Generation of a Mn(IV)-Peroxo or Mn(III)-Oxo-Mn(III) Species upon Oxygenation of Mono- and Binuclear Thiolate-Ligated Mn(II) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.7b01513

A thiolate-bridged binuclear complex [PPN]₂[(Mn^II(^TMSPS3))₂] (1, PPN = bis(triphenylphosphine)iminium and ^TMSPS3H₃ = (2,2′,2″-trimercapto-3,3′,3″-tris(trimethylsilyl)triphenylphosphine)), prepared from the reaction of MnCl₂/[PPN]Cl and Li₃[^TMSPS3], converts into a mononuclear complex [PPN][Mn^II(^TMSPS3)(DABCO)] (2) in the presence of excess amounts of DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane). Variable temperature studies of solution containing 1 and DABCO by UV-vis spectroscopy indicate that 1 and 2 exist in significant amounts in equilibrium and mononuclear 2 is favored at low temperature. Treatment of 1 or 2 with the monomeric O₂-side-on-bound [PPN][Mn^IV(O₂)(^TMSPS3)] (3) produces the mono-oxo-bridged dimer [PPN]₂[(Mn^III(^TMSPS3))₂(μ-O)] (4). The electrochemistry of 1 and 2 reveals anodic peak(s) for a Mn^III/Mn^II redox couple at shifted potentials against Fc/Fc⁺, indicating that both complexes can be oxidized by dioxygen. The O₂ activation mediated by 1 and 2 is investigated in both solution and the solid state. Microcrystals of 2 rapidly react with air or dry O₂ to generate the Mn(IV)-peroxo 3 in high yield, revealing a solid-to-solid transformation and two-electron reduction of O₂. Oxygenation of 1 or 2 in solution, however, is affected by diffusion and transient concentration of dioxygen in the two different substrates, leading to generation of 3 and 4 in variable ratios.

Full text of DOI:10.1021/acs.inorgchem.7b01513

Article
pubs.acs.org/IC
Generation of a Mn(IV)−Peroxo or Mn(III)−Oxo−Mn(III) Species upon
Oxygenation of Mono- and Binuclear Thiolate-Ligated Mn(II)
Complexes
Chien-Ming Lee,*,† Wun-Yan Wu,† Ming-Hsi Chiang,*,‡ D. Scott Bohle,*,§ and Gene-Hsiang Lee∥
†Department of Applied Science, National Taitung University, Taitung 950, Taiwan
‡Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan
§Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada
∥Instrumentation Center, National Taiwan University, Taipei 107, Taiwan
S
* Supporting Information
ABSTRACT: A thiolate-bridged binuclear complex
[PPN]2[(MnII(TMSPS3))2] (1, PPN = bis(triphenylphosphine)-
iminium and TMSPS3H3 = (2,2′,2″-trimercapto-3,3′,3″-tris-
(trimethylsilyl)triphenylphosphine)), prepared from the reaction
of MnCl2/[PPN]Cl and Li3[TMSPS3], converts into a mono-
nuclear complex [PPN][MnII(TMSPS3)(DABCO)] (2) in the
presence of excess amounts of DABCO (DABCO = 1,4-
diazabicyclo[2.2.2]octane). Variable temperature studies of
solution containing 1 and DABCO by UV−vis spectroscopy
indicate that 1 and 2 exist in significant amounts in equilibrium and mononuclear 2 is favored at low temperature. Treatment of 1
or 2 with the monomeric O2-side-on-bound [PPN][MnIV(O2)(TMSPS3)] (3) produces the mono-oxo-bridged dimer
[PPN]2[(MnIII(TMSPS3))2(μ-O)] (4). The electrochemistry of 1 and 2 reveals anodic peak(s) for a MnIII/MnII redox couple
at shifted potentials against Fc/Fc+, indicating that both complexes can be oxidized by dioxygen. The O2 activation mediated by 1
and 2 is investigated in both solution and the solid state. Microcrystals of 2 rapidly react with air or dry O2 to generate the
Mn(IV)−peroxo 3 in high yield, revealing a solid-to-solid transformation and two-electron reduction of O2. Oxygenation of 1 or
2 in solution, however, is affected by diffusion and transient concentration of dioxygen in the two different substrates, leading to
generation of 3 and 4 in variable ratios.
than one intermediate is involved (black arrows in Scheme 1),
but the reaction includes a structurally characterized peroxo-
bridged binuclear Mn(III) complex which slowly converts to
the mono-oxo-bridged binuclear Mn(III) species.14 This
example also reveals that the thiolate ligand is capable of
stabilizing metal−peroxo species. Very recently, oxygenation of
a dimercapto-bridged MnII−thiolate dimer reported by Duboc’s
INTRODUCTION
■
Coordination compounds with Mn−peroxo moieties have
attracted considerable attention,1−21 due to their varied roles in
key biological processes which include the activation of
molecular oxygen,22−25 detoxification of superoxide and
hydrogen peroxide,26−29 and water-splitting chemistry.30−32
The metastable Mn−peroxo intermediates that undergo O−O
bond cleavage produce high-valent Mn−oxo adducts which are
responsible for substrate oxidation and are also of interest in
biological33,34 and synthetic chemistry.16,35−39 In this regard,
understanding the mechanisms of Mn-mediated dioxygen
activation remains a significant challenge. Based on the key
intermediates such as metal−superoxo, −peroxo, −hydro-
peroxo, or−oxo obtained in enzymatic and biomimetic systems
(metal = iron or copper), a potential mechanism for metal-
promoted dioxygen activation has been established.40 Com-
pared to the Fe-39−41 and Cu-mediated42−44 dioxygen
chemistry, the reported chemistry relative to Mn-mediated
activation of O2 is scarce.2,5,16,19−21,37,39 Recently reported
examples of mononuclear and binuclear MnII−thiolate
complexes include one by Kovacs et al. which shows that a
series of five-coordinate mononuclear thiolate-coordinated
Mn(II) complexes can react with O2.12,14,18,21 Here, more
Scheme 1
Received: June 14, 2017
© XXXX American Chemical Society
A
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group resulted in the isolation of a di-μ-oxo Mn(IV) dimer that
may be generated following homolytic O−O bond cleavage of
peroxo-bridged binuclear Mn(III) species (blue arrows in
Scheme 1).21 In this system, additional MnII−thiolate dimer is
required to convert the di-μ-oxo Mn(IV) dimer to mono-oxo-
bridged binuclear Mn(III) species (via a comproportionation
reaction).
Treatment of transition-metal−thiolate complexes with O2
frequently causes ligand-centered oxidation, resulting in the
formation of metal−sulfenate, −sulfinate, or −sulfonate
species.45−48 On the other hand, coordination of chelating
ligands containing strongly donating thiolato sulfur(s) is found
to help metal-based O2 activation by lowering the metal redox
potential.16,18,21,49 Thiolates with noninnocent character also
serve as good chelators to help stabilize high-valent complexes.
One example of this class is the tetradentate-deprotonated
TMSPS3H3 ligand which contains three thiolates and phos-
phine.50−55 In previous studies, we have demonstrated that
treatment of a thiolate-ligated Mn(I) complex containing a
pendant thiol group with O2 can generate a monomeric O2-
side-on-bound [PPN][MnIV(TMSPS3)(O2)] which is metastable
in organic solvent and stable in the solid state at ambient
temperature (Scheme 2).55 The activation of O2 is proposed to
in solution and in the solid state, leading to solid-to-solid direct
oxygenation of 2 by O2.
RESULTS AND DISCUSSION
■
Preparation of Binuclear 1, Mononuclear 2, and
Mono-Oxo-Bridged Dimeric 4. When a THF solution of
deprotonated TMSPS33− ligand (as a trilithium salt) is added to
a CH3CN solution of MnCl2/[PPN]Cl mixture in a 1:1:1
molar ratio, an immediate change in solution color from light
yellow to orange red is observed. The reaction mixture leads to
the isolation of dimeric [PPN]2[(MnII(TMSPS3))2] (1, 95%
yield) after recrystallization from vapor diffusion of Et2O into
CH3CN solution of 1 under N2 at room temperature (Scheme
3). The optical spectrum of 1 in CH3CN solution is featureless
at wavelengths above 550 nm (Figure 1). Upon addition of
Scheme 2
Figure 1. UV−vis spectra (in CH3CN) for 1 (red line), 2 (black line),
and 4 (blue line) at room temperature (ε, M−1 cm−1).
excess amounts of DABCO (100 equiv) into a CH3CN
solution of 1, the resulting mixture immediately turns purple.
The change is also observed in the UV−vis spectrum in which a
535 nm absorption band is responsible for purple color of
DABCO adduct (Figure 1). In titration experiments, as
observed by UV−vis spectroscopy (Figure 1S), ∼50 equiv of
DABCO is needed to maximize the growth of the peak at 535
nm. Dark purple crystals of a DABCO adduct suitable for X-ray
crystallography are obtained by slowly adding the diethyl ether
to layer above the mixture (90% yield). Characterization by X-
ray crystallography revealed the purple DABCO adduct to be a
five-coordinate monomeric [PPN][MnII(TMSPS3)(DABCO)]
(2).
go through a four-coordinated [MnII(TMSPS3)]− intermediate.
In this work, we report the synthesis of mononuclear and
binuclear thiolate-ligated Mn(II) complexes,
[PPN]2[(MnII(TMSPS3))2] (1) and [PPN][MnII(TMSPS3)-
(DABCO)] (2), by utilizing MnCl2 as Mn(II) ion source
(Scheme 3). Reaction of 1 and 2 with different oxidants e.g.,
[PPN][MnIV(TMSPS3)(O2)] (3) and O2, has been investigated
Scheme 3
Upon treatment of peroxomanganese(IV) 355 with 2 in
CH3CN at ambient temperature under N2, a green adduct with
absorption bands at 450 (ε = 5410) and 670 (ε = 3760) nm is
immediately formed. Dark green crystals obtained by vapor
diffusion of Et2O into CH3CN solution and characterized by X-
ray crystallography reveal the green adduct to be a mono-oxo-
bridged dimeric [PPN]2[(MnIII(TMSPS3))2(μ-O)] (4) (95%
yield, Scheme 3).
Molecular Structures of Complexes 1, 2, and 4.
ORTEP diagrams of anions 1, 2, and 4 are presented in
Figures 2−4 with selected bond distances and angles being
given in the figure captions. The two Mn sites of 1 are
crystallographically equivalent, and the two [Mn2S2] cores
appear as a coplanar diamond shape with a zero dihedral angle
crystallographically imposed between the S1MnS1A and
S1MnAS1A planes. The distance between two Mn(II) ions is
3.0055(13) Å, which is too long for a direct metal−metal
B
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Figure 2. ORTEP diagrams of dianion 1 with thermal ellipsoids drawn
at the 50% probability level. Hydrogen atoms and solvent of
crystallization are omitted for clarity. Selected bond distances (Å)
and angles (deg): Mn−S1 2.5438(14); Mn−S2 2.4627(13); Mn−S1A
2.5045(14); Mn−S3A 2.4254(14); Mn−P1A 2.6140(13); S1−Mn−S2
102.57(4); S1−Mn−S3A 119.08(5); S1−Mn−S1A 106.93(4); S1−
Mn−P1A 88.80(4); S2−Mn−S1A 97.08(5); S2−Mn−S3A 94.62(5);
S2−Mn−P1A 168.50(5); S1A−Mn−S3A 128.41(5); S1A−Mn−P1A
77.71(4); S3A−Mn−P1A 81.06(4); Mn−S1−MnA 73.07(4).
Figure 4. ORTEP diagrams of dianion 4 with thermal ellipsoids drawn
at the 50% probability level. Hydrogen atoms and solvent of
crystallization are omitted for clarity. Selected bond distances (Å)
and angles (deg): Mn1−S1 2.4031(19); Mn1−S2 2.3779(18); Mn1−
S3 2.3861(18); Mn1−P1 2.3208(17); Mn1−O1 1.774(3); Mn2−S4
2.3553(19); Mn2−S5 2.3938(17); Mn2−S6 2.3738(17); Mn2−P2
2.3328(16); Mn2−O1 1.775(3); S1−Mn1−S2 116.58(7); S1−Mn1−
S3 116.19(7); S2−Mn1−S3 120.57(7); O1−Mn1−P1 177.79(14);
O1−Mn2−P2 178.54(14).
distance of 2 (2.5108(9)) is longer than that of five-coordinate
mononuclear thiolate-coordinated [MnII(SMe2N4(6-Me-
DPEN)](BF4)]+ (6-Me-DPEN = N,N-bis(6-methyl-2-
pyridylmethyl)ethane-1,2-diamine)12 It can be attributed to
rich charge density on the Mn(II) center, provided by three
thiolate donors, reducing the interaction between Mn ion and
thiolato sulfurs. The geometry around both central Mn(III) in
4 adopt trigonal bipyramidal geometry (τ = 0.95) with three
thiolates located in equatorial positions and the phosphorus
occupying an axial position trans to the bridged-oxo ligand. The
distances of Mn1−O1 and Mn2−O2 are nearly identical, and
the Mn1···Mn2 separation is 3.548 Å, both of which are
comparable with other examples containing a single,
unsupported oxo-bridged Mn(III) dimer.12,56−62 The mean
Mn(III)−SR bond distance of 4 (2.390(2) Å) is longer than
those of unsupported oxo-bridged Mn(III)−thiolate dimers
(range from 2.255 to 2.297 Å),12 and dinuclear [MnIII2(edt)4]2−
(Mn−Sterminal = 2.32 Å, edt = 1,2-ethenedithiolate)63 and
[Mn2(Im)(edt)4]− (the mean Mn−S = 2.335 Å, Im− = anion
imidazole).64 The shorter mean Mn−SR bond distance of 4
than that of 1 or 2 is indicative of an increase in oxidation state
of Mn ion from Mn(II) to Mn(III).
Figure 3. ORTEP diagrams of anion 2 with thermal ellipsoids drawn
at the 50% probability level. Hydrogen atoms and solvent of
crystallization are omitted for clarity. Selected bond distances (Å)
and angles (deg): Mn−S1 2.5295(8); Mn−S2 2.4987(8); Mn−S3
2.5041(9); Mn−N1 2.226(2); Mn−P1 2.4429(8); S1−Mn−S2
117.67(3); S1−Mn−S3 121.44(3); S2−Mn−S3 112.94(3); S1−
Mn−N1 94.77(7); S1−Mn−P1 79.47(3); S2−Mn−N1 105.41(6);
S2−Mn−P1 80.96(3); S3−Mn−N1 98.54(6); S3−Mn−P1 81.31(3);
N1−Mn−P1 172.99(7).
Magnetic Properties of Complexes 1, 2, and 4.
Magnetic susceptibility (χM) of microcrystalline samples of 1,
2, and 4 is measured under an external field of 2000 G,
respectively. The χM value of 1 decreases from 0.0114 cm3
mol−1 at 300 K to a minima of 2.339 × 10−3 cm3 mol−1 at 12 K
and increases to 4.253 × 10−3 cm3 mol−1 at 2 K (Figure 5a).
The corresponding χMT value of 1 between 300 and 2 K
decreases from 3.4109 to 8.256 × 10−3 cm3 mol−1 K. The value
at 300 K for 1 is significantly deviated from the theoretical value
of 8.75 cm3 mol−1 K for a system composed of two non-
interacting high-spin MnII centers (S = 5/2, g = 2). This
suggests that a strong antiferromagnetic interaction is present
between the Mn centers of 1. The χMT data is fitted to an
interaction. The geometry about both central Mn(II) can be
regarded as distorted trigonal bipyramidal (τ = 0.67) with three
thiolates located in equatorial positions and the phosphorus
occupying an axial position trans to the fourth thiolato sulfur.
The average Mn−Sbridge and Mn−Sterminal bond lengths of 1 are
2.5242(14) and 2.4441(13) Å, respectively, which are
comparable to those of [MnII (LS)(LSH)]ClO4 (LS = 2,2′-
2
(2,2′-bipyridine-6,6′-diyl)bis(1,1-diphenylethanethiolate)).18
The geometry of anion 2 (τ = 0.86) exhibits closer to the ideal
trigonal bipyramidal than that of 1 with three thiolates located
in equatorial positions and the phosphorus occupying an axial
position trans to DABCO. The mean Mn(II)−SR bond
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centers via an oxo bridge, consistent with the observation
that an oxo group is a good spin mediator.65 The χMT data is
fitted to an expression of H = −2J·S1·S2 (S1 = S2 = 2) in which
2J represents the magnetic exchange parameter. A satisfactory
fit is obtained between 100 and 300 K: g = 2.01(3), 2J =
−152(3) cm−1, which falls into the range of known mono-oxo-
bridged Mn(III) dimers12,58−62,66 and reveals that the high-spin
MnIII ions of 4 are strongly antiferromagnetically coupled.
Electrochemical and EPR Spectra of Complexes 1 and
2. The electrochemical behavior of 1 (1.0 mM) measured by
cyclic voltammetry (CV) in CH3CN with 0.1 M [n-Bu4N]-
[PF6] as supporting electrolyte, under N2, reveals two
successive and reversible redox processes at E1/2 = −1.10 V
and E1/2 = −0.77 V, respectively (vs Fc/Fc+). The electro-
chemistry of 2 shows only one reversible redox process at E1/2
= −1.16 V against Fc/Fc+ (Figure 6). In comparison with redox
Figure 6. Cyclic voltammograms of 1 (solid line) and 2 (dashed line)
measured in a 1 mM CH3CN solution with 0.1 M [n-Bu4N][PF6] as
the supporting electrolyte at room temperature, scan rate 0.1 V/s. E1/2
= −1.16 V (Ep = 89 mV) for 2; E1/2 = −1.10 V (Ep = 70 mV) and E1/2
= −0.77 V (Ep = 73 mV) for 1.
Figure 5. (a) Plots of χM (open circles) and χMT (open squares)
versus temperature for 1. The solid line is the best fit of the
experimental data to the theoretical expression. (b) Plots of χM (open
circles) and 1/χM (open squares) versus temperature for 2. The solid
line is the best fit of the experimental data to the Curie−Weiss law.
properties of Li3TMSPS3 (Figure S3), ligand-centered redox
processes of 1 and 2 can be ruled out.67−69 The event at −1.10
V can be assigned to a MnIIIMnII/MnIIMnII redox couple, and
the electrochemically generated MnIIMnIII species can be
further oxidized to MnIIIMnIII at −0.77 V. The reversible
redox process at E1/2 = −1.16 V of 2 is assigned to the MnIII/
MnII redox couple. Within the CH3CN solvent window, no
redox wave is observed for the MnIV/MnIII couple of 1 and
expression of H = −2J·S1·S2 (S1 = S2 = 5/2) in which 2J
represents the magnetic exchange parameter. A satisfactory fit is
obtained: g = 1.991(9), 2J = −57.0(5) cm−1, which is
comparable to that of [MnII (LS)(LSH)]ClO4 (J = −22(1)
2
cm−1),18 revealing that the high-spin MnII ions of 1 are strongly
antiferromagnetically coupled.
As shown in Figure 5b, the χM value of microcrystalline
samples of 2 increases from 0.0136 cm3 mol−1 at 300 K to
2.0667 cm3 mol−1 at 2 K. The corresponding inverse χM value
of 2 displays a linear relationship against temperature,
indicating the Curie−Weiss paramagnetic behavior for a S =
5/2 spin ground state system (C = 4.04 cm3 K mol−1, θ =
0.1436 K). The results from the magnetic investigation suggests
a high-spin MnII center in 2.12
The χM value of mono-oxo-bridged dimeric
[PPN]2[(MnIII(TMSPS3))2(μ-O)] (4) gradually decreases
from 4.451 × 10−3 cm3 mol−1 at 300 K to 3.017 × 10−3 cm3
mol−1 at 50 K and then increases to 0.011 cm3 mol−1 at 2 K
(Figure S2). The corresponding χMT value between 300 and 2
K decreases from 1.335 to 0.022 cm3 mol−1 K. The value at 300
K is significantly deviated from the theoretical value of 6 cm3
mol−1 K for a system composed of two non-interacting high-
spin MnIII centers (S = 2, g = 2). Thus, a strong
antiferromagnetic interaction is present between the Mn
2.55,70 A dimercapto-bridged dimer [MnII (LS)(LSH)]ClO4
2
with a pendant thiol group (its CV has an irreversible anodic
peak at −0.01 V vs Fc/Fc+) and the deprotonated form
[MnII (LS)2] which shows a reversible peak at −0.45 V vs Fc/
2
Fc+ have been recently reported.18,21 The assignment of these
redox events as a pair of one-electron oxidations for MnIIMnII
to MnIIIMnIII couple reveals different electrochemical behavior
from that of 1. The drop in potential of 1 may be attributed to
coordinated TMSPS33− ligand that contains three thiolates with
better donor ability than thiol to place the Mn(II) ion in an
electron-rich condition. The electrochemical stability of a
mixed-valence MnII/MnIII species of 1 can be attributed to
relatively rigid tetradentate ligand and the redox noninnocence
of TMSPS33−.67,68 Those factors also lend the support to the
explanation of more negative potential of mononuclear 2
compared to other monomeric thiolate-ligated Mn(II)
complexes such as [MnII(SMe2N4(6-Me-DPEN)](BF4)]+ with
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a reversible MnIII/II redox couple at E1/2 = 0.41 V (vs SCE;
0.035 V vs Fc/Fc+).12 Moreover, the lower potentials associated
with the MnIII/II redox couple indicate that 1 and 2 are much
easier to oxidize by an oxidant such as O2.
Although the CVs of 1 and 2 indicate that the solid-state
structure of dimeric 1 is mostly retained in CH3CN (a weaker
donor than DABCO), the partial dissociation of 1 in CH3CN
to form mononuclear solvent-bound [MnII(TMSPS3)-
(NCCH3)]− is not ruled out. The X-band EPR spectrum of
mononuclear 2 recorded at 77 K displays an intense broad
signal at g⊥ = 5.21 and a less intense signal at g∥ = 1.95 (Figure
S4), again consistent with an axial high-spin MnII center in 2. It
is noted that the 77 K EPR spectrum of dimeric 1 in CH3CN
shows very weak signals, the g-values of which are similar to
those of 2 (Figure S4). In the solid state, 1 shows strong
antiferromagnetic interaction between two Mn(II) centers,
suggesting that the EPR spectrum of 1 could be silent at low
temperature. The resonance signals observed by EPR of 1 in
CH3CN may be attributed to mononuclear solvent-bound
[MnII(TMSPS3)(NCCH3)]− species. Similarly, very weak peaks
are observed in the ESI-MS (electrospray ionization mass
spectrum) at m/z = 667.2 ([MnII(TMSPS3)(NCCH3)]−, m/z =
667.1 (calcd); Figure S5).
Van’t Hoff Plot for Conversion of 1 to 2. Variable
temperature studies of solutions containing 1 and excess
amounts of DABCO by UV−vis spectroscopy indicate that 1
and 2 exist in significant amounts in equilibrium. Based on the
equilibrium manner in eq 1, the equilibrium constant (Keq) is
9(1) at 25 °C, which is comparable to the Keq observed
between [CuIII(TMSPS3)(Cl)]− and CuIII(TMSPS3)(DABCO) in
CH3CN.51 An analysis of the Van’t Hoff plot from 298 to 248
K for this reaction displays the activation parameters ΔH° =
−16(1) kJ mol−1, ΔS° = −37(2) J K−1 mol−1, indicating that
the monomeric 2 is favored at low temperature (Figure 7).
Figure 8. UV−vis spectra of complexes 3 (red) and 4 (black),
respectively. Changes in UV−vis spectra (gray) after treating 3 with
various equivalents of 2 in CH3CN at room temperature. Inset:
absorbance changes at 670 nm upon addition of 2.
3[MnII(TMSPS3)(DABCO)]− + [MnIV(TMSPS3)(O2)]−
→ 2[(MnIII(TMSPS3))2(μ‐O)]2− + 3DABCO
(2)
Recently, a mono-oxo-bridged {[MnIII(SMe2N4(6-Me-
DPEN)]2(μ-O)}2+ reported by Kovacs’s group was generated
from the thermal decomposition of metastable peroxo-bridged
{[MnIII(SMe2N4(6-Me-DPEN)]2(trans-μ-1,2-O2)}2+.14 The
mechanism for the formation this binuclear Mn(III)−peroxo
species has been demonstrated to involve a mononuclear
Mn(III)−superoxo intermediate that reacts with the second
equivalent of [MnII(SMe2N4(6-Me-DPEN)]+ (black arrows in
Scheme 1).16 By analogy with widely accepted pathways to
explain the formation of μ-peroxo and -oxo dimetallic
species,16,39−41 we propose that mononuclear Mn(II) 2 reacts
with peroxomanganese(IV) 3 to yield a binuclear [(TMSPS3)-
MnIII−(μ-O22−)−MnIII(TMSPS3)]2− (intermediate A, Scheme
3). Low-temperature UV−vis spectroscopy is utilized to detect
the peoxo-to-manganese charge transfer band which has been
observed at higher energy visible region,8,16 but no
intermediates are observed upon mixing 2 and 3 in
CH3CH2CN at −70 °C. In related systems, peroxo-bridged
dimanganese intermediates have been observed and their
stability has been attributed to ligand intramolecular
interactions, including aromatic ring π-stacking, which stabilize
these reactive species.14
[(MnII(TMSPS3))2]2− + 2DABCO ⇌ 2[MnII(TMSPS3)(DABCO)]−
(1)
Oxidation of 1 or 2 with Mn(IV)−Peroxo Species.55 In
titration experiments, as observed by UV−vis spectroscopy
(Figure 8), ∼3.0 equiv of mononucler 2 is needed to fully
transform 3 into 4 and the formation of 4 is nearly quantitative
based on the amount of peroxomanganese(IV) 3 (eq 2).
It is noted that stoichiometric quantities for this reaction are
three equiv of 2 per equiv of 3 (eq 2). An independent
experiment shows that 2 can react with iodosylbenzene (PhIO;
0.5 equiv), an oxygen-atom transfer reagent, to produce 4 in
nearly quantitative yield. These observations suggest that the
formation of 4 involves a high-valent Mn−oxo transient species
that, in the case of O2 addition, would be generated from O−O
bond cleavage in A (Scheme 3).12 Then, the generated Mn−
oxo species reacts rapidly with 2 (2 equiv) to form 2 equiv of μ-
oxo dimeric 4.21,39,41 Therefore, the total consumption for 2 is
3 equiv, which is consistent with the titration experiments.
In a competition experiment of 2 with triphenylphosphine
(PPh3) for oxygen atom transfer mediated by Mn−oxo species
we observe that the yield of 4 is unperturbed based on UV−vis
spectroscopy when reacting 2 and 3 in the presence of excess
amounts of PPh3. The formation of OPPh3 is not observed in
this reaction presumably due to the fast reaction between Mn−
oxo transient species and mononuclear 2. This observation also
suggests that intermediary complexes do not have electrophilic
Figure 7. Changes of UV−vis spectra of CH3CN solution containing 1
(0.60 mM) and DABCO (13.8 mM) observed from 25 to −25 °C.
Inset: Van’t Hoff plot of equilibrium data based on eq 1.
E
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oxygens and that they are thus relatively electron rich. Binuclear
1 also reacts with 3 to generate 4, but the yield of 4 from this
reaction is decreased to 75% based on the absorbance peaks at
670 (ε = 3760) of 4 (Figure S6).
Oxidation of 1 and 2 with Dioxygen, Respectively.
Complex 2 is highly reactive with dioxygen both in solution and
in the solid state. Since the oxidation of 2 with O2 in solution is
more complicated, we discuss the reaction in the solid state
first. Microcrystals of 2 are placed under air or dry O2 at
ambient temperature for 2 h. The color change during
oxidation of solid-state 2 with O2 is subtle, from light purple
to dark red-purple (Figure S7). The UV−vis spectrum of solid-
to-solid oxygenation product dissolved in CH3CN under N2
atmosphere shows three features at 490, 550, and 755 nm,
indicating the formation of peroxomanganese(IV) 3 (Scheme
4; 95% yield based on the ε value at 550 nm).71 The peak at
Figure 9. Comparisons of UV−vis spectra between purging O2 into
and layering O2 above CH3CN solution of 2 (0.2 mM).
Scheme 4
(IV) 3 first in solution as well as in the solid state (Scheme 4).
This can be rationalized as follows: in solution, the diffusion
rate of 2 is fast enough to react with 3 and vice versa to produce
4, which is consistent with a separate study of the reaction 2
with 3 (Scheme 3). However, in the solid state, which prevents
rapid diffusion of the nongaseous reagents, there is the high
yield conversion to the peroxomanganese(IV) 3. Moreover,
treatment of 2 and O2 (layered above the solution) in
CH3CH2CN at −80 °C results in an isolation of 3 (Figure S12)
that is similar to oxygenation of 2 in the solid state. This can be
attributed to the solubility/diffusion rate of the intermediate
being decreased in EtCN at lower temperature. It is also noted
that most of mononuclear 2 are converted into the Mn(IV)−
O2 species without a detectable intermediate upon reaction of
O2 in EtCN at −80 °C.
Analysis by cyclic voltammetry of CV’s responses of 1 and 2
suggests that both complexes can be oxidized by O2. In contrast
to 2, solid-state oxidation of 1 with O2 does not generate
Mn(IV)−peroxo 3 as evidenced by the absence a νOO band at
903 cm−1 in ATR-FTIR spectroscopy (Scheme 4; Figure S13).
Orange-red microcrystals of 1 gradually convert to a yellow-
brown solid upon contacting with excess amounts of dry O2 at
ambient temperature for 2 h (Figure S14). The yellow-brown
species can dissolve in THF and has a featureless UV−vis
spectrum at wavelengths above 500 nm. Attempts to isolate this
adduct have been unsuccessful.
903 cm−1 (νOO) is observed after microcrystals of 2 are stood in
open air at ambient temperature for 2 h (Figure S8), which is
consistent with the formation of 3 in the solid state. When 18O2
is used during solid-state oxygenation of 2, we observe the shift
of νOO to lower energy (∼861 cm−1, Figure S8), confirming
that O2 is the source of peroxo ligand in 3.55 However, lattice
parameters recorded for single-crystal 2 before and after
exposure to air for 30 min at room temperature are the same.
This observation may indicate that solid-state oxygenation of 2
occurs on the surface of particles. Prolonged exposure of
microcrystals of 2 to air leads to a loss of crystallinity of 2 that is
confirmed by powder X-ray diffraction (Figure S9). The
presence or absence of solvent like n-hexane in the solid state
does not affect dioxygen binding to 2. No re-formation of 2
upon prolonged evacuation of 3 is observed at room
temperature, indicating that the binding of O2 to 2 is
irreversible.
As shown in Figure 10, treatment of CH3CN solution of 1
with excess amounts of O2 at ambient temperature also
produces mixed products, 3 and 4 based on UV−vis
In CH3CN solution, treatment of 2 with excess O2 at
ambient temperature results in the formation of mixed products
as evidenced by UV−vis spectroscopy (Figure 9). Calculations
from spectral deconvolution revealed that 3 (63%) and 4 (8%)
are responsible for this pattern (Figure S10). As shown in
Figure 9, the ratio between generated 3 and 4 in this reaction
depends upon the transient oxygen concentration.21 For
example, the yield of 3 increases when the solution is purged
with a vigorous stream of O2 into the solution of 2, and the
yield is higher than that when gas O2 is layered above the
solution (Figure S11). Given these observations, a sequence of
isolated products after mixing O2 with 2 is peroxomanganese-
Figure 10. Comparisons of UV−vis spectra between purging O2 into
and layering O2 above CH3CN solution of 1 (0.16 mM).
F
DOI: 10.1021/acs.inorgchem.7b01513
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
spectroscopy. Compared to the oxidation of solution 2 with O2
(Figure 9), the ratio between the generated 3 and 4 in this
reaction is less dependent upon the oxygen addition method
(Figure S15). The formation of 3 in oxidation of CH3CN
solution of 1 with O2 is observed; however, as indicated in
solid-to-solid oxygenation of 1 (Figure S13), none can evolve
into 3. Presumably, the dissociation of binuclear 1 to
mononuclear solvent-bound [MnII(TMSPS3)(NCCH3)]− occurs
in CH3CN solution (Scheme 4). Like oxygenation of
mononuclear 2, solvent-bound [MnII(TMSPS3)(NCCH3)]−
can react with O2 to yield mononuclear 3, and then the
generated 3 can react with 1 to produce dinuclear 4 (Scheme
3). The second hypothesis for formation of 4 in this reaction
may involve direct insertion of O2 into two coordinate-
unsaturated Mn(II) centers of 1, resulting in the formation of
intermediate A. As indicated in Scheme 3, intermediate A may
undergo homolytic O−O bond cleavage and the generated
Mn−oxo species reacts rapidly with 1 to form dimeric 4 (via a
comproportionation reaction).21 The ESI-MS of 1 in CH3CN
shows some oxygenated fragments in which the m/z at 658.0 is
complex 3 ([Mn(TMSPS3)(O2)]− (3), m/z = 658.1 (calcd);
Figure S5).72 However, the factors for 4 being generated
preferentially and independent of the oxygen addition method
in this reaction are not clear.
species upon oxidation of these thiolate-ligated-manganese
complexes.
EXPERIMENTAL SECTION
■
General Procedures. Manipulations and reactions are conducted
under a pure nitrogen atmosphere according to Schlenk techniques or
in a glovebox (nitrogen atmosphere). Solvents are purified and
distilled under nitrogen by utilizing appropriate reagents (diethyl ether
from CaH2; acetonitrile from CaH2−P2O5; methylene chloride from
CaH2; hexane and tetrahydrofuran (THF) from sodium benzophe-
none) and stored in dried, N2-filled flasks over 4 Å molecular sieves.
The reagent 18O2 (99 atom % 18O, Sure-Pac from Aldrich) is used as
received. 2,2′,2″-Trimercapto-3,3′,3″-tris(trimethylsilyl)-
triphenylphosphine ligand (TMSPS3H3) is synthesized according to
published procedures. Li3[TMSPS3] is prepared from reaction of
TMSPS3H3 and n-butyllithium (2.5 M in hexane) at −20 °C. Infrared
spectra (IR) are recorded either on a SHIMADZU FTIR-8400S with
sealed solution cells (0.1 mm, KBr windows) or on a ATR (attenuated
total reflectance)-FTIR (PerkinElmer, Frontier). UV−vis spectra are
recorded on a SCINCO S-4100 or on an Agilent 8454
spectrophotometer equipped with a UNICOKU liquid N2 cryostat.
NMR spectra are obtained on an Agilent 400-MR DD2. GC−MS (an
Agilent 7890A gas chromatograph connected with an Agilent 5975C
mass selective detector) is used to detect the organic products.
Analyses of carbon, hydrogen, and nitrogen are obtained with a CHN
analyzer (Heraeus).
Physical Measurements. Electrochemical measurements are
recorded on a CH Instruments 630C electrochemical potentiostat
using a gas-tight three-electrode cell under N2 at room temperature. A
glassy carbon electrode (3 mm in diameter) and a platinum wire are
used as working and counter electrode, respectively. Reference
electrode is a nonaqueous Ag/Ag+ electrode. All potentials are
reported against ferrocene/ferrocenium (Fc/Fc+). The magnetic data
of the microcrystalline samples of 1, 2, and 4 are recorded on a
SQUID magnetometer (SQUID-VSM, Quantum Design) under an
external magnetic field (0.2 T) in the temperature range of 2−300 K.
The magnetic susceptibility data are corrected with ligands’
diamagnetism by the tabulated Pascal’s constants and the sample
holder.74 The X-band EPR measurements are recorded at 77 K on a
Bruker E580 CW/Pulse EPR. The X-ray single crystal crystallographic
data collections for 1, 2, and 4 are carried out at 150 K with a Bruker
SMART APEX CCD four-circle diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) outfitted with a
low-temperature, nitrogen-stream aperture. The structures are solved
by direct methods, in conjunction with standard difference Fourier
techniques and refined by full-matrix least-squares procedures. A
summary of the crystallographic parameters for the complexes 1, 2,
and 4 is shown in Table S1. An empirical absorption correction
(multiscan) is applied to the diffraction data for all structures. All non-
hydrogen atoms are refined anisotropically, and all hydrogen atoms are
placed in geometrically calculated positions by the riding model. All
software used for diffraction data processing and crystal structure
solution and refinement are contained in the SHELXL-97 program
suites.
CONCLUSION
■
We describe a thiolate-bridged binuclear complex
[PPN]2[(MnII(TMSPS3))2] (1) which converts to the mono-
nuclear complex [PPN][MnII(TMSPS3)(DABCO)] (2) in the
presence of excess amounts of DABCO. The activation
parameters obtained from studies of variable-temperature
UV−vis spectroscopy are consistent with an equilibrium in
which mononuclear 2 is favored at low temperature. The CVs
of 1 and 2 reveal anodic peak(s) for MnIII/MnII redox couple at
much negative potentials against Fc/Fc+, indicating rich
oxidative chemistry with O2 and other oxidants. Oxidative
reactions are first examined with a Mn(IV)−peroxo 3, leading
to the formation of an unsupported oxo-bridged Mn(III) dimer
4. The generation of 4 is proposed via a peroxo-bridged
dimanganese(III) intermediate in which the O−O bond is
much weaker and more readily undergoes O−O bond cleavage
than that of 3. Although the intermediate is not detected in this
case, even at low temperature, a well-characterized peroxo-
bridged Mn(III) dimer has been reported recently.
The cyclic voltammetry of 2 under inert atmosphere shows a
reversible MnIII/MnII redox couple which indicates that a stable
mononuclear Mn(III) [Mn(TMSPS3)(DABCO)] can be elec-
trochemically generated.73 Chemically, oxidation of 2 with O2
in both solution and the solid state generates a mononuclear
Mn(IV)−peroxo 3. Factors which allow for the isolation of 3
may include a redox noninnocent TMSPS33− which stabilizes a
formally high-valent Mn(IV) species.
Preparation of [PPN]2[(MnII(TMSPS3))2] (1). A THF/CH3CN
solution of Li3[TMSPS3] (9:1 v/v; 5 mL, 0.1 M) is added to a
suspended CH3CN solution (2 mL) containing MnCl2 (0.063 g, 0.50
mmol) and PPNCl (0.288 g, 0.50 mmol) by syringe under N2. The
reaction mixture is stirred for 30 min at ambient temperature. The
resulting orange-red solution is reduced under vacuum, and diethyl
ether (50 mL) is added to precipitate the orange-red solid
[PPN]2[(MnII(TMSPS3))2] (1) (1.110 g, 95%). Diffusion of diethyl
ether into a THF/CH3CN (3:1 v/v) solution of 1 at −20 °C leads to
red crystals suitable for X-ray crystallography. UV−vis THF/CH3CN,
1:1 v/v): λmax (ε, M−1 cm−1) = 420 nm (650, sh). Magnetic
susceptibility (solid state, 2−300 K, antiferromagnetically coupled):
calcd for g = 1.991(9), 2J = −57.0(5) cm−1. ESI-MS: [(Mn-
The O2 activation mediated by 1 and 2 is investigated in both
solution and the solid state. Since the movement of ions is
restricted in the solid state, Mn(IV)−peroxo 3 generated from
reaction of mononuclear Mn(II) 2 and gas O2 is not further
oxidized by another 2 to form oxo-bridged Mn(III) dimer 4. In
solution, however, the diffusion rate of ions is fast enough and
mixed products are isolated. Significantly, the oxygenation of 1
or 2 does not lead to the oxidation of thiolate donors. This is
attributed to the rigidity of multidentate chelating TMSPS33−
ligand. Further studies seek to characterize the intermediate
(
TMSPS3))2]−, expected m/z for C54H72P2S6Si6Mn2 = 1252.1, found
m/z = 1252.2.
G
DOI: 10.1021/acs.inorgchem.7b01513
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Inorganic Chemistry
Article
Preparation of [PPN][MnII(TMSPS3)(DABCO)] (2). A THF/
CH3CN solution (3:1 v/v, 20 mL) of 1 (0.466 g, 0.20 mmol) is
added to a THF solution of DABCO (20 mL, 1 M) by syringe under
N2. The reaction mixture is stirred for 10 min at ambient temperature.
The resulting purple solution is reduced to 10 mL under vacuum, and
a diethyl ether solution of DABCO (30 mL, 0.2 M) is added to
precipitate the purple solid [PPN][MnII(TMSPS3)(DABCO)] (2)
(0.460 g, 90%). Crystals of 2 suitable for X-ray crystallography are
grown by slowly adding the diethyl ether solution of DABCO (5 mL, 1
M) to layer above the CH3CN solution of 2 (2 mL, 0.05 M) at −20
°C under N2 for 1 week. UV−vis (CH3CN): λmax (ε, M−1 cm−1) = 370
(2450, sh), 535 nm (540). Magnetic susceptibility (solid state, 300 K):
5.71 μB. EPR spectrum (CH3CN glass): g⊥ = 5.21 and g∥ = 1.95. Peaks
of m/z for 2 ([Mn(TMSPS3)(DABCO)]−, expected m/z for
C33H48PS3Si3Mn = 738.1) are not able to be detected by ESI-MS,
presumably because of oxygenation of 2 with air during injection of
sample into the instrument (Figure S17).
Equilibrium Constant Measurement. In a glovebox (N2
atmosphere), solids of 1 (0.029 g, 0.013 mmol) are mixed with excess
amounts of DABCO (0.035 g, 0.32 mmol) in 25 mL of CH3CN. The
values for [1]0 and [DABCO]0 are 0.50 and 12.5 mM, respectively,
where [1]0 and [DABCO]0 are initial concentrations for 1 and
DABCO. Other sets of concentrations for [1]0 and [DABCO]0 (0.67
and 13.4, or 0.60 and 13.8 mM, respectively) are also prepared for
equilibrium constant measurement. The mixture is then loaded into a
4 mL UV cell. The equilibrium concentration of 2 ([2]) at 25 °C can
be determined from the absorption band at 535 nm (ε = 540) where
the ε values for 1 and DABCO are minor contributors. According to
eq 1, the equilibrium constant (Keq = 9(1), the mean value is obtained
from three measurements) is expressed as eq 3,
and diethyl ether (30 mL) is added to precipitate the dark-green solid
[PPN]2[(MnIII(TMSPS3))2(μ-O)] (4) (0.220 g, 70%).
Method C: Reaction of 2 with Iodosylbenzene (PhIO). A
suspended CH3CN solution (10 mL) of PhIO (0.035 g, 0.16 mmol)
is added to a THF/CH3CN solution (1:1 v/v, 30 mL) containing 2
(0.383 g, 0.3 mmol) and DABCO (1.68 g, 15 mmol) by syringe under
N2. The reaction mixture is stirred for 60 min at ambient temperature
under N2. Analysis of the dark-green solution by UV−vis spectroscopy
reveals the formation of 4. Diethyl ether is added to precipitate the
dark-green solid, 4 (0.450 g, 96%).
Reaction of 1 with Dioxygen in the Solid State. Orange-red
microcrystals of 1 (0.055 g, 0.020 mmol) are placed in a vial and then
exposed to air or dry O2 for 2 h. During this period, a color change of
microcrystals of 1 is observed from orange-red to yellow-brown. IR
(solid, cm−1): 3060(w), 2950(w), 2890(w), 1588(w), 1554(w),
1532(w), 1482(w), 1438(m), 1350(m), 1238(m), 1192(w),
1114(m), 1044(w), 998(w), 848(s), 830(s), 799(w), 781(w),
750(m), 722(s), 690(s). The UV−vis spectrum of the yellow-brown
species (THF) is featureless above 500 nm. Characterization of this
species was unsuccessful.
Reaction of 1 with Dioxygen in Solution. Oxygen gas (excess)
is purged through a CH3CN (25 mL) solution of 1 (0.130 g, 0.050
mmol) at ambient temperature for 30 min. A change of color from
orange-red to dark-green is observed. Calculations from UV−vis
spectral deconvolution reveal the formation of 3 (24% yield based on ε
at 550 nm) and 4 (50% yield based on ε at 670 nm), respectively.
When excess amounts of O2 are slowly added to layer above the
mixture containing 1 (0.130 g, 0.050 mmol) at ambient temperature
for 30 min, the color of solution changes from orange-red to green.
Analysis of UV−vis spectra obtained that the yields of 3 and 4 are 12%
and 68%, respectively.
Reaction of 2 with Dioxygen in the Solid State. Purple
microcrystals of 2 (0.064 g, 0.050 mmol) are loaded into a vial and
then exposed to air or excess amounts of dry 16O2 or 18O2 for 2 h.
During this period, a color change of microcrystals of 2 is observed
from purple to dark-purple. The reaction mixture is then kept under
vacuum to remove the remaining 16O2 or 18O2 and is sent to a
glovebox (O2 < 0.5 ppm, H2O < 0.5 ppm). A weak peak at 903 cm−1
(νOO) observed by FTIR (KBr, 861 cm−1 for using 18O2) and three
absorption bands at 490, 550, and 755 nm (dissolved in CH3CN under
N2 in the glovebox) in the UV−vis spectroscopy confirm the
formation of 3 (95% yield based on ε at 550 nm). In comparison,
microcrystals of 2 are dissolved in CH3CN under N2 in the golvebox.
None of the three absorption bands at 490, 550, and 755 nm are
observed by UV−vis spectroscopy.
[2]2
Keq
=
[2]
2
[1]0 −
(
([DABCO]0 − [2])2
)
(3)
The temperature dependence of Keq (25, 15, 5, −5, −15 and −25
°C) for the same UV cell is recorded on an Agilent 8454
spectrophotometer equipped with a UNICOKU liquid N2 cryostat.
The van’t Hoff equation is used to calculate ΔH° and ΔS°. The
average value for ΔH° is −16(1) kJ mol−1 (−16, −16, and −17) and
for ΔS° is −37(2) J K−1 mol−1 (−39, −36, and −35). In comparison,
the changes of UV−vis spectra of 1 (0.50 mM) without addition of
DABCO and 1 (0.50 mM) with excess amounts of DABCO (100
equiv) are also examined in the temperature range from 25 to −25 °C,
respectively. The intensities at 535 nm of individual spectra of 1 and 2
(suggesting 100% conversion from 1 with excess amounts of DABCO)
show minor temperature dependence in the temperature range from
25 to −25 °C (Figure S18).
Reaction of 2 with Dioxygen in Solution. Oxygen gas (excess)
is purged through a CH3CN (25 mL) solution containing 2 (0.064 g,
0.050 mmol) and DABCO (0.28 g, 2.5 mmol) at ambient temperature
for 10 min. A change of color from purple to red-purple is observed.
Calculations from UV−vis spectral deconvolution reveal the formation
of 3 (63% yield based on ε at 550 nm) and 4 (8% yield based on ε at
670 nm), respectively. When excess amounts of O2 are slowly added to
layer above the mixture containing 2 (0.064 g, 0.050 mmol) and
DABCO (0.28 g, 2.5 mmol) at ambient temperature for 30 min, the
color of solution changes from purple to brown. Analysis of UV−vis
spectra obtained that the yields of 3 and 4 are 37% and 25%,
respectively.
Preparation of [PPN]2[(MnIII(TMSPS3))2(μ-O)] (4). Method A:
Reaction of 2 with [PPN][MnIV(O2)(TMSPS3)] (3).55 A CH3CN solution
(10 mL) of 3 (0.120 g, 0.10 mmol) is added to a THF/CH3CN
solution (1:1 v/v, 30 mL) containing 2 (0.383 g, 0.30 mmol) and
DABCO (1.680 g, 15 mmol) by syringe under N2. The reaction
mixture is stirred for 30 min at ambient temperature. Analysis of the
dark-green solution by UV−vis spectroscopy reveals the formation of
4. Diethyl ether is added to precipitate the dark-green solid,
[PPN]2[(MnIII(TMSPS3))2(μ-O)] (4; 0.446 g, 95%). Diffusion of
diethyl ether into a CH3CN solution of 4 at −20 °C leads to dark-
green crystals suitable for X-ray crystallography. UV−vis (CH3CN):
λmax (ε, M−1 cm−1) = 450 (5410), 670 nm (3760). Magnetic
susceptibility (solid state, 100−300 K, antiferromagnetically coupled):
calcd for g = 2.01(3), 2J = −152(3) cm−1. ESI-MS: [(Mn-
ASSOCIATED CONTENT
■
S
* Supporting Information
(
TMSPS3))2(μ-O)]−, expected m/z for C54H72O1P2S6Si6Mn2
=
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01513.
1268.1, found m/z = 1268.2. Anal. Calcd for C126H132N2OP6S6Si6Mn2:
C, 64.48; H, 5.67; N, 1.19. Found: C, 64.30; H, 5.79; N, 1.37.
Method B: Reaction of 1 with [PPN][MnIV(O2)(TMSPS3)] (3).55
A
CH3CN solution (5 mL) of 3 (0.08 g, 0.067 mmol) is added to a
CH3CN solution (10 mL) of 1 (0.233 g, 0.10 mmol) by syringe under
N2. The reaction mixture is stirred for 30 min at ambient temperature.
The resulting dark-green solution is reduced to 5 mL under vacuum,
UV−vis, FTIR, ESI-MS, EPR, SQUID, and powder X-ray
diffraction data, ab initio calculations, and crystallo-
graphic parameters (PDF)
H
DOI: 10.1021/acs.inorgchem.7b01513
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(9) Shook, R. L.; Borovik, A. S. Role of the Secondary Coordination
Sphere in Metal-Mediated Dioxygen Activation. Inorg. Chem. 2010, 49,
3646−3660.
(10) Shook, R. L.; Peterson, S.; Greaves, J.; Moore, C.; Rheingold, A.
L.; Borovik, A. S. Catalytic Reduction of Dioxygen to Water with a
Monomeric Manganese Complex at Room Temperature. J. Am. Chem.
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(11) Coggins, M. K.; Kovacs, J. A. Structural and Spectroscopic
Characterization of Metastable Thiolate-Ligated Manganese(III)
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(12) Coggins, M. K.; Toledo, S.; Shaffer, E.; Kaminsky, W.; Shearer,
J.; Kovacs, J. A. Characterization and Dioxygen Reactivity of a New
Series of Coordinatively Unsaturated Thiolate-Ligated Manganese(II)
Complexes. Inorg. Chem. 2012, 51, 6633−6644.
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Correlation Between Structural, Spectroscopic, and Reactivity Proper-
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(III)−Alkylperoxo Complexes. J. Am. Chem. Soc. 2013, 135, 4260−
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Accession Codes
CCDC 1556237−1556239 and 1563888 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: cmlee@nttu.edu.tw.
*E-mail: mhchiang@chem.sinica.edu.tw.
*E-mail: Scott.Bohle@mcgill.ca.
ORCID
Chien-Ming Lee: 0000-0001-8529-4279
Ming-Hsi Chiang: 0000-0002-7632-9369
D. Scott Bohle: 0000-0001-5833-5696
(14) Coggins, M. K.; Sun, X.; Kwak, Y.; Solomon, E. I.; Rybak-
Akimova, E.; Kovacs, J. A. Characterization of Metastable
Intermediates Formed in the Reaction between a Mn(II) Complex
and Dioxygen, Including a Crystallographic Structure of a Binuclear
Mn(III)−Peroxo Species. J. Am. Chem. Soc. 2013, 135, 5631−5640.
(15) Ghachtouli, S. E.; Ching, H. Y. V.; Lassalle-Kaiser, B.; Guillot,
R.; Leto, D. F.; Chattopadhyay, S.; Jackson, T. A.; Dorlet, P.;
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́ ̀
Anxolabeher
e-Mallart, E. Electrochemical formation of MnIII-peroxo
C.-M.L. thanks Dr. Lai-Chin Wu (National Synchrotron
Radiation Research Center, Taiwan) for collection of powder
X-ray diffraction data and is thankful for the support from the
Ministry of Science and Technology of Taiwan (Grant 105-
2113-M-143-001).
complexes supported by pentadentate amino pyridine and imidazole
ligands. Chem. Commun. 2013, 49, 5696−5698.
(16) Kovacs, J. A. Tuning the Relative Stability and Reactivity of
Manganese Dioxygen and Peroxo Intermediates via Systematic Ligand
Modification. Acc. Chem. Res. 2015, 48, 2744−2753.
(17) Rees, J. A.; Martin-Diaconescu, V.; Kovacs, J. A.; DeBeer, S. X-
ray Absorption and Emission Study of Dioxygen Activation by a Small-
Molecule Manganese Complex. Inorg. Chem. 2015, 54, 6410−6422.
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