Unprecedented pendant group exchange of a porphyrinato platinum(II) in benzonitrile

Article abstract of DOI:10.1246/cl.2004.450

5-(4-cyanophenyl)-10,15,20-triphenylporphyrinato platinum(II) (3) and 5-(4-methoxycarbonyrphenyl)-10,15,20-triphenylporphyrinato platinum(II) (2) were isolated from a reaction of 5-(4-methoxycarbonylphenyl)-10,15,20-triphenyl porphyrin (1) with K₂

Full text of DOI:10.1246/cl.2004.450

450
Chemistry Letters Vol.33, No.4 (2004)
Unprecedented Pendant Group Exchange of a Porphyrinato Platinum(II) in Benzonitrile
Naoko Araki, Makoto Obata, Akio Ichimura,y Yuji Mikata,yy and Shigenobu Yanoꢀ
Division of Natural Science and Ecological Awareness, Graduate School of Humanities and Sciences,
Nara Women’s University, Nara 630-8506
yDepartment of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585
yyKYOSEI Science Center, Nara Women’s University, Nara 630-8506
(Received January 20, 2004; CL-040072)
5-(4-cyanophenyl)-10,15,20-triphenylporphyrinato platinu-
m(II) (3) and 5-(4-methoxycarbonylphenyl)-10,15,20-triphenyl-
porphyrinato platinum(II) (2) were isolated from a reaction of 5-
(4-methoxycarbonylphenyl)-10,15,20-triphenyl porphyrin (1)
with K2[PtCl4] in benzonitrile. Seemingly, 3 was generated
through the functional group substitution reaction of the phenyl
group of tetraphenylporphyrin during platinum ion insertion into
umn chromatography to afford the 5-(4-methoxycarbonylphen-
yl)-10,15,20-triphenylporphyrinato platinum(II) (2) in 29.8%
yield and 5-(4-cyano phenyl)-10,15,20-triphenylporphyrinato
platinum(II) (3) in 52.7% yield, respectively (Scheme 1b).6 On
the other hand, 2 was obtained as main product from the Scheme
1c in yield 95.4%.7 When a mixture of 2 and K2[PtCl4] dissolved
in anhydrous benzonitrile was heated to 170 ꢁC, no 3 was detect-
able in the 1H NMR spectrum. Thus, 3 was not supposedly gen-
1
1 and was characterized by H NMR, mass spectroscopy, ele-
mental analysis, and X-ray crystallography.
erated from 2. The structure of 3 was established by 1H and 13
C
NMR, mass spectroscopy, elemental analysis, and X-ray crystal-
lography.
In the 1H NMR spectrum of 3, the methyl ester peak at
4.09 ppm (for 2) was no longer present. However, the peaks in
the aromatic region clearly show that 3 is a tetraphenylporphyrin
derivative in which one of the four phenyl groups has been re-
placed by a p-substituted phenyl group. In the UV–vis spectrum
of 3 (Soret-band at ca. 402.0 nm and two Q-bands at ca. 509.5
and 535.5 nm), the Soret-band is shifted towards shorter wave-
length compared with the starting material 1 (ca. 420.0 nm and
four Q-bands at ca. 518.5, 550.0, 590.5, and 645.0 nm), and is
quite similar to that of 2 (ca. 402.0 nm and two Q-bands at ca.
509.5 and 535.5 nm). This observation suggests that platinum
ion was inserted into the porphyrin ring. The shapes of the Sor-
et-band and Q-bands were comparable with those of known nor-
mal metalloporphyrins, so it was suggested that the electronic
structure of 3 belongs to a normal porphyrin type such as
Pt(II)TPP. FAB mass spectroscopy and elemental analysis of 3
supported the formula of 5-(4-cyanophenyl)-10,15,20-triphenyl-
porphinato platinum(II) (Pt1C45H27N5). Unfortunately, the cya-
no carbon peak could not be distinguished in the 13C NMR spec-
trum, because it is in the same position as the pyrrole carbon.
Recrystallization of 3 from CH2Cl2–MeOH afforded X-ray qual-
ity crystals (Figure 1).8 The diffraction data revealed a tetragonal
crystal system, I-42d space group, and Z ¼ 4. This indicates that
the orientation of the cyano group is statistically disordered to
give pseudo four-fold symmetry. The cyano group was found
on a differential electron density map, and refined with an iso-
tropic displacement parameter with an occupancy of 1/4. The
Porphyrin compounds are of great interest in the fields of bi-
oorganic chemistry and material science.1 The electronic and op-
tical properties of porphyrins can be tuned by metal ion inser-
tion.2 Recently, platinum porphyrin derivatives have been used
for oxygen sensing.3 In order to improve oxygen sensitivity, con-
siderable effort has been devoted to the synthesis of porphyrinato
platinum(II) analogs. In our research on porphyrinato plati-
num(II) derivatives, we discovered that a unique reaction occur-
red during the insertion of platinum into a 5,10,15,20-tetraphen-
ylporphyrin derivative in benzonitrile.4
Condensation of pyrrole with aldehydes by Lindsey’s meth-
od afforded 5-(4-methoxycarbonylphenyl)-10,15,20-triphenyl
porphyrin (1) in 17.7% yield (Scheme 1a).5 1 and K2[PtCl4] dis-
solved in anhydrous benzonitrile was heated to 170 ꢁC for 72 h
under N2, and the crude product was purified by silica gel col-
ꢀ
N(2)–C(12) bond distance was 1.15(3) A and the N(2)–C(12)–
C(9) bond angle was 177(2)ꢁ, which resembles that of meso-tet-
rakis(4-cyanophenyl)porphyrinato zinc(II) (C-N triple bond dis-
ꢁ
9
ꢀ
tance, 1.13 A, and C–C–N bond angle, 176.7 ). The crystal of
tetraphenylporphirinato platinum(II) (PtTPP) is also tetragonal,
I-42d space group, and Z ¼ 4. The lattice volume of 3 is bigger
than that of PtTPP, which reflects the additional volume of the
cyano group.4c These findings indicate that a novel substitution
reaction occurs when the porphyrin ring is heated with K2[PtCl4]
in benzonitrile.
Scheme 1. Conditions: a (i) BF3ꢂOEt2, CHCl3 (ii) p-chloranil;
b K2[PtCl4], Ph-CN; c CH3COONa, K2[PtCl4], CH3COOH/
Ph–Cl.
Recently, many reactions about porphyrins are reported and
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.4 (2004)
451
1.60 mmol) was added and the mixture was stirred at room temper-
ature for 19 h under Ar, after which p-chloranil (9.65 g, 39.3 mmol)
was added. The mixture was maintained at room temperature for
1 day, then the solvent was evaporated. The crude product was puri-
fied by silica gel column chromatography eluted with a mixture of
CH2Cl2/acetone (12/1, v/v). Precipitation from CH2Cl2/methanol
afforded a purple powder (1.46 g, 2.18 mmol, 17.7%, Rf ¼ 0:79
(CH2Cl2/acetone 12/1, v/v)) of 1. 1H NMR (CDCl3): ꢀ 8.87–8.85
(m, 6H, pyrrole-ꢁH), 8.78 (d, 3J ¼ 4:58 Hz, 2H, pyrrole-ꢁH), 8.42
(d, 3J ¼ 8:24 Hz, 2H, ArH), 8.29 (d, 3J ¼ 8:55 Hz, 2H, ArH),
8.23–8.19 (m, 6H, o-PhH), 7.77–7.74 (m, 9H, m, p-PhH), 4.10 (s,
3H, –COOCH3), ꢃ2:78 (s, 2H,–2NH).
6
1 (0.53 g, 0.80 mmol) and K2[PtCl4] (0.78 g, 1.89 mmol) were dis-
solved in anhydrous benzonitrile (50 mL). The mixture was stirred
at 170 ꢁC for 72 h under N2 until no free base was apparent in the
UV–vis spectrum. The solvent was removed by vacuum distillation
and the crude product was purified by silica gel column chromatog-
raphy eluted with CH2Cl2/hexane (15/8, v/v). Two orange bands
were separated and precipitated from CH2Cl2/methanol to afford 2
as a reddish orange solid (0.20 g, 0.24 mmol, 29.8%, Rf ¼ 0:67
(CH2Cl2/hexane 15/8, v/v)) and 3 also as a reddish orange solid
(0.35 g, 0.42 mmol, 52.7%, Rf ¼ 0:69 (CH2Cl2/hexane 15/8, v/
v)). 1H NMR(CDCl3) of 2: ꢀ 8.79–8.73 (m, 6H, pyrrole-ꢁH), 8.67
(d, 3J ¼ 5:19 Hz, 2H, pyrrole-ꢁH), 8.39 (d, 3J ¼ 8:24 Hz, 2H,
ArH), 8.22 (d, 3J ¼ 8:54 Hz, 2H, ArH), 8.16–8.12 (m, 6H, o-PhH),
7.78–7.68 (m, 9H, m, p-PhH), 4.09 (s, 3H, –COOCH3). Anal. Calcd.
for C46H30O2N4Pt: C, 63.81; H, 3.49; N, 6.47. Found: C, 62.38; H,
3.31; N, 6.54%. FAB–MS of 2: m=z 866.3 ([M + H]þ). 1H NMR
(CDCl3) of 3: ꢀ (ppm) = 8.82–8.74 (m, 6H, pyrrole-ꢁH), 8.62 (d,
3J ¼ 5:19 Hz, 2H, pyrrole-ꢁH), 8.27 (d, 3J ¼ 8:24 Hz, 2H, ArH),
8.16–8.12 (m, 6H, o-PhH), 8.03 (d, 3J ¼ 8:54 Hz, 2H, ArH), 7.80–
7.71 (m, 9H, m, p-PhH). Anal. Calcd. for C45H27N5Pt: C, 64.90;
H, 3.27; N, 8.41. Found: C, 64.86; H, 3.20; N, 8.51%. FAB–MS of
3: m=z 833.3 ([M + H]þ).
1 (1.43 g, 2.13 mmol), sodium acetate (3.76 g, 45.9 mmol), and
K2[PtCl4] (2.34 g, 5.64 mmol) were dissolved in CH3COOH
(80 mL) and chlorobenzene (100 mL). The mixture was stirred at
150–160 ꢁC for 96 h under N2. The solvent was removed by vacuum
distillation and the crude product was purified by silica gel column
chromatography eluted with CH2Cl2/hexane (15/8, v/v). An orange
band was separated and precipitated from CH2Cl2/methanol to af-
ford 2 as a reddish orange solid (1.76 g, 2.03 mmol, 95.4%, Rf ¼
0:67 (CH2Cl2/hexane 15/8, v/v)).
Figure 1. ORTEP drawings of 3 showing 50% probability. All
hydrogen atoms and other three cyano groups disordered statisti-
cally were omitted for clarity.
it is well known that the meso position of a porphyrin ring has
high reactivity. For example, addition reaction of functional
groups to the meso position of porphyrins were reported, and
the porphyrin which the additional functional group was attach-
ed to a meso position is called an isoporphyrin.10 However, to
our knowledge, no exchange reaction via an isoporphyrins inter-
mediate was reported, although synthesises of isoporphyrins are
realized by means of chemical and electrochemical ap-
proaches.11 Thus, the functional group substitution reaction of
the phenyl group of tetraphenylporphyrin is not reported. There-
fore, it is suggested that the functional group substitution reac-
tion of porphyrin, which we discovered, should be a new reac-
tion in the field of porphyrin chemistry. This is expected to be
a significant result for the synthesis of metal-containing porphy-
rins. We are now studying the scope of this reaction and are also
examining the substitution mechanism.
7
The authors would like to thank Professor Akio Toshimitsu
(Kyoto University) and Professor Kiyomi Kakiuchi (Nara Insti-
tute of Science and Technology) for their helpful discussions.
This research was supported by a Grant-in-Aid for Scientific Re-
search from the Ministry of Education, Culture, Sports, Science
and Technology, Japan (15033246, 14045252, 13557211), and
by grants from OSAKA GAS and San-Ei Gen Foundation for
Food Chemical Research.
8
A violet crystal of 3 was mounted on a glass fiber and cooled in a
stream of cold N2 gas. The reflections were collected on Rigaku/
MSC Mercury CCD X-ray diffractometer, with graphite-monochro-
mated Mo Kꢂ radiation, controlled by the Crystal Clear program (Ri-
gaku). The structure was solved by direct methods (SIR92). Crystal
data for 3: C45H27N5Pt, Mr ¼ 832:83, tetragonal, a ¼
ꢀ
ꢀ
ꢀ 3
15:4029ð10Þ A, c ¼ 13:8930ð11Þ A, V ¼ 3296:1ð4Þ A , T ¼ 173 K,
space group I-42d(#122), Z ¼ 4, ꢃ(Mo Kꢂ) = 42.83 cmꢃ1, 12773
reflections measured, 1047 unique (Rint ¼ 0:050) which were used
in all calculations. Final R1 ¼ 0:025 with I > 2:00 ꢄðIÞ, R ¼
0:034, wRðF2Þ ¼ 0:062 for all 1047 data, and GOF ¼ 0:93. Details
of the crystallographic data (excluding structure factor) for the struc-
tures reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-215090. Copies of the data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk).
R. K. Kumar, S. Balasubramanian, and I. Goldberg, Inorg. Chem.,
37, 541 (1998).
References and Notes
1
a) H. Hillebrandt and M. Tanaka, J. Phys. Chem. B, 105, 4270
(2001). b) K. Uosaki, T. Kondo, X. Zhang, and M. Yanagida, J.
Am. Chem. Soc., 119, 8367 (1997). c) T. Mizutani, K. Wada, and
S. Kitagawa, J. Am. Chem. Soc., 121, 11425 (1999). d) R. Bonnett,
Chem. Soc. Rev., 1995, 19.
2
3
4
H. R. Frederick and G. David, in ‘‘Porphyrins and Metalloporphy-
rins,’’ ed. by K. M. Smith, Elsevier Scientific Pubilishing Company,
New York (1975), Chap. 16, p. 668.
a) Y. Amao, K. Asai, T. Miyashita, and I. Okura, Anal. Commun., 36,
367 (1999). b) S. Lee and I. Okura, Anal. Commun., 34, 185 (1997).
c) X. Lu and M. A. Winnik, Chem. Mater., 13, 3449 (2001).
a) D. W. Thomas and A. E. Martell, J. Am. Chem. Soc., 81, 5111
(1959). b) R. C. Kwong, C. Sibley, T. Dubovoy, M. Baldo, S. R.
Forrest, and M. E. Thompson, Chem. Mater., 11, 3709 (1999). c)
A. Hazell, Acta Crystallogr., Sect. C, 40, 751 (1984).
9
10 W. R. Fawcett, M. Fedurco, K. M. Smith, and H. Xie, J. Electroanal.
Chem., 354, 281 (1993).
11 a) W. A. Lee and T. C. Bruice, Inorg. Chem., 25, 131 (1986). b) A.
Gold, W. Ivey, G. E. Toney, and R. Sangaiah, Inorg. Chem., 23, 2932
(1984). c) A. Harriman and P. Walters, Inorg. Chim. Acta, 83, 151
(1984). d) Y. Takeda, S. Takahara, Y. Kobayashi, H. Misawa, H.
Sakuragi, and K. Tokumaru, Chem. Lett., 1990, 2103. e) Y. Oliver,
D. Kim, and T. G. Spiro, J. Electroanal. Chem., 246, 363 (1988).
5
Pyrrole (4.5 mL, 44.5 mmol) and methyl 4-formylbenzoate (2.01 g,
12.3 mmol) were dissolved in CHCl3 (800 mL). BF3ꢂOEt2 (0.2 mL,
Published on the web (Advance View) March 20, 2004; DOI 10.1246/cl.2004.450