Synthesis and catalytic study of ruthenium carbene catalyst containing a Zn-porphyrin ligand

Article abstract of DOI:10.1002/cjoc.201500614

A ruthenium carbene complex containing a Zn-porphyrin ligand has been developed. The complex was characterized by ¹H NMR, IR, HRMS and elemental analysis. The catalytic activity of the ruthenium carbene complex for olefin metathesis reactions w

Full text of DOI:10.1002/cjoc.201500614

NOTE
DOI: 10.1002/cjoc.201500614
Synthesis and Catalytic Study of Ruthenium Carbene Catalyst
Containing a Zn-Porphyrin Ligand
Ying Xu, Huizhu Zhang, Xinyuan Wang, and Guiyan Liu*
Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of
Inorganic-Organic Hybrid Functional Material Chemistry (Tianjin Normal University), Ministry
of Education; College of Chemistry, Tianjin Normal University, Tianjin, 300387, China
A ruthenium carbene complex containing a Zn-porphyrin ligand has been developed. The complex was charac-
terized by 1H NMR, IR, HRMS and elemental analysis. The catalytic activity of the ruthenium carbene complex for
olefin metathesis reactions was also investigated. The complex exhibited excellent performance for both
ring-closing and cross metathesis reactions at 35 ℃.
Keywords olefin metathesis, ruthenium carbene, catalyst, Zn-porphyrin
Introduction
that possess 22 π electrons and based on Hückel’s rule,
they are highly aromatic. These aromatic properties are
responsible for many of the useful porphyrin applica-
tions, particularly in the field of medicine.[7,8] Bulky
porphyrins also have excellent stability and can effec-
tively stabilize Ru catalysts.[9] So, in this work the effect
of using a porphyrin in the isopropoxystyrene ligand
was investigated. A ruthenium carbene complex con-
taining a Zn porphyrin ligand was synthesized, charac-
terized and investigated as a catalyst for ring-closing
and cross metathesis reactions.
Olefin metathesis is one of the most flexible, efficient
and widely used methods for the construction of car-
bon-carbon double bonds.[1] In 1992, Grubbs and co-
workers reported the first well-defined ruthenium-based
olefin metathesis catalyst (1, Figure 1).[2] Since then, a
series of modified catalysts have been synthesized in-
cluding 2 in which one of the tricyclohexylphosphine
ligands in 1 was replaced with a bulky N-heterocyclic
carbene (NHC) ligand, H2IMes (Figure 1).[3] In addition,
more stable Hoveyda-type complexes 3 and 4 (Figure 1)
have also been developed.[4] Complex 4, which has an
O-chelated NHC ruthenium isopropoxybenzylidene, is
very important because it has excellent stability and
remarkable catalytic activity in olefin metathesis.[5]
Many other complexes based on 4 have also been de-
signed by changing the strength of the Ru－O bond
which has a pronounced effect on the catalytic activ-
ity.[6]
Experimental
Elemental analyses were determined using an Ele-
1
mentar Vario EL cube analyzer. H NMR spectra were
obtained on a 400 or 500 MHz spectrometer and 13C
NMR spectra were obtained on a 500 MHz spectrometer
with CDCl3 as the solvent and TMS as the internal ref-
erence. High-resolution (HR) mass analysis was deter-
mined by Fourier transform ion cyclotron resonance
mass spectrometry (MS).
L
L
Cl
Cl
Ru
L = PCy3
The (E)-4-bromo-1-isopropoxy-2-(prop-1-enyl) ben-
zene was prepared according to a literature method.[10]
Synthesis of compound 5 A flask was charged
with 1.50 g (5.91 mmol) of (E)-4-bromo-1-isopropoxy-
2-(prop-1-enyl)benzene (precursor for 5) and 5 mL of
anhydrous diethyl ether. The solution was cooled to −78
℃, and then 4.27 mL of n-BuLi (1.66 mol/L in hexane,
7.08 mmol, 1.2 equiv.) was slowly added via a syringe.
The reaction mixture was then allowed to slowly warm
to room temperature. After stirring for 1 h at room tem-
perature, the reaction mixture was cooled to −78 ℃. To
Ru
1, 3
2, 4
Cl
Cl
Ph
PCy3
O
L =
MesN
NMes
1, 2
3, 4
Figure 1 Catalysts for olefin metathesis.
It is well known that a change in the isopropoxysty-
rene ligand can result in a change in the activity of the
catalyst. For example, increasing the steric bulk of the
ligand can improve the leaving-group ability of the sty-
rene ligand. Porphyrins are tetrapyrrole macrocycles
*
E-mail: guiyanliu2013@163.com
Received August 26, 2015; accepted November 1, 2015; published online December 15, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500614 or from the author.
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Xu et al.
NOTE
this mixture, 0.43 g of DMF (5.91 mmol, 1 equiv.) was
slowly added via a syringe and the resulting solution
was stirred for 1 h at this temperature. The mixture was
then concentrated under vacuum to obtain a thick oil
residue. Next, 20 mL of dichloromethane was added to
the residue. After being washed four times with water,
the organic layer was dried over magnesium sulfate.
Removal of the solvent by filtration gave an oil residue.
The residue was purified by silica gel chromatography
using pentane/CH2Cl2 (1∶1) as the eluent. The desired
compound 5 was obtained as a yellow oil (0.67 g, 3.28
mmol, 56%). 1H NMR (500 MHz, CDCl3) δ: 9.88 (s, 1H,
COH), 7.949 (s, 1H, CH), 7.70 (d, 3J(H, H)＝11.0 Hz, 1H,
tion by silica gel chromatography using pentane/CH2Cl2
(1∶1) as the eluent. Yield 78.4% (140 mg, 0.18 mmol).
1H NMR (500 MHz, CDCl3) δ: 8.99 (s, 8H, CH), 8.25
(d, 3J(H, H)＝7.5 Hz, 8H, CH), 7.81－7.77 (m, 10H, CH),
7.02 (d, 3J(H, H)＝20.0 Hz, 1H, CH), 6.43－6.37 (m, 1H,
CH), 4.90－4.87 (m, 1H, CH), 1.94 (d, 3J(H, H)＝7.5 Hz,
3H, CH3), 1.62 (d, 3J(H, H)＝7.5 Hz, 6H, CH3); 13C NMR
(125 MHz, CDCl3) δ: 18.9, 22.5, 71.1, 112.1, 121.0,
121.1, 121.2, 121.4, 125.9, 126.1, 126.5, 126.7, 127.5,
131.9, 132.0, 132.1, 132.2, 132.8, 133.7, 134.4, 135.0,
142.8, 142.9, 143.0, 150.2, 150.3, 150.7, 154.3; IR (KBr)
v: 2922, 2850, 1596, 1484, 1439, 1339, 1242, 1122,
1068, 1003, 994, 797, 700 cm−1. Anal. calcd for
C50H38N4OZn: C 77.36, H 4.83, N 7.22; found C 77.41,
H 4.95, N 7.32.
Synthesis of complex 8 Grubbs catalyst 2 (17 mg,
0.020 mmol) and CuCl (2.0 mg, 0.020 mmol) were
added to a Schlenk flask under N2. A solution of 7 (14
mg, 0.018 mmol) in 5 mL dry dichloromethane was
poured into the reaction mixture at room temperature.
The resulting mixture was then stirred for 3 h at 40 ℃.
After being cooled to room temperature, the reaction
mixture was filtered and the clear filtrate was collected.
The solvent from the filtrate was evaporated under vac-
uum to obtain a residue. The desired product 8 was ob-
tained as a green-purple crystalline solid after purifica-
tion by silica gel chromatography using pentane/CH2Cl2
(1∶1) as the eluent. Yield 36.2% (8 mg, 0.0065 mmol).
1H NMR (400 MHz, CDCl3) δ: 16.70 (s, 1H, Ru-H),
9.03 (s, 2H, CH), 8.96－8.94 (m, 6H, CH), 8.33－8.17
(m, 7H, CH), 7.83－7.77 (m, 10H, CH), 7.18－7.16 (m,
1H, CH), 6.99－6.94 (m, 3H, CH), 5.20－5.17 (m, 1H,
CH), 4.19 (s, 4H, CH2), 2.52 (s, 12H, CH3), 1.49 (d,
3J(H, H)＝6.4 Hz, 6H, CH3); IR (KBr) v: 2966, 2925,
2849, 1617, 1482, 1261, 1101, 1002, 796, 700 cm−1;
HRMS calcd for C69H59Cl2N6OZnRu [M−H]+
1153.3085, found 1153.3088. Anal. calcd for
C69H60Cl2N6OZnRu: C 67.56, H 4.93, N 6.85; found C
67.77, H 4.84, N 6.95.
3
CH), 6.95 (d, J(H, H) ＝8.4 Hz, 1H, CH), 6.71 (d,
3J(H, H)＝20 Hz, 1H, CH), 6.38－6.33 (m, 1H, CH),
3
4.71－4.67 (m, 1H, CH), 1.93 (d, J(H, H)＝8.0 Hz, 3H,
3
CH3), 1.41 (d, J(H, H)＝7.5 Hz, 6H, CH3); 13C NMR
(125 MHz, CDCl3) δ: 18.9, 21.9, 70.7, 112.5, 124.8,
127.6, 128.0 128.3, 129.2, 130.2, 159.5, 190.9. Anal.
calcd for C13H16O2: C 76.44, H 7.90; found C 76.77, H
7.85.
Synthesis of compound 6 A flask was charged
with compound 5 (1 g, 4.9 mmol), benzaldehyde (1.56 g,
14.7 mmol) and propionic acid (60 mL). The mixture
was brought to a boil and then pyrrole (1.32 g, 19.6
mmol) was added via a syringe. The mixture was then
stirred for 8 h under reflux and the propionic acid was
removed under vacuum. Next, dichloromethane (50 mL)
was added to the residue, and the organic layer was
separated and washed four times with water. The or-
ganic layers were combined and washed with saturated
salt water, dried over magnesium sulfate, filtered and
concentrated. The desired product 6 was obtained as a
purple solid after purification by silica gel chromatog-
raphy using pentane/CH2Cl2 (1∶1) as the eluent. Yield:
9.1% (0.27 g, 0.33 mmol). 1H NMR (500 MHz, CDCl3)
δ: 8.95 (d, 3J(H, H)＝5.5 Hz, 2H, CH), 8.86（s, 6H, CH),
3
3
8.23 (d, J(H, H)＝8.0 Hz, 8H, CH), 7.77 (d, J(H, H)＝9.0
Hz, 10H, CH), 7.05－7.01 (m, 1H, CH), 6.40 (dd,
3J(H, H)＝8.5 Hz, 19.5 Hz, 1H, CH), 4.93－4.84 (m, 1H,
Kinetics study of 8 and 4 A Schlenk flask was
charged with catalyst (0.02 mmol, 1.0 mol%) and dry
CH2Cl2. The sample was equilibrated at 30 ℃ and then
diethyl diallylmalonate 9 was added via a syringe. Ali-
quots were taken from the reaction mixture at the ap-
propriate time using a syringe and were quenched im-
mediately with 0.1 mol/L PEI in CH2Cl2. The resulting
solution was then subjected to short column chroma-
tography to remove any Ru metal residue using CH2Cl2
as the eluent. The solvent from the collected solution
was evaporated under vacuum. The conversion yield
was determined by comparing the ratio of the integrals
3
CH), 1.94 (d, J(H, H)＝8.0 Hz, 3H, CH3), 1.61 (d,
3J(H, H)＝7.5 Hz, 6H, CH3), −2.72 (s, 2H, NH); 13C NMR
(125 MHz, CDCl3) δ: 19.0, 22.5, 71.0, 112.1, 119.9,
120.1, 120.2, 120.5, 125.9, 126.2, 126.7, 126.8, 127.7,
128.0, 133.0, 133.9, 134.0, 134.4, 134.6, 142.3, 154.5,
167.2; IR (KBr) v: 3402, 2961, 2923, 2852, 1653, 1259,
1107, 800, 701 cm−1. Anal. calcd for C50H40N4O: C
84.24, H 7.66, N 6.86; found C 84.31, H 7.55, N 6.92.
Synthesis of compound 7 A mixture of compound
6 (165 mg, 0.23 mmol) and Zn(OAc)2•2H2O (389 mg,
2.3 mmol) was dissolved in DMF (5 mL) and CH2Cl2
(10 mL). Then the mixture was placed in a 250 mL flask
and refluxed for 20 min under N2. After cooling to room
temperature, the solvent was evaporated under vacuum.
The residue was dissolved in dichloromethane and
washed with water. Then the organic layer was dried
with magnesium sulfate and concentrated. The desired
product 7 was obtained as a purple solid after purifica-
1
of the H NMR methylene proton peaks in the starting
material with those in the product.
Catalytic study of the ruthenium carbene com-
plex 8 The general procedure for the metathesis reac-
tions with the ruthenium carbene complex 8 is as fol-
lows: 0.0005 mmol of catalyst 8 suspended in 1.0 mL of
dry CH2Cl2 was placed in a Schlenk flask, and heated to
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Chin. J. Chem. 2015, 33, 1393—1397

Synthesis and Catalytic Study of Ruthenium Carbene Catalyst Containing a Zn-Porphyrin Ligand
35 ℃ in an oil bath under nitrogen. Then, the desired
amount of substrates was added with stirring. The reac-
Catalyst
( 1 mol%)
CO2Et
CO2Et
CO2Et
tion mixture was stirred for 1－12 h. At the end of the
reaction, the catalysts were separated by silica gel
chromatography using CH2Cl2 as the eluent to remove
CO2Et
CH2Cl2
30 OC, 0.5 h
9
10
any trace amounts of the Ru residue. The yield is re-
ported as isolated yield.
100
80
Results and Discussion
The reaction of compound 5 with benzaldehyde and
60
pyrrole gave compound 6 which contains a porphyrin
(Scheme 1). Next, 6 was treated with Zn(OAc)2•4H2O
4
8
40
in N,N-dimethylformamide to give ligand 7 in good
yield. As described by Kingsbury et al,[4b] the treatment
20
of 7 with 2 in the presence of CuCl in CH2Cl2 at 40 ℃
resulted in the exchange of the styrene group to give 8, a
ruthenium complex, as a green-purple crystalline solid.
0
0
5
10
15
Time/min
20
25
30
The catalytic activity of 8 and the unmodified
Hoveyda second generation catalyst 4 were tested for
the ring-closing metathesis (RCM) reaction using di-
ethyl diallylmalonate 9 as the substrate. The relative
conversion rates are shown in Figure 2. Although 8 has
a lower initiation rate than 4, both catalysts had high
RCM conversions (＞95%) after 30 min.
The catalytic efficiency of complex 8 for different
RCM substrates was then investigated (Table 1). The
ring closure of the N-protected substrates 11, 13, 15 and
21 and the oxygen containing dienes 15, 19 and 23 led
to either five-, six-, or seven-membered rings with di-,
or tri-substituted double bonds, respectively (Table 1,
Entries 1－8). High yields were obtained with a low
Figure 2 Catalytic activities of 8 and 4 in the RCM of diallyl
diethylmalonate.
catalyst loading (0.1－0.5 mol% [Ru]).
The usefulness of catalyst 8 for the cross metathesis
(CM) reaction of 25 and 26 was also examined (Table 2).
Catalyst 8 exhibited a high activity in this reaction with
a loading of 1.5 mol%. The dimerization of olefin 27 to
E-stilbene was achieved which is similar to the results
for 4.[11] The reaction proceeded smoothly for methyl
acrylate 26 and olefins (25a－25d) which had different
substituted groups on the benzene rings including
Scheme 1 Synthesis of ruthenium carbene complex 8 (Mes＝2,4,6-trimethylphenyl)
Chin. J. Chem. 2015, 33, 1393—1397
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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Xu et al.
NOTE
Table 1 Application of catalyst 8 to different RCM substratesa
Product Cat./mol%
Entry
1
Substrate
t/h
Yieldb/%
EtO2C
EtO2C
10
EtO2C CO2Et
0.1
0.1
0.1
0.1
0.1
2.0
98
97
97
98
90
9
Ts
N
TsN
12
2
3
4
5
1.5
1.5
1.5
1.5
11
N
PhCON
COPh
14
13
Ts
N
TsN
15
16
O
O
17
18
O
O
O
O
O
O
O
6
1.0
12
96
O
20
19
N
TsN
Ts
7
8
0.5
0.5
1.0
1.5
97
93
21
22
O
O
24
23
a Reactions were conducted in CH2Cl2 at 35 ℃. b Isolated yield.
Table 2 Application of catalyst 8 to different CM substrates
ucts (27a－27e) were obtained in good to high yields
(60%－98%). Even with an o-substituted substrate 25f,
a moderate yield (27f, 40%) was obtained.
O
O
Catalyst
(1.5 mol%)
CH2Cl2, 35 oC
O
25
+
O
R
O
Conclusions
27
All E isomer
R
12 h
O
In summary, a new Hoveyda-Grubbs type metathesis
catalyst containing a Zn-porphyrin ligand has been pre-
pared. This complex exhibits high activity and selectiv-
ity for a series of RCM and CM reactions with different
substrates.
26
2 equiv.
Entry
Substrate
Product
Yielda/%
1
25a (R＝H)
27a
27b
27c
27d
27e
27f
93
98
96
95
60
40
2
25b (R＝4-OCH3)
25c (R＝4-Br)
25d (R＝4-CH3)
25e (R＝4-NO2)
25f (R＝2-Br)
3
Acknowledgement
4
This work was supported by the National Natural
Science Foundation of China (grant No. 21102102).
5
6
a Isolated yield.
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Chin. J. Chem. 2015, 33, 1393—1397

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