Far-red absorbing azodipyrrin dyes synthesis, X-ray crystallographic, and spectral characterization of 1,9-diazodipyrrins and their metal complexes

Article abstract of DOI:10.1139/V10-173

A series of novel 1,9-diazodipyrrins (4) were readily synthesized by reacting aryldiazonium salts with 5-aryldipyrromethanes under both acidic and basic conditions. The zinc complex of 1,9-diphenylazodipyrrin (5aZn) was confirmed by X-ray crystallographic

Full text of DOI:10.1139/V10-173

481
Far-red absorbing azodipyrrin dyes — Synthesis,
X-ray crystallographic, and spectral
characterization of 1,9-diazodipyrrins and their
metal complexes
Yan Li and David Dolphin
Abstract: A series of novel 1,9-diazodipyrrins (4) were readily synthesized by reacting aryldiazonium salts with 5-aryldi-
pyrromethanes under both acidic and basic conditions. The zinc complex of 1,9-diphenylazodipyrrin (5aZn) was confirmed
by X-ray crystallographic analysis, and 1,9-diazodipyrrins and their zinc and nickel complexes (5M) were characterized by
1H and 13C NMR, IR, UV–vis, and MS. All of the metal complexes absorb almost all colours of the rainbow; the absorp-
tion maximums are >650 nm and the half-band widths are over 100 nm. The fluorescence of the zinc complexes of 1,9-di-
phenylazodipyrrin (5aZn) and 1,9-di(2-iodophenylazo)dipyrrin (5cZn) were also explored.
Key words: dipyrrin, dipyrromethane, azo dye, boron-dipyrromethene (BODIPY), fluorescence.
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Resume : On a facilement realise la synthese d’une serie de nouvelles 1,9-diazodipyrrines (4) en faisant reagir des sels
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d’aryldiazonium avec des 5-aryldipyrromethanes dans des conditions acides ou basiques. On a confirme la structure du
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complexe de zinc de la 1,9-diphenylazodipyrrine (5aZn) par diffraction des rayons-X alors que les 1,9-diazodipyrrines et
1
leurs complexes avec le zinc et le nickel (5M) ont ete caracterises par leurs spectres RMN du H et du 13C, leurs spectres
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IR, UV–vis et leurs spectres de masse. Tous les complexes metalliques absorbent pratiquement toutes les couleurs de l’arc-
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en-ciel; les maxima d’absorption sont superieurs a 650 nm et les largeurs des bandes a demi-hauteur s’etalent sur 100 nm.
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On a aussi examine la fluorescence des complexes de zinc de la 1,9-diphenylazodipyrrine (5aZn) et de la 1,9-di(2-iodophe-
nylazo)dipyrrine (5cZn).
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Mots-cles : dipyrrine, dipyrromethane, colorant azo, bore-dipyrromethene (BODIPY), fluorescence.
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[Traduit par la Redaction]
and NR2) have absorption maxima >650 nm. Herein, we re-
port the synthesis, X-ray crystallographic, and spectral char-
acterization of novel 1,9-diazodipyrrins (4) and their zinc
and nickel complexes (5M).
Introduction
Dipyrrins are well-known as important building blocks in
supramolecular chemistry and as subunits of porphyrins
(Fig. 1).1 Owing to the fluorescent characteristics of their
BF2 complexes (boron-dipyrromethene (BODIPY) dyes),
publications related to dipyrrins have increased dramatically
during the past two decades.2 In comparison with their
bridged nitrogen analogues, azadipyrromethenes,3 dipyrrins
have smaller absorption maxima, which has limited their po-
tential use as photosensitizers for photodynamic therapy.4
The design and synthesis of dipyrrin derivatives with longer
wavelength absorption has been a challenge in this field.
Nucleophilic substitutions and catalyzed coupling reactions
on 1,9-dichloro-BODIPY have been adapted to produce
BODIPYs with greater absorption maxima (1), but their ab-
sorption maxima are still <620 nm.5,6 Until now, among the
numerous known dipyrrin derivatives, only a few 1,9-distyr-
yldipyrrin-BF2 (2)7 and rigid 1,5,9-triaryldipyrrin-BF2 (3)8
complexes with strong electron-donating substituents (OR
Results and discussion
Synthesis of 1,9-diazodipyrrins
In our initial studies, we employed the use of dipyrrome-
thanes9 to react with diazonium salts to form the desired
1,9-diazodipyrrins. Unfortunately, the reaction of dipyrrome-
thanes with phenyldiazonium chloride did not afford 2,2’-
di(phenylazo)dipyrromethane (6) but rather 2,5-diphenylazo-
pyrrole (7) was isolated in a 61% yield (Scheme 1). This is
the same product that would result from reacting diazonium
salts with pyrrole.10 The degradation reactions between di-
pyrromethanes and aryldiazonium salts leading to monopyr-
rollic products are known in the literature and can be
assumed to be the result of the strong electrophilic nature of
pyrrole.11,12 Depraetere and Dehaen12 reported the structure
Received 3 August 2010. Accepted 30 November 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on 18 March
2011.
Y. Li and D. Dolphin.1 Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1,
Canada.
1Corresponding author (e-mail: david.dolphin@ubc.ca).
Can. J. Chem. 89: 481–487 (2011)
doi:10.1139/V10-173
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Can. J. Chem. Vol. 89, 2011
Fig. 1. Structures of dipyrrin–BF2 (1), distyryldipyrrin–BF2 (2), and
the rigid 1,5,9-triaryldipyrrin–BF2 (3) complexes, and 1,9-diazodi-
pyrrins (4) and their metal complexes (5M).
Scheme 2. The reaction between 5-phenyldipyrrin and phenyl-
diazonium dichloroacetic salt.
Fig. 2. ORTEP view of 5aZn (hydrogen atoms are not shown).
Scheme 1. The reaction between a dipyrromethane and phenyl-
diazonium chloride.
of 1,9-diphenylazo-5,5-dipropyl-dipyrromethane in 2003, but
did not provide any supporting analytical data.
While dipyrrins are relatively electron deficient, they can
also act as nucleophiles in the presence of Lewis acids to
form porphyrins.13 This characteristic prompted us to inves-
tigate the reaction between 5-phenyldipyrrin and phenyl-
diazonium salt (Scheme 2). 5-Phenyldipyrrin was readily
prepared by the reaction of trimethyl orthobenzoate with
pyrrole and an excess of dichloroacetic acid.14 The phenyl-
diazonium salt was formed by reacting aniline with sodium
nitrite – aqueous dichloroacetic acid at temperatures <5 8C.10
After neutralization with triethylamine and treatment with
0.5 equiv. of 5-phenyldipyrrin in methanol, a red mixture
was formed. Chromatography on a silica gel column pro-
vided a small amount of purple product that was identified
as 1,9-diazodipyrrin 4a by NMR and MS. When an acidic
solution of the phenyldiazonium salt was added directly to
the methanol solution of 5-phenyldipyrrin, the same purple
compound was isolated in a 15% yield. Further reaction of
4a with zinc acetylacetonate provided the complex 5aZn.
With the growth of diffraction-quality crystals of 5aZn by
the slow evaporation of a dichloromethane–hexane solution
at –5 8C, the structure of complex 5aZn was confirmed by
X-ray crystallographic analysis (Fig. 2; also see the Supple-
mentary data).
With the confirmed structure of the 1,9-diazodipyrrin in
hand, we turned our attention to exploration of an alternate
synthetic method to improve the yield of 1,9-diazodipyrrins.
Interestingly, in contrast to the dipyrromethane, 5-(4-
iodophenyl)dipyrromethane15 was found to react with phe-
nyldiazonium chloride under basic conditions to form 1,9-
di(phenylazo)-5-(4-iodophenyl)dipyrromethane (6d) (route 1
in Scheme 3). When air was bubbled into an ethyl acetate
solution of 6d for several hours, 6d was converted into 1,9-
(diphenylazo)-5-(4-iodophenyl)dipyrrin (4d). Following this
method, the reaction of 5-(2,4,6-trimethoxyphenyl)dipyrro-
methane16 with phenyldiazonium chloride afforded 1,9-
(diphenylazo)-5-(2,4,6-trimethoxyphenyl)dipyrrin (4e) in a
moderate yield. Furthermore, when the reactions between 5-
phenyldipyrrin with aryldiazonium dichloroacetic salts were
carried out under acidic conditions, 1,9-diazodipyrrins (4b:
Published by NRC Research Press

Li and Dolphin
483
Table 1. Crystal data and structure refinements for
5aZn.
Scheme 3. Synthesis of 1,9-diazodipyrrin complexes starting from
5-aryldipyrromethane and aryldiazonium dichloroacetic salt.
Formula
Mw
C60H52N12Zn
1006.51
Orthorhombic
Pbca (No. 61)
10.0893(3)
20.2261(7)
50.323(2)
90
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90
90
3
˚
V (A )
10 269.2(6)
8
1.302
Z
Dc (g/cm3)
m (cm–1)
5.31
Unique (Rint = 0.075)
Reflection/parameter ratio
R1; wR2
6791
9.20
0.116; 0.120
1.12
GoF
No. of obs. data (I > 2s(I)) 4340
R1; wR2
0.063; 0.104
Table 2. Selected bond distances and angles for 5aZn.
˚
Bond distances (A)
N—N
Ar’ = Ph, Ar = 2-Me2CH-Ph; 4c: Ar’ = Ph, Ar = 2-I-Ph)
were formed directly in a one-pot synthesis (route 2 in
Scheme 3). All of the 1,9-diazodipyrrins (4) reacted with a
zinc salt to form complexes (5aZn, 5bZn, 5cZn, 5dZn, and
5eZn) and 4a reacted with nickel acetate to form the nickel
complex 5aNi (route 3 in Scheme 3). Whereas complexes
5aZn, 5aNi, 5bZn, 5cZn, and 5dZn are fully characterized
by NMR, MS, and UV–vis spectra, complex 5eZn was un-
stable even when stored at low temperature.
1.264(5), 1.265(5), 1.262(5), 1.264(5)
N(azo)—C(pyrrole)
N(azo)—C(phenyl)
Zn—N
Bond angles (8)
N–N–C(pyrrole)
N–N–C(phenyl)
N(1)–Zn–N(2,3,4)
N(2)–Zn–N(3,4)
N(3)–Zn–N(4)
C–N–N–C
1.403(6), 1.399(6), 1.401(6), 1.398(6)
1.444(6), 1.431(6), 1.417(6), 1.425(6)
1.983(4), 1.984(4), 1.981(4), 1.981(4)
112.6(4), 113.2(4), 113.4(4), 113.9(4)
112.8(4), 113.5(4), 113.0(4), 111.8(4)
92.2(2), 116.2(2), 117.5(2)
123.4(2), 117.8(2)
91.8(2)
X-ray crystal structure of 5aZn
176.8(4), 174.8(4), 177.1(4), 178.1(4)
The structure of 5aZn was determined by X-ray crystallog-
raphy and is shown in Fig. 2. Data were collected at –170.0
0.1 8C with maximum 2q values of 45.18 on a Bruker APEX
II diffractometer with graphite-monochromated Mo Ka radi-
ation. The structures were solved by direct methods.17 The
material crystallizes with one disordered phenyl ring (C43–
C48), which was modeled in two orientations with restraints
to maintain the hexagonal character of the phenyl ring. All
refinements were performed using the SHELXL-9718 via
the WinGX19 interface. Crystal data and structure refine-
ments are summarized in Table 1, and selected bond lengths
and angles are listed in Table 2.
Fig. 3. Top and side views of 5aZn (hydrogen atoms are not
shown).
for their N=N–C(pyrrole) configurations,10 all N=N–
C(pyrrole) configurations in structure 5aZn are in the trans–
trans form as a result of the coordination to the central zinc
ion. The diazodipyrrin ligands are slightly distorted, where
the dihedral angles between the dipyrrin planes and phenyl
planes are 188 and 168 for the ligand of C5 and 198 and 238
for the ligand of C14, respectively. The 5-phenyl groups are
not perpendicular to their dipyrrin planes, thus, not parallel
to the dipyrrin planes of the other ligands. The 5-phenyl
group C25–C30 has angles of 638 to the parent dipyrrin
plane and 338 to that of the other ligand; the 5-phenyl group
C43–C48 has angles of 638 and 568 to the parent dipyrrin
Complex 5aZn has a tetrahedral structure around the cen-
tral zinc ion. The Zn–N(pyrrole) bond distances are
˚
1.983(4), 1.984(4), 1.981(4), and 1.981(4) A, respectively,
but the N–Zn–N angles within the same diazodipyrrin ligand
(92.2(2)8 and 91.8(2)8) are smaller than those between two
ligands (116.2(2)8, 117.5(2)8, 123.4(2)8, and 117.8(2)8).
5aZn exhibits N=N bond distances between 1.262 and
˚
1.265 A, which are slightly longer than that of free 2-
˚
phenylazopyrrole (1.253(2) A) and shorter than those of
10
˚
2,5-diazopyrroles (1.283–1.293 A).
Figure 3 shows the top and side view representations of
5aZn. Whereas 2,5-diazopyrroles have the trans–cis form
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484
Can. J. Chem. Vol. 89, 2011
1
plane and 338 and 298 to that of the other ligand, respec-
tively. Furthermore, the mean deviations of carbon and ni-
trogen atoms from the p-delocalized skeletons of the
Fig. 4. The partial H NMR spectra of 4a, 5aZn, and 5cZn at tem-
peratures between 25 and –80 8C.
˚
diazodipyrrin ligands are 0.14 and 0.16 A, respectively.
1H NMR spectra
1,9-Diazodipyrrin (4a and 4c–4e) and their complexes
(5aZn, 5aNi, 5cZn, and 5dZn) exhibit symmetric proton
signals in their 1H NMR spectra, but the bulky ortho-
isopropyl substituents of 4b and 5bZn distort their ligand
planes and result in distinct proton signals for the two arylazo
and two pyrrole groups.
1H NMR spectra were generated at various temperatures
between 25 and –80 8C for 4a, 5aZn, and 5cZn, and their
pyrrolic proton signals are shown in Fig. 4. Azo dyes have
cis and trans isomers, which exist in an equilibrium specific
to the solvent and temperature. Upon decreasing the temper-
ature, the equilibrium between the cis and trans isomers
shifts toward the cis isomer.20 The planar 1,9-diazodipyrrin
4a has two pyrrolic proton signals at 7.05 and 6.78 ppm at
room temperature. No significant change was observed for
the chemical shift difference of the two pyrrolic protons
(0.27 ppm) from 25 to –80 8C (0.25 ppm). This suggests
the phenylazo groups have little influence on the pyrrolic
proton signals in the same 1,9-diazodipyrrin ligand regard-
less of whether the cis or trans configuration dominates.
However, the chemical shift difference of two pyrrolic pro-
tons of 5aZn increases from 0.00 ppm at 25 8C to 0.31 ppm
at –80 8C. This phenomenon suggests that the trans–trans
form of the N=N–C(pyrrole) configuration in structure
5aZn at room temperature shifts toward the cis–trans form
at –80 8C, so that the phenylazo group is further away from
the pyrrolic groups in an adjacent 1,9-diazodipyrrin ligand
and has less influence on their pyrrolic proton signals. Inter-
estingly, the chemical shift difference of the two pyrrolic
protons of 5cZn shows little change from 0.28 ppm at
25 8C to 0.31 ppm at –80 8C. This may be explained by the
large radius of the iodo substituent at the ortho position of
the –N=N–, which restricts the azo cis/trans isomerization.
Table 3. The UV–vis absorption data of 1,9-diazodi-
pyrrins (4) and their complexes (5M) in CHCl3.
Half-band width
Compd.
4a
4b
4c
4d
lmax (log 3) (nm)
574 (4.47)
580 (4.49)
582 (4.52)
573 (4.50)
(nm)
119
136
149
130
144
4e
573 (4.54)
5aZn
5aNi
5bZn
5cZn
5dZn
5eZn
613 (4.61), 659 (4.67) 108
655 (4.62) 155
615 (4.66), 674 (4.68) 136
631 (4.80), 683 (4.83) 122
615 (4.63), 662 (4.67) 128
628, 674
128
UV–vis spectra
Table 3 lists the UV–vis absorption data of 4 and com-
plexes 5M. Figure 5 shows the UV–vis absorption spectra
of 4a, 5aZn, and 5aNi. 4a has its visible absorption maxi-
mum at 528 nm and a half-band width of 119 nm that re-
flects the overlap of absorptions between the arylazo and
dipyrrin chromophores. Complexation with the zinc ion in
5aZn shifts the absorption maximum bathochromically and
forms two distinct and sharper absorptions at 613 and
659 nm with a total half-band width of 108 nm. The absorp-
tion on the blue side should be attributed to the azo chromo-
phore as it is less affected by the metal ion; correspondingly,
the lower energy absorption can be assigned to the dipyrrin
chromophore. With the introduction of the iodo atom, the
corresponding absorptions of 5cZn shift further to 631 and
683 nm. In contrast, complexation with nickel in 5aNi shifts
the absorption maximum to 655 nm and produces a half-
band width of 155 nm. As the analogue of 4a, the 1,9-distyryl-
dipyrrin–BF2 complex has its absorption maximum at
630 nm.21
Fluorescence
Since the zinc complexes of dipyrrins are reported to be
fluorescent,22 the fluorescence of complexes 5aZn and
5cZn were examined at room temperature. When 5aZn was
excited at a wavelength of 630 nm, a weak but noticeable
emission was detected with a maximum wavelength of
690 nm (Fig. 6). Complex 5eZn might have better emission
because of the restricted rotation of the bulky 5-(2,4,6-
trimethoxy)phenyl group,22,23 but it decomposed during the
detection process. Interestingly, 5cZn, which is stable, did
not fluoresce when excited at 650 nm, which is consistent
with the heavy atom effect of the iodines.4,24
Conclusion
In this work, we report the facile synthesis of 1,9-diazodi-
pyrrins and select metal complexes as novel dipyrrin and
azo dye derivatives. Along with only a few 1,9-distyryldi-
pyrrin–BF2 and rigid 1,5,9-triaryldipyrrin–BF2 complexes
Published by NRC Research Press

Li and Dolphin
485
Fig. 5. Absorption spectra of 4a (black line) and complexes 5aZn
(purple line) and 5aNi (blue line) in chloroform.
residual nondeuterated solvent (CHCl3). UV–vis spectra
were measured in CHCl3. IR spectra were measured as solid
samples and N=N stretching vibrations were designated re-
ferring to the literature.25 Mass spectra were measured using
ESI and MALDI-TOF.
General procedure for the preparation of 1,9-
diazodipyrrins 4a–4c
To a suspension of the aromatic amine (4.0 mmol) in
water (8 mL) was added dichloroacetic acid (12 mmol,
1.0 mL). The solution was cooled and kept at 0–5 8C in an
ice bath and diazotized by addition of a solution of sodium
nitrite (4.1 mmol, 0.283 g) in water (3 mL), followed by
stirring for 30 min at 0–5 8C. To a solution of the dipyrrin
(2 mmol) and dichloroacetic acid (2 mmol, 0.17 mL) in
methanol (80 mL) was slowly added a solution of the diazo-
nium salt at 0–5 8C. The resulting mixture was stirred for
5 h and then evaporated under vacuum to dryness. The resi-
dues were purified by column chromatography, eluting with
a gradient mixture of ethyl acetate and hexane (1:20 to 1:10)
for 4a and dichloromethane and hexane (2:3) for 4b and 4c.
Fig. 6. Fluorescence spectrum of 5aZn in chloroform with excita-
tion at 630 nm.
1,9-Diphenylazo-5-phenyldipyrrin (4a)
Yield: 42%; mp 133–134 8C. UV–vis (1.05 Â 10–5 mol/L,
CH2Cl2) lmax (log 3): 367 (4.69), 574 (4.47). IR
1
(N=N, cm–1) n: 1053. H NMR (CDCl3) d: 13.05 (b, 1H),
8.04 (d, 4H, J = 6.9), 7.59–7.52 (m, 11H), 7.04 (d, 2H, J =
4.7), 6.76 (d, 2H, J = 4.4). 13C NMR (CDCl3) d: 163.4,
153.6, 143.1, 143.0, 136.4, 131.9, 131.3, 130.6, 129.6,
129.4, 128.1, 123.6, 115.2. ESI MS (M + H)+ m/z: 429.
Anal. calcd for C27H20N6Á1/4C6H14 (solvent of crystallization
determined by NMR): C 76.06, H 5.26, N 18.67; found: C
76.07, H 4.89, N 18.62.
1,9-Di(2-isopropylphenylazo)-5-phenyldipyrrin (4b)
Yield: 34%; mp 123–124 8C. UV–vis (1.13 Â 10–5 mol/L,
CHCl3) lmax: 372 (4.66), 580 (4.49). IR (N=N, cm–1) n:
1
1038. H NMR (CD2Cl2) d: 13.20 (b, 1H), 7.81 (d, 2H, J =
8.0), 7.59–7.48 (m, 9H), 7.33–7.28 (m, 2H), 7.04 (d, 2H, J =
4.5), 6.78 (d, 2H, J = 4.5), 4.23–4.16 (m, 2H), 1.39 (s, 6H),
1.38 (s, 6H). 13C NMR (CD2Cl2) d: 164.0, 150.8, 150.0,
143.3, 136.7, 132.8, 131.6, 130.7, 130.0, 128.5, 127.2,
126.8, 126.4, 116.1, 115.6, 28.5, 24.3. ESI MS (M + H)+ m/z:
513.4. Anal. calcd for C33H32N6: C 77.31, H 6.29, N 16.39;
found: C 77.35, H 6.58, N 16.26.
with strong electron-donating substituents, these compounds
constitute a rare group of dipyrrin derivatives with absorp-
tion maxima >650 nm, an important feature for potential
photodynamic therapy (PDT) agents. As well, initial studies
show the 5aZn complex exhibits weak fluoresence. Future
work entails the introduction of p-conjugated substituents
(SR, OR, I, Br, and NO2) to the two ortho positions of the
arylazo group to restrict cis/trans isomerization of the –N=N–
bond. These changes, as well as complexation with BF2,
should enhance fluorescence efficiency.
1,9-Di(2-iodophenylazo)-5-phenyldipyrrin (4c)
Yield: 38%; mp 159–160 8C. UV–vis (9.9 Â 10–6 mol/L,
CHCl3) lmax: 376 (4.63), 582 (4.52). IR (N=N, cm–1) n:
1
1065. H NMR (CD2Cl2) d: 13.3 (1H), 8.08 (d, 2H, J =
8.0), 7.80 (d, 2H, J = 6.8), 7.59–7.53 (m, 5H), 7.50–7.47
(m, 2H), 7.24–7.21 (m, 2H), 7.10 (d, 2H, J = 4.6), 6.79 (m,
2H, J = 4.5). 13C NMR (CD2Cl2) d: 163.4, 152.2, 144.2,
143.7, 140.7, 136.3, 133.7, 131.6, 131.0, 130.2, 129.6,
128.6, 117.6, 117.3, 105.0. ESI MS (M + H)+ m/z: 681.1.
Anal. calcd for C27H18I2N6: C 47.67, H 2.67, N 12.35;
found: C 47.92, H 2.81, N 12.00.
Experimental
All starting materials, reagents, and solvents were com-
mercially available and used as received. Column chroma-
tography was performed using 230–400 mesh silica gel.
1
Melting points are uncorrected. H and 13C NMR spectra
General procedure for the preparation of 1,9-
diazodipyrrins 4d and 4e
To a suspension of the aromatic amine (4.0 mmol) in
were recorded in CDCl3 with a 400 MHz spectrometer (J in
Hz); the chemical shifts (d, ppm) are quoted relative to the
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486
Can. J. Chem. Vol. 89, 2011
water (8 mL) was added dichloroacetic acid (12 mmol,
1.0 mL). The solution was cooled and kept at 0–5 8C in an
ice bath and diazotized by addition of a solution of sodium
nitrite (4.1 mmol, 0.283 g) in water (3 mL), followed by
stirring for 30 min at 0–5 8C. To a solution of the dipyrrin
(2 mmol) and triethylamine (25 mmol, 3.5 mL) in methanol
(80 mL) was slowly added a solution of the diazonium salt
at 0–5 8C. The resulting mixture was stirred for 5 h and then
evaporated under vacuum to dryness. The residues were dis-
solved in ethyl acetate and washed with water. Air was
bubbled into the organic phase for 4 h and then evaporated
and purified by column chromatography, eluting with a mix-
ture of ethyl acetate and hexane (1:20).
tion determined by NMR): C 70.40, H 4.77, N 17.28; found:
C 70.08, H 4.62, N 16.90.
Zinc complex of 1,9-di(2-isopropylphenylazo)-5-
phenyldipyrrin (5bZn)
Yield: 88%. UV–vis (1.06 Â 10–5 mol/L, CHCl3) lmax
(log 3): 367 (4.66), 615 (4.66), 674 (4.68). IR (N=N, cm–1)
1
n: 1047. H NMR (CD2Cl2) d: 7.67–7.59 (m, 10H), 7.34–
7.31 (m, 8H), 7.02 (d, 4H, J = 8.0), 6.95–6.88 (m, 8H),
6.79 (d, 4H, J = 4.5), 3.93–3.86 (m, 4H), 1.19 (s, 12H),
1.17 (s, 12H). 13C NMR (CD2Cl2) d: 167.4, 150.7, 149.0,
148.6, 142.8, 138.2, 133.9, 131.7, 131.4, 129.3, 127.7,
126.4, 126.2, 115.1, 108.4, 27.6, 23.6. ESI MS (M + H)+ m/z:
1087.8. Anal. calcd for C66H62N12ZnÁ2/3C6H14 (solvent of
crystallization determined by NMR): C 73.36, H 6.27, N
14.67; found: C 73.53, H 6.22, N 14.68.
1,9-Diphenylazo-5-(4-iodophenyl)dipyrrin (4d)
Yield: 43%; mp 164–166 8C. UV–vis (1.03 Â 10–5 mol/L,
CHCl3) lmax: 372 (4.63), 573 (4.50). IR (N=N, cm–1) n:
1
Zinc complex of 1,9-di(2-iodophenylazo)-5-phenyldipyrrin
(5cZn)
1044. H NMR (CD2Cl2) d: 8.06 (d, 4H, J = 6.8), 7.91 (d,
2H, J = 8.3), 7.64–7.57 (m, 6H), 7.35 (d, 2H, J = 8.3), 7.07
(d, 2H, J = 4.4), 6.77 (d, 2H, J = 4.4). 13C NMR (CD2Cl2) d:
163.3, 153.4, 142.7, 137.4, 135.7, 132.8, 132.1, 130.2,
129.4, 129.2, 123.4, 122.1, 115.6. ESI MS (M + H)+ m/z:
555.2. Anal. calcd for C27H19IN6Á2/5C6H14 (solvent of crys-
tallization determined by NMR): C 59.97, H 4.21, N 14.27;
found: C 60.24, H 3.78, N 14.09.
Yield: 92%. UV–vis (1.50 Â 10–5 mol/L, CHCl3) lmax
(log 3): 370 (4.69), 631 (4.80), 683 (4.83). IR (N=N, cm–1)
1
n: 1051. H NMR (CD2Cl2) d: 7.93–7.92 (dd, 2H, J = 7.0,
2.0), 7.66–7.57 (m, 10H), 7.15–7.12 (dt, 4H, J = 8.1, 1.3),
7.08–7.04 (m, 4H), 6.94–6.93 (dd, 2H, J = 6.4, 2.5), 6.91–
6.88 (q, 4H, J = 9.9), 6.76–6.75 (dd, 4H, J = 8.0, 1.4),
6.47–6.44 (dt, 4H, J = 7.9, 1.5). 13C NMR (CD2Cl2) d:
167.1, 153.0, 144.0, 140.4, 139.4, 134.8, 132.9, 131.8, 129.9,
128.3, 120.2, 117.7, 115.1, 110.4, 103.9. MALDI-TOF
MS m/z: 1421.8. Anal. calcd for C54H34I4N12ZnÁ1/2CH2Cl2
(solvents of crystallization determined by NMR): C 44.64,
H 2.41, N 11.46; found: C 44.23, H 2.63, N 11.42.
1,9-Diphenylazo-5-(2,4,6-trimethoxyphenyl)dipyrrin (4e)
Yield: 40%; mp 180–181 8C. UV–vis (1.06 Â 10–5 mol/L,
CHCl3) lmax: 351 (4.60), 573 (4.54). IR (N=N, cm–1) n:
1
1050. H NMR (CD2Cl2) d: 12.78 (b, 1H), 8.04 (d, 4H, J =
7.4), 7.59 (t, 4H, J = 7.5), 7.54 (t, 2H, J = 7.2), 6.99 (d, 2H,
J = 4.5), 6.69 (d, 2H, J = 4.4), 6.30 (s, 2H), 3.92 (s, 3H),
3.74 (s, 6H). 13C NMR (CD2Cl2) d: 162.2, 162.0, 158.9,
152.9, 143.8, 136.1, 131.2, 128.8, 128.7, 122.7, 114.8,
105.3, 90.1, 55.5, 55.0. ESI MS (M + H)+ m/z: 519.4. Anal.
calcd for C30H26N6O3Á1/5C6H14 (solvent of crystallization
determined by NMR): C 69.94, H 5.42, N 15.68; found: C
69.78, H 5.33, N 15.33.
Zinc complex of 1,9-diphenylazo-5-(4-iodophenyl)dipyrrin
(5dZn)
Yield: 85%. UV–vis (9.42 Â 10–6 mol/L, CHCl3) lmax
(log 3): 369 (4.68), 615 (4.63), 662 (4.67). IR (N=N, cm–1)
1
n: 1040. H NMR (CD2Cl2) d: 7.90 (d, 4H, J = 8.6), 7.42 (d,
8H, J = 7.1), 7.38 (t, 4H, J = 7.3), 7.29 (t, 8H, J = 7.7), 7.19
(d, 4H, J = 8.4), 6.89 (d, 4H, J = 4.6), 6.83 (d, 4H, J = 4.4).
13C NMR (CD2Cl2) d: 166.9, 154.1, 148.5, 143.2, 138.1,
137.3, 134.2, 133.4, 131.8, 129.5, 123.5, 112.6, 95.9. ESI MS
(M + H)+ m/z: 1171.1. Anal. calcd for C54H36I2N12ZnÁ4/7C6H14
(solvent of crystallization determined by NMR): C 56.47, H
3.63, N 13.76; found: C 56.01, H 3.62, N 13.38.
General procedure for the preparation of zinc complexes
of 1,9-diazodipyrrins (5Zn)
The solution of 1,9-diazodipyrrin (0.06 mmol), zinc acetyl-
acetonate hydrate (0.03 mmol, 8 mg), and triethylamine
(0.2 mmol, 28 mL) in dry dichloromethane (30 mL) was re-
fluxed for 1 h and then evaporated under vacuum to dryness.
The residue was purified by column chromatography, elut-
ing with a mixture of ethyl acetate and hexane (1:20) for
5aZn, 5dZn, and 5eZn and dichloromethane and hexane
(2:3) for 5bZn and 5cZn.
Zinc complex of 1,9-diphenylazo-5-(2,4,6-
trimethoxyphenyl)dipyrrin (5eZn)
Yield: 76%. UV–vis (CHCl3) lmax: 356, 628, 674. IR
(N=N, cm–1) n: 1048. MALDI-TOF MS (M + H)+ m/z:
1099.4.
Zinc complex of 1,9-diphenylazo-5-phenyldipyrrin (5aZn)
Yield: 90%. UV–vis (1.03 Â 10–5 mol/L, CH2Cl2) lmax
(log 3): 361 (4.64), 613 (4.61), 659 (4.67). IR (N=N, cm–1)
Preparation of the nickel complex of 1,9-diphenylazo-5-
phenyldipyrrin (5aNi)
A solution of 4a (0.06 mmol, 25.7 mg), nickel acetate tet-
rahydrate (0.03 mmol, 7.5 mg), and triethylamine
(0.2 mmol, 28 mL) in dry dichloromethane (30 mL) was re-
fluxed for 1 h and then evaporated under vacuum to dryness.
The residue was purified by column chromatography, elut-
ing with a mixture of ethyl acetate and hexane (1:20) to
give the product. Yield: 92%. UV–vis (1.10 Â 10–5 mol/L,
CHCl3) lmax (log 3): 361 (4.84), 655 (4.62). IR
1
n: 1043. H NMR (CDCl3) d: 7.56 (t, 1H, J = 7.4), 7.50 (t,
2H, J = 7.5), 7.43 (dd, 6H, J = 7.6, 1.3), 7.32 (t, 2H, J =
7.2), 7.25 (t, 4H, J = 7.55), 6.83 (d, 2H, J = 4.5), 6.79 (d,
2H, J = 4.5). 13C NMR (CDCl3) d: 166.4, 153.8, 149.4,
143.2, 138.4, 133.9, 131.4, 131.0, 129.2, 129.0, 127.6,
123.3, 111.8. MALDI-TOF MS (M)+ m/z: 918. Anal. calcd
for C54H38N12ZnÁ1/2H2OÁ1/2C6H14 (solvents of crystalliza-
Published by NRC Research Press

Li and Dolphin
487
1
(N=N, cm–1) n: 1054. H NMR (CD2Cl2) d: 7.64 (9H), 7.50
(4H), 6.89 (6H). 13C NMR (CDCl3) d: 170.0, 146.1, 141.8,
138.1, 132.9, 131.3, 130.0, 129.7, 129.1, 128.7, 122.9,
121.7, 104.2. ESI MS (M + Na)+ m/z: 935.3. Anal. calcd
for C54H38N12NiÁ1/2H2O: C 70.29, H 4.26, N 18.22; found:
C 70.11, H 4.24, N 17.93.
Chem. Asian J. 2006,
1
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200600042.; (b) Zheng, Q.; Xu, G.; Prasad, P. N. Chem.
Eur. J. 2008, 14 (19), 5812. doi:10.1002/chem.200800309.;
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Supplementary data
Supplementary data (1H NMR, 13C NMR, and UV–vis
spectra) are available with this article through the journal
Web site (www.nrcresearchpress.com/cjc). CCDC 784639
contains the X-ray data in CIF format for this manuscript.
These data can be obtained, free of charge, via http://www.
ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.
cam.ac.uk).
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Acknowledgement
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This work was supported by QLT Inc., Vancouver, British
Columbia, and the Natural Sciences and Engineering Re-
search Council of Canada (NSERC). We thank the NMR,
Mass Spectroscopy, and Elemental Analysis labs of the
Chemistry Department at the University of British Colum-
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