Biscopper complexes of meso-aryl-substituted hexaphyrin: Gable structures and varying antiferromagnetic coupling

Article abstract of DOI:10.1021/ja046102x

The copper metalation into the hexaphyrins is accompanied by large structural changes to give four complexes exhibiting gable structures and varying antiferromagnetic couplings. Copyright

Full text of DOI:10.1021/ja046102x

Published on Web 09/08/2004
Biscopper Complexes of meso-Aryl-Substituted Hexaphyrin: Gable
Structures and Varying Antiferromagnetic Coupling
Soji Shimizu,† Venkataramanarao G. Anand,† Ryuichiro Taniguchi,† Ko Furukawa,‡ Tatsuhisa Kato,*,§
Toshihiko Yokoyama,‡ and Atsuhiro Osuka*,†
Department of Chemistry, Graduate School of Science, Kyoto UniVersity, and
Core Research for EVolutional Science and Technology (CREST), Japan Science and Technology Agency,
Sakyo-ku, Kyoto 606-8502, Japan, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan, and
Department of Chemistry, Josai UniVersity, Keyakidai, Sakado 350-0295, Japan
Received July 1, 2004; E-mail: osuka@kuchem.kyoto-u.ac.jp; rik@josai.ac.jp
Recently, increasing attention has been focused on expanded
porphyrins that have a conjugated pyrrolic macrocycle larger than
porphyrins.1 One of the promising potentials of expanded porphyrins
relies on their rich metalation chemistry, which may allow formation
of discrete dinuclear metal complexes with notable metal-metal
interaction, as anticipated from their large cavities. This is in contrast
to the metalation of porphyrins, in which metal ions are usually
coordinated in a 1:1 fashion. Despite this promise, there are only
limited examples of such dinuclear metal complexes in the
literature.2-6 Gossauer et al. were the first to prepare â-dodecaalkyl-
substituted [26]hexaphyrins and their dinuclear zinc(II) and palla-
Figure 1. X-ray crystal structures of 3 (left), 4 (middle), and 6 (right).
dium(II) complexes, though they never characterized them struc-
The thermal ellipsoids were scaled to the 50% probability level. meso-
Pentafluorophenyl substituents, â-hydrogen atoms, and solvent molecules
were omitted for clarity.
turally.4 Recent structurally characterized examples include dinuclear
metal complexes of amethyrin5 and doubly N-confused hexaphyrin.6
Here we report copper(II) metalation of meso-aryl-substituted
hexaphyrins 1 and 2 (chart 1). Hexaphyrin 1 displays pronounced
intense absorption spectrum (Supporting Information, SI). Complex
4 exhibits a similar gable structure (Figure 1, middle), in which
the two copper ions are bound to the meso-attached bridging oxygen
aromaticity along rectangular conjugated 26π-network,7a while a
thermally stable form of perfluorinated analogue 2 is nonaromatic
[28]hexaphyrin with a figure eight conformation.7c As such, these
atom and three pyrrolic nitrogen atoms in a square-planar fashion
molecules occupy a central position of meso-aryl-expanded por-
with smaller displacements of the copper ions (0.08 and 0.05 Å).10
The perfluorinated hexaphyrin 2 gave complex 5 as a sole product
phyrins that are real homologues of meso-tetraaryl porphyrins,7 but
their metalation has not been reported yet.8
(96%) upon treatment with CuCl2, while 5 and 6 were obtained in
A solution of 1 in CH2Cl2 was stirred at room temperature in
26 and 56% from the reaction with Cu(OAc)2. The HR FAB-MS
the presence of anhydrous CuCl2 and NaOAc for 4 h. After usual
spectra displayed a molecular ion peak at m/z ) 1815.8092 for 5
workup, dinuclear copper complex 3 was isolated in 84% yield.
(calcd for C66F42N6OCu2: 1815.8055) and at m/z ) 1832.8089 for
6 (calcd for C66HF42N6O2Cu2: 1832.8082). The structures of 5 and
Interestingly, the metalation with anhydrous Cu(OAc)2 led to
isolation of a different dinuclear copper complex 4 in 90% yield.
6 were also determined by X-ray crystallographic analysis. The
The high-resolution (HR) FAB-MS spectra of 3 and 4 indicated
structure of 5 is quite similar to that of 4 in respect of the square-
planar coordination with the meso-attached bridging oxygen atom
and three pyrrolic nitrogen atoms (SI).11 Complex 6 takes a different
the presence of two copper ions and one oxygen atom; 3: m/z:
1600.9256, calcd for C66H13F30N6OCu2: 1600.9264 and 4: m/z:
1599.9168, calcd for C66H12F30N6OCu2: 1599.9186. The structures
structure (Figure 1, right), in which the two copper ions are not
directly bridged by oxygen atom but rather separately bound to
the different tripyrrolic ligand and meso-attached oxygen atom.12
The oxygen ligands have been revealed to be tertiary alcohol and
alkoxide, which are hydrogen-bonded with an O-O distance of
2.366(4) Å. The presence of a hydroxy group was shown by H-D
exchange upon treatment with D2O, which has been probed by the
FAB-MS spectroscopy (SI). Importantly, this structure leads to the
assignment of 6 as Cu(I)-Cu(II) mixed valence. Collectively, the
biscopper complexes 3-6 take the similar gable structures, in which
the symmetric two tripyrrolic semimacrocycles are obliquely
arranged with varying dihedral angles (3, 118°; 4, 108°; 5, 109°;
6, 79°) and Cu-Cu distances (3, 3.469(2) Å; 4, 3.708(2) Å; 5,
3.603(1) Å; 6, 3.906(1) Å). The source of the meso-attached oxygen
atoms has been assigned to adventitious water in the reaction
mixture on the basis of the metalation experiments carried out in
of 3 and 4 have been confirmed by X-ray crystallographic analysis.
In 3 (Figure 1, left), the two copper ions are each bound to the
bridging chloride atom, the oxygen atom attached at the meso-
position, and three pyrrolic nitrogen atoms of the semi-planar
tripyrrolic ligand attached in a square pyramidal fashion with the
chloride atom as an apical ligand.9 Displacements of the copper
ions from the mean plane defined by the three nitrogen atoms and
oxygen atom are 0.23 and 0.24 Å. The gable structure of 3 is caused
by addition of oxygen and hydrogen atoms at the opposite meso-
positions and flipping of the two inverted pyrroles in 1 to constitute
two semi-planar tripyrrolic units. The resulting rehybridization of
the methene bridges, from sp2 to sp3, serves to interrupt the
conjugation of the ligand, which was also confirmed by its less
† Kyoto University and Japan Science and Technology Agency.
‡ Institute for Molecular Science.
§ Josai University.
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J. AM. CHEM. SOC. 2004, 126, 12280-12281
10.1021/ja046102x CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
Chart 1. Structures of meso-Aryl Hexaphyrins 1 and 2 and Their
Biscopper Complexes 3, 4, 5, and 6
conformation, electronic demands, and the number of NH available
for the metalation. Metalation of meso-aryl-substituted hexaphyrins
and other expanded porphyrins is an attractive subject and worthy
of further investigation.
Acknowledgment. This work was supported by Grant-in-Aids
for Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology of Japan. S.S. thanks the JSPS for
the Research Fellowship for Young Scientists. V.G.A. thanks the
JSPS for the postdoctoral fellowship.
Supporting Information Available: Synthetic procedures and
spectral data of complexes 3, 4, 5, and 6, including magnetic
susceptibility and ESR spectra (PDF). CIF files for the X-ray structural
analysis. This material is available free of charge via the Internet at
http://pubs.acs.org.
References
(1) (a) Jasat, A.; Dolphin, D. Chem. ReV. 1997, 97, 2267. (b) Lash, T. D.
Angew. Chem., Int. Ed. 2000, 39, 1763. (c) Furuta, H.; Maeda, H.; Osuka,
A. Chem. Commum. 2002, 1795. (d) Sessler, J. L.; Seidel, D. Angew.
Chem., Int. Ed. 2003, 42, 5134.
(2) Dolphin, D.; Rettig, S. J.; Tang, H.; Wijesekera, T.; Xie, L. Y. J. Am.
Chem. Soc. 1993, 115, 9301.
(3) (a) Werner, A.; Michels, M.; Zander, L.; Lex, J.; Vogel, E. Angew. Chem.,
Int. Ed. 1999, 38, 3650. (b) Vogel, E.; Michels, M.; Zander, L.; Lex, J.;
Tuzun, N. S.; Houk, K. N. Angew. Chem., Int. Ed. 2003, 42, 2857. (c)
Tanaka, Y.; Hoshino, W.; Shimizu, S.; Youfu, K.; Aratani, N.; Maruyama,
N.; Fujita, S.; Osuka, A. J. Am. Chem. Soc. 2004, 126, 3046. (d) Veauthier,
J. M.; Cho, W.-S.; Lynch, V. M.; Sessler, J. L. Inorg. Chem. 2004, 43,
1220.
(4) (a) Gossauer, A. Bull. Soc. Chim. Belg. 1983, 92, 793. (b) Charrie`re, R.;
Jenny, T. A.; Rexhausen, H.; Gossauer, A. Heterocycles 1993, 36, 1561.
(5) (a) Sessler, J. L.; Weghorn, S. J.; Hisaeda, Y.; Lynch, V. Chem. Eur. J.
1995, 1, 56. (b) Weghorn, S. J.; Sessler, J. L.; Lynch, V.; Baumann, T.
F.; Sibert, J. W. Inorg. Chem. 1996, 35, 1089. (c) Hannah, S.; Seidel, D.;
Sessler, J. L.; Lynch, V. Inorg. Chim. Acta 2001, 317, 211.
(6) Srinivasan, A.; Ishizuka, T.; Osuka, A.; Furuta, H. J. Am. Chem. Soc.
2003, 125, 878.
the presence of a small amount of H218O, which afforded 18O-
incorporated products as determined by the FAB-MS spectros-
copy.13
Complexes 3, 4, and 5 exhibit magnetic behaviors typical of
antiferromagnetically coupled biscopper(II) pairs in the variable-
temperature magnetic susceptibility measurements (2-300 K), while
complex 6 exhibits temperature-independent susceptibility øpT value
(0.4229 emu K mol-1), which corresponds to S ) 1/2 state in
agreement with Cu(I)-Cu(II) mixed valence state (SI).14 The least-
squares fit of the experimental data through the Bleaney-Bowers
equation gave -J values of 8.27 cm-1 for 3, 87.6 cm-1 for 4, and
42.1 cm-1 for 5. Different -J values for 4 and 5 are interesting
despite the similar coordination environments and Cu-Cu distances.
Provided that magnetic interaction propagates predominantly
through the Cu-O-Cu bond for 4 and 5, the larger -J value in 4
compared with 5 may be explained in terms of more electron-
withdrawing ligand in 5. The small -J value in 3 may be ascribed
to the presence of the bridging chloride atom, which might act a
mediator of superexchange ferromagnetic interaction through
bridge.15,16 Alternatively, the square pyramidal coordination caused
by the chloride bridge may influence the magnetic interaction.
As noted above, the absorption spectra of 3-6 are less intense
compared with that of the aromatic hexaphyrin 1 (SI). Curiously,
very broad absorption bands around near-IR region are observed
in the spectra of 4 (λmax ) 1498 nm), 5 (λmax ) 1475 nm), and 6
(λmax ) 1842 nm) with molar absorption coefficients of ca. 104
cm-1 M-1. Though origins of these bands are not clear at this stage,
preliminary spectroelectrochemical studies suggest that they may
be ligand-derived absorptions.
(7) (a) Neves, M. G. P. M. S.; Martins, R. M.; Tome´, A. C.; Silvestre, A. J.
D.; Silva, A. M. S.; Fe´lix, V.; Drew, M. G. B.; Cavaleiro, J. A. S. Chem.
Commun. 1999, 385. (b) Shin, J.-Y.; Furuta, H.; Yoza, K.; Igarashi, S.;
Osuka, A. J. Am. Chem. Soc. 2001, 123, 7190. (c) Shimizu, S.; Shin,
J.-Y.; Furuta, H.; Ismael, R.; Osuka, A. Angew. Chem., Int. Ed. 2003, 42,
78.
(8) Reports (ref 3) on the metalation of octaphyrins encourage new potentials
of expanded porphyrins.
(9) Crystallographic data of 3:
C68H15N6F30Cu2O1.61Cl7, Mw ) 1886.88,
monoclinic, space group C2/c (No. 15), a ) 18.37(3), b ) 16.20(2), c )
25.17(4) Å, â ) 113.52(9)°, V ) 6866(16) Å3, Dc ) 1.825 g/cm3, Z ) 4,
R ) 0.095, Rw (I > 3.0σ(I)) ) 0.135, GOF ) 1.070 (I > 3.0σ(I)).
(10) Crystallographic data of 4: C67H12N6F30Cu2O4Cl2, Mw ) 1732.82, triclinic,
space group P1h (No. 2), a ) 13.979(3), b ) 15.646(3), c ) 15.932(4) Å,
R ) 78.753(4), â ) 73.062(4), γ ) 74.027(4)°, V ) 3179(1) Å3, Dc )
1.810 g/cm3, Z ) 2, R ) 0.104, Rw (all data) ) 0.265, GOF ) 1.097 (I
> 2.0σ(I)).
(11) Crystallographic data of 5: C69N6F42O1Cu2Cl6, Mw ) 2066.54, monoclinic,
space group P21/n (No.14), a ) 22.60(1), b ) 13.063(5), c ) 25.05(1)
Å, â ) 109.73(3)°, V ) 6960(5) Å3, Dc ) 1.972 g/cm3, Z ) 4, R )
0.092, Rw (all data) ) 0.310, GOF ) 1.269 (I > 2.0σ(I)).
(12) Crystallographic data of 6: C69H3N6F42Cu2O3Cl5, Mw ) 2066.11, triclinic,
space group P1h (No. 2), a ) 13.964(6), b ) 16.264(7), c ) 16.295(8) Å,
R ) 86.66(4), â ) 74.89(4), γ ) 84.63(4)°, V ) 3554(2) Å3, Dc ) 1.930
g/cm3, Z ) 2, R ) 0.065, Rw (I > 3.0σ(I)) ) 0.076, GOF ) 1.340 (I >
3.0σ(I)).
(13) The biscopper complexes 3, 4, and 5 formed in the presence of H218O
exhibit a cluster of peaks that fit well with the respective formula with
18O in the FAB-MS spectra. 3: 1603, calcd for C66H13F30N618OCu2:
1602.9307, 4: 1602, calcd for C66H12F30N618OCu2: 1601.9228, and 5:
1818, calcd for C66F42N618OCu2: 1817.8098 (SI).
(14) Consistent with this assignment, the ESR spectrum of 6 at 1.5 K can be
simulated as a single-spin system, and the XPS measurements revealed
that the satellite peak associated with Cu(II) ion in 6 was weaker in
comparison to 3 and 5 (SI).
(15) Geertsma, W.; Khomskii, D. Phys. ReV. B 1996, 54, 3011.
(16) Interestingly, a smaller antiferromagnetic interaction (-J ) 5 cm-1) was
reported for bis[(µ-chloro)copper(II)] amethyrin with a Cu-Cu distance
of 2.76 Å (ref 5b).
In summary, the hexaphyrins 1 and 2 can serve as an effective
ligand for two copper ions with unexpected but rather common
large structural changes to provide the gable biscopper complexes
3-6 that exhibit varying antiferromagnetic couplings. This is a new
mode of metalation of meso-aryl-expanded porphyrins. Relatively
similar structures of 3-6 are remarkable, considering a large
difference between 1 and 2 in respects of aromaticity, stable
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