Palladium aminopyridine complexes catalyzed selective benzylic C-H oxidations with peracetic acid

Article abstract of DOI:10.1039/d0dt02247k

Four palladium(ii) complexes with tripodal ligands of the tpa family (tpa = tris(2-pyridylmethyl)amine) have been synthesized and X-ray characterized. These complexes efficiently catalyze benzylic C-H oxidation of various substrates with peracetic acid, affording the corresponding ketones in high yields (up to 100%), at <1 mol% catalyst loadings. Complex [(tpa)Pd(OAc)](PF6) with the least sterically demanding ligand tpa demonstrates the highest substrate conversions and ketone selectivities. Preliminary mechanistic data provide evidence in favor of metal complex-mediated rate-limiting benzylic C-H bond cleavage by an electron-deficient oxidant.

Full text of DOI:10.1039/d0dt02247k

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Palladium Aminopyridine Complexes Catalyzed Selective Benzylic C-H
View Article Online
DOI: 10.1039/D0DT02247K
Oxidations with Peracetic Acid
a,b
a,b
b,c
b,d
Dmitry P. Lubov, Oleg Yu. Lyakin, Denis G. Samsonenko, Tatyana V. Rybalova, Evgenii
a,b
a,b
P. Talsi, Konstantin P. Bryliakov*
a
Boreskov Institute of Catalysis, Pr. Lavrentieva 5, Novosibirsk 630090, Russia
Novosibirsk State University, Pirogova 1, Novosibirsk 630090, Russia
b
c
Nikolaev Institute of Inorganic Chemistry, Pr. Lavrentieva 3, Novosibirsk 630090, Russia
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Pr. Lavrentieva 9, Novosibirsk 630090,
d
Russia
E-mail: bryliako@catalysis.ru
Abstract
Four palladium(II) complexes with tripodal ligands of the tpa family (tpa = tris(2-
pyridylmethyl)amine) have been synthesized and X-ray characterized. These complexes efficiently
catalyze benzylic C-H oxidation of various substrates with peracetic acid, affording the
corresponding ketones in high yields (up to 100 %), at <1 mol. % catalyst loadings. Complex
[
(tpa)Pd(OAc)](PF ) with the least sterically demanding ligand tpa demonstrates the highest
6
substrate conversions and ketone selectivities. Preliminary mechanistic data provide evidence in
favor of metal complex-mediated rate-limiting benzylic C-H bond cleavage by an electron-deficient
oxidant.
Keywords
C-H activation, selective oxidation, mechanism, palladium, peracetic acid
1

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Page 2 of 18
Introduction
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DOI: 10.1039/D0DT02247K
Developing efficient approaches to late-stage activation and functionalization of C-H bonds in
complex organic molecules has been considered as a challenging goal; novel catalysts, capable of
conducting these transformations in a predictably selective fashion, could revolutionize current
synthetic approaches to biomolecules derivatization and metabolites synthesis in today’s drug
discovery.1–3 Designing catalysts for such processes is not trivial, since C-H groups are often
thought of as ‘un-functional groups’, with the common representation of organic molecules with
‘
invisible’ hydrogens reflecting both their ubiquitous nature and lack of reactivity.4
To date, a broad range of C–H functionalization reactions, with formation of new C-X,
including C-O, bonds, have been reported, the majority of those relying on transition metal based
catalysts.5–8 Palladium compounds have been extensively used as reagents and catalysts for organic
synthesis,9,10 including the oxidation of alkenes11,12 and alcohols.13–16 However, unlike first-row
transition metal complexes, the involvement of palladium in selective benzylic C-H oxidations has
so far been rather limited.17,18 The Pd-mediated C-H bond oxygenations, reported to date, have
invoked both Pd(0)/Pd(II) and Pd(II)/Pd(IV) catalytic cycles;19,20 typically, such processes are
carried out through inner-sphere mechanism21,22 via the formation of organopalladium intermediates
in the presence of directing groups.23,24
As part of our longstanding interest in designing transition metal based catalyst systems for
the selective oxygenation of aliphatic and aromatic C-H groups,25–29 we sought catalysts, capable of
mediating selectively activating benzylic CH groups of substrates with various C-H bonds
2
(aromatic, aliphatic), with formation of ketone functionalities. The present work has been inspired
by the success of tripodal N -donor tpa-type ligand in bioinspired oxidations, mediated by various
4
transition metal complexes.30–34 Herein, we present the synthesis and characterization of a series of
palladium(II) complexes with ligands of the tpa family, that have been shown to catalyze the
selective benzylic C-H oxidations with peracetic acid as terminal oxidant, demonstrating high
efficiency, as well as regio- and chemoselectivity.
2

Page 3 of 18
Dalton Transactions
Results and discussion
View Article Online
DOI: 10.1039/D0DT02247K
Palladium (II) complexes 1-4 (Figure 1) were prepared from the corresponding N -donor tripodal
4
ligands and either Pd(OAc) (complexes 1, 2) or [Pd(CH CN) ](OTf) (complexes 3, 4). N donor
2
3
4
2
4
ligands of the tpa family were synthesized according to modified literature procedures (see SI for
details). Complexes 1 and 2 were prepared by heating a mixture of ligands with palladium acetate in
methanol with subsequent addition of ammonium hexafluorophosphate, while 3 and 4 were
obtained by treating [Pd(CH CN) ](OTf) with the corresponding ligand in acetonitrile at ambient
3
4
2
temperature. X-ray quality crystals of 1-4 were grown from CH CN, layered with Et O.
3
2
PF6
O
PF6
N
N
Pd
N
O
N
O
Pd
N
N
O
N
O
O
N
CH3
CH3
CH CN
3
O
1
2
(OTf)2
(OTf)2
N
N
N
N
Pd
Pd
N
N
NCCH3
NCCH3
N
N
H O
2
3
4
PF6-
+
N
N
1
) Pd(OAc)2,
Pd
R
MeOH, 60°C;
N
OAc
2) NH PF ;
N
4
6
R
R
R
N
R
1 and 2
N
N
OTf-
2+
2
N
N
N
Pd(CH CN) ](OTf)
R
R
3
4
2
Pd
N
CH CN, r.t.
N
NCCH3
3
R
R
3
and 4
Figure 1. Structure of palladium complexes 1-4 considered in this study (top) and their synthesis
–
(
bottom). OTf is trifluoromethanesulfonate anion.
3

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Page 4 of 18
Molecular crystal structures of complexes 1-4, established on the basis of single-crystal X-
View Article Online
DOI: 10.1039/D0DT02247K
ray diffraction studies (see SI for details), are shown in Figure 2. All complexes contain cations
8
with the metal ion in a nearly square planar environment, typical for d Pd (II) complexes.
Complexes 1 and 2, stemming from Pd(OAc) , bear one acetate anion in the first coordination
2
sphere of the central atom, while in 3 and 4, this position is occupied by an acetonitrile molecule.
Complexes 1, 3, and 4 crystallize in a triclinic crystal system (P-1), while the 2 features additional
elements of symmetry (P2 /c). In all complexes, one of the three pycolyl nitrogens does not form
1
metal-N bond (Figure 2). This structural peculiarity was previously documented for other
3
5,36
palladium(II) complexes with tripodal N -donor ligands.
A notable structural feature of complex
, owing to the presence of 6-Me substituents in the pyridyl moieties, is the much more restricted
cone trajectory available for the substrate to reach the Pd site (ca. 88 º vs. ca. 117 º for complexes 1,
4
4
2
and 3, Figure 3), which may account for its markedly different catalytic reactivity, see below.
4

Page 5 of 18
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Figure 2. Molecular structure of complexes 1-4. Thermal ellipsoids are drawn at the 50%
View Article Online
DOI: 10.1039/D0DT02247K
probability level. Pd: blue, O: red, N: light blue, C: grey, P: orange, S: light orange, F: yellow.
Hydrogens are omitted for clarity. In 2, only one of the two Pd atoms of the unit cell is shown. In 3
and 4, co-crystallized molecules (CH CN and H O, respectively) are omitted.
3
2
N
N
X
N
N
X
Pd
N
H
Pd
N
CH3
N
N
H
117 °
CH3
88 °
Figure 3. Restriction of the cone of available substrate trajectories upon insertion of β-pyridine
Me substituents.
Complexes 1-4 were examined as catalyst in the oxidation of ethylbenzene, using different
terminal oxidants. First of all, different oxidants were tested in combination with complex 1 (Table
1
). Peroxyacids (AcOOH, mCPBA: entries 1, 2) demonstrated good conversions and ketone
selectivities, with minor by-products 1-phenylethanol acetate and 1-phenylethanol. With
H O /AcOH no reaction was the case (entry 3). With tert-butyl hydroperoxide as oxidant, 1-
2
2
phenylethyl hydroperoxide was the major reaction product (entry 4). Iodosylbenzene and
iodobenzene diacetate showed high ketone selectivity, but substrate conversion was poor (entries 5,
6
). Sodium periodate demonstrated even poorer conversion (entry 7).
Table 1. Ethylbenzene oxidation in the presence of complex 1 and different oxidants.a
H
H
O
1
+
by-products
CH CN
3
oxidant
60°C, 24 h
conversion yield of ketone
entry
oxidant
b
b
(%)
(%)
AcOOH c
85
82
1
2
3
4
mCPBA
66
0
54
0
3 f
d
H O (30% aq)
2
2
TBHP e
49
5

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Page 6 of 18
5
6
7
PhIO
15
19
6
13
18
4
View Article Online
DOI: 10.1039/D0DT02247K
PhI(OAc)2
NaIO4 g
a
Reaction conditions: 60 °C; ethylbenzene (100 μmol), oxidant (4 equiv.), catalyst (0.6 mol. % Pd), CH CN
3
b
(
200 μL); oxidant was added in one portion, and the mixture was stirred for 24 h. conversion and yield were
c
d
determined by HPLC and NMR. 35wt. % solution in diluted acetic acid. 4 equiv. H O and 175 µmol of
2
2
e
f
AcOH was added.
Added as 5.5 M solution in decane. The major product was 1-phenylethyl
g
hydroperoxide (ca. 40%). in CH CN/H O (250 µL:100 µL).
3
2
The best oxidation results were achieved with 0.6 mol. % of catalyst 1, 4 equiv. of AcOOH,
and conducting the reaction for 24 h at 60°C (Table 2, entries 1-3). Adding more oxidant did not
lead to meaningful conversion growth (entry 3). Increasing the catalyst loading slightly deteriorated
both the conversion and ketone yield (entry 4). Lowering the temperature reduced the conversion
(entry 5).
Table 2. Ethylbenzene oxidation with AcOOH in the presence of Pd complexes 1-4. a
O
OAc
H
H
Pd complex
other products
of oxidation
+
+
CH CN
3
AcOOH
60°C, 24 h
conversion, % c yield of ketone,
% c
catalyst loading,
AcOOH,
equiv. b
entry
catalyst
mol. %
1
2
3
4
5
6
7
8
9
1
1
0.6
0.6
0.6
0.8
0.6
0.6
0.6
−
3
4
5
4
4
4
4
4
70
85
87
81
49
61
81
0
68
82
85
77
47
1
1
1 d
2
60
76
0
3
− e
[Pd(CH CN) ](OTf)
2
0.6
0.6
4
4
23
23
18
17
77
3
4
1
1
1
1
0
1
2
3
Pd(OAc)2
1 f
0.6
1
1
4
4
4
80
36
38
g
4
21
34
f
h
4
6

Page 7 of 18
Dalton Transactions
a
Reaction conditions: 60 °C; ethylbenzene (100 μmol), AcOOH, catalyst, CH CN (200 μL); oxidant was
3
View Article Online
b
c
added in one portion and the mixture was stirred for 24 h. vs. ethylbenzene. ConversionDO
a
I
n
: 1
d
0.1
y
0
i
3
e
9
l
/
d
D0
w
DT
e
02247K
r
e
d
e
f
g
determined by HPLC. T = 30°C. Blank experiment (without catalyst). Under an agron atmosphere. The
main (10 %) by-product was 1-phenylethyl hydroperoxide, along with 1-phenylethanol and 1-phenylethyl
h
acetate (ca. 5 % together). Byproducts: 1-phenylethanol and 1-phenylethyl acetate (ca. 4 % together).
Complexes 1 and 3 demonstrated comparable catalytic efficiency and selectivity in
ethylbenzene oxidation (cf. entry 7 vs. 2), while with 2, the conversion was markedly lower (entry
6
). Blank experiment (without catalyst) showed no product formation without catalyst (Table 2,
entry 8). Replacing the Pd complexes with salts, [Pd(CH CN) ](OTf) and Pd(OAc) , resulted in a
3
4
2
2
dramatic drop of the substrate conversion and ketone yield (entries 9, 10), thus reflecting the key
role of the chelating N-donor ligands in ensuring the catalytic activity of the Pd complexes.
Atmospheric oxygen is not substantially involved in the oxidations in the presence of complex 1:
conducting the oxidation under inert atmosphere did not (within experimental error ± 5 %) affect the
reaction outcome (entry11 vs. 2 and 7).
Contrastingly, complex 4 showed much poorer conversion (36 %, even at higher catalyst
loading of 1 mol %, cf. entries 12 and 2). Significantly, formation of sizeable amounts of 1-
phenylethyl hydroperoxide as by-product was detected. Conducting the reaction in the presence of 4
under inert atmosphere dramatically improved the ketone yield and selectivity, with no evidence for
hydroperoxide formation (entry 13). These observations apparently reflect significant contribution
of free-radical driven oxidation pathway in the case of 4 under aerobic conditions. Most plausibly, it
is increased steric hindrance of the central atom in 4 (owing to 6-methyl groups) which restricts the
access of reactants to the metal center, thus suppressing the contribution of the main (presumably
transition-metal mediated) reaction pathway, and facilitating the radical-driven oxidation.
Next, the benzylic oxidation of a range of arylalkyl substrates was examined under the
optimized reaction conditions. The results of oxidations in the presence of complex 1 are
summarized in Table 3, with the ketone yields ranging from moderate to very high (39-98 %).
7

Dalton Transactions
Page 8 of 18
Under the same conditions, complex 2 in most cases showed lower conversions and ketone yields
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DOI: 10.1039/D0DT02247K
(see Table S1, SI).
Table 3. Benzylic oxidation of arylalkanes with AcOOH in the presence of complex 1. a
O
OAc
1
(0.6 mol %)
R2
R2
R2
+
CH CN
3
R1
R1
R1
AcOOH (4 equiv.)
0°C, 24 h
6
entry
1
substrate
conversion (%) ketone yield (%)
85
70
73
82
68
69
2
3
4
Cl
Br
59
50
O N
2
5
6
7
8
9
<30% b
<7% b
MeO
80
79
66
76
46 c
33 d
62
99
47
83
52
84
1
1
1
1
1
1
1
0
1
2
3
4
5
6
39
77
1
00
100
90
O
9
2
O
99
98
>99
97 e
8

Page 9 of 18
Dalton Transactions
a
Reaction conditions: 60 °C; substrate (100 μmol), AcOOH (0.4 mmol), catalyst (0.6 μmol Pd), CH CN (200
3
View Article Online
μL); oxidant was added in one portion, and the mixture was stirred for 24 h. ConversionDO
a
I
n
:
d
10.1
y
0
i
3
e
9
l
/
d
D0
w
DT
e
02247K
r
e
b
determined by HPLC and NMR.
Conversion and yield was estimated by GC-MS. 2-methoxy-5-
ethylhydroquinone (<9%) and 2-ethylhydroquinone (<9%) were the main byproducts. c Main byproducts
d
were 3-ethyl- and 3-acetylbenzoic acids (up to 20%). The main byproducts were 1-(o-tolyl)ethanol (8%), 2-
ethylbenzoic acid (5%), N-(1-(o-tolyl)ethyl)acetamide (7%). e Yield of the major product, 9,10-diketone
(anthraquinone).
The selectivity of the Pd catalysts for the ketone has been very high; either by using lower
catalyst loadings or lower temperatures, significant amount of alcohol could not be obtained. The
presence of electron-withdrawing substituents in the substrates slightly reduced the conversion
(
Table 3, entries 2-4). Interestingly, p-methoxy group directed the oxidation preferentially toward
the aromatic ring (entry 5). The main products in the latter case were substituted hydroquinones
estimated <18% by GC/MS). The oxidation of substrates having benzylic methylene and methyl
positions (o-, m-, p-ethyltoluenes) occurred preferentially at the methylenic group (Table 3, entries
-8). Upon the oxidation of isobutylbenzene, ketone formation (52 % yield, entry 9) was
(
6
accompanied by the emergence of minor product of tertiary C-H group oxidation (α,α-
dimethylphenetyl alcohol, <4 %). The oxidation of cyclic substrates in most cases afforded the
ketones in excellent yields (entries 10-14). In the case of phthalane, the reaction proceeded with
9
9% conversion, with excellent selectivity for phthalide (entry 15). The oxidation of
dihydroanthracene gave the corresponding diketone in high yield (entry 16).
Some insight into the mechanism of the palladium catalyzed benzylic C-H oxidation was
obtained. First of all, the documented excellent selectivities for ketone, in case of 1, suggest ruling
out the radical chain autoxidation (involving participation of long-lived alkyl radicals, capable of
capturing dissolved dioxygen) as the rate-limiting C-H breaking step in arylalkanes: in that case,
alcohol/ketone ratios of ≈ 1, accompanied by formation of significant amounts of alkyl
hydroperoxides would be expected.37-39
9

Dalton Transactions
Page 10 of 18
Secondly, primary kinetic isotope effect (KIE) was measured in ethylbenzene/d -
1
0
View Article Online
DOI: 10.1039/D0DT02247K
ethylbenzene competitive oxidations in the presence of complexes 1 and 2 (Figure 4a). The
resulting high k /k values (6.3 and 6.2, respectively; see SI for details) are substantially higher
H
D
than those characteristic of C-H abstractions by HO˙ (1-2) and RO˙ (ca. 4) radicals.40–43 On the
other hand, these KIE values are substantially lower than those documented for benzylic C-H
4
4
abstractions by less reactive ROO˙ (KIE 14-16) radicals, which argues against participation of the
latter in our system.
Actually, the observed k /k values fall within the range of 3-10, typically reported for C-H
H
D
oxidations by electron-deficient transition metal complexes,27,45–56 including platinum group metal
oxo complexes,57–60 therefore, in addition, clearly indicating that benzylic hydrogen lies on the
reaction coordinate at the rate-limiting step. Competitive oxidations of 1-phenylethanol and 1-d-1-
phenylethanol were also conducted (Figure 4b), expectedly25,61 revealing lower primary k /kD
H
values, still pointing to rate-limiting C-H bond breaking step.
H
D
D
H
CD3
O
O
CD3
1
or 2
+
+
D
+
by-products
a)
D
AcOOH
CH CN, 60°C
3
k /k = 6.3 (for complex 1);
H
D
k /k = 6.2 (for complex 2).
H
D
HO
O
H(D)
1
or 2
b)
+ by-products
AcOOH
CH CN, 60°C
3
k /k = 2.4 (for complex 1);
H
D
k /k = 3.0 (for complex 2).
H
D
Figure 4. Kinetic isotope effect measurements: a) for C-H oxidation of ethylbenzene and d -
1
0
ethylbenzene; b) for oxidation of 1-phenylethanol and 1-d-1-phenylethanol. For details see SI.
Further, competitive oxidations of substituted ethylbenzenes were performed, providing very
+
close, moderately negative ρ values (-1.04 for 1 and -0.99 for 2) in linear log(k /k ) correlation
X
H
1
0

Page 11 of 18
Dalton Transactions
+
versus Brown-Okamoto polar substituent parameters σ (Figure 5 and Figure S2). This reflects
View Article Online
DOI: 10.1039/D0DT02247K
6
2
electron-deficient transition state, possibly preceding the formation of a radical intermediate. Such
+
57
slope value (cf. ρ -2.0 for Ru porphyrin mediated C-H oxidation ) indicates moderate charge
6
3
separation, comparable to that occurring upon hydrogen atom abstractions by bromine atoms. The
+
64
observed ρ value is closer to that reported for the C-H oxidations by cytochrome P-450 (-1.6),
6
5
56,58
perferryl complexes (-0.8), high-valent oxoruthenium complexes (-1.4).
For comparison, the
slopes documented for oxidations with rate-limiting C-H bond breaking by RO˙ and ROO˙ radicals
typically fall within the range -0.3 to -0.6.66-69
+
Actually, the observed ρ value nearly coincides with that documented for benzylic C-H
oxidations, mediated by bis-amino-bis-pyridine manganese complexes, in which case C-H bond
breaking by high-valent terminal metal-oxo complex with formation of a radical intermediate was
presumed.46
These preliminary data look intriguing, since the formation of terminal palladium oxo
complexes, yet occasionally invoked as active species of oxidative C-H functionalization
1
7
70
reactions, have never been supported by compelling evidence. We look forward to collecting
more experimental data and hypothesizing on the role of the pending pyridyl moiety, as well as on
the overall oxidation mechanism in a separate in-depth mechanistic study.
Figure 5. Hammett plot for the competitive oxidation of substituted ethylbenzenes with AcOOH in
the presence of complex 1. For details see SI.
1
1

Dalton Transactions
Page 12 of 18
Conclusions
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DOI: 10.1039/D0DT02247K
Four novel palladium(II) complexes with tripodal ligands of the tpa family (tpa = tris(2-
pyridylmethyl)amine) have been synthesized and X-ray characterized. In spite of the N -donor
4
nature of the tpa-type ligands, all complexes feature square-planar topology, with one of the pyridyl
arms remaining unbound. These complexes have been shown to efficiently (at <1 mol. % catalyst
loading) catalyze benzylic C-H oxidation of various substrates with peracetic acid, affording the
corresponding ketones in high yield (up to 100 %). Methylene groups are preferentially oxidized in
the presence of methyl groups. To the best of our knowledge, this is the first example of highly
selective palladium mediated oxidation of substrates with benzylic CH groups to the corresponding
2
ketones by peracetic acid.
In the series, palladium complexes with the least sterically demanding ligand,
[
(tpa)Pd(OAc)](PF ) (1) and [(tpa)Pd(CH CN)](OTf) (3), demonstrate the highest ketonization
6 3 2
selectivity. The introduction of Me and OMe substituents into the ligand pyridyl rings (complexes 2
and 4) reduces the substrate conversions and (in case of 4) leads to formation of significant amounts
of C-H hydroperoxidation byproducts.
In case of catalysts 1-3, high to excellent ketone formation selectivities may indicate the
absence of statistically meaningful contribution of radical chain autoxidation pathways to the
overall process. This agrees with the observation that for catalyst 1, conducting the oxidations under
ambient air and under inert atmosphere showed identical results. The oxidations demonstrate
sizeable primary deuterium KIE of 6.2…6.3 (ethylbenzene/d -ethylbenzene), typical for rate-
1
0
limiting C-H abstractions by electron-deficient high-valent transition metal complexes. The
+
moderately negative slope (ρ of -1.0) of the Brown-Okamoto correlations for the oxidation of p-
substituted ethylbenzenes falls within the range typical for C-H oxidations occurring via rate-
limiting metal-mediated hydrogen atom abstractions, with generation of electron-deficient transition
state.
1
2

Page 13 of 18
Dalton Transactions
At the same time, at least in the case of complex 4, oxidations under ambient air and argon
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DOI: 10.1039/D0DT02247K
(Table 2, entries 12 and 13) showed significantly differing results, thus witnessing that possible
contribution of radical authoxidation into the overall reaction should not be completely ruled out.
Further studies, focused on extensive investigation of the ligand effects on the catalytic C-H
oxidation reactivity of Pd complexes, and detailed evaluation of the reaction mechanism, are
underway in our laboratory.
Experimental
Standard catalytic oxidation procedure
Substrate (0.10 mmol) was added to the solution of the desired palladium complex (0.6 μmol of Pd)
in CH CN (0.20 mL). Then, peracetic acid (0.40 mmol, 35wt.% solution in dilute acetic acid) was
3
added in one portion. The resulting mixture was stirred at 60°C for 24 h and then subjected to
HPLC, NMR, or GC-MS analysis. The amount of 1-phenylethylhydroperoxide (Table 2, entries 12,
1
3) was quantified by GC-MS using Shul’pin triphenylphosphine test.71
More data (The detailed experimental procedures and the X-ray data for complexes 1-4) are
provided in the Supporting Information.
ORCID
Konstantin P. Bryliakov: 0000-0002-7009-8950
Dmitry P. Lubov: 0000-0002-8991-580X
Oleg Yu. Lyakin: 0000-0001-8540-8707
Denis G. Samsonenko: 0000-0003-2688-4521
Tatyana V. Rybalova: 0000-0003-2398-5271
Evgenii P. Talsi: 0000-0003-0756-1401
Conflict of interests
There are no conflicts of interest to declare.
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DOI: 10.1039/D0DT02247K
Acknowledgements
This work was conducted with the financial support from the Russian Science Foundation (project
7-13-01117). The authors thank Dr. M.V. Shashkov for GC-MS measurements. The authors thank
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Novosibirsk State University, the Center of Collective Use “National Center of Catalysis Research”
and Multi-Access Chemical Research Center SB RAS for providing the access to spectral and
analytical facilities.
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TOC entry
View Article Online
DOI: 10.1039/D0DT02247K
PF6
N
N
Pd
N
OAc
N
H
H
O
(0.6 mol %)
R2
R2
AcOOH
R1
R1
up to 100 % yield
CH CN
3
60°C
R = H, alkyl, halogen, NO
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2
R = alkyl, aryl, alkoxy
2
Palladium complexes with tripodal ligands of the tpa family efficiently catalyze benzylic C-H
oxidation of various substrates with peracetic acid, affording the corresponding ketones in high
yields (up to 100 %), at <1 mol. % catalyst loadings.
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