Palladium(II)-triggered rearrangement of heptaphyrins to N-confused porphyrins

Article abstract of DOI:10.1002/anie.201100243

More confused: Metalation reactions of [32]heptaphyrins(1.1.1.1.1.1.1) with Pd^II ions result in a rearrangement to form Pd^II complexes that contain an N-confused-porphyrin (NCP) framework (see scheme). This rearrangement was also dem

Full text of DOI:10.1002/anie.201100243

DOI: 10.1002/anie.201100243
Porphyrinoids
Palladium(II)-Triggered Rearrangement of Heptaphyrins to
N-Confused Porphyrins**
Tomoki Yoneda, Shohei Saito, Hideki Yorimitsu, and Atsuhiro Osuka*
A recent surge in the chemistry of expanded porphyrins is
largely due to their attractive optical, electrochemical,
and coordination properties, which arise from their large
p-conjugated frameworks.[1] The unique chemical reactivity of
expanded porphyrins means that they often undergo metal-
ation-induced skeletal rearrangements, as metalation reac-
tions require specific coordination structures and expanded
porphyrins have flexible electronic systems that are reactive
toward such structural distortions.[2,3] The first examples of
expanded porphyrins were the octaphyrins(1.1.1.0.1.1.1.0)
reported by Vogel et al.,[2] which were followed by our reports
on 1) the splitting reaction of a bis(CuII octaphyrin) into two
CuII porphyrins,[3a,b] 2) the boron(III)-triggered splitting reac-
tion of CuII heptaphyrins to CuII porphyrins and BIII
subporphyrins,[3c,d] and 3) the boron(III)-induced rearrange-
ment of a hexaphyrin(1.1.1.1.1.1) to form a hexaphyr-
in(2.1.1.0.1.1).[3e] These skeletal rearrangements are intriguing
in making “chemical connections” between important por-
phyrinoids such as octaphyrins, heptaphyrins, hexaphyrins,
porphyrins, and subporphyrins. Despite these results,
N-confused porphyrins (NCPs), which have a key position
in porphyrin chemistry,[1d,4,5] have not been included in this
approach to date. Herein, we report that an NCP-type
the yield of 2 (Scheme 1). High-resolution electrospray
ionization time-of-flight mass spectroscopy (HR-ESI-TOF
MS) indicated the parent ion peak of 3 at m/z 1659.7423
(calcd for C77H34N7Cl14Pd [MÀH]À: 1659.7485). The structure
of 3 was unambiguously determined by single-crystal X-ray
Scheme 1. Metalation of 1 with PdII ions. Ar=2,6-dichlorophenyl.
conjugated
system
is
formed
from
[32]hepta-
phyrin(1.1.1.1.1.1.1) upon rearrangement triggered by metal-
ation with PdII ions.
diffraction analysis.[8] To our surprise, complex 3 contains a
PdII NCP-type framework, across which a tripyrromethene
unit is attached at the a- and g-positions, C(19) and C(17), of
the N-confused pyrrole (pyrrole D in Figure 1). The
Pd···N(1), Pd···N(2), Pd···N(3), and Pd···C(17) distances are
2.01, 2.08, 1.99, and 2.07 ꢁ, respectively. As seen in other
NCPs, the three pyrrole units are almost planar with the
mean-plane deviation of 0.07 ꢁ, to which the inverted
pyrrole D is tilted with a dihedral angle of 38.908. The
carbon atom C(17), which is bound to the PdII ion, is sp3-
hybridized.[9] The existence of aromatic NCP network is also
indicated by the chemical shifts of Ha (d = 1.99 ppm) and Hb
(d = 4.84 ppm) protons, which are located above the NCP ring
and thus are considerably upfield-shifted because of the 18p
diatropic ring current. The UV/Vis absorption spectrum of 3
meso-Aryl-substituted [32]heptaphyrins(1.1.1.1.1.1.1) are
interesting macrocycles[6] in terms of their flexible conforma-
tions,[7a] multiple N-fusion reactions,[7b] facile formation of
twisted Mꢀbius aromatic species upon protonation,[7c] forma-
tion of three-coordinated CuII complexes,[7d] and oxidative
ring opening to form conjugated helical molecules.[7e] We have
previously reported that a Mꢀbius aromatic complex, 2, was
formed in 88% yield from meso-heptakis(2,6-dichloro-
phenyl)-substituted [32]heptaphyrin 1 upon treatment with
Pd(OAc)2 in CH2Cl2.[7c] Careful examination of this reaction
led to an isolation of brown complex 3 as a side-product in 9%
yield. When the metalation reaction was carried out in
acetone, the yield of 3 was improved to 22% at the expense of
[*] T. Yoneda, Dr. S. Saito, Prof. Dr. H. Yorimitsu, Prof. Dr. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
Fax: (+81)75-753-3970
E-mail: osuka@kuchem.kyoto-u.ac.jp
[**] This work was supported by Grants-in-Aid (nos. 22245006 (A) and
20108006 “pi-Space”) from MEXT. S.S. acknowledges a JSPS
Fellowship for Young Scientists.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201100243.
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Scheme 2. Metalation of 5 with PdII ions. Ar=pentafluorophenyl.
istic properties of the complex 6 are analogous to those of 3,
thus suggesting an NCP-embedded framework for 6 that is
practically the same as that of 3. The structure of the complex
7 has been shown by single-crystal X-ray diffraction analysis
to contain two PdII ions at the NCP-type site and the
tripyrromethene site. The coordination geometry of the NCP
moiety is analogous to that of 3, in which the Pd(1)···N(1),
Pd(1)···N(2), Pd(1)···N(3), and Pd(1)···C(17) distances are
1.98, 2.00, 2.00, and 2.05 ꢁ, respectively, and the inverted
pyrrole is tilted from the rest of the planar tripyrromethene
part with an angle of 36.698. The other PdII ion is bound with
Figure 1. X-ray crystal structure of 3: a) top view and b) side view.
meso-2,6-Dichlorophenyl substituents and solvent molecules are omit-
ted for clarity. Thermal ellipsoids are drawn at the 50% probability
level.
NNNC in
a square-planar manner with Pd(2)···N(4),
Pd(2)···N(5), Pd(2)···N(6), and Pd(2)···C(18) distances of
1.93, 1.93, 1.92, and 2.10 ꢁ, respectively (Figure 3). The
shows Soret-like bands at 419 and 449 nm, which are
considerably attenuated and blue-shifted from that of hepta-
phyrin 1, but are rather similar to that of the reference
compound PdII NCP 4 (Figure 2).[10]
The same rearrangement reaction proceeded for meso-
heptakis(pentafluorophenyl)-substituted [32]heptaphyrin 5,
to provide either monopalladium(II) complex 6 or bispalla-
dium(II) complex 7, depending upon the amount of PdII salt
present (Scheme 2). According to spectroscopic data, includ-
1
ing H NMR and UV/Vis absorption spectra, the character-
Figure 3. X-ray crystal structure of 7. meso-Pentafluorophenyl substitu-
ents and solvent molecules are omitted for clarity. Thermal ellipsoids
are drawn at the 20% probability level.
latter coordination causes the disruption of NCP conjugated
network. Consistent with this structure, the 13C NMR spec-
trum of 7 shows signals at d = 76.09 and 81.16 ppm that arise
from the sp3-hybridized carbon atoms C(17) and C(18), and
the 1H NMR spectrum indicates only marginal high-field
shifts for Ha (d = 4.01 ppm) and Hb (d = 6.11 ppm) protons.
The absorption spectrum of 7 is clearly different from those of
3 and 6 (see the Supporting Information).[11]
Interestingly, a similar transformation from heptaphyrin
to NCP also occurred for monozinc(II) complex 8 that has an
enforced figure-eight conformation. Upon treatment with
Pd(OAc)2 in the presence of triethylamine in acetone, 8
underwent a rearrangement to afford the PdII–ZnII hybrid
complex 9 in 62% yield (Scheme 3). The structure of 9 has
been also shown by X-ray diffraction analysis to have the
Figure 2. UV/Vis absorption spectra of 1 (b), 3 (c), and 4 (a)
in CH2Cl2.
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[1] a) J. L. Sessler, A. Gebauer, S. J. Weghorn in The Porphyrin
Handbook, Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard),
Academic Press, San Diego, 1999, p. 55; b) A. Jasat, D. Dolphin,
Chem. Rev. 1997, 97, 2267; c) T. D. Lash, Angew. Chem. 2000,
112, 1833; Angew. Chem. Int. Ed. 2000, 39, 1763; d) H. Furuta, H.
Maeda, A. Osuka, Chem. Commun. 2002, 1795; e) J. L. Sessler,
D. Seidel, Angew. Chem. 2003, 115, 5292; Angew. Chem. Int. Ed.
2003, 42, 5134; f) T. K. Chandrashekar, S. Venkatraman, Acc.
Chem. Res. 2003, 36, 676.
Scheme 3. Metalation of 8 with PdII ions. Ar=pentafluorophenyl.
[2] E. Vogel, M. Michels, L. Zander, J. Lex, N. S. Tuzun, K. N. Houk,
Angew. Chem. 2003, 115, 2964; Angew. Chem. Int. Ed. 2003, 42,
2857.
same rearranged skeleton (Figure 4). The PdII NCP moiety is
similar to those of the complexes 6 and 7, in which the
Pd···N(1), Pd···N(2), Pd···N(3), and Pd···C(17) distances are
2.02, 2.05, 2.03, and 2.07 ꢁ, respectively. The distorted square-
planar N,N,N,N coordination of the ZnII ion in 8 was changed
[3] a) Y. Tanaka, W. Hoshino, S. Shimizu, K. Youfu, N. Aratani, N.
Maruyama, S. Fujita, A. Osuka, J. Am. Chem. Soc. 2004, 126,
3046; b) Y. Tanaka, H. Shinokubo, Y. Yoshimura, A. Osuka,
Chem. Eur. J. 2009, 15, 5674; c) S. Saito, K. S. Kim, Z. S. Yoon, D.
Kim, A. Osuka, Angew. Chem. 2007, 119, 5687; Angew. Chem.
Int. Ed. 2007, 46, 5591; d) R. Sakamoto, S. Saito, S. Shimizu, Y.
Inokuma, N. Aratani, A. Osuka, Chem. Lett. 2010, 39, 439; e) K.
Moriya, S. Saito, A. Osuka, Angew. Chem. 2010, 122, 4393;
Angew. Chem. Int. Ed. 2010, 49, 4297.
[4] H. Furuta, T. Asano, T. Ogawa, J. Am. Chem. Soc. 1994, 116, 767.
´
[5] P. J. Chmielewski, L. Latos-Graz˙ynski, K. Rachlewicz, T. Glow-
law, Angew. Chem. 1994, 106, 805; Angew. Chem. Int. Ed. Engl.
1994, 33, 779.
[6] P. J. Chmielewski, Angew. Chem. 2010, 122, 1399; Angew. Chem.
Int. Ed. 2010, 49, 1359.
[7] a) S. Saito, J.-Y. Shin, J. M. Lim, K. S. Kim, D. Kim, A. Osuka,
Angew. Chem. 2008, 120, 9803; Angew. Chem. Int. Ed. 2008, 47,
9657; b) S. Saito, A. Osuka, Chem. Eur. J. 2006, 12, 9095; c) 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; Angew. Chem. Int. Ed.
2008, 47, 681; d) S. Saito, K. Furukawa, A. Osuka, Angew. Chem.
2009, 121, 8230; Angew. Chem. Int. Ed. 2009, 48, 8086; e) S. Saito,
K. Furukawa, A. Osuka, J. Am. Chem. Soc. 2010, 132, 2128.
[8] Crystal data for 3: C82.13H41.63Cl17.38N7O2.38Pd1 (Mr = 1886.69),
monoclinic, space group C2/c (no. 15), a = 23.965(7), b =
28.506(10), c = 24.994(8) ꢁ, b = 107.418(6), V= 16291(9) ꢁ3,
Z = 8, 1calcd = 1.538 gcmÀ3, T= 90(2) K, R1 = 0.1117 (I > 2s(I)),
Figure 4. X-ray crystal structure of 9. meso-Pentafluorophenyl substitu-
ents and solvent molecules are omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level.
to a distorted tetrahedral coordination with the tripyrrome-
thene unit and a water molecule with distances of 1.96, 1.94,
1.97, and 2.06 ꢁ for Zn···N(5), Zn···N(6), Zn···N(7), and
Zn···O, respectively. The distances between the ZnII ion and
C(18) and C(19) are 2.940 and 2.916 ꢁ, which are too long for
a bonding interaction. The relatively high-yielding conversion
of 8 to 9 is important, as it shows the generality of the process
and the possible involvement of only two pyrrole units in the
rearrangement. The mechanism of this rearrangement, which
apparently consists of several steps, is unclear at present.
However, it is likely that coordination of PdII ions triggers the
rearrangement, in which the transannular interactions and
energetic stabilization associated with creation of an aromatic
NCP network play important roles (see the Supporting
Information for a possible mechanism).
In summary, we have reported the rearrangement of free-
base [32]heptaphyrins(1.1.1.1.1.1.1) to PdII NCP complexes
bridged by a tripyrromethene unit. This rearrangement has
been demonstrated even for a monozinc(II) heptaphyrin
complex with a figure-eight conformation. The occurrence of
these transformations has shown that NCPs can now be
considered as a member of the expanded porphyrin family.
RW = 0.3230 (all data), GOF = 0.988. Crystal data for 7:
ꢀ
C
81.5H22F35N7Pd2 (Mr = 1977), triclinic, space group P1 (no. 2),
a = 15.0620(6), b = 15.7271(5), c = 17.6854(6) ꢁ, a = 111.681(2),
b = 94.995(3), g = 111.708(3), V= 3493.3(2) ꢁ3, Z = 2, 1calcd
=
1.879 gcmÀ3, T= 93(2) K, R1 = 0.1113 (I > 2s(I)), RW = 0.3630
(all data), GOF = 0.920. Crystal data for 9: C85H32F35N7Pd1Zn1
ꢀ
(Mr = 2004), triclinic, space group P1 (no. 2), a = 14.4760(5), b =
15.0800(5),
c = 20.3770(8) ꢁ,
a = 100.1770(10),
b =
100.1180(10), g = 115.1180(10) V= 3804.2(2) ꢁ3, Z = 2, 1calcd
=
1.749 gcmÀ3, T= 90(2) K, R1 = 0.0566 (I > 2s(I)), RW = 0.1387
(all data), GOF = 0.939. CCDC 807128 (3), CCDC 807129 (7),
and CCDC 807130 (9) 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.
[9] For examples of this type of complex with other metals, see
´
Ni(II) and Pt(II):a) P. J. Chmielewski, L. Latos-Graz˙ynski, T.
Glowlaw, J. Am. Chem. Soc. 1996, 118, 5690; b) I. Schmidt, P. J.
Chmielewski, Chem. Commun. 2002, 92; c) I. Schmidt, P. J.
Chmielewski, Z. Ciunik, J. Org. Chem. 2002, 67, 8917; d) I.
Schmidt, P. J. Chmielewski, Inorg. Chem. 2003, 42, 5579; e) P. J.
Chmielewski, I. Schmidt, Inorg. Chem. 2004, 43, 1885; f) P. J.
Chmielewski, Inorg. Chem. 2007, 46, 1617; g) P. J. Chmielewski,
Inorg. Chem. 2009, 48, 432; h) H.-W. Jiang, Q.-Y. Chen, J.-C.
Xiao, Y.-C. Gu, Chem. Commun. 2009, 3732; i) P. J. Chmielew-
ski, L. Szterenberg, M. Siczek, Chem. Eur. J. 2011, 17, 1009; Pt
Received: January 12, 2011
Published online: March 10, 2011
Keywords: heptaphyrins · metalation · palladium ·
.
porphyrinoids · rearrangement
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Communications
complex: j) D.-H. Won, M. Toganoh, H. Uno, H. Furuta, Dalton
Trans. 2009, 6151.
PdII ion is coordinated to the double bond of NCP macrocycle in
a h2 fashion.
[10] A planar N-confused Pd porphyrin complex has been reported
to have a relatively strong absorption coefficient: H. Furuta, N.
Kubo, H. Maeda, T. Ishizuka, A. Osuka, H. Nanami, T. Ogawa,
Inorg. Chem. 2000, 39, 5424.
[11] Concerning the structure of 7, one of the reviewers commented
that the chemical shifts of Ha and Hb as well as C(17) and C(18)
cannot be explained by solely considering the structure that
contains two sp3-hybridized carbon atoms. We suggest some
contribution of the structure shown below, in which the second
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