Investigations on the directive effects of a single meso-substituent via nitration of 5,12,13,17,18-pentasubstituted porphyrins: Syntheses of conjugated β-nitroporphyrins

Article abstract of DOI:10.1016/S0040-4020(01)00329-5

Vilsmeier formylation of 5-substituted 1,9-diunsubstituted dipyrromethanes afforded 1,9-diformyldipyrromethanes in good yields. Their MacDonald condensation with tetra-β-alkyldipyrromethanes produced 5,12,13,17,18-pentasubstituted porphyrins. A meso-electron-donating group, presumably acting by destabilizing the porphyrin a_2u ground state, directs the nitrations to the meso-carbons. β-Nitration takes place on porphyrins bearing a meso-electron-withdrawing group. Unhindered β-nitro groups are shown to exert stronger electronic effects relative to meso-nitro groups by conjugating effectively with the porphyrin macrocycle.

Full text of DOI:10.1016/S0040-4020(01)00329-5

TETRAHEDRON
Pergamon
Tetrahedron 57 72001) 4261±4269
Investigations on the directive effects of a single meso-substituent
via nitration of 5,12,13,17,18-pentasubstituted porphyrins:
syntheses of conjugated b-nitroporphyrins
Anura Wickramasinghe, Laurent Jaquinod, Daniel J. Nurco and Kevin M. Smithp
Department of Chemistry, University of California, Davis, CA 95616, USA
Received 2 February 2001; accepted 10 March 2001
AbstractÐVilsmeier formylation of 5-substituted 1,9-diunsubstituted dipyrromethanes afforded 1,9-diformyldipyrromethanes in good
yields. Their MacDonald condensation with tetra-b-alkyldipyrromethanes produced 5,12,13,17,18-pentasubstituted porphyrins. A meso-
electron-donating group, presumably acting by destabilizing the porphyrin a2u ground state, directs the nitrations to the meso-carbons. b-
Nitration takes place on porphyrins bearing a meso-electron-withdrawing group. Unhindered b-nitro groups are shown to exert stronger
electronic effects relative to meso-nitro groups by conjugating effectively with the porphyrin macrocycle. q 2001 Elsevier Science Ltd. All
rights reserved.
1.Introduction
From these previous studies, we can assume that meso-
substituents have an important electronic in¯uence upon
the outcome of the nitration reaction. Effects of a single
meso-substituent on the reactivity of the porphyrin system
were investigated using 5-phenyl-12,13,17,18-tetraethyl-
porphyrin.11 As expected, bromination of this porphyrin
took place under strong steric regulation at an unhindered
b-position. Nitration reactions, which are little in¯uenced
by steric crowding, are better suited to investigate the direc-
tive effect 7if any) of a single meso-substituent on the reac-
tivity of pentasubstituted porphyrins. Herein, we report
the synthesis and N2O4 nitrations of a series of zinc7II)
and nickel7II) complexes of 5,12,13,17,18-pentasubstituted
porphyrins. Conditions to obtain porphyrins bearing b-nitro
substituents free of ¯anking meso- and/or b-substituents and
concomitantly displaying strongly perturbed optical spectra
are discussed. Prior to this work a few meso-unsubstituted-
b-nitroporphyrins12 and a 2,3-dinitroporphyrazine13 have
been prepared, but the strong p-acceptor nitro groups were
sterically prevented from conjugation with the porphyrin ring.
Electrophilic, nucleophilic, and radical reactions on porphy-
rins bearing vacant meso- and b-positions occur preferen-
tially at the methine bridges.1,2 Exceptions leading to b-
functionalizations result from the core-complexation of
electropositive metals such as nickel7II) or palladium7II),3
steric impediments 7e.g. upon bromination, formylation,
mercuration)4 or changes in the physical state of the initial
products 7e.g. upon sulfonation).5 Nitration reactions are
particularly insensitive to peripheral crowding and prevail
at the meso-positions 7for example nitrations of unsubsti-
tuted porphyrin,1c 5,15-diarylporphyrin,2b,c deuteroporphy-
rin6 and octaethylporphyrin7). Nitrations of the zinc7II) or
magnesium7II) meso-tetraphenylporphyrins 7TPPs) take
place at the crowded meso-positions,8a but use of bulkier
meso-substituents such as 2,6-dichlorophenyl inhibits such
ipso-attacks.9
Complexation with electronegative metals 7Cu7II), Ni7II),
Pd7II)) ensure b-nitrations and afford 2-nitro-tetraphenyl-
porphyrins in good yields.8 However, electronegative
metals do not always promote b-functionalizations of
tetra-meso-substituted porphyrins. Indeed, reactions of
nickel7II) or copper7II) 5,10,15,20-tetrapropylporphyrin
with N2O4 resulted in electrophilic dealkylative nitration
7affording 5-nitro-10,15,20-tripropylporphyrin) or ring-
opening of the porphyrin macrocycle.10
2.Results and discussion
b-Nitration of the porphyrin periphery has been recognized
to advantageously alter the chemical reactivities at the
various pyrrolic positions.14 b-Nitroporphyrins have been
used in various nucleophilic addition15 and substitution
reactions,16 and have been investigated for their nonlinear
optical,17 catalytic18 and photophysical properties.19,20 We
prepared a ®rst coplanar b-nitroporphyrin 1 by nitration of
the nickel7II) complex of a meso-free hexa-b-alkylporphy-
rin,10 and 7erroneously) assumed that the predominant
Keywords: nitroporphyrin; porphyrin; regioselective nitration; Vilsmeier
formylation.
Corresponding author. Tel.: 1530-752-4091; fax: 1530-754-2100;
e-mail: kmsmith@ucdavis.edc
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020701)00329-5

4262
A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
electronic effect leading to meso-nitration could be over-
ridden by a careful balance of steric effects. As a result, 5-
substituted-12,13,17,18-tetraalkylporphyrins were targeted
as they offer similar structural features 7two sterically
unhindered b-unsubstituted positions), but could be readily
prepared from meso-substituted b-free dipyrromethanes.
b-Free dipyrromethanes are useful synthetic porphyrin
intermediates,21 which have also been oxidized to dipyrro-
methenes,22 mono- and di-acylated with pyridyl thioester,23
and brominated.24 Two examples of Vilsmeier reactions
were reported to afford 1,9-diformyl-5-7aryl)-dipyrro-
methanes.25,26 These can also be obtained in three steps
via the cyanovinyl protection of 2-formylpyrrole.27 Herein,
we extend the Vilsmeier reaction to a series of b-unsub-
stituted-5-7alkyl)-dipyrromethanes.
Two b-tetraethyl-5-phenylporphyrins have been obtained
by acid-catalyzed condensation of two 1,19-di-unsubsti-
tuted-a,c-biladienes with benzaldehyde followed by oxi-
dation with DDQ.11 We followed a modi®ed MacDonald
7212) pathway and reacted 1,9-diformyldipyrromethanes
7, 8 and 10 with 3,7-diethyl-2,8-dimethyldipyrromethane-
1,9-dicarboxylic acid 1331 in CH2Cl2 in the presence of
TFA; this afforded, after oxidation with DDQ and chromato-
graphic puri®cations, penta-substituted porphyrins 14, 15
and 18 in 17±32% yield. Of note is that 1,9-diformyl-
2,3,7,8-tetraethyldipyrromethane failed to condense with 2
to give a tetraethylporphyrin analogue of 14.25 1,1-Bis75-
formylpyrrol-2-yl)ethene 12 was reacted with 2,3,7,8-tetra-
ethyldipyrromethane in the presence of TFA to give
porphyrin 20 after DDQ oxidation and migration of the
exocyclic double bond.
2.2. Nitrations of metalated 5,12,13,17,18-penta-
substituted porphyrins
2.1. Synthesis of 5,12,13,17,18-pentasubstituted
porphyrins
Many studies have focused attention on the nitration of
16a
porphyrins; various reagents such as N2O4,8a,10 AgNO2/I2
or Cu7NO3)2/AcOH/Ac2O,8b,c have been used. The nature of
z
Condensation of p-anisaldehyde, propionaldehyde and
isobutyraldehyde with excess pyrrole28 in the presence of
tri¯uoroacetic acid 7TFA) gave moderate yields of 5-
substituted dipyrromethanes 2±4. Treatment of 2 equiv. of
pyrrole with tri¯uoroacetaldehyde or hepta¯uorobutyralde-
hyde 7as their hydrate or hemiacetal) afforded per¯uoroalkyl-
dipyrromethanes 5 and 6.29 Reaction of dipyrromethanes
2±5 with excess POCl3/DMFin dichloromethane followed
by hydrolysis with saturated aqueous K2CO3 produced
bench-stable 1,9-diformyldipyrromethanes 7±10. meso-
Hepta¯uoropropyldipyrromethane 6, when reacted with
POCl3/DMF, gave traces of diformyldipyrromethane 11.
Instead, upon hydrolysis, a base-catalyzed elimination of
the nitrating species 7NO2 or NO21) and the nitration
mechanisms are ambiguous and could involve radical
combination of the porphyrin p-cation radical with NO2 ,
z 8a
NO2 electrophilic substitution10 and/or charge-transfer
1
1
process 7likely between NO2 and low redox potential
porphyrin derivatives).32 Reaction of the zinc complex 17
with AgNO2/I2 in CH3CN/CH2Cl2 yielded simultaneously
the brown-red 10-nitro-21 and 10,15-dinitro-22 products
along with some starting material. Upon HNO3 nitration
of 5-nitroporphyrin in H2SO4, a 5,10-dinitro-product was
also obtained and its formation was rationalized by consid-
ering the relative stabilities of the two potential s-
complexes leading to the nitration 75,10 vs 5,15) products.2c
The 5,10-disubstituted products are favored as no resonance
structure with a positive charge on the meso-carbon bearing
the 5-nitro group can be written upon nitronium attack at the
10-position. When the nickel7II) complex 16 was nitrated
with AgNO2/I2, N2O4 or Cu7NO3)2, the meso-nitroporphyrin
HFyielded 1,1-bis75-formylpyrrol-2-yl)ethene
12. In
dichloromethane, bis7pyrrolyl)ethene 12 exists in the
methylidene form 7as shown) rather than as the conjugated
dipyrromethene tautomer.30 Addition of TFA turned the
yellow solution to red, as expected for dipyrromethene salts.

A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
4263
23 was obtained in moderate yield. In contrast to the zinc
complex, further nitration took place at unsubstituted b-
positions giving rise to a regioisomeric mixture of green
dinitroporphyrins 24 7characterized by mass spectrometry
1
and H NMR spectroscopy). Bulkier b-substituents [as in
nickel7II) 5,12,18-triisopropyl-13,17-dimethylporphyrin,
not shown] did not prevent meso-nitrations.
Strong electron-withdrawing meso-groups are known to
preferentially stabilize the a2u porphyrin orbitals 7which
has large amplitude at the meso-positions) relative to the
highest occupied a1u orbitals 7with a large amplitude on
the a and b-carbons).19 Therefore, to favor b- over meso-
nitration, we turned our attention to 5-per¯uoroalkyl-
porphyrins hoping to perturb the porphyrin electronic
distribution by altering the macrocycle frontier orbitals.
Indeed, N2O4 nitration of nickel7II) 5-tri¯uoromethyl-
12,18-dimethyl-13,17-diethylporphyrin 19 [or the nickel7II)
complex of 20, not shown] gave rise simultaneously to three
mono-nitroporphyrins 725±27) as shown by thin layer
chromatography 7TLC). Some meso-nitration occurred and
the red meso-nitroporphyrin 27 was obtained in 38% yield.
Two green b-nitro derivatives were isolated in a combined
yield of 53%. The preferential formation of the crowded
b-nitroporphyrin 25 relative to the truly b-coplanar-nitro-
porphyrin 26 may result from the relative ability of their
likely charged intermediates to accommodate a positive
charge. AgNO2/I2 nitration of zinc7II) 5-tri¯uoromethyl-
12,18-dimethyl-13,17-diethylporphyrin gave a regioiso-
meric mixture of mono-meso-nitroporphyrin 7not shown),
showing that a meso-electron-withdrawing group did not
upset the strong meso-directive effect of an electropositive
metal.
1
The H NMR spectra of coplanar b-nitroporphyrins re¯ect
the magnetic anisotropy and resonance effect of the nitro
group. A coplanar b-nitro group places the adjacent b- and
meso-protons in a region of strong negative shielding
7porphyrin 26, b-H at d 9.75 and meso-H at 9.92), whereas
the shielding of the other meso-protons 7d 9.10±9.15) stems
from a reduced aromatic ring current. The absorption spec-
tra were more sensitive to the nitration site and re¯ect the
orientation of the nitro group relative to the macrocycle 7for
Figure, see ref. 10). meso-Nitration only slightly red-shifted
the optical spectra relative to the starting porphyrins. b-
Nitration resulted in an intense Q-band absorption, the
signature of an effective intramolecular charge transfer.34
The absorption spectrum of b-nitroporphyrin 26 also
displayed split Soret bands at 370 and 421 nm. Theoretical
calculations on b-nitroporphyrins have shown that a
coplanar nitro group would result in such splitting of the
Soret band.20 Two b-nitrovinyl porphyrins prepared by
direct nitrosation of protoporphyrin IX displayed similar
N2O4 nitration of nickel7II) 2,3,7,8-tetraethylporphyrin 28
produced four nitroporphyrins: the red meso-nitroporphyrin
29, two non-separable green b-nitroporphyrins 30, and the
brown meso-nitroporphyrin 31 in a roughly 2:4:1 ratio
7respectively). The formation of these two b-nitro deriva-
tives 7despite the presence of an unhindered meso-position)
suggests that the four b ethyl groups alone do not induce a
large electronic perturbation and presumably preserve the
a1u ground state of the unsubstituted porphyrin.33

4264
A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
coplanar aromatic nitro group.36 For b-nitroporphyrin 25,
this peak was found at an intermediate frequency
71349 cm21) and supports some conjugation of the nitro
group with the p-system.
The molecular structures of 25 and 27, as determined by
X-ray crystallography, are shown in Figs. 1 and 2, respect-
ively. Selected geometrical features for all reported meso
and b substituted mono- and di-nitroporphyrin crystal
structures are given in Table 1. The macrocycle of 25
exhibited a non-planar ruf¯ed distortion, a nitro-to-PMP
7porphyrin mean plane) dihedral angle of 21.58, and an
Ê
average Ni±N bond length of 1.933[5] A. Steric strain
between the nitro and tri¯uoromethyl groups along with
the tendency of Ni7II) ions to contract porphyrin 4N cores
were causative factors for the non-planar distortion. The
macrocycle of 27 was only slightly non-planar with a
predominantly ruf¯ed distortion, a nitro-to-PMP dihedral
angle of 69.58 7within the range observed for meso-nitro-
porphyrins, Table 1), and an average Ni±N bond length of
Ê
1.962[5] A.
The structure of 25, along with those of 2-nitro-TPP39 7nitro-
to-PMP dihedral angleˆ48.18), and 2,13-dinitro-TPP40
7nitro-to-PMP dihedral anglesˆ42.78 and 45.18) represent
the only published crystal structure determinations of
b-nitroporphyrins. While taking into account steric restric-
tions to nitro rotation 7imposed by adjacent meso substitu-
ents) it is clear from these data that the b-nitro groups tend
towards coplanarity with their porphyrin macrocycles.
In contrast, meso-nitroporphyrins exhibit nitro-to-PMP
dihedral angles that approximate perpendicularity 7Table
1). Once structural investigations into porphyrins with
unhindered b-nitro groups 7such as 26 or 30) are obtained
we will have better physical evidence pertaining to the
geometry and electronic interactions involved in these
systems.
Figure 1. The molecular structure of 25; 7top) top view, 7bottom) side view.
Hydrogens have been omitted for clarity.
split Soret bands, while their IR spectra suggested the
presence of a conjugated nitro-group.35
In the infrared spectra spectra of meso-nitroporphyrins such
as 27, peaks at 1362 cm21 were attributed to the symmetric
stretching mode of NO2. In the IR spectrum of 26 the occur-
rence of the symmetric mode at lower frenquencies
71331 cm21) is in accord with structures containing a
3.Conclusions
meso-Substituted 1,9-diformyldipyrromethanes were pre-
pared in good yields by Vilsmeier formylation of
a,b-di-unsubstituted dipyrromethanes. Their MacDonald
condensation with tetraalkyldipyrromethane afforded
5,12,13,17,18-pentasubstituted porphyrins. b-Nitration of
these porphyrins can compete with meso-nitration depend-
ing upon an appropriate choice of metal 7nickel) and meso-
substituent 7electron-withdrawing groups). The steric
effects were found to be negligible. The effect of a meso-
electron-donating group was more pronounced, and resulted
in exclusive meso-nitrations presumably by destabilizing
the porphyrin a2u ground state 7which has large amplitude
at the meso-positions). Alternatively, a single meso-
per¯uoroalkyl group did not suf®ciently stabilize the a2u
porphyrin orbitals to induce exclusive b-nitration. While
most substituents exert stronger electronic effects at the
meso-positions than at the b-positions, unhindered b-nitro
groups are an exception as they are sterically allowed to lie
in the plane of the porphyrin and can conjugate effectively
with the macrocycle, thus resulting in strongly perturbed
electronic spectra.
Figure 2. The molecular structure of 27; 7top) top view, 7bottom) side view.
Hydrogens have been omitted for clarity.

A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
4265
Table 1. Selected geometrical features for all reported meso and b substituted mono- and di-nitro porphyrin crystal structures
a
MDPMP 7A)
CSD refcode41
Nitro/PMPb dihedral angle 78)
Ê
Compound
725), Ni7II) 13,17-diethyl-12,18-dimethyl-3-nitro-5-tri¯uoromethyl Pc
727), Ni7II) 13,17-diethyl-12,18-dimethyl-10-nitro-5-tri¯uoromethyl Pc
5-Nitro-10,20-diphenyl Pc,d,2b
±
±
0.250
0.096
0.134
0.088
0.093
0.029
0.028
0.041
0.025
0.284
21.5
69.5
62.4
48.1
84.0
86.0
87.6
87.7
NESHOI
NOZKUI
TOYSAB
WAVLOU
WAVMAH
WAVLUA
WAVMEL
HAVFUF
2-Nitro-TPPd,e,39
[Fe7III)Cl] 5-nitro-OEPf,42
5-nitro-OEPd,f,43
[Zn7II)] 5-nitro-OEPf,43
[Zn7II)-pyridine] 5-nitro-OEPf,43
[Zn7II)-MeOH] 5-nitro-OEPf,43
2,13-dinitro-TPPd,e,40
89.4
42.7, 45.1
a
MDPMPˆThe mean deviation of the 24 macrocyclic atoms from their least-squares plane.
PMPˆPorphyrin mean plane, calculated as the 24 atom macrocyclic least-squares plane.
Pˆporphyrin.
b
c
d
e
f
In free base form.
TPPˆ5,10,15,20-tetraphenylporphyrin.
OEPˆ2,3,7,8,12,13,17,18-octaethylporphyrin.
4.Experimental
7m, 2H), 3.86 7t, Jˆ7.6 Hz, 1H), 6.09 7s, 2H), 6.16 7m, 2H),
6.60 7s, 2H), 7.66 7br s, 2H); Anal. Calcd for C11H14N2: C,
75.82; H, 8.10; N, 16.08; Found: C, 76.02; H, 8.20; N,
15.96. MS: m/e 174.1 792), 157.1 760), 145.1 7±Et, 100).
4.1. General
Mps were measured on a Thomas/Bristoline microscopic
hot stage apparatus and were uncorrected. Silica gel 60
770±230 and 230±400 mesh) was used for column chroma-
tography. Preparative thin layer chromatography was
carried out on 20£20 cm glass plates coated with Merck
G 254 silica gel 71±2 mm thick). Analytical thin layer
chromatography 7TLC) was performed using Macherey±
Nagel Polygram SIL G/UV254 7precoated silca gel sheets,
0.2 mm thick). 1H NMR spectra were obtained in deuterio-
chloroform solution at 300 MHz using a General Electric
QE300 spectrometer; chemical shifts are expressed in ppm
relative to chloroform 77.26 ppm). Elemental analyses were
performed at the Midwest Microlab., Inc., Indianapolis, IN.
Electronic absorption spectra were measured in dichloro-
methane solution using a Hitachi U-2000 spectrophoto-
meter. Mass spectra were obtained at the Mass
Spectrometry Facility, University of California, San
Francisco, CA, and at the Facility for Advanced Instru-
mentation, University of California, Davis, CA 7LDI-
TOF). N2O4 gas was prepared by reacting concentrated
HNO3 with zinc metal.15e 5-7p-Methoxyphenyl)dipyrro-
methane, 5-7tri¯uoromethyl)dipyrromethane, 5-7hepta¯uoro-
methyl)dipyrromethane 6, and 2,8-dimethyl-3,7-diethyl-
dipyrromethane-1,9-dicarboxylic acid 13 were prepared
according to the literature 7vide infra).
4.1.2. 5-Isopropyldipyrromethane 4. Pyrrole 769.4 mL,
1 mol) and 2-methylpropionaldehyde 72.88 g, 0.04 mol)
were reacted by the procedure described for 3 7silica gel
column eluted with CH2Cl2). Recrystallization from
CH2Cl2/petroleum ether afforded 4 as white crystals
74.36 g, 58%), mp 83±848C. 1H NMR d 0.95 7d,
Jˆ6.4 Hz, 6H), 2.30 7m, 1H), 3.78 7d, Jˆ6.4 Hz, 1H),
6.07 7m, 2H), 6.16 7m, 2H), 6.62 7m, 2H), 7.79 7br s, 2H);
Anal. Calcd for C12H16N2: C, 76.56; H, 8.57; N, 14.88;
Found: C, 76.32; H, 8.46; N, 14.63. MS: m/e 188.2.
4.1.3. 1,9-Diformyl-5-/p-methoxyphenyl)-dipyrromethane
7. POCl3 75 mL, 0.054 mmol) was added dropwise to a
250 mL three necked round bottomed ¯ask charged with
DMF715 mL) at 0 8C under an inert atmosphere. The
mixture was stirred for 30 min before adding 5-7p-methoxy-
phenyl)dipyrromethane 2 72.2 g, 8.72 mmol) dissolved in
CH2Cl2 7150 mL). The ice bath was removed and the
mixture was re¯uxed for 2 h. The reaction mixture was
poured into water, followed by slow addition of K2CO3
until a pH .11 was reached. After 1 h, additional K2CO3
was added and the mixture was left stirring overnight. The
organic phase was separated and the aqueous phase was
extracted twice with CH2Cl2. The combined organic phases
were washed several times with water and evaporated
to dryness. The residue was recrystallized from CH2Cl2/
hexane to yield 2.19 g of white±beige powder 786%), mp
197±1998C; 1H NMR d 3.79 7s, 3H), 5.51 7s, 1H, CH), 6.06
7m, 2H), 6.86 7m, 2H), 6.87 7d, 2H), 7.20 7d, 2H), 9.20 7s,
2H), 10.37 7br s, 2H); Anal. Calcd For C18H16N2O2: C,
68.91; H, 5.44; N, 9.45. Found: C, 69.17; H, 5.27; N,
9.13. MS: m/e 308.12 7M1, 100).
4.1.1. 5-Ethyldipyrromethane 3. A mixture of pyrrole
769.4 mL, 1 mol) and propionaldehyde 72.9 mL, 0.04 mol)
in a round bottomed ¯ask was degassed with argon for
5 min. Tri¯uoroacetic acid 70.58 mL, 7.5 mmol) was
added and the solution was stirred for 5 min at room
temperature under argon. The reaction mixture was
quenched with 0.1 M NaOH. Ethyl acetate was added and
the organic phase was washed with water, dried and evapo-
rated under vacuum to afford a brownish oil. Excess pyrrole
was removed by vacuum distillation at room temperature
and the residue was chromatographed on silica gel 7eluting
with CH2Cl2) to yield the product as off white crystals
73.85 g, 55%). It was recrystallized from CH2Cl2/petroleum
ether, mp 47±488C. 1H NMR d 0.93 7t, Jˆ7.6 Hz, 3H), 1.97
4.1.4. 5-Ethyl-1,9-diformyldipyrromethane 8. Vilsmeier
reagent was prepared by adding POCl3 74 mL, 0.043 mol)
dropwise to dimethylformamide 726.6 mL) at 08C under
argon. 5-Ethyldipyrromethane 3 73.13 g, 0.018 mol) was
dissolved in CH2Cl2 760 mL) and the solution was cooled
to 08C. To this solution was added dropwise the Vilsmeier

4266
A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
reagent 72.4 equiv.) and the mixture was stirred at 08C for
2 h under argon. Saturated aq. Na2CO3 solution 7200 mL)
was added carefully and solid Na2CO3 was added until the
solution was basic 7pH around 12). After 1 h, additional
Na2CO3 was added and the mixture was left stirring over-
night at room temperature. The solution was extracted with
CH2Cl2 and the extracts were washed with brine. Evapo-
ration of the solvent gave a brown oil which was chromato-
graphed on silica gel eluting with ethyl acetate/cyclohexane
72:3) to yield the product as an off white powder. It was
recrystallized from hexane/CH2Cl2 72.73 g, 66%), mp 128±
mixture was reduced under vacuum to 10 mL and ®ltered
successively through a short silica gel plug and an alumina
7Grade III) plug 7eluting with CH2Cl2). After evaporation of
the solvent, the residue was recrystallized from CH2Cl2/
MeOH to yield 540 mg of purple powder 732%), mp
.3008C. UV±Vis: lmax 402 nm 7e 226000), 498 714500),
529 73500), 567 75000). 1H NMR d 23.40 7s, 2H), 1.81 7t,
6H), 3.58 7s, 6H), 4.10 7q, 4H), 4.12 7s, 3H), 7.33 7d,
Jˆ7.8 Hz, 2H), 8.18 7d, Jˆ7.8 Hz, 2H), 9.05 7d,
Jˆ3.6 Hz, 2H), 9.30 7d, Jˆ3.6 Hz, 2H), 10.0 7s, 1H),
10.15 7s, 2H). Anal. Calcd for C33H32N4O: C, 79.17; H,
6.44; N, 11.19; Found: C, 79.06; H, 6.54; N, 11.05. MS:
m/e 501.1 7MH1, 100).
1
1298C. H NMR d 0.95 7t, Jˆ7.2 Hz, 3H), 2.19 7m, 2H),
4.11 7t, Jˆ7.2 Hz, 1H), 6.21 7m, 2H), 6.94 7m, 2H), 9.43 7s,
2H), 11.38 7br s, 2H). Anal. Calcd for C13H14N2O2: C, 67.81;
H, 6.13; N, 12.17; Found: C, 67.60; H, 6.03; N, 11.95. MS:
m/e 230.2 7100, M1).
4.1.9. 5,13,17-Triethyl-12,18-dimethylporphyrin 15. 3,7-
Diethyl-2,8-dimethyldipyromethane-1,9-dicarboxylic acid
13 7796 mg, 2.5 mmol) was stirred in 5 mL of TFA for
5 min at room temperature under argon. The mixture was
diluted with water and extracted twice with CH2Cl2; the
combined organic layers were washed with saturated
NaHCO3, dried over anhydrous Na2SO4, and the volume
of CH2Cl2 was reduced to 250 mL. 5-Ethyl-1,9-diformyl-
dipyromethane 8 7575 mg, 2.5 mmol) was added and the
solution was purged with argon for 5 min. TFA 70.05 mL)
was then added and the mixture was stirred at room
temperature for 16 h under argon before addition of chlor-
anil 7613 mg, 2.5 mmol) and stirring for another 4 h at room
temperature. The reaction mixture was passed through an
alumina 7Grade III) plug, eluting with CH2Cl2. Evaporation
of the solvent gave a residue which was chromatographed
on a silica gel column eluting with CH2Cl2 to give 230 mg
722%) of the product as red crystals after recrystallization
from methanol/CH2Cl2, mp 252±2538C. UV±Vis: lmax
395 nm 7e 225000), 497 714500), 529 73100), 568 75300),
620 71500). 1H NMR d 23.10 7br s, 2H), 1.87 7t, Jˆ7.6 Hz,
6H), 2.20 7t, Jˆ7.6 Hz, 3H), 3.59 7s, 6H), 4.04 7q, Jˆ7.6 Hz,
4H), 5.09 7q, Jˆ7.6 Hz, 2H), 9.36 7d, Jˆ4.6 Hz, 2H), 9.60
7d, Jˆ4.6 Hz, 2H), 9.88 7s, 1H), 10.05 7s, 2H). Anal. Calcd
for C28H30N4: C, 79.59; H, 7.16; N, 13.26; Found: C, 79.20;
H, 7.16; N, 13.24. MS: m/e 422.3 7MH1, 100).
4.1.5. 1,9-Diformyl-5-isopropyldipyrromethane 9. 5-Iso-
propyldipyrromethane 4 73.38 g, 0.018 mol) was reacted
with the Vilsmeier reagent using the procedure described
for 8 [silica gel column eluted with ethyl acetate/cyclohex-
ane 71:1)]. Recrystallization from hexane/CH2Cl2 gave 9
1
72.72 g, 62%) as off white crystals, mp 182±1838C. H
NMR d 0.96 7d, Jˆ6.3 Hz, 6H), 2.62 7m, 1H), 3.77 7d,
Jˆ6.4 Hz, 1H), 6.26 7m, 2H), 6.92 7m, 2H), 9.48 7s, 2H),
11.62 7br s, 2H). Anal. Calcd for C14H16N2O2: C, 68.83; H,
6.60; N, 11.47; Found: C, 68.37; H, 6.02; N, 11.28. MS: m/e
244.2 7M1, 100).
4.1.6. 1,9-Diformyl-5-tri¯uoromethyldipyrromethane 10.
5-Tri¯uoromethyldipyrromethane 529 72.57 g, 0.012 mol)
was reacted with the Vilsmeier reagent using the procedure
described for 8. The reaction mixture was heated under
re¯ux for 1 h. The silica gel column was eluted with ethyl
acetate/cyclohexane 71:1). Recrystallization from hexane/
CH2Cl2 gave 10 72.60 g, 79%) as off white crystals, mp
1
174±1758C. H NMR d 5.11 7q, Jˆ9.0 Hz, 1H), 6.43 7m,
2H), 6.99 7m, 2H), 9.52 7s, 2H), 11.15 7br s, 2H). Anal.
Calcd for C12H9F3N2O2: C, 53.34; H, 3.36; N, 10.37;
Found: C, 53.08; H, 3.29; N, 10.13. MS: m/e 270.2 7M1,
100).
4.1.10. Nickel/II) 5,13,17-triethyl-12,18-dimethylpor-
phyrin 16. 5,13,17-Triethyl-12,18-dimethylporphyrin 15
7105 mg, 0.25 mmol) and nickel acetylacetonate 7257 mg,
4 equiv.) were re¯uxed in toluene for 16 h. Toluene was
evaporated and the residue was puri®ed on a silica gel
column eluting with CH2Cl2/cyclohexane 71:1) to give
112 mg 793%) of the title compound, mp 210±2118C.
UV±Vis: lmax 393 nm 7e 270000), 513 710500), 547
712000). 1H NMR d 1.77 7t, Jˆ7.8 Hz, 6H), 2.12 7t,
Jˆ7.7 Hz, 3H), 3.38 7s, 6H), 3.82 7q, Jˆ7.8 Hz, 4H), 4.74
7q, Jˆ7.7 Hz, 2H), 9.11 7d, Jˆ4.6 Hz, 2H), 9.44 7d,
Jˆ4.6 Hz, 2H), 9.54 7s, 1H), 9.62 7s, 2H). Anal. Calcd for
C28H28N4Ni.2H2O: C, 65.27; H, 6.26; N, 10.87; Found: C,
65.88; H, 5.77; N, 10.57. MS: m/e 478.3 7M1, 100).
4.1.7. 1,1-Di/5-formylpyrrol-2-yl)-2-¯uoro-2-/penta¯uoro-
ethyl)ethene 12. 5-Hepta¯uoropropyldipyrromethane 629
76.28 g, 0.02 mol) was reacted with the Vilsmeier reagent
by using the procedure described for 8. The reaction mixture
was heated under re¯ux for 1 h. The silica gel column was
eluted with ethyl acetate/cyclohexane 71:1). Recrystalli-
zation from hexane/CH2Cl2 gave 12 75.71 g, 82%) as off
1
white crystals, mp 159±1608C. H NMR d 6.58 7m, 1H),
6.75 7m, 1H), 6.92 7m, 1H), 7.04 7m, 1H), 9.14 7s, 1H), 9.21
7s, 1H), 10.41 7br s, 1H), 11.06 7br s, 1H). Anal. Calcd for
C14H8F6N2O2 0.5H2O: C, 46.81; H, 2.52; N, 7.79; Found: C,
.
47.27; H, 2.29; N, 7.75. MS: m/e 350.0 7100, M1).
4.1.8. 13,17-Diethyl-5-/p-methoxyphenyl)-12,18-dimethyl-
porphyrin 14. To a light-shielded suspension of 7 71.0 g,
3.2 mmol) and 3,7-diethyl-2,8-dimethyldipyrromethane-
1,9-dicarboxylic acid13 71.10 g, 1 equiv) in degassed
CH2Cl2 7250 mL) was added 8 mL of TFA. The reaction
mixture was further degassed with argon for 5 min and
stirred for 16 h. Chloranil 7790 mg, 3.2 mmol) was added
all at once and the mixture was stirred for 4 h. The reaction
4.1.11. Zinc/II) 5,13,17-triethyl-12,18-dimethylporphyrin
17. 5,13,17-Triethyl-12,18-dimethylporphyrin 15 7106 mg,
0.25 mol) and zinc acetate 7220 mg, 4 equiv.) were re¯uxed
in CHCl3/Methanol 71:1) for 1 h. The solvents were evapo-
rated and the residue was puri®ed on a silica gel column
eluting with CH2Cl2/cyclohexane 71:1) to give 105 mg
787%) of the title product, mp 295±2968C. UV±Vis: lmax

A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
4267
1
401 nm 7e 300000), 530 715000), 568 75500). H NMR d
1.82 7t, Jˆ7.6 Hz, 6H), 2.18 7t, Jˆ7.6 Hz, 3H), 3.51 7s, 6H),
3.96 7q, Jˆ7.6 Hz, 4H), 5.06 7q, Jˆ7.6 Hz, 2H), 9.26 7br s,
2H), 9.58 7br s, 2H), 9.71 7s, 1H), 9.86 7s, 2H). Anal. Calcd
for C28H28N4Zn´0.5CH3OH: C, 68.20; H, 6.02; N, 11.16;
Found: C, 68.50; H, 6.36; N, 10.58. MS: m/e 484.16 7M1,
100).
solvents under vacuum, the residue was puri®ed by chroma-
tography on preparative silica gel plates.
4.2.1. General procedure for AgNO2/I2 nitration of nickel
/II) or zinc/II) porphyrins. To a solution of the zinc7II) or
nickel7II) porphyrin 7e.g. 0.1 mmol) in a mixture of CH2Cl2
710 mL) and CH3CN 74 mL) at 08C and protected from light,
was added AgNO2 721 mg, 0.13 mmol) in CH3CN 74 mL)
followed by I2 716.5 mg, 0.067 mmol) in CH2Cl2 74 mL).
The reaction mixture was stirred under argon for 2 h at
08C and then ®ltered. The solvents were evaporated under
vacuum and the residue was puri®ed by chromatography on
preparative silica gel plates.
4.1.12. 13,17-Diethyl-12,18-dimethyl-5-tri¯uoromethyl-
porphyrin 18. 3,7-Diethyl-2,8-dimethyldipyromethane-
1,9-dicarboxylic acid 13 71.27 g, 4.0 mmol) and 5-tri¯uoro-
methyl-1,9-diformyldipyrromethane 10 71.08 g, 4.0 mmol)
were reacted by the procedure described for 15 7silica
gel column eluted with CH2Cl2). Recrystallization from
methanol/CH2Cl2 yielded 318 mg 717%) of the title
compound, mp 310±3118C. UV±Vis: lmax 393 nm 7e
163000), 498 710500), 534 710500), 569 75500), 621
4.2.2. Zinc/II) 5,13,17-triethyl-12,18-dimethyl-10-nitropor-
phyrin 21. AgNO2/I2 nitration of 17 748.5 mg, 0.1 mmol)
gave porphyrins 21 and 22 [running slower on TLC 7silica,
CH2Cl2/cyclohexane 1:1)]. The more polar compound 7brown
red) was identi®ed as 22 7recrystallized from methanol/
CH2Cl2, 13 mg, 25%). The less polar compound 7brown
red) was identi®ed as 21 7recrystallized from methanol/
CH2Cl2, 28 mg, 53%), mp .3008C. UV±Vis: lmax
1
77500). H NMR d 24.05 7br s, 1H), 23.60 7br s, 1H),
1.80 7t, Jˆ7.6 Hz, 6H), 3.52 7s, 6H), 4.00 7q, Jˆ7.6 Hz,
4H), 9.41 7d, Jˆ4.8 Hz, 2H), 9.74 7m, 2H), 9.96 7s, 1H),
10.12 7s, 2H). Anal. Calcd for C27H25F3N4: C, 70.12; H,
5.45; N, 12.11; Found: C, 69.88; H, 5.44; N, 12.10. MS:
m/e 462.4 7M1, 100).
1
403 nm 7e 220000), 535 714000), 569 77000). H NMR d
1.76 7m, 6H), 2.08 7t, Jˆ7.6 Hz, 3H), 3.23 7s, 3H), 3.45 7s,
3H), 3.94 7m, 4H), 4.98 7q, Jˆ7.6 Hz, 2H), 9.13 7d,
Jˆ4.6 Hz, 1H), 9.20 7d, Jˆ4.6 Hz, 1H), 9.48 7d,
Jˆ4.6 Hz, 1H), 9.58 7d, Jˆ4.6 Hz, 1H), 9.83 7s, 1H), 9.88
7s, 1H). Anal. Calcd for C28H27N5O2Zn.0.5H2O: C, 62.29; H,
5.23; N, 12.97; Found: C, 62.19; H, 5.24; N, 12.64. MS: m/e
529.2 7M1, 100).
4.1.13. Nickel/II) 13,17-diethyl-12,18-dimethyl-5-tri¯uoro-
methylporphyrin 19. 13,17-Diethyl-12,18-dimethyl-5-
tri¯uoromethylporphyrin 18 7231 mg, 0.5 mmol) and nickel
acetylacetonate 7257 mg, 1 mmol) were re¯uxed in toluene
720 mL) for 16 h. The toluene was evaporated under
vacuum and the residue was puri®ed on a silica gel column
eluting with CH2Cl2/cyclohexane 71:2) to give 228 mg
788%) of the product, mp 229±2308C. UV±Vis: lmax
4.2.3. Zinc/II) 5,13,17-triethyl-12,18-dimethyl-10,15-dini-
troporphyrin 22. Obtained in 25% yield 713 mg). Mp:
decomposed without melting. UV±Vis: lmax 407 nm 7e
1
391 nm 7e 165000), 526 710000), 565 719500). H NMR d
1.72 7t, Jˆ7.6 Hz, 6H), 3.25 7s, 6H), 3.73 7q, Jˆ7.6 Hz, 4H),
8.98 7d, Jˆ4.8 Hz, 2H), 9.35 7s, 1H), 9.36 7s, 2H), 9.47 7m,
2H). Anal. Calcd for C27H23F3N4Ni: C, 62.46; H, 4.47; N,
10.79; Found: C, 62.16; H, 4.51; N, 10.69. MS: m/e 518.1
7M1, 100).
1
141000), 540 711000), 594 74500). H NMR d 1.33 7t,
Jˆ7.6 Hz, 3H), 1.67 7t, Jˆ7.6 Hz, 3H), 1.83 7t, Jˆ7.6 Hz,
3H), 3.31 7s, 3H), 3.40 7s, 3H), 3.61 7q, Jˆ7.6 Hz, 2H), 3.79
7q, Jˆ7.6 Hz, 2H), 3.89 7q, Jˆ7.6 Hz, 2H), 7.66 7d,
Jˆ4.6 Hz, 1H), 7.86 7d, Jˆ4.6 Hz, 1H), 8.52 7s, 1H), 8.87
7d, Jˆ4.6 Hz, 1H), 8.94 7d, Jˆ4.6 Hz, 1H). Anal. Calcd for
C28H26N6O4Zn´3H2O: C, 53.38; H, 5.12; N, 13.34; Found:
C, 53.79; H, 4.55; N, 12.54. MS: m/e 574.2 7M1, 100).
4.1.14. 12,13,17,18-Tetraethyl-5-/3,3,3,2,2,1-hexa¯uoro-
propyl)-porphyrin 20. 2,3,7,8-Tetraethyldipyromethane-
1,9-dicarboxylic acid 71.04 g, 3.0 mmol) and 1,1-dipyrro-
ethene 12 71.05 g, 3.0 mmol) were reacted following the
procedure described for 5 [silica gel column eluted
with CH2Cl2/cyclohexane 71:1)]. Recrystallization from
methanol/CH2Cl2 gave 480 mg 728%) of the product, mp
228±2298C. UV±Vis: lmax 396 nm 7e 168000), 498
4.2.4. Nickel/II) 5,13,17-triethyl-12,18-dimethyl-10-nitro-
porphyrin 23. AgNO2/I2 nitration of 16 747.8 mg,
0.1 mmol) gave porphyrin 23 [running slower on TLC
7silica, CH2Cl2/cyclohexane 1:1)]. Recrystallized from
methanol/CH2Cl2 725 mg, 48%). A more polar compound
7green) was found to be a regioisomeric mixture of b-nitro-
10-nitroporphyrins 24 712.4 mg, 22%). 23: mp .3008C.
UV±Vis: lmax 395 nm 7e 140000), 519 710000), 553
1
711000), 533 77500), 568 75200), 620 74500). H NMR d
23.99 7br s, 1H), -3.40 7br s, 1H), 1.92 7m, 12H), 4.07 7m,
8H), 8.56 7m, 1H), 9.48 7d, Jˆ4.8 Hz, 2H), 9.64 7br s, 2H),
10.07 7s, 1H), 10.21 7s, 2H). Anal. Calcd [Ni7II) complex]
C31H28F6N4Ni: C, 59.17; H, 4.49; N, 8.90; Found: C, 59.05;
H, 4.55; N, 8.79. MS: m/e 572.2 7MH1, 100).
1
711000). H NMR d 1.68 7m, 6H), 1.97 7t, Jˆ7.6 Hz, 3H),
3.15 7s, 3H), 3.24 7s, 3H), 3.68 7q, Jˆ7.6 Hz, 2H), 3.75 7q,
Jˆ7.6 Hz, 2H), 4.48 7q, Jˆ7.6 Hz, 2H), 8.86 7d, Jˆ4.8 Hz,
1H), 9.01 7d, Jˆ4.8 Hz, 1H), 9.17 7d, Jˆ4.8 Hz, 1H), 9.28
7d, Jˆ4.8 Hz, 1H), 9.30 7s, 1H), 9.32 7s, 1H). Anal. Calcd
for C28H27N5O2Ni.0.5H2O: C, 63.07; H, 5.29; N, 13.13;
Found: C, 63.34; H, 5.20; N, 13.19. MS: m/e 523.4 7100,
M1) IR: 1529 7nas-NO2), 1361 7ns-NO2).
4.2. General procedure for N2O4 nitration of nickel/II)
porphyrins
A solution of nickel7II) porphyrin 7e.g. 100 mg) in dichloro-
methane 740 mL) was stirred vigorously. A N2O4 solution in
petroleum ether was added dropwise.15e Close reaction
monitoring by TLC 7SiO2, CH2Cl2/cyclohexane 2:3) is
crucial to avoid over-nitration. After evaporation of the
4.2.5. Nickel/II) 13,17-diethyl-12,18-dimethyl-3-nitro-5-
tri¯uoromethylporphyrin 25. N2O4 nitration of 19
745 mg, 0.085 mmol) gave three nitroporphyrins 25±27

4268
A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
[all running slower on TLC 7silica, CH2Cl2/cyclohexane
1:1). Separation was carried out on preparative silica plates
eluting with CH2Cl2/cyclohexane 71:1)]. The least polar
compound 7red) was identi®ed as 27 7recrystallized from
CH2Cl2/methanol, 13.8 mg, 28%). The next compound
7green) was identi®ed as 26 7recrystallized from CH2Cl2/
methanol, 7.5 mg, 15%). The most polar and major
compound 7green) was identi®ed as 25 7recrystallized
from CH2Cl2/methanol, 18.6 mg, 38%), mp .3008C
7decomp.). UV±Vis: lmax 410 nm 7e 84000), 601 715500).
1H NMR d 1.68 7m, 6H), 3.26 7s, 3H), 3.29 7s, 3H), 3.75 7m,
4H), 8.99 7d, Jˆ4.8 Hz, 1H), 9.28 7s, 1H), 9.35 7s, 1H), 9.37
7s, 1H), 9.39 7m, 1H), 9.42 7s, 1H). Anal. Calcd for
C27H22F3N5O2Ni´1.5H2O: C, 54.85; H, 4.26; N, 11.85;
Found: C, 54.88; H, 4.09; N, 11.40. MS: m/e 563.1. IR:
1349 7ns-NO2).
1H), 9.81 7s, 1H). MS: m/e 522.15 7M1, 100). Amount of
®nal products was insuf®cient for elemental analyses. The
substituent regiochemistry of porphyrin 29 was further
con®rmed by X-ray crystallography.38
4.2.10. Regioisomeric mixture of nickel/II) 2,3,7,8-tetra-
ethyl-12-nitroporphyrin and 2,3,7,8-tetraethyl-13-nitro-
porphyrin 30. UV±Vis: lmax 7rel. int.) 364 nm 70.74), 423
71.0), 591 70.32). Anal. Calcd for C28H27N5NiO2´0.25H2O:
C, 63.60; H, 5.24; N, 13.24; Found: C, 63.53; H, 5.32; N,
13.06. MS: m/e 522.31 7M1, 100). IR: 1462 7nas-NO2),
1342, 1333 7sh) 7ns-NO2).
4.2.11. Nickel/II) 2,3,7,8-tetraethyl-15-nitroporphyrin 31.
Mp: 225±2308C. UV±Vis: lmax 390 nm 7e 69500), 559
1
78500). H NMR d 1.74 7m, 12H), 3.83 7m, 8H), 9.15 7d,
Jˆ4.8 Hz, 2H), 9.29 7d, Jˆ4.8 Hz, 2H), 9.63 7s, 1H), 9.71
7s, 2H). MS: m/e 522.35 7M1, 100). Amount of ®nal product
was insuf®cient for elemental analyses. The substituent
regiochemistry of porphyrin 31 was further con®rmed by
X-ray crystallography.38
4.2.6. Nickel/II) 13,17-diethyl-12,18-dimethyl-2-nitro-5-
tri¯uoromethylporphyrin 26. Mp: decomposed without
melting. UV±Vis: lmax 370 nm 7e 31000), 421 761500),
1
609 716000). H NMR d 1.65 7m, 6H), 3.23 7s, 3H), 3.26
7s, 3H), 3.71 7m, 4H), 8.74 7d, Jˆ4.8 Hz, 1H), 8.97 7s, 1H),
9.10 7s, 1H), 9.15 7m, 1H), 9.75 7m, 1H), 9.92 7s, 1H). Anal.
Calcd for C27H22F3N5O2Ni´H2O: C, 55.70; H, 4.16; N,
12.03; Found: C, 55.89; H, 4.04; N, 11.52. MS: m/e 563.1.
IR: 1331 7ns-NO2).
4.3. Crystal structure data for 25 and 27
Crystals were grown by slow evaporation of a CDCl3 solu-
tion of 25 and by solvent diffusion from CH2Cl2/MeOH
for 27 [regioisomers with C27H22F3N5NiO2, F Wˆ564.21].
For 25, the purple prismatic crystal 70.08£0.33£0.54 mm)
4.2.7. Nickel/II) 13,17-diethyl-12,18-dimethyl-10-nitro-
5-tri¯uoromethylporphyrin 27. Mp.3008C 7decomp).
UV±Vis: lmax 395 nm 7e 70000), 521 75000), 567 79500).
1H NMR d 1.74 7m, 6H), 3.15 7s, 3H), 3.25 7s, 3H), 3.75 7m,
4H), 8.99 7d, Jˆ4.8 Hz, 1H), 9.07 7d, Jˆ4.8 Hz, 1H), 9.37
7s, 1H), 9.38 7m, 1H), 9.42 7s, 1H), 9.45 7m, 1H). Anal.
Calcd for C27H22F3N5O2Ni´0.5H2O: C, 56.58; H, 4.04; N,
12.22; Found: C, 56.75; H, 3.93; N, 12.07. MS: m/e 563.1.
IR: 1362 7ns-NO2).
ꢀ
had a triclinic unit cell, space group P1; with cell
Ê
dimensions aˆ9.269074), bˆ11.163474), cˆ13.132875) A,
aˆ109.27471)8, bˆ96.80371)8, gˆ107.80471)8, Vˆ
Ê 3
1184.35713) A , and Zˆ2. For 27, the red parallelepiped
crystal 70.04£0.16£0.40 mm) had a triclinic unit cell,
ꢀ
space group P1, with cell dimensions aˆ9.449873), bˆ
Ê
11.659674), cˆ12.111274) A, aˆ104.8400710)8, bˆ
Ê 3
106.0690710)8, gˆ107.5700710)8, Vˆ1135.3276) A , and
Zˆ2. Data were collected on a Bruker SMART 1000
diffractometer with a sealed tube source [l 7MoKa)ˆ
4.2.8. Nickel/II) 2,3,7,8-tetraethylporphyrin 28. Conden-
sation of 1,9-diformyldipyrromethane37 with 2,3,7,8-tetra-
ethyldipyrromethane-1,9-dicarboxylic acid followed by
DDQ oxidation afforded 2,3,7,8-tetraethylporphyrin in 25%
yield.11 2,3,7,8-Tetraethylporphyrin 763.3 mg, 0.15 mmol)
and nickel acetylacetonate 764 mg, 0.25 mmol) were re¯uxed
in toluene 710 mL) for 16 h. The toluene was evaporated
under vacuum and the residue was puri®ed on a silica gel
column eluting with CH2Cl2/petroleum ether 72:3) to give
66 mg 792%) of the product, mp: 183±1848C. UV±Vis:
Ê
0.71073 A] at 9072) K. A 2u cutoff of 608 was applied to
both datasets to afford 12287 and 15330 total re¯ections
7when two values are given they refer to 25 and 27, respec-
tively) of which 6787 and 6567 were unique and of those
5839 and 5490 were observed 7I.2s) [Rintˆ0.0314, 0.0247;
Tminˆ0.65, 0.71; Tmaxˆ0.93, 0.96; mˆ0.880, 0.918 mm21].
An empirical absorption correction was applied to the data-
sets 7SADABS 2.0, Sheldrick 2000). The structures were
solved by direct methods and re®ned 7based on F2 using
all data) by full matrix least-squares methods with 347
and 365 parameters 7Bruker shelxs-97, shelxl-97). All
hydrogen atom positions were re®ned with a riding model.
Final R factors were R1ˆ0.042, 0.044 7observed data) and
wR2ˆ0.125, 0.110 7all data).
1
lmax 385 nm 7e 190000) 507 710500), 541 721000). H
NMR d 1.84 7m, 12H), 3.96 7m, 8H), 9.26 7m, 4H), 9.85
7s, 1H), 9.90 7s, 2H), 9.97 7s, 1H). MS: m/e 479.2 7M1, 100).
4.2.9. Nickel/II) 2,3,7,8-tetraethyl-10-nitroporphyrin 29.
N2O4 nitration of 28 740 mg, 0.08 mmol) gave three nitro-
porphyrins 29±31 running slower on TLC 7SiO2, CH2Cl2/
cyclohexane 2:3). The most polar compounds 7green) were
identi®ed as 30 7recrystallized from CH2Cl2/MeOH, 15 mg,
37% yield). The second band 7brown) and the third band
7red) were identi®ed as 31 and 29, respectively. Separation
was carried out on preparative silica gel plates eluting with
CH2Cl2/cyclohexane 2:3. Mp: 145±1508C. UV±Vis: lmax
Acknowledgements
This work was supported by grants from the National
Science Foundation 7CHE-99-04076) and the National
Institutes of Health 7HL-22252). Mass spectrometric
analyses were performed by the UCSFMass Spectrometry
Facility 7A. L. Burlingame, Director) supported by the
Biomedical Research Technology Program of the National
Center for Research Resources, NIH NCRR BRTP 01614.
1
387 nm 7e 110000), 514 77000), 549 711500). H NMR: d
1.61 7t, Jˆ7.5 Hz, 3H), 1.85 7m, 9H), 3.63 7q, Jˆ7.5 Hz,
2H), 3.90 7m, 6H), 9.16 7m, b-H, 4H), 9.71 7s, 1H), 9.76 7s,

A. Wickramasinghe et al. / Tetrahedron 57 %2001) 4261±4269
4269
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The Bruker SMART 1000 diffractometer was funded in part
by NSFinstrument grant CHE-98-08259.
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