Syntheses, structures, and crystal packing of n-confused 5,20-diphenylporphyrin and Ag(III) complex

Article abstract of DOI:10.1021/ol034172n

(Matrix presented) β-Unsubstituted meso partially free N-confused porphyrin, N-confused 5,20-diphenylporphyrin (NCDPP, 3), was synthesized in 7% yield by [3 + 1] condensation reaction followed by oxidation. The structures of the free base and its Ag(III)

Full text of DOI:10.1021/ol034172n

ORGANIC
LETTERS
2003
Vol. 5, No. 9
1427-1430
Syntheses, Structures, and Crystal
Packing of N-Confused
5,20-Diphenylporphyrin and Ag(III)
Complex
,†
,‡
Hiroyuki Furuta,* Tatsuki Morimoto,‡ and Atsuhiro Osuka*
Department of Chemistry & Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, Fukuoka 812-8581, Japan, and Department of Chemistry,
Graduate School of Science, Kyoto UniVersity, Kyoto 606-8502, Japan
hfuruta@cstf.kyushu-u.ac.jp
Received January 30, 2003
ABSTRACT
â-Unsubstituted meso partially free N-confused porphyrin, N-confused 5,20-diphenylporphyrin (NCDPP, 3), was synthesized in 7% yield by [3
+ 1] condensation reaction followed by oxidation. The structures of the free base and its Ag(III) complex were elucidated by the single-crystal
X-ray analyses. The Ag(III) complex was more planar than the free base and formed columnar structures stacking to each other with a 3.3 Å
distance in the crystal.
Comparison of similarity and differences is one effective
method in approaching the subject concerned. In porphyrin
chemistry, a new series of porphyrin analogues such as core-
modified, expanded, and contracted porphyrins has emerged
and is growing progressively. Among them, porphyrin
isomers are of particularly interest because they exhibit
chemistry analogous to that of the parent normal porphyrin
and reveal completely different properties in some cases. In
the study of N-confused porphyrin (NCP), we and others
have shown the peculiar chemistry in the structures, metal
coordinations, and reactivities.1 In this paper, we focus on
the similar aspects in turn, and show the important nature
of the meso-substituents on the molecular planarity and
crystal packing. For this study, meso-diphenyl derivatives
and Ag metal complexes of both NCP and normal porphyrin
were newly synthesized.
Toward “N-confused porphin”, a standard of NCP having
only a basic framework, we started the syntheses of meso-
tri-, di-, and monosubstituted NCP derivatives. Pre-
viously, meso-free NCPs having alkyl groups at outer R-
and â-positions were synthesized.2 Such alkyl groups may
(1) (a) Furuta, H.; Maeda, H.; Osuka, A. Chem. Commun. 2002, 1795.
(b) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767.
(c) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak, T.
Angew. Chem., Int. Ed. Engl. 1994, 33, 779.
(2) (a) Liu, B. Y.; Bruckner, C.; Dolphin, D. Chem. Commun. 1996,
2141. (b) Lash, T. D.; Chaney, S. T.; Richter, D. T. J. Org. Chem. 1998,
63, 9076.
† Kyushu University.
‡ Kyoto University.
10.1021/ol034172n CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/02/2003

be important for the syntheses and the stabilization of
NCP. Here, we chose N-confused 5,20-diphenylporphyrin
(NCDPP, 3) as an initial target of outer R,â-free NCP with
less than four meso-substituents (Figure 1).
Scheme 1. Synthesis of 5,20-Diphenyl-NCP (NCDPP, 3)
R-proton of the confused ring (C3-H) and â-protons are
shifted slightly downfield (8.8-9.1 ppm) compared to
NCTPP (8.5-9.0 ppm). In addition, two new singlet signals
at 9.4 and 9.5 ppm assignable to meso-protons (C10-H and
C15-H) were observed.
Figure 1. Framework and atom numbering system of porphyrin
and N-confused porphyrin (NCP).
The UV/vis spectrum of 3 showed the absorption maxima
at 430 (Soret), 527, 566, and 705 nm (Q-bands) in CH2Cl2.
The spectrum was similar to that of NCTPP with respect to
the shape but showed hypsochromic shifts compared to
NCTPP.10 On the other hand, in DMF, the Soret band was
bathochromic shifted (434 nm) and the appearance of
characteristic Q-bands (579, 626, 679 nm) indicates the
formation of another tautomer of the inner-2H-type as
demonstrated in NCTPP (Figure 2).11
NCDPP (3) was synthesized according to the Scheme 1.
In the synthesis, we have used [3 + 1] condensation reac-
tion of 2,4-bis(phenylhydroxymethyl)pyrrole (1) and meso-
unsubstituted tripyrrane (2) referring to the successful
procedures used in the syntheses of hetero-NCP3 and
porphin.4At first, 2,4-dibenzoylpyrrole5 was reduced to the
corresponding dicarbinol (1) and the resulting diol was
reacted with tripyrrane (2)6 in the presence of an acid catalyst.
After the oxidation with o-chloranil, followed by column
chromatography on alumina and silica gel sequentially, the
target compound 3 was isolated in 7% yield and no other
NCP derivatives were obtained. Formation of meso-phenyl-
substituted porphyrins (<1%) was only detected in a trace
amount by NMR, UV/vis, and FABMS,7 which indicates that
the scrambling of phenyl groups was not significant in this
NCP formation reaction. When MSA (methanesulfonic acid),
a known effective acid for tetraaryl-NCP synthesis,8 was
applied instead of BF3‚MeOH, the yield of NCDPP decreased
to 3%.
In the 1H NMR spectrum of 3 in CDCl3, the inner C21-H
signal was observed at -5.9 ppm, which was shifted up-
field compared to that of N-confused tetraphenylporphyrin,
NCTPP, at -5.1 ppm. Such a substituent effect is known in
the normal porphyrin systems and is attributable to the
enhancement of the ring current as the result of the removal
of the electron-withdrawing meso-phenyl groups.9 The outer
Figure 2. Absorption spectra of 3 in CH2Cl2 (solid line) and in
DMF (broken line).
In a single crystal of 3, the two independent NCDPP
molecules form a pair with stacking to each other in the same
direction. The intermolecular distances between the porphyrin
rings are 3.55 Å in the pair (r1) and 3.69 Å between the
(3) (a) Heo, P.-Y.; Shin, K.; Lee, C.-H. Tetrahedron Lett. 1996, 37, 197.
(b) Heo, P.-Y.; Shin, K.; Lee, C.-H. Tetrahedron Lett. 1996, 37, 1521.
(4) Taniguchi, S.; Hasegawa, H.; Nishimura, M.; Takahashi, M. Synlett
1999, 73.
(5) Cadamuro, S.; Degani, I.; Dughera, S.; Fochi, R.; Gatti, A.; Piscopo,
L. J. Chem. Soc., Perkin Trans. 1 1993, 273.
(6) High-yield and stepwise synthesis of 2: Taniguchi, S.; Hasegawa,
H.; Yanagiya, S.; Tabeta, Y.; Nakano, Y.; Takahashi, M. Tetrahedron 2001,
57, 2103. Another one-pot synthesis: Ka, J.-W.; Lee, C.-H. Tetrahedron
Lett. 2000, 41, 4609.
(7) Formation of a trace amount of porphine, mono-, di-, and tri-
phenylporphyrins was detected by NMR and FABMS. meso-Diphenyl-â-
benzylporphyrin was also produced according to the quenching procedure
in the reduction step.
(9) Chemical shifts of the inner NH signal of TPP, 5,10-DPP, and porphin
were reported -2.76, -3.34, and -3.76 ppm, respectively. See, ref 17b
and: Medforth, C. J. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 5, Chapter
35.
(10) Such shifts were also observed in normal porphyrins. For example,
the Soret bands of TPP and 5,10-DPP were observed at 419 and 405 nm in
CH2Cl2, respectively.
(8) Geier, G. R., III; Haynes, D. M.; Lindsey, J. S. Org. Lett. 1999, 1,
1455.
(11) Furuta, H.; Ishizuka, T.; Osuka, A.; Dejima, H.; Nakagawa, H.;
Ishikawa, Y. J. Am. Chem. Soc. 2001, 123, 6207.
1428
Org. Lett., Vol. 5, No. 9, 2003

Figure 4. Molecular structure of 3-Ag(III): (a) top view, (b) side
view, and (c) packing diagram from the b-axis. r1 and r2 denote
the interplane distances between the paired and unpaired porphyrins
(see text). Solvent molecules are omitted for clarity.
Figure 3. Molecular structure of 3: (a) top view, (b) side view,
and (c) packing diagram from the c-axis. r1 and r2 denote the
interplane distances between the paired and unpaired porphyrins
(see text). Solvent molecules are omitted for clarity.
complex shows the planar structure with the mean deviation
of 0.02 Å, which is rather smaller than that of NCTPP-Ag(III)
complex (0.19 Å). Interestingly, the crystal packing is
dramatically different from the free base (3). In a columnar
packing of 3-Ag(III), NCP skeletons are almost parallel to
each other (dihedral angle < 1°) and perpendicular to the
b-axis of the column.16 The NCP molecules stack in an
opposite direction to each other with the distances of 3.30
and 3.31 Å (r1 and r2, see Figure 4), and the Ag(III) metals
are located along a zigzag line with a distance of 3.73 Å. In
the case of the NCTPP-Ag(III) complex, the distances
between the two molecular planes are 3.90 and 3.83 Å, and
the Ag(III) metals are arranged along a zigzag line with
alternate distances of 5.10 and 5.13 Å.
nearest unpaired porphyrins (r2), respectively (Figure 3).12
The confused pyrrole ring of 3 is tilted by 21.6° from the
mean plane consisting of 24 atoms of NCP skeleton, and
the other pyrroles are canted by 5.7, 3.5, and 8.4°, respec-
tively. The confused ring of the opposite NCP is tilted by
16.4° from the plane, and the remaining pyrroles by 10.6,
2.0, and 11.4°, respectively. Such tilting of the confused
pyrrole rings is commonly observed in the inner-3H-type of
the NCP tautomer, which is not the case in the normal
porphyrin.
Next, NCDPP was complexed with Ag(III) ions using
excess Ag(I) trifluoroacetate in CH2Cl2/MeOH. As reported
previously, NCP ligand can form a neutral square-planar
complex with Ag(III) ion,13,1a which is in marked contrast
to normal porphyrin, which forms a neutral square-planar
complex with Ag(II).14 The X-ray structure of NCDPP-
Ag(III) complex (3-Ag(III)) is shown in Figure 4.15 The
To clarify the factors for the change of the crystal packing
of NCDPP, we synthesized the Ag(II) complex of normal
5,10-diphenylporphyrin (4-Ag(II)) as a control.17 If the
(15) Crystal data for 3-Ag(III): C32H17N4‚H2O, Mw ) 583.40, mono-
clinic, space group P21/c (no. 14), a ) 15.224(2), b ) 6.6255(7), c )
24.759(3) Å, â ) 102.717°, V ) 2436.2(5) Å3, Z ) 4, Dcalcd ) 1.590 g/cm3,
T ) -150 °C, R ) 0.076, Rw ) 0.125, GOF ) 1.919.
(16) In CH2Cl2 and DMF solutions, compound 3 and 3-Ag(III) exist as
monomers and do not form dimers or aggregates, as judged by UV/vis
spectra at various concentrations.
(17) (a) Hatscher, S.; Senge, M. O. Tetrahedron Lett. 2003, 44, 157. (b)
Brinas, R. P.; Bruckner, C. Tetrahedron 2002, 58, 4375. (c) Adler, A. D.;
Longo, F. R.; Kampas, F.; Kim, J. J. Inorg. Nucl. Chem. 1970, 32, 2443.
(12) Crystal data for NCDPP (3): C32H22N4, Mw ) 462.55, orthorhombic,
space group P21212 (no. 18), a ) 21.176(2), b ) 22.188(2), c ) 9.8918(8)
Å, V ) 4647.5(7) Å3, Z ) 8, Dcalcd ) 1.322 g/cm3, T ) -150 °C, R )
0.078, Rw ) 0.097, GOF ) 0.918.
(13) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676.
(14) Scheidt, W. R.; Mondal, J. U.; Eigenbrot, C. W.; Adler, A.;
Radonovich, L. J.; Hoard, J. L. Inorg. Chem. 1986, 25, 795.
Org. Lett., Vol. 5, No. 9, 2003
1429

0.02 Å. Although it is not simple to interpret the relation
between the substituent effects and the planarity of the
porphyrin rings in general, it is likely that the complementary
molecular structures favorable for the stacking could induce
the planarity of the ring, at least in the present diphenyl
derivative of NCP and normal porphyrin cases (3 and 4).
The additional characteristic for both the crystal packing of
3-Ag(III) and 4-Ag(II) was short a lateral shift (LS)19
between the porphyrin rings, 1.71 and 1.67 Å, respectively.
These values were much smaller than those of NCTPP-
Ag(III) and TPP-Ag(II), 3.32 and 5.04 Å, respectively,
supporting the complementary packing of the silver complex
of diphenyl derivatives. Deviation of the core atoms (∆),
C-Ag and averaged N-Ag bond lengths, and LS are
summarized in Table 1.
Table 1. Deviations of Core Atoms from the Mean Plane
(×10-2 Å), Ag-C and Averaged Ag-N Bond Lengths (Å),
Mean Plane Deviation (∆, Å), and Lateral Shifts (LS, Å) in
NCTPP-Ag(III), 3-Ag(III), TPP-Ag(II), and 4-Ag(II)
Complexes
In conclusion, N-confused 5,20-diphenylporphyrin (NCD-
PP) was synthesized by [3 + 1] condensation reaction, and
the structure was determined by single-crystal X-ray analysis.
The Ag(III) complex was found to stack regularly in the
crystal, in which the packing mode was rather different from
the free base form and NCTPP-Ag(III) but the same as that
of the corresponding Ag(II) complex of the diphenyl deriva-
tive. Because of the resemblance to the normal porphyrin
and the facile modification at meso-positions, we believe that
this unsubstituted type of NCP will be useful for introducing
local perturbation into the porphyrin-based molecular ar-
chitecture.20 Furthermore, the potential alignment of the
coordinated metals in close proximity in the crystals might
be of interest in applying these diphenyl-substituted porphyrin
and NCP ligands for the development of conductive materi-
als21 or one-dimensional magnetic systems.22
Acknowledgment. We thank Prof. Shozo Taniguchi at
Ibaraki National College of Technology for the valuable
suggestion for the synthesis of 3.
packing structure of 4-Ag(II) is the same as that of 3-Ag(III),
the structural similarity of having only two phenyl groups
is the likely main reason. If the packing structure differs
largely, then the unusual electronic states of metals, Ag(II)
vs Ag(III), need to be taken into account.
Interestingly, the observed crystal packing of 4-Ag(II) is
almost same as that of 3-Ag(III).18 Moreover, the molecular
planarity of 4-Ag(II) was much enhanced compared with
TPP-Ag(II) as judged by the mean deviation values, 0.02
and 0.05 Å, respectively. In the complexation of Ag(III) with
a smaller ionic size, the NCTPP core was slightly distorted
from planarity with a deviation of 0.19 Å; on the other hand,
complex 3-Ag(III) was almost planar with a deviation of
Supporting Information Available: Experimental pro-
cedures, spectral data of NCDPP (3), 3-Ag(III), and 4-Ag(II),
a crystal packing diagram of 4-Ag(II), and crystallographic
data (CIF) for 3, 3-Ag(III), and 4-Ag(II). This material is
available free of charge via the Internet at http://pubs.acs.org.
OL034172N
(19) Scheidt, W. R. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 3, Chapter
16.
(20) (a) Aratani, N.; Osuka, A. Org. Lett. 2001, 3, 4213. (b) Sugiura,
K.; Fujimoto, Y.; Sakata, Y. Chem. Commun. 2000, 1105. (c) Liu, V. S.-
Y.; DiMagno, S. G.; Therien, M. J. Science 1994, 264, 1105.
(21) Miller, D. C.; Bollinger, J. C.; Hoffman, B. M.; Ibers, J. A. Inorg.
Chem. 1994, 33, 3354.
(18) Crystal data for 4-Ag(II): C32H20N4Ag‚0.42CH2Cl2, Mw ) 604.08,
monoclinic, space group P21/c (no. 14), a ) 15.635(6), b ) 6.623(2), c )
24.964(9) Å, â ) 104.14(3)°, V ) 2506.8(2) Å3, Z ) 4, Dcalcd ) 1.600
g/cm3, T ) -150 °C, R ) 0.045, Rw ) 0.052, GOF ) 0.907. The crystal
packing diagram is shown in Supporting Information.
(22) Caneschi, A.; Gatteschi, D.; Lalioti, N.; Sangregorio, C.; Sessoli,
R.; Venturi, G.; Vindigni, A.; Rettori, A.; Pini, M. G.; Novak, M. A. Angew.
Chem., Int. Ed. 2001, 40, 1760.
1430
Org. Lett., Vol. 5, No. 9, 2003