Diruthenium(II,III) tetracarboxylates catalyzed H2O2 oxygenation of organic sulfides

Article abstract of DOI:10.1016/j.ica.2014.07.046

Diruthenium(II,III) tetracarboxylates, Ru₂(OAc)₄Cl (A), Ru₂(esp)₂Cl (B, esp = tetramethyl-1,3-benzenedipropionate) and Ru₂(3-HB)₄Cl (C, 3-HB = 3-hydroxybenzoate) were investigated for activating hydrogen peroxide in organic sulfide oxygenation. The speciation of the substrate and potential products, sulfoxide and sulfone, were investigated for each catalyst. With methyl phenyl sulfide as the substrate, A simultaneously produces sulfoxide and sulfone, B yields the highest turnover with complete conversion to sulfoxide at 6 min before sulfone appears, and C facilitates complete conversion to sulfoxide in 20 min but little subsequent conversion to sulfone. The dependence of the initial reaction rate on catalyst and H₂O₂ concentrations were investigated. A small set of other sulfides were subjected to catalytic reactions with C, and all reactions resulted in near quantitative conversion. Finally, the sulfide oxygenation activity and stability towards hydrogen peroxide of the diphosphonate complex Na₄[Ru₂(hedp)₂(H₂O)Cl] (D, hedp = 1-hydroxyethylidenediphosphonate) was investigated, and D was found to be an effective catalyst, which retains its activity over an extended period of time due to its robustness at the (III,III) oxidation state.

Full text of DOI:10.1016/j.ica.2014.07.046

Inorganica Chimica Acta 424 (2015) 150–155
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Inorganica Chimica Acta
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Diruthenium(II,III) tetracarboxylates catalyzed H2O2 oxygenation
of organic sulfides
Dylan J. Thompson a, Julia E. Barker Paredes b, Leslie Villalobos a, Marco Ciclosi a, Rachel J. Elsby b, Bin Liu a,
Phillip E. Fanwick a, Tong Ren a,b,
⇑
a Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
b Department of Chemistry, University of Miami, Coral Gables, FL 33146, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 May 2014
Received in revised form 12 July 2014
Accepted 20 July 2014
Available online 28 July 2014
Diruthenium(II,III) tetracarboxylates, Ru2(OAc)4Cl (A), Ru2(esp)2Cl (B, esp = tetramethyl-1,3-benzenedi-
propionate) and Ru2(3-HB)4Cl (C, 3-HB = 3-hydroxybenzoate) were investigated for activating hydrogen
peroxide in organic sulfide oxygenation. The speciation of the substrate and potential products, sulfoxide
and sulfone, were investigated for each catalyst. With methyl phenyl sulfide as the substrate, A simulta-
neously produces sulfoxide and sulfone, B yields the highest turnover with complete conversion to
sulfoxide at 6 min before sulfone appears, and C facilitates complete conversion to sulfoxide in 20 min
but little subsequent conversion to sulfone. The dependence of the initial reaction rate on catalyst and
H2O2 concentrations were investigated. A small set of other sulfides were subjected to catalytic reactions
with C, and all reactions resulted in near quantitative conversion. Finally, the sulfide oxygenation activity
and stability towards hydrogen peroxide of the diphosphonate complex Na4[Ru2(hedp)2(H2O)Cl] (D,
hedp = 1-hydroxyethylidenediphosphonate) was investigated, and D was found to be an effective
catalyst, which retains its activity over an extended period of time due to its robustness at the (III,III)
oxidation state.
Keywords:
Sulfide oxygenation
Hydrogen peroxide
Diruthenium(II,III)
Diruthenium(III,III)
Stepwise reaction
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
as allylic/benzylic oxidation and amine oxidation, where the redox
flexibility of dirhodium species is a key [9–14]. Diruthenium tetra-
Catalytic conversion of organic sulfides to sulfoxides and subse-
quently sulfones is a topic of interest in several chemical areas. In
medicinal chemistry, chiral sulfoxide intermediates and products
play a crucial role in pharmaceuticals such as omeprazole [1–3].
For the decontamination of chemical warfare agents such as mus-
tard gas, selective conversion to sulfoxide largely eliminates the
toxicity of the compounds, while complete oxygenation leaves
the compound nearly as toxic as the initial sulfide [4]. On the other
hand, complete conversion to sulfone is essential for the detoxifi-
cation of V-type agents [5]. Lastly, in the field of fuel desulfuriza-
tion, the oxygenation of refractory sulfides (ODS) is proposed to
enable a more complete desulfurization than the traditional
hydrodesulfurization (HDS) approach [6].
carboxylates and related compounds with N,N0-bidentate ligands
are highly redox active with formal oxidation states ranging from
Ru2(I,II) to Ru2(III,IV) [15–19]. Inspired by Doyle’s success on
dirhodium catalysis, our laboratory has examined organic sulfide
oxygenation reactions catalyzed by diruthenium species: tert-butyl
hydroperoxide (TBHP) oxygenation by Ru2(esp)2Cl [20,21], aerobic
oxygenation by Ru2(O2CR)3(CO3) [22] and H2O2/TBHP oxygenation
by diruthenium(II,III) tetraamidate [23]. Reported herein are the
H2O2 oxygenation facilitated by diruthenium catalysts including
Ru2(OAc)4Cl (A), Ru2(esp)2Cl (B) and Ru2(3-hydroxybenzoate)4Cl
(C), and related reaction kinetics. Also investigated is the activity
and catalyst longevity of Na4[Ru2(hedp)2(H2O)Cl] (D, hedp = 1-
hydroxyethylidenediphosphonate) [24], which is known to be
stable in both the (II,III) and (III,III) states [25].
Bimetallic compounds have been explored as the group transfer
catalysts for decades, and a prime example is the carbene transfer
reactions using dirhodium compounds studied by Doyle and many
others [7,8]. In addition, dirhodium compounds have been found
active in facilitating various oxidative organic transformations, such
2. Results and discussion
2.1. Preparation and characterization ofRu2(3-hydroxybenzoate)4Cl (C)
⇑
Compound C was prepared by refluxing Ru2(OAc)4Cl in metha-
nol with 3-hydroxybenzoic acid for 24 h, and the product was
Corresponding author at: Department of Chemistry, Purdue University, West
Lafayette, IN 47907, USA.
http://dx.doi.org/10.1016/j.ica.2014.07.046
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

D.J. Thompson et al. / Inorganica Chimica Acta 424 (2015) 150–155
151
authenticated using both mass spectrometry and elemental analy-
100
80
60
40
20
0
sis. Single crystals suitable for X-ray diffraction analysis were
grown via slow diffusion of hexanes into a THF solution of C, and
the molecular structure of C is shown in Fig. 1. Similar to other
structurally determined diruthenium(II,III) tetracarboxylates
[20,26,27], Ru2(3-HB)4Cl displays the classical paddlewheel motif
and some relevant geometric parameters are listed in Fig. 1. The
Ru–Ru bond length (2.2774(5) Å) falls in the range of 2.25–2.29 Å
observed for other diruthenium(II,III) tetracarboxylates [15,16].
In addition to the expected axial coordination by the chloro ligand,
the other axial site is occupied by a coordinating THF molecule,
which prevents the formation of the 1-D chain structure that is a
common occurrence for Ru2(O2CR)4X [15,16]. Ru2(3-HB)4Cl is para-
magnetic with a room temperature effective magnetic moment of
A
MPS
MPSO
MPSO2
3.97 lB, which corresponds to an S = 3/2 ground state that is com-
mon among Ru2(II,III) species [15,16]. The Vis–NIR absorption
spectrum of C features absorptions at ca. 460 and 640 nm, which
0
10
20
30
40
50
60
are attributed to the
p
(Ru–O, Ru2) ? p⁄(Ru2) transition and the
Time (min)
d(Ru2) ? p⁄(Ru2) transition, respectively, according to Miskowski
and Gray [28].
Fig. 2. Speciation of MPS, MPSO and MPSO2 during H2O2 oxygenation catalyzed by
A. Conditions: 1.25 mmol MPS, 1 mol% A, 8 equivalents H2O2, in 25 mL CH3CN.
2.2. Ru2(OAc)4Cl (A), and Ru2(esp)2Cl (B) and Ru2(3-HB)4Cl (C) as
H2O2 activators
100
B
Given the capacity of diruthenium species A and B as TBHP acti-
vators [20,21], we started testing their capacity in activating
hydrogen peroxide with methyl phenyl sulfide (MPS, also known
as thioanisole) as the benchmark substrate. In a typical reaction,
MPS was mixed with 1 mol% of the catalyst in acetonitrile and
the reaction was initiated by the addition of hydrogen peroxide
(8 equiv). The distribution of the products was monitored with
gas chromatography over the course of the reaction. The results
of the reactions catalyzed by compounds A, B and C are shown
Figs. 2–4, respectively (See scheme 1).
80
60
MPS
MPSO
MPSO2
40
20
0
0
10
20
30
40
50
60
Time (min)
Fig. 3. Speciation of MPS, MPSO and MPSO2 during H2O2 oxygenation catalyzed by
B. Conditions identical to that of Fig. 2.
100
C
80
60
MPS
MPSO
MPSO2
40
20
0
Fig. 1. ORTEP plot of C.thf. Hydrogen atoms were omitted for clarity. Selected bond
lengths (Å) and angles (°): Ru1–Ru2, 2.2774(5); Ru1–Cl1, 2.5309(9); Ru2–O51,
2.299(2); Ru1–O1, 2.010(2); Ru1–O3, 2.008(2); Ru1–O5, 2.020(2); Ru1–O7,
2.023(2); Ru2–O2, 2.023(2); Ru2–O4, 2.015(2); Ru2–O6, 2.030(2); Ru2–O8,
2.006(2); Ru(2)–Ru(1)–Cl(1), 177.72(3); O(51)–Ru(2)–Ru(1), 176.89(6).
0
10
20
30
40
50
60
Time (min)
Fig. 4. Speciation of MPS, MPSO and MPSO2 during H2O2 oxygenation catalyzed by
C. Conditions identical to that of Fig. 2.

152
D.J. Thompson et al. / Inorganica Chimica Acta 424 (2015) 150–155
Table 1
O
S
O
O
Sulfide substrates catalyzed by C with 8 equivalents H2O2.
S
H2O2
S
+
Substrate
BPS
Entry
Hours
% RSR0
% RSOR0
% RSO2R0
TOFa
Catalyst
1
2
3
4
5
6
7
8
9
10
11
12
13
0.33
2.0
5.0
24
0.33
2.0
24
0.33
2.0
24
0.33
2.0
24
15
0
0
82
82
76
63
50
72
93
97
93
80
92
86
50
1
17
22
37
0
0
3
1
7
19
0
13
49
255
58
24
6
150
36
4
300
54
5
280
56
6
MPS
MPSO
MPSO2
0
Scheme 1. Conversion of methyl phenyl sulfide to sulfoxide and sulfone.
PPS
4BT
PTE
50
27
4
0
0
0
7
0
0
It is clear from Fig. 2 that the reaction catalyzed by A has no
observable induction period. It is also obvious that the conversion
of sulfoxide to sulfone becomes concurrent with the conversion of
sulfide to sulfoxide after an appreciable amount of sulfoxide (ca.
40%) is formed. At 60 min, the reaction has resulted in the disap-
pearance of 96% of sulfide with the formation of 85% sulfoxide
and 11% sulfone.
a
Turnover frequency (hourꢀ1) = {[RSOR0] + 2[RSO2R0]}/[Cat]*time (hour).
Slightly different from that of A, the reaction with catalyst B dis-
plays a short induction period (the first 2 min) followed by rapid
conversion of sulfide to sulfoxide (Fig. 3). Yet, the reaction pro-
ceeded much faster than that with A and is step-wise: conversion
of MPS to MPSO completed in 6 min with almost no MPSO2, and
88% of MPSO2 was present at 60 min.
As shown in Fig. 4, the reaction catalyzed by C displayed an
induction period similar to that observed for B. The conversion of
sulfide to sulfoxide completed in 15 min, slower than that with B
but faster than that with A. On the other hand, the sulfoxide to sul-
fone conversion is very slow with C and only 3% of sulfone was
detected at 60 min. Thus C proceeds not only in a stepwise progres-
sion but is rather selective for sulfoxide formation.
There are two notable features in the activity of catalysts A, B
and C. First, MPS is fully consumed in 6 and 15 min. with B and
C, respectively, whereas 5% of MPS remains with A in 60 min. Sec-
ond, reactions with B and C are stepwise: there is no production of
sulfone till the complete consumption of sulfide. On the other
hand, sulfone started appearing around 15 min while a substantial
amount of sulfide (>40%) was still present in the reaction with A. It
is well established that while the oxygenation of sulfide can be
accomplished through either electrophilic or nucleophilic attack,
the oxygenation of sulfoxide is accomplished through nucleophilic
attack [29]. The insignificant sulfone production seems to indicate
that the active species derived from C is significantly more electro-
philic than these derived from both A and B. The structural differ-
ences among the three compounds may play a role in selectivity as
well. The large difference in steric bulk from the relatively unhin-
dered A to the bulkier B and C may also explain some of the latter’s
preference for the sulfoxide formation since the sulfur center in
sulfide is easier to access than that in sulfoxide.
were investigated under conditions similar to the MPS reactions in
Section 2.2. Product yields were assessed with gas chromatogra-
phy. The results of these experiments are summarized in Table 1.
The reaction with the bulky BPS yielded 82% conversion to sulf-
oxide, 1% to sulfone and 14% residual sulfide at 20 min, corre-
sponding to a TOF of 255 hꢀ1, and 82% sulfoxide and 17% sulfone
at 2 h. The reaction with bulkier and less electron rich PPS resulted
in only 50% sulfoxide and no sulfone at 20 min (TOF of 150 hꢀ1),
and 72% of sulfoxide and 27% of unreacted sulfide at 2 h. The reac-
tion with 4BT yielded similar results to that with MPS: 97% sulfox-
ide, 1% sulfone and no detectable sulfide (TOF: 300 hꢀ1) at 20 min,
and 93% sulfoxide and 7% sulfone at 2 h. Similarly, the reaction
with PTE resulted in 92% sulfoxide and 7% sulfide at 20 min, and
86% sulfoxide and 13% sulfone at 2 h. It is clear from these reactiv-
ity data that catalyst C favors the fast and selective formation of
sulfoxide, while it is much slower in the conversion to sulfone.
Also, the reaction with the most sterically hindered and electron
deficient PPS is substantially slower than the other three
substrates.
2.4. Rate dependence on [H2O2]
The efficacy of catalysts A, B and C in activating H2O2 for sulfide
oxygenation encourages further study of the reaction kinetics,
which is largely based on the initial rates method by monitoring
of the disappearance of MPS at 290 nm that has been used effec-
tively in analysis of MPS oxygenation [20,21,30–32]. First analyzed
was the rate dependence on [H2O2].
For each catalyst the dependence on hydrogen peroxide con-
centration was investigated using 5–50 equiv of hydrogen perox-
ide with respect to the substrate (2.0 mM). The ln(Abs290) versus
time plots during the first 15 min were consistent with pseudo-
first order kinetics. The kobs obtained were plotted against the
equiv of H2O2 in Fig. 5 with catalysts A, B and C. For all three cat-
alysts, the rate dependence followed a pseudo-first order pattern
until reaching saturation.
2.3. Catalytic oxygenation of other sulfides C
Because of both the fast turnover and selectivity in producing
sulfoxide with catalyst C, additional sulfide substrates (Scheme 2)
The [H2O2] needed to reach saturation was found to be similar
between catalysts A and B at 30 equiv and 25 equiv, respectively.
However, catalyst C reaches saturation at the significantly lower
[H2O2] of 15 equiv, which is consistent with C being more electro-
philic than A and B. For all three catalysts krel[H2O2] was found
from the linear regression of the pseudo-first order region of the
equivalents H2O2 versus kobs plots. In all three cases the linear fit
was forced through the origin as there is no conversion of sulfide
to sulfoxide in the presence of catalyst without hydrogen peroxide.
The resulting krel data are in the order of C > B > A, with that of C
S
S
Benzyl phenyl sulfide (BPS)
Phenyl sulfide (PPS)
S
S
OH
Br
4-Bromo thioanisole (4BT)
Phenyl thioethanol (PTE)
being the highest at 4.3 ꢁ 10ꢀ3 minꢀ1, followed by 3.8 ꢁ 10ꢀ3
-
Scheme 2. Sulfide substrates oxygenated with hydrogen peroxide via catalysis
with C.
minꢀ1 and 2.5 ꢁ 10ꢀ3 minꢀ1 for B and A, respectively. Lastly, it is

D.J. Thompson et al. / Inorganica Chimica Acta 424 (2015) 150–155
153
0.1
0.08
0.06
0.04
0.02
0
0.15
0.1
A
B
C
0.05
A
B
C
0
2 10-5
4 10-5
6 10-5
8 10-5
0
0.0001
0
10
20
30
40
50
60
[Cat.]
Equiv. H2O2
Fig. 6. Rate dependence on the loading of catalysts A–C.
Fig. 5. Rate dependence on H2O2 for Ru2(OAc)4Cl (A), Ru2(esp)2Cl (B) and Ru2(3-
HB)4Cl (C).
when completed at saturation conditions is consistent with the
krel(H2O2) results.
important to note for the kinetic investigation of [cat] in the next
section that A and C have similar saturation rates: 0.077 and
0.073 minꢀ1 for A and C, respectively, while that for B is about
0.095 minꢀ1. The saturation kinetics observed for all three com-
pounds imply that the H2O2 coordinates to the catalyst to yield
the active oxygen donor [21].
2.6. Possible role of Ru2(III,III) species
In all the reactions discussed above, compounds A, B and C
undergo a change of color from reddish brown to dark blue/purple
upon the addition of H2O2. For C the absorption initially at 460 nm
shifts to 580 nm within the first 40 min of the reaction, after which
the intensity of the 580 nm peak decreases steadily over the next
24 h. Furthermore, addition of fresh aliquots of sulfide and hydro-
gen peroxide to these solutions after standing 24 h under ambient
conditions resulted in no further conversion, indicating a complete
degradation of the active species. The initial spectral shift is spec-
ulated to be associated with the formation of a transient Ru2(III,III)
species, which is difficult to ascertain due to the instability of the
Ru2(III,III) tetracarboxylates. A diphosphonate supported diruthe-
nium(II,III) compound Na4[Ru2(hedp)2(H2O)Cl] (D) discovered in
the laboratory of Zheng in 2003 [24,33] caught our attention since
its (III,III) surrogate, namely Na4[Ru2(hedp)2Cl2], has been isolated
recently [25]. Both the activity of D in the MPS oxygenation and the
effect of H2O2 in large excess have been investigated.
The MPS oxygenation reaction with compound D was carried
out using the same stoichiometry as those described in Section
2.2, i.e. 1.25 mmol MPS, 1 mol% D and 8 equiv H2O2, with the use
of acetone:water as the solvent because of D’s insolubility in aceto-
nitrile and other common organic solvents. The disappearance of
MPS in this reaction is plotted together with the MPS disappear-
ances from Figs. 2–4 in Fig. 7. It is clear that while D has a substan-
tial induction period (15 min), it displays a post-induction rate
between that of A and that of C, and the reaction resulted in a com-
plete consumption of MPS in 120 min. Subsequently, the aliquots
of MPS (1.25 mmol) and H2O2 (8 equiv) were added to this reaction
mixture, and complete consumption of MPS was achieved in 4 h.
During the first reaction, the color of the solution changed from
orange-red to deep purple in a fashion similar to the reactions with
A–C. Yet, the catalytic species formed in situ remains active during
the subsequent reactions.
2.5. Rate dependence on catalyst loading
The influence of catalyst concentration on the rate of the reac-
tion was also investigated with the initial-rates technique as previ-
ously described. In this case the [MPS] was 2.0 mM and the [H2O2]
was kept constant at 200 mM ensuring that H2O2 is at saturation
for all catalysts and that the kinetics would mimic steady state
conditions. The concentration of each catalyst was varied from
0.0094 to 0.094 mM (0.47–4.7 mol% with respect to [MPS]). Extrap-
olation of the slope of the lines from ln(Abs290) versus t for the first
15 min of the reaction yielded kobs, which was in turn plotted ver-
sus [cat] for krel. (Fig. 6) The resulting rate constant (krel, kobs = krel[-
cat]) was 1.2 ꢁ 103 minꢀ1 and 3.6 ꢁ 103 minꢀ1 for
A
and B,
respectively. For B, pseudo-first order kinetics behavior was
observed until 3.8 ꢁ 10ꢀ2 mM catalyst (2%), after which saturation
was observed. In contrast, A approached saturation more slowly
with the pseudo-first order region lasting through 5.6 ꢁ 10ꢀ2 mM
(about 3%) with saturation beginning shortly thereafter. The effect
of [C] is similar to that of B in that the pseudo-first order region
ends at comparable concentration of catalyst (2.8 ꢁ 10ꢀ2 mM)
while not fully reaching saturation until 5.6 ꢁ 10ꢀ2 mM (about
3%). Upon completing the same analysis of initial rates under
pseudo-first order conditions using catalyst C (Fig. 6), the extracted
rate constant was found to be krel = 1.6 ꢁ 103 minꢀ1 for C. The
pseudo-first order dependence observed for all three compounds
indicates that a single molecule of A, B or C is involved in the cat-
alytic cycle.
The krel(cat) data for the three catalysts initially appears diver-
gent from both the results from [H2O2] variation kinetics as well as
the catalytic reactions in solution. Here krel(cat) indicates a rate
ordering of B > C > A. This result is due to the experimental condi-
tions of utilizing [H2O2] above saturation for all three catalysts. It
was remarked in Section 2.4 that C reaches saturation at approxi-
mately the same krel(H2O2) as A. Therefore the similar krel(cat)
To further explore the origin of color change, aliquots of hydro-
gen peroxide (100 equiv) were added to a cuvette containing an
aqueous solution of D. The spectrum of the resultant solution,
along with those of D and Na4[Ru2(hedp)2Cl2] (D(III,III)) are shown
in Fig. 8. The (II,III) species D has characteristic peaks at 275, 320
and 465 nm, while the (III,III) species has characteristic peaks at

154
D.J. Thompson et al. / Inorganica Chimica Acta 424 (2015) 150–155
resultant spectrum appears to be the superposition of these of D
100
80
60
40
20
0
(minor) and its (III,III) surrogate (major). These peak shiftings are
responsible for the observed color change during the catalytic reac-
tion. The resultant color (and new peaks) upon the addition of
H2O2 sustained days standing in solution containing excess H2O2.
Taking into account the reactivity data gathered, a plausible
mechanism of H2O2 activation is outlined in Scheme 3. It is likely
that hydrogen peroxide approaches the vacant (or water coordi-
nated) axial site to form an axial hydroperoxide ligand with con-
current one-electron oxidation of the Ru2 center, yielding the
intermediate 3a. Sulfide substrate approaches the Ru-bound
hydroperoxide in the transition state 3b, from which a concerted
oxo-transfer produces sulfoxide and regenerates 3a with the addi-
tion of another hydrogen peroxide. Similar cycle can be envisioned
for converting sulfoxide to sulfone.
A
B
C
D
0
20
40
60
80
100
120
3. Conclusions
Time (min)
Results reported herein demonstrated that diruthenium tetra-
carboxylates A–C are all effective in activating hydrogen peroxide
in sulfide oxygenation reactions. In addition, catalysts B and C
facilitate stepwise oxygenation, a feature that is potentially useful
in medicinal chemistry. Using a diruthenium complex supported
by bridging diphosphonates, D, it is demonstrated that (i) the
active catalyst is likely to be a Ru2(III,III) species and (ii) the robust-
ness of the (III,III) species assures the longevity of the catalyst.
Given the recent resurgence of interest in the synthesis and reac-
tivity of diruthenium paddlewheel species [34–43], new com-
pounds with robust Ru2(III,III) formal oxidation state are
expected and their ability to facilitate oxidative transformations
should be tested. The activity of D in promoting organic transfor-
mations beside sulfide oxygenation is being explored in our
laboratory.
Fig. 7. Disappearance of MPS in reactions with catalysts A, B, C and D.
6000
D (II,III)
D (II,III) + 100 eq. H2O2
D (III,III)
5000
4000
ε
3000
2000
1000
0
4. Experimental
4.1. General
250
300
350
400
450
500
550
600
Solvent acetonitrile and organic reagents were purchased from
Sigma Aldrich. Ru2(OAc)4Cl [44], Ru2(esp)2Cl [20] and Na4[Ru2
(hedp)2(H2O)Cl] [25] were prepared according to the literature
procedures. Organic sulfides were purchased from ACROS Organ-
ics. Hydrogen peroxide (30%) was purchased from Macron Fine
Chemicals and standardized via iodometric titration. Samples of
oxygenation reactions were analyzed by Agilent 7890A GC system
equipped with a flame ionization detector. The separation of sub-
strate and products was achieved using an Agilent HP-5 column
with dimensions of 30 m ꢁ 0.320 mm with 25 micron film thick-
ness. Reaction kinetics was followed via UV–Vis spectroscopy on
a JASCO V-670 Spectrophotometer.
λ (nm)
Fig. 8. Spectra of genuine D(II,III) and D(III,III), and D(II,III) + 100 equiv H2O2.
3a
O
O
O
O
H2O2
O
O
O
O
RuIII
O
RuIII
O
O
Cl
RuIII
O
RuII
O
Cl
O
O
O
O
O
S
H
H+ + e-
R
R
S
O
R
R
+ H2O
H2O2
4.2. Synthesis of Ru2(3-HB)4Cl
O
O
O
O
Ru2(OAc)4Cl (200 mg, 0.422 mmol) and 3-hydroxybenzoic acid
(466 mg, 3.37 mmol) were refluxed in 15 mL of MeOH for 48 h.
After cooling, the MeOH was removed under reduced pressure
and the red-orange precipitate was collected and recrystallized
from a minimum of MeOH (279 mg, 84% based on Ru). Orange
crystals suitable for single crystal X-ray diffraction were grown
via slow diffusion of hexanes into a THF solution. Elemental Anal-
ysis for C28H28ClO14Ru2 (Ru2(3HB)4ClꢂH2O), Found (Calc.): C 40.34
Cl
RuIII
O
RuIII
O
O
O
O
O
H
3b
Scheme 3. Plaussible mechanism of H2O2 activation.
270, 319 and 510 nm. The solution from treating D with 100 equiv
of H2O2 displays a dramatic intensification of the 320 nm peak as
well as a red shift of the 460 nm peak to ca. 500 nm, and the
(40.71), H 3.12 (3.42).
leff: 3.97
lB, UV–Vis: kmax 460 nm (e
1600 Mꢀ1 cmꢀ1); 640 nm (
e
810 Mꢀ1 cmꢀ1).

D.J. Thompson et al. / Inorganica Chimica Acta 424 (2015) 150–155
155
4.3. Speciation monitored catalyst reactions
Acknowledgement
To a solution of 1.25 mmol of methyl phenyl sulfide in 25 mL
CH3CN, 1% catalyst A, B, or C was dissolved along with 1.0 mmol
1,2 dichlorobenzene for internal standard. Initiating the reaction
with 8.0 equivalents of hydrogen peroxide was carried out by add-
ing the hydrogen peroxide drop wise over about 30 s. Samples
We thank both Purdue University and the US Army Research
Office (Grants DAAD 190110708 and W911NF-06-1-0305) for
financial support. Leslie Villalobos was supported in part by an
AGEP Supplement from the US National Science Foundation (CHE
1057621).
were taken at the indicated times by removing 300
mixture and quenching the hydrogen peroxide with about 5 mg
of MnO2. From this sample, 2 L of solution was injected into GC
lL of reaction
Appendix A. Supplementary material
l
for analysis under the conditions described above. For catalyst D,
the reactions were completed in the same fashion, except that
water: acetone (3:2, v/v) was used as solvent.
CCDC 1003707 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
4.4. Oxygenation of other sulfides with Ru2(3-HB)4Cl (C)
References
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1,2-dichlorobenzene, and 8 equiv hydrogen peroxide. The reac-
tions were sampled at the indicated times by quenching the unre-
acted hydrogen peroxide with MnO2 as above. Samples were
analyzed via gas chromatography and percentages determined
via standard curves for purchased sulfides and synthesized sulfox-
ides and sulfones.
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[45] The DIRDIF2008 Program System, Crystallography Laboratory, University of
Nijmegen, The Netherlands, 2008.
From the same stock solutions as above, reactions were per-
formed in a similar fashion. Reactions consisted of 1.0 mL MPS
solution, a standard 100 equivalents of H2O2 (1.0 mL H2O2 solu-
tion) and varying amounts of catalyst solution in the range of
0.5–5% catalyst with respect to MPS were added to initiate the
reaction after enough acetonitrile was added to reach 3.0 mL solu-
tion. The krel data were extracted by plotting the kobs from lnAbs
versus time versus the concentration of catalyst. The linear fit of
the pseudo-first order region yielded krel[cat].
4.7. X-ray crystallography
Single crystals of Ru2(3-HB)4Cl (C) were grown via slow
diffusion of hexanes into a THF solution of Ru2(3-HB)4Cl. X-ray
diffraction data were collected on a Rigaku Rapid II image plate dif-
fractometer equipped with a MicroMax002 + high intensity copper
(k (Ka) = 1.54 Å) X-ray source at 180 K. The structure was solved
using the structure solution program DIRDIF2008 [45] and refine-
ment was performed using SHELX2013 [46]. Crystal data for C.thf:
C
32H28ClO13Ru2, FW = 858.15, monoclinic, P21/c, a = 10.7503(3),
b = 18.8725(6), c = 20.8024(7) Å, b = 94.753(2)°, V = 4206.0(2) Å3,
Z = 4, Dcalc = 1.583 g cmꢀ3. Of 35885 reflections measured, 7774
were unique. Least squares refinement based on 7108 reflections
[46] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
with I P 2r(I) and 539 parameters led to convergence with final
R1 = 0.047 and wR2 = 0.134.