Coupled X-ray Absorption/UV-vis Monitoring of Fast Oxidation Reactions Involving a Nonheme Iron-Oxo Complex

Article abstract of DOI:10.1021/jacs.8b08687

Time-resolved X-ray absorption (XAS) and UV-vis spectroscopies with millisecond resolution are used simultaneously to investigate oxidation reactions of organic substrates by nonheme iron activated species. In particular, the oxidation processes of arylsulfides and benzyl alcohols by a nonheme iron-oxo complex have been studied. We show for the first time that the pseudo-first-order rate constants of fast bimolecular processes in solution (milliseconds and above) can be determined by time-resolved XAS technique. By following the Fe K-edge energy shift, it is possible to detect the rate of iron oxidation state evolution that matches that of the bimolecular reaction in solution. The kinetic constant values obtained by XAS are in perfect agreement with those obtained by means of the concomitant UV-vis detection. This combined approach has the potential to provide unique insights into reaction mechanisms in the liquid phase that involve changes of the oxidation state of a metal center, and it is particularly useful in complex chemical systems where possible interferences from species present in solution could make it impossible to use other detection techniques.

Full text of DOI:10.1021/jacs.8b08687

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Article
Coupled X-Ray Absorption/ UV-Vis Monitoring of Fast
Oxidation Reactions Involving a Non-Heme Iron Oxo Complex.
Giorgio Capocasa, Francesco Sessa, Francesco Tavani, Giorgio Olivo, Manuel Monte,
Sakura Pascarelli, Osvaldo Lanzalunga, Stefano Di Stefano, and Paola D'Angelo
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 16 Jan 2019
Downloaded from http://pubs.acs.org on January 16, 2019
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Coupled X-Ray Absorption/ UV-Vis Monitoring of Fast Oxidation
Reactions Involving a Non-Heme Iron Oxo Complex.
Giorgio Capocasa,†, §,¶ Francesco Sessa,† ,¶ Francesco Tavani,†, ¶ Manuel Monte,‡ Giorgio Olivo,†
Sakura Pascarelli,‡ Osvaldo Lanzalunga,†, §,* Stefano Di Stefano,†,§,* and Paola D’Angelo,†,*
† Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro 5, 00185 Roma, Italy.
‡ European Synchrotron Radiation Facility, 71, Avenue des Martyrs, Grenoble, France.
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§ Istituto CNR di Metodologie Chimiche (IMC-CNR), Sezione Meccanismi di Reazione, P.le A. Moro 5, 00185 Roma,
Italy.
ABSTRACT: Time-resolved X-ray absorption (XAS) and UV-Vis spectroscopies with millisecond resolution are used
simultaneously to investigate oxidation reactions of organic substrates by non-heme iron activated species. In particular,
the oxidation processes of arylsulfides and benzyl alcohols by a non-heme iron oxo-complex have been studied. We show
for the first time that the pseudo first-order rate constants of fast bimolecular processes in solution (milliseconds and
above) can be determined by time-resolved XAS technique. By following the Fe K-edge energy shift it is possible to detect
the rate of iron oxidation state evolution that matches that of the bimolecular reaction in solution. The kinetic constant
values obtained by XAS are in perfect agreement with those obtained by means of the concomitant UV-Vis detection.
This combined approach has the potential to provide unique insights into reaction mechanisms in the liquid phase that
involve changes of the oxidation state of a metal center and it is particularly useful in complex chemical systems where
possible interferences from species present in solution could make impossible the use of other detection techniques.
INTRODUCTION
showed that radiation damage may occur during in situ
reactions of copper containing samples.3
The comprehension of reactivity is one of the main topics
of chemical science since its very beginning. The
knowledge of the reaction mechanisms is indeed an
indispensable tool to control chemical transformations
and to direct them into the desired outputs. Due to the
increasing complexity of the chemical systems
investigated by contemporary researchers, the need is
strong for innovative techniques capable of providing
both an easy and selective monitoring of the process of
interest. This exigency is even stronger when chemical
reactions are fast on human timescales (seconds and
below).
Recently, we have shown that time-resolved EDXAS and
UV-Vis spectroscopy can be used in combination, to
follow fast chemical processes (halftimes from
milliseconds to seconds) by the direct observation of the
intermediates succeeding one another during the
reaction.4 In particular, time-resolved XAS allowed us to
monitor the evolution of the oxidation state of the iron
metal center present in the prototypical non-heme
complex FeII(tris(2-pyridylmethyl)amine) ([TPA•FeII]2+)
and of the first coordination sphere around the metal
itself, when the complex was subjected to the action of
oxidizing species like hydrogen peroxide or peroxyacetic
acid (AcOO2H). Concomitant UV-Vis monitoring of the
reaction enabled us to unambiguously assign the
identities to the several reaction intermediates.
Experimentally, XAS and UV-Vis techniques were coupled
by means of perpendicular detections carried out in the
probe of a stopped-flow apparatus.
X-ray absorption spectroscopy (XAS) allows one to gain
information on the local structure and electronic
configuration of a selected atom both on solid and liquid
systems. It is therefore a very powerful tool to follow the
structural and electronic evolution taking place during
chemical reactions that generally occur in solution on a
timescale of milliseconds and above. In a pioneering
investigation time-resolved energy dispersive X-ray
absorption spectroscopy (EDXAS) was synchronized with
a stopped flow experiment to monitor the reactions
involving nickel, iron and iridium complexes. This work
showed the potentialities of this combined approach.1
Afterward, simultaneous structural and kinetic
information was obtained from a combined stopped flow,
UV-Vis spectroscopy and energy dispersive extended X-
ray absorption fine structure (EXAFS) experiment on a
two-step prototypical oxidative reaction of Pd complexes
in solution. This reaction occurs in the second time scale
and this allowed EXAFS spectra to be collected.2 Further,
a combined in-situ UV-Vis XAS spectroscopic setup
2+
CH3
2+
2+
C
N
N
O
IV
Fe
N
NCCH3
NCCH3
N
II
Fe
N
N
N
N
II
Fe
N
N
N
N
N
N
N
[TPA FeII]2+
[N4Py FeII]2+
[N4Py FeIV(O)]2+
Figure 1. Molecular structures of the non-heme iron
complexes.
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+
SCH3
+ [N4Py FeIV(O)]2+
SCH3
ET
b
+ [N4Py FeIII(O)]+
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X
X
S(O)CH3
+ [N4Py FeII]2+
a
c
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DOT
OT
X
Scheme 1. Mechanistic dicothomy in the [N4Py•FeIV(O)]2+ oxydation of arylsulfide: (a) the DOT mechanism, (b-c) the ET-
OT mechanism.
Here, we report that the use of the time resolved
XAS/UV-Vis coupled technique is not limited to the
RESULTS AND DISCUSSION
The XAS/UV-Vis coupled technique was used to follow
the oxidation of a series of thioanisoles, differently
substituted in the para position of the aromatic ring, to
the corresponding methylphenyl sulfoxide (CH3CN, 25 °C)
by the oxidant [N4Py•FeIV(O)]2+ freshly prepared by
reaction between [N4Py•FeII]2+ and peroxyacetic acid. In
general, sulfoxidation of aryl sulfides promoted by high-
valent iron(IV)-oxo complexes in non-heme iron
oxygenases and their synthetic non-heme models is
characterized by a mechanistic dichotomy between the
direct oxygen transfer or “oxene process” (DOT) and
electron transfer followed by oxygen transfer (ET-OT)
mechanisms.13-18 As reported by Nam and Fukuzumi,
analysis of the activation of the metal complex in the
presence of suitable oxidants but it can also be extended
to the investigation of the oxidation reactions of organic
substrates by the non-heme iron activated species. In
particular, we have focused our attention on the oxidation
processes of synthetic interest such as sulfide and alcohol
oxidation, by the oxo-complex [N4Py•FeIV(O)]2+ derived
from the other paradigmatic non-heme iron complex
[N4Py•FeII]2+
(N4Py=N,N-bis(2-pyridylmethyl)-N-bis(2-
pyridyl)methylamine) reported in Figure 1. In this work,
we show for the first time that the pseudo first-order rate
constants of fast bimolecular processes in solution
(milliseconds and above) can be determined by the time-
resolved XAS technique. In particular, following the Fe
K-edge energy shift it is possible to determine the rate of
the iron oxidation state evolution that matches that of the
bimolecular reaction in solution. The kinetic constant
values obtained by XAS are indeed in perfect accordance
with those obtained by means of the concomitant UV-Vis
detection.
This innovative approach was possible using the energy
dispersive XAS technique now available at third
generation synchrotron light sources that allows one to
collect time resolved X-ray absorption near edge spectra
with good signal to noise ratio with a time resolution of 10
ms for photoabsorber concentrations of few mM under
operand conditions.
sulfoxidation
of
thioanisoles
promoted
by
[N4Py•FeIV(O)]2+ occurs by a DOT mechanism (Scheme 1,
path a) in the absence of acid additives or in the presence
of perchloric acid (70% HClO4).19,20 A mechanistic switch
to an ET-OT mechanism or better to a metal ion-coupled
electron transfer/proton-coupled electron transfer occurs
when the same reaction is carried out in the presence of
Sc(OTf)3 or triflic acid (HOTf), respectively (Scheme 1,
path b,c).19,21 An ET reaction followed by a fast oxygen
rebound is also operating in the sulfoxidation of cumyl or
arylethyl aryl sulfides promoted by [N4Py•FeIV(O)]2+ and
other high-valent iron-oxo complexes.22-24 Under our
conditions, where no additive other than [N4Py•FeIV(O)]2+
is added, the aryl sulfides oxidation should proceed
through a simple DOT mechanism (Scheme 1, path a),
that is an elementary reaction. Figure 2 shows the results
related to the oxidation of thioanisole (PhSCH3) by
[N4Py•FeIV(O)]2+. The reaction was carried out under
pseudo-first order conditions with the concentration of
PhSMe (350 mM) exceeding that of [N4Py•FeIV(O)]2+ (15
mM) by a factor of 23. Figure 2A shows the continuous
evolution of the Fe K-edge normalized time-resolved
EDXAS spectra during the course of the reaction.
The choice of [N4Py•FeIV(O)]2+ as the oxidizing agent was
guided by both the ever-growing interest on non-heme
iron complexes as catalysts for the oxidation of organic
compounds mainly due to the cheap and environmentally
friendly conditions under which these kind of reactions
can be carried out,5-10 and the high stability of such
particular
oxo-complex
that
guarantees
easy
manipulation and monitoring.11,12
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Figure 2. Oxidation of PhSMe by [N4Py•FeIV(O)]2+ in CH3CN at 25 °C followed by the coupled XAS/UV-Vis technique. (A)
Time evolution of the XANES spectra at selected times from reaction start. A magnification of Fe K-edge region is shown
in the inset. (B) E0 vs time (the points with colored marks correspond to the spectra with the same color reported in
panels A and C). E0 is the difference between the K-edge energy position of the XANES spectra at time t and the K-edge
position of the first XANES spectrum at t=0 s. Blue curve derives from a first-order kinetic treatment of experimental
points. (C) Difference between the XANES spectrum at time t and XANES spectrum at t=0 s related to panel A. (D)
UV/Vis monitoring of [N4Py•FeIV(O)]2+ (downward triangles at =690 nm) and [N4Py•FeII]2+ (upward triangles at =513
nm) during the reaction. Blue and red curves are derived from a first-order kinetic treatment of experimental points.
The XANES spectra show a shift of the Fe K edge position
towards lower energy values due to the reduction of the
iron oxidation state from FeIV to FeII during the reaction.
The time resolved EDXAS spectra were recorded every 120
ms and the reaction was followed for 10 s. Previous works
have demonstrated the potential of Fe K-edge XANES
spectroscopy for the quantitative determination of
FeII/FeIII ratio in different materials.25-28 The X-ray
absorption Fe K-edge comprises features that have been
ascribed to transition from core to bound states, namely
looking at the difference spectra shown in Figure 2C and
it corresponds to the first maximum region of the
difference spectra. Figure 2B shows the evolution of E0
during the reaction, where E0 is the difference between
the Fe K-edge energy position of the XANES spectra at
time t and the edge position of the first XANES spectrum
at t=0 s. The blue curve in Figure 2B is the first-order
kinetic plot obtained by fitting the experimental data with
the following equation:
1s3d (pre-edge), 1s4s (edge shoulder) and 1s4p
(edge crest). The 1s4s transition usually forbidden is
enabled by strong orbital mixing between the 4s and 4p
orbitals.27,28 The energy of the 1s4s edge shoulder was
found to correlate linearly with the iron oxidation state.27
Exploiting this potential we have followed the variation of
this spectral feature to detect the rate of reduction of FeIV
to FeII during the reaction. In particular, we measured the
energy of the main absorption edge at a height of 0.3 as a
function of time. The value 0.3 was chosen in an attempt
to determine the energy of the threshold while
minimizing the distortions arising from transitions to
bound states. Note that this value has been chosen
(1)
E0

t



E0

i

 E0

f


ekt  E0
 
f
where E0(i) is the K-edge energy at t=0 s, E0(f) is the K
edge energy at the end of the reaction and k is the kinetic
constant. From this analysis the k value turned out to be
0.54±0.06 s-1.
Spectrophotometric data related to the experiment are
reported in Figure 2D. Absorbance variation at 513 nm is
due to the increase of the concentration of [N4Py•FeII]2+
which is the reduction product of [N4Py•FeIV(O)]2+. The
concentration decrease of the latter species is confirmed
by the concomitant decrease of the absorbance at
690 nm, the maximum visible absorption wavelength of
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this species and by the shift of the XANES Fe K-edge. Red
and blue curves in Figure 2D are first-order kinetic plots
with independently obtained kinetic constants of k of
0.53±0.02 and 0.54±0.02 s-1, respectively, well in keeping
with literature data.29,30 It was gratifying to observe that
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Figure 3. Time evolution of the Fe K-edge EDXAS spectra of the reactions between (A) p-CH3OC6H4SCH3 (MeOPhSMe),
(C) PhSCH3 and (E) p-CNC6H4SCH3 (CNPhSMe) with [N4Py•FeIV(O)]2+ in CH3CN at 25 °C. Magnifications of Fe K-edge regions
are shown in the insets. (B,D,F) E0 vs time (the points with colored marks correspond to the spectra with the same color
reported in panels A,C,E). E0 is the difference between the edge energy position of the XANES spectra at time t and the edge
position of the first XANES spectrum at t=0 s. Blue curves in panel B, D, F derive from a first-order kinetic treatment of EDXAS
experimental points.
CH2OH
+ [N4Py FeIV(O)]2+
CHO
CHOH
+ [N4Py FeIII(OH)]2+
b
a
+ [N4Py FeII]2+
-H2O
HAT
Scheme 2. Mechanism for the oxidation of benzyl alcohol by [N4Py•FeIV(O)]2+. After a rate determining hydrogen atom
transfer from the benzylic C-H bond to the oxidant a fast second oxidation and a subsequent proton loss from
intermediate lead to benzaldehyde.
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these values are identical to that obtained from the
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EDXAS spectra. This experiment proofs that the
quantitative analysis of the shift of the XANES E0 value
during the reaction, which is a direct observation of the
change of the iron metal oxidation state from FeIV to FeII,
may serve for the kinetic analysis of fast reacting chemical
systems (in this case a half-life of 1.3 s is measured).
In order to investigate the potentiality of time-resolved
XAS technique for kinetic measurements we also used
other arylsulfides with different reactivity, whose
oxidation by [N4Py•FeIV(O)]2+ is known to be faster and
slower than that of PhSMe. Thus, para-methoxy and para-
cyano thioanisoles were also included in this study and
the related results are shown in Figure 3 where selected
XANES
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Figure 4. Oxidation of PhCH2OH by [N4Py•FeIV(O)]2+ in CH3CN at 25 °C followed by the coupled XAS/UV-Vis technique.
(A) Time evolution of the XANES spectra at selected times from reaction start. A magnification of Fe K-edge region is
shown in the inset. (B) E0 vs time (the points with colored marks correspond to the spectra with the same color reported
in panel A). E0 is the difference between the K-edge energy position of the XANES spectra at time t and the K-edge
position of the first XANES spectrum at t=0 s. Blue curve derives from a first-order kinetic treatment of experimental
points. (C) Difference between the XANES spectrum at time t and XANES spectrum at t=0 s related to panel A. (D) UV-
Vis monitoring of [N4Py•FeIV(O)]2+ (downward triangles at =690 nm) and [N4Py•FeII]2+ (upward triangles at =513 nm)
during the reaction. Blue and red curves are derived from a first-order kinetic treatment of experimental points.
more reactive than the parent compound and the reaction
was followed for 10 s while collecting the EDXAS spectra
every 100 ms (Figure 3A). The first order kinetic constant
spectra at different times and E0 experimental data
points with the related first-order fits carried out with eq.
(1) are reported. The reactions were carried out under
pseudo first-order kinetic conditions, p-CH3OC6H4SCH3
100 mM + [N4Py•FeIV(O)]2+ 15 mM and p-CNC6H4SCH3
800 mM + [N4Py•FeIV(O)]2+ 15 mM in CH3CN at 25 °C. As
expected the para-methoxy derivative is significantly
obtained by fitting the E0 values as a function of t with
eq ( 1) (Figure 3B) was k of 1.23±0.05 s-1 (half-life 0.56
s).
Conversely, the para-cyano derivative is less
reactive in this case the EDXAS spectra were collected
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every 1.8 s and the reaction was followed for 150 s (Figure
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In this work we show that it is possible to use the time
resolved XAS technique to carry out kinetic
measurements related to bimolecular fast chemical
reactions in solution. In particular, it is demonstrated
that, when the EDXAS and UV-Vis techniques are
coupled by means of perpendicular detections in the
probe of a stopped-flow apparatus, the kinetic measures
derived from both XANES E0 and UV-Vis monitoring are
coincident within experimental errors. This makes time
resolved XAS technique a helpful tool to follow fast
chemical reactions which involve changes of the
oxidation state of a metal center. The advantage is
particularly remarkable in complex chemical systems
under reaction, where possible interferences from the
species present in solution could make impossible the use
of any other detection technique. Finally, a significant
progress has recently been achieved concerning the
development of advanced multivariate analysis able to
capture the XANES signature of each species formed in
the reaction course.34-36 This approach would allow one
not only to determine the kinetic constant values but also
to provide a structural characterization of all the species
involved in the reaction. Additional investigations are
underway to pursue this goal.
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3E). The first order kinetic constant as determined from
the XANES spectra (Figure 3F) was k = 0.08±0.04 s-1 (half-
life 8.6 s). These values, the latter of which is in good
accordance with literature data,31 reflect the electrophilic
character of the oxidizing species [N4Py•FeIV(O)]2+.
In order to further check the reliability of our results a
different method based on the deconvolution of the
threshold region of the Fe K-edge spectra as a sum of an
arctangent function describing the transition into the
continuum, and a Lorentzian function representing the
1s4s transition has been carried out. This analysis has
been applied to the oxidation of p-CH3OC6H4SCH3 by
[N4Py•FeIV(O)]2+ providing the same value of the kinetic
constant within the experimental error (see SI for details).
The XAS/UV-Vis coupled technique was also used to
follow the oxidation of benzyl alcohol to benzaldehyde by
[N4Py•FeIV(O)]2+. This reaction has a more complex
mechanism than that related to the [N4Py•FeIV(O)]2+
oxidation of the aryl methylsulfides, which is reported in
Scheme 2. The mechanistic details of the oxidation of
benzyl alcohol with [(N4Py)FeIV(O)]2+ have been disclosed
by Nam and coworkers.32 From the results of the
oxidation of benzyl alcohol with an 18O labeled iron(IV)-
oxo complex, [N4Py•FeIV(18O)]2+, it was found that the
oxygen atom in the benzaldehyde product does not derive
from the ferryl oxygen atom. Thus benzaldehyde is
formed by a first hydrogen atom transfer (HAT) from the
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ASSOCIATED CONTENT
Supporting Information. The Supporting Information is
available free of charge on the ACS Publications website at
DOI:
benzylic C-H bond to [N4Py•FeIV(O)]2+ to produce the -
Experimental details and EDXAS data treatment.
hydroxybenzyl radical and the iron hydroxo complex
[N4Py•FeIII(OH)]2+ (step a in Scheme 2). In the second
step, a second fast oxidation of the former species
followed by proton loss leads to products, as reported in
path b of Scheme 2. Figure 4 shows the results obtained
when the XAS/UV-Vis coupled technique was applied for
monitoring the reaction of Scheme 2. Again, the reaction
was carried out under pseudo-first order conditions
(benzyl alcohol 2.18 M and [N4Py•FeIV(O)]2+ 15 mM). The
panels of the Figure 4 have to be read with the same
rational of those of Figure 2. UV-Vis experimental data
points (Figure 4D) related to the disappearance of
[N4Py•FeIV(O)]2+ followed at = 690 nm and appearance
of [N4Py•FeII]2+ (absorption at  = 513 nm), fitted with a
first order equation gave k values of 0.15±0.01 s-1 and
0.14±0.01 s-1 (half-life 4.7 s), respectively, which are again
in accordance with literature data.33 In this case the
EDXAS spectra were recorded every 300 ms and the
reaction was followed for 40 s (Figure 4A). The first order
treatment of the related XANES E0 values vs t data
reported in Figure 4B provided a k value of 0.11±0.05 s-1
(half-life 6.2 s) which, within the experimental error,
coincides with the values obtained from UV-Vis data,
again confirming the validity of the time-resolved XAS
technique in the kinetic analysis of fast chemical
reactions.
AUTHOR INFORMATION
Corresponding Author
* p.dangelo@uniroma1.it
* stefano.distefano@uniroma1.it
*osvaldo.lanzalunga@uniroma1.it
ORCID
Giorgio Capocasa: 0000-0002-9725-2727
Paola D’Angelo: 0000-0001-5015-8410
Stefano Di Stefano 0000-0002-6742-0988
Osvaldo Lanzalunga 0000-0002-0532-1888
Author Contributions
¶Equal contribution.
Note
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the University of Rome “La
Sapienza” (Progetti Ateneo 2015 C26H159F5B). ESRF is
acknowledged for the provision of synchrotron beam time.
REFERENCES
(1) Abdul Rahman, M. B. B.; Bolton, P. R.; Evans, J.; Dent, A. J.;
Harvey, I.; Diaz-Moreno, S. Application of stopped flow
techniques and energy dispersive EXAFS for investigation of the
reactions of transition metal complexes in solution: Activation of
CONCLUSION
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nickel β-diketonates to form homogeneous catalysts, electron
transfer reactions involving iron(III) and oxidative addition to
iridium(I). Farday Discuss. 2002, 122, 211.
manganese(V) Corroles to Sulfides. J. Am. Chem. Soc. 2010, 132,
15233.
(19) Park, J.; Morimoto, Y.; Lee, Y.-M.; Nam, W.; Fukuzumi, S.
1
2
3
4
5
6
7
8
9
(2) Guilera, G.; Newton, M. A.; Polli, C.; Pascarelli, S.; Guino,
M.; Hii, K. K. In situ investigation of the oxidative addition in
homogeneous Pd catalysts by synchronised time resolved UV-
Vis/EXAFS. Chem. Commun. 2006, 41, 4306.
(3) Mesu, J. G.; van der Eerden, A. M. J.; de Groot, F. M. F.;
Weckhuysen, B. M. Synchrotron Radiation Effects on Catalytic
Systems As Probed with a Combined In-Situ UV−Vis/XAFS
Spectroscopic Setup J. Phys. Chem. B 2005, 109, 4042.
(4) Olivo, G.; Barbieri, A.; Dantignana, V.; Sessa, F.; Migliorati,
V.; Monte, M.; Pascarelli, S.; Narayanan, T.; Lanzalunga, O.; Di
Stefano, S.; D’Angelo, P. Following a Chemical Reaction on the
Millisecond Time Scale by Simultaneous X-ray and UV/Vis
Spectro-scopy. J. Phys. Chem. Lett. 2017, 8, 2958.
(5) Chen, K; Que, L., Jr. Stereospecific Alkane Hydroxylation
by Non-Heme Iron Catalysts: Mechanistic Evidence for an
FeV═O Active Species. J. Am. Chem. Soc. 2001, 123, 6327.
(6) Chen, K.; Costas, M.; Kim, J.; Tipton, A. K.; Que, L., Jr.
Olefin cis-dihydroxylation versus epoxidation by non-heme iron
catalysts: two faces of an Fe(III)-OOH coin. J. Am. Chem. Soc.
2002, 124, 3026.
(7) Nam, W. High-Valent Iron(IV)–Oxo Complexes of Heme
and Non-Heme Ligands in Oxygenation Reactions. Acc. Chem.
Res. 2007, 40, 522.
(8) Talsi, E. P.; Bryliakov, K. P. Chemo- and stereoselective C-
dihydroxylations with H. Coord. Chem. Rev. 2012, 256, 1418.
(9) Nam, W.; Lee, Y.-M.; Fukuzumi, S. Tuning reactivity and
mechanism in oxidation reactions by mononuclear non heme
iron(IV)-oxocomplexes. Acc. Chem. Res. 2014, 47, 1146.
(10) Oloo, W. N.; Que, L., Jr. Bioinspired Non heme Iron
Catalysts for C–H and C═C Bond Oxidation: Insights into the
Nature of the Metal-Based Oxidants. Acc. Chem. Res. 2015, 48,
2612.
(11) Kaizer, J.; Klinker, E. J.; Oh, N. Y.; Rohde, J.-U.; Song, W. J.;
Stubna, A.; Kim, J.; Münck, E.; Nam, W.; Que, L., Jr. Non
hemeFeIVO complexes that can oxidize the C-H bonds of
cyclohexane at room temperature. J. Am. Chem. Soc. 2004, 126,
472.
(12) Lubben, M.; Meetsma, A.; Wilkinson, E. C.; Feringa, B.;
Que, L., Jr. Non heme Iron Centers in Oxygen Activation:
Characterization of an Iron(III) Hydroperoxide Intermediate.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1512.
(13) Peñéñory, A. B.; Argüello, J. E.; Puiatti, M. Novel Model
Sulfur Compounds as Mechanistic Probes for Enzymatic and
Biomimetic Oxidations. Eur. J. Org. Chem. 2005, 114, 122.
(14) Baciocchi, E.; Gerini, M. F.; Lanzalunga, O.; Lapi, A.; Lo
Piparo, M. G. Mechanism of the oxidation of aromatic sulfides
catalysed by a water soluble iron porphyrin. Org. Biomol. Chem.
2003, 1, 422.
Metal Ion-Coupled Electron Transfer of a Nonheme Oxoiron(IV)
Complex: Remarkable Enhancement of Electron-Transfer Rates
by Sc3+. J. Am. Chem. Soc. 2011, 133, 5236.
(20) Park, J.; Morimoto, Y.; Lee, Y.-M.; Nam, W.; Fukuzumi, S.
Proton-Promoted Oxygen Atom Transfer vs Proton-Coupled
Electron Transfer of a Non-Heme Iron(IV)-Oxo Complex. J. Am.
Chem. Soc. 2012, 134, 3903.
(21) Park, J.; Morimoto, Y.; Lee, Y.-M.; Nam, W.; Fukuzumi, S.
Unified view of oxidative C-H bond cleavage and sulfoxidation
by a non heme iron(IV)-oxo complex via Lewis acid-promoted
electron transfer. Inorg. Chem. 2014, 53, 3618.
(22) Barbieri, A.; Di Stefano, S.; Lanzalunga, O.; Lapi, A.;
Mazzonna, M.; Olivo, G. Role of electron transfer processes in
the oxidation of arylsulfides catalyzed by non heme iron
complexes. Phosphorus, Sulfur and Silicon 2017, 192, 241.
(23) Barbieri, A.; Del Giacco, T.; Di Stefano, S.; Lanzalunga, O.;
Lapi, A.; Mazzonna, M.; Olivo, G. Electron Transfer Mechanism
in the Oxidation of Aryl 1-Methyl-1-phenylethyl Sulfids
Promoted by Non heme Iron(IV)–Oxo Complexes: The Rate of
the Oxygen Rebound Process. J. Org. Chem. 2016, 81, 12382.
(24) Barbieri, A.; De Carlo Chimienti, R.; Del Giacco, T.; Di
Ste-fano, S.; Lanzalunga, O.; Lapi, A.; Mazzonna, M.; Olivo, G.;
Sa-lamone, M. Oxidation of Aryl Diphenylmethyl Sulfides
Promoted by a Nonheme Iron(IV)-OxoComplex: Evidence for an
Electron Transfer-Oxygen Transfer Mechanism. J. Org. Chem.
2016, 81, 2513.
(25) Westre, T.-E.; Kennepohl, P.; DeWitt, J.-G.;Hedman,
B.;Hodgson, K.-O.; Solomon, E.-I. A Multiplet Analysis of Fe K-
Edge 1s→3d Pre-Edge Features of Iron Complexes. J. Am. Chem.
Soc. 1997, 119, 6297.
(26) D’Angelo, P.; Lucarelli, D.; Della Longa, S.; Benfatto, M.;
Hazemann, J.-L.; Feis, A.; Smulevich, G.; Ilari, A.; Bonamore,
A.; Boffi, A. Unusual heme iron-lipid acyl chain coordination in
Escherichia coli flavohemoglobin. Biophys. J. 2004, 86, 3882.
(27) Berry, A.-J.; Yaxley, G.-M.; Woodland, A.-B.; Foran, J.-G.A
XANES calibration for determining the oxidation state of iron in
mantle garnet. Chem. Geol. 2010, 278, 31.
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25
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41
42
43
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45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(28) Shulman, R.G.; Yafet, Y.; Eisenberger, P.; Blumberg, W.E.
Observation and interpretation of X-ray absorption edges of iron
compounds and proteins. PNAS 1976, 73, 1384.
(29) For thioanisole a k2 of 0.87 M-1 s-1 is reported in ref. 20
which, under our conditions corresponds to k=k2×[Substrate] =
0.30 s-1 to be compared with 0.53 s-1. It has to be remarked that
the k value reported in ref. 20 was obtained at much lower
concentrations.
(30) The fair agreement between our and literature data
allows us to rule out any damage due to the X-ray beam that was
previously found to occur for reactions involving copper
containing samples (ref. 3).
(15) Baciocchi, E.; Lanzalunga, O.; Malandrucco, S.; Ioele, M.;
Steenken, S. Oxidation of Sulfides by Peroxidases. Involvement
of Radical Cations and the Rate of the Oxygen Rebound Step. J.
Am. Chem. Soc. 1996, 118, 8973.
(16) Goto, Y.; Matsui, T.; Ozaki, S.; Watanabe, Y.; Fukuzumi, S.
Mechanisms of Sulfoxidation Catalyzed by High-Valent
Intermediates of Heme Enzymes:ꢀ Electron-Transfer vs O-xygen-
Transfer Mechanism. J. Am. Chem. Soc. 1999, 121, 9497.
(17) Khenkin, A. M.; Leitus, G.; Neumann, R. Electron
Transfer−Oxygen Transfer Oxygenation of Sulfides Catalyzed by
the H5PV2Mo10O40 Polyoxometalate. J. Am. Chem. Soc. 2010, 132,
11446.
(31) For para-cyano thioanisole a k2 of 0.044 M-1 s-1 is reported
in ref. 20 which, under our conditions corresponds to
k=k2×[Substrate] = 0.04 s-1 to be compared with 0.08 s-1. It has to
be remarked that the k value reported in ref. 20 was obtained at
much lower substrate concentrations.
(32) Oh, N. Y.; Suh, Y.; Park, M. J.; Seo, M. S.; Kim, J.; Nam, W.
Mechanistic insight into alcohol oxidation by high-valent iron-
oxo complexes of heme and non heme ligands Angew. Chem. Int.
Ed. 2005, 44, 4235.
(33) For benzyl alcohol a k2 of 0.10 M-1 s-1 can be calculated
from data in ref. 32 which, under our conditions corresponds to
k=k2×[Substrate] = 0.28 s-1 to be compared with 0.13 s-1. It has to
be remarked that the k value in reported in ref 10 was obtained
in lower concentrations.
(18) Kumar, A.; Goldberg, I.; Botoshansky, M.; Buchman, Y.;
Gross, Z. Oxygen Atom Transfer Reactions from Isolated (Oxo)
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(34) Smolentsev1, G,; Guilera, G.; Tromp, M.; Pascarelli, S.;
Soldato, A. V. Local structure of reaction intermediates probed
by time-resolved x-ray absorption near edge structure
spectroscopy. J. Chem. Phys. 2009, 130, 174508.
(35) Martini, A. ; Borfecchia, E.; Lomachenko, K. A.; Pankin, I.
A. ; Negri, C. ; Berlier, G.; Beato, P.; Falsig, H.; Bordiga, S.;
Lamberti, C. Composition-driven Cu-speciation and reducibility
in Cu-CHA zeolite catalysts: a multivariate XAS/FTIR approach
to complexity. Chem. Sci. 2017, 8, 6836.
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(36) Pappas, D. K.; Martini, A.; Dyballa, M.; Kvande, K.;
Teketel, S.; Lomachenko, K. A.; Baran, R.; Glatzel, P.; Arstad, B.;
Berlier, G.; Lamberti, C.; Bordiga, S.; Olsbye, U.; Svelle, S.; Beato,
P.; Borfecchia, E. The Nuclearity of the Active Site for Methane
to Methanol Conversion in Cu-Mordenite: A Quantitative
Assessment. J. Am. Chem. Soc. 2018, 140, 15270.
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