Journal of the American Chemical Society
COMMUNICATION
’ ACKNOWLEDGMENT
The work at Kyoto was supported by Grants-in-Aid (Nos.
22245006 (A) and 20108001 “pi-Space”) for Scientific Research
from MEXT. E.T. and Y.I. acknowledge JSPS Fellowship for
Young Scientists. This work at Seoul was supported by the Star
Faculty and World Class University (R32-2009-000-10217-0),
Programs of the Ministry of Education, Science and Technology
(MEST) of Korea, and an AFSOR/AOARD Grant (FA2386-09-
1-4092) (D.K.).
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Figure 3. MO diagrams of 1a, 2a, and 3a calculated with Gaussian 09
package.11 (All energy levels were calculated at the B3LYP/6-311G(d)
level. And each MO was visualized with cubegen program.)
-0.05 and 0.43 V, and -0.18 and 0.35 V, respectively. Char-
acteristically high oxidation potentials of subbacteriochlorins are
in accord with their easily oxidizable propensity with molecular
oxygen.
Finally, 3a was found to be smoothly and selectively oxidized
to 2a with Ag2O in 86% yield. Therefore, the initial reduction of
subporphyrin to subbacteriochlorin followed by oxidation with
Ag2O constitutes a novel synthetic route to subchlorins that is
superior to our previous direct route of the reduction of 1 with
p-tosylhydrazide.7 Actually, subchlorin 2a was prepared in 74%
from 1a via the two-step route involving the Raney nickel reduction
and the Ag2O oxidation without isolation of unstable 3a.
In summary, subbacteriochlorins were synthesized by the
hydrogenation of subporphyrins with Raney nickel. Despite
double β-hydrogenation, subbacteriochlorins are modestly aro-
matic owing to the 14π-electronic circuit that involves the lone
pair electrons of the nitrogen atom and exhibit characteristic
blue-shifted Soret-like bands, red-shifted Q-like bands, enhanced
fluorescence, and high oxidation potentials. Incorporation of this
interesting porphyrinic chromophore into novel functional mo-
lecular systems is now actively pursued in our laboratories.
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(10) Spectroscopic data of 3d; see Figure S4 of SI. At the present
time, we isolated almost pure 3d but failed its complete purification.
(11) For the full Gaussian citation, see SI.
’ ASSOCIATED CONTENT
S
Supporting Information. Preparation and analytical data
b
for samples, crystallographic data for 3a-OEt (CIF), cyclic
voltammograms, calculated molecular orbitals, and time-resolved
fluorescence decays and nanosecond time-resolved transient
absorption decays. Complete ref 11. This material is available
(12) Crystallographic data for 3a-OEt: 2(C35H30B1N3O1) C2H3N1,
3
M = 1079.91, monoclinic, space group P21 (no. 4), a = 12.251(4) Å, b =
18.924(6) Å, c = 13.226(5) Å, β = 115.098(12)°, V = 2776.9(16) Å3, T =
123 K, Fcalcd = 1.292 gcm-3, Z = 2, R1 = 0.0631 (I > 2σ(I)), Rw = 0.1840
(all data), GOF = 1.016. CCDC-806996.
(13) (a) Keegan, J. D.; Stolzenberg, A. M.; Lu, Y.-C.; Linder, R. E.;
Barth, G.; Moscowitz, A.; Bunnenberg, E.; Djerassi, C. J. Am. Chem. Soc.
1982, 104, 4305. (b) Burkhalter, F. A.; Meister, E. C.; Wild, U. P. J. Phys.
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’ AUTHOR INFORMATION
Corresponding Author
dongho@yonsei.ac.kr; osuka@kuchem.kyoto-u.ac.jp
(14) Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138.
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dx.doi.org/10.1021/ja200669a |J. Am. Chem. Soc. 2011, 133, 4254–4256