Non-redox metal ions promoted oxidative dehydrogenation of saturated C[sbnd]C bond by simple Pd(OAc)2 catalyst

Article abstract of DOI:10.1016/j.catcom.2016.11.007

Adding non-redox metal ions to simple Pd(OAc)₂ catalyst can remarkably promote oxidative dehydrogenation of saturated C[sbnd]C bond, and the activity improvement is Lewis acidity strength dependent. Through UV–vis and NMR characterizations of the catalyst, it was proposed that in-situ generated heteronuclear Pd(II)/Zn(II) dimer is the key active species for dehydrogenation.

Full text of DOI:10.1016/j.catcom.2016.11.007

Catalysis Communications 90 (2017) 5–9
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Non-redox metal ions promoted oxidative dehydrogenation of saturated
C\\C bond by simple Pd(OAc) catalyst
2
Chenlin Lou, Shuhao Qin, Sicheng Zhang, Zhanao Lv, Ahmed M. Senan, Zhuqi Chen, Guochuan Yin ⁎
School of Chemistry and Chemical Engineering, Key Laboratory of Material Chemistry for Energy Conversion and Storage (Huazhong University of Science and Technology), Ministry of Education,
Hubei Key Laboratory of Material Chemistry and Service Failure, Huazhong University of Science and Technology, Wuhan 430074, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 August 2016
Received in revised form 19 October 2016
Accepted 3 November 2016
Available online 09 November 2016
Adding non-redox metal ions to simple Pd(OAc) catalyst can remarkably promote oxidative dehydrogenation of
saturated C \\ C bond, and the activity improvement is Lewis acidity strength dependent. Through UV–vis and
NMR characterizations of the catalyst, it was proposed that in-situ generated heteronuclear Pd(II)/Zn(II) dimer
is the key active species for dehydrogenation.
2
©
2016 Published by Elsevier B.V.
Keywords:
Oxidative dehydrogenation
Palladium(II)
Lewis acid
Active heterobimetallic species
1
. Introduction
oxidations in addition to its redox properties [15], and next explored
Al(III) promoted benzene hydroxylation by Pd(II)(bpym) catalyst,
non-redox metal ions promoted olefin isomerization and oxidative cou-
Oxidative dehydrogenation of saturated C\\C bond around ambient
temperature represents one of the promising protocols to obtain the
2
pling of indole with olefin by Pd(OAc) catalyst [16–18]. The promotion
functionalized compounds like olefin, aromatics, and heterocycles [1–
effects were attributed to the formation of heterometallic Pd(II)/Lewis
acid complexes which improved C\\H bond activation capability of
Pd(II) cation. Herein we demonstrate another example of non-redox
metal ions promoted C\\H activation by Pd(II) catalyst, that is, the pres-
ence of non-redox metal ions can remarkably improve the catalytic effi-
ciency of simple Pd(OAc) catalyst in aerobic dehydrogenation of the
2
saturated C\\C bond to obtain indoles from heterocyclic compounds,
and phenols from cycloketone.
3
]. Traditionally, those bulky olefinic and aromatic compounds like pro-
pylene and styrene are commercially produced by heterogeneous cata-
lysts at high temperature with the release of hydrogen (H ), which are
2
not suitable for many fine and pharmaceutical products [4,5]. Alterna-
tively, through oxidative dehydrogenation, the energy compensation
from water formation can drive the dehydrogenation reaction happens
around ambient temperature. In 2011 and later, Stahl and co-workers
reported a Pd(II)-catalyzed aerobic dehydrogenation of substituted cy-
clohexanones to phenols, in which the presence of organic ligands are
essential to achieve the good yields [6,7]. Balcells and co-workers alter-
natively demonstrated another example of dehydrogenation using
2. Experimental
2.1. Materials and methods
2 2
H O as oxidant, in which copper complexes could catalyze oxidative
dehydrogenation of alkane including robust n-hexane or cycloalkane
to n-hexene and cycloalkenes, respectively [8]. Liu also reported that re-
action-activated palladium catalyst can dehydrogenate substituted cy-
All chemical reagents are commercially available and used without
further purification. UV–vis spectra were studied on Analytikjena
specord 205 UV–vis spectrometer, NMR analysis was performed on
Bruker AV400.
clohexanones to phenols and H
acceptors [9].
2
without oxidants and hydrogen
Recently, non-redox metal ions promoted stoichiometric and cata-
lytic oxidations by redox metal ions have attracted much attention
2.2. General procedure for indoline dehydrogenation reaction by Pd(OAc)
with Zn(OTf)
2
2
[10–14]. In particular, we further found that the Lewis acid properties
of copper(II) play a significant role in Pd(II)-catalyzed Wacker-type
Pd(OAc)
2
(1.12 mg, 0.005 mmol), Zn(OTf)
2
(3.63 mg, 0.01 mmol)
were dissolved in 5 mL acetonitrile in a glass tube, after stirring for
0 min, indoline (60 mg, 0.5 mmol) were added. The glass tube was
equipped with a reflux condenser. Next, the reaction solution was
1
⁎
Corresponding author.
E-mail address: gyin@hust.edu.cn (G. Yin).
http://dx.doi.org/10.1016/j.catcom.2016.11.007
566-7367/© 2016 Published by Elsevier B.V.
1

6
C. Lou et al. / Catalysis Communications 90 (2017) 5–9
magnetically stirred at 353 K in oil bath for 6 h with O
product analysis was performed by GC using the internal standard
method. Control experiments including using Pd(OAc)
alone were carried out in parallel.
2
balloon. The
experiments using Lewis acid as catalyst demonstrated ignorable activ-
ity for dehydrogenation, thus eliminated the role of impurities in
dehydrogenation.
2 2
, or Zn(OTf)
The influence of Zn(II)/Pd(II) ratio on indoline dehydrogenation was
2 2
displayed in Fig. S2. Increasing the ratio of Zn(OTf) /Pd(OAc) up to 4
3
. Results and discussion
still continuously improved the dehydrogenation efficiency, which is
similar to that in Lewis acid promoted Wacker-type oxidation by
To screen the Lewis acid for the Pd(OAc)
2
catalyzed dehydrogena-
2
Pd(OAc) catalyst, but different from that in olefin isomerization [15,
tion, an easy substrate, indoline, was first tested for aerobic oxidative
dehydrogenation, and the reactions were conducted in acetonitrile
17]. In olefin isomerization, increasing the ratio of Al(III)/Pd(II) from 0
to 1 can sharply improve the isomerization efficiency, while further in-
creasing the ratio does not show significant improvement. Catalytic ki-
netics of 2-methylindoline dehydrogenation also disclosed that adding
with O
2
balloon at 353 K with stirring. The results are listed in Table 1.
alone can offer
8.7% conversion of indoline with 34.3% yield of indole. Without
One may see that, in the control experiment, Pd(OAc)
3
2
2 2
Zn(OTf) displays a clear faster reaction rate than using Pd(OAc)
Pd(OAc)
2
, exposing indoline to the reaction conditions also provided
alone. As shown in Fig. 1, Lewis acid alone as catalyst shows the identical
dehydrogenation rate as that of no catalyst added, supporting that
1
3.2% conversion with 10.8% yield of indole due to its instability. Adding
NaOTf to Pd(OAc) did not improve its dehydrogenation efficiency,
while adding 2 equiv. of bivalent metal ions like Ca , Mg , and
2
Zn(OTf)
Pd(OAc)
2
alone cannot catalyze the reaction. Without Lewis acid,
alone is active but the dehydrogenation rate is pretty slow,
2
+
2+
2
2
+
Ba clearly improved the catalytic efficiency of Pd(OAc)
adding Zn(OTf) to Pd(OAc) improved the yield of indole up to 71.0%
with 74.2% conversion. However, in the case of trivalent metal ions
2
; in particular,
2 2
however, adding Zn(OTf) to Pd(OAc) greatly accelerates the dehydro-
genation reaction and demonstrates a higher yield of the 2-
methylindole product.
The catalytic dehydrogenation of other N-heterocyclic compounds
which contain secondary amine functional groups also clearly supports
2
2
like Sc3 and Al , the catalytic efficiency slightly decreased, giving
+
3+
6
1.9% and 55.4% of indoline conversion with 49.0% and 44.2% yield of in-
dole, respectively. This phenomenon is different from those observed in
Wacker-type oxidation, olefin isomerization and indole coupling reac-
tions in which a stronger Lewis acid can offer better promotion effect
that adding Zn(OTf)
by Pd(OAc) catalyst. For examples, in dehydrogenation of 1,2,3,4-
tetrahydroquinoline, adding Zn(OTf) offered 59.8% conversion with
55.1% yield of quinoline in 12 h at 353 K, whereas using Pd(OAc) alone
as catalyst only provided 36.2% of conversion with 23.6% yield of quino-
line (Table 2). The relatively low conversion of substrate can be attributed
2
greatly accelerates the dehydrogenation reaction
2
2
3
+
[
15,17,18]. Here, the lower efficiency of strong Lewis acid like Sc
2
3
+
and Al
can be attributed to its interaction with indoline substrate
and indole product which is basic. As shown in entry 9 in Table 1, adding
−
6
equiv. of NaOTf, which contains identical amounts of OTf anion as
those in 2 equiv. of Sc(OTf) , does not improve the catalytic efficiency
of Pd(OAc) , whereas 2 equiv. of Zn(OTf) significantly improved the
to the plausible interaction of indole product with Pd(OAc)
which blocks the promotion effect by added Lewis acid. In the case of 2-
methylindoline, adding Zn(OTf) to Pd(OAc) provided 74.0% yield of 2-
methylindole with 97.6% conversion of substrate, while Pd(OAc) alone
2
catalyst
3
2
2
2
2
−
dehydrogenation efficiency. To exclude the role of OTf anion in cataly-
2
sis, we further conducted complimentary experiments for Zn2 with
+
gave 43.2% yield with 51.0% conversion. In particular, in a 1 g scale dehy-
drogenation of 2-methylindoline, a 79.7% yield of 2-methylindole was
achieved. In a complementary test, tetrahydrothiopene was employed
as substrate, and it provided only 5% of thiopene as product. However,
in the absence of Lewis acid, no formation of thiopene was observed,
other counter-ions. While Zn(OAc)
soluble in acetonitrile, Zn(NO is soluble, and it demonstrated similar
promotional effect as well as Zn(OTf) , providing 62.8% yield of indole
with 95.2% of conversion. It clearly demonstrated that it is non-redox
2 4 3 2
, ZnSO , ZnCO and Zn(OH) are in-
3 2
)
2
2
+
−
metal ion like Zn , rather than OTf , plays the significant role in accel-
thus also evidenced the promotional effect of Lewis acid in Pd(OAc)
2
cat-
erating Pd(II)-catalyzed dehydrogenation. In addition, minor palladium
alyzed oxidative dehydrogenation.
black was observed after reaction in the case of using Pd(OAc)
lyst or adding NaOTf to Pd(OAc) , while adding other bivalent or triva-
lent Lewis acid to Pd(OAc) prevented the palladium black formation,
which is similar to those observed in Lewis acid promoted Wacker-
type oxidation by Pd(OAc) catalyst [15]. It is worth to mention that
2
as cata-
As reported elsewhere, a stronger Lewis acid may have a better pro-
2
motional effect on the redox metal ion mediated oxidations [10–14].
Here, due that the strong Lewis acid like Sc3 and Al
+
3+
can interact
2
with the tested N-heterocyclic compounds and related products which
are basic, the promotional effect of trivalent Lewis acids was not
2
added Lewis acid alone does not catalyze dehydrogenation as shown
in the parentheses of Table 1. In certain cases, the trace metal impurities
played significant roles in catalysis [19–22]. In our studies, the control
Pd(OAc) +Zn(OTf)
2 2
Pd(OAc)2
Zn(OTf)2
w
i
t
h
o
u
t
P
d
(
O
A
c
)
a
n
d
Z
n
(
O
T
f
)
Table 1
100
2
2
Lewis acid promoted oxidative dehydrogenation of indoline to indole.
8
0
0
6
Entry
Catalyst
Lewis acid
Conv. %
Yield %
1
2
3
4
5
6
7
8
9
–
–
–
13.2
38.7
10.8
34.3
40
20
0
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
2
2
Sc(OTf)
Al(OTf)
Zn(OTf)
Ca(OTf)
Mg(OTf)
Ba(OTf)
6NaOTf
3
61.9(12.4)
55.4(17.0)
74.2(13.8)
65.8(15.3)
52.5(12.9)
70.5(14.1)
38.8(11.3)
49.0(9.2)
44.2(12.9)
71.0(11.2)
62.4(13.2)
37.8(7.8)
67.4(8.4)
34.7(6.0)
3
2
2
2
0
50
100
150
200
2
2
Time / min
Conditions: Pd(OAc)
loon, 353 K, 6 h. The data in parentheses represent the control experiment without
Pd(OAc)
2 3 2
1 mM, Lewis acid 2 mM, CH CN 5 mL, Substrate: 100 mM, O bal-
Fig. 1. Time course of dehydrogenation from 2-methylindoline. Conditions: Pd(OAc)
1 mM, Lewis acid 2 mM, CH CN 5 mL, substrate 100 mM, O balloon, 353 K.
2
2
.
3
2

C. Lou et al. / Catalysis Communications 90 (2017) 5–9
7
Table 2
Dehydrogenation of different N-heterocyclic compounds by Pd(OAc)
2
in the presence of Zn(OTf)
2
.a
Entry
1
Substrate
T/h
6
Conv. %
Products
Yield %
77.4(34.4)
97.6(51.0)
59.8(26.2)
71.0(32.6)
2
3
74.0(43.2)
55.1(23.6)
3b
12
4c
24
24
47.0(23.3)
62.1(46.9)
34.0(18.7)
50.9(37.6)
5d
The data in parentheses come from control experiments using Pd(OAc)
2
alone.
a
b
c
Conditions: Pd(OAc)
Substrate (50 mM).
2
(1 mol%, 1 mM), Zn(OTf)
2
(2 mol%, 2 mM), CH CN (5 mL), substrate (100 mM), O balloon, 353 K.
3
2
Substrate (100 mM), 363 K.
Substrate (20 mM), 363 K.
d
Table 3
Lewis acid promoted oxidative dehydrogenation of cyclic ketone by Pd(OAc)
2
catalyst.
Entry
Lewis acid
Conv. [%]
Yield A [%]
Yield B [%]
1
2
3
4
–
8.9
4.6
7.6
28.7
37.7
–
–
10.3
15.7
Zn(OTf)
Al(OTf)
Sc(OTf)
2
14.1
68.2
64.3
3
3
Reaction conditions: CH
3
CN 3 mL, Pd(OAc)
2
8 mM, Lewis acid 16 mM, 4-tert-butyl-cyclohexanone 80 mM, 20 atm O
2
, 353 K, 24 h.
impressively observed in dehydrogenation. Compared with amines, cy-
clic ketones are mostly neutral, and have much more robust C\\H bond.
Here, 4-t-butyl-cyclohexanone was selected as substrate for oxidative
dehydrogenation, and the results are summarized in Table 3. Clearly,
due to the robust C\\H bond in ketone, the promotional effect of Zn2
is minor, providing only 14.1% conversion of ketone with only 7.6%
yield of 4-t-butyl-cyclohexenone and no t-butylphenol formation was
2
dehydrogenation by Pd(OAc) catalyst as well those in previous studies
[15,17,18]. Although it is not clear the dehydrogenation of indoline pro-
ceeds by C\\C or C\\N (followed by tautomerization) bond oxidation
(vide supra), the oxidative dehydrogenation of cycloketone to the phe-
+
nols has clearly indicated that adding Lewis acid to simple Pd(OAc)
2
can
substantially improve its hydrogen atom abstraction ability.
As well as in indoline dehydrogenation, increasing the ratio of Pd(II)/
Sc(III) from 1:0.5 to 1:1 sharply improves the dehydrogenation efficien-
cy of 4-t-butyl-cyclohexenone, while further increasing ratio still im-
proves the dehydrogenation efficiency as shown in Table 4. In
detected, however, it is still slightly better than using Pd(OAc)
Adding Al(OTf) to Pd(OAc) giving 68.2% conversion of ketone with
8.7% yield of 4-t-butyl-cyclohexenone and 10.3% yield of t-butylphenol
formation. Remarkably, adding 2 equiv. of Sc(OTf) to Pd(OAc) offered
7.7% yield of 4-t-butyl-cyclohexenone with 15.7% yield of 4-t-
2
alone.
3
2
2
3
2
3
particular, increasing the Sc(OTf) loading sharply drives the transfor-
3
mation of 4-t-butyl-cyclohexenone to 4-t-butylphenol. In the 1:1 ratio
butylphenol product, while the conversion is 64.3%. Clearly, stronger
Lewis acid can provide much better promotional effect in oxidative
2
1
1
0
.0
.6
.2
.8
Zn(OTf) 2 mM
2
Table 4
Pd(OAc) 1 mM
2
The influence of Pd(OAc)/Sc(OTf)
3
on 4-t-butyl-cyclohexenone.
Pd(OAc) 1 mM
2
+ Zn(OTf) 2 mM
2
Entry
Pd(OAc)
2
:Sc(OTf)
3
Conv. [%]
Yield A [%]
Yield B [%]
0.4
1
2
3
4
1:0.5
1:1
1:2
15.2
52.3
64.3
75.3
7.4
–
0
.0
200
41.2
37.7
26.1
2.6
15.7
23.2
300
400
500
600
1:4
nm
3 2
Reaction conditions: CH CN 3 mL, Pd(OAc) 8 mM, 4-tert-butyl-cyclohexanone 80 mM, 20
atm O , 353 K, 24 h.
2
Fig. 2. The UV–visible spectra of the Pd(OAc)
2
plus Zn(OTf)
2
in acetonitrile.

8
C. Lou et al. / Catalysis Communications 90 (2017) 5–9
Fig. 3. 1H NMR spectra of Pd(OAc)
/Zn(OTf)
with related compounds in acetonitrile-d
Scheme 1. Proposed heteronuclear Pd(II)/Zn(II) dimer for dehydrogenation.
2
2
3
.
of Pd(II)/Sc(III), it provided 41.2% yield of 4-t-butyl-cyclohexenone with
only 2.6% yield of 4-t-butylphenol, while in the case of 1:4 ratio, it of-
fered 26.1% yield of 4-t-butyl-cyclohexenone with 23.2% yield of 4-t-
butylphenol, and the conversion of 4-t-butyl-cyclohexanone is 75.3%.
To address the origins of the promotional effect in dehydrogenation
4. Conclusions
This work demonstrated that adding non-redox metal ions to simple
Pd(OAc) catalyst can remarkably improve its dehydrogenation activity
2
for feasible C\\H bond in indolines to indole and derivatives, and for the
robust C\\H bond in cyclic ketone to enone and phenols; in particular,
the activity improvement is Lewis acidity strength dependent
on added non-redox metal ions. Through UV–vis and NMR characteriza-
tions of the catalyst, it was proposed that in-situ generated
heteronuclear Pd(II)/Zn(II) dimer is the key active species for
dehydrogenation.
2 2
by Pd(OAc) /Zn(OTf) , the catalytic system was characterized by UV–
vis and NMR technologies. As shown in Fig. 2, in acetonitrile Pd(OAc)
2
alone demonstrates a yellowish colour, having a shoulder absorbance
band above 400 nm involving the ligand-to-metal charge transfer as ex-
pected. Adding 2 equiv. of Zn(OTf)
bance band with a maximum near 320 nm, indicating the formation of
a new Pd(II) species, which is similar to that adding Sc(OTf) to
in acetonitrile [15]. In H NMR spectra (Fig. 3), the chemical
shift of 1.97 ppm of Pd(OAc) alone can be assigned to the methyl
group of acetate in the Pd (OAc)
Adding Zn(OTf) to Pd(OAc)
2 2
to Pd(OAc) yields a new absor-
3
1
Pd(OAc)
2
Acknowledgments
2
3
6
trimer as those in literature [23,24].
2
downshifts this methyl group to
This work was supported by the National Natural Science Founda-
tion of China (No. 21273086 and 21573082). The GC–MS analysis was
performed in the Analytical and Testing Center of Huazhong University
of Science and Technology.
Supplementary materials include detailed experimental procedures,
UV–vis characterization of catalyst, graph of Zn(II)/Pd(II) ratio on cata-
lytic efficiency, and GC–MS graphs of 4-t-butyl cyclohexanone.
2
1
3
2
.01 ppm. In C NMR spectra (Fig. 4), Pd(OAc)
shift at 21.15 ppm and another at 173.73 ppm, corresponding to the
methyl and carbonyl groups of acetate bridges in Pd (OAc) , respective-
ly. Adding Zn(OTf) downshifts the carbonyl group to 178.56 ppm and
2
displays one chemical
3
6
2
the methyl group to 22.03 ppm, also indicating the new coordination
environment of acetate. All of these UV–vis and NMR characterization
clearly evidenced the formation of new Pd(II) species after adding
Appendix A. Supplementary data
Zn(OTf)
studies in similar Pd(OAc)
ported formation of heterobimetallic Pd(II) dimers with Ba , Ca
2
to the acetonitrile solution of Pd(OAc)
2
. According to previous
2
/Lewis acid system [15,17,18], and the re-
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2016.11.007.
2
+
2+
,
2
+
2+
2+
2+
4+
Mn , Ni , Cd , Zn
here, similar Pd(II)/Zn(II) dimer with acetate bridge can be reasonably
proposed in this Pd(OAc) /Zn(OTf) system (Scheme 1), and it serves
as the key active species for oxidative dehydrogenation.
and Ce
through acetate bridge [25,26],
References
2
2
[1] B.M. Stoltz, Chem. Lett. 33 (2004) 362–367.
[
2] W. Zhou, P. Taboonpong, A.H. Aboo, L. Zhang, J. Jiang, J. Xiao, Synlett 27 (2016)
1806–1809.
[
[
[
[
[
[
3] A.E. Wendlandt, S.S. Stahl, J. Am. Chem. Soc. 136 (2014) 11910–11913.
4] J.C. Bricker, Top. Catal. 55 (2012) 1309–1314.
5] F. Cavani, F. Trifiro, Appl. Catal. A Gen. 133 (1995) 219–239.
6] Y. Izawa, D. Pun, S.S. Stahl, Science 333 (2011) 209–213.
7] T. Diao, D. Pun, S.S. Stahl, J. Am. Chem. Soc. 135 (2013) 8205–8212.
8] A. Conde, L. Vilella, D. Balcells, M.M. Diaz-Requejo, A. Lledos, P.J. Perez, J. Am. Chem.
Soc. 135 (2013) 3887–3896.
[
9] J. Zhang, Q. Jiang, D. Yang, X. Zhao, Y. Dong, R. Liu, Chem. Sci. 6 (2015) 4674–4680.
[
[
[
[
10] P. Leeladee, R.A. Baglia, K.A. Prokop, R. Latifi, S.P. de Visser, D.P. Goldberg, J. Am.
Chem. Soc. 134 (2012) 10397–10400.
11] J. Park, Y. Morimoto, Y.M. Lee, W. Nam, S. Fukuzumi, J. Am. Chem. Soc. 133 (2011)
5236–5239.
12] W.W.Y. Lam, S.M. Yiu, J.M.N. Lee, S.K.Y. Yau, H.K. Kwong, T.C. Lau, D. Liu, Z. Lin, J. Am.
Chem. Soc. 128 (2006) 2851–2858.
13] L. Dong, Y. Wang, Y. Lv, Z. Chen, F. Mei, H. Xiong, G. Yin, Inorg. Chem. 52 (2013)
5418–5427.
[14] Z. Chen, L. Yang, C. Choe, Z. Lv, G. Yin, Chem. Commun. 51 (2015) 1874–1877.
[15] S. Qin, L. Dong, S. Zhang, Z. Chen, G. Yin, Dalton Trans. 44 (2015) 17508–17515.
[16] H. Guo, Z. Chen, F. Mei, D. Zhu, H. Xiong, G. Yin, Chem. Asian. J. 8 (2013) 888–891.
[17] A.M. Senan, S. Qin, S. Zhang, C. Lou, Z. Chen, R. Liao, G. Yin, ACS Catal. 6 (2016)
4144–4148.
[
18] S. Zhang, Z. Chen, S. Qin, C. Lou, A.M. Senan, R. Liao, G. Yin, Org. Biomol. Chem. 14
Fig. 4. 13C NMR spectra of Pd(OAc)
/Zn(OTf)
with related compounds in acetonitrile-d
(2016) 4146–4157.
2
2
3
.

C. Lou et al. / Catalysis Communications 90 (2017) 5–9
9
[19] T. Lauterbach, M. Livendahl, A. Rosellón, P. Espinet, A.M. Echavarren, Org. Lett. 12
[24] D.D. Kragten, R.A. van Santen, Inorg. Chem. 38 (1999) 331–339.
(2010) 3006–3009.
[25] N.Y. Kozitsyna, S.E. Nefedov, F.M. Dolgushin, N.V. Cherkashina, M.N. Vargaftik, I.I.
[
[
[
20] I. Thomé, A. Nijs, C. Bolm, Chem. Soc. Rev. 41 (2012) 979–987.
Moiseev, Inorg. Chim. Acta 359 (2006) 2072–2086.
[26] N.S. Akhmadullina, N.V. Cherkashina, N.Y. Kozitsyna, A.E. Gekhman, M.N. Vargaftik,
Kinet. Catal. 50 (2009) 396–400.
21] K. Inamoto, L.D. Campbell, T. Doi, K. Koide, Tetrahedron Lett. 53 (2012) 3147–3148.
22] C. Lübbe, A. Dumrath, H. Neumann, M. Schäffer, R. Zimmermann, M. Beller, R.
Kadyrov, ChemCatChem 6 (2014) 684–688.
[23] V.I. Bakhmutov, J.F. Berry, F.A. Cotton, S. Ibragimov, C.A. Murillo, Dalton Trans. 34
(2005) 1989–1992.