Mechanistic insights into catalytic linear cross-dimerization between conjugated dienes and styrenes by a ruthenium(0) complex

Article abstract of DOI:10.1016/j.jorganchem.2015.08.022

The mechanistic studies for linear cross-dimerization between 2,3-dimethylbuta-1,3-diene and styrene by a Ru(0) complex, Ru(η⁶-naphthalene)(η⁴-1,5-COD) (1), are performed both by kinetic and computational studies. This reaction is ba

Full text of DOI:10.1016/j.jorganchem.2015.08.022

Journal of Organometallic Chemistry 797 (2015) 174e184
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mechanistic insights into catalytic linear cross-dimerization between
conjugated dienes and styrenes by a ruthenium(0) complex
Masafumi Hirano a
,
b
,
*
, Takao Ueda , Nobuyuki Komine , Sanshiro Komiya
a
a
a, 1
,
c
c
b, c, **
Saki Nakamura , Hikaru Deguchi , Susumu Kawauchi
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei,
Tokyo 184-8588, Japan
Japan Science and Technology Agency (JST), ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, Ookayama 2-12-1,
a
b
c
Meguro-ku, Tokyo 152-8552, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 June 2015
Received in revised form
The mechanistic studies for linear cross-dimerization between 2,3-dimethylbuta-1,3-diene and styrene
6
4
by a Ru(0) complex, Ru(h -naphthalene)(h -1,5-COD) (1), are performed both by kinetic and computa-
tional studies. This reaction is basically zero-order to both of the diene and styrene concentrations and
first-order to the catalyst concentration. The Hammett plot using p-substituted styrenes gives a linear
15 August 2015
Accepted 23 August 2015
Available online 29 August 2015
relationship with a positive slope (
r
¼ þ0.482). The deuterium isotope experiment clearly shows the
present reaction being a formal 1,4-addition of a CeH bond in styrene to cisoid-1,3-diene. These kinetic
studies show the reaction proceeding via oxidative coupling mechanism that is also supported by the
DFT calculations.
Keywords:
Cross-dimerization
Ruthenium(0)
Mechanism
©
2015 Elsevier B.V. All rights reserved.
Oxidative coupling
1. Introduction
proceed by an oxidative coupling mechanism, this pioneering work
does not report the conclusive mechanistic evidence. The other
Direct carbonecarbon bond formation by use of simple com-
modity chemicals has garnered much attention as a straightfor-
ward transformation process to give complex and valuable
molecules with high atom and step economy [1]. The cross-
dimerizations between conjugated dienes and alkenes have been
documented by using the Ziegler-type catalyst systems, and com-
binations of transition-metal salt with alkylaluminum [2]. Similar
catalytic 1,4-addition reactions of styrene to conjugated diene are
recently documented by in situ reductions of Fe(II) [3] and Co(II) [4]
with Mg and Zn metals, respectively. Although the cross-
dimerization catalyzed by the Fe(II)/Mg system is proposed to
potential mechanisms for a cross-dimerization are hydride-
insertion mechanism [5] and CeH bond activation mechanism [6].
We have documented a series of homo- and cross-dimerization
reactions between conjugated compounds and/or substituted al-
kenes by a Ru(0) catalyst. A considerable mechanistic breakthrough
1
was isolation of a ruthenacyclopentane, trans-[Ru[C H(CO
2
Me)
4
2
1
4
4
C
2
H
4
C H(CO
2
Me)-
k
-C C ]( ] out of the reac-
-naphthalene)(h -1,5-COD)] (1) with methyl acrylate
h
-1,5-COD)(NCMe)
2
6
4
tion of [Ru(
h
(Scheme 1), and the isolated ruthenacyclopentane also catalyzed
tail-to-tail dimerization of methyl acrylate [7].
These findings were the first solid evidence in support of an
oxidative coupling mechanism for tail-to-tail dimerization between
substituted alkenes. On another front, we have also documented
catalytic cross-dimerization between conjugated dienes and
substituted alkenes [8]. However, we do not have adequate mech-
anistic evidence for the cross-dimerization. Although we have
*
Corresponding author. Department of Applied Chemistry, Graduate School of
Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho,
Koganei, Tokyo 184-8588, Japan.
1
3
*
* Corresponding author. Department of Organic and Polymeric Materials, Grad-
uate School of Science and Engineering, Tokyo Institute of Technology, Ookayama 2-
2-1, Meguro-ku, Tokyo 152-8552, Japan.
observed the formation of an
of [Ru(h -buta-1,3-diene)(h
[
h
:
h
-ruthenacycle by the treatment
-1,5-COD)(NCMe)] with vinyl acetate
Eq. (1)], this compound does not show the catalytic activity and
4
4
1
E-mail addresses: hrc@cc.tuat.ac.jp (M. Hirano), skawauch@polymer.titech.ac.jp
therefore we cannot exclude the possibility of this compound being
a dead-end species.
(
S. Kawauchi).
Present address: Gakushuin University.
1
http://dx.doi.org/10.1016/j.jorganchem.2015.08.022
022-328X/© 2015 Elsevier B.V. All rights reserved.
0

M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
175
In this paper, we now disclose a solid evidence to support an
oxidative coupling mechanism by the kinetic studies and DFT cal-
culations for a catalytic cross-dimerization between conjugated
diene and substituted alkenes.
2
. Results and discussion
Scheme 1. Isolation of trans-2,5-bis(methoxycarbonyl)ruthenacyclopentane.
2.1. Cross-dimerization between diene and styrenes
on the diene and styrene concentrations was observed in this
range, this reaction is roughly regarded as a zero-order reaction to
both of the concentrations [9]. The double logarithmic plot for the
The naphthalene complex 1 (2 mol%) catalyzed the cross-
dimerization between 2,3-dimethylbuta-1,3-diene (2) and styrene
ꢀ
(
(
(
3a) in toluene at 60 C for 2 h to give the coupling products 4a
71%) and 5a (9%) along with 6 minor isomers (12% in total) [Eq.
2)]. No homo-dimers were observed in this reaction. The upmost
ꢀ
catalyst concentration and the rate at 40 C shows a good linear
relationship with a positive slope of þ0.878, which is consistent
with the first-order to the catalyst concentration. Therefore, the
present reaction can be summarized as the zero-order to both of
diene and styrene concentrations and first-order to the catalyst
concentration.
minor product is 5a, a regioisomer of the C]C bond of the major
product 4a. Notably, the relative 4a/5a ratio diminished with in-
crease of the catalyst concentration (Table 1).
Fig. 2 shows Hammett plot for cross-dimerization between 2,3-
dimethylbuta-1,3-diene and a series of p-substituted styrenes 3a-f
in toluene, showing the linear dependence with a positive slope
(
r
¼ þ0.482) (Fig. 2).
Eyring plot for overall formation reaction of 4a and 5a by 1
s
ꢁ1
(
D
2 mol%) was measured in toluene:
G
DH
¼ 70.2 kJ mol
,
s
ꢁ1
s
ꢁ1
ꢁ1
298 ¼ 104 kJ mol , and
DS
¼ ꢁ115 J K mol . The large
negative entropy of activation suggests involvement of a distorted
transition state.
In order to confirm whereabouts of the cleaved hydrogen, we
0
have employed styrene-
b,
b
-d
2
(95 atom % D) for this cross-
dimerization. In the cross-dimer, the deuterium atoms were
distributed among the (Z)-1-, 4-, and 5-positions, and the deute-
rium atoms were not found in the other positions in the product 4a
(Table 2).
Based on the time-course of the reaction monitored by NMR, the
The isolated 4a did not cause spontaneous conversion into 5a at
ꢀ
deuterium atoms exclusively located among the (Z)-1- and 5-
positions at the initial stage, and then a H/D exchange reaction
occurs between the 4- and 5-positions while the deuterium content
at the (Z)-1-position remains intact throughout the reaction. The
total sum of deuterium atoms in 4a roughly indicates two D atoms
being incorporated in 4a regardless of the reaction time, suggesting
the following H/D exchange reaction between the 4- and 5-
4
0 C in benzene-d
6
but the treatment of 4a with a catalytic amount
of 1 (10 mol%) under the same conditions gave a mixture of 4a and
a. The final 4a/5a ratio was 1/2 under these conditions after 148 h.
These facts suggest the primary kinetic product 4a being converted
into the thermodynamic product 5a by a Ru catalyst, and an equi-
librium exists between them [Eq. (3)].
5
2
positions to be an intramolecular process in 4a-d . Note that only
the methyl group [(Z)-C(1)], cis to the styryl fragment, was
deuterated and no incorporation of the D atom was observed in the
0
trans-methyl [(E)-C(1 )] position (Scheme 2). These facts suggest
the present initial reaction being regarded as a 1,4-addition of
Table 1
2.2. Kinetic studies
The relation between catalyst concentration and major/minor ratio.
Entry
1a/mol%
Total yield/%
4a/5a
The time-course curves for the reaction of 2,3-dimethylbuta-
,3-diene with styrene by 1 were monitored by GLC, and the total
sum yield of the cross-dimers, 4a and 5a, showed a linear increase
with time, suggesting a zero-order reaction. Fig. 1 shows the double
logarithm plots for the relation of the formation rate of the prod-
1
2
3
4
5
6
0.5
1.0
2.0
4.0
10
39
52
74
74
65
61
6/1
6/1
6/1
4.5/1
2.6/1
1.3/1
1
20
ucts (v
p
) with the diene (Fig. 1A), styrene (Fig. 1B) and catalyst
concentrations (Fig. 1C). Although a slight dependence of the rate
Conditions: [2]/[3a] ¼ 1.3/1, 40 ꢀC, in toluene, 8 h.

176
M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
Fig. 2. Hammett plot for cross-dimerization between 2,3-dimethylbuta-1,3-diene and
p-substituted styrenes. Conditions: [1]
diene] ¼ 0.71 M, [p-substituted styrene] ¼ 0.61 M, temp ¼ 40 C, solvent ¼ toluene.
¼
0.01 M, [2,3-dimethylbuta-1,3-
ꢀ
observed by the competitive reaction in a same vessel. This fact
may be consistent with the CeH bond cleavage step being an
irreversible process after a rate-determining step in a multi-step
process [10]. Note that the KIE for the behydride elimination was
reported to be around 2e3 for the syn elimination, and around 5e7
for the anti elimination, and the KIE for reductive elimination was
reported to be 1.3e3 [11].
2.3. Stoichiometric reactions in relation to the mechanism
In order to understand the mechanism, we performed the
stoichiometric reactions. Because the NMR experiments for the
stoichiometric reaction using 2,3-dimethylbuta-1,3-diene and sty-
rene gave a complex mixture, we described the mimic reaction of
4
4
[Ru(
h
-buta-1,3-diene)(
h
-1,5-COD)(NCMe)] (6) with methyl
Table 2
Distribution of deuterium atoms in the major product 4a.
a
Fig. 1. Double-logarithm plots for the cross-dimerization between 2,3-dimethylbuta-
,3-diene and styrene. (A) Effect of concentration of diene on the rate. (B) Effect of
1
concentration of styrene on the rate. Conditions: [diene]
¼
0.59e5.58 M,
ꢀ
[
styrene] ¼ 1.18e7.78 M. [1] ¼ 0.011 M, temp ¼ 50 C, solvent ¼ toluene. (C) Effect of
concentration of 1 on the rate. Conditions: [1] ¼ 0.003e0.12 M, [2,3-dimethylbuta-1,3-
diene] ¼ 0.75 M, [styrene] ¼ 0.62 M, temp ¼ 40 ꢀC, solvent ¼ toluene.
Time/min
C(1) atom % D
C(4) atom % D
C(5) atom % D
5
70
88
89
21
35
83
68
trans-
b
-CꢁD bond in styrene to cisoid-2,3-dimethylbuta-1,3-diene,
and then a site-selective H/D exchange reaction between 4- and 5-
positions occurs by an intramolecular process.
a
The deuterium content was calculated based on the one proton at each carbon.
For the minor conjugated product 5a, the deuterium atoms also
found at the (Z)-1, 4-, 5- and 6-positions (Chart 1). The total sum of
D atoms was around two, suggesting an intramolecular deuterium
2
distribution process in the cross-dimer-d .
It is noteworthy that the one deuterium atom has mainly moved
to the (Z)-C(1) position (90% atom D) and the other deuterium atom
was distributed among C(4), C(5) and C(6) positions.
Although this process involves complicated isomerization pro-
cesses for the deuterium distribution in 4a and 5a as shown above,
H D
the KIE values (k /k ) for the present cross-dimerization were
measured using the initial rate. The KIE measured from the inde-
pendent reactions was 0.99(4), but a very small KIE [1.30(3)] was
Scheme 2. Site-selective distribution of deuterium atoms in 4a-d2.

M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
177
3
1
H), the diastereotopic methylene protons at
H) and 2.58 (s, 1H), and two coordinated alkenyl protons at
d
2.46 (br.d, J ¼ 4 Hz,
d 4.61
(
br.dd, J ¼ 9, 4 Hz,1H) and 4.70 (br.d, J ¼ 9 Hz,1H). These resonances
are consistent with the coordinated 4,5-dimethyl-1,4-
hexadienylbenzene moiety in D [13].
The other transient new species remains obscure because of
severe overlapping among complex broad resonances. However, it
2
Chart 1. Deuterium distribution in 5a-d .
contains characteristic singlets at
d
ꢁ1.05 and
d 1.86 around 1:3
ꢀ
ratio, respectively, at ꢁ80 C. A possible explanation for these res-
onances is due to the endo-methylene and methyl protons in the
coordinated 2,3-dimethylbuta-1,3-diene, as observed for butadiene
complex 7. Thus we presumed formation of a diene complex
acrylate at first. Complex 6 reacted with methyl acrylate and the
1
reaction at room temperature gave broad resonances in the H NMR
ꢀ
spectrum. On cooling to ꢁ60 C, those resonances sharpened and
4
2
4
the signals assignable to the coordinated and free methyl acrylate
appeared separately. We have tentatively assigned this species as
[Ru(
h -2,3-dimethylbuta-1,3-diene)(h -styrene)(h -1,5-COD)] (A)
[14].
4
2
4
1
[
Ru(h -buta-1,3-diene)(h -methyl acrylate)(h -1,5-COD)] (7) by H
1
1
NMR and He H COSY (Scheme 3).
2.4. Possible catalytic cycle
The most characteristic feature of 7 in 1H NMR spectrum in
ꢀ
toluene-d
6
at ꢁ60 C is a 3H singlet at
d 3.44 assignable to the
All these experimental data are consistent with the catalytic
cycle shown in Scheme 5.
In order to clarify the fate of the cleaved hydrogen, the reaction
2
using styrene-d is depicted in Scheme 5. Since the present reaction
obeys zero-order kinetics to both of the diene and styrene con-
centrations, the presence of A is supported. The intermediate A is
methyl group of the coordinated methyl acrylate. Consistently, the
buta-1,3-diene group was observed unsymmetrically and all reso-
nances appeared separately, suggesting the coordination of a
prostereogenic mono-substituted alkene. The alkenyl protons of
acrylate obscured probably overlapped with the 1,5-COD protons.
4
Complex 7 gradually converted into [Ru(
h
-methylhepta-2,4-
formed by displacement of the 6
dimethylbuta-1,3-diene and styrene as 4
p
naphthalene ligand with 2,3-
and 2 donors, respec-
4
dienoate)(
h -1,5-COD)(NCMe)] (8) [8] upon warming to room
p
p
temperature. The observation of 7 affords collateral evidence for
tively. This substrate selectivity is owing to the hapticity and is
origin of the cross-dimerization. In fact we observed the related
compound 7. Then an oxidative coupling reaction occurs at A to give
a ruthenacycle B. Note that we have obtained an analog of B in the
4
2
4
the formation of [Ru(
h -diene)(h -alkene)(h -1,5-COD)]. Note that
we have also documented observation of a similar intermediate
4
2
4
[
Ru(
COD)] at ꢁ60 C by H NMR, where the
is labile and undergoes rapid exchange with free buta-1,3-diene
h
-cisoid-buta-1,3-diene)(
h
-transoid-buta-1,3-diene)(
h
-1,5-
ꢀ
1
2
4
4
h
-transoid-buta-1,3-diene
reaction of [Ru(
h -cisoid-buta-1,3-diene)(h -1,5-COD)(NCMe)]
with vinyl acetate [Eq. (1)] [8].
4
while the
12].
Because stoichiometric reaction of 6 with styrene gave a com-
h -cisoid-buta-1,3-diene binds tightly to the Ru center
As shown in Fig. 2, this cross-dimerization is promoted by
electron deficient styrene. This fact can be explained by two rea-
sons: (i) facile coordination of the electron deficient styrene to the
Lewis basic Ru(0) center, and/or (ii) lowering the energy of the
LUMO in styrene fragment to enhance the oxidative coupling re-
action. However, because present reaction is regarded as a zero-
order to the styrene concentration, we believe the reason (ii) be-
ing responsible for this enhancement effect. Thus, the rate-
determining step seems to involve the oxidative coupling step.
The KIE values for this reaction are also consistent with this hy-
[
plex mixture, we tried the stoichiometric reaction of the naph-
thalene complex 1 with substrates. This experiment also gave less
clear results than 7 because of following reasons: (i) only a portion
of 1 reacted with substrates at low temperature, (ii) concomitant
formation of at least two new species were observed even at low
temperature, and (iii) dynamic behaviors of these new species and
added styrene resonances were observed. However, growth of the
broad resonances assignable to one of the new species was
pothesis. Subsequent b-hydride elimination gives C followed by the
reductive elimination giving D. The stoichiometric reaction also
supports D as the final compound in the catalytic cycle. Finally,
ꢀ
observed upon warming the mixture to þ10 C. In order to freeze
ꢀ
the dynamic behavior, we measured it at ꢁ80 C, and the broad
resonances relatively sharpened. We tentatively assigned this
2
non-conjugated cross-dimer 4a-d is released. This mechanism
4
4
species as [Ru(
COD)] (D) (Scheme 4). The H NMR spectrum of this species con-
tains three methyl peaks at 0.83 (s, 3H), 1.32 (s, 3H) and 1.67 (s,
h -4,5-dimethyl-1,4-hexadienylbenzene) (h -1,5-
well explains the formal 1,4-addition of styrene to diene as shown
1
4
5
above. The Z configuration of the C ]C bond in 4a-d
2
is also
d
consistent with this mechanism which extends back to the cisoid
Scheme 3. Reaction of [Ru( 4-buta-1,3-diene)(h4-1,5-COD)(NCMe)] (6) with methyl acrylate.
h

178
M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
Scheme 4. Reaction of [Ru( 4-naphthalene)(h4-1,5-COD)] (1) with 2,3-dimethylbuta-1,3-diene and styrene.
h
coordination of the diene in A.
products denoted in Fig. 3 are collected in the Fig. 4. As shown in
The site selective H/D exchange process and isomerization of the
C]C bond are rather speculative but these processes are consistent
with the pathways shown in Scheme 6. The intermediate D having
Figs. 3 and 4, two intermediates, INT1 and INT2, are participated in
the
b-hydride elimination and reductive elimination steps,
respectively. Interestingly, they are relatively stable complexes in
which a hydride is attached to a carbon atom in the COD ligand. As a
result, five transition states (TS1-TS5) were located in the cross-
dimerization reaction. As shown in Fig. 4, the structures of TS2-
TS5 resemble each other. However, they are clearly different each
other because of distinct imaginary frequencies corresponding to
each reaction coordinates and they are verified by the IRC
calculations.
4
a-1,5-d
oxidative addition of the CꢁD bond occurs to give F, followed by
hydride elimination to give an allene intermediate G or H. Another
possible pathway is formation of C from D, followed by -deuteride
elimination to give G or H. Note that we have documented coor-
2
fragment causes a subsequent reaction involving an
b
-
b
4
dination of cumulenes to the Ru(
Then the hydride and deuteride get back to the internal C]C bond
in allene to give either 4a-1,4-d or 5a-d
h -1,5-COD) fragment [15,16].
2
2
.
Many intermediates and transition states were obtained during
investigation but the reaction paths directly connecting from B to C,
and from C to D without passing through the intermediates, INT1
and INT2, were failed to be located. In oxidative coupling step, the
CeC bond distance for coupling between diene and styrene
changes from 3.021 Å of A to 1.522 Å of B via 1.962 Å of TS1 as
2.5. DFT calculations
In order to understand the detailed mechanism for the cross-
dimerization, we have performed the DFT calculations. The calcu-
lated energy profile is illustrated in Fig. 3. It corresponds to the
main catalytic cycle from initial complex A to final complex D as
ꢁ1
shown in Fig. 4. TS1 has an imaginary frequency of 204.4i cm
corresponding to the reaction coordinate of CeC coupling. The
ꢁ
ꢁ1
1
shown in Scheme 5, composed of oxidative coupling step,
b-hy-
activation energy for oxidative coupling is 16.9 kcal mol
ꢁ1
dride elimination step, and reductive elimination step, respectively.
The optimized geometries of the reactants, transition states, and
(70.8 kJ mol ) and the heat of reaction is 11.2 kcal mol
ꢁ
1
(46.9 kJ mol ) endothermic as shown in Fig. 4.
Then, the -hydride elimination step followed from B to C was
examined carefully. The optimized geometries of transition states
TS2 and TS3), intermediate (INT1), and C are also shown in Fig. 4.
The structure of TS2 is very close to that of C, but the RueH bond
1.684 Å) is quite elongated than that in C (1.585 Å), and has an
imaginary frequency of 596.8i cm corresponding to the hydride
transfer from a carbon of styrene moiety to a carbon of the COD
ligand. The following reaction proceeds from INT1 to C through TS3.
The structure of TS3 is also close to that of C as shown in the figure,
b
(
(
ꢁ1
ꢁ
1
but TS3 has an imaginary frequency of 659.3i cm corresponding
to hydride transfer from INT1 to C. The activation energy of TS2 is
0.4 kcal mol (43.6 kJ mol ) measured from B and that of TS3 is
ꢁ
1
ꢁ1
ꢁ1
1
8
ꢁ1
.1 kcal mol (34.8 kJ mol ) measured from INT1. The heats of
reaction for INT1 and C are both exothermic. It is noteworthy that
the hydride transfer from a carbon atom of the COD in INT1 to an
adjoining carbon atom in the COD is difficult to occur because the
ꢁ
1
ꢁ1
reaction is 2.9 kcal mol (12.2 kJ mol ) endothermic with rela-
ꢁ
1
ꢁ1
tively high activation energy of 35.5 kcal mol (148.7 kJ mol
)
(these structures and energies are shown in Supporting Informa-
tion). This is consistent with the experimental result in Table 2,
where the contribution of hydride scrambling in deuterium dis-
tribution in the major product 4a is small.
The present calculations suggest the COD ligand being not a
Scheme 5. Overall mechanism for the cross-dimerization of the product.

M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
179
stands at the
and coworkers have documented electron-withdrawing groups at
the eposition in an alkyl complex suppressing ehydride elimi-
aeposition in a ruthenacycle. It is notable that Myers
a
b
nation [19], but our system contradicts this feature. The isotopic
labeling studies also show the CeH bond cleavage step being an
irreversible process after a rate-determining step. These kinetic
results are consistent with the oxidative coupling step being rate-
determining. In the energy profile by DFT calculations, the high-
est transition state in the energy diagram is TS2, which concerns
the behydride elimination, but the transition state that requires the
largest activation energy is TS1 in the oxidative coupling step (cf.
Fig. 3). There is an argument of which step should be called as the
rate-determining step. If the
enough, the oxidative coupling step would constitute an equilib-
rium, that means the ehydride elimination step being controlled
by the concentration of B. On the other hand, the ehydride
behydride elimination step is slow
b
b
elimination step is quick enough, produced B would be consumed
rapidly. In this case, the oxidative coupling step will govern the
reaction. Unfortunately, we do not have information about
reversibility of the oxidative coupling step, but this step is largest
endothermic step in the present catalytic cycle. The energy differ-
ence means that this step largely leis on the A side (K
e
¼ [B]/
ꢁ
9
[A] ~ 10 at 298 K) even if this step were reversible. Therefore, the
overall reaction would strongly depend on the oxidative coupling
step and we can call this step being a practical rate-determining
step. In fact, we obtained a good linear relationship between the
logarithm of experimental relative rate constants and the calcu-
lated activation energies for the oxidative coupling reaction as
shown in Fig. 5.
3. Conclusion
Scheme 6. Possible mechanism for H/D exchange and isomerization of the product.
The present study supports an oxidative coupling mechanism
simple spectator ligand, and the Ru center mediates the hydride
for cross-dimerization between conjugated diene and alkene both
by the kinetic and theoretical studies. The kinetic studies suggest
prior coordination of both of diene and styrene to the Ru(0) center
and the electron deficient styrene promotes the cross-dimerization.
The computational studies are also consistent with the kinetic re-
sults and engage the oxidative coupling step to govern the overall
reaction. This is the first solid evidence in support of oxidative
mechanism for the cross-dimerizations between dienes and al-
kenes. The calculations also suggest that the COD ligand is actually
not a simple spectator ligand but it engages to assist the hydrogen
migration steps.
transfer from a methylene carbon in the ruthenacycle to the COD
4
ligand. Such migration of a hydride in RueH to
h
-1,5-COD ligand
3
normally comes down an allylic
8
h -1-3-C H13 ligand [17]. However,
1
2
a similar hydride migration giving
h
-5:
-1,5-COD)(NH NMe
-1,2-C 13) (CNR) ]PF
The energy profile of reductive elimination step is also shown in
h
-1,2-C
]PF
[18].
8
H
13 is reported in
with isocyanide
4
the reaction of [RuH(
h
2
2
)
3
6
1
2
to yield [Ru(
h
-5:
h
8
H
4
6
ꢁ
1
Fig. 3. The intermediate (INT2) has lower energy of 3.7 kcal mol
ꢁ1
(
15.5 kJ mol ) than C. Transition state (TS4) can be located among
them with barrierless. The transition state (TS5) followed by INT2
ꢁ
1
ꢁ1
has activation energy of 14.3 kcal mol (59.9 kJ mol ) and the
ꢁ
1
final complex D has small endothermicity of 3.5 kcal mol
14.7 kJ mol ) relative to INT2.
These calculation results clearly show that the oxidative
ꢁ
1
4. Experimental
(
4.1. General procedures
coupling step requires the largest activation barrier for TS1
throughout the reactions. To confirm this, the effect of substituents
of styrene on activation energy of the oxidation coupling was
investigated as shown in Fig. 5. The excellent linear relationship
clearly indicates the electronic nature of styrene governs the rate of
the overall reactions.
All manipulations and reactions were performed under dry ni-
trogen or argon with use of standard Schlenk and vacuum line
techniques. Benzene, toluene, hexane, tetrahydrofuran (THF) and
Et
2
O were purified by Glass Contour Ultimate Solvent Purification
and toluene-d were dried over sodium wire,
System. Benzene-d
6
8
and these solvents were stored under vacuum. 2,3-Dimethylbuta-
1,3-diene (99.0% pure) was purchased from Aldrich and used as
received. [Ru(h -naphthalene)(h -1,5-COD)] (1) was prepared ac-
2.6. Discussion
6
4
The present studies strongly support an oxidative coupling
cording to the literature procedure [2]. All other reagents were
obtained from commercial suppliers (Wako Pure Chemical In-
dustry, Aldrich, or TCI) and used as received. NMR spectra were
mechanism for this reaction. These kinetic studies basically suggest
the reaction to be a zero-order reaction to both of the diene and
styrene concentrations. In other words, coordination of these
substrates is not a rate-determining step. Therefore the Hammett
1
13
recorded on JEOL ECX400P ( H at 399.8 MHz, C at 100.5 MHz)
1
spectrometer. Tetramethylsilane was used as reference for H and
13
plot with a positive
promote the subsequent steps. In our system,
tion would proceed from B (cf. Scheme 5), where an aryl group
r
value suggests electron-deficient styrene to
C spectra. The GLC analyses were performed on Shimadzu GC14B
behydride elimina-
equipped with a TC-WAX (0.25 mmf x 30 m) under the following
conditions: initial temp. ¼ 50 ꢀC, initial time ¼ 5 min, program

180
M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
Fig. 3. Energy profile for the cross-dimerization reaction between 2,3-dimethylbut-1,3-diene and styrene. Energy values in parentheses are measured from a) B, b) INT1, c) C, and d)
INT2, respectively.
ꢀ
ꢀ
rate ¼ 5 ꢀC /min, final temp. ¼ 220 C, injector temp. ¼ 200 C, de-
0.05927 mol) in 100% yield (99% atom D). [PPh
3 3
(CD )]I (24.3235 g,
ꢀ
tector temp. ¼ 200 C. GCeMS was measured on a Shimadzu
0.0593 mmol) was suspended in Et O (80 ml) and tert-BuOK
2
QP2010 by use of the electron impact method.
(6.3078 g, 0.5621 mol) was added into the reaction mixture, during
which the white suspension turned to yellow suspension. After 2 h,
benzaldehyde (5.8 ml, 0.0568 mol) was slowly dropped into the
4
.2. Reactions of 2,3-dimethylbuta-1,3-diene with styrene
ꢀ
solution at ꢁ65 C to give a white suspension. The reaction mixture
A toluene solution (2 ml) of 2,3-dimethylbuta-1,3-diene (2)
ml, 1.77 mmol) and styrene (3a) (170 ml, 1.48 mmol) was
was stirred for a night and was allowed to rise to room temperature.
Then, water (30 ml) was added into the suspension and the product
(
200
6
4
added into Ru(
h
-naphthalene)(
h
-1,5-COD) (1) (10.3 mg,
2
was extracted with Et O. The ether solution was washed with
ꢀ
0
.03 mmol, 2 mol%) and the reaction mixture was stirred at 50 C
NaHSO aq (10 ml), and brine (10 ml), and then dried with MgSO .
3
4
for 5 h. The product yield and product ratio were determined by
GC analysis using dibenzyl (49.9 mg, 0.27 mmol) as an initial
standard. Yield 84% (4a/5a/isomers ¼ 79/13/8). These products
were identified by NMR spectra after purification by silicagel
chromatography with hexane as an eluent. (E)-(4,5-dimethyl-1,4-
The solution was concentrated under atmospheric pressure and the
product was purified with silicagel chromatography using pentane
as an eluent. The product was dried with CaH and was distilled
0
under vacuum to give styrene-
b
,
b
-d
2
(3a-d
2
). Yield: 3.7317 g (3a-
d
2
/pentane ¼ 4.7/1, net 3a-d
2
¼ 0.0288 mol, 49%).
1
hexadienyl)benzene (4a). H NMR (400 MHz, chloroform-d, r.t.):
d
7.35 (d, J ¼ 8.0 Hz, 2H, ePh), 7.26 (t, J ¼ 8.0 Hz, 2H, ePh), 7.16 (t,
J ¼ 7.4 Hz, 1H, ePh), 6.33 (d, J ¼ 16.0 Hz, 1H, ]CHe), 6.14 (dt,
J ¼ 16.0 Hz, 6.3 Hz, 1H, ]CHe), 2.90 (d, J ¼ 6.3 Hz, 2H, eCH e),
.69 (s, 3H, 1-Me cis to methylene), 1.67 (s, 3H, 3-Me), 1.65 (s, 3H,
4.4. Effect of substrate concentrations
2
Similar to above reaction, the reactions were repeated with
different substrate concentrations at 50 C for 5 h: 2 (1660
ꢀ
1
m
l,
1
2
-Me): These assignments were confirmed by NOESY. H NMR
400 MHz, benzene-d , r.t.): 7.25 (m, 2H, ePh), 7.12 (m, 2H,
ePh), 7.03 (m, 1H, ePh), 6.36 (d, J ¼ 15.5 Hz, 1H, ]CHe), 6.11 (dt,
J ¼ 15.4 Hz, 6.8 Hz, 1H, ]CHe), 2.84 (d, J ¼ 6.3 Hz, 2H, eCH e),
.64 (s, 6H, -Me), 1.62 (s, 3H, -Me). C{ H} NMR (100 MHz,
benzene-d , r.t.): 141.0 (s), 131.0 (s), 129.0 (s), 128.9 (s), 126.0 (s),
25.0 (s), 40.1 (s), 21.6 (s), 21.0 (s), 14.6 (s). GCeMS: m/z ¼ 186
14.7 mmol), 3a (170
(0.8 ml), yield 90% (4a/5a/isomers ¼ 87/9/4). 2 (830
3a (170 l, 1.48 mmol), 1 (10.0 mg, 0.03 mmol), toluene (1.6 ml),
yield 86% (4a/5a/isomers ¼ 82/12/6). 2 (330 l, 2.93 mmol), 3a
(170 l, 1.48 mmol), 1 (10.1 mg, 0.03 mmol), toluene (2 ml), yield
88% (4a/5a/isomers ¼ 78/9/13). 2 (166 l, 1.48 mmol), 3a (340 l,
2.96 mmol), 1 (9.8 mg, 0.03 mmol) toluene (2 ml), yield 64% (4a/5a/
l, 1.48 mmol), 3a (830 l, 7.25 mmol) in
ml, 1.48 mmol), 1 (10.0 mg, 0.03 mmol), toluene
(
6
d
m
l, 7.37 mmol),
m
2
m
13
1
1
m
6
d
m
m
1
þ
1
(
(
M ). (E)-(4,5-dimethyl-2,4-hexadienyl)benzene (5a). H NMR
400 MHz, benzene-d , r.t.): 7.16 (m, 4H, ePh), 7.05 (m, 1H,
isomers ¼ 34/59/6). 2 (167
m
m
6
d
toluene (1.5 ml) were added into Ru(naphthalene) (COD) 1
(10.0 mg, 0.03 mmol), yield 65% (4a/5a/isomers ¼ 63/32/5). 2
ePh), 6.66 (d, J ¼ 14.8 Hz, 1H, ]CHe), 5.71 (dt, J ¼ 15.4 Hz, 6.8 Hz,
e), 1.70 (s, 6H, -Me), 1.62
s, 3H, -Me). 13C{ H} NMR (100 MHz, benzene-d
, r.t.): 138.26
1
H, 2-CH), 3.36 (d, J ¼ 6.9 Hz, 2H, eCH
2
(167 ml, 1.48 mmol), 3a (1690 ml, 14.77 mmol), 1 (10.0 mg,
1
(
(
6
d
0.03 mmol), toluene (0.6 ml) yield 58% (4a/5a/isomers ¼ 74/21/5).
s), 130.49 (s), 128.61 (s), 127.08 (s), 38.36 (s), 20.67 (s), 20.26 (s),
þ
1
8.56 (s). GCeMS: m/z ¼ 186 (M ).
4.5. Effect of catalyst concentration
0
4.3. Synthesis of styrene-
b
,
b
-d
2
2 (200
ml, 1.77 mmol), 3a (170 ml, 1.48 mmol), 1 (10.0 mg,
ꢀ
0
.03 mmol), toluene (2 ml), 40 C. 9 h. Yield: 62% (4a/5a/
In a 500 ml Schlenk tube, PPh
placed and THF (90 ml) was added. CD
3
(15.5466 g, 0.05927 mol) was
I (3.8 ml, 0.05927 mmol)
isomers ¼ 77/15/8). 2 (200
m
l, 1.77 mmol), 3a (170
m
l, 1.48 mmol), 1
ꢀ
3
(4.93 mg, 0.015 mmol), toluene (2 ml), 50 C, 10 h. Yield: 52% (4a/
was added into the solution and the reaction mixture was refluxed
for an hour. After cooling to room temperature, the resulting white
5a/isomers ¼ 83/12/5). 2 (200
m
l, 1.77 mmol), 3a (170
m
l,
ꢀ
1.48 mmol), 1 (19.7 mg, 0.058 mmol), toluene (2 ml), 50 C, 8 h.
solid was separated and was washed with Et
dried under reduced pressure to give [PPh
2
O (20 ml, twice) and
(CD )]I (24.3235 g,
Yield: 74% (4a/5a/isomers ¼ 74/16/9). 2 (100
m
l, 1.77 mmol), 3a
ꢀ
3
3
(170
m
l, 1.48 mmol), 1 (19.7 mg, 0.058 mmol), toluene (2 ml), 50 C,

M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
181
Fig. 4. Optimized structures for the cross-dimerization reaction between 2,3-dimethylbuta-1,3-diene and styrene as denoted in Fig. 3. Structures of intermediates and transition-
states are also depicted below each ball-and-stick model. Selected bond lengths (Å) are shown in the figure. The transferring hydride is highlighted in green. (For interpretation of
the references to colour in this figure legend, the reader is referred to the web version of this article.)

182
M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
1
(
eC
4d). H NMR (400 MHz, benzene-d
6
, r.t.):
d
7.06 (d, J ¼ 8.6 Hz, 2H,
6
H
4
e), 6.89 (d, J ¼ 8.6 Hz, 2H, eC
6 4
H
e), 6.15 (d, J ¼ 15.5 Hz,1H, ]
CHe), 5.94 (dt, J ¼ 16.0 Hz, 6.3 Hz, 1H, ]CHe), 2.79 (d, J ¼ 6.3 Hz,
2
H, eCH
2
e), 1.69 (s, 6H, -Me), 1.62 (s, 3H, -Me). GCeMS: m/z ¼ 220
þ
(
M ). (E)-1-chloro-4-(4,5-dimethyl-2,4-hexadienyl)benzene (5d):
1
H NMR (400 MHz, benzene-d
eC
6
, r.t.):
d
7.10 (d, J ¼ 9.2 Hz, 2H,
6
H
4
e), 6.80 (d, J ¼ 8.6 Hz, 2H, eC
6
H
4
e), 6.58 (d, J ¼ 15.5 Hz,1H, ]
CHe), 5.56 (dt, J ¼ 15.5 Hz, 7.4 Hz,1H, ]CHe), 3.16 (d, J ¼ 6.9 Hz, 2H,
þ
eCH
2
e),1.69 (s, 6H, -Me),1.62 (s, 3H, -Me). GCeMS: m/z ¼ 220 (M ).
2
(200 ml, 1.77 mmol), p-trifluoromethylstyrene (3e) (325 ml,
1.01 mmol), 1 (6.82 mg, 0.02 mmol), toluene (2 ml), Yield: 74% (4e/
5
e/isomers ¼ 85/12/3). The products were purified by silicagel
chromatography with hexane as an eluent and were identified by
NMR spectra. (E)-1-trifluoromethyl-4-(4,5-dimethyl-1,4-
hexadienyl)benzene (4e): H NMR (400 MHz, chloroform-d, r.t.):
1
d
6
7.51 (d, J ¼ 8.6 Hz, 2H, eC
.36 (d, J ¼ 16.0 Hz, 1H, ]CHe), 6.25 (dt, J ¼ 16.0 Hz, 6.3 Hz, 1H, ]
e), 1.73 (s, 3H, -Me), 1.70 (s, 3H,
Me), 1.64 (s, 3H, -Me). H NMR (400 MHz, benzene-d , r.t.): 7.29
d, J ¼ 8.0 Hz, 2H, eC ), 6.96 (d, J ¼ 8.0 Hz, 2H, C ), 6.16 (d,
J ¼ 15.1 Hz, 1H, ]CHe), 6.01 (dt, J ¼ 6.8 Hz, 1H, ]CHe), 2.78 (d,
6
H
4
e), 7.41 (d, J ¼ 8.6 Hz, 2H, eC
6 4
H e),
Fig. 5. Hammett-like plot against calculated activation energies for oxidative coupling
reaction.
CHe), 2.93 (d, J ¼ 6.3 Hz, 2H, eCH
2
1
-
(
6
d
6
H
4
6 4
H
4
3
5
h. Yield: 65% (4a/5a/isomers ¼ 60/23/17). 2 (100
m
l, 0.88 mmol),
13
1
J ¼ 6.8 Hz, 2H, eCH
benzene-d , r.t.): 141.4 (s), 131.5 (s), 129.0 (s), 126.4 (s), 124.6 (s),
8.3 (s), 20.7 (s), 20.3 (s), 18.5 (s): In this spectrum, the CF
2
e), 1.62 (s, 9H, -Me). C{ H} NMR (100 MHz,
a (85
ml, 0.74 mmol), 1 (50.4 mg, 0.149 mmol), toluene (1 ml),
d
ꢀ
6
0
C, 3 h. Yield: 61% (4a/5a/isomers ¼ 43/33/24). 2 (200
ml,
3
3
d
reso-
ꢁ61.9
1.77 mmol), 3a (170
m
l, 1.48 mmol), 1 (2.61 mg, 0.0077 mmol),
19
nance was not observed. F NMR (376 MHz, benzene-d
6
):
ꢀ
toluene (2 ml), 50 C, 11 h. Yield: 39% (4a/5a/isomers ¼ 82/13/5).
þ
(s). GCeMS: m/z
¼
254 (M ). (E)-1-trifluoromethyl-4-(4,5-
1
dimethyl-2,4-hexadienyl)benzene (5e): H NMR (400 MHz, ben-
zene-d , r.t.): e), 7.30 (d, J ¼ 8.0 Hz, 2H,
7.53 (d, J ¼ 8 Hz, 2H, eC
eC
e), 6.61 (d, J ¼ 14.9 Hz, 1H, ]CHe), 5.65 (dt, J ¼ 15.5 Hz,
6.9 Hz, 1H, ]CHe), 3.50 (d, J ¼ 6.9 Hz, 2H, eCH e), 1.81 (s, 3H, -Me),
1.77 (s, 3H, -Me), 1.74 (s, 3H, -Me). C{ H} NMR (100 MHz, benzene-
, r.t.): 145.5 (s), 131.7 (s), 129.1 (s), 126.0 (s), 125.1 (s), 39.6 (s),
4.6. Hammett plot
6
d
6 4
H
6 4
H
2
(200 l, 1.77 mmol), styrene (3a) (170
m
ml, 1.48 mmol), 1
2
13
1
(
10.0 mg, 0.03 mmol), toluene (2 ml). Yield: 75% (4a/5a/
isomers ¼ 80/13/7).
d
6
d
19
2
(200
m
l, 1.77 mmol), p-methoxy styrene (3b) (210
ml,
21.6 (s), 20.2 (s), 14.6 (s). F NMR (376 MHz, benzene-d
(s). GCeMS: m/z ¼ 254 (M ).
6
):
d
ꢁ61.8
ꢀ
þ
1.48 mmol),1 (10.0 mg, 0.03 mmol), toluene (2 ml), 50 C, 8 h. Yield:
4
9% (4a/isomer ¼ 92/8). The products were purified by silicagel
2 (200 ml, 1.77 mmol), p-nitrostyrene (3f) (235 ml, 1.48 mmol), 1
column chromatography with hexane as an eluent and were
(10.0 mg, 0.03 mmol), toluene (2 ml). Yield: 87% (4f/isomers ¼ 85/
identified by NMR spectra. (E)-1-methoxy-4-(4,5-dimethyl-1,4-
15). The product was purified by silicagel column chromatography
1
hexadienyl)benzene (4b): H NMR (400 MHz, benzene-d
6
, r.t.):
e),
.38 (d, J ¼ 15.4 Hz, 1H, ]CHe), 6.04 (dt, J ¼ 15.4 Hz, 6.9 Hz, 1H, ]
e), 1.68 (s, 6H,
Me), 1.63 (s, 3H, -Me). 1 C{ H} NMR (100 MHz, benzene-d
, r.t.):
159.31 (s), 130.01 (s), 127.29 (s), 126.33 (s), 114.24 (s), 54.70 (s),
with hexane as an eluent and were identified by NMR spectra. (E)-
1
d
6
7.21 (d, J ¼ 9.2 Hz, 2H, eC
6
H
4
e), 6.76 (d, J ¼ 11.4 Hz, 2H, eC
6
H
4
1-nitro-4-(4,5-dimethyl-1,4-hexadienyl)benzene (4f):
(400 MHz, benzene-d , r.t.):
7.83 (d, J ¼ 9.2 Hz, 2H, eC
(d, J ¼ 8.6 Hz, 2H, eC e), 6.06 (d, J ¼ 16 Hz, 1H, ]CHe), 5.98 (dt,
J ¼ 16 Hz, 6.3 Hz, 1H, ]CHe), 2.76 (d, J ¼ 6.3 Hz, 2H, ]CH e), 1.61
133.67 (s),
H
NMR
6
d
6
H
4
e), 6.79
CHe), 3.28 (s, 3H, -OMe), 2.89 (d, J ¼ 6.8 Hz, 2H, eCH
2
6 4
H
3
1
-
6
2
13
1
d
(m, 9H, -Me). C{ H} NMR (100 MHz, benzene-d
6
, r.t.):
d
þ
3
8.39 (s), 20.68 (s), 20.29 (s), 18.59 (s). GCeMS: m/z ¼ 216 (M ).
(200 l,1.77 mmol) p-methylstyrene (3c) (195 l,1.48 mmol),1
10.0 mg, 0.03 mmol), toluene (2 ml), Yield: 51% (4c/5c/
128.38 (s), 126.39 (s), 123.88 (s), 38.36 (s), 20.64 (s), 20.27 (s), 18.58.
þ
2
m
m
GCeMS: m/z ¼ 231 (M ).
ꢁ
1
(
The observed initial formation rate rint (M s ) of 4 (the number
ꢁ7
isomers ¼ 90/2/8). These products were purified by silicagel col-
in parentheses indicates concentrations (M) of 1); 4a: 1.80 ꢂ 10
7
ꢁ
ꢁ7
umn chromatography with hexane as an eluent and were identified
(0.0125), 4b: 1.22 ꢂ 10 (0.0124), 4c: 1.24 ꢂ 10 (0.0124), 4d:
ꢁ7
ꢁ7
ꢁ7
by NMR spectra. (E)-1-methyl-4-(4,5-dimethyl-1,4-hexadienyl)
2.48 ꢂ 10 (0.0124), 4e: 1.16 ꢂ 10 (0.0080), and 4f: 4.06 ꢂ 10
1
benzene (4c). H NMR (400 MHz, benzene-d
6
, r.t.):
e), 6.95 (d, J ¼ 8 Hz, 2H, eC e), 6.39 (d,
J ¼ 16 Hz,1H, ]CHe), 6.11 (dt, J ¼ 15 Hz, 6.9 Hz,1H, ]CHe), 2.87 (d,
J ¼ 6.8 Hz, 2H, eCH e), 2.10 (s, 3H, -Me),1.65 (s, 6H, -Me),1.62 (s, 3H,
Me). C{ H} NMR (400 MHz, benzene-d , r.t.): 130.45 (s), 129.44
s), 127.56 (s), 38.40 (s), 21.10 (s), 20.68 (s), 20.28 (s), 18.59 (s). (E)-1-
d
7.22 (d,
(0.0122).
J ¼ 8 Hz, 2H, eC
6
H
4
6 4
H
4.7. Isotopic labeling experiments
2
13
1
0
-
6
d
(Method A): 2 (200
m
l, 1.77 mmol) and styrene-
b
,
b
ꢁd
2 2
(3a-d )
(
(175
m
l, 1.48 mmol), 1 (10.01 mg, 0.030 mmol), toluene (2 ml),
1
ꢀ
methyl-4-(4,5-dimethyl-2,4-hexadienyl)benzene (5c).
400 MHz, benzene-d , r.t.):
7.10 (d, J ¼ 8 Hz, 2H, eC
J ¼ 8 Hz, 2H, eC e), 6.67 (d, J ¼ 15.5 Hz, 1H, ]C He), 5.75 (dt,
e), 2.13
H
NMR
40 C, 8 h. Yield: 79% (4a-d
2
/5a-d
2
/isomers ¼ 78/14/8). These
(
6
d
6
H
4
e), 7.06 (d,
products were purified by silicagel column chromatography with
6
H
4
hexane as an eluent and were identified by NMR spectra. (E)-2,3,6-
1
J ¼ 15.5 Hz, 6.8 Hz, 1H, ]CHe), 3.39 (d, J ¼ 7.5 Hz, 2H, eCH
2
triduterium-(4,5-dimethyl-1,4-hexadienyl)benzene (4a-d
2
):
H
(
s, 3H, -Me), 1.71 (s, 6H, -Me), 1.62 (s, 3H, -Me).
(200 l,1.77 mmol), p-chlorostyrene (3d) (190
10.0 mg, 0.03 mmol), toluene (2 ml). Yield: 89% (4d/5d/
NMR (400 MHz, benzene-d
6
, r.t.):
d
7.25 (d, J ¼ 7.4 Hz, 2H,
2
m
ml,1.48 mmol),1
eC
eC
6
6
H
H
4
e), 7.11 (d, J ¼ 8 Hz, 2H, eC
6 4
H
e), 7.02 (t, J ¼ 5.2 Hz, 1H,
(
4
e), 6.37 (d, J ¼ 12 Hz, 1H, ]CHe), 6.0 (dt, J ¼ 16 Hz, 6.9 Hz,
isomers ¼ 75/19/6). The products were purified by silicagel chro-
2
0.33H, ]CHe), 2.83 (m, 1.58H, ]CH e), 1.64 (s, 2.69H, -Me), 1.62
(s, 3H, -Me). H NMR (61 MHz, benzene, r.t.):
2
matography with hexane as an eluent and were identified by NMR
d
6.12 (m, 0.67D),
þ
spectra.
(E)-1-chloro-4-(4,5-dimethyl-1,4-hexadienyl)benzene
2.79 (m, 0.42D), 1.61 (m, 0.71D). GCeMS: m/z ¼ 188 (M ). (E)-

M. Hirano et al. / Journal of Organometallic Chemistry 797 (2015) 174e184
183
1
,2,3,6-tetraduterium-(4,5-dimethyl-2,4-hexadienyl)benzene (5a-
frequency corresponding to the reaction coordinate. Additionally,
the intrinsic reaction coordinate (IRC) calculations [24,25] were
carried out to check whether the transition state leads to the
reactant and the product, or not. Relative energies were corrected
by adding the unscaled zero-point vibrational energy. All calcula-
tions were carried out using the Gaussian 09 program [26].
2
d
2
): H NMR (61 MHz, benzene, r.t.):
d 6.62 (m, 0.12D), 5.69 (m,
0
.62D), 3.32 (m, 0.25D), 1.63e1.69 (m, 0.90D). (Method B): In an
NMR tube, dibenzyl (3.44 mg, 0.0188 mmol) was dissolved in
benzene-d (300 l). Then, 2 (16.6 l, 0.148 mmol), 3a (8.4 l,
.073 mmol) and 3a-d (8.8 l, 0.073 mmol) were added into the
solution. After measurement the first NMR spectra, 1 (1.03 mg,
.00305 mmol) was added and then benzene-d was added to
6
m
m
m
0
2
m
0
6
Acknowledgments
adjust the volume being 0.600 ml. The NMR tube was heated at
ꢀ
4
0
C for the catalysis.
The numerical calculations were carried out on the TSUBAME2.5
supercomputer at the Tokyo Institute of Technology, Tokyo, Japan,
and on the supercomputer at the Research Center for Computa-
tional Science, Okazaki, Japan. This work was financially supported
by Japan Science and Technology Agency (JST), ACT-C.
4.8. Eyring plot
The reactions were carried out under the following conditions
and the reaction was monitored by GLC. Conditions: 2 (200
m
l,
l, 1.48 mmol), toluene (2.00 ml), 1 (10 mg,
.03 mmol), dibenzyl as an internal standard (67 mg, 0.37 mmol).
1
0
.77 mmol), 3a (170
m
Appendix A. Supplementary data
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
The reaction was performed at 41 C, 46 C, 49 C, 55 C, 59 C,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.08.022.
ꢀ
ꢀ
6
5 C, or 71 C.
4.9. Reaction of 6 with methyl acrylate
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(
4
.10. Reaction of 1 with 2,3-dimethylbuta-1,3-diene and styrene
(
Complex 1 (10.1 mg, 0.030 mmol) was placed in an NMR tube to
(
which toluene-d
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8
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[
(
m
(
ꢀ
ꢀ
ml,
0
ꢀ
1
temperature range of ꢁ80 to þ10 C. The H NMR spectrum of the
1
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ꢀ
d
8
, ꢁ80 C):
d
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0
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.11. DFT calculations
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(
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