Tetraazaoctaphyrin - A biimidazole-containing expanded porphyrin

Article abstract of DOI:10.1139/V06-068

A series of expanded porphyrins, incorporating biimidazoles and bipyrroles within their macrocyclic framework, has been synthesized. Insights into the complex conformational characteristics of these systems were obtained from two-dimensional NMR spectrosc

Full text of DOI:10.1139/V06-068

1218
Tetraazaoctaphyrin — A biimidazole-containing
expanded porphyrin1
Jonathan L. Sessler, Bobbi L. Rubin, Marcin St“pie½, Thomas Köhler,
G. Dan Pantos, and Vladimir Roznyatovskiy
Abstract: A series of expanded porphyrins, incorporating biimidazoles and bipyrroles within their macrocyclic frame-
work, has been synthesized. Insights into the complex conformational characteristics of these systems were obtained
from two-dimensional NMR spectroscopic studies. The relative energy values for the various asymmetric structures in-
ferred from these analyses were compared using DFT molecular modeling calculations.
Key words: macrocycles, expanded porphyrins, imidazoles, pyrroles, biimidazoles, supramolecular chemistry,
heterocycles.
Résumé : On a réalisé la synthèse d’une série de porphyrines agrandies qui incorporent des biimidazoles et des bipyr-
roles dans le squelette de leur macrocycle. Sur les bases des études de spectroscopie RMN bidimensionnelle, on a ex-
trait des donnés qui permettent de mieux comprendre les caractéristiques conformationnelles complexes de ces
systèmes. On a comparé les valeurs relatives d’énergie de diverses structures asymétriques déduites de ces analyses à
celles obtenues par des calculs de modélisation moléculaire sur la base de la théorie de la fonctionnelle de densité.
Mots clés : macrocycles, porphyrines agrandies, imidazoles, pyrroles, biimidazoles chimie macromoléculaire, hétérocycles.
[Traduit par la Rédaction] Sessler et al. 1225
Introduction
Most known expanded porphyrins, with the exception of
Schiff-base macrocycles, have been constructed from pyrrole
and its closely related heterocyclic analogues, furan, thio-
phene, and selenophene. Recently, efforts have shifted to-
wards incorporating imidazoles and biimidazoles into
porphyrin-like structures. Youngs et al. (8) reported the syn-
thesis of a series of cyclophane complexes, or porphyrinoids,
which contained imidazoliums incorporated into the skeletal
framework of the macrocycle. In 2003, the research groups
of Allen (9) and Nonell (10) separately reported the first
biimidazole-based porphycene analog, imidacene. There
have also been a number of reports that describe the incor-
poration of imidazole or imidazolium cations into other
macrocyclic structures (11–14). These systems show great
promise in both anionic and cationic recognition and are
made especially interesting because they are potentially ca-
pable of recognition both inside and outside the skeletal
framework. In spite of this promise, biimidazoles, as
opposed to imidazoles, have yet to be incorporated into
expanded porphyrin-type frameworks. We report here the
A new subdiscipline of porphyrin chemistry, involving the
synthesis and study of large oligopyrrole macrocycles, so-
called expanded porphyrins, was instigated by the serendipi-
tous discovery of sapphyrin by Woodward and co-workers in
the mid 1960s (1). In the decades since that time, the field of
expanded porphyrin chemistry has grown into a large and vi-
brant subfield of macrocyclic chemistry (2). Expanded por-
phyrins have been studied in the context of molecular
recognition with anionic, cationic, and neutral substrates (3).
Part of what is driving this research is the promise that these
systems show in various practical applications, ranging from
drug development to anion recognition (4–7). Work in this
area has also been inspired by less prosaic motivations, in-
cluding the synthetic challenge of constructing new oligo-
pyrrolic macrocycles and their inherent aesthetic appeal.
Received 11 October 2005. Accepted 30 November 2005.
Published on the NRC Research Press Web site at
http://canjchem.nrc.ca on 8 June 2006.
first example of such
a system, namely 3,6,21,24-
tetraaza[32]octaphyrin(1.0.1.0.1.0.1.0).
J.L. Sessler,2 B.L. Rubin, M. St“pie½, T. Köhler,
G.D. Pantos, and V. Roznyatovskiy.3 Department of
Chemistry and Biochemistry, The University of Texas at
Austin, 1 University Station A5300, Austin, TX 78712-0165,
USA.
Results and discussion
The synthesis of tetraazaoctaphyrin target 3 was carried
out in a single step via the condensation of biimidazole 1
1This article is part of a Special Issue dedicated to Dr. Alfred
Bader.
with bis-α-free bipyrrole
2
under dilute conditions
2Corresponding author (e-mail: sessler@mail.utexas.edu).
3Present address: Department of Chemistry, M.V. Lomonosov
Moscow State University, Leninskie Gory, 119899 Moscow,
Russian Federation.
(Scheme 1). Biimidazole 1a was prepared according to the
literature and 1b was synthesized using an extension of this
same basic methodology (10). Bipyrroles 2a–2c were syn-
thesized according to the literature (15, 16).4 The condensa-
tion of biimidazole 1 with bipyrrole 2 was performed in a
4J.L. Sessler and J.T. Lee. Unpublished results.
Can. J. Chem. 84: 1218–1225 (2006)
doi:10.1139/V06-068
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Sessler et al.
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Fig. 1. Absorbance (᎐᎐) and fluorescence spectra (----) of 3b in
methanol–tetrahydrofuran (THF) mixture using trifluoroacetic
acid (TFA) as the acid catalyst. After column chromato-
graphic work-up over silica gel, tetraazaoctaphyrins 3a–3e
were obtained in yields ranging from 26% to 69%, depend-
ing on the substrates used. The compounds obtained in this
way are unstable when exposed to oxygen and decompose
over time. Thus, they were stored in a freezer under a blan-
ket of argon. Under these conditions, little decomposition
was seen for a period of 1 week. Elemental analysis was
used as a means of characterization and repeatedly resulted
in total carbon, hydrogen, and nitrogen counts of 95%–96%
of the theoretical values. XPS analysis revealed the presence
of silicon and oxygen, which is supported by a singlet near
CH2Cl2.
1
0 ppm observed in the H NMR spectra of 3a–3e, attribut-
able to a dimethyl siloxane compound. Efforts to remove the
impurity included recrystallization, trituration, and extrac-
tion, but unfortunately all proved unsuccesful. If, however,
the carbon, hydrogen, and nitrogen percentage is normalized
to 100% and compared with a theoretical percentage of the
same elements, thus accounting for the amount of impurity
in these percentages, the experimental results fall within ac-
ceptable error values (i.e., ∆ < 0.20%). In an additional ex-
periment, the solvent was passed through a blank column
under identical conditions and the siloxane was identified in
Fig. 2. Dilute solution tetraazaoctaphyrin 3b in methylene chlo-
ride in the absence (left) and presence (right) of an illuminating
black light (365 nm).
1
the eluate by XPS and H NMR spectroscopy, thus estab-
lishing the silica gel as the likely source of the impurity.
The UV–vis absorption spectrum of 3b, the prototypical
tetraazaoctaphyrin chosen for detailed study, is characterized
by a Soret-type band at 299 nm and a Q-type band at
633 nm (Fig. 1). These features, particularly the latter long-
wavelength absorption band, are considered diagnostic of an
extended conjugated system (17). Dilute solutions of tetra-
azaoctaphyrin 3 in methylene chloride are blue and fluoresce
red (Fig. 2). For the fluorescence emission experiments, ex-
citation was performed at 578 nm, while the emission maxi-
mum was observed at 670 nm.
The one-dimensional 1H NMR spectrum of 3b recorded in
dichloromethane-d2 is shown in Fig. 3. It is apparent from an
inspection of this spectrum that the solution structure of 3b
does not exhibit the fourfold symmetry implied by the repre-
sentation of the macrocycle given in Scheme 1. The actual
conformation has only twofold symmetry, which can be in-
ferred from the doubled number of peaks in the aromatic and
alkyl regions. The signal at 9.87 ppm integrates to two pro-
tons and most likely corresponds to a pyrrole NH proton.
When studied as a solution in DMSO-d6, an additional peak
with the same integral intensity can be observed at
10.8 ppm. In dichloromethane-d2, this signal is broadened
by exchange and cannot be observed. Such a solvent de-
pendence is typically found for imidazole NH protons.
Based on these findings, the signal is assigned as an
imidazole NH; however, its exact placement on the
biimidazole unit could not be determined. Chemical shifts of
the NH and meso protons indicate an absence of overall
macrocyclic aromaticity.
this basis cannot be separated by chromatography (all sam-
ples yield a single peak on the HPLC chromatogram). While
the identity of the additional species could not be ascer-
tained, it is thought that it may correspond to a different
symmetrical conformation for each of the different deriva-
tives of 3.
The assignment of the signals presented in Fig. 3 follows
the labeling pattern given in Scheme 2. These assignments
were deduced using two-dimensional NMR spectroscopy
(COSY and ROESY maps). Figure 4 shows representative
expansions of the COSY spectrum, used to establish connec-
tivity within the aryl rings and alkyl chains. There is a sig-
nificant crowding of signals in the alkyl region, which was
resolved on the COSY map. Further insight into the struc-
ture and conformation of 3b was gained from an analysis of
the ROESY spectrum (Fig. 5).
The doubled spectral pattern, indicative of symmetry low-
ering, is also seen for the other tetraazaoctaphyrin deriva-
tives. It should, however, be noted that the doubled signals
assigned to the dominant species present in solution are of-
ten accompanied by ones ascribable to an impurity, which
gives rise to a single set of peaks. The admixture inferred on
Based on selected ROE cross-peaks, it was possible to
assign unequivocally each of the signals to one of the two
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Can. J. Chem. Vol. 84, 2006
Scheme 1. Synthesis of tetraazaoctaphyrin 3.
R' R'
R
R
R''
R''
R
H
OHC
N
N
N
N
H
TFA
MeOH/THF
N
N
H
N
N
N
HN
N
N
CHO
R''
R
1a R = Me
1b R = n-Bu
NH
N
H
N
N
R' R'
R''
R''
R''
R
R
R' R'
N
N
H
H
3a R = n-Bu, R' = R'' = Et
3b R = n-Bu, R' = Me, R'' = Et
3c R = Me, R' = R'' = Et
3d R = Me, R' = Me, R'' = Et
3e R = n-Bu, R' = CH2CH2COOMe, R'' = Me
2a R' = Me, R'' = Et
2b R' = R'' = Et
2c R' = CH2CH2COOMe, R'' = Me
1
1
Fig. 3. H NMR spectrum of compound 3b (500 MHz, CD2Cl2,
Scheme 2. Labeling scheme used in the analysis of H NMR
spectra of 3b. For simplification, π bonding in the macrocycle is
not shown. Placement of pyrrole and imidazole NH protons is
arbitrary.
298 K). Labeling of peaks follows that given in Scheme 2.
δ-Bu
γ-Bu β-Bu
α-Bu
ortho
meta
N
N
N
α-Et
N
H
meso
β-Et
N
HN
N
Me
NH
H
N
N
N
N
nonequivalent subunits 1 and 2 (Scheme 3). Each of the sub-
units contains one pyrrole ring and one imidazole ring
linked by a meso-bridging carbon atom. In addition, four
special ROE correlations provided the information necessary
to determine the arrangement of constituent rings in each
subunit. The meso signal of subunit 1 (meso1, 7.04 ppm)
correlates with the ortho signal of the adjacent aryl ring
(ortho1, 7.59 ppm, peak A in Fig. 5), as well as with one of
the ethyl CH3 signals (β-Et1, 1.04 ppm, peak C). In the
other subunit, the meso signal (meso2, 6.95 ppm) only corre-
lates with the respective ethyl group (β-Et2, 1.21 ppm, peak
D) and shows no cross-peak to the ortho signal (ortho2,
7.72 ppm). However, the latter yields an unexpected correla-
tion with the pyrrolic NH (peak B). This latter correlation
can be rationalized by assuming a “kinked” conformation
for subunit 2, in which the meso CH fragment is turned
away from the aryl ring (Scheme 3).
meet the above criterion are shown in Fig. 6. In arrange-
ments A and B, the sequence of subunits in the ring is
1–2–1–2, whereas, in arrangements C and D, the sequence is
1–1–2–2. Furthermore, the aryl rings pointing towards the
inside of the macrocycle are positioned on the same side of
the macrocyclic plane (in arrangements A and C) or on the
opposite sides (B and D). As a result, we obtain four distinct
conformers, two of which are chiral (A and D).
Inspection of the molecular models leads to the inference
that arrangement B is the least congested of the four con-
formers and hence the one with the lowest energy. This con-
clusion is supported by DFT calculations performed at the
TZ2p atomic level. Optimized geometries and relative
Macrocycle 3 should contain two subunits of type 1 and
two of type 2 combined in such a way that the entire struc-
ture exhibits twofold symmetry. The four arrangements that
© 2006 NRC Canada

Sessler et al.
1221
1
1
Fig. 4. H COSY spectrum of 3b (500 MHz, CD2Cl2, 298 K).
Fig. 5. H ROESY spectrum of 3b (500 MHz, CD2Cl2, 298 K).
Parts (A) and (B) show the expansions of aromatic–aromatic and
aliphatic–aromatic regions, respectively. The spectrum is phased
to give positive ROE crosspeaks.
Parts (A) and (B) show expansions of the aromatic and aliphatic
regions, respectively. Peaks corresponding to the symmetrical
form are not labeled.
has any exchange been noted between the major asymmetri-
cal form and the symmetrical admixture mentioned earlier.
In point of fact, the lines remain sharp even at 130 °C in
DSMO-d6. However, significant broadening is observed at
room temperature for the ortho and meta signals of the aryl
rings (Fig. 3). This broadening is most readily interpreted in
terms of the aryl moieties being in an unsymmetrical envi-
ronment and undergoing slow rotation, conclusions that are
consistent with the nonplanar conformation noted above.
Interestingly, the conformation proposed for 3 has no
apparent precedent among the structures of octaphyrins
energy values are given in Table 1. Conformer B is the most
stable, closely followed in energy by conformer D (Fig. 6);
not surprisingly, conformations A and C are higher in en-
ergy, likely reflecting the cis arrangement of the phenyl
rings within the cavity. Additionally, conformer C, expected
to have a symmetry plane (Cs symmetry), collapsed upon
optimization into a completely nonsymmetrical geometry.
The conformation of 3 observed in solution appears to be
rigid. No exchange cross-peaks in the room temperature
ROESY and NOESY spectra have been observed between
topologically equivalent signals (e.g., meso1 and meso2); nor
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Can. J. Chem. Vol. 84, 2006
Fig. 6. Possible conformers of tetraazaoctaphyrin 3 (top). The bottom part shows the DFT optimized structures and their point symme-
tries. Within the optimized structures, subunit 1 is highlighted in blue, while subunit 2 is highlighted in red for clarity. With the excep-
tion of the NH hydrogen atoms, all the hydrogen atoms have been removed for clarity.
Scheme 3. Illustration of the two subunit structure of 3b, as de-
termined from the interpretation of the ROESY spectrum. The π
electron extended conjugation is removed for clarity.
Table 1. Minimization energy values for molecular arrangements
A–D.
Arrangement
Energy (kcal/mol)
Relative energy
A
B
C
D
–321 084.01
–321 067.25
–321 053.80
–321 064.63
16.76
0
13.45
2.62
B
C
H
H
H
H
H
N
Note: 1 cal = 4.184 J.
A
N
N
N
N
H
N
H
Fig. 7. Tetraazaoctaphyrin 3b in acetonitrile in the absence (left)
and presence of tetrabutylammonium chloride (middle) and
tetrabutylammonium bromide (right).
D
Subunit 1
Subunit 2
reported to date. For [32]octaphyrin(1.0.1.0.1.0.1.0), re-
ported by Vogel and co-workers (18), a D2-symmetrical fig-
ure eight conformation with transoid bipyrrole subunits
located at the figure eight intersection was observed in the
crystal structure. A similar conformation was conjectured for
a closely related macrocycle obtained by Setsune et al. (19).
Another type of figure eight conformation was observed for
[36]octaphyrin(1.1.1.1.1.1.1.1), reported by Furuta, Osuka
and co-workers. (20), and for its thiophene analogue ob-
tained by Spruta and Latos-Graóy½ski (21). However, the
presence of four imidazole rings in system 3 and a different
substitution pattern (aryl groups at the β-pyrrole positions)
may explain why this new macrocycle adopts a conforma-
tion different from that of its all-pyrrole analogue (18).
were formed from the condensation of biimidazole dialde-
hydes 2a and 2b with bis-α-free bipyrroles 2a–2c. The high
density of NH functionality makes these systems of potential
interest as anion receptors. Initial qualitative tests of this
postulate have been performed on tetraazaoctaphyrin 3. We
have found that the neutral host (3b) undergoes a naked-eye
detectable color change in the presence of fluoride, bromide
Conclusion
The design and synthesis of a novel expanded porphyrin
has been described. The series of tetraazaoctaphyrins 3a–3e
© 2006 NRC Canada

Sessler et al.
1223
(Fig. 7), cyanide, hydroxyde, acetate, nitrate, dihydrogen-
phosphate anions (studied in the form of their respective
tetrabutylammonium salts). On the other hand, no change in
the spectral properties of 3b was noted upon addition of
chloride, iodide, hypochlorate, nitrite, benzoate, and hydro-
gensulfate anions. Such observations lead us to propose that
this or other neutral biimidazole-incorporated expanded por-
phyrins may emerge as useful anion sensors.
dried under vacuum to give the desired compound in the
form of a white solid in 78% yield; mp 160–180 °C. H
1
NMR (400 MHz, DMSO-d6) δ: 2.37 (s, 6H), 7.33 (d, J =
7.6 Hz, 4H), 7.79 (d, J = 8.4 Hz, 4H), 9.88 (s, 2H). 13C
NMR (500 MHz, DMSO-d6) δ: 21.00, 125.30, 126.81,
128.73, 128.97, 129.30, 129.58, 129.72, 133.12, 139.25,
140.01, 182.60. HR-MS (CI+) m/z (M + H+) calcd. for
C22H18N4O2: 371.1508; found: 371.1521.
General procedure for the preparation of
tetraazaoctaphyrin derivatives (3)
Experimental
Biimidazole dialdehyde 1 (0.184 mmol) was dissolved in
200 mL of dry 2:1 methanol–THF containing 1 mL of TFA.
Bipyrrole 2 (0.184 mmol) was separately dissolved in 40 mL
of the same solvent ratio and placed in an addition funnel.
The bipyrrole solution was added dropwise to the
biimidazole solution over 30 min and after several hours of
stirring at room temperature, an additional 1 mL of TFA was
added to the reaction. Stirring was continued overnight with
the reaction left open to the atmosphere. After 12 h, the deep
blue-black solution was concentrated in vacuo to give a deep
purple oil, which was taken to dryness on the vacuum line to
remove any residual trifluoroacetic acid. Column chromatog-
raphy was performed twice over silica gel, eluting initially
with methylene chloride before the polarity of the eluent was
slowly increased to 3% methanol in methylene chloride. The
desired fractions were combined and concentrated in vacuo
to give a lustrous blue-black solid. The material was then
redissolved in methylene chloride, washed with 5% aqueous
sodium bicarbonate, dried over sodium sulfate, filtered, con-
centrated in vacuo to a blue-black solid, and dried under
vacuum. The solid was triturated with distilled pentane to re-
move any remaining grease. The desired tetraazaoctaphyrin
was obtained as a blue-black lustrous solid.
Elemental analysis was pursued as a means of character-
ization and repeatedly resulted in carbon, hydrogen, and
nitrogren counts of 95%–96% of the theoretical values. XPS
analysis revealed the presence of 3.14% silicon in the sam-
ple of 2.5b. Taking into account this silicon percentage, the
calculated impurity reveals 1.40 equiv. of the siloxane for
each equivalent of the host 2.5b. Anal. calcd. for
C84H92N12·1.4SiO2(CH3)2: C 74.72, H 7.20, N 12.05; found:
C 74.71, H 7.09, N 12.22. Efforts to remove the impurity in-
cluded recrystallization, trituration, and extraction, but un-
fortunately all proved unsuccesful.
General information
All reagents and solvents were purchased from Sigma-
Aldrich Corporation, Fischer Scientific, or Fluka and used
without further purification with the following exceptions.
Dichloromethane was dried by distillation under argon over
calcium hydride. Dimethylformamide was dried by passage
through two columns of molecular sieves. Tetrahydrofuran
(THF) was dried by passage through two columns of acti-
vated alumina. Toluene was dried by passage through two
columns of activated alumina. N-Bromosuccinimide was
recrystallized from boiling water. For column chromatogra-
phy, silica gel (Scientific Adsorbents Inc., particle size 32–
63 µm) was used as the immoble phase.
1-((2-(Trimethylsilyl)ethoxy)methyl)-2-(1-((2-
(trimethylsilyl)ethoxy)methyl)-5-formyl-4-p-tolyl-1H-
imidazol-2-yl)-4-p-tolyl-1H-imidazole-5-carbaldehyde
4,4′-Dibromo-1,1′-bis[(trimethylsilyl)ethoxymethyl]-2,2′-
biimidazole-5,5′-dicarbaldehyde (10) (1.68 mmol) and p-
methylphenyl boronic acid (3.36 mmol) were degassed for
20 min in 9.2 mL of 2 mol/L sodium carbonate and 4 mL of
ethanol by purging the solution with argon. Palladium
tetrakistriphenylphosphine (10% mol) was added and the re-
action was heated to reflux for 7 h using an oil bath. The re-
action flask was removed from the oil bath, cooled, and the
mixture was diluted with ethyl acetate, dried with sodium
sulfate, filtered, and concentrated in vacuo to give an oil.
Column chromatography was performed using silica gel as
the solid support, eluting initially with hexanes and slowly
increasing the polarity to 20% ethyl acetate in hexanes. De-
sired fractions were combined, concentrated in vacuo, and
1
dried to give an off-white solid in 89% yield. H NMR
(CDCl3, 400 MHz) δ: –0.13 (m, 9H), –0.08 (m, 9H), 2.02 (s,
3H), 2.42 (s, 3H), 3.58 (m, 4H), 4.10 (m, 4H), 6.31 (s, 2H),
6.37 (s, 2H), 7.30 (d, J = 8.0 Hz, 4H), 7.61 (d, J = 7.6 Hz,
4H), 9.88 (s, 1H), 9.96 (s, 1H). 13C NMR δ: 14.17, 17.86,
21.35, 60.39, 66.41, 127.14, 127.55, 128.75, 128.95, 129.29,
120.49, 129.525, 139.71, 141.16, 154.49, 171.17, 181.00.
HR-MS (CI+) m/z (M + H+) calcd. for C22H18N4O2:
371.1508; found: 371.1521.
2,7,20,25-Tetra-p-butylphenyl-11,12,15,16,29,30,33,34-
octaethyl–3,6,21,24-tetraaza[32]octaphyrin(1.0.1.0.1.0.1.0)
(3a)
The compound was obtained from the condensation of
biimidazole 1b (10) with bipyrrole 2b (16)4 in 69% yield,
following the general procedure given above. UV–vis
2-(5-Formyl-4-p-tolyl-1H-imidazol-2-yl)-4-p-tolyl-1H-
imidazole-5-carbaldehyde (1a)
(CH3CN, nm (ε)) λmax: 296 (85 800), 534 (41 100), 631
1
(94 300). H NMR (500 MHz, CD2Cl2) δ: 0.95–1.09 (comp,
24H, CH2CH3, CH2CH2CH2CH3), 1.13–1.21 (comp, 8H,
CH2CH3), 1.39–1.49 (comp, 8H, CH2CH2CH2CH3), 1.61–
1.75 (comp, 8H, CH2CH2CH2CH3), 2.34 (m, 8H, CH2CH3),
2.65–2.77 (comp, 12H, CH2CH3 & CH2CH2CH2CH3), 2.97
(m, 4H, CH2CH2CH2CH3), 6.94 (s, 2H, meso-H), 7.080 (s,
2H, meso-H), 7.27 (d, J = 8.0 Hz, 4H), 7.38 (d, J = 8.5 Hz,
4H), 7.53 (d, J = 8.0 Hz, 4H), 7.82 (d, J = 8.0 Hz, 4H), 9.98
The previous compound (0.457 mmol) was dissolved in
10 mL ethanol. Ten milliliters of 10% HCl was added and
the reaction was heated to reflux for 1 h using an oil bath.
The flask was removed from the oil bath, cooled, and the so-
lution was carefully neutralized with 10% aqueous sodium
carbonate. At this juncture, a solid precipitated out of solu-
tion. It was filtered and washed with ice-cold water, and
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Can. J. Chem. Vol. 84, 2006
(s, 2H, NH), 11.70 (br, NH). 13C NMR (500 MHz, CD2Cl2)
δ: 12.95, 13.095, 13.18, 15.12, 16.33, 17.11, 17.21, 18.19,
21.44, 21.59, 32.26, 32.43, 34.59, 34.64, 117.92, 123.68,
126.87, 127.59, 128.09, 128.45, 134.20, 134.86, 136.08,
137.16, 139.27, 141.34, 144.15, 144.29, 148.18, 150.13,
158.59.
129.74, 131.69, 137.54, 138.09, 138.83, 139.80, 147.35,
148.89, 150.94.
2,7,20,25-Tetra-p-butylphenyl-11,16,29,34-tetramethyl-
12,15,30,33-tetracarboxylate-3,6,21,24-
tetraaza[32]octaphyrin(1.0.1.0.1.0.1.0) (3e)
The compound was obtained from the condensation of
biimidazole 1b (10) with bipyrrole 2c (17) in 26% yield, fol-
lowing the general procedure given above. UV–vis (CH3CN,
nm (ε)) λmax: 275 (34 300), 609 (4790). 1H NMR (400 MHz,
CD2Cl2) δ: 0.98 (m, 12H, CH2CH2CH2CH3), 1.44 (m,
8H, CH2CH2CH2CH3), 1.67 (m, 8H, CH2CH2CH2CH3),
2.05 (s, 12H, CH3), 2.45 (t, J = 7.4 Hz, 4H, CH2CH2), 2.62–
2.77 (comp, 12H, CH2CH2), 3.02 (t, J = 7.6 Hz,
CH2CH2CH2CH3), 3.21 (t, J = 7.2 Hz, 4H, CH2CH2CH2CH3),
3.30 (s, 6H, CO2CH3), 3.56 (s, 6H, CO2CH3), 7.00 (s, 2H,
meso-H), 7.13 (s, 2H, meso-H), 7.30 (d, J = 7.6 Hz, 4H),
7.41 (d, J = 8.0 Hz, 4H), 7.62 (d, J = 8 Hz, 4H), 7.82 (d, J =
8 Hz, 4H), 10.02 (s, 2H, NH).
2,7,20,25-Tetra-p-butylphenyl-11,16,29,34-tetraethyl-
12,15,30,33-tetramethyl-3,6,21,24-tetraaza[32]octaphyrin-
(1.0.1.0.1.0.1.0) (3b)
The compound was obtained from the condensation of
biimidazole 1b (10) with bipyrrole 2a (16)4 in 54% yield,
following the general procedure given above. UV–vis
(CH3CN, nm (ε)) λmax: 299 (139 000), 536 (68 500), 633
(142 000). 1H NMR (500 MHz, CD2Cl2) δ: 0.93–1.04
(comp, 18H, CH2CH3, CH2CH2CH2CH3), 1.16–1.21 (m, 6H,
CH2CH3), 1.36–1.47 (m, 8H, CH2CH2CH2CH3), 1.59–1.69
(comp, 8H, CH2CH2CH2CH3), 2.00 (s, 6H, CH3), 2.39–2.47
(comp, 14H, CH3 and CH2CH2CH2CH3), 2.61–2.72 (comp,
8H, CH2CH2CH2CH3), 6.87 (br, 2H, meso-H), 6.95 (s, 1H,
meso-H), 7.04 (br, 1H, meso-H), 7.19 (m, 2H), 7.25 (m, 2H),
7.46 (br, 4H), 7.49 (m, 2H), 7.59 (br, 2H), 7.72 (br, 4H),
9.87 (br, 2H). 13C NMR (500 MHz, CD2Cl2) δ: 10.95, 11.67,
14.11, 14.38, 15.64, 18.16, 18.69, 22.81, 33.98, 35.84,
119.71, 121.37, 126.50, 128.68, 129.10, 129.14, 129.42,
137.88, 143.97, 144.85, 147.48, 159.16.
Molecular modelling studies
Molecular modelling studies were performed using semi-
empirical calculations at the PM3 level, using HyperChem®
V7.1, for preoptimization. Density functional theory (DFT)
calculations were then performed using PRIRODA-04 (22).
A PBE functional that includes the electron density gradient
was used. The TZ2p atomic basis sets of grouped Gaussian
functions were used to solve the Kohn–Sham equations. The
criterion for convergence was to reach a difference in energy
gradient between two sequential structures below
0.01 kcal/mol/Å (1 cal = 4.184 J). A PDB file for each opti-
mized structure is included in the Supplementary informa-
tion.5
2,7,20,25-Tetra-p-methylphenyl-11,12,15,16,29,30,33,34-
octaethyl-3,6,21,24-tetraaza[32]octaphyrin(1.0.1.0.1.0.1.0)
(3c)
The compound was obtained from the condensation of
biimidazole 1a with bipyrrole 2b (16)4 in 62% yield, follow-
ing the general procedure given above. UV–vis (CH3CN, nm
(ε)) λmax: 299 (78 400), 540 (40 900), 634 (92 400). 1H
NMR (400 MHz, CD2Cl2) δ: 0.90–1.25 (comp, 24H,
CH2CH3), 2.36–2.99 (comp, 28H, CH3, CH2CH3), 6.89 (s,
1H, meso-H), 6.99 (s, 2H, meso-H), 7.06 (s, 1H, meso-H),
7.22–7.31 (comp, 4H), 7.39 (d, J = 7.6 Hz, 2H), 7.54 (m,
4H), 7.72 (d, J = 8.4 Hz, 2H), 7.84 (d, J = 7.6 Hz, 4H),
10.02 (s, 2H). 13C NMR (500 MHz, CD2Cl2) δ: 14.81,
15.22, 15.30, 16.86, 18.17, 18.61, 19.18, 19.54, 21.50,
127.81, 128.92, 129.73, 135.12, 138.73, 147.10, 148.25.
HR-MS (FAB+) m/z (M + H+) calcd. for C76H77N12:
1157.6394; found: 1157.6383.
Acknowledgements
This project was supported by the National Science Foun-
dation Integrative Graduate Education and Research
Traineeship Program (grant No. DGE 9870653) and the Na-
tional Science Foundation (grant No. CHE 0515670 to JLS).
We would also like to acknowledge Mr. Jeong Tae Lee for
providing bipyrrole 2c and Dr. Dmitri Laikov for providing
the DFT software PRIRODA-04.
References
2,7,20,25-Tetra-p-methylphenyl-11,16,29,34-tetraethyl-
12,15,30,33-tetramethyl-3,6,21,24-tetraaza[32]octaphyrin-
(1.0.1.0.1.0.1.0) (3d)
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