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DOI: 10.1002/anie.201410595
Aromaticity

Oxatriphyrins(2.1.1) Incorporating an ortho-Phenylene Motif**

Miłosz Pawlicki,* Mateusz Garbicz, Ludmiła Szterenberg, and Lechosław Latos-Grażyński*

Abstract: An understanding of fundamental aspects of arche- mented for protonated structures.[5] The ortho-phenylene is
typal organic structural motifs remains a key issue faced by the rarely represented in porphyrinoids and reported for aro-
experimental and theoretical chemists. Two possible bonding matic porphycenes[6] and texaphyrins,[7] as well as for non-
modes for a disubstituted benzene ring, that is a meta and para, aromatic calixpyrroles,[8] but it can potentially lead to a fully
determines the p delocalization for oligomeric structures. aromatic macrocyclic architecture and still remains an unex-
When the less abundant ortho-substituted variant is introduced plored aspect of porphyrinoid reactivity.
into a triphyrin(2.1.1) skeleton an aromatic molecule is Herein we present oxatriphyrins(2.1.1) with an ortho-
obtained and the carbocyclic ring participates in the conjuga- phenylene motif serving as a C2 meso-bridge. The initial step
tion of the macrocycle. The two-electron reduction and in formation of the desired structures requires the synthesis of
introduction of boron(III) changes the aromatic character 1 (Scheme 2) wherein a benzene ring is incorporated. By
and results in an anti-aromatic structure which has been
confirmed by single-crystal analysis and supported by theoret-
ical calculations.

Benzene, 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-
molecules, noticeably distinguishing between the ortho-, phere, BF3·Et2O, DDQ; b) MeOH/Et3N (1:1); c) CH2Cl2, HCl; d) 2,5-
bis(hydroxydiphenylmethyl)furan, CH2Cl2, inert atmosphere, BF3·Et2O.
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 using the palladium-catalyzed Suzuki coupling for 1,2-dibro-
aromaticity. While the para isomer can be illustrated as an mobenzene and N-Boc-pyrrol-2-yl-boronic acid,[9] followed
aromatic macrocycle,[3] the meta variant is mostly described as by deprotection, 1 was obtained in 68 % yield. The conden-
an example wherein m-phenyl blocks effective macrocyclic sation of 1 with 2,5-bis(hydroxymethyltolyl)furan in equimo-
delocalization.[4] However, there are some exceptions docu- lar ratio (Scheme 1) followed by oxidation with dichlorodi-
cyano-p-quinone gave the oxatriphyrin(2.1.1) 2-H, which was
[*] Dr. M. Pawlicki, M. Garbicz, Dr. L. Szterenberg, isolated solely in the monocationic form. The counterion, was
Prof. L. Latos-Grażyński identified as a dichlorodicyano-hydroquinone anion and
Department of Chemistry, University of Wrocław replaced with a chloride by quantitative transformation into
F. Joliot-Curie 14, 50383 Wrocław (Poland) phlorin (3) followed by acidic removal of the methoxy
E-mail: milosz.pawlicki@chem.uni.wroc.pl substituent (Scheme 2), and finally giving 2-HCl in 20 %
lechoslaw.latos-grazynski@chem.uni.wroc.pl
yield. The remarkable affinity of 2 toward protons reveals the
Homepage: http://llg.chem.uni.wroc.pl/
structural suitability of the porphyrinoid core for formation of
[**] Financial support from the Ministry of Science and Higher
Education (Grant N N204 021939) and the National Science Centre an intramolecular hydrogen bond. The behavior resembles
(2012/04/A/ST5/00593) is kindly acknowledged. The DFT calcula- that of other triphyrins(n.1.1).[10]
tions were carried out at the Poznań Supercomputing Centre. To explore the wider applicability of the presented
Supporting information for this article is available on the WWW synthetic approach, the calix-triphyrin 4 was synthesized
under http://dx.doi.org/10.1002/anie.201410595. and used here as an appropriate reference point to analyze

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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 Figure 2. Absorption spectra for 2-HCl (solid line), 4 (dotted line), and
hydrogen atoms. The 1H NMR spectrum of 2-H suggests 6 (dashed line). All experiments performed in CH2Cl2 at 298 K.
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 1 A)
relative to the resonances for the non-aromatic 3 and 4
(Figure 1 B,C). A similar trend was previously reported for

Scheme 3. 14 p versus 18 p delocalization in 2-H.

typical shape of 14 p 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
16 p/20 p 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 Scheme 4. Reactivity of 2-HCl. Reaction conditions: a) Zn/Hg, CDCl3,
in Scheme 1. inert atmosphere; b) toluene (reflux), Et3N, PhBCl2, inert atmosphere.

ortho-phenylene incorporated into the porphycene skele- system, of the ortho-phenylene, located at d = 7.05 ppm (H11,
ton.[6a] The b-hydrogen atoms of pyrroles and furan resonate H21) and 6.80 ppm (H12, H22), which are shifted slightly up-
at d = 8.80 ppm (H4, H15), 8.45 ppm (H9, H10), and 8.28 ppm field (by ca. 0.5 ppm) compared to those of 4 (Figure 1).
(H5, H14) and are consistent with the aromaticity of 2-HCl. A Evidently a different spectroscopic picture was observed for
strongly downfield-shifted NH proton (d ~ 14.2 ppm) has the boron(III) complex of 5, that is, 6 (Scheme 3) which was
a significant influence on the internal hydrogen bond which obtained by reaction of 2-H with PhBCl2 in the presence of
overshadows the upfield ring current contribution. Such an Et3N and using the procedure reported for thiophene-fused
effect is typical for triphyrins(n.1.1).[9, 10] oxatriphyrins(2.1.1)[9] and for furan fused oxatriphyrin-
The electronic spectrum of 2-H is consistent with the (3.1.1).[12]
NMR-derived conclusions. An intense Soret-like band is The insertion of boron(III) results in systematic upfield
accompanied by a set of Q-bands (Figure 2). The observed relocation of the b-hydrogen resonances of the pyrroles [d =
pattern suggests a contribution of both available delocaliza- 5.84 ppm (H4, H15) and 5.61 ppm (H5, H14)] and furan [d =
tion paths (14 p/18 p; Scheme 3) as it does not present the 5.23 ppm (H9, H10); Figure 3 B]. Also the ortho-phenylene

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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
lengths of the furan fragment (C7 C8 1.432(7), C8 C9
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
Figure 3. 1H NMR (CDCl3, 300 K, 600 MHz) spectra for a) 5 and b) 6
(inset presents the axial s-phenyl resonances).
furan,[16] which is expected for macrocyclic aromaticity.
Analogous bonds in 6 alternate (C7 C8 1.355(4), C8 C9
1.422(3), C9 C10 1.354(4), C10 C11 1.416(3) and C11 C12
resonances move significantly upfield (ca. 1 ppm with respect 1.355(4), C8 O 1.440(4), C11 O 1.431(4) ) but in a fashion
to 4) to d = 6.61 ppm (H12, H22) and 6.49 ppm (H11, H21). opposite to that of the free furan, thus reflecting the anti-
Significantly the paratropicity of 6 is reflected by a marked aromatic features of 6. Similar changes are observed for
downfield relocation of the axially coordinated s-phenyl (o- pyrroles linked directly to the benzene ring. The bonds
Ph: d = 8.78 ppm, m-Ph: d = 7.66 ppm, and p-Ph: d = between the benzene and pyrroles (C1 C16 1.470(7) for 2-H
7.58 ppm).[9, 11, 12] The electronic properties recorded for 6 and C1 C16 1.477(3) and C2 C3 1.475(3)  for 6) approach
(Figure 2) resemble the picture characteristic of anti-aromatic the distance of an C(sp2) C(sp2) bond (C(meso) C(ipso):
delocalization in triphyrins,[9] tetraphyrins,[14] and expanded 1.485(7)  for 2-H and 1.480(3)  for 6), thus suggesting
porphyrins.[15] isolation of a benzene fragment from the rest of the macro-
2-H crystalizes as a cation with a dichlorodicyano-hydro- cycle. Nevertheless the spectroscopically documented merg-
quinone dianion as the counteranion with an NH hydro- ing of benzene with the macrocyclic conjugation is supported
gen atom entrapped within the macrocycle (Figure 4). by the bond lengths observed for the ortho-benzene fragment
Oxatriphyrin(2.1.1) presents a planar structure with hydrogen (from 1.386(11) to 1.420(10) for 2-H and from 1.368(4) to
firmly held between two nitrogen atoms, thus confirming the 1.424(4)  for 6; see the Supporting Information), thus
hydrogen bond responsible for a downfield shift of the NH 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 = 8.7 ppm (2-H), 1.4 ppm (4),
+ 3.7 ppm (5), and + 8.4 ppm (6), NICS(0)] are consistent
with 1H NMR features. The NICS(0) values at the center of
the ortho-phenylene ring [d = 13.7 ppm (2-H), 8.7 ppm
(4), 5.5 ppm (5), and 3.3 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
Figure 4. X-Ray structures[20] (left) and DFT models (right) for a) 2-H distances (2.566 , 2.564 , and 2.566 , respectively) within
and b) 6. Thermal ellipsoids in crystal structures present at 50 % the cavity of the theoretical models optimized for 2-H are
probability. The NH hydrogen atoms in (A) are arbitrarily located. In
comparable with those observed for the crystal structures,
the crystal structures oxygen atoms are presented as spheres with
black filling, nitrogen atoms are presented as white spheres, and the thus supporting the origins of a strong hydrogen bond. The
central atoms (hydrogen for 2-H and boron for 6) are presented in Wiberg indices[19] calculated in 2-H (N17 H 0.5663, N19 H
gray. 0.1631, O18 H 0.0096) confirm a strong interaction within the

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coordination cavity and a strong hydrogen bond observed for Srinivasan, Org. Lett. 2011, 13, 2498 – 2501; c) D. Kuzuhara, Y.
the N-O-N group within involving the neighboring oxygen Sakakibara, S. Mori, T. Okujima, H. Uno, H. Yamada, Angew.
atom. Chem. Int. Ed. 2013, 52, 3360 – 3363; Angew. Chem. 2013, 125,
3444 – 3447; d) A. Krivokapic, A. R. Cowley, H. L. Anderson, J.
In conclusion the skeleton of oxatriphyrin(2.1.1) has been
Org. Chem. 2003, 68, 1089 – 1096; e) M. Pawlicki, L. Latos-
significantly modified by integrating an ortho-phenylene Grażyński, L. Szterenberg, J. Org. Chem. 2002, 67, 5644 – 5653;
fragment which merges with the macrocyclic p system. The f) M. Pawlicki, D. Bykowski, L. Szterenberg, L. Latos-Grażyń-
molecule reveals either an aromatic or anti-aromatic macro- ski, Angew. Chem. Int. Ed. 2012, 51, 2500 – 2504; Angew. Chem.
cyclic p delocalization which is consistent with a significant 2012, 124, 2550 – 2554.
contribution of either the corresponding 18 p or 20 p elec- [11] a) R. Myśliborski, L. Latos-Grażyński, L. Szterenberg, T. Lis,
Angew. Chem. Int. Ed. 2006, 45, 3670 – 3674; Angew. Chem.
tronic system. Additionally a strong, three-centered hydrogen
2006, 118, 3752 – 3756; b) D. Kuzuhara, Z. L. Xue, S. Mori, T.
bond has been documented for the N-O-N surrounding. Okujima, H. Uno, N. Aratani, H. Yamada, Chem. Commun.
2013, 49, 8955 – 8957.
Received: October 30, 2014 [12] M. Pawlicki, A. Ke˛dzia, D. Bykowski, L. Latos-Grażyński,
Published online: December 21, 2014 Chem. Eur. J. 2014, 20, 17500 – 17506.

.
Keywords: aromaticity · boron · density functional calculations ·
macrocycles · structure elucidation
[13]

[14]
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.
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.
[1] a) B. Szyszko, L. Latos-Grażyński, L. Szterenberg, Angew. Yamamoto, Chem. Eur. J. 2011, 17, 7768 – 7771.
Chem. Int. Ed. 2011, 50, 6587 – 6591; Angew. Chem. 2011, 123, [15] S. Cho, Z. S. Yoon, K. S. Kim, M.-C. Yoon, D.-G. Cho, J. L.
6717 – 6721; b) B. Szyszko, K. Kupietz, L. Szterenberg, L. Latos- Sessler, D. Kim, J. Phys. Chem. Lett. 2010, 1, 895 – 900.
Grażyński, Chem. Eur. J. 2014, 20, 1376 – 1382; c) M. Ste˛pień, L. [16] a) A. R. Katrizky, A. F. Pozharskii, Handbook of Heterocyclic
Latos-Grażyński, Acc. Chem. Res. 2005, 38, 88 – 98. Chemistry, 2nd ed., Elsevier Pergamon, Oxford, 2000; b) J. A.
[2] a) S. M. Mathew, C. S. Hartley, Macromolecules 2011, 44, 8425 – Joule, K. Mills, Heterocyclic Chemistry, 5th ed., Wiley-Black-
8432; b) C. S. Hartley, J. Org. Chem. 2011, 76, 9188 – 9191; c) K. well, Oxford, 2010.
Matsuda, M. T. Stone, J. S. Moore, J. Am. Chem. Soc. 2002, 124, [17] E.-K. Sim, S.-D. Jeong, D.-W. Yoon, S.-J. Hong, Y. Kang, Ch.-H.
11836 – 11837. Lee, Org. Lett. 2006, 8, 3355 – 3358.
[3] M. Ste˛pień, L. Latos-Grażyński, J. Am. Chem. Soc. 2002, 124, [18] P. von R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R.
3838 – 3839. van Eikema Hommes, J. Am. Chem. Soc. 1996, 118, 6317 – 6318.
[4] a) K. Berlin, E. Breimaier, Angew. Chem. Int. Ed. Engl. 1994, 33, [19] K. B. Wiberg, Tetrahedron 1968, 24, 1083 – 1096.
1246 – 1247; Angew. Chem. 1994, 106, 1356 – 1357; b) M. Ste˛pień, [20] Low-temperature (100 K) single-crystal diffraction data were
L. Latos-Grażyński, Chem. Eur. J. 2001, 7, 5113 – 5117. collected on Nonius Kappa CCD diffractometer. Data were
[5] a) J. T. Szymanski, T. D. Lash, Tetrahedron Lett. 2003, 44, 8613 – solved and refined with the SHELXS-97. Crystallographic data
8616; b) T. D. Lash, J. T. Szymanski, G. M. Ferrence, J. Org. (excluding structure factors) have been deposited with the
Chem. 2007, 72, 6481 – 6492. Cambridge Crystallographic Data Centre [CCDC 1031417 (2-H)
[6] a) F. DSouza, P. L. Boulas, M. Kisters, L. Sambrotta, A. M. and 1031416 (6)] which contain the supplementary crystallo-
Aukauloo, R. Guilard, K. M. Kadish, Inorg. Chem. 1996, 35, graphic data for this paper. These data can be obtained free of
5743 – 5746; b) W.-M. Dai, W. L. Mak, Tetrahedron Lett. 2000, charge from The Cambridge Crystallographic Data Centre via
41, 10277 – 10280. www.ccdc.cam.ac.uk/data_request/cif. Single crystal X-ray dif-
[7] J. L. Sessler, G. Hemmi, T. D. Mody, T. Murai, A. Burrell, S. W. fraction data for 2-H: C34H27N2O·C8N2Cl2, Mr = 707.40, ortho-
Young, Acc. Chem. Res. 1994, 27, 43 – 50. rhombic (Pnma), a = 31.185(2) , b = 30.231(2) , c =
[8] B. Chandra, S. P. Mahanta, N. N. Pati, S. Baskaran, R. K. 3.8539(4) , a = b = g = 90.008, V = 3633.2(5) 3, Z = 4, m =
Kanaparthi, Ch. Sivasankar, P. K. Panda, Org. Lett. 2013, 15, 1.761 mm 1, Dc = 1.293 Mg m 3,T = 100(2) K, 2956 independent
306 – 309. reflections, R1 = 0.0736, wR2 = 0.1997 [I > 2s(I)], S = 0.807;
[9] M. Pawlicki, K. Hurej, L. Szterenberg, L. Latos-Grażyński, Single crystal X-ray diffraction data for 6: C40H29BN2O, Mr =
Angew. Chem. Int. Ed. 2014, 53, 2992 – 2996; Angew. Chem. 564.46, monoclinic (P21/c), a = 7.8597(4) , b = 22.9416(9) ,
2014, 126, 3036 – 3040. c = 16.5956(6) , a = 90.008, b = 102.210(4)8, g = 90.008, V =
[10] a) Z.-L. Xue, Z. Shen, J. Mack, D. Kuzuhara, H. Yamada, T. 2924.7(2) 3, Z = 4, m = 0.589 mm 1, Dc = 1.282 Mg m 3, T =
Okujima, N. Ono, X.-Z. You, N. Kobayashi, J. Am. Chem. Soc. 100(2) K, 6184 independent reflections, R1 = 0.0907, wR2 =
2008, 130, 16478 – 16479; b) K. S. Anju, S. Ramakrishnan, A. 0.2371 [I > 2 s(I)], S = 0.981.

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