Epoxidation of Cyclooctene Using Water as the Oxygen Atom Source at Manganese Oxide Electrocatalysts

Article abstract of DOI:10.1021/jacs.9b02345

Epoxides are useful intermediates for the manufacture of a diverse set of chemical products. Current routes of olefin epoxidation either involve hazardous reagents or generate stoichiometric side products, leading to challenges in separation and significant waste streams. Here, we demonstrate a sustainable and safe route to epoxidize olefin substrates using water as the oxygen atom source at room temperature and ambient pressure. Manganese oxide nanoparticles (NPs) are shown to catalyze cyclooctene epoxidation with Faradaic efficiencies above 30%. Isotopic studies and detailed product analysis reveal an overall reaction in which water and cyclooctene are converted to cyclooctene oxide and hydrogen. Electrokinetic studies provide insights into the mechanism of olefin epoxidation, including an approximate first-order dependence on the substrate and water and a rate-determining step which involves the first electron transfer. We demonstrate that this new route can also achieve a cyclooctene conversion of ～50% over 4 h.

Full text of DOI:10.1021/jacs.9b02345

Article
pubs.acs.org/JACS
Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Epoxidation of Cyclooctene Using Water as the Oxygen Atom
Source at Manganese Oxide Electrocatalysts
Kyoungsuk Jin, Joseph H. Maalouf, Nikifar Lazouski, Nathan Corbin, Dengtao Yang,
and Karthish Manthiram*
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
S
* Supporting Information
ABSTRACT: Epoxides are useful intermediates for the manufacture of a
diverse set of chemical products. Current routes of olefin epoxidation either
involve hazardous reagents or generate stoichiometric side products, leading
to challenges in separation and significant waste streams. Here, we
demonstrate a sustainable and safe route to epoxidize olefin substrates
using water as the oxygen atom source at room temperature and ambient
pressure. Manganese oxide nanoparticles (NPs) are shown to catalyze
cyclooctene epoxidation with Faradaic efficiencies above 30%. Isotopic
studies and detailed product analysis reveal an overall reaction in which water
and cyclooctene are converted to cyclooctene oxide and hydrogen.
Electrokinetic studies provide insights into the mechanism of olefin
epoxidation, including an approximate first-order dependence on the substrate
and water and a rate-determining step which involves the first electron
transfer. We demonstrate that this new route can also achieve a cyclooctene
conversion of ∼50% over 4 h.
in water and acetonitrile mixtures to catalyze electrochemical
epoxidation of olefin substrates.20−22Hydrolysis of bromine in
water generates HOBr, which transfers oxygen into olefin
substrates. In addition, photochemical epoxidation has been
studied using various transition-metal-based complexes with
water as oxygen source.23−27For example, visible light
irradiation with chemical oxidants such as K2PtCl6 can activate
a ruthenium(II) porphyrin to make a RuO species from
water, which can transfer oxygen into an olefin substrate to
make an epoxide. Similarly, a combination of a photosensitizer,
[RuII(bpy)3]2+ (bpy: 2,2′-bipyridine), and a one-electron
oxidant, [CoIII(NH3)5Cl]2+, has been utilized to produce
metal−oxo species, which can catalyze olefin epoxidation.26
[(bTAML)FeIII-OH (bTAML = biuret-modified tetraamido
macrocyclic ligand),26 [(R,R-BQCN)MnII]2+ (R,R-BQCN =
N,N′-dimethyl-N,N-bis(8-quinolyl)cyclohexanediamine),27
and [Ru (TMP)(CO)] (TMP = tetramesitylporphyrin)
catalysts23,25 have shown high selectivity and yield for
photochemical epoxidation. Although these catalysts exhibit
high selectivity and yield, several limitations still remain: (i)
required operating temperature (∼80−100 °C), (ii) difficulty
of separating homogeneous catalysts following the reaction,
(iii) required additional reagents such as chemical oxidants and
photosensitizer, and (iv) risk of explosion due to the
combination of oxidizing agents (oxygen and hydrogen
peroxide) and fuels (flammable solvents and organics).28,29
INTRODUCTION
■
The direct transfer of an oxygen atom into a target substrate is
a fundamental reaction in organic chemistry. Over several
decades, oxygen-atom transfer reactions have been investigated
to make diverse chemicals,1−3 including epoxides. Epoxides
are versatile intermediates for the manufacture of many
chemical products including surfactants,4 epoxy resins,5 and
pharmaceuticals.6 These epoxides are often prepared by
oxidation of olefins. Ethylene is among a small number
of olefin substrates that can be oxidized to the corresponding
epoxide using molecular oxygen through heterogeneous,
thermochemical routes; in the case of ethylene, the reaction
is conducted at 270−290 °C and 20 bar with Ag-based
catalysts.7,8 Most alkene epoxidation reactions employ
peroxide-based oxidants, such as tert-butyl hydroperoxide
(TBHP) or m-chloroperoxybenzoic acid (mCPBA), or are
conducted through the chlorohydrin process. Both of these
routes involve difficult to handle reagents and generate
undesirable stoichiometric byproducts.9,10
To avoid generation of side products, some processes use
catalysts that generate hydrogen peroxide in situ as the
oxidant.11,12 Hydrogen peroxide is produced in situ by either
reducing oxygen or oxidizing water. In either case, this in situ
approach to hydrogen peroxide generation has been proposed
in both a chemical and an electrochemical fashion. Epoxidation
catalysts explored in this context include bioinspired
homogeneous complexes,2,13−15 transition-metal-based poly-
oxometalates (POM),16−18metal clusters,19 and nanopar-
ticles.12 Sodium bromide has also been studied as an additive
Received: March 2, 2019
© XXXX American Chemical Society
A
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NPs were transformed into the Mn3O4 phase, as confirmed by powder
X-ray diffraction (PXRD) measurement (Figure S4). Scanning
electron microscope (SEM) analysis confirmed that the Mn3O4
nanoparticles were deposited on the carbon paper electrode (Figure
S5).
In this regard, we propose that water would be attractive as a
sustainable, abundant, and safe oxygen atom source for
electrochemical epoxidation reactions, especially if a hydrogen
peroxide intermediate can be avoided (Scheme 1). Although
Electrochemical experiments were conducted using a one-compart-
ment electrochemical cell. Acetonitrile with 0.1 M tetrabutyl-
ammonium tetrafluoroborate (TBABF4) was used as the solvent
with varying concentrations of cis-cyclooctene and water. A platinum
foil and manganese oxide-loaded carbon paper were used as the
counter and working electrodes, respectively. A Ag/AgCl electrode
(Innovative Instruments) was used as the reference, and aluminum
foil was used as the current collector. All potentials were 85% IR
compensated using electrochemical impedance spectroscopy (EIS)
techniques and were calibrated by measuring the redox potentials of 5
mM ferrocene/ferrocenium (Figure S7).
Scheme 1. Electrochemical Epoxidation Using Water as the
Oxygen Source
olefin substrates are normally inert to water, we demonstrate in
this study that the equilibrium can be shifted toward epoxide
through the application of an anodic potential in an
electrochemical reactor at ambient conditions, allowing for
catalytic epoxidation of olefins with water as the sole oxygen
atom source. Among the many candidate catalysts that could
be explored for this new reaction, we were interested in
manganese oxide nanoparticles. Previously, manganese oxide
nanoparticles have been investigated as efficient water
oxidation catalysts. According to recent studies, reactive
high-valent Mn(IV)O intermediate species are generated
during water oxidation catalysis,30 which we hypothesized may
act as an oxygen atom donor to the target olefin substrate.
RESULTS AND DISCUSSION
■
Cyclic voltammetry (CV) analysis was conducted to
investigate the effect of water, cyclooctene, and manganese
oxide NPs on the epoxidation reaction (Figure 1B). The
distinct redox features of manganese oxide NPs appeared at
approximately 0.7 V vs Fc/Fc+ with 5 M H2O and 200 mM
cyclooctene. The redox behavior only appeared in the presence
of water and manganese oxide catalysts, which indicated that
manganese redox originates from the added water. According
to previous electrochemical studies,30 the observed redox peaks
may correspond to the Mn(III)/Mn(IV) redox couple (Figure
S8).
EXPERIMENTAL SECTION
■
Monodisperse manganese oxide nanoparticles (NPs) were prepared
using a hot injection method (Figure 1A).30 A ligand exchange
procedure was performed on the NPs to replace hydrophobic myristic
acid ligands on the manganese oxide NPs with NOBF4 ligands.31
Manganese oxide NPs dispersed in ethanol were then drop-cast onto
hydrophilic carbon paper and subsequently annealed in a muffle
furnace at 400 °C for 5 h (see the Supporting Information for a
detailed procedure). During the annealing process, synthesized MnO
To confirm the identity of the products, we performed
chronoamperometry at various potentials by passing 20 C of
charge, which is equivalent to a maximum conversion of ∼13%
of the substrate (Figure 1C). All the products were collected
and analyzed by nuclear magnetic resonance (NMR) and
quantified using gas chromatograph−mass spectrometry (GC-
MS) (Figure S9; see the Supporting Information for full
details). We were able to detect cyclooctene oxide (epoxide) as
the major product starting from 0.8 V vs Fc/Fc+, which is well
matched with the Mn redox features. The only detectable side
product was cyclooctanone (ketone). Interestingly, at lower
potentials, we only detected the epoxide without the formation
of any ketone, while at higher potentials, both products were
detected. The product ratio of epoxide and ketone at 1.45 V vs
Fc/Fc+ was approximately 3.91:1. In the absence of Mn3O4 NP
catalysts, only about 8% of Faradaic efficiency toward epoxide
was obtained at 1.45 V vs Fc/Fc+, which corresponds to 0.34
mA/cm2 of iepoxide (Figure S10), whereas ∼30% of FE with 2.5
mA/cm2 was obtained in the presence of Mn3O4 NP with 5 M
H2O and 200 mM cyclooctene (Figure S11).
Having water serve as the only oxygen atom source for the
epoxidation reaction is crucial. More detailed insights into the
nature of the epoxide/ketone formation step are provided from
measurements of the isotopic distributions of epoxide/ketone
product obtained from the electrolysis with H218O-enriched
electrolyte. We conducted GC-MS of synthesized epoxide
(Figure 1D). The prominent ion peaks at a mass-to-charge
ratio (m/z) of 125 and 126 were shifted to 127 and 128,
respectively, when the electrolysis was conducted with a H218O
oxygen source. We also excluded the involvement of free
hydrogen peroxide in the epoxidation reaction by assay tests.
We were not able to detect any hydrogen peroxide species
during the anodic reaction with or without cyclooctene
substrate (Figure S12). Thus, the spectroscopic data clearly
Figure 1. Mn3O4 nanoparticles for cyclooctene epoxidation. (A)
TEM image of as-synthesized 10 nm sized manganese oxide
nanoparticles and (B) cyclic voltammetry curves of Mn3O4 nano-
particles varying substrate and water condition (scan rate: 50 mV/s; 5
M water and 200 mM cyclooctene were used). (C) Faradaic efficiency
for epoxide at various potentials and (D) GC-MS spectrum of the
epoxide product generated from the epoxidation reaction by Mn3O4
NPs. Inset figures show the isotopic distribution patterns obtained
from H216O (left) and H218O (right) (see Figure S6 for identification
of the fragments).
B
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indicate the oxygen in cyclooctene oxide comes from the
added water without involving a soluble peroxide intermediate.
Because water and cyclooctene are the species that are being
oxidized into epoxide or ketone products, we sought to
understand the impact of concentration of those species on the
Faradaic efficiency toward epoxidation. As the concentration of
either cyclooctene or water increased, the total current density
at 1.45 V vs Fc/Fc+ remained unchanged (Figure S13), which
suggests the current is limited by a competition for the same
manganese active sites. In terms of selectivity, the FEepoxide
increased linearly with the cyclooctene concentration (Figure
2A). The higher cyclooctene concentration likely enables it to
ment allows for theinterrogation of the reaction order of
reactant species.32,33
The cyclooctene order dependence was obtained by plotting
the partial current density for epoxide iepoxide versus the
concentration of cyclooctene with 5 M H2O (Figure 3A).
While no clear dependence on total current density exists
(Figure S13), a roughly first-order dependence is obtained
from the log(iepoxide) vs log(Ccyclooctene) plot. The water order
dependence of catalytic current at Mn3O4 NPs was then
examined by varying the concentration of water from 0.5 to 15
M at 200 mM cyclooctene. Similar to the substrate
dependence, a roughly first-order dependence on water
concentration was observed from 0.5 to 5 M water, whereas
a negative-order water dependence is observed beyond 5 M
H2O due to the reduced solubility of cyclooctene.
The current−potential (Tafel) behavior of the Mn3O4 NPs
in the region of olefin oxidation was measured from 1.25 to
1.45 V vs Fc/Fc+ in 50 mV increments. The chronoamper-
ometry analysis was conducted at each potential in 5 M H2O
and 200 mM cyclooctene condition until total passed charge
reached 20 C. The Tafel slope of the Mn3O4 NPs is 150 12
mV/dec (Figure 3C), which suggests that the rate-determining
step (RDS) contains an electron transfer and there are no prior
electron transfers that affect the RDS for the overall
epoxidation reaction.34
Figure 2. Variation in the Faradaic efficiency toward cyclooctene
oxide as a function of (A) cyclooctene (with 5 M H2O) and (B) water
(with 200 mM cyclooctene) concentrations at 1.45 V versus Fc/Fc+.
The FE increased monotonically as cyclooctene concentration
increased while the FE slightly decreased when the water
concentration exceeded 10 M. Each error bar denotes the standard
deviation of data from three experiments.
Taken together, the electrokinetic study and isotopic
labeling experiments lead us to suggest the following
electrochemical rate law:
i
EF
2.54RT
y
iepoxide = 2Fk0θ[cyclooctene]0.70[water]0.77 exp
j
j
j
z
z
z
k
{
compete better for oxygen-atom intermediates at Mn active
sites. On the other hand, FEepoxide initially increased with the
water concentration, reaching a maximum FEepoxide at 10 M
H2O and then monotonically decreased when the water
concentration was over 10 M (Figure 2B). This can be
rationalized by the fact that at water concentrations where the
solubility of cyclooctene drops below 200 mM (>10 M H2O)
the electrolyte becomes slightly turbid, and the concentration
of cyclooctene is reduced, resulting in attenuated Faradaic
efficiency toward epoxide.
where θ is coverage of surface Mn active sites, k0 is a potential-
independent rate constant, F is Faraday’s constant, T is the
absolute temperature, and R is the ideal gas constant. On the
basis of the equation, we can propose an electrochemical
epoxidation reaction mechanism (Scheme 2 and section E in
Scheme 2. Proposed Mechanism for Electrochemical
Epoxidation by Manganese Oxide Nanoparticles
Electrokinetic measurements were conducted to understand
the electrochemical epoxidation mechanism. The dependence
of the partial current density on the concentration of
cyclooctene and water was ascertained from chronoamperom-
etry measurements at 1.45 V vs Fc/Fc+ (see the Supporting
Information for full details). Chronoamperometry measure-
Figure 3. Electrokinetic studies. (A) Cyclooctene concentration (at 5 M H2O) and (B) water concentration (at 200 mM cyclooctene)
dependences of epoxide partial current at 1.45 V vs Fc/Fc+. (C) Tafel plot for cyclooctene oxide formation with 5 M H2O and 200 mM
cyclooctene. Each error bar denotes the standard deviation of data from three experiments.
C
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the Supporting Information). We hypothesize a Mn(IV)O
species as the resting state, which was reported in previous
studies on manganese oxide catalysts for water oxidation.30,35
In addition, Mn(IV)O has also been regarded as the resting
state for homogeneous epoxidation reactions.36,37 Addition of
cyclooctene to the Mn(IV)O will make cyclooctene oxide,
leaving Mn(II)-vacant sites. We consider a reversible oxygen
atom transfer step that exists as a pre-equilibrium step, which
was previously observed in other oxygen atom transfer
reactions.38,39 To probe the nature of the pre-equilibrium
step, we added 1,2-epoxyoctane to the electrolyte during an
electrochemical epoxidation reaction of cyclooctene. Gener-
ation of 1-octene was confirmed by GC-MS analysis (Figure
S14), demonstrating the existence of reversible oxo-transfer
steps during the epoxidation reaction. While the quantitative
order dependence on added product is of smaller magnitude
than expected (∼−0.3), this may be due to further oxidation of
the added product. We found that the H/D kinetic isotope
effect (KIE) value was 1.54, which does not provide evidence
for the involement of a proton in the rate-determining step
(Figure S15).
remaining FE is largely attributable to ketone formation
(∼7.7%) as well as solvent oxidation. To fully understand the
overall reaction in the electrochemical cell, we checked the
products of the cathode using gas chromatography and
confirmed that only hydrogen gas was produced with 94
5% Faradaic efficiency (Figure 4B). Taken together with the
data of the product analysis, isotopic labeling experiments, and
electrokinetic studies, the overall electrochemical epoxidation
reaction is proposed to involve the reaction of cyclooctene and
water to generate cyclooctene oxide and hydrogen gas (Figure
4C). Hence, compared to a conventional water electrolyzer
which produces valuable hydrogen and vents oxygen gas, we
can make use of the anodically produced oxygen atoms to
conduct an epoxidation reaction.
Lastly, we have attempted to apply our method to other
olefin substrates. Investigation of a wider range of substrates is
imperative to show the broader applicability of our concept.
Hence, a series of linear, cyclic, and other aliphatic substrates
have been examined (Scheme 3). The concentrations of water
Scheme 3. Epoxidation of Other Olefin Substrates
As shown in Scheme 2, nucleophilic attack of water to vacant
Mn(II) sites is proposed as the rate-determining step,
accompanied by a one-electron transfer, resulting in the
formation of Mn(III)−OH2. Indeed, for water oxidation
catalysis by manganese oxide, one-electron oxidation of Mn(II)
to Mn(III)−OH2 has been considered as the rate-determining
step.40−42 Strong Jahn−Teller distortion increases the
instability of Mn(III) species, which leads to high energy
barriers.41,43 We believe a similar phenomenon occurs for
epoxidation reactions as well. This mechanism has a first-order
dependence on cyclooctene and water concentrations and a
theoretical 120 mV/dec Tafel slope, consistent with our
experimental data. There are additional proposed mechanisms
which may also be consistent with the experimental data
(Figure S18 and see the Supporting Information section E).
Long-term electrolysis was conducted to demonstrate
sustainable chemical production. Epoxide products were
analyzed at 25, 50, 75, and 100 C of passed charge (Figure
4A and Figure S16). Epoxide production was confirmed over a
4 h electrolysis with ∼50% total conversion. The drop in FE
during electrolysis is due to substrate depletion, which is
consistent with our data showing the dependence of FE on
cyclooctene concentration (Figure 2A). We believe that the
and substrates were varied depending on the solubility of
substrates in the water/acetonitrile mixture (Tables S1 and
S3). We were able to obtain >50% selectivity toward epoxide
from most of the olefin substrates. Detailed reaction conditions
and results are summarized in the Supporting Information
section F. We found that selectivity toward epoxide decreased
as chain length of linear aliphatic olefin substrates increased.
For instance, selectivity among observed products for 1-hexene
epoxidation was 92.6%, while 25.4% selectivity was obtained
using 1-dodecene (Table S2). Ketone and aldehyde were
generated as side products (Figure S21). On the other hand,
more selective epoxidation was achieved as ring size increased.
Ring contraction reaction occurred when the ring size was
smaller than n = 8 (Figure S23). For instance, cyclopentyl
aldehyde and cyclohexanone were the major products for
cyclohexene oxidation reaction. Cyclic alkene substrates of
smaller ring size (n < 8) have higher strain energy,44 which
could cause them to preferentially go through ring contraction
reactions. Only 8.0% selectivity was observed for cyclohexene,
whereas 72.1% selectivity toward epoxide was achieved from
cyclooctene oxidation. We believe higher Faradaic efficiencies
and yields could be obtained through further engineering,
which we are undertaking in future work.
CONCLUSIONS
■
In summary, we have developed a new electrochemical method
to epoxidize olefin substrates at room temperature and
ambient pressure using water as the sole oxygen atom source
and monodisperse manganese oxide nanoparticles as the
catalyst. From electrokinetic studies, a reaction mechanism
was proposed where epoxide formation is a pre-equilibrium
step to a rate-limiting electron transfer. In addition, >30%
Figure 4. Overall reaction. (A) Chronoamperometry curves and
FEepoxide of Mn3O4 NPs at 1.45 V vs Fc/Fc+ and (B) FE for hydrogen
at the cathode. (C) Complete reaction scheme of electrochemical
cyclooctene epoxidation. Each error bar denotes the standard
deviation of data from three experiments.
D
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(10) Kim, C.; Traylor, T. G.; Perrin, C. L. MCPBA Epoxidation of
Alkenes: Reinvestigation of Correlation between Rate and Ionization
Potential. J. Am. Chem. Soc. 1998, 120 (37), 9513−9516.
(11) Nishihara, H.; Pressprich, K.; Murray, R. W.; Collman, J. P.
Electrochemical Olefin Epoxidation with Manganese Meso-Tetraphe-
nylporphyrin Catalyst and Hydrogen Peroxide Generation at
Polymer-Coated Electrodes. Inorg. Chem. 1990, 29 (5), 1000−1006.
(12) Espinal, L.; Suib, S. L.; Rusling, J. F. Electrochemical Catalysis
of Styrene Epoxidation with Films of MnO2 Nanoparticles and H2O2.
J. Am. Chem. Soc. 2004, 126 (24), 7676−7682.
(13) Basu, P.; Kail, B. W.; Young, C. G. Influence of the Oxygen
Atom Acceptor on the Reaction Coordinate and Mechanism of
Oxygen Atom Transfer from the Dioxo-Mo(VI) Complex,
TpiPrMoO2(OPh), to Tertiary Phosphines. Inorg. Chem. 2010, 49
(11), 4895−4900.
Faradaic efficiency toward epoxidation was achieved at the
anode, while hydrogen was coproduced at the cathode with
>94 5% Faradaic efficiency. We believe that these results will
provide a new pathway to catalyze oxygen atom transfer
reactions electrochemically.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.9b02345.
Experimental methods, additional electrochemical data,
and mechanistic analysis (PDF)
(14) Reddy, P. R.; Holm, R. H.; Caradonna, J. P. Kinetics,
Mechanisms, and Catalysis of Oxygen Atom Transfer Reactions of S-
Oxide and Pyridine N-Oxide Substrates with Molybdenum(IV,VI)
Complexes: Relevance to Molybdoenzymes. J. Am. Chem. Soc. 1988,
110 (7), 2139−2144.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: karthish@mit.edu.
ORCID
Kyoungsuk Jin: 0000-0003-3009-6691
Dengtao Yang: 0000-0002-8315-5467
Karthish Manthiram: 0000-0001-9260-3391
(15) Jin, S.; Makris, T. M.; Bryson, T. A.; Sligar, S. G.; Dawson, J. H.
Epoxidation of Olefins by Hydroperoxo-Ferric Cytochrome P450. J.
Am. Chem. Soc. 2003, 125 (12), 3406−3407.
(16) Hua, L.; Qiao, Y.; Yu, Y.; Zhu, W.; Cao, T.; Shi, Y.; Li, H.;
Feng, B.; Hou, Z. A Ti-Substituted Polyoxometalate as a
Heterogeneous Catalyst for Olefin Epoxidation with Aqueous
Hydrogen Peroxide. New J. Chem. 2011, 35 (9), 1836−1841.
Notes
The authors declare no competing financial interest.
́
(17) Jimenez-Lozano, P.; Skobelev, I. Y.; Kholdeeva, O. A.; Poblet, J.
́
M.; Carbo, J. J. Alkene Epoxidation Catalyzed by Ti-Containing
ACKNOWLEDGMENTS
■
Polyoxometalates: Unprecedented β-Oxygen Transfer Mechanism.
Inorg. Chem. 2016, 55 (12), 6080−6084.
(18) Neumann, R.; Dahan, M. A Ruthenium-Substituted Poly-
oxometalate as an Inorganic Dioxygenase for Activation of Molecular
Oxygen. Nature 1997, 388 (6640), 353−355.
(19) Tian, S.; Fu, Q.; Chen, W.; Feng, Q.; Chen, Z.; Zhang, J.;
Cheong, W.-C.; Yu, R.; Gu, L.; Dong, J.; Chen, C.; Peng, Q.; Draxl,
C.; Wang, D. Carbon Nitride Supported Fe2 Cluster Catalysts with
Superior Performance for Alkene Epoxidation. Nat. Commun. 2018, 9
(1), 2353.
We gratefully acknowledge Kindle Williams for insightful
discussions and experimental assistance. We also thank the
MIT Department of Chemistry Instrumentation Facility
(DCIF) for the use of their NMR spectrometer. Funding for
this research was provided by the Department of Chemical
Engineering at MIT. J.H.M., N.L., and N.C. were supported by
National Science Foundation Graduate Research Fellowships
under Grant 1122374.
(20) Torii, S.; Uneyama, K.; Tanaka, H.; Yamanaka, T.; Yasuda, T.;
Ono, M.; Kohmoto, Y. Efficient Conversion of Olefins into Epoxides,
Bromohydrins, and Dibromides with Sodium Bromide in Water-
Organic Solvent Electrolysis Systems. J. Org. Chem. 1981, 46 (16),
3312−3315.
REFERENCES
■
(1) Yan, M.; Kawamata, Y.; Baran, P. S. Synthetic Organic
Electrochemical Methods since 2000: On the Verge of a Renaissance.
Chem. Rev. 2017, 117 (21), 13230−13319.
(2) Holm, R. H. Metal-Centered Oxygen Atom Transfer Reactions.
Chem. Rev. 1987, 87 (6), 1401−1449.
(21) Torii, S.; Uneyama, K.; Ono, M.; Tazawa, H.; Matsunami, S. A
Regioselective Epoxidation. Tetrahedron Lett. 1979, 20 (48), 4661−
4662.
(3) Xia, Q.-H.; Ge, H.-Q.; Ye, C.-P.; Liu, Z.-M.; Su, K.-X. Advances
in Homogeneous and Heterogeneous Catalytic Asymmetric Epox-
idation. Chem. Rev. 2005, 105 (5), 1603−1662.
(22) Torii, S.; Uneyama, K.; Matsunami, S. Alicyclic Terpenoids
from Cyclocitryl Phenyl Sulfides. 11. Stereoselective Synthesis of
( )-Irones. J. Org. Chem. 1980, 45 (1), 16−20.
(23) Inoue, H.; Takagi, S.; Funyu, S.; Isobe, T.; Tryk, D. A. Highly
Efficient and Selective Epoxidation of Alkenes by Photochemical
Oxygenation Sensitized by a Ruthenium(II) Porphyrin with Water as
Both Electron and Oxygen Donor. J. Am. Chem. Soc. 2003, 125 (19),
5734−5740.
(24) Takagi, S.; Honna, R.; Tatsumi, D.; Shimada, T.; Tsukamoto,
T.; Hoshino, S. Highly Selective Photochemical Epoxidation of
Cyclohexene Sensitized by Ru(II) Porphyrin−Clay Hybrid Catalyst.
Chem. Lett. 2017, 46 (9), 1311−1314.
(25) Ishikawa, A.; Sakaki, S. Theoretical Study of Photoinduced
Epoxidation of Olefins Catalyzed by Ruthenium Porphyrin. J. Phys.
Chem. A 2011, 115 (18), 4774−4785.
(4) Liu, Y.; Deng, K.; Wang, S.; Xiao, M.; Han, D.; Meng, Y. A
Novel Biodegradable Polymeric Surfactant Synthesized from Carbon
Dioxide, Maleic Anhydride and Propylene Epoxide. Polym. Chem.
2015, 6 (11), 2076−2083.
(5) Moon, S. J.; Kang, T. J. Effects of Epoxide and Silicone Polymers
on the Mechanical and Performance Properties of Wool Fabric. Text.
Res. J. 2000, 70 (12), 1063−1069.
(6) Nakajima, H.; Hori, Y.; Terano, H.; Okuhara, M.; Manda, T.;
Matsumoto, S.; Shimomura, K. New Antitumor Substances,
FR901463, FR901464 and FR901465. II. Activities against Exper-
imental Tumors in Mice and Mechanism of Action. J. Antibiot. 1996,
49 (12), 1204−1211.
(7) Nguyen, N. L.; De Gironcoli, S.; Piccinin, S. Ag-Cu Catalysts for
Ethylene Epoxidation: Selectivity and Activity Descriptors. J. Chem.
Phys. 2013, 138 (18), 184707.
(8) Christopher, P.; Linic, S. Engineering Selectivity in Heteroge-
neous Catalysis : Ag Nanowires as Selective Ethylene Epoxidation. J.
Am. Chem. Soc. 2008, 130 (34), 11264−11265.
(9) Dryuk, V. G. The Mechanism of Epoxidation of Olefins by
Peracids. Tetrahedron 1976, 32 (23), 2855−2866.
(26) Chandra, B.; Singh, K. K.; Gupta, S. S. Selective Photocatalytic
Hydroxylation and Epoxidation Reactions by an Iron Complex Using
Water as the Oxygen Source. Chem. Sci. 2017, 8 (11), 7545−7551.
(27) Lee, Y.-M.; Fukuzumi, S.; Nam, W.; Shen, D.; Saracini, C.; Sun,
W. Photocatalytic Asymmetric Epoxidation of Terminal Olefins Using
Water as an Oxygen Source in the Presence of a Mononuclear Non-
E
DOI: 10.1021/jacs.9b02345
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Heme Chiral Manganese Complex. J. Am. Chem. Soc. 2016, 138 (49),
15857−15860.
(28) Astbury, G. R. Safe Scale-up of Oxidation by Hydrogen
Peroxide in Flammable Solvents. Org. Process Res. Dev. 2002, 6 (6),
893−895.
(29) Mackenzie, J. Considerations for the Safe Design of Processes
Using Hydrogen Peroxide and Organics. Plant/Oper. Prog. 1991, 10
(3), 164−170.
(30) Jin, K.; Seo, H.; Hayashi, T.; Balamurugan, M.; Jeong, D.; Go,
Y. K.; Hong, J. S.; Cho, K. H.; Kakizaki, H.; Bonnet-Mercier, N.; Kim,
M. G.; Kim, S. H.; Nakamura, R.; Nam, K. T. Mechanistic
Investigation of Water Oxidation Catalyzed by Uniform, Assembled
MnO Nanoparticles. J. Am. Chem. Soc. 2017, 139 (6), 2277−2285.
(31) Dong, A.; Ye, X.; Chen, J.; Kang, Y.; Gordon, T.; Kikkawa, J.
M.; Murray, C. B. A Generalized Ligand-Exchange Strategy Enabling
Sequential Surface Functionalization of Colloidal Nanocrystals. J. Am.
Chem. Soc. 2011, 133 (4), 998−1006.
(32) Bediako, D. K.; Surendranath, Y.; Nocera, D. G. Mechanistic
Studies of the Oxygen Evolution Reaction Mediated by a Nickel-
Borate Thin Film Electrocatalyst. J. Am. Chem. Soc. 2013, 135 (9),
3662−3674.
(33) Surendranath, Y.; Kanan, M. W.; Nocera, D. G. Mechanistic
Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate
Catalyst at Neutral PH. J. Am. Chem. Soc. 2010, 132 (14), 16501−
16509.
(34) Bard, A. J.; Faulkner, L. R. Electrochemical Methods.
Fundamentals and Applications, 2nd ed.; Harris, D., Swain, E.,
Robey, C., Aiello, E., Eds.; John Wiley & Sons, Inc.: Phoenix, 2001.
́
(35) Zaharieva, I.; Gonzalez-Flores, D.; Asfari, B.; Pasquini, C.;
Mohammadi, M. R.; Klingan, K.; Zizak, I.; Loos, S.; Chernev, P.; Dau,
H. Water Oxidation Catalysis-Role of Redox and Structural Dynamics
in Biological Photosynthesis and Inorganic Manganese Oxides. Energy
Environ. Sci. 2016, 9 (7), 2433−2443.
(36) Kim, S.; Cho, K. B.; Lee, Y. M.; Chen, J.; Fukuzumi, S.; Nam,
W. Factors Controlling the Chemoselectivity in the Oxidation of
Olefins by Nonheme Manganese(IV)-Oxo Complexes. J. Am. Chem.
Soc. 2016, 138 (33), 10654−10663.
(37) Shen, D.; Saracini, C.; Lee, Y. M.; Sun, W.; Fukuzumi, S.; Nam,
W. Photocatalytic Asymmetric Epoxidation of Terminal Olefins Using
Water as an Oxygen Source in the Presence of a Mononuclear Non-
Heme Chiral Manganese Complex. J. Am. Chem. Soc. 2016, 138 (49),
15857−15860.
(38) Jin, N.; Bourassa, J. L.; Tizio, S. C.; Groves, J. T. Rapid,
Reversible Oxygen Atom Transfer between an Oxomanganese(v)
Porphyrin and Bromide: A Haloperoxidase Mimic with Enzymatic
Rates. Angew. Chem., Int. Ed. 2000, 39 (21), 3849−3851.
(39) Xiao, J.; Li, X. Gold α-Oxo Carbenoids in Catalysis: Catalytic
Oxygen-Atom Transfer to Alkynes. Angew. Chem., Int. Ed. 2011, 50
(32), 7226−7236.
(40) Takashima, T.; Hashimoto, K.; Nakamura, R. Mechanisms of
pH-Dependent Activity for Water Oxidation to Molecular Oxygen by
MnO2 Electrocatalysts. J. Am. Chem. Soc. 2012, 134 (3), 1519−1527.
(41) Takashima, T.; Hashimoto, K.; Nakamura, R. Inhibition of
Charge Disproportionation of MnO2 Electrocatalysts for Efficient
Water Oxidation under Neutral Conditions. J. Am. Chem. Soc. 2012,
134 (44), 18153−18156.
(42) Nakamura, R.; Hayashi, T.; Takashima, T.; Hashimoto, K.;
Yamaguchi, A.; Inuzuka, R. Regulating Proton-Coupled Electron
Transfer for Efficient Water Splitting by Manganese Oxides at Neutral
PH. Nat. Commun. 2014, 5 (1), 1−6.
(43) Hirai, S.; Yagi, S.; Seno, A.; Fujioka, M.; Ohno, T.; Matsuda, T.
Enhancement of the Oxygen Evolution Reaction in Mn3+-Based
Electrocatalysts: Correlation between Jahn-Teller Distortion and
Catalytic Activity. RSC Adv. 2016, 6 (3), 2019−2023.
(44) Traynham, J. G.; Sehnert, M. F. Ring Size and Reactivity of
Cyclic Olefins: Complexation with Aqueous Silver Ion. J. Am. Chem.
Soc. 1956, 78 (16), 4024−4027.
F
DOI: 10.1021/jacs.9b02345
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX