Self-assembly of zinc aminoporphyrins

Article abstract of DOI:10.1039/a807876i

The aniline-zinc porphyrin interaction is an order of magnitude weaker than the corresponding pyridine-zinc porphyrin interaction, but it is still strong enough to cause self-assembly of zinc aminoporphyrins in solution. Three isomeric systems are reporte

Full text of DOI:10.1039/a807876i

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Self-assembly of zinc aminoporphyrins
Mark Gardner,b Andrea J. Guerin,a Christopher A. Hunter,*a Ulrike Michelsena and
Carmen Rotger¤
a Krebs Institute for Biomolecular Science, Department of Chemistry, University of Sheffield,
Sheffield, UK S3 7HF
b Discovery Chemistry, PÐzer L td, Sandwich, UK CT 13 9NJ
Received (in Cambridge, UK) 9th October 1998, Accepted 4th November 1998
The anilineÈzinc porphyrin interaction is an order of magnitude weaker than the corresponding pyridineÈzinc
porphyrin interaction, but it is still strong enough to cause self-assembly of zinc aminoporphyrins in solution. Three
isomeric systems are reported, two form self-assembled dimers, but the geometry of the third forces it to form an
open chain oligomer. The stabilities and structures of the complexes have been determined using 1H NMR
spectroscopy.
for the signals due to the protons on the aniline ring which
suggested that the lone pair of the aniline nitrogen of one
Introduction
Self-assembly is the spontaneous generation of well-deÐned
molecular assemblies via non-covalent interactions, such as
hydrogen-bonding and metalÈligand coordination.1h12
Porphyrins are popular building blocks because they are
easily synthesized and functionalised, they are large and rigid,
they are spectroscopically rich, and they have interesting
photochemical and redox properties.13h16 We have been
investigating the use of pyridineÈzinc porphyrin coordination
interactions for the self-assembly of oligomeric arrays of these
chromophores.17h19 In the course of this work, we prepared a
range of di†erent aminoporphyrins, and when these com-
pounds were metallated with zinc, they displayed some
unusual spectroscopic properties. These are reported in this
paper along with structural characterization of the complexes.
We show that the anilineÈzinc porphyrin coordination bond,
although weaker than the pyridineÈzinc porphyrin inter-
action,20 is strong enough to yield stable self-assembled com-
plexes.
porphyrin was coordinated to the vacant zinc binding site on
the face of another porphyrin. This would bring the aniline
into the shielding region of the coordinated porphyrinÏs ring
current. To test this hypothesis, a 1H NMR titration was
carried out to measure the strength of the zincÈaniline inter-
action: a millimolar solution of 1 in d-chloroform was titrated
with aliquots of a molar solution of L5. The association con-
stant is 130 ^ 10 M~1, and the limiting complexation-induced
changes in chemical shift are shown in Fig. 1. The aniline
clearly coordinates to the zinc and lies over the face of the
porphyrin.
The self-assembly properties of the three zinc amino-
porphyrins were therefore investigated by quantitative 1H
NMR dilution experiments. The results for each system are
discussed in turn.
Complex 2
At a concentration of 25 mM, the 1H NMR spectrum of 2 was
surprisingly complicated, and COSY and ROESY experi-
ments were required to fully assign all of the signals. The com-
plexity is caused by non-equivalence of the two faces of the
porphyrin and slow rotation about all four meso-phenyl bonds
Results and discussion
The three isomeric zinc aminoporphyrins, 2, 3 and 4, were all
synthesised using the same procedure (Scheme 1).21,22 Starting
from the appropriate nitrobenzaldehyde, a statistical reaction
with pyrrole and n-pentylbenzaldehyde gave a mixture of
porphyrin products. These were separated by column chroma-
tography to give the mononitroporphyrin (H L6, H L7 or
2
2
H L8) and the tetraalkylporphyrin (H L1) which was used for
2
2
control binding experiments. Each of the nitroporphyrins was
reduced with stannous chloride and metallated with zinc
acetate to give 2, 3 and 4 in essentially quantitative yields.
-1.3
-4.5
H L1 was similarly metallated to give 1.
2
The Ðrst evidence for the self-assembly of the three zinc
NH2
aminoporphyrins came from the 1H NMR spectra which were
recorded at millimolar concentrations. The spectra were all
concentration-dependent and surprisingly complex with many
more signals than the corresponding free base porphyrins. At
high concentrations, there were particularly large upÐeld shifts
N
N
Zn
N
N
Fig. 1 Structure of the 1 Æ L5 complex, showing the limiting
complexation-induced changes in chemical shift from the 1H NMR
titration in chloroform (some of the porphyrin meso substituents are
omitted for clarity).
¤
Current address: Department of Chemistry, Universitat de les Illes
Balears, 07071 Palma de Mallorca, Spain.
New J. Chem., 1999, 309È316
309

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Scheme 1
on the NMR timescale. Clearly the rate of rotation about the
meso-aniline bond is much slower than for the other three tor-
sions due to the ortho substituent, but nevertheless on the
NMR timescale, all are in slow exchange. In other systems
such as H L2 and H L6, this slow exchange has no impact on
be 10 ^ 5 M~1 which is signiÐcantly lower than the dimer-
isation constant for 2. Thus 2 self-assembles via a cooperative
process which suggests that the structure of the complex is a
closed macrocyclic dimer held together by two zincÈaniline
interactions (Fig. 3).23 Of course, larger macrocyclic structures
are also consistent with this data, but a dimer is entropically
favoured, and this structure is supported by the chemical shift
data discussed below.
2
2
the appearance of the 1H NMR spectrum, because there is
very little di†erence between the environments on the two
faces of the porphyrin. It is the self-assembly process that
causes the di†erence between these two enviroments in 2.
A detailed 1H NMR dilution study was carried out on 2 in
d-chloroform. The data could be Ðtted reasonably well to
either a dimerisation isotherm or a non-cooperative linear
polymerisation isotherm, but the dimer model was marginally
better. The dimerisation constant is 160 ^ 20 M~1 which is
similar in magnitude to the value for the simple zincÈaniline
interaction in 1 Æ L5 and suggests that there is no cooperative
self-assembly process in this system. However, this is not an
appropriate comparison, because there is signiÐcant steric hin-
drance of the amine binding site in the ortho-derivative. In
N
H
N
N
H
+
0.1
N
-0.2
0.3
-
NH2
Zn
-
1.8
N
N
order to quantify this e†ect, we measured the 1 Æ H L2 associ-
N
N
2
ation constant (Fig. 2). It is difficult to obtain accurate values
for the binding constant and complexation-induced changes in
chemical shift for this complex, because it is very weakly
bound, and it is therefore not possible to reach saturation in
the binding isotherm. We estimate the association constant to
Fig. 2 Structure of the 1 É H L2 complex, showing the limiting
2
complexation-induced changes in chemical shift from the 1H NMR
titration in chloroform (some of the porphyrin meso substituents are
omitted for clarity).
310
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C5H11
C5H11
H2L1 M= 2H
M= Zn
H2L3 M= 2H
1
3 M= Zn
N
N
N
N
N
N
H11C5
M
N
C5H11
H11C5
M
N
NH2
C5H11
C5H11
C5H11
C5H11
H2L4 M= 2H
H2L4 M= 2H
M= Zn
4
M= Zn
2
N
N
N
N
N
M
N
NH2
H11C5
M
N
H11C5
N
NH2
C5H11
C5H11
L5
H13C6
NH2
The limiting complexation-induced changes in chemical
ments were required to fully assign the spectrum. The two
faces of the porphyrin are again di†erent, and rotation about
the meso-phenyl bonds is slow on the NMR timescale. The
low concentration spectrum and the spectra of the corre-
sponding free base porphyrins H L3 and H L7 are relatively
shift (CIS) for 1 Æ H L2 and (2) are shown in Fig. 2 and 3
2
2
respectively. Although the magnitudes of the values for
1
Æ H L2 are subject to a large error due to the low stability of
2
the complex, the pattern of shift changes is accurate and is
2
2
quite di†erent from that found for (2) indicating that the anil-
simple which implies that it is the self-assembly process which
causes the two faces of the porphyrin to become non-
equivalent. A 1H NMR dilution study was carried out in d-
chloroform. The data could be Ðtted equally well to either a
dimerisation isotherm or a non-cooperative linear polymeris-
ation isotherm, but the association constants are an order of
magnitude larger than the value for the simple zincÈaniline
interaction in 1 Æ L5 (the association constant for dimerisation
is 1080 ^ 90 M~1). This implies that formation of the complex
is a cooperative process involving more than one coordination
bond, i.e. the complex is a closed macrocycle held together by
two zincÈaniline interactions per monomer. Entropically, the
most favourable structure is a dimer (Fig. 5), and this is sup-
ported by the CIS data discussed below.
2
ines are bound in di†erent orientations in the two systems.
Very large changes in chemical shift are found for the porphy-
rin b-pyrrole signals as well as the signals due to the protons
on the aniline ring. CIS values can be used in a quantitative
manner to obtain more detailed information about the struc-
tures of porphryin complexes of this type.24h26 We have
recently developed a computational method for deriving high
resolution three-dimensional structural information on supra-
molecular complexes from complexation-induced changes in
chemical shift,27 and this was used to obtain the three-
dimensional structure of (2) which is shown in Fig. 4 (see
2
Experimental section for details). The CIS values for the opti-
mised dimer structure agree extremely well with the experi-
mental data: root mean square di†erence (rmsd) \ 0.03 ppm.
The limiting complexation-induced changes in chemical
shift for (3) are shown in Fig. 5. The pattern of shift changes
2
is similar to that found for 2 except that the values for the
Complex 3
porphyrin b-pyrrole signals are signiÐcantly smaller. These
CIS values were used in conjunction with the computational
method discussed above to obtain a three-dimensional struc-
Like 2, the 1H NMR spectrum of 3 was surprisingly compli-
cated at high concentrations, and COSY and ROESY experi-
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311

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R
R
-0.1
-0.5
0.0
-0.2
+
0.1
-2.1
-0.7
0
.0
-0.6
-0.3
+
0.2
-0.5
+
0.1
N
N
N
-0.9
+
0.1
N
N
N
0.0
R
Zn
-3.3
NH2
R
Zn
-1.1
4.1
N
N
-
+0.1 +0.2
-3.7
+
0.2 +0.3
NH2
-
0.3
-
0.6
0.1
+
0.1
+
+
0.1
0.1
+
0.1
+0.2
-
R
R
N
N
N
Zn
N
N
N
N
N
Zn
NH2
Zn
H2N
H2N
NH2
N
N
N
N
N
N
Zn
N
N
Fig. 3 Limiting complexation-induced changes in chemical shift
from the 1H NMR dilution of 2 (the signals due to the anilino protons
were difficult to identify reliably and reproducibly). The structure of
the self-assembled dimer is also shown. Some of the porphyrin meso
substituents are omitted for clarity.
Fig. 5 Limiting complexation-induced changes in chemical shift
from the 1H NMR dilution of 3 (the signals due to the anilino protons
were difficult to identify reliably and reproducibly). The structure of
the self-assembled dimer is also shown. Some of the porphyrin meso
substituents are omitted for clarity.
ture (Fig. 6). The calculated CIS values for the optimised
dimer structure agree extremely well with the experimental
data: rmsd \ 0.02 ppm. The reason for the di†erence in the
pattern of chemical shift changes for 2 and 3 can easily be seen
by comparing the structures in Fig. 4 and 6: in 2, the b-
pyrrole protons on the edge of one porphyrin lie over the
centre of the ring current of the neighbouring molecule, but
moving the substituent from the ortho to the meta position
increases the lateral displacement of the porphyrin rings and
signiÐcantly reduces the extent of overlap.
Complex 4
The behaviour of 4 was quite di†erent from the other two
systems. All of the signals in the 1H NMR spectrum of 4 were
broad at a concentration of 25 mM but became much sharper
at lower concentrations. The line-broadening suggests that
self-assembly generates a high molecular weight oligomeric
species (a chemical exchange process is an alternative
explanation). A 1H NMR dilution study was carried out in
d-chloroform. The data could be Ðtted equally well to either a
dimerisation isotherm or a non-cooperative linear oligomeri-
sation isotherm, but the association constants are very similar
to the value for the simple zincÈaniline interaction in 1 Æ L5
(the association constant for open chain oligomerisation is
190 ^ 20 M~1). This implies that there are no cooperative
processes in this system and suggests that an open linear oli-
gomer is the most likely structure of the complex (Fig. 7).23
The limiting complexation-induced changes in chemical shift
are shown in Fig. 7. The values for the aniline ring protons are
comparable with those found for the 1 Æ L5 complex (Fig. 1)
Fig. 4 Two views of the three-dimensional structure of the self-
assembled dimer (2) . The structure was determined by matching cal-
2
culated complexation-induced changes in 1H NMR chemical shift
with the experimental values.
312
New J. Chem., 1999, 309È316

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upright structure for this complex with the 10- and 20-meso
substituents lying over the ring current of the neighbouring
molecule. Attempts to use the CIS values to determine the
three-dimensional structure of a closed dimer failed for this
system: the conformational search was unable to locate a
compatible dimeric structure. Thus the CIS data also support
formation of a simple oligomeric aggregate for 4. This behav-
iour can easily be rationalised on the basis of the geometry of
the system: it is not sterically possible to form a closed
dimeric complex with the para- substituent.
Further evidence for the structures of the assemblies was
sought from mass spectrometry and vapor pressure osmom-
etry, but the complexes are not sufficiently stable to be charac-
terized using these techniques. Similarly, self-assembly does
not take place at concentrations suitable for UV/Visible
absorption spectroscopy.
Conclusions
The stability constant for coordination of a zinc porphyrin by
aniline is approximately 100 M~1. This is one order of magni-
tude weaker than the stability of pyridineÈzinc porphyrin
complexes. Nevertheless stable oligomeric assemblies of zinc
aminoporphyrins are formed in solution. The ortho and meta
zinc amino porphyrin derivatives, 2 and 3, form closed dimers
with signiÐcant cooperativity between the two zincÈnitrogen
bonds which hold the macrocycle together. The geometry of
the para derivative precludes the formation of macrocyclic
dimers, and so this compound forms an open chain linear oli-
gomer with no cooperativity. The large ring current shifts in
the 1H NMR spectra provide detailed information about the
three-dimensional structures of the complexes and have been
used to derive high resolution structures of the two dimers.
Fig. 6 Two views of the three-dimensional structure of the self-
assembled dimer (3) . The structure was determined by matching cal-
2
culated complexation-induced changes in 1H NMR chemical shift
with the experimental values.
indicating that the aniline is bound in a similar orientation in
both systems. The pattern of shifts on the porphyrin ring are
similar to 3, but the meso substituents experience much larger
ring current-induced upÐeld shifts. This suggests a more
Fig. 7 Limiting complexation-induced changes in chemical shift from the 1H NMR dilution of 4 (the signals due to the anilino protons were
difficult to identify reliably and reproducibly). The structure of the self-assembled oligomeric chain is also shown. Some of the porphyrin meso
substituents are omitted for clarity.
New J. Chem., 1999, 309È316
313

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The conformational searches were carried out using the
same protocol for each system. The structures of the zinc
porphyrins were taken from the X-ray crystal structure
analysis of the pyridine complex of zinc tetraphenylporphyrin,
and amine groups were added using standard bond lengths
and angles in Macromodel.29 A genetic algorithm was used to
optimise the conformation of the complex so that the calcu-
lated CIS values matched the experimental values as closely as
possible. We allowed intermolecular translation (^10 AŽ ) and
rotation (^180¡) as well as intramolecular torsional changes
(^180¡) for all four meso-phenyl bonds in each molecule. To
restrict the search space, the amine nitrogens were constrained
Experimental
1H NMR dilution experiments
A sample of known concentration (of the order 10È100 mM)
in CDCl was prepared and a 1H NMR spectrum was record-
3
ed on a 0.8 ml sample. From this sample, 0.4 ml was removed
and replaced by 0.4 ml of solvent. After shaking to mix the
solvents, a second 1H NMR spectrum was recorded. This pro-
cedure was repeated until there was no further change in
chemical shift or the sample was too dilute to record a spec-
trum. For signals that moved more than 0.01 ppm over the
whole concentration range, the chemical shifts at each concen-
tration were recorded and Ðtted to a dimerisation or non-
cooperative linear polymerisation isotherm using purpose
written software on an Apple Macintosh microcomputer,
NMRDil Dimer or NMRDil Agg. These programs use a
Simplex procedure to Ðt the experimental data to the follow-
ing equations to determine the optimum solutions for the
association constant, and the limiting bound and free chemical
shifts.
to be within 2.1 ^ 0.5 A
clashes were penalised at distances of less than 3 A
molecular clashes and 2 A for intramolecular clashes for non-
Ž
of the zinc atoms, and van der Waals
Ž
for inter-
Ž
hydrogen atoms. The searches for both 2 and 3 converged to
values of R /R of 9.0 and 13.5 respectively in about 2000
generations for a population of 100 (R
experimentally observed CIS values, and R is the rms di†er-
ence between the calculated and experimental values). The 4
search failed to converge to a satisfactory solution: the
expt *d
is the rms of the
expt
*
d
NMRDil Dimer Ðts the data to a dimerisation isotherm by
solving the following equations:
maximum R /R value reached was 1.9.
expt *d
Preparation of porphyrins
] 4K [A] [ JM1 ] 8K [A] N
[
AA] \ 1
d
0
d
0
(1)
(2)
(3)
8K
Freshly distilled pyrrole (1.39 ml, 0.02 mol, 1 equivalent), the
appropriate nitrobenzaldehyde (1.207 g, 0.008 mol, 0.4
equivalent), 4-n-pentylbenzaldehyde (2.112 g, 0.012 mol, 0.6
equivalent), dry EtOH (13 ml) and dry dichloromethane (2 l)
were stirred under N for 5 min. BF OEt (1 ml, 6.6 mmol,
d
[
A] \ [A] [ 2[AA]
0
\ 2
[AA]
d ]
[A]
[A]
d
d
2
3
2
obs
[A]
d
f
0
.33 equivalent) was added via a septum, and the reaction
0
0
mixture was protected from light and stirred under nitrogen
for 70 min. 2,3-Dicyano-5,6-dichloro-1,4-benzoquinone
where [A] is the total concentration, [A] is the concentration
of unbound free species, [AA] is the concentration of dimer,
0
(DDQ) (4.54 g, 0.02 mol, 1 equivalent) was added, and the
K is the dimerisation constant, d is the free chemical shift,
d
f
reaction mixture was stirred for a further 90 min before the
addition of triethylamine (2.8 ml). The solvent was removed in
vacuo, and the black residue was washed with methanol in a
Soxhlet to remove polymeric material. The solid residue was
dissolved in dichloromethane and passed through a short plug
and d is the limiting bound chemical shift of the dimer.
d
NMRDil Agg Ðts the data to a non-cooperative linear
oligomerisation/polymerisation isotherm by solving the fol-
lowing equations:
of Florisil eluting with light petroleumÈCHCl (1 : 1, bp range
for light petroleum; 40È60 ¡C) to remove any remaining
polymer. The solvent was removed in vacuo, and the porphy-
rin products were separated by column chromatography on
G
2
H
3
[
Agg] \ [A] 1 [
(4)
(5)
(6)
0
1 ] JM1 ] 4K[A] N
0
[
A] \ [A] [ [Agg]
0
silica eluting with light petroleumÈCHCl (2 : 1). The Ðrst
3
band was H L1 which was recrystallised from
2
\ 2
[Agg]
[A]
[A]
d
d ]
d
CHCl ÈCH OH to give purple plates (0.3È0.8 g, 8È16%). The
obs
[A]
b
f
3
3
0
0
second band was the mononitroporphyrin which was rec-
rystallised in the same manner to give a dark purple powder.
where [A] is the total concentration, [A] is the concentration
of sites which are unbound (this is the sum of the free species
0
and the ends of the aggregate which are not bound), [Agg] is
the concentration of sites involved in intermolecular inter-
actions in the aggregate, K is the association constant for
5,10,15,20 - Tetrakis(4 - pentylphenyl) - 21H,23H - porphine
H L1. Mp 313È316 ¡C (Found: C, 85.66; H, 7.88; N, 6.24.
2
Calc. for C
H N : C, 85.86; H, 7.88; N, 6.26%); j
6
4 70 4
max
chain extension of the aggregate, d is the free chemical shift,
(CH Cl )/nm 420 (e/dm3 mol~1 cm~1 530 000), 517 (25 000),
f
2 2
and d is the limiting bound chemical shift of the bound sites
551 (16 000) and 598 (9 300); d (CDCl ) 8.87 (8H, s, b-pyrrolic
b
H
3
in the aggregate.
H), 8.12 (8H, d, J 7, ArH ), 7.56 (8H, d, J 7, ArH ), 2.96 (8H, t,
o
m
Several signals were followed in each experiment, and the
value quoted for the association constant is the weighted
average based on the observed changes in chemical shift. The
errors quoted are twice the standard error (95% conÐdence
limit).
J 7, ArCH ), 1.93 (8H, qn, J 7, CH ), 1.52 (16H, m, 8 ] CH ),
2
2
2
1.03 (12H, t, J 7Hz, CH ), [2.75 (2H, s, NH); m/z (FAB) 895
3
(M`, C
H
N requires 895.2962).
6
4 70 4
5
-(2-Nitrophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
porphine H L6. Yield 0.44 g, 10%; mp 199È201 ¡C; j
2
max
(
5
CH Cl )/nm 423 (e/dm3 mol~1 cm~1 640 000), 518 (13 400),
Complexation-induced change in chemical shift calculations
2
2
54 (6 810), 593 (3 990) and 649 (3 070); d (CDCl ) 8.88 (2H, d,
H
3
The method used to determine three-dimensional structures
from complexation-induced changes in chemical shift has been
described in detail elsewhere.27 In this work, the porphyrin
ring current shifts were calculated using the eight loop HaighÈ
Mallion model developed by Cross and Wright with ring
current intensity factors of 1.99 for the six-membered rings
and 0.55 for the Ðve-membered rings.28
J 7, b-pyrrolic H), 8.86 (4H, s, b-pyrrolic H), 8.64 (2H, d, J 7,
b-pyrrolic H), 8.45 (1H, d, J 7, 5-H ), 8.24 (1H, d, J 7, 5-H ),
6
3
8.10 (6H, m, 10-, 15- and 20-H ), 7.95 (2H, m, 5-H and 5-H ),
o
4
5
7.50 (6H, d, J 7, 10-, 15- and 20-H ), 2.94 (6H, t, J 7, ArCH ),
1.95 (6H, qn, J 7, CH ), 1.50 (12H, m, 6 ] CH ), 1.05 (9H, t, J
7Hz, CH ), [2.72 (2H, s, NH); m/z (FAB) 870 (M`,
m
2
2
2
3
C
H
N O requires 870.1793).
59 59 5 2
314
New J. Chem., 1999, 309È316

View Article Online
5
-(3-Nitrophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
(2H, d, J 7, 5-H and 5-H ), 7.55 (6H, d, J 7, 10-, 15- and
2
6
porphine H L7. Yield 0.22 g, 5%; mp 259È261 ¡C; j
20-H ), 7.10 (2H, d, J 7, 5-H and 5-H ), 4.05 (2H, s, NH ),
2
max
m
3
5
2
(
CH Cl )/nm 421 (e/dm3 mol~1 cm~1 360 000), 518 (19 000),
2.95 (6H, t, J 7, ArCH ), 1.90 (6H, qn, J 7, CH ), 1.4È1.6 (12H,
2
2
2
2
5
5
54 (9 590), 592 (5 890) and 648 (4 710); d (CDCl ) 9.10 (1H, s,
m, 6 ] CH ), 1.05 (9H, t, J 7Hz, CH ), [2.75 (2H, s, NH); m/z
(FAB) 840 (M`, C
H
3
2
3
-H ), 8.92 (2H, d, J 7, b-pyrrolic H), 8.87 (4H, s, b-pyrrolic
H
N requires 840.1644).
2
59 61 5
H), 8.70 (2H, d, J 7, b-pyrrolic H), 8.68 (1H, d, J 7, 5-H ), 8.58
4
(
1H, d, J 7, 5-H ), 8.15 (6H, m, 10-, 15- and 20-H ), 7.95 (1H, t,
6
o
General procedure for the metallation of porphyrins
J 7, 5-H ), 7.60 (6H, d, J 7, 10-, 15- and 20-H ), 2.97 (6H, t, J
5
m
7
1
(
, ArCH ), 1.94 (6H, qn, J 7, CH ), 1.50 (12H, m, 6 ] CH ),
The free base porphyrin (36 mg, 0.04 mmol, 1 equivalent) was
2
2
2
.05 (9H, t, J 7Hz, CH ), [2.75 (2H, s, NH); m/z (FAB) 870
dissolved in CH Cl ÈCH OH (3 : 1, 30 ml) and zinc acetate
3
2
2
3
M`, C59 59 5 2
H
N O requires 870.1793).
(94 mg, 0.4 mmol, 10 equivalents) was added. The reaction
mixture was protected from light and stirred at room tem-
perature for 60 min. The solvent was removed in vacuo, and
the product was puriÐed by column chromatography on basic
alumina eluting with CH Cl ÈCH OH (99 : 1). Rec-
5
-(4-Nitrophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
porphine H L4. Yield 0.56 g, 13%; mp 243È245 ¡C; j
2
max
(
5
CH Cl )/nm 421 (e/dm3 mol~1 cm~1 330 000), 518 (18 000),
2
2
2
3
2
3
54 (11 000), 593 (6 500) and 649 (5 300); d (CDCl ) 8.92 (2H,
rystallisation from CHCl ÈCH OH yielded the product as a
H
3
3
purple powder (37 mg, 96%).
d, J 7, b-pyrrolic H), 8.88 (4H, s, b-pyrrolic H), 8.73 (2H, d, J
, b-pyrrolic H), 8.63 (2H, d, J 7, 5-H and 5-H ), 8.40 (2H, d,
7
2
6
J 7, 5-H and 5-H ), 8.12 (6H, d, J 7, 10-, 15- and 20-H ), 7.56
[5,10,15,20-Tetrakis(4-pentylphenyl)-21H,23H-porphinato] -
zinc 1. Mp 309È311 ¡C (Found: C, 80.23; H, 7.25; N, 5.87.
3
5
o
2
(
(
6H, d, J 7, 10-, 15- and 20-H ), 2.96 (6H, t, J 7, ArCH ), 1.93
m
6H, qn, J 7, CH ), 1.54 (12H, m, 6 ] CH ), 1.05 (9H, t, J 7Hz,
Calc. for C
64 68 4
(CH Cl )/nm 422 (e/dm3 mol~1 cm~1 650 000), 551 (26 000)
H N Zn: C, 80.19; H, 7.15; N, 6.26%); j
2
2
max
and 592 (8 300); d (CDCl ) 8.98 (8H, s, b-pyrrolic H), 8.12 (8H,
CH ), [ 2.75 (2H, s, NH); m/z (FAB) 870 (M`, C
H
N O
3
59 59 5 2
2 2
requires 870.1793).
H
3
d, J 7, ArH ), 7.55 (8H, d, J 7, ArH ), 2.96 (8H, t, J 7, ArCH ),
.93 (8H, qn, J 7, CH ), 1.52 (16H, m, 8 ] CH ), 1.03 (12H, t,
J 7Hz, CH ); m/z (FAB) 957 (M`, C
o
m
2
1
General procedure for reduction of nitroporphyrins
2
2
H
N Zn requires
3
64 68 4
The mononitroporphyrin (200 mg, 0.230 mmol, 1 equivalent)
957.51).
was dissolved in 1,4-dioxane (45 cm3). SnCl É 2H O (600 mg,
2
2
2
.66 mmol, 12 equivalents) and concentrated HCl (70 cm3)
[5-(2-Aminophenyl)-10,15,20-(4-pentylphenyl)-21H,23H-por-
phinato]zinc 2. Mp 227È230 ¡C; j (CH Cl )/nm 423 (e/dm3
were added. The reaction vessel was protected from light and
heated for 60 min under argon using a preheated oil bath
max
2 2
mol~1 cm~1 61 500), 549 (29 100) and 589 (6 760); d (CDCl )
H
3
(
70 ¡C). After removing the heat source, the hot reaction
concentration-dependent, 9.04 (2H, d, J 7, b-pyrrolic H), 8.92
(2H, d, J 7, b-pyrrolic H), 8.70 (2H, d, J 7, b-pyrrolic H), 8.28
(1H, d, J 7, 15-H ), 8.20 (1H, d, J 7, 15-H ), 8.17 (2H, d, J 7,
mixture was basiÐed by adding concentrated NH and then
3
allowed to cool to room temperature. The product was
o
o
extracted with ethyl acetate (3 ] 50 cm3). The organic frac-
10- and 20-H ), 8.08 (2H, d, J 7, b-pyrrolic H), 7.93 (2H, d, J 7,
o
tions were combined, washed with water, dried over Na SO
10- and 20-H ), 7.75 (1H, d, J 7, 15-H ), 7.60 (1H, d, J 7,
15-H ), 7.60 (2H, d, J 7, 10- and 20-H ), 7.48 (2H, d, J 7, 10-
and 20-H ), 7.48 (1H, d, J 7, 5-H ), 7.08 (1H, t, J 7, 5-H ), 6.94
2
4
o
m
and Ðltered. The solvent was removed in vacuo, and the
product was puriÐed by column chromatography on silica
eluting with light petroleumÈCH Cl (1 : 4). The product was
m
m
m
6
4
(1H, t, J 7, 5-H ), 4.91 (1H, d, J 7, 5-H ), 2.85 (6H, t, J 7,
2
3
2
5
3
recrystallised from CH Cl ÈCH OH giving a purple powder
ArCH ), 1.88 (6H, qn, J 7, CH ), 1.48 (12H, m, 6 ] CH ), 1.00
2
2
2
2
2
(
0.18 g, 95%).
(9H, t, J 7Hz, CH ), 0.60 (2H, s, NH ); m/z (FAB) 903 (M`,
3
H N Zn requires 903.4886).
2
C59 59 5
5
-(2-Aminophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
(cyclohexane)/nm 423
porphine H L2. Mp 169È171 ¡C; j
[5-(3-Aminophenyl)-10,15,20-(4-pentylphenyl)-21H,23H-por-
2
max
e/dm3 mol~1 cm~1 94 500), 517 (19 200), 553 (9 240), 592
(
phinato]zinc 3. Mp 169È172 ¡C; j
(CHCl )/nm 422 (e/dm3
max
3
(
8
(
(
2
6
(
5 550) and 647 (4 540); d (CDCl ) 8.80 (8H, s, b-pyrrolic H),
mol~1 cm~1 307 000), 549 (14 600) and 589 (2 940); d (CDCl )
H
3
H
3
.05 (6H, m, 10-, 15- and 20-H ), 7.84 (1H, d, J 7, 5-H ), 7.53
concentration-dependent, 9.03 (2H, d, J 7, b-pyrrolic H), 8.95
(2H, d, J 7, b-pyrrolic H), 8.71 (2H, d, J 7, b-pyrrolic H), 8.25
o
6
m
1H, t, J 7, 5-H ), 7.50 (6H, d, J 7, 10-, 15- and 20-H ), 7.25
1H, t, J 7, 5-H ), 7.10 (1H, d, J 7, 5-H ), 3.50 (2H, s, NH ),
.94 (6H, t, J 7, ArCH ), 1.95 (6H, qn, J 7, CH ), 1.50 (12H, m,
] CH ), 1.05 (9H, t, J 7Hz, CH ), [2.80 (2H, s, NH); m/z
FAB) 840 (M`, C
4
5
(2H, m, b-pyrrolic H), 8.29 (2H, d, J 7, 10- and 20-H ), 8.20
3
2
o
(1H, d, J 7, 15-H ), 8.16 (1H, d, J 7, 15-H ), 7.94 (2H, d, J 7,
2
2
o
o
10- and 20-H ), 7.69 (1H, d, J 7, 15-H ), 7.62 (2H, d, J 7, 10-
2
3
o
m
H
N requires 840.1644).
and 20-H ), 7.57 (1H, d, J 7, 15-H ), 7.46 (2H, d, J 7, 10- and
5
9 61 5
m
m
2
0-H ), 7.32 (1H, d, J 7, 5-H ), 6.62 (1H, t, J 7, 5-H ), 3.83 (2H,
m
6
5
5
-(3-Aminophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
m, 5-H and 5-H ), 2.96 (6H, t, J 7, ArCH ), 1.94 (6H, qn, J 7,
CH ), 1.50 (12H, m, 6 ] CH ), 1.04 (9H, t, J 7Hz, CH ); m/z
(FAB) 903 (M`, C
2
4
2
porphine H L3. Mp 153È155 ¡C; j (CH Cl )/nm 421 (e/dm3
2
max
2
2
2
2
3
mol~1 cm~1 328 000), 517 (13 000), 552 (6 890), 593 (3 840) and
H
N Zn requires 903.4886).
5
9 59 5
6
(
48 (3 500); d (CDCl ) 8.93 (2H, d, J 7, b-pyrrolic H), 8.84
H
3
4H, s, b-pyrrolic H), 8.82 (2H, d, J 7, b-pyrrolic H), 8.10 (6H,
[5-(4-Aminophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
(CH Cl )/nm 425
d, J 7, 10-, 15- and 20-H ), 7.62 (1H, t, J 7, 5-H ), 7.50 (7H, m,
porphinato]zinc 4. Mp 101È104 ¡C; j
o
6
max
2 2
1
0-, 15- and 20-H and 5-H ), 7.47 (1H, d, J 7, 5-H ), 7.10 (1H,
d, J 7, 5-H ), 3.94 (2H, s, NH ), 2.94 (6H, t, J 7, ArCH ), 1.95
(e/dm3 mol~1 cm~1 100 000), 551 (35 400) and 592 (12 900);
d (CDCl ) concentration-dependent, 9.11 (2H, d, J 7, b-
m
2
5
4
2
2
H
3
(
6H, qn, J 7, CH ), 1.50 (12H, m, 6 ] CH ), 1.05 (9H, t, J 7Hz,
pyrrolic H), 8.98 (2H, d, J 7, b-pyrrolic H), 8.45 (2H, d, J 7,
b-pyrrolic H), 8.36 (2H, d, J 7, b-pyrrolic H), 8.30 (2H, d, J 7,
15-H ), 7.64 (2H, d, J 7, 15-H ), 7.86 (4H, d, J 7, 10- and
2
2
CH ), [2.80 (2H, s, NH); m/z (FAB) 841 (M ] 1, C
H N
3
59 61 5
requires 840.1644).
o
o
m
2
0-H ), 7.08 (6H, m, 10- and 20-H and 5-H and 5-H ), 3.71
m
2
6
5
-(4-Aminophenyl)-10,15,20-tris(4-pentylphenyl)-21H,23H-
(2H, d, J 7, 5-H and 5-H ), 3.04 (2H, t, J 7, ArCH ), 2.75 (4H,
3
5
2
porphine H L4. Mp 147È149 ¡C; j
(CH Cl )/nm 422 (e/dm3
t, J 7, ArCH ), 2.00 (2H, qn, J 7, CH ), 1.73 (4H, qn, J 7,
CH ), 1.45 (2H, m, CH ), 1.30 (4H, m, 2 ] CH ), 1.11 (3H, t, J
7, CH ), 0.93 (6H, t, J 7Hz, CH ), 0.35 (2H, s, NH ); m/z
2
max
2
2
2
2
mol~1 cm~1 290 000), 519 (15 000), 557 (10 000), 594 (4 600)
and 650 (5 300); d (CDCl ) 8.91 (4H, m, b-pyrrolic H), 8.87
4H, s, b-pyrrolic H), 8.10 (6H, d, J 7, 10-, 15- and 20-H ), 8.00
2
2
2
H
3
3
3
2
(
(FAB) 903 (M`, C
H
N Zn requires 903.4886).
o
59 59 5
New J. Chem., 1999, 309È316
315

View Article Online
1
1
3 C. M. Drain, R. Fischer, E. G. Nolen and J. M. Lehn, J. Chem.
Soc., Chem. Commun., 1993, 243.
Acknowledgements
We thank PÐzer and the EPSRC (AJG), the Spanish govern-
ment (CR) and the Lister Institute (CAH) for Ðnancial
support.
4 C. M. Drain and J. M. Lehn, J. Chem. Soc., Chem. Commun., 1994,
2
313.
15 H. L. Anderson, Inorg. Chem., 1994, 33, 972.
16 P. J. Stang, J. Fan and B. Olenyuk, Chem. Commun., 1997, 1453.
17 C. A. Hunter and L. D. Sarson, Angew. Chem., Int. Ed. Engl., 1994,
33, 2313.
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