Synthesis and characterization of novel fused porphyrinoids based on cyclic carbazole[2]indolones

Article abstract of DOI:10.1021/ol300585v

The carbazole- and indolone-based porphyrinoids 3 and 4 were synthesized by stepwise transition-metal-catalyzed coupling reactions. Palladium metalation of 4 produced 4Pd, which exhibits near-infrared absorption.

Full text of DOI:10.1021/ol300585v

ORGANIC
LETTERS
2012
Vol. 14, No. 8
2122–2125
Synthesis and Characterization of Novel
Fused Porphyrinoids Based on Cyclic
Carbazole[2]indolones
Chihiro Maeda* and Naoki Yoshioka*
Department of Applied Chemistry, Faculty of Science and Technology, Keio University,
Kohoku-ku, Yokohama 223-8522, Japan
cmaeda@applc.keio.ac.jp; yoshioka@applc.keio.ac.jp
Received March 15, 2012
ABSTRACT
The carbazole- and indolone-based porphyrinoids 3 and 4 were synthesized by stepwise transition-metal-catalyzed coupling reactions. Palladium
metalation of 4 produced 4Pd, which exhibits near-infrared absorption.
Porphyrins are a class of tetrapyrrolic ligands that are of
exceptional importance in various biological processes
such as photosynthesis, and which also have applications
in catalysis, anion sensing, and optical devices.1 Porphyr-
ins typically absorb strongly in the visible region of the
spectrum, although the fusion of additional aromatic rings
to the core porphyrin structure results in expanded
π-conjugation and additional absorption within the
near-infrared (NIR) region.2 Fused porphyrins absorbing
in the NIR are anticipated to have applications in photo-
dynamic therapy, since they allow the use of harmless low
energy excitation wavelengths, as well as in the production
of dye-sensitized solar cells.
Carbazole derivatives have often been studied as novel
materials since they are highly emissive, electron conduct-
ing, easily modified, and chemically stable.3 Since carba-
zole is a benzene-fused pyrrole, its incorporation into fused
porphyrins presents interesting possibilities. We recently
reported the synthesis of the carbazole-based porphyrinoid 1,
which exhibits distinct aromaticity and NIR absorption
owing to extended π-conjugation over the macrocycle.4
(1) (a) Smith, K. M. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 1999; Vol. 1,
Chapter 1, p 1. (b) Lindsey, J. S. In The Porphyrin Handbook; Kadish,
K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 1999;
Vol. 1, Chapter 2, p 45. (c) Smith, K. M. In The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego,
1999; Vol. 1, Chapter 3, p 119.
(3) (a) Grazulevicius, J. V.; Strohriegl, P.; Pielichowski, J.; Pieli-
chowski, K. Prog. Polym. Sci. 2003, 28, 1297. (b) Morin, J. F.; Leclere,
M.; Ades, D.; Siove, A. Macromol. Rapid Commun. 2005, 26, 761.
(c) Blouin, N.; Leclerc, M. Acc. Chem. Res. 2008, 41, 1110.
(4) Maeda., C.; Yoneda, T.; Aratani, N; Yoon, M.-C.; Lim, J. M.;
Kim, D.; Yoshioka, N.; Osuka, A. Angew. Chem., Int. Ed. 2011, 50,
5691.
(2) (a) Callot, H. J.; Schaeffer, E.; Cromer, R.; Metz, F. Tetrahedron
1990, 46, 5253. (b) Crossley, M. J.; Burn, P. L.; Chew, S. S.; Cuttance,
F. B.; Newsom, I. A. J. Chem. Soc., Chem. Commun. 1991, 1564.
(c) Richeter, S.; Jeandon, C.; Gisselbrecht, J. P.; Ruppert, R.; Callot,
H. J. J. Am. Chem. Soc. 2002, 124, 6168. (d) Tsuda, A.; Osuka, A. Science
2001, 293, 79. (e) Gill, H. S.; Harmjanz, M.; Santamaria, J.; Finger, I.;
Scott, M. J. Angew. Chem., Int. Ed. 2004, 43, 485. (f) Fox, S.; Boyle,
R. W. Chem. Commun. 2004, 1322. (g) Yamane, O.; Sugiura, K.;
Miyasaka, H.; Nakamura, K.; Fujimoto, T.; Nakamura, K.; Kaneda,
T.; Sakata, Y.; Yamashita, M. Chem. Lett. 2004, 33, 40. (h) Shen, D.-M.;
Liu, C.; Chen, Q.-Y. Chem. Commun. 2005, 4982. (i) Kurotobi, K.; Kim,
K. S.; Noh, S. B.; Kim, D.; Osuka, A. Angew. Chem., Int. Ed. 2006, 45,
3944. (j) Davis, N. K. S.; Pawlicki, M.; Anderson, H. L. Org. Lett. 2008,
10, 3945. (k) Tokuji, S.; Takahashi, Y.; Shinmori, H.; Shinokubo, H.;
Osuka, A. Chem. Commun. 2009, 1028. (l) Davis, N. K. S.; Thompson,
A. L.; Anderson, H. L. J. Am. Chem. Soc. 2011, 133, 30.
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126, 16073. (b) Arnold, L.; Norouzi-Arasi, H.; Wagner, M.; Enkelmann,
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V.; Mullen, K. Chem. Commun. 2011, 970.
(6) Cabazole-containing porphyrins were formed as a consequence of
Bergman cyclization of β,β0-diethynylated porphyrins: (a) Aihara, H.;
Jaquinod, L.; Nurco, D. J.; Smith, K. M. Angew. Chem., Int. Ed. 2001,
40, 3439. (b) Nath, M.; Huffman, J. C.; Zaleski, J. M. J. Am. Chem. Soc.
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r
10.1021/ol300585v
Published on Web 04/10/2012
2012 American Chemical Society

Despite the potential usefulness of such carbazole-based
porphyrinoids, only a few examples have been reported to
date.5,6 Here we report the synthesis of the novel porphyr-
inoids 2, 3, and 4, containing both carbazole and indole
moieties (Figure 1).
X-ray diffraction analysis unambiguously demonstrates
that the structure of 3 contains indolone units (Figure 2).9,10
˚
The mean plane deviation of the macrocycle is 0.083 A,
indicating a highly planar structure. Within the crystal
packing structure, molecules of 3 self-stack at intervals of
˚
3.3 A, as a result of πꢀπ interaction (Figure S11 in the
Supporting Information).
Scheme 1. Synthesis of 2, 3, and 4
Figure 1. Structures of carbazole-based porphyrinoids 1ꢀ4.
Our synthetic methodology is shown in Scheme 1. The
initial intent was to synthesize 2, which is similar in
structure to 1 with regard to the benzo-fused positions,
via the annulation reaction of 9 with Na2S.7 In the first
synthetic step, starting compound 3,6-di-tert-butyl-1,8-
bis(trimethylsilylethynyl)carbazole (5) was coupled with
4-tert-butyl-2,6-diiodoaniline via the Sonogashira reac-
tion. The subsequent InCl3-catalyzed cyclization reaction8
of 6 produced the bis(7-iodoindol-2-yl)-substituted carba-
zole (7). Ethynyl groups were introduced to 7 via the
Sonogashira coupling reaction followed by trimethylsilyl
deprotection with K2CO3, resulting in 8. The Glaser
coupling reaction of 8 gave a red-colored product, which
we expected would be 9. Spectral analyses, however,
established that the product was instead 3, the oxygen
adduct of 9. High-resolution electrospray-ionization (HR-
ESI) mass spectral data show the parent ion peak of 3 at an
m/z value of 696.3607 (calcd for C48H45N3O2 [M þ H]þ =
696.3585). Furthermore, the 13C NMR spectrum of this
product exhibits a carbonyl peak at δ = 194.83 ppm. Slow
diffusion of acetonitrile vapor into a chloroform solution
of 3 resulted in the formation of well-defined crystals.
(7) (a) Lagan, J.; Arora, S. K. J. Org. Chem. 1983, 43, 4317.
€
(b) Kromer, J.; Rios-Carreras, I.; Fuhrmann, G.; Musch, C.; Wunderlin,
M.; Debaerdemaeker, T.; Mena-Osteritz, E.; Bauerle, P. Angew. Chem.,
€
Int. Ed. 2000, 39, 3481. (c) Sumi, N.; Nakanishi, H.; Ueno, S.; Takimiya,
K.; Aso, Y.; Otsubo, T. Bull. Chem. Soc. Jpn. 2001, 74, 979.
(d) O’Connor, M. J.; Haley, M. M. Org. Lett. 2008, 10, 3973.
(8) Sakai, M.; Annaka, K.; Fujita, A.; Sato, A.; Konakara, T. J. Org.
Chem. 2008, 73, 4160.
Additionally, the Stille coupling reaction of 7 with bis-
(tributylstannyl)thiophene afforded the core modified iso-
phrolin 2. The HR-ESI mass spectrum of 2 shows the
parent ion peak at an m/z value of 700.3744 (calcd for
C48H51N3S [M ꢀ H]ꢀ = 700.3731). Interestingly, it was
found that 2 could be converted into the dioxygenated
product 4 through MnO2 oxidation.
The 1H NMR spectrum of 3 exhibits a single set of peaks
with downfield shifts for carbazole protons (9.32 and 8.82
ppm), indicating a diatropic ring current. Such shifts were
not observed for 4 (see the Supporting Information). The
UVꢀvis absorption spectra of 2, 3, and 4 are shown in
Figure 3. While the spectrum of 2 exhibits absorption
primarily in the UV region, the spectra of 3 and 4 are
(9) Crystallographic data for 3: formula C48H45N3O2, Mw = 695.87,
˚
triclinic, space group P1, a = 13.6171(3), b = 19.1937(4), c = 20.4913(6) A,
R = 116.6655(10), β = 102.6618(10), γ = 97.2168(14)°, V =
4512.92(19) A , Z = 4, Fcalcd = 1.024 g cmꢀ3, T = ꢀ180 °C, 4345
3
˚
3
measured reflections, 12895 unique reflections (Rint = 0.0881), R1
=
0.0938 (I > 2σ(I)), wR2 = 0.2198 (all data), GOF = 1.051. The
contribution to the scattering arising from the presence of disordered
solvents in the crystals was removed by using the utility SQUEEZE in
the PLATON software package.14
(10) For examples of indolone-containing porphyrinoids, see: (a)
Boyle, R. W.; Dolphin, D. J. Chem. Soc., Chem. Commun. 1994, 21,
2463. (b) Richeter, S; Jeandon, C.; Gisselbrecht, J.-P.; Graff, R.;
Ruppert, R.; Callot, H. J. Inorg. Chem. 2004, 43, 251. (c) Smith,
K. M.; Vicente, M. G. H. Sci. Synth. 2004, 17, 1081. (d) Jeandon, C.;
Ruppert, R.; Callot, H. J. Chem. Commun. 2004, 1090. (e) Fouchet, J.;
Jeandon, C.; Ruppert, R.; Callot, H. J. Org. Lett. 2005, 7, 5257.
(f) Jeandon, C.; Ruppert, R.; Callot, H. J. J. Org. Chem. 2006, 71, 3111.
(g) Nakamura, S.; Hiroto, S.; Shinokubo, H. Chem. Sci. 2012, 2, 524.
Org. Lett., Vol. 14, No. 8, 2012
2123

Figure 3. UVꢀvis absorption spectra in CH2Cl2 (black line, 2;
red line, 3; blue line, 4).
Figure 2. X-ray crystal structure of 3. tert-Butyl groups and
hydrogen atoms except for the NH proton are omitted for
clarity. The thermal ellipsoids were at a 50% probability level.
considerably broader and extend into the visible region.
The addition of TFA to CH2Cl2 solutions of either 2, 3, or
4 resulted in a significant change in the color of the
solutions as a result of red-shifted absorption (Figure S8
in the Supporting Information).
Cyclic voltammetry of 3 and 4 was performed in order to
estimate the relatively narrow optical HOMOꢀLUMO
gap. The cyclic voltammogram of 3 exhibits one irrever-
sible oxidation wave (0.73 V) and one reduction wave
(ꢀ1.06 V), while that of 4 exhibits two reversible oxidation
waves (0.40, 0.69 V) and reduction waves (ꢀ1.19, ꢀ1.30 V)
(Figure 4). It is worth noting that the two reversible oxida-
tions and reductions seen with 4 are typical for porphyr-
inoids, where the electrochemical HOMOꢀLUMO band
gap (1.59 V) is relatively narrow, likely because of extended
π-conjugation.
Figure 4. Cyclic voltammograms of (a) 3 and (b) 4 (solvent,
CH2Cl2; supporting electrolyte, Bu4NPF6 (0.10 M); counter
electrode, Pt; reference electrode, Ag/Agþ; scan rate, 0.01 V/s).
DFT calculations were performed in order to further
elucidate the structures and electronic properties of these
compounds (Figure 5).11 The calculated HOMOꢀLUMO
gaps of 3 and 4 are narrower than in 2, which is consistent
with the absorption spectroscopy results. Interestingly, the
LUMO and LUMO þ 1 of 3 and 4 exhibit large electronic
coefficients related to the indolone moieties, suggesting
that indolones act as an acceptor, and observed broad
absorption bands in the visible region are due to intramo-
lecular charge transfer. The NICS values at the center
positions of 2 and 4 were calculated to be 2.02, ꢀ0.71,
respectively, while the values at inner positions of 3 are
negative, although the absolute values were not so high.
(11) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian03, revision B.04; Gaussian, Inc.:
Pittsburgh, PA, 2003.
1
These NICS results, along with the results of H NMR
(12) For examples of metal complexes of monothiaporphyrin, see: (a)
_ ꢀ
Latos-Grazynski, L; Lisowski, J.; Olmstead, M. M.; Balch, A. L. Inorg.
Chem. 1989, 28, 3328. (b) Pandian, R. P.; Chandrashekar, T. K. J. Chem.
_ ꢀ
Soc., Dalton Trans. 1993, 119. (c) Latos-Grazynski, L; Lisowski, J.;
Chmielewski, P.; Grzeszczuk, M.; Olmstead, M. M.; Balch, A. L. Inorg.
Chem. 1994, 33, 192. (d) Hung, C.-H.; Ou, C.-K.; Lee, G.-H.; Peng,
S.-M. Inorg. Chem. 2001, 40, 6845. (e) Chuang, C.-H.; Ou, C.-K.; Liu,
S.-T.; Kumar, A.; Ching, W.-M.; Chiang, P.-C.; dela Rosa, M. A. C.;
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Org. Lett., Vol. 14, No. 8, 2012

Scheme 2. Synthesis of 4Pd
Figure 5. Molecular orbital diagrams of (a) 2, (b) 3, and (c) 4
calculated at the B3LYP/6-31G* level.
analysis, indicate that 3 is weakly aromatic, whereas 2 and
4 are essentially nonaromatic. Because the π-conjugation
pathwaysof both4 and 3 can beconsideredas18π-electron
systems, 4 will show aromaticity after proper modifica-
tions.
Figure 6. UVꢀvis/NIR absorption spectra in CH2Cl2 (blue line, 4;
pink line, 4Pd).
is similar to the Pd-complex of a thiaporphyrin (Figure S10 in
the Supporting Information).12c
The complexation reaction of 4 with palladium was
carried out, in order to hinder potential rotation of the
thiophene spacer unit.12 Treatment of 4 with Pd(OAc)2
and subsequent brine addition afforded the Pd com-
plex 4Pd (Scheme 2).13 The HR-ESI mass spectrum
of the product shows a parent ion peak at an m/z value
In summary, we have synthesized the novel benzo-
fused porphyrinoids 3 and 4, containing both carbazole
and indolone moieties, through metal-mediated synthe-
sis. Furthermore, palladium complexation of 4 afforded
4Pd, which exhibits weak aromaticity and NIR absorp-
tion. Further exploration of novel porphyrinoids and
their metal complexes are currently underway in our
laboratory.
of 834.2390 (calcd for C48H46N3O2SPd [M ꢀ Cl]ꢀ
=
834.2356). The UVꢀvis/NIR absorption spectrum of 4Pd
exhibits a red-shift into the NIR region (Figure 6). The 1H
NMR spectrum of 4Pd exhibits downfield shifts for the
peripheral protons as compared to the spectrum of 4,
indicating a diatropic ring current for 4Pd (see the Supporting
Information). Both the red-shifted absorption and the ring
current effect observed for 4Pd are considered to be due to an
increase in structural rigidity of the molecule as a result of the
palladium metalation. The cyclic voltammogram of 4Pd
exhibits two reduction waves at ꢀ0.92 and ꢀ1.19 V, which
Acknowledgment. This work was supported by Grants-
in-Aid for Young Scientists (No. 23750231 (B)) from
MEXT, Japan. WethankProf. A. Osuka(KyotoUniversity)
for X-ray diffraction analyses and HR-ESI-MS measure-
ments.
Supporting Information Available. Experimental pro-
cedures, compound data, and crystallographic data for 3
in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
(13) Because the 1H NMR spectrum of 4Pd is different from that of
the crude Pd-complex before brine addition, we assigned the coordina-
tion of chloride to Pd center.
(14) (a) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht, The Netherlands, 2005. (b) Sluis, P.; van der; Spek, A. L. Acta
Crystallogr., Sect. A 1990, 46, 194.
The authors declare no competing financial interest.
Org. Lett., Vol. 14, No. 8, 2012
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