A six-coordinated cationic ruthenium carbyne complex with liable pyridine ligands: Synthesis, structure, catalytic investigation, and DFT study on initiation mechanism

Article abstract of DOI:10.1016/j.tet.2014.05.060

A novel six-coordinated high-valence cationic ruthenium carbyne complex bearing two liable pyridine ligands was prepared in high yield by the reaction of the ruthenium-based complex (IMesH₂)(Cl)₂(C ₅H₅N)₂RuCHPh [IMesH₂=1,3-dimesityl- 4,5-dihydroimida-zol-2-ylidene] with excess iodine as an oxidant in CH ₂Cl₂ at 25 °C under N₂. The new ruthenium carbyne-based complex shows moderate to good catalytic activity for ring-closing metathesis reactions. Importantly, no double bond isomerization by-product was produced at elevated reaction temperatures (100 °C-137 °C) in the reaction catalyzed by the synthesized ruthenium carbyne complex. A mechanism involving the in situ conversion of the ruthenium carbyne through the addition of an iodide to the carbyne carbon was also proposed, and DFT calculations were performed to explain the initiating mechanism.

Full text of DOI:10.1016/j.tet.2014.05.060

Tetrahedron 70 (2014) 4718e4725
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A six-coordinated cationic ruthenium carbyne complex with liable
pyridine ligands: synthesis, structure, catalytic investigation, and
DFT study on initiation mechanism
,
b
b
a
b
b
Guiyan Liu a , Lu Zheng , Mingbo Shao , Huizhu Zhang , Weixia Qiao , Xiaojia Wang ,
*
Bowen Liu b, Haitao Zhao b , Jianhui Wang
,
b,
*
*
a College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of Inorganic-Organic Hybrid
Functional Material Chemistry, Ministry of Education, Tianjin Normal University, Tianjin 300387, PR China
b Department of Chemistry, College of Science, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel six-coordinated high-valence cationic ruthenium carbyne complex bearing two liable pyridine
ligands was prepared in high yield by the reaction of the ruthenium-based complex (IM-
esH2)(Cl)2(C5H5N)2RuꢀCHPh [IMesH2¼1,3-dimesityl-4,5-dihydroimida-zol-2-ylidene] with excess iodine
as an oxidant in CH2Cl2 at 25 ꢁC under N2. The new ruthenium carbyne-based complex shows moderate
to good catalytic activity for ring-closing metathesis reactions. Importantly, no double bond isomeriza-
tion by-product was produced at elevated reaction temperatures (100 ꢁCe137 ꢁC) in the reaction cata-
lyzed by the synthesized ruthenium carbyne complex. A mechanism involving the in situ conversion of
the ruthenium carbyne through the addition of an iodide to the carbyne carbon was also proposed, and
DFT calculations were performed to explain the initiating mechanism.
Received 4 March 2014
Received in revised form 6 May 2014
Accepted 19 May 2014
Available online 23 May 2014
Keywords:
Olefin isomerization
Olefin metathesis
Ruthenium carbynes
Ring-closing metathesis
N-Heterocyclic carbene
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
than 4 and 5 toward the metathesis reaction because of the rapid
liberation of the chelating phenoxy ligand in this catalyst. The
Olefin metathesis is a powerful tool for the construction of CeC
double bonds in organic synthesis and materials chemistry.1 In
particular, ruthenium-based catalysts are receiving considerable
attention because they can provide a catalytic system more tolerant
to a large number of organic functional groups than other types of
currently available catalysts.2 The successful application of olefin
metathesis in the organic synthesis and materials chemistry largely
depends on the discovery of catalysts 1 and 2 by Grubbs.3 After the
discovery of catalysts 1 and 2, many efforts have been devoted to
the development of new catalysts to improve the activity, selec-
tivity, and stability of the catalysts. For example, the ruthenium
carbene complexes 4 and 5 developed by Hoveyda et al.4 show
excellent stability toward air and moisture by the introduction of
a chelating phenoxy group. Blechert5 showed that 6 with a phenyl
next to the chelating phenoxy group has a higher initiation rate
ruthenium-indenylidene complexes 7 and 8 reported by Monsaert
and Verpoort6 show excellent application profiles. In particular,
high selectivity is observed in cross-metathesis with low catalyst
loadings. The ruthenium carbene complex 9 reported by Grubbs,7
which contains substitutionally labile pyridine ligands, can serve
as a rapid initiator for the olefin metathesis reaction. The labile
pyridine and chloride ligand in this catalyst can also activate itself
to become a versatile starting material for the preparation of
structurally diverse ruthenium olefin metathesis catalysts. Six-
coordinate carbene complexes of 10 developed by Grela,8 in
which a carbonyl oxygen of the ester was functionalized as a ligand
to coordinate to the ruthenium metal center, show high activity for
olefin metathesis reactions. Ruthenium complexes of 11aec with
N,O-chelates from a Schiff base ligand reported by Raines et al.9a
and Verpoort et al.9bee can efficiently catalyze the ring-closing re-
action of diethyl 2,2-diallylmalonate and other diene substrates in
protic media. Through the introduction of chiral carbene ligands,
the ruthenium carbene catalysts of 12,10 13, and 1411 show asym-
metric conversions of substrates having a prochiral center with
high enantioselectivity. Recently, the new ruthenium catalysts 15
and 16 reported by Grubbs et al.12aed are found to extend
* Corresponding authors. Tel.: þ86 022 23766515; fax: þ86 022 23766532 (G.L.);
tel.: þ86 022 27892497; fax: þ86 22 27403475 (H.Z.); tel.: þ86 022 27892497; fax:
þ86 22 27403475 (J.W.); e-mail addresses: guiyanliu2013@163.com (G. Liu),
htzhao@tju.edu.cn (H. Zhao), wjh@tju.edu.cn (J. Wang).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.05.060

G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
4719
dramatically the scope of olefin metathesis to produce (Z)-olefins
selectively in cross-metathesis reactions. The first broadly appli-
cable set of protocols for efficient Z-selective formation of macro-
cyclic disubstituted alkenes through catalytic ring-closing
metathesis (RCM) is described by Hoveyda and Schrock.12eei These
newly developed ruthenium carbene olefin metathesis catalysts are
facilitating the application of this method in many fields, including
polymer chemistry,13 organic synthesis,14 and green chemistry.15
These newly developed ruthenium catalysts for olefin metathesis,
which have a carbene-metal core structure, are generally highly
active for olefin metathesis. However, an increasing number of
reports on olefin isomerizations reveal that these ruthenium car-
bene catalysts are problematic in olefin metathesis reactions under
harsh reaction conditions.16 Such harsh conditions significantly
decrease the yield of the desired product, and the isomerized side
products are often difficult to remove through standard purification
techniques. Hence, the development of olefin metathesis catalysts
suitable for harsh reaction conditions is highly important.
In recent years, many transition-metal carbyne complexes have
been developed and prepared not only because of their unusual
type of bonding but also because of their increasing applications in
organic synthesis and alkyne metathesis.17 After Fischer et al.18
reported the preparation and structural characterization of the
first prototypes of metal carbynes in 1973, various synthesis routes
for compounds with a metal-carbon triple bond have been de-
veloped, including the conversion of coordinated carbenes, vinyl-
idenes, allenylidenes, and even alkynyls into corresponding metal
carbyne units.19,20 Caulton21 disclosed the unexpected formation
of square-planar Ruecarbyne complexes Ru(CPh)(PR3)2(OPh)
(R¼i-Pr, Cy). Similarly, Fogg22 prepared Ru(CPh)(PCy3)2(OC6F5)
from 1 by reaction with TlOC6F5. By the conversion of coordinated
ruthenium carbenes and vinylidenes, many ruthenium carbyne
complexes have been developed and prepared.23 However, unlike
the molybdenum and tungsten analogs of these complexes, the
nature of their catalytic behavior remains elusive. Some of these
ruthenium carbyne complexes are known for their ability to cat-
alyze the dimerization of alkynes instead of alkyne metathesis.23a
Reports of ruthenium carbyne complexes exhibiting catalytic ac-
tivity toward olefin metathesis are also extremely rare,24 and
a general belief exists that ruthenium carbyne complexes are inert
toward olefin metathesis.25 These complexes must first be con-
verted to allenylidene- or alkylidene-ruthenium complexes to
initialize an olefin metathesis reaction.26 In our previous work,
Chart 1. Catalysts for olefin metathesis.
atmosphere (Scheme 1). Unlike its bisphosphine analogs,22 the
new Ruecarbyne complex did not exist as a neutral, six-coordinate
Ruecarbyne structure (18a and 18b). This finding may be due to
the large steric effect of N-heterocyclic carbene, which inhibits the
addition of iodine to the ruthenium center. Similar to the pre-
viously reported ruthenium complex 17, 18 was formed as a six-
coordinated high-valence cationic ruthenium carbyne complex
bearing two liable pyridine ligands. The complex was character-
ized by X-ray diffraction, and the exact molecular structure is
shown in Fig. 1. The coordination geometry around the metal
center of the ruthenium cation corresponded to that of a distorted
octahedron with two pyridines and two trans-disposed chlorines.
The atoms C(27) and C(28) of the alkynyl ligand and NHC ligand
lied in the same plane. In contrast to the nearly linear Cl(1)e
RueCl(2) axis (176.9ꢁ), the C(27)eRueN(4) axis (166.6ꢁ) was
slightly bent, with the carbon atoms pointing away from the NHC
a
five-coordinate dichloro(tricyclohexylphosphine) ruthenium
carbyne complex 17 has been prepared via oxidation of 2 with an
excess amount of I2 and was used to initiate olefin metathesis
reactions with moderate to good activities.27 However, iron pow-
der (5.0 mol %) need to be added to accelerated the catalyst re-
action. Designing new ruthenium carbyne complexes, which have
high initiation rate without the help of iron powder become the
goal of our new research. Compared with 2, complex 9 led to
greatly increased initiation rates by replacing the phosphanes with
labile pyridines.7 We proposed that the initiation rates will be
significant increased if the phosphane was replaced by a labile
pyridine. Thus, a stable six-coordinate ruthenium carbyne com-
plex 18 bearing labile pyridine ligands was prepared via oxidation
of 9 with an excess amount of I2. This complex can initiate olefin
metathesis reactions at elevated temperatures. The initiating
mechanism, including the in situ conversion of ruthenium carbyne
to ruthenium carbene, was explained using DFT calculations
(Chart 1).
2. Results and discussion
Complex 18 was prepared in 90% isolated yield through the
oxidation of 9 with excess I2 in CH2Cl2 at 25 ꢁC under N2
Scheme 1. Synthesis of ruthenium carbyne complex 18.

4720
G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
Under the optimized reaction conditions (1.0 M substrate in
toluene at 100 ꢁC), the RCM of the N-protected substrates 19, 21, 23,
25, 29 and 31 (Table 1, entries 1e4 and entries 6e7), as well as
diethyl diallymalonate 27 (Table 1, entry 5), leading to the forma-
tion of five-, six-, or seven-membered carbo- or heterocyclic
structures smoothly proceeded when 18 was used (1.0 mol %).
Table 1
Olefin metathesis reactions catalyzed by the Ruecarbyne complex 18a
Entry
Diene
Product
18 Ru mol % Yieldb (%)
(time)a
1
2
1.0%(2 h)
1.0%(2 h)
99
98
Fig. 1. Molecular structure of the ruthenium carbyne 18; the Iꢂ3 was omitted for clarity;
selected bond lengths [A] and angles [ ]: RueCl(1) 2.4590(8), RueCl(2) 2.4655(8),
RueN(3) 2.1867(9), RueN(4) 2.3709(7), RueC(27) 1.6010(9), RueC(10) 2.071(1); Cl(1)e
RueCl(2) 176.9(1), N(3)eRueN(4) 75.1(4).
ꢁ
ꢀ
moiety. The formation of a ruthenium carbyne complex was in-
dicated by the Ru(1)eC(27) bond length (1.601 A), which was
3
4
5
1.0%(2 h)
1.0%(3 h)
1.0%(3 h)
98
98
96
ꢀ
much shorter than the bond in the ruthenium carbene complex 9
7
ꢀ
(1.873 A). This bond length was consistent with the bond lengths
previously reported for ruthenium carbyne complexes.22,27 The
ꢀ
RueN bond lengths of 2.1867(9) and 2.3709(7) A lied within the
expected range, and were nearly identical to those found in six-
coordinate ruthenium carbene 9 complex containing a [RuPy2]
fragment.7
The ring-closing metathesis (RCM) activity of 17 and 18 were
examined using the N-protected diallylamine 19 as a test substrate
with 2.5 mol % ruthenium precatalyst loading. When the reaction
was carried out in toluene (1 M) at 100 ꢁC, the catalytic activity of
17 and 18 was sharply increased. A complete conversion of 18
(>98%) and a good conversion of 17 (>92%) were observed in
20 min (Fig. 2, a). In order to clearly compare the efficiencies of 17
and 18, the reaction was performed at 60 ꢁC. The desired RCM
products were obtained in 65% yields (complex 17) and 85% yields
(complex 18) in 6 h (Fig. 2, b). The catalytic activity of 18 is higher
than that of 17.
6
7
8
2.0%(2 h)
2.0%(3 h)
2.5%(12 h)
96
94
4
9
1.0%(2 h)
94
91
10
1.0%(12 h)
11
2.0%(12 h)
90
12
13
2.5%(12 h)
2.5%(12 h)
88
85
Fig. 2. Kinetic curves for the RCM of diene 19 using 17 and 18 as a precatalyst: (a) at
100 ꢁC; (b) at 60 ꢁC.

G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
4721
Table 1 (continued )
such as that between olefins 45 and 46. The corresponding product
47 was obtained in 92% yield (E/Z>20/1). These results clearly
showed that 18 was an olefin metathesis catalyst with moderate to
good activity. Moreover, its performance was highly similar to those
of many other well known olefin metathesis catalysts in terms of
substrate scope and functional group tolerance.28
Entry
Diene
Product
18 Ru mol % Yieldb (%)
(time)a
14
5.0%(12 h)
92
E/Z>20:1
Similar to previously reported ruthenium carbyne-based com-
plex 17, complex 18 can also initiate olefin metathesis reactions at
a high temperature without interference from olefin isomerization
side reactions. A comparative study of 18 and several well known
catalysts, such as 1, 2, 5, 9, and 17 was then conducted. The results
are shown in Table 2. The RCM of the tosylamide dienes 19, 21, 23,
and 25 using the Ru carbene complexes 1, 2, 5, or 9 in toluene at
100 ꢁC resulted in the formation of an undesired side product in
each case caused by the isomerization of the initially formed RCM
product (Table 2, entries 1e4). When using 17 as catalyst under the
same reactions, no complication caused by the double bond
isomerization of the products, but proceeded in low yields (<50%).
However, using 18 with under identical conditions in high yields
(>98%) and no isomerization was observed. These results revealed
an interesting feature of the Ru carbyne-based complex 18, i.e., the
absence of olefin isomerization tendencies, which are common in
olefin metathesis with Ru carbene-based catalysts under harsh
reaction conditions.16 Another example for the unique application
of 18 was found in the metathetical dimerization of allybenzene 50
(Table 2, entry 5). The use of 2, 5, and 9 as catalysts gave the desired
product 51 in low yield (7% for 2; 33% for 5, 11% for 9) in CH2Cl2 at
40 ꢁC, along with the side products 1-((E)-prop-1-enyl)benzene 50a
(22% for 2; 1% for 5, 2% for 9), (E)-1,3-diphenylprop-1-ene 51a (33%
for 2; 54% for 5, 73% for 9), and (E)-1,2-diphenylethene 51b (36% for
2; 6% for 5, 7% for 9). The use of 1 as the catalyst gave the desired
product 51 in higher yield (62%), but the side products 1-((E)-prop-
1-enyl)benzene 50a (13%), and the (E)-1,3-diphenylprop-1-ene 51a
15
10.0%(12 h)c 90
Z/E¼2.4:1
a
Reaction conditions: in toluene (1.0 mol/L) at 100 ꢁC under nitrogen.
b
Isolated yields after silica gel chromatography. Yields determined by 1H NMR
spectroscopy.
c
Yields determined by GCeMS analysis of the crude reaction mixture. E/Z ratio
was obtained by GCeMS analysis of the product.
The RCM of the sulfur-containing substrate 35 (Table 1, entry 9),
the oxygen-containing substrates 37 and 39 (Table 1, entries
10e11), and the enyne substrate 41 and 43 (Table 1, entry 12 and 13)
uneventfully proceeded (yields from 85% to 90%) under similar
conditions. Only little RCM product (yields 4%) was observed when
a more challenging substrate, such as the tetrasubstituted diene 33
(Table 1, entry 8), was used. The RCM of 48 to form the 21-
membered macrocyclic lactone 49 proceeded smoothly and gave
49 in 90% yields without any indication for the formation of by-
product (Table 1, entries 15). Complex 18 was also an effective
catalyst for typical cross-metathesis reactions (Table 1, entry 14),
Table 2
Comparison of 18 with 1, 2, 5, and 17 for different substrates in model metathesis reactions and CM reactionsa
Entry
Diene
Cat.
Productb
(Ru mol %)a
1
1 (1.0)
2 (1.0)
5 (1.0)
9 (1.0)
17 (1.0)
18 (1.0)
97%
84%
90%
93%
48%
100%
3%
16%
10%
7%
0%
0%
2
1 (1.0)
2 (1.0)
5 (1.0)
9 (1.0)
17 (1.0)
18 (1.0)
100%
84%
90%
100%
49%
100%
0%
16%
10%
0%
0%
0%
3
1 (1.0)
2 (1.0)
5 (1.0)
9 (1.0)
17 (1.0)
18 (1.0)
100%
87%
91%
100%
48%
100%
0%
13%
9%
0%
0%
0%
(continued on next page)

4722
G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
Table 2 (continued )
Entry
Diene
Cat.
Productb
(Ru mol %)a
4
1 (1.0)c
2 (1.0)c
5 (1.0)c
9 (1.0)c
17 (1.0)c
18 (1.0)c
58%
94%
89%
78%
25%
100%
1%
2%
6%
0%
0%
0%
0%
2%
1%
0%
0%
0%
5
1 (5.0)(73%)c,d,e
2 (5.0)(98%)c,d,e
5 (5.0)(95%)c,d,e
9 (5.0)(93%)c,d,e
17(5.0)(34%)c,d,f
18(5.0)(89%)c,d,f
13% (E only)
22% (E only)
1% (E only)
2% (E only)
0%
62% (4.5:1)
7% (4.8:1)
33% (5.6:1)
11% (5.2:1)
34% (1.5:1)
89% (2.2:1)
0%
11% (E only)
33% (E only)
54% (E only)
73% (E only)
0%
0%
36% (E only)
6% (E only)
7% (E only)
0%
0%
0%
a
Except noticed, the reactions were conducted in toluene at 100 ꢁC for 2 h under nitrogen (1.0 mol/L).
Conversions were determined by 1H NMR analysis of the crude reaction mixture.
Conversions were determined by GCeMS analysis of the crude reaction mixture.
E/Z ratio was obtained by GCeMS analysis of the product.
In CH2Cl2 at 40 ꢁC.
b
c
d
e
f
In xylene at 137 ꢁC.
(11%) were also produced. When 5 mol % 17 was used as the catalyst
conducted using the M06 functional,31 and the results are sum-
marized in Fig. 3. The nucleophilic addition of I-3 to the carbon-
metal triple bonds of I produced the iodized ruthenium carbene
II by TS (I/II) with a barrier of 14.5 kcal/mol. The transformation
of I to II was endergonic by 12.0 kcal/mol. After I2 was released,
a pyridine ligand dissociated from II to produce III with an energy
decrease of 5.5 kcal/mol. The energy decrease indicated that the
steric hindrance of the metal center in II was released by the
liberation of a pyridine ligand. However, when the other pyridine
ligand in III was freed to yield IV, the energy increased by 3.8 kcal/
mol, which was unsurprising. The Ru(II) metal center in IV co-
ordinated with an ethylene to form V with an energy increase of
6.4 kcal/mol, and the pyridine ligand was released at the same
time. A [2þ2] intramolecular cycloaddition in V gave the metal-
lacyclobutane complex VI through TS (V/VI) with a free energy
increase of 4.6 kcal/mol. Then, ring-opening through TS (VI/VII)
in xylene at 137 ꢁC for 12 h, no by-products were observed, but the
product 51 was given in low yield (34%). Under the similar condi-
tions, the use of 5 mol % 18, the dimerization of 50 proceeded
smoothly to give 51 in a higher yield (89%) without any side
products. Although the [Ru] complexes 2 and 17, 9, and 18 have
similar structures, but under the same conditions to initiate olefin
metathesis reactions at a high temperature can produce different
products. For the complexes 17 and 18, no isomerization was
observed.
Similar to our previous work, when exchanging with AgBF4 to
eliminate the Ie3 (and hence, Ie) from the reaction system, the cat-
alytic activity of 18 was completely shut down. This finding in-
dicated an initiating mechanism similar to that of the previously
reported complex. Accordingly, we propose a similar catalytic
mechanism involving two main steps. First is the in situ conversion
of 18 to the
addition of Iꢂ to either 18 or its resonance structure 52
(Scheme 2).29 Second is the reaction of the
-iodobenzylidene
complex 53 with an olefin to generate the 14-electron Ru complex
55, which participates in subsequent catalytic cycles. Notably, the
formation of 53 from 18 was a rare but potentially general approach
for the formation of halocarbene complexes even though the ad-
dition of hetero-nucleophiles to carbon-metal triple bonds is well
documented.30
The initiating mechanism of the complex was further in-
vestigated by performing DFT calculations to obtain the free en-
ergies and enthalpies of all transition states (TSs) and
intermediates of the situ conversion of 18. DFT calculations were
a
-iodobenzylidene complex 53 by the nucleophilic
affords VII with a barrier of 12.4 kcal/mol. Subsequently, a-iodo-
benzylidene was released from VII to produce VIII, which partic-
ipated in subsequent catalytic cycles. This step was associated
with a free energy decrease of 3.6 kcal/mol. The entire initiation
process of the complex was endergonic by 22.2 kcal/mol.
The highest reaction barrier of 14.5 kcal/mol occurred in steps I to
II.
Therefore, steps I to II were the rate-determining steps. The
conversion of 18 to the metathesis catalytic active species VI or VIII
was an endothermic process. This result was consistent with the
fact that the initiation of the complex required elevated tempera-
tures. The calculation results strongly supported the proposed
initiating mechanism.
a

G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
4723
procedures. Other chemicals or reagents were obtained from
commercial sources.
4.1.1. Preparation of ruthenium carbyne 18. Ruthenium carbene
complex
9 (100.0 mg; 137.6 mmol) and iodine (104.9 mg;
412.8 mmol) were added to a flask under N2. Dry dichloromethane
(10.0 mL) was added to the mixture using a syringe under N2. The
resulting mixtures were then stirred at room temperature for
30 min and were concentrated under a vacuum. The residual solid
was washed with hexane until the solution was colorless. The
residue was purified by flash column chromatography on neutral
aluminum oxide using CH2Cl2 as eluant to produce the desired
product 18 as a yellow solid (137 mg, 90%). Anal. found (calcd) for
Scheme 2. Proposed mechanism for the olefin metathesis activity of 18.
Fig. 3. Calculated energy profiles for the initiation pathway of 18. The relative free energies and electronic energies (in parentheses) are given in kilocalories per mole.
3. Conclusions
C38H41Cl2I3N4Ru: C 40.87 (41.25), H 3.20 (3.73), N 4.69 (5.06); 1H
NMR (400 MHz, CDCl3): 8.68e8.71 (m, 4H, pyridine), 7.50e7.47
d
The cationic complex 18 reported in this paper was an efficient
RCM and CM catalyst bearing a ruthenium carbyne core structure.
Importantly, no double bond isomerization by-product was formed
even at a high temperature in the RCM reactions and CM reactions
catalyzed by 18. The in situ conversion of the ruthenium carbyne to
a metathesis active species was explained by DFT calculations.
(m, 7H, CH, pyridine), 6.95e7.03 (m, 4H, CH), 6.43e6.51 (m, 3H,
pyridine), 4.20 (s, 4H, CH2CH2), 2.46e2.60 (m, 18H, Mes CH3). 13C
NMR (400 MHz, CDCl3):
d 313.2, 200.0, 149.2, 148.0, 140.9, 139.2,
139.0, 136.7, 136.5, 130.9, 129.4, 128.7, 128.1, 127.0, 125.2, 124.1, 53.7,
51.3, 31.5, 22.6, 21.1, 18.9.
4.2. General procedures for olefin metathesis reactions
4. Experiment section
4.1. General
4.2.1. RCM
and
enyn
metathesis. A
solution
of
18
(0.001e0.0025 mmol, 1.00 mol %e10.0 mol %) was added to a so-
lution of alkene (0.10 mmol) in toluene (0.10 mL; 1.0 M) under ni-
trogen. The resulting mixture was stirred at 100 ꢁC for 2e12 h.
Then, the solvent was removed under reduced pressure to yield
a crude product, which was purified by flash chromatography (c-
hexaneeCH2Cl2) to remove the Ru residue. Conversions were ob-
tained as confirmed by 1H NMR spectroscopy by comparing the
ratios of the integrals of the starting materials with those of the
Unless otherwise noted, all reactions were performed under an
atmosphere of dry N2 using oven-dried glassware and anhydrous
solvents. Toluene was dried from sodium/benzophenone under
a
N2 atmosphere, and distilled prior to use. Silica gel
(200e300 mesh) was used for flash chromatography. The starting
materials were synthesized and purified according to literature

4724
G. Liu et al. / Tetrahedron 70 (2014) 4718e4725
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4.2.2. Cross-metathesis. To a mixture of alkene (0.10 mmol) and
cross-metathesis partner (0.20 mmol) in toluene (0.10 mL, c¼1.0 M)
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Acknowledgements
This work was supported by grants from the National Natural
Science Foundation of China (NSFC 21102102, 21372175, 20872109,
and 21072149).
€
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Supplementary data
Details for crystal structure determination, crystallographic
parameters, 1H, and 13C NMR spectra are given. Supplementary data
related to this article can be found at http://dx.doi.org/10.1016/
j.tet.2014.05.060.
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