Oxatriphyrins(2.1.1) incorporating an ortho-phenylene motif

Article abstract of DOI:10.1002/anie.201410595

An understanding of fundamental aspects of archetypal organic structural motifs remains a key issue faced by the experimental and theoretical chemists. Two possible bonding modes for a disubstituted benzene ring, that is a meta and para, determines the p

Full text of DOI:10.1002/anie.201410595

Angewandte
Chemie
DOI: 10.1002/anie.201410595
Aromaticity
Oxatriphyrins(2.1.1) Incorporating an ortho-Phenylene Motif**
´
˙
Miłosz Pawlicki,* Mateusz Garbicz, Ludmiła Szterenberg, and Lechosław Latos-Grazynski*
Abstract: An understanding of fundamental aspects of arche-
typal organic structural motifs remains a key issue faced by the
experimental and theoretical chemists. Two possible bonding
modes for a disubstituted benzene ring, that is a meta and para,
determines the p delocalization for oligomeric structures.
When the less abundant ortho-substituted variant is introduced
into a triphyrin(2.1.1) skeleton an aromatic molecule is
obtained and the carbocyclic ring participates in the conjuga-
tion of the macrocycle. The two-electron reduction and
introduction of boron(III) changes the aromatic character
and results in an anti-aromatic structure which has been
confirmed by single-crystal analysis and supported by theoret-
ical calculations.
mented for protonated structures.[5] The ortho-phenylene is
rarely represented in porphyrinoids and reported for aro-
matic porphycenes[6] and texaphyrins,[7] as well as for non-
aromatic calixpyrroles,[8] but it can potentially lead to a fully
aromatic macrocyclic architecture and still remains an unex-
plored aspect of porphyrinoid reactivity.
Herein we present oxatriphyrins(2.1.1) with an ortho-
phenylene motif serving as a C2 meso-bridge. The initial step
in formation of the desired structures requires the synthesis of
1 (Scheme 2) wherein a benzene ring is incorporated. By
B
enzene, as an integral part of macrocyclic motifs brings to
the light new aspects of carbocyclic reactivity enforced by the
environment and type of substitution.[1] The bonding arrange-
ment (Scheme 1) determines the properties of the target
Scheme 1. Bonding modes for incorporation of benzene into macro-
cyclic loops.
Scheme 2. Formation of ortho-phenylene oxatriphyrins(2.1.1). Reaction
conditions: a) 2,5-bis(hydroxymethyltolyl)furan, CH2Cl2, inert atmos-
phere, BF3·Et2O, DDQ; b) MeOH/Et3N (1:1); c) CH2Cl2, HCl; d) 2,5-
bis(hydroxydiphenylmethyl)furan, CH2Cl2, inert atmosphere, BF3·Et2O.
molecules, noticeably distinguishing between the ortho-,
meta-, and para-phenylenes incorporated into either a macro-
cycle[1c] or oligophenylene.[2]
In porphyrinoids the orientation of benzene modifies the
conjugation, thus eventually determining the macrocyclic
aromaticity. While the para isomer can be illustrated as an
aromatic macrocycle,[3] the meta variant is mostly described as
an example wherein m-phenyl blocks effective macrocyclic
delocalization.[4] However, there are some exceptions docu-
using the palladium-catalyzed Suzuki coupling for 1,2-dibro-
mobenzene and N-Boc-pyrrol-2-yl-boronic acid,[9] followed
by deprotection, 1 was obtained in 68% yield. The conden-
sation of 1 with 2,5-bis(hydroxymethyltolyl)furan in equimo-
lar ratio (Scheme 1) followed by oxidation with dichlorodi-
cyano-p-quinone gave the oxatriphyrin(2.1.1) 2-H, which was
isolated solely in the monocationic form. The counterion, was
identified as a dichlorodicyano-hydroquinone anion and
replaced with a chloride by quantitative transformation into
phlorin (3) followed by acidic removal of the methoxy
substituent (Scheme 2), and finally giving 2-HCl in 20%
yield. The remarkable affinity of 2 toward protons reveals the
structural suitability of the porphyrinoid core for formation of
an intramolecular hydrogen bond. The behavior resembles
that of other triphyrins(n.1.1).[10]
[*] Dr. M. Pawlicki, M. Garbicz, Dr. L. Szterenberg,
´
Prof. L. Latos-Graz˙ynski
Department of Chemistry, University of Wrocław
F. Joliot-Curie 14, 50383 Wrocław (Poland)
E-mail: milosz.pawlicki@chem.uni.wroc.pl
lechoslaw.latos-grazynski@chem.uni.wroc.pl
Homepage: http://llg.chem.uni.wroc.pl/
[**] Financial support from the Ministry of Science and Higher
Education (Grant N N204 021939) and the National Science Centre
(2012/04/A/ST5/00593) is kindly acknowledged. The DFT calcula-
To explore the wider applicability of the presented
synthetic approach, the calix-triphyrin 4 was synthesized
and used here as an appropriate reference point to analyze
´
tions were carried out at the Poznan Supercomputing Centre.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201410595.
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
macrocyclic conjugation. The synthetic approach involves the
same strategy as that applied for 2-H, but using 2,5-
bis(hydroxydiphenylmethyl)furan (Scheme 1). All synthetic
steps are effective and lead to isolation of the desired
macrocycles in good yields.
Based on the different structures one can expect drasti-
cally dissimilar electronic properties for all three of the
oxatriphyrins(2.1.1) 2-HCl, 3, and 4. 2-HCl shows an aromatic
character with downfield-shifted resonances for the perimeter
hydrogen atoms. The 1H NMR spectrum of 2-H suggests
a significant involvement of the carbocyclic fragment in p-
delocalization of the macrocyclic as the AA’BB’ spin system
characteristic for ortho benzene is shifted downfield [d =
9.68 ppm (H11, H21) and 8.35 ppm (H12, H22)] (Figure 1A)
relative to the resonances for the non-aromatic 3 and 4
(Figure 1B,C). A similar trend was previously reported for
Figure 2. Absorption spectra for 2-HCl (solid line), 4 (dotted line), and
6 (dashed line). All experiments performed in CH2Cl2 at 298 K.
Scheme 3. 14p versus 18p delocalization in 2-H.
typical shape of 14p triphyrins(2.1.1),[10c] but approaches the
situation observed for thiophene-fused triphyrins(2.1.1).[9]
The electronic spectrum for 4 reflects a complete blockage
of the macrocyclic conjugation as the absorbance does not
exceed l = 350 nm.
The reduction of 2-HCl with a zinc amalgam in an inert
atmosphere (Scheme 4) affords 5, the form which can be
potentially described as an anti-aromatic compound with
16p/20p electron delocalization path. All b-resonances of 5
are similar to those of the non-aromatic 1 and 4. Nevertheless
the most informative structural fragment is the AA’BB’ spin
Figure 1. 1H NMR spectra for a) 2-HCl (MeOD, 300 K; inset presents
NH group observed in CDCl3), b) 4 (CD2Cl2, 300 K), and c) 3 (CD2Cl2,
300 K). The peak assignments follow the numbering scheme presented
in Scheme 1.
Scheme 4. Reactivity of 2-HCl. Reaction conditions: a) Zn/Hg, CDCl3,
inert atmosphere; b) toluene (reflux), Et3N, PhBCl2, inert atmosphere.
ortho-phenylene incorporated into the porphycene skele-
ton.[6a] The b-hydrogen atoms of pyrroles and furan resonate
at d = 8.80 ppm (H4, H15), 8.45 ppm (H9, H10), and 8.28 ppm
(H5, H14) and are consistent with the aromaticity of 2-HCl. A
strongly downfield-shifted NH proton (d ~ 14.2 ppm) has
a significant influence on the internal hydrogen bond which
overshadows the upfield ring current contribution. Such an
effect is typical for triphyrins(n.1.1).[9,10]
The electronic spectrum of 2-H is consistent with the
NMR-derived conclusions. An intense Soret-like band is
accompanied by a set of Q-bands (Figure 2). The observed
pattern suggests a contribution of both available delocaliza-
tion paths (14p/18p; Scheme 3) as it does not present the
system, of the ortho-phenylene, located at d = 7.05 ppm (H11,
H21) and 6.80 ppm (H12, H22), which are shifted slightly up-
field (by ca. 0.5 ppm) compared to those of 4 (Figure 1).
Evidently a different spectroscopic picture was observed for
the boron(III) complex of 5, that is, 6 (Scheme 3) which was
obtained by reaction of 2-H with PhBCl2 in the presence of
Et3N and using the procedure reported for thiophene-fused
oxatriphyrins(2.1.1)[9] and for furan fused oxatriphyrin-
(3.1.1).[12]
The insertion of boron(III) results in systematic upfield
relocation of the b-hydrogen resonances of the pyrroles [d =
5.84 ppm (H4, H15) and 5.61 ppm (H5, H14)] and furan [d =
5.23 ppm (H9, H10); Figure 3B]. Also the ortho-phenylene
2
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
proton in the 1H NMR spectrum.[9,10a,11a,13] The N–N and N–O
distances (2.550 ꢀ and 2.490 ꢀ, respectively) locate this
hydrogen bond in the region of strong interaction which is
characteristic of triphyrins,[9,10a,b,11a,13] but it is observed for
a cavity introducing a new type of environment for a three-
centered hydrogen bond which has not been reported before
for triphyrins(2.1.1). The coordination of boron(III) distorts
the planarity observed for 2-H. The central boron(III) cation
is displaced from the macrocyclic plane (defined by C3, C7,
C12 and C16) by 0.7 ꢀ, confirming the presence of a small
cavity for this oxatriphyrin(2.1.1), which is similar to nitrogen
analogues.[11b]
A careful analysis of bond lengths within the tri-hetero-
cyclic portion of 2-H and 6 (pyrrole-furan-pyrrole) clearly
reflects the differences in electronic structure. The bond
À
À
lengths of the furan fragment (C7 C8 1.432(7), C8 C9
À
À
1.389(7), C8 O 1.369(7), and C9 C10 1.382(10) ꢀ) in 2-H
equalize, thus showing a delocalization, as compared to a free
furan,[16] which is expected for macrocyclic aromaticity.
Figure 3. 1H NMR (CDCl3, 300 K, 600 MHz) spectra for a) 5 and b) 6
(inset presents the axial s-phenyl resonances).
À
À
Analogous bonds in 6 alternate (C7 C8 1.355(4), C8 C9
À
À
À
1.422(3), C9 C10 1.354(4), C10 C11 1.416(3) and C11 C12
À
À
resonances move significantly upfield (ca. 1 ppm with respect
to 4) to d = 6.61 ppm (H12, H22) and 6.49 ppm (H11, H21).
Significantly the paratropicity of 6 is reflected by a marked
downfield relocation of the axially coordinated s-phenyl (o-
Ph: d = 8.78 ppm, m-Ph: d = 7.66 ppm, and p-Ph: d =
7.58 ppm).[9,11,12] The electronic properties recorded for 6
(Figure 2) resemble the picture characteristic of anti-aromatic
delocalization in triphyrins,[9] tetraphyrins,[14] and expanded
porphyrins.[15]
2-H crystalizes as a cation with a dichlorodicyano-hydro-
quinone dianion as the counteranion with an NH hydro-
gen atom entrapped within the macrocycle (Figure 4).
Oxatriphyrin(2.1.1) presents a planar structure with hydrogen
firmly held between two nitrogen atoms, thus confirming the
hydrogen bond responsible for a downfield shift of the NH
1.355(4), C8 O 1.440(4), C11 O 1.431(4) ꢀ) but in a fashion
opposite to that of the free furan, thus reflecting the anti-
aromatic features of 6. Similar changes are observed for
pyrroles linked directly to the benzene ring. The bonds
À
between the benzene and pyrroles (C1 C16 1.470(7) for 2-H
À
À
and C1 C16 1.477(3) and C2 C3 1.475(3) ꢀ for 6) approach
2
2
À
À
the distance of an C(sp ) C(sp ) bond (C(meso) C(ipso):
1.485(7) ꢀ for 2-H and 1.480(3) ꢀ for 6), thus suggesting
isolation of a benzene fragment from the rest of the macro-
cycle. Nevertheless the spectroscopically documented merg-
ing of benzene with the macrocyclic conjugation is supported
by the bond lengths observed for the ortho-benzene fragment
(from 1.386(11) to 1.420(10) for 2-H and from 1.368(4) to
1.424(4) ꢀ for 6; see the Supporting Information), thus
showing a significant difference when compared to the meta
variant (1.378(2) to 1.399(2) ꢀ) where isolation of the
benzene ring from a macrocyclic conjugation has been
documented.[4b,17] The data is similar to that of the para
system (1.365(2) to 1.411(2) ꢀ) which is shown to be part of
the conjugated system.[3]
The DFT-optimized geometries of oxatriphyrins(2.1.1)
(Figure 4; see the Supporting Information) present similar
bond lengths and geometries as those observed for the crystal
structures. The NICS (nucleus independent chemical shifts)[18]
values calculated for the middle of macrocyclic plane for all
four compounds [d = À8.7 ppm (2-H), À1.4 ppm (4),
+ 3.7 ppm (5), and + 8.4 ppm (6), NICS(0)] are consistent
1
with H NMR features. The NICS(0) values at the center of
the ortho-phenylene ring [d = À13.7 ppm (2-H), À8.7 ppm
(4), À5.5 ppm (5), and À3.3 ppm (6)] demonstrate a visible
influence of the macrocycle on the properties of the
carbocyclic unit.[18] The N17 N19, N17 O18, and N19 O18
distances (2.566 ꢀ, 2.564 ꢀ, and 2.566 ꢀ, respectively) within
the cavity of the theoretical models optimized for 2-H are
comparable with those observed for the crystal structures,
thus supporting the origins of a strong hydrogen bond. The
À
À
À
Figure 4. X-Ray structures[20] (left) and DFT models (right) for a) 2-H
and b) 6. Thermal ellipsoids in crystal structures present at 50%
probability. The NH hydrogen atoms in (A) are arbitrarily located. In
the crystal structures oxygen atoms are presented as spheres with
black filling, nitrogen atoms are presented as white spheres, and the
central atoms (hydrogen for 2-H and boron for 6) are presented in
gray.
Wiberg indices[19] calculated in 2-H (N17 H 0.5663, N19 H
0.1631, O18 H 0.0096) confirm a strong interaction within the
À
À
À
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
Srinivasan, Org. Lett. 2011, 13, 2498 – 2501; c) D. Kuzuhara, Y.
Sakakibara, S. Mori, T. Okujima, H. Uno, H. Yamada, Angew.
Chem. Int. Ed. 2013, 52, 3360 – 3363; Angew. Chem. 2013, 125,
3444 – 3447; d) A. Krivokapic, A. R. Cowley, H. L. Anderson, J.
Org. Chem. 2003, 68, 1089 – 1096; e) M. Pawlicki, L. Latos-
coordination cavity and a strong hydrogen bond observed for
the N-O-N group within involving the neighboring oxygen
atom.
In conclusion the skeleton of oxatriphyrin(2.1.1) has been
significantly modified by integrating an ortho-phenylene
fragment which merges with the macrocyclic p system. The
molecule reveals either an aromatic or anti-aromatic macro-
cyclic p delocalization which is consistent with a significant
contribution of either the corresponding 18p or 20p elec-
tronic system. Additionally a strong, three-centered hydrogen
bond has been documented for the N-O-N surrounding.
´
Graz˙ynski, L. Szterenberg, J. Org. Chem. 2002, 67, 5644 – 5653;
´
f) M. Pawlicki, D. Bykowski, L. Szterenberg, L. Latos-Graz˙yn-
ski, Angew. Chem. Int. Ed. 2012, 51, 2500 – 2504; Angew. Chem.
2012, 124, 2550 – 2554.
´
´
[11] a) R. Mysliborski, L. Latos-Graz˙ynski, L. Szterenberg, T. Lis,
Angew. Chem. Int. Ed. 2006, 45, 3670 – 3674; Angew. Chem.
2006, 118, 3752 – 3756; b) D. Kuzuhara, Z. L. Xue, S. Mori, T.
Okujima, H. Uno, N. Aratani, H. Yamada, Chem. Commun.
2013, 49, 8955 – 8957.
Received: October 30, 2014
Published online: && &&, &&&&
´
[12] M. Pawlicki, A. Ke˛dzia, D. Bykowski, L. Latos-Graz˙ynski,
Chem. Eur. J. DOI: 10.1002/chem.201404570.
[13] a) H. Furuta, T. Ishizuka, A. Osuka, T. Ogawa, J. Am. Chem.
Soc. 1999, 121, 2945 – 2946; b) H. Furuta, H. Maeda, A. Osuka, J.
Am. Chem. Soc. 2001, 123, 6435 – 6436.
[14] a) J. A. Cissell, T. P. Vaid, G. P. A. Yap, Org. Lett. 2006, 8, 2401 –
2404; b) T. Kakui, S. Sugawara, Y. Hirata, S. Kojima, Y.
Yamamoto, Chem. Eur. J. 2011, 17, 7768 – 7771.
[15] S. Cho, Z. S. Yoon, K. S. Kim, M.-C. Yoon, D.-G. Cho, J. L.
Sessler, D. Kim, J. Phys. Chem. Lett. 2010, 1, 895 – 900.
[16] a) A. R. Katrizky, A. F. Pozharskii, Handbook of Heterocyclic
Chemistry, 2nd ed., Elsevier Pergamon, Oxford, 2000; b) J. A.
Joule, K. Mills, Heterocyclic Chemistry, 5th ed., Wiley-Black-
well, Oxford, 2010.
[17] E.-K. Sim, S.-D. Jeong, D.-W. Yoon, S.-J. Hong, Y. Kang, Ch.-H.
Lee, Org. Lett. 2006, 8, 3355 – 3358.
[18] P. von R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R.
van Eikema Hommes, J. Am. Chem. Soc. 1996, 118, 6317 – 6318.
[19] K. B. Wiberg, Tetrahedron 1968, 24, 1083 – 1096.
Keywords: aromaticity · boron · density functional calculations ·
macrocycles · structure elucidation
.
´
[1] a) B. Szyszko, L. Latos-Graz˙ynski, L. Szterenberg, Angew.
Chem. Int. Ed. 2011, 50, 6587 – 6591; Angew. Chem. 2011, 123,
6717 – 6721; b) B. Szyszko, K. Kupietz, L. Szterenberg, L. Latos-
´
´
Graz˙ynski, Chem. Eur. J. 2014, 20, 1376 – 1382; c) M. Ste˛pien, L.
´
Latos-Graz˙ynski, Acc. Chem. Res. 2005, 38, 88 – 98.
[2] a) S. M. Mathew, C. S. Hartley, Macromolecules 2011, 44, 8425 –
8432; b) C. S. Hartley, J. Org. Chem. 2011, 76, 9188 – 9191; c) K.
Matsuda, M. T. Stone, J. S. Moore, J. Am. Chem. Soc. 2002, 124,
11836 – 11837.
´
´
[3] M. Ste˛pien, L. Latos-Graz˙ynski, J. Am. Chem. Soc. 2002, 124,
3838 – 3839.
[4] a) K. Berlin, E. Breimaier, Angew. Chem. Int. Ed. Engl. 1994, 33,
[20] Low-temperature (100 K) single-crystal diffraction data were
collected on Nonius Kappa CCD diffractometer. Data were
solved and refined with the SHELXS-97. Crystallographic data
(excluding structure factors) have been deposited with the
Cambridge Crystallographic Data Centre [CCDC 1031417 (2-H)
and 1031416 (6)] which contain the supplementary crystallo-
graphic 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. Single crystal X-ray dif-
fraction data for 2-H: C34H27N2O·C8N2Cl2, Mr = 707.40, ortho-
rhombic (Pnma), a = 31.185(2) ꢀ, b = 30.231(2) ꢀ, c =
3.8539(4) ꢀ, a = b = g = 90.008, V= 3633.2(5) ꢀ3, Z = 4, m =
1.761 mmÀ1, Dc = 1.293 MgmÀ3,T= 100(2) K, 2956 independent
reflections, R1 = 0.0736, wR2 = 0.1997 [I > 2s(I)], S = 0.807;
Single crystal X-ray diffraction data for 6: C40H29BN2O, Mr =
564.46, monoclinic (P21/c), a = 7.8597(4) ꢀ, b = 22.9416(9) ꢀ,
c = 16.5956(6) ꢀ, a = 90.008, b = 102.210(4)8, g = 90.008, V=
´
1246 – 1247; Angew. Chem. 1994, 106, 1356 – 1357; b) M. Ste˛pien,
´
L. Latos-Graz˙ynski, Chem. Eur. J. 2001, 7, 5113 – 5117.
[5] a) J. T. Szymanski, T. D. Lash, Tetrahedron Lett. 2003, 44, 8613 –
8616; b) T. D. Lash, J. T. Szymanski, G. M. Ferrence, J. Org.
Chem. 2007, 72, 6481 – 6492.
[6] a) F. DꢁSouza, P. L. Boulas, M. Kisters, L. Sambrotta, A. M.
Aukauloo, R. Guilard, K. M. Kadish, Inorg. Chem. 1996, 35,
5743 – 5746; b) W.-M. Dai, W. L. Mak, Tetrahedron Lett. 2000,
41, 10277 – 10280.
[7] J. L. Sessler, G. Hemmi, T. D. Mody, T. Murai, A. Burrell, S. W.
Young, Acc. Chem. Res. 1994, 27, 43 – 50.
[8] B. Chandra, S. P. Mahanta, N. N. Pati, S. Baskaran, R. K.
Kanaparthi, Ch. Sivasankar, P. K. Panda, Org. Lett. 2013, 15,
306 – 309.
´
[9] M. Pawlicki, K. Hurej, L. Szterenberg, L. Latos-Graz˙ynski,
Angew. Chem. Int. Ed. 2014, 53, 2992 – 2996; Angew. Chem.
2014, 126, 3036 – 3040.
[10] a) Z.-L. Xue, Z. Shen, J. Mack, D. Kuzuhara, H. Yamada, T.
Okujima, N. Ono, X.-Z. You, N. Kobayashi, J. Am. Chem. Soc.
2008, 130, 16478 – 16479; b) K. S. Anju, S. Ramakrishnan, A.
2924.7(2) ꢀ3, Z = 4, m = 0.589 mmÀ1 Dc = 1.282 MgmÀ3
, , T=
100(2) K, 6184 independent reflections, R1 = 0.0907, wR2 =
0.2371 [I > 2s(I)], S = 0.981.
4
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
Communications
Aromaticity
Staying close: Oxatriphyrin(2.1.1) incor-
porating an ortho-phenylene moiety leads
to an aromatic compound in which the
benzene fragment participates in p de-
localization. The proximity of the heter-
oatoms (N,O,N) results in a strong
intramolecular three-centered hydrogen
bond. The introduction of boron(III)
leads to a complex having a paratropic
current.
M. Pawlicki,* M. Garbicz, L. Szterenberg,
´
L. Latos-Graz˙ynski*
&&&& — &&&&
Oxatriphyrins(2.1.1) Incorporating an
ortho-Phenylene Motif
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!