A bis-Au(III) [28]hexaphyrin triphenylphosphine adduct

Article abstract of DOI:10.1142/S1088424616500097

Triphenylphosphine was added regioselectively at the C(3) position of bis-Au(III) complex of [26]hexaphyrin 5 in the presence of trifluoroacetic acid to produce [28]hexaphyrin triphenylphosphine adduct 6 in 62% yield, which has been fully characterized by NMR, UV-vis/NIR absorption, and MS spectroscopies, and X-ray diffraction analysis. The rigid planar structure forces 6 to take Hückel antiaromaticity, which has been supported by its ¹H NMR spectrum. Curiously, the detailed structural analysis elucidated that the triphenylphosphine moiety exists as a phosphorane form in the solid state. A plausible mechanism via a double protonated 5 is proposed, which can explain the observed regioselectivity.

Full text of DOI:10.1142/S1088424616500097

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2016; 20: 1–5
DOI: 10.1142/S1088424616500097
Published at http://www.worldscinet.com/jpp/
A Bis-Au(III) [28]hexaphyrin triphenylphosphine adduct
Koji Naoda and Atsuhiro Osuka*◊
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
Dedicated to Professor Tomas Torres on the occasion of his 65th birthday
Received 20 November 2015
Accepted 3 December 2015
ABSTRACT: Triphenylphosphine was added regioselectively at the C(3) position of bis-Au(III)
complex of [26]hexaphyrin 5 in the presence of trifluoroacetic acid to produce [28]hexaphyrin
triphenylphosphine adduct 6 in 62% yield, which has been fully characterized by NMR, UV-vis/NIR
absorption, and MS spectroscopies, and X-ray diffraction analysis. The rigid planar structure forces
1
6 to take Hückel antiaromaticity, which has been supported by its H NMR spectrum. Curiously, the
detailed structural analysis elucidated that the triphenylphosphine moiety exists as a phosphorane form
in the solid state. A plausible mechanism via a double protonated 5 is proposed, which can explain the
observed regioselectivity.
KEYWORDS: expanded porphyrin, hexaphyrin, triphenylphosphine, phosphonium ylide, phosphorane.
conformationalchangesfromplanarHückelformtotwisted
Möbius-strip like form. Characteristically, triphenyl-
phosphine moiety dominantly exists as a phosphorane
form 2b in free base 2 while a phosphonium ylide form
4a is more important in palladium complex 4. Inspired by
these results, we herein tried the reaction of bis-Au(III)
[26]hexaphyrin 5 [13] with triphenylphosphine. Addition
INTRODUCTION
In the last two decades, considerable efforts have been
devoted to the development of expanded porphyrins that
consist of more than five pyrroles, which are ring extended
porphyrin analogs, since they display intriguing optical,
electronic, and structural properties that significantly
differ from those of porphyrin [1]. In particular, expanded
of triphenylphosphine proceeded regioselectively to
porphyrins have been demonstrated to realize Hückel and
furnish bis-Au(III) [28]hexaphyrin triphenylphosphine
Möbius(anti)aromaticity[2,3],anionreceptors[4],various
adduct 6 in a good yield. The structural rigidity of 5 did
metal complexes [5], near-infrared (NIR) absorption dyes
not allow large conformational change observed for the
[6], and stable organic radicals [7]. In addition to these
free base [26]hexaphyrin and its Pd complex, and the
unique properties, the reactivity of expanded porphyrin
adduct 6 displayed Hückel antiaromaticity. In addition,
has been studied and discovered sometimes in an
the triphenylphosphine moiety was found to exist as a
unprecedented manner, such as skeleton rearrangement
phosphorane contribution in the solid state.
[8], cell division like splitting reaction [9], pericyclic
reaction [10], electrophilicity [11], and nucleophilicity
[12]. Previously, we have reported that nucleophilic
addition of triphenylphosphine to [26]hexaphyrin free
base 1 and palladium complex 3 gave the corresponding
[28]hexaphyrin triphenylphosphine adducts 2 and 4,
respectively [11] (Scheme 1). These reactions caused
RESULTS AND DISCUSSION
The reaction of bis-Au(III) complex of [26]hexaphyrin
5 with 1 equivalent of triphenylphosphine in the presence
of trifluoroacetic acid (TFA) gave [28]hexaphyrin
triphenylphosphine adduct 6 in 62% yield along with
formation of [28]hexaphyrin 7 in 29% yield (Scheme 2).
The high-resolution electrospray-ionization time-of-
flight (HR-ESI-TOF) mass spectrum of 6 indicated the
parent ion peak at m/z = 2109.0477 [M – H]- (calcd. for
◊ SPP full member in good standing
*Correspondence to: Atsuhiro Osuka, email: osuka@kuchem.
kyoto-u.ac.jp, tel: +81 075-753-4008, fax: +81 075-753-3970
Copyright © 2016 World Scientific Publishing Company

2
K. NAODA AND A. OSUKA
Ar
Ar
Ar
Ar
N
N
N
N
HN
HN
N
NH
PPh3, TFA
CH2Cl2
Ar
Ar
Ar
Ar
N
N
Ar
Ar
Ar
Ar
NH
NH
HN
N
HN
HN
PPh3
PPh3
N
N
Ar
Ar
Ar
Ar
Ar
Ar
1
2a
(ylide form)
2b
(phosphorane form)
(26π)
Ar
Ar
PPh3
PPh3
Ar
Ar
H
N
N
N
N
N
N
N
N
N
PPh3
Ar
Ar
Pd
Pd
Ar
Ar
N
H
N
Ar
Ar
Pd
Ar
Ar
Ar
H
CH2Cl2
N
HN
N
N
N
N
N
Ar
Ar
Ar
Ar
H
H
Ar
3
4a
4b
(26π)
(ylide form)
(phosphorane form)
Scheme 1. Synthesis of [28]hexaphyrin triphenylphosphine adducts 2 and 4 and possible resonance between phosphonium ylide a
and phosphorane b in 2 and 4. Ar = pentafluorophenyl. The bold line represents a conjugated circuit
Ar
Ar
Ar
Ar
Ar
Ar
H
N
H
N
N
PPh3 (1 equiv.)
TFA
N
N
N
N
N
N
N
N
N
Ar
Ar
PPh3
Ar
PPh3
Ar
Au
Au
Ar
Au
Au
Ar
Ar
Au
Au
Ar
CH2Cl2, rt, 30 min
N
N
N
C(3)
N
N
N
C(2)
Ar
Ar
Ar
Ar
5
6a
6b
+
(26π)
(ylide form)
(phosphorane form)
Ar
Ar
H
N
N
N
N
Reduction
Oxidation
Ar
Ar
Au
Au
N
N
H
7
Ar
Ar
(28π)
Scheme 2. Synthesis of a bis-Au(III) [28]hexaphyrin triphenylphosphine adduct 6 and possible resonance between phosphonium
ylide 6a and phosphorane 6b. Ar = pentafluorophenyl. The bold line represents a conjugated circuit
2109.0490, C84H22N6F30PAu2). It is thought that there
are two kinds of triphenylphosphine adducts since there
are two reactive positions C(2) and C(3) in 5. However,
only one isomer was obtained, indicating the reaction
proceeded regioselectively.
The structure of 6 has been unambiguously determined
by X-ray diffraction analysis, which revealed the addition
of triphenylphosphine reacted at the C(3) position
(Fig. 1). The bond length of P–C(3) is 1.77 Å (1.77 Å),
which is shorter than a typical bond length of P–C
(1.82 Å) observed in b-diphenylphosphine-substituted
porphyrins [14]. The angle of C–N–C in the pyrrole C
is 110.0° (109.0°), while that in the pyrrole F is 103.9°
(104.3°), implying that the pyrrole C is amino-type
pyrrole and the pyrrole F is imino-type pyrrole. While
ylide form 6a and phosphorane form 6b are resonance
hybrid contributors of 6, these observations indicated that
6b is more important than 6a in the solid state.
1
The H NMR spectrum of 6 revealed that signals
due to the outer b protons are observed in the range of
2.62–3.43 ppm and the outer NH proton is observed
at 2.45 ppm. These data indicate a strong paratropic
ring current, and hence antiaromaticity for 6, similarly
to [28]hexaphyrin 7. The nuclear independent
chemical shift (NICS) values of 6 at the center of
gravity exhibited positive values (NICS(+1) = +19.4
ppm and NICS(-1) = +21.7 ppm), also suggesting the
antiaromaticity [15].
In the absorption spectrum of 6, an intense absorption
band was observed at 572 nm and weak absorption
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 2–5

A BIS-AU(III) [28]HEXAPHYRIN TRIPHENYLPHOSPHINE ADDUCT
3
Fig. 1. X-ray crystal structure of 6. (a) Top view. (b) Side view. The thermal ellipsoids are scaled to 50% probability level. Solvent
molecules and hydrogen atoms except for NH are omitted for clarity. One of two independent structures in the lattice is shown
EXPERIMENTAL
General
All reagents were of the commercial reagent grade
and were used without further purification except
where noted. Silica gel column chromatography was
performed on Wakogel C-300. UV-vis/NIR absorption
spectra were recorded on a Shimadzu UV-3600PC
1
spectrometer. H, 19F, and 31P NMR spectra were
recorded on
a
JEOL ECA-600 spectrometer
Fig. 2. UV-vis/NIR absorption spectrum of 6 in CH2Cl2
(operating as 600.17 MHz for 1H, 564.73 MHz for 19F,
and 242.95 MHz for 31P) using the residual solvent
1
as the internal reference for H (d = 7.26 ppm in
bands at 665 and 743 nm. The broad and quite weak
absorption band that reached around 2000 nm was also
detected because of the transition to the dark state,
which was characteristic of antiaromatic porphyrinoids
[16] (Fig. 2).
CDCl3), hexafluorobenzene as the external reference for
19F (d = -162.9 ppm), and 85% phosphoric acid as the
external reference for 31P (d = 0.00 ppm). NMR signals
were assigned from the H–1H COSY spectrum, and
1
the comparison with the spectra in the presence of D2O
(signals assigned for NH protons disappear in the presence
of D2O). High-resolution electrospray-ionization time-
of-flight mass spectroscopy (HR-ESI-TOF-MS) was
recorded on a BRUKER micrOTOF model using negative
mode for acetonitrile solutions of samples.
A plausible reaction mechanism was shown in
Scheme 3. Addition of triphenylphosphine to
5
proceeded smoothly in the presence of TFA but did not
occur in the absence of TFA, indicating that protonated
[26]hexaphyrin would be a key intermediate. Thus,
we took doubly protonated species 5H as a reaction
intermediate and calculated its molecular orbitals by
the density functional theory (DFT) method. Curiously,
the lowest unoccupied molecular orbital (LUMO) of
5H shown in Scheme 3b nicely explains the observed
highly regioselective addition of triphenylphosphine at
the C(3) position. Rearomatization of 5P and subsequent
deprotonation of 6H furnished the final adduct 6. The
doubly protonated hexaphyrin could be easily reduced
to afford 7, and thus it is conceivable that the reduction
of the protonated [26]hexaphyrin 5H competes with the
nucleophilic attack of triphenylphosphine.
Crystal data
X-ray crystallographic data were collected on a Rigaku
XtaLAB P200 apparatus at -180°C using graphite-
monochromated CuKa radiation (l = 1.54187 Å).
The structures were solved by direct method SIR-97 and
refined by SHELXL-97 program.
6. 2(C84H23N6F30Au2P)·3.5(C8H18)·1.69(C7H8), Mw
=
4776.88, monoclinic, space group C2/c (no. 15), a =
41.025(7) Å, b = 27.969(3) Å, c = 36.794(8) Å, b =
120.951(5)°, V = 36207(11) Å3, T = 93 K, rcalcd = 1.753
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 3–5

4
K. NAODA AND A. OSUKA
Ar
(b)
Ar
(a)
Ar
H
N
Ar
N
Protonation
+ 2 H+
N
N
N
N
N
N
N
Au
Au
Ar
Ar
Ar
Ar
Au
Au
N
C(3)
C(3)
N
H
N
C(2)
Ar
Ar
Ar
Ar
C(2)
5H
(26π)
5
5H
(26π)
(26π)
PPh Addition
×
3
Reduction
+ 2 e–
PPh3 Addition
Ar
Ar
Ar
Ar
H
N
H
N
Ar
Ar
H
N
Deprotonation
Rearomatization
PPh3 Addition
– 1 H+
– 1 H+
N
N
N
N
N
N
N
N
N
N
Au
Ar
Au
Au
Au
Ar
PPh3
Ar
Ar
Ar
Ar
6
Ar
Au
Au
Ar
×
(28π)
N
N
PPh3
H
N
H
N
H
N
H
Ar
Ar
Ar
Ar
6H
(28π)
7
5P
(28π)
Scheme 3. (a) A plausible mechanism of the nucleophilic addition of triphenylphosphine to 6. (b) LUMO of 5H. Ar =
pentafluorophenyl. The bold line represents a conjugated circuit
g.cm-3, Z = 8, R1 = 0.0635 (I > 2s (I)), Rw = 0.1780 (all
data), GOF = 1.055.
(m, 2F; para-C6F5), -158.7 (t, J = 22.0 Hz, 2F; meta-
C6F5), -159.4 (t, J = 17.5 Hz, 2F; meta-C6F5), -159.9 (t,
J = 22.0 Hz, 2F; meta-C6F5), -160.4 (m, 2F; meta-C6F5),
-164.3 (t, J = 22.0 Hz, 2F; meta-C6F5), and -164.5 (t, J =
21.5 Hz, 2F; meta-C6F5). 31P NMR (242.95 MHz; CDCl3;
85% phosphoric acid): dP, ppm 14.0 (s, 1P; decoupled with
13C). MS (ESI-TOF-MS): m/z 2109.0477 [M–H]- (calcd.
for 2109.0490. C84H23N6F30PAu2). UV-vis (CH2Cl2): l,
nm (e) 354 (26100), 572 (134400), 665 (13700), 743
(9100), and 1405 (1200).
Synthesis
Bis-Au(III) [26]hexaphyrin(1.1.1.1.1.1) 5. The titled
compound was synthesized according to the literature
[13c].
Bis-Au(III) [28]hexaphyrin(1.1.1.1.1.1) triphenyl-
phosphine adduct 6. Bis-Au(III) [26]hexaphyrin 5
(20 mg, 11 mmol) and PPh3 (2.5 mg, 1 equiv.) were
dissolvedinCH2Cl2 (1.0mL)underinertatmosphere. One
drop of TFA was added to the solution and the color of the
solution immediately changed from green to purple.After
stirred for 30 min, the resulting mixture was quenched by
addition of aqueous NaHCO3 solution. Then, the mixture
was washed with water, extracted with CH2Cl2, and dried
over Na2SO4. The residual solvent was removed under
reduced pressure. Silica gel column chromatography
using CH2Cl2/AcOEt (20/1) as an eluent afforded bis-
Au(III) [28]hexaphyrin 7 (5.8 mg, 29%) [13a] as the first
red fraction and the titled compound 6 (14 mg, 62%) as a
purple fraction. 1H NMR (600.17 MHz; CDCl3): dH, ppm
7.63 (t, J = 7.4 Hz, 3H; phenyl), 7.52 (m, 6H; phenyl),
7.18 (m, 6H; phenyl), 3.43 (d, J = 5.0 Hz, 1H; b), 3.36 (d,
J = 5.5 Hz, 1H; b), 3.31 (d, J = 5.5 Hz, 2H; b), 3.20 (d,
J = 5.9 Hz, 1H; b), 3.13 (d, J = 5.5 Hz, 1H; b), 2.62 (d,
JH–P = 8.3 Hz, 1H; b) and 2.45 (s, 1H; NH). 19F NMR
(564.73 MHz; CDCl3; hexafluorobenzene): dF, ppm
-131.6 (d, J = 18.6 Hz, 2F; ortho-C6F5), -137.3 (m, 4F;
ortho-C6F5), -138.3 (m, 4F; ortho-C6F5), -138.6 (m, 2F;
ortho-C6F5), -151.5 (t, J = 22.0 Hz, 1F; para-C6F5), -152.2
(t, J = 23.4 Hz, 1F; para-C6F5), -153.4 (t, J = 23.4 Hz, 1F;
para-C6F5), -154.1 (t, J = 21.4 Hz, 1F; para-C6F5), -157.3
CONCLUSION
In conclusion, the reaction of bis-Au(III) [26]
hexaphyrin 5 with triphenylphosphine in the presence of
TFA afforded [28]hexaphyrin triphenylphosphine adduct
6, which was fully characterized by NMR and UV-vis/
NIR absorption spectroscopy and X-ray diffraction
1
analysis. Judging from the H NMR and absorption
spectroscopies, adduct 6 has been assigned as a distinct
Hückel antiaromatic macrocycle. It was found that the
phosphorane form 6b is more important in the solid state.
A plausible reaction mechanism via a doubly protonated
species was suggested for the regioselective addtion of
triphenylphosphine to 5.
Acknowledgements
This work was supported by Grant-in-Aid (No.
25220802(S)) for Scientific Research from MEXT of
Japan. K.N. acknowledges a JSPS Fellowship for Young
Scientists.
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 4–5

A BIS-AU(III) [28]HEXAPHYRIN TRIPHENYLPHOSPHINE ADDUCT
5
Supporting information
and Anand VG. Angew. Chem. Int. Ed. 2014; 53:
10984. (c) Hisamune Y, Nishimura K, Isakari K,
Ishida M, Mori S, Karasawa S, Kato T, Lee S, Kim D
and Furuta H. Angew. Chem. Int. Ed. 2015; 54: 7323.
8. (a) Vogel E, Michels M, Zander L, Lex J, Tuzun
NS and Houk KN. Angew. Chem. Int. Ed. 2003; 42:
2857. (b)Yoneda T, Saito S,Yorimitsu H and Osuka
A. Angew. Chem. Int. Ed. 2011; 50: 3475. (c) Tanaka
Y, Mori H, Koide, T, Yorimitsu H, Aratani N and
Osuka A. Angew. Chem. Int. Ed. 2011; 50: 11460.
9. (a) Tanaka Y, Hoshino W, Shimizu S, Youfu K,
Aratani N, Maruyama N, Fujita S and Osuka A. J.
Am. Chem. Soc. 2004; 126: 3046. (b) Saito S, Kim
KS, Yoon ZS, Kim D and Osuka A. Angew. Chem.
Int. Ed. 2007; 46: 5591.
The chart of NMR and MS spectra, crystallographic
details, and theoretical calculations (Figs S1–S4, Tables
S1–S2) are given in the supplementary material. This
material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data for compound 6 have been
deposited at the Cambridge Crystallographic Data
Center (CCDC) under number CCDC-1437331. Copies
can be obtained on request, free of charge, via www.
ccdc.cam.ac.uk/data_request/cif or from the Cambridge
Crystallographic Data Center, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223-336-033 or
email: data_request@ccdc.cam.ac.uk).
10. (a) Hata H, Shinokubo H and Osuka A. Angew.
Chem. Int. Ed. 2005; 44: 932. (b) Hata H, Kamimura
Y, Shinokubo H and Osuka A. Org. Lett. 2006; 8:
1169.
11. (a) Youfu K and Osuka A. Org. Lett. 2005; 7: 4381.
(b) Inoue M, Yoneda T, Youfu K, Aratani N and
Osuka A. Chem. Eur. J. 2011; 17: 9028.
12. (a) Suzuki M and Osuka A. Chem. Commun. 2005:
3685. (b) Yoneda T and Osuka A. Chem. Eur. J.
2013; 19: 7314.
REFERENCES
1. (a) Jasat A and Dolphin D. Chem. Rev. 1997; 97:
2267. (b) Misra R and Chandrashekar TK. Acc.
Chem. Res. 2008; 41: 265. (c) Sessler JL and Seidel
D. Angew. Chem. Int. Ed. 2003; 42: 5134. (d) Stępień
M, Sprutta N and Latos-Grażyński L. Angew. Chem.
Int. Ed. 2011; 50: 4288. (e) Saito S and Osuka A.
Angew. Chem. Int. Ed. 2011; 50: 4342.
2. For Hückel (anti)aromaticity, see (a) Shin JY, Furuta
H, Yoza K, Igarashi S and Osuka A. J. Am. Chem.
Soc. 2001; 123: 7190. (b) SungYM, Yoon MC, Lim
JM, Rath H, Naoda K, Osuka A and Kim D. Nat.
Chem. 2015; 7: 418.
13. (a) Mori S and Osuka A. J. Am. Chem. Soc. 2005;
127: 8030. (b) Mori S, Kim KS, Yoon ZS, Noh SB,
Kim D and Osuka A. J. Am. Chem. Soc. 2005; 127:
8030. (c) Naoda K, Mori H and Osuka A. Chem.
Lett. 2013; 42: 2224.
3. For Möbius (anti)aromaticity, see (a) Stępień M,
Latos-Grażyński L, Sprutta N, Chwalisz P and
Szterenberg L. Angew. Chem. Int. Ed. 2007; 46:
7869. (b) Sankar J, Mori S, Saito S, Rath H, Suzuki
M, Inokuma Y, Shinokubo H, Kim KS, Yoon ZS,
Shin JY, Lim JM, Matsuzaki Y, Matsushita O,
Muranaka A, Kobayashi N, Kim D and Osuka A.
J. Am. Chem. Soc. 2008; 130: 13568. (c) Higashino
T, Lim JM, Miura T, Saito S, Shin JY, Kim D and
Osuka A. Angew. Chem. Int. Ed. 2010; 49: 4950.
4. (a) Sessler JL, Mody TD, Ford DA and Lynch
V. Angew. Chem. Int. Ed. Engl. 1992; 31: 452.
(b) Köhler T, Seidel D, Lynch V, Arp FO, Ou Z,
Kadish KM and Sessler JL. J. Am. Chem. Soc.
2003; 125: 6872.
5. (a) Sessler JL and Tomat E. Acc. Chem. Res. 2007;
40: 371. (b) Shimizu S and Osuka A. Eur. J. Inorg.
Chem. 2006: 1319.
6. (a) Tanaka T, Aratani N, Lim JM, Kim KS, Kim D
and Osuka A. Chem. Sci. 2011; 2: 1414. (b) Naoda
K, Mori H, Aratani N, Lee BS, Kim D and Osuka
A. Angew. Chem. Int. Ed. 2012; 51: 9850. (c) Mori
H, Tanaka T, Lee S, Lim JM, Kim D and Osuka A.
J. Am. Chem. Soc. 2015; 137: 2097.
14. Fujimoto K, Yoneda T, Yorimitsu H and Osuka A.
Angew. Chem. Int. Ed. 2014; 53: 1127.
15. (a) Schleyer PvR, Maerker C, DransfeldA, Jiao H and
Hommes NJRvE. J. Am. Chem. Soc. 1996; 118: 6317.
(b) Chen Z, Wannere CS, Corminboeuf C, Puchta R
and Schleyer PvR. Chem. Rev. 2005; 105: 3842.
16. Shin JY, Kim KS, Yoon MC, Lim JM, Yoon, ZS,
OsukaA and Kim D. Chem. Soc. Rev. 2010; 39: 2751.
17. Gaussian 09, RevisionA.02, Frisch MJ, Trucks GW,
Schlegel HB, Scuseria GE, Robb MA, Cheeseman
JR, Scalmani G, Barone V, Mennucci B, Petersson
GA, Nakatsuji H, Caricato M, Li X, Hratchian HP,
Izmaylov AF, Bloino J, Zheng G, Sonnenberg JL,
Hada M, Ehara M, Toyota K, Fukuda R, Hasegawa
J, Ishida M, Nakajima T, Honda Y, Kitao O, Nakai
H, Vreven T, Montgomery JA, Jr., Peralta JE, Ogli-
aro F, Bearpark M, Heyd JJ, Brothers E, Kudin
KN, Staroverov VN, Kobayashi R, Normand J,
Raghavachari K, Rendell A, Burant JC, Iyengar SS,
Tomasi J, Cossi M, Rega N, Millam JM, Klene M,
Knox JE, Cross JB, Bakken V, Adamo C, Jaramillo
J, Gomperts R, Stratmann RE,Yazyev O, Austin AJ,
Cammi R, Pomelli C, Ochterski JW, Martin RL,
Morokuma K, Zakrzewski VG, Voth GA, Salvador
P, Dannenberg JJ, Dapprich S, Daniels AD, Farkas
O, Foresman JB, Ortiz JV, Cioslowski J and Fox DJ.
Gaussian, Inc., Wallingford CT, 2009.
7. (a) Koide T, Furukawa K, Shinokubo H, Shin JY,
Kim KS, Kim D and Osuka A. J. Am. Chem. Soc.
2010; 132: 7246. (b) Gopalakrishna TY, Reddy JS
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