A flexible porphyrin-annulene hybrid: A nonporphyrin conformation for meso-tetraaryldivacataporphyrin

Article abstract of DOI:10.1002/chem.201002765

An annulene-porphyrin hybrid, the diaaza-deficient porphyrin 5,10,15,20-tetraaryl-21,23-divacataporphyrin, has been synthesized by an extrusion of tellurium atom(s) from 5,10,15,20-tetraaryl-21,23- ditelluraporphyrin under treatment with HCl. In addition,

Full text of DOI:10.1002/chem.201002765

DOI: 10.1002/chem.201002765
A Flexible Porphyrin–Annulene Hybrid: A Nonporphyrin Conformation for
meso-Tetraaryldivacataporphyrin
Ewa Pacholska-Dudziak, Ludmiła Szterenberg, and Lechosław Latos-Grazyn´ski*[a]
˙
Abstract:
An
annulene–porphyrin
as UV/Vis and NMR spectroscopy.
These aromatic molecules preserve the
fundamental structural and spectro-
scopic features of the parent tetraaryl-
porphyrin. The X-ray crystal structures
of 21,23-divacataporphyrin and 21-tel-
lura-23-vacataporphyrin show typical
porphyrin patterns. The molecules are
not strictly planar and show distortion
of the annulene moieties. The
N22···N24 distances (5.23 and 5.09 ꢂ)
are considerably longer than in regular
porphyrins. For 21,23-divacataporphyr-
hybrid, the diaaza-deficient porphyrin
5,10,15,20-tetraaryl-21,23-divacatapor-
phyrin, has been synthesized by an ex-
trusion of tellurium atom(s) from
5,10,15,20-tetraaryl-21,23-ditellurapor-
phyrin under treatment with HCl. In
1
in, variable-temperature H NMR spec-
troscopy data allowed the identification
of divacataporphyrin stereoisomers dif-
ferentiated by the geometry of the bu-
tadiene bridges. The forms remain in
thermodynamic equilibrium.
addition,
a
monoaza-deficient
5,10,15,20-tetraaryl-21-tellura-23-vaca-
taporphyrin was formed in the same re-
action. The two new members of the
vacataporphyrin family were character-
ized by X-ray crystallography, as well
Keywords: annulenes · aromaticity ·
isomerization · porphyrinoids · tel-
lurium
ꢀ ꢀ
N
Introduction
charged
links.[10,11] According to probably the most
widespread concept, a diaza[18]annulene skeleton needs two
aza and two ethylene bridges to form a porphyrin (1;
Scheme 1). The relationship of the annulene and porphyrin
structures was highlighted by Sondheimer et al. as early as
in 1962,[12] shortly after the first synthesis of [18]annulene.[13]
Thus, the stepwise bridging of [18]annulene 4 eventually af-
fords porphyrin 1, as shown in Scheme 1. The reverse of this
concept, that is, the formation of annulene 4 from porphyrin
1 via 3 by way of the removal of bridges and replacement of
nitrogen atoms is essential for this contribution.
The idea of treating porphyrins or porphyrinoids as bridged
annulenes has been an inspiration for developing new fields
and refreshing discussions in porphyrinoid chemistry.[1–7] In
relation to Hꢀckelꢁs aromaticity rules, three annulenic
models of porphyrins were practical in describing their elec-
tronic structure. A porphyrin may be regarded as 1) a tet-
ꢀ
ꢀ
raaza[16]annulene dianion with four C2H2 bridges con-
taining isolated double bonds,[8,9] or 2) a [20]annulene dicat-
ion with two neutral bivalent NH and two negatively
Scheme 1. 5,10,15,20-Tetraaryl-21,23-divacataporphyrin (3) as a diaza-deficient porphyrin and as a doubly bridged aza[18]annulene.
Importantly, from the perspective of an annulene chemist,
[a] Dr. E. Pacholska-Dudziak, Dr. L. Szterenberg,
´
Prof. L. Latos-Graz˙ynski
an ancestor of a porphyrin may be constructed by the incor-
poration of two CH2 and two CH=CH bridges to the mater-
nal [18]annulene, resulting in a peculiar aromatic tetracyclo-
pentadienic hydrocarbon 6.[7,14] To date, hydrocarbon 6,
named quatyrin,[15,16] has yet be synthesized, although the
importance of 6 in both annulene and porphyrin fields has
Department of Chemistry, University of Wrocław
ul. F.Joliot-Curie 14, 50-383 Wrocław (Poland)
Fax : (+48)71-3282348
E-mail: llg@wchuwr.pl
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002765.
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FULL PAPER
been highlighted.[16,17] Recently, a relevant molecular pattern
has been identified in tetraazuliporphyrin tetracation.[17]
An analogous relationship that intertwines the hypotheti-
cal [18]annulenes of C2h or lower symmetry, the porphyrin
structural isomers and their bridged variants have been ex-
tensively explored to afford a whole class of porphyrin con-
stitutional isomers.[2,6,18–22] For instance, a porphycene mole-
cule (8) imprints an [18]annulene frame of C2h symmetry
(7).[18,23]
theoretical point of view, including the very first Mçbius an-
nulenes[29,30] or porphyrinoids.[31,32]
If only partial bridging is introduced into [18]annulene 4,
it may preserve some degree of flexibility, some core steric
repulsions, and may be placed on the borderline between an
annulene and a porphyrin. In this class of borderline com-
pound, there is the relatively conformationally mobile,
doubly bridged annulene 9, which is the oxygen analogue of
the hypothetical structure 5 (Scheme 1).[33] The imprint of 5
may be also found in rigid dicarbaporphyrin 12.[34] The
bridging scheme in 3 has already been realized in 7,8,17,18-
tetraphenyl-21,23-dideazaporphyrin (11), very recently re-
ported by Lash and co-workers.[35] Molecule 11 is in fact an
isomer of 3 with a different type of periphery substitution.
On the path between an [18]annulene and “half-porphyrin”
3, is aza[18]annulene[36,37] 10 with a nitrogen atom (if unpro-
tonated) exclusively occupying an internal position of the
ring perimeter.
On the other hand, [18]annulene 4 itself is not just a trivi-
al standard of aromaticity, but a fluxional molecule, affected
by steric interactions of internal protons.[24,25] Although an
[18]annulene complies with the spectral and structural crite-
ria of aromaticity, as a consequence of the conformational
flexibility it is a relatively reactive molecule, which decom-
poses at elevated temperatures with the tendency for addi-
tion/polymerization rather than electrophilic substitution re-
actions.[26,27] The last decade of the 20th century heralded a
renaissance of annulene chemistry.[28] A number of synthetic
discoveries in organic chemistry gave the ability to create
new annulenes with a variety of uses or interest from the
Abstract in Polish: Pod wpływem działania HCl-u na
5,10,15,20-tetraarylo-21,23-ditelluraporfiryne˛
otrzymano
5,10,15,20-tetraarylo-21,23-diwakataporfiryne˛, czyli porfiryne˛
pozbawiona˛ dwꢀch atomꢀw azotu rdzenia, be˛da˛ca˛ hybryda˛
annulenu i porfiryny. W powyz˙szej reakcji powstaje takz˙e
Bridging a diaza[18]annulene by three linkages, two
porACHTUNGTRENNUNGfiryna pozbawiona tylko jednego heteroatomu, tj.
ꢀ
ꢀ
ꢀ
ꢀ
C2H2 and only one N(H) , is sufficient to assure stabili-
ty and a porphyrinic structure (in a geometric and spectro-
scopic sense) in the molecule. In 2002 we synthesized such a
porphyrin–annulene hybrid, 2, belonging to the meso-tet-
raaryl-substituted series (Scheme 1).[38]
5,10,15,20-tetraarylo-21-tellura-23-wakataporfiryna. Obydwa
produkty, nalez˙a˛ce do rodziny wakataporfiryn, scharaktery-
zowano za pomoca˛ rentgenografii strukturalnej, spektrosko-
pii UV/Vis i NMR. Zwia˛zki te sa˛ aromatyczne, a parametry
spektroskopowe sa˛ podobne jak dla typowych tetraarylopor-
firyn. Badania krystalograficzne 21,23-diwakataporfiryny i
21-tellura-23-wakataporfiryny dowodza˛ pofałdowania cza˛ste-
It was named 21-vacataporphyrin, in relation to 21-heter-
oporphyrins[39] and emphasizing the vacant space instead of
a heteroatomic bridge. In fact the presence of four meso-
aryl groups additionally limits the conformational possibili-
ties and stabilizes the molecule. Therefore, the planarity, sta-
bility, and aromaticity of 2 is similar to that of 1. However,
metal coordination makes a substantial difference in the en-
ergetics of the system and traps other conformers and exotic
topologies.[40,41] The tripyrrene pincer holds a metal ion
(CdII, NiII, ZnII, or PdII) close to the nonbridged annulenic
´
czek. Odległosci niewia˛z˙a˛ce N22···N24 (5.23 i 5.09 ꢁ) sa˛
znacznie wie˛ksze niz˙ w normalnych porfirynach. Dla 21,23-
1
diwakataporfiryny pomiary zmiennotemperaturowe H NMR
pozwoliły na identyfikacje˛ stereoizomerꢀw rꢀz˙nia˛cych sie˛
geometria˛ mostkꢀw butadienowych (fragmentꢀw annuleno-
wych). Dwie formy pozostaja˛ w rꢀwnowadze termodyna-
micznej.
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´
L. Latos-Graz˙ynski et al.
fragment, which coordinates in several modes (structures
13–17), including organometallic s coordination in 15 and
different p modes in 14, 16, and 17. Two compounds require
special attention, that is, 16 and 17, in which the 18-electron
p system acquires Mçbius strip topology and represents one
of very few examples of Mçbius antiaromaticity.[41,42]
Scheme 2. Synthesis of 5,10,15,20-tetraaryl-21,23-divacataporphyrin (3Ar
Ar=Ph, or p-MeOPh).
;
of heteroporphyrins that, although fastidious ligands, show
unusual reactivity of the core atoms, catalytic activity, and
extraordinary flexibility, such as ditelluraporphyrin, which is
a porphyrin with one tellurophene ring rotated around the
Cmeso Ca bonds (Scheme 2).[44–46] The tellurium atom in 21-
ꢀ
telluraporphyrin can be replaced with oxygen under the in-
fluence of peroxide without damage to the porphyrin skele-
ton. In the reaction with HCl each tellurium atom exchanges
for two hydrogen atoms, the heterocycle opens, and heteroa-
tom-deficient vacataporphyrins are produced.
Herein, we report the synthesis of the next member of the
Telluraporphyrin 18Ph was heated with concentrated hy-
drochloric acid and the reaction yielded, depending on the
conditions, exclusively telluravacataporphyrin 19Ph (after
15 min in boiling toluene) or a mixture of vacataporphyrins
19Ph and 3Ph if the prolonged reaction was carried out in
boiling o-dichlorobenzene. The ease of the first tellurium
atom extrusion was not surprising in view of the 21,23-ditel-
5,10,15,20-tetraaryl
aza-deficient
porphyrin
family—
5,10,15,20-tetraaryl-21,23-divacataporphyrin—a half-porphy-
rin half-annulene molecule 3Ar (from this point we will indi-
cate the meso substituents by subscripts: 3Ph for tetraphenyl,
3Me for tetra(4-methoxyphenyl) derivatives). This porphyri-
noid may also be formally named [18]diphyrinACHTNUTRGNE(NUG 6.6) because
ꢀ
it contains only two pyrrolic units and two six-carbon links
or in a carbaporphyrin-like fashion, dibutadieneporphyrin,
because it has two butadiene chains in place of pyrrole
rings.[43]
luraporphyrin conformation with Te C bonds exposed to re-
actant attack. After chromatographic workup and recrystal-
lization, divacataporphyrin 3Ph was isolated in up to 25%
yield, and telluravacataporphyrin 19Ph in up to 80%. The
yields depend on the reaction time and the solvent, and are
truly not reproducible. Telluravacataporphyrin 19Ph is stable
under normal laboratory conditions and, contrary to 21-tel-
luraporphyrin, is resistant to air.[45] In independent experi-
ments, we have determined that 19Ph is not practical as a
starting material to obtain 3Ph. Heating 19Ph in o-dichloro-
benzene with hydrochloric acid gave 3Ph in very low and not
reproducible yield.
Results and Discussion
Synthesis: The synthesis of 3Ar seems to be quite challenging
when considering a rational approach by assembling all ap-
propriate synthons. The above-mentioned isomer of 3Ph, that
is, the tetraphenyl-b-substituted molecule 11 was elegantly
synthesized by Lash and co-workers in a McMurry coupling
reaction.[35] We have considered the “reversed” route, start-
ing from a porphyrin to form diaza-deficient porphyrins, and
presumed that 5,10,15,20-tetraaryl-21,23-divacataporphyrin
can be formed from 5,10,15,20-tetraaryl-21,23-diheteropor-
phyrin merely by extrusion of two bridging heteroatoms fol-
lowed by the addition of four hydrogen atoms. Such a con-
cept succeeded previously in formation of 5,10,15,20-tetra-
The detected degradation of 3Ph over the course of purifi-
cation prompted us to make an effort to synthesize an ana-
logue of divacataporphyrin with different meso substituents,
namely, derivative 3Me. Such a substitution required the syn-
thesis of a commercially unavailable starting material, 1-(p-
methoxyphenyl)prop-2-yn-1-ol, and motivated us to make a
revision of the usual troublesome procedure of preparing
2,5-bis(arylhydroxymethyl)tellurophene;[47] the crucial sub-
strate in the ditelluraporphyrin synthesis. The synthetic
work is summarized in Scheme 3.[48–50] In fact, compound 3Me
proved to be not much more stable than 3Ph, but was easier
to purify.
ACHTUNGTRENNUNG
heating
a
tellurium-containing macrocyclic substrate,
5,10,15,20-tetraaryl-21,23-ditelluraporphyrin (18Ar),[44] with
The replacement of HCl by DCl produced deuterated de-
rivative [Dx]3Me in which deuterium atoms not only substi-
concentrated HCl. Telluraporphyrins constitute a small class
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A Flexible Porphyrin–Annulene Hybrid
FULL PAPER
Scheme 3. Synthesis of 5,10,15,20-tetra(4-methoxyphenyl)-21,23-ditellura-
porphyrin 18Me. TMEDA=N,N,N’,N’-tetramethylethylenediamine.
tute the tellurium atoms, but also replace, to some degree,
the b-tellurophene and b-pyrrole protons, which proves their
acidic nature. If a mixture of DCl in D2O and HCl in H2O is
used in the reaction (6:1 v/v), the deuteration level equals
92% for the H-1,4,11,14 positions, 30% for the H-2,3,12,13
positions, and 70% for the b-pyrrolic positions, as shown by
1H NMR spectroscopy. Selectively deuterated divacatapor-
phyrin was instrumental in the analysis of conformational
equilibria.
Crystal structures of 3Ph and 19Ph: Both vacataporphyrins 3Ph
and 19Ph were characterized by X-ray crystallography
(Figure 1). The X-ray quality crystals were obtained for the
tetraphenyl derivatives by slow diffusion of n-hexane into a
1:1 solution of the porphyrin and C60 in chloroform/benzene
(1:1). The C60 molecules did not cocrystallize with the por-
phyrin, but their presence somehow facilitated crystal
growth.
Both structures of 3Ph and 19Ph have the typical porphyrin-
ic skeleton, with the butadiene fragments in an “out” con-
formation, which remains in contrast with the unorthodox
structure of the parent 21,23-ditelluraporphyrin 18Ph.[44] Evi-
dently the butadiene fragment flips out easily after tellurium
extrusion. The structure of 19Ph suffers from a disorder that
involves the tellurophene moiety and the butadiene frag-
ment on the opposite side of the molecule, thus the precise
geometrical parameters within these parts cannot be dis-
cussed. Nevertheless, the nonplanarity of the butadiene
moiety is not in question (Figure 1b), with hydrogen atoms
pointing in opposite directions of the porphyrin plane, likely
as a result of steric repulsion of closely located hydrogen
atoms. The tellurophene ring on the other side of the macro-
cyclic core is nearly planar and in plane with the meso-
carbon atoms.
Divacataporphyrin 3Ph is not strictly planar and shows a
substantial wavelike distortion of the skeleton, in contrast to
almost planar isomeric 11. The four meso-carbon atoms of
3Ph form a distinct rectangular pattern with the 6-carbon
chain side considerably longer (C5···C20=5.714(3) ꢂ) than
the pyrrolic side (C5···C10=4.813(3) ꢂ). The distance be-
tween potentially coordinating nitrogen atoms, that is,
N22···N24 (5.230(4) ꢂ), is rather large compared with
4.20 ꢂ in the regular 5,10,15,20-tetraphenylporphyrin 1[51] or
Figure 1. Molecular structure of a) 3Ph and b) 19Ph (top: perspective view,
vibrational ellipsoids represent 50% probability; bottom: side view,
phenyl groups omitted for clarity).
4.65 ꢂ in 21-telluraporphyrin.[45] Similarly to 19Ph, the fold-
ing of the 3Ph structure relieves some steric repulsion be-
tween neighboring inner hydrogen atoms. Subtle deviations
discussed in reference [35] for 11 were attributed to crowd-
ing of internal hydrogen atoms. In 19Ph, the N22···N24 dis-
tance (5.094(4) ꢂ) is smaller than that in 3Ph owing to the
bridging tellurium atom.
Electronic spectroscopy: The electronic absorption spectra
of 3Me and 19Me are presented in Figure 2 and the positions
of bands are gathered in Table 1.
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´
L. Latos-Graz˙ynski et al.
tendency was observed in the series 21-monoheteroporphyr-
ins and the shift value was dependent on the heteroatom
size.[39]
A comparison of the UV/Vis spectrum of 11 (Soret:
401 nm, Q: 565 nm) with that of 3 suggests that the electron-
ic structures of 3 and 11 differ more than that expected for
different periphery substitution.[35]
1H NMR spectrum of 19Ph: The fundamental structural fea-
tures of 19Ph and 3Ph determined in the solid state are pre-
1
served in solution, as determined by H NMR spectroscopy
for both species. Telluravacataporphyrin 19Ph, in fact a side
product of divacataporphyrin synthesis, does not require in-
1
depth discussion. H NMR spectroscopy data of 19Ph proves
that this molecule fits well into the tetraaryl-21-heteropor-
phyrin family and to the new class of vacataporphyrins as
1
well. The H NMR spectrum is a superposition of vacatapor-
phyrin and telluraporphyrin spectra. On two edges of the
spectrum, the fingerprint of vacataporphyrins, the AA’XX’
system, is present with typical parameters (d=10.13 and
ꢀ3.98 ppm; J11,12 =14.4, J12,13 =8.2, J11,13 =ꢀ1.3 Hz) and the
b-tellurophene protons give a characteristically downfield-
shifted singlet at d=10.54 ppm (see the Supporting Informa-
tion).
Figure 2. UV/Vis spectra in CH2Cl2 of a) divacataporphyrin 3Me (c)
compared with spectra of vacataporphyrin 2Me (a) and porphyrin 1Me
(g), and b) 21-tellura-23-vacataporphyrin 19Me (c) compared with
the spectrum of 21-telluraporphyrin (a).
Table 1. Electronic absorption spectra of selected vacata- and tellurapor-
phyrins.
Porphyrinoid[a]
Band
1
NMR spectroscopic studies of 3: H NMR spectra of both
Soret
Q
divacataporphyrins 3Ph and 3Me were recorded and the differ-
ences were insignificant, therefore, most NMR spectroscopy
studies were carried out for the more easily available deriva-
tive 3Me (Figure 3a). The large, easily visible signals in the
1H NMR spectrum come from the major divacataporphyrin
isomer 3Me-A (signals marked A; the existence of a second
1Me
2Me
3Me
422
440
448
447
469
518
526
532
540
561
556
593
675
792
629
747
650
751
882
690
832
555
559
610
693
21-telluraporphyrin
19Me
583
598
680
[a] All of the data are for tetra(4-methoxyphenyl) derivatives.
Generally, the spectroscopic properties of 3 and 19 indi-
cate their aromatic character, consistent with the presence
of 18 p electrons. A distinction can be made, by analogy to
the regular porphyrins, between the intense Soret band in
the near ultraviolet and Q bands in the visible region. Sys-
tematic redshifts were found for the Soret and all Q bands
in the series: porphyrin 1Me, vacataporphyrin 2Me, divacata-
porphyrin 3Me. The Soret band of 3Me is redshifted by 8 nm
compared with 2Me and 26 nm to 1Me. The remarkable
changes are visible in the long-wavelength region of the
spectrum—the Q-I band moves from 650 nm in 1Me to
751 nm in 2Me and 882 nm in 3Me. The intensity of the Soret
bands decreases, but the intensity of the long-wavelength Q-
band increases substantially (Figure 2a).
At this point, one can conclude that formal removal of ni-
trogen atoms results in redshifts of the bands, which increase
as the number of nitrogen atoms decreases. This tendency is
also clear for the pair 21-telluraporphyrin and 19Me (Fig-
ure 2b).
A comparison of the electronic spectra of vacataporphyrin
3Me and its monohetero-derivative, 19Me, shows that incorpo-
ration of a tellurium atom instead of a nitrogen one, shifts
all of the bands to the longer wavelength region. The similar
Figure 3. Selected regions of the 1H NMR (CDCl3, 260 K) spectrum of
a) 3Me (A and B correspond to the major 3Me-A and minor 3Me-B isomers,
1
respectively). The numbering follows Scheme 2. b) The H NMR (CDCl3,
260 K) spectrum of deuterated derivative [Dx]3Me. The residual solvent
peak and its satellites are indicated by s. The insets (with the vertical
scale enlarged 20 times) show the minor isomer 3Me-B more clearly.
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Chem. Eur. J. 2011, 17, 3500 – 3511

A Flexible Porphyrin–Annulene Hybrid
FULL PAPER
isomer (B) will be discussed below, see Figure 7). The very
simple NMR pattern is composed of one pyrrolic singlet,
one AA’XX’ pattern of the butadiene fragment, one set of
aryl signals, and is consistent with the high effective symme-
try (D2h) of the 3Me-A molecule. The spectral parameters of
the b-pyrrole protons do not differ from those typical for
porphyrins and heteroporphyrins[39] and have similar values
3
to those of 21-vacataporphyrin (dpyrr =8.39 ppm, Jpyrr
=
4.1 Hz, 300 K, CDCl3).[38]
The AA’XX’ pattern of the C1-C2-C3-C4 fragment shows
chemical shifts consistent with the presence of a strong dia-
magnetic ring current, dH-2 =9.69 ppm and dH-1 =ꢀ2.04 ppm
(3Me, CDCl3, 300 K), similar to that obtained for 11 (d=
9.88, 9.96, and ꢀ2.52 ppm).[35] The trans–cis–trans configura-
tion of the butadiene fragments of 3 is evident from the
chemical shifts and coupling constants. In fact, the AA’XX’
multiplets serve as the fingerprint of the annulene (non-
Figure 4. The temperature dependence of the 1H NMR chemical shifts
(CDCl3, 200–320 K) of H-1 and H-2 for divacataporphyrin 3Me-A. The
1
bridged) moiety (C1-C2-C3-C4). Remarkably, the H NMR
&
*
left axis and represent the H-1 (inner) signal; the right axis and rep-
resent the H-2 (outer) signal. The spectrum at 200 K was measured for a
supercooled solution. The parabolic lines are for illustrative purposes
only.
spectroscopic parameters match those of [18]annulene be-
cause the 1H NMR spectrum (CDCl3, 213 K) of [18]an-
nulene is characterized by quartet at d=9.17 ppm and a
quintet at d=ꢀ2.96 ppm for the external and internal pro-
tons, respectively.[25,52]
3Ph-A (for the details see below), we suggest that the mole-
cule adopts several very easily convertible conformations
with different arrangements of the four internal hydrogen
atoms (up or down with respect to the C5C10C15C20 plane,
Scheme 4). This exchange does not involve cis-trans isomeri-
zation of the butadiene linker (see below).[25] The preference
for a folded geometry can be explained by a tendency to
maximize the nonbonded H-1···H-4 distance to minimize the
steric repulsion.[24,25,53] The analogous conformational equi-
librium effect was found to be instrumental in analysis of
the temperature dependence of the chemical shifts detected
for [16]- and [18]annulene.[25]
Variable-temperature
studies:
Variable-temperature
1H NMR spectroscopy measurements have been carried out
to search for observable spectroscopic features to confirm
the feasible conformational flexibility of 3Me in solution. The
lines are narrow over the whole temperature range (200–
320 K) available for the standard solvents (CDCl3 or
CD2Cl2), but apparent temperature dependence of the
chemical shifts has been observed. In particular, remarkable
changes have been noted for the inner and outer butadiene
hydrogen atoms (Figure 4; DdH-2 =0.30 and DdH-1 =ꢀ0.95,
whereas Dd=d200 Kꢀd320 K). This way the chemical shift dif-
ference between the outer and inner hydrogen atoms of this
aromatic macrocycle, which is a simple measure of diatro-
picity, increases with the temperature decrease (from
Ddout-in =11.53 ppm at 320 K to
The pyrrole rings can be tilted out of the C5C10C15C20
plane in the same or opposite directions, albeit the coplanar
arrangement cannot be excluded. In fact, the waved confor-
12.77 ppm at 200 K).
The thermal dependence of
the chemical shifts of 3Me-A is
not accompanied by the sub-
stantial broadening of the sig-
nals in the upper or lower tem-
perature limits. The process re-
sponsible for the chemical-shift
variation, which does not even
begin to slow at the lowest tem-
peratures, must be fast on the
1H NMR timescale. Thus, the
mechanism should involve very
similar molecular structures and
very low energy barriers. After
the analysis of the X-ray struc-
ture and the DFT (B3LYP/6-
31G**) optimized model of Scheme 4. Possible conformers of 3-A. A tilt of the pyrrole rings is not shown.
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´
L. Latos-Graz˙ynski et al.
mation of the macrocycle has been determined by X-ray
crystallography (tilt angle 13.5(1)8), but the almost coplanar
arrangement of the pyrrole rings has been found in the DFT
optimized structure (tilt angle 6.08). Thus, the tilt angle of
the pyrrole units can be considered as the additional struc-
tural factor possibly varied by temperature. Presumably, as
the temperature of the solution of 3Me-A is lowered, the con-
formation of the macrocycle approaches the DFT-optimized
geometry. Consequently, this results in the enforcement of
macrocyclic p delocalization and the accompanying increase
in diatropicity of the porphyrinoid system.
1H NMR chemical shifts have been calculated by using
the GIAO-B3LYP method for the DFT-optimized geometry
of 3Ph-A (see below). There is only qualitative agreement
for a considered set of theoretical and experimental data
(see the Supporting Information). The calculated diatropici-
ty is highly overestimated, for instance, the maximal differ-
Figure 6. Dependence of the calculated (GIAO-B3LYP for B3LYP/6-
31G**-optimized geometries) and measured chemical shifts for divacata-
2+
1
porphyrin dication 3Me-H2
.
ence in calculated and experimental H NMR spectroscopic
shifts reached about 5 ppm for H-1. It is known that a good
agreement between calculated and measured chemical shifts
is expected only when the calculations are based on correct
geometries.[53] We conclude that the experimental data re-
flect, in fact, the averaged value to which the DFT-opti-
mized geometry and the appropriate chemical shifts contrib-
ute only to a limited extent, which increases once the tem-
perature is lowered.
paratropicity, and diatropicity of annulenes were quite sensi-
tive to steric interactions involving their internal pro-
tons.[25,54,55] In a clever experiment, they demonstrated that
modification of the steric interactions through isotopic sub-
stitution H!D (intrinsic steric isotope effects)[56] influences
the aromaticity, that is, increases the antiaromaticity of
[16]annulene and aromaticity of [18]annulene.[25]
The protonated divacataporphyrin provides us with argu-
ments that verify the above hypothesis. For divacataporphy-
ACHTUNGTRENNUNGrin dication, (3Me-A)H2 (formed from 3Me and an excess of
A similar strategy has been applied herein to confirm the
nature of the detected 3Me-A conformational equilibrium.
As already shown (Figure 3a), the 1H NMR spectrum
(600 MHz, 260 K, CDCl3) of 3Me-A demonstrates the charac-
teristic AA’XX’ multiplets at d=ꢀ2.34 and 9.78 ppm for the
internal and external hydrogen atoms, respectively. The
analogous spectrum of [Dx]3Me-A reveals increased diatropic
shifts of the internal protons due to site-specific deuteration.
To provide an internal reference, 1H NMR spectra of
[Dx]3Me with added protic 3Me were also recorded. Under
such experimental conditions, the signals of the external
protons H-2 of [Dx]3Me-A are practically unchanged, but the
internal proton signal (H-1) of 3-A-2 are shifted upfield by
36 ppb compared with the protic reference (Scheme 5 and
2+
HBF4), with a skeleton substantially distorted from planari-
ty, as the DFT model shows (see Figure 8 below), but likely
nondynamic structure, the chemical shifts of diagnostic H-1
and H-2 are practically temperature independent (Figure 5)
in contrast to neutral 3Me-A. It is also worth noting that the
calculated chemical shifts for the dication (Figure 6) are in
very good accordance with the experimental data, proving
that the rigid DFT model is a proper and sufficient descrip-
tion of the molecule.
ꢀ
Figure 3b). Since the C D bond is known to be shorter than
[25,54–59]
ꢀ
the C H bond,
the increased diatropic shifts of
Figure 5. 1H NMR (600 MHz, CDCl3) spectra of a) 3Me at 300 K, b) the
2+
dication 3Me-H2 obtained by the addition of HBF4 (8 equiv) at 300 K,
2+
and c) the dication 3Me-H2 at 220 K.
Scheme 5. The crucial deuterated derivatives of 3-A used in the investiga-
1
tion of intrinsic isotope effects. The H NMR spectroscopically detectable
inner hydrogen and the adjacent hydrogen or deuterium atoms are
framed (see also Figure 3b).
In the inspiring contributions by Stevenson and co-work-
ers, it was demonstrated that the conformational equilibria,
3506
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Chem. Eur. J. 2011, 17, 3500 – 3511

A Flexible Porphyrin–Annulene Hybrid
FULL PAPER
3
[Dx]3Me-A has been accounted for by an increased planarity
rameters (d260 K =8.12 and 8.23 ppm; J=4.3 Hz). Two buta-
and consequently larger diatropic ring current.
diene linkages are equivalent and demonstrate the ABXY
pattern with two multiplets in the high and two in the low-
frequency regions of the spectra (d260 K: 9.58 (H-1), ꢀ1.25
(H-2), 10.03 (H-3), ꢀ2.13 ppm (H-4)). The chemical shifts
are consistent with an all-trans conformation, as well as the
NMR spectroscopic studies of 3Me-B: After a careful exami-
nation of the spectra over a broad temperature range (200–
320 K), we noticed a second set of resonances of very low
intensity. Under standard experimental conditions (CDCl3,
300 K, cMffi8 mm), those resonances were too broad to be in-
dependently interpreted, but at 260 K (or below) they were
well resolved, although the intensities were comparable to
the intensity of the solvent satellites (Figure 3a, signals la-
beled B). The new pattern has been readily assigned to
second isomer 3Me-B with lower symmetry (C2h), which in
comparison to 3Me-A acquires a different configuration of
the butadiene linkers, that is, trans–trans–trans instead of
trans–cis–trans detected for 3Me-A (Figure 7). Possible inter-
mediates (energetically accessible, see below for the DFT
calculations) 3-C and 3-D forms are also included.
3J
ACTHNUTRGNEUNG(H,H) coupling constant equal to 13.5 Hz, which is consis-
tent with the trans geometry of coupled protons.
Variable-temperature 1H NMR spectroscopy data ob-
tained at 600 MHz provide insight into the dynamics of iso-
mers 3Me-A and 3Me-B, which are in dynamic equilibrium
(Figure 7). The isomerization process 3Me-AQ3Me-B is slow
on the NMR spectroscopy timescale and the corresponding
exchange rate is much lower than that for the rearrange-
ment of the internal protons in 3-A described above. Signifi-
cantly, the 2D NOESY experiment carried out at 260 K re-
vealed EXSY correlations between the appropriate resonan-
ces of 3Me-A and 3Me-B and within the 3Me-B signals. This ex-
periment provided evidence for the conversion of 3Me-A
into 3Me-B (which requires the cis–trans rearrangement of
the butadiene backbone) and the isodynamic conversion of
3
Me-BQ3Me-B’.
For the minor isomer, 3Me-B, the temperature dependence
of the hydrocarbon fragment chemical shift is evident, al-
though the differences in the chemical shifts are lower than
those for the A isomer, that is, Dd=ꢀ0.66 for the inner and
0.13 for the outer protons in the temperature range from
310 to 200 K (Dd=d200 Kꢀd310 K).
The observed conformers raised the question of their ther-
modynamic stability. The relative concentration of the two
isomers has been measured as a function of temperature for
the spectra that demonstrate acceptable signal-to-noise
ratios for the resonances of 3Me-B, that is, in the range 200–
320 K. The relative molar ratio [3Me-B]/ACHTNUGRTNEUNG[3Me-A] varied from
1:70 at 200 K to approximately 1:18 at 320 K. The tempera-
ture dependence of the equilibrium constant, defined as K=
[3Me-B]/ACHTNUGRTNEUNG[3Me-A] allows the following thermodynamic param-
eters to be calculated: DHo =1.55(5) kcalmolꢀ1, DSo =
ꢀ0.9(2) calmolꢀ1 Kꢀ1. The corresponding value of DG at
300 K is 1.81(6) kcalmolꢀ1. For a similar isomerization pro-
cess observed in isoporphycene, EQZ, the Gibbs free
energy, derived from NMR spectroscopy data is DG0 =
2.5 kcalmolꢀ1 and the E isomer is energetically favored.[60]
The addition of HBF4 to the equilibrium mixture of [3Me
A] and [3Me-B] resulted in dication formation, 3Me-H2
-
,
2+
which exists as only one isomer to preserve the structure of
Me-A (Figure 8).
3
DFT calculations: Herein, we have considered several novel
geometries of divacataporphyrin that are inspired by the ex-
perimentally determined structures. Several stereoisomers of
5,10,15,20-tetraphenyl-21,23-divacataporphyrin were subject-
ed to DFT optimization at the B3LYP/6-31G** level of
theory. The isomers important for discussing alongside the
experimental data and four other geometries with interest-
ing topologies are gathered in Figure 9 and are ordered by
their total calculated energies (by B3LYP/6-31G**//B3LYP/
Figure 7. Isomerization of divacataporphyrin 3Ph (DFT-optimized geome-
tries, B3LYP/6-31G**) with two possible intermediates.
In 3Me-B, pyrrole b protons are no longer equivalent and
give an AB pattern with typical tetraphenylporphyrin pa-
Chem. Eur. J. 2011, 17, 3500 – 3511
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3507

´
L. Latos-Graz˙ynski et al.
As expected, the porphyrin-like isomer 3-A has the
lowest energy, which accounts for the preference of 3-A in
solution and in the solid state. The experimentally observed
minor isomer, 3-B, is 1.57 kcalmolꢀ1 higher in energy than
the calculated energy for tetraphenyl derivative 3Ph-A, and
1.42 kcalmolꢀ1 higher in energy than the calculated energy
for the tetra(4-methoxyphenyl) derivative 3Me-A; this is in
excellent accordance with the experimental data (DHo =
1.55(5) kcalmolꢀ1 for 3Me). The next two isomers on the
energy scale, 3-C and 3-D, with one butadiene chain config-
uration unchanged with respect to 3-A, may be regarded as
half way from A to B and are good candidates for inter-
mediate forms (Figure 7). The energy of the other stereoiso-
mers excludes their contribution to experimentally detected
conformational equilibria. However, we selected them to
underline the diversity of conformational and topological
possibilities for divacataporphyrin. Three of them, E, F, G
(Figure 9) have the Mçbius strip conjugation path, and
isomer H has a doubly twisted figure-of-eight topology.
Isomer F is directly related to the known vacataporphyrin
complex 17.[41]
Figure 8. DFT-optimized (B3LYP/6-31G**) geometry of dication of
2+
3Me-H2
.
6-31G** approach). For the isomers studied by 1H NMR
spectroscopy, the 5,10,15,20-tetra(4-methoxyphenyl) deriva-
tives were the also subject of calculations: 3Me-A, 3Me-B, and
2+
3
Me-H2 .
Figure 9. Geometries, calculated energies (in kcal), and NICS values (in ppm) of chosen tetraphenyl-21,23-divacataporphyrins stereoisomers obtained by
DFT optimization (B3LYP/6-31G**). Isomers with the lowest energy (A, B, C, D), with Mçbius strip topology (E, F, G), and with figure-of-eight topolo-
gy (H) are shown. In the side-view projections the phenyl groups have been omitted for clarity.
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Chem. Eur. J. 2011, 17, 3500 – 3511

A Flexible Porphyrin–Annulene Hybrid
FULL PAPER
the potential energy surface; the resulting zero-point vibrational energies
were included in the calculation of relative energies. NICS values and
proton chemical shifts were calculated at the GIAO-B3LYP/6-31G**
level for the optimized structures. The Cartesian coordinates for the cal-
culated structures are given in the Supporting Information.
Thermodynamics calculations: DHo and DSo for the reaction [3Me-A]Q
AHCTUNGTRENNUNG
Chemical shifts and NICS calculations: Nucleus-indepen-
ACHTUNGTRENNUNG
dent chemical shift (NICS) values[60–62] were calculated for
divacataporphyrin molecules for the central 18-membered
ring (Figure 9). A comparison of the central ring NICS
values shows that they are good indicators of macrocyclic ar-
omaticity for a group of stereoisomers from 3-A to 3-H. For
the Hꢀckel aromatic systems, which were experimentally
identified as 3-A and 3-B, the central NICS values are nega-
tive (ꢀ12.1 and ꢀ12.4 ppm respectively) and comparable
with that reported for a porphyrin (ꢀ16.5 ppm).[63] For the
Mçbius antiaromatic conformers 3-E, 3-F, and 3-G, the
NICS values equal +3.7, +3.0, and +2.5 These values are
smaller than the NICS obtained for [20]annulene
(+12.1 ppm),[64] but resemble values determined previously
for the antiaromatic tautomer of 22-hydoxybenziporphyrin
ACHTUNGTRENNUNG
were obtained from integration of 1H NMR signals from spectra mea-
sured at temperatures ranging from 200 to 320 K. For this purpose, 32k
FIDs of 120 scans were collected with 4 s repetition time and before inte-
gration a baseline correction was done. Both downfield (H-2 of 3Me-A
and H-1, H-3 of 3Me-B) and upfield (H-1 of 3Me-A and H-2, H-4 of 3Me-B)
annulene signals were integrated if no overlap was present.
1-(4-Methoxyphenyl)prop-2-yn-1-ol: The synthesis of 1-(4-methoxyphe-
nyl)prop-2-yn-1-ol was based on a literature procedure involving com-
mercially available 1-phenylprop-2-yn-1-ol.[48] Ethynylmagnesium bro-
mide (12.0 mL, 0.5m in THF, 6 mmol) was added to a solution of anisol
aldehyde (0.6 mL, 5 mmol) in anhydrous THF (5 mL) at room tempera-
ture under nitrogen. The reaction mixture was stirred for 1 h, then
quenched with water (100 mL) and extracted with CH2Cl2 (100 mL). The
organic layer was washed with distilled water (50 mL) and a saturated
aqueous solution of NaCl (50 mL), and dried over Na2SO4. The solvent
was evaporated to give 1-(4-methoxyphenyl)prop-2-yn-1-ol as a light
solid (0.77 g, 95%). 1H NMR (CDCl3, 600 MHz): d=7.48 (d, J=8.0, 2H;
o-Ar), 6.91 (d, J=8.0, 2H; m-Ar), 5.42 (d, J=5.8, 1H; H-1), 3.81 (s, 3H;
OCH3), 2.65 (s, 1H; H-3), 2.35 ppm (d, J=5.8, 1H; OH).
ACHTUNGTRENNUNG
(+5.0 ppm)[65] or vacataporphyrin (+6 and +4 ppm).[41]
Conclusion
meso-Tetraaryl-21,23-divacataporphyrin—a half porphyrin
half annulene—was synthesized by the extrusion of two tel-
lurium atoms from 21,23-ditelluraporphyrin. This hybrid
molecule exhibits some properties characteristic for por-
phyrins and some typical for nonbridged annulenes. The
porphyrin-like structure and aromaticity of this molecule
was proven by X-ray crystallography and by the spectro-
scopic properties of the main form of divacataporphyrin
1,6-Bis(4-methoxyphenyl)hexa-2,4-diyne-1,6-diol: The synthesis of 1,6-
bis(4-methoxyphenyl)hexa-2,4-diyne-1,6-diol was based on a literature
procedure.[49] A mixture of TMEDA (0.06 mL, 0.4 mmol), CuI (19 mg,
0.1 mmol), and NiCl2·6H2O (24 mg, 0.1 mmol) in THF (5 mL) was stirred
at room temperature. 1-(4-Methoxyphenyl)prop-2-yn-1-ol (0.325 g,
2 mmol) dissolved in THF (5 mL) was added slowly and oxygen was bub-
bled through the solution. After completion of the reaction (1 h), as indi-
cated by TLC analysis, the mixture was concentrated in vacuo and puri-
fied by column chromatography on silica gel. The product was eluted
with 20% ethyl acetate in CH2Cl2 to give, after solvent evaporation, 1,6-
bis(4-methoxyphenyl)hexa-2,4-diyne-1,6-diol as pale yellow solid (0.30 g,
93%). Data for 4-methoxyphenyl derivative: 1H NMR (CDCl3,
600 MHz): d=7.44 (d, J=8.6 Hz, 4H; o-Ar), 6.91 (d, J=8.6 Hz, 4H; m-
Ar), 5.48 (d, J=6.0 Hz, 2H; H-1), 3.82 (s, 6H; OCH3), 2.13 ppm (d, J=
6.0 Hz, 2H; OH); 13C NMR (CDCl3, 150 MHz): d=159.7 (p-Ar), 132.4
1
(UV/Vis and H NMR spectroscopy). The typically annulen-
ic nature of this hybrid molecule is expressed by its flexibili-
ty, which results in the existence of a second, minor confor-
mer in a solution. The latter form is also aromatic and dif-
ferent from the main form in the configuration of the 6-
carbon bridge. In spite of the lack of two nitrogen atoms, di-
vacaporphyrin conserves the essential characteristic of the
maternal tetraphenylporphyrin structure, but allows for an
unprecedented flexibility in a porphyrin.
ꢁ
ꢁ
(ipso-Ar), 128.1 (o-Ar), 114.0 (m-Ar), 80.0 (C ), 69.9 (C ), 64.0 (C-1),
55.3 ppm (OMe).
2,5-Bis[(4-methoxyphenyl)hydroxymethyl]tellurophene: The synthesis
was adapted from a published procedure..[50] A 250 mL three-necked
flask equipped with a nitrogen inlet, reflux condenser, and addition
funnel was filled with nitrogen and loaded with tellurium (0.5 g, 4 mmol),
NaBH4 (0.6 g, 16 mmol), and distilled water (10 mL). The mixture was
vigorously stirred under nitrogen for 30 min and turned a pink–purple
Experimental Section
General: THF was dried and distilled from sodium/benzophenone imme-
diately prior to use under a nitrogen atmosphere. CH2Cl2 was distilled
from calcium hydride.
color.
A deoxygenated solution of 1,6-bis(4-methoxyphenyl)hexa-2,4-
diyne-1,6-diol (1.0 g, 3.1 mmol) in MeOH (12 mL) with AgOAc (50 mg)
was added dropwise and the mixture was stirred overnight. Water
(100 mL) was added and the product was extracted with benzene/ethyl
ether (1:1, 150 mL). The extract was washed with water, dried over
Na2SO4, and dried in vacuo to give 2,5-bis[(4-methoxyphenyl)hydroxy-
NMR spectroscopy: NMR spectra were recorded on high-field spectrom-
eters (1H frequency 500.13 or 600.15 MHz) equipped with a broadband
inverse gradient probe head. Spectra were calibrated to the residual sol-
vent signals (CDCl3, d1H =7.26, d13C =77.16 ppm).
AHCTUNGTRENNUNG
X-ray analysis: CCDC-794452 and 794453 contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
AHCTUNGTRENNUNG
Ar), 5.77 (2ꢄd, Jffi3 Hz, 2H; CH), 3.89, 3.79 (2ꢄs, 6H; OCH3), 2.45 ppm
(2ꢄd, Jffi3 Hz, 2H; OH); 13C NMR (CDCl3/CD3OD, 150 MHz): d=159.0
(p-Ar), 156.8 (a-tell), 137.0 (ipso-Ar), 132.54 and 132.45 (b-tell), 127.4
(o-Ar), 113.8 and 113.7 (o-Ar), 76.0 (Csp3), 55.2 ppm (O-CH3);
Theoretical calculations: DFT calculations were performed with the
Gaussian 03 program.[66] Starting geometries were obtained by using mo-
lecular mechanics and semiempirical calculations. Geometry optimiza-
tions were carried out within unconstrained C1 symmetry. Beckeꢁs three-
parameter exchange functional[67] with the gradient-corrected correlation
formula of Lee, Yang, and Parr (B3LYP)[68] was used with the 6-31G**
basis set. The structures were found to have converged to a minimum on
5,10,15,20-Tetra(4-methoxyphenyl)-21,23-ditelluraporphyrin (18Me): The
synthesis was carried out as a slight modification to our previously re-
ported method.[44] 2,5-Bis[(4-methoxyphenyl)hydroxymethyl]tellurophene
(1.35 g, 3 mmol), pyrrole (0.21 mL, 3 mmol), and freshly distilled CH2Cl2
(400 mL) were placed in a three-necked flask equipped with a reflux con-
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ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3509

´
L. Latos-Graz˙ynski et al.
denser and gas inlet. Nitrogen was bubbled through the solution for
20 min, the flask was protected from light, then BF3·Et2O (0.4 mL) was
added and the mixture was stirred for 1 h under nitrogen. Chloranil
(1.1 g, 4.5 mmol) was added and the solution was heated at reflux for
40 min. The solvent was condensed, the solution was passed through
basic Al2O3/CH2Cl2, then it was condensed again and purified by column
chromatography on silica gel. The first green fraction eluted with CH2Cl2
was recrystalized from CH2Cl2 and hexane to yield 18Me as a dark green
solid in (0.34 g, 23%). 1H NMR (CDCl3, 600 MHz, 325 K): d=7.83 (brd,
8H; o-Ar), 7.71 (brs, 4H; pyrr), 7.32 (v brs, 4H; tell), 7.10 (d, J=8.4 Hz,
8H; m-Ar), 3.94 ppm (s, 12H; OMe); 13C NMR (CDCl3, 150 MHz,
325 K): d=160.3, 154.6, 141.2, 134.6, 134.1, 133.9, 132.7, 114.0, 55.6 ppm;
UV/Vis (CH2Cl2): l=469, 684 nm; HRMS (ESI): m/z calcd for
815 nm (3.6); HRMS (ESI): m/z calcd for C44H31N2O130Te [M+O+H+]
733.1493; found: 733.1459.
Acknowledgements
Financial support from the Ministry of Science and Higher Education
(grant no. N204 013536) is kindly acknowledged. DFT calculations were
´
carried at the Supercomputer Center of Poznan.
+
C48H37N2O4Te2 [M+H+]: 965.0878; found: 965.0872.
[1] E. Vogel, Pure Appl. Chem. 1993, 65, 143–152.
5,10,15,20-Tetra(4-methoxyphenyl)-21,23-divacataporphyrin (3Me): Con-
centrated (35–38%) hydrochloric acid (4 mL) was added dropwise under
nitrogen to the oxygen-free, boiling solution of 18Me (15 mg, 1.5ꢄ
10ꢀ5 mol) in o-dichlorobenzene (12 mL). The mixture was stirred vigo-
rously for 90 min, then all of the solvents were distilled off. The solid res-
idue was dissolved in dichloromethane, half a teaspoon of basic Al2O3
was added to neutralize the protonated porphyrins, and the solution was
purified by column chromatography on SiO2. The first red fraction eluted
with CH2Cl2 was 19Me, the second eluted with 1% MeOH in CH2Cl2 was
[2] J. L. Sessler, S. J. Weghorn, Expanded, Contracted, and Isomeric Por-
phyrins, Elsevier, Oxford, New York Tokyo, 1997.
[3] J. L. Sessler, A. Gebauer, S. J. Weghorn in The Porphyrin Hand-
book, Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), Aca-
demic Press, San Diego, 2000, pp. 55–124.
´
´
[4] M. Ste˛pien, L. Latos-Graz˙ynski, Top. Heterocycl. Chem. 2009, 19,
83–154.
´
[5] E. Pacholska-Dudziak, L. Latos-Graz˙ynski, Coord. Chem. Rev. 2009,
253, 2036–2048.
3
Me. 3Me: Yield: 15–30%; UV/Vis (CH2Cl2): l (loge): 448 (4.7), 532 (3.9),
´
[6] M. Pawlicki, L. Latos-Graz˙ynski in Handbook of Porphyrin Science,
559 (sh), 693 (2.3), 792 (2.3), 882 nm (3.5); HRMS (ESI): m/z calcd for
Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), World Scien-
tific Publishing, Singapore, 2010, pp. 104–192.
+
C48H41N2O4 [M+H+]: 709.3066; found: 709.3051.
3
Me-A: 1H NMR
(CDCl3, 300 K, 600 MHz): d=9.69 (AA’XX’, J1,2 =14.8, J2,3 =8.2, J1,3
=
[7] E. Vogel, Pure Appl. Chem. 1990, 62, 557–564.
[8] H. Scheer, J. J. Katz in Porphyrins and Metalloporphyrin (Eds.:
K. M. Smith), Elsevier, Amsterdam, 1975, p. 399.
ꢀ1.4 Hz, 4H; H-2), 8.39 (s, 4H; H-6), 8.12 (d, J=8.35 Hz, 8H; o-Ar),
7.35 (d, J=8.35 Hz, 8H; m-Ar), 4.07 (s, 12H; OCH3), ꢀ2.04 ppm
(AA’XX’, J1,2 =14.8, J2,3 =8.2, J1,3 =ꢀ1.4 Hz, 4H; H-1); 13C NMR (CDCl3,
260 K, 150.9 MHz): d=159.9 (C-6), 159.7 (p-Ar), 140.2 (C-5), 135.3 (o-
Ar), 134.0 (C-7), 133.5 (C-2), 131.3 (ipso-Ar), 126.2 (C-1), 113.9 (m-Ar),
55.7 ppm (OCH3). 3Me-B: 1H NMR (CDCl3, 260 K, 600 MHz): d=10.03
(t, Jffi13.1 Hz, 2H; H-3), 9.58 (d, J=13.5 Hz; H-1), 8.23 (d, J=4.3 Hz,
2H; pyrr), 8.12 (d, J=4.3 Hz, 2H; pyrr), 8.04 (d, J=8.4 Hz, 8H; o-Ar),
7.26 (m-Ar, overlapping with residual solvent), 4.02 (s, 12H; OCH3),
ꢀ1.25 (t, Jffi13.4 Hz, 2H; H-2), ꢀ2.13 ppm (d, J=13.5 Hz, 2H; H-4).
´
[9] M. K. Cyranski, T. M. Krygowski, M. Wisiorowski, N. J. R. van Eike-
ma Hommes, P. von Raguꢅ Schleyer, Angew. Chem. 1998, 110, 187–
190; Angew. Chem. Int. Ed. 1998, 37, 177–180.
[10] J. Michl, J. Am. Chem. Soc. 1978, 100, 6801–6811.
[11] J. Waluk, J. Michl, J. Org. Chem. 1991, 56, 2729–2735.
[12] F. Sondheimer, R. Wolovsky, Y. Amiel, J. Am. Chem. Soc. 1962, 84,
274–284.
[13] F. Sondheimer, R. Wolovsky, Tetrahedron Lett. 1959, 1, 3–6.
[14] E. Vogel, W. Haas, B. Knipp, J. Lex, H. Schmickler, Angew. Chem.
1988, 100, 445–448; Angew. Chem. Int. Ed. Engl. 1988, 27, 406–409.
[15] T. D. Lash, Synlett 2000, 279–295.
5,10,15,20-Tetraphenyl-21,23-divacataporphyrin (3Ph): This compound was
synthesized under the same conditions as those used for the 4-methoxy-
phenyl derivative, 3Me.
1H NMR (CDCl3, 300 K, 600 MHz): d=9.71
[16] D. A. Colby, T. D. Lash, J. Org. Chem. 2002, 67, 1031–1033.
(AA’XX’, J1,2 =14.8, J2,3 =8.1, J1,3 =ꢀ1.5 Hz, 4H; H-2), 8.39 (s, 4H; H-7),
8.17 (d, J=8 Hz, 8H; o-Ph), 7.80 (t, J=7 Hz, 8H; m-Ph), 7.73 (t, J=
8 Hz, 4H; p-Ph), ꢀ2.10 ppm (AA’XX’, J1,2 =14.8, J2,3 =8.1, J1,3 =ꢀ1.5 Hz,
4H; H-1); 13C NMR (CDCl3, 300 K, 150 MHz): d=160.1, 140.7, 138.7,
134.0 (H-7), 133.6 (o-Ph), 133.4 (H-2), 128.2 (m-Ph), 128.1 (p-Ph),
126.3 ppm (H-1); UV/Vis (CH2Cl2): l (loge): 438 (4.7), 525 (3.9), 556
(sh), 683 (2.3), 776 (2.3), 866 nm (3.5); HRMS (ESI): m/z calcd for
C44H33N2 [M+H+] 589.2643; found: 589.2645.
´
[17] N. Sprutta, S. Mackowiak, M. Kocik, L. Szterenberg, T. Lis, L.
´
Latos-Graz˙ynski, Angew. Chem. 2009, 121, 3387—3391; Angew.
Chem. Int. Ed. 2009, 48, 3337–3341.
[18] E. Vogel, M. Kçcher, H. Schmickler, J. Lex, Angew. Chem. 1986, 98,
262–264; Angew. Chem. Int. Ed. Engl. 1986, 25, 257–259.
[19] E. Vogel, Pure Appl. Chem. 1996, 68, 1355–1360.
[20] J. L. Sessler, A. Gebauer, E. Vogel in The Porphyrin Handbook,
Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), Academic
Press, San Diego, 2000, pp. 1–54.
5,10,15,20-Tetraphenyl-21-tellura-23-vacataporphyrin (19Ph): (The tetra(4-
methoxyphenyl) derivative gave a much lower yield of 19Me in such con-
ditions and was very difficult to purify from the substrate, 19Me.) Concen-
trated (35–38%) hydrochloric acid (4 mL) was added dropwise under ni-
trogen to the oxygen-free, boiling solution of 18Ph (15 mg, 1.5ꢄ10ꢀ5 mol)
in toluene (12 mL). The mixture was stirred vigorously for 5 min, then all
of the solvents were distilled off. The solid residue was dissolved in di-
chloromethane, half a teaspoon of basic Al2O3 was added to neutralize
the protonated porphyrins, and the solution was purified by column chro-
matography on SiO2. The first red fraction eluted with CH2Cl2 was 19Ph
(10 mg, 80%). 1H NMR (CDCl3, 300 K, 600 MHz): d=10.54 (s, 2H; H-
2), 10.13 (AA’XX’, J11,12 =14.4, J12,13 =8.2, J11,13 =ꢀ1.3 Hz, 2H; H-12),
8.66 (d, J=4.3 Hz, 2H; pyrr), 8.60 (d, J=4.3 Hz, 2H; pyrr), 8.27 (m, 4H;
o-Ph-10,15), 8.21 (m, 4H; o-Ph-5,10), 7.85 (m, 4H; m-Ph-10,15), 7.82 (m,
4H; m-Ph-5,20), 7.77 (m, 4H; p-Ph), ꢀ3.98 ppm (AA’XX’, J11,12 =14.4,
´
[21] J. Skonieczny, L. Latos-Graz˙ynski, L. Szterenberg, Inorg. Chem.
2009, 48, 7394–7407.
´
[22] A. Młodzianowska, L. Latos-Graz˙ynski, L. Szterenberg, Inorg.
Chem. 2008, 47, 6364–6374.
[23] E. Vogel, M. Sicken, P. Rçhrig, H. Schmickler, J. Lex, O. Ermer,
Angew. Chem. 1988, 100, 450–453; Angew. Chem. Int. Ed. Engl.
1988, 27, 411–414.
[24] J. F. M. Oth, Pure Appl. Chem. 1971, 25, 573–622.
[25] C. D. Stevenson, T. L. Kurth, J. Am. Chem. Soc. 2000, 122, 722–723.
[26] K. Stçckel, P. J. Garratt, F. Sondheimer, J. Am. Chem. Soc. 1972, 94,
8644–8645.
[27] J. F. M. Oth, J.-M. Gilles, J. Phys. Chem. A 2000, 104, 7980–7994.
[28] E. L. Spitler, C. A. Johnson II, M. M. Haley, Chem. Rev. 2006, 106,
5344–5386.
[29] D. Ajami, O. Oeckler, A. Simon, R. Herges, Nature 2003, 426, 819–
821.
J
12,13 =8.2,
J
11,13 =ꢀ1.3 Hz, 4H; H-11); 13C NMR (CDCl3, 300 K,
150 MHz): d=160.7, 157.2, 153.8, 144.3 (C-2), 143.8 (C-5), 135.4 (b-pyrr),
134.12 (o-Ph), 134.03 (o-Ph), 133.96 (C-12), 139.0 (C-10), 133.1 (b-pyrr),
128.5 (m-Ph), 128.2 (p-Ph), 127.96 (C-11), 127.86 ppm (m-Ph); UV/Vis
(CH2Cl2): l (loge): 459 (4.6), 554 (3.7), 590 (3.5), 661 (2.6), 732 (2.7),
[30] D. Ajami, K. Hess, F. Kçhler, C. Nꢆther, O. Oeckler, A. Simon, C.
Yamamoto, Y. Okamoto, R. Herges, Chem. Eur. J. 2006, 12, 5434–
5445.
3510
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 3500 – 3511

A Flexible Porphyrin–Annulene Hybrid
FULL PAPER
´
´
[31] M. Ste˛pien, L. Latos-Graz˙ynski, N. Sprutta, P. Chwalisz, L. Szteren-
berg, Angew. Chem. 2007, 119, 8015–8019; Angew. Chem. Int. Ed.
2007, 46, 7869–7874.
[53] C. S. Wannere, K. W. Sattelmeyer, H. F. Schaefer III, P. von
Raguꢅ Schleyer, Angew. Chem. 2004, 116, 4296–4302; Schleyer,
Angew. Chem. 2004, 116, 4296–4302; Angew. Chem. Int. Ed. 2004,
43, 4200–4206.
[54] C. D. Stevenson, T. L. Kurth, J. Am. Chem. Soc. 1999, 121, 1623–
1624.
[55] T. L. Kurth, E. C. Brown, A. I. Smirnov, R. C. Reiter, C. D. Steven-
son, J. Phys. Chem. A 1999, 103, 8566–8572.
[56] K. Ibrom, G. Kohn, K. U. Boeckmann, R. Kraft, P. Holba-Schulz, L.
Ernst, Org. Lett. 2000, 2, 4111–4113.
[32] Y. Tanaka, S. Saito, S. Mori, N. Aratani, H. Shinokubo, N. Shibata,
Y. Higuchi, Z. S. Yoon, K. S. Kim, S. B. Noh, J. K. Park, D. Kim, A.
Osuka, Angew. Chem. 2008, 120, 693–696; Angew. Chem. Int. Ed.
2008, 47, 681–684.
[33] H. Ogawa, N. Sadakari, T. Imoto, I. Miyamoto, H. Kato, Y. Tanigu-
chi, Angew. Chem. 1983, 95, 412–413; Angew. Chem. Int. Ed. Engl.
1983, 22, 417–418.
[34] T. D. Lash, J. L. Romanic, M. J. Hayes, J. D. Spence, Chem.
Commun. 1999, 819–820.
[57] S. Aonuma, H. Sawa, R. Kato, J. Chem. Soc. Perkin Trans. 2 1995,
1541–1549.
[35] T. D. Lash, S. A. Jones, G. M. Ferrence, J. Am. Chem. Soc. 2010,
132, 12786–12787.
[58] L. S. Bartell, E. A. Roth, C. Hollowell, K. Kuchitsu, J. E. Young, J.
Chem. Phys. 1965, 42, 2683–2686.
[36] W. Gilb, G. Schrçder, Angew. Chem. 1979, 91, 332–333; Angew.
Chem. Int. Ed. Engl. 1979, 18, 312–313.
[37] W. Gilb, G. Schrçder, Chem. Ber. 1982, 115, 240–247.
[59] S. Berger, H. Kunzer, Tetrahedron 1983, 39, 1327–1329.
[60] E. Vogel, P. Scholz, R. Demuth, C. Erben, M. Brçring, H. Schmick-
ler, Y.-D. Wu, Angew. Chem. 1999, 111, 3100–3105; Angew. Chem.
Int. Ed. 1999, 38, 2919–2923.
´
[38] E. Pacholska, L. Latos-Graz˙ynski, Z. Ciunik, Chem. Eur. J. 2002, 8,
5403–5406.
[61] P. von Raguꢅ Schleyer, C. Meaerker, A. Dransfeld, H. Jiao, N. J. R.
van Eikema Hommes, J. Am. Chem. Soc. 1996, 118, 6317–6318.
[62] Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta, P. von Raguꢅ
Schleyer, Chem. Rev. 2005, 105, 3842–3888; Schleyer, Chem. Rev.
2005, 105, 3842–3888.
´
[39] L. Latos-Graz˙ynski in The Porphyrin Handbook, Vol. 2 (Eds.: K. M.
Kadish, K. M. Smith, R. Guilard), Academic Press, San Diego, 2000,
pp. 361–416.
[40] E. Pacholska-Dudziak, J. Skonieczny, M. Pawlicki, L. Latos-Graz˙yn-
´
´
ski, L. Szterenberg, Inorg. Chem. 2005, 44, 8794–8803.
[63] M. K. Cyranski, T. M. Krygowski, M. Wisiorowski, N. J. R. van Eike-
[41] E. Pacholska-Dudziak, J. Skonieczny, M. Pawlicki, L. Szterenberg,
ma Hommes, P. von Raguꢅ Schleyer, Angew. Chem. 1998, 110, 187–
190; Angew. Chem. Int. Ed. 1998, 37, 177–180.
´
Z. Ciunik, L. Latos-Graz˙ynski, J. Am. Chem. Soc. 2008, 130, 6182–
6195.
[64] C. Castro, C. M. Isborn, W. L. Karney, M. Mauksch, P. von Raguꢅ
Schleyer, Org. Lett. 2002, 4, 3431–3434; Schleyer, Org. Lett. 2002, 4,
3431–3434.
[42] T. Higashino, J. M. Lim, T. Miura, S. Saito, J.-Y. Shin, D. Kim, A.
Osuka, Angew. Chem. Int. Ed. 2010, 49, 4950–4954.
´
´
[43] The new macrocycle 3 is directly related to 5,10,15,20-tetraaryl-
21,23-heteroporphyrins, but instead of a heteroatomic bridge there
are two vacant spaces. Accordingly, the prefix vacata- means the re-
placement of a nitrogen atom by a vacancy. Alternatively, one can
point out that the NH group has been replaced by two hydrogen
atoms yielding a core-modified porphyrin with two (C)H hydrogen
atoms in the coordination core, 5,10,15,20-tetraaryl-1,4,11,14-tetra-
hydro-21,23-dideazaporphyrin; see ref. [17] in ref. [38].
[65] M. Ste˛pien, L. Latos-Graz˙ynski, L. Szterenberg, J. Org. Chem. 2007,
72, 2259–2270.
[66] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford CT, 2004.
´
[44] E. Pacholska, L. Latos-Graz˙ynski, Z. Ciunik, Angew. Chem. 2001,
113, 4598–4601; Angew. Chem. Int. Ed. 2001, 40, 4466–4469.
´
[45] L. Latos-Graz˙ynski, E. Pacholska, P. J. Chmielewski, M. M. Olm-
stead, A. L. Balch, Angew. Chem. 1995, 107, 2467–2469; Angew.
Chem. Int. Ed. Engl. 1995, 34, 2252–2254.
[46] M. Abe, Y. You, M. R. Detty, Organometallics 2002, 21, 4546–4551.
[47] A. Ulman, J. Manassen, F. Frolow, D. Rabinowich, Tetrahedron Lett.
1978, 19, 1885–1886.
[48] P. C. Chen, R. E. Wharton, P. A. Patel, A. K. Oyelere, Bioorg. Med.
Chem. 2007, 15, 7288–7300.
[49] W. Yin, C. He, M. Chen, H. Zhang, A. Lei, Org. Lett. 2009, 11, 709–
712.
[50] D. P. Sweat, C. E. Stephens, J. Organomet. Chem. 2008, 693, 2463–
2464.
[67] A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100.
[68] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[51] M. J. Hamor, T. A. Hamor, J. L. Hoard, J. Am. Chem. Soc. 1964, 86,
1938.
[52] J. F. M. Oth, H. Baumann, J. M. Giles, G. Schrçder, J. Am. Chem.
Soc. 1972, 94, 3498–3512.
Received: September 27, 2010
Revised: December 1, 2010
Published online: February 22, 2011
Chem. Eur. J. 2011, 17, 3500 – 3511
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3511