Formation of a ruthenium(IV)-oxo complex by electron-transfer oxidation of a coordinatively saturated ruthenium(II) complex and detection of oxygen-rebound intermediates in C-H bond oxygenation

Article abstract of DOI:10.1021/ja2037645

A coordinatively saturated ruthenium(II) complex having tetradentate tris(2-pyridylmethyl)amine (TPA) and bidentate 2,2′-bipyridine (bpy), [Ru(TPA)(bpy)]²⁺ (1), was oxidized by a Ce(IV) ion in H₂O to afford a Ru(IV)-oxo complex, [Ru(O)(H⁺TPA)(bpy)]³⁺ (2). The crystal structure of the Ru(IV)-oxo complex 2 was determined by X-ray crystallography. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated. The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to -20 ppm, was determined to be an intermediate spin (S = 1) by the Evans' method with ¹H NMR spectroscopy in acetone-d₆. The reaction of 2 with various oraganic substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex, [Ru(H⁺TPA)(bpy)(CH₃CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated C-H bonds with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12, respectively. The second-order rate constants of C-H oxygenation in the first step exhibited a linear correlation with bond dissociation energies of the C-H bond cleavage.

Full text of DOI:10.1021/ja2037645

ARTICLE
pubs.acs.org/JACS
Formation of a Ruthenium(IV)-Oxo Complex by Electron-Transfer
Oxidation of a Coordinatively Saturated Ruthenium(II)
Complex and Detection of Oxygen-Rebound Intermediates
in CꢀH Bond Oxygenation
,
†
‡
§
§
,‡,||,^
Takahiko Kojima,* Kazuya Nakayama, Kenichiro Ikemura, Takashi Ogura, and Shunichi Fukuzumi*
†
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tennoudai, Tsukuba,
Ibaraki 305-8571
‡
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Japan
ALCA, Japan Science and Technology Agency (JST), 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
§
Graduate School of Life Science, University of Hyogo, Kouto, Hyogo 678-1297, Japan
^Department of Bioinspired Science, Ewha Womans University, Seoul, South Korea
S Supporting Information
b
ABSTRACT: A coordinatively saturated ruthenium(II) com-
plex having tetradentate tris(2-pyridylmethyl)amine (TPA) and
0
2+
bidentate 2,2 -bipyridine (bpy), [Ru(TPA)(bpy)] (1), wasoxi-
dized by a Ce(IV) ion in H O to afford a Ru(IV)-oxo complex,
2
+
3+
[
Ru(O)(H TPA)(bpy)] (2). The crystal structure of the
Ru(IV)-oxo complex 2 was determined by X-ray crystallogra-
phy. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated.
The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to ꢀ20 ppm, was determined to be an
1
intermediate spin (S = 1) by the Evans’ method with H NMR spectroscopy in acetone-d . The reaction of 2 with various oraganic
6
substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex,
+
[
Ru(H TPA)(bpy)(CH CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated CꢀH bonds
3
with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from
the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic
isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12,
respectively. The second-order rate constants of CꢀH oxygenation in the first step exhibited a linear correlation with bond
dissociation energies of the CꢀH bond cleavage.
’
INTRODUCTION
via proton-coupled electron transfer to afford the high-valent
metalꢀoxo complexes.
High-valent metalꢀoxo complexes are known to act as reac-
Thus, although being the majority of coordination com-
pounds, coordinatively saturated metal complexes in which all
the coordination sites are occupied by chelating ligands have
been excluded as precursor complexes to afford high-valent
metalꢀoxo complexes. However, if high-valent metalꢀoxo com-
plexes can be formed using coordinatively saturated metal
complexes, the possibility will be widely expanded in application
of metal complexes to form high-valent metalꢀoxo species as
responsible intermediates in substrate oxidations. As a strategy to
make it possible to apply coordinatively saturated metal com-
plexes to oxidation reactions involving the generation of high-
valent metalꢀoxo complexes, structural change such as partial
ligand dissociation is required in the course of the reaction to
tive species for oxidation of various substrates in both biolo-
gical and chemical systems.
been devoted to understand the structures and reactivities of
high-valent metalꢀoxo complexes, which have normally been
produced by reactions of metal complexes with active oxygen
species such as iodosylbenzene (PhIO), m-chloroperbenzoic
acid (m-CPBA), and hydroperoxides (H O and ROOH), or
1
ꢀ3
Extensive efforts have so far
2
2
4
ꢀ8
with O in the presence of electron and proton donors.
2
To promote those reactions, it is required for the metal com-
plexes to have a vacant site or a labile ligand such as a solvent
molecule or halides to accommodate the coordination of the
oxidant for its activation. Alternatively, high-valent metalꢀ
oxo intermediates have been produced by the two-electron
oxidation of metal complexes with water as an oxygen source
9
ꢀ11
for the oxo ligand.
a water molecule as a ligand have been required to be oxidized
In this process, aqua complexes having
Received: April 24, 2011
Published: June 22, 2011
r 2011 American Chemical Society
11692
dx.doi.org/10.1021/ja2037645
|J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
Scheme 1
Figure 2. Positive-ion ESI-MS spectra of 2 in CH
3
CN. (a) Peak cluster
+
ꢀ
6
)} ; (b) peak cluster at
+
+
at m/z 709.1 assigned to {2 ꢀ H ꢀ 2(PF
1
8
+
ꢀ
6
)} . Red lines show
m/z = 711.1 assigned to {2( O) ꢀ H ꢀ 2(PF
the computer-simulated isotope patterns.
observation of the oxygen-rebound process in the course of
hydroxylation of saturated CꢀH bonds.
’
RESULTS AND DISCUSSION
Characterization of a Ruthenium(IV)ꢀOxo Complex.
18
A Ru(II) complex, [Ru(TPA)(bpy)](PF ) (1), having a tetra-
6
2
dentate ligand of TPA and a bidentate ligand of bpy as ligands
IV
was oxidized by (NH ) [Ce (NO ) ] (CAN) in H O at room
4
2
3 6
2
temperature. In the UVꢀvis spectrum, the MLCT band peculiar
to 1 disappeared by the addition of CAN to an aqueous solution
of 1 (see Figure S1 in Supporting Information). The reaction
afforded a light-green complex 2 and its crystal structure was
determined by X-ray crystallography. The crystal structure of the
cation part of 2 is depicted in Figure 1 with a partial numbering
Figure 1. ORTEP drawing of the cation moiety of 2 using 50%
probability thermal ellipsoids with numbering scheme for the heteroa-
toms. Hydrogen atoms are omitted for clarity except the hydrogen on
the uncoordinated pyridine nitrogen (N2). O2 represents the water
molecule of crystallization. Selected bond lengths (Å): Ru1ꢀO1
19
scheme. The light-green complex was revealed to be a Ru-
+
1
.771(4), Ru1ꢀN1 2.242(4), Ru1ꢀN2 2.083(4), Ru1ꢀN4 2.072(4),
(IV)ꢀoxo complex, [Ru(O)(H TPA)(bpy)](PF ) (2), bear-
6
3
Ru1ꢀN5 2.070(4), Ru1ꢀN6 2.073(4).
ing an oxo ligand, the bpy ligand, and a protonated TPA ligand
H TPA) in a facial and tridentate coordination mode. In the
+
(
course of the formation of 2, the complex was revealed to
accommodate a coordination site for the formation of the oxo ligand.
However, there has so far been no report on generation of high-
valent metalꢀoxo complexes starting from coordinatively saturated
metal complexes through proton-coupled electron transfer.
undergo structural change, which is reminiscent of the photo-
18
chromic behavior of 1, in terms of the coordination mode of the
TPA ligand involving its partial dissociation. The bond length of
RuꢀO bond is 1.771(4) Å, which is in the range of those of
20
High-valent metalꢀoxo complexes are capable of hydroxyla-
Ru(IV)ꢀoxo bonds reported so far. The uncoordinated pyr-
idine moiety is protonated and the proton attached to the
pyridine nitrogen atom forms a hydrogen bond with a water
tion of a CꢀH bond, which has been believed to proceed via an
12
“
oxygen-rebound” mechanism as shown in Scheme 1. Hydro-
ꢀ
gen atom transfer from substrates to high-valent metalꢀoxo
complexes affords the hydrogen abstracted radicals and the
hydoxo complexes, followed by oxygen-rebound between them
to produce the corresponding alcohols. Although much effort has
been devoted to gain mechanistic insights into proving the
molecule of crystallization and one of fluorine atoms of PF6
(N2 O2: 2.738(8) Å, N2 F: 2.899(6) Å).
3
3 3
3 3 3
ESI-MS spectrometry was applied to detect the signal due to
+
ꢀ
+
{2 ꢀ H ꢀ 2(PF )} at m/z = 709.1 in CH CN prepared in
6
3
1
6
H
O, and the mass number was shifted to m/z = 711.1 for the
18
2
13
14
rebound mechanism by experiments as well as calculations,
direct observation of the oxygen-rebound intermediates has yet
to be achieved.
sample prepared in H2 O as shown in Figure 2. These results
indicate that the Ru(IV)ꢀoxo complex 2 is stable in solution to
maintain the oxo ligand and that the oxo-oxygen comes from
water.
1
5ꢀ17
We report herein the first example of generation of a high-
valent metalꢀoxo complex using a coordinatively saturated
metal complex, which is stabilized by two chelating ligands
without aqua ligand. The electron-transfer oxidation of a hex-
acoordinated ruthenium(II) complex having tris(2-pyridyl-
The Ru(IV)-oxo complex 2 showed paramagnetically shifted
NMR signals in the range of 60 to ꢀ20 ppm, and the spin state
was determined to be an intermediate spin (S = 1) by the Evans’
21
1
method with H NMR spectroscopy in acetone-d (see Figure
6
0
methyl)amine (TPA) and 2,2 -bipyridine (bpy) as chelating
S2 in Supporting Information).
The resonance Raman spectrum of 2 prepared in H2 O was
2+
18
16
ligands, [Ru(TPA)(bpy)] (1), with a Ce(IV) ion afforded
+
+
the corresponding Ru(IV)ꢀoxo complex, [Ru(O)(H TPA)-
measured by the laser excitation at 363.8 nm with an Ar laser.
3
+
ꢀ1
(
bpy)] (2). Successful isolation and determination of the
A peak obsreved at 805 cm was assigned to the Raman scattering
ꢀ
1
crystal structure of 2 have allowed us to examine the mechanism
of the CꢀH bond activation with 2 including the first direct
of the RudO moiety (ν(RudO)), which shifted to 764 cm
18
when 2 was prepared in H2 O as shown in Figure 3. The shift
1
1693
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
ꢀ
1
value (Δν = 41 cm ) agrees with the calculated value (Δνcalcd
=
The one-electron reduction potential of 2 was determined
to be 0.70 V (versus SCE) by SHACV (second harmonic ac
voltammetry) in the presence of 0.1 M of [(n-butyl) N]PF as an
ꢀ1
4
0 cm ) for ν(RudO). The Raman shift of the ν(RudO) for 2
is comparable to that (805 cm ) observed for [Ru (O)(TPA)-
OH )] in the intermediate spin state and falls in the lower
range of those of Ru dO bonds.
ꢀ
1 IV
4
6
2
+
10a
(
electrolyte in CH CN at room temperature under Ar and 0.80 V
2
3
IV
20a,22
(vs SCE) by SHACV in the presence of 0.1 M of Na SO as an
2
4
electrolyte at pH = 1 adjusted by aqueous H SO at room temp-
2
4
erature under Ar (see Figure S3 in Supporting Information). This
IV
III
potential is comparable to those of Ru /Ru redox couples
IV
2+
10a
IV
ꢀ
for [Ru (O)(TPA)(H O)] (0.74 V) and [Ru (6-COO -
2
+
10b
TPA)(O)(H O)] (0.68 V) in a Britton-Robinson buffer at
2
pH = 2.
Oxidation Reactions of Organic Substrates by 2 Involving
Hydrogen Abstraction. The complex 2 was employed for
oxidation of various organic substrates in CH CN at room
3
temperature. Substrates used and their bond dissociation en-
ergies (BDEs), methods, products and their yields are summar-
ized in Table 1. When 10-methyl-9,10-dihydroacridine (entry 1)
was used as a substrate, the two-electron oxidized product
16
2
18
Figure 3. Resonance Raman spectra of 2 in (a) H O and (b) H2 O.
16
18
(c) Differential spectrum of ( O ꢀ O).
Table 1. Yields of Products in Oxidation of Various Substrates by 2 (5 mM) in Acetonitrile under Inert Atmosphere at Room
Temperature
a
b
c
d
Adapted from ref 23. Oxidation efficiency (%) = [{[Product(s)]/(2 ꢁ [2])} ꢁ N(oxidation equivalent)] ꢁ 100. Adapted from ref 24. Adapted
e
f
from ref 25. Adapted from ref 26. Adapted from ref 27. Methods: w, by NMR in CD CN; x, by NMR in CDCl ; y, by GC-MS in CH CN; z, by NMR
3
3
3
and GC-MS in CD
3
CN (wꢀy, 1,4-cyclohexadione as an internal reference; z, methoxybenzene as internal references). Product yields are based on 2.
1
1694
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
Figure 4. Absorption spectral change in the course of the reaction of 2
Figure 6. (a) Concentration dependence of pseudo-first-order rate
(0.1 mM) with cumene (200 mM) in CH
3
CN under Ar at 298 K: (a)
constants for the first step of the reaction of 2 with cumene in CH CN
3
0ꢀ650 s; (b) 650ꢀ3000 s.
at 298 K: red, cumene; blue, cumene-d12. (b) Concentration depen-
dence of pseudo-first-order rate constants for the second step of reaction
3
of 2 with cumene in CH CN at 298 K: red, cumene; blue, cumene-d12.
Figure 7. Concentration dependence of pseudo-first-order rate con-
stants for the reaction of 2 with (a) DHA and (b) DHA-d in CH CN
4 3
at 298 K.
(
23%) with the overall oxidation efficiency of 46%. The low
oxidation efficiency for toluene may stem from its high BDE
ꢀ
1
value (88.5 kcal mol ) compared to that of OꢀH bond formed
by the hydrogen abstraction by 2.
Figure 5. Absorbance change at 319 nm (red line) and 420 nm (black
line) in the course of the reaction of 2 (0.1 mM) with cumene (200 mM)
Kinetic Analysis of Reaction Mechanisms. To obtain the
mechanistic insight into the oxidation of substrates with 2, we
in CH
3
CN under Ar at 298 K: (a) 0ꢀ3200 s; (b) 0ꢀ650 s (the first
step); (c) 650ꢀ3000 s (the second step).
conducted the kinetic analysis in deaerated CH CN using
3
UVꢀvis spectroscopy. The absorption spectrum of 2 in the
reaction with cumene exhibited a two-step spectral change as
shown in Figure 4a and b. In the first step up to 650 s after mixing,
the spectral change was observed as an increase in a broad
absorption band ranging from 330 to 450 nm with isosbestic
points at 306 and 316 nm (Figure 4a). The time profile of the
absorption change obeyed pseudo-first-order kinetics as shown
in Figure 5. The pseudo-first-order rate constant (kobs) increased
linearly with increasing cumene concentration (red squares in
(
10-methylacridinium ion) was obtained in 100% yield. 9,
0-Dihydroanthracene (DHA; entry 2) was converted to the
1
two-electron oxidized product, anthracene (20%), and the eight-
electron oxidized product, anthraquinone (18%). 9-Oxo-10-
hydroanthracene (anthrone, entry 3) was converted to the four-
electron oxidized product, anthraquinone (46%). Cyclohexene
(
entry 4) was also oxidized to the four-electron oxidized product,
cyclohexene-1-one (44%), and the two-electron oxidized pro-
duct, cyclohexen-1-ol (5%). The overall oxidant efficiency of
these substrates, which have lower BDE values than 82 kcal
Figure 6a). The second-order rate constant (k ) for the first step
1
was determined from the slope of the linear plot in Figure 6a
ꢀ
1
ꢀ2
ꢀ1 ꢀ1
mol , with 2 is higher than 90%. Diphenylmethane (entry 5)
was converted to benzophenone (18%) and diphenylmethanol
(
to be (3.2 ( 0.1) ꢁ 10
M
s
s
. Virtually the same value
ꢀ
2
ꢀ1 ꢀ1
[(3.3 ( 0.1) ꢁ 10
M
] was obtained under O (see
2
12%). The lower oxidant efficiency should stem from steric
Figure S4 in Supporting Information).
hindrance in the access of bulky diphenylmethane to the oxo
ligand. Cumene (entry 6) was also converted to the two-electron
oxidized product, 2-phenyl-2-propanol (cumyl alcohol: 54%),
R-methylstyrene (6%), and the four-electron oxidized product,
acetophenone (6%), when the overall oxidation efficiency is 72%.
Ethylbenzene (entry 7) underwent benzylic oxygenation to yield
the two-electron oxidized product, benzyl alcohol (25%) and
styrene (trace), and the four-electron oxidized products, acet-
ophenone (15%) and benzaldehyde (8%) with the overall
oxidation efficiency of 81%. Toluene (entry 8) was also oxyge-
nated to yield the four-electron oxidized product, benzaldehyde
When cumene was replaced by the corresponding deuterated
compound (cumene-d ), the second-order rate constant was
12
ꢀ3
ꢀ1 ꢀ1
determined to be (2.74 ( 0.14) ꢁ 10
M
s
(blue points in
Figure 6a), which is significantly smaller that the value of cumene.
From the rate constants of cumene and cumene-d , the kinetic
12
isotope effect (KIE) was determined to be 12 for the first step of
the cumene oxygenation.
The oxidation of 9,10-dihydroanthracene (DHA) and the
deuterated compound (DHA-d ) with 2 also proceeded by
4
the two steps. The pseudo-first-order rate constant increased
linearly with increasing DHA concentration as shown in Figure 7.
1
1695
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
Figure 10. (a) Concentration dependence of pseudo-first-order rate
0
Figure 8. Plot of logk vs BDEs of substrates for oxidation of substrates
1
constants of reaction of 2 with cyclohexene in CH CN at 298 K: red, the
3
3
with 2 in CH CN at 298 K.
first step; blue, the second step. (b) Eyring plot for the second-order rate
ꢀ1
ꢀ1
constants of the first step (k , M
s ) in the reaction of 2 with
1
cyclohexene.
Figure 9. Eyring plots for the oxidation of cumene with 2 (red: the first
ꢀ1
ꢀ1
ꢀ1
step (k , M
s ); blue: the second step (k , s )).
1
2
The second-order rate constants for the first step in the oxidation
of DHA and DHA-d with 2 were determined to be (1.05 (
4
2
ꢀ1 ꢀ1
ꢀ1 ꢀ1
0
.05) ꢁ 10 M
s
and 2.13 ( 0.09 M
s , respectively,
from which the KIE value was determined to be 49. In this case,
the hydrogen atom transfer probably occurs via proton-coupled
electron transfer with tunneling. The large KIE value indicates
that the first step should be the hydrogen abstraction from
substrates by 2.
Figure 11. Time-course of ESI-MS spectra of the reaction mixture of 2
28
(0.1 mM) and cumene (200 mM) in CH CN (purple line: 0 min, red
3
line: 15 min, blue line; 300 min). (a) Range, m/z = 700ꢀ745; (b) range,
m/z = 815ꢀ840.
The second-order rate constants for the first step in the
oxidation of other substrates were also determined from plots
of the observed pseudo-first-order rate constant vs concentration
of substrates (see Figure S5 in Supporting Information for an
oxidation of cumene with 2 in CH CN are compared in the
Eyring plots (Figure 9). The activation parameters of the first
3
q
ꢀ1
step was determined to be ΔH = 10 ( 0.40 kcal mol and
q
ꢀ1 ꢀ1
example of the case of ethylbenzene). The logarithm of the
ΔS = ꢀ31 ( 1.5 cal mol
K
. The activation enthalpy of the
0
q
ꢀ1
normalized second-order rate constants (k ) for the first step in
second step (ΔH = 7.3 ( 0.9 kcal mol ) is smaller than the
1
q
ꢀ1
oxidation of various substrates by 2 exhibited a linear relationship
with the bond dissociation energies of the CꢀH bond of the
corresponding substrates as shown in Figure 8, where the
observed second-order rate constants are divided by the number
of equivalent hydrogen atoms to be abstracted at the same
value of the first step (ΔH = 10 ( 0.40 kcal mol ), whereas
q
ꢀ1 ꢀ1
the activation entropy (ΔS = ꢀ47 ( 3.1 cal mol
K ) is
q
more negative than the value of the first step (ΔS = ꢀ31 (
ꢀ1
ꢀ1
1.5 cal mol
K ).
The activation parameters for the first step in the oxidation of
cyclohexene with 2 to give cyclohexene-1-one (entry 4 in
0
29,30
position to obtain k .
The linear correlation between log
1
0
q
ꢀ1
k1 and BDE in Figure 8 strongly indicates that the hydrogen
Table 1) were also determined to be ΔH = 7.2 ( 1.0 kcal mol
q
ꢀ1 ꢀ1
atom abstraction occurs in a common mechanism for all the
and ΔS = ꢀ36 ( 3.5 cal mol
K
as shown in Figure 10.
11b,30
investigated substrates.
These values are virtually identical with those obtained in the
IV
The spectral change in the second step at later than 650 s after
mixing of cumene with 2 is shown in Figure 3b, where a new
isosbestic point is observed at 319 nm. The rate of the second
step also obeyed first-order kinetics. The first-order rate con-
reaction of the same substrate (cyclohexene) with [Ru (O)-
2
+
q
ꢀ1
q
(bpy) (py)] (ΔH = 7.4 ( 0.1 kcal mol and ΔS = ꢀ34 (
2
ꢀ
1
ꢀ1 31
3.4 cal mol
K ). The identical reactivity of 2 may result
from the nearly the same one-electron reduction potential of 2
IV
2+
stants (k ) of the second step in the oxygenation of cumene,
(0.80 V at pH = 1 in water) as that of [Ru (O)(bpy) (py)]
2
32
2
cyclohexene, and ethybenzene were determined to be 1.17,
(0.85 V at pH = 1 in water).
ꢀ
1
1
.03, and 1.09 s , respectively. In contrast to the case of the first
Detection of Intermediates in Substrate Oxygenation
Reactions. ESI-MS spectrometry was applied in order to detect
intermediates in the two-step processes for the oxidation of
step (Figure 5a), the observed first-order rate constant shows
no dependence on the substrate concentration as shown in
Figure 5b and Figure 6 (blue points). The temperature depen-
dence of the rate constants of the first and the second steps in the
substrates with 2 in CH CN, In the course of the reaction of 2
3
+
ꢀ
+
({2 ꢀ H ꢀ 2(PF6 )} , m/z = 709.1) with cumene in CH CN
3
1
1696
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
II
+
at room temperature, signals due to a Ru(III)-hydroxo complex
complexes were finally converted to [Ru (H TPA)(bpy)-
III
+
2+
+ +
3+
+ +
[
Ru (OH)(H TPA)(bpy)] (3) ({3 ꢀ H } , m/z = 710.1)
(CH CN)] (5) ({5 ꢀ H } , m/z = 734.1) at the end of the
3
III
and a Ru(III)-cumyl alkoxo complex, [Ru (OC(CH ) -
(
observed as shown in Figure 11 (see also Figure S6 in Support-
ing Information). The isotope patterns agree with those obtained
by computer simulations (Figure S7 in Supporting Information).
reaction (blue line in Figure 11a).
3
2
+
2+
+ +
C H ))(H TPA)(bpy)] (4) ({4 ꢀ H } , m/z = 828.2) were
The Ru(III)ꢀhydroxo complex 3 and the Ru(III)-alkoxo
complex 4 may be formed via the oxygen-rebound reaction as
shown in Scheme 2 in the case of oxidation of cumene with 2.
The complex 1 is rapidly oxidized with CAN with water as an
oxygen source to afford 2. In the first step, hydrogen atom
transfer from cumene to 2 occurs to produce cumyl radical and
the Ru(III)ꢀhydroxo complex 3. The oxygen rebound between
cumyl radical and 3 affords the Ru(II)-alcohol complex. The
Ru(II)ꢀalcohol complex may be readily oxidized by 2 via
hydrogen atom transfer to produce 3 and the Ru(III)ꢀalkoxo
complex 4. The formation of Ru(III) complexes 3 and 4 in the
6
5
18
18
+
When the O-labeled complex, [Ru( O)(H TPA)(bpy)](PF )
6
3
1
8
(
2- O), was employed as the starting material, the signals due to
and 4 were shifted to m/z = 712.1 and m/z = 830.2, respectively
Figure 12). Formation of Ru(III)ꢀalkoxo complexes was also
observed in the reactions of 2 with cyclohexene, dihydro-
3
(
3
3
anthracene, anthrone, ethylbenzene, and diphenylmethane
(Figures S8ꢀ12 in Supporting Information). All the alkoxo
reaction of 2 with cumene in CH CN detected by ESI-MS
3
spectra in Figure 11 was confirmed by the EPR spectroscopic
measurements at 8 K as shown in Figure 13. The observed EPR
signal at g = 1.89, 2.16, and 2.40 in Figure 13 is typical for Ru(III)
34
complexes. The reverse reaction may also occur to reproduce
the Ru(II)ꢀcumyl alcohol complex, which slowly dissociates
II
+
by ligand substitution with CH CN to yield [Ru (H TPA)-
3
3+
(
bpy)(CH CN)] (5) and cumyl alcohol as the final products.
3
As mentioned above, the negative activation entropy for the
second step in the oxygenation of cumene indicates that this
ligand substitution process proceeds via an associative mechan-
1
8b
ism as observed in thermal ligand dissociation in 1 to afford 5.
Complex 5 in the presence of large excess cumyl alcohol was not
Figure 12. ESI-MS spectra of the mixture of cumene (200 mM)
II
+
3+
1
8
converted to [Ru (H TPA)(bpy)(cumyl alcohol)] , due to
and 2( O) (0.1 mM) in CH CN. (a) Peak cluster at m/z = 712.1
3
18
+ +
35
assigned to {3( O) ꢀ H } ; (b) peak cluster at m/z = 830.2 assigned
strong interaction of CH CN with the Ru(II) center. Also,
3
18
+ +
to {4( O) ꢀ H } .
cumyl alcohol is not oxidized by 2 under the same reaction
Scheme 2
1
1697
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
first example of the direct observation of“oxygen-rebound” process,
which has been proposed as a fundamental reaction mechanism for
hydroxylation of CꢀH bond by high-valent metalꢀoxo complexes.
The hydrogen atom abstraction by 2 proceeds via a compact and
well-ordered transition state as demonstrated by the activation
parameters and with large KIE values.
’
EXPERIMENTAL SECTION
IV
Materials. (NH ) [Ce (NO ) ] (CAN) was used as received and
4
2
3 6
Figure 13. EPR spectrum of the reaction mixture of 2 and cumene in
its purity was determined to be 67% by iodometry. CH CN was used
3
CH
3
CN at 8 K.
after distillation over CaH
2
. All other solvents were of special grade and
were used as received from commercial sources without further purifi-
conditions due to the stronger OꢀH bond than the tertiary
41
42
36
cation. TPA 3HClO
4
,
[RuCl(TPA)]
2
(ClO
4
)
2
,
[Ru(TPA)(bpy)]-
3
CꢀH bond in cumene.
18
6 2
(PF )
were synthesized as reported previously. Cyclohexene was
According to Scheme 2, the first step corresponds to the
hydrogen abstraction from cumene by 2 to produce the Ru-
purified by passage through a column of alumina to remove the BHT
stabilizer. Dihydroanthracene (DHA) was recrystallized twice from
absolute ethanol.
(
II)ꢀcumyl alcohol complex, when the rate is proportional to
concentration of cumene with the large kinetic isotope effect.
Instrumentation. UVꢀvis spectra were recorded on a Hewlett-
The second step corresponds to the ligand displacement of the
1
Packard HP8453 photodiode array spectrophotometer. H NMR spec-
Ru(II)ꢀcumyl alcohol complex by CH CN to release cumyl
3
tra were recorded on a JEOL JMN-AL-300 NMR spectrometer at room
temperature. Electrochemical measurements were carried out using a
BAS 100W electrochemical analyzer. Gas chromatographic analyses
were performed on a Shimadzu GC-17A equipped with DB-5 ms
(Agilent J&W, 30 m) or Inertcap 5 ms/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.
Stopped-flow measurements were performed with a UNISOKU RSP-
601 stopped-flow spectrophotometer with an MOS-type high selective
photodiode array. EPR spectra were recorded on a JEOL JEXREIXE
alcohol, which competes with the oxidation by 2 to produce 3
and 4, which were detected as intermediates by ESI-MS. The
equilibrium between the hydrogen atom transfer from Ru-
(
II)ꢀcumyl alcohol complex to 2 and the backward hydrogen
atom transfer from 3 to 4 in Scheme 2 lies to the right side (3 and
), because only 3 and 4 were detected by ESI-MS. As the ligand
4
substitution of the Ru(II)ꢀcumyl alcohol complex proceeds in
the second step, 3 and 4 are converted to 5. Because the rate-
determining step in the second step involved no reaction with
cumene and hydrogen abstraction, the rate is independent of
cumene concentration with no kinetic isotope effect (Figure 5b)
and regardless of deuterium substitution of the alcohol OꢀH
2+
spectrometer, and g values were determined using an Mn marker.
IV
+
[Ru (O)(H TPA)(bpy)](PF
30 mmol) were added to a solution of (NH
9 mmol) in water (3 mL) and stirred vigorously for several minutes. When
the orange power of [Ru(TPA)(bpy)](PF dissolved, light green solution
was obtained. KPF (50 mg 270 mmol) were added to afford light-green
powder. The light-green precipitate was washed with small amount of ether
and then dried (24 mg. Yield: 83%). Anal. Calcd for C28 18Ru: C,
6 3
6 2
) (2). [Ru(TPA)(bpy)](PF )
(25mg,
) [Ce (NO ) ] (65 mg
4 2 3 6
IV
7
group by addition of excess amount of D O (2 M) (Figure S13 in
2
6 2
)
Supporting Information). In addition, since the complex 5 is
intact in the presence of excess amount of cumyl alcohol, it cannot
be a precursor to afford the Ru(II)ꢀcumyl alcohol complex.
Mayer and co-workers have previously reported the trapping
6
6 3
H27ON P F
3
3.65; H, 2.72; N, 8.41. Found: C, 33.42; H, 2.70; N, 8.45. ESI-MS: 709.1
of radical species by O in the cumene oxygenation by
2
+
IV
2+
2 3
37
({M ꢀ PF } ).
6
[
Ru (O)(bpy) (py)] in CH CN. In our case, however, no
Resonance Raman Spectroscopy. Samples were prepared
effect of O was observed on the rate of the reaction of 2 with
2
16
+
3+
under following conditions. For [Ru( O)(H TPA)(bpy)] : To a
1
cumene (vide supra). The products also remained the same in
the presence of O as those in the absence of O . In addition, no
1
6
mL of H
2 6 2
O solution of [Ru(TPA)(bpy)](PF ) (1.7 mg, 2.0 μmol)
2
2
was added a CAN (4.4 mg, 8.0 μmol) and stirred for 2 min. For
organic radical was detected by EPR measurements in Figure 13.
Moreover, the addition of CH Br or CBr used as radical traps
1
8
+
3+
18
[
Ru( O)(H TPA)(bpy)] : To a 120 μL of H O solution of [Ru-
2
2
2
4
(TPA)(bpy)](PF
6 2
) (0.3 mg, 0.36 μmol) was added a CAN (2.2 mg,
resulted in no effect on the product distribution without forming
4
.0 μmol) and stirred for 2 min. Resonance Raman scattering was made
38
any brominated products. Thus, we concluded that the nascent
radical species formed by the hydrogen abstraction is not
released from a solvent cage and resides in the second coordina-
+
by excitation at 363.8 nm with an Ar laser (Spectra Physics, 2080ꢀ25/
2
1
580C), dispersed by a single polychromator (Ritsu Oyo Kogaku, MC-
00DG) and detected by a liquid-nitrogen-cooled CCD detector (Roper
39,40
tion sphere to undergo a fast oxygen-rebound reaction.
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.
X-Ray Crystallography on 2. A single crystal of 2 was obtained by
6 2
standing a mixture of [Ru(TPA)(bpy)](PF ) and CAN overnight in
’
SUMMARY AND CONCLUSION
We have synthesized an intermediate-spin (S = 1) Ru(IV)-oxo
complex from a coordinatively saturated Ru(II) complex without
aqua ligand via structural change involving partial dissociation of
a multidentate ligand, followed by proton-coupled electron
transfer. The Ru(IV)ꢀoxo complex was characterized by crystal-
lographic, spectroscopic, and electrochemical methods. We have
succeeded in the direct observation of “oxygen-rebound” process
in the course of hydroxylation of a saturated CꢀH bond by the
Ru(IV)ꢀoxo complex by using ESI-MS spectrometry. This is the
water at room temperature. The crystals 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 KR
radiation (λ = 0.71073 Å). The data 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. Refine-
ment was carried out with full-matrix least-squares on F with scattering
4
3
44
factors and including anomalous dispersion effects. All calculations
1
1698
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
ARTICLE
were performed using the Crystal Structure crystallographic software
package, and structure refinements were made by using SHELX-97.
General Procedure for Oxygenation Reactions. A solution
Education and Research Center for Bio-Environmental Chem-
istry” from the Japan Society of Promotion of Science (JSPS), the
Ministry of Education, Science, Technology of Japan, and by
KOSEF/MEST through WCU project (R31-2008-000-10010-0).
T.K. also appreciates financial support from The Asahi Glass
Foundation.
45
46,47
was prepared in 0.6 mL of CD CN to contain 3 μmol of 2 and fixed
3
amount of 1,4-cyclohexadione or methoxybenzene as an internal standard
for NMR and GC-MS quantification. To the solution, 0.006ꢀ0.3 mmol of
a substrate was added and the mixture was stirred at room temperature at
least 120 min. ESI-MS measurements were performed to clarify the end of
1
reaction. The solution was directly analyzed by H NMR spectroscopy
’
REFERENCES
and GC-MS analysis to obtain quantitative data for the products. All
reactions were conducted in an inert atmosphere.
(1) (a) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of
Organic Compounds; Academic Press: New York, 1981. (b) Activation
Kinetic Studies. All kinetic experiments on the oxidation of
ethylbenzene, cumene and cyclohexene were performed using a photo-
diode array with 1 cm cell in acetonitrile and oxidation of dihydroan-
thracene was performed on a UNISOKU RSP-601 stopped-flow
spectrometer equipped with a MOS-type highly sensitive photodiode
array or a Hewlett-Packard 8453 photodiode-array spectrophotometer
at 298 K in acetonitrile. The reactions were monitored by absorbance
changes at 318 or 319 nm for the first step and 420 nm for the second
step. The rate constants in the first step were determined from the
and Functionalization of Alaknes; Hill, C. L., Ed.: Wiley: New York, 1989.
(
c) The Activation of Dioxygen and Homogeneous Catalytic Oxidation;
Barton, D. H. R., Martell, A. E., Sawyer, D. T., Eds.; Plenum: New York,
993. (d) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879–2932.
e) Meunier, B. Biomimetic Oxidations Catalyzed by Transition Metal
1
(
Complexes; Imperial College Press: London, 1998. (f) Gunay, A.;
Theopold, K. H. Chem. Rev. 2010, 110, 1060–1081.
(2) (a) Dawson, J. H.; Sono, M. Chem. Rev. 1987, 87, 1255–1276.
(b) Sono, M.; Roach, M. P.; Coulter, E. D.; Dawson, J. H. Chem. Rev.
1996, 96, 2841–2888. (c) Denisov, I. D.; Makris, T. M.; Sliger, S. G.;
Schlichting, I. Chem. Rev. 2005, 105, 2253–2277. (d) Schlichting, I.;
Berendzen, J.; Chu, K.; Stock, A. M.; Maves, S. A.; Benson, D. E.; Sweet,
R. M.; Ringe, D.; Petsko, G. A.; Sligar, S. G. Science 2000, 287, 1615–
gradient of the plot of ln(AꢀA
∞ ∞
) at 318 or 319 nm vs time, where A
was the absorbance at 318 or 319 nm at the end of the first reaction. The
rate constants in the second step were determined by using the fitting equa-
tion as follows: f(t) = a + b(1 ꢀ exp(ꢀkobst)), where f(t) was absorbance at
1622.
420 nm at certain time (t sec), kobs was the first-order rate constant in the
(3) (a) Wallar, B. J.; Lipscomb, J. D. Chem. Rev. 1996, 96, 2625–
second step; a and b were coefficients. The initial concentrations of
ꢀ4
2658. (b) Lippard, S. J. J. Chem. Soc., Dalton Trans. 1997, 3925–3932.
(c) Costas, M.; Mehn, M. P.; Jensen, M. P.; Que, L., Jr. Chem. Rev. 2004,
Ru(IV)ꢀoxo complexes were fixed to be 1.0 ꢁ 10 M, and the concen-
ꢀ
3
ꢀ2
tration of the substrates was varied from 3.0 ꢁ 10 to 1.5 ꢁ 10 M for
1
04, 939–986. (d) Abu-Omar, M. M.; Loaiza, A.; Hontzeas, N. Chem.
Rev. 2005, 105, 2227–2252.
4) Fe: (a) Hessenauer-Ilicheva, N.; Franke, A.; Meyer, D.; Woggon,
ꢀ
1
ꢀ2
dihydroanthracene, 3.0 ꢁ 10 to 1.8 M for ethylbenzene, 5.0 ꢁ 10 to
ꢀ1
ꢀ3
ꢀ2
5
.0 ꢁ 10 Mforcumene, and5.0ꢁ 10 to 4.0 ꢁ 10 M for cyclohexene.
(
All reactions were conducted under inert atmosphere.
W.-D.; van Eldik, R. J. Am. Chem. Soc. 2007, 129, 12473–12479. (b) Lee,
K. A.; Nam, W. J. Am. Chem. Soc. 1997, 119, 1916–1922. (c) Jackson,
T. A.; Rohde, J.-U.; Seo, M. S.; Sastri, C. V.; DeHont, R.; Stubna, A.;
Ohta, T.; Kitagawa, T.; M €u nck, E.; Nam, W.; Que, L. J. Am. Chem. Soc.
2008, 130, 12394–12407. (d) Chen, K.; Que, L. J. Am. Chem. Soc. 2001,
123, 6327–6337.
EPR Spectroscopy. EPR spectra were recorded on a JEOL
2
+
JEXREIXE spectrometer, and g values were determined using an Mn
marker. ESR spectra were measured at 8 K. A solution were prepared in
+
0.6 mL of CH
3 6 3
CN to contain 2 ([Ru(O)(H TPA)(bpy)](PF ) )
(1 mM), cumene (100 mM) and 2,6-lutidine(10 mM) under Ar
atmosphere. We confirmed that no Ru(III)ꢀOH were left and alkoxo
(5) Mn: (a) Fukuzumi, S.; Kishi, T.; Kotani, H.; Lee, Y.-M.; Nam, W.
Nat. Chem. 2011, 3, 38–41. (b) Groves, J. T.; Lee, J.; Marla, S. S. J. Am.
Chem. Soc. 1997, 119, 6269–6273. (c) Pitie, M.; Bernadou, J.; Meunier, B.
J. Am. Chem. Soc. 1995, 117, 2935–2936. (d) Parsell, T. H.; Yang, M.-Y.;
Borovik, A. S. J. Am. Chem. Soc. 2009, 131, 2762–2763. (e) Larsen, A. S.;
Wang, K.; Lockwood, M. A.; Rice, G. L.; Won, T.-J.; Lovell, S.; Sadilek,
complex existed by using ESI-MS before measurement.
Electrochemical Measurements. Cyclic voltammetry was em-
ployed in acetonitrile in the presence of TBAPF (0.1 M) as an
6
electrolyte under Ar at room temperature with use of a glassy carbon
electrode as a working electrode, a saturated calomel electrode (SCE) as
a reference electrode, and Pt wire as an auxiliary electrode. Cyclic
voltammetry in water were also employed with same electrodes in the
ꢀ
M.; Turecdk, F.; Mayer, J. M. J. Am. Chem. Soc. 2002, 124, 10112–10123.
(f) Wang, K.; Mayer, J. M. J. Am. Chem. Soc. 1997, 119, 1470–1471.
(g) Bryant, J. R.; Taves, J. E.; Mayer, J. M. Inorg. Chem. 2002, 41, 2769–
presence of Na
2 4
SO (0.1 M) as an electrolyte under Ar at room
2776.
temperature. pH value was adjusted by H SO . The concentration of
2
4
(6) Ru:(a) Yip, W.-P.; Yu, W.-Y.; Zhu, N.; Che, C.-M. J. Am. Chem.
0
+
2
(for acetonitrile as solvent) or 2 ([Ru(O)(H TPA)(bpy)](ClO
4 3
)
Soc. 2005, 127, 14239–14249. (b) Goldstein, A. S.; Beer, R. H.; Drago,
R. S. J. Am. Chem. Soc. 1994, 116, 2424–2429. (c) Thompson, M. S.;
Meyer, T. J. J. Am. Chem. Soc. 1982, 104, 4106–4115. (d) Okumura, T.;
Morishima, Y.; Shiozaki, H.; Yagyu, T.; Funahashi, Y.; Ozawa, T.; Jitsukawa,
K.; Masuda, H. Bull. Chem. Soc. Jpn. 2007, 80, 507–517. (e) Lam, W. W. Y.;
Man, W.-L.; Leung, C.-F.; Wong, C.-Y.; Lau, T.-C. J. Am. Chem. Soc. 2007,
for water as solvent) was 1.0 mM and a scan rate was 0.1 V/s.
’
ASSOCIATED CONTENT
S
Supporting Information. Figures S1ꢀ13 and crystal-
b
1
4
29, 13646–13652. (f) Seok, W. K.; Meyer, T. J. Inorg. Chem. 2005,
4, 3931–3941.
lographic data of 2 in the cif format. This material is available free
of charge via the Internet at http://pubs.acs.org.
(7) For porphyrin complexes: (a) Groves, J. T.; Nemo, T. E. J. Am.
Chem. Soc. 1983, 105, 6243–6248. (b) Groves, J. T.; Watanabe, Y. J. Am.
Chem. Soc. 1988, 110, 8443–8452. (c) Fujii, H. J. Am. Chem. Soc. 1993,
’
AUTHOR INFORMATION
1
15, 4641–4648. (d) Auclair, K.; Hu, Z.; Little, D. M.; Ortiz de
Montellano, P. R.; Groves, J. T. J. Am. Chem. Soc. 2002, 124, 6020–6027.
8) For nonheme model complexes: (a) Que, L., Jr.; Tolman, W. B.
Corresponding Author
kojima@chem.tsukuba.ac.jp; fukuzumi@chem.eng.osaka-u.ac.jp
(
Angew. Chem., Int. Ed. 2002, 41, 1114–1137. (b) Rohde, J.-U.; In, J.-H.;
Lim, M. H.; Brennessel, W. W.; Bukowski, M. R.; Stubna, A.; M €u nck, E.;
Nam, W.; Que, L., Jr. Science 2003, 299, 1037–1039. (c) Nam, W. Acc.
Chem. Res. 2007, 40, 522–531. (d) Que, L., Jr. Acc. Chem. Res. 2007,
40, 493–500. (e) Fiedler, A. T.; Que, L., Jr. Inorg. Chem. 2009,
’
ACKNOWLEDGMENT
This work was supported by Grants-in-Aid (Nos. 21350035,
2
1750146 and 20108010), a Global COE program, “the Global
1
1699
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700

Journal of the American Chemical Society
8, 11038–11047. (f) Hirao, H.; Chen, H.; Carvajal, M. A.; Wang, Y.;
Shaik, S. J. Am. Chem. Soc. 2008, 130, 3319–3327. (g) Takahashi, A.;
Kurahashi, T.; Fujii, H. Inorg. Chem. 2007, 46, 6227. (h) Yip, W.-P.; Yu,
W.-Y.; Zhu, N.; Che, C.-M. J. Am. Chem. Soc. 2005, 127, 14239–14249.
ARTICLE
4
(24) Fukuzumi, S.; Ohkubo, K.; Suenobu, T.; Kato, K.; Fujitsuka,
M.; Ito, O. J. Am. Chem. Soc. 2001, 123, 8459–8467.
(25) Griller, D.; Martinho Sim o~ es, J. A.; Mulder, P.; Sim, B. A.;
Wayner, D. D. M. J. Am. Chem. Soc. 1989, 111, 7872–7876.
(26) Siu, T.; Picard, C. J.; Yudin, A. K. J. Org. Chem. 2005, 70, 932–
937.
(9) (a) Moyer, B. A.; Thompson, M. S.; Meyer, T. J. J. Am. Chem. Soc.
1
980, 102, 2310–2312. (b) Moyer, B. A.; Meyer, T. J. Inorg. Chem. 1981,
20, 436–444. (c) Che, C.-M.; Yam, V. W.-W.; Mak, T. C. W. J. Am. Chem.
(27) Fujita, M.; Ishida, A.; Takamuku, S.; Fukuzumi, S. J. Am. Chem.
Soc. 1990, 112, 2284–2291. (d) Meyer, T. J.; Huynh, M. H. V. Inorg.
Chem. 2003, 42, 8140–8160. (e) Szczepura, L. F.; Maricich, S. M.; See,
R. F.; Churchill, M. R.; Takeuchi, K. J. Inorg. Chem. 1995, 34, 4198–4205.
Soc. 1996, 118, 8566–8574.
(28) (a) Wu, A.; Mayer, J. M. J. Am. Chem. Soc. 2008,
130, 14745–14754. (b) Pan, Z.; Horner, J. H.; Newcomb, M. J. Am.
Chem. Soc. 2008, 130, 7776–7777.
(
f) Dhuri, S. N.; Seo, M. S.; Lee, Y.-M.; Hirao, H.; Wang, Y.; Nam, W.;
Shaik, S. Angew. Chem., Int. Ed. 2008, 47, 3356–3359.
10) (a) Hirai, Y.; Kojima, T.; Mizutani, Y.; Shiota, Y.; Yoshizawa, K.;
(29) (a) Yoon, J.; Wilson, S. A.; Jang, Y. K.; Seo, M. S.; Nehru, K.;
Hedman, B.; Hodgson, K. O.; Bill, E.; Solomon, E. I.; Nam, W. Angew.
Chem., Int. Ed. 2009, 48, 1257–1261. (b) Che, C.-M.; Zhang, J.-L.;
Zhang, R.; Huang, J.-S.; Lai, T.-S.; Tsui, W.-M.; Zhou, X.-G.; Zhou, Z.-Y.;
Zhu, N.; Chang, C. K. Chem.ꢀEur. J. 2005, 11, 7040–7053. (c) Kaizer, J.;
Klinker, E. J.; Oh, N. Y.; Rohde, J.-U.; Song, W. J.; Stubna, A.; Kim, J.;
M €u nck, E.; Nam, W.; Que, L. J. Am. Chem. Soc. 2004, 126, 472.
(30) (a) Bryant, J. R.; Mayer, J. M. J. Am. Chem. Soc. 2003,
125, 10351–10361. (b) Lam, W. W. Y.; Yiu, S. M.; Yiu, D. T. Y.; Lau,
T. C.; Yip, W. P.; Che, C. M. Inorg. Chem. 2003, 42, 8011–8018.
(31) Stultz, L. K.; Huynh, M. H. V.; Binstead, R. A.; Curry, M.;
Meyer, T. J. J. Am. Chem. Soc. 2000, 122, 5984–5996.
(32) Lebeau, E. L.; Binstead, R. A.; Meyer, T. J. J. Am. Chem. Soc.
2001, 123, 10535–10544.
(
Fukuzumi, S. Angew. Chem., Int. Ed. 2008, 47, 5772–5776. (b) Kojima,
T.; Hirai, Y.; Ikemura, K.; Ogura, T.; Shiota, Y.; Yoshizawa, K.;
Fukuzumi, S. Angew. Chem., Int. Ed. 2010, 49, 8449–8453. (c) Lee, Y.-M.;
Dhuri, S. N.; Sawant, S. C.; Cho, J.; Kubo, M.; Ogura, T.; Fukuzumi, S.
Angew. Chem., Int. Ed. 2009, 48, 1803–1806. (d) Sawant, S. C.; Wu, X.; Cho,
J.;Cho, K.-B.;Kim, S. H.; Seo, M. S.; Lee, Y.-M.; Kubo, M.;Ogura, T.;Shaik,
S.; Nam, W. Angew. Chem., Int. Ed. 2010, 49, 8190–8194.
(11) (a) Lee, Y.-M.; Hong, S.; Morimoto, Y.; Shin, W.; Fukuzumi, S.;
Nam, W. J. Am. Chem. Soc. 2010, 132, 10668–10670. (b) Bryant, J. R.;
Mayer, J. M. J. Am. Chem. Soc. 2003, 125, 10351–10361. (c) Lam,
W. W. Y.; Yiu, S. M.; Yiu, D. T. Y.; Lau, T. C.; Yip, W. P.; Che, C. M.
Inorg. Chem. 2003, 42, 8011–8018.
(
12) (a) Groves, J. T.; McCluskey, G. A. J. Am. Chem. Soc. 1976,
8, 859–861. (b) Groves, J. T. J. Chem. Educ. 1985, 62, 928–931. (c)
Sono, M.; Roach, M. P.; Coulter, E. D.; Dawson, J. H. Chem. Rev. 1996,
9
1
(33) In this case, a peak cluster due to a complex bearing an alkoxo
ligand derived from oxygenation of anthrone as a precursor of anthra-
quinone was observed at m/z = 902.2 (Figure S8c in the Supporting
Information).
9
6, 2841–2888. (d) Strassner, T.; Houk, K. N. J. Am. Chem. Soc. 2000,
22, 7821–7822.
(34) Miyazaki, S.; Kojima, T.; Sakamoto, T.; Matsumoto, T.; Ohkubo,
(
13) Stone, K. L.; Hoffart, L. M.; Behan, R. K.; Krebs, C.; Green,
M. T. J. Am. Chem. Soc. 2006, 128, 6147.
14) (a) Schoneboom, J. C.; Cohen, S.; Lin, H.; Shaik, S.; Thiel, W.
K.; Fukuzumi, S. Inorg. Chem. 2008, 47, 333–343.
(35) Kojima, T.; Hayashi, K.; Shiota, Y.; Tachi, Y.; Naruta, Y.;
Suzuki, T.; Uezu, K.; Yshizawa, K. Bull. Chem. Soc. Jpn. 2005, 78,
2152–2158.
(
J. Am. Chem. Soc. 2004, 126, 4017–4034. (b) Sharma, P. K.; de Visser,
S. P.; Ogliaro, F. O.; Shaik, S. J. Am. Chem. Soc. 2003, 125, 2291–2300.
c) de Visser, S. P.; Ogliaro, F. o.; Sharma, P. K.; Shaik, S. J. Am. Chem.
(36) Usually BDEs of OꢀH bonds in alcohols are more than 90 kcal
ꢀ
1
(
mol : see ref 23.
Soc. 2002, 124, 11809–11826. (d) Yoshizawa, K.; Kamachi, T.; Shiota, Y.
J. Am. Chem. Soc. 2001, 123, 9806–9816. (e) Hata, M.; Hirano, Y.;
Hoshino, T.; Tsuda, M. J. Am. Chem. Soc. 2001, 123, 6410–6416.
(37) Bryant, J. R.; Matsuo, T.; Mayer, J. M. Inorg. Chem. 2004,
43, 1587–1592.
(38) (a) Kojima, T.; Leising, R. A.; Yan, S.; Que, L., Jr. J. Am. Chem.
Soc. 1993, 115, 11328–11335. (b) Mathew, L.; Warkentin, J. Can. J.
Chem. 1988, 66, 11–16. (c) Groves, J. T.; Nemo, T. E. J. Am. Chem. Soc.
1983, 105, 6243–6248.
(15) An oxygen-rebound intermediate has been detected in the
peroxynitrite formation by an Fe(IV)-oxo species of myoglobin: Su, J.;
Groves, J. T. J. Am. Chem. Soc. 2009, 131, 12979–12988.
(
16) An sulfoxide-bounded complex has been detected by Ru(IV)-
(39) Radical species have an extremely short lifetime: Newcomb, M.;
Le Tadic-Biadatti, M.-H.; Chestney, D. L.; Roberts, E. S.; Hollenberg,
P. F. J. Am. Chem. Soc. 1995, 117, 12085–12094.
oxo species: Roecker, L.; Dobson, J. C.; Vining, W. J.; Meyer, T. J. Inorg.
Chem. 1987, 26, 779–781.
(
17) An phenol-bounded complex has been detected by Ru(IV)-oxo
species: Seok, W. K.; Dobson, J. C.; Meyer, T. J. Inorg. Chem. 1988, 27, 3–5.
18) (a) Kojima, T.; Sakamoto, T.; Matsuda, Y. Inorg. Chem. 2004,
3, 2245–2247. (b) Kojima, T.; Morimoto, T.; Sakamoto, T.; Miyazaki,
S.; Fukuzumi, S. Chem.ꢀEur. J. 2008, 14, 8904–8915.
19) Crystallographic data for 2: Crystal system orthorhombic, space
(40) Fokin, A. A.; Schreiner, P. R. Chem. Rev. 2002, 102, 1551–1593.
(41) (a) Anderegg, G; Wenk, F. Helv. Chim. Acta 1967,
50, 2330–2332. (b) Gafford, B. G.; Holewerda, R. A. Inorg. Chem. 1989,
28, 60–66.
(42) Kojima, T.; Amano, T.; Ishii, Y.; Ohba, M.; Okaue, Y.; Matsuda,
Y. Inorg. Chem. 1998, 37, 4076–4085.
(
4
(
group Pbca, T = 123 K, a = 19.516(4) Å, b = 12.763(2) Å, c = 28.775(5) Å,
V = 7167(2) Å , Z = 8, no. of reflections 52108, no. of observations 8201,
parameters 528, R1 = 0.087 (I > 2σ(I)), wR = 0.201, GOF = 1.24.
(43) Creagh, D. C.; McAuley, W. J. International Tables for Crystal-
lography; Wilson, A. J. C., Ed.; Kluwer, Academic Publishers: Boston,
1992; Vol. C, Table 4.2.6.8, pp 219ꢀ222.
3
(
20) (a) Che, C.ꢀM.; Lai, T.ꢀF.; Wong, K.ꢀY. Inorg. Chem. 1987,
(44) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(45) CrystalStructyre 3.7.0: Crystal Structure Analysis Package; Rigaku
and Rigaku/MSC: The Woodlands, TX, 2000ꢀ2005
(46) Sheldrick, G. M. SIR 97 and SHELX 97, Programs for Crystal
Structure Refinement; University of Gottingen: Gottingen, Germany, 1997.
(47) We could not determine the positions of the hydrogen atoms of
the water molecule of crystallization, which should attach to O2.
2
ꢀ
6, 2289–2299 and references cited therein. (b) Cheng, W.ꢀC.; Yu, W.
Y.; Zhu, J.; Cheung, K.ꢀK.; Peng, S.ꢀM.; Poon, C.ꢀK.; Che, C.ꢀM.
Inorg. Chim. Acta 1996, 24, 105–113. (c) Che, C. M.; Tang, W. T.; Wong,
W. T.; Lai, T. F. J. Am. Chem. Soc. 1989, 111, 9048–9056. (d) Aoyagi, K.;
Yukawa, Y.; Shimizu, K.; Mukaida, M.; Takeuchi, T.; Kakihana, H. Bull.
Chem. Soc. Jpn. 1986, 59, 1493–1499.
(
21) Evans, D. F.; Jakubovic, D. A. J. Chem. Soc., Dalton Trans.
988, 2927–2933.
22) (a) Yamada, H.; Koike, T.; Hurst, J. K. J. Am. Chem. Soc. 2001,
1
(
123, 12775–12780. (b) Paeng, I. R.; Nakamoto, K. J. Am. Chem. Soc.
1
990, 112, 3289.
(23) Luo, Y.-R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: Boca Raton, FL, 2003.
1
1700
dx.doi.org/10.1021/ja2037645 |J. Am. Chem. Soc. 2011, 133, 11692–11700