Dramatic Effect of Ancillary NHC Ligand in the Highly Selective Catalytic Oxidative Carbon-Carbon Multiple Bond Cleavage

Article abstract of DOI:10.1021/acs.organomet.6b00337

Selective and controlled oxidation of olefins to aldehydes is a commonly used important transformation in chemistry. However, chemists still use the dangerous and inconvenient ozonolysis method or the less selective, low-yielding Lemieux-Johnson protocol. In a program of developing effective catalysts for this important reaction, we disclose here that an ancillary ligand can play a dramatic role in the above catalytic phenomenon, depending on the design of the ligand precursor chosen. Proof-of-principle is demonstrated with the help of two newly designed [L_nRu^II-NHC] precatalysts (NHC = an imidazolydene-based NHC, Im-NHC, or a triazolydene-based NHC, Trz-NHC; L_n = para-cymene) for catalytic selective oxidation of olefins/alkynes to carbonyl compounds. With the electron-deficient Trz-NHC ligand, [(para-cymene)Ru^II(Im-Trz)]⁺ precatalyst was found to be an order of magnitude more efficient than the [(para-cymene)Ru^II(Im-NHC)]⁺ precatalyst.

Full text of DOI:10.1021/acs.organomet.6b00337

Article
pubs.acs.org/Organometallics
Dramatic Effect of Ancillary NHC Ligand in the Highly Selective
Catalytic Oxidative Carbon−Carbon Multiple Bond Cleavage
Suraj K. Gupta, Sandeep K. Sahoo, and Joyanta Choudhury*
Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research
Bhopal, Bhopal 462 066, India
*
S Supporting Information
ABSTRACT: Selective and controlled oxidation of olefins to aldehydes
is a commonly used important transformation in chemistry. However,
chemists still use the dangerous and inconvenient ozonolysis method or
the less selective, low-yielding Lemieux−Johnson protocol. In a program
of developing effective catalysts for this important reaction, we disclose
here that an ancillary ligand can play a dramatic role in the above catalytic
phenomenon, depending on the design of the ligand precursor chosen.
Proof-of-principle is demonstrated with the help of two newly designed
II
[
L Ru -NHC] precatalysts (NHC = an imidazolydene-based NHC, Im-
n
NHC, or a triazolydene-based NHC, Trz-NHC; L = para-cymene) for catalytic selective oxidation of olefins/alkynes to carbonyl
n
II
+
compounds. With the electron-deficient Trz-NHC ligand, [(para-cymene)Ru (Im-Trz)] precatalyst was found to be an order
of magnitude more efficient than the [(para-cymene)Ru (Im-NHC)] precatalyst.
II
+
II
INTRODUCTION
Ru Im-NHC catalytic center by accelerating the generation of
■
15
active catalyst. This enhancement was suggested due to
electronic reasons, translated to the catalytic center from the
remote tuner. Herein we show that the ancillary NHC ligand
itself, when properly modified, can impose a dramatic electronic
bias at the Ru(II) center, which ultimately leads to the
development of a superior catalyst for the above reaction. It is
noteworthy that only a few moderately active NHC-based
Modification of the electronic/steric properties of a catalyst can
easily tune the catalytic performance by influencing the rate-
limiting step, and undoubtedly ligands play a vital role in such
controlled manipulation activity. Selective oxidation of alkenes
to the corresponding carbonyl compounds, free from the
subsequent overoxidation to carboxylic acids, is an indispensible
1
reaction in synthetic chemistry. It transforms hydrocarbons to
more valuable oxygenated derivatives and is used in biomass
processing and for the synthesis of bioactive compounds, thus
rendering the process both industrially and academically
relevant. Unfortunately, to achieve this, we are still seriously
limited by the use of either the dangerous and inconvenient
ruthenium complexes are known to carry out this important
12,14
catalysis.
In this report, the catalytic activity of
2
3
II
“
L Ru (NHC)”-based precatalysts 1-Cym and 2-Cym as
n
depicted in Figure 1 (L = para-cymene and NHC = an
n
imidazolydene-based NHC, Im-NHC, or a triazolydene-based
NHC, Trz-NHC) was explored to demonstrate the significant
role of the Trz-NHC ligand for selective oxidation of alkenes
and alkynes to the corresponding carbonyl compounds.
2
,3a,c,4,5
ozonolysis method with a reductive workup
selective and low-yielding Lemieux−Johnson oxidation proto-
9
or the less
6
7
8
col. Strong oxidants and OsO /oxidant and RuCl /NaIO
4
4
3
systems are also known to carry out these transformations with
major limitations. Although a few solitary moderately effective
catalysts have been reported to date based on well-defined
RESULTS AND DISCUSSION
■
II
+
−
The [(para-cymene)Ru (NHC)Cl] Br type of complexes 1-
Cym (NHC = Im-NHC) and 2-Cym (NHC = Trz-NHC)
were synthesized in 89% and 78% overall yields by first
deprotonation of quaternized NHC-ligand precursors using
10−14
ruthenium complexes,
major problems related to efficient
catalyst design remained unaddressed partly due to the lack of a
systematic structure−activity study to evaluate the associated
controlling and tuning factors of the catalytically relevant steps.
Ag O as a mild base to provide “Ag-NHC” intermediate
2
16
II
complexes followed by transmetalation to [(para-cymene)-
Ru Im-NHC-based (Im-NHC = an imidazolydene-based N-
II
1
Ru Cl ] . Both the complexes were fully characterized by H,
heterocyclic carbene) transition metal complexes have been
extensively reported in the literature to carry out a series of
transformations, which include cross-coupling (homo and
hetero) reactions, C−H activation reactions, water oxidation,
and transfer hydrogenation reactions. As an important
application for the oxidative cleavage of carbon−carbon
2 2
13
1
C{ H}, and 2D NMR spectroscopic and mass spectrometric
methods (details provided in the Supporting Information).
The proposed structures of 1-Cym and 2-Cym based on the
above techniques were unambiguously confirmed by X-ray
multiple bonds, recently we disclosed that a remote
Received: April 26, 2016
II
coordination site, Ru (terpy) , enhances the efficiency of a
2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00337
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Article
Table 1. Comparative Study of 1-Cym- and 2-Cym-Catalyzed
a
Oxidation of Olefins/Alkynes
Figure 1. Molecular structures of the ruthenium(II) precatalysts used
in oxidative cleavage of olefins/alkynes to carbonyl compounds.
ORTEPs were drawn at the 30% ellipsoid probability level. Hydrogen
atoms and counteranions are removed for clarity.
diffraction studies. 1-Cym and 2-Cym showed three-legged
piano-stool geometries around the ruthenium center with
II
CNHC−Ru −C
bite angles of 76.59(5)° and 76.61(6)°
pyridine
II
and CNHC−Ru bond lengths of 2.009(15) and 2.009(16) Å,
respectively. Complexes 1-Cym and 2-Cym showed Ru
II/III
redox potential values of 1.392 and 1.484 V vs SCE,
respectively (Figure 2). The potential for 2-Cym was found
Figure 2. Differential pulse voltammetric plots of 1-Cym and 2-Cym
in CH CN.
3
a
Reaction conditions: substrate, 0.4 mmol; NaIO , 1.0 mmol; cat,
to be anodically shifted by ∼92 mV compared to that for 1-
Cym. This shift may be attributed to the inherent poor σ-donor
and better π-acceptor properties of Trz-NHC compared to Im-
4
0
.002 mmol; acetone/H O (1:1), 6 mL; room temp; time, 15−240
2
min. Yields were determined by GC. TOF = mmol (product)/{mmol
(cat)·time (min)}. 4-(2-Oxoethoxy)benzaldehyde also appeared in
<
b
1
7
NHC.
5% yield.
Both the complexes were utilized as precatalysts (0.5 mol %
loading) for selective oxidation of various alkenes and alkynes
to the corresponding aldehydes and ketones using NaIO as a
efficiently to the corresponding oxygen-inserted products in
good to excellent yields. It is evident from Table 1 that 2-Cym
is a much more efficient catalyst than 1-Cym. This trend was
further verified and confirmed by more reliable kinetic profiles
4
sacrificial mild oxidant in acetone/H O solvent mixture at
2
ambient temperature. The results are shown in Table 1. With
the best precatalyst, 2-Cym, all the substrates were converted
B
DOI: 10.1021/acs.organomet.6b00337
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Article
of the reactions (Figure 3), which indeed supported the much
higher reaction rate with 2-Cym as compared to 1-Cym for the
Figure 4. UV−vis study with 1-Cym (left) and 2-Cym (right).
verify it, the catalytic oxidation of 4-methylstyrene with 2-Cym
was carried out in the presence of added para-cymene. The
decrease in the yield of aldehyde was observed when excess
para-cymene was added to the reaction mixture (Figure 5, left).
Notably, para-cymene was found to remain unreacted in the
Figure 3. Reaction kinetics profile of the precatalysts for the oxidation
of styrene to benzaldehyde.
1
catalytic conditions, which was confirmed by H NMR studies
(
see the Supporting Information).
oxidation of styrene to benzaldehyde. The difference in the rate
of the reaction can be attributed to the change in the NHC
backbone of the precatalysts and the contrasting electronic
effects thereof, as evident from Figure 2.
To understand the effect of the NHC ligands Im-NHC vs
Trz-NHC, the kinetic orders of dependency for the Ru(II)
precatalysts, oxidant NaIO , and alkene were determined by the
4
initial rate method for the oxidation of 4-methylstyrene to 4-
methylbenzaldehyde. For both complexes, the kinetics data
showed first-order rate dependency on precatalyst as well as
Figure 5. Effect of added para-cymene (left) and different arenes
right) on the catalytic oxidation of 4-methylstyrene with 2-Cym (0.5
mol %) as the precatalyst (RSM = recovered starting material).
(
NaIO and zero-order rate dependency on the alkene substrate
4
(
Supporting Information). Nonetheless, in general, it is
noteworthy that these results were found to be different from
literature reports, where first-order rate dependency on
precatalyst and substrate and zero-order rate dependency on
Interestingly, the decrease in the yield was also found in the
presence of other electron-rich arenes (Figure 5, right). These
studies suggested that in the case of 1-Cym and 2-Cym step I is
a key step of the proposed catalytic cycle in the subsequent
formation of the active catalyst. Since the Trz-NHC-based
complex 2-Cym is more electron-deficient than the Im-NHC-
based complex 1-Cym (confirmed from electrochemical
studies), easy release of para-cymene is expected in the case
of 2-Cym under catalytic conditions (owing to strong Ru →
Trz-NHC and poor Ru → para-cymene back-donation),
making it a more active precatalyst. It is noteworthy to
NaIO were reported, suggesting the alkene association as the
4
13,14
rate-determining step.
Therefore, in the case of the present
reactions, the rate-limiting step might not involve substrate, but
it involved Ru(II) complex and NaIO . The possible steps in
4
the plausible catalytic cycle are shown in Scheme 1. The
Scheme 1. Suggested Catalytic Steps
II
mention that “LnRu NHC”-type complexes have previously
been reported for the oxidative cleavage of carbon−carbon
double bonds by using NaIO as a sacrificial oxidant, and it was
4
shown that the NHC backbone is quite robust under these
12,14
oxidizing conditions.
To check the integrity of the NHC-
ligand backbone under the oxidizing catalytic conditions, a few
control experiments were conducted. The reaction of 4-
methylstyrene with 1-Cym and with 2-Cym (1-Cym:-
NaIO :4-methylstyrene; 1:25:10, and 2-Cym:NaIO :4-methyl-
4
4
1
styrene; 2:125:50) was monitored by time-dependent H NMR
spectroscopic studies in a CD CN/D O solvent mixture. These
3
2
studies showed that the NHC-ligand backbone remained intact
for both the catalyst precursors with a ∼15% and ∼2% decrease
of peak intensity after 15 min for 2-Cym and 1-Cym,
respectively. 4-Methylstyrene was found to be converted to 4-
methylbenzaldehyde gradually with time (Figures S42 and S43,
Supporting Information). Next, for the more active catalyst
precursor 2-Cym, a 1:1 stoichiometric reaction of 2-Cym and
proposed generation of ruthenium(VI)-dioxo species and its
reaction with alkene to form a metallacycle followed by its
cleavage to aldehyde was monitored by UV−vis spectroscopy
along the line of Che’s work, supporting a similar course of
13
reaction (Figure 4; see Supporting Information for details).
1
Step I is proposed to be reversible loss of para-cymene for the
precatalysts 1-Cym and 2-Cym in the presence of NaIO /H O.
NaIO was investigated in CD CN/D O. H NMR studies
4
3
2
indicated the existence of the (Trz-NHC)Ru(para-cymene)
backbone along with only free para-cymene and no free/
4
2
This step seems to be the key step for these complexes. To
C
DOI: 10.1021/acs.organomet.6b00337
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Article
transformed NHC ligand residues (Figure S44, Supporting
the products was verified by GC and GC-MS with known samples. In a
few cases, H NMR spectroscopy was also used to match the products
with the known samples.
Synthesis of 1-Phenyl-4-(pyridin-2-yl)-1H-1,2,4-triazol-4-ium
Bromide. 1-Phenyl-1H-1,2,4-triazole (350.4 mg, 2.0 mmol) and 2-
bromopyridine (314 mg, 2.0 mmol) were mixed in a pressure tube and
stirred under neat conditions at 140 °C for 48 h. After this, the
reaction mixture was allowed to cool to room temprature. After
cooling to room temprature, the formed solid was washed with THF
1
Information). However, with excess NaIO (20 equiv for 1
4
1
equiv of 2-Cym) the H NMR spectrum of the reaction mixture
exhibited broadening of the peaks corresponding to bound Trz-
NHC and para-cymene moieties (Figure S45, Supporting
Information). No oxidized NHC derivatives could be detected
1
by H NMR spectroscopy when a reaction of 2-Cym (0.03
mmol) and NaIO (10 mmol) under the standard conditions
4
but in the absence of substrate was analyzed (Figure S46,
Supporting Information). Moreover, ESI-MS study of a
and dried under high vacuum for 1 h to afford the desired product.
1
Yield: 392 mg (65%). H NMR (500 MHz, CDCl , 300 K): δ 13.61 (s,
3
1
H), 9.51 (s, 1H), 9.29 (d, J = 8.2 Hz, 1H), 8.56 (dd, J = 4.7, 1.1 Hz,
reaction mixture of 2-Cym/NaIO /4-methylstyrene (in
4
1
(
H), 8.45 (dd, J = 7.7, 1.6 Hz, 2H), 8.11 (td, J = 8.1, 1.7 Hz, 1H), 7.63
1
:25:10 molar ratio) in acetone/water showed the presence
m, 2H), 7.56 (m, 2H) ppm. 13C{ H} NMR (125 MHz, CDCl , 300
1
3
of parent precursor cation ([(Trz-NHC)Ru(para-cymene)-
Cl] ) along with two (Trz-NHC)Ru-oxo species, [(Trz-
K): δ 149.2, 144.4, 141.4, 140.3, 138.9, 134.8, 131.5, 130.5, 126.4,
+
1
20.9, 117.1 ppm. HRMS (ESI, positive ion): m/z = 223.09 (calcd for
13 11 4
+
+
NHC)RuO] and [(Trz-NHC)Ru(OH )(O) ] (Figure
+
2
2
[C H N ] = 223.0978).
S47, Supporting Information). All of the above studies
suggested the stability of the NHC-Ru backbone under
catalytic conditions. It is notable that any paramagnetic oxo-
Synthesis of 1-Cym. Silver(I) oxide (26 mg, 0.11 mmol) and
ligand precursor (62 mg, 0.2 mmol) were mixed in degassed
acetonitrile (8 mL) in a Schlenk tube. The reaction mixture was
stirred for 6 h at room temperature under dark conditions. [Ru(para-
cym)Cl ] (62 mg, 0.1 mmol) was added to the reaction mixture. This
IV
4
VI
2
Ru (d )-NHC or oxo-Ru (d )-NHC species would be
invisible in H NMR spectroscopy and hence might account
1
2 2
reaction mixture was again stirred overnight under dark conditions.
The resulting yellow solution was filtered through a Celite plug. The
yellow filtrate was reduced to 0.5 mL under vacuum. Addition of
diethyl ether to this concentrated solution resulted in a large amount
of precipitate. This precipitate was filtered and washed with diethyl
for the partial loss of peak intensity. The variable catalytic
activity and rate with 2-Cym and 1-Cym might be therefore
related to the different electronic perturbation of Trz-NHC and
18
Im-NHC ligands within the corresponding complexes.
ether to afford the desired product (Scheme S1). Yield: 102 mg (89%).
1
SUMMARY
H NMR (500 MHz, CDCl , 300 K): δ 9.46 (d, J = 5.5 Hz, 1H), 9.16
■
3
(
s {br}, 1H), 8.73 (d, J = 8.2 Hz, 1H), 8.05 (t, J = 7.7 Hz, 1H), 7.85−
In summary, with the help of two newly designed
II
7.79 (m, 2H), 7.65 (dd, J = 6.9, 3.4 Hz, 3H), 7.48 (d, J = 1.9 Hz, 1H),
“L Ru (NHC)”-type complexes, it was shown that just by
n
7
5
6
3
1
.47−7.42 (m, 1H), 5.97 (d, J = 6.1 Hz, 1H), 5.66 (d, J = 6.2 Hz, 1H),
.13 (d, J = 6.0 Hz, 1H), 4.63 (d, J = 6.0 Hz, 1H), 2.29 (dt, J = 13.8,
.9 Hz, 1H), 2.11 (s, 3H), 0.87 (d, J = 6.9 Hz, 3H), 0.84 (d, J = 6.9 Hz,
introducing a nitrogen atom at the C4/C5 position of an
imidazole-based ligand backbone, that is, modifying Im-NHC
to 1,2,4-Trz-NHC, the catalytic efficiency for the oxidation of
carbon−carbon multiple bonds was found to increase by an
order of magnitude. Electrochemical and a few other controlled
studies suggested that the Trz-NHC-based catalyst precursors
are electron deficient, wherein the key step involving reversible
loss of para-cymene controlled the observed enhanced
reactivity. Detailed mechanistic investigations including DFT
calculations are under way in our laboratory.
13
1
H). C{ H} NMR (125 MHz, CDCl , 300 K): δ 184.0, 156.1, 151.7,
3
41.8, 139.3, 130.4, 130.1, 126.5, 125.5, 124.0, 119.5, 114.5, 109.0,
106.7, 92.3, 89.1, 86.9, 82.9, 31.3, 22.9, 22.1, 19.3. HRMS (ESI,
+
positive ion): m/z = 492.0771 (calcd for [C H N ClRu]
492.0778). Anal. Found: C, 42.75; H, 3.90; N, 6.23. Calcd for
C H N ClRuBr·1.5CH Cl ·H2O: C, 42.79; H, 4.19; N, 5.87.
Synthesis of 2-Cym. This complex was synthesized by following
the same procedure as used for the synthesis of 1-Cym but in CH Cl
solvent (Scheme S1). Yield: 90 mg (78%). H NMR (500 MHz,
=
24
25
3
24 25
3
2
2
2
2
1
CDCl , 300 K): δ 10.83 (s, 1H), 9.49 (d, J = 4.5 Hz, 1H), 9.13 (d, J =
3
EXPERIMENTAL SECTION
■
6.4 Hz, 1H), 8.10 (s {br}, 1H), 7.94 (m, 2H), 7.65 (m, 3H), 7.53 (s
{br}, 1H), 6.03 (d, J = 4.4 Hz, 1H), 5.74 (d, J = 5.3 Hz, 1H), 5.35 (d, J
= 5.7 Hz, 1H), 4.93 (d, J = 5.8 Hz, 1H), 2.34−2.39 (m, 1H), 2.14 (s,
3H), 0.90 (dd, J = 8.9, 7.1 Hz, 6H) ppm. 13C{ H} NMR (125 MHz,
1
13
1
General Information. H and C{ H} NMR spectra were
recorded on Bruker AVANCE III 400 and 500 MHz NMR
spectrometers at room temperature unless mentioned otherwise.
Chemical shifts (δ) are expressed in ppm using the residual proton
1
CDCl , 300 K): δ 184.8, 156.8, 149.0, 142.4, 141.9, 138.7, 130.8,
3
resonance of the solvent as an internal standard (CHCl : δ = 7.26 ppm
129.9, 125.9, 125.4, 116.5, 109.0, 108.7, 92.6, 89.3, 87.7, 84.0, 31.4,
3
1
13
1
for H spectra, 77.2 ppm for C{ H} spectra; CH COCH : δ = 2.05
23.0, 22.0, 19.4 ppm. HRMS (ESI, positive ion): m/z = 493.0744
3
3
1
13
1
+
ppm for H spectra, 29.8 ppm for C{ H} spectra; CH CN: δ = 1.94
ppm for H spectra, 118.3 and 1.3 ppm for C{ H} spectra). All
(calcd for [C H N RuCl] = 493.0730). Anal. Found: C, 47.95; H,
3
23 24
4
1
13
1
4.48; N, 9.70. Calcd for C H N ClRuBr: C, 48.25; H, 4.19; N, 9.79.
23 24 4
coupling constants (J) are expressed in hertz (Hz) and only given for
H− H couplings unless mentioned otherwise. The following
abbreviations were used to indicate multiplicity: s (singlet), d
Electrochemical Analysis of the Complexes. A three-electrode
configuration was used to carry out the electrochemical studies (DPV).
Working electrode: Pt disk (1 mm diameter); counter electrode: a Pt
wire; reference electrode: saturated calomel electrode, SCE. Both
samples were prepared in dry deoxygenated acetonitrile. Hexafluor-
ophosphate salts of 1-Cym and 2-Cym were used for this study. A 0.1
1
1
(
(
doublet), t (triplet), q (quartet), dd (doublet of doublets), dt
doublet of triplets), m (multiplet). ESI mass spectroscopy was
performed on a Bruker microTOF QII spectrometer. GC-MS analysis
was performed on a Agilent 7890A GC/5975C MS system. The UV−
visible absorption and kinetic studies were carried out on a Cary 100
UV−vis spectrophotometer using 1.0 cm quartz cuvettes at room
temperature. The electrochemical measurements (differential pulse
voltammetry, DPV) were carried out using a CHI 620E electro-
chemical analyzer at room temperature. Dry solvents and reagents
were obtained from commercial suppliers and used without further
purification. RuCl ·xH O and deuterated solvents were purchased
M solution of [NBu ]PF solution was used as the supporting
4 6
+
electrolyte. Ferrocene (E1/2, Fc/Fc = 0.37 V vs SCE) was used as an
external calibration standard for all the experiments.
General Procedure for the Catalysis Studies. Substrate (0.4
mmol) in 1 mL of acetone and catalyst (0.5 mol %, bromide salts)
were taken in a round-bottom flask. A 2 mL amount of acetone and 2
mL of H O were added to it. NaIO4 (213 mg, 1.0 mmol) was
2
dissolved in 1 mL of H O and transferred to the reaction mixture. The
3
2
2
19
from Aldrich. [Ru(para-cymene)Cl ] and 1-phenyl-3-(pyridin-2-yl)-
H-imidazol-3-ium bromide were prepared by following a reported
reaction mixture was stirred at room temprature for ∼15−240 min.
2
2
20
1
After this time, Na SO (2.0 mmol) was added to the reaction mixture
2
3
method. All the products were previously reported, and the identity of
followed by the addition of 2 mL of dichloromethane (DCM) and 3
D
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Article
mL of H O. The reaction mixture was further stirred for 10 min.
(6) Pappo, R.; Allen, D. S., Jr.; Lemieux, R. U.; Johnson, W. S. J. Org.
Chem. 1956, 21, 478−479.
2
Standard (ethylbenzene, mesitylene, stilbene, or acetophenone) was
added as a reference, and the reaction mixture was again stirred for 5
min. It was then transferred to a separating funnel with the help of 3
(7) (a) Travis, B. R.; Narayan, R. S.; Borhan, B. J. Am. Chem. Soc.
2002, 124, 3824−3825. (b) Berkowitz, L. M.; Rylander, P. N. J. Am.
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H. M. S.; Eberlin, M. N.; Stefani, H. A. Tetrahedron Lett. 2009, 50,
2312−2316.
mL of H O and 8 mL of DCM. The organic layer was separated, and
2
the aqueous layer was again extracted with 5 mL of DCM (two times).
The combined organic layer was washed with 20 mL of brine solution.
Products and unreacted substrates were analyzed by GC-MS. The
yields of the products were calculated by GC analyses.
(8) (a) Milas, N. A.; Trepagnier, J. H.; Nolan, J. T., Jr.; Iliopulos, M.
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
■
*
S
(9) (a) Carlsen, P. H. J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J.
.
Org. Chem. 1981, 46, 3936−3938. (b) Yang, D.; Zhang, C. J. Org.
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(
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Additional experimental details and schemes, character-
ization data, kinetic data, and additional figures (PDF)
Crystallographic data for 1-Cym (CCDC 1441844) and
(
2-Cym (CCDC 1441846) (CIF)
(
2
(
AUTHOR INFORMATION
Corresponding Author
E-mail (J. Choudhury): joyanta@iiserb.ac.in.
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Notes
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16) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251, 642−670.
17) (a) Teng, Q.; Huynh, H. V. Inorg. Chem. 2014, 53, 10964−
tz, J.; Frey, G. D.; Herdtweck, E.
Organometallics 2006, 25, 2437−2448.
18) We compared the catalytic activity of the 2-Cym/NaIO system
The authors declare no competing financial interest.
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0973. (b) Herrmann, W. A.; Schu
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ACKNOWLEDGMENTS
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J.C. sincerely thanks DST and IISER Bhopal for generous
financial support. S.K.G. is a recipient of a CSIR doctoral
fellowship. S.K.S. thanks DST-INSPIRE for a BSMS fellowship.
We thank Professor Robert H. Crabtree for helpful discussions.
(
4
with the RuCl /NaIO system for 1-octene and cyclooctene oxidation
3
4
(see the Supporting Information for details). The disparate results
obtained thus far suggested that the active catalysts might be different
in these two systems. However, the possibility of generation of a trace
amount of RuO via complete degradation of all organic ligands in the
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DOI: 10.1021/acs.organomet.6b00337
Organometallics XXXX, XXX, XXX−XXX