136.3, 132.8, 132.7, 131.7, 130.2, 129.2, 127.1, 124.7, 122.5,
120.9, 115.4, 106.5, 35.3, 32.0; m/z (FAB) 897.5 (Mϩ,
C56H57N5O2Zn requires 897.47).
Imine-linked porphyrin dimer 18
Aminoporphyrin 13 (18.1 mg, 23.6 µmol), formylporphyrin 16
(20.2 mg, 26.0 µmol) and Amberlyst 15 (20 mg) were mixed
with toluene (15 cm3) and pyridine (0.005 cm3) then brought to
reflux over a Soxhlet containing 3 Å molecular sieves. TFA
(0.015 cm3) was added and the mixture refluxed for 48 h. Et3N
(approx. 1 cm3) was added, and the solids were filtered off and
the filtrate evaporated to dryness. Column chromatography
on silica in 10 : 1 : 0.1 60–80 petroleum ether–EtOAc–pyridine
separated unreacted 16, while changing to 1 : 1 60–80 petroleum
ether–CHCl3 was required to elute the dimer. Pure 18 (11.4 mg,
32%) was obtained by recrystallising from CH2Cl2 by the
layered addition of methanol. λmax(CH2Cl2–1% pyridine)/nm
427 (log ε 5.32), 443 (5.31), 565 (4.31), 622 (4.32), 663 (4.31);
(4.43); νmax(KBr)/cmϪ1 2194 (C᎐C); δ (500 MHz; CDCl , d -
᎐
᎐
H
3
5
pyridine) 10.10 (1 H, s, meso H ), 9.85 (2 H, d, J 4.5, βH), 9.28 (2
H, d, J 4.5, βH), 9.05 (2 H, d, J 4.5, βH), 9.02 (2 H, d, J 4.5, βH),
8.09 (4 H, d, J 1.6, But aryl H ), 8.05 (2 H, d, J 7.4, phenyl H ),
7.83 (2 H, t, J 1.6, But aryl H ), 7.56 (2 H, t, J 7.4, phenyl H ),
7.47 (1 H, t, J 7.4, phenyl H ), 1.58 (36 H, s, But H ); δC(125
MHz; CDCl3, d5-pyridine) 152.0, 150.9, 150.1, 149.6, 148.6,
142.2, 133.0, 132.6, 131.7, 131.6, 130.5, 130.3, 128.8, 128.2,
124.9, 122.7, 120.8, 107.4, 99.1, 95.6, 94.1, 35.2, 32.0; m/z (FAB)
850 (Mϩ, C56H56N4Zn requires 850.47).
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-(4-nitrophenylethynyl)-
porphyrinato]zinc(II) 9b
νmax(KBr)/cmϪ1 1591 (C᎐N); δ (500 MHz; CDCl , d -pyridine)
᎐
H
3
5
11.68 (1 H, s, N᎐CH ), 10.55 (2 H, d, J 4.7, βH), 10.21 (1 H, s,
᎐
Pd2(dba)3 (4.0 mg, 4.3 µmol), PPh3 (9.5 mg, 36 µmol) and CuI
(3.4 mg, 18 µmol) were dissolved in Et3N (11 cm3) and the
solution warmed at 70 ЊC for 30 min. 20 (60.0 mg, 72 µmol) and
4-nitrophenylacetylene 21b (32.0 mg, 217 µmol) were dissolved
in dry toluene (11 cm3) and pyridine (0.25 cm3) in a separate
flask. The active catalyst solution was transferred to the reac-
tion flask via cannula and the mixture heated at 80 ЊC. The
solution was cooled after 1 h, filtered through a silica plug and
then chromatographed in 10 : 1 : 0.1 60–80 petroleum ether–
EtOAc–pyridine. Recrystallisation from CHCl3 by layered
addition of methanol yielded 9b (59.7 mg, 92%). λmax(CH2Cl2–
1% pyridine)/nm 452 (log ε 5.48), 579 (4.30), 637 (4.81);
meso H ), 9.96 (1 H, s, meso H ), 9.89 (2 H, d, J 4.5, βH), 9.35
(2 H, d, J 4.4, βH), 9.27 (2 H, d, J 4.4, βH), 9.18 (2 H, d, J 4.7,
βH), 9.06 (2 H, d, J 4.4, βH), 9.05 (2 H, d, J 4.4, βH), 9.04 (2 H,
d, J 4.5, βH), 8.16 (4 H, d, J 1.7, But aryl H ), 8.14 (4 H, d, J 1.7,
But aryl H ), 7.82 (2 H, t, J 1.7, But aryl H ), 7.79 (2 H, t, J 1.7,
But aryl H ), 1.57 (72 H, m, But H ); δC(125 MHz; CDCl3, d5-
pyridine) 151.6, 151.2, 150.5, 150.0, 149.8, 149.7, 149.0, 148.3,
148.2, 147.6, 144.0, 142.4, 142.0, 135.8, 134.0, 132.7, 132.2,
131.7, 131.4, 130.8, 129.9, 129.8, 128.7, 123.2, 123.1, 121.7,
120.6, 120.3, 110.8, 108.6, 103.4, 35.0, 34.9, 31.7 (2 C); m/z
(MALDI-TOF) 1525.8 (Mϩ, C97H103N9Zn2 requires 1525.7).
λem(CH2Cl2–1% pyridine)/nm 649 (λex 450 nm); νmax(KBr)/cmϪ1
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-bromoporphyrinato]-
zinc(II) 20
᎐
2185 (C᎐C), 1517 (NO ), 1338 (NO ); δ (500 MHz; CDCl ,
᎐
2
2
H
3
d5-pyridine) 10.04 (1 H, s, meso H ), 9.36 (2 H, d, J 4.3, βH),
9.29 (2 H, d, J 4.2, βH), 9.09 (2 H, d, J 4.2, βH), 9.06 (2 H, d,
Zinc porphyrin 10 (400 mg, 0.533 mmol) was dissolved in
CHCl3 (120 cm3) and pyridine (0.5 cm3). The solution was
cooled to 0 ЊC and N-bromosuccinimide (123 mg, 0.693 mmol)
added. The reaction was stirred for 15 min, quenched with
acetone and then the solvents were removed under reduced
pressure. The residue was washed with copious methanol to
give a mixture of mono- and di-brominated products. This
mixture was washed with CHCl3 and both the filtrate and the
remaining residue were then separately chromatographed on
silica eluting with 10 : 1 : 0.1 60–80 petroleum ether–EtOAc–
pyridine. The fractions containing the mono-brominated
product 20 were evaporated to dryness and crystallised from
CHCl3 by layered addition of 30–40 petroleum ether to yield
the pure product as a pink solid (263 mg, 59%): λmax(CH2Cl2–
1% pyridine)/nm 319 (log ε 4.29), 429 (5.68), 563 (4.24), 603
(3.87); δH(500 MHz; CDCl3, d5-pyridine) 10.05 (1 H, s, meso
H ), 9.71 (2 H, d, J 4.5, βH), 9.24 (2 H, d, J 4.5, βH), 8.98 (4 H,
app. t, J 5.5, βH), 8.01 (4 H, d, J 1.8, aryl H ), 7.77 (2 H, t,
J 1.8, aryl H ), 1.50 (36 H, s, But H ); δC(125 MHz; CDCl3,
d5-pyridine) 150.7, 150.6, 150.1, 149.1, 148.4, 142.0, 133.1,
132.9, 132.3, 131.7, 130.1, 123.7, 120.7, 106.0, 104.1, 35.0, 31.8;
m/z (FAB) 829 (Mϩ, C48H51N4BrZn requires 829.23).
J 4.3, βH), 8.90 (1 H, s, N᎐CH ), 8.40 (4 H, two s, phenyl H ),
᎐
8.15 (4 H, s, But aryl H ), 7.87 (2 H, s, But aryl H ), 1.75–1.50
(36 H, m, But H ); δC(125 MHz; CDCl3, d5-pyridine) 165.7,
150.3, 150.1, 149.2, 148.4, 145.1, 143.1, 142.1, 141.7, 132.9,
131.8, 131.3, 130.0, 129.5, 127.7, 124.2, 122.5, 122.1, 120.6,
104.8, 35.0, 31.8; m/z (MALDI-TOF) 895.6 (Mϩ, C56H55-
N5O2Zn requires 895.46).
[5,15-Bis(3,5-di-tert-butylphenyl)-10-trimethylsilylethynylpor-
phyrinato]zinc(II)
Bromoporphyrin 20 (300 mg, 0.362 mmol), Pd2(dba)3 (10 mg,
0.012 mmol), PPh3 (23 mg, 0.087 mmol) and CuI (8 mg, 0.044
mmol) were dried under vacuum and then dissolved in dry
toluene (75 cm3), pyridine (2.25 cm3) and Et3N (35 cm3). The
solution was degassed and trimethylsilylacetylene (0.112 cm3,
0.796 mmol) added and the reaction stirred under inert atmos-
phere at 45 ЊC for 15 h. On completion, the reaction mixture
was washed with water (2 × 100 cm3), the organic phase
evaporated to dryness and the residue chromatographed on
silica eluting with 60–80 petroleum ether–EtOAc–pyridine
(10 : 1 : 0.1). Crystallisation from chloroform by layered addition
of 1% water–methanol yielded pure [5,15-bis(3,5-di-tert-
butylphenyl)-10-trimethylsilylethynylporphyrinato]zinc() as a
green solid (254 mg, 83%). λmax(CH2Cl2–1% pyridine)/nm 319
(log ε 4.24), 434 (5.50), 440 (5.47), 571 (4.13), 617 (4.12);
[5,15-Bis(3Ј,5Ј-di-tert-butylphenyl)-10-phenylethynylporphyr-
inato]zinc(II) 9a
Pd2(dba)3 (1.5 mg, 0.0014 mmol), PPh3 (3.0 mg, 0.0116 mmol)
and CuI (1.0 mg, 0.0058 mmol) were dried under vacuum and
Et3N (5 cm3) added. The solution was degassed and then heated
at 70 ЊC for 1.5 h. Simultaneously, bromoporphyrin 20 (40 mg,
νmax(KBr)/cmϪ1 2138 (C᎐C); δ (500 MHz; CDCl , d -pyridine)
᎐
᎐
H
3
5
10.19 (1 H, s, meso H ), 9.81 (2 H, d, J 4.5, βH), 9.34 (2 H, d,
J 4.5, βH), 9.08 (4 H, d, J 4.5, βH), 8.11 (4 H, d, J 1.8, But aryl
328
J. Chem. Soc., Perkin Trans. 1, 2002, 320–329

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H ), 7.85 (2 H, t, J 1.8, But aryl H ), 1.59 (36 H, s, But H ), 0.64
(9 H, TMS); δC(125 MHz; CDCl3, d5-pyridine) 152.4, 151.0,
150.4, 149.6, 148.9, 141.8, 133.3, 132.8, 131.9, 131.0, 130.1,
122.9, 121.1, 108.6, 107.7, 100.8, 99.6, 35.3, 32.0, 0.7; m/z (FAB)
847 (Mϩ, C53H60N4SiZn requires 846.6).
2 S. M. LeCours, H.-W. Guan, S. G. DiMagno, C. H. Wang and
M. J. Therien, J. Am. Chem. Soc., 1996, 118, 1497.
3 K. S. Suslick, C.-T. Chen, G. R. Meredith and L.-T. Cheng, J. Am.
Chem. Soc., 1992, 114, 6928.
4 H. L. Anderson, S. J. Martin and D. D. C. Bradley, Angew. Chem.,
Int. Ed. Engl., 1994, 33, 655.
5 J. R. G. Thorne, S. M. Kuebler, R. G. Denning, I. M. Blake,
P. N. Taylor and H. L. Anderson, Chem. Phys., 1999, 248, 181;
S. M. Kuebler, R. G. Denning and H. L. Anderson, J. Am. Chem.
Soc., 2000, 122, 339.
6 H. L. Anderson, Tetrahedron Lett., 1992, 33, 1101.
7 H. L. Anderson, A. P. Wylie and K. Prout, J. Chem. Soc., Perkin
Trans. 1, 1998, 1607.
8 L. R. Milgrom, G. Yahioglu, D. W. Bruce, S. Morrone, F. Z. Henari
and W. J. Blau, Adv. Mater., 1997, 9, 313.
9 F. Z. Henari, W. J. Blau, L. R. Milgrom, G. Yahioglu, D. Phillips and
J. A. Lacey, Chem. Phys. Lett., 1997, 267, 229.
[5,15-Bis(3,5-di-tert-butylphenyl)-10-ethynylporphyrinato]-
zinc(II) 22
[5,15-Bis(3,5-di-tert-butylphenyl)-10-trimethylsilylethynylpor-
phyrinato]zinc() (200 mg, 0.236 mmol) was dissolved in dry
CH2Cl2 (80 cm3) and TBAF (0.354 cm3 of a 1 M solution in
THF, 0.354 mmol) added. The reaction was stirred at room
temperature for 15 min and then quenched by adding acetic
acid (0.020 cm3, 0.354 mmol). The pure product 22 was precipi-
tated from the reaction mixture with 1% water in methanol as
purple crystals (166 mg, 91%). λmax(CH2Cl2–1% pyridine)/nm
10 A. Krivokapic, H. L. Anderson, G. Bourhill, R. Ives, S. Clark and
K. J. McEwan, Adv. Mater., 2001, 13, 652.
11 K. Müllen and G. Wegner, Electronic Materials: The Oligomer
Approach; Wiley-VCH, Chichester, 1998.
426 (log ε 5.60), 560 (4.24); νmax(KBr)/cmϪ1 2089 (C᎐C); δ (500
᎐
᎐
H
MHz; CDCl3, d5-pyridine) 10.15 (1 H, s, meso H ), 9.78 (2 H, d,
J 4.5, βH), 9.31 (2 H, d, J 4.5, βH), 9.06 (2 H, d, J 4.5, βH), 9.03
(2 H, d, J 4.5, βH), 8.08 (4 H, d, J 1.8, But aryl H ), 7.82 (2 H, t,
12 R. E. Martin and F. Diederich, Angew. Chem., Int. Ed., 1999, 38,
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10, 753.
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18 M. Traetteberg, I. Hilmo, R. J. Abraham and S. Ljunggren, J. Mol.
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20 J. O. Morley, J. Chem. Soc., Perkin Trans. 2, 1995, 731.
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23 J.-H. Fuhrhop in The Porphyrins, ed. D. Dolphin, Academic Press,
New York, 1978, vol. 2, ch. 5.
t
t
᎐
J 1.8, Bu aryl H ), 4.15 (1 H, s, C᎐C–H ), 1.59 (36 H, s, Bu H );
᎐
δC(125 MHz; CDCl3, d5-pyridine) 152.6, 151.2, 150.5, 149.7,
148.8, 142.4, 133.4, 132.7, 131.9, 130.8, 130.4, 122.8, 121.0,
107.8, 97.5, 87.8, 82.8, 35.4, 32.2; m/z (FAB) 774 (Mϩ,
C50H52N4Zn requires 774.4).
Acetylene-linked porphyrin dimer 23
Ethynylporphyrin 22 (100 mg, 0.129 mmol), bromoporphyrin
20 (210 mg, 0.258 mmol), Pd2(dba)3 (3.4 mg, 0.004 mmol), PPh3
(7.9 mg, 0.030 mmol) and CuI (2.9 mg, 0.015 mmol) were dried
under vacuum and dissolved in dry toluene (25 cm3), pyridine
(0.5 cm3) and Et3N (25 cm3). The solution was degassed and the
reaction stirred under inert atmosphere for 1.5 h at 80 ЊC. On
completion, the mixture was passed through a short silica plug
and the product then separated from excess bromoporphyrin
20 on a silica column eluting with 60–80 petroleum ether–
CH2Cl2–pyridine (10 : 1 : 0.1 and then increasing the polarity to
2 : 1 : 0.1). 1% Pyridine in chloroform was required to remove
all the product from the column. Crystallisation from chloro-
form by layered addition of methanol yielded the pure dimer as
a black solid (138 mg, 70%). λmax(CH2Cl2–1% pyridine)/nm 415
24 M. J. Billig and E. W. Baker, Chem. Ind., 1969, 654.
25 S. Nishitani, N. Kurata, Y. Sakata, S. Misumi, M. Migita, T. Okada
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28 V. S.-Y. Lin, S. G. DiMagno and M. J. Therien, Science, 1994, 264,
1105.
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31 S. M. LeCours, S. G. DiMagno and M. J. Therien, J. Am. Chem.
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32 C. J. Brown, Acta Crystallogr., 1966, 21, 146.
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58, 5983.
(log ε 5.21), 434 (5.17), 481 (5.59), 710 (4.84); νmax(KBr)/cmϪ1
᎐
2155 (C᎐C); δ (500 MHz; CDCl , d -pyridine) 10.48 (4 H, d,
᎐
H
3
5
J 4.4, βH), 10.03 (2 H, s, meso H ), 9.22 (4 H, d, J 4.4, βH), 9.14
(4 H, d, J 4.4, βH), 8.97 (4 H, d, J 4.4, βH), 8.09 (8 H, d, J 1.5,
But aryl H ), 7.79 (4 H, t, J 1.5, But aryl H ), 1.52 (72 H, s, But
H ); δC(125 MHz; CDCl3, d5-pyridine) 152.6, 150.8, 150.1,
149.7, 148.6, 142.2, 133.0, 132.5, 131.4, 130.5, 129.9, 122.8,
120.7, 107.0, 101.3, 100.9, 35.1, 31.8; m/z (FAB) 1523 (Mϩ,
C98H102N8Zn2 requires 1522.7).
35 K. Susumu, T. Shimidzu, K. Tanaka and H. Segawa, Tetrahedron
Lett., 1996, 37, 8399.
36 S. Anderson, Chem. Eur. J., 2001, 7, 4706.
37 SIR92 – A program for crystal structure solution A. Altomare,
G. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl.
Crystallogr., 1993, 26, 343.
38 SHELXL93 – Program for Crystal Structure Refinement. G. M.
Sheldrick, Institüt für Anorganische Chemie der Universität,
Tammanstrasse 4, D-3400 Göttingen, Germany, 1993.
39 CRYSTALS. D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W.
Better, Chemical Crystallography Laboratory, Oxford, UK, 1996.
40 G. M. Sheldrick, SHELXTL version 5, Bruker AXS Inc., Madison,
Wisconsin, USA, 1997.
Acknowledgements
This work was supported by the Engineering and Physical
Sciences Research Council (EPSRC) and the Defence Science
and Technology Laboratory (DSTL, Malvern). Dr David J.
Watkin provided valuable advice on crystallography. We are
also grateful to the EPSRC Mass Spectrometry Service in
Swansea for FAB mass spectra.
41 J. A. Cowan and J. K. M. Sanders, J. Chem. Soc., Perkin Trans. 1,
1987, 2395.
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M. Zojaji, Aust. J. Chem., 1997, 50, 495.
44 R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384.
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