Synthesis, properties, and reactivities of ruthenium (II) carbonyl 5,15-diazaporphyrins

Article abstract of DOI:10.1246/cl.170363

We have succeeded in the synthesis of ruthenium(II) carbonyl 5,15-diazaporphyrin complexes 2 having pyridines as axial ligands. The structures, properties, and reactivities under photoirradiation of 2 are compared with those of the corresponding ruthenium

Full text of DOI:10.1246/cl.170363

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Synthesis, Properties, and Reactivities of Ruthenium(II) Carbonyl 5,15-Diazaporphyrins
Tsubasa Nishimura, Yoshihiro Miyake,* and Hiroshi Shinokubo
Advance Publication on the web May 2, 2017
doi:10.1246/cl.170363
© 2017 The Chemical Society of Japan
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1
Synthesis, Properties, and Reactivities of Ruthenium(II) Carbonyl 5,15-Diazaporphyrins
Tsubasa Nishimura, Yoshihiro Miyake,* and Hiroshi Shinokubo
Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603
E-mail: miyake@chembio.nagoya-u.ac.jp
We have succeeded in the synthesis of ruthenium(II)
(Scheme 1). Further treatment of 2a with pyridine (1.1
equiv) and N,N-dimethyl-4-aminopyridine (DMAP) (1.1
equiv) in THF at room temperature for 1 h smoothly
furnished the corresponding ruthenium complexes 2b and 2c
having pyridine and DMAP as axial ligands in 43% and 70%
yields, respectively. Formation of these ruthenium
carbonyl 5,15-diazaporphyrin complexes 2 having pyridines
as axial ligands. The structures, properties, and reactivities
under photoirradiation of 2 are compared with those of the
corresponding ruthenium porphyrins.
1
complexes 2a–2c was confirmed by their H and 13C NMR
Metalloporphyrins based on a variety of transition
metals such as iron, manganese, ruthenium, and so on have
attracted considerable attention as catalysts for selective
oxidation of saturated C–H bonds1,2 since the discovery of
the enzymes cytochrome P450. In particular, ruthenium
porphyrin complexes are extensively studied as effective
catalysts for epoxidation of alkenes, oxidation of alcohols,
oxidation of sulfides, hydroxylation of alkanes.3-7 Electron
deficient ruthenium porphyrins, where electron withdrawing
groups are introduced to the porphyrin ligands, exhibit high
catalytic activity for the oxidation of organic compounds.
For example, Groves and co-workers have reported that
and high-resolution electro-spray ionization time-of-flight
(HR-ESI-TOF) mass spectra. 1H NMR spectra of 2 displayed
three methyl protons on the mesityl group, suggesting the
presence of axial ligands such as CO, pyridine, and DMAP.
The complex 2a is insoluble in toluene, CH2Cl2, and CHCl3,
but soluble in THF. The coordination of THF to the
ruthenium center as an axial ligand may prevent the
aggregation of 2a. In fact, the complexes 2b and 2c having
pyridine and DMAP as axial ligands are soluble in toluene,
CH2Cl2, and CHCl3.
Mes
O
carbonylruthenium(II)
5,10,15,20-
C
Mes
N
Ru3(CO)12
(1.0 equiv)
NH
N
N
tetrakis(pentafluorophenyl)porphyrin 3a works as an
efficient catalyst for the oxidation of alkenes (Chart 1).7-8
5,15-Diazaporphyrins 1M are 18p porphyrinoids, which
exhibit electron deficient nature owing to imine-type sp2-
hybridized nitrogen atoms at meso-positions (Chart 1).10-12
We have explored unique reactivities and properties of 5,15-
diazaporphyrins.11a-11d As an extension of our study, we have
developed the synthesis of carbonylruthenium(II) 5,15-
diazaporphyrins 2, which are expected to work as an
oxidation catalyst because of their electron deficient nature.
Here we disclose the structures, properties, and reactivities of
2.
N
N
Ru
N
N
N
N
N
o-C6H4Cl2
HN
160 °C, 5 h
Mes
2a: 29%
Mes
1H2
O
C
Mes
N
L
N
(1.1 equiv)
N
Ru
L
N
N
N
THF
rt, 1 h
Mes
2b (L = pyridine): 43%
2c (L = DMAP): 70%
Scheme 1. Synthesis of carbonylruthenium(II) 5,15-
diazaporphyrins 2.
Mes
O
C
Mes
N
Recrystallization of ruthenium diazaporphyrins 2b and
2c from CHCl3/hexane and CH2Cl2/methanol afforded single
crystals suitable for X-ray diffraction analysis, which
unambiguously confirmed the molecular structures of 2b and
2c (Figures 1a and 1b).13,14 The structure of diazaporphyrin
core in 2b was quite similar to that in 2c. The mean plane
deviations in 2b and 2c are 0.08108 and 0.08468 Å,
suggesting their planar structures. The bond lengths of C–O
bond in 2b (1.139(4) Å) and 2c (1.148(3) Å) are shorter than
those in ruthenium porphyrin 4b (1.165(11) and 1.153(10)
Å) (Figure S2).14 This fact clearly shows that the electron
deficient nature of diazaporphyrins affects the p-back
donating ability of the ruthenium center.
N
N
N
N
N
N
M
N
N
Ru
N
N
N
L
Mes
1M
2
Mes
O
O
C
Ar
C
Ar
N
N
N
N
N
Ru
Ar
Ar
Ru
Ar
Ar
N
N
N
Ar
L
Ar
3a (Ar = C6F5)
4a (Ar = mesityl)
3b (Ar = C6F5, L = pyridine)
4b (Ar = mesityl, L = pyridine)
Chart 1. Carbonylruthenium(II) porphyrins and 5,15-
diazaporphyrins.
In IR spectra, ruthenium diazaporphyrins 2 exhibited
strong CO stretching absorption, of which positions are
influenced by the nature of the second ligands (Table 1).15
The nCO frequencies of diazaporphyrin complexes 2a and 2b
Treatment of free-base diazaporphyrin 1H2 (Mes =
2,4,6-trimethylphenyl) with Ru3(CO)12 (1.0 equiv) in o-
dichlorobenzene at 160 °C for
5
h
afforded
carbonylruthenium 5,15-diazaporphyrin 2a in 29% yield

2
are higher than those of 4a and 4b, while the spectra of 2a
and 2b show lower absorption bands than those of 3a and 3b.
These results suggest that the order in the electron deficient
nature as a ligand is 3b > 2b > 4b.
photoreaction of 2b proceeded, new absorption bands
appeared around 390 and 550 nm (Figure 3a). The
observation of isobestic points clearly supports the direct
transformation of 2b into 2d. A similar spectral change of 4b
also suggests that the photosubstitution reaction occurs
(Figure 3b). From the absorption changes of the Q-band, we
conducted the kinetic analysis (Figure S1): the rate constants
of the photosubstitution reaction of 2b and 4b are determined
to be 6.8 × 10–4 and 1.1 × 10–3 s–1, respectively.
(a)
(b)
3.0
2b
4b
2.5
2.0
1.5
1.0
(c)
ε
0.5
0
300
400
500
λ / nm
600
700
Figure 2. Absorption spectra of 2b and 4b (CH2Cl2).
O
C
L
Mes
N
Mes
N
N
N
N
N
Ru
L
Ru
L
N
N
N
N
N
N
Figure 1. Crystal structures of (a) 2b, (b) 2c, and (c) 2d.
Hydrogen atoms and mesityl groups are omitted for
clarity. The thermal ellipsoids are scaled at 50%
probability level.
Mes
Mes
pyridine
(excess)
2b (L = pyridine)
2d (L = pyridine)
benznene
(10 µM)
O
C
L
Ar
Ar
hν (>380 nm)
Table 1. nCO Frequencies of diazaporphyrin complexesa
rt
N
N
N
N
Ru
L
Ar
Ru
L
Ar
Ar
Ar
CO (cm–1)
1952
1954
1975
1963
1944
1948
N
N
N
N
compounds
n
Ar
Ar
2a
2b
3a
3b
4a
4b
4b (Ar = mesityl, L = pyridine)
4d (Ar = mesityl, L = pyridine)
Scheme 2. Photosubstitution reaction of 2b and 4b.
(a)
(b)
1.2
1.0
0 s
3.0
2.5
0 s
30 s
30 s
a
60 s
60 s
All spectra were measured using FT-IR spectrometer
180 s
180 s
300 s
300 s
equipped with an ATR apparatus.
0.8
0.6
2.0
1.5
600 s
900 s
1800 s
600 s
900 s
1800 s
Electronic absorption spectra of 2b and 4b were
measured in CH2Cl2 (Figure 2). As compared to 4b, the Q-
band of 2b (lmax = 556 nm) was slightly bathochromic
shifted and the molar extinction coefficient (e) was similar,
while the Soret band (lmax = 400 nm) was blue-shifted and
was weakened.
3600 s
3600 s
0.4
0.2
1.0
0.5
0
0
300 400 500 600 700
300 400 500 600 700
Photosubstitution reactions of the CO ligand in
carbonylruthenium porphyrins have been extensively studied
because the dissociation of CO ligand is an important step
for their catalysis.16,17 We conducted the photosubstitution
reaction of 2b and 4b. Dissociation of CO from 2b and 4b
upon visible-light (>380 nm) excitation in the presence of an
excess amount of pyridine effectively provided the
corresponding bis-pyridine complexes 2d and 4d (Scheme 2).
The molecular structure of 2d was confirmed by X-ray
diffraction analysis (Figure 1c).18 UV-Vis spectra changes
during photoirradiation are shown in Figure 3. As the
λ / nm
λ / nm
Figure 3. Absorption spectral changes of (a) 2b and (b)
4b during the photoirradiation.
We then investigated the catalytic activity of 2 and 4 in
oxidation of alkenes (Scheme 3). Treatment of p-
chlorostyrene with 1.2 equiv of 2,6-dichloropyridine N-oxide
in the presence of 0.5 mol% of 4a in toluene at room
temperature for 19 h afforded the corresponding epoxide in
77% yield. On the other hand, the use of the complex 2a

3
6
7
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Umezawa, T. Higuchi, J. Am. Chem. Soc. 2005, 127, 834.
afforded none of the epoxide probably because of the low
solubility of 2a in toluene. Furthermore, pyridine complexes
2b and 4b showed no catalytic activity. Increase of catalyst
loading of 2b (2.5 mol%) did not affect the yield of epoxide.
Unfortunately, the photoirradiation was not effective for this
catalytic system. At present, we have not clarified the reason,
but an axial ligand like pyridine may prevent the formation
step of the reactive intermediate including the oxidation of
2b.
a) J. T. Groves, R. Quinn, Inorg. Chem. 1984, 23, 3844. b) J. T.
Groves, R. Quinn, J. Am. Chem. Soc. 1985, 107, 5790. c) J. T.
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8
9
Porphyrins 3a and 4a have already been synthesized.7d,9
O
D. P. Rillema, J. K. Nagle, L. F. Barringer, Jr. T. J. Meyer, J. Am.
Chem. Soc. 1981, 103, 56.
Y. Matano, Chem. Rev. 2017, 117, 3138.
cat. (0.5 mol%)
+
toluene
rt, 19 h
Cl
N
O
Cl
10
11
Cl
Cl
For b-unsubstituted diazaporphyrins, see: a) M. Horie, Y. Hayashi,
S. Yamaguchi, H. Shinokubo, Chem. Eur. J. 2012, 18, 5919. b) A.
Yamaji, S. Hiroto, J.-Y. Shin, H. Shinokubo, Chem. Commun.
2013, 49, 5064. c) A. Yamaji, J.-Y. Shin, Y. Miyake, H.
Shinokubo, Angew. Chem. Int. Ed. 2014, 53, 13924. d) A. Yamaji,
H. Tsurugi, Y. Miyake, K. Mashima, H. Shinokubo, Chem. Eur. J.
2016, 22, 3956. e) Y. Matano, T. Shibano, H. Nakano, H. Imahori,
Chem. Eur. J. 2012, 18, 6208. f) Y. Matano,; T. Shibano, H.
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119, 7328. i) S. Omomo, K. Furukawa, H. Nakano, Y. Matano, J.
Porphyrins Phthalocyanines 2015, 19, 775. j) Y. Matano, D. Fujii,
T. Shibano, K. Furukawa, T. Higashino, H. Nakano, H. Imahori,
Chem. Eur. J. 2014, 20, 3342. k) M. Yamamoto, Y. Takano, Y.
Matano, K. Stranius, N. V. Tkachenko, H. Lemmetyinen, H.
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Haberland, A. Müller, Justus Liebigs Ann. Chem. 1936, 521, 122.
b) H. Ogata, T. Fukuda, K. Nakai, Y. Fujimura, S. Neya, P.
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Inorg. Chem. 2010, 49, 4802. h) P. A. Stuzhin, A. Ul-Haq, S. E.
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cat.
2a
yield (%)
0
77
4a
2b
4b
0
trace
Scheme 3. Epoxidation of p-chlorostyrene.
In summary, we have succeeded in the synthesis of
carbonylruthenium(II) 5,15-diazaporphyrins 2 having axial
ligands. From X-ray analysis and IR spectra, we have found
that 5,15-diazaporphyrin works as an electron deficient
ligand to the ruthenium center. The photosubstitution
reaction of the CO ligand in 2 proceeds smoothly. We
believe these findings suggest the possibility of 5,15-
diazaporphyrin as a useful ligand for unique molecular
transformation. Further work is currently in progress in our
group to develop 5,15-diazaporphyrin transition metal
complexes as the oxidation catalyst of alkenes and alkanes.
12
This work was supported by JSPS KAKENHI Grant
Numbers (26102003 and 16H01013) in Grant-in-Aids for
Scientific Research on Innovative Area “pi-System
Figuration” and “Precisely Designed Catalysts with
Customized Scaffolding” from the Japanese Ministry of
Education, Culture, Sports, Science & Technology (MEXT),
as well as the Program for Leading Graduate Schools
“Integrative Graduate Education and Research in Green
Natural Sciences”, MEXT, Japan.
Supporting
Information
is
available
on
http://dx.doi.org/10.1246/cl.******.
13
14
Crystallographic data for 2b: C42H35N4ORu, Mw = 754.84,
monoclinic, P21/c, a = 14.6827(7), b = 18.3386(8), c = 13.7446(7)
Å, b = 106.2410(10), V = 3553.2(3) Å3, Z = 4, R = 0.0326 (I >
2.0 σ(I)), wR2 = 0.1286 (all data), GOF = 1.096. Crystallographic
data for 2b has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-1542190.
References and Notes
1
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Chem. Res. 2015, 48, 1727.
Crystallographic data for 2c: C44H40N8ORu, Mw
= 797.91,
2
a) P. R. Ortiz de Montellano, Chem. Rev. 2010, 110, 932. b) J. T.
Groves, Nat. Chem. 2014, 6, 89.
monoclinic, P21/c, a = 14.9323(7), b = 18.2032(9), c = 13.8978(7)
Å, b = 96.4600(10), V = 3753.7(3) Å3, Z = 4, R = 0.0230 (I >
2.0 σ(I)), wR2 = 0.0607 (all data), GOF = 1.046. Crystallographic
data for 2c has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-1542191.
For experimental details of the synthesis of 3b and 4b, see:
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15
16

4
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18
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Porphyrins Phthalocyanines 2015, 19, 233.
Crystallographic data for 2d: C46H40N8Ru, Mw
= 805.93,
monoclinic, C2/c, 14.7049(15), 19.366(2), c =
a
=
b
=
13.4556(15) Å, b = 102.850(3), V = 3735.9(7) Å3, Z = 4, R =
0.0644 (I > 2.0 σ(I)), wR2 = 0.1910 (all data), GOF = 1.090.
Crystallographic data for 2c has been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-1542192.