Redox Reactivity of a Mononuclear Manganese-Oxo Complex Binding Calcium Ion and Other Redox-Inactive Metal Ions

Article abstract of DOI:10.1021/jacs.8b11492

Mononuclear nonheme manganese(IV)-oxo complexes binding calcium ion and other redox-inactive metal ions, [(dpaq)Mn^IV(O)]⁺-Mⁿ⁺ (1-Mⁿ⁺, Mⁿ⁺ = Ca²⁺, Mg²⁺, Zn²⁺, Lu³⁺

Full text of DOI:10.1021/jacs.8b11492

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Article
Redox Reactivity of a Mononuclear Manganese-Oxo Complex
Binding Calcium Ion and Other Redox-Inactive Metal Ions
Muniyandi Sankaralingam, Yong-Min Lee, Yuliana Pineda-Galvan, Deepika G. Karmalkar,
Mi Sook Seo, So Hyun Jeon, Yulia N. Pushkar, Shunichi Fukuzumi, and Wonwoo Nam
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 24 Dec 2018
Downloaded from http://pubs.acs.org on December 24, 2018
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†
†
‡
†
†
Muniyandi Sankaralingam, Yong-Min Lee, Yuliana Pineda-Galvan, Deepika G. Karmalkar, Mi Sook Seo, So
†
,‡
,†,§
,†
Hyun Jeon, Yulia N. Pushkar,* Shunichi Fukuzumi,* and Wonwoo Nam*
†
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
Department of Physics and Astronomy, Purdue University, 525 Northwestern Ave., West Lafayette, Indiana 47907, USA
Faculty of Science and Engineering, SENTAN, Japan Science and Technology Agency (JST), Meijo University, Nagoya, Aichi 468-
‡
§
8
502, Japan
ABSTRACT: Mononuclear nonheme manganese(IV)-oxo complexes binding calcium ion and other redox-inactive metal ions,
(dpaq)Mn (O)] -M (1-M , M = Ca , Mg , Zn , Lu , Y , Al and Sc ) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-
acetamidate), were synthesized by reacting a hydroxomanganese(III) complex, [(dpaq)Mn (OH)] , with iodosylbenzene (PhIO) in the
presence of redox-inactive metal ions (M ). The Mn(IV)-oxo complexes were characterized using various spectroscopic techniques. In
IV
+
n+
n+
n+
2+
2+
2+
3+
3+
3+
3+
[
III
+
n+
n+
n+
reactivity studies, we observed contrasting effects of M on the reactivity of 1-M in redox reactions such as electron-transfer (ET), oxygen
n+
3+
atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. In the OAT and ET reactions, the reactivity order of 1-M , such as 1-Sc
3
+
3+
3+
2+
2+
2+
n+
≈ 1-Al > 1-Y > 1-Lu > 1-Zn > 1-Mg > 1-Ca , follows the Lewis acidity of M bound to the Mn-O moiety; that is, the stronger is the
n+
n+
n+
Lewis acidity of M , the higher becomes the reactivity of 1-M . In sharp contrast, the reactivity of 1-M in HAT reaction was reversed, giving
the reactivity order of 1-Ca > 1-Mg > 1-Zn > 1-Lu > 1-Y > 1-Al ≈ 1-Sc ; that is, the higher is the Lewis acidity of M , the lower
becomes the reactivity of 1-M in HAT reaction. The latter result implies that the Lewis acidity of M bound to the Mn-O moiety can modulate
the basicity of the metal-oxo moiety, thus influencing the HAT reactivity of 1-M ; Cytochrome P450 utilizes the axial thiolate ligand to increase
2
+
2+
2+
3+
3+
3+
3+
n+
n+
n+
n+
the basicity of iron-oxo moiety that enhances the reactivity of Compound I in C-H bond activation reactions.
Mn(IV)-oxo complexes, thereby enhancing their reactivities in
OAT and ET reactions but diminishing their reactivities in hydrogen
atom transfer (HAT) reactions. Goldberg and co-workers re-
ported the influence of a redox-inactive Zn ion on a valence tau-
tomerization of a Mn(V)-oxo corrolazine complex and the change
of the reactivity of the Mn(V)-oxo complex in ET and HAT reac-
tions. The redox-inactive metal ion effect has also been demon-
strated in the catalytic oxidation of organic substrates by terminal ox-
idants, in which high-valent metal(IV)-oxo species binding Sc ion
was proposed as an active oxidant.
26
High-valent manganese-oxo complexes play pivotal roles as reactive
intermediates in enzymatic reactions; one example is the water oxi-
dation by the oxygen-evolving complex (OEC) in Photosystem II
PS II), where Ca ion is an essential component for the dioxygen
evolution in the catalytic water oxidation reaction. The role of the
Ca ion, which is a redox-inactive metal ion, has been proposed to
facilitate the O-O bond formation step occurring between a high-va-
lent Mn(V)-oxo intermediate and an aqua (or hydroxide) ligand
2+
2+
(
2
7
1-5
2+
3
+
2
8
2
+
2+
bound to the Ca ion, although the exact role of the Ca ion has yet
As alluded above, the effects of redox-inactive metal ions on the
chemical properties of Mn-oxo complexes have merited significant
interest due to the vital role of Ca ion in OEC in PS II as well as the
desire for the development of efficient catalytic oxidation systems.
However, non-heme Mn(IV)-oxo complexes binding calcium ion
6
-8
to be clearly clarified.
2+
Recently, a large number of high-valent metal-oxo complexes bear-
ing nonheme ligands have been successfully synthesized and charac-
terized spectroscopically and/or structurally in biomimetic studies.
Their reactivities have also been investigated intensively in various
oxidation reactions. In addition, factors that modulate the reactiv-
ities and reaction mechanisms of the high-valent metal-oxo com-
plexes have been the focus of current research. For example, it has
been shown that binding of redox-inactive metal ions, such as scan-
dium ion (Sc ), to nonheme metal-oxo complexes enhanced their
reactivities greatly in oxygen atom transfer (OAT) and electron-
Further, enhancement of the oxidizing
power of nonheme iron(IV)-oxo complexes in the presence of re-
dox-inactive metal ions was shown to be correlated with the Lewis
acidity of the redox-inactive metal ions. In Mn-oxo complexes,
binding of Sc ion(s) to nonheme Mn(IV)-oxo complexes resulted
in a large positive shift in the one-electron reduction potentials of the
9-
3
+
20
and other redox-inactive metal ions other than Sc have yet to be
reported. Herein, we report the synthesis and characterization of
Mn(IV)-oxo complexes binding a series of redox-inactive metal ions,
9-20
IV
+
n+
n+
n+
2+
2+
2+
3+
3+
2
1-26
[(dpaq)Mn (O)] -M (1-M , M = Ca , Mg , Zn , Lu , Y ,
3
+
3+
Al , and Sc ) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quino-
lin-8-yl-acetamidate), by reacting a hydroxomanganese(III) com-
3
+
III
+
plex, [(dpaq)Mn (OH)] , with iodosylbenzene (PhIO) in the pres-
ence of redox-inactive metal ions (M ) (Scheme 1, reaction a). In
n+
2
2-26
transfer (ET) reactions.
n+
the absence of M , a bis(µ-oxo)dimanganese(III,IV) complex,
III
IV
+
[
(dpaq)Mn (O)
2
Mn -(dpaq)] , was produced (Scheme 1, reac-
2
5
tion b). We also report the contrasting effects of redox-inactive metal
ions (M ) on the redox reactivity of 1-M in OAT, ET, and HAT
reactions (Scheme 1). Interestingly, we found that the reactivities of
n+
n+
3
+
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Scheme 1. Effects of Redox-Inactive Metal Ions on the Synthesis and
Page 2 of 13
1
2
3
4
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
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5
5
6
Reactivity of Mn(IV)–Oxo Complex
0
1
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0
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0
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9
0
Scheme 2. The Ligand (H-dpaq) and the Mn(III) Complex,
[(dpaq)Mn (OH)] , Used in This Study
III
+
OH
N
N
N
N
N
MnIII
N
N
N
N
NH
O
O
III
H-dpaq
[(dpaq)Mn (OH)]+
n+
1
-M differed markedly in the OAT, ET, and HAT reactions, de-
n+
n+
pending on the Lewis acidity of M in 1-M . For example, as the
Lewis acidity of M increases, the reactivity of 1-M becomes
n+
n+
greater in the OAT and ET reactions (Scheme 1). In sharp contrast,
n+
1
-M becomes a weaker oxidant in the HAT reaction as the Lewis
n+
acidity of M increases (Scheme 1). The latter result implies that the
Figure 1. (a) Visible-NIR absorption spectral changes showing the for-
mation of bis(μ-oxo)dimanganese(III,IV) complex
reaction of
(dpaq)Mn (OH)] (1.0 mM) and PhIO (0.50 mM) in the presence
O (20 μL) in deaerated MeCN at 263 K. Inset shows the time
course of the reaction monitored at 520 nm. (b) Visible-NIR absorp-
n+
n+
Lewis acidity of M modulates the reactivity of 1-M in abstracting
hydrogen atom (H-atom) from substrate C-H bonds by controlling
the basicity of metal-oxo moiety; it has been discussed in the com-
munities of bioinorganic/biomimetic and biological chemistry that
Cytochrome P450 enzymes utilize the axial thiolate ligand to modu-
late the basicity of iron-oxo moiety that influences the reactivity of
Compound I in C-H bond activation reactions. To the best of our
knowledge, the present study reports for the first time the synthesis
of Mn(IV)-oxo complexes binding various redox-inactive metal ions,
a
III
IV
+
(
[
[(dpaq)Mn (O)
2
Mn (dpaq)] )
in
the
III
+
of H
2
IV
+
tion spectral changes showing the formation of [(dpaq)Mn (O)] -
3+
3+
III
+
Sc (1-Sc ) in the reaction of [(dpaq)Mn (OH)] (0.50 mM) and
PhIO (1.5 mM) in the presence of Sc(OTf) (1.0 mM) in deaerated
3
MeCN at 253 K. Inset shows the time course of the reaction monitored
2
+
2+
2+
3+
3+
3+
3+
3+
such as Ca , Mg , Zn , Lu , Y , Al , and Sc , which provides us
with an excellent opportunity to investigate the redox-inactive metal
ion effect on the chemical properties of high-valent metal-oxo spe-
cies systematically.
at 700 nm. (c) CSI-MS spectrum of 1-Sc . The peaks at 945.0 and
IV
+
986.0 correspond to [(dpaq)Mn (O)] –Sc(OTf)
3
(calc. m/z =
(calc. m/z =
IV
+
944.9) and [(dpaq)Mn (O)(CH
3
CN)] –Sc(OTf)
3
9
85.9), respectively. Insets show the observed isotope distribution pat-
3
+ 16
3+ 18
terns for 1-Sc - O (left panel) and 1-Sc - O (right panel); the 1-
Sc - O and 1-Sc - O complexes were prepared by reacting
3
+ 16
3+ 18
III
+
16
18
[
(
(dpaq)Mn (OH)] (0.25 mM) with PhI O (0.75 mM) and PhI O
0.75 mM), respectively, in the presence of Sc(OTf) (0.50 mM) in
IV
n+
Synthesis and Characterization of Mn (O)-M . The starting
3
III
+
[(dpaq)Mn (OH)] complex was synthesized according to the lit-
erature methods (see Scheme 2 for the structures of the dpaq ligand
18
deaerated MeCN at 253 K. The percentage of O incorporation in 1-
Sc was determined to be 85(5)%.
3+
III
+
and the [(dpaq)Mn (OH)] complex; also see the X-ray crystal
1
III
+
structure and H NMR spectrum of [(dpaq)Mn (OH)] (Support-
29,30
29a
ing Information (SI), Figures S1 and S2);
very recently that the [(dpaq)Mn (OH)] complex is in equilib-
rium with a -oxodimanganese(III,III) complex, [(dpaq)
O)] . When the solution of [(dpaq)Mn (OH)] was reacted
with PhIO in acetonitrile (MeCN) at 263 K, we observed the for-
mation of a green-colored species with broad absorption bands at
it has been reported
identified as a dinuclear bis(μ-oxo)dimanganese complex,
III
+
III
IV
+
[(dpaq)Mn (O)
2
Mn (dpaq)] , by electron paramagnetic reso-
III
nance (EPR) spectroscopy (SI, Figure S3); the yield of
2
Mn
2
(-
III
IV
+
2
+ 30b
III
+
[
(dpaq)Mn (O) Mn (dpaq)] was determined to be ~90% by
2
comparing the doubly integrated value of the EPR signal with that of
the reference signal of 2,2-diphenyl-1-picrylhydrazyl radical
•
(
DPPH ) (SI, Figure S3).
~
520 nm within 2 min (Figure 1a). The manganese product was
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Scheme 3. DFT Optimized Structure of the Redox-Inactive Metal Ion
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3+
3+
(
Sc )-Bound Mn(IV)–Oxo Complex (1-Sc )
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Interestingly, when we reacted the solution of
III
+
[(dpaq)Mn (OH)] containing redox-inactive metal ions, such as
Sc(OTf) , with PhIO in MeCN at 253 K, we observed the formation
3
of a green-colored species with two electronic absorption bands at
3
+
510 and 700 nm (Figure 1b); this intermediate is denoted as 1-Sc
(see Scheme 3 for the DFT-optimized schematic structure). 1-Sc
3
+
Figure 2. (a) Normalized Mn K-edge XANES spectra of
was metastable (t1/2 ~1 day at 253 K), allowing us to characterize it
with cold-spray ionization time-of-flight mass spectrometry (CSI-
III
+
3+
[(dpaq)Mn (OH)] (blue line) and 1-Sc (red line). (b) Fourier
III
+
3+
transformed EXAFS for [(dpaq)Mn (OH)] (blue line) and 1-Sc
(red line) (k = 3.5 – 10.9 Å ).
3
+
–
1
MS) and EPR. The CSI-MS of 1-Sc exhibits a prominent ion peak
at a mass-to-charge (m/z) ratio of 945.0 (Figure 1c), whose mass
3
+
and
isotope
distribution
pattern
corresponds
to
This result suggests the binding of the Sc ion to the Mn-oxo moiety,
not to the carbonyl group in the dpaq ligand.
+
[(dpaq)Mn(O)Sc(OTf)
3
] (calc. m/z = 944.9). When the reaction
1
8
was performed with isotopically labeled PhI O, the mass peak at
m/z = 945.0 shifted to m/z = 947.0, indicating that this intermediate
possesses one oxygen atom. The EPR spectrum exhibits signals at geff
n+
We have also observed the formation of 1-M binding a series of
n+
2+
2+
2+
3+
3+
redox-inactive metal ions (M ), such as Ca , Mg , Zn , Lu , Y ,
3
+
III
+
and Al , in the reactions of [(dpaq)Mn (OH)] (0.50 mM) with
PhIO (1.5 mM) in the presence of Ca(OTf) (200 mM), Mg(OTf)
25 mM), Zn(OTf) (5.0 mM), Lu(OTf) (1.5 mM), Y(OTf) (1.0
mM), and Al(OTf) (1.0 mM) in MeCN at 253 K; those are denoted
as 1-Ca , 1-Mg , 1-Zn , 1-Lu , 1-Y , and 1-Al , respectively. In
the case of weak Lewis acidic redox-inactive metal ions, higher con-
centration of the redox-inactive metal ions is needed because the
=
=
5.4, 4.0 and 1.81 (SI, Figures S4 and S5), suggesting a high-spin S
3/2 Mn species.
2
2
IV
26,31
(
2
3
3
3
+
1
-Sc was further characterized using Mn K-edge X-ray absorp-
3
2
+
2+
2+
3+
3+
3+
tion spectroscopy (XAS). Figure 2a shows the comparison of X-ray
absorption near edge structure (XANES) spectra for
III
+
3+
[
(dpaq)Mn (OH)] (blue line) and 1-Sc (red line). Shift in the
3
+
III
+
edge position of 1-Sc , compared with [(dpaq)Mn (OH)] , indi-
cates that the Mn oxidation state in 1-Sc is higher than Mn . Pre-
edge structure characteristic for Mn complexes at ~6539 eV de-
creased in intensity, which is consistent with the binding of Sc ion
at Mn =O fragment.
EXAFS) data for [(dpaq)Mn (OH)] and 1-Sc are shown in Fig-
3
+
III
IV
31b
3
+
IV
26a,31b
Extended X-ray absorption fine structure
III
+
3+
(
ure 2b. Fit results for both curves are provided in SI, Tables S1 and
S2, and the comparisons of best-fit curve with Fourier transformed
3+
(
1
FT) EXAFS of 1-Sc is shown in SI, Figure S6. EXAFS analysis of
3
+
-Sc spectrum indicates the presence of a 1.68 Å Mn-O interaction,
which is close to the result obtained with Sc ion-bound
[(N4Py)Mn (O)] (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-
3
+
IV
2+
2
6a
pyridyl)methylamine) reported previously. The EXAFS data also
3
+
reveal a short Mn-Sc distance (3.99 Å), which clearly indicates that
3
+
3+
Sc ion binds to the Mn-O moiety in 1-Sc . Very recently, we have
shown the binding of Sc ion to the Mn(V)-oxo complex bearing a
tetraamido macrocyclic ligand, [Mn (O)(TAML)] ; the binding
3
+
IV
+
n+
n+
n+
2+
Figure 3. UV-vis spectra of [(dpaq)Mn (O)] –M (1-M ; M = Ca ,
V
– 32
2+
2+
3+
3+
3+
3+
n+
Mg , Zn , Lu , Y , Al and Sc ). 1-M were generated by reacting
[(dpaq)Mn (OH)] (0.50 mM) with PhIO (1.5 mM) in the presence
of metal ions (Ca , 200 mM; Mg , 25 mM; Zn , 5.0 mM; Lu , 1.5
mM; Y , 1.0 mM; Al , 1.0 mM; Sc , 1.0 mM) in deaerated MeCN at
53 K.
III
+
3
+
site of the Sc ion was proposed at the carbonyl group of the TAML
2
+
2+
2+
3+
3
+
ligand with the Mn-Sc bond length of ~6.0 Å , whereas in the pre-
3+
3+
3+
3
+
sent case, we observed a shorter bond length of Mn-Sc (3.99 Å).
2
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acidity is not enough to obtain the product or prohibit the dimer for-
Page 4 of 13
n+
n+
2+
2+
2+
3+
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
mation. The UV-vis spectra of 1-M (M = Ca , Mg , Zn , Lu ,
3
+
3+
Y , and Al ) exhibit two absorption bands, such as 500 and 580 nm
for 1-Ca , 500 and 580 nm for 1-Mg , 500 and 590 nm for 1-Zn ,
510 and 684 nm for 1-Lu , 510 and 690 nm for 1-Y , and 510 and
695 nm for 1-Al (see Figure 3). The metastable 1-M intermedi-
ates (t1/2 >4h at 253 K) were further characterized using CSI-MS and
EPR spectroscopic techniques (SI, Figures S4, S5, S7 and S8).
2
+
2+
2+
3
+
3+
3
+
n+
n+
The EPR spectra of 1-M exhibit signals at geff = 3.7 and 1.96 for
2+
2
2+
3+
3+
1
-Ca , 1-Mg , and 1-Zn and geff = 5.4, 4.0 and 1.81 for 1-Y , 1-Lu ,
3
+
n+
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
and 1-Al (SI, Figures S4, S5 and S7), indicating that all 1-M are
high-spin S = 3/2 Mn species irrespective of the kind of M .
The CSI-MS spectra of 1-Zn , 1-Lu , and 1-Y exhibited promi-
nent ion peaks at m/z = 815.1, 1075.1, and 989.0, respectively (SI,
Figure S8); the mass and isotope distribution patterns of the ion
peaks at m/z = 815.1, 1075.1, and 989.0 correspond to
(dpaq)Mn (O)Zn(OTf)
(dpaq)Mn (O)Lu(OTf)
(dpaq)Mn (O)Y(OTf) ] (calc. m/z = 988.9), respectively. We
have also confirmed the oxidation state of 1-Zn and 1-Lu using
Mn K-edge X-ray absorption spectroscopy (SI, Figure S9); in the
IV
n+ 26,31
2
+
3+
3+
IV
+
[
[
[
2
]
(calc.
(calc. m/z
m/z
=
=
815.1),
IV
+
3
]
1075.1), and
IV
+
3
2+
3+
III
+
2+
3+
XANES spectra of [(dpaq)Mn (OH)] , 1-Zn , and 1-Lu , the
shift in the edge position of 1-M , compared to
n+
III
+
[
1
(dpaq)Mn (OH)] , indicates that oxidation state of the Mn ion in
n+
III
3+
-M is higher than Mn , as shown in the case of 1-Sc (Figure 2;
3+
vide supra). EXAFS analysis of 1-Lu spectrum indicates the Mn-O
and Mn-Lu distances are 1.73 and 4.25 Å, respectively (SI, Table
3+
S3 and Figure S10). Based on the spectroscopic characterization
n+
IV
+
discussed above, 1-M is assigned as [(dpaq)Mn (O)] binding a
n+
IV
+
n+
n+
redox-inactive metal ion (M ), [(dpaq)Mn (O)] –M (1-M ;
n+
2+
2+
2+
3+
3+
3+
3+
M = Ca , Mg , Zn , Lu , Y , Al , and Sc ).
•+
IV
+
n+
Figure 4. (a) Absorption spectra of TBPA produced in electron trans-
Reactivity Studies of [(dpaq)Mn (O)] –M . In this section, we
3+
fer from TBPA (0 – 0.12 mM) to 1-Sc (0.050 mM) in MeCN at 253 K.
(b) Plot of concentration of TBPA produced in ET from TBPA to 1-
Sc (0.050 mM) vs initial concentration of TBPA, [TBPA] . (c) Plot of
– 1 (where α = [TBPA ]/[TBPA] )
to determine the equilibrium constant (Ket) of electron transfer from
TBPA to 1-Sc upon addition of TBPA to an MeCN solution of 1-Sc
at 253 K (see eq 9 in Experimental Section).
report the redox-inactive metal ion effects on the reactivities of the
•
+
IV
+
n+
n+
[
(dpaq)Mn (O)] –M (1-M ) complexes in ET, OAT, and HAT
3
+
0
reactions. It should be noted that the bis(-oxo)dimanganese(III,IV)
–
1
–1
3+
•+
(α – 1) vs [1-Sc ]
0
/α[(TBPA]
0
0
III
IV
+
complex, [(dpaq)Mn (O)
2
+
Mn (dpaq)] , produced by the oxida-
III
n+
tion of [(dpaq)Mn (OH)] by PhIO in the absence of M exhib-
ited no reactivity towards thioanisole, cyclohexadiene and
3+
3+
II
2+
[
Fe (Me
2
bpy)
3
] (SI, Figure S11).
n+
(
i) Redox Properties of 1-M . The one-electron reduction potential
Table 1. Second-Order Rate Constants (ket and kox) for Oxidation
n+
3+
II
2+
n+
of 1-M , such as 1-Sc , was determined by performing the ET titra-
tion with tris(4-bromophenyl)amine (TBPA, Eox = 1.08 V vs
SCE). When 1-Sc was employed as an electron acceptor, effi-
cient ET occurred from TBPA to 1-Sc (Figure 4a), where the ab-
sorption band at 705 nm is assigned due to TBPA (ε = 32,000 M
of [Fe (Me
2
bpy)
3
] , Thioanisole, and CHD by 1-M in Deaerated
MeCN at 253 K
33,34
3+
3
+
–1 –1
k
et or kox, M s
•+
–1
metal ion
II
]2+
[
Fe (Me
2
bpy)
3
thioanisole
CHD
–
1
35
3+
cm at max = 705 nm). The ET from TBPA to 1-Sc was found to
•+
be in equilibrium, where the concentration of TBPA produced in-
creased with increasing the initial concentration of TBPA, as shown
in Figure 4b. The equilibrium constant (Ket) was determined to be
Ca2+
2
–2
–1
–1
–2
–2
–2
–2
–2
1.9(2) × 10
5.8(5) × 10
1.5(1) × 10
4.7(4) × 10
7.4(5) × 10
9.0(7) × 10
3.4(3)
1.3(1) × 10
1.0(1) × 10
7.1(6) × 10
2.3(2) × 10
2.1(2) × 10
1.8(1) × 10
1.6(1) × 10
Mg2+
Zn2+
3.2(3) × 10
2
–1
–1
–1
–1
•+
7
0 at 253 K by fitting the plot of [TBPA ] vs [TBPA]
0
with the use
2
3
3
3
3
4.8(4) × 10
4.8(3) × 10
6.0(5) × 10
7.8(5) × 10
8.4(7) × 10
of the ET equilibrium equations (eqs 7 – 9) in Experimental Section
3+
(
Figure 4c). The one-electron reduction potential (Ered) of 1-Sc
was determined to be 1.17 V vs SCE from the Ket value of 70 and the
ox value of TBPA (1.08 V vs SCE) using the Nernst equation (eq
Lu3+
E
1
Y3+
36
).
Al3+
Sc3+
Ered = Eox + (RT/F)lnKet
(1)
2.2(2)
The rate of ET from a coordinatively saturated metal complex, such
II
2+
as [Fe (Me
2
bpy)
3
] (Me bpy = 4,4’-dimethyl-2,2’-bipyridine), to 1-
2
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Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 6. Driving force (–ΔGet) dependence of logarithm of rate con-
II
2+
stants (log ket) of ET from one-electron donors [(1) [Fe (Me
2
bpy) ] ,
3
3
2+
II
2+
II
2+
II
(
2) [Fe (bpy)
3
] , (3) [Fe (phen)
3
] , and (4) [Ru (Me
-Sc , and logarithm of rate constants (log kox) determined in the oxi-
2
bpy) ] ] to
3
+
1
dation of substrates [(5) p-methylthioanisole, (6) thioanisole, (7) p-
chlorothioanisole and (8) p-bromothioanisole, (9) xanthene, (10)
3
+
DHA, and (11) CHD] by 1-Sc in MeCN at 253 K. The black and blue
lines are drawn according to eq 2 with the  values of 1.79 and 1.85 eV,
respectively.
Figure 5. (a) Visible-NIR absorption spectral change observed in the re-
action of 1-Sc3+ (0.25 mM) with thioanisole (15 mM) in deaerated
MeCN at 253 K. Inset shows time profile of absorbance at 700 nm. (b)
Plot of pseudo-first-order rate constant (kobs) vs the concentration of
thioanisole for the reaction of 1-Sc3+ with thioanisole in MeCN at 253
K.
ure S15a indicates that electron transfer is involved in the rate-deter-
24a,24d,26a
mining step (vide infra).
of rate constant as a function of σ shows a good Hammett correla-
In addition, a plot of the logarithm
p
+
tion with a largely negative ρ value of –4.5 (SI, Figure S15b).
The product(s) formed in this reaction was analyzed using ESI-
MS and EPR. Analysis of the Mn product by ESI-MS showed that a
III
Mn species was formed as a major product with an impurity scale
3
+
Sc obeyed the first-order kinetics and the pseudo-first-order rate
constant (k was proportional to the concentration of
II
3+
of Mn in the sulfoxidation reaction by 1-Sc (SI, Figure S16a). In
1
)
II
the EPR analysis, an impurity scale (< 1%) of Mn was observed (SI,
Figure S16b), confirming that a Mn species was formed as the ma-
jor product. It has been reported that (dpaq)Mn is not stable under
II
2+
[Fe (Me
2
bpy)
3
] , affording the second-order rate constant (ket) of
III
3
–1
–1
8.4 × 10
M
s
in MeCN at 253 K for the ET from
II
II
2+
3+
[Fe (Me
2
bpy) ] to 1-Sc (SI, Figure S12a). Similarly, ket values of
3
certain circumstances and reacts with
O
2
to form the
ET from various one-electron donors (i.e., coordinatively saturated
III
+
30a
[(dpaq)Mn (OH)] complex. The organic product analysis of
II
2+
metal complexes, such as [Fe (bpy)
3
]
(bpy = 2,2’-bipyridine),
1,10-phenonthroline), and
] ) to 1-Sc (vide infra) were determined and listed
the reaction solution revealed that methyl phenyl sulfoxide was
formed quantitatively. It was confirmed that oxygen in methyl phe-
II
2+
[
Fe (phen)
3
]
(phen
=
II
2+
3+
[
Ru (Me
2
bpy)
3
3+
nyl sulfoxide derived from the oxo group of 1-Sc , not from water,
in SI, Table S4 (also see SI, Figure S12). The ket values of ET from
18
3+
by using O-labeled 1-Sc as shown in SI, Figure S17, as the case of
II
2+
n+
[
Fe (Me
2
bpy) ] to other 1-M were also determined and listed in
3
3
+
anthracene oxidation by 1-Sc to produce anthraquinone in which
two oxygen atoms originated from the oxo group of 1-Sc .
Table 1 (also see SI, Figure S13).
3
37
n+
(ii) Sulfoxidation Reaction by 1-M . Oxygen atom transfer (OAT)
n+
The oxidation of thioanisole by other 1-M was also performed in
MeCN at 253 K (SI, Figure S18), and the second-order rate con-
stants (kox) determined were listed in Table 1. The kox value in-
creased with increasing the Lewis acidity of redox-inactive metal
n+
3+
reactions by 1-M , such as 1-Sc , were performed using thioanisole
derivatives as substrates in MeCN at 253 K. Upon addition of thi-
3
+
oanisole to an MeCN solution of 1-Sc , the absorption band at 700
3
+
nm corresponding to 1-Sc disappeared with the first-order decay
kinetics profile (Figure 5a). Pseudo-first-order rate constants, deter-
mined by the first-order fitting of the kinetic data for the decay of 1-
IV
23,38
ions bound to the Mn (O) moiety. Thus, the reactivity order of
n+
1
-M in the oxidation of thioanisole (i.e., OAT reaction) was deter-
mined to be 1-Al > 1-Sc > 1-Y > 1-Lu > 1-Zn > 1-Mg > 1-
3+
3+
3+
3+
2+
2+
3
+
Sc , increased linearly with an increase in thioanisole concentration,
2+
Ca .
–
1
–1
giving the second-order rate constant (kox) of 2.2 M s at 253 K
Figure 5b). Similarly, the oxidation of other para-substituted thi-
oanisoles (para-X-thioanisoles; X = OMe, Me, H, Cl, and Br) by 1-
(
The dependence of logarithm of the second-order rate constants
3
+
of ET(ket) from electron donors to 1-Sc (vide supra) on the ET
3
+
Sc was also performed, and the second-order rate constants (kox),
determined by the plots of pseudo-first-order rate constants vs con-
centrations of thioanisole derivatives (SI, Figure S14), were listed in
SI, Table S5. The logarithm of kox values is linearly correlated with
the one-electron oxidation potentials of para-X-thioanisoles (SI, Fig-
ure S15a), where the kox value increases as the electron-donating abil-
driving force [–G (eV) =e(E – E )] is shown in Figure 6, where
et
red
ox
the logarithm of the second-order rate constants (k ) of sulfoxida-
ox
3
+
22a
tion of thioanisole derivatives by 1-Sc is also plotted. The driving
force dependence of the ET rate constants is well fitted by the Mar-
cus theory of outer-sphere electron transfer (eq 2),
2
21,22
k
et = Zexp[–(λ/4)(1 + ΔGet/λ) /k
B
T
(2)
ity of the para-substituent increases. The slope of –15 in SI, Fig-
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 13
3+
in MeCN at 253 K. Addition of DHA to an MeCN solution of 1-Sc
resulted in the disappearance of the absorption band at 700 nm due
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
+
to 1-Sc (SI, Figure S19a). Pseudo-first-order rate constants, deter-
mined by the first-order fitting of the kinetic data for the decay of 1-
3
+
Sc , increased linearly with an increase in DHA concentration, giv-
–1
–1 –1
ing the second-order rate constant (kox) of 2.5 × 10 M s at 253
K (Figure 7a). The C-H bond activation reactions were also investi-
gated with other weak C-H bonds, such as xanthene and CHD. The
–
1
–2
–1 –1
second-order rate constants (kox) of 4.9 × 10 and 1.6 × 10 M s
3
+
were determined in the oxidation of xanthene and CHD by 1-Sc ,
respectively (Figure 7a). As expected, the second-order rate con-
stants decreased with an increase in the C-H BDEs of alkyl hydro-
carbons, showing a correlation between the log kox’ values and the C-
H BDEs of the substrates with a slope of –0.54 (SI, Figure S19b).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
+
The oxidation of DHA-h
4
and DHA-d by 1-Sc was also investi-
4
gated, affording the kinetic isotope effect (KIE) value of 2.3(1) (Fig-
ure 7a). These results indicate that the C-H bond activation of alkyl
3+
hydrocarbons by 1-Sc occurs via an H-atom abstraction mecha-
3+
nism and the H-atom abstraction by 1-Sc is the rate-determining
step.
The product(s) formed in the oxidation reactions was analyzed us-
ing ESI-MS and EPR spectroscopic techniques. Analysis of the Mn
III
product by ESI-MS shows that an Mn species was formed as a ma-
Figure 7. (a) Plots of pseudo-first-order rate constant (kobs) against sub-
strate concentration to determine the second-order rate constants in
II
jor product with an impurity scale of Mn in the C-H bond activation
3
+
3
+
reaction by 1-Sc (SI, Figure S20a), as observed in the oxidation of
the reactions of 1-Sc with xanthene (black circle), DHA-h
cle), DHA-d (red circle), and CHD (blue circle) in MeCN at 253 K.
b) Plots of pseudo-first-order rate constant (kobs) against CHD con-
4
(green cir-
3
+
4
thioanisole derivatives by 1-Sc (vide supra). In the EPR analysis, a
II
(
trace amount of Mn active signal was observed (SI, Figure S20b),
-1
-1
III
centration to determine the second-order rate constants (M s ) in the
reactions of 1-M with CHD in MeCN at 253 K (see Table 1).
confirming that a Mn species was the major product. The product
n+
analysis of the reaction solution of xanthene revealed that xanthone
was formed as the sole product. In addition, by carrying out the oxi-
1
8
3+
1
1
–1 –1
dation of xanthene with the O-labeled 1-Sc , the oxygen atom in
where Z is the collision frequency taken as 1 × 10 M s , λ is the
reorganization energy of ET, k is the Boltzmann constant, and T is
the absolute temperature. The best fit λ value of ET from metal
1
8
3+
the xanthone was found to derive from the O-labeled 1-Sc (SI,
Figure S21).
B
3
9
3
+
The CHD was chosen as the C-H bond substrate to compare the
complexes to 1-Sc is 1.85 eV (blue line in Figure 6), which is similar
n+
oxidizing ability of 1-M complexes in MeCN at 253 K. The second-
to the best fit λ value (1.79 eV) of sulfoxidation of thioanisole deriv-
n+
3
+
order rate constants of 1-M were determined and listed in Table 1
atives by 1-Sc (black line in Figure 6). Such an agreement strongly
3
+
(see also Figure 7b). Interestingly, the k values decreased with in-
ox
indicates that sulfoxidation of thioanisole derivatives by 1-Sc pro-
ceeds via the rate-determining ET (vide supra). It should be noted
that the λ values (1.79 and 1.85 eV) are significantly smaller than
creasing the Lewis acidity of redox-inactive metal ions bound to the
n+
Mn-oxo moiety. Thus, the reactivity order of 1-M in the oxidation
IV
2+
3+
of CHD (i.e., HAT reaction) is opposite to that obtained in the ET
those of ET reactions of [(Bn-TPEN)Mn (O)] -(Sc )
TPEN N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-dia-
minoethane; λ = 2.12 eV) and [(N4Py)Mn (O)] -(Sc )
2
(Bn-
n+
2+
and OAT reactions by 1-M ; that is, the reactivity order is 1-Ca >
=
2
+
2+
3+
3+
3+
3+
IV
2+
3+
1-Mg > 1-Zn > 1-Lu > 1-Y > 1-Al ≥ 1-Sc in the HAT reac-
tion (vide infra). The reason why the reactivity order of 1-M in
2
(λ = 2.21
n+
26b
eV), probably because of the more rigid structure of the dpaq lig-
and that contains a quinoline moiety. On the other hand, the reor-
ganization energy of electron exchange between thioanisole and thi-
oanisole radical cation was determined to be 0.80 eV from the rate
HAT is opposite that in ET and OAT is discussed as follows.
There are two extreme mechanisms for hydrogen atom transfer
(HAT) reactions. The first one is electron transfer, followed by pro-
ton transfer, referred to ET-PT. In this case, the HAT reactivity is in
parallel with the ET reactivity. The other one is proton transfer fol-
lowed by electron transfer (PT-ET), when the HAT reactivity is in
parallel with the PT reactivity, which is opposite to the ET reactivity,
because the stronger base for the PT reaction acts as the weaker elec-
tron acceptor for the ET reaction. A change of the mechanism be-
tween ET-PT and PT-ET was reported as a V-shaped Hammett plot
for the HAT from para-substituted 2,6-di-tert-butylphenols to an
7
–1 –1 40
constant of the electron exchange (1 × 10 M s ) using eq 2 when
Get =0. The observed reorganization energy of electron transfer
3
+
from thioanisole to 1-Sc ( = 1.79 eV in Figure 6) is much larger
than that of electron exchange between thioanisole and thioanisole
radical cation (0.80 V). It should be noted that the observed reor-
ganization energy (1.79 eV) is the average of the reorganization en-
ergy of electron exchange between thioanisole and thioanisole radi-
cal cation (0.80 eV) and that of electron exchange between
V
IV
+
3+
III
+
3+
imido manganese(V) corrole (tpfc)Mn (NTs) where tpfc =
[
(dpaq)Mn (O)] -Sc and [(dpaq)Mn (O)] -Sc (2.78 eV).
43
5
,10,15-tetrakis(pentafluoro-phenyl)corrole. As the more with-
n+
(
iii) C-H Bond Activation by 1-M . The hydrogen atom (H-atom)
drawing substituents are employed, the acidity of the phenolic pro-
ton increases to enhance the initial rate-determining proton transfer
n+
3+
abstraction reactions of 1-M , such as 1-Sc , with hydrocarbons
having weak C-H bond dissociation energies (BDEs), such as xan-
thene (75.5 kcal mol ), dihydroanthracene (DHA; 77.0 kcal mol ),
–
1
–1
–1
41
and 1,4-cyclohexadiene (CHD; 78.0 kcal mol ), were performed
ACS Paragon Plus Environment

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Journal of the American Chemical Society
Scheme 4. Influence of Axial Ligand and Lewis Acid Metal Ion on the
Basicity of the Oxo Ligand
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
one-electron reduced species of electron acceptors generally results
in the large positive shift in the one-electron reduction potentials of
electron acceptors.
8c,21,22,45,46
Figure 8. Plots of logarithm of the second-order rate constants in the
oxidation (kox) of thioanisole (red line) and CHD (green line) by 1-
In the case of HAT reaction, however, the log kox values decrease
as the Lewis acidity of the redox-inactive metal ions increases (green
line in Figure 8). It has been reported previously that the basicity of
the metal-oxo group determines the capability of high-valent metal-
oxo intermediates in abstracting H-atom from substrate C-H bonds.
One notable example is the role of the thiolate ligand in Cytochrome
n+
II
2+
M and in the electron transfer (ket) from [Fe (Me
2
bpy)
3
] (blue
n+
line) to 1-M vs a quantitative measure of Lewis acidity of metal ions
42
(
ΔE). The ΔE value of the Al(OTf)
3
was determined using fluores-
complex
cence maximum of 10-methylacridone (AcrCO)-Al(OTf)
SI, Figure S22).
3
42f
(
4
7
P450 enzymes. It has also been demonstrated in synthetic metal-
oxo complexes that the HAT reactivity of high-valent metal-oxo
complexes increases as the axial ligand becomes a better electron do-
V
from the phenolic proton to (tpfc)Mn NTs, followed by fast elec-
4
3
tron transfer. When electron-donating substituents are employed,
the rate-determining step is changed from PT-ET to ET-PT, exhib-
48
nor (Scheme 4A). In the present study, we have shown for the first
4
3
iting a V-shaped Hammett plot. In most cases, however, ET and
PT may occur in a concerted manner. In such a case, the HAT reac-
tivity may be determined by the compensation between the ET and
time that the basicity of the metal-oxo group can be tuned by binding
redox-inactive metal ions (Scheme 4B). For example, the Mn(IV)-
n+
2+
oxo group of 1-M binding Ca (ΔE = 0.58 eV) is more basic than
44
3+
PT reactivity depending on the ET and PT driving force. In the case
that binding Sc (ΔE = 1.00 eV), resulted in showing a higher reac-
tivity in the HAT reaction by 1-Ca (green circles in Figure 8). In
addition, based on the reactivity of 1-M in the HAT reaction, we
can predict that the basicity of the metal-oxo moiety for 1-Ca is the
n+
2+
of 1-M , the HAT reactivity seems to be determined by the PT re-
n+
activity rather than the ET reactivity, because the stronger is the
n+
IV
2+
Lewis acidity of M binding to the Mn (O) moiety, the weaker is
the basicity of the oxo group in the PT reaction. The decreased reac-
2
+
2+
2+
highest and decreases in the order of 1-Ca > 1-Mg > 1-Zn > 1-
IV
3+
3+
3+
3+
tivity of a trivalent metal ion-bound Mn (O) complex such as 1-
Lu > 1-Y > 1-Al > 1-Sc . Further investigation is underway to
fully understand the redox-inactive metal ion effect on the basicity of
metal-oxo moiety and the reactivity of metal-oxo species in HAT re-
actions.
IV
Sc(OTf)
3
as compared with a divalent metal ion-bound Mn (O)
complex such as 1-Ca(OTf)
2
may also result from the steric effects
of Sc(OTf)
3
that binds with the oxo moiety stronger than Ca(OTf) .
2
IV
Materials. Commercially available chemicals were used without
further purification unless otherwise indicated. 8-Aminoquinoline,
bromoacetyl bromide, dipicolylamine, sodium carbonate, trifluro-
Redox-inactive metal ion-bound Mn (O) complexes,
IV
+
n+
n+
n+
2+
2+
2+
3+
3+
[
(dpaq)Mn (O)] –M (1-M ; M = Ca , Mg , Zn , Lu , Y ,
3
+
3+
Al and Sc ), were synthesized in the oxidation of a mononuclear
III
+
methanesulfonic acid, manganese powder, (diacetoxyiodo)benzene,
hydroxomanganese(III) complex, [(dpaq)Mn (OH)] , by PhIO in
the presence of various metal triflates, M (OTf)
–
n+
sodium hydroxide, calcium triflate (Ca(OTf)
magnesium triflate (Mg(OTf)
2
) (OTf = SO
3
CF
3
),
n
, whereas a bis-µ-
III
IV
+
), magnesium perchlorate
), zinc triflate (Zn(OTf) ), scandium triflate
), aluminium triflate (Al(OTf) ), yttrium triflate
) and acetonitrile were pur-
oxo dimer, [(dpaq)Mn (O)
2
Mn (dpaq)] , was formed in the ab-
2
n+
(
(
(
Mg(ClO
Sc(OTf)
4
)
3
2
2
sence of M (OTf)
n
. Although the bis(µ-oxo)dimanganese(III,IV)
n+
complex exhibited no reactivity in OAT and HAT reactions, 1-M
oxidized thioanisoles and CHD efficiently via ET and HAT reac-
tions, respectively. Interestingly, when the log kox values obtained in
the OAT (e.g., thioanisole) and HAT (e.g., CHD) reactions as well
as the log ket values of ET (e.g., [Fe (Me
against a quantitative measure of Lewis acidity of metal ions (ΔE),
3
Y(OTf)
3
), lutetium triflate (Lu(OTf)
3
chased from Aldrich chemical Co. 2,2-Diphenyl-1-picrylhydrazyl
•
radical (DPPH ) was purchased from Wako Pure Chemicals (Osaka,
1
8
18
II
2+
Japan). H
2
O (95% O-enriched) was purchased from ICON Ser-
2
bpy) ] ) were plotted
3
49
4
2
vices Inc. (Summit, NJ, USA). Iodosylbenzene (PhIO) and
II
50
Mn (OTf)
2
·2CH CN were prepared by the literature method.
3
the reactivity trends differed markedly (Figure 8). For example, the
log kox values of the oxidation of thioanisole (red line in Figure 8),
which proceeds via ET, and the log ket values of ET of
The dpaq ligand (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-
quinolin-8-yl-acetamidate) was synthesized according to the previ-
29
18
II
2+
ously reported methods. PhI O was prepared by the addition of
[
Fe (Me
2
bpy) ] (blue line in Figure 8) increase with an increase in
3
1
8
16
H O (140 mM, 5 μL) to the PhI O (50 μL) in trifluoroethanol at
2
the Lewis acidity (ΔE), since the stronger is the Lewis acidity of the
1
8
298 K and wait for 20 min for the exchange. Then use the PhI O to
synthesis the O-labeled 1-Sc . The [(dpaq)Mn (OH)](OTf)
complex was synthesized by mixing the stoichiometric amounts of
redox-inactive metal ions bound to the Mn-oxo moiety, the faster be-
1
8
3+
III
n+
comes ET to 1-M due to the more positive shift in the one-electron
n+ 21,22
reduction potentials of 1-M . The binding of metal ions to the
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 13
the dpaq ligand and Mn(OTf)
tion, followed by the addition of triethylamine. The deuterated
2
in an oxygen-saturated MeCN solu-
5300PC fluorescence spectrophotometer with the excitation and
emission slit widths are 2 nm.
2
9
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
5
1
DHA-d
mmol) was reacted with NaH (0.20 g, 8.1 mmol) in DMSO-d
mL) under an Ar atmosphere. The deep red solution was stirred at
room temperature for 8 h and then quenched with D O (5.0 mL).
The crude product was filtered and washed with copious amounts of
4
was synthesized by a literature method: DHA (0.50 g, 2.7
IV
+
n+
IV
Generation of [(dpaq)Mn (O)] -M (OTf) . [(dpaq)Mn -
n
6
(3.0
+
n+
n+
n+
2+
2+
2+
3+
3+
3+
(
O)] -M (OTf)
n
(1-M ; M = Ca , Mg , Zn , Lu , Y , Al , and
Sc ) complexes were generated by adding iodosylbenzene (PhIO;
equiv dissolved in methanol/trifluoroethanol) into the solution of
(dpaq)Mn (OH)] (0.50 mM) in the presence of Ca(OTf)
mM), Mg(OTf) (25 mM), Zn(OTf) (5.0 mM), Lu(OTf)
mM), Y(OTf) (1.0 mM), Al(OTf) (1.0 mM), and Sc(OTf)
mM) in MeCN at 253 K, respectively. 1-M species were also gen-
erated in the solvent mixture (i.e., MeCN/trifluoroethanol (v/v
1:1)). The characteristic peaks of 1-M species were red-shifted as
3
+
2
3
[
III
+
2
(200
(1.5
(1.0
1
distilled H
NMR.
2
O. Purity of >99% deuteration was confirmed by H
2
2
3
3
3
3
n+
Instrumentation. UV-vis spectra were recorded on a Hewlett
Packard 8453 diode array spectrophotometer equipped with a
UNISOKU Scientific Instruments Cryostat USP-203A for low-tem-
perature experiments or on a Hi-Tech Scientific (U.K.) SF-61 DX2
cryogenic stopped-flow spectrophotometer equipped with a Xe arc
lamp and a KinetaScan diode array rapid scanning unit. The cold-
spray ionization time-of-flight mass (CSI-MS) spectral data were
collected on a JMS-T100CS (JEOL) mass spectrometer equipped
with the CSI source. Typical measurement conditions are as follows:
Needle voltage, 2.2 kV; orifice 1 current, 50 – 500 nA; orifice 1 volt-
age, 0 to 20 V; ring lens voltage, 10 V; ion source temperature, 5°C;
spray temperature, –40 °C. Electrospray ionization mass (ESI-MS)
spectra were collected using Thermo Finnigan (San Jose, CA, USA)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
n+
compared with those in MeCN (data are not shown).
XAS and EXAFS Measurements. X-ray absorption spectra were
collected at the Advanced Photon Source (APS) at Argonne Na-
tional Laboratory on bending magnet beamline 20 at electron en-
ergy 6 keV and average current of 100 mA. The radiation was mon-
ochromatized by a Si(110) crystal monochromator. The intensity of
the X-rays was monitored by three ion chambers (I
with 20% nitrogen and 80% helium and placed before the sample (I
and after the sample (I and I ). KMnO powder was placed between
and I and its absorption was recorded with each scan for energy
0
, I
1
, and I
2
) filled
0
)
1
2
4
I
1
2
TM
LCQ Advantage MAX quadrupole ion trap instrument, by infus-
calibration. Plastic (Lexan) EXAFS sample holders (inner dimen-
sions of 12 mm × 2 mm × 3 mm) filled with frozen solutions were
inserted into a cryostat pre-cooled to 20 K. The samples were kept
at 20 K in a He atmosphere at ambient pressure. Data were recorded
as fluorescence excitation spectra using a 13-element energy-resolv-
ing detector. In order to reduce the risk of sample damage by X-ray
defocused mode (beam size 1 × 2 mm) was used and no damage was
observed. Shutter was synchronized with the scan software prevent-
ing exposure to X-rays in between scans and during spectrometer
movements. Mn XAS energy was calibrated by the maximum of the
pre-edge feature of the potassium permanganate powder XANES
–1
ing samples directly into the source at 20 µL min using a syringe
pump. The spray voltage was set at 4.7 kV while the capillary tem-
perature was maintained at 80 C. X-band EPR spectra were rec-
o
orded at 5 K using X-band Bruker EMX-plus spectrometer equipped
with a dual mode cavity (ER 4116DM). Low temperature was
achieved and controlled with an Oxford Instruments ESR900 liquid
He quartz cryostat with an Oxford Instruments ITC503 tempera-
ture and gas flow controller. The experimental parameters for EPR
measurements were as follows: microwave frequency = 9.647 GHz,
microwave power = 1.0 mW, modulation amplitude = 10 G, gain =
3
1 × 10 , modulation frequency = 100 kHz, time constant = 40.96 ms,
spectrum (6543.3 eV), which was placed between I
1
and I ionization
2
and conversion time = 81.00 ms. EPR spectra were also recorded at
77 K with use of JEOL X-band spectrometer (JES-FA100). The spin
amount of the bis-µ-oxo dimer produced in the reaction of
chambers. EXAFS scans with 5 eV steps in the pre-edge region
(6437.67 – 6529.67 eV), 0.5 eV steps (6529.67 – 6637.67 eV)
–
1
–1
through the edge and 0.05 Å steps from k = 2.0 – 12 Å were used.
III
+
[
(dpaq)Mn (OH)] with PhIO in MeCN at 263 K was determined
EXAFS Data Analysis. Athena software was used for data pro-
5
2
by the double integration of the EPR signal at 77 K, which was com-
pared with that obtained from DPPH used as a reference. The g
cessing. Energy scale for each scan was normalized using potassium
permanganate powder standard and scans for same samples were
added. Data in energy space were pre-edge corrected, normalized,
and background corrected. The processed data were converted to
•
2
+
value was calibrated using the Mn marker. The EPR spectra were
recorded under non-saturating microwave power conditions. The
magnitude of modulation was chosen to optimize the resolution and
the signal-to-noise (S/N) ratio of the observed spectra. The experi-
mental parameters for EPR measurements by JES-FA100 were as
follows: microwave frequency = 9.028 GHz, microwave power = 1.0
mW, modulation amplitude = 3.0 G, modulation frequency = 100
kHz and time constant = 0.03 s. The product analyses were per-
formed with an Agilent 6890N gas chromatograph (GC) and a
FOCUS DSQ (dual-stage quadrupole) mass spectrometer (Thermo
Finnigan, Austin, TX, USA) interfaced with a Finnigan FOCUS gas
chromatograph (GC-MS). Product analysis of thioanisole oxidation
was performed on High Performance Liquid Chromatography
(HPLC, DIOMEX Pump Series P580) equipped with a variable
wavelength UV-200 detector and Diacel OD-H column (4.6 mm ×
25 cm). The fluorescence spectra were recorded using a four faced
quartz cuvette (10 mm i.d.), which containing 10-methylacridone
3
the photoelectron wave vector (k) space and weighted by k . The
electron wave number is defined as in eq 3,
2
1/2
k = [{2m(E – E
0
)}/η ]
(3)
where E is the threshold energy. k-space data were truncated near
0
zero crossings and Fourier-transformed into R-space. Artemis soft-
ware was used for curve fitting. In order to fit the data, the Fourier
peaks were isolated separately, or entire experimental spectrum was
fitted. The individual Fourier peaks were isolated by applying a Han-
ning window. Curve fitting was performed using ab initio-calculated
phases and amplitudes from the FEFF8 program from the University
of Washington. Ab initio-calculated phases and amplitudes were
5
3
used in the EXAFS equation (eq 4):
(4)
(AcrCO) with Al(OTf)
3
in deaerated MeCN at 298 K, was irradi-
ated with monochromatic light of 430 nm from a Shimadzu RF-
ACS Paragon Plus Environment

Page 9 of 13
where N
Journal of the American Chemical Society
is the distance between the concentrations of substrates, from which second-order rate con-
th
j
is the number of atoms in j shell; R
j
th
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
the absorbing atoms and the atoms in j shell; feff j is the ab initio am-
stants were determined.
2
2
2 j k
Product Analysis. Products formed in the oxidation of thioanisole
by 1-Sc in MeCN at 253 K were analyzed by HPLC and GC-MS.
Phenyl methyl sulfoxide was formed as a sole product in the oxida-
plitude function for j, and e
counting for damping due to thermal and static disorder in the shell.
is Debye-Waller factor for shell j ac-
3
+
–2Rj/λj(k)
The mean free path term (e
tic scattering. The oscillations in the EXAFS spectrum are reflected
in the sin(2kR +φij(k)) term, where φij(k) is the ab initio phase func-
tion for the shell j. S is an amplitude reduction factor. The EXAFS
equation was used to fit experimental data using N, E
variable parameters, while S was kept fixed. The quality of fit was
) accounts for losses due to inelas-
3
+
tion of thioanisole by 1-Sc . Products formed in the oxidation of
3
+
xanthene by 1-Sc were analyzed by GC, and GC-MS. Quantitative
analysis was performed by comparison against standard curves pre-
pared with known authentic samples and using decane as an internal
standard. In the reaction of 1-Sc and xanthene, xanthone was ob-
tained as sole product. The manganese products formed in the reac-
tion of 1-Sc with thioanisole and xanthene were analyzed by ESI-
MS and EPR techniques. In both the reactions, Mn species were
produced as a major product.
j
0
2
0
, R and σ as
3
+
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
evaluated by R-factor: if R-factor is less than 2% then the fit is good
3
+
2
enough. Reduced χ was used to justify the addition of new absorber-
III
backscatter shells.
Spectral Redox Titration for the ET Equilibrium Constant (Ket).
Redox titration of ET from tri(4-bromophenyl)amine (TBPA) to 1-
3
+
Sc was examined with various concentrations of TBPA in MeCN
at 253 K using a Hewlett Packard 8453 photodiode-array spectrom-
eter with a quartz cuvette (path length = 1.0 cm). Typically, a deaer-
ated MeCN solution of TBPA (0.00 – 0.12 mM) was added to a de-
Spectral and kinetic data (Figures S1 – S22)
and EXAFS data (Tables S1 – S3) and kinetic data (Tables S4 and S5).
This material is available free of charge via the Internet at
http://pubs.acs.org.
3
+
aerated MeCN solution containing 1-Sc (0.050 mM). The concen-
•+
tration of TBPA was determined from the absorption band at λ =
4
–1
–1
3+
3
–1
–1
7
05 nm (ε
1
= 3.2 × 10 M cm ), and 1-Sc (ε = 1.2 × 10 M cm )
3+
2
using eq 5 derived from eq 6, where [1-Sc ]
0
is the initial
3+
3+
3+
•+
wwnam@ewha.ac.kr, fukuzumi@chem.eng.osaka-u.ac.jp, ypush-
kar@purdue.edu
concentration of 1-Sc and [1-Sc ] = [1-Sc ] – [TBPA ].
0
•
+
3+
[
TBPA ] = (Abs705 – ε
2
[1-Sc ]
0
)/(ε
1
– ε
2
)
(5)
(6)
•+
3+
Abs705 = ε
1
[TBPA ] + ε
2
[1-Sc ]
This work was supported by the NRF of Korea through CRI (NRF-
2012R1A3A2048842 to W.N.), GRL (NRF-2010-00353 to W.N.)
and Basic Science Research Program (2017R1D1A1B03029982 to
Y.-M.L. and 2017R1D1A1B03032615 to S.F.), and a Grant-in-Aid
(no. 16H02268 to S.F.) from the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), a SENTAN project from
Japan Science and Technology (JST) to S.F, and also by the U.S. De-
partment of Energy, Office of Sciences, Office of Basic Energy Sci-
ences under Grant Numbers DE-FG02-10ER16184 (Y.P.) Use of
the Advanced Photon Source, an Office of Science User Facility op-
erated by the U.S. Department of Energy (DOE) Office of Science
by Argonne National Laboratory, was supported by the U.S. DOE
under Contract DE-AC02-06CH11357.
•
+
4
–1
–1
The ε
1
value of TBPA (3.2 × 10 M cm ) was confirmed by the
standard authentic sample of tris(4-bromo-phenyl)ammoniumyl
hexachloroantimonate, [(4-BrC N]-SbCl , in MeCN at 253 K.
The expression used for determination of Ket was derived according
to our previous work. The equilibrium constant (Ket) in eq 1 is ex-
pressed by eq 7, from which eq 8 is derived,
6
H
4
)
3
6
5
4
•+
III
3+
3+
K
et = [TBPA ] [Mn (O)Sc ]/[TBPA] [1-Sc ]
(7)
•+
3+
•+
•+ 2
K
et–1 = ([TBPA]
0
– [TBPA ])([1-Sc ] – [TBPA ])/[TBPA ]
0
•
+
3+
•+
=
([TBPA]
0
/[TBPA ] – 1) ([1-Sc ]
0
/[(TBPA )] – 1)
(8)
III
3+
•+
•+
where [Mn (O)Sc ] = [TBPA ], [TBPA]
= [1-Sc ] + [Mn (O)Sc ]. [1-Sc ]
are the initial concentrations of [1-Sc ], and [TBPA], respectively.
0
= [TBPA] + [TBPA ],
3
+
3+
III
3+
3+
and [1-Sc ]
0
0
and [TBPA]
0
3
+
•+
Equation 9 is derived from eq 8, where α = [TBPA ]/[TBPA] .
0
(
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0
/α[TBPA]
0
– 1)
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/α[TBPA]
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– 1 as shown in Figure
4
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First-order rate constants for the oxidation of substrates by
IV
+
n+
n+
n+
2+
2+
2+
3+
[(dpaq)Mn (O)] -M (OTf) (1-M ; M = Ca , Mg , Zn , Lu ,
n
3
+
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