Photochemical activation of ruthenium(II)-pyridylamine complexes having a pyridine- N -oxide pendant toward oxygenation of organic substrates

Article abstract of DOI:10.1021/ja207572z

Ruthenium(II)-acetonitrile complexes having η³-tris(2- pyridylmethyl)amine (TPA) with an uncoordinated pyridine ring and diimine such as 2,2′-bipyridine (bpy) and 2,2′-bipyrimidine (bpm), [Ru ^II(η³-TPA)(diimine)(CH₃CN)]²⁺, reacted with m-chloroperbenzoic acid to afford corresponding Ru(II)-acetonitrile complexes having an uncoordinated pyridine-N-oxide arm, [Ru^II(η ³-TPA-O)(diimine)(CH₃CN)]²⁺, with retention of the coordination environment. Photoirradiation of the acetonitrile complexes having diimine and the η³-TPA with the uncoordinated pyridine-N-oxide arm afforded a mixture of [Ru^II(TPA)(diimine)] ²⁺, intermediate-spin (S = 1) Ru(IV)-oxo complex with uncoordinated pyridine arm, and intermediate-spin Ru(IV)-oxo complex with uncoordinated pyridine-N-oxide arm. A Ru(II) complex bearing an oxygen-bound pyridine-N-oxide as a ligand and bpm as a diimine ligand was also obtained, and its crystal structure was determined by X-ray crystallography. Femtosecond laser flash photolysis of the isolated O-coordinated Ru(II)-pyridine-N-oxide complex has been investigated to reveal the photodynamics. The Ru(IV)-oxo complex with an uncoordinated pyridine moiety was alternatively prepared by reaction of the corresponding acetonitrile complex with 2,6-dichloropyridine-N-oxide (Cl ₂py-O) to identify the Ru(IV)-oxo species. The formation of Ru(IV)-oxo complexes was concluded to proceed via intermolecular oxygen atom transfer from the uncoordinated pyridine-N-oxide to a Ru(II) center on the basis of the results of the reaction with Cl₂py-O and the concentration dependence of the consumption of the starting Ru(II) complexes having the uncoordinated pyridine-N-oxide moiety. Oxygenation reactions of organic substrates by [Ru^II(η³-TPA-O)(diimine)(CH ₃CN)]²⁺ were examined under irradiation (at 420 ± 5 nm) and showed selective allylic oxygenation of cyclohexene to give cyclohexen-1-ol and cyclohexen-1-one and cumene oxygenation to afford cumyl alcohol and acetophenone.

Full text of DOI:10.1021/ja207572z

ARTICLE
pubs.acs.org/JACS
Photochemical Activation of Ruthenium(II)ꢀPyridylamine Complexes
Having a Pyridine-N-Oxide Pendant toward Oxygenation of Organic
Substrates
,
†
‡
z
z
‡,^
Takahiko Kojima,* Kazuya Nakayama, Miyuki Sakaguchi, Takashi Ogura, Kei Ohkubo, and
,‡,§,^
Shunichi Fukuzumi*
†
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba,
Ibaraki 305-8571, Japan
‡
^
Department of Material and Life Science, Graduate School of Engineering, Osaka University, and ALCA, Japan Science and
Technology Agency (JST), 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
z
Graduate School of Life Science, University of Hyogo, Kouto, Hyogo 678-1297, Japan
§
Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, South Korea
S Supporting Information
b
ABSTRACT: Ruthenium(II)ꢀacetonitrile complexes having
3
η -tris(2-pyridylmethyl)amine (TPA) with an uncoordinated
0
0
pyridine ring and diimine such as 2,2 -bipyridine (bpy) and 2,2 -
II
3
2+
bipyrimidine (bpm), [Ru (η -TPA)(diimine)(CH CN)] ,
3
reacted with m-chloroperbenzoic acid to afford corresponding
Ru(II)ꢀacetonitrile complexes having an uncoordinated pyr-
II
3
2+
idine-N-oxide arm, [Ru (η -TPA-O)(diimine)(CH CN)] ,
3
with retention of the coordination environment. Photoirradia-
3
tion of the acetonitrile complexes having diimine and the η -
TPA with the uncoordinated pyridine-N-oxide arm afforded a
II
2+
mixture of [Ru (TPA)(diimine)] , intermediate-spin (S = 1) Ru(IV)ꢀoxo complex with uncoordinated pyridine arm, and
intermediate-spin Ru(IV)ꢀoxo complex with uncoordinated pyridine-N-oxide arm. A Ru(II) complex bearing an oxygen-bound
pyridine-N-oxide as a ligand and bpm as a diimine ligand was also obtained, and its crystal structure was determined by X-ray
crystallography. Femtosecond laser flash photolysis of the isolated O-coordinated Ru(II)ꢀpyridine-N-oxide complex has been
investigated to reveal the photodynamics. The Ru(IV)ꢀoxo complex with an uncoordinated pyridine moiety was alternatively
prepared by reaction of the corresponding acetonitrile complex with 2,6-dichloropyridine-N-oxide (Cl py-O) to identify the
2
Ru(IV)ꢀoxo species. The formation of Ru(IV)ꢀoxo complexes was concluded to proceed via intermolecular oxygen atom transfer
from the uncoordinated pyridine-N-oxide to a Ru(II) center on the basis of the results of the reaction with Cl py-O and the
2
concentration dependence of the consumption of the starting Ru(II) complexes having the uncoordinated pyridine-N-oxide moiety.
II
3
2+
Oxygenation reactions of organic substrates by [Ru (η -TPA-O)(diimine)(CH CN)] were examined under irradiation (at
3
4
20 ( 5 nm) and showed selective allylic oxygenation of cyclohexene to give cyclohexen-1-ol and cyclohexen-1-one and cumene
oxygenation to afford cumyl alcohol and acetophenone.
’
INTRODUCTION
complexes has been investigated for use in substrate oxygenation
using metalꢀporphyrin complexes via homolytic cleavage of the
In the course of the oxidative conversion of organic substrates,
ꢀ
21
ClꢀO bond in coordinated ClO by laser flash photolysis.
4
high-valent transition metalꢀoxo complexes play a pivotal role as
1ꢀ6
As a strategy for the formation of reactive species in metal-
catalyzed oxidation reactions, pyridine-N-oxides, such as 2,6-
dichloropyridine-N-oxide, have been adopted asterminal oxidants,
responsible species of the reactions.
Not only substrate oxida-
tion with high-valent metalꢀoxo complexes to afford oxidized
7
ꢀ9
products
but also formation of the high-valent metalꢀoxo
22,23
especially for ruthenium complexes as catalysts.
A benefit to
complexes have been intensively investigated to elucidate activation
8ꢀ11
use of pyridine-N-oxides as oxidants is the prevention of radical
chain reactions that may result in complicated reaction pathways
affording less-selective formation of oxidation products. As a
mechanisms of oxidants at the metal centers.
metalꢀoxo complexes have been formed mainly by reactions of
The high-valent
1
2ꢀ14
metal complexes through dioxygen activation,
with active
19
4,15ꢀ18
oxygen species such as peroxides
also through proton-coupled electron-transfer oxidation. On the
and iodosylarenes, and
20
Received: August 11, 2011
other hand, photochemical formation of high-valent metalꢀoxo
Published: September 26, 2011
r 2011 American Chemical Society
17901
dx.doi.org/10.1021/ja207572z
|J. Am. Chem. Soc. 2011, 133, 17901–17911

Journal of the American Chemical Society
ARTICLE
Scheme 1
Figure 2. ORTEP drawing of the cation part of 3a with partial
numbering scheme (50% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
Figure 1. ORTEP drawing of the cation part of 2a with partial
numbering scheme (50% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(
deg): Ru1ꢀN1 2.123(2), Ru1ꢀN3 2.050(3), Ru1ꢀN4 2.078(3),
Ru1ꢀN5 2.054(3), Ru1ꢀN6 2.074(3), Ru1ꢀN7 2.031(2), O1ꢀN2
(deg): Ru1ꢀN1 2.115(5), Ru1ꢀN3 2.053(5), Ru1ꢀN4 2.083(5),
1
.309(4); N1ꢀRu1ꢀN3 81.93(10), N1ꢀRu1ꢀN4 80.86(11), N3ꢀ
Ru1ꢀN5 2.057(5), Ru1ꢀN6 2.072(6), Ru1ꢀN7 2.011(5); N1ꢀ
Ru1ꢀN3 81.9(2), N1ꢀRu1ꢀN4 81.4(2), N3ꢀRu1ꢀN4 81.8(2),
N5ꢀRu1ꢀN6 78.9(2).
Ru1ꢀN4 82.25(12), N5ꢀRu1ꢀN6 78.77(13).
was also investigated to clarify the oxidizing ability of the photo-
generated Ru(IV)ꢀoxo complex.
milder oxidant, pyridine-N-oxides have been reported to be
2
4
essential for selective oxidation processes. The reactions of
pyridine-N-oxides with metal complexes, which require photo-
irradiation, have been proposed to afford high-valent metalꢀ
’
RESULTS AND DISCUSSION
22
oxo complexes as reactive species in catalytic oxidation reactions.
Reaction of m-Chloroperbenzoic Acid To Form Ru(II) Com-
plexes with Pyridine-N-Oxide Arm. Ru(II)-TPA-diimine com-
Such photochemical reactions with mild oxidants such as pyr-
idine-N-oxides would provide versatile pathways to produce
high-valent metalꢀoxo complexes. However, there has been no
report on the direct detection or isolation of high-valent metalꢀ
oxo complexes in photochemical reactions of metal complexes
with mild oxidants.
0
plexes, [Ru(TPA)(diimine)](PF ) (diimine = 2,2 -bipyridine
6
2
0
(bpy, 1a); 2,2 -bipyrimidine (bpm, 1b)), undergo a complete
3
thermal structural change in CH CN to give [Ru(η -TPA)-
3
(diimine)(CH CN)](PF ) (diimine = bpy (2a); bpm (2b)), in
3
6 2
which the TPA ligand binds to the Ru(II) center as a tridentate
We report herein photochemical formation of high-valent
metalꢀoxo complexes for the first time by using a Ru(II)ꢀ
diimine complex having an uncoordinated pyridine-N-oxide
ligand in a facial configuration with an uncoordinated pyridine
arm. The reaction of m-chloroperbenzoicacid (mCPBA) with2a
25
and 2b gave complexes bearing a uncoordinated pyridine-N-oxide
3
3
arm (TPA-O) derived from the η -tris(2-pyridylmethyl)amine
arm, [Ru(η -TPA-O)(diimine)(CH CN)](PF ) (diimine = bpy
3
6 2
II
3
2+
(
TPA) ligand, [Ru (η -TPA-O)(diimine)(CH CN)] , which
(3a); bpm (3b)), as described in Scheme 1. The second-order rate
3
has been newly synthesized and structurally characterized by
X-ray crystallography. The photochemical formation of Ru(IV)ꢀ
oxo complexes together with the O-coordinated Ru(II)ꢀ
constant for the reaction of 2a with mCPBA to form 3a was
ꢀ
2
ꢀ1 ꢀ1
determined to be (1.45 ( 0.16) ꢁ 10
M
s
in CH CN at
3
323 K (Figure S1 in the Supporting Information (SI)). The
oxidation state of the ruthenium center remains +2, even in the
presence of an excess amount of mCPBA.
II
3
pyridine-N-oxide complex, derived from [Ru (η -TPA-O)-
2
+
(
diimine)(CH CN)] , was compared with the photochemical
3
II
3
2+
reaction of [Ru (η -TPA)(diimine)(CH CN)] without an
The crystal structure of 2a was determined by X-ray crystal-
lography. Its ORTEP drawing is depicted in Figure 1 involving
partial numbering scheme with 50% thermal ellipsoids and selected
bond lengths and angles are given in the figure caption. It is clear
3
uncoordinated pyridine-N-oxide arm with an external oxidant,
2
,6-dichloropyridine-N-oxide. The oxygenation of substrates with
II 3 2+
[Ru (η -TPA-O)(diimine)(CH CN)] under photoirradiation
3
1
7902
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Journal of the American Chemical Society
ARTICLE
that this complex has an uncoordinated pyridine moiety and an
acetonitrile ligand. The TPA ligand acts as a facial tridentate ligand
in sharp contrast to that in 1, in which TPA binds to the Ru(II)
center as a tetradentate ligand. The bond length of Ru1ꢀN7-
and S4 in SI). In the ESI-MS spectrum, the N-oxide-appended
complexes 3a and 3b exhibited peak clusters at m/z = 750.1 for
3
+
3a ({[Ru(η -TPA-O)(bpy)(CH CN)](PF )} ) and at m/z =
3
6
3
+
752.1 for 3b ({[Ru(η -TPA-O)(bpm)(CH CN)](PF )} ) as
3
6
(
acetonitrile) is 2.011(5) Å, which is the shortest coordination
shown in Figure 3.
Photochemical Reactions of Ruthenium Complexes Hav-
ing Pyridine-N-Oxide Pendant. Photoirradiation of complexes
bond in 2a. This strong interaction causes elongation of the bond
length of Ru1ꢀN1(tert-amino nitrogen) to be 2.115(5) Å, due to
the trans influence of the acetonitrile ligand.
3a at 420 nm and 3b at 450 nm in CD CN at room temperature
3
X-ray crystallography on 3a allowed us to access a unique
structure involving an uncoordinated pyridine-N-oxide moiety.
So far, no example has been reported on a metal complex bearing
an uncoordinated pyridine-N-oxide moiety. An ORTEP drawing
of the cation part of 3a is shown in Figure 2, involving numbering
scheme with 50% probability thermal ellipsoids, and selected
bond lengths and angles are given in the figure caption. In this
complex, the TPA ligand maintains a facial tridentate coordina-
tion mode and the nitrogen atom of the uncoordinated pyridine
pendant is oxygenated by mCPBA to give rise to an uncoordi-
nated pyridine N-oxide moiety. The bond length of Ru1ꢀN7-
resulted in formation of the O-coordinated Ru(II)ꢀpyridine-N-
oxide complex ([(Ru-O-TPA)(bpm)](PF ) 4b) and Ru(IV)ꢀ
6
2
oxo complexes, [Ru(O)(TPA)(diimine)](PF ) (5a with bpy
6
2
and 5b with bpm), and small amount of Ru(IV)ꢀoxo complexes
3
with uncoordinated pyridine-N-oxide pendant, [Ru(O)(η -
TPA-O)(diimine)](PF ) (6a for bpy and 6b for bpm), as well
6
2
as 1a and 1b as shown in Scheme 2. The identification of each
product in Scheme 2 is described below. As for the bpy complex
3a, the corresponding O-coordinated Ru(II)ꢀpyridine-N-oxide
complex, [(Ru-O-TPA)(bpy)](PF ) (4a), was not detected by
6
2
1
H NMR spectrometry, in contrast to the case of 3b to from 4b.
(
acetonitrile) is shortest to be 2.031(2) Å and the Ru1ꢀN1(tert-
In the ESI-MS spectrum of the reaction mixture including
amino nitrogen) bond is elongated to be 2.123(2) Å as well as
3b with bpm under photoirradiation at 450 nm in CD CN
3
that in 2a. The bond length of N(2)ꢀO(1) of the N-oxide is
(Figure 4), we could observe a peak cluster ([) assignable to
both pyridine-N-oxide-coordinated {[(Ru-O-TPA)(bpm)]-
1
.309(4) Å.
+
+
In the absorption spectra of 3a and 3b in CH CN, no
(PF )} ({4b ꢀ (PF )} ) and the Ru(IV)ꢀoxo complex
3
6
6
significant change was observed in comparison with those of
a and 2b (Figure S2 in SI). In the NMR spectra of 3a and 3b in
2
CD CN, a downfield shift was observed for a doublet due to the
3
methylene group of a coordinating pyridylmethyl arm (Figures S3
Figure 3. ESI-MS spectra of 3a (a) and 3b (b). The red lines are
simulated isotopic patterns.
Figure 4. Time course of ESI-MS spectra of 3b under photoirradiation
at 450 nm in CD CN.
3
Scheme 2
1
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Journal of the American Chemical Society
ARTICLE
1
IV
1
IV
3
Figure 6. H NMR spectra of a solution containing [Ru (O)-
(
Figure 5. H NMR spectra of a solution containing [Ru (O)(η -
+
+
H TPA)(bpm)](PF
in CD CN at room temperature (red trace) and the solution of 3b
5 mM) after photoirradiation at 450 nm for 3 h in CD
temperature (black trace).
6 3
) (5 mM) formed by oxidation of 1b by CAN
TPAH )(bpy)](PF
CD CN at room temperature (red trace) and the solution of 3a (5 mM)
after photoirradiation at 420 nm for 3 h in CD CN at room temperature
3
black trace).
6 3
) (5 mM) formed by oxidation of 1a by CAN in
3
3
(
3
CN at room
(
3
+
{
(
7
{
[Ru(O)(η -TPA)(bpm)](PF )} at m/z = 711.1 ({5b ꢀ
6
+
PF )} ) as main products. As a minor peak cluster, at m/z =
6
3
+
27.1 is assigned to {[Ru(O)(η -TPA-O)(bpm)](PF )} (+,
6
+
6b ꢀ (PF )} ). The isotopic patterns of those peak clusters are
6
consistent with simulated patterns as shown in Figure S5 (SI). In
+
addition, small peak clusters due to {[Ru(TPA)(bpm)](PF )}
6
+
3
at m/z = 695.1 (f, {1b ꢀ (PF )} ) and {[Ru(η -TPA)-
6
+
+
(
CD CN)(bpm)](PF )} at m/z = 739.1 (O, {2b ꢀ (PF )} )
3
6
6
were observed at the end of the reaction. The peak due to the
3
+
starting {[Ru(η -TPA-O)(CH CN)(bpm)](PF )} at m/z =
3
6
+
7
52.1 (., {3b ꢀ (PF )} ) lowered its intensity and shifted to
6
3
+
that due to {[Ru(η -TPA-O)(CD CN)(bpm)](PF )} at m/z =
3 6
+
7
55.1 (9, {3b ꢀ (PF )} ) because of photoinduced ligand
6
substitution of CH CN by the deuterated solvent, CD CN.
3
3
The formation of 1b and 6b in Scheme 2 suggests that an oxo
transfer reaction occurs between two molecules of 3b. ESI-MS
measurements on 3a under photoirradiation at 420 nm in
1
6
3
+
3+
Figure 7. Resonance Raman spectra of [Ru( O)(η -TPAH )(bpm)]
1
8
3
+
3+
(a), [Ru( O)(η -TPAH )(bpm)] (b), and their differential spec-
1
6
18
CD CN allowed us to observe peak clusters assigned to
trum ( O ꢀ O) (c).
3
3
+
+
{
7
[Ru(O)(η -TPA)(bpy)](PF )} ({5a ꢀ (PF )} ) at m/z =
6
6
3
+
+
+
3+ 26
09.1, {[Ru(O)(η -TPA-O)(bpy)](PF )} ({6a ꢀ (PF )} )
TPAH )(bpy)] . Thus, we concluded that the photoirradia-
tion of 3a can afford two kinds of Ru(IV)ꢀoxo complexes in the
S = 1 spin state. As for 3b, the spectrum of the photoproduct
(black trace in Figure 6) was similar to that (red trace in
6
6
+
+
at m/z = 725.1, {[Ru(TPA)(bpy)](PF )} ({1a ꢀ (PF )} ) at
6
6
3
+
m/z = 693.1 and {[Ru(η -TPA)(bpy)(CD CN)](PF )} ({2a ꢀ
3
6
+
(
PF )} ) at m/z = 737.1 (Figures S6 and S7 in SI). In the NMR
6
3
+
3+
spectrum, signals assigned to those of 1a were detected, however,
no signals due to the O-coordinated Ru(II)ꢀpyridine-N-oxide
Figure 6) of [Ru(O)(η -TPAH )(bpm)] , which was formed
IV
4 2 3 6
by the reaction of 1b with (NH
) [Ce (NO ) ] (CAN) in
3
complex (4a) were observed in CD CN. This is probably due to
water. In the resonance Raman spectrum of [Ru(O)(η -
TPAH )(bpm)] , a Raman scattering due to the RudO
moiety was observed at 800 cm (Figure 7(a)), which was
close to those of [Ru (O)(η -TPAH )(bpy)] (805 cm
)] (806 cm ). The peak shifted
to 763 cm (Figure 7(b)) by using H
3
+
3+
stronger interaction of the N-oxide oxygen with the Ru(II) center
of 4b than that in 4a: The pyrimidine may act as a better π-
acceptor for the π-back bonding than pyridine to enhance the
electron donation from the N-oxide oxygen as a π-donor to
ꢀ
1
IV
3
+
3+
ꢀ1 25
)
IV
2+
ꢀ1 27
18
and [Ru (O)(TPA)(OH
2
20
ꢀ1
strengthen the interaction. In addition, the difference may stem
from that of the quantum yields of the coordination of the N-
2
O as a solvent to
generate the Ru(IV)ꢀoxo complex; the isotope shift is con-
ꢀ
1
oxide oxygen via the release of CH CN. The quantum yields of
sistent with the calculated value (Δν = 40 cm ) as shown in
3
1
the reaction from 2 to 1 have been determined to be 0.0057 for
Figure 7(c). The H NMR spectrum of 5b was identical to that
3
+
3+
2
a and 0.028 for 2b, and those of the reverse reaction (1 to 2)
of [Ru(O)(η -TPAH )(bpm)] , supporting the formation of
5b in the photoreaction of 3b. Thus, we concluded that the
Ru(II)-diimine complexes having the pyridine-N-oxide pen-
dant, 3a and 3b, can be converted to the corresponding
intermediate-spin Ru(IV)ꢀoxo complexes by means of photo-
irradiation. This is the first confirmation of the photochemical
formation of high-valent Ruꢀoxo complexes with use of
pyridine-N-oxides as oxygen sources.
Concerning the O-coordinated Ru(II)ꢀpyridine-N-oxide com-
plex, we could obtain a single crystal of 4b to determine its crystal
structure. As depicted in Figure 8, the oxygen atom of the
pyridine-N-oxide arm coordinates to the Ru(II) center to form
25a
have been reported to be 0.0021 for 1a and 0.0017 for 1b.
Thus, more efficient structural change can be expected for 2a to
consume 4a for further reactions.
1
In the H NMR spectra of photoirradiated solutions of 3a and
b, paramagnetically shifted signals were observed in the range of
3
6
0 to ꢀ20 ppm. Photoirradiation of 3a at 420 nm in CD CN gave
3
rise to two sets of paramagnetically shifted peaks, suggesting one
major and one minor products, as can be seen in the black trace in
Figure 5. The chemical shifts of those signals are consistent with or
close to those for a crystallographycally characterized inter-
IV
3
mediate-spin (S = 1) Ru(IV)ꢀoxo complex, [Ru (O)(η -
1
7904
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Journal of the American Chemical Society
ARTICLE
a six-membered chelate ring. This is the first example of a
structurally characterized ruthenium complex having a pyri-
dine-N-oxide as a ligand. The bond length of Ru1ꢀO1 was
Therefore, we examined the conversion of 4b to a high-valent
rutheniumꢀoxo complex. Contrary to our expectation, the
complex 4b was consumed very slowly under photoirradiation
and was intact upon heating and was proved to be stable under
catalytic conditions.
2
.083(3) Å and the bond angle of Ru1ꢀO1ꢀN2 was 115.4(2)ꢀ.
The bond length of O1ꢀN2 was 1.323(5) Å, which was a little
longer than that of the uncoordinated pyridine-N-oxide moiety
in 3b; it was also comparable to those of terminal and bridging
pyridine-N-oxide ligands in the first-row transition metal com-
In order to understand the photostability of 4b, femtosecond
laser flash photolysis of 4b in CH CN was examined by photo-
3
excitation at 420 nm to observe transient absorption spectra as
shown Figure 9a. Analysis of the time-course of absorbance at
510 nm by using double-exponential curve-fitting (Figure 9b)
allowed us to reveal two-step very fast reaction processes
2
8
plexes reported so far.
Pyridine-N-oxides have been known as oxygen atom donors
to perform catalytic oxidation of organic substrates in the
2
2
10 ꢀ1
ꢀ1
presence of Ru(II) complexes under photoirradiation. The
reaction mechanism has been proposed to involve the coordi-
nation of the N-oxide followed by the formation of putative
showing first-order rate constants of 2.5 ꢁ 10
s
((40 ps) )
9
ꢀ1
ꢀ1
and 1.1 ꢁ 10 s ((930 ps) ). These two processes can be
ascribed to the NꢀO bond cleavage and its recombination,
respectively, suggesting a very short lifetime of the corresponding
Ruꢀoxo complex (5b) formed from the photoreaction of 4b.
Thus, we ruled out the participation of 4b as an intermediate for
the oxidation of substrates by 3b.
2
2b
high-valent ruthenium-oxo complexes as reactive species.
Photoirradiation of the solutions of 3 in CH CN allowed us to
3
observe complicated change of absorption spectra. Therefore,
1
the reactions were followed by H NMR spectroscopy to observe
change of peak integration. The spectral change was assigned to
the consumption of 3 to form 1, 2, and 5 and/or 6. As mentioned
above, in addition to those complexes, the formation of the
closed N-oxide complex 4b was observed for 3b. The complex 1
has been demonstrated to exhibit photochromic structural
25
change to reach a photostationary state involving 2. The initial
decay rates (bpy for 100 min and bpm for 80 min) of 3
determined by NMR measurements were revealed to show linear
correlations to the initial concentration of 3 as depicted in
Figure 10. This result also indicates that the consumption of 3
occurs intermolecular reactions rather than intramolecular reac-
tions. As can be seen in Figure 10, no intercept was observed for
3a in contrast to 3b showing remarkable intercept. This differ-
ence may stem from the formation of the dead-end compound 4b
through the intramolecular reaction of 3b (vide supra) in
contrast with the lack of the formation of the corresponding
N-oxide-coordinated complex from 3a.
Figure 8. ORTEP drawing of the cation part of 4b with partial
numbering scheme (50% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
The quantum yields of the consumption of 3 were determined
to be 0.0055 for 3a and 0.019 for 3b, respectively. These values
are lower than those for 2a and 2b to afford 1a (0.0057) and 1b
(
deg): Ru1ꢀO1 20.84(3), Ru1ꢀN1 2.081(2), Ru1ꢀN3 2.069(3),
Ru1ꢀN4 2.056(3), Ru1ꢀN5 2.091(3), Ru1ꢀN6 2.047(3), O1ꢀN2
.323(5); O1ꢀRu1ꢀN1 89.13(12), N1ꢀRu1ꢀN3 81.72(14),
N1ꢀRu1ꢀN4 81.24(13), N5ꢀRu1ꢀN6 78.38(12).
1
25
(0.028), respectively. The reason for the lower quantum yields
Figure 9. Femtosecond laser flash photolysis of 4b in CH CN upon photoexcitation at 420 nm: (a) transient absorption spectra and (b) time course of
3
absorbance at 510 nm.
1
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Journal of the American Chemical Society
ARTICLE
may result from the intermolecular conversions of 3 to 5 and 6 in
contrast with the intramolecular conversions of 2a and 2b to 1a
and 1b, respectively.
In order to examine intermolecular oxygen atom transfer from
the pendant pyridine N-oxide arm to another Ru(II) center, we
conducted the reaction of 2 with excess amount of 2,6-dichloro-
N-oxide arm (6b). The complex 1b undergoes photochromic
structural change to give 2b as previously reported. The
2
5
CH CN complex 2b can react with the N-oxide moiety of 3b
3
to form the 5b (pathway (z)). Alternatively, the complex 2b can
react with 6b to generate 5b via the intermolecular oxygen atom
transfer (pathway (y)).
pyridine-N-oxide (Cl py-O) used as an external oxygen donor in
Substrate Oxygenation by 3a under Photoirradiation. We
also examined oxygenation reactions of organic substrates
(50 mM) with 3a (5 mM) by photoirradiation at 420 nm under
Ar at room temperature. The results were summarized in Table 1.
Cyclohexene was oxidized to afford cyclohexen-1-ol (14%)
2
1
CD CN under visible light irradiation. The H NMR spectrum of
3
the photoirradiated reaction mixture of 2b and Cl py-O exhib-
2
ited paramagnetically shifted peaks, which were consistent with
those of 5b formed by photoirradiation of 3b as shown in
3
+
3+
IV
3
Figure 11, as well as those of [Ru(O)(η -TPAH )(bpm)]
and cyclohexen-1-one (34%). With use of isolated [Ru (O)(η -
+
3+
formed by the reaction of 1b with CAN (see Figure 6). These
results also support the intermolecular oxo transfer between two
TPAH )(bpy)] synthesized by using CAN in CH CN at room
3
temperature, cyclohexene was oxidized to be cyclohexen-1-ol
26
3
b molecules to generate 6b.
(5%) and cyclohexen-1-one (46%). This discrepancy may stem
from the difference in the concentration of the oxidant: In light of
the low quantum yield (0.0055) of the consumption of 3a (vide
supra), the concentrations of the reactive Ru(IV)ꢀoxo com-
plexes 5a and 6a formed by the photoreaction of 3a should be
Based on the observations described above, the photochemical
reactions of 3b are summarized in Scheme 3. The complex 3b is
excited by photoirradiation to perform structural change by
releasing the CH CN ligand to afford the N-oxide-bound com-
3
IV
3
+
plex 4b formed by the intramolecular reaction (pathway (w)).
On the other hand, the intermolecular reaction (pathway (x))
affords 1b and the Ru(IV)ꢀoxo complex with the appended
inevitably lower than that of isolated [Ru (O)(η -TPAH )-
3+
(bpy)] . When cumene was used as a substrate, cumyl alcohol
(24%) and acetophenone (6%) via β-scission of cumyl alkoxyl
1
IV
3
Figure 11. H NMR spectrum of a solution containing [Ru (O)(η -
+
TPAH )(bpm)](PF
CD CN at room temperature (red trace), that of the reaction product by
photoirradiation of 3b (5 mM) in CD CN at room temperature (green
6 3
) (5 mM) formed by oxidation of 1b by CAN in
3
3
Figure 10. Dependence of decay rates of 3a (black line) and 3b (red
line) and that by photoirradiation of the mixture of 2b (5 mM) and 2,6-
dichloropyridine N-oxide (100 mM) at 450 nm at room temperature
(black line).
3
line) in CD CN under photoirradiation on the initial concentrations of
3
a and 3b, respectively.
Scheme 3
1
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Journal of the American Chemical Society
ARTICLE
Table 1. Yields of Products in Oxidation of Various Substrates by 3a (5 mM) in Acetonitrile by Photoirradiation at 420 nm under
Inert Atmosphere at Room Temperature
a
b
c
Taken from ref 29. Taken from ref 30. Taken from ref 31. Methods: y, by GC-MS in CH CN; z, by NMR and GC-MS in CD CN (y, 1,4-
3
3
d
cyclohexadione as internal reference; z, methoxybenzene as internal reference). Products and their yields are based on 3a. Oxidation efficiency (%) =
{[product(s)]/(2 ꢁ [3a])} ꢁ N(oxidation equivalent)] ꢁ 100.
[
3
2
radical were obtained by photoirradiation at 420 nm under Ar
N-oxide-chelated Ru(II) complex for the bpm complex and
2+ 4
at room temperature. α-Methyl styrene, which can be formed by
[Ru(TPA)(diimine)] with η -TPA, in addition to intermedi-
IV
3
+
further oxidation of cumyl alcohol by [Ru (O)(η -TPAH )-
ate-spin (S = 1) Ru(IV)ꢀoxo complexes in CH CN. The
3
3
+ 26
(
bpy)] , was not obtained under photoirradiation of 3a. This
difference may be derived from the presence of proton in
formation of the Ru(IV)ꢀoxo complexes was revealed to
proceed via photoinduced intermolecular oxygen atom transfer
from the pyridine-N-oxide pendant to a Ru(II) center of another
IV
3
+
3+
[
Ru (O)(η -TPAH )(bpy)] to catalyze the dehydration of
cumyl alcohol to give α-methyl styrene, while no proton is
available for the reaction of 3a. However, the ratio of [cumyl
alcohol]/[acetophenone] (= 4) was similar to that observed in
complex having CH CN as the leaving ligand. The Ru(IV)ꢀoxo
3
3
2+
complex derived from [Ru(η -TPA-O)(bpy)(CH CN)] was
3
demonstrated to oxygenate organic substrates. The results pre-
sented here have given the first clear evidence for the formation
of high-valent Ruꢀoxo complexes by the reaction of pyridine-N-
oxide with Ru(II) complexes via intermolecular pathway, even
though the Ru(II) complex possesses a pyridine-N-oxide moiety.
Together with the importance of pyridine-N-oxides as cleaner
and safer terminal oxidants in organic synthesis than peroxides,
the clarification of the reaction pathway of photoactivation of
pyridine-N-oxides at the metal center to generate the reactive
metalꢀoxo species provides valuable mechanistic insights into
important oxidation processes.
IV
3
+
3+ 26
the reaction with use of [Ru (O)(η -TPAH )(bpy)] . When
toluene was used as a substrate, benzaldehyde (6%) was obtained
as the sole product. This result is consistent with that of isolated
IV
3
+
3+
[
Ru (O)(η -TPAH )(bpy)] used as an oxidant with respect
26
to the product. The lower oxidation efficiency in the toluene
oxygenation compared to that (23%) of the isolated [Ru (O)-
η -TPAH )(bpy)] may result from the thermal self-decay of
IV
3
+
3+
(
5
a and 6a by the heat of the light source.
In the oxygenation reaction of cyclohexene (50 mM) with 3a
(
5 mM) under air, an unexpectedly large amount of cyclo-
1
hexen-1-hydroperoxide (5.6 mM) was detected by H NMR
33
spectroscopy (Figure S8 in SI). This product may come from
’
EXPERIMENTAL SECTION
the oxidation not by the Ruꢀoxo complex, but by singlet
3
4
oxygen because cyclohexene hydroperoxide is known to be
formed by the reaction between cyclohexene and singlet oxygen
derived from the photoirradiation of 9-phenylacridine in the
Materials. Acetonitrile in extra-pure grade was used without further
purification. Diimine ligands were purchased from commercial sources
and used without further purification. All other solvents were of special
grade and were used as received from commercial sources without further
35
presence of dioxygen. Because it is well-known that the singlet
3
7
38
oxygen can be produced by photosensitization with
purification. TPA 3HClO
4
,
[RuCl(TPA)]
2
(ClO
4
)
2
,
[Ru(TPA)-
[Ru(TPA)-
were synthe-
II
2+
36
3
2
5
3
25a
25a
[
Ru (bpy) ] under air, the Ru(II)-bpy moiety of 3a may
3
(bpy)](PF ) , [Ru(η -TPA)(bpy)(CH CN)](PF ) ,
6
2
3
6 2
25a
3
6 2 3 6 2
also act as a photosensitizer to afford singlet oxygen by photo-
irradiation under aerobic atmosphere to give cyclohexen-1-
hydroperoxide.
(
bpm)](PF ) , [Ru(η -TPA)(bpm)(CH CN)](PF )
sized in the procedure reported previously. m-Chloroperbenzoic acid
39
(mCPBA) was purified by the literature method. Cyclohexene was purified
by passage through a column of alumina to remove the BHT stabilizer.
Instrumentation. UVꢀvis spectra were collected on a Hewlett-
’
SUMMARY AND CONCLUSION
1
Packard HP8453 photodiode array spectrophotometer. H NMR spec-
1
Ru(II)ꢀdiimine complexes having a η -CH CN ligand and a
3
tra were recorded on JEOL JMN-AL-300 and Varian UNITY-600 NMR
spectrometers at room temperature. Gas chromatographic analyses were
performed on an Inertcap 5ms/sil column (GL Science, 30 m) and a
mass spectrometer (Shimadzu QP 5000) as a detector. ESI-MS spectra
were recorded on a Perkin-Elmer API-150 spectrometer. An Asahi
Spectra MAX-301 was used for the light source.
3
η -TPA ligand in a facial fashion with an uncoordinated pyridine
arm, [Ru(TPA)(diimine)(CH CN)] , reacted with mCPBA
2+
3
to undergo oxygenation of the uncoordinated pyridine nitro-
gen. The Ru(II) complexes having uncoordinated pyridine-
N-oxide arm exhibited photochemical transformation to afford an
1
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Journal of the American Chemical Society
ARTICLE
3
[
Ru(η -TPA-O)(bpy)(CH CN)](PF ) (3a). mCPBA (98 mg,
five-hours intervals by observing time course of the signals due to the
axial methylene protons of 2a and 3a. The time-course of [3a]/{[2a] +
[3a]} was plotted and curve-fitting of the data was made by using the
following equation:
3
6 2
3
0
(
.569 mmol) was added to a solution of [Ru(η -TPA)(bpy)(CH CN)]-
PF ) (100 mg, 0.114 mmol) in CH CN (100 mL). The mixture was
6 2 3
heated to 50 ꢀC for 24 h and evaporated to dryness to obtain a light
orange powder. The powder was washed with diethyl ether and then
dried in vacuo (85.1 mg, yield 83%). Anal. Calcd for C H ON
7-
3
FðtÞ ¼ A þ B expð ꢀ kobstÞ
30
29
2
P F12Ru: C, 40.28; H, 3.27; N, 10.96. Found: C, 40.42; H, 3.14; N,
where A and B are coefficients, t is the reaction time (s), and kobs is the
1
10.87. H NMR (CD
3 6
CN): 8.92 (d, 2H, J = 6 Hz, bpy-H ), 8.53 (d, 2H, J
pseudo-first-order rate constant, respectively.
3
+
=
7 Hz, pyr-H (equatorial)), 8.40 (d, 2H, J = 6 Hz, pyr-H (equatorial)),
6
3
Resonance Raman Spectroscopy on [Ru(O)(η -TPAH )-
3+
8
1
1
.14 (td, 2H, J = 8 and 2 Hz, pyr-H
Hz, pyr-H (free)), 7.79 (td, 2H, J = 8 and 2 Hz, bpy-H
H, J = 8 and 6 and 1 Hz, pyr-H (equatorial)), 7.43 (dd, 1H, J = 8 and 2
5
(equatorial)), 8.13 (dd, 1H, J = 7 and
(
[
bpm)] . Samples were prepared by the following procedures. For
1
6
3
+
3+
6
4
), 7.57 (ddd,
Ru( O)(η -TPAH )(bpm)] , CAN (8.8 mg, 16.0 μmol) was added
1
6
4
to 1 mL of a H
2 6 2
O solution of [Ru(TPA)(bpm)](PF ) (1.7 mg, 2.0
1
8
3
+
3+
Hz, pyr-H (free)), 7.37 (ddd, 1H, J = 8 and 7 and 2 Hz, pyr-H (free)),
3
5
μmol) and stirred for 2 min. For [Ru( O)(η -TPAH )(bpm)] , CAN
1
8
7
7
.36 (dd, 2H, J = 8 and 6 Hz, bpy-H
.30 (td, 1H, J = 8 and 1 Hz, pyr-H (free)), 4.92 and 4.11 (ABq, 4H,
4
5
3
), 7.31 (d, 2H, J = 8 Hz, bpy-H ),
(1.8 mg, 3.2 μmol) was added to 200 μL of a H
2
O solution of
[
Ru(TPA)(bpm)](PF (0.3 mg, 0.4 μmol) and stirred for 2 min.
6 2
)
JAB = 17 Hz, CH (equatorial)), 3.48 (s, 2H, CH (free)), 2.29 (s, 3H,
2
2
Resonance Raman scattering was made by excitation at 363.8 nm with an
+
+
CH ). ESI-MS (m/z): 750.1 ({M ꢀ (PF )} ). Absorption maximum
3
6
Ar laser (Spectra Physics, 2080-25/2580C), dispersed by a single
(
λ
max, nm): 426. A single crystal of this compound was obtained by
polychromator (Ritsu Oyo Kogaku, MC-100DG) and detected by a
liquid-nitrogen-cooled CCD detector (Roper Scientific, LNCCD-1100-
PB). The resonance Raman measurements were carried out at 22 ꢀC
using a spinning cell (outer diameter = 3 mm, wall thickness = 1 mm) at
90ꢀ scattering geometry.
recrystallization from acetonitrile with vapor diffusion of diethyl ether.
3
[
Ru(η -TPA-O)(bpm)(CH CN)](PF ) (3b). mCPBA (98 mg,
3 6 2
3
0
.569 mmol) was added to a solution of [Ru(η -TPA)(bpm)(CH
3
-
CN)](PF (100 mg, 0.114 mmol) in CH CN (100 mL). The mixture
6
)
2
3
was heated to 50 ꢀC for 24 h and evaporated to dryness to obtain a light
orange powder. The powder was washed with diethyl ether and then
Photochemical Reactions. Photoirradiation of the samples was
performed by using the light source of an Asahi Spectra MAX-301 at
dried in vacuo. (83.2 mg Yield 81%. Anal. Calcd for C28
H
27ON9-
monochromated wavelengths (420 ( 5 or 450 ( 5 nm) in CD CN at
3
P F Ru: C, 37.43; H, 3.04; N, 14.06. Found: C, 37.51; H, 3.08; N,
room temperature. The reaction was done in an NMR tube or a 10 mm
2
12
1
1
4.14. H NMR (CD CN): 9.20 (dd, 2H, J = 5 and 2 Hz, bpm-H ), 8.91
quartz cell to monitor the progress of the reaction by NMR and
absorption spectroscopy, respectively. All experiments were per-
formed under an inert atmosphere using standard techniques unless
otherwise noted.
3
6
(
d, 2H, J = 6 Hz, pyr-H
6
(equatorial)), 8.61 (dd, 2H, J = 4 and 2 Hz, bpm-
4 6
H ), 8.14 (d, 1H, J = 6 Hz, pyr-H (free)), 7.84 (td, 2H, J = 8 and 1 Hz,
pyr-H (equatorial)), 7.70 (dd, 2H, J = 5 and 4 Hz, bpm-H ), 7.45 (dd,
4
5
1H, J = 8 and 2 Hz, pyr-H
3
(free)), 7.41 (t, 2H, J = 6 Hz, pyr-
Photoreactions of 3a, 3b, and 4b in the Absence of Sub-
strate. The complexes (3.0 μmol) were dissolved in CD CN (600 μL)
H
5
(equatorial)), 7.39 (ddd, 2H, J = 8 and 6 and 2 Hz, pyr-H
5
(free)),
3
7
.35 (d, 2H, J = 8 Hz, pyr-H (equatorial), 7.32 (td, 1H, J = 8 and 1 Hz,
3
and irradiated by using the light source of an Asahi Spectra MAX-301 at
3
pyr-H (free)), 4.92 and 4.14 (ABq, 4H, J = 16 Hz, CH (equatorial)),
monochromated wavelengths ([Ru(η -TPA-O)(bpy)(CH CN)](PF )
4
AB
2
3
6 2
3
3.64 (s, 2H, CH
2
(free)), 2.29 (s, 3H, CH
)} ). Absorption maximum (λmax, nm): 449.
3
). ESI-MS (m/z): 752.0 ({M
(3a), 420 nm; [Ru(η -TPA-O)(bpm)(CH CN)](PF ) (3b), 450 nm;
3 6 2
+
ꢀ
(PF
[
6
[(Ru-O-TPA)(bpm)](PF ) (4b), 450 nm). The reactions were mon-
6 2
3
1
(Ru-O-TPA)(bpm)](PF ) (4b).[Ru(η -TPA-O)(bpm)(CH CN)]-
itored by H NMR measurements every hour.
6
2
3
(
PF
6
)
2
(5 mg, 0.0057 mmol) was irradiated at 420 nm for 3 h in CH
3
CN
Determination of the Initial Decay Rate of Photoreactions
of 3a and 3b in the Absence of Substrate. The complexes (3.3,
6.2, 12, 16, 25 mM for 3a; 3.3, 6.2, 12, 19, 25 mM for 3b) were dissolved
(0.6 mL). A dark brown single crystal of 4b was obtained by recrystallization
of the mixture from acetonitrile with vapor diffusion of diethyl ether.
Ru(TPA)(bpm)](PF (1b) will be obtained as a mixture when
too much ether is added. Anal. Calcd for C26 12Ru: C,
6.50; H, 2.83; N, 13.10. Found: C, 36.64; H, 2.99; N, 12.84. H NMR
CD CN): 10.38 (dd, 1H, J = 6 and 5 Hz, bpm-N5,7-H ), 9.21 (dd, 1H,
J = 5 and 2 Hz, bpm-N5,7-H ), 9.14 (dd, 1H, J = 6 and 2 Hz, bpm-N6,8-
[
6
)
2
in CD CN (600 μL) and photoirradiated by using an Asahi Spectra
3
3
H
24ON
8
P
2
F
MAX-301 at monochromated wavelengths: For ([Ru(η -TPA-O)-
(bpy)(CH CN)](PF ) (3a), 420 nm; for [Ru(η -TPA-O)(bpm)-
1
3
3
(
3
6 2
3
6
3 6 2
(CH CN)](PF ) (3b), 450 nm). The reactions were monitored by
1
H NMR measurements every 20 min. The decay rates were determined
4
H
6
), 8.79 (dd, 1H, J = 5 and 2 Hz, bpm-N6,8-H
pyr-N3-H ), 8.01 (dd, 1H, J = 6 and 5 Hz, bpm-N5,7-H
J = 8 and 2 Hz, pyr-N3-H ), 7.74 (ddd, 1H, J = 8 and 7 and 1 Hz, pyr-
4
), 8.61 (d, 1H, J = 7 Hz,
using the following equation:
6
5
), 7.76 (dd, 1H,
decay rate ¼ ꢀ d½3ꢂ=dt ¼ ð½3ꢂ ꢀ ½3ꢂ Þ=t
0
t
3
N4-H
and 1 Hz, pyr-N4-H
J = 6 and 1 Hz, pyr-N2-H ), 7.45 (dd, 1H, J = 6 and 5 Hz, bpm-N6,8-
5
), 7.64 (dd, 1H, J = 9 and 8 Hz, pyr-N3-H
4
), 7.63 (dd, 1H, J = 7
t 0
where [3] is concentration of 3 at certain time t (s), [3] is a initial
3
), 7.59 (d, 1H, J = 8 Hz, pyr-N4-H
6
), 7.53 (dd, 1H,
concentration of 3 and t (s) is reaction time, which was 6000 s (100 min)
for 3a and 4800 s (80 min) for 3b. Therefore, the decrease in the
concentration of 3 for 100 min for 3a and 80 min for 3b were divided by
6000 and 4800, respectively.
6
H
5
), 7.37 (dd, 1H, J = 8 and 7 Hz, pyr-N2-H
4
), 7.36 (ddd, 1H, J = 9 and
7
and 2 Hz, pyr-N3-H , 7.16 (t, 1H, J = 7 Hz, pyr-N4-H ), 7.07 (d, 1H,
5
4
J = 8 Hz, pyr-N2-H
and 5.09 (ABq, 2H, JAB = 18 Hz, CH
3
), 6.74 (dd, 1H, J = 7 and 6 Hz, pyr-N2-H
), 5.28 and 5.20 (ABq, 2H, JAB
6 Hz, CH (pyr-N3 and N4)), 4.49 and 3.65 (ABq, 4H, J = 13 Hz,
5
), 5.34
Photoirradiation in the Presence of Substrate. In a 10 mm
quartz cell, a complex (4.5 μmol) and a substrate (45ꢀ450 μmol) were
2
=
1
added in CD CN (900 μL) and photoirradiated under Ar atmosphere
2
AB
3
CH
2
(pyr-N2)). Absorption maximum (λmax, nm): 493. ESI-MS
by using the light source of an Asahi Spectra MAX-301 at monochro-
+
3
(
m/z): 711.1 ({M ꢀ (PF
6
)} ). A single crystal of this compound
mated wavelengths ([Ru(η -TPA-O)(bpy)(CH CN)](PF ) (3a),
3
6 2
1
was obtained by recrystallization from acetonitrile with vapor diffusion
of diethyl ether.
6 2
420 nm; [(Ru-O-TPA)(bpm)](PF ) (4b), 450 nm). H NMR and
GC-MS measurements were made after 30 h.
Kinetic Analysis of the Reaction of 2a with mCPBA. mCPBA
X-ray Crystallography. The crystals of 2a, 3a, and 4b were
mounted on a glass capillary with epoxy resin. All measurements were
performed on a Rigaku Mercury CCD diffractometer at ꢀ150 ꢀC with a
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The data
(
(
2.9 mM, 5.8 mM, or 11.6 mM) was added to a CD
1.15 mM). The reaction was performed in an oil bath kept at 323 K. H
3
CN solution of 2a
1
NMR spectra were recorded to monitor the reaction for one-hour or
1
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dx.doi.org/10.1021/ja207572z |J. Am. Chem. Soc. 2011, 133, 17901–17911

Journal of the American Chemical Society
Table 2. X-ray Crystallographic Data for [Ru(η -TPA)(bpy)(CH CN)](PF ) (2a), [Ru(η -TPA-O)(bpy)(CH CN)](PF )
6 2
ARTICLE
3
3
3
6 2
3
(
3a), and [(Ru-O-TPA)(bpm)](PF ) (4b)
6 2
2
a
3a
OP
4b
OP
formula
fw
C
30
H
29
F
12
7 2
N P Ru
C
30
H
29
N
7
2
F
12Ru
C
26
H
24
N
8
2
F12Ru
878.60
monoclinic
P2 /n
894.61
monoclinic
P2 /n
855.53
triclinic
P1
crystal system
space group
T, K
1
1
123
123
123
a, Å
19.25(8)
9.01(4)
21.80(9)
19.373(3)
8.841(1)
21.969(3)
11.343(2)
12.621(3)
12.733(3)
72.79(6)
77.87(6)
74.91(6)
1663.7(6)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
115.04(2)
114.9229(4)
3
V, Å
3427(25)
4
3412.6(8)
4
Z
no. of reflections
no. of observations
no. of parameters
26126
7740
470
25656
7574
479
13225
7303
479
a
R1 (I > 2.0σ(I))
0.101
0.238
1.22
0.053
0.138
1.11
0.055
b
wR2 (all data)
0.147
GOF
1.05
a
b
2
2 2
2 2 1/2
R1 =||F | ꢀ |F ||/∑ |F |. wR2=[ ∑(w (F ꢀ F ) )/∑ w(F ) ]
.
o
c
o
o
c
o
were collected up to 2θ = 55.0ꢀ. The structure was solved by direct
methods and expanded using Fourier techniques. All non-hydrogen
atoms were refined anisotropically. Refinement was carried out with full-
but also unnecessary wavelengths, the latter was deviated using a wedge
prism with wedge angle of 18 degree. The desirable beam was
irradiated at the sample cell with a spot size of 1 mm diameter where
it was merged with the white probe pulse in a close angle (<10 degree).
The probe beam after passing through the 2 mm sample cell was
focused on a fiber optic cable, which was connected to a CCD
spectrograph for recording the time-resolved spectra (470ꢀ
40
matrix least-squares on F with scattering factors and including
41
anomalous dispersion effects. All calculations were performed using
42
the Crystal Structure crystallographic software package, and structure
43
refinements were made by using SHELX-97. Crystallographic data are
summarized in Table 2.
1
600 nm). Typically, 3000 excitation pulses were averaged for 3 s to
Quantum Yield Determination. Quantum yields of the reac-
tions were determined by a standard method using an actinometer
obtain the transient spectrum at a set delay time. Kinetic traces at
appropriate wavelengths were assembled from the time-resolved
spectral data. All measurements were conducted at room tempera-
ture, 295 K.
3
(potassium ferrioxalate) in CD CN at room temperature with photo-
irradiation at 420 nm. Absorbance of the complex and that of the
actinometer were uniformed at 420 nm to determine the quantum
yields. The reactions were monitored at the decay of the peak of 3
(
7.5 mM) in NMR spectra and the data at the initial stage, where the
’
ASSOCIATED CONTENT
time-course of the spectral change was linear, were used to determine the
quantum yields.
S
Supporting Information. Figures S1ꢀS8 and crystallo-
b
3
Femtosecond Laser Flash Photolysis of 4b. A CH CN
graphic data for 2a, 3a, and 4b in CIF format. This material is
solution of 4b (0.083 mM) was prepared for laser flash photolysis.
Femtosecond transient absorption spectroscopy experiments were
conducted using an ultrafast source: Integra-C (Quantronix Corp.),
an optical parametric amplifier: TOPAS (Light Conversion Ltd.) and a
commercially available optical detection system: Helios provided by
Ultrafast Systems LLC. The source for the pump and probe pulses
were derived from the fundamental output of Integra-C (780 nm,
available free of charge via the Internet at http://pubs.acs.org.
’
AUTHOR INFORMATION
Corresponding Author
kojima@chem.tsukuba.ac.jp; fukuzumi@chem.eng.osaka-u.ac.jp
2
mJ/pulse and fwhm = 130 fs) at a repetition rate of 1 kHz. 75% of the
fundamental output of the laser was introduced into TOPAS which has
optical frequency mixers resulting in tunable range from 285 to
’
ACKNOWLEDGMENT
1
660 nm, while the rest of the output was used for white light
We appreciate financial support provided by Grants-in-Aid
generation. Prior to generating the probe continuum, a variable neutral
density filter was inserted in the path in order to generate stable
continuum, then the laser pulse was fed to a delay line that provides an
experimental time window of 3.2 ns with a maximum step resolution of
(Nos. 21350035, 23750014 and 20108010), a Global COE
program, “the Global Education and Research Center for Bio-
Environmental Chemistry” from the Japan Society of Promotion
of Science (JSPS), the Ministry of Education, Science, Technol-
ogy of Japan, and by KOSEF/MEST through WCU project
(R31-2008-000-10010-0) from Korea. T.K. also thanks The
Asahi Glass Foundation for support.
7
fs. Excitation wavelength at 420 nm of TOPAS output, which is
fourth harmonic of signal or idler pulses, was chosen as the pump
beam. As this TOPAS output consists of not only desirable wavelength
1
7909
dx.doi.org/10.1021/ja207572z |J. Am. Chem. Soc. 2011, 133, 17901–17911

Journal of the American Chemical Society
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