Nonredox Metal-Ion-Accelerated Olefin Isomerization by Palladium(II) Catalysts: Density Functional Theory (DFT) Calculations Supporting the Experimental Data

Article abstract of DOI:10.1021/acscatal.6b01061

Redox metal-ion-catalyzed olefin isomerization represents one of the important chemical processes. This work illustrates that nonredox metal ions can sharply accelerate Pd(II)-catalyzed olefin isomerization, while Pd(II) alone is very sluggish. Nuclear magnetic resonance (NMR) and ultraviolet-visible light (UV-vis) characterizations disclosed that the acceleration effect originates from the formation of heterobimetallic Pd(II) species with added nonredox metal ions, which improves the C-H activation capability of the Pd(II) moiety. Density functional theory (DFT) calculations further confirmed the sharp decrease of the energy barrier in C-H activation by the heterobimetallic Pd(II)/Al(III) species.

Full text of DOI:10.1021/acscatal.6b01061

Letter
pubs.acs.org/acscatalysis
Nonredox Metal-Ion-Accelerated Olefin Isomerization by
Palladium(II) Catalysts: Density Functional Theory (DFT) Calculations
Supporting the Experimental Data
†
†
Ahmed M. Senan, Shuhao Qin, Sicheng Zhang, Chenling Lou, Zhuqi Chen, Rong-Zhen Liao,*
and Guochuan Yin*
School of Chemistry and Chemical Engineering, Key Laboratory of Material Chemistry for Energy Conversion and Storage, and
Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, Huazhong University of Science and
Technology, Wuhan 430074, People’s Republic of China
*
S Supporting Information
ABSTRACT: Redox metal-ion-catalyzed olefin isomerization represents one of
the important chemical processes. This work illustrates that nonredox metal ions
can sharply accelerate Pd(II)-catalyzed olefin isomerization, while Pd(II) alone is
very sluggish. Nuclear magnetic resonance (NMR) and ultraviolet−visible light
(
UV-vis) characterizations disclosed that the acceleration effect originates from
the formation of heterobimetallic Pd(II) species with added nonredox metal ions,
which improves the C−H activation capability of the Pd(II) moiety. Density
functional theory (DFT) calculations further confirmed the sharp decrease of the
energy barrier in C−H activation by the heterobimetallic Pd(II)/Al(III) species.
KEYWORDS: olefins, isomerization, density functional theory, energy barrier, nonredox metal ions
ate-transition-metal ions play significant roles in versatile
C−H activation and functionalization, and in certain cases,
metal-ion-promoted olefin isomerization by simple Pd(OAc)2
L
catalyst. It was found that adding nonredox metal ions can
sharply accelerate Pd(II)-catalyzed olefin isomerization, and the
catalytic efficiency is highly Lewis acidity strength-dependent,
the counteranion of the redox metal ions may significantly
1
affect the reactivity. To achieve the efficient oxidative C−H
bond activation by palladium(II) catalyst, copper(II) salts were
popularly employed as stoichiometric oxidant or co-catalyst
whereas Pd(OAc) alone is very sluggish. Detailed density
2
functional theory (DFT) calculations provided more-detailed
information about the roles of the nonredox metal ions in
improving the catalytic efficiency of Pd(II) in olefin isomer-
ization. The strategy of catalyst design demonstrated here may
offer those sluggish Pd(II)-based catalysts new opportunity in
olefin isomerization, which has a great market in the perfumery,
fragrance, and food industries.
To explore nonredox metal-ion-promoted olefin isomer-
ization with Pd(II) catalyst, we first focused on allylbenzene as
a substrate, using simple Pd(OAc) as a catalyst, and the results
2
are summarized in Table 1. In acetonitrile at 30 °C, in the
2
,3
when dioxygen was employed as the terminal oxidant.
Unprecedentedly, we recently observed that, in Wacker-type
oxidations, nonredox metal ions like Sc(III) can accelerate4
Pd(II)-catalyzed olefin oxidation even better than Cu(II),
implicating that the Lewis acid properties of Cu(II) may play
significant role as well as its redox properties, and a
heterobimetallic Pd(II)/Sc(III) dimer having diacetate bridge
was proposed as the key active species for oxidation. In fact,
bimetallic catalysis has been applied in versatile organic
5
synthesis as well as Ziegler catalysis. We also observed that
adding nonredox metal ions can substantially accelerate redox
metal ions such as manganese- and iron-mediated catalytic
absence of Lewis acid, Pd(OAc) alone as a catalyst is inactive
2
II
for olefin isomerization. It can be rationalized by the fact that
there is no extra protonic source such as alcohol in the reaction
mixture to facilitate the formation of the Pd(II) hydride moiety
to initialize the [1,2]-hydrogen shift mechanism, while the
Pd(II)/Pd(IV) catalytic cycle for the [1,3]-hydrogen shift
oxidations, and adding Al(III) to the Pd (bpym) complex can
promote its benzene hydroxylation to phenol (bpym = 2,2′-
II
bipyrimidine), whereas Pd (bpym) alone is very sluggish in
6
,7
activating the C−H bond of benzene. The recovered C−H
II
activation ability of the Pd (bpym) was attributed to binding of
3+
nonredox Al through two remote N atoms in the bpym ligand
II
3+
to generate Pd -bpym-Al complex, which positively shifts the
redox potential of Pd(II) species. Inspired by these Lewis-acid-
promoted C−H bond activations, herein, we report a nonredox
Received: April 13, 2016
Revised: May 18, 2016
©
XXXX American Chemical Society
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ACS Catalysis
Letter
Table 1. Nonredox Metal-Ion-Promoted Allylbenzene
well-disclosed in Table 1, Figure 1 further confirms that the
isomerization rate increases in the order of added monovalent,
a
Isomerization by Pd(OAc) Catalyst
2
Yield (%)
entry
Lewis acid
conversion (%)
trans
0.02
cis
1
2
3
4
5
6
7
8
Na(OTf)
Mg(OTf)2
Ca(OTf)2
Zn(OTf)2
0.09
46.5
44.2
55.4
85.6
98.9
87.1
81.5
12.5
40.2
37.3
45.9
82.5
1.9
2.5
3.5
1.2
0.7
1.9
1.2
Figure 1. UV-vis spectra of (a) kinetic formation of heterobimetallic
Pd(II)/Al(III) dimer and (b) Pd(OAc) , Al(OTf) , or final Pd-
Cu(OTf)2
2
3
Al(OTf)3
97,2
(OAc) /Al(OTf) in acetonitrile.
2 3
Sc(OTf)3
Y(OTf)3
Al(OTf)3
85.0
77.8
9.2
divalent, and trivalent metal ions, which is consistent with their
increased Lewis acidity. The influence of the Al(III)/Pd(II)
ratio on the Pd(II)-catalyzed allylbenzene isomerization was
also investigated (see Figure S2 in the Supporting Information).
It was found that increasing the ratio of Al(III)/Pd(II) from 0
to 1 sharply accelerates the isomerization reaction, while
increasing the ratio to 2 just slightly improves the catalytic
efficiency; further increasing the ratio to 3 or 4 demonstrates a
slightly negative effect, which is different from Pd(II)/Sc(III)-
b
9
a
Conditions: acetonitrile volume, 3 mL; Pd(OAc) concentration, 1
2
mM; Lewis acid concentration, 2 mM; allylbenzene 100 mM, 30 °C
under air, 2 h. Using isopropanol (3 mL) as the solvent.
b
mechanism is energetically unfavorable, as are those in the
literature. Adding monovalent NaOTf to the Pd(OAc)2
8
catalyst does not generate any improvement for isomerization.
However, adding divalent metal ions such as Mg(II), Ca(II),
and Zn(II) substantially promote the catalytic activity of the
Pd(II) catalyst, providing 40.2%, 37.3%, and 45.9% of trans-
methylstyrene product (E isomer) with 1.9%, 2.5%, and 3.5%
cis-methylstyrene product (Z isomer), respectively. In partic-
4
catalyzed Wacker-type oxidation. In Pd(II)/Sc(III)-catalyzed
olefin oxidation, the ratio of 4 is much more efficient than that
of 1. In that reaction, the roles of Sc(III) cation were explained
in two aspects: one is to ligate with Pd(II) through two acetate
bridges to accelerate Pd(II)-catalyzed olefin oxidation, and the
other is to generate a Sc(III)···H−Pd(II) intermediate, thus
facilitating the insertion of dioxygen to generate the HOO−
Pd(II) intermediate. Thereof, the presence of excess Sc(III) is
critical for efficient Pd(II)-catalyzed Wacker-type oxidation. In
this work, dioxygen insertion of the H−Pd(II) bond is not an
elementary step in olefin isomerization, thus extra amounts of
Al(III) are not essential for the Pd(II) catalyst here.
Next, the substrate scope of olefin isomerization was
investigated, and the results are summarized in Table 2. One
may see that, as well as allylbenzene, its derivatives can also be
isomerized feasibly at ambient temperature. For example,
isomerization of 2,4-dimethoxyl allylbenzene offered 99.5%
ular, adding Cu(OTf) can offer 82.5% E isomer with 1.2% Z
2
isomer within 2 h. Compared with other divalent metal ions
such as Zn(II), Cu(II) is redox active and widely employed as
stoichiometric oxidant or co-catalyst in versatile Pd(II)-
2
,3
catalyzed oxidative C−H activations.
Here, in Pd(II)-
catalyzed olefin isomerization, the redox properties of Cu(II)
are apparently not essential, since there is no extra oxidant
required for olefin isomerization. More importantly, nonredox
trivalent metal ions such as Al(III) can accelerate Pd(II)-
catalyzed olefin isomerization more efficiently than Cu(II),
providing 97.2% E isomer with 0.7% Z isomer within 2 h;
adding Sc(III) to Pd(OAc) also gave 85% E isomer with 1.9%
Z isomer. In control experiments, using Al(OTf) alone as a
2
3
catalyst is inactive for olefin isomerization. Clearly, adding
nonredox metal ions would greatly promote Pd(II)-catalyzed
olefin isomerization, and the improvement is highly Lewis-acid-
strength-dependent on added metal ions. Compared with
acetonitrile solvent, using isopropanol as a solvent sharply
retards the reaction, providing only 9.2% E isomer within 2 h,
with no detectable Z isomer with Pd(II)/Al(III) catalyst. In
addition, the preliminary DFT calculations also support that
isopropanol is a poor solvent for this catalysis (see Figures S15
and S16 in the Supporting Information). In the literature,
isopropanol and other protonic solvents were generally
employed as co-catalysts or additives for in situ generation of
Table 2. Substrate Scope of Olefin Isomerization by
a
Pd(OAc) /Al(OTf)
2
3
Yield (%)
time
(h)
conversion
entry
substrate
(%)
trans
97.2
cis
1
2
allybenzene
2
2
98.9
99.9
0.7
0.9
4-methoxyl
allylbenzene
98.7
3
2,4-dimethoxyl
allylbenzene
4
99.5
97.8 (87)
94.2 (83)
1.7
5.1
4
5
6
7
8
eugenol
4
99.7
99.5
99.8
99.9
99.9
99.2
1-hexene
0.3
0.3
0.3
0.3
24
95.3 (isomers)
94.1 (isomers)
95.2 (isomers)
8
the active metal-hydride moiety to initiate olefin isomerization.
1-dodecene
1-octene
Apparently, the invalidity of isopropanol as a solvent indicates
an alternative mechanism other than [1,2]-hydrogen shift
operates here.
4-methylpentene
1,5-COD
95.2 (isomers)
b
c
d
9
95.6
2.3
Reaction kinetics further confirmed the promotional effect of
nonredox metal ions in Pd(II)-catalyzed olefin isomerization.
As shown in Figure S1 in the Supporting Information, adding
NaOTf does not show any promotional effect, while other
metal ions substantially accelerate isomerization. Notably, as
a
Conditions: acetonitrile, 3 mL; Pd(OAc) , 1 mM; Al(OTf) , 2 mM;
2
3
b
olefin, 100 mM; 30 °C, data in brackets represent isolated yield. 2
mM Pd(OAc) , 4 mM Al(OTf) , 100 mM olefin, 90 °C. Yield of 1,3-
COD. Yield of 1,4-COD.
c
2
3
d
4
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ACS Catalysis
Letter
conversion with 97.8% yield of the E isomer and 1.7% yield of
Z isomer at 30 °C within 4 h. In particular, it is worth
mentioning that the ratio of E:Z isomer generated here is
remarkably high. Also, in the isomerization of eugenol, the yield
of trans-isoeugenol is 94.2% with a 5.1% yield of cis-isoeugenol
demonstrates three chemical shifts for the carbonyl group
(181.78, 173.10, and 167.48 ppm) and two for the methyl
group (24.49 and 21.05 ppm), indicating the occurrence of
three categories of acetate in this Pd(II)/Al(III) solution. The
downshifts of carbonyl at 181.78 ppm with methyl at 24.49
ppm suggest that a more electron-deficient group than Pd(II)
has become linked to acetate, while the chemical shifts at
173.10 and 21.05 ppm indicate that free Pd (OAc) trimer still
when Al(OTf) was employed as additives. More importantly,
3
in a 10 g scale isomerization of eugenol with only 0.1 mmol %
Pd(OAc) and 0.2 mmol % Al(OTf) loading, a yield of 96%
2
3
3
6
can be achieved with an E/Z isomer ratio of 95:5 in 12 h at 50
C. It was reported that the ongoing commercial process with
H SO and KOH generally only gives a 82:18 ratio of E/Z
exists. However, the shift at 167.48 ppm for carbonyl group
further implies that the third category of acetate exists in
solution, which has indistinguishable methyl chemical shifts in
°
2
4
1
13
isoeugenol, with a total yield of 56%, and the reaction
both H and C NMR graphs from those of Pd (OAc) trimer,
3 6
9
1
13
temperature is as high as 200 °C. Because cis-isoeugenol has
which was further evidenced by H− C HSQC NMR (see
Figure S4 in the Supporting Information). In the comple-
mentary experiments, the Al NMR studies were conducted as
shown in Figure S9 in the Supporting Information. In
an unpleasant taste and, in some cases, a toxic character in food
industries, the content of cis-isoeugenol should be <1%.
Apparently, the Pd(II)/Al(III) catalyst demonstrated here is
much more attractive than the ongoing commercial process,
not only because of the high ratio of E/Z isomer formation, but
also its simplicity and more environmentally benign process. As
well as arylalkenes, linear olefins, such as 1-hexene, 1-octene, 1-
dodecene, and even 4-methylpentene can be feasibly
isomerized to the corresponding internal olefin mixtures in
27
acetonitrile, Al(OTf) alone displayed several peaks between
3
3
+
1
10 ppm and −20 ppm, indicating the presence of several Al
species having an octahedral coordination environment;
1
however, in Pd(OAc) /Al(OTf)3 solution (ratio 1:1), the
2
peaks change sharply to a broadened resonance between 10
ppm and −10 ppm, clearly indicating that an interaction
between Pd(II) and Al(III) cations exists. According to these
changes with DFT calculations (vide infra), the acetate ligands
in this Pd(II)/Al(III) system can be assigned in three forms:
2
0 min at 30 °C. Isomerization of cyclic olefin is generally very
sluggish, because of its steric hindrance. Here, isomerization of
,5-cyclooctadiene (1,5-COD) required 24 h at 90 °C to
1
achieve 99.2% conversion, providing a 95.6% yield of 1,3-
cyclootadiene (1,3-COD) with a 2.3% yield of 1,4-cyclo-
octadiene (1,4-COD), and the Pd(II)/Al(III) loading must be
doubled. Because of serious steric hindrance, 4-ethenyl-
cyclohexene cannot be isomerized by the Pd(II)/Al(III)
catalyst here.
(
a) heterobimetallic Pd(II)/Al(III) dimer, having two acetate
bridges; (b) heterobimetallic Pd(II)/Al(III) dimer, having one
acetate bridge with another acetate ligated to Pd(II) cation
(
Figure 3); and (c) original Pd (OAc) .
3 6
In UV-vis characterizations of the catalyst (Figure 1), adding
Al(OTf) to the acetonitrile solution of Pd(OAc) triggered the
3
2
immediate formation of an intermediate, having the absorbance
band maximum at 278 nm. This intermediate decays gradually
to form a stable species having a characteristic absorbance band
at ∼310 nm, and the original yellow color of the Pd(II) species
changes to a pale yellow of the new species. In particular,
adding olefin to this new species in acetonitrile can immediately
trigger the formation of the above intermediate again (see
Figure 3. Proposed heterobimetallic Pd(II)/Al(III) dimer having (a)
two acetate bridges and (b) one acetate bridge, based on NMR studies.
1
Figure S3 in the Supporting Information). In H NMR spectra
In order to understand the effect of Lewis acid on the Pd(II)-
(
Figure 2), Pd(OAc) alone in acetonitrile-d reveals a chemical
2
3
catalyzed allylbenzene isomerization, we performed DFT
12
calculations for the catalytic systems with and without
Al(OTf) . The calculated Gibbs free energy diagram is shown
3
in Figure 4 (for optimized structures, see Figures S11−S19).
The most striking difference between catalytic systems with and
without Al(OTf) comes from the energetics for the generation
3
of the active catalytic species. For Pd(OAc) alone, the trimeric
2
10,13
form Pd (OAc) is the most stable form in solution,
and
3
6
the formation of the monomeric species Pd(OAc)2 is
endergonic by 14.8 kcal/mol. The addition of Al(OTf)3
Figure 2. NMR spectra of Pd(OAc) /Al(OTf)3 with related
compounds in acetonitrile-d3.
2
facilitates the decomposition of Pd (OAc)6 to generate a
3
dimeric Pd(II)/Al(III) species, and this process becomes
exergonic by as much as 22.8 kcal/mol. The calculations
agree quite well with our NMR studies, which suggest a
heterobimetallic Pd(II)/Al(III) dimeric species.
shift of 1.97 ppm, which can be assigned to the methyl group of
acetate in Pd (OAc) trimer in which all of the acetates serve as
3
6
10
a bridge like those in the literature. Adding Al(OTf) to the
For Pd(OAc) -catalyzed isomerization, the reaction starts
3
2
acetonitrile solution of Pd(OAc) slightly shifts the chemical
with the coordination of the substrate allyl double bond to
2
shift of methyl group of acetate from 1.97 ppm to 1.98 ppm
with another chemical shift at 2.06 ppm, indicating the
Pd(II), This is followed by proton transfer (TS1) from C1 to
3
acetate to form a η -allyl Pd(II) intermediate, and no stable
1
3
formation of the new species. In C NMR spectra, adding
Pd(IV)-hydride intermediate can be located. This type of base-
Al(OTf) causes the chemical shifts at 173.73 and 21.15 ppm
assisted C−H activation mechanism has also been observed in
3
14,15
for Pd(OAc) in acetonitrile-d to become complicated. It
several Pd-, Ir-, and Ru-catalyzed reactions.
Importantly,
2
3
4
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ACS Catalysis
Letter
In summary, this work demonstrated the first example that
bridging nonredox metal ions to the simple Pd(II) catalyst can
sharply promote its activity in olefin isomerization, and DFT
calculations convincingly support the experimental data. The
catalyst strategy introduced here may offer new opportunities
for versatile olefin isomerization processes, which has a great
market in the perfumery, fragrance, and food industries.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acscatal.6b01061.
■
*
S
Detailed experimental procedures, UV-vis, NMR graphs,
and calculation procedures (PDF)
AUTHOR INFORMATION
Corresponding Authors
E-mail: rongzhen@hust.edu.cn (R.-Z. Liao).
E-mail: gyin@hust.edu.cn (G. Yin).
■
*
*
Author Contributions
†
Figure 4. Calculated Gibbs free-energy diagram for (top) Pd(OAc)2-
These authors equally contribute to this work.
catalyzed allylbenzene isomerization and (bottom) Pd(OAc) /Al-
2
Funding
(
OTf) -catalyzed allylbenzene isomerization.
3
This work was supported by the National Natural Science
Foundation of China (Nos. 21303063, 21273086, 21573082,
and 21503083).
the oxidation addition mechanism to generate Pd(IV)-hydride
Notes
15
was found to be unfavorable. Subsequently, isomerization and
proton transfer (TS2) proceed to form the final product. The
first step (TS1) was calculated to be the rate-limiting step, with
a total barrier of 29.5 kcal/mol for the trans pathway. The
corresponding barrier for the cis pathway is 3.7 kcal/mol higher.
It is pertinent to mention that constrained geometry
optimization could obtain a Pd(IV)-hydride-like structure, but
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The GC-MS analysis was performed in the Analytical and
Testing Center of Huazhong University of Science and
Technology.
its energy is much higher than that of TS1 (see Figure S13 in
the Supporting Information), which further supports the
proton transfer mechanism.
t
REFERENCES
■
(
1) (a) Gulzar, N.; Schweitzer-Chaput, B.; Klussmann, M. Catal. Sci.
Technol. 2014, 4, 2778−2796. (b) Shi, W.; Liu, C.; Lei, A. Chem. Soc.
The overall mechanism of the Pd(II)/Al(III) -catalyzed
3
Rev. 2011, 40, 2761−2776. (c) Yeung, C. S.; Dong, V. M. Chem. Rev.
allylbenzene isomerization is quite similar to that without
2
011, 111, 1215−1292. (d) Hartwig, J. F. Angew. Chem., Int. Ed. 1998,
Al(OTf) , but with very different energetics. TS2′ is now the
3
t
37, 2046−2067. (e) Chen, X.; Engle, K. M.; Wang, D.; Yu, J. Angew.
Chem., Int. Ed. 2009, 48, 5094−5115. (f) Fu, G. C. Acc. Chem. Res.
2008, 41, 1555−1564. (g) Weaver, J. D.; Recio, A.; Grenning, A. J.;
Tunge, J. Chem. Rev. 2011, 111, 1846−1913. (h) Bajwa, S. E.; Storr, T.
E.; Hatcher, L. E.; Williams, T. J.; Baumann, C. G.; Whitwood, A. C.;
Allan, D. R.; Teat, S. J.; Raithby, P. R.; Fairlamb, I. J. S. Chem. Sci.
rate-determining step for the trans pathway, with a barrier of
2
4.9 kcal/mol. For the cis pathway, TS1′ is rate-limiting with a
c
barrier of 25.3 kcal/mol. The barrier is 4.6 kcal/mol lower than
that without Al(OTf) , suggesting a critical role of Lewis acid in
3
the Pd(II)-catalyzed isomerization reaction. In addition, it is
very important to point out that TS1′ is the selectivity-
determining step, which favors the trans pathway, with a barrier
difference of 5.5 kcal/mol. Our experimental data (98.8% trans
vs 0.8% cis) gives a barrier difference of 2.85 kcal/mol. The
2
(
1
(
012, 3, 1656−1661.
2) (a) Liang, Z.; Zhao, J.; Zhang, Y. J. Org. Chem. 2010, 75, 170−
77. (b) Ying, C.; Yan, S.; Duan, W. Org. Lett. 2014, 16, 500−503.
c) Wei, Y.; Su, W. J. Am. Chem. Soc. 2010, 132, 16377−16379.
(
d) Maehara, A.; Tsurugi, H.; Satoh, T.; Miura, M. Org. Lett. 2008, 10,
calculations thus somewhat overestimate the difference. If Int2′
t
1159−1162. (e) Stuart, D. R.; Fagnou, K. Science 2007, 316, 1172−
1175. (f) Zhang, X.; Dai, H.; Wasa, M.; Yu, J. J. Am. Chem. Soc. 2012,
134, 11948−11951.
and Int2′ can be easily interconverted, then TS2′ is the
c
selectivity-determining step, which would give the wrong
selectivity. However, interconversion between Int2′ and Int2′
(3) (a) Timokhin, V. I.; Anastasi, N. R.; Stahl, S. S. J. Am. Chem. Soc.
2003, 125, 12996−12997. (b) Dwight, T. A.; Rue, N. R.; Charyk, D.;
Josselyn, R.; DeBoef, B. Org. Lett. 2007, 9, 3137−3139. (c) Tang, R.;
Guo, X.; Xiang, J.; Li, J. J. Org. Chem. 2013, 78, 11163−11171. (d) Li,
B.; Tian, S.; Fang, Z.; Shi, Z. Angew. Chem., Int. Ed. 2008, 47, 1115−
t
c
should be very difficult as the rotation of a double bond is very
energy-demanding. Notably, formation of the C1 intermediate
requires the dissociation of one acetate bridge between Pd(II)
and Al(III). This is very consistent with the experimental fact
that adding olefin to the acetonitrile solution of Pd(II)/Al(III)
catalyst will generate an intermediate having absorbance
identical to that adding Al(OTf)3 to Pd(OAc)2 solution,
which has been proposed as the heterobimetallic Pd(II)/Al(III)
dimer having two acetate bridge by NMR studies (see Figure
1
7
(
118. (e) Zhao, J.; Zhang, Y.; Cheng, K. J. Org. Chem. 2008, 73, 7428−
431.
4) Qin, S.; Dong, L.; Zhang, S.; Chen, Z.; Yin, G. Dalton Trans.
2015, 44, 17508−17515.
5) (a) Huang, G.; Li, J.; Huang, J.; Lin, J.; Chuang, G. J. Chem.
J.; Braunstein,
(
Eur. J. 2014, 20, 5240−5243. (b) Buchwalter, P.; Rose,
́
3).
P. Chem. Rev. 2015, 115, 28−126. (c) Wu, B.; Gallucci, J. C.;
4
147
DOI: 10.1021/acscatal.6b01061
ACS Catal. 2016, 6, 4144−4148

ACS Catalysis
Letter
Parquette, J. R.; RajanBabu, T. V. Angew. Chem., Int. Ed. 2009, 48,
1
126−1129. (d) Dang, L.; Shibl, M. F.; Yang, X.; Alak, A.; Harrison, D.
J.; Fekl, U.; Brothers, E. N.; Hall, M. B. J. Am. Chem. Soc. 2012, 134,
481−4484.
6) (a) Dong, L.; Wang, Y.; Lv, Y.; Chen, Z.; Mei, F.; Xiong, H.; Yin,
4
(
G. Inorg. Chem. 2013, 52, 5418−5427. (b) Chen, Z.; Yang, L.; Choe,
C.; Lv, Z.; Yin, G. Chem. Commun. 2015, 51, 1874−1877. (c) Zhang,
Z.; Coats, K. L.; Chen, Z.; HuBin, T. J.; Yin, G. Inorg. Chem. 2014, 53,
1
1937−11947. (d) Choe, C.; Yang, L.; Lv, Z.; Mo, W.; Chen, Z.; Li,
G.; Yin, G. Dalton Trans. 2015, 44, 9182−9192.
7) Guo, H.; Chen, Z.; Mei, F.; Zhu, D.; Xiong, H.; Yin, G. Chem.
Asian J. 2013, 8, 888−891.
8) (a) Sen, A.; Lai, T. Inorg. Chem. 1981, 20, 4036−4038.
b) Cramer, R. J. Am. Chem. Soc. 1966, 88, 2272−2282. (c) Kim, I. S.;
Dong, G. R.; Jung, Y. H. J. Org. Chem. 2007, 72, 5424−5426.
d) Mirza-Aghayan, M.; Boukherroub, R.; Bolourtchian, M.; Hoseini,
M.; Tabar-Hydar, K. J. Organomet. Chem. 2003, 678, 1−4.
9) Scarso, A.; Colladon, M.; Sgarbossa, P.; Santo, C.; Michelin, R.
A.; Strukul, G. Organometallics 2010, 29, 1487−1497.
10) (a) Kragten, D. D.; van Santen, R. A.; Crawford, M. K.; Provine,
(
(
(
(
(
(
W. D.; Lerou, J. J. Inorg. Chem. 1999, 38, 331−339. (b) Nosova, V. M.;
Ustynyuk, Y. A.; Bruk, L. G.; Temkin, O. N.; Kisin, A. V.; Storozhenko,
P. A. Inorg. Chem. 2011, 50, 9300−9310. (c) Bakhmutov, V. I.; Berry,
J. F.; Cotton, F. A.; Ibragimov, S.; Murillo, C. A. Dalton Trans. 2005,
4
(
4, 1989−1992.
11) (a) Tayade, K. N.; Mishra, M.; K, M.; Somani, R. S. Catal. Sci.
Technol. 2015, 5, 2427−2440. (b) Haouas, M.; Taulelle, F.; Martineau,
C. Prog. Nucl. Magn. Reson. Spectrosc. 2016, 94−95, 11−36.
(
12) Computational details are given in the Supporting Information.
(
13) (a) Giri, R.; Lan, Y.; Liu, P.; Houk, K. N.; Yu, J.-Q. J. Am. Chem.
Soc. 2012, 134, 14118−14126. (b) Yang, Y.-F.; Cheng, G.-J.; Liu, P.;
Leow, D.; Sun, T.-Y.; Chen, P.; Zhang, X.; Yu, J.-Q.; Wu, Y.-D.; Houk,
K. N. J. Am. Chem. Soc. 2014, 136, 344−355. (c) Dang, Y.; Qu, S.;
Nelson, J. W.; Pham, D. H.; Wang, Z.-X.; Wang, X. J. Am. Chem. Soc.
2
(
7
3
015, 137, 2006−2014.
14) (a) Balcells, D.; Clot, E.; Eisenstein, O. Chem. Rev. 2010, 110,
49−823. (b) Jiang, J.; Yu, J.-Q.; Morokuma, K. ACS Catal. 2015, 5,
648−3661. (c) Ozdemir, I.; Demir, S.; Cetinkaya, B.; Gourlaouen, C.;
Maseras, F.; Bruneau, C.; Dixneuf, P. H. J. Am. Chem. Soc. 2008, 130,
1
156−1157. (d) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K.
J. Am. Chem. Soc. 2006, 128, 8754−8756. (e) Zhang, Q.; Yu, H.-Z.; Fu,
Y. Organometallics 2013, 32, 4165−4173.
(
15) (a) Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. J. Am.
Chem. Soc. 2005, 127, 13754−13755. (b) Davies, D. L.; Donald, S. M.
A.; Al-Duaij, O.; Macgregor, S. A.; Polleth, M. J. Am. Chem. Soc. 2006,
1
28, 4210−4211.
4
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DOI: 10.1021/acscatal.6b01061
ACS Catal. 2016, 6, 4144−4148