Stable meso-Aryl β-Alkyl Hybrid Sapphyrin with a Warped π-Conjugation Circuit and Neo-Confused Sapphyrin–Silver(I) Complex

Article abstract of DOI:10.1002/asia.201800286

A meso-aryl and β-alkyl substituted sapphyrin and its rhodium(I) and silver complexes were synthesized. This sapphyrin was so stable that the non-inverted and warped structure could be analyzed by X-ray crystallography even in its neutral state. Its bis-r

Full text of DOI:10.1002/asia.201800286

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Accepted Article
Title: Stable meso-Aryl β-Alkyl Hybrid Sapphyrin with a Warped π-
Conjugation Circuit and Neo-Confused Sapphyrin-AgI Complex
Authors: Tomoki Yoneda, Daiki Mori, Tyuji Hoshino, and Saburo Neya
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To be cited as: Chem. Asian J. 10.1002/asia.201800286
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Stable meso-Aryl β-Alkyl Hybrid Sapphyrin with a Warped π-
Conjugation Circuit and Neo-Confused Sapphyrin–AgI Complex
Daiki Mori, Tomoki Yoneda*, Tyuji Hoshino and Saburo Neya*
Abstract: A meso-aryl and β-alkyl substituted new sapphyrin 1 and
its rhodium(I) and silver complexes were synthesized. Sapphyrin 1
was so stable that the non-inverted and warped structure could be
analyzed by X-ray crystallography even in its neutral state. The bis-
rhodium(I) complex 1Rh2 has a more planar structure than 1 with
enhanced aromaticity over the conjugation circuit. On the other hand,
silver metalation into 1 caused a marked core rearrangement into neo-
confused sapphyrin 1Ag with a C(α)-N bond and a twisted
macrocycle.
the center. The structures of sapphyrins with an all inward-
pointing neutral pyrrole rings stabilized only by internal hydrogen
bonding remain to be elucidated.
Over the long history of sapphyrins, their coordination
chemistry has not been studied in sufficient detail. Zn(II) and
Co(II) complexes of sapphyrin have been reported, but their
crystal structures have not been unveiled yet.[2a,b] Some Rh(I) or
Ir(I) metallo-dicarbonyl complexes have been reported,[2b,6] where
one or two rhodium or iridium ions protrude from their sapphyrin
planes in an η2-type ordinal coordination. The sole example of η5-
type coordination system is the U(Vl) complex of sapphyrin with
five nitrogen atoms ligating to the central UO2 moiety.[7] The poor
metalation property of sapphyrins might arise from the low stability
of the sapphyrins themselves.
Sapphyrin (pentaphyrin(1.1.1.1.0)) is the first expanded
porphyrin to have been discovered,[1] and bears five pyrroles
connected through four meso-carbons and one α,α-bond. The
initial β-substituted sapphyrin was synthesized by a [2+3]
methodology. Later, meso-substituted sapphyrins were reported.
However, a meso-pentafluorophenyl-substituted sapphyrin is
insufficiently stable.[2] Sapphyrins include some structural
frustration caused by the insertion of a pyrrole unit to the planar
porphyrin. To resolve this, sapphyrins sometimes take up an
inverted form; inversion of the pyrrole unit C (Chart 1) induces a
larger internal angle consisting of two C(meso)-C(α) bonds than
that of the non-inverted one, stabilizing the planar 22π conjugation
circuit of sapphyrin. Indeed, the sole X-ray crystal structure of
sapphyrin in the neutral state[3] shows high planarity.
In contrast, we already have reported stable aromatic meso-
free
[22]pentaphyrin(1.1.1.1.1)
and
antiaromatic
[24]pentaphyrin(2.1.1.1.1) with β-substituted pyrrole units.[8]
Therefore, we expected that blocking of reactive β-positions by
alkyl groups would prevent their decomposition. β-Alkyl
substituents tend to be on the outer periphery of sapphyrins. We
planned to synthesize sapphyrin 1 with meso-aryl and β-alkyl
substituents with cross-condensation of meso-pentafluorophenyl
substituted tripyrrane dicarbinol A and β-substituted bipyrrole B
(Scheme 1). The meso- and β-substituted sapphyrin 1 was so
stable that its warped X-ray crystal structure could be analyzed.
In addition, the silver complex of sapphyrin with a rearranged neo-
confused π-conjugation circuit was synthesized.
Chart 1. Conformers of sapphyrins obtained by X-ray crystal structural analysis.
However, the crystal structure of non-inverted neutral
sapphyrin has not been obtained yet. Since sapphyrins are also
versatile anion-binding agents, some crystal structures of β-
substituted sapphyrins have been obtained only in their
protonated form in their non-inverted forms with counteranions at
[a]
D. Mori, Dr. Tomoki Yoneda, Dr. Tyuji Hoshino, Prof. Dr. Saburo
Neya
Department of Pharmaceutical Sciences, Chiba University
1-8-1, Inohana, Chuo-ku, Chiba, 260-8675, Japan
E-mail: yoneda@chiba-u.jp
Scheme 1. Synthesis of sapphyrin 1.
Supporting information for this article is given via a link at the end of
the document.
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UV/vis absorption spectrum of 1 exhibited a sharp Soret band at
484 nm and a Q band at 702 nm—a typical feature of aromatic
expanded porphyrins (Figure 2).
20
15
10
5
0
300
400
500
600
700
800
900
1000
Figure 2. UV/Vis absorption spectra of 1(black), 1-Rh2(red), and 1-Ag(blue) in
CH2Cl2.
Figure 1. X-ray crystal structure of sapphyrin 1. a) Top view and b) side view.
Solvent molecules and meso-pentafluorophenyl groups in side view are omitted.
Thermal ellipsoids are shown in 50% probability.
Following our previous works to synthesize hybrid expanded
porphyrins,[8] we treated a solution of tripyrrane dicarbinol A[9] and
4,4’-diethyl-3,3-dimethyl-2,2-bipyrrole B[10] in CH2Cl2 with 0.3
equivalent of p-toluenesulfonic acid under nitrogen atmosphere.
The resulting mixture was oxidized with 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ) to give green sapphyrin 1 in 10% yield
(Scheme 1). Compound 1 was so stable under ambient conditions
Scheme 2. Synthesis of 1Rh2.
that
1 was isolated in its pure form by florisil column
chromatography and recrystallization with hexane. High-
resolution electrospray ionization time of flight mass spectroscopy
(HR-ESI-TOF MS) indicated the parent ion peak of 1 at m/z =
1124.1923 (calcd for C54H26N5F20 [M+H]+: 1124.1869). The 1H
NMR spectrum of 1 showed one singlet and two doublets due to
the outer β protons at 8.54 and 8.40 and 8.29 ppm, indicating a
strong diatropic ring current. The singlet due to methyl groups at
3- and 22-positions was observed at 2.47 ppm and the quartet
and triplet derived from ethoxycarbonyl groups at 2- and 23-
positions were observed at 3.78 ppm and 1.25 ppm, respectively.
A peak from three NH protons was at –0.88 ppm, suggesting their
fast exchange in the strong intermolecular hydrogen-bonding
network. The structure of 1 was unambiguously determined by X-
ray analysis[11] of the crystal, obtained by slow diffusion of octane
into its toluene solution (Figure 1). No counteranion or -cation was
observed in the crystal, indicating that 1 is a neutral molecule. The
solid-state structure of 1 was a highly warped with all inward-
pointing pyrrole units. Since the reported structures of protonated
sapphyrins involve central counteranions and the neutral
sapphyrin contains an inverted pyrrole ring, our data indicates a
new conformer of sapphyrin. The mean plane deviations (MPD)
of the main pentaphyrin skeleton of 1 were calculated to be 0.585
and 0.582 Å, which are much larger than 0.259 Å of inverted
neutral sapphyrin,[5] suggesting a warped structure for 1. The
Figure 3. X-ray crystal structure of 1Rh2. a) Top view and b) side view. Solvent
molecules and meso-pentafluorophenyl groups in side view are omitted.
Thermal ellipsoids are shown in 50% probability.
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Figure 4. Mean-plane deviation diagram calculated from the 24 core atoms for
1 (black and gray) and 1Rh2 (red).
Next, we synthesized the rhodium(I) complex of 1 by treating
it with [RhCl(CO)2]2 in dichloromethane in the presence of sodium
acetate to produce the bis-rhodium(I) complex 1Rh2 as a pink
solid in 83% yield. HR-ESI-TOF MS indicated the parent ion peak
–
of 1Rh2 at m/z = 1409.9513 (calcd for C57H22N5F20Rh2O3 [M–
CO–H]–: 1409.9498), which suggests the insertion of double
RhI(CO)2 groups. The 1H NMR spectrum of 1Rh2 showed peaks
derived from outward-pointing β-protons at 8.94, 9.08, and 9.19
ppm and alkyl groups, indicating the strong aromatic character of
1Rh2. The structure of 1Rh2 was also determined by X-ray crystal
analysis to comprise a planar sapphyrin moiety with two Rh(CO)2
groups in a trans arrangement (Figure 3).[12] The mean plane
deviation (MPD) of the main pentaphyrin skeleton of 1Rh2 was
calculated to be 0.294 Å, which revealed that the π-conjugation
circuit of 1Rh2 was more planar than that of 1 (Figure 4). The
UV/vis absorption spectrum of 1Rh2 showed a sharp Soret band
at 512 nm and Q-bands at 666 and 754 nm (Figure 2), suggesting
that the aromatic character of 1 has also been preserved.
Figure 5. X-ray crystal structure of 1Ag obtained from an acetonitrile/water
solution. a) Top view and b) side view. Solvent molecules,
a meso-
pentafluorophenyl group on C20 in top view, and meso-pentafluorophenyl
groups and -alkyl substituents in side view are omitted. Thermal ellipsoids are
shown in 50% probability.
In the chemistry of expanded porphyrins, unique
rearrangements[13] or ring contractions[14] triggered by metalation
have sometimes been observed. However, in the case of
sapphyrins, despite many synthetic reports, specific
rearrangements or ring contractions have not been observed. We
tested the metalation of 1 with silver acetate in a CH2Cl2/methanol
solution. After stirring for 12 h, chromatographic separation gave
a brown band for 1Ag in 23% yield (Scheme 3). X-ray diffraction
analysis identified this product to be the rearranged sapphyrin
(Figure 5).[15] In the structure, accompanying silver metalation, a
C24 atom was substituted by two methoxy groups, the C1-C24
bond was cleaved, and a new C1-N5 bond was formed. This form
of expanded porphyrins with C-N bond is said to be “Neo-
confused”,[16] and 1Ag was considered to be the neo-confused
sapphyrin(1.1.1.1.0). The “neo-confused” conjugated macrocycle
of 1Ag with a C(α)-N pyrrole linkage is also interpreted as an aza-
Chart 2. Neo-confused porphyrinoids. The “neo-confused” pyrroles whose
nitrogens are connected to carbons are shown in red.
derivative of hypothetical [20]porphyrin(3.1.1.1)[17]
.
The
mechanism of this rearrangement is unclear, but is thought to
have been triggered by the nucleophilic attack of two methoxy
groups of methanol at the C24 position. The lengths of Ag-N
bonds are in the range of 2.284-2.436 Å, thus we assigned 1Ag
as a Ag(I) complex. In addition, the overall topology of the π-
Scheme 3. Synthesis of 1Ag.
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conjugation circuit showed a Möbius-type twist. The 1H NMR
spectrum of 1Ag indicates its asymmetric structure with six
doublets at 7.00–7.37 ppm derived from β-protons, suggesting its
nonaromatic or weakly aromatic character. The UV/vis absorption
spectrum of 1Ag drastically attenuated from that of 1, exhibiting a
weak absorption band at 468 nm and a Q-like broad band at 780
nm. (Figure 2).
[8]
[9]
a) T. Yoneda, T. Hoshino, S. Neya, Chem. Asian J. 2016, 22, 4413; b) T.
Yoneda, T. Hoshino, S. Neya, J. Org. Chem. 2017, 82, 10737
V. G. Anand, S. Saito, S. Shimizu, A. Osuka, Angew. Chem. Int. Ed. 2005,
44, 7244.
[10] R. Grigg, A. W. Johnson, J. W. F. Wasley, J. Chem. Soc. 1963, 359.
[11] X-ray data of 1, 2(C54H25F20N5)･1.5(octane)･4(toluene) (Mr = 2745.11),
Triclinic, space group P-1 (No. 2), a = 12.2322(2), b = 12.8560(3), c =
32.0662(6) Å, α = 87.9129(7)°, β = 81.6249(7)°, γ = 77.6816(7)°, V =
6390.4(2) Å3, Z = 2, ρcalcd = 1.427 gcm-3, T = 93(2) K, R1 = 0.1041 ( I >
2σ(I)), wR2 = 0.3595 (all data), GOF = 0.997. CCDC 1816959 contains
the supplementary crystallographic data for this paper. These data are
provided free of charge by the Cambridge Crystallographic Data Centre.
[12] X-ray data of 1Rh2, C58H23F20N5O2Rh2･3(acetonitrile) (Mr = 1562.79),
To obtain further insight into the reactivity and the aromatic
properties of 1, 1Rh2, and 1Ag, we performed DFT calculations
(B3LYP/6-31G(d)/LANL2DZ level).[18] (see SI). The HOMO–
LUMO gaps for 1 and 1Rh2 were calculated to be 2.03 eV and
2.16 eV, respectively, and highly degenerated HOMO/HOMO–1
and LUMO/LUMO+1 were observed, consistent with their
aromatic character. The nucleus-independent chemical shift
(NICS) values[19] at the center of the macrocycles were calculated
to be –10.80 and –13.80 ppm for 1 and 1Rh2, respectively. These
results are in line with the aromaticity of 1 and the stronger
aromaticity of 1Rh2 than that of 1.
Orthorhombic, space group Pbcn (No. 60),
a = 35.3723(6), b =
13.0209(2), c = 26.4217(5) Å, V = 12169.3(4) Å3, Z = 8, ρcalcd = 1.706
gcm-3, T = 93(2) K, R1 = 0.0575 ( I > 2σ(I)), wR2 = 0.1233 (all data), GOF
= 0.990. CCDC 1816960 contains the supplementary crystallographic
data for this paper. These data are provided free of charge by the
Cambridge Crystallographic Data Centre.
[13] a) E. Vogel, M. Michels, L. Zander, J. Lex, N. S. Tuzun, K. N. Houk,
Angew. Chem. Int. Ed. 2003, 42, 2857; b) G. Hohlneicher, D. Bremm, J.
Wytko, J. Bley-Escrich, J.-P. Gisselbrecht, M. Gross, M. Michels. K. Lex,
E. Vogel, Chem. Eur. J. 2003, 9, 5636. c) M. Suzuki, M.-C. Yoon, D. Y.
Kim, J. H. Kwon, H. Furuta, D. Kim, A. Osuka, Chem. Eur. J. 2006, 12,
1754; d) S. Saito, K. Furukawa, A. Osuka, J. Am. Chem. Soc. 2010, 132,
2128; e) T. Yoneda, S. Saito, H. Yorimitsu, A.Osuka, Angew. Chem. Int.
Ed. 2011, 50, 11460; f) Y. Tanaka, H. Mori, T. Koide, H. Yorimitsu, N.
Aratani, A. Osuka, Angew. Chem. Int. Ed. 2011, 50, 11460.
In summary, we synthesized a new sapphyrin moiety 1 that
shows a highly warped but aromatic conjugation circuit in its X-
ray crystal structure. In addition, its Rh(I) complex 1Rh2, with
stronger aromaticity, and a rearranged neo-confused sapphyrin-
Ag(I) complex 1Ag, with a twisted topology, were obtained. The
characteristic property and reactivity of these complexes may
arise from strain release from 1. The possible applications of
strained but highly stable hybrid sapphyrin and its complexes are
now under investigation in our laboratory.
[14] a) C. Brückner, J. Akhigbe, L. P. Samankumara, in Handbook of
Porphyrin Science: with Applications to Chemistry, Physics, Material
Science, Engineering, Biologh and Medicine, ed. K. M. Kadish, M. Smith,
R. Guilard, World Scientific Publishing, Sinfapore, 2010; b) H. J. Callot,
Dalton Trans, 2008, 6346; c) B. Szyszko, L. Latos-Grażyński, Chem. Soc.
Rev. 2015, 44, 3588.
[15] X-ray data of 1Ag, C56H28F20N5O2Ag (Mr = 1290.71), Monoclinic, space
group P21/a (No. 14), a = 15.1003(4), b = 12.0691(3), c = 27.1125(7) Å,
β = 91.4584(14)°, V = 4936.6(2) Å3, Z = 4, ρcalcd = 1.737 gcm-3, T = 93(2)
K, R1 = 0.0855 ( I > 2σ(I)), wR2 = 0.2250 (all data), GOF = 1.030. CCDC
1816958 contains the supplementary crystallographic data for this paper.
These data are provided free of charge by the Cambridge
Crystallographic Data Centre.
Acknowledgements
This work was supported by JSPS KAKENHI for young scientist
No.17K14445(B) and the Program to Disseminate Tenure
Tracking System from MEXT of Japan.
[16] a) K. Fujino, Y. Hirota, Y. Kawabe, T. Orimoto, A. Srinivasan, M. Toganoh,
Y. Miseki, A. Kudo, H. Furuta, Angew. Chem. Int. Ed. 2011, 50, 6855; b)
T. D. Lash, A. D. Lammer, G. M. Ferrence, Angew. Chem. Int. Ed. 2011,
50, 9718, c) Y. Xie, P. Wei, X. Li, T. Hong, K. Zhang, H. Furuta, J. Am.
Chem. Soc. 2013, 135, 19119; d) P. Wei, K. Zhang, X. Li, D. Meng, H.
Ågren, Z. Ou, S. Ng, H. Furuta, Y. Xie, Angew. Chem. Int. Ed. 2014, 53,
14069; e) K. Zhang, J. Zhang, X. Li, R. Guo, H. Ågren, Z. Ou, M. Ishida,
H. Furuta, Y. Xie, Org. Lett. 2015, 17, 4806.
Keywords: Sapphyrin • Aromaticity • Warped π-conjugation
circuit •Rearrangement• Neo-confused porphyrinoid
[1]
a) A. Jasat, D. Dolphin, Chem. Rev. 1997, 97, 2267; b) J. L. Sessler, J.
M. Davis, Acc. Chem. Res. 2001, 34, 989; c) J. L. Sessler, D. Seidel,
Angew, Chem. Int. Ed. 2003, 42, 5134. d) J. L. Sessler, E. Tomat, Acc.
Chem.Soc. 2007, 40, 371; e) T. Chatterjee, A. Srinivasan, M. Ravikanth,
T. K. Chandrashekar, Chem. Rev. 2017, 117, 3329.
[17] J. L. Sessler, D. Seidel, Angew. Chem. Int. Ed. 2003, 42, 5134.
[18] Gaussian 09, Revision A.02, M. J. Frisch. et al., Gaussian, Inc.,
Wallingford, CT, 2009 (Full citation in SI).
[2]
a) V. J. Bauer, D. L. J. Clive, D. Dolphin, J. B. Paine III, F. L. Harris, M.
M. King, J. Loder, S.-W. C. Wang. R. B. Woodward, J. Am. Chem. Soc.
1983, 105, 6429; b) J. L. Sessler, M. J. Cyr, V. Lynch, E. McGhee, J. A.
Ibers, J. Am. Chem. Soc. 1990, 112, 2810. c) J. L. Sessler, M. Cyr, A. K.
Burrell, Tetrahedron 1992, 48, 9661.
[19] a) P. v. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R. v. E.
Hommes, J. Am. Chem. Soc. 1996, 118, 6317; b) Z. Chen, C. S.
Wannerere, C. Corminboeuf, R. T. Puchta, P. v. R. Schleyer, Chem. Rev.
2005, 105, 3842.
[3]
[4]
a) P. J. Chemielewski, L. Latos-Grażyński, K. Rachlewicz, Chem. Eur. J.
1995, 1, 68. b) L. Simkhovich, S. Rosenberg, Z. Gross, Tetrahedron Lett.
2001, 42, 4929; c) S. Kang, H. Hayashi, T. Umeyama, Y. Matano, N. V.
Tkachenko, H. Lemmetyinen, H. Imahori, Chem. Asian J. 2008, 3, 2065.
a) J. L. Sessler, J. Lisowski, K. A. Boudreaux, V. Lynchm J. Barry, T. J.
Kodadek, J. Org. Chem. 1995, 60, 5975; b) C. Bruckner, E. D. Sternberg,
R. W. Boyle, D. Dolphin, Chem. Commun. 1997, 1689.
[5]
[6]
[7]
W. Huang, Z. Ou, X. Chen, Z. Xue, G. Lu, H. Wang, J. Xiao, Y. Fang, K.
M. Kadish, J. Porphyrins Phthalocyanines 2015, 19, 794.
A. K. Burrel, J. L. Sessler, M. J. Cyr, E. McGhee, J. A. Ibers, Angew.
Chem. Int. Ed. 1991, 30, 91.
A. K. Burrell, M. J. Cyr, V. Lynch, J. L. Sessler, J. Chem. Soc., Chem.
Commun. 1991, 1710.
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COMMUNICATION
A novel meso- and β-substituted
sapphyrin and its rhodium(I) and
silver(I) complexes were synthesized.
The non-inverted and warped
Daiki Mori, Tomoki Yoneda*, Tyuji
Hoshino, Saburo Neya*.
Page No. – Page No.
structure for the neutral state of
sapphyrin was analyzed by X-ray
crystallography. Rhodium(I)
metalation enhanced the aromaticity
of the warped structure. Silver
Stable meso-Aryl β-Alkyl Hybrid
Sapphyrin with a Warped π-
Conjugation Circuit and Neo-
Confused Sapphyrin-AgI Complex.
metalation caused a rearrangement
giving neo-confused (C(α)-N bonded)
sapphyrin with a twisted structure.
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