Facile synthesis of meso-arylamino- and alkylaminosubporphyrins

Article abstract of DOI:10.1002/chem.201201256

Newcomers: meso-Arylamino- and meso-alkylaminosubporphyrins have been synthesized by the Pd-catalyzed aminations of meso-bromosubporphyrin 1 as the first example of subporphyrins containing heteroatom substituents at the meso-position. The X-ray structura

Full text of DOI:10.1002/chem.201201256

COMMUNICATION
DOI: 10.1002/chem.201201256
Facile Synthesis of meso-Arylamino- and Alkylaminosubporphyrins
Masaaki Kitano, Shin-ya Hayashi, Takayuki Tanaka, Naoki Aratani, and
[
a]
Atsuhiro Osuka*
Subporphyrins are relatively newcomers, first synthesized
[1]
in 2006, but have been shown to be very promising func-
tional molecules in light of their attractive attributes, such as
1
4p-electronic aromaticity, bright fluorescence, and tunable
[2,3]
optical properties.
By virtue of almost free rotation,
meso-aryl substituents provide significant influences on the
electronic nature of subporphyrins as seen in meso-(oligo-
1
,4-phenyleneethynylene)- and meso-(4-aminophenyl)-sub-
[4]
stituted subporphyrins. During the last five years, new sub-
porphyrins have been continuously developed: this includes
meso-alkyl-substituted subporphyrins, meso-oxocyclohexa-
dienylidene-substituted subporphyrins, subchlorins, sub-
bacteriochlorins, and subporphyrin borenium cations.
[5]
[6]
[7]
[8]
[9]
Despite these progresses, the repertoire of subporphyrins
still remains very poor compared with porphyrins, and thus
the exploration of new subporphyrins is desirable for their
further development. In particular, there is no example of
subporphyrin containing heteroatom substituents, except
halogen atom at meso-position.
Scheme 1. Synthesis of meso-aminosubporphyrins 3–6.
meso-Aminoporphyrins occupy a unique position in por-
phyrin chemistry in terms of perturbed electronic natures,
stable radical cations, and effective chromophores in dye-
stituent. In addition, we have revealed the unique two-way
structural distortions of the meso-anilino groups that depend
upon their electronic properties and the perturbed optical
properties of meso-aminated subporphyrins.
[10]
sensitized solar cells. These molecules have been prepared
by transition-metal-catalyzed amination reactions of meso-
[11]
halogenated porphyrins. Based on facts that electron-do-
nating amino groups are often quite effective to perturb the
Following the meso-aminations of porphyrins developed
[
11a,c]
by Zhang and co-workers,
(3.6 equiv) in THF was heated at reflux for 12 h in the pres-
ence of 5 mol% of [Pd(OAc) ] and 7.6 mol% of bis(2-di-
a solution of 2 and aniline
[4b,12]
optical properties of subporphyrins,
meso-aminosubpor-
phyrins would display largely perturbed optical and electro-
chemical properties. Quite recently, we have explored meso-
bromosubporphyrin 2, with N-bromosuccinimide (NBS) bro-
ACHTUNGTRENNUNG
2
phenylphosphinophenyl)ether (DPEphos), and Cs CO3
2
(1.4 equiv) under inert atmosphere. After usual work up,
meso-anilinosubporphyrin 3 was isolated in 72% yield as
red solids. The high-resolution electrospray ionization time-
of-flight (HR ESI TOF) mass spectrum of 3 revealed an in-
tense borenium cation peak at m/z 485.1944 (calcd for
[12]
mination of meso-free subporphyrin 1 (Scheme 1).
Be-
cause this bromide is a straightforward precursor for meso-
aminosubporphyrins, we set up a study to find appropriate
synthetic conditions for the meso-aminations of subporphyr-
ins. Herein, we report the synthesis of meso-arylamino- and
meso-alkylamino-substituted subporphyrins as the first ex-
ample of subporphyrins containing meso-heteroatom sub-
+
1
C H B N 485.1938 [3ÀOMe] ). The H NMR spectrum
3
3
22
1
4
indicated a set of doublets due to the pyrrolic b-protons ad-
jacent to the meso-anilino substituent at d=7.90 and
7
.78 ppm (J=4.4 Hz), which are upfield shifted from those
of 2 at d=8.22 and 8.09 ppm (J=4.6 Hz). The structure of 3
[
a] M. Kitano, S. Hayashi, Dr. T. Tanaka, Dr. N. Aratani,
Prof. Dr. A. Osuka
Department of Chemistry
Graduate School of Science, Kyoto University
Sakyo-ku, Kyoto 606-8502 (Japan)
Fax : (+81)75-753-3970
was unambiguously determined by X-ray single-crystal dif-
[13]
fraction analysis (Figure 1). The bowl depth was calculat-
ed to be 1.355 ꢀ, and CmesoÀN and NÀC bond lengths are
ipso
1
.393 and 1.427 ꢀ, respectively. The C ÀN bond length is
meso
[14]
distinctly shorter than usual CÀN bonds (1.402–1.417 ꢀ)
E-mail: osuka@kuchem.kyoto-u.ac.jp
[11f]
and that of
a meso-morpholinoporphyrin (1.434 ꢀ),
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201256.
hence suggesting the contribution of resonance structure A,
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Figure 2. X-ray crystal structures of compounds a) 4, b) 5, and c) 6. Sol-
vent molecules are omitted for clarity; ellipsoids are set to 50% probabil-
ity.
Figure 1. a) X-ray crystal structure of 3 and b) packing structure of 3. El-
lipsoids are set to 50% probability.
in which the anilino group serves as an electron-donating
substituent to the subporphyrin core (Figure 3). Interesting-
ly, in the solid state, the meso-amino proton is bonded to
the axial oxygen atom of another subporphyrin core to form
one-dimensional chain by hydrogen-bonding interaction
with an NÀO separation of 2.89 ꢀ. Under similar conditions,
(
4-dimethylaminophenyl)amino- and (4-nitrophenyl)amino-
substituted subporphyrins 4 and 5 were prepared in 64 and
8% yield, respectively. The spectroscopic data of 4 and 5
7
Figure 3. Resonance structures of meso-aminosubporphyrins.
are fully consistent with their structures (see the Supporting
Information), and their final structural proof has come from
the X-ray structural analysis (Figure 2). The bowl depths are
[
15]
(Scheme 1). The spectroscopic data of 6 support its struc-
tures (see the Supporting Information), and its crystal struc-
ture was again determined by X-ray analysis (Figure 2).
[13]
1
.401 and 1.363 ꢀ for 4 and 5, respectively, and the hydro-
gen-bond networks are similarly observed for 4 and 5. Inter-
estingly, CmesoÀN and NÀC
bond lengths are 1.374 and
The bowl depth was calculated to be 1.332 ꢀ, and CmesoÀN
and NÀC bond lengths are 1.414 and 1.438 ꢀ, respectively.
sp3
ipso
1.416 ꢀ for 4, and 1.405 and 1.379 ꢀ for 5, respectively. In
These data suggest smaller structural distortions in 6 as com-
pared with 3–5.
comparison with 3, both CmesoÀN and NÀC
bond lengths
ipso
are shortened in 4, whereas CmesoÀN bond length is longer
The UV/Vis absorption spectra of 3–6 are shown in Fig-
ure 4a along with that of meso-triphenylsubporphyrin 7 as
a reference that exhibits a Soret-like band at l=373 nm and
Q-band-like bands at l=461 and 484 nm. Compared with
these, the Soret-like bands of 3–6 are redshifted, appearing
at l=389 nm for 3, 365 and 380 nm for 4, 381 nm for 5, and
380 nm for 6, respectively, and the Q-band-like bands are
broadened and redshifted, appearing at l=524 nm for 3,
528 nm for 4, 512 nm for 5, and 510 nm for 6, respectively. It
is likely that the absorption spectra are more perturbed by
and NÀC bond length is shorter in 5. The former feature
ipso
indicates larger contribution of resonance structure A in 4,
whereas the latter suggests the importance of the opposite
resonance contribution B in 5, in which the lone-pair elec-
trons of the anilino nitrogen atom are delocalized toward
the nitro group (Figure 3). meso-Morpholinosubporphyrin 6,
an alkylaminosubporphyrin, was prepared in 66% yield with
Pd-PEPPSI-IPent (PEPPSI=pyridine-enhanced precatalyst
preparation stabilization and initiation) as
a catalyst
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Facile Synthesis of meso-Arylamino- and Alkylaminosubporphyrins
COMMUNICATION
Bu NPF (0.1m) as a supporting electrolyte (see the Sup-
4
6
porting Information). The first one-electron oxidation and
reduction potentials of 3–6 were observed at 0.22, À0.18,
0
.42, and 0.11 V, and at À2.05, À2.14, À1.87, and À2.09 V,
respectively, which are all considerably shifted to the nega-
tive side compared with the parent subporphyrin 7 that ex-
hibits the first oxidation potential at 0.71 V and reduction
potential at À1.97 V. On the basis of these data, the elec-
trochemical HOMO–LUMO gaps of 3–6 have been calculat-
ed to be 2.27, 1.96, 2.29, and 2.20 eV, respectively.
[4a]
We have previously reported that meso-triaryl-substituted
subporphyrins possess quite porphyrin-like four orbitals,
HOMOÀ1, HOMO, LUMO, and LUMO+1, as typically
shown for 7 (Figure 5). The HOMOÀ1 and HOMO of 7 re-
semble to the a (HOMOÀ1) and a (HOMO) orbitals of
1
u
2u
Figure 4. a) UV/Vis absorption and b) fluorescence spectra of subpor-
phyrins 3–7 in CH Cl .
2 2
more electron-rich meso-amino substituents. As an extreme
case, the Soret-like band of 4 is split to l=365 and 380 nm.
Such split Soret-like bands were observed for subporphyrins
containing strongly electron-donating meso-substituents,
[4b]
such as 4-dibenzylaminophenyl group
ACHTUNGTRENNUNGa minophenyl)ethynyl group.
and (4-dimethyl-
[12]
As shown in Figure 4b, the fluorescence spectra of 3 and
are enhanced and redshifted compared with that of 7,
6
whereas the fluorescence spectra of 4 and 5 are very weak.
More precise measurements of the fluorescence by using
[16]
a sphere-type digital photon counting instrument recorded
the fluorescence quantum yields to be 0.43, 0.001, 0.001, and
0.39 for 3–6, respectively, in accordance with the steady-
state fluorescence measurements. The observed efficient
fluorescence quenching of 4 and 5 may be ascribed to the in-
tramolecular electron transfer, but the final conclusion must
wait for the detailed photophysical studies based on laser-
based ultrafast measurements.
Figure 5. MO diagrams of compounds 3, 4, 5, and 7 calculated with Gaus-
The electrochemical potentials of 3–6 were measured by
cyclic voltammetry (CV) experiments in CH Cl containing
[16]
sian 09 package.
(All energy levels were calculated at the B3LYP/6-
311G(d) level, and each MO was visualized with cubegen program).
2
2
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A. Osuka et al.
[
17]
meso-tetraphenylporphyrin (TPP), as HOMOÀ1 of 7 and
a1u of TPP have nodes at meso-positions and HOMO of 7
da, N. Kobayashi, J. Am. Chem. Soc. 2007, 129, 8271; c) T. Xu, R.
Lu, X. Liu, P. Chen, X. Qiu, Y. Zhao, Eur. J. Org. Chem. 2008, 2008,
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47, 4840; b) Y. Inokuma, S. Easwaramoorthi, Z. S. Yoon, D. Kim, A.
Osuka, J. Am. Chem. Soc. 2008, 130, 12234.
[2d]
and a2u of TPP have large coefficients at meso-positions.
Similarly, the LUMO and LUMO+1 of 7 resemble to eg
[
(
LUMO and LUMO+1) orbitals of TPP. In contrast, meso-
aminosubporphyrins 3–6 exhibit rather perturbed molecular
orbital (MO) diagrams as shown in Figure 5 (for the MO di-
agram of 6, see the Supporting Information). HOMOÀ1 of
[
5] S. Hayashi, Y. Inokuma, S. Easwaramoorthi, K. S. Kim, D. Kim, A.
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4
9, 321.
3
–6 are relatively unperturbed by the meso-amino substitu-
[
6] S. Hayashi, J. Sung, Y. M. Sung, Y. Inokuma, D. Kim, A. Osuka,
ents, whereas HOMO of 3, 4, and 6 are distinctly destabi-
lized due to the electron-donating meso-amino substituents,
which leads to redshifted and intensified Q-band-like bands
through more effective break down of the HOMO degener-
acy. This effect is the largest for 4. In addition, in the case of
Angew. Chem. 2011, 123, 3311; Angew. Chem. Int. Ed. 2011, 50,
3
253.
[
[
7] E. Tsurumaki, S. Saito, K. S. Kim, J. M. Lim, Y. Inokuma, D. Kim,
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4
, even HOMOÀ1 suffers perturbations from the meso-
[9] E. Tsurumaki, S. Hayashi, F. S. Tham, C. A. Reed, A. Osuka, J. Am.
Chem. Soc. 2011, 133, 11956.
amino substituent, which is not seen for either 3 or 6. On
the other hand, the MO diagram of 5 suggested that 4-nitro-
anilino group serves as an electron-withdrawing substituent
towards subporphyrin, seemingly consistent with possible
contribution of resonance structure B. HOMO–LUMO gaps
for 3–6 have been estimated from the absorption and fluo-
rescence spectra to be 2.28, 2.30, 2.32, and 2.29 eV, respec-
[
10] a) R. Sakamoto, T. Sasaki, N. Honda, T. Yamamura, Chem.
Commun. 2009, 5156; b) R. Sakamoto, M. Nishikawa, T. Yamamura,
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1
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2
[18]
tively.
Chandiran, M. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Za-
keeruddin, M. Grꢂtzel, Science 2011, 334, 629.
In summary, meso-arylamino- and meso-alkylamino- sub-
stituted subporphyrins have been synthesized by the Pd-cat-
alyzed aminations of meso-bromosubporphyrin 2 as the first
example of subporphyrins containing heteroatom-substitu-
ents at meso-position. The X-ray structural analyses have re-
vealed the significant structural distortions of meso-amino-
subporphyrins due to the effective electronic interactions
between the meso-amino substituents and subporphyrin
core, which were clearly observed from the absorption and
fluorescence spectra. By using the same synthetic strategy,
we are now investigating new subporphyrins containing vari-
ous meso-heteroatom substituents, which will be soon re-
ported elsewhere.
[
11] a) Y. Chen, X. P. Zhang, J. Org. Chem. 2003, 68, 4432; b) T. Takana-
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2
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[
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5
1, 5593.
13] CCDC-875385 (3), CCDC-875384 (4), CCDC-875383 (5), CCDC-
75382 (6) contain the supplementary crystallographic data for this
8
paper. These data can be obtained free of charge from The Cam-
Acknowledgements
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_-
À1
request/cif.Crystal data for 3: C34
H
25
B
1
N
4
O
1
; M
w
=516.39 gmol ; tri-
This work was supported by the Global COE Program “International
Center for Integrated Research and Advanced Education in Materials
Science” (No. B-024) and Grants-in-Aid (Nos. 22245006 (A) and
0108001 “pi-Space”) for Scientific Research from MEXT. T.T. thanks
the JSPS Research Fellowship for Young Scientists.
¯
clinic; space group P1; a=10.4856(3), b=14.5752(5), c=
1
2
2
8.2283(7) ꢀ; a=78.831(2), b=74.352(2), g=75.7766(19)8; V=
3
À3
1
576.00(15) ꢀ ; T=93 K; 1calcd =1.332 gcm ; Z=4; R =0.0801 [I>
2
s(I)]; R =0.1522 (all data); GOF=1.007. Crystal data for 4:
w
À1
C
36
H
30
B
1
N
5
O
1
·
A
H
N
T
E
N
N
w
M =587.47 gmol ; monoclinic; space
group P2
8.147(3)8; V=2953.9(3) ꢀ ; T=93 K; 1calcd =1.321 gcm ; Z=4;
1
3
À3
9
Keywords: amination
porphyrinoids · subporphyrins
·
cross-coupling
·
palladium
·
R
1
=0.0604 [I>2s(I)]; R
w
=0.1736 (all data); GOF=1.084. Crystal
À1
data for 5: C34
H
24
B
1
N
5
O
3
·0.5(chloroform); M
¯
w
=620.57 gmol ; tri-
clinic; space group P1; a=7.1645(4), b=10.6692(6), c=
9.6188(12) ꢀ; a=83.228(3), b=84.741(3), g=76.290(3)8; V=
1
3
À3
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1443.60(14) ꢀ ; T=93 K; 1calcd =1.428 gcm ; Z=2; R
2s(I)]; R =0.2917 (all data); GOF=1.031. Crystal data for 6:
C
space group P1; a=11.0193(5), b=12.2054(5), c=13.0442(5) ꢀ; a=
64.579(2), b=68.982(2), g=74.190(2)8; V=1464.41(11) ꢀ ; T=
1
=0.0981 [I>
w
À1
[
32
H
27
B
1
N
4
O
2
·0.73(dichloromethane); M
¯
w
=572.02 gmol ; triclinic;
3
2
2
834; c) A. Osuka, E. Tsurumaki, T. Tanaka, Bull. Chem. Soc. Jpn.
011, 84, 679; d) Y. Inokuma, Z. S. Yoon, D. Kim, A. Osuka, J. Am.
À3
93 K; 1calcd =1.297 gcm ; Z=2, R
(all data); GOF=1.051.
1 w
=0.0905 [I>2s(I)]; R =0.2376
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[
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7
72; Angew. Chem. Int. Ed. 2007, 46, 758; b) Y. Takeuchi, A. Matsu-
&
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Facile Synthesis of meso-Arylamino- and Alkylaminosubporphyrins
COMMUNICATION
[
15] a) K. H. Hoi, S. C¸ alimsiz, R. D. J. Froese, A. C. Hopkinson, M. G.
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the very weak and broad fluorescence around l=550 nm (see the
Supporting Information). Judging from the observed large Stokes
shifts commonly observed for meso-aminated subporphyrins, the
1
8, 145; c) C. Valente, S. C¸ alimsiz, K. H. Hoi, D. Mallik, M. Sayah,
M. G. Organ, Angew. Chem. 2012, 124, 3370; Angew. Chem. Int. Ed.
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real S
1
-state may be more delocalized and, hence lying at much
lower energy level, but completely nonfluorescent.
2
[
[
[
16] See the Supporting Information.
17] M. Gouterman, J. Mol. Spectrosc. 1961, 6, 138.
18] The discrepancy between the estimated HOMO–LUMO gaps for 4
may arise from the inaccurate estimation of the S-state energy from
Received: April 13, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
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A. Osuka et al.
Newcomers: meso-Arylamino- and
Cross-Coupling
meso-alkylaminosubporphyrins have
been synthesized by the Pd-catalyzed
aminations of meso-bromosubpor-
phyrin 1 as the first example of subpor-
phyrins containing heteroatom sub-
stituents at meso-position. The X-ray
structural analyses have revealed sig-
nificant structural distortions of meso-
aminosubporphyrins 2 due to the effec-
tive electronic interaction (see
M. Kitano, S. Hayashi, T. Tanaka,
N. Aratani, A. Osuka* . . . . . . &&&& — &&&&
Facile Synthesis of meso-Arylamino-
and Alkylaminosubporphyrins
scheme).
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Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!