N-confused porphyrin-bearing meso-perfluorophenyl groups: A potential agent that forms stable square-planar complexes with Cu(II) and Ag(III)

Article abstract of DOI:10.1021/ol034227l

(Matrix presented) N-Confused porphyrin (NCP) bearing pentafluorophenyl groups at meso-positions, which were obtained from N-confused dipyrromethane in ca. 20% yield, can form Cu(II) complex as well as Ag(III), Ni(II), and Pd(II) complexes. The square-pla

Full text of DOI:10.1021/ol034227l

ORGANIC
LETTERS
2003
Vol. 5, No. 8
1293-1296
N-Confused Porphyrin-Bearing
meso-Perfluorophenyl Groups: A
Potential Agent That Forms Stable
Square-Planar Complexes with Cu(II)
and Ag(III)
Hiromitsu Maeda,† Atsuhiro Osuka,† Yuichi Ishikawa,‡ Isao Aritome,§
Yoshio Hisaeda,§ and Hiroyuki Furuta*
,†,§
Department of Chemistry, Graduate School of Science, Kyoto UniVersity,
Kyoto 606-8502, Japan, Department of Applied Chemistry, Faculty of Engineering,
Oita UniVersity, Oita 870-1192, Japan, and Department of Chemistry and
Biochemistry, Graduate School of Engineering, Kyushu UniVersity,
Fukuoka 812-8581, Japan
hfuruta@cstf.kyushu-u.ac.jp
Received February 7, 2003
ABSTRACT
N-Confused porphyrin (NCP) bearing pentafluorophenyl groups at meso-positions, which were obtained from N-confused dipyrromethane in
ca. 20% yield, can form Cu(II) complex as well as Ag(III), Ni(II), and Pd(II) complexes. The square-planar structures of all these metal complexes
were elucidated by X-ray single-crystal analyses.
In recent years, there has been much attention on the
syntheses of porphyrinoids bearing electron-withdrawing
groups because of the catalytic reactivity of the metal
complexes. For example, pentafluorophenyl (C6F5)-substi-
tuted corrole was synthesized in good yield by solvent-free
acid-catalyzed pyrrole-aldehyde condensation, and the Fe(IV)
and Rh(III) complexes were shown to catalyze the cyclo-
propanation reaction effectively.1 Similarly, the Rh(II)
complex of perfluorinated meso-tetraarylporphyrin was used
for C-H activation of methane.2 Furthermore, the efficient
one-pot syntheses of a series of meso-C6F5 substituted
expanded porphyrins were recently reported.3 Such examples
prompted us to synthesize meso-C6F5-substituted N-confused
porphyrin (C6F5-NCP), because we hope that the C6F5
substituent may stabilize the metal complexes which are
(2) (a) Woller, E. K.; DiMagno, S. G. J. Org. Chem. 1997, 62, 1588.
(b) Leroy, J.; Bondon, A.; Toupet, L.; Rolando, C. Chem. Eur. J. 1997, 3,
1890. (c) Smirnov, V. V.; Woller, E. K.; DiMagno, S. G. Inorg. Chem.
1998, 37, 4971. (d) Nelson, A. P.; DiMagno, S. G. J. Am. Chem. Soc. 2000,
122, 8569.
(3) (a) Shin, J.-Y.; Furuta, H.; Osuka, A. Angew. Chem., Int. Ed. 2001,
40, 619. (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. (d) Neves, M.
G. P. M. S.; Martins, R. M. M.; Tome, A. C.; Silvestre, A. J. D.; Silva, A.
M. S.; Drew, M. G. B.; Cavaleiro, J. A. S. Chem. Commun. 1999, 385. (e)
Srinivasan, A.; Ishizuka, T.; Osuka, A.; Furuta, H. J. Am. Chem. Soc. 2003,
125, 878.
† Kyoto University.
‡ Oita University.
§ Kyushu University.
(1) (a) Gross, Z.; Galili, N.; Saltsman, I. Angew. Chem., Int. Ed. 1999,
38, 1427. (b) Gross, Z.; Galili, N.; Simkhovich, L.; Saltsman, I.; Boto-
shansky, M.; Bla¨ser, D.; Boese, R.; Goldberg, I. Org. Lett. 1999, 1, 599.
(c) Simkhovich, L.; Mahammed, A.; Goldberg, I.; Gross, Z. Chem. Eur. J.
2001, 7, 1041.
10.1021/ol034227l CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/18/2003

difficult to prepare from the standard meso-phenyl deriva-
tive.4-9 In addition, C6F5-NCP may serve as an appropriate
reference to the existing cis-doubly N-confused porphyrin
(cis-N2CP, Figure 1) that can stabilize the unusual higher
of 2, and the subsequent oxidation by 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) (Scheme 1b). The advan-
tage of using dibenzoyl-substituted dipyrromethane is well
documented in the syntheses of porphyrins bearing different
meso-substituents.13,14 This type of [2+2] condensation was
previously reported for the syntheses of â-alkyl-substituted
NCP,15 but not applied for meso-aryl-type NCP synthesis.
1
The H NMR spectrum of C6F5-NCP in CDCl3 showed
an aromatic feature, in which the signals of two inner NH
and CH are observed at -2.57 and -5.26 ppm, and those
of the peripheral CH appeared around 8.96-8.55 ppm,
respectively. Interestingly, the electron-deficient π-system
was reflected from the absorption spectrum of C6F5-NCP in
methanol, where the weak aromatic inner 2H-tautomer is
predominant. In the case of NCTPP, aromatic inner 3H-
tautomer was favored by using the same solvent.16
NCP is known to behave as either trianionic or dianionic
ligands according to the center metals (e.g. Ag(III),5 Ni(II),4b,6
and Pd(II)7) affording square-planar complexes. As expected,
C6F5-NCP complexed with Ag(III), Ni(II), Pd(II), and Cu(II)9
was obtained in modest yields compared to NCTPP (Scheme
2). The complexes 4-Ag, 4-Ni, and 4-Pd showed the
Figure 1. The structures of N-confused porphyrin (NCP) and cis-
doubly N-confused porphyrin (cis-N2CP).
oxidation states of metals such as Cu(III).10 Herein, we report
the synthesis of C6F5-NCP (4) and the X-ray structures of
Ag(III), Ni(II), Pd(II), and Cu(II) complexes. To the best of
our knowledge, the Cu(II) complex is the first example of
an organocopper(II) complex of aromatic porphyrinoid to
be characterized by X-ray crystallography.11
The initial attempt to obtain C6F5-NCP from the Rothe-
mund-type condensation reaction between pyrrole and penta-
fluorobenzaldehyde was hampered by the preferential forma-
tion of a series of expanded porphyrins (Scheme 1(a)).3a-d
Scheme 2. Metal Complexation of C6F5-NCP (4)
Scheme 1. Synthesis of C6F5-NCP (4): (a) One-Pot Route3b
and (b) [2+2] Stepwise Route
diamagnetic features of the d8 configuration as judged by
1
the resonance of H NMR spectra in the normal region
(10.0-7.4 ppm for the peripheral protons). Among them,
outer NH and the neighboring R-CH signals were observed
(4) (a) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116,
767. (b) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak,
T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779. (c) Geier, G. R., III; Haynes,
D. M.; Lindsey, J. S. Org. Lett. 1999, 1, 1455. (d) Latos-Graz˘yn´ski, L. In
The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, CA, 2000; Vol. 2, Chapter 14. (e) Furuta, H.;
Maeda, H.; Osuka, A. Chem. Commun. 2002, 1795.
The isolated yield of C6F5-NCP was quite low (<0.1%),
therefore we decided to synthesize C6F5-NCP by a stepwise
[2+2] condensation route (Scheme 1b).
(5) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676.
A key starting unit, bis(pentafluorobenzoyl) N-confused
dipyrromethane 2, was synthesized by Friedel-Crafts reac-
tion of corresponding dipyrromethane 1.10a,12 N-Confused
tetrakis(pentafluorophenyl)porphyrin (C6F5-NCP, 4) was
obtained in 21% yield by the acid-catalyzed condensation
between normal dipyrromethane 3 and the carbinol derivative
(6) (a) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. J. Chem. Soc., Perkin
Trans. 2 1995, 503. (b) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Głowiak,
T. J. Am. Chem. Soc. 1996, 118, 5690. (c) Chmielewski, P. J.; Latos-
Graz˘yn´ski, L. Inorg. Chem. 1997, 36, 840. (d) Chmielewski, P. J.; Latos-
Graz˘yn´ski, L. Inorg. Chem. 2000, 40, 5639. (e) Lash, T. D.; Richter, D. T.;
Shiner, C. M. J. Org. Chem. 1999, 64, 7973.
(7) Furuta, H.; Kubo, N.; Maeda, H.; Ishizuka, T.; Osuka, A.; Nanami,
H.; Ogawa, T. Inorg. Chem. 2000, 39, 5424.
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Org. Lett., Vol. 5, No. 8, 2003

Figure 2. X-ray single-crystal structures of (a) 4-Ag, (b) 4-Ni, and (c) 4-Pd (top and side view). Meso-substituents are omitted for clarity
in the side view. The thermal ellipsoids were scaled to the 50% probability levels. Due to the disorder of the nitrogen atom at the confused
pyrrole ring, one of the eight possible structures is shown in each complex.
in 4-Ni (9.94 and 8.45 ppm, J ) 2.7 Hz) and 4-Pd (9.87
and 8.38 ppm, J ) 2.7 Hz), but only the R-CH signal was
resonated at 9.38 ppm in 4-Ag as expected from the
structures. On the other hand, the signals of 4-Cu were not
detected in the region from -30 to +40 ppm, which proved
that the complex was paramagnetic and the Cu(II) was in
the d9 configuration. FAB-MS of each complex was also
consistent with the formulation above.
average bond lengths of Ag(III) and coordinating atoms (C
and N) are 2.033(4) and 2.039(4) Å, which are comparable
to those of the Ag(III) complex of NCTPP (2.03-2.08 Å).5
The corresponding values are 1.933(3) and 1.955(3) Å in
4-Ni and 2.004(4) and 2.026(4) Å in 4-Pd, which are similar
to those of the N-confused tetra(p-tolyl)porphyrin (NCTTP)
Ni(II) complex (1.955(3) and 1.963(3) Å)4b and Pd(II)NCTTP
(2.016(4) and 2.023(5) Å).7
The explicit evidence of the square-planar coordination
in the N3C cores of 4-Ag, 4-Ni, and 4-Pd was afforded by
X-ray single-crystal analyses (Figure 2).17-19 In 4-Ag, the
The coordination mode of the Cu(II) complex of NCP (4-
Cu) was also elucidated by X-ray analysis (Figure 3).20 The
(8) (a) Ogawa, T.; Furuta, H.; Morino, M.; Takahashi, M.; Uno, H. J.
Organomet. Chem. 2000, 611, 551. (b) Srinivasan, A.; Furuta, H.; Osuka,
A. Chem. Commun. 2001, 1666. (c) Furuta, H.; Ishizuka, T.; Osuka, A. J.
Am. Chem. Soc. 2002, 124, 5622. (d) Chen, W.-C.; Hung, C.-H. Inorg.
Chem. 2001, 40, 5070. (e) Bohle, D. S.; Chen, W.-C.; Hung, C.-H. Inorg.
Chem. 2002, 41, 3334. (f) Hung, C.-H.; Chen, W.-C.; Lee, G.-H.; Peng,
S.-M. Chem. Commun. 2002, 1516. (g) Harvey, J. D.; Ziegler, C. J. Chem.
Commun. 2002, 1942.
(9) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. Inorg. Chem. 2000, 40, 5475.
(10) (a) Furuta, H.; Maeda, H.; Osuka, A. J. Am. Chem. Soc. 2000, 122,
803. (b) Furuta, H.; Maeda, H.; Osuka, A.; Yasutake, M.; Shinmyozu, T.;
Ishikawa, Y. Chem. Commun. 2000, 1143. (c) Furuta, H.; Maeda, H.; Osuka,
A. J. Am. Chem. Soc. 2001, 123, 6435. (d) Araki, K.; Winnischofer, H.;
Toma, H. E.; Maeda, H.; Osuka, A.; Furuta, H. Inorg. Chem. 2000, 40,
2020. (e) Araki, K.; Engelmann, F. M.; Mayer, I.; Toma, H. E.; Baptista,
M. S.; Maeda, H.; Osuka, A.; Furuta, H. Chem. Lett. 2003, 32, 244.
(11) Furuta, H.; Ishizuka, T.; Osuka, A.; Uwatoko, Y.; Ishikawa, Y.
Angew. Chem., Int. Ed. 2001, 40, 2323.
(12) Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.; O’Shea,
D. F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 1391.
(13) (a) Rao, P. D.; Littler, B. J.; Geier, G. R., III; Lindsey, J. S. J. Org.
Chem. 2000, 65, 1084. (b) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J.;
Lindsey, J. S. J. Org. Chem. 2000, 65, 7323.
(14) Acid-catalyzed condensation of NC-dipyrromethane 1, normal
dipyrromethane 3, and pentafluorobenzaldehyde affords the complicated
mixture of expanded porphyrins and a trace of 4.
Figure 3. X-ray single-crystal structure of 4-Cu (top and side
view). Meso-substituents are omitted for clarity in the side view.
The thermal ellipsoids were scaled to the 30% probability levels.
The position of the nitrogen at confused pyrrole is disordered, so
one of the eight possible forms is shown.
(15) Liu, B. Y.; Bru¨ckner, C.; Dolphin, D. Chem. Commun. 1996, 2141.
(16) Furuta, H.; Ishizuka, T.; Osuka, A.; Dejima, H.; Nakagawa, H.;
Ishikawa, Y. J. Am. Chem. Soc. 2001, 123, 6207.
center Cu(II) is coordinated in a square-planar fashion as
expected.9 The average bond lengths between Cu(II) and
ligand atoms are 1.980(9) and 2.018(9) Å, which are longer
(17) Crystal data for 4-Ag: C44H7N4F20Ag‚0.5H2O, Mw ) 1088.42,
trigonal R3h(h) (no. 148), a ) b ) 20.29(1) Å, c ) 24.25(3) Å, V ) 8647.4(1)
Å3, Dc ) 1.881 g/cm3, Z ) 9, R ) 0.057, wR ) 0.081, GOF ) 0.998 (I >
3.0σ(I)). Hydrogen atoms of water molecules incorporated in the crystal
were omitted for the refinement due to the significant disorder of the solvent.
(18) Crystal data for 4-Ni: C44H8N4F20Ni, Mw ) 1031.25, trigonal R3h(h)
(no. 148), a ) b ) 19.6856(10) Å, c ) 24.831(3) Å, V ) 8333.5(11) Å3,
Dc ) 1.849 g/cm3, Z ) 9, R ) 0.0489, wR ) 0.1207, GOF ) 1.046 (I >
2.0σ(I)).
(19) Crystal data for 4-Pd: C44H8N4F20Pd, Mw ) 1078.94, trigonal R3h(h)
(no. 148), a ) b ) 19.6798(10) Å, c ) 25.097(3) Å, V ) 8417.6(11) Å3,
Dc ) 1.916 g/cm3, Z ) 9, R ) 0.0478, wR ) 0.1148, GOF ) 0.997 (I >
2.0σ(I)).
Org. Lett., Vol. 5, No. 8, 2003
1295

than those of the cis-N2CP-Cu(III) complex (1.934-1.969
Å)10a reflecting the larger Cu(II) radius than that of Cu(III).
The ESR parameters of 4-Cu (giso ) 2.09, g ) 2.12, [A ]
unit in NCP is reflected in the Cu(II/III) redox couple at
+0.14 V (vs Fc/Fc+), which is shifted to higher potential
compared with that of NCTPP at -0.11 V.9 In other words,
the electron-withdrawing C6F5 groups decrease the electron
density of the π system, including the center metal, as a
result, the reactivity of the inner carbon bound to Cu(II)
decreases to afford sufficient stability to grow single crystals.
In the case of the NCTPP-Cu(II) complex, the core frame-
work is easily cleaved and fragmented to transform into the
tripyrrinone-Cu(II) complex under aerobic conditions.22 In
the case of 4-Cu, however, the complex retains its framework
under similar aerobic conditions.23
||
||
)168 G in toluene (4 mM) at 77 K) are also consistent with
the square-planar structure.21
The absorption spectra of the free base form of C6F5-NCP
and the Ag(III) and Cu(II) complexes in CHCl3 are shown
in Figure 4. The Soret band of 4-Cu shows the peak at 428.0
In summary, we have succeeded in synthesizing the meso-
pentafluorophenyl-substituted NCP (C6F5-NCP, 4) in good
yield. C6F5-NCP can form square-planar complexes with a
variety of metals such as Ag(III), Ni(II), Pd(II), and Cu(II).
The stabilizing effect of the electron-withdrawing C6F5
substituents was demonstrated explicitly by the preparation
of single crystals of the Cu(II) complex, which are not
available from the meso-phenyl derivative due to the instabil-
ity of the complex.24 C6F5-NCP is, thus, attractive as a
potential ligand in complexing various metals that can exhibit
the catalytic activity as shown in the corrole complexes.1c
Furthermore, the stepwise synthesis used for C6F5-NCP
would be applicable for the preparation of NCP derivatives
with various functional group at meso-positions.
Figure 4. UV/vis absorption spectra of C6F5-NCP (4) (solid line),
4-Ag (broken line), and 4-Cu (bold line) in CHCl3.
Acknowledgment. The authors thank Dr. Kenji Matsuda
at Kyushu University and Mr. Soji Shimizu at Kyoto
University for FAB-MS measurements. H.M. thanks JSPS
for a Research Fellowship for Young Scientists.
nm and a characteristic shoulder around 440 nm. The last
Q-band reaches to 739.0 nm, which is 27 and 103 nm red-
shifted compared to those of 4 and 4-Ag, respectively, but
is more blue-shifted than other divalent metal complexes (4-
Ni, 810.0 nm; 4-Pd, 762.0 nm; see Supporting Information).
Interestingly, the oxidation state of the copper ion changes
in NCP (Cu(II)) and N2CP (Cu(III)), whereas that of silver
is kept in the same (Ag(III)) state, despite the same group
11 elements. As meso-substituents are identical in both NCP
and N2CP, we can clearly state that the introduction of a
second confused ring in the NCP core facilitates to stabilize
the higher oxidation state of metals, just as the first confusion
does in the NCP-Ag(III) complex. The effect of the C6F5
Supporting Information Available: Synthetic procedures
and spectral data of dipyrromethane (2), free base (4), and
the metal complexes, UV/vis absorption spectra of 4-Ni and
4-Pd, and CIF files for the X-ray structural data of 4-Ag,
4-Ni, 4-Pd, and 4-Cu. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL034227L
(22) (a) Furuta, H.; Maeda, H.; Osuka, A. Org. Lett. 2002, 4, 181. (b)
Furuta, H.; Maeda, H.; Osuka, A. Inorg. Chem. Commun. 2003, 6, 162.
(23) The details of the oxidation of 4-Cu are under investigation. The
complexation of Cu(II) under toluene reflux conditions yielded the
unidentified product different from tripyrrinone-Cu(II) complex,22 quanti-
tatively.
(24) Introduction of electron-withdrawing groups directly at the NCP
core may also be helpful to stabilize the metal complexes. In fact, an air-
stable Cu(II) complex was also obtained from CN-substituted NCTPP at
the confused pyrrole ring. Ishikawa, Y.; Dejima, H.; Furuta, H. Manuscript
in preparation.
(20) Crystal data for 4-Cu: C44H8N4F20Cu, Mw ) 1036.09, trigonal R3h(h)
(no. 148), a ) b ) 20.1647(9) Å, c ) 23.941(2) Å, V ) 8430.4(9) Å3, Dc
) 1.837 g/cm3, Z ) 9, R ) 0.0707, wR ) 0.1996, GOF ) 1.017 (I >
2.0σ(I)).
(21) The obtained values are slightly different from the reported Cu(II)-
NCTPP complex, giso ) 2.070, g ) 2.139, [A ] )143 G in toluene/CH2Cl2
||
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(80/20, v/v) at 77 K. See ref 9.
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Org. Lett., Vol. 5, No. 8, 2003