Tautomerism-Induced Cis-Trans Isomerization of Pyridylethenyl N-Confused Porphyrin

Article abstract of DOI:10.1021/acs.joc.7b01770

Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized, and their cis-trans isomerization was studied. Among four possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in the vicinity. The thermal cis-trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the system. The kinetic studies revealed that the isomerization reaction was second-order and the activation energy of the thermal isomerization from cis to trans isomer was ΔG₀^?_cis→trans = 35.7 kcal/mol at 298 K, which is significantly smaller than that of Ni complex (42.3 kcal/mol). An intermolecular proton transfer induced cis-trans isomerization mechanism was proposed.

Full text of DOI:10.1021/acs.joc.7b01770

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Article
Tautomerism-induced Cis-Trans Isomerization
of Pyridylethenyl N-Confused Porphyrin
Ryuichi Sakashita, Yasutaka Oka, Hisanori Akimaru, Praseetha E. Kesavan, Masatoshi
Ishida, Motoki Toganoh, Tomoya Ishizuka, Shigeki Mori, and Hiroyuki Furuta
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01770 • Publication Date (Web): 26 Jul 2017
Downloaded from http://pubs.acs.org on July 26, 2017
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The Journal of Organic Chemistry
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Tautomerism-induced Cis-Trans Isomerization of Pyridylethenyl
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N-Confused Porphyrin
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Ryuichi Sakashita, Yasutaka Oka, Hisanori Akimaru, Praseetha E. Kesavan, Masatoshi Ishida, Motoki
†
‡
§
†
Toganoh, Tomoya Ishizuka, Shigeki Mori, and Hiroyuki Furuta*
†
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan
Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571, Japan
Advanced Research Support Center, Ehime University, Matsuyama 790-8577, Japan
‡
§
ABSTRACT: Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized and their cis-trans isomerization was studied.
Among 4 possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely,
were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in
the vicinity. The thermal cis-trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the
system. The kinetic studies revealed the isomerization reaction was second order and the activation energy of the thermal isomerization from
‡
cis to trans isomer was DG
o
cis®trans = 35.7 kcal/mol at 298 K, which is significantly smaller than that of Ni complex, 42.3 kcal/mol. Intermo-
lecular proton transfer induced cis-trans isomerization mechanism was proposed.
INTRODUCTION
NH tautomerism can be controlled by the external molecules such
5 6
as solvents or anions , and each tautomeric form can be fixed by
A set of interconvertible isomers, of which structures and electronic
properties differ largely, is an attractive candidate for the applica-
tions such as optical memories and switches at the molecular level.
II 7a
II 4b
II 7b
II 7c
II 7d
metalation (e.g., Co , Ni , Cu , Pd , Pt , for 2H-form and
III 7e
III 7f
III 7g
8
1
Co , Cu , Ag for 3H-form).
A variety of isomerization systems, such as cis-trans azobenzenes,
ring open-closed diarylethenes, keto-enol tautomers, etc., have been
Scheme 1. Cis-Trans Isomerization of Alkene with Interacting
groups: a) Conceptual Illustration, b) Py-C=C-Pyr, and c)
Pyridylethenyl NCP
2
so far developed for such purpose. Among them, the usage of cis-
trans isomerization of simple diarylethene is rather limited com-
pared with that of azo systems because of the smaller difference in
the optical properties between the cis-trans pair and succeeding
ring-forming reactions. If one of the isomers largely alters its elec-
tronic state through a specific interaction between the aryl groups
at both ends, a distinct difference could be anticipated. One of the
strategies to cause such a change is to make the two aryl groups
bifunctional and interactive each other in the cis-form. (Schemes
a)
c)
N
N
H
N
N
b)
H
N
H
NH
HN
N
N
N
H
N
1
a). The acid-base pair could be anticipated as a candidate for the
N
HN
trans-3H
cis-2H
HN
aryl groups, and actually, an olefin molecule with a pyrrole-pyridine
substituent-pair, 2-[2-(2-pyrrolyl)ethenyl]pyridine (Py-C=C-Pyr),
was reported to show a distinct difference in the fluorescence spec-
Py-C=C-Pyr
3
tra; cis: lmax = 570 nm and trans: lmax = 430 nm (Schemes 1b).
From the structural point of view, NCPs can be regarded as ex-
panded pyridine and/or expanded pyrrole (and expanded imidazole
in the case of doubly N-confused porphyrins) according to the
tautomeric forms, because an outward-pointing nitrogen atom
exists at the periphery of a large conjugated macrocycle. In fact, we
have already demonstrated the pyrrole-like anion binding, pyri-
Meanwhile, we have been working on the N-confused porphyrin
4
(NCP) since its discovery. NCP can take two NH tautomeric
forms, inner 3H- and inner 2H-form, electronic states of which are
9
5
totally different. Namely, the 3H-tautomer, which possesses three
6
,10
protons inner core (2NH, 1CH) as well as an imino-type N at the
periphery, exhibits a strong aromaticity due to the complete annu-
lenic circuit in the porphyrin skeleton. On the other hand, 2H-
tautomer possesses only two inner protons (1NH, 1CH) and an
amino-type outer NH, annulenic circuit of which is incomplete. As
the result, the two tautomers show the electronic properties with
1
1
dine-like metal coordination, and imidazole-like acid-base interac-
1
2
tions with NCPs. Thus, we could develop a Gulliver-type pyri-
dine/pyrrole chemistry by utilizing NCPs to enlarge the functional-
ity. Here, the idea is to expand the 6p-based isomerization system
to the 18p NCP-based one by simply changing the aryl groups. In
this study, we synthesized pyridylethenyl-NCP (1), in which a
5
marked difference. These tautomers interconvert easily and this
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pyrrole moiety of Py-C=C-Pyr was replaced with NCP. The regu- Scheme 2. Synthesis of a) Pyridylethenyl NCPs and b) Porphy-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
lar porphyrin derivative (7) was also synthesized for a reference
(Scheme 2). We found the colors of the solutions of two isomers,
cis-2H-1 and trans-3H-1, were largely different and the trans iso-
mer showed the intense emission. Surprisingly, the cis-trans thermal
isomerization of 1 proceeded even at 30 °C, while the correspond-
ing regular porphyrin 7 required above 100 °C for isomerization.
Herein, we describe the unprecedented NH tautomerism-induced
cis-trans isomerization of 1. A plausible mechanism is discussed
based on the kinetic and thermodynamic studies.
rin (7)
a)
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9
0
RESULTS AND DISCUSSION
Synthesis. The title compounds 1a and 1b were synthesized ac-
cording to Scheme 2a. p-Trifluoromethylphenyl groups were em-
ployed as meso-substituents to make the NCP macrocycle more
electron-deficient and acidic to form a stronger intramolecular
hydrogen bond between the outer NH of the confused pyrrole and
1
3
the pyridyl moiety in cis-form. At first, N-confused tetrakis(p-
b)
1
4
trifluoromethylphenyl)porphyrin (2) was treated with sodium
cyanide in dimethylformamide (DMF) to yield 3-cyano-NCP (3).
To avoid the aluminium metal insertion in the core during the reac-
tion with diisobutylaluminium hydride (DIBAL-H), 3 was first
metalated with nickel(II) acetate, and then reduced to 3-formyl-
II
NCP Ni complex (5). Subsequent Wittig reaction afforded a mix-
II
ture of cis- and trans-isomers of 3-[(2-pyridyl)ethenyl]-NCP Ni
complexes (cis-1-Ni and trans-1-Ni), both of which were isolated
by silica gel column chromatography. Then, cis-1-Ni was demeta-
lated with methanesulfonic acid to give a mixture of cis- and trans-
isomers of freebase pyridylethenyl-NCPs (1), which were separat-
ed on a silica gel column. Notably, only cis-2H-1 and trans-3H-1
were isolated among the four possible isomers (Figure 1). Both cis-
i) NaCN/DMF, ii) Ni(acac) /toluene/MeOH, iii) DIBAL-H/toluene,
2
iv) PyCH PPh Cl, DBU/CH Cl , v) CH SO H/CH Cl , vi) AgO-
2
3
2
2
3
3
2
2
Ac/CH
2
Cl
2
, vii) 2-formylpyridine, DBU/CH
2
2
Cl .
1
and trans-1 were recrystallized below 25 °C to avoid the isomeri-
R
R
zation. Furthermore, to fix to a 3H-model, trans-3H-1a was con-
verted to the silver(III) complex, trans-1a-Ag, by treating with
N
N
7
g
trans
silver acetate (Scheme 2a). Likewise, the porphyrin derivative (7)
1
5
N
HN
was synthesized according to Scheme 2b.
Ar
Ar
Ar
Ar
Ar
Ar
Ar
X-ray crystallography. Single crystal X-ray analyses of cis-1a-Ni
and trans-1a-Ag were successfully performed (Figures 2 and S15,
Table S6). As expected, cis-1a-Ni revealed the intramolecular hy-
drogen bond between the N atoms of the confused pyrrole ring and
the pyridyl group, judging from the N····N atomic distance
NH
HN
N
N
H
N
N
Ar
trans-3H
stable
trans-2H
R
(
2.718(7) Å), N····H-N angle (137.05°), and the dihedral angle
between two rings (21.8°) (Figure 2a). Interestingly, the pyridyl
N
N
ring of cis-1a-Ni shows the bond alternation with a value of har-
N
16
H
monic-oscillator model for aromaticity (HOMA), 0.520, which is
R
N
Ar
Ar
Ar
Ar
Ar
Ar
Ar
remarkably smaller than that of the silver(III) complex, trans-1a-
Ag, 0.901 (Figure 3). Thus, the aromaticity of the pyridyl ring
seems largely affected by the hydrogen bonding between the
pyridyl and confused pyrrole moieties in cis-1a-Ni. Furthermore,
the bond length of the ethenyl double bond in cis-1a-Ni (1.351(7)
Å) is longer than that of trans-1a-Ag (1.318(8) Å) (Figure 2b).
This could be attributed to the extension of p-conjugation from the
NCP macrocycle to the pyridyl moiety in cis-1a-Ni as schematical-
ly shown in Scheme 2 (bold blue line). This tendency was modestly
reflected in the density functional theory (DFT) calculations on
1b: the calculated bond lengths of ethenyl moieties were 1.363 and
1.351 Å for cis-2H-1b and trans-3H-1b, respectively (Figure S31).
NH
HN
N
N
H
N
N
cis
Ar
cis-3H
cis-2H
stable
3H
2H
Figure 1. Possible isomers of 1.
The effective p-conjugation through the 3-position of NCP has
1
7
been illustrated with the divalent metal complexes of 2H-form.
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bly due to their low stability resulting from a lack of intramolecular
1
2
3
4
5
6
7
8
9
hydrogen bonding. Also, the repulsion between the lone pair elec-
trons of two adjacent N atoms could not be ignored in the cis-3H.
Optical properties. The cis- and trans-isomers of 1 exhibited the
distinct optical features. In the absorption spectra of the freebase 1
in CH
2
2
Cl , the Soret-band of cis-2H-1b was observed at 495 nm,
which was 23 nm red-shifted compared to trans-3H-1b (Figure 4).
In addition, the spectral profiles in the Q-bands region of two iso-
mers were largely different, reflecting the structural features of 2H-
5
and 3H-tautomers. This large shift is a characteristic of NCP de-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
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31
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43
44
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49
50
51
52
53
54
55
56
57
58
59
60
rivatives, and was not seen with the regular porphyrin 7, the shift of
the Soret-band of which was only 5 nm (Figure S19). Interestingly,
the emission of cis-2H-1b is significantly quenched compared with
trans-3H-1b though both cis-7 and trans-7 showed intense fluo-
rescence (Figures 4 and S19). The large differences in the optical
properties between the isomers of 1 would be advantageous for the
application such as molecular memory.
1
4
Figure 2. Top and side views of the X-ray structures of (a) cis-1a-Ni
and (b) trans-1a-Ag, with 50% thermal ellipsoid probability. Hydro-
gen atoms except for the confused pyrrolic N–H are omitted for clarity.
1
2
10
8
(a)
(b)
1
.381
1
.375
1
.353
0.520
1.393
1.369
6
1
.422
0.901
.362
1
.389
1
.392
.325
1.325
1.488
1.462
4
1
1
1
.390
1
.351
1.318
1.462
2
1.433
0
400
600
800
1000
1200
wavelength (nm)
Figure 4. Absorption spectra of (a) trans-3H-1b (——) and (b) cis-
H-1b (——), and fluorescence spectra of (c) trans-3H-1b (-----) and
d) cis-2H-1b (-----) in CH Cl . Excited at 495 nm (cis) and 472 nm
trans).
2
(
(
2
2
Figure 3. Selected bond lengths (Å) and HOMA values for pyridyl
rings of (a) cis-1a-Ni and (b) trans-1a-Ag.
NMR study. Cis and trans isomers of 1 and 1-Ni were identified by
3
the coupling constants of the olefinic protons, Jcis = 13.4–13.7 Hz
3
1
and Jtrans = 15.5–16.5 Hz, respectively (Figure S16). The H NMR
spectra of 1-Ni and the freebase 1 revealed the presence of strong
intramolecular hydrogen bonding in the cis-isomers in CDCl .
3
Namely, the signals of outer NH proton in cis-1a-Ni and cis-1b-Ni
were observed at d = 16.9 and 17.3 ppm, respectively, while the
corresponding NH signals appeared at d = 9.86 and 9.83 ppm in
the case of trans-1a-Ni and trans-1b-Ni, respectively. The ob-
served higher cis/trans ratio of 1b-Ni (31:69) than 1a-Ni (21:79)
in the synthesis (Scheme 1) could be attributed to the stronger
intramolecular hydrogen bonding in 1b-Ni, pyridine moiety (R =
OMe) of which is more basic. Similarly, the outer NH signals of the
free bases, cis-2H-1a and cis-2H-1b, appeared at d = 16.50 and
Figure 5. Molecular orbital energy diagrams of 1b and 2 calculated at
**
the B3LYP/6-31G level.
1
6.82 ppm, respectively (Figure S16a). The remaining trans-3H
isomers, which lack the outer NH, showed the stronger aromaticity
18
Calculations. The nucleus independent chemical shift (NICS)
as indicated by the highly shielded inner CH signals at d = –4.78
and –4.77 ppm for trans-3H-1a and trans-3H-1b, respectively
values of 1b at the mass center of the macrocycle were calculated to
be –5.09 ppm for cis-2H and –11.70 ppm for trans-3H (Figure
S31). These results indicate that cis-2H is less aromatic than trans-
(
Figure S16b). The cis/trans ratio of the freebases 1a and 1b could
5
a
not be determined accurately because of the facile isomerization
during the work-up after demetalation of cis-1-Ni. Absence of oth-
er isomers, trans-2H and cis-3H, in the isolated products is proba-
3H in accordance with the previous report on NCPs. Molecular
orbital energy diagrams of 1b and reference NCP 2 are shown in
Figure 5. Trans-3H-1b has comparatively degenerated LUMO and
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LUMO+1, similar to 3H-2 or regular porphyrins. The 2H-type
(a)
-1
(b)
-2.5
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
isomers have higher HOMO energies, and the pyridylethenyl sub-
stituent raises the HOMO and HOMO-1 levels of both cis-2H-1b
and trans-3H-1b, and as a result, cis-2H-1b has a narrower
HOMO-LUMO gap than trans-3H-1b. The time-dependent
-
2.6
2.7
-
1.5
-
-2
2.2
-2.8
-
2.5
-3
-2.9
(
TD)-DFT calculations showed the first excitation energy corre-
-3
sponding to the Q-band of 1b is 832 nm for cis-2H and 694 nm for
trans-3H (Figure S32-S33, Table S9). The difference in the Q-
band transition between the cis/trans isomers of 1b (138 nm) is
much larger than that of 2 (60 nm), reflecting the conjugation
pathway elongated to the pyridylethenyl-substituent in the cis-2H-
1b (Table S10).
-3.5
-4
-3.1
-3.2
0
0.2 0.4 0.6 0.8
1
1.2
-1
-0.5
0
0.5
1
1.5
log([1b])
log([Py])
Figure 7. Logarithmic plots of (a) concentration of 1b vs initial rate
) and (b) pyridine concentration vs initial rate: [1b] =1.2 µM,
measured by UV/Vis absorbance in CH Cl at 50 °C.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
v
0
2
2
Thermal isomerization: Effects of concentration and added
pyridine. The thermal cis-trans isomerization of 1 (Scheme 1c)
was studied in CH
2
2
Cl using 1b in the dark. Surprisingly, the isom-
erization proceeded very rapidly and occurred even at 30 °C, while
the corresponding regular porphyrin cis-7 required much higher
Table 1. Isomerization Initial Rates of 1b (1.2
ous Additives (25 mM) in CH Cl at 50
µ
M) with Vari-
2
2
°
C
temperature (≥100 °C in toluene-d ) and trans-Py-C=C-Pyr did
8
not show any sign of isomerization at 150 °C for 5 days (Figures 6,
S27–28).
Initial rate (v
(µM/min)
0
)
Relative initial rate
Additive
(vs None)
Notably, the isomerization of 1b was significantly affected by its
concentration as well as the pyridine added to the system (Figure
–4
None
Pyridine
3.11 × 10
1
–
3
6
2
). For [1b] = 15 µM, the initial rate (v
0
) of isomerization from cis-
3.10 × 10
2.58 × 10
7.52 × 10
5.92 × 10
5.35 × 10
5.36 × 10
9.97
0.83
2.42
1.90
1.72
1.72
–
2
H-1b to trans-3H-1b was v = 7.42 × 10 µM/min at 50 °C,
0
–
4
–4
whereas it decreased to 3.11 × 10 µM/min upon dilution ([1b] =
.2 µM). Logarithmic plots of concentrations versus initial rates
2,6-Lutidine
Quinoline
Acridine
1
–
–
4
4
showed that the reaction order was ca. 2, indicating that two mole-
cules of 1b participated in the cis-trans isomerization (Figure 7a).
Apart from the above, when an excess amount of pyridine (25
mM) was added to the diluted solution ([1b] =1.2 µM), the isom-
–4
–4
4
-Cyanopyridine
–
3
erization reaction was accelerated by 10-fold (v = 3.10 × 10
0
µM/min) (Figure 6). The logarithmic plots of pyridine concentra-
tions versus initial rates showed a nonlinearly curved line, which
suggests that there are at least two pathways of isomerization. The
isomerization was not significantly affected by the low concentra-
tion of pyridine (reaction order of pyridine <0.1), while the isomer-
ization was highly accelerated in the presence of a large amount of
pyridine (>10 mM: reaction order of pyridine >1) (Figure 7b). In
case of cis-7, the addition of pyridine did not function in the ther-
mal isomerization under the similar conditions (at 50 °C in tolu-
4
-Dimethylaminopyridine
When 2,6-lutidine was added in place of pyridine, the acceleration
was not observed or rather the isomerization was decelerated (Ta-
ble 1, Figure S26). On the other hand, the addition of larger and
planar pyridine derivatives, such as quinoline and acridine, acceler-
ated the isomerization of 1b, but the effects were significantly lower
than pyridine. Furthermore, the addition of electron-rich (4-
dimethylamino-) or electron-deficient (4-cyano-) pyridines also
accelerated the isomerization but the effects were small in either
case. These results may indicate the less steric hindrance and prop-
er basicity are necessary for the additives to accelerate the isomeri-
zation, probably due to their two-way role, proton-capture and
proton-transfer, in the NH tautomerism which coupled to the cis-
trans isomerization. Moreover, for the thermal cis-trans isomeriza-
ene-d ). These results suggest that the pyridine molecule plays an
8
important role in the transition state of this isomerization when an
excess amount of pyridine is present in the solution.
1
0.8
0.6
0.4
tion of 1a-Ni, which proceeded very slowly in toluene-d at 100 °C
8
and reached the equilibrium with the ratio of cis-1a-Ni : trans-1a-
Ni = 79 : 21 after 60 days (Figure S20), the acceleration by the
pyridine or its derivatives was not observed. In the pyridine titra-
0.2
1
tion experiments of trans-1b-Ni using H NMR, the outer NH
0
signal gradually shifted to a lower field region, while the other sig-
nals remained unchanged, indicating the hydrogen bonding be-
tween the outer NH and the added pyridine (Figure 8).
0
50
100 150 200 250 300
time (min)
Figure 6. Time-courses of the thermal isomerization of 1b in CH
at 50 °C; [1b] = 1.2 µM ( ), [1b] = 15 µM ( ), and [1b] = 1.2 µM
and [pyridine] = 25 mM ( ).
2
Cl
2
○
-
□
-
◇
-
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The Journal of Organic Chemistry
A)
OMe
MeO
4
3
2
1
0
1
1
2
3
4
N
N
H
N
R’
Ar
Ar
Ar
Ar
Ar
Ar
N
Ar
N
NH HN
N
N
N
N
H
N
Ar
HN
5
Ar
Ar
cis-2H-1b
trans-3H-1b
D
Ar
6
7
8
9
d
N
Ni
N
b
E
cis-2H
(1.37)
N
cis-3H
e
Ar
(7.20)
c
trans-2H
trans-1b-Ni
(3.74)
-
a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-2
0
2
4
6
8
10
12
Pyridine (M)
2
H
Figure 8. Changes of the chemical shifts of outer NH proton of trans-
cis
m
–
1
cis-tran
eris
1
b-Ni (5 mM) upon addition of pyridine-d
5
in CDCl . K = 0.99 M
3
m
s
is
R
to
u
)
was estimated from the curve fitting analysis.
omeriza
trans-3H
ta
(O
(PT
(0)
)
ti
trans
NH
kcal/mol)
o
3H
n
(
Mechanism of the cis-trans isomerization. Characteristics of
present isomerization system can be summarized as follows: 1)
B)
d
e
replacing a 6p pyrrole ring in Py-C=C-Pyr with a large 18p sub-
stituent, either NCP or porphyrin, is effective in decreasing the
activation energy of the cis-trans isomerization, 2) free base NCP
derivative isomerizes much faster than its nickel complex and cor-
responding porphyrin derivative, which implies the participation of
NCP NH tautomerism in the isomerization process, 3) addition of
pyridine to the system largely accelerates the isomerization, which
suggests its dual role, proton capture and transfer, in the NH tau-
tomerism of NCP moiety, 4) two 1b molecules are involved in the
isomerization, suggesting a similar role of the pyridyl moiety in 1b
as added pyridine.
OR
PT
90°-2H
4
0.1
1.37
cis-2H
3.74
0
trans-2H
trans-3H
b
c
PT
OR
9
0°-3H
37.5
1.37
cis-2H
7.20
cis-3H
0
To get the insight into the mechanism of present cis-trans isomer-
ization, the thermodynamic energy profile of the system was first
considered. Basically, three trails on the energy surface of the
ground state were assumed for the isomerization of 1b (Figure 9).
One is path-a, in which proton transfer (PT) and olefin rotation
trans-3H
a
OR
PT
(
(
OR) proceed concertedly. Others are path-(b®c) and path-
d®e), in which PT-OR or OR-PT proceeds stepwise (Figure 9A).
ΔG‡
Namely, the path-b and path-e correspond to the NH tautomerism
PT) and the path-c and path-d are cis-trans isomerization (OR)
1.37
0
cis-2H
trans-3H
(
Reaction Coordinate
process. Calculations on the transition states of each path were so
far difficult, thus, we simply compared the relative energies of the
hypothetical structures in the transition state where the olefin moi-
ety is twisted by 90° (Figure 10, Table S7). For path-c and path-d,
Figure 9. Schematic illustration of free energy profiles of cis-trans
isomerization and NH tautomerism between cis-2H-1b and trans-3H-
1
b. OR: olefin rotation, PT: proton transfer.
‡
‡
DG
o
path-c = 37.5 kcal/mol and DG path-d = 40.1 kcal/mol (vs DGo trans-
o
(b)
3
H
= 0 kcal/mol) were obtained. On the other hand, for path-b and
(a)
50
‡
50
40
path-e, we adapted the values of DG
o
3H®2H = 29.9 kcal/mol and
4
0
‡
DG
o
2H®3H = 28.5 kcal/mol, which were derived from the NH tau-
30
20
10
0
30
tomerism of N-confused tetraphenylporphyrin (NCTPP) (vide
19
infra). By using these values, we can schematically depict the en-
20
10
0
ergy profiles of isomerization for each pathway as shown in Figure
9
B. In the stepwise cases, the activation energies of OR processes
are larger than those of NH tautomerism, indicating that OR (path-
c and path-d) is the rate-determining step. However, the results
that the addition of pyridine accelerated the cis-trans isomerization
of 1b but not 1a-Ni would not be compatible with the stepwise
mechanism if the rate-determining steps are the same OR process
in the both systems.
0
cis
45
90
135
180
trans
0
cis
45
90
135
180
trans
C=C dihedral angle
C=C dihedral angle
Figure 10. Calculated Gibbs free energies of (a) 1a-Ni (– ○- –) and (b)
H form of 1b: (-- □- --) and 3H form of 1b: (– ○- –) with various dihedral
angles of olefin moiety (B3LYP/6-31G** for C, H, F, N, and LanL2DZ
for Ni).
2
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In order to estimate the activation parameters of independent
pathways of NH tautomerism (path-b and path-e), we measured
the rate constants of NCTPP tautomerism in the pyridine-
Table 2. Activation Parameters of NH Tautomerism of
®
NCTPP (3H 2H)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
DG ‡
DH ‡
DS
‡
o 3H®2H
d
5
/CDCl
ed for the concurrent detection of 2H- and 3H-tautomers by
NMR, since the 3H-type tautomer is predominantly formed in the
CD Cl or CDCl only solution due to the higher stability of the
3
mixture solutions. This mixed solvent system was select-
o
3H®2H
o
3H®2H
solvents
1
H
[kcal/mol]
16.12
[kcal/mol]
1.93
[cal/mol·K]
–47.6
Pyridine-d
5
2
2
3
5
0% Pyridine-d
CDCl
5
5
/
/
5
a
‡
24.58
16.40
–27.5
3H-type than 2H-tautomer. The values of DG
o
3H®2H = 29.9
3
‡
kcal/mol and DG
o
2H®3H = 28.0 kcal/mol at 298 K in CDCl
3
only
30% Pyridine-d
2
5.31
21.19
–13.8
‡
CDCl
3
solution were derived from the plots of DG
o
against the pyridine
] = 0
Figure 11, Table 2). These values are much higher than the NH
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CDCl
30.32*
29.83*
–1.59*
concentrations, by extrapolating to the point at [pyridine-d
5
3
(
*Obtained from extrapolation of the plot lines in Figure 11.
‡
tautomerism of regular porphyrin (DG ~12 kcal/mol) where the
tautomerism occurs only inside of the core. The larger DG of
o
20
‡
o
NCP should be explained by the different mechanism from the
3
2
0
0
–50
21
tunneling model of the regular porphyrin. Because of the solvent
‡
dependence of DG
o
and the long-range proton transfer from the
–
40
inner to the outer, a possibility of ring rotation mechanism was
22
proposed based on the calculation study but the detailed mecha-
–30
nism of NH tautomerism of NCP still remains challenging.
From the variable-temperature kinetic experiments, the activation
10
–
20
10
free energy of the thermal isomerization of 1b from cis to trans was
‡
determined to be DG
o
cis®trans = 35.7 kcal/mol, while that of 1a-Ni
–
100
was 42.3 kcal/mol at high concentration ([1b]: 680 µM, [1a-Ni]:
.8 mM) (Tables S1, S3). The calculated free energy differences for
the hypothetical OR transition states of 1b and 1a-Ni are similar
0
0
20
40
60
80
1
Pyr-d in CDCl , v/v%
5
3
Figure 11. The activation parameters of the NH tautomerism of
values of 38.7 and 38.9 kcal/mol, respectively (Figure 9, Table
‡
‡
2
3
NCTPP (20 mM) in pyridine-d
5
(Pyr-d
5
)/CDCl
3
. DG
o
( ), DH
o
S7). The compound 7 showed the similar trend with the energy
‡
(
), DS
o
(
).
differences of 35.4~39.0 kcal/mol (Figure S30 and Table S8). Thus,
the large decrease of activation energy of 1b from that of Ni com-
‡
plex (DDG
o
cis®trans = 6.6 kcal/mol) could be attributed to the NH
Scheme 3. A Plausible Isomerization Mechanism of 1 in the
Presence of Pyridine
tautomerism during the cis-trans isomerization. Here, it should be
noted that the added pyridine accelerates the NH tautomerism of
NCP, that is, lowers the activation energy of NH tautomerism,
probably by mediating the proton migration (Table 2). If the pyri-
dine participated in both the tautomerism and cis-trans isomeriza-
tion to assist the breaking of the intramolecular hydrogen bonding
in cis-2H-1b and twisting the pyridylethenyl moiety favorable for
the cis-trans isomerization through the steric repulsion (Scheme 3),
then, the rotation of C=C double bond and proton transfer occur
concertedly, which could reduce the activation energy of double
bond rotation lower than the stepwise pathways. Although the
above mechanism is highly speculative and needs more detailed
studies including calculations, it is likely that PT process is merged
with the OR process (path-a) to account for the acceleration of the
cis-trans isomerization reaction. Considering the observed result
that the isomerization is second-order to the concentration of 1b, it
is highly probable that the pyridine moiety in trans-3H-1b plays
the similar role as added pyridine in the cis-trans isomerization.
Photo-isomerization. Lastly, photoisomerization of 1b was inves-
tigated by monitoring the fluorescence changes at 20 °C, where the
thermal isomerization was negligible (Figure 12). Upon irradiation
at the Soret band (496 nm) of cis-2H-1b, isomerization to trans-
–4
3
H-1b proceeded with the initial rate of v
0
= 8.12 × 10 µM/min.
At the photostationary state, the ratio of isomers, cis-2H : trans-3H,
reached ca. 6 : 4, which is different from that of thermal isomeriza-
tion, 4 : 6, at 30 °C. The acceleration effect of added pyridine in this
photoisomerization system was modest compared with the thermal
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chemical shifts were reported relative to a residual proton of a deu-
one. In the case of Py-C=C-Pyr, the excited state intramolecular
proton transfer (ESIPT) mechanism was demonstrated in the
2
4
13
1
terated solvent, CHCl (d = 7.26) in ppm. C NMR spectra were
3
3
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
photoisomerization. Thus, in the present isomerization, there is a
recorded at either 75 MHz (JNM-AL 300) or 150 MHz (Bruker
possibility of ESIPT from the confused pyrrole to the pyridyl moie-
ty of cis-2H-1b under photo-irradiation. For a further discussion,
however, the fast time-resolved spectroscopic study is indispensa-
ble.
AVANCE III 600) and chemical shifts were reported relative to
19
either CDCl
3
(d = 77.13) or THF-d
8
(d = 25.31) in ppm. F NMR
spectra were recorded on a JNM-AL 300 (270 MHz) and chemical
shifts were reported relative to perfluorobenzene (d = –164.9) in
ppm. UV/vis absorption spectra were recorded on a UV-3150PC
spectrometer (Shimadzu). Fluorescence spectra were recorded on
an SPEX Fluorolog spectrometer (HORIBA) with photomultiplier
module (Hamamatsu R928P) and InGaAs photodiode array. High-
resolution mass spectra were measured with a JMS-T100CS (ESI-
TOF mode, JEOL). Absolute quantum yields of emission were
measured with PL quantum yield measurement system (C9920-02,
Hamamatsu).
1
0.8
0.6
0.4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.2
0
Time-course measurements of isomerization. Time-course
studies of the thermal cis-trans isomerization were performed by
0
20
40
60
80
100
time (min)
1
following the changes in the H NMR spectra (at high concentra-
Figure 12. Time-courses of the photoisomerization of 1b (1.2 µM)
monitored by the fluorescence at 800 nm in CH Cl at 20 °C upon
tion) or UV/vis absorption spectra (at low concentration). Integra-
tion of olefinic proton signals or intensity of the Soret-band was
used to calculate the cis/trans molar ratios. Sample solution was
prepared by dissolving the pure isomer in the cold solvent to sup-
press the isomerization before measurements. The sealed NMR
tube or tightly capped UV cell was placed into the thermostat bath.
The first point was measured immediately after reaching the de-
sired temperature. Because of the facile isomerization of the free
base 1b, the compound has already isomerized at the first meas-
urement point (ca. 0.2 molar ratio).
2
2
irradiation at 496 nm: (a) without pyridine (black) and (b) with excess
pyridine (25 mM) (blue).
CONCLUSION
In summary, we have synthesized a novel type of diarylethenes, cis-
and trans-pyridylethenyl N-confused porphyrins (1) and investi-
gated the thermal cis-trans isomerization in detail. The cis-isomer
was largely stabilized by the intramolecular hydrogen bonding be-
tween the pyrrolic-NH of NCP and the pyridinic-N in the vicinity.
The freebase 1 isomerized readily even at 30 °C, accompanied by
the NH tautomerism of NCP moiety. The isomerization was accel-
erated by increasing the concentration of 1 or by the addition of
pyridine. The kinetic studies revealed the isomerization reaction
Synthesis. N-confused tetrakis(p-trifluoromethylphenyl)-
porphyrin (2): To a 3 L flask, CH
2
Cl
2
(3 L), pyrrole (2 mL), and
4
-(trifluoromethyl)benzaldehyde (4 mL) were added. The reaction
was initiated by addition of methanesulfonic acid (1.4 mL). The
reaction mixture was stirred at room temperature for 30 min. DDQ
(
6.0 g) was added and the mixture was allowed to stir for 2 min and
then the acid was quenched by addition of triethylamine (12 mL).
Impurity was removed by passage through alumina and silica gel.
After evaporation, the residue was separated by silica gel column
was second order and the activation energy of this thermal isomeri-
‡
zation from cis- to trans-isomer was DG
o
cis®trans = 35.7 kcal/mol at
298 K, which is much smaller than that of Ni complex, 42.3
kcal/mol. In addition, photoisomerization was also observed at
20 °C, where the thermal isomerization was negligible. The cou-
pling of NCP tautomerism and cis-trans isomerization enabled us to
develop a new isomerization system that affords two interchangea-
ble isomers, electronic properties of which are significantly differ-
ent. The present study demonstrated the design of diarylethene,
to make the two aryl groups bifunctional and interactive each other in
the cis-form, is effective to cause the change of tautomer’s electronic
state largely, and the NCP could serve as an expanded pyrrole
and/or expanded pyridine.
chromatography with 10% hexane in CH
2
Cl
2
. Concentration of the
Cl /hexane
, 300 MHz,
ppm): d –5.11 (s, 1H, inner CH), –2.50 (br s, 2H, inner NH), 8.05
d, J = 7.5 Hz, 4H, m-ArH), 8.12 (d, J = 8.3 Hz, 2H, m-ArH), 8.14
fraction and recrystallization of the residue from CH
2
2
1
afforded 2. Yield: 1.57 g (24%). H NMR (CDCl
3
(
(d, J = 8.9 Hz, 2H, m-ArH), 8.28 (d, J = 7.5 Hz, 2H, o-ArH), 8.30
(d, J = 7.5 Hz, 2H, o-ArH), 8.45 (d, J = 8.9 Hz, 2H, o-ArH), 8.48 (d,
J = 8.3 Hz, 2H, o-ArH), 8.52 (d, J = 5.1 Hz, 1H, b-H), 8.55 (d, J =
5
1
.1 Hz, 1H, b-H), 8.57 (d, J = 5.0 Hz, 1H, b-H), 8.62 (d, J = 5.0 Hz,
H, b-H), 8.75 (s, 1H, a-H), 8.93 (d, J = 5.0 Hz, 1H, b-H), 8.98 (d,
13
J = 5.0 Hz, 1H, b-H); C NMR (CDCl
3
, 75 MHz, ppm): d 99.0,
1
1
16.3, 117.9, 122.30, 122.32, 122.4, 123.3, 123.77, 123.81, 123.83,
23.85, 123.88, 123.93, 124.07, 124.10, 124.14, 124.2, 124.34,
EXPERIMENTAL SECTION
General Methods. Commercially available solvents and reagents
were used without further purification unless otherwise mentioned.
Thin-layer chromatography (TLC) was carried out on aluminum
sheets coated with silica gel 60 F254 (MERCK). Preparative sepa-
ration was performed by silica gel flash column chromatography
124.36, 124.38, 124.41, 124.44, 124.48, 125.41, 125.44, 125.46,
125.51, 125.54, 125.55, 125.59, 125.90, 125.93, 126.1, 126.36,
126.40, 126.44, 126.5, 127.8, 127.90, 127.93, 127.95, 127.99,
128.23, 128.25, 128.27, 128.31, 128.34, 129.51, 129.53, 129.77,
129.87, 129.92, 130.1, 130.2, 130.3, 130.4, 130.6, 133.7, 134.29,
134.36, 134.41, 134.5, 135.0, 136.4, 136.51, 136.59, 136.66, 136.70,
136.9, 139.0, 139.7, 142.28, 142.30, 142.45, 142.47, 144.72, 144.73,
144.76, 144.77, 149.1, 155.8, 156.8; Due to the severe spectral
(
KANTO Silica Gel 60 N, spherical, neutral, 40–50 µm) or silica
gel gravity column chromatography (KANTO Silica Gel 60 N,
spherical, neutral, 63–210 µm). H NMR spectra were recorded on
1
2
13
a JNM-AL 300 FT-NMR spectrometer (JEOL) at 300 MHz, and
complexity in the sp -carbon region, the C-F coupled splitting
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1
9
19
could not be assigned. F NMR (CDCl
F, CF ), –60.52 (s, 6F, CF ), –60.57 (s, 3F, CF
max/nm (e)): 724 (10500), 581 (11600), 540 (10400),
3
, 270 MHz): d –60.48 (s,
144.05, 144.1, 146.6, 146.9, 150.5, 151.5, 155.0, 156.3, 190.7;
NMR (CDCl , 270 MHz): d –65.46 (s, 6F, CF
CF ), –65.67 (s, 3F, CF ); UV-vis (CH Cl , lmax/nm (e)): 913
(2050), 815 (2620), 651 (7180), 569 (8630), 527 (5720), 429
(55000), 356 (41400); Anal. Calcd for 3c (C49 Ni): C
F
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
l
3
3
3
); UV-vis (CH Cl
2
2
,
3
3
), –65.48 (s, 3F,
3
3
2
2
+
4
C
40(176000); HRMS (ESI-TOF) m/z: [M+H] Calcd for
48
H
26
F
12
N
4
887.20441; Found 887.20283.
H
23
F
12
N
5
6
0.77; H 2.39; N 7.23. Found: C 60.38; H 2.34; N 7.15.
3
-Cyano-N-Confused Tetrakis(p-trifluoromethylphenyl)-porphyrin
(
3): To a 500 mL DMF solution of 2 (400 mg, 0.45 mmol), sodium
cyanide (322 mg, 10 mmol) was added and stirred for 12 h. After
the solvent was evaporated, the residue was dissolved in CH Cl
and the solution was washed with water and brine. The organic
layer was separated and dried over Na SO . After evaporation, the
residue was separated by silica gel column chromatography with
CH Cl /hexane. Concentration of the fraction and recrystallization
3-Formyl-N-Confused
Tetrakis(p-trifluoromethylphenyl)-
porphyrin Ni(II) Complex (5): To a 260 mL solution of 4 (370
mg, 0.38 mmol) in toluene, 1.0 M DIBAL-H in toluene (2.3 mL,
2.3 mmol) was added under nitrogen at 0 °C. After 5 min, the reac-
tion was quenched by 5 mL of 1.0 M hydrochloric acid and the
solution was stirred at 0 °C for 30 min. The organic layer was
washed with water and dried over Na
residues were separated by silica gel column chromatography with
CH Cl /hexane. The fraction was concentrated and the residue
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
4
2
2
2
SO . After evaporation, the
4
of the residue from CH
2
Cl
2
/MeOH afforded 3. Yield: 308 mg
1
(
75%). H NMR (CDCl
3
, 300 MHz, ppm): d –4.42 (s, 1H, inner
2
2
CH), –1.60 (br s, 2H, inner NH), 8.04 (d, J = 7.9 Hz, 2H, m-ArH),
was recrystallized from MeOH/CH Cl to give 5. Yield: 170 mg
2
2
8
8
8
8
.05 (d, J = 7.9 Hz, 2H, m-ArH), 8.12 (d, J = 8.2 Hz, 2H, m-ArH),
.14 (d, J = 8.5 Hz, 2H, m-ArH), 8.23 (d, J = 7.9 Hz, 2H, o-ArH),
.26 (d, J = 7.9 Hz, 2H, o-ArH), 8.38–8.43 (m, 4H, o-ArH, b-H),
.44 (d, J = 7.9 Hz, 2H, o-ArH), 8.47 (d, J = 5.1 Hz, 1H, b-H), 8.51
1
(
46%). H NMR (CDCl
3
): d 7.13 (d, J = 4.9 Hz, 1H, b-H), 7.19 (d,
J = 5.2 Hz, 1H, b-H), 7.36 (s, 2H, b-H), 7.41 (d, J = 4.9 Hz, 1H, b-
H), 7.42 (d, J = 5.2 Hz, 1H, b-H), 7.70 (d, J = 8.4 Hz, 2H, m-ArH),
7
.72 (d, J = 8.4 Hz, 2H, m-ArH), 7.76 (d, J = 8.4 Hz, 2H, m-ArH),
(
d, J = 5.2 Hz, 1H, b-H), 8.90 (d, J = 5.2 Hz, 1H, b-H), 8.92 (d, J =
7.78 (d, J = 8.4 Hz, 4H, o,m-ArH), 7.85 (d, J = 8.4 Hz, 2H, o-ArH),
1
3
13
5
1
1
1
1
1
1
1
1
1
1
1
2
.1 Hz, 1H, b-H); C NMR (CDCl
3
, 75 MHz, ppm): d 93.6, 115.2,
8.46 (s, 1H, CHO), 9.97 (br s, 1H, outer NH); C NMR (CDCl ,
3
16.3, 118.1, 118.6, 122.18, 122.23, 122.3, 123.87, 123.97, 124.00,
24.05, 124.10, 124.12, 124.17, 124.20, 124.21, 124.24, 124.26,
24.31, 124.36, 124.38, 124.64, 124.67, 124.70, 124.74, 124.78,
24.80, 124.83, 124.85, 124.86, 124.89, 124.91, 125.79, 125.83,
25.9, 126.02, 126.07, 126.11, 126.13, 126.16, 127.28, 127.29,
27.31, 127.35, 127.41, 129.40, 129.44, 129.49, 129.69, 129.71,
29.77, 129.83, 129.89, 139.95, 130.1, 130.2, 130.3, 130.4, 130.57,
30.63, 130.8, 130.96, 130.99, 131.2, 131.3, 131.4, 131.8, 134.3,
34.4, 135.16, 135.19, 135.25, 135.29, 135.33, 135.79, 135.83,
75 MHz, ppm): d 117.0, 117.3, 120.3, 120.8, 122.15, 122.20, 122.5,
123.96, 124.01, 124.07, 124.25, 124.28, 124.33, 124.37, 124.42,
124.68, 124.75, 124.79, 124.84, 125.01, 125.02, 125.3, 125.4,
125.76, 125.81, 126.1, 129.3, 129.7, 130.0, 130.5, 130.9, 131.0,
131.1, 131.4, 131.6, 132.42, 132.48, 132.54, 132.8, 133.31, 133.34,
133.4, 133.6, 134.0, 134.6, 134.7, 139.5, 139.6, 143.0, 143.29,
143.32, 143.39, 143.41, 143.8, 148.6, 148.7, 152.2, 152.9, 157.5,
1
–
19
58.6, 180.7; F NMR (CDCl
3
, 270 MHz): d –60.71 (s, 6F, CF
3
),
60.74 (s, 3F, CF
3
), –60.92 (s, 3F, CF ); UV-vis (CH Cl , lmax/nm
3
2
2
35.9, 136.1, 137.0, 137.3, 137.5, 141.3, 141.4, 141.50, 141.52,
(
(
e)): 867 (872), 672 (5310), 587 (12600), 545 (6730), 437
54300), 366 (46700); HRMS (ESI-TOF) m/z: [M-H] Calcd for
19
41.8, 142.6, 144.00, 144.02, 146.3, 157.6, 159.0; F NMR (CDCl
3
,
–
70 MHz): d –60.53 (s, 3F, CF
F, CF ); UV-vis (CH Cl , lmax/nm (e)): 774 (16500), 596 (3250),
51 (13500), 455 (186000), 387 (44700); Anal. Calcd for 2c
): C 64.55; H 2.76; N 7.68. Found: C 64.63; H 2.82;
3
), –60.61 (s, 6F, CF
3
), –60.63 (s,
C
49
H
24
F
12
N
4
NiO 969.10296; Found 969.10337.
3
5
3
2
2
((4-Methoxypyridin-2-yl)methyl)-triphenylphosphonium
2
3
Chloride: 2-Hydroxymethyl-4-methoxypyridine (100 mg, 0.72
mmol) was dissolved in CH Cl (3 mL) and treated with thionyl
chloride (0.063 mL) at room temperature for 1 h. The reaction
mixture was neutralized with saturated aqueous NaHCO solution,
extracted with CH Cl , and dried over Na SO . After evaporation,
2-chloromethyl-4-methoxypyridine was obtained. This was reacted
with an equimolar amount of triphenylphosphine in toluene (2
mL) at reflux for 21 h. The solvent was evaporated and the residue
was washed with ether to give a 170 mg of Wittig reagent after dry-
ing in vacuo. H NMR (CDCl
Hz, 2H, CH
and Py), 8.0 (d, J = 6.0 Hz, 1H, Py); C NMR (CDCl3, 75 MHz): d
32.6 (d, JC-P = 51.7 Hz, CH
111.9 (d, JC(3)-P = 8.1 Hz, C(3), Py), 119.0 (d, Jc(i)-P = 86.55 Hz, C(i),
Ph), 129.8 (d, JC(o)-P = 12.5 Hz, C(o), Ph), 134.3 (d, JC(m)-P = 10.0
Hz, C(m), Ph), 134.5 (d, JC(p)-P = 3.1 Hz, C(p), Ph), 149.2 (s, C(H),
Py), 151.8 (d, JC(2)-P = 8.1 Hz, C(2), Py), 166.3 (s, C(H), Py).
(
C
49
H
25
F
12
N
5
2
2
N 7.47.
3
-Cyano-N-Confused
Tetrakis(p-trifluoromethylphenyl)-
3
porphyrin Ni(II) Complex (4): Compound 3 (300 mg, 0.33
mmol) and nickel acetylacetate (452 mg) were dissolved in tolue-
ne/ methanol and refluxed for 4 h under Ar atmosphere. The reac-
tion mixture was washed with water and the separated organic layer
2
2
2
4
was dried over Na
decomposition of the product.) The solvent was evaporated and
the residue was recrystallized from CH
Yield: 297 mg (96%). H NMR (CDCl
J = 5.5 Hz, 1H, b-H), 7.29 (d, J = 5.2 Hz, 1H, b-H), 7.43 (d, J = 5.2
Hz, 1H, b-H), 7.45 (d, J = 5.2 Hz, 1H, b-H), 7.49 (d, J = 5.5 Hz, 1H,
b-H), 7.53 (d, J = 4.9 Hz, 1H, b-H), 7.75–7.87 (m, 14H, o,m-ArH),
2
SO
4
. (Quick work up was necessary to avoid the
1
3
): d 3.78 (s, 3H, CH ), 5.65 (d, J = 14
3
2
Cl /hexane to afford 4.
, 300 MHz, ppm): d 7.21 (d,
2
2
), 6.60 (d, J = 6.0 Hz, 1H, Py), 7.58–7.89 (m, 16H, Ph
1
3
13
2
-P), 55.9 (s, CH ), 111.0 (s, C(H), Py),
3
1
3
7.93 (d, J = 7.9 Hz, 2H, o-ArH); C NMR (THF-d , 75 MHz,
8
ppm): d 115.9, 116.7, 117.5, 122.40, 122.43, 122.46, 123.75,
123.77, 123.81, 123.86, 123.90, 123.95, 124.00, 124.02, 124.05,
124.09, 124.13, 124.18, 124.19, 124.6, 126.00, 126.03, 126.06,
128.6, 129.01, 129.08, 129.12, 129.17, 129.4, 129.57, 129.60,
1
1
1
1
3
-(2-(2-Pyridyl)ethenyl)-N-Confused
Tetrakis(p-
trifluoromethylphenyl)porphyrin Ni(II) Complex (1a-Ni):
Compound 5 (20 mg, 0.021 mmol) and triphenyl(pyridin-2-
ylmethyl)phosphonium chloride (8 mg, 0.021 mmol) were dis-
29.63, 129.66, 129.69, 129.72, 129.74, 129.76, 129.80, 129.81,
29.86, 129.91, 130.0, 130.1, 130.6, 131.6, 132.4, 132.60, 132.63,
32.71, 132.76, 132.78, 133.15, 133.24, 133.69, 134.31, 134.33,
34.35, 134.37, 134.39, 134.41, 134.45, 140.6, 141.8, 144.03,
solved in CH
2
Cl
2
(15 mL) and DBU (3.1 µL, 0.021 mmol) was
added. The solution was stirred for 15 min at room temperature.
8
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The Journal of Organic Chemistry
The resulting solution was evaporated and the residue was separat-
ed by silica gel column chromatography with CH Cl /hexane. The
first and third fractions were recrystallized from CH Cl /hexane to
ly. Yield: cis-1b-Ni; 11.3 mg (17%), trans-1b-Ni; 24.7 mg (37%).
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
2
2
cis-1b-Ni: H NMR (CDCl ): d 3.87 (s, 3H, CH ), 6.15 (d, J = 13.4
3
3
2
2
Hz, 1H, olefin), 6.23 (d, J = 13.4 Hz, 1H, olefin), 6.59 (dd, J = 6.0,
2.3 Hz, 1H, Py), 6.78 (d, J = 5.8 Hz, 1H, Py), 6.82 (d, J = 2.1 Hz,
give cis-1a-Ni and trans-1a-Ni, respectively. Yield: cis-1a-Ni, 3.3
1
mg (15%), trans-1a-Ni, 12.0 mg (55%). cis-1a-Ni: H NMR
1
H, Py), 7.61 (d, J = 4.8 Hz, 1H, b-H), 7.67 (d, J = 5.7 Hz, 1H, b-
H), 7.77 (d, J = 5.7 Hz, 1H, b-H), 7.79 (d, J = 4.8 Hz, 1H, b-H),
.80 (s, 2H, b-H), 7.84 (d, J = 7.6 Hz, 2H, m-ArH), 7.85 (d, J = 8.4
(
CDCl ): d 6.17 (d, J = 13.7 Hz, 1H, olefin), 6.30 (d, J = 13.7 Hz,
3
1H, olefin), 6.96 (dd, J = 5.2, 1.5 Hz, 1H, Py), 7.09 (dd, J = 7.0, 5.2
Hz, 1H, Py), 7.34 (d, J = 8.5 Hz, 1H, Py), 7.61 (d, J = 5.2 Hz, 1H, b-
H), 7.66 (d, J = 5.5 Hz, 1H, b-H), 7.74 (ddd, J = 7.5, 7.5, 2.7 Hz,
7
Hz, 2H, m-ArH), 7.87 (d, J = 7.6 Hz, 2H, m-ArH), 7.92 (d, J = 7.6
Hz, 2H, o-ArH), 7.94 (d, J = 8.4 Hz, 2H, o-ArH), 7.96 (d, J = 7.6 Hz,
1
H, Py), 7.77 (d, J = 5.5 Hz, 1H, b-H), 7.78 (d, J = 5.2 Hz, 1H, b-
2H, o-ArH), 7.97 (d, J = 7.9 Hz, 2H, m-ArH), 8.15 (d, J = 7.9 Hz,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
H), 7.78 (d, J = 5.5 Hz, 2H, b-H), 7.85 (d, J = 7.5 Hz, 2H, m-ArH),
2H, o-ArH), 17.3 (br s, 1H, outer NH); C NMR (CDCl
3
, 75
7
7
7
8
.94 (d, J = 7.5 Hz, 2H, o-ArH), 7.84 (d, J = 6.9 Hz, 2H, m-ArH),
.87 (d, J = 7.5 Hz, 2H, m-ArH), 7.92 (d, J = 6.9 Hz, 2H, o-ArH),
MHz): d 55.5, 109.2, 113.1, 116.0, 117.1, 121.2, 121.8, 122.0,
122.49, 122.58, 122.62, 122.88, 122.92, 123.94, 123.98, 124.07,
124.1, 124.2, 124.3, 124.35, 124.39, 124.44, 126.05, 126.09, 126.18,
126.22, 127.6, 129.0, 129.19, 129.21, 129.5, 129.6, 129.9, 130.0,
130.4, 130.9, 131.0, 131.3, 132.2, 132.4, 133.2, 133.7, 134.0, 143.3,
.96 (d, J = 7.5 Hz, 2H, o-ArH), 7.98 (d, J = 7.9 Hz, 2H, m-ArH),
13
.16 (d, J = 7.9 Hz, 2H, o-ArH), 16.9 (br s, 1H, outer NH);
C
NMR (CDCl3, 150 MHz): d 116.1, 117.1, 121.3, 121.6, 122.8,
1
1
1
1
1
1
23.1, 123.39, 123.46, 123.52, 124.00, 124.02, 124.10, 124.13,
24.16, 124.19, 124.21, 124.47, 124.49, 124.52, 125.19, 125.27,
25.33, 127.58, 127.61, 129.1, 129.3, 129.6, 129.8, 130.17, 130.23,
30.39, 130.44, 130.7, 131.4, 132.3, 132.4, 133.22, 133.24, 133.3,
144.9, 145.0, 145.5, 146.2, 148.0, 149.1, 151.3, 152.6, 152.9, 154.3,
19
166.9; F NMR (CDCl
3
, 270 MHz): d –60.37 (s, 3F, CF ), –60.42
3
(s, 6F, CF ), –60.61 (s, 3F, CF ); UV-vis (CH Cl , l (nm)) 886
3
3
2
2
max
(2020), 797 (2510), 615 (17300), 491 (29200), 455 (30600), 390
+
33.7, 133.8, 138.1, 143.3, 144.7, 144.8, 145.0, 145.5, 146.3, 146.8,
(29600); HRMS (ESI-TOF) m/z: [M]
Calcd for
19
1
48.1, 149.2, 151.5, 152.7, 152.8, 152.8; F NMR (CDCl
3
, 270
), –60.51 (s, 3F,
, lmax (nm)) 800 (3900),
16 (21900), 492 (37000), 454 (40200), 393 (38600); HRMS
C H F N NiO 1075.16905; Found 1075.16932. trans-1b-Ni: H
5
6
31 12
5
MHz): d –60.46 (s, 3F, CF
CF ), –60.75 (s, 3F, CF ); UV-vis (CH
3
), –60.50 (s, 3F, CF
Cl
3
NMR (CDCl ): d 3.86 (s, 3H, CH ), 6.56 (d, J = 1.8 Hz, 1H, Py),
3
3
3
3
2
2
6.72 (dd, J = 1.8, 5.5 Hz, 1H, Py), 6.88 (d, J = 16.5 Hz, 1H, olefin),
7.01 (d, J = 16.5 Hz, 1H, olefin), 7.59 (d, J = 4.9 Hz, 1H, b-H), 7.67
6
+
(
ESI-TOF) m/z: [M] Calcd for C55
H
29
F
12
N
5
Ni 1045.15848;
Found 1045.15846. trans-1a-Ni: H NMR (CDCl ): d 6.72 (d, J =
6.5 Hz, 1H, olefin), 6.95 (d, J = 8.2 Hz, 1H, Py), 7.08 (d, J = 16.5
(
d, J = 4.9 Hz, 1H, b-H), 7.77 (d, J = 4.9 Hz, 1H, b-H), 7.78 (d, J =
1
3
4
.9 Hz, 1H, b-H), 7.80 (d, J = 4.9 Hz, 1H, b-H), 7.84 (d, J = 4.9 Hz,
1
1
H, b-H), 7.85–7.98 (m, 14H), 8.03 (d, J = 7.9 Hz, 2H, o-Ar), 8.34
Hz, 1H, olefin), 7.19 (dd, J = 7.0, 4.9 Hz, 1H, Py), 7.60 (d, J = 5.4
Hz, 1H, b-H), 7.62 (ddd, J = 7.8, 7.8, 1.5 Hz, 1H, Py), 7.67 (d, J =
13
(
(
d, J = 5.5 Hz, 1H, Py), 9.83 (br s, 1H, outer NH); C NMR
CDCl
3
, 75 MHz): d 54.9, 115.8, 117.06, 117.09, 117.2, 119.4,
5
1
.2 Hz, 1H, b-H), 7.76 (d, J = 5.1 Hz, 1H, b-H), 7.80 (d, J = 5.1 Hz,
H, b-H), 7.81 (d, J = 5.4 Hz, 1H, b-H), 7.83 (d, J = 5.2 Hz, 1H, b-
1
21.3, 121.92, 121.94, 121.98, 122.03, 122.05, 122.06, 122.08,
122.10, 122.3, 123.9, 124.50, 124.54, 124.59, 125.5, 125.8, 125.9,
126.0, 128.8, 128.9, 129.1, 129.2, 129.5, 129.6, 129.7, 129.9, 130.1,
131.3, 131.9, 132.1, 132.5, 132.9, 133.1, 133.5, 140.67, 140.69,
H), 7.85 (d, J = 9.0 Hz, 2H, m-ArH), 7.86 (d, J = 9.0 Hz, 2H, m-
ArH), 7.91 (d, J = 9.0 Hz, 2H, m-ArH), 7.94 (d, J = 9.0 Hz, 4H, o-
ArH), 7.99 (d, J = 9.0 Hz, 2H, o-ArH), 7.97 (d, J = 9.0 Hz, 2H, m-
ArH), 8.03 (d, J = 9.0 Hz, 2H, o-ArH), 8.53 (d, J = 4.0 Hz, 1H, Py),
140.71, 143.81, 143.85, 143.89, 143.90, 143.92, 144.0, 144.2, 144.3,
19
1
44.6, 146.1, 148.0, 149.4, 151.4, 152.6, 153.2; F NMR (CDCl3,
1
3
9
1
1
1
1
1
1
.86 (br s, 1H, outer NH); C NMR (CDCl , 75 MHz): d 116.3,
3
270 MHz): d –60.51 (s, 3F, CF
3F, CF ), –60.64 (s, 3F, CF ); UV-vis (CH
(3550), 602 (26000), 452 (59900), 382 (52300); HRMS (ESI-
3
), –60.52 (s, 3F, CF
3
), –60.63 (s,
17.6, 119.9, 121.28, 121.32, 121.8, 122.4, 122.6, 122.7, 123.6,
24.30, 124.35, 124.38, 124.43, 134.5, 125.05, 125.10, 125.14,
25.2, 126.0, 126.2, 126.3, 126.5, 129.5, 129.6, 129.8, 130.1, 130.2,
30.4, 130.6, 130.8, 130.9, 131.3, 131.8, 132.3, 132.5, 132.7, 132.9,
33.3, 133.6, 134.0, 136.7, 141.1, 144.6, 144.71, 144.73, 145.2,
3
3
2
2
Cl , lmax/nm (e)): 799
+
TOF) m/z: [M+H] Calcd for C56
H
31
F
12
N
5
NiO 1076.17419;
Found 1076.17687.
1
9
3-(2-(2-Pyridyl)ethenyl)-N-Confused
Tetrakis(p-
46.6, 148.6, 150.01, 150.08, 152.1, 152.6, 153.9, 154.0; F NMR
CDCl , 270 MHz): d –60.53 (s, 3F, CF ), –60.54 (s, 3F, CF ), –
0.52 (s, 3F, CF ), –60.68 (s, 3F, CF ); UV-vis (CH Cl
trifluoromethylphenyl)porphyrin (1a): trans-1a-Ni (27.6 mg,
0.026 mmol) was dissolved in 20 mL of dichloromethane and me-
thanesulfonic acid (0.1 mL) was added. The solution was stirred
(
6
3
3
3
3
3
2
2
, lmax/nm
(
(
e)): 800 (4190), 602 (30200), 452 (68500), 382 (61200); HRMS
for 30 min, and aqueous NaHCO solution was added. The reac-
3
–
ESI-TOF) m/z: [M-H] Calcd for C55
H
29
F
12
5
N Ni 1044.15083;
tion mixture was washed with water, and the organic layer was sep-
arated. After the solvent was evaporated, the residue was separated
by silica gel column chromatography with 1% triethylamine in
Found 1044.15066.
3-(2-(4-Methoxy-2-Pyridyl)ethenyl)-N-Confused Tetrakis(p-
trifluoromethylphenyl)porphyrin Ni(II) Complex (1b-Ni):
Compound 5 (60 mg, 0.062 mmol) and ((4-methoxypyridin-2-
yl)methyl)triphenylphosphonium chloride (26 mg, 0.062 mmol)
CH
2
C1
2
to afford trans-3H-1a (22.0 mg, 84%) and cis-2H-1a (3.5
1
mg, 13%) trans-3H-1a: H NMR (CDCl , 300 MHz, ppm): d –
.
3
4.78 (s, 1H, inner CH), –2.00 (br s, 2H, inner NH), 6.97 (d, J =
15.3 Hz, 1H, olefin), 7.09 (d, J = 7.6 Hz, 1H, Py), 7.12 (dd, J = 3.4,
7.6 Hz, 1H, Py), 7.58 (ddd, J = 3.4, 7.6, 7.8 Hz, 1H, Py), 7.94 (d, J =
15.3 Hz, 1H, olefin), 8.04 (d, J = 8.3 Hz, 2H, m-ArH), 8.04 (d, J =
8.1 Hz, 2H, m-ArH), 8.11 (d, J = 8.3 Hz, 2H, m-ArH), 8.12 (d, J =
7.2 Hz, 4H, m-ArH), 8.27 (d, J = 8.3 Hz, 2H, o-ArH), 8.30 (d, J =
were dissolved in 30 mL CH
2
2
Cl and DBU (9.0 µL, 0.061 mmol)
was added. The solution was stirred for 15 min in room tempera-
ture. After the solvent was removed by evaporation, the residue was
separated by silica gel column chromatography with
CH
from CH
2
Cl
2
/hexane. The first and third fractions were recrystallized
Cl /hexane to give cis-1b-Ni and trans-1b-Ni respective-
2
2
8.1 Hz, 2H, o-ArH), 8.43 (d, J = 5.8 Hz, 1H, b-H), 8.45 (d, J = 4.9
9
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The Journal of Organic Chemistry
Page 10 of 13
Hz, 1H, b-H), 8.47 (d, J = 5.8 Hz, 1H, b-H), 8.48 (d, J = 7.2 Hz, 2H,
o-ArH), 8.50 (d, J = 3.4 Hz, 1H, Py), 8.51 (d, J = 5.2 Hz, 1H, b-H),
NMR: Because of the isomerization during the measurement, dis-
1
9
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
tinct spectrum was unable to obtain; F NMR (CDCl
d –60.38 (s, 3F, CF ), –60.52 (s, 6F, CF ), –60.67 (s, 3F, CF
vis (CH Cl , lmax/nm (e)): 740 (12200), 663 (16500), 613
3
, 270 MHz):
3
3
3
); UV-
8
.54 (d, J = 8.3 Hz, 2H, o-ArH), 8.84 (d, J = 4.9 Hz, 1H, b-H), 8.85
1
3
2
2
(
d, J = 5.2 Hz, 1H, b-H); C NMR: Because of the isomerization
(
12000), 495 (113000), 375 (54500); HRMS (ESI-TOF) m/z:
during the measurement, distinct spectrum was unable to obtain;
+
1
9
[M+H] Calcd for AgC55
H
28AgF12
N
5
1020.25717; Found
F NMR (CDCl
CF ), –60.61 (s, 3F, CF
10900), 558 (20200), 472 (162000), 374 (53200); HRMS (ESI-
3
, 270 MHz): d –60.37 (s, 3F, CF
3
), –60.50 (s, 6F,
1
020.25703.
3
3
); UV-vis (CH Cl , lmax/nm (e)): 765
2
2
3
-(2-(2-Pyridyl)ethenyl)-N-Confused
Tetrakis(p-
(
–
trifluoromethylphenyl)porphyrin Ag(III) Complex (trans-1a-
Ag): trans-1a (25.0 mg, 0.025 mmol) was dissolved in 20 mL of
TOF) m/z: [M-H] Calcd for C55
H
31
F
12
N
5
988.23096; Found
1
9
88.23060. cis-2H-1a: H NMR (CDCl
3
): d 1.60 (s, 1H, inner
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CH
2
2
Cl and silver(I) acetate (21.5 mg, 0.125 mmol) was added.
CH), 4.09 (br s, 1H, inner NH), 6.02 (d, J = 13.6 Hz, 1H, olefin),
.20 (d, J = 13.6 Hz, 1H, olefin), 6.90 (d, J = 4.9 Hz, 1H, Py), 7.03
dd, J = 7.0, 5.2 Hz, 1H, Py), 7.25 (d, J = 8.9 Hz, 1H, Py), 7.40 (d, J
4.2 Hz, 1H, b-H), 7.46 (d, J = 4.2 Hz, 1H, b-H), 7.68 (t, J = 8.2
Hz, 1H, Py), 7.68 (s, 2H, b-H),7.78 (d, J = 4.2 Hz, 1H, b-H), 7.85
d, J = 4.2 Hz, 1H, b-H), 7.86 (d, J = 8.3 Hz, 4H, m-ArH), 7.91 (d, J
7.3 Hz, 2H, m-ArH), 7.96 (d, J = 8.3 Hz, 4H, o-ArH), 8.02 (d, J =
.3 Hz, 2H, m-ArH), 8.08 (d, J = 7.3 Hz, 2H, o-ArH), 8.26 (d, J =
The solution was stirred for 2 h, and then the solvent was evapo-
rated. The residue was separated by silica gel column chromatog-
6
(
=
raphy with 1% methanol in CH
2
Cl to afford trans-1a-Ag (15.7 mg,
2
1
5
1
1
7%). H NMR (CDCl
H, olefin), 7.14 (d, J = 8.2 Hz, 1H, Py), 7.18 (dd, J = 6.0, 7.9 Hz,
H, Py), 7.19 (dd, J = 7.7, 7.7 Hz, 1H, Py), 8.03 (d, J = 15.6 Hz, 1H,
3
, 300 MHz, ppm): d 7.05 (d, J = 15.6 Hz,
(
=
olefin), 8.02–8.07 (m, 8H, m-ArH), 8.14 (d, J = 7.7 Hz, 2H, o-ArH),
8
8
8
.24 (d, J = 8.2 Hz, 2H, o-ArH), 8.27 (d, J = 8.1 Hz, 2H, o-ArH),
1
3
.3 Hz, 2H, o-ArH), 16.5 (br s, 1H, outer NH); C NMR: Because
8
.37 (d, J = 7.9 Hz, 2H, o-ArH), 8.52 (d, J = 5.0 Hz, 1H, b-H), 8.57
of the isomerization during the measurement, distinct spectrum
1
9
(d, J = 5.0 Hz, 1H, b-H), 8.57 (d, J = 5.0 Hz, 1H, b-H), 8.60 (s, 1H,
Py), 8.62 (d, J = 4.5 Hz, 1H, b-H), 8.66 (d, J = 5.0 Hz, 1H, b-H),
was unable to obtain; F NMR (CDCl
F, CF ), –60.52 (s, 6F, CF ), –60.72 (s, 3F, CF
max/nm (e)): 742 (16400), 664 (23200), 664 (32200), 614
3
, 270 MHz): d –60.39 (s,
3
l
3
3
3
); UV-vis (CH Cl ,
2
2
1
3
8
.85 (d, J = 4.5 Hz, 1H, b-H); C NMR (CDCl
3
, 150 MHz): d
+
118.9, 119.8, 120.8, 121.9, 122.6, 123.5, 123.6, 123.79, 123.82,
(17300), 497 (154000); HRMS (ESI-TOF) m/z: [M+H] Calcd
: 990.24661; Found 990.24663.
1
1
1
1
1
1
23.84, 124.2, 124.3, 124.46, 124.48, 124.50, 125.3, 125.4, 125.5,
25.6, 126.1, 127.5, 128.2, 128.5, 128.6, 128.8, 129.15, 129.18,
29.6, 129.81, 129.83, 130.06, 130.09, 130.3, 130.5, 130.6, 130.7,
30.8, 130.9, 131.0, 131.5, 133.3, 134.1, 135.7, 136.2, 137.7, 138.84,
38.86, 138.90, 138.92, 139.1, 139.9, 140.5, 141.5, 143.1, 144.2,
for C55
H
31
F
12
N
5
3-(2-(4-Methoxy-2-Pyridyl)ethenyl)-N-Confused Tetrakis(p-
trifluoromethylphenyl)porphyrin (1b): trans-1b-Ni (29.6 mg,
0.027 mmol) was dissolved in 10 mL of dichloromethane and me-
thanesulfonic acid (0.1 mL) was added. The solution was stirred
1
9
44.9, 149.8, 155.4, 164.5; F NMR (CDCl
s, 3F, CF ), –60.55 (s, 3F, CF ), –60.58 (s, 3F, CF
); UV-vis (CH Cl , lmax/nm (e)): 581 (6860), 534 (8140), 467
3
, 270 MHz): d –60.36
for 20 min and aqueous NaHCO solution was added. The reaction
3
(
CF
3
3
3
), –60.59 (s, 3F,
mixture was washed with water and the organic layer was separated.
After the solvent was removed by evaporation, the residue was
separated by silica gel column chromatography with 1% triethyla-
3
2
2
(
52800), 387 (19700), 332 (17500); HRMS (ESI-TOF) m/z:
+
[
M+H] Calcd for C55
H
28
F
12
5
N Ag 1094.12821; Found 1094.12823.
mine in CH
1b (9.4 mg, 33%)
ppm): d –4.77 (s, 1H, inner CH), –1.99 (br s, 2H, inner NH), 3.85
(s, 3H, OCH ), 6.65–6.67 (m, 2H, Py), 7.04 (d, J = 15.5 Hz, 1H,
2
Cl
2
to afford trans-3H-1b (18.0 mg, 64%) and cis-2H-
1
.
trans-3H-1b: H NMR (CDCl
3
, 300 MHz,
3-(2-(2-Pyridyl)ethenyl)tetraphenylporphyrin
(7):
Tri-
phenyl[(5,10,15,20-tetraphenylporphyrin-2-
1
7b
yl)methyl]phosphonium chloride (200 mg, 0.22 mmol) and 2-
formylpyridine (46.3 mg, 0.43 mmol) were dissolved in 20 mL
3
olefin), 7.86 (d, J = 15.5 Hz, 1H, olefin), 8.04 (d, J = 6.6 Hz, 4H, m-
ArH), 8.11 (d, J = 7.8 Hz, 4H, m-ArH), 8.27 (d, J = 7.4 Hz, 2H, o-
ArH), 8.29 (d, J = 7.4 Hz, 2H, o-ArH), 8.31 (d, J = 6.0 Hz, 1H, Py),
CH
2
2
Cl and DBU (100 µL, 0.68 mmol) was added. The reaction
mixture was stirred for 10 min at room temperature. After the sol-
vent was removed by evaporation, the residue was separated by
8
.47 (d, J = 7.8 Hz, 2H, o-ArH), 8.55 (d, J = 7.8 Hz, 2H, o-ArH),
silica gel column chromatography with CH
and third fractions were recrystallized from CH
2
Cl
2
2
/hexane. The first
Cl /hexane to give
8.42 (d, J = 4.9 Hz, 1H, b-H), 8.45 (d, J = 5.1 Hz, 1H, b-H), 8.46 (d,
J = 6.0 Hz, 1H, b-H), 8.50 (d, J = 4.9 Hz, 1H, b-H), 8.84 (d, J = 4.9
2
1
3
cis-7 and trans-7, respectively. Yield: cis-7 33.0 mg (21%), trans-7
Hz, 2H, b-H); C NMR: Because of the isomerization during the
1
1
9
80.0 mg (52%). trans-7: H NMR (CDCl
3
, 300 MHz, ppm): d –
measurement, distinct spectrum was unable to obtain; F NMR
CDCl , 270 MHz): d –60.41 (s, 3F, CF ), –60.54 (s, 6F, CF ), –
0.65 (s, 3F, CF ); UV-vis (CH Cl , lmax/nm (e)): 765 (5880),
58 (13500), 472 (138000), 379 (43100); HRMS (ESI-TOF)
2
.55 (br s, 2H, inner NH), 7.12–7.18 (m, 2H, Py), 7.21 (d, J = 16.2
Hz, 1H, olefin), 7.50 (d, J = 16.2 Hz, 1H, olefin), 7.64 (dd, J = 7.3,
.3 Hz, 1H, Py), 7.78–7.81 (m, 12H, m, p-Ph), 8.23–8.25 (m, 8H,
(
3
3
3
6
5
3
2
2
7
+
m, o-Ph), 8.58 (d, J = 4.6 Hz, 1H, Py), 8.77 (d, J = 4.8 Hz, 1H, b-H),
8.82 (d, J = 4.8 Hz, 1H, b-H), 8.86 (d, J = 4.6 Hz, 4H, b-H), 9.13 (s,
m/z: [M+H] Calcd for
C
56
H
33
F
12
N
5
O
3
1020.25717; Found
): d 1.56 (s, 1H, inner
), 6.00 (d, J = 13.4
Hz, 1H, olefin), 6.13 (d, J = 13.4 Hz, 1H, olefin), 6.54 (dd, J = 6.0,
.0 Hz, 1H, Py), 6.72–6.74 (m, 2H, Py), 7.41 (d, J = 4.9 Hz, 1H, b-
H), 7.47 (d, J = 4.6 Hz, 1H, b-H), 7.69 (br s, 2H, b-H), 7.78 (d, J =
1
1
020.25707. cis-2H-1b: H NMR (CDCl
1H, b-H); UV-vis (CH
2
2
Cl , lmax/nm (e)): 657 (1510), 600 (3960),
CH, 3.99 (br s, 1H, inner NH), 3.84 (s, 3H, CH
3
562 (6050), 524 (11300), 427 (141000); HRMS (ESI-TOF) m/z:
+
[M+H] Calcd for C51
H
35
N 718.29707; Found 718.29739. cis-7:
5
2
1
H NMR (CDCl ): d –2.72 (br s, 2H, inner NH), 6.43 (d, J = 12.2
3
Hz, 1H, olefin), 6.71 (d, J = 12.2 Hz, 1H, olefin), 6.97–7.03 (m, 3H,
Py), 7.57 (t, J = 7.3 Hz, 1H, Py), 7.63–7.68 (m, 3H, m, p-Ph), 7.75–
7.77 (m, 8H, m, p-Ph), 7.98 (d, J = 7.0 Hz, 2H, o-Ph), 8.08 (d, J =
7.0 Hz, 2H, o-Ph), 8.20 (d, J = 7.5 Hz, 4H, o-Ph), 8.52–8.54 (m, 2H,
4
4
.9 Hz, 1H, b-H), 7.86 (d, J = 4.9 Hz, 1H, b-H), 7.86 (d, J = 8.2 Hz,
H, m-Ar), 7.91 (d, J = 8.1 Hz, 2H, m-Ar), 7.96 (d, J = 8.2 Hz, 4H,
o-Ar), 8.02 (d, J = 8.1 Hz, 2H m-Ar), 8.08 (d, J = 8.1 Hz, 2H o-Ar),
8
1
3
.26 (d, J = 8.1 Hz, 2H o-Ar), 16.82 (br s, 1H, outer NH); C
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The Journal of Organic Chemistry
b-H, Py), 8.76–8.84 (m, 6H, b-H);UV-vis (CH
2
Cl
2
, lmax/nm (e)):
Calculation data (PDF)
X-ray crystallographic data for compound cis-1a-Ni (CIF)
X-ray crystallographic data for compound trans-1b-Ag (CIF)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
51 (2750), 596 (5460), 556 (6740), 520 (17600), 422 (272000);
+
HRMS (ESI-TOF) m/z: [M+H] Calcd for C51
H
35
5
N 718.29707;
Found 718.29709.
AUTHOR INFORMATION
Corresponding Author
* hfuruta@cstf.kyushu-u.ac.jp
ORCID
Hiroyuki Furuta: 0000-0002-3881-8807
Masatoshi Ishida: 0000-0002-1117-2188
X-ray crystallography. 1a-Ni: X-ray analysis was performed on a
Rigaku VariMax with RAPID equipped with an imaging plate using
CuK
a
(multi-layer mirror, monochromated, l = 1.54187 Å) radia-
2
5
tion. The structure was solved by the direct method of SIR2004
2
6
and refined using the SHELXL-2016/6 program. The positional
parameters and thermal parameters of non-hydrogen atoms were
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
refined anisotropically on F by the full-matrix least-squares meth-
od. Hydrogen atoms were placed at calculated positions and re-
fined riding on their corresponding carbon atoms. 1a-Ag: X-ray
analysis was performed on a Rigaku Saturn 724 equipped with a
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
CCD detector using MoKa (graphite, monochromated, l =
0
.71069 Å) radiation. The structure was solved by the direct meth-
The work was supported by the Grant-in-Aid (no. 15K13646 to H.F;
16K05700 and 17H05377 to M.I.) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan. The financial support from a
bilateral program between JSPS and the National Research Foundation
(NRF) of South Africa is also acknowledged. P.K.E thanks to the financial
support from the internship program of IIT Gandhinagar and Kyushu
University.
27
od of SIR92 and refined using the SHELXL-2016/6 program.
The positional parameters and thermal parameters of non-
hydrogen atoms were refined anisotropically on F by the full-
2
matrix least-squares method. Hydrogen atoms were placed at calcu-
lated positions and refined riding on their corresponding carbon
28
atoms. PLATON/SQUEEZE was used to correct the data for the
presence of the disordered solvent.
2
9
Calculation Details: All density functional theory calculations
REFERENCES
30
were achieved with a Gaussian09 program package. The basis sets
(
(
1) Molecular Switches, Feringa, B. L., Ed.; Wiley: Weinheim, 2001.
2) (a) Dugave, C.; Demange, L. Chem. Rev. 2003, 103, 2475–2532. (b)
31
implemented in the program were used. The B3LYP density func-
tional method was used with the 6-31G** (for C, H, N, F) and
LanL2DZ (for Ni) basis set for structural optimizations. Equilibri-
um geometries were fully optimized and verified by the frequency
calculations, where no imaginary frequency was found.
cis-trans Isomerization in Biochemistry, Dugave, C., Ed.; Wiley: Wein-
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Ed.; Wiley: Weinheim, 2014. (f) Tautomerism: Concepts and Applica-
tions in Science and Technology, Antonov, L., Ed.; Wiley: Weinheim,
2016.
3
2
Saturation Transfer Experiment. The determination of the rate
constant for NCTPP tautomerism was performed on a JEOL a-
1
5
00 spectrometer (operating at 500.00 MHz for H) with a spin
(3) (a) Obi, M.; Sakuragi, H.; Arai, T. Chem. Lett. 1998, 27, 169–170.
(
b) Lewis, F. D.; Yoon, B. A.; Arai, T.; Iwasaki, T.; Tokumaru, K. J.
saturation transfer method. The spin relaxation times were estimat-
ed by an inversion recovery method. In this experiment, mainly we
used the signal of the inner CH. The tautomerism kinetics are
shown, where [3H] and [3H*] are the lower and upper spin-state
populations for the inner CH of tautomer-3H, and [2H] and
Am. Chem. Soc. 1995, 117, 3029–3036. (c) Kurihara, S.; Nishimura, Y.;
Arai, T. Bull. Chem. Soc. Jpn. 2015, 88, 963–965.
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7
67–768. (b) Chmielewski, P. J.; Latos-Grażyński, L.; Rachlewicz, K.;
Głowiak, T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779–781.
[
2H*] are those for the inner CH of tautomer-2H, respectively. T
and T1 2H are the spin lattice relaxation times for the inner CH of
-3H and 2-2H, and k , k are the rate constants of the tautomerism.
1
(5) (a) Furuta, H.; Ishizuka, T.; Osuka, A.; Dejima, H.; Nakagawa, H.;
Ishikawa, Y. J. Am. Chem. Soc. 2001, 123, 6207–6208. (b) Alemán, E.
A.; Rajesh, C. S.; Ziegler, C. J.; Modarelli, D. A. J. Phys. Chem. A 2006,
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Nemykin, V. N. J. Phys. Chem. A 2013, 117, 11499–11508. (d) Shaw, J.
L.; McMurry, J. L.; Salehi, P.; Stovall, A. J. Porphyrin Phthalocyanines
3
H
2
f
b
Here, the signals of 2-2H were saturated. With a sufficiently long
irradiation of the decoupler r. f. pulse, the spin states of the 2-2H
can be saturated; i.e. [2H] = [2H*]. Over time, the saturated spin
population is transferred to the signal of 2-2H via tautomerism,
resulting in partial loss of net magnetization of the P(3H) signal
2
014, 18, 231–239. (e) Alemán, E. A.; Jojo, J.; Modarelli, D. A. J. Org.
Chem. 2015, 80, 11031–11038. (f) Marchand, G.; Roy, H.; Mendive-
Tapia, D.; Jacquemin, D. Phys. Chem. Chem. Phys. 2015, 17, 5290–
5297. (g) Ou, Z.; Chen, X.; Ye, L.; Xue, S.; Fang, Y.; Jiang, X.; Kadish,
K. M. J. Porphyrin Phthalocyanines 2015, 19, 251–260.
(6) Maeda, H.; Morimoto, T.; Osuka, A.; Furuta, H. Chem. Asian J.
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from its thermal equilibrium value. Then, k were calculated accord-
f
ing to the equation below.
1
æ I
0
ö
ø
(1)
kf
=
-1
T
1P(3H) è I
(
7) (a) Zilbermann, I.; Maimon, E.; Ydgar, R.; Shames, A. I.; Korin, E.;
I
0
is the signal intensity in the thermal equilibrium, and I is that in
Soifer, L.; Bettelheim A. Inorg. Chem. Commun. 2004, 1238–1241. (b)
Chmielewski, P. J.; Latos-Grażyński, L.; Schmidt, I. Inorg. Chem. 2000,
saturation.
3
9, 5475–5482. (c) Furuta, H; Kubo, N.; Maeda, H.; Ishizuka, T.; Osuka,
A.; Nanami, H.; Ogawa, T. Inorg. Chem. 2000, 39, 5424–5425. (d) Fu-
ruta, H.; Youfu, K.; Maeda, H.; Osuka, A. Angew. Chem. Int. Ed. 2003,
42, 2186–2188. (e) Harvey, J. D.; Ziegler, C. J. Chem. Commun. 2004,
ASSOCIATED CONTENT
1
666–1667. (f) Maeda, H.; Ishikawa, Y.; Matsuda, T.; Osuka, A.; Furuta,
Supporting Information.
1
13
19
H. J. Am. Chem. Soc. 2003, 125, 11822–11823. (g) Furuta, H.; Ogawa,
T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999, 38, 2676–2682.
H, C, and F NMR spectra of compounds (PDF)
UV-vis-NIR and FL spectra of compounds (PDF)
Kinetic data of isomerization (PDF)
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Page 12 of 13
Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200–1211. (d) Stephens, P.
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(
8) Toganoh, M.; Furuta, H., In Handbook of Porphyrin Science: With
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Applications to Chemistry, Physics, Materials Science, Engineering,
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(
(
9
(
9
9) Toganoh, M.; Furuta, H. Chem. Commun. 2012, 48, 937–954.
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6
(
3
151–6158.
11) Morimoto, T.; Uno, H.; Furuta, H. Angew. Chem. Int. Ed. 2007, 46,
672–3675.
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H. Chem.–Eur. J. Accepted article: DOI: 10.1002/chem.201701958.
(
1
(
1
13) Sakashita, R.; Ishida, M.; Furuta, H. J. Phys. Chem. A 2015, 119,
013–1022.
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455–1458.
15) A Zn complex of b-(4-pyridylethenyl)-tetraphenylporphyrin was
synthesized and its cis-trans isomerization by the photoirradiation or I
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
2
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‡
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Pyridylethenyl-substituted N-confused porphyrin showed the thermal cis-trans isomerization at 30 °C in solution. The kinetics
‡
study revealed the activation energy from cis to trans isomer is lowered significantly to DGo
lecular proton transfer induced cis-trans isomerization mechanism was proposed.
®
= 35.7 kcal/mol. The intermo-
cis trans
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