In Situ routes to catalytically active Ru(0) Species by reduction of readily available, air-stable precursors

Article abstract of DOI:10.1021/acs.organomet.7b00882

Cross-dimerization of a conjugated diene with a substituted alkene catalyzed by in situ reduction of an air-stable Ru(II) catalyst precursor has been achieved. Reaction of 2,3-dimethylbutadiene with styrene is catalyzed by [Ru(acac)₂(η⁴-1,5-COD)] (2a) (5 mol %) with BuLi (10 mol %) at 50 °C for 6 h in hexane, giving the cross-dimers in 99% yield ((E)-4,5-dimethyl-1-phenylhexa-1,4-diene (3a)/(E)-4,5-dimethyl-1-phenylhexa-2,4-diene (3b)/isomers = 84/9/7). Because neither 2a nor BuLi separately catalyzes the cross-dimerization and reduction of 2a with BuLi in the presence of naphthalene produces [Ru(η⁶-naphthalene)(η⁴-1,5-COD)] (1a), the active species in this catalysis is considered to be a Ru(0) compound. Interestingly, this in situ reduction method of Ru(II) using BuLi can be applied to the cross-dimerization using an ester such as methyl acrylate. Alternatively, an air-stable Ru(II) complex having a labile arene ligand such as [RuCl₂(η⁶-anisole)]₂ (5c) (5 mol %) with Na₂CO₃ (40 mol %) in the presence of 1,5-COD (20 mol %) at 100 °C for 6 h in 2-butanol also catalyzes the same cross-dimerization in 62% yield. These protocols provide facile methods for production of unsaturated linear compounds by the cross-dimerization using air-stable Ru(II) catalyst precursors.

Full text of DOI:10.1021/acs.organomet.7b00882

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
In Situ Routes to Catalytically Active Ru(0) Species by Reduction of
Readily Available, Air-Stable Precursors
,
†
†
†
†
†
Masafumi Hirano,* Hideyuki Kobayashi, Takao Ueda, Yuki Hiroi, Ryota Abe,
Nobuyuki Komine,† Annie L. Colebatch,‡,§ and Martin A. Bennett*,‡
†Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16
Nakacho, Koganei, Tokyo 184-8588, Japan
‡
Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia
*
S Supporting Information
ABSTRACT: Cross-dimerization of a conjugated diene with a substituted alkene
catalyzed by in situ reduction of an air-stable Ru(II) catalyst precursor has been
achieved. Reaction of 2,3-dimethylbutadiene with styrene is catalyzed by
4
[
Ru(acac) (η -1,5-COD)] (2a) (5 mol %) with BuLi (10 mol %) at 50 °C for 6
2
h in hexane, giving the cross-dimers in 99% yield ((E)-4,5-dimethyl-1-phenylhexa-
,4-diene (3a)/(E)-4,5-dimethyl-1-phenylhexa-2,4-diene (3b)/isomers = 84/9/7).
Because neither 2a nor BuLi separately catalyzes the cross-dimerization and
1
6
4
reduction of 2a with BuLi in the presence of naphthalene produces [Ru(η -naphthalene)(η -1,5-COD)] (1a), the active species
in this catalysis is considered to be a Ru(0) compound. Interestingly, this in situ reduction method of Ru(II) using BuLi can be
applied to the cross-dimerization using an ester such as methyl acrylate. Alternatively, an air-stable Ru(II) complex having a labile
6
arene ligand such as [RuCl (η -anisole)] (5c) (5 mol %) with Na CO (40 mol %) in the presence of 1,5-COD (20 mol %) at
2
2
2
3
1
00 °C for 6 h in 2-butanol also catalyzes the same cross-dimerization in 62% yield. These protocols provide facile methods for
production of unsaturated linear compounds by the cross-dimerization using air-stable Ru(II) catalyst precursors.
6
4
16
INTRODUCTION
[Ru(η -naphthalene)(η -cyclic diene)] (1), where the cyclic
■
diene ligand acts as an important ancillary ligand for the activity
and selectivity. Typical examples are the cross-dimerization of
,3-dienes with acrylates, the tail-to-tail dimerization of
acrylates, and the chemo- and stereoselective cross-dimeriza-
tion of methyl methacrylate or methacrylamide with unsatu-
Catalytic cross-dimerization between conjugated dienes and
substituted alkenes is a reliable and promising method for
production of linear organic molecules with high atom and step
economy. Following the first brief report by Wittenberg of Co-
catalyzed cross-dimerizations of dienes, various catalytic
systems based on transition metal compounds from groups
0 to 8 have been reported (Table 1).
documented regio- and enantioselective cross-dimerizations
between conjugated dienes and substituted alkenes catalyzed by
17
1
18
1
19
rated five-membered-ring compounds.
The detailed mechanism of operation of this catalytic system
has been established by isolation/observation of the inter-
mediates, kinetic studies, and DFT calculations. These
2
−15
1
We have
2
0
6
reactions are initiated by displacement of the labile η -
naphthalene ligand to generate a formal “Ru(cyclic diene)”
4
Table 1. Selected Groups 10 to 8 Catalyst Systems for Cross-
Dimerization using Conjugated Dienes/Related Compounds
(A) with a 6e vacant site, to which a η -conjugated compound
2
(4π) and η -unsaturated compound (2π) selectively coordinate,
and the subsequent C−C coupling proceeds by an oxidative
catalyst system
Ni(η -1,5-COD) ]/AlEt /PPh(OMe)
ref
coupling mechanism. Scheme 1 outlines the mechanism for the
4
[
[
[
[
[
[
2
6
4
2
3
2
cross-dimerization catalyzed by [Ru(η -naphthalene)(η -1,5-
COD)] (1a).
PdCl (DMA) ]/AgBF /P(C H )
17 3
3
2
2
4
8
3
PdCl(η -C H )] /BF ·PPh
3
4
3
5
2
3
Although this is a potentially useful catalytic system for the
cross-dimerization, one must first prepare the thermally
unstable and air-sensitive naphthalene complex 1a. For the
practical use of this catalysis, it would be desirable to generate
1
2
4
Co(η :η -cyclooct-4-en-1-yl)(η -1,5-COD)]
5
CoBr (SchmalzPhos)]/ZnI /activated Zn
6, 7
8
2
2
CoBr (diphosphine)]/NaBARF/Zn
2
RhCl ·H O/EtOH
9
3
2
in situ catalytically active Ru(0) species A by reduction of
[
[
[
Fe(acac) ]/AlEt
10
11
12
13
14
15
4
3
3
readily available, air-stable precursors such as [Ru(acac) (η -
2
4
6
Ru(η -1,5-COD)(η -1,3,5-COT)]
6
1
,5-COD)] (2a) and [RuCl (η -arene)] (5) (Scheme 1). In
2
2
4
RuCp*Cl(η -1,5-COD)]
this paper, we report two different methods for the facile
FeCl /iminopyridine/activated Mg
2
RuCl ·3H O/Zn-Cu/EtOH/CO
3
2
6
Received: December 11, 2017
[
RuCl (η -p-cymene)] /HCO Na/PCyPh
2 2 2 2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4
Scheme 1. Outline of Catalytic Linear Cross-Dimerization of
Diene with Alkene
Table 2. Screening of Reductants for [Ru(acac) (η -1,5-
COD)] (2a)
2
a
reductant
cross-dimers
entry
amt (mol %) yield (%) 3a/3b/isomers
1
2
none
Mg
0
10
10
10
10
10
10
10
64
10
10
10
10
4
0
21
1
b
3
Mg*
Zn*
Na/naphthalene
Li/naphthalene
NaBH4
80/10/10
100/0/0
72/14/14
78/13/9
100/0/0
72/11/17
67/20/13
81/11/8
c
4
d
5
57
32
1
d
6
7
8
9
LiAlH4
76
46
26
0
NaH
1
1
1
1
0
1
2
3
MeMgBr
e
Et Zn
2
MeLi
BuLi
BuLi
BuLi
BuLi
75
73
14
13
0
74/11/15
82/8/10
86/14/0
85/15/0
f
generation of the “Ru(1,5-COD)” and related “Ru(cyclic
diene)” species by in situ reduction of ruthenium(II)
compounds.
14
15
g
h
10
10
1
6
a
Typical conditions: 2a (0.05 mmol), 2,3-dimethylbutadiene (1.0
mmol), styrene (1.0 mmol), hexane (1.5 mL), 50 C, 6 h. Yields and
ratios of the cross-dimers were determined by GLC analysis. Rieke
RESULTS AND DISCUSSION
In Situ Reduction of [Ru(acac) (η -1,5-COD)] (2a) as
the Catalyst Precursor. A series of [Ru(acac) (η -cyclic
̊
■
b
4
2
c
d
4
Mg. Rieke Zn. Metal/naphthalene was prepared in another vessel
2
e
and was transferred into the catalytic system by a cannula tube. [2,3-
diene)] (2) complexes is readily prepared by treatment of
f
g
dimethylbutadiene]/[styrene] = 2/1. 2a (2 mol %). Temperature 30
[
Ru(acac) ] with cyclic dienes in the presence of Zn in wet
h
3
°
C. In the absence of 2a.
2
1
THF. We focused on the air- and moisture-stable compound
[
4
Ru(acac) (η -1,5-COD)] (2a) as a catalyst precursor for the
2
present cross-dimerization. We employed the cross-dimeriza-
tion of 2,3-dimethylbutadiene with styrene as a model reaction,
The optimized conditions for the cross-dimerization of 2,3-
dimethylbutadiene with styrene catalyzed by 2a (5 mol %) and
BuLi were established; the results are given in Table 3. The
optimal BuLi/2a ratio was found to be 2/1, which gave cross-
dimers in 87% yield. The yield was reduced slightly, to 81%, by
use of a BuLi/2a ratio of 4/1, but use of a large excess of BuLi
(8 equiv) stopped the reaction completely (entry 4), probably
because of competing anionic polymerization of 2,3-dimethyl-
butadiene and/or styrene. Finally, a slight excess of 2,3-
dimethylbutadiene over styrene, with 10 mol % BuLi, furnished
the cross-dimers almost quantitatively (entry 9).
6
because this reaction is catalyzed by the Ru(0) complex [Ru(η -
4
naphthalene)(η -1,5-COD)] (1a) and the reaction mechanism
20a
is well-established. Table 2 illustrates the results of screening
of several reductants for 2a. In this catalysis, the major and
primary minor products were (E)-3a and (E)-3b, respectively.
We also detected several minor isomers having the same
molecular weight as 3 by GC/GC-MS analyses, but their
detailed structures are still unclear. The divalent Ru complex 2a
precursor alone showed no catalytic activity (entry 1).
A reductant was therefore required to generate a Ru(0)
species, but Mg metal did not work at all (Table 2, entry 2).
More active metal powders, prepared by a reduction of the
corresponding anhydrous metal chloride with an alkali metal
such as K, Na, and Li, are known as Rieke metals. However,
both Rieke Mg (Mg*) and Rieke Zn (Zn*) were very
inefficient (entries 3 and 4). Sodium/naphthalene and lithium/
naphthalene yielded the cross-dimers in moderate yields
Because the yield and distribution of the products by this
catalysis (Table 3, entry 7) are similar to those observed in the
Ru(0)-catalyzed reaction (entry 9), the 2a/BuLi system is likely
to act by the same mechanism as 1a.
2
2
The GLC analysis for reduction of 2a with 2 equiv of BuLi in
hexane showed evolution of butane (17.6%), 1-butene (5.0%),
(E)-2-butene (1.8%), and octane (6.9%), and (Z)-2-butene was
not observed. This observation supports formation of a Ru(0)
species by the in situ reduction. Although the present data
suggest that this system reduces a limited amount of Ru(II)
species, further addition of BuLi does not improve the catalysis
(Table 3). In another effort to obtain evidence for generation of
a Ru(0) species by this in situ reduction, we performed the
stoichiometric reaction of 2a with 2 equiv of BuLi in the
(
entries 5 and 6). Among the hydride reagents screened,
LiAlH gave the desired cross-dimers in promising yield (entry
4
8
), although NaBH4 was almost ineffective (entry 7).
Alkylmetal reagents such as MeLi and BuLi furnished the
cross-dimers in good yields (entries 12 and 13). We focused on
BuLi, as a mild reductant with low nucleophilicity, for reduction
of 2a.
6
presence of naphthalene. The Ru(0) complex [Ru(η -
B
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 3. Optimizations for Reaction of 2,3-
a
Dimethylbutadiene with Styrene
amt (mol %)
x/y
cross-dimers
entry
z
yield (%)
3a/3b/isomers
1
2
3
4
5
6
7
8
2/1
2/1
2/1
2/1
1/3
1/2
1/1
3/1
1.2/1
5
80
87
81
0
84/9/7
10
20
40
10
10
10
10
0
83/10/7
80/9/11
81
82
73
99
84
62/31/7
65/26/9
82/8/10
84/9/7
4
6
provided by the treatment of [Ru(η -1,5-COD)(η -1,3,5-
COT)] with dcype and acetylacetone at 70 °C (eq 3).
b
9
79/13/8
Single crystals suitable for X-ray analysis were obtained by
recrystallization from acetone/hexane for 2b and from THF/
hexane for 2c,d, respectively (Figure 1). Although complexes 2
bearing an unsymmetrical bidentate ligand potentially produce
a diastereomeric mixture arising from the Δ and Λ forms of the
two chelating acac ligands, the single crystals of 2b−d were
obtained as single diastereomers of rac-Λ-2b, rac-Δ-2c, and rac-
Δ-2d. Knowing the X-ray structures, we could determine the
diastereomer ratios of the original samples of 2b−d from the
NMR data to be rac-Δ-2b/rac-Λ-2b = 62/38, rac-Δ-2c/rac-Λ-
a
Conditions unless specified otherwise: 2a (0.05 mmol), 2,3-
dimethylbutadiene (1.04−2.99 mmol), styrene (1.04−2.96 mmol), in
BuLi (0.049−0.396 mmol), hexane (1.5 mL), temperature 50 °C, time
6
h. Yields and product ratios were determined by GLC analysis.
Conditions: 1a (0.03 mmol), 2,3-dimethylbutadiene (1.77 mmol),
b
styrene (1.48 mmol), temperature 50 °C, time 5 h.
4
naphthalene)(η -1,5-COD)] (1a) was certainly produced,
although it was obtained in only 8% yield (eq 1) and the
2
c = 85/15, and rac-Δ-(S)-2d/rac-Λ-(S)-2d = 79/21,
respectively.
Under the optimized conditions, cross-dimerization between
,3-dimethylbutadiene and styrene was catalyzed by the in situ
2
reduction of 2/BuLi (Table 4), the process being most efficient
for 2a. The cross-dimerization was also catalyzed by 2b/BuLi
and 2c/BuLi in moderate yields (entries 2 and 3), but the
product yield was much lower in the case of 2d/BuLi (entry 4),
while the system [Ru(acac) (dcype)] (2e) gave no cross-dimer
2
6
4
other products were not well characterized. We know little
about the course of reaction. However, 2a was almost
completely consumed and very broad resonances were
observed in the aliphatic region in the H NMR spectrum. It
appears that a ruthenium(0) species was formed under the
at all. Note that although [Ru(η -naphthalene)(η -1,5-COD)]
24
4
(1a) is readily obtained by treatment of [Ru(acac) (η -1,5-
2
2
4a
COD)] (2a) with 2 equiv of sodium naphthalene,
all
1
6
attempts to prepare the corresponding [Ru(η -naphthalene)L]
complexes from 2b (L = 2-phenylbicyclo[3.3.1]nona-2,6-diene
(L2)), 2c (L = 2,5-dimethyl-7,8-(tetrafluorobenzo)-
bicyclo[2.2.2]octatriene (L3)), and 2d (L = (3,5-dioxa-4-
phosphacyclohepta[2,1-a:3,4-a′]dinaphthalen-4-yl)-
iminostilbenzene (L4)) failed even at low temperature; thus,
their catalytic behavior could not be examined.
reaction conditions, among other unidentified products.
Synthesis of and Cross-Dimerization by [Ru(acac) L]
2) as the Catalyst Precursor. With the optimized conditions
2
(
for reduction of 2a in hand, we explored the scope of the
catalyst [Ru(acac) L] (2) (5 mol %) in the presence of BuLi
2
(
10 mol %). A series of new [Ru(acac) L] complexes (L = 2-
No cross-dimers were obtained when BuLi was added to a
mixture of 2,3-dimethylbutadiene and methyl acrylate in hexane
containing the catalyst precursor 2a (Table 5, entry 1),
probably owing to the undesirable competing reaction of BuLi
with methyl acrylate. However, when 2,3-dimethylbutadiene
and methyl acrylate were added after pretreatment of 2a (5 mol
%) with BuLi (10 mol %) for 1 h at room temperature, the
result was more promising, the cross-dimers being obtained in
35% yield (entry 2). In THF, under the same conditions with
the pretreatment, the cross-dimers were obtained almost
quantitatively (entry 4).
2
phenylbicyclo[3.3.1]nona-2,6-diene (L2), 2,5-dimethyl-7,8-
tetrafluorobenzo)bicyclo[2.2.2]octatriene (L3), (3,5-dioxa-4-
(
phosphacyclohepta[2,1-a:3,4-a′]dinaphthalen-4-yl)-
iminostilbene (L4)) was prepared from [Ru(acac) ] according
3
21
to our previous method (eq 2). Oligomeric complexes
1
[
Ru(acac) (μ ,κ P-L) ] are formed initially in the case of L =
2 2 2 n
dppe, dppp under these conditions, and heating to 140 °C is
required to convert them into monomeric cis-[Ru-
2
1b,23
(
acac) L].
However, [Ru(acac) ] in the presence of Zn
3
2
reacted with dcype in refluxing THF to give cis-[Ru-
acac) (dcype)] (2e) directly, although in only moderate
(
The results obtained with a range of catalyst precursors
under optimized conditions are shown in Table 6. In this
2
yield (16%). More efficient access to 2e (80% yield) was
C
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Cross-Dimerization of 2,3-Dimethylbutadiene with
a
Styrene Catalyzed by [Ru(acac) L]/BuLi
2
cross-dimers
entry
catalyst precursor
time (h)
yield (%)
3a/3b/isomers
1
2
3
4
5
2a
2b
2c
2d
2e
6
2
99
77
66
22
0
84/9/7
73/13/14
74/14/12
73/9/18
2
15
6
a
Conditions: 2a−e (0.0398−0.0500 mmol), BuLi (0.10 mmol), 2,3-
dimethylbutadiene (1.49−2.11 mmol), styrene (1.00−1.04 mmol),
THF (1.5 mL).
Table 5. Cross-Dimerization of 2,3-Dimethylbutadiene with
Methyl Acrylate Catalyzed by [Ru(acac) (1,5-COD)] (2a)/
2
a
BuLi
cross-dimers
pretreatment
(h)
time
(h)
yield
(%)
E-4a/Z-4a/4b/
entry
1
solvent
isomers
hexane
hexane
THF
0
1
0
1
1
1
6
6
0
35
65
97
41
57
b
2
74/20/6/0
67/9/22/2
69/8/21/2
68/17/12/3
75/14/9/2
3
6
b
4
THF
4
b
5
b
toluene
benzene
10
10
6
a
Conditions: 2a (0.0498−0.0506 mmol), BuLi (0.093−0.10 mmol),
,3-dimethylbutadiene (1.05 mmol), methyl acrylate (1.56 mmol),
2
temperature 50 °C. Yields and product ratios were determined by
b
GLC analysis. The substrates were added after pretreatment of 2a
with BuLi for 1 h at room temperature.
Figure 1. Molecular structures determined by single-crystal X-ray
diffraction for Λ-2b (A), Δ-2c (B), and Δ-2d (C). All hydrogen atoms
and incorporated molecules are omitted for clarity. Ellipsoids represent
6
4
a series of [Ru(η -arene)(η -1,5-COD)] complexes, analogous
to the naphthalene compound, which, if the arene is sufficiently
labile, are potential precursors to a coordinatively unsaturated
50% probability.
4
24
6
“
Ru(η -1,5-COD)” species. If the [RuCl (η -arene)] com-
2 2
reaction, the major product was (E)-4a along with (Z)-4a and
b as the prime minor products. The GC/GC-MS analyses also
suggested formation of isomers having the same molecular
weight as 4, but their detailed structures are unknown. When a
slight excess of methyl acrylate was used, the reaction occurred
in excellent yield (entry 1), but an increase in the amount of
plex is readily available starting from RuCl , it can be converted
into [Ru(η -arene)(η -1,5-COD)] by treatment with 1,5-COD
3
6
4
4
in 2-propanol or ethanol in the presence of anhydrous Na CO .
2
3
p-
2
5,26
This procedure has been used for the C Me ,
6
6
2
7,28
28
cymene,
and benzene complexes. More versatile
procedures employ labile ruthenium(0) systems as starting
4
6
2
,3-dimethylbutadiene decreased the product yield (entry 2).
materials: e.g. [Ru(η -1,5-COD)(η -1,3,5-COT)] with an arene
29
6
4
As in the 2,3-dimethylbutadiene/styrene cross-dimerization,
in the presence of hydrogen or [Ru(η -naphthalene)(η -1,5-
24
complex 2a showed the highest activity of these precursors.
COD)] (1a) with an arene in the presence of acetonitrile. We
used the second method to make the complexes of benzene
(1b), anisole (1c), dimethylaniline (1d), acetophenone (1e)
6
Synthesis of and Cross-Dimerization by [Ru(η -arene)-
η -1,5-COD)] (1). We examined initially the catalytic ability of
4
(
D
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 6. Cross-Dimerization of 2,3-Dimethylbutadiene with
Methyl Acrylate Catalyzed by [Ru(acac) (L)] (2)/BuLi in
2
a
THF
cross-dimers
entry catalyst precursor time (h)
yield (%)
E-4a/Z-4a/4b/isomers
b
1
2
3
4
5
2a
2a
2b
2c
2d
4
4
6
3
4
97
63
10
46
49
69/8/21/2
81/3/14/2
90/0/10/0
78/4/18/0
74/18/8/0
a
Conditions: 2 (0.0487−0.0506 mmol), BuLi (0.10 mmol), pretreat-
ment 1 h at room temperature, 2,3-dimethylbutadiene (2.02−2.11
mmol), methyl acrylate (1.00 mmol), temperature 50 °C.Yields and
b
product ratios were determined by GLC. 2,3-Dimethylbutadiene
(
1.05 mmol) and methyl acrylate (1.56 mmol) were used for the
catalysis.
and 1,2-, 1,3-, and 1,4-dimethoxybenzene (1f−h, respectively);
complexes 1b,c had already been made by the first method
2
9
1
13
(
Chart 1). They were characterized by H and C NMR
spectroscopy and elemental analysis and by X-ray analyses for
d,g,h.
1
Chart 1
Figure 2. Molecular structures by single-crystal X-ray diffration for 1d
(A), 1g (B), and 1h (C). All hydrogen atoms are omitted for clarity.
Ellipsoids represent 50% probability.
6
In addition to the naphthalene complex, several of the [Ru(η -
4
arene)(η -1,5-COD)] compounds containing electron-donating
substituents catalyzed the formation of cross-dimers in
moderate to high yield (entries 1−5). The acetophenone
complex 1e was completely inactive (entry 6), probably
because the electron-withdrawing COMe substituent stabilizes
The molecular structures of 1d,g,h determined by X-ray
analysis are depicted in Figure 2, and the Ru−C(arene)
distances are given in Table 7. In the reported structure of 1b,
the Ru−C(arene) distances fall in the range 2.199(7)−2.261(7)
6
η coordination, thus disfavoring arene dissociation. It is worth
3
0
Å. Similar Ru−C(arene) distances to the unsaturated carbon
atoms are observed in 1d,g,h, but some of the Ru−C(ipso)
distances in 1g,h are slightly above this range (Ru−C(3) in 1g
noting that the 1,3-dimethoxybenzene complex 1g produced
cross-dimers in 74% yield after 14 h at 50 °C (entry 9), whereas
the 1,2- and 1,4-analogues (1f,h) were much less active under
similar conditions; the reasons for this difference remain
unclear. As noted above, the N,N-dimethylaniline complex 1d
contains one remarkably long Ru−C(arene) bond, indicating
that the arene in this case might be fairly weakly bound, but 1d
is nevertheless not the most active catalyst. Finally, we note that
the isomeric ratio 4a/4b of the cross-dimers catalyzed by the
anisole complex 1c at 100 °C for 4 h is strongly in favor of 4b
2
.304(6) Å; Ru−C(4) in 1h 2.310(4) Å), while in 1d the Ru−
C(1) distance of 2.385(3) Å to the ipso carbon atom bearing
the strongly electron-donating substituent NMe is well above
2
the range.
6
4
The catalytic activities of [Ru(η -arene)(η -1,5-COD)] (1)
for cross-dimerization between 2,3-dimethylbutadiene with
methyl acrylate were tested; the results are shown in Table 8.
E
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Table 7. Distortions of the Aromatic Fragment in 1d,f.g and
Selected Bond Distances between Ruthenium and the
Aromatic Carbons (Å)
was based on elemental analysis and H NMR data, though it
was noted that the product contained about 10% of the
6
benzene complex [RuCl (η -benzene)] (5b), arising from
2
2
competing demethoxylation of anisole. Soleimannejad and
32
White also re-examined and reported on this chemistry. We
attempted to prepare 5c from methanolic RuCl3 and 1-
methoxycyclohexa-1,4-diene (Scheme 2: method A). The
Scheme 2
1
d
1g
1h
Ru−C(1)
Ru−C(2)
Ru−C(3)
Ru−C(4)
Ru−C(5)
Ru−C(6)
2.385(3)
2.210(3)
2.264(3)
2.284(4)
2.204(3)
2.275(3)
2.279(4)
2.200(4)
2.304(6)
2.279(5)
2.189(4)
2.274(4)
2.297(4)
2.185(4)
2.258(4)
2.310(4)
2.205(4)
2.259(4)
Table 8. Cross-Dimerization of 2,3-Dimethylbutadiene with
6
4
Methyl Acrylate Catalyzed by [Ru(η -arene)(η -1,5-COD)]
a
(
1)
initially formed, poorly soluble green-brown solid was
Soxhlet-extracted with hot chloroform to give a brown solution,
from which a green-brown solid was obtained after evaporation
1
of the solvent. The H NMR spectrum in DMSO-d indicated it
cross-dimers
entry catalyst temp (°C) time (h) yield (%) E-4a/Z-4a/4b/isomers
6
to be a mixture of the anisole complex 5c (89%) and the
benzene complex 5b (11%), but the estimated yield remained
1
2
3
4
5
6
7
8
9
1a
1b
1c
1c
1d
1e
1f
30
100
100
80
2
10
4
98
63/4/30/3
20/6/57/17
3/6/81/9
generally in the range of only 10−17%. Note that Iwata and
54
33
Ogata
reported that these compounds also contain
85
6
[
RuCl (η -arene)] [RuCl ] (m/n = 0.1−0.2 for arene =
2
n
2 m
4
25
49/7/25/20
46/12/35/18
benzene; m/n = 0.4−0.5 for arene = mesitylene; m/n = 1−2
70
8
26
for arene = 1,3,5-triphenylbenzene), rather than the previously
50
4
trace
8
6
assumed [RuCl (η -arene)] . Our elemental analyses are fairly
2
2
50
14
14
13
58/9/33/0
6
consistent with the empirical formula [RuCl (η -anisole)]-
RuCl2]0.22, and the chemical reactions of this product with
PMe3 are also consistent with this composition (see the
Supporting Information).
Following the procedure of Vitulli et al., we prepared an
analytically pure sample of 5c as an orange powder in 83% yield
based on Ru by treatment of [Ru(η -anisole)(η -1,5-COD)]
2
1g
1h
50
74
47/22/30/1
[
50
trace
a
Conditions: 1 (0.029−0.030 mmol), 2,3-dimethylbutadiene (0.89
29
mmol), methyl acrylate (0.70 mmol). Yields and product ratios were
determined by GLC.
6
4
(
5
entry 3), in marked contrast with the results reported in Table
. This apparent reversal in regioselectivity is probably caused
with hydrochloric acid (method B). Except for the absence of
peaks due to 5b, the H NMR spectrum of this solid in DMSO-
1
by thermal, Ru-catalyzed isomerization of initially formed 4a as
the kinetic product of the coupling. In agreement, the isomeric
ratio of the cross-dimerization product after 4 h at 80 °C using
d6 was identical with that of the green-brown solid made by
method A.
6
Similar attempts to prepare [RuCl (η -1,3-dimethoxyben-
2
1c as catalyst favors 4a over 4b. The occurrence of the
zene)] (5f) by heating 1,3-dimethoxy-1,4-cyclohexadiene with
2
isomerization of cross-dimer 3a to 3b has been demonstrate-
methanolic RuCl at 50 °C for 2 days failed, the only product
3
2
0a
d.
isolated being 3-methoxy-2-cyclohexenone.
6
6
Synthesis of [RuCl (η -anisole)] (5c). These promising
Catalytic Cross-Dimerization by [RuCl (η -anisole)]
2
2
2
2
4
results with cross-dimerization using the Ru(η -1,5-COD)
(5c) as the Catalyst Precursor. Using 5c with a reductant
and 1,5-COD, a catalytic cross-dimerization between 2,3-
dimethylbutadiene with styrene was performed (Table 9).
In a typical experiment, a suspension of 5c (5 mol %), 1,5-
COD (20 mol %), and Na CO (20 mol %) was heated in a
complexes of anisole (1c) and 1,3-dimethoxybenzene (1g) as
II
catalysts prompted us to examine the Ru Cl complexes of
2
these aromatics, 5c,g, respectively, as possible precursors. A
6
product formulated as [RuCl (η -anisole)] (5c) was first
2
2
2
3
i
reported briefly by Bennett and Smith in 1974 as a brown solid,
obtained from the reaction of hydrated RuCl3 with 1-
methoxycyclohexa-1,4-diene, the Birch reduction product of
Schlenk tube in PrOH at 100 °C for 1 h, and after the reaction
mixture was cooled to room temperature, 2,3-dimethylbuta-
diene and styrene were added. After 6 h at 100 °C, the cross-
dimers were obtained in 8% yield (Table 9, entry 1). The
31
anisole, in refluxing methanol in 25% yield. The formulation
F
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 9. Catalytic Cross-Dimerization between 2,3-
Dimethylbutadiene with Styrene Catalyzed by [RuCl (η -
catalytically less active than 1a. However, presumably one
needs only a minor amount of a Ru(0) species for the catalysis
to be effective. Controls of the regioselective formation of the
CC bond and enantioselective cross-dimerizations remain
the challenges in the future for the preparative-scale catalysis.
6
2
a
anisole)] (5c) with 1,5-COD in the Presence of Na CO
2
2
3
EXPERIMENTAL SECTION
■
General Procedures. All manipulations and reactions were
performed under dry nitrogen with use of standard Schlenk and
vacuum line techniques. Diethyl ether, THF, benzene, toluene, and
hexane were dried and deoxygenated with a Glass Contour Ultimate
Solvent System. The following starting materials were prepared
amt (mol %)
1,5-COD
cross-dimers
1
3
22
4
according to literature methods: Rieke Mg and Rieke Zn,
entry
1
Na CO
solvent
iPrOH
iPrOH
iPrOH
yield (%) 3a/3b/isomers
34
35
2
3
4
6
[
Ru(acac)3], [Ru(η -1,5-COD)(η -1,3,5-COT)], [Ru(acac) (η -
2
36
6
4
24
20
20
20
40
20
20
20
0
20
20
40
40
40
40
40
40
40
8
47
55
44
1
12/50/38
21/43/36
19/26/10
20/39/41
1
,5-COD)], [Ru(η -naphthalene)(η -1,5-COD)] (1a), and [Ru-
26
b
b
b
,
c
,
c
,
c
6
4
6
2
3
4
5
6
7
8
9
(η -benzene)(η -1,5-COD)] (1b). The known complexes [Ru(η -
29
4
arene)(η -1,5-COD)] (arene = anisole, acetophenone) were made
from 1a and the arene in the presence of acetonitrile by use of the
iPrOH
2
4
6
literature procedure. [RuCl (η -anisole)] (5c) was also prepared by
the literature method. 2-Phenylbicyclo[3.3.1]nona-2,6-diene was
2
DMSO
1-BuOH
2-BuOH
2-BuOH
iPrOH
31
1
19b
prepared according to the modification of the reported procedure.
62
0
24/40/36
18/44/38
Solutions of BuLi (1.003 M) were standardized by titration with 1,10-
phenanthroline/sec-BuOH (1.003 M) prior to use. 2,5-Dimethyl-7,8-
b
,
d
37
20
45
(tetrafluorobenzo)bicyclo[2.2.2]octatriene
and (3,5-dioxa-4-
38
a
phosphacyclohepta[2,1-a:3,4-a′]dinaphthalen-4-yl)iminostilbene
In all reactions, 2,3-dimethylbutadiene and styrene were added after
pretreatment of 5c with 1,5-COD and Na CO at 100 °C (oil bath
were prepared by literature methods. dcype was prepared according to
2
3
39
literature methods. All other reagents were obtained from
temperature) for 1 h: 2,3-dimethylbutadiene (0.88 mmol), styrene
b
c
commercial suppliers and used as received. Chromatographic
(
0.75 mmol). This reaction was carried out in an autoclave. Time 10
d
6
separation was carried out on Al O (Merck, Activity I, 250 mesh).
h. [Ru(OAc) (η -anisole)] (prepared by treatment of 5c with an
2
3
2
1
13
31
1
H, C, and P{ H} NMR spectra were recorded on JEOL ECX-
00P (400 MHz for H) and JEOL Lambda-300 (300 MHz for H)
excess of AgOAc) was used for the catalyst precursor.
1
1
4
instruments. Benzene-d was distilled over sodium wire and stored
6
under vacuum. Chemical shifts (δ) are given in ppm, relative to
reaction in an autoclave improved the product yield (47%
yield), probably by preventing the loss of 2,3-dimethylbuta-
diene. When the relative amount of Na CO was increased to
1
13
internal TMS for H and C. All coupling constants are given in Hz.
Most elemental analyses were carried out on a PerkinElmer 2400
series II CHN analyzer; some C, H, Cl analyses on 5c were done at the
Center for Organic Elemental Microanalysis, Department of
Pharmaceutical Sciences, Kyoto University, and at the Campbell
Microanalytical Laboratory, the University of Otago, Otago, New
Zealand. IR spectra were recorded on a JASCO FT/IR-4100
instrument with use of KBr disks. GLC analysis was performed on a
Shimadzu GC-14B instrument with a FID detector equipped with a
ZB-WAX plus column (0.25 mm i.d. × 30 m). The GC-MS analyses
were performed on a Shimadzu QP2010 instrument.
2
3
40 mol %, there was a small increase in the yield of the cross-
dimers (55% yield). With 2-butanol, the product yield increased
to 62% but the reaction using 1-butanol significantly decreased
the product yield (entries 6 and 7). The high efficiency of
secondary alcohols suggests that the reduction of 5c occurs via
β-hydride elimination from an alkoxoruthenium species. The
cross-dimerization did not occur in the absence of 1,5-COD
(
entry 8).
Preparations of [Ru(acac) (2-phenylbicyclo[3.3.1]nona-2,6-
2
diene)] (2b). Complex 2b was prepared according to our previous
CONCLUDING REMARKS
21c
■
report
using [Ru(acac) ] (1.5427 g, 3.8723 mmol) with 2-
3
We have shown that a catalytically active species for the one-
pot C−C coupling between 2,3-dimethylbutadiene and styrene
or methyl acrylate can be generated in situ by reduction of
phenylbicyclo[3.3.1]nona-2,6-diene (795.6 mg, 4.053 mmol) and Zn
dust (2.5 g, 39 mmol) in THF (39 mL) and water (1 mL).
Crystallization of the resulting oil from cold (−20 °C) hexane (10
mL) gave orange plates of 2b (57% yield, 1.0916 g, 2.2027 mmol, rac-
Δ-(S,S)-2b/rac-Λ-(S,S)-2b = 62/38). From the mother liquor, 2b was
4
6
[
Ru(acac) (η -cyclic diene)] (2) with BuLi or of [RuCl (η -
2
2
arene)] (5)/1,5-COD with Na CO . With these procedures, it
2
3
obtained (24% yield, 488.0 mg, 0.9847 mmol, rac-Δ-(S,S)-2b/rac-Λ-
is not necessary to isolate the air-sensitive Ru(0) species which
is the actual catalyst precursor. This is a clear advantage over
the corresponding Ru(0) naphthalene system 1a, although the
latter is probably catalytically more active. Moreover, the
present methods could generate a catalytically active Ru(0)
1
(
(
3
S,S)-2b = 93/7). Data for rac-Δ-(S,S)-2b are as follows. H NMR
400 MHz, CDCl ): δ 1.58 (br s, 2H, CH ), 1.73 (s, 3H, Me), 1.81 (s,
3
2
H, Me), 1.85 (s, 3H, Me), 2.15 (s, 3H, Me), 2.3−2.6 (m, 5H, CH and
2
3
CH), 2.65 (br s, 1H, bridge head), 4.09 (dd, J
CH), 4.32 (dd, J
= 7.8, 5.2 Hz, 1H,
H−H
3
3
= 7.8, 4.0 Hz, 1H, CH), 5.16 (d, J
=
H−H
H−H
6
species, even if [Ru(η -naphthalene)L] cannot survive during
2.9 Hz, 1H, CH), 5.29 (s, 1H, CH in acac), 5.38 (s, 1H, CH in
13
1
the reduction using sodium naphthalene. Of the two present
procedures starting from Ru(II) complexes, in situ reduction of
acac), 7.04−7.16 (m, 5H, Ph). C{ H} NMR (100.5 MHz, CDCl
3
): δ
2
8
1
7.03, 27.29, 28.30, 28.39, 29.51, 34.37, 35.62, 38.59, 38.94, 78.17,
6.32, 92.49, 93.15, 98.37, 98.82, 125.57, 126.21 (2C), 126.25 (2C),
43.54, 184.37, 186.15 (2C), 186.25. IR (KBr, cm ): 3086 (w), 3016
[
Ru(acac) L] with 2 equiv of BuLi is probably the more facile,
2
−1
reliable, and practical protocol for generating an active Ru(0)
species that is capable of catalyzing the cross-dimerization of
conjugated dienes and substituted alkenes. With this amount,
BuLi probably cannot reduce the Ru(II) species completely.
However, further addition of BuLi causes undesirable polymer-
ization of substrates. This is probably why the present system is
(
1
6
w), 2966 (w), 2910 (m), 2836 (m), 1576 (vs), 1519 (vs), 1401 (vs),
271 (m), 1196 (m), 1184 (m), 1017 (s), 933 (m), 764 (s), 691 (m),
11 (m), 436 (m). Anal. Calcd for C H O Ru: C, 60.59; H, 6.10.
25
30
4
1
Found: 60.57; H, 5.98. Data for rac-Λ-(S,S)-2b are as follows. H
NMR (400 MHz, CDCl ): δ 1.63 (s, 3H, Me), 1.65 (br s, overlapped,
3
2H, CH ), 1.81 (s, 3H, Me), 1.82 (s, 3H, Me), 2.13 (s, 3H, Me), 2.3−
2
G
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4
2
.5 (m, 3H, CH and CH), 2.65 (br s, 1H, bridge head), 3.18 (dt,
h in 16% yield. A higher yield of 2e was obtained as follows: [Ru(η -
2
3
3
6
JH−H = 14.3, 4.0 Hz, 1H, CH ), 3.23 (dt, J
CH ), 3.65 (dd, J
8
= 14.3, 4.0 Hz, 1H,
1,5-COD)(η -1,3,5-COT)] (546 mg, 1.73 mmol) and 1,2-bis-
2
H−H
3
3
= 8.3, 5.2 Hz, 1H, CH ), 4.30 (dd, J
=
H−H
(dicyclohexylphosphino)ethane (756 mg, 1.80 mmol) in benzene (7
mL) were treated with acetylacetone (541 μL, 5.2 mmol) at room
temperature. After 48 h, the initially orange solution had turned red.
After evaporation of all volatile material under reduced pressure, an
orange oil remained, which on recrystallization from cold hexane gave
2
H−H
2
.3, 4.3 Hz, 1H, CH ), 4.47 (s, 1H, CH in acac), 5.15 (s, 1H, CH in
2
3
acac), 5.39 (d, J
= 4.0 Hz, 1H, CH), 6.97−7.02 (m, 3H, Ph),
H−H
13
1
7
.04−7.16 (m, 2H, Ph). C{ H} NMR (100.5 MHz, CDCl ): δ 26.89
3
(
s), 26.97 (s), 28.40 (s), 28.88 (s), 29.72 (s), 35.06 (s), 25.81 (s),
7.10 (s), 37.40 (s), 81.90 (s), 85.53 (s), 89.29 (s), 91.66 (s), 97.61
s), 98.19 (s), 125.31 (s, 2C), 125.53 (s), 126.74 (s, 2C), 143.08 (s),
85.07 (s), 185.32 (s), 185.81 (s), 186.79 (s).
Ru(acac) (2,5-dimethyl-7,8-(tetrafluorobenzo)bicyclo-
3
(
1
analytically pure orange crystals of 2e (80% yield, 1.00 g, 1.39 mmol).
1
H NMR (300 MHz, C
D
6
): δ 1.14−2.68 (m, 48H, PCy and PC H P),
6
2 4
1.82 (s, 6H, Me in acac), 2.01 (s, 6H, Me in acac), 5.41 (s, 2H, CH in
acac). 31P{ H} NMR (121 MHz, C D ): δ 88.2 (s). Anal. Calcd for
1
[
2
6
6
[2.2.2]octatriene)] (2c). 2c was prepared from [Ru(acac) ] (410.4
C H O P Ru: C, 59.90; H, 8.66. Found: C, 60.21; H, 8.69.
36 62 4 2
3
mg, 1.030 mmol) with 2,5-dimethyl-7,8-(tetrafluorobenzo)-
bicyclo[2.2.2]octatriene (275.8 mg, 1.085 mmol) and Zn dust (0.7
g, 11 mmol) (79% yield, 448.0 mg, 0.8094 mmol, rac-Δ-(S,S)-2c/rac-
Catalytic Cross-Dimerization of 2,3-Dimethylbutadiene with
4
Styrene in the Presence of [Ru(acac) (η -1,5-COD)] (2a) with/
2
4
without Reductant. [Ru(acac)
(η -1,5-COD)] (2a) (20.63 mg,
2
1
Λ-(S,S)-2c = 85/15). Data for rac-Δ-(S,S)-2c are as follows. H NMR
0.0506 mmol) and dibenzyl as an internal standard (36.6 mg, 0.201
mmol) were placed in a 25 mL Schlenk tube, into which hexane (1.5
mL), styrene (120 μL, 1.04 mmol), 2,3-dimethylbutadiene (120 μL,
1.05 mmol), and BuLi (40 μL, 2.33 M, 0.093 mmol) were placed from
a hypodermic syringe. The reaction mixture was warmed to 50 °C for
(
400 MHz, CDCl ): δ 1.48 (s, 6H, Me), 1.86 (s, 6H, Me in acac), 2.25
3
3
(
s, 6H, Me in acac), 3.69 (d, J
= 6.3 Hz, 2H, CH), 4.79 (d,
H−H
3
J
= 6.3 Hz, 2H, CH in bridge head), 5.35 (s, 2H, CH in acac).
H−H
1
3
1
C{ H} NMR (100.5 MHz, CDCl ): δ 17.47 (Me), 27.14 (Me in
3
6
3
h, and the product yields were estimated by GLC (73% total yield,
a/3b/isomers = 82/8/10). The other evaluations of reductants are
acac), 28.36 (Me in acac), 47.51 (bridge head), 69.24 (CH), 84.13
(
1
C<), 99.30 (acac), 127.1−127.4 (m, aromatic), 186.57 (CO),
−1
summarized in the Supporting Information.
Effect of Amount of BuLi to [Ru(acac) (η -1,5-COD)] (2a) on
87.10 (CO). IR (KBr, cm ): 2975 (w), 2896 (m), 1594 (vs), 1580
4
(
1
7
vs), 1519 (vs), 1489 (vs), 1368 (m), 1297 (s), 1269 (s), 1200 (m),
2
Cross-Dimerization of 2,3-Dimethylbutadiene with Styrene.
Similar to the standard reaction of 2,3-dimethylbutadiene with styrene
catalyzed by 2a/BuLi described above, the following experiments were
performed. 2a (20.49 mg, 0.0502 mmol), hexane (1.5 mL), styrene
(120 μL, 1.04 mmol), 2,3-dimethylbutadiene (240 μL, 2.11 mmol),
BuLi (21 μL, 2.3 M, 0.049 mmol): 80% total yield, 3a/3b/isomers =
84/9/7. The other screening data for the amount of BuLi are
175 (m), 1135 (m), 1106 (m), 1085 (m), 1024 (s), 998 (m), 930 (s),
72 (s), 699 (w), 617 (m), 437 (m). Anal. Calcd for C H F O Ru:
24
24
4
4
C, 52.08; H, 4.37. Found: C, 51.81; H, 4.54. Data for rac-Λ-(S,S)-2c
1
are as follows. H NMR (400 MHz, CDCl ): δ 1.21 (s, 6H, Me), 1.88
3
3
(
2
s, 6H, Me in acac), 2.28 (s, 6H, Me in acac), 4.13 (d, J
= 5.2 Hz,
H−H
3
H, CH), 4.97 (d, J
= 5.2 Hz, CH in bridge head), 5.34 (s, 2H,
H−H
13
1
CH in acac). C{ H} NMR (100.5 MHz, CDCl ): δ 18.35 (s, Me),
3
summarized in the Supporting Information.
Effect of Diene/Styrene Ratio on [Ru(acac) (η -1,5-COD)]
2a)-Catalyzed Cross-Dimerization of 2,3-Dimethylbutadiene
7.18 (s, Me in acac), 28.30 (s, Me in acac), 47.39 (s, bridge head),
1.59 (s, CH), 85.18 (s, CH), 98.74 (s, CH in acac), 127.1−127.4
4
2
(
with Styrene. Similar to the standard reaction of 2,3-dimethylbuta-
diene with styrene catalyzed by 2a/BuLi described above, the
following experiments were performed. 2a (20.44 mg, 0.0501
mmol), hexane (1.5 mL), styrene (340 μL, 2.96 mmol), 2,3-
dimethylbutadiene (120 μL, 1.05 mmol), BuLi (43 μL, 2.3 M, 0.10
mmol): 81% total yield, 3a/3b/isomers = 62/31/7. The other
screening data for the diene/styrene ratio are summarized in the
Supporting Information.
[
Ru(acac) (3,5-dioxa-4-phosphacyclohepta[2,1-a:3,4-a’]-
2
dinaphthalen-4-yl)iminostilbene] (2d). 2d was prepared from
Ru(acac) ] (651.5 mg, 1.635 mmol) with (3,5-dioxa-4-
[
3
phosphacyclohepta[2,1-a:3,4-a’]dinaphthalene-4-yl)iminostilbene
(
870.3 mg, 1.715 mmol) and Zn dust (1.0 g, 15 mmol) as an
analytically pure pale yellow powder (88% yield, 1.3208 g, 1.5028
mmol, rac-Δ-(S)-2d/rac-Λ-(S)-2d = 79/21). Data for rac-Δ-(S)-2d
1
are as follows. H NMR (400 MHz, CDCl ): δ 0.60 (s, 3H, Me), 1.59
3
Effect of [Ru(acac) L] (2) on Cross-Dimerization of 2,3-
2
(
s, 3H, Me), 2.04 (s, 3H, Me), 2.08 (s, 3H, Me), 4.67 (s, 1H, CH in
Dimethylbutadiene with Styrene in the Presence of BuLi.
Similar to the standard reaction of 2,3-dimethylbutadiene with styrene
catalyzed by 2a/BuLi described above, the following experiments were
3
3
acac), 4.90 (d, J
1
= 10.0 Hz, 1H, CH), 5.33 (d, J
= 10.0 Hz,
= 8.6 Hz, 1H,
H−H
H−H
3
H, CH), 5.46 (s, 1H, CH in acac), 7.01 (d, J
H−H
aromatic), 7.1−7.2 (m, 5H, aromatic), 7.2−7.25 (m, 2H, aromatic),
7
aromatic), 7.58 (d, J
performed. [Ru(acac) (2-phenylbicyclo[3.3.1]nona-2,6-diene)] (2b)
2
.3−7.35 (m, 3H, aromatic), 7.4 (m, 2H, aromatic), 7.43 (m, 1H,
(
24.72 mg, 0.0498 mmol), THF (1.5 mL), styrene (115 μL, 1.00
mmol), 2,3-dimethylbutadiene (240 μL, 2.11 mmol), BuLi (43 μL, 2.3
M, 0.10 mmol): 77% total yield, 3a/3b/isomers = 73/13/14. The
3
3
= 9.2 Hz, 1H, aromatic), 7.62 (d, J
= 7.5
H−H
H−H
3
Hz, 1H, aromatic), 7.79 (d, J
= 8.6 Hz, 2H, aromatic), 7.92 (d,
H−H
3
3
J
= 8.6 Hz, 1H, aromatic), 7.93 (d, J
= 8.0 Hz, 1H, aromatic).
H−H
H−H
other screening of [Ru(acac) L] are summarized in the Supporting
1
3
1
2
C{ H} NMR (100 MHz, CDCl ): δ 25.30 (s), 27.68 (s), 28.53 (s),
3
Information.
2
(
(
(
(
(
(
d, J
= 8.6 Hz), 28.77 (s), 80.38 (s), 83.88 (s), 98.53 (s), 98.97
C−P
Cross-Dimerization of 2,3-Dimethylbutadiene with Methyl
4
s), 121.83 (s), 122.16 (s), 122.83 (s), 124.55 (s), 124.86 (s), 125.52
s), 125.93 (s), 126.51 (s), 126.70 (s), 126.93 (s), 127.06 (s), 127.43
s), 127.50 (s), 127.93 (s), 128.15 (s), 129.19 (s), 129.28 (s), 129.43
Acrylate. [Ru(acac) (η -1,5-COD)] (2a) (20.66 mg, 0.0506 mmol)
2
and dibenzyl as an internal standard (35.71 mg, 0.196 mmol) were
placed in a 25 mL Schlenk tube, into which hexane (1.5 mL), 2,3-
dimethylbutadiene (120 μL, 1.05 mmol), methyl acrylate (140 μL,
1.56 mmol), and BuLi (40 μL, 2.3 M, 0.093 mmol) were placed by a
hypodermic syringe. The reaction mixture was warmed to 50 °C for 6
h, and the product yields were estimated by GLC. The total yield of
cross-dimers was 0%. A similar reaction was carried out in THF with
2a (20.33 mg, 0.0498 mmol), THF (1.5 mL), BuLi (40 μL, 0.093
mmol), 2,3-dimethylbutadiene (120 μL, 1.05 mmol), and methyl
acrylate (140 μL, 1.56 mmol), and the product yields were measured
by GLC: 65% total yield, E-4a/Z-4a/4b/isomers = 67/9/22/2. The
other screenings of the catalysis are summarized in the Supporting
Information.
s), 129.78 (s), 130.31 (s), 131.06 (s), 131.28 (s), 131.63 (s), 132.07
2
s), 132.75 (s), 141.63 (s), 131.86 (s), 141.91 (s), 142.91 (d, J
=
C−P
2
6
1
.7 Hz), 142.73 (d, J
= 5.8 Hz), 147.77 (s), 149.07 (s), 185.75 (s),
C−P
31
1
85.87 (s), 187.41 (s), 187.46 (s). P{ H} NMR (162 MHz, CDCl ):
3
1
δ 192.10 (s). Data for rac-Λ-(S)-2d are as follows. H NMR (400
MHz, CDCl ): δ 1.14 (s, 3H, Me), 1.82 (s, 3H, Me), 1.95 (s, 3H, Me),
2
CH in acac), 5.31 (s, 1H, CH in acac), 5.52 (d, J
CH), 6.8−7.7 (m, overlapped, 20H, aromatic). P{ H} NMR (162
MHz, CDCl ): δ 192.24 (s). 2d: Anal. Calcd for C H NO PRu: C,
3
3
.05 (s, 3H, Me), 5.12 (d, J
= 9.7 Hz, 1H, CH), 5.28 (s, 1H,
H−H
3
= 9.7 Hz, 1H, 
H−H
3
1
1
3
48 44
7
6
5.59; H, 5.05; N, 1.59. Found: C, 65.10; H, 4.78; N, 1.54.
[
Ru(acac) (1,2-bis(dicyclohexylphosphino)ethane)] (2e).
2
Effect of [Ru(acac) L] (2) on Cross-Dimerization of 2,3-
2
Complex 2e was prepared from [Ru(acac) ] (199.6 mg, 0.5010
Dimethylbutadiene with Methyl Acrylate in the Presence of
BuLi. Similar to the standard reaction of 2,3-dimethylbutadiene with
methyl acrylate catalyzed by 2a with pretreatment of the catalyst
3
mmol) with 1,2-bis(dicyclohexylphosphino)ethane (222.1 mg, 0.5255
mmol) and Zn (327.1 mg, 5.003 mmol) in refluxing THF/H O for 11
2
H
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
precursor with BuLi, the following experiments were performed.
days. 1h was obtained as yellow plates (67% yield, 136.5 mg, 0.392
1
[
Ru(acac) (1,5-COD)] (2a) (20.63 mg, 0.0506 mmol), THF (1.5
mmol). H NMR (400 MHz, C D ): δ 2.37−2.42 (m, 8H, CH in
2
6
6
2
mL), BuLi (43 μL, 0.10 mmol), 2,3-dimethylbutadiene (230 μL, 2.02
mmol), methyl acrylate (90 μL, 1.00 mmol): 63% total yield, E-4a/Z-
COD), 3.25 (s, 6H, OMe), 3.35 (m, 4H, CH in COD), 4.62 (s, 4H,
aromatic). 13C{ H} NMR (100 MHz, C D ): δ 34.86 (s, CH in
1
6
6
2
4
a/4b/isomers = 81/3/14/2. The other screening data of the catalyst
COD), 55.50 (s, OMe), 63.55 (s, CH in COD), 70.08 (s, arene),
136.62 (s, arene). Satisfactory elemental analysis data were not
obtained, and this compound was characterized by spectroscopic
methods.
are summarized in the Supporting Information.
4
Reaction of [Ru(acac) (η -1,5-COD)] (2a) with 2 equiv of
2
4
BuLi. [Ru(acac) (η -1,5-COD)] (2a) (20.3 mg, 0.0500 mmol) was
2
6
dissolved in hexane (1.5 mL), and BuLi (2.49 M, 40.0 μL, 0.996
mmol) was added to the solution under reduced pressure by a
hypodermic syringe. Then, methane (99.8 μL, 1019 hPa, 10 °C) was
added to the system as an internal standard. An orange suspension
formed immediately. The system was stirred at 0 °C for 5 min, and the
GC analysis (Unicarbon column, 1 m × 3 mmϕ) suggests generation
of butane (17.6%), 1-hexene (5.0%), and (E)-2-butene (1.8%). (Z)-2-
Butene was not observed. Then, cyclooctane (2.0 μL, 0.015 mmol)
was added to the system as an internal standard. The GLC analysis
Synthesis of [RuCl (η -anisole)] (5c). Method A. According to
2
2
3
1
the literature method, RuCl ·3H O (2.054 g, 7.8955 mmol) was
3
2
dissolved in methanol (80 mL) and 1-methoxy-1,4-cyclohexadiene
(5.4 mL, 39.59 mmol) was added. The reaction mixture was refluxed
for 24 h to give a brown precipitate. The product was obtained by
extraction with a Soxhlet extraction apparatus with hot chloroform of
the initially formed, poorly soluble green-brown solid and isolated as a
green-brown solid by evaporation of the chloroform in 17% crude
1
yield (378 mg, 0.65 mmol). The H NMR spectrum of the obtained
(
(
OV-1 column, 30 m × 0.25 mm i.d.) indicated formation of octane
6.9%).
green-brown solid in DMSO-d indicated it to be a mixture of 5c
6
1
(89%) and 5b (11%). Data for 5c are as follows. H NMR (400 MHz,
4
3
Reaction of [Ru(acac) (η -1,5-COD)] (2a) with 2 equiv of BuLi
22.2 °C, DMSO-d ): δ 3.90 (s, 6H, OMe), 5.36 (t, J
= 4.3 Hz, 2H,
= 4.9 Hz,
H−H
2
6
H−H
4
3
3
in the Presence of Naphthalene. [Ru(acac) (η -1,5-COD)] (2a)
2
arene), 5.53 (d, J
= 5.2 Hz, 4H, arene), 6.15 (t, J
H−H
(
20.44 mg, 0.0501 mmol) and naphthalene (12.90 mg, 0.1008 mmol)
4
H, arene). Typical analytical data of two different batches of this
compound made in Kyoto and Canberra are as follows Found: C,
6.99, 27.03; H, 2.50, 2.68; N, 0, <0.3; Cl, 28.18, 27.86. A sample of
were dissolved in THF (1.5 mL), and BuLi (43 μL, 0.10 mmol) was
added to the solution. After removal of volatile materials, triphenyl-
methane (5.54 mg, 0.022 mmol) was added as an internal standard.
2
the solid that had not been extracted with chloroform but only dried in
vacuo was analyzed as follows. Found: C, 25.59; H, 2.53; Cl, 28.28.
Calcd for C H Cl ORu: C, 30.02; H, 2.88; N, 0; Cl, 25.31. Calcd for
1
a: 0.004 mmol, 8% yield.
6
4
6
[
Ru(η -N,N-dimethylaniline)(η -1,5-COD)] (1d). [Ru(η -
4
7
8
2
naphthalene)(η -1,5-COD)] (1a) (203.8 mg, 0.604 mmol) was
treated with MeCN (1 mL, 20 mmol) and N,N-dimethylaniline (1
mL, 8 mmol) in THF (10 mL) at room temperature for 17 h. After
concentration of the solution, the product was purified by alumina
chromatography using hexane and all volatile matter was removed
under reduced pressure. Recrystallization of the resulting solid from
cold hexane produced yellow plates of 1d (54% yield, 107.8 mg, 0.326
C H Cl ORu·0.22RuCl : C, 26.44; H, 2.54; Cl, 27.21.
7
8
2
2
2
4
6
Method B. According to the literature method, [Ru(η -anisole)-
4
6
(
η -1,5-COD)] (1c) was prepared by the reaction of [Ru(η -
4
naphthalene)(η -1,5-COD)] (1a) (264.2 mg, 0.7839 mmol) with
excess anisole (4.6041 g, 42.63 mmol) in the presence of MeCN (60
μL, 0.952 mmol) at room temperature for 2 days (96% yield, 239.5
mg, 0.756 mmol). Following the procedure of ref 29, this was
dissolved in acetone (5 mL) and HCl (36 M, 0.20 mL, 7.2 mmol) was
added to the solution at room temperature. An orange-brown
precipitate deposited immediately. The dark red supernatant was
removed by cannula, and the resulting orange powder was washed
twice with acetone (2 mL) and dried under vacuum (83% yield based
1
mmol). H NMR (400 MHz, C D ): δ 2.29 (s, 6H, NMe), 2.35−2.48
6
6
3
(
m, 8H, CH in COD), 3.43 (d, J
= 9.2 Hz, 4H, CH in COD),
2
H−H
3
4
2
.46 (d, J
= 5.7 Hz, 2H, 2-CH in aromatic ring), 4.71−4.77 (m,
H−H
3
H, 3-CH in aromatic ring), 5.06 (t, J
= 5.7 Hz, 1H, 4-CH in
H−H
13
1
aromatic ring). C{ H} NMR (100 MHz, C D ): δ 34.69 (s, CH in
6
6
2
1
COD), 29.88 (s, Me), 58.78 (s, = CH in COD), 69.60 (s, arene), 82.22
s, arene), 90.14 (s, arene), 130.16 (s, arene). Satisfactory elemental
on Ru, 175.1 mg, 0.3127 mmol). H NMR (400 MHz, 22.3 °C,
3
(
DMSO-d ): δ 3.29 (s, OMe), 5.38 (t, J
JH−H = 5.7 Hz, 2H, Ph), 6.17 (t, J
= 5.4 Hz, 1H, Ph), 5.54 (d,
= 5.7 Hz, 2H, Ph). Anal. Calcd
6
H−H
3
3
analysis data were not obtained, and this compound was characterized
by spectroscopic methods.
H−H
for C H Cl ORu: C, 30.02; H, 2.88; N, 0. Found: C, 30.38; H, 2.61;
7
8
2
6
4
[
Ru(η -1,2-dimethoxybenzene)(η -1,5-COD)] (1f). Similar to
N, 0.22.
the case for 1d, 1f was prepared by the reaction of 1a (203.2 mg, 0.602
mmol), MeCN (1 mL, 20 mmol), and 1,2-dimethoxybenzene (600 μL,
6
4
Synthesis of [Ru(η -anisole)(η -1,5-COD)] (1c) by Use of 5c. A
crude mixture of 5c and 5b (91 mg, 0.15 mmol, 5c/5b = 89/11) and
Na CO (160 mg, 1.52 mmol) was dissolved in 2-propanol (10 mL),
4.69 mmol) in THF (16 mL) at room temperature for 4 days. 1f was
2
3
1
obtained as yellow plates (25% yield, 53.1 mg, 0.153 mmol). H NMR
and 1,5-COD (1 mL, 8 mmol) was added to the solution. After the
solution was heated to 100 °C for 30 min, it was concentrated and
purified by alumina column chromatography with THF. The yellow
(
400 MHz, C D ): δ 2.37−2.39 (m, 8H, CH in COD), 3.35 (s, 6H,
6
6
2
OMe), 3.43 (m, 4H, CH in COD), 4.46 (s, 2H, aromatic), 4.95 (s,
H, aromatic). 13C{ H} NMR (100 MHz, C D ): δ 34.57 (s, CH in
1
2
6
6
2
fraction was evaporated under reduced pressure to give a brown oil
COD), 57.40 (s, OMe), 61.43 (s, CH in COD), 72.88 (s, arene),
1
(
72 mg). The H NMR analysis suggested formation of 1c (60% yield)
8
5
3.35 (s, arene), 126.0 (s, arene). Anal. Calcd for C H O Ru: C,
16 22 2
5.31; H, 6.38. Found: C, 55.31; H, 6.59.
as an inseparable mixture with 1b (8% yield).
Cross-Dimerization of 2,3-Dimethylbutadiene with Styrene
6
4
6
[
Ru(η -1,3-dimethoxybenzene)(η -1,5-COD)] (1g). Similar to
the case for 1d, 1g was prepared by the reaction of 1a (106.2 mg,
.315 mmol), MeCN (1 mL, 20 mmol), and 1,3-dimethoxybenzene
150 μL, 1.00 mmol) in THF (10 mL) at room temperature for 42 h.
g was obtained as yellow plates (25% yield, 51.4 mg, 0.148 mmol).
Catalyzed by [RuCl (η -anisole)] (5c). Complex 5c (21.07 mg,
2
2
0.376 mmol), Na CO (32.04 mg, 0.302 mmol), and dibenzyl (45.07
2
3
0
(
1
mg, 0.251 mmol) as an internal standard were dissolved in 2-butanol
(2 mL), and 1,5-COD (20 μL, 0.15 mmol) was added to the solution.
After the mixture was heated to 100 °C for 1 h, to the solution at room
temperature were added 2,3-dimethylbutadiene (100 μL, 0.88 mmol)
and styrene (86 μL, 0.75 mmol) in an autoclave. The reaction mixture
was heated at 100 °C for 6 h, during which the reaction course was
monitored by GLC: 62% total yield, 3a/3b/isomers = 24/40/36.
Similar experiments were performed. 5c (21.2 mg, 0.0378 mmol),
Na CO (16.1 mg, 0.152 mmol) 2-propanol (2 mL), 1,5-COD (20 μL,
1
H NMR (400 MHz, C D ): δ 2.37 (m, 8H, CH in COD), 3.23 (s,
6
6
2
3
6
H, OMe), 3.40 (m, 4H, CH in COD), 4.03 (t, J
= 5.6 Hz, 1H,
= 5.6 Hz, 2H, aromatic), 4.96 (s, 1H,
H−H
3
aromatic), 4.82 (d,
J
H−H
aromatic). 13C{ H} NMR (100 MHz, C D ): δ 34.64 (s, CH in
1
6
6
2
COD), 55.95 (s, OMe), 62.25 (s, CH in COD), 67.54 (s, arene),
73.51 (s, arene), 74.36 (s, arene), 136.19 (s, arene). Anal. Calcd for
2
3
C H O Ru: C, 55.31; H, 6.38. Found: C, 55.39; H, 6.28.
0.152 mmol), 2,3-dimethylbutadiene (100 μL, 0.88 mmol), and
styrene (86 μL, 0.75 mmol) in Schlenk tube: 8% total yield, 3a/3b/
isomers = 12/50/38. 5c (20.8 mg, 0.0371 mmol), Na CO (16.0 mg,
0.151 mmol), 2-propanol (2 mL), 1,5-COD (20 μL, 0.152 mmol), 2,3-
dimethylbutadiene (100 μL, 0.88 mmol), and styrene (86 μL, 0.75
16
22
2
6
4
[
Ru(η -1,4-dimethoxybenzene)(η -1,5-COD)] (1h). Similar to
the case for 1d, 1h was prepared by the reaction of 1a (199.2 mg,
.590 mmol), MeCN (2 mL, 40 mmol), and 1,4-dimethoxybenzene
297.5 μL, 2.153 mmol) in THF (15 mL) at room temperature for 2
2
3
0
(
I
DOI: 10.1021/acs.organomet.7b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mmol) in autoclave: 47% total yield, 3a/3b/isomers = 21/43/36. 5c
Notes
(
(
21.1 mg, 0.0377 mmol), Na CO (32.0 mg, 0.302 mmol), 2-propanol
2 mL), 1,5-COD (20 μL, 0.15 mmol), 2,3-dimethylbutadiene (100
2 3
The authors declare no competing financial interest.
μL, 0.88 mmol), and styrene (86 μL, 0.75 mmol) in autoclave: 55%
total yield, 3a/3b/isomers = 16/47/36. 5c (20.9 mg, 0.0373 mmol),
Na CO (31.9 mg, 0.301 mmol), 2-propanol (2 mL), 1,5-COD (40
μL, 0.30 mmol), 2,3-dimethylbutadiene (31.7 mg, 0.299 mmol),
DMSO (2 mL), 1,5-COD (20 μL, 0.15 mmol), 2,3-dimethylbutadiene
ACKNOWLEDGMENTS
■
2
3
We thank Prof. M. Akita and Dr. Y. Tanaka (Tokyo Institute of
Technology) for MALDI-TOF MS analyses and Dr. S. Kiyota
for elemental analyses. We also thank the Campbell micro-
analytical laboratory at the University of Otago, Otago, New
Zealand. A part of this work was financially supported by the
Japan Science and Technology Agency (JST), ACT-C
(JPMJCR12Z2), and a part of this work was also supported
by a JSPS Grant-in-Aid for Scientific Research on Innovative
Areas “3D Active-Site Science” (26105003).
(
100 μL, 0.88 mmol), and styrene (86 μL, 0.75 mmol) in a Schlenk
tube: 1% yield. 5c (20.9 mg, 0.0373 mmol), Na CO (30.2 mg, 0.289
2
3
mmol), 1-butanol (2 mL), 1,5-COD (20 μL, 0.15 mmol), 2,3-
dimethylbutadiene (100 μL, 0.88 mmol), and styrene (86 μL, 0.75
mmol) in a Schlenk tube: 1% yield. 5c (21.1 mg, 0.0376 mmol),
Na CO (32.0 mg, 0.302 mmol), 2-butanol (2 mL), 1,5-COD (20 μL,
2
3
0
(
=
.15 mmol), 2,3-dimethylbutadiene (100 μL, 0.88 mmol), and styrene
86 μL, 0.75 mmol) in a Schlenk tube: 62% total yield, 3a/3b/isomers
24/40/36. 5c (21.0 mg, 0.0375 mmol), Na CO (31.8 mg, 0.300
2
3
ABBREVIATIONS
mmol), 2-butanol (2 mL), 2,3-dimethylbutadiene (100 μL, 0.88
mmol), and styrene (86 μL, 0.75 mmol) in a Schlenk tube: 0% yield.
■
COD,cyclooctadiene (C H ); COT,cyclooctatriene (C H );
8
12
8
10
6
c (21.5 mg, 0.00656 mmol), Na CO (31.9 mg, 0.301 mmol), 2-
2 3
DMA,dimethylacetamide (C H ON); acac,acetylacetonate
4
9
propyl alcohol (2 mL), 1,5-COD (20 μL, 0.15 mmol), 2,3-
dimethylbutadiene (100 μL, 0.88 mmol), and styrene (86 μL, 0.75
mmol) in autoclave: 45% total yield, 3a/3b/isomers = 18/44/38.
X-ray Analyses. A single crystal was selected using a polarized
microscope and was mounted on a glass capillary by use of Paratone-N
oil. A Rigaku AFC-7R Mercury II diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.71075 Å) was used for data
collection. The collected data were solved by direct methods and
refined by a full-matrix least-squares procedure using the Crystal-
(
C H O ); Cp*,pentamethylcyclopentadienyl (C H );
5 7 2 10 15
THF,tetrahydrofuran (C H O); dcype,1,2-bis-
4
8
(
dicyclohexylphosphino)ethane (C H P ); DMSO,dimethyl
26 48 2
sulfoxide (C H OS); Schmalzphos,(3aR,8aR)-6-((3-
3
6
(
diphenylphosphaneyl)[1,1′-biphenyl]-2-yl)oxy)-2,2-dimethyl-
4,4,8,8-tetraphenyltetrahydro-[1,3]dioxolo[4,5-e][1,3,2]-
dioxaphosphepine (C H O P )
55
46
5 2
40,41
Structure program (ver. 4.2).
All hydrogen atoms were treated as a
REFERENCES
riding model. The optimized structures are depicted by use of the
■
42
POV-Ray program (ver. 3.6.2). Incorporation of THF and 5H-
dibenzo[b.f ]azepine molecules were observed in a unit cell of 2d.
CCDC 1567421, 1567423, 1567422, 1567420, 1567419, and 1567438
contain the supplementary crystallographic data for 1d,g,h and 2b−d,
respectively.
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̈
ASSOCIATED CONTENT
■
*
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Supporting Information
(
̈
The Supporting Information is available free of charge on the
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met.7b00882.
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Accession Codes
Jpn. 1967, 40, 1889−1893.
CCDC 1567419−1567423 and 1567438 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
■
Corresponding Authors
E-mail for M.H.: hrc@cc.tuat.ac.jp.
E-mail for M.A.B.: martin.a.bennett@anu.edu.au.
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ORCID
Organometallics 2017, 36, 3931−3939.
Masafumi Hirano: 0000-0001-7835-1044
Nobuyuki Komine: 0000-0003-1744-695X
Annie L. Colebatch: 0000-0001-6920-3744
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