Selective photocatalytic hydroxylation and epoxidation reactions by an iron complex using water as the oxygen source

Article abstract of DOI:10.1039/c7sc02780j

The iron complex [(bTAML)Fe^III-OH₂]^- (1) selectively catalyses the photocatalytic hydroxylation and epoxidation reactions of alkanes and alkenes, respectively, using water as the oxygen-atom source. Upon the oxidation of unactivated alkanes, which included several substrates including natural products, hydroxylation was observed mostly at the 3° C-H bonds with 3° :2° selectivity up to ～100:1. When alkenes were used as the substrates, epoxides were predominantly formed with high yields. In the presence of H₂¹⁸O, more than 90% of the ¹⁸O-labelled oxygen atoms were incorporated into the hydroxylated and epoxide product indicating that water was the primary oxygen source. Mechanistic studies indicate the formation of an active [{(bTAML)Fe^IV}₂-μ-oxo]^2- (2) dimer from the starting complex 1via PCET. The subsequent disproportionation of 2 upon addition of substrate, leading to the formation of Fe^V(O), renders the high selectivity observed in these reactions.

Full text of DOI:10.1039/c7sc02780j

View Article Online
View Journal
Chemical
Science
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: B. Chandra, K. K.
Singh and S. Sen Gupta, Chem. Sci., 2017, DOI: 10.1039/C7SC02780J.
This is an Accepted Manuscript, which has been through the
Volume
7 Number 1 January 2016 Pages 1–812
Royal Society of Chemistry peer review process and has been
accepted for publication.
Chemical
Science
Accepted Manuscripts are published online shortly after
www.rsc.org/chemicalscience
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2041-6539
EDGE ARTICLE
Francesco Ricci et al.
Electronic control of DNA-based nanoswitches and nanodevices
rsc.li/chemical-science

Please do not adjust margins
Chemical Science
Page 1 of 8
View Article Online
DOI: 10.1039/C7SC02780J
Journal Name
ARTICLE
Selective Photocatalytic Hydroxylation and Epoxidation Reaction
by an Iron Complex Using Water as the Oxygen Source
Bittu Chandra#, Kundan K. Singh# and Sayam Sen Gupta*a
Received 00th January 20xx,
Accepted 00th January 20xx
The iron complex, [(bTAML)FeIII-OH2]- (1), selectively catalyses the photocatalytic hydroxylation and epoxidation reactions
of alkanes and alkenes respectively using water as the oxygen-atom source. Upon oxidation of unactivated alkanes, which
included several substrates including natural products, hydroxylation was observed mostly at the 3° C-H bonds with 3°:2°
selectivity up to ~100:1. When alkenes were used as substrates, epoxides were predominantly formed with high yields. In
presence of H218O, more than 90% of the 18O-labelled oxygen atom was incorporated into the hydroxylated and epoxide
product indicating water to be the primary oxygen source. Mechanistic studies indicate formation of an active
[{(bTAML)FeIV}2-µ-oxo]2- (2) dimer from the starting complex 1 via PCET. The subsequent disproportionation of 2 upon
addition of substrate, leading to formation of FeV(O), renders the high selectivity observed in these reactions.
DOI: 10.1039/x0xx00000x
www.rsc.org/
[Mn(N)(CN)4]2-,10c that have been shown to be active catalysts
for photocatalytic oxygenation reactions where water was
used as the oxygen source. Although ruthenium and
Introduction
Conversion of sunlight to chemical energy has been one of the
grand challenges for chemists in the quest for a sustainable
world.1 The inspiration for such a process comes from
photosynthesis, wherein sunlight is used to accomplish the
energetically uphill water oxidation reaction.2 During
photosynthesis, a high-valent manganese-oxo cluster has been
proposed to be the active intermediate for water oxidation.3
Similarly, high-valent iron-oxo complexes have been shown to
be the active intermediate for heme/non-heme enzymes and
their model complexes which catalyse hydrocarbon oxidation
using O2 as the oxidant.4 Combining these concepts, Inoue et
al. first demonstrated that visible light can be utilized for the
oxidation of organic substrates using water as the oxygen
atom source.5 Gray et al. have also developed a photochemical
method to generate the intermediate “Compound I” and
“Compound II” from peroxidases by using [RuII(bpy)3]2+ (bpy =
2,2′-bipyridine) as a photosensitizer and [CoIII(NH3)5Cl]2+ as a
mild one electron oxidant in aqueous medium.6 Using these
strategies, several photochemical oxygenation systems based
on metal complexes (mostly Ru and Mn) as catalysts have
been evolved. Examples include various Ru-Complexes7,8 and
Mn-Complexes such as Mn-Porphyrin9, [(R,R-BQCN)MnII(OTf)2]
manganese based metal complexes have been explored for
photochemical alcohol, olefin and sulfide oxidation reactions,
they have not been shown to catalyse oxidation of unactivated
C-H bonds.7,8,9,10 The likely reason is that Ru-oxo and Mn-oxo
intermediates, formed during these reactions, do not cleave
unactivated C-H bonds with rates fast enough to function as
catalysts for C-H bond oxidation reactions. In contrast, iron
based metalloenzymes (sMMO,11a,b heme and non-heme
enzymes4,11c,d) and their synthetic models4b,c,e exhibit excellent
reactivity and selectivity towards hydrocarbon oxidation.
However, for synthetic systems, very few examples are known
where cheap and environmentally benign metal like iron has
been used as a catalyst for photochemical oxidation reactions.
Recently, photochemical generation of oxoiron(IV) have been
demonstrated using [FeII(N4Py)]2+ [N4Py
pyridylmethyl)-N-bis(2-pyridyl)methylamine]12
=
N,N-bis(2-
and
[FeII(MePy2tacn)]2+ [MePy2tacn = N-methyl-N,N-bis(2-picolyl)-
1,4,7-triazacyclononane].13 The complex [FeII(MePy2tacn)]2+,
along with [RuII(bpy)3]2+ as a photosensitizer and sodium
persulfate as a sacrificial oxidant under light irradiation has
been shown to catalyse sulfoxidation reaction albeit with low
yields. However, the photochemical hydroxylation of
unactivated C-H bonds using [FeII(MePy2tacn)]2+ complex
described above has not been reported. Mechanistic studies
on iron catalysed hydroxylation reactions have revealed that in
both chemical and biological systems, efficient and selective
hydroxylation of unactivated C-H bonds have been mostly
catalysed by reactive intermediates such as oxoiron(V)
(synthetic systems),14,15,19 the isoelectronic oxoiron(IV) radical
cation (heme enzymes)4a,11c,d and the [(μ-O)2FeIV2] (methane
monooxygenase11a,b). None of these intermediates were
(BQCN
cyclohexanediamine)10a,b
=
N,N‘-dimethyl-N,N‘-bis(8-quinolyl)
and Mn(V)-Nitrido complex,
a.Dr. Sayam Sen Gupta
Department of Chemical Sciences
Indian Institute of Science Education and Research Kolkata
Mohanpur, West Bengal, India-741246
E-mail:sayam.sengupta@iiserkol.ac.in
[#]Both authors contributed equally to this work
†Electronic Supplementary Information (ESI) available: materials, general
instrumentation and additional figures, See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 2 of 8
View Article Online
DOI: 10.1039/C7SC02780J
ARTICLE
Journal Name
formed in the photochemical systems reported till date using
[FeII(N4Py)]2+ and [FeII(MePy2tacn)]2+ complexes which explains
the absence of iron catalysts catalysing photochemical C-H
bond oxidation in the literature.
Results and discussion
We focused our attention to peroxidase mimicking iron(III)
bTAML14
Photocatalytic Oxidation of Alkanes
complex
of
(bTAML
=
biuret-modified
All the photocatalytic hydroxylation reactions were performed
by employing catalyst
(~3-7mol% loading), [RuII(bpy)3]Cl2 and
tetraamidomacrocyclic ligand) synthesized in our laboratory
where the highly electron donating tetraanionic N-donors are
well-known to stabilize high valent iron-oxo species such as
[(bTAML)FeV(O)]- and [(bTAML)FeIV(O)]2- (subsequently
referred to as FeV(O) and FeIV(O) respectively).15 Moreover,
1
[CoIII(NH3)5Cl]Cl2 in acetonitrile-phosphate buffer solution
mixture in presence of light (3W blue LED, 440nm) under
argon atmosphere. Photocatalytic hydroxylation of alkanes
having different unactivated 3o and activated 2o C-H bonds was
attempted under optimized reaction conditions. Adamantane
having twelve 2° and four 3° C-H bonds was used as a
substrate probe to study the regioselectivity using the
photocatalytic system. Upon completion of reaction, 1-
adamantanol was formed in good yields (88%) and the 3°:2°
selectivity for adamantane oxidation was calculated to be
~100:1 (Table 1; Entry 1). In case of cumene, which contains six
1o and one benzylic 3o C-H bonds, 3o hydroxylated product was
formed as the major product (67% yield; Table 1, Entry 2).
Next, cis-1,2-dimethylcyclohexane and cis-decalin were chosen
as substrates to examine the stereoselectivity of this oxidation.
Reaction of cis-1,2-dimethylcyclohexane and cis-decalin
displayed primarily 3o hydroxylated product (99% and 96%
yield respectively) with more than ~97% retention of
configuration under the reaction condition (Table 1; Entry 3,
4). The high stereo-retention observed excluded the possibility
of radical processes since cis-1,2-dimethylcyclohexane and cis-
decalin are known to epimerize to the trans isomer if radical
processes are operational. In cyclohexane derivatives, the
stereochemical orientation of the 3° C-H bonds (axial or
equatorial) determines the regioselective outcome of the
reaction. For catalytic hydroxylation of trans-decalin, the
reaction was comparatively slower with lower yield (60%) of
the oxidized product (Table 1, Entry 5) in contrast to that of
the cis isomer. Oxidation of trans-decalin also exhibits
oxidation at the methylenic C-H bonds unlike its cis congener,
resulting in the formation of both alcohol (99% retention of
configuration) and ketone at a ratio of 3:2. The difference in
reactivity between the cis and trans isomers can be attributed
to the strain release in the transition state for the cis-
isomers.20 In short, the hydroxylated products formed after the
reaction displayed very high regioselectivity of 3o over 2o C-H
bonds (Table 1; Entry 3, 4, 6) where 3o hydroxylated products
were formed predominantly. This result is consistent with
complex 1 in combination with chemical oxidants, catalyses
the oxidation of unactivated alkanes, alkenes and alcohols
selectively.15b,17b,18,19 The high selectivity obtained has been
attributed
[{(bTAML)FeIV}2(µ-O)]2-
reactions. We have also shown that the oxidant [RuIII(bpy)3]3+,
generated either chemically or photochemically, is
competent oxidant to oxidize [(bTAML)FeIII(OH2)]- (
) complex
in solution to the catalytically active [{(bTAML)FeIV}2(µ-O)]2-
dimer ( along
).16 We therefore hypothesized that complex
to
the presence of
oxoiron(V)
and
(
2) as active intermediates in these
a
1
2
1
with [RuII(bpy)3]2+ and [CoIII(NH3)5Cl]2+, can be a competent
system to catalyse the photochemical oxidation of
synthetically challenging reactions such as selective
hydroxylation of unactivated C-H bonds and epoxidation
reactions. Development of such iron-based catalysts would
become transformational in the goal to achieve green methods
for selective oxidation of C-H bonds.
Herein, we report selective photocatalytic alkane
hydroxylation and olefin epoxidation by employing
[Et4N][(bTAML)FeIII(OH2)] (1) as a catalyst, [RuII(bpy)3]Cl2
as a photosensitizer, [CoIII(NH3)5Cl]Cl2 as a mild one
electron acceptor and water as the oxygen atom
source. We also demonstrate that under the reaction
conditions, intermediate 2 was generated and found to
be the active oxidant (Scheme 1). To the best of our
knowledge, this represents the first example for the
use of iron-complex to catalyse photochemical
selective oxidation of unactivated C-H bonds and C=C
bonds using water as O-atom donor.
similar oxidation reported by us using complex
1 and mCPBA
as the oxidant.19 Further the regioselective oxidation of 3o C-H
bonds in natural product derivative of cedrol, cedryl acetate,
was performed. Cedrol is a sesquiterpene alcohol found in
essential oil, having a very rigid structure with five 3o C-H
positions. The substrate was hydroxylated very selectively with
good yield albeit low conversion (Table 1, Entry 6). In order to
find the O-atom source in the product formed, oxidation
reactions of cis-1,2-dimethylcyclohexane and adamantane
were carried out in a mixture of CH3CN and H218O (3:2 v/v). We
observed >90% and >95% incorporation of 18O-labelled oxygen
Scheme 1 Photocatalytic oxygenation of hydrocarbons.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 3 of 8
View Article Online
DOI: 10.1039/C7SC02780J
Journal Name
ARTICLE
atom in 1-adamantanol (Fig. 2D) and (1S,2R or 1R,2S)-1,2-
dimethylcyclohexanol (Fig. S1†) respectively which confirmed
water as the O-atom source. This also precluded the
involvement of O2 based radical pathway during the reaction.
Table 2 Effect of substrate concentration on photocatalytic hydroxylation of 2o C-H
bond by 1 using water as the oxygen source.
Table 1 Photocatalytic hydroxylation of different alkanes by 1 using water as the
oxygen source.
Reaction conditions: 1 (1.0 × 10-4 M), [Ru(bpy)3]2+ (2.0 × 10-3 M), [Co(NH3)5Cl]2+
(2.0 × 10-2 M); acetonitrile-aqueous phosphate buffer (3:2 v/v, 10 mM, pH 10),
photoirradiation with LED (3W, 440 nm), room temperature (27 oC), under argon,
40 mins.
Photocatalytic Oxidation of Alkenes
Epoxidation of various alkenes were also performed under
optimized reaction conditions by employing catalyst
1 (2 mol%
loading) (Fig. S3†). Analysis of the products indicated
predominant formation of alkene oxides in moderate to high
yields (79-84%) and only trace amount of the side-product
aldehyde (~5-7% with respect to epoxide) was observed. At
first, styrene was chosen as the substrate for photocatalytic
epoxidation reaction where styrene oxide was obtained as the
predominant product. Subsequently, different para substituted
styrene derivatives such as 4-chlorostyrene and 4-
methoxystyrene were investigated and their corresponding
epoxides were obtained with yields up to 92% (Table 3; Entry
Reaction conditions: 1 (1.0 × 10-4 M), [Ru(bpy)3]2+ (2.0 × 10-3 M), [Co(NH3)5Cl]2+
(2.0 × 10-2 M) and substrate (3.0 × 10-3 M), acetonitrile-aqueous phosphate buffer
(3:2 v/v, 10 mM, pH 10), photoirradiation with LED (3W, 440 nm), room
temperature (27 oC), under argon, 40 mins. aCatalyst 1 (2.0 × 10-4 M). bYields are 1, 2 & 3). The higher amount of epoxide formation for para-
based on substrate conversion (amount of side products indicated inside the
substituted electron donating group on styrene in comparison
parenthesis are not included); yields and conversions were estimated by GC.
to electron withdrawing group supports the likely involvement
of an electrophilic high-valent iron-oxo intermediate, as has
Finally, the selective oxidation of substrates bearing activated
been reported earlier by us.17b For cis-stilbene, a substrate
methylenic and benzylic C-H bonds were explored. In case of
which contains a sterically constrained double bond, a lower
the substrate ambroxide, oxidation at the α-ethereal C-H bond
conversion of 58% and a moderate yield of 79% (Table 3; Entry
occurred predominantly among numerous other electronically
1
4). The cis/trans product ratio 19:2 was estimated by H-NMR
and sterically accessible secondary and tertiary sites (Table 1;
(Fig. S4†) (Note: additional stereo-scrambling in cis/trans ratio
Entry 7). At lower substrate concentration, over-oxidized
was observed in GC run). The substrate scope was further
ketone was the major product formed (Table 1; Entry 7, 8). The
expanded to include cyclooctene and norbornene (Table 3;
alcohol to ketone product ratio increased with increasing
Entry 5 and 6) where 94% yield of cyclooctene oxide and 92%
substrate concentration (3 mM to 40 mM; Table 2) under the
yield of exo-norbornene oxide indicate selectivity for C=C bond
same reaction condition. Similar results were found when
over C-H bonds. For the epoxidation of alkenes, a maximum
diphenylmethane was employed as substrate (Table 1; Entry
quantum yield of 18.7% for 4-methoxystyrene was observed
8). This formation of ketone was attributed to the over-
(Table S2†).
oxidation of the hydroxylated product, which was first formed
during the hydroxylation reaction (cyclohexanol oxidation has
been shown to be 400 times faster than cyclohexane
oxidation18). The incorporation of ~80% 18O-labelled oxygen
atom in the ketone product of ambroxide (Fig. S2†) also
supports this hypothesis. The quantum yields for the
photocatalytic oxidation of alkanes were determined using a
standard actinometer (potassium ferrioxalate) and a maximum
value of 12.2% was observed in case of cis-decalin
hydroxylation (Table S1†).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 4 of 8
View Article Online
DOI: 10.1039/C7SC02780J
ARTICLE
Journal Name
Table 3 Photocatalytic epoxidation of different alkenes by 1 using water as the oxygen
source.
Fig. 1 UV-vis spectral scan of a photochemical reaction mixture of 1 (1.0 ×10-4 M),
[RuII(bpy)3]2+ (2.0 ×10-5 M) and [CoIII(NH3)5Cl]2+ (6.0 ×10-4 M) in acetonitrile-aqueous
phosphate buffer (3:2) solvent.
Reaction conditions: 1 (1.0 × 10-4 M), [Ru(bpy)3]2+ (2.0 × 10-3 M), [Co(NH3)5Cl]2+
(2.0 × 10-2 M) and substrate (5.0 × 10-3 M), acetonitrile-aqueous phosphate buffer
(3:2 v/v, 10 mM, pH 10), photoirradiation with LED (3W, 440 nm), room
temperature (27 oC), under air, 40 mins.Yields are based on substrate conversion
(the amount of side products are not included); yields and conversions were
estimated by GC.
We have demonstrated earlier that independently synthesized
[RuIII(bpy)3]3+ was competent to oxidize
1
to form the complex
2 16
.
We therefore propose that [RuIII(bpy)3]3+, which is
generated due to one electron transfer from the excited state
of [RuII(bpy)3]2+ to the sacrificial oxidant [CoIII(NH3)5Cl]2+,
oxidizes
1 containing an axial H2O ligand, to generate a
putative [(bTAML)FeIV-OH]- species by one electron and one
proton transfer process (PCET). This proposition is based on
previous electrochemical studies reported by us.15c,d Under
neutral or basic condition (pH 10 in this case), FeIV-OH species
Mechanistic Insight
Since the operation of free radical oxidation was ruled out,
involvement of high-valent iron-oxo intermediate during the
reaction was investigated. Upon irradiation with blue LED light
(λmax = 440 nm) to the mixture of 1
, Ru2+ and Co3+ in 3:2
dimerizes immediately to form complex 2 as shown below.
CH3CN-phosphate buffer solution mixture, a broad absorption
band in the region of 800-1000 nm was observed (Fig. 1; violet
colour spectrum). This new species was assigned as the
previously characterized dimer, [{(bTAML)FeIV}2(µ-O)]2-
which is consistent with the UV-vis spectrum of chemically
synthesized dimer
(Fig. S5†). This intermediate species was
(2
),15b
2
This
is
in
contrast
to
[(N4Py)FeII]2+
and
not observed in the absence of any one of the components
(catalyst, Ru2+, Co3+ or light). Upon addition of substrate
[(MePy2tacn)FeII]2+complexes where the FeIII-OH species is
oxidized by [RuIII(bpy)3]3+ to form the corresponding
FeIV(O).12,13 The reactivity of both the FeIV complexes, i.e. the
(alkenes or alkanes) to this solution,
2
reacted with substrate
(Fig. S6†), which
and regenerated the parental complex
1
FeIV(O) and [(μ-O)FeIV2] dimer (
2) differ. While the high-valent
would restart the catalytic cycle upon light irradiation with
concomitant formation of oxygenated product (alcohol or
epoxide).
[(N4Py)FeIV(O)] and [(Me2Pytacn)FeIV(O)] [Me2Pytacn = 1-(2-
pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane] species
are competent to cleave strong C-H bonds selectively, the low
redox potential of FeIII-OH formed prevents the subsequent
“rebound” process, thus leading to free radical auto-
oxidation.22 In contrast, our investigations on the reactivity of
the [{(bTAML)FeIV}2-µ-oxo]2-
alcohols demonstrate that the dimer exists in equilibrium with
the corresponding FeV(O) and FeIII
). Such a proposal is based
on our previously reported kinetic and mass spectral studies
with 2 17b
Upon addition of substrate, the dimer
disproportionates into FeV(O) and FeIII ), and the FeV(O)
(2) with alkanes, alkenes and
(1
.
(2)
(1
intermediate remains the active oxidant. The primarily
formation of the cis-hydroxylated product (Table 1; Entry 3) for
reactions with cis-1,2-dimethylcyclohexane also supports our
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 5 of 8
View Article Online
DOI: 10.1039/C7SC02780J
Journal Name
ARTICLE
reported mechanism that involves C-H bond abstraction by was explained due to the formation of an excited state via spin
FeV(O) and subsequent formation of hydroxylated product by a change. Such possibility of rate enhancements in the reactivity
“rebound” mechanism.15b H218O labelling experiments with of
2 due to the presence of light clearly exists and is currently
styrene and adamantane results in the formation of more than being investigated.
90% 18O-labelled epoxide and hydroxylated product
respectively which clearly indicates water is the primary
oxygen atom source (Fig. 2).
Scheme 2 Proposed reaction mechanism.
Conclusions
In conclusion, we have demonstrated the first example of an
iron-complex catalysed photocatalytic hydroxylation and
epoxidation reaction with variety of substrates using water as
the oxygen source. The [{(bTAML)FeIV}2(µ-O)]2-
(2) dimer,
produced by oxidative activation of water molecule, remains
the active oxidant and results in hydroxylation or epoxidation
with such high selectivity. 18O-labelling experiments support a
metal based selective and controlled oxygenation of substrates
having C-H and C=C bonds. Although the reactivity of this
photochemical system is lower as compared to the FeIII-
bTAML/NaOCl system and the use of [Co(NH3)5Cl]2+ as the
electron acceptor is not optimal, we believe that conjugating
Fig. 2 GC-MS spectra of products after photochemical reaction with A) styrene in H216O,
B) styrene in H218O,C) adamantane in H216O, D) adamantane in H218O.
Proposed Photocatalytic Reaction Cycle
Finally, on the basis of product analysis, UV-vis spectroscopy,
18O-labelling experiments, mass analysis and previously
reported observations, we propose the following catalytic
cycle for photochemical oxygenation reaction (Scheme 2). In
complex
1 to a light harvesting system can increase its
efficiency many-fold. Such work is being attempted currently
in our laboratory.
water, FeIII-bTAML (
1) upon irradiation with light (3W blue LED,
440nm) in presence of photosensitizer [RuII(bpy)3]2+ and Experimental Section
electron acceptor [CoIII(NH3)5Cl]2+ gets oxidized to
General Procedure for the Photocatalytic Hydroxylation Reactions
[(bTAML)FeIV-OH]- which immediately gets converted into
The photocatalytic oxidation of alkanes were carried out under
argon atmosphere in acetonitrile and phosphate buffer (pH 10,
10 mM) (3:2 v/v) mixed solvent. The reaction solution (1.0 mL)
dimer
2
.
Upon addition of substrate, the dimer
). For hydroxylation
disproportionates to the FeV(O) and FeIII
(
1
reaction, the mechanism likely involves a C-H bond abstraction
followed by a rebound process to generate the corresponding
alcohol. For epoxidation reactions, formation of a radical
intermediate upon electrophilic attack of the FeV(O) onto the
alkene followed by a fast ring closing step is expected.17b
containing catalyst 1
(1.0 × 10-4M) [Ru(bpy)3]Cl2.6H2O (2.0 × 10-
3M), [Co(NH3)5Cl]Cl2 (2.0 × 10-2M) and substrate (3.0 × 10-3 M)
was irradiated with a blue LED light source (3W, 440 nm) and
stirred for 40 mins at room temperature. The temperature was
kept constant by using a water circulating system during the
whole reaction. The final reaction mixture was extracted with
dichloromethane (five times with 2 mL of dichloromethane
each time) and dried over Na2SO4. After concentrating the
reaction solution by purging with nitrogen gas, product was
identified and quantified by GC-MS. Control experiments were
performed at the same condition as mentioned above.
Before concluding, one important point is worth noting.
Irradiation with visible and UV light has been shown to alter
the reactivity of intermediates such as [(corrole)FeIV}2-µ-oxo],
[FeIV(O)(MePy2tacn)]2+ and cofacial bis-porphyrin-diiron(III)-μ-
oxo complexes as has been reported by Newcomb et al.21b
Lloret-Fillol et al.13 and Nocera et al.21a respectively. For FeIV
,
intermediates, light was shown to disproportionate
[(corrole)FeIV}2-µ-oxo]
[(corrole)FeV(O)] hence increasing its reactivity. For the
corresponding [FeIV(O)(MePy2tacn)]2+, the increase in reactivity
to
form
the
corresponding
General Procedure for the Photocatalytic Epoxidation Reactions
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 6 of 8
View Article Online
DOI: 10.1039/C7SC02780J
ARTICLE
Journal Name
2
3
4
(a) B. Loll, J. Kern, W. Saenger, A. Zouni and J. Biesiadka, Nature,
2005, 438, 1040ꢀ1044; (b) J. P. McEvoy and G. W. Brudvig, Chem.
The photocatalytic epoxidation of alkenes were carried out in
acetonitrile and phosphate buffer (pH 10, 10 mM) (3:2 v/v)
mixed solvent. The reaction solution (1.0 mL) containing
Rev., 2006, 106, 4455ꢀ4483; (c) J. Barber, Chem. Soc. Rev., 2009, 38
,
185ꢀ196.
catalyst
1
(1.0 × 10-4 M) [Ru(bpy)3]Cl2.6H2O (2.0 × 10-3 M),
(a) K. N. Ferreira, T. M. Iverson, K. Maghlaoui, J. Barber and S. Iwata,
Science, 2004, 303, 1831ꢀ1838; (b) J. Yano, J. Kern, K. Sauer, M. J.
Latimer, Y. Pushkar, J. Biesiadka, B. Loll, W. Saenger, J. Messinger, A.
Zouni and V. K. Yachandra, Science, 2006, 314, 821ꢀ825.
[Co(NH3)5Cl]Cl2 (2.0 × 10-2 M) and substrate (5.0 × 10-3 M) was
irradiated with a blue LED light source (3W, 440 nm) and
stirred for 40 min at room temperature (27oC). The
temperature was kept constant by using a water circulating
system during the whole reaction. After 40 mins, reaction
mixture was extracted with dichloromethane (five times with 2
mL of dichloromethane each time) and dried over Na2SO4.
After concentrating the reaction solution by purging with
nitrogen gas, product was identified and quantified using GC-
MS.
(a) B. Meunier, S. P. de Visser and S. Shaik, Chem. Rev., 2004, 104
,
3947ꢀ3980; (b) M. Costas, M. P. Mehn, M. P. Jensen and L. Que, Jr.,
Chem. Rev., 2004, 104, 939ꢀ986; (c) C. Krebs, D. G. Fujimori, C. T.
Walsh and J. M. Bollinger, Jr., Acc. Chem. Res., 2007, 40, 484ꢀ492; (d)
W. Nam, Acc. Chem. Res. 2007, 40, 522ꢀ531; (e) L. Que, Jr. and W. B.
Tolman, Nature, 2008, 455, 333ꢀ340; (g) L. Shu, J. C. Nesheim, K.
Kauffmann, E. Munck, J. D. Lipscomb and L. Que, Jr., Science, 1997,
275, 515ꢀ518; (h) M. Costas, J. ꢀU. Rohde, A. Stubna, R. Y. N. Ho, L.
Quaroni, E. Munck and L. Que, Jr., J. Am. Chem. Soc., 2001, 123
,
12931ꢀ12932.
5
6
H. Inoue, M. Sumitani, A. Sekita and M. Hida, J. Chem. Soc., Chem.
Commun., 1987, 1681ꢀ1682.
18O-labelling Experiment
The 18O-labelling experiments were carried out for the
photochemical oxidation of styrene, adamantane, cis-1,2-
dimethylcyclohexane and ambroxide. A mixture of acetonitrile
and H218O (3:2 v/v) solution containing catalyst
[Ru(bpy)3]Cl2.6H2O (2.0 × 10-3 M), [Co(NH3)5Cl]Cl2 (2.0 × 10-2 M)
and substrates (styrene, adamantane, cis-1,2-
dimethylcyclohexane and ambroxide) (5.0 × 10-3 M) were
stirred and irradiated with light (3W Blue LED, 440 nm) for 40
mins at room temperature. The resulted solution was
extracted with dichloromethane and products were analyzed
by GC-MS.
(a) D. W. Low, J. R Winkler and H. B. Gray, J. Am. Chem. Soc., 1996,
118, 117ꢀ120; (b) J. Berglund, T. Pascher, J. R. Winkler and H. B. Gray,
J. Am. Chem. Soc., 1997, 119, 2464ꢀ2469.
7
(a) S. Funyu, T. Isobe, S. Takagi, D. A. Tryk and H. Inoue, J. Am.
Chem. Soc., 2003, 125, 5734ꢀ5740; (b) F. Li, M. Yu, Y. Jiang, F. Huang,
Y. Li, B. Zhanga and L. Sun, Chem. Commun., 2011, 47, 8949ꢀ8951; (c)
D. Kalita, B. Radaram, B. Brooks, P. P. Kannam and X. Zhao,
1
(1.0 × 10-4 M),
ChemCatChem., 2011, 3, 571ꢀ573; (d) P. Guillo, O. Hamelin, P. Batat,
G. Jonusauskas, N. D. McClenaghan and S. Ménage, Inorg. Chem.,
2012, 51, 2222ꢀ2230; (e) D. Chao and W. F. Fu, Chem. Commun.,
2013, 49, 3872ꢀ3874; (f) T. V. Pho, M. V. Sheridan, Z. A. Morseth, B. D.
Sherman,T. J. Meyer, J. M. Papanikolas, K. S. Schanze and J. R.
Reynolds, ACS Appl. Mater. Interfaces, 2016, 8, 9125ꢀ9133; (g) L. Bai,
F. Li, Y. Wang, H. Li, X. Jianga and L. Sun, Chem. Commun., 2016, 52
,
9711ꢀ9714.
UV-vis Experiment
8
9
S. Ohzu, T. Ishizuka, Y. Hirai, S. Fukuzumi, and T. Kojima, Chem.- Eur.
J., 2013, 19, 1563ꢀ1567.
The photochemical generation of [{(bTAML)FeIV}2-µ-oxo]2-
(2)
(a) S. Fukuzumi, T. Kishi, H. Kotani, Y.ꢀM. Lee and W. Nam, Nat.
was observed in UV-vis spectroscopy. A solution mixture of
acetonitrile and phosphate buffer (3:2) containing catalyst (1.0
× 10-4 M), [Ru(bpy)3]Cl2.6H2O (2.0 × 10-5 M) and [Co(NH3)5Cl]Cl2
(6.0 × 10-4 M) were taken in to a 1.0 cm (path length) quartz
cuvette and spectra was recorded at 0, 1 and 3 mins of
photoirradiation with a blue LED light source (3W, 440 nm).
Chem., 2011,
3, 38ꢀ41; (b) S. Fukuzumi, T. Mizuno and T. Ojiri, Chem.
Eur. J., 2012, 18, 15794ꢀ15804.
10 (a) X. Wu, X. Yang, Y. M. Lee, W. Nam and L. Sun, Chem. Commun.,
2015, 51, 4013ꢀ4016; (b) D. Shen, C. Saracini, Y.ꢀM. Lee, W. Sun, S.
Fukuzumi and W. Nam, J. Am. Chem. Soc., 2016, 138, 15857ꢀ15860;
(c) G. Chen, L. Chen, L. Ma, H.ꢀK. Kwong and T.ꢀC. Lau, Chem.
Commun., 2016, 52, 9271ꢀ9274.
The chemical formation of [{(bTAML)FeIV}2-µ-oxo]2-
(2) was
11 (a) A. C. Rosenzweig, C. A. Frederick, S. J. Lippard and P. Nordlund,
Nature, 1993, 336, 537ꢀ543; (b) R. L. Lieberman and A. C. Rosenzweig,
Nature, 2005, 434, 177ꢀ182; (c) I.G. Denisov, T.M. Makris, S.G. Sligar
and I. Schlichting, Chem. Rev., 2005, 105, 2253ꢀ2278; (d) J. Rittle and
M.T. Green, Science,2010, 330, 933ꢀ937.
also examined from changes in the absorption spectra of
solution mixture of acetonitrile and phosphate buffer (3:2 v/v)
containing catalyst (1
) and NaOCl (0.5 equivalent) (Fig. S5†).
12 H. Kotani, T. Suenobu, Y. ꢀM. Lee, W. Nam and S. Fukuzumi, J. Am.
Chem. Soc., 2011, 133, 3249ꢀ3251.
13 A. Company, G. Sabenya, M. Gonza´lezꢀBe´jar, L. Go´mez, M.
Cle´mancey, G. Blondin, A. J. Jasniewski, M. Puri, W. R. Browne, J.
Latour, L. Que, Jr., M. Costas, J. Pe´rezꢀPrieto and J. LloretꢀFillol, J.
Am. Chem. Soc., 2014, 136, 4624ꢀ4633.
Acknowledgements
S.S.G. acknowledges SERB, New Delhi (Grant no
EMR/2014/00016) and IISER-Kolkata (“Start-up Grant”) for
funding. K.K.S. and B.C. acknowledge UGC-New Delhi for
fellowship.
14 (a) S. Sen Gupta, M. Stadler, C. A. Noser, A. Ghosh, B. Steinhoff, D.
Lenoir, C. P. Horwitz, K.ꢀW. Schraman and T. J. Collins, Science, 2002,
296, 326ꢀ328; (b) T. J. Collins, Acc. Chem. Res., 2002, 35, 782ꢀ790; (c)
T. J. Collins, Acc. Chem. Res., 1994, 27, 279ꢀ285; (d) B. C. Ellis, C. T.
Tran, M. A. Denardo, A. Fischer, A. D. Ryabov and T. J. Collins, J. Am.
Chem. Soc., 2009, 131, 18052ꢀ18053; (e) C. Panda, M. Ghosh, T.
Notes and references
Panda, R. Banerjee and S. Sen Gupta, Chem. Commun., 2011, 47
,
8016ꢀ8018.
1
(a) N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. U. S. A., 2006,
103, 15729ꢀ15735; (b) A. Magnuson, M. Anderlund, O. Johansson, P.
Lindblad, R. Lomoth, T. Polivka, S. Ott, K. Stensjö, S. Styring, V.
Sundström and L. Hamarström, Acc. Chem. Res., 2009, 42, 1899ꢀ1909.
15 (a) F. T. de Oliveira, A. Chanda, D. Banerjee, X. Shan, S. Mondal, L.
Que, Jr., E. L. Bominaar, E. Münck and T. J. Collins, Science, 2007,
315, 835ꢀ838; (b) M. Ghosh, K. K. Singh, C. Panda, A. Weitz, M. P.
Hendrich, T. J. Collins, B. B. Dhar and S. Sen Gupta, J. Am. Chem.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 7 of 8
View Article Online
DOI: 10.1039/C7SC02780J
Journal Name
ARTICLE
Soc., 2014, 136
, 9524ꢀ9527; (c) S. Pattanayak, A. Rana, A. J.
Jasniewski, K. K. Singh, A. Weitz, M. Hendrich, L. Que Jr., A. Dey and
S. Sen Gupta, 2017, Inorg. Chem., 2017, 56, 6352−6361; (d) S.
Pattanayak, D. R. Chowduri, B. Garai, K. K. Singh, A. Paul, B. B. Dhar
and S. Sen. Gupta, Chem. Eur. J., 2017, 23, 3414ꢀ3424.
16 C. Panda, J. Debgupta, D. Diaz Diaz, K. K. Singh, S. Sen Gupta and B.
B. Dhar, J. Am. Chem. Soc., 2014, 136, 12273ꢀ12282.
17 (a) K. K. Singh, M. k. Tiwari, M Ghosh, C. Panda, A. Weitz, M. P.
Hendrich, B. B. Dhar, K. Vanka, and S. Sen Gupta, Inorg. Chem.,2015,
54, 1535ꢀ1542; (b) K. K. Singh, M. k. Tiwari, B. B. Dhar, K. Vanka and
S. Sen Gupta, Inorg. Chem., 2015, 54, 6112ꢀ6121.
18 M. Ghosh, Y. L. K. Nikhil, B. B. Dhar and S. Sen Gupta, Inorg. Chem.,
2015, 54, 11792ꢀ11798.
19 S. Jana, M. Ghosh, M. Ambule and S. Sen Gupta, Org. Lett. 2017, 19
,
746−749.
20 K. Chen, A. Eschenmoser and P. S. Baran, Angew. Chem. Int. Ed.,
2009, 48, 9705ꢀ9708.
21 (a) J. Rosenthal, J. Bachman, J. L. Dempsey, A. J. Esswein, T. G. Gray,
J. M. Hodgkiss, D. R. Manke, T. D. Luckett, B. J. Pistorio, A. S. Veige
and D. G. Nocera, Coord. Chem. Rev., 2005, 249, 1316–1326; (b) D. N.
Harischandra, G. Lowery, R. Zhang and M. Newcomb, Org. Lett., 2009,
11, 2089ꢀ2092.
22 K.ꢀB. Cho, H. Hirao, S. Shaik and W. Nam, Chem. Soc. Rev., 2016, 45
,
1197ꢀ1210.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 8 of 8
View Article Online
DOI: 10.1039/C7SC02780J
ARTICLE
Journal Name
TOC:
Selective
photocatalytic
hydroxylation
and
epoxidation reaction by an iron complex using water as the
oxygen source
.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins