A General Strategy for Open-Flask Alkene Isomerization by Ruthenium Hydride Complexes with Non-Redox Metal Salts

Article abstract of DOI:10.1002/cctc.201700687

A homogenous metal hydride (M?H) catalyst for isomerization normally requires rigorous air-free techniques. Here, we demonstrate a highly efficient protocol in which simple non-redox metal ions as Lewis acids can promote olefin isomerization dramatically with a commercially available RuH₂(CO)(PPh₃)₃ complex in an open-flask system. Isomerization can be accomplished within a short time, and a satisfactory selectivity for different types of unsaturated compounds can be obtained. Meanwhile, an excellent turnover number up to 17208 was achieved under air, and open-flask gram-scale experiments further demonstrated the efficiency of the RuH₂(CO)(PPh₃)₃/non-redox-metals system. We used FTIR spectroscopy, GC–MS, NMR spectroscopy and kinetics studies to evidence that in the sluggish RuH₂(CO)(PPh₃)₃ catalyst, bloated PPh₃ ligands cause steric hindrance for the coordination of the free alkene. Alternatively, the addition of non-redox metal ions could induce the dissociation of the PPh₃ ligand to offer unoccupied coordination sites for the alkene and to form the Mg-bridged adduct OC?Ru?H₂?Mg²⁺ as the highly active species, which benefited the isomerization significantly through the metal hydride addition–elimination pathway. Finally, this strategy was demonstrated as an impactful approach for hydride catalysts of other transition metals such as Os.

Full text of DOI:10.1002/cctc.201700687

Accepted Article
Title: A General Strategy for Open Flask Alkene Isomerization by
Ruthenium Hydride Complexes with Non-Redox Metal Salts
Authors: Zhanao Lv, Zhuqi Chen, Yue Hu, Wenrui Zheng, Haibin
Wang, Wanling Mo, and Guochuan Yin
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A General Strategy for Open Flask Alkene Isomerization by
Ruthenium Hydride Complexes with Non-Redox Metal Salts
Zhanao Lv, Zhuqi Chen,* Yue Hu, Wenrui Zheng, Haibin Wang, Wanling Mo, Guochuan Yin*
Abstract: Homogenous metal hydride (M-H) catalyst for
isomerization normally required rigorous air-free techniques. This
work demonstrated a highly efficient protocol that simple non-redox
metal ions as Lewis acids can dramatically promote olefin
isomerization by commercially available RuH2(CO)(PPh3)3 complex
in open flask system. Isomerization can be accomplished within
short time, and satisfying selectivity for different types of unsaturated
compounds can be obtained. Meanwhile, an excellent turnover
number (TON) up to 17208 was achieved under air, and open flask
gram scale experiments further demonstrated the efficiency of
Grubbs metathesis catalysts7. Moreover, the double bond
migration catalyzed by Ru-H catalyst is one important pathway
in methodology of organic synthesis by tandem processes, such
as the synthesis of 1,2-annulated trans-tetrahydrofurans with
Chaudret’s catalyst ([RuH(η5-C8H11)2][BF4]),8 heterocycles by
isomerization and cycloisomerization,9 C-C bond forming using
RuHCl(CO)(PPh3)3/Brønsted acid binary catalytic system10 and
aromatic oxazaheterocycles11.
Nevertheless, most of these cases were highly sensitive to
oxygen and moisture, which demanded standard Schlenk
RuH2(CO)(PPh3)3/non-redox-metals system. Through FT-IR, GC-MS, techniques with protective atmosphere, or even extremely
NMR and kinetics studies, it was evidenced that in sluggish
RuH2(CO)(PPh3)3 catalyst, bloated PPh3 ligands caused the steric
hindrance for the coordination of free alkene. Alternatively, the
addition of non-redox metal ions induced the dissociation of PPh3
ligand, offered unoccupied coordination sites for alkene, and formed
the magnesium-bridged adduct OC-Ru-H2---Mg2+ as the highly active
species which significant benefited the isomerization through metal
hydride addition-elimination pathway. Last but not least, this strategy
was also demonstrated as an impactful approach for hydride
catalysts of other transition metals such as osmium.
rigorous conditions such as glove-box for the whole synthetic
procedure, and all the reagent required being purged and
degassed with dry argon prior to use. For instance, the
[Ru(CO)H(PNN)] pincer complex exhibited forceful ability to
isomerize alkenes when the reaction was carried out under the
protective nitrogen atmosphere using a glove-box and Schlenk
techniques, however, the reactions was straightway quenched
by exposure to air.12 Therefore, an efficient catalytic system in
open flask is still of great demand for isomerization of extensive
unsaturated compounds.
We recently observed that non-redox metal ions as Lewis
acids can modulate the reactivity of transition metal catalysis in
versatile homogeneous reactions.13 For instance, the strategy of
introducing of non-redox metal ions remarkably promoted redox
metal ions such as iron-, manganese-, vanadium- and
palladium-mediated catalytic reactions, including hydroxylation,
C-C coupling, isomerization and epoxidation.14 Evidenced by
mechanism studies, the presence of non-redox metal ions can
substantially manipulate the coordination structure of reactive
species, thus further regulate their catalytic activities.14b-g The
presence of non-redox metals may also alter the reaction
pathway, and control the yield distribution of different oxidative
products.14h Particularly in the case of ruthenium catalysts, we
further found that the addition of non-redox metal ions as Lewis
acids can accelerate the catalytic epoxidation of olefins and
saturated C-C bond dehydrogenation.15 Above examples
unambiguously specified an alternative approach to regulate the
catalytic properties of those sluggish transition metal catalysts.
Herein, the isomerization of extensive unsaturated
compounds was investigated, whereas one commercially
available Ru-H complex, RuH2(CO)(PPh3)3, was conducted as
the model catalyst. Unprecedentedly, the isomerization could be
remarkably promoted by cheap inorganic magnesium salts to
introduce non-redox metal ions. This simple catalytic system
showed an outstanding efficiency for various types of olefins
under mild conditions with significant tolerance to oxygen and
moisture. A primary mechanism for this non-redox metal-ions-
promoted isomerization by ruthenium hydride species was
further explored. Furthermore, similar promotional effect can
also be observed in sluggish OsH2(CO)(PPh3)3, which further
Introduction
Alkene isomerization have attracted considerable interests due
to its widespread applications in chemical, biological and
pharmaceutical synthesis.1 This process was normally catalyzed
by transition metals such as Fe, Pd, Rh, Ni, Ir, Cr and Ru,2
among which ruthenium hydride complexes have been
demonstrated with a strong affinity to facilitate hydrometallation
of versatile olefins and are widely applied in the C=C bond
migration reactions, for instance, the isomerization of S-allyl, O-
allyl
and
N-allyl
compounds
by
air-sensitive
[RuClH(CO)(PPh3)3],2c,2d,3 allylic alcohols to saturated ketones
by ruthenium-cyclopentadienyl complexes,4 isomerization of
terminal alkenes by cationic version of [RuCl(PPh3)2(3-
phenylindenyl)],5 (C5Me5)Ru complexes6 and the classical
Z. Lv, Dr. Z. Chen, Y. Hu, W. Zheng, H. Wang, Dr. W. Mo, Prof. Dr.
G. Yin
School of Chemistry and Chemical Engineering. Key laboratory of
Material Chemistry for Energy Conversion and Storage (Huazhong
University of Science and Technology), Ministry of Education, Hubei
Key Laboratory of Material Chemistry and Service Failure,
Huazhong University of Science and Technology, Wuhan 430074,
PR China
E-mail: zqchen@hust.edu.cn for Zhuqi Chen; gyin@hust.edu.cn for
Guochuan Yin.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201700687
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verified the feasibility of our strategy that may offer an alternative
opportunity to those air-sensitive metal hydride catalysts for
open flask olefin isomerization.
redox metals with transition metal complexes through metal-oxo-
metal or metal-H-metal bonds. This interaction has been
observed in both our previous studies 14b-f, 15 and other reports13d,
18. Thus, the presence of Ru-H in RuH2(CO)(PPh3)3/Mg2+ system
was essential to initiate the promoted isomerization, as
compared with the case of Ru(CO)3(PPh3)2, and from which it
was speculated that the regulation from non-redox metals to the
ruthenium center may originate through metal-H-metal bonds.
Results and Discussion
Non-redox metal ions promoted olefins isomerization
Initial assays were performed with classic Ru-H complex
RuH2(CO)(PPh3)3 as the catalyst, which could be purchased
commercially or easily synthesized.16,17 Eugenol was chosen as
the model substrate because eugenol has been widely used in
perfumes, flavorings, and essential oils. The synergistic effect
between non-redox metal ions and RuH2(CO)(PPh3)3 was
compiled in Table 1. RuH2(CO)(PPh3)3 alone was very sluggish,
Table 1. Effects of different non-redox metal ions on catalytic isomerization of
eugenol by ruthenium complexes.
exhibiting only 18.7
% conversion and 17.8 % yield of
Yield (%)
Conversion
(%)
Entry
additive
isoeugenol (Table 1, entry 1). Alternatively, introducing the
divalent non-redox metal ions such as Ca2+ and Mg2+
dramatically promoted the performance, accompanying 77.4 %
conversion with 74.6 % (24.7 % cis-isoeugenol and 49.9 %
trans-isoeugenol) yield and 99.9 % conversion with 98.8 %
(6.4 % cis-isoeugenol and 92.4 % trans-isoeugenol) yield,
respectively. Meanwhile, trivalent non-redox metal ions, such as
Sc3+, In3+, Yb3+, Y3+, can also obviously accelerate the efficiency
of RuH2(CO)(PPh3)3 catalyst, in which more than 80 % eugenol
was isomerized within 30 min. When the reaction time was
extended to 1 h, almost 100 % conversion could be gained in
the presence of these trivalent non-redox metal ions. Among all
the tested non-redox metal salts, Mg(OTf)2 displayed the best
enhancement for eugenol isomerization with high selectivity. On
the other hand, the addition of 6 equiv. of monovalent NaOTf
provided only 35.8 % conversion with 34.0 % yield, including
11.6 % cis-isoeugenol and 22.4 % trans-isoeugenol, and the
promotional effect was much lower than other triflate salts of
divalent or trivalent metals. These data clearly revealed that the
synergistic effect was not originated from the influence of OTf-
anion because the concentration of OTf- in 6 equiv. of NaOTf
Cis-
6.0
Trans-
11.8
22.4
49.9
36.3
31.1
92.4
61.2
13.4
59.7
64.1
62.4
13.1
92.3
76.9
67.2
6.8
1
-
18.7
35.8
77.4
57.7
41.8
99.9
84.7
23.0
82.5
86.3
85.9
19.4
99.8
90.8
86.7
9.3
2a
3
NaOTf
11.6
24.7
19.7
7.6
Ca(OTf)2
Ba(OTf)2
Zn(OTf)2
Mg(OTf)2
Sc(OTf)3
Al(OTf)3
4
5
6
6.4
7
19.9
8.0
8
9
In(OTf)3
20.2
19.0
19.9
5.6
10
11
12
13
14
15
16b
Yb(OTf)3
Y(OTf)3
Mg(CH3COO)2•4H2O
MgCl2•6H2O
Mg(NO3)2•6H2O
MgSO4
was identical to
2 equiv. of trivalent metals. To further
7.1
demonstrate the promotional effect, different magnesium salts
were also tested. MgCl2, Mg(NO3)2 and MgSO4 induced similar
improvement for isomerization with the case of Mg(OTf)2. For
example, introducing MgCl2 to RuH2(CO)(PPh3)3 catalyst led to
99.8 % conversion and 98.4 % yield (7.1 % cis-isoeugenol and
13.1
17.1
2.3
Mg(OTf)2
91.3
% trans-isoeugenol, Table 1, entry 13). However,
isomerization performance was not much influenced with the
addition of Mg(CH3COO)2, which can be explained by the poor
solubility of Mg(CH3COO)2 in the ethanol solvent. The control
experiments with non-redox metals alone as the catalysts were
also performed under identical conditions. Only trace conversion
was demonstrated and no isomerization product was detected in
all cases. Interestingly, Ru(CO)3(PPh3)2 was also synthesized
and conducted as the catalyst (Table S3). However, no
synergetic effect could be found between Ru(CO)3(PPh3)2
catalyst and Mg(OTf)2, providing only 9.3 % conversion and
9.1 % yield of isoeugenol (Table 1, entry 16). This phenomenon
was suggestive to the mechanism because the manipulation on
catalytic properties always originated from the interaction of non-
Conditions: solvent C2H5OH 2 mL, eugenol 200 mM, RuH2(CO)(PPh3)3 1 mM,
non-redox metal salt 2 mM, 30 min, 80 ℃, under air; a:NaOTf 6 mM; b:
Ru(CO)3(PPh3)2 1 mM, Mg(OTf)2 2 mM, 60 min.
The influence of solvent (Table S1) and temperature (Table
S2) on the catalytic isomerization provided further clue to the
synergetic effect between Ru-H complex and non-redox metals.
Trace conversion was observed but no isomerization product
was detected in CH3CN and DMSO, which was probably due to
6a, 19
the co-coordinating properties of solvent molecules.3a,
16.3 % conversion was observed in the case of 1,4-dioxane and
N,N-dimethylethanamide, while alcoholic solvent such as
methanol, ethanol, isopropanol and tert-butanol exhibited better
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performance. The plausible explanation is that the alcohols are
hydrogen donor solvent and the beneficial effect can be
attributed to their ability to stabilize the catalytically active
ruthenium-hydride species.12,20 In all the alcoholic solvents,
ethanol is the most effective solvent with 99.9 % conversion and
98.8 % yield including 6.4 % yield of cis-isoeugenol and 92.4 %
yield of trans-isoeugenol (Table S1). Noticeably, alcoholic
solvents show beneficial effect for the isomerization reaction but
are apparently not essential in the catalytic system. 99.7 %
conversion with total 96.0 % yield of isoeugenol could still be
obtained in the case of CHCl3 as the solvent (Table S1, entry 5).
Meanwhile, employing toluene as solvent could also lead to
good reaction activity in the case of certain chain olefins and
cyclic olefins (Table 2, entry 8-14). RuH2(CO)(PPh3)3/Mg2+
system also demonstrated excellent efficiency under mild
conditions. As showed in Table S2, eugenol could be completely
converted with high configuration selectivity at the reaction
temperature of 80 ℃ in ethanol. In the cases of 1-hexane, 4-
methyl-1-pentene and 1,5-cyclooctadiene, the catalytic system
exhibited good performance when the reaction temperature was
reduced to 50 ℃.
To further explore the interaction between RuH2(CO)(PPh3)3
and non-redox metal salts, isomerization of eugenol by different
ratios of Mg(OTf)2 was conducted and listed in Table S5 and
Figure S3. 97.5 % conversion with 95.3 % yield could be
achieved in the presence of 200 equiv. of substrate within 30
min when only 0.5 equiv. Mg(OTf)2 was employed (Table S5,
entry 3). It was speculated that RuH2(CO)(PPh3)3/Mg2+ system
was so efficient in catalyzing the isomerization that the influence
of RuH2(CO)(PPh3)3/Mg2+ ratio on the performance could not be
distinguished. Thus this comparison was conducted with 1000
equiv. of substrate in 30 min (Table S5, Figure S3). The
continuously sharp acceleration was obtained with the
increasing Mg(OTf)2/RuH2(CO)(PPh3)3 ratio from 0 to 0.5, 1 then
to 2, during which the conversion was increased from 5.6 % to
50.1%, 73.0% then to 92.5 %. Alternatively, the conversion
continuous decreasing, while the yield of trans-isoeugenol kept
increasing continuously, which indicated the configurational
isomerization process form cis-isoeugenol to trans-isoeugenol
by RuH2(CO)(PPh3)3/Mg2+ system. This isomerization may be
attributed to the fact that trans-isoeugenol was a thermodynamic
favored product comparing with cis-isoeugenol. Additionally, the
generation of cis-isoeugenol suggested the detailed pathway of
eugenol isomerization, which will be further explained in the
mechanism section.
100
80
Conv.: Ru(II)+Mg2+
Yield: Ru(II)+Mg2+ E isomer
Yield: Ru(II)+Mg2+ Z isomer
60
Conv.: Ru(II)
40
Yield: Ru(II) Z isomer
Yield: Ru(II) E isomer
20
0
0
20
40
60
80
100
t (time)
Figure 1. Non-redox metal ion accelerated isomerization kinetics by the
ruthenium complex. Conditions: solvent C2H5OH 2 mL, eugenol 1000 mM,
RuH2(CO)(PPh3)3 1 mM, Mg(OTf)2 2 mM, 80℃, under air.
The accelerated double bond migration by adding non-
redox metal ions was investigated in different types of olefins,
including allylbenzene derivatives, chain olefins, cyclic olefins,
O-allyl systems and cis-stilbene, and the results were displayed
in Table 2. The obvious promotion could be observed in all of
the investigated olefins. For example, isomerization of 4-allyl-
1,2-dimethoxybenzene by RuH2(CO)(PPh3)3 alone gave 35.7 %
conversion with 34.1 % yield of isomers while the addition of
Mg2+ exhibited 99.4 % conversion with 5.4 % yield of cis-isomer
and 93.6 % yield of trans-isomer in 800 equiv. of substrate within
only 30 min under air (Table 2, entry 3). 96.7 % conversion with
95.4 % yield of 4-methyl-2-pentene was obtained when the
control experiment with RuH2(CO)(PPh3)3 alone as catalyst
offered only 6.7 % conversion (Table 2, entry 10). Significantly,
when 4-methyl-1-pentene was tested as substrate, the double
bond isomerization occurred over only one position leading to a
product of 4-metahyl-2-pentene as demonstrated in 1H NMR
(Figure S8), whereas further isomerization was resisted. Same
phenomenon could also be observed in the case of 5-vinyl-2-
norbornene (Figure S17 and Table 2, entry 13). This trend was
attributed to the steric hindrance with substituents close to the
double bond that affected the reactivity and stereoselectivity.5
The promotional isomerization strategy was also successfully
applied to cyclic olefins such as 1,5-cyclooctadiene and O-allyl
system such as allyl phenyl ether. In particular, cis-stilbene was
selected as model substrate for the purpose of configurational
isomerization and mechanism information. Dramatically
decreased
to
84.2
%
when
the
ratio
of
Mg(OTf)2/RuH2(CO)(PPh3)3 was further increased to 4. The
results have clearly revealed that 2 equiv. of non-redox metal ion
(relative to Ru catalyst) has already demonstrated a saturated
promotional effect for olefin isomerization. In the isomerization
reaction, the role of Mg2+ was speculated to interact with the
RuH2(CO)(PPh3)3 and 2 equiv. of Mg2+ was considered as a
saturated amount to accomplish the process, thus extra
amounts of Mg(OTf)2 was not essential for the Ru catalyst, even
slightly disturbed the active ruthenium species.
The detailed catalytic process by RuH2(CO)(PPh3)3 in the
presence/absence of non-redox metals was further disclosed by
the catalytic kinetics (Figure 1). Catalytic isomerization of
eugenol was obviously sluggish in the absence of non-redox
metals, and was sharply accelerated by introducing 2 equiv. of
Mg2+. 410 turnover numbers could be achieved in the initial 5
min. Conversion could be reached beyond 90% within 30 min
and the 1000 equiv. of substrate was completely isomerized in
100 min, providing 6.1 % cis-isomer and 93.4 % trans-isomer.
More importantly, from Figure 1, one may see that the yield of
cis-isoeugenol increased sharply in the initial 20 min followed by
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Table 2. Substrate scope of olefin isomerization by RuH2(CO)(PPh3)3 and non-redox metal ions.
Yield (%)
Entry
1a
Substrate
conditions
product
Conversion (%)
99.9 (18.7)
Cis-
Trans-
200 mM, 30 min
6.4 (6.0)
92.4 (11.8)
2a
3a
1000 mM, 100 min
800 mM, 30 min
99.9 (10.2)
99.4 (35.7)
6.1 (4.2)
93.4 (5.8)
5.4 (12.3)
93.6 (21.8)
4a
5a
400 mM, 30 min
200 mM, 40 min
95.6 (27.6)
96.3 (45.2)
9.4 (10.6)
9.2 (10.6)
85.7 (15.3)
85.7 (32.8)
6a
7a
8b
400 mM, 20 min
1000 mM, 30 min
400 mM, 3 h
94.1 (15.2)
92.6 (42.3)
94.2 (15.4)
93.7 (14.8)
91.7 (38.1)
93.5 (15.1)
isomers
isomers
9c
200 mM, 90 min
200 mM, 3 h
96.7 (9.8)
96.7 (6.7)
95.6 (9.0)
95.4 (4.2)
isomers
10c
11c
400 mM, 30 min
91.6 (8.2)
74.2d (1.7)
16.5e (3.4)
isomers
12b
13b
200 mM, 25 min
200 mM, 5 h
98.6 (12.4)
89.6 (2.4)
97.5 (11.6)
88.1 (2.1)
14a
200 mM, 2 h
90.7 (15.8)
89.4 (15.2)
Conditions: solvent C2H5OH 2 mL (entry 1-7) or toluene 2 mL (entry 8-14), RuH2(CO)(PPh3)3 1 mM, Mg(OTf)2 2 mM (entry 1-7) or Al(OTf)3 2 mM (entry 8-14),
under air. a: 80℃; b: 60℃; c: 50℃; d: yield of 1,3-cyclooctadiene; e: yield of 1,4-cyclooctadiene. The data in parentheses represent control experiments with
RuH2(CO)(PPh3)3 alone as catalyst.
accelerated effect has also been observed with 89.4 % yield of
trans-stilbene in the presence of non-redox metal ions, which
further implied that the metal hydride addition-elimination
mechanism(vide infra) was proceeded in RuH2(CO)(PPh3)3/Mg2+
system.
accelerated efficiency but also open flask procedure, which
placed RuH2(CO)(PPh3)3/Mg2+ on the top of list among various
ruthenium based homogenous catalysts. For instance, the
isomerization reaction was evaluated under different
atmosphere (Table S6). A conversion of 28.5 % with 27.1% yield
was achieved by using RuH2(CO)(PPh3)3 alone as catalyst
under the inert atmosphere such as Ar. Once again this result
revealed the poor active of RuH2(CO)(PPh3)3, which was not
originated from the influence of air. Isomerization with
RuH2(CO)(PPh3)3/Mg2+ demonstrated 99.9 % conversion and
99.0 % yield of isoeugenol (7.7 % cis-isoeugenol and 91.3 %
Open flask synthesis and gram scale tests
The above data clearly disclose the promotional effect on the
performance of Ru-H catalysts by introducing simple non-redox
metal ions. Comparing with previously reported systems,
significant advantages of this strategy were not only its
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10.1002/cctc.201700687
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trans-isoeugenol) under the protection of Ar, and this
performance was identical to the case of open flask procedure.
This advantage of open flask reaction in RuH2(CO)(PPh3)3/Mg2+
system was a significant advantage comparing with other
ruthenium catalysts for olefin isomerization, in which air-free
conditions were always required (Table 3). Our mechanism
study further revealed that the improved tolerance to air may rise
from the interaction between Mg2+ and ruthenium center.
93.0 % trans-isoeugenol when the reaction time was extended
to
3 h (Table S4, entry 10). Furthermore, 4-allyl-1,2-
dimethoxybenzene (perfume industry) and 1-octene (oil
feedstock) were chosen as model substrates of important
resources. TON and TOF for the isomerization of 4-allyl-1,2-
dimethoxybenzene reached up to 17208 and 124 min-1 under air,
respectively (Table 4).
Table 4. Performance of RuH2(CO)(PPh3)3 in the presence of non-redox metal
ions with model compounds.
Table 3. Olefins isomerization reaction catalyzed by different ruthenium
complexes.
Entry
1
Substrate
TONa
4044
TOF (min-1)b
Catalyst (mol%)
Conditions
Ref.
21
RuCl2(PPh3)3 (0.2)
130 ℃, 45 h, N2
98
THF, 80 ℃, 5.5 h, Ar and
Schlenk techniques
[RuCp(CH3CN)2(PPh3)]+ (0.6)
22
2
3
17208
3198
124
107
[RuClH(CO)(PPh3)3] (1.2)
80 ℃, 3 h, Ar
100 ℃, 2 h, Ar
23
3b
[RuCl2(cod)]x(2)+PPh3 + LiAlH4
Conditions: C2H5OH 2 mL, RuH2(CO)(PPh3)3 1 mM, Mg(OTf)2 2 mM, substrate
(more than 6000 mM for entry 1 and 3.), 80℃, under air. a: 10 h; b:the initial
10 minutes.
Grubbs catalyst (5)
50℃, 3 h, silyl enol ether, Ar
24
25
RT or 70-130 ℃ 16 h, N2
and glove box, Schlenk
techniques
In particular, the isomerization of eugenol was also
performed in a scale of 3 g with 0.03 mol % RuH2(CO)(PPh3)3
and 0.06 mol % Mg(OTf)2, accompanying a yield of 98.6 % with
an trans/cis isomer ratio of 94:6 under air (Table S7). More
importantly, the commercially available catalyst and cheap non-
redox metal ion loading could be decreased to less than 0.01
mol % and 0.02 mol %, respectively. Under the same conditions,
a conversion of 99.9 % with 98.9 % yield of isomers were
achieved (5.6 % cis-isomer and 93.3 % trans-isomer) in the case
of 4.2 g (12000 equiv. of substrate with respect to Ru catalyst)
4-allyl-1,2-dimethoxybenzene (Table S8). Previous studies have
displayed the ongoing commercial process to perform with
H2SO4 and KOH. However, longer reaction times (12 h) and
higher temperatures (ca. 200 ℃) were required, and lower yields
(56 %) of isoeugenol with quite moderate selectivity toward the
trans-isomer (trans : cis = 82:18) was obtained.32 In some cases,
the existence of cis-isoeugenol will cause an unpleasant taste
and even a poisonous character in food industries, so the
content of cis-isoeugenol should be less than 1%.14i Manifestly,
this bimetallic catalyst system through introducing simple non-
redox metal ions to RuH2(CO)(PPh3)3 showed more attractive
performance than aforementioned ongoing commercial process,
not only because of the high ratio of trans/cis isomer
components, but also due to its simplicity in conditions.
[Ru(CO)H(PNN)] (2.5)
Grubbs
second-generation
60 ℃, 12 h
10b,7g
26
catalyst (10)
60-100 ℃ ,12 h, Ar and
Schlenk techniques
[(η6-p-cymene)RuCl(L)] (0.1)
[RuCl2(η6-C6H5OCH2CH2OH)(L)]
(1)
80 ℃, 5 min-7 h, N2
27
5
[RuCl(PPh3)2(3-phenylindenyl)]
(0.25)
110 ℃ , 16 h, glove box
techniques
RuHCl(PPh3)3(s) (<0.5)
RuCl2(PPh3)3 (0.08)
120-180 ℃, 30 min, N2
28
29
85 ℃, 3 h, alcoholic solvent
80 ℃ ,
5 h, Schlenk and
[RuHCl(PPh3)3] (1)
7f
glove box techniques
60-100 ℃ , 12 h, Ar and
Schlenk techniques
Ru(PPh3)2(CO)H(Ln) (0.1)
Ru(CO)3(PPh3)2 (1)
30
31
120 ℃, 3 h, N2 and He
50-80 ℃, 30 min,
open flask reaction
This
work
RuH2(CO)(PPh3)3 (0.01-0.5)
Additionally, we have also attempted to extend this novel
strategy to other metal complexes. A common osmium hydride
complex of OsH2(CO)(PPh3)3 was selected as the catalyst. As
disclosed in Table S9, the catalytic efficiency of
OsH2(CO)(PPh3)3 alone was very sluggish, by which only 18.9 %
conversion and 17.7 % yield of isomers were obtained (Table S9,
entry 2). The addition of 2 equiv. of Sc(OTf)3 as additive to
OsH2(CO)(PPh3)3 can obviously accelerate the isomerization of
The
performance
of
non-redox-metal-promoted
RuH2(CO)(PPh3)3 was also evaluated by its catalytic turnover
number (TON) and turnover frequency (TOF). As shown in
Table S4, 600 equiv. of eugenol (relative to Ru catalyst) could
be completely converted, while in the case of 1000 equiv.
substrate, 92.5 % conversion with 87.8 % could be achieved
within 30 min. When the concentration of eugenol was further
increased to 1600 equiv., conversion still reached 100 % with
4-allyl-1,2-dimethoxybenzene under air, accompanying
a
conversion of 99.5 % and a yield of 98.5 % (3.8 % cis-isomer
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10.1002/cctc.201700687
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FULL PAPER
and 94.7 % trans-isomer). The results clearly illustrated that the
synergetic catalyst strategy with simple non-redox metal ions
can be feasible in the cases of different metal catalysts for
various olefin isomerization reactions.
promotional activity was still observed in the presence of Mg2+
as non-redox metal ion with 98.2 % conversion and 97.7 % yield
(6.1 % cis-isomer and 91.6 % trans-isomer), while only 61.6 %
conversion with 60.6 % yield (10.2 % cis-isomer and 50.4 %
trans-isomer) was obtained in the addition of HOTf. The result
with Mg(OTf)2 was obviously much better than the case of
proton acid. Moreover, the control experiments by injecting
certain amount of water were also conducted in the presence of
non-redox metal salts. Both the conversion of 4-allyl-1,2-
dimethoxybenzene and yield of isomers were visibly decreased
with increase of the amount of extra water, which also excluded
the possibility that the synergistic activity was originated from the
hydrolysis product of non-redox metal salts.
The evidence to display the interaction between
RuH2(CO)(PPh3)3 and non-redox metal ions was further
demonstrated by 31P NMR. As shown in Figure 2, 31P NMR
spectrum of RuH2(CO)(PPh3)3 was identical to the reported
value with the PC signal at 57.5 ppm and PD signal at 45.4
ppm.17 A weak signal located at 24.7 ppm could be observed
after the RuH2(CO)(PPh3)3 was stirred at 70 ℃ for 5 min (Figure
2a), which was possible due to the dissociation of PPh3 ligand
and further oxidation to O=PPh3. The addition of 2 equiv. of
Mg(OTf)2 to the RuH2(CO)(PPh3)3 catalyst led to the generation
of two distinct signals at 24.7 and -5.2 ppm identified as O=PPh3
and free PPh3 (Figure 2c) in 31P NMR spectrum, whereas the
original signal of PC and PD in RuH2(CO)(PPh3)3 still existed but
exhibited weaker intensity. However, only moderate peaks were
detected in the case of 4 equiv. of NaOTf under identical
Mechanism studies
Generally two established pathways for transition metal-
catalyzed olefin isomerization have been proposed: 1) the π-allyl
mechanism and 2) the metal hydride addition-elimination
31,
mechanism (Scheme 1)2e,
33. In this report, metal hydride
addition-elimination was suggested as the dominant pathway
based on following arguments. 1) the isomerization was
catalyzed by RuH2(CO)(PPh3)3/Mg2+, but in the case of
Ru(CO)3(PPh3)2 the reaction was infeasible (Table S3); 2) cis-
stilbene could also be isomerized (Table 2 entry 14) in which no
allyl hydrogen beside C=C bond could be migrated ; 3) alcohols
as hydrogen donor solvent were beneficial (Table S1) due to
their ability to stabilize the catalytically active ruthenium-hydride
species;12,20 4) 1H NMR spectra displayed the disappear of Ru-H
signal immediately after the addition of alkene (vide infra). In
metal hydride addition-elimination mechanism, free alkene
coordinates to ruthenium hydride species, then insertion into the
metal-hydride bond yields a secondary metal-alkyl, subsequent
β-hydride elimination yields the isomerized product and
regenerates the initial ruthenium hydride catalyst (Scheme
1).2a,3a,4,5,7c,8,11,23,28,34 Thus, in this process the cis-isomer and
trans-isomer should be both generated. As evidenced by the
kinetic study in Figure 1, both cis-isomer and trans-isomer were
generated, and the isomerization from cis-isomer to trans-isomer
conditions
(Figure
2b).
Considering
the
fact
that
RuH2(CO)(PPh3)3 itself also contained very small amount of
O=PPh3 and free PPh3 (Figure 2a), the interaction between
NaOTf and RuH2(CO)(PPh3)3 was negligible. Above data clearly
revealed that the presence of non-redox metals would induce
the dissociation of PPh3 ligand from RuH2(CO)(PPh3)3 catalyst,
and certain amount of dissociated PPh3 ligand could be further
oxidized to O=PPh3. This process was further evidenced by GC-
MS analysis as disclosed in Figure S10, S15 and S16.
could be conducted because trans-isoeugenol was
a
thermodynamic favored product comparing with cis-isoeugenol.
To investigate the origin of the accelerating effect and reaction
pathway of catalytic isomerization by RuH2(CO)(PPh3)3 plus
non-redox
metal
ions,
additional
experiments
and
characterizations of FT-IR, 1H NMR and 31P NMR were
conducted.
Scheme 1. Generally accepted mechanisms for the metal-catalyzed
isomerization of olefins.
Firstly, Crochet and co-workers reported that pH of solution
can influence the isomerization rate by the addition of H2SO4 in
the aqueous media.27 There is one possible speculation that the
promotional isomerization was from the hydrolysis reaction of
trifluoromethanesulfonate salts with trace amount of water to
form HOTf, thus induced the synergetic effect. To exclude the
influence of proton acid, isomerization of 4-allyl-1,2-
dimethoxybenzene was conducted in the presence of HOTf or
Mg(OTf)2 with Schlenk system and dehydrated solvent in the
supplementary experiments. As displayed in Table S10,
♣
♥
★
▲
PC
PD
Free PPh
O=PPh3
3
Figure 2. The 31P NMR spectra of RuH2(CO)(PPh3)3 in the absence/presence
of non-redox metal ions. Conditions: toluene-d8, RuH2(CO)(PPh3)3 1 mM,
Mg(OTf)2 2 mM, NaOTf 4 mM, triethyl phosphate as internal standard, 70 ℃, 5
min, under air.
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10.1002/cctc.201700687
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One may concern how this dissociation of PPh3 ligand
would benefit the isomerization performance. Thus, a series of
kinetic studies on the isomerization of eugenol by
RuH2(CO)(PPh3)3/Mg2+ system were conducted through the
externally addition of PPh3. The concentration of extra PPh3 had
a negative influence on the rate of the isomerization reaction
(Table S11) and a linear dependence between the reciprocal of
the rate constant and the concentration of added PPh3 was
obtained (Figure 3), which was in good agreement with other
reports.35 Above results from 31P NMR, GC-MS and kinetic
studies clearly indicated that the dissociation of PPh3 ligand from
RuH2(CO)(PPh3)3 was an important step in the isomerization
similarly to other previous studies.7f,11,27,34a,36 Dissociation of
PPh3 formed unoccupied coordination site for alkene, thus
benefitted the catalytic isomerization.
RuH2(CO)(PPh3)3 was also consistent with its identical signals in
both 31P and 1H NMR (vide infra).
The extra signal at 1973 cm-1 was more distinct with the
increase Mg2+/RuH2(CO)(PPh3)3 ratio from 0 to 2 (Figure 4a).
FT-IR spectra of RuH2(CO)(PPh3)3 with different non-redox
metal salts were also investigated (Figure 4b). These changes in
FT-IR spectra were Lewis acidity strength dependent on added
non-redox metal ions and were also consistent with the trend of
above isomerization reaction data (Table 1), namely, more
obvious changes were induced and higher promotional effect on
olefin isomerization was observed in the case of metal ions with
higher positive charge, such as Mg2+, Sc3+ or Yb3+. Interestingly,
the wavenumber of ν(C=O) after the addition of each non-redox
metals of Mg2+, Sc3+ or Yb3+ was obviously different, indicating
each non-redox metals may alter the frequency of ν(C=O) in
varying degrees, which was in good agreement with the fact that
the performance of RuH2(CO)(PPh3)3 with different non-redox
metals varied from each other. To sum up, these changes in FT-
IR further suggested that non-redox metals as Lewis acids may
80
70
60
50
40
bind
and
influence
the
coordination
structure
of
RuH2(CO)(PPh3)3 through the linkage of OC-Ru-H2---Mg2+ or H2-
Ru-CO---Mg2+.
Ru(II):Mg2+=1:0
(a)
Ru(II):Mg2+=1:0.5
1943
1937
0
2
4
6
8
10
12
14
16
1973
[PPh3]add / mM
Ru(II):Mg2+=1:1
Ru(II):Mg2+=1:2
Figure 3. Effect of concentration of externally added PPh3 on the rate of
catalytic isomerization of eugenol. Conditions: C2H5OH 2 mL, eugenol 1000
mM, RuH2(CO)(PPh3)3 1 mM, PPh3 0-15 mM, Mg(OTf)2 2 mM, 80 ℃, under air,
15 min.
1973
1973
1943
1943
2100
2050
2000
1950
1900
1850
Wavenumber / cm-1
Mg2+ influenced of catalytic property of RuH2(CO)(PPh3)3
through coordinative interaction onto Ru species and formed
catalytically active species. However, the binding site between
Ru-H center and non-redox metals was not clear yet, and the
difference between various non-redox metals in regulating the
performance of RuH2(CO)(PPh3)3 remained elusive. In Figure 4,
FT-IR spectra of RuH2(CO)(PPh3)3 in the absence/presence of
different non-redox metals were recorded. The infrared spectrum
showed a very strong band at 1943 cm-1. In previous reports, the
remarkable and characteristic IR absorption at 1940 cm-1 was
assigned to ν(C=O) and weak bands at 1960 cm-1 and 1900 cm-1
was attributed to ν(Ru-H), and it was usually frustrated to
observe the signals of Ru-H in infrared spectrum due to its
weaker band and being obscured by the strong absorption of
C=O bond.17b,37 With the addition of Mg(OTf)2 (enlarged spectra
in Figure 4 and full-scale spectra in Figure S18), one obvious
shoulder band around 1973 cm-1 could be obtained. The
formation of new signals at 1973 cm-1 was possibly from the
active catalytic species generated by the dissociation of PPh3
and interaction with Mg2+, while the original signal around 1937
cm-1 suggested that part of RuH2(CO)(PPh3)3 complex remained
undissociated. The existence of certain amount of
(b)
Ru(II)
Ru(II)+Na+
1943
1975
Ru(II)+Mg2+
Ru(II)+Al3+
1936
1943
1973
1982
Ru(II)+Sc3+
Ru(II)+Yb3+
1938
1932
1973
1971
1934
2100
2050
2000
1950
1900
1850
Wavenumber / cm-1
Figure 4. FT-IR spectra of RuH2(CO)(PPh3)3 with (a) different concentrations
of Mg(OTf)2 and (b) different non-redox metal salts. Conditions: solvent CHCl3
5 mL, RuH2(CO)(PPh3)3 2 mM, non-redox metal salt 4 mM, 60℃, 10 min,
under air, solvent was remove by vacuum evaporation.
In previous reports, the [(π-C5H5)Ru(CO)2]2-AlR3 system
contained two carbonyl groups, and one of them can bind to
AlR3.38a This binding of AlR3 led to a 30 cm-1 increase in
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10.1002/cctc.201700687
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frequency for the free terminal Ru-CO stretching and a decrease
of 115 cm-1 for the bridging carbonyl in Ru-CO-AlR3. The same
trend has also been found in other transition metal complexes,
such as Fe, Mo, Re and Mn.38b-e Similarly, in our case, if the
addition of the electron acceptor (Al3+) was directly coordinated
to the oxygen atom of CO, it would increase the Ru-CO back-π-
bonding, imply an increase in electron density on the bridging
carbonyl ligand, and then cause the decrease in frequency.
Alternatively, if this binding of electron acceptor was through Ru-
H, it would decrease the electron density on the terminal
carbonyl ligand and then cause the increase in frequency. Thus,
it was speculated that the non-redox metal ions interacted with
ruthenium species through the linkage of OC-Ru-H2---Mg2+,
which led to the increased wavenumbers of carbonyl group,
rather than H2-Ru-CO---Mg2+. The plausible form of OC-Ru-H2---
Mg2+ was further evidenced by the 1H NMR spectra.
hydrogen atom should be decreased after the binding of Mg2+.
Indeed, after the addition of Mg(OTf)2 or Ba(OTf)2, this additional
resonance was found at -4.46 ppm, a lower field compared with
the hydride resonance from residual RuH2(CO)(PPh3)3 complex
at -6.9 ppm and -8.8 ppm. Noticeably, these two hydrides
around Ru center were equivalent in chemical environment,
giving us one more evidence supporting the proposed structure
of OC-Ru-H2---Mg2+. Additionally, this Ru-H signal at -4.46 ppm
immediately vanished with the addition of eugenol, which clearly
indicated that the new species (with Ru-H at - 4.46 ppm) was
responsible for the isomerization reaction through metal hydride
addition-elimination mechanism. This phenomenon once again
demonstrated the catalytic active OC-Ru-H2---Mg2+ species was
remarkably active in isomerization, which in turn improved the
stability of the catalytic system in open flask operation because
the chance of oxygen atom to attack reactive ruthenium center
was significantly decreased.
As shown in Figure 5, RuH2(CO)(PPh3)3 alone gave two
characterized resonances with the same integral area at -8.8
ppm for HB and -6.9 ppm for HA (Figure 5a).17 No additional
signal was obtained with the addition of NaOTf (Figure 5b).
However, a new Ru-H signal located at -4.46 ppm was found in
presence of non-redox metals (Figure 5c and 5d, detailed in
Figure S19), which clearly demonstrated the change of the
37a, 39
coordination structure around ruthenium center.30,
Meanwhile, resonances at -8.8 ppm and -6.9 ppm still existed,
suggesting that certain amount of RuH2(CO)(PPh3)3 complex
remained undissociated, and was highly consistent with the
results in FT-IR and 31P NMR. Two additional doubles at -2.5
and -3.3 ppm were obtained, which were very imperceptible and
possibly from the trace of undefined Ru-H species generated by
the decomposition of RuH2(CO)(PPh3)3 in the presence of
Mg(OTf)2 or Ba(OTf)2.
(a) RuH2(CO)(PPh3)3
(b) RuH2(CO)(PPh3)3+NaOTf
Scheme 2. Reaction pathways of isomerization accelerated by the non-redox
metal ions.
(c) RuH2(CO)(PPh3)3+Ba(OTf)2
(d) RuH2(CO)(PPh3)3+Mg(OTf)2
Taken
characterizations,
together
the
reaction
performance
and
HB
HA
a
possible reaction pathway and the
interaction of RuH2(CO)(PPh3)3 with Mg(OTf)2 was proposed as
displayed in Scheme 2. RuH2(CO)(PPh3)3 was a stable complex
under air, with saturated six coordination atoms in its first
coordination sphere. The bloated PPh3 ligands caused the steric
hindrance for free alkene to coordinate to metal hydride, and
poor activity was demonstrated in the olefin isomerization by
RuH2(CO)(PPh3)3 itself. The addition of non-redox metal ions
such as Mg2+ formed a magnesium-bridged species like OC-Ru-
H2---Mg2+, in which these two hydrides around Ru center were
equivalent in chemical environment (Scheme 2). The role of
Mg2+ mainly embodied in the two key processes: 1) the twisting
of the first co-ordination sphere of ruthenium center. This
twisting, together with steric hinder from OTf- anions, induced
the dissociation of PPh3 ligand and the formation of unoccupied
coordination site for alkene; 2) the interaction with Ru center
(e) RuH2(CO)(PPh3)3+Mg(OTf)2+eugenol
Figure 5. 1H NMR spectra of RuH2(CO)(PPh3)3 with different non-redox metal
salts. Conditions: chloroform-d, RuH2(CO)(PPh3)3 2 mM, Mg(OTf)2 4 mM,
NaOTf 8 mM, 60 ℃, 10 min, under air.
Previously we speculated the catalytic active Ru-H species
as OC-Ru-H2---Mg2+ due to the change of FT-IR spectra.
Theoretically, hydrogen atoms in OC-Ru-H2---Mg2+ should locate
at
a
lower field in 1H NMR comparing with original
RuH2(CO)(PPh3)3 complex because the electron density of
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10.1002/cctc.201700687
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through hydride, because of which the strain associated with Ru-
H bond could be relieved by invoking a magnesium-bridged
species that benefitted the isomerization of alkene.14f,14i,40 This
acceleration was similarly to the case of redox isomerization of
propargyl alcohols, in which the interaction of In3+ to Ru species
through Ru-Cl---In3+ also benefitted the isomerization process.40
Compared with RuH2(CO)(PPh3)3, significantly higher activity of
OC-Ru-H2---Mg2+ species guaranteed the whole isomerization
feasible in open flask system. Complete reaction pathway
through metal hydride addition-elimination mechanism was
Ba(OTf)2 and Al(OTf)3 were purchased from Shanghai DiBai
Chemical
Co.
Triphenylphosphine
and
sodium
hexachloroosmate(IV) dihydrate came from Alfa Aesar.
Common solvents and inorganic magnesium salts were
purchased from Sinopharm Chemical Reagent Co., Ltd. Olefins
and some isomerization products were purchased from either
Aldrich or Alfa Aesar.
The osmium catalyst OsH2(CO)(PPh3)3 and ruthenium complex
Ru(CO)3(PPh3)2 were synthesized according to the literature.16
The ruthenium catalyst RuH2(CO)(PPh3)3 was synthesized
17
shown in Scheme 2. Because trans-isoeugenol was
a
according to the literatures.16,
The detailed procedures for
thermodynamic favored product, the generation of trans-isomer
was attributed to both the position isomerization of substrate and
the configurational isomerization of cis-isomer. In some cases,
steric hindrance with substituents close to the double bond may
affect the reactivity and prevent further isomerization (4-methyl-
catalyst synthesis was exhibited in the supporting information.
1
The H NMR and 31P NMR spectra of RuH2(CO)(PPh3)3 were
shown in Figure S1 and S2, respectively. 1H NMR (400 MHz,
Toluene-d8) δ = -6.87 (Ru-HA, 1H, tdd, JPC-HA = 30.9 Hz, JPD-HA
=
15.2 Hz, JHA-HB = 6.3 Hz), -8.76 (Ru-HB, 1H, dtd, JPD-HB = 74.3 Hz,
1-pentene and 5-vinyl-2-norbornene, Entry 10 and 13 in Table 2). JPC-HB = 28.5 Hz, JHA-HB = 6.4 Hz); 31P NMR (162 MHz, Toluene-
Alternatively, cis-isomer as the major product in the case of allyl
phenyl ether was attributed to the coordination of the ruthenium
to functional group, which was an important factor to Z-E
selectivity.2c, 2d, 3a, 3b
d8) δ = 57.45 (d, J = 18.2, 4.6 Hz), 45.36 (t, J = 18.3 Hz).
Gas chromatography-mass spectrometry (GC-MS) analysis
was performed on an Agilent 7890A/5975C spectrometer. FT-IR
1
spectra were obtained on Bruker VERTEX70. H and 31P NMR
spectra were collected on a Bruker AV-400 using TMS as an
internal reference.
CONCLUSIONS
Crystal structure analysis
RuH2(CO)(PPh3)3 (40 mg) was dissolved in CHCl3 (20 mL) and
the light yellow solution was stirred at room temperature for 10
min. Single crystal of RuH2(CO)(PPh3)3 suitable for X-ray
crystallography were grown by slow vapor diffusion of diethyl
ether into the above solution at 278 K. A colorless prism-shaped
crystal was selected for X-ray structure analysis. Intensity data
for this compound were collected on a Bruker D8 Quest
diffractometer at 172.15 K using graphite-monochromated Mo
In summary, this work demonstrated one general strategy that
the addition of common non-redox metal salts to commercially
available RuH2(CO)(PPh3)3 complex could remarkably promote
the valuable alkene isomerization with high selectivity, while
RuH2(CO)(PPh3)3 alone was very sluggish. This catalytic system
showed excellent tolerance to oxygen and moisture, and was
widely feasible for different types of olefins for open flask gram
scale tests (up to 17208 TON). Furthermore, the strategy could
also be extended to other transition metal catalysts such as
OsH2(CO)(PPh3)3. The remarkable performance was attributed
to the alternation of reaction pathway, in which non-redox metal
ions as Lewis acids could dramatically accelerate the
dissociation of PPh3 ligand and the alkene insertion into the
metal-hydride bond by the formation of magnesium-bridged
species of OC-Ru-H2---Mg2+. This approach may offer new
opportunities to those sluggish metal catalysts in versatile olefin
isomerization processes, and may overcome the shortage of
classic metal hydride catalysts in open flask reactions.
Kα radiation (λ=0.71073Å) with
a ω-scan method. The
centrosymmetric monoclinic space group P21/n was determined
by systematic absences and statistical tests and verified by
subsequent refinement. The structure was solved by direct
methods and refined by full-matrix least-squares methods on F2.
One target molecule was co-crystallized with 1 equiv. of diethyl
ether. The crystal data and structure refinement results of
RuH2(CO)(PPh3)3 were given in Table S12-S16 and the
structure of the six-coordinate complex is shown Figure S20.
General procedure for catalytic reaction
All the reagents were used as purchased without further
treatments. In a typical experiment, 1 mM ruthenium(II) complex,
2 mM non-redox metal salt and 200 mM alkenes (or more
concentration for different alkenes) were added into 2 mL of
solvent in a glass tube. The ruthenium complex and inorganic
salts were completely soluble under the experimental conditions
used. Then the reaction mixture was magnetically stirred at
80 ℃ under air in an oil bath for 30 minutes. After the reaction,
the qualitative analysis was conducted by GC-MS and/or 1H
NMR and the quantitative analysis was performed by GC using
the internal standard method. Chloroform-d or toluene-d8 was
selected as the reaction solvent for qualitative analysis in 1H
NMR. Control experiments using RuH2(CO)(PPh3)3 or non-redox
EXPERIMENTAL SECTION
All chemical reagents were commercially available and used
without
Ruthenium(III)
further
purification
chloride
unless
otherwise
hydrate,
stated.
ytterbium
yttrium
trifluoromethanesulfonate
(Yb(OTf)3)
and
trifluoromethanesulfonate (Y(OTf)3) were purchased from Accela
ChemBio Co., Ltd. Sodium trifluoromethanesulfonate (NaOTf),
magnesium trifluoromethanesulfonate (Mg(OTf)2), indium
trifluoromethanesulfonate
trifluoromethanesulfonate (Sc(OTf)3) came from Aladdin. Other
trifluoromethanesulfonates including Ca(OTf)2, Zn(OTf)2,
(In(OTf)3),
scandium
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10.1002/cctc.201700687
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FULL PAPER
Penczek, J. Rzepa, J. Mrowiec-Białoń, J. Mol. Catal. A: Chem. 2004,
219, 29-40;
metal salts individually as the catalyst were carried out in parallel.
Reactions were performed at least in triplicate, and average data
were used in the results and discussion section.
[4]
[5]
[6]
B. Martín-Matute, K. Bogár, M. Edin, F. B. Kaynak, J.-E. Bäckvall,
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S. Manzini, D. J. Nelson, S. P. Nolan, ChemCatChem 2013, 5, 2848-
2851.
General Procedure for kinetics study
In a typical experiment, 1 mM ruthenium(II) complex, 2 mM non-
redox metal salt and 1000 mM alkenes were added in 2 mL of
solvent in a glass tube. Then the reaction solution was
magnetically stirred at 80 ℃ under air in an oil bath. The
quantitative product analysis was conducted by GC using the
internal standard method at set intervals. Control experiments
using RuH2(CO)(PPh3)3 or non-redox metal salt alone as
catalyst were also carried out in parallel. Reactions were
performed at least in triplicate, and average data were used in
the catalytic kinetics results.
a) D. B. Grotjahn, C. R. Larsen, J. L. Gustafson, R. Nair, A. Sharma, J.
Am. Chem. Soc. 2007, 129, 9592-9593; b) C. R. Larsen, D. B. Grotjahn,
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a) T. J. Donohoe, T. J. C. O’Riordan, C. Rosa, Angew. Chem. Int. Ed.
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General Procedure for FT-IR Study
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In a typical experiment, 2 mM RuH2(CO)(PPh3)3, 4 mM non-
redox metal salt were added in 5 mL of chloroform in a glass
tube. Then the mixture solution was magnetically stirred at 60 ℃
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was dried in vacuum for 10 minutes. Then the solid sample was
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Acknowledgements
This study was supported by the National Natural Science
Foundation of China (No. 21671072 and 21573082) and Chutian
Scholar Foundation from Hubei province. The GC-MS analysis
was performed in the Analytical and Testing Center of Huazhong
University of Science and Technology.
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Keywords: Ruthenium hydride complex • isomerization •
unsaturated compound • non-redox metal ions • open flask
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Simple non-redox metal salts can
dramatically promote olefin
isomerization by commercially
available metal hydrid complexes
in open flask system.
Zhanao Lv, Zhuqi Chen,* Yue Hu,
Wenrui Zheng, Haibin Wang,
Wanling Mo, Guochuan Yin*
Page No. – Page No.
A General Strategy for Open Flask
Alkene Isomerization by
Ruthenium Hydride Complexes
with Non-Redox Metal Salts
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