Efficient and Recyclable RuCl3 ? 3H2O Catalyst Modified with Ionic Diphosphine for the Alkoxycarbonylation of Aryl Halides

Article abstract of DOI:10.1002/open.201800266

A series of ionic (mono-/di-)phosphines (L2, L4, and L6) with structural similarity and their corresponding neutral counterparts (L1, L3, and L5) were applied to modulate the catalytic performance of RuCl₃ ? 3H₂O. With the involvement of the ionic diphosphine (L4), in which the two phosphino-fragments were linked by butylene group, RuCl₃ ? 3H₂O with advantages of low cost, robustness, and good availability was found to be an efficient and recyclable catalyst for the alkoxycarbonylation of aryl halides. The L4-based RuCl₃ ? 3H₂O system corresponded to the best conversion of PhI (96 %) along with 99 % selectivity to the target product of methyl benzoate as well as the good generality to alkoxycarbonylation of different aryl halides (ArX, X=I and Br) with alcohols MeOH, EtOH, i-PrOH and n-BuOH. The electronic and steric effects of the applied phosphines, which were analyzed by the ³¹P NMR for ¹J³¹_P-⁷⁷_Se¹J measurement and single-crystal X-ray diffraction, were carefully co-related to the performance RuCl₃ ? 3H₂O catalyst. In addition, the L4-based RuCl₃ ? 3H₂O system could be recycled successfully for at least eight runs in the ionic liquid [Bmim]PF₆.

Full text of DOI:10.1002/open.201800266

Full Papers
DOI: 10.1002/open.201800266
1
2
3
4
5
6
7
8
9
Efficient and Recyclable RuCl3 ·3H2O Catalyst Modified with
Ionic Diphosphine for the Alkoxycarbonylation of Aryl
Halides
Qing Zhou, Lei Liu, Wen-Di Guo, Wen-Yu Liang, Yong Lu, and Ye Liu*[a]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
A series of ionic (mono-/di-)phosphines (L2, L4, and L6) with
structural similarity and their corresponding neutral counter-
parts (L1, L3, and L5) were applied to modulate the catalytic
performance of RuCl3 ·3H2O. With the involvement of the ionic
diphosphine (L4), in which the two phosphino-fragments were
linked by butylene group, RuCl3 ·3H2O with advantages of low
cost, robustness, and good availability was found to be an
efficient and recyclable catalyst for the alkoxycarbonylation of
aryl halides. The L4-based RuCl3 ·3H2O system corresponded to
the best conversion of PhI (96%) along with 99% selectivity to
the target product of methyl benzoate as well as the good
generality to alkoxycarbonylation of different aryl halides (ArX,
X=I and Br) with alcohols MeOH, EtOH, i-PrOH and n-BuOH. The
electronic and steric effects of the applied phosphines, which
1
77
were analyzed by the 31P NMR for J31
1J measurement and
P- Se
single-crystal X-ray diffraction, were carefully co-related to the
performance RuCl3 ·3H2O catalyst. In addition, the L4-based
RuCl3 ·3H2O system could be recycled successfully for at least
eight runs in the ionic liquid [Bmim]PF6.
1. Introduction
edge, it is enlightened that the utilization of RuCl3 ·3H2O as the
viable catalyst absolutely requires a kind of electron-deficient
phosphines to guarantee their co-existence and then the
expected complexation without redox process.
The transition-metal-catalyzed carbonylation of aryl halides in
the presence of nucleophiles is an important methodology for
the preparation of aromatic esters and derivatives.[1,2] Aromatic
esters are significant and versatile compounds, known as
important ingredients in food, beverages, cosmetics, pharma-
ceuticals, agrochemicals, detergents and as intermediates for
the synthesis of polymers.[2–4] So far, palladium complexes are
the most studied catalytic systems for alkoxycarbonylation of
aryl halides.[5] In addition, the other metals such as nickel,[6,7]
cobalt,[8] platinum,[9] rhodium[10] also could be applied as the
viable catalysts with the involvement of suitable ligands.
In comparison, RuCl3 ·3H2O-based complexes have been
rarely used to catalyze alkoxcarbonylation of alkenes/aryl halide.
As for the high valence state RuCl3 ·3H2O-based complexes, the
existence of the common electron-rich phosphines (as the
strong σ-donors) and Ru-ion in +3 valence are incompatible
because of the unavoidable redox reaction between them in
the course of complexation.[11] Hence, even if RuCl3 ·3H2O is
used as the precursor, the real catalyst is still Ru(II)/Ru(0)-based
complex due to the in situ unavoidable reduction of Ru(III)-ion
by the involved electron-rich phosphines. Based on this knowl-
The typical examples of electron-deficient ligands are
phosphinites, phosphonites, phosphites,[12] and fluoroarylphos-
phines,[13] which are in great concerns in the coordinating
chemistry and homogeneous catalysis while providing the
essential difference in coordinating nature as well as in catalytic
performance. However, the PÀ O bonds of phosphinites,
phosphonites, and phosphites are instable and sensitive to
protic cleavage.[14,15] Although fluoroarylphosphines with inert
PÀ C linkages can be considered as alternatives, their structural
diversity is limited.[16] Compared to the functional groups of À F,
À CF3, À NO2, À COR etc., the positively charged quaternary
ammoniums are the most intensive electron-withdrawing
moieties. Hence, the ionic phosphines tailed with the positively
charged imidazolium vicinal to the P(III) atom are the alternative
electron-deficient ligand candidates[17–21] with the apparent
robustness against oxidative degradation and versatile sources.
Our group already reported some imidazolium-based phos-
phines as the electron-deficient ligands for transition metal
complex catalyzed carbonylations.[22–25] However, it should be
noted that such electron-deficient ionic phosphine also can
serve as the N-heterocyclic carbene precursors upon cleavage
of PÀ C(imidazolium) bonds even by the attack of the weak
nucleophiles like ClÀ .[26]
[a] Q. Zhou, L. Liu, W.-D. Guo, W.-Y. Liang, Prof. Y. Lu, Prof. Y. Liu
Shanghai Key Laboratory of Green Chemistry & Chemical Processes
East China Normal University
3663 North Zhongshan Road, 200062 Shanghai, China
E-mail: yliu@chem.ecnu.edu.cn
As for alkoxycarbonylation of aryl halides, the reductive
reagents are present universally such as CO, the base of organic
amine (as HX scavenger), the involved phosphines, water etc.
The use of RuCl3 ·3H2O was initiated by the sensitive nature of
Pd(II) complexes to the ingredients (CO, the base and water)
existed this reaction, which often resulted in the deactivation of
Pd(II)-catalyst with the precipitation of Pd(0)-black.[27–29] In
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/open.201800266
© 2018 The Authors. Published by Wiley-VCH AG. This is an open access
article under the terms of the Creative Commons Attribution Non-Com-
mercial NoDerivs License, which permits use and distribution in any med-
ium, provided the original work is properly cited, the use is non-commercial
and no modifications or adaptations are made.
ChemistryOpen 2019, 8, 166–172
166
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
comparison, RuCl3 ·3H2O is advantageous with apparent robust-
ness against CO, organic amine and water.
Herein a series of ionic phosphines (L2, L4, and L6) as the
electron-deficient ligands were applied with RuCl3 ·3H2O togeth-
er to catalyze alkoxycarbonylation of aryl halides (Scheme 1).
Table 1. Methoxycarbonylation of PhI catalyzed by RuCl3 ·3H2O with the
1
2
3
4
5
6
7
8
9
involvement of different phosphines.[a]
Entry
Ligand
Conv.[b] [%]
Sel.ester[b] [%]
Sel.acid[b] [%]
1
2
3
4
L1
L2
L3
L4
75
87
88
96
78
82
96
43
86
96
93
99
81
96
98
95
14
4
7
1
19
4
5
L5
6
L6
7[c]
8
RuIII-L4
–
2
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
[a] RuCl3 ·3H2O 0.01 mmol (Ru 0.5 mol%), monophosphine 0.008 mmol,
diphosphine 0.004 mmol, (P/Ru=0.8 molar ratio), iodobenzene 2 mmol,
CH3OH 10 mmol, NEt3 5 mmol, CO 2 Mpa, N-methyl pyrrolidone (NMP)
°
3 mL, 120 C, 16 h. [b] Determined by GC. Sel.ester represents selectivity to
methyl benzoate; Sel.acid represents selectivity to benzoic acid. [c] The as-
synthesized complex of RuIII-L4 (0.005 mmol) was used instead of mixing
RuCl3 ·3H2O (0.01 mmol) and L4 (0.004 mmol).
Even over L3 with the very structural similarity to L4, 88%
conversion of PhI was obtained along with the formation of by-
product of benzoic acid in selectivity of 7% (Entry 3). When the
complexes of RuIII-L4 was used to replace the mixture of
RuCl3 ·3H2O and L4 as the pre-catalyst, nearly the same yield of
methyl benzoate was obtained, indicating the in situ formed
complex exhibited the identical activity as the as-synthesized
one (Entry 7 vs 4). Without the involvement of any phosphine
ligand, RuCl3 ·3H2O itself couldn’t enable the rapid conversion
of PhI to the target product as a result of only 43% conversion
(Entry 8).
Scheme 1. The neutral and ionic phosphines (L1–L6) and related RuIII
complexes (RuIII-L2’, RuIII-L4) for alkoxycarbonylation of aryl halides.
For comparison, their corresponding neutral counterparts
(L1, L3, and L5) with structural similarity were investigated in
parallel in order to elucidate the electronic and steric effects of
the involved phosphines on the catalytic performance of
RuCl3 ·3H2O.
In addition, the recyclability of the ionic phosphine based
RuCl3 ·3H2O in combination of the room temperature ionic
liquid (RTIL) of [Bmim]PF6 (as the reaction medium) was also
investigated. The method in combination of transition metal
complex coordinated by ionic phosphines and RTIL medium
has been accepted as an easy operation and efficient alternative
to immobilize a homogeneous transition metal catalyst for
recovery and recycling in green chemistry in recent years.[30–33]
The effect of Ru- and Pd-precursors on this reaction was
summarized in Table 2. It was noted that over the different Ru-
Table 2. Comparison of methoxycarbonylation of PhI catalyzed by differ-
ent Ru- and Pd complex precursors with involvement of L4.[a]
Entry
Precursor
Conv.[b] [%]
Selester[b] [%]
Sel.acid[b] [%]
1
2
3
RuCl3 ·3H2O
Ru(COD)Cl2
Ru3(CO)12
Pd(OAc)2
PdCl2
Pd(MeCN)2Cl2
96
84
86
89
89
77
99
97
97
93
94
91
1
3
3
7
6
9
4*c
5*
6*
[a] M (metal) 0.5 mol%, L4 0.004 mmol, P/M=0.8 molar ratio, iodobenzene
2 mmol, MeOH 10 mmol, NEt3 5 mmol, CO 2 MPa, N-methyl pyrrolidone
2. Results and Discussion
°
(NMP) 3 mL, 120 C, 16 h. [b] Determined by GC. Sel.ester represents
selectivity to methyl benzoate; Sel.acid represents selectivity to benzoic acid;
* Pd(0)-black precipitated upon reaction. [c] The Pd-black residue was
collected after washing by diethyl ether completely to repeat the reaction.
Under the optimal conditions (P/Ru=0.8 molar ratio, NEt3 as
°
base, CO 2 MPa, NMP as solvent, 120 C, 16 h; see Table S1 in
the Supporting Information), the ligand effect on the perform-
ance of RuCl3 ·3H2O catalyst was summarized in Table 1. It was
noticed that benzoic acid was universally formed during the
reaction, which was derived from the hydrolysis of methyl
benzoate or the direct hydrocarboxylation of PhI. Over the
neutral phosphines (L1, L3 and L5), the selectivities to benzoic
acid were much higher than those over the ionic ones (L2, L4
and L6). The highest conversion of PhI (96%) along with the
best selectivity to methyl benzoate (99%) was observed on L4-
based RuCl3 ·3H2O system (Entry 4), and the other phosphines
just corresponded to the relatively slow transformation of PhI.
based precursors such as RuCl3 ·3H2O, Ru(COD)Cl2 and Ru3(CO)12,
only RuCl3 ·3H2O exhibited the best activity towards methox-
ycarbonylation of PhI with the involvement of L4 (Entries 1 vs 2
and 3). When the Pd-based precursors were used instead, not
only the relatively lower yield of methyl benzoate was
observed, but the Pd(0)-black was seriously precipitated upon
the reaction which indicated the rapid deactivation of these Pd-
catalysts even with the presence of L4 (Entries 4–6; pictures of
the slurry mixture upon reaction were provided in the
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
167
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
Table 3. The structures and the selected bond distance of RuIII-L2’, RuIII-L4,
L5, L6.
Supporting Information). When the precipitated Pd(0)-black
(Entry 4) was collected after washing by diethyl ether com-
pletely to repeat the reaction under the same condition, it was
found that Pd(0)-black exhibited the poor activity towards
methoxycarbonylation of iodobenzene with 7% yield of methyl
benzoate. Based on this experiment, we could rule out the
catalytic activity of Pd-black for this reaction. These obtained
results further confirmed the much better tolerance of Ru-based
catalyst against reduction to atom state in the reductive
1
2
3
4
5
6
7
8
9
Structures
Bond distances [Å]
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Cl(1a)
Ru(1)-Cl(2a)
Ru(1)-P(1)
2.3441(10)
2.3614(9)
2.3441(10)
2.3614(9)
2.4056(9)
2.4056(9)
Ru(1)-P(1a)
environment than that of Pd-based ones.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
77
It has been reported that the magnitude of 1J31 Se coupling
P-
constant in the 77Se isotopomer of the corresponding
phosphine-selenide in 31P NMR spectra can evaluate the π-
acceptor ability of different phosphines. An increase of J31
1
77
P- Se
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Cl(3)
Ru(1)-Cl(4)
Ru(1)-P(1)
Ru(1)-P(2)
2.3755(12)
2.3806(14)
2.3599(12)
2.3571(14)
2.4109(15)
2.4119(15)
indicates an increase in the character of the π-acceptor ability
(i.e., less σ-donor ability). [34–36] In this work, the measurement of
77
1J31
of the phosphines of L1–L6 upon reacting with
P- Se
elemental selenium by 31P NMR spectroscopy was given in
Figure 1. It was demonstrated that that the values of J31
of
1
77
P- Se
P(1)-C(1)
P(1)-C(7)
P(1)-C(13)
1.8290(16)
1.8398(17)
1.8279(16)
P(1)-C(1)
1.8261(2)
1.8406(2)
1.8329(18)
1.8365(19)
1.8340(2)
1.8324(19)
P(1)-C(12)
P(1)-C(13)
P(2)-C(26)
P(2)-C(27)
P(2)-C(33)
Figure 1. 31P NMR spectra (202 MHz) of the selenides of L1–L6:[37] reacting
°
elemental selenium with a) L1 in CDCl3 at 70 C for 12 h; b) L2 in CDCl3 at
°
°
°
70 C for 12 h; c) L3 in CDCl3 at 70 C for 12 h; d) L4 in CDCl3 at 70 C for 12 h;
°
°
e) L5 in CDCl3 at 70 C for 12 h; f) L6 in CD3COCD3 at 70 C for 24 h.
À
[a] RuIII-L2’ with counter-anion of PF6 possesses the same cation as RuIII-
L2. [b] The related structural data were provided in the Supporting
Information.
the ionic phosphines universally higher than their neutral
analogues, which means a dramatic increase in the character of
π-acceptor ability for the ionic phosphines due to the intensive
electron-withdrawing effect from the positive-charged imidazo-
lium. Although the ionic phosphines of L2, L4[37] and L6 all
ionic phosphine (L2 or L4) and the high valence state Ru3+ was
avoided completely as expected. As shown in Table 3, Ru(III)
(d5)-center of RuIII-L2’[38] and RuIII-L4[22] is in six-coordinated
octahedral configuration with paramagnetism. In RuIII-L2’, the
tailed butylimidazolium moieties are located in trans-positions.
RuIII-L4 is a dimer analogue of RuIII-L2’ in which the two
butylenyl-linked imidazolium moieties are reversed to cis-
positions to form a quadrilateral ring dinuclear Ru(III) complex.
It was found in RuIII-L4 that the distance of the four RuÀ Cl
bonds was in the range of 2.36~2.38 Å, and the two RuÀ Cl
bonds inside the quadrilateral ring were dramatically length-
ened due to the additional developed hydrogen bonding of ClÀ
1
77
possessed the very similar magnitude of J31 Se, they demon-
P-
strated quite different promoting effect on the performance of
RuCl3 ·3H2O. Evidently, only L4 enabled RuCl3 ·3H2O to exhibit
the best activity for methoxcarbonylation of PhI (Entry 4 of
Table 1), which implied that the steric effect of these phos-
phines played more predominant role in tailoring the behavior
of RuCl3 ·3H2O over their electronic effect.
The molecular structures of the complexes of RuIII-L2’ and
RuIII-L4 reported in our previously published work [22,38] can help
us understand the steric effect of L2 and L4 on the performance
of RuCl3 ·3H2O (Table 3). Undoubtedly, the redox between the
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
168
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
with H-butylenyl group. In contrast, in RuIII-L2’, the distances of
the four RuÀ Cl bonds are much shorter in the range of 2.34~
2.36 Å. Hence, when RuIII-L4 or L4-based RuCl3 ·3H2O (in situ
formation of RuIII-L4) were applied as the catalysts for
methoxycarbonylation of PhI in Table 1 (Entries 7 and 4), the
weakened RuÀ Cl bonds inside the quadrilateral ring were able
to be cleaved preferentially to provide unsaturation site for
oxidative addition of PhI and coordination of CO for the
formation of Ru-acyl intermediate (responsible for the efficient
methoxycarbonylation). As for L5 and L6 with long dangling
linker of n-octylenyl, the expected dinuclear complex with
structural similarity to RuIII-L4 was not obtained successfully
while reacting RuCl3 ·3H2O with L5 and L6 respectively.
Accordingly, the uncompetitive performance over L5 or L6
based catalyst was observed in comparison to that over L4
(Entries 6 vs 4 of Table 1).
In addition, as an ionic phosphine, L4-based Ru-catalyst
could be used with the room temperature ionic liquid (RTIL)
solvent to fulfil the recovery and recycling of transition metal
catalysts. [Bmim]PF6 was selected as the most suitable medium
after comparing to [Bmim]BF4 (1-butyl-3-methylimidazolium
tetrafluoroborate) and [Bmim]Cl (1-butyl-3-methylimidazolium
chloride) (See Table S2). As shown in Figure 2, in the first 6 runs,
The generality of RuCl3 ·3H2O-L4 catalytic system for alkox-
ycarbonylation of different aryl and heteroaryl halides was
summarized in Table 4. It was found that the para-positioned
aryl iodides all converted to the corresponding methyl esters in
excellent yields (80~92%) without discrimination on the
1
2
3
4
5
6
7
8
9
Table 4. Generality of L4-based RuCl3 ·3H2O for alkoxycarbonylation.[a]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Entry Substrate
Alcohol Product
Conv.[b]
[%]
Yield[b]
[%]
1
2
3
4
MeOH
MeOH
MeOH
MeOH
93
82
88
90
90
80
84
86
5
6
7
MeOH
MeOH
MeOH
90
95
86
83
92
80
8
9
MeOH
MeOH
67
51
64
43
Figure 2. The recycling uses of RuCl3 ·3H2O with the involvement of L4 in
[Bmim]PF6 for methoxycarbonylation of iodobenzene [Ru 0.01 mmol, L4
0.004 mmol, iodobenzene 2 mmol, MeOH 10 mmol, NEt3 5 mmol, [Bmim]PF6
10
11
MeOH
MeOH
63
70
57
63
3 mL, CO 2 MPa, 120 C, 16 h; * In the 7th run, the reaction slurry was washed
°
by H2O to remove the formed ammonium salt of Et3N·HI.
12
MeOH
MeOH
7
4
L4-RuCl3 ·3H2O system could be successfully recycled affording
86–96% yield of methyl benzoate. However, in the 7th run, the
conversion of PhI dropped slightly due to the inefficient stirring
of the slurry mixtures contain [Bmim]PF6 and the formed
Et3N·HI salt. Subsequently, the slurry was washed by water to
remove Et3N·HI and then the hydrophobic [Bmim]PF6 was
refreshed to use in the next run. In the 8th run, the competitive
yield (84%) was obtained. The ICP-OES analysis demonstrated
that, after 8 runs, the loss of Ru and P (coming from L4 and
[Bmim]PF6) in the combined organic phase was 1.6% and 6.2%
respectively, indicating that the catalyst could be locked in
[Bmim]PF6 medium tightly only with very low leaching into the
organic phase.
13[c]
84
80
14
15
16
EtOH
95
91
89
90
66
81
i-PrOH
n-
BuOH
[a] RuCl3 ·3H2O 0.5 mol%, L4 0.004 mmol (P/Ru=0.8 molar ratio), aryl or
heteroaryl halides 2 mmol, alcohol 10 mmol, NEt3 5 mmol, CO 2 MPa, N-
°
methyl pyrrolidone (NMP) 3 mL, 120 C, 16 h. [b] Determined by GC. [c] 140
°
C.
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
169
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
electronic effect of the substituted groups (Entries 1–6). The
steric effect of the substituents at meta- or ortho-position
obviously influenced the reaction rate. For example, 1-iodo-3-
nitrobenzene corresponded to 80% yield of the product
(Entry 7) whereas 1-iodo-2-nitrobenzene gave only 64% yield of
methyl 2-nitrobenzoate (Entry 8). Notably, 1,2-diiodobenzene
was subjected to the double methoxycarbonylation to produce
insertion of CO into RuÀ Ar bond leads to an acylruthenium
intermediate (C) which is attacked by nucleophile of alcohol to
give the desired product (ester) along with the regeneration of
the active Ru(I)-intermediate complex (A) via reductive elimi-
nation.
1
2
3
4
5
6
7
8
9
dimethyl phthalate at 43% yield (Entry 9). Heteroaryl halides 3. Conclusions
could afford the corresponding esters in the moderate yields of
57–63% under the applied conditions (Entries 10 and 11).
Unfortunately, L4-based RuCl3 ·3H2O catalytic system exhibited
poor activity towards methoxycarbonylation of bromobenzene
(Entry 12). However, when 1-bromo-4-nitrobenzene was applied
to repeat the reaction, 80% yield of methyl 4-nitrobenzoate
The low-cost and robust RuCl3 ·3H2O was successfully applied as
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
an efficient and recyclable catalyst for alkoxycarbonylation of
aryl halides with the involvement of the unique ionic
diphosphine of L4. Due to the electron-deficient nature of L4,
the redox between L4 and the high valence state Ru3+ was
avoided completely to guarantee the catalysis of Ru(III)-center.
On the other hand, the unique steric effect of L4 with ability to
form a quadrilateral ring dimer of RuIII-L4 along with the
differentiated hydrogen bond interaction further facilitated the
activity of this Ru(III)-catalyst. As a result, L4-based RuCl3 ·3H2O
catalyst led to the best conversion of PhI (96%) along with 99%
selectivity to the target product of methyl benzoate as well as
the good generality to alkoxycarbonylation of different aryl
halides (ArX, X=I and Br) with alcohols (MeOH, EtOH, i-PrOH and
n-BuOH). In addition, L4-based RuCl3 ·3H2O system could be
recycled successfully at least 8 runs in the hydrophobic ionic
liquid of [Bmim]PF6.
°
was obtained at the temperature of 140 C (Entry 13), indicating
that the conjugated and inductive effects of À NO2 group
dramatically increased the reactivity of the corresponding
substrate. In addition to methanol, ethanol, isopropanol and 1-
butanol were also suitable for this reaction to give the
corresponding esters in good yields (66%–90%, Entries 14–16).
Notably, besides the target esters, the corresponding acids
were observed universally. For example, the use of i-PrOH in
place of MeOH afforded isopropyl benzoate in the yield of 66%
along with 25% yield of benzoic acid due to the dramatically
increased steric hindrance of i-PrOH (Entry 15).
The catalytic mechanism for alkoxycarbonylation of aryl
halides over L4-based RuCl3 ·3H2O was tentatively proposed in
Scheme 2. In the catalytic cycle, the available active Ru(I)-
intermediate complex (A) upon reduction of the L4-ligated Ru Experimental Section
(III) complex (RuIII-L4) by CO is oxidatively added by aryl halide
to afford an arylruthenium complex (B). Then, the migratory
General Procedures
The chemical reagents used in this work were purchased from
Shanghai Aladdin Chemical Reagent Co., Ltd., and TCI Shanghai.
Unless otherwise specified, the chemical reagents were used as
received. The 1H and 31P NMR spectra for the analyses of the
common compounds were recorded on
a Bruker ARX 500
spectrometer at ambient temperature. The 31P NMR spectra were
referenced to 85% H3PO4 sealed in a capillary tube as an internal
standard. Gas chromatography (GC) analysis was performed on a
SHIMADZU-2014 equipped with a DM-Wax capillary column (30 m×
0.25 mm×0.25 μm). GC-mass spectrometry (GC-MS) which
equipped with
a DB-Wax capillary column (30 m×0.25 mm×
0.25 μm) was recorded on an Agilent 6890 instrument equipped
with an Agilent 5973 mass selective detector. TG/DTG analysis was
performed on a thermo gravimetric analyzer (TGA/SDTA/SF/1100/
851e). The amount of Ru and P in the sample was quantified by
using an inductively coupled plasma optical emission spectrometer
(ICP-OES) on an Optima 8300 instrument (PE Corporation).
Synthesis of L1–L4
The phosphine ligands of L1–L4 were prepared according to the
procedures reported by our group previously.[22,37]
Synthesis of L5 and L6[39]
Under N2 atmosphere, imidazole (2.86 g, 42 mmol) was added into
the distilled DMF (25 mL), then NaH (1.76 g, 60% dispersion in
mineral oil, 44 mmol) were added into the mixtures carefully and
Scheme 2. The proposed catalytic mechanism over L4-based Ru(III) complex
for alkoxycarbonylation of aryl halides
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
170
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
slowly. Next, the mixture was stirred vigorously at ice-water bath
for 1 h. After the mixtures restored room temperature, 1,8-
dibromooctane (5.44 g, 20 mmol) was added into the mixtures and
NEt3 (5 mmol), iodobenzene (2 mmol) sequentially to form a
homogenous reaction solution. Upon reaction completion, anhy-
drous diethyl ether (20 mL) was added to the yellow reaction
solution. Then the upper transparent phase was decanted from the
obtained biphasic mixture. The remaining RTIL phase was washed
with anhydrous diethyl ether (3 mL×3) to extract the reactants and
products completely. The yield and selectivity to the target product
was analyzed by GC and the remaining RTIL phase was reused
without further treatment for the next run. Then the amount of Ru
and P in the organic phase was quantified by ICP-OES.
1
2
3
4
5
6
7
8
°
the mixtures were stirred vigorously at 70 C for 4 h. The excess
NaH in reaction mixtures was treated with 100 mL of deionized
water. Then the reaction mixture was extracted with dichloro-
methane (100 mL×3). After dried with anhydrous sodium sulfate
the combined organic phase was concentrated under vacuum to
give yellow liquid as the product of 1,1’-(1,8-octanediyl)bis
(imidazole) with the yield of 64% (3.15 g).
9
Under N2 atmosphere, when a solution of 1,1’-(1,8-octanediyl)bis
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
(imidazole) (1.23 g, 5 mmol) in 50 mL of distilled THF was cooled to
°
À 78 C, 5 mL of n-BuLi (2.5 M in hexane, 12.5 mmol) was added
Acknowledgements
dropwise in 30 min. After stirring vigorously for 1 h, the obtained
reaction mixture was added with chlorodiphenylphosphine (PPh2Cl,
2.32 g, 10.5 mmol) dropwise in 30 min. The reaction mixture was
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21673077 and 21473058), and
the Science and Technology Commission of Shanghai Municipality
(18JC1412100).
°
stirred for another 1 h at À 78 C and then warmed up to room
temperature naturally. After quenching excess n-BuLi with 100 mL
deionized water, the mixture was stripped of solvent in vacuo and
then extracted with dichloromethane (100 mL×3). After dried by
anhydrous sodium sulfate and concentrated under vacuum, the
mixture was further purified by column chromatography on silica
gel, using dichloromethane/ethyl acetate (40:1) as an eluent, to
give a white solid as the product of L5 with the yield of 55%
(1.69 g). 1H NMR (δ, ppm, CD3COCD3): 7.53 (s, 8H, HAr), 7.33-7.32 (m,
14H, HAr), 7.15 (s, 2H, HAr), 4.25 (t, J=10 Hz, 4H, NCH2CH2), 1.64 (m,
4H, NCH2CH2CH2), 1.06 (s, 8H, NCH2CH2CH2CH2CH2CH2CH2CH2N). 31P
NMR (δ, ppm, CD3COCD3): À 23.02 (s, PPh2).
Conflict of Interest
The authors declare no conflict of interest.
Keywords: Alkoxycarbonylation
diphosphines · Ru(III) complex · catalyst recyclability
·
aryl halides
·
ionic
A solution of L5 (1.23 g, 2 mmol) in 30 mL of distilled dichloro-
°
methane was cooled to À 78 C and then MeOTf (0.67 g, 4.1 mmol)
was added dropwise in 30 min. The reaction mixture was stirred at
°
À 78 C for another 1 h and then warmed up to room temperature
naturally. Upon completion, the mixture was stripped of solvent in
vacuo to give a white solid. Then the white solid product was
washed by diethyl ether completely to give the product L6 in 90%
[1] A. Brennführer, H. Neumann, M. Beller, Angew. Chem. Int. Ed. 2009, 48,
4114–4133; Angew. Chem. 2009, 121, 4176–4196
[2] P. Kalck, M. Urrutigoïty, Inorg. Chim. Acta. 2015, 431, 110–121.
[3] A. G. A. SÁ, A. C. d. Meneses, P. H. H. d. Araújo, D. d. Oliveira, Trends
Food Sci. Technol. 2017, 69, 95–105.
[4] C. Zhang, M. Li, H.-Y. Lu, C.-F. Chen , RSC Adv. 2018, 8, 1014–1021.
[5] C. F. J. Barnard, Organometallics 2008, 27, 5402–5422.
[6] T. Fujihara, K. Nogi, T. Xu, J. Terao, Y. Tsuji, J. Am. Chem. Soc. 2012, 134,
9106–9109.
yield (1.70 g). H NMR (δ, ppm, CD3COCD3): 8.08 (s, 2H, N+CHCHN),
1
7.96 (s, 2H, N+CHCHN), 7.59–7.53 (m, 20H, HAr), 4.45 (t, J=10 Hz,
4H, NCH2CH2), 3.70 (s, 6H, N+CH3), 1.63-1.61 (d, J=10 Hz, 4H,
NCH2CH2CH2), 1.05 (s, 8H, NCH2CH2CH2CH2CH2CH2CH2CH2N). 31P NMR
(δ, ppm, CD3COCD3): À 28.78 (s, PPh2).
[7] N. Iranpoor, H. Firouzabadi, E. Etemadi-Davan, A. Nematollahi, H. R.
Firouzi, New J. Chem. 2015, 39, 6445–6452.
[8] R. Vanderesse, J. Marchal, P. Caubère, Synth. Commun. 1993, 23, 1361–
1370.
General Procedures for Alkoxycarbonylation of Aryl Halides in
38 Alcohols
39
[9] R. Takeuchi, Y. Tsuji, M. Fujita, T. Kondo, Y. Watanabe, J. Org. Chem.
1989, 54, 1831–1836.
In
a 50 mL sealed Teflon-lined stainless-steel autoclave, the
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
[10] T. Mizuno, H. Alper, J. Mol. Catal. A 1997, 123, 21–24.
[11] S. Kannan, K. N. Kumar, R. Ramesh, Polyhedron 2008, 27, 701–708.
[12] Y. Yan, Y. Chi, X. Zhang, Tetrahedron: Asymmetry 2004, 15, 2173–2175.
[13] C. L. Pollock, G. C. Saunders, E. C. M. Sarah. Smyth, V. I. Sorokin, J.
Fluorine Chem. 2008, 129, 142–166.
commercial complex of RuCl3 ·3H2O (0.01 mmol Ru 0.5%) and pure
L4 (0.004 mmol) were mixed with methanol (10 mmol, or the other
alcohols), NEt3 (5 mmol), iodobenzene (2 mmol, or the other aryl
iodides and aryl bromides) and N-methyl pyrrolidone (NMP) 3 mL
(solvent). The autoclave was purged with CO (0.5 MPa) for three
times and pressured by CO to 2.0 MPa. The reaction mixture was
[14] H. Tricas, O. Diebolt, P. W. N. M. van Leeuwen, J. Catal. 2013, 298, 198–
205.
[15] N. Sakai, S. Mano, K. Nozaki, H. Takaya, J. Am. Chem. Soc. 1993, 115,
7033–7034.
[16] M. L. Clarke, D. Ellis, K. L. Mason, A. Guy Orpen, P. G. Pringle, R. L.
Wingad, D. A. Zaher, R. Tom Bake, Dalton Trans. 2005, 1294–1300.
[17] Y. Canac, N. Debono, L. Vendier, R. Chauvin, Inorg. Chem. 2009, 48,
5562–5568.
°
stirred vigorously at 120 C for 16 h. Upon reaction completion, the
reactor was cooled down to room temperature and depressurized
carefully. The reactor vessel was washed with anhydrous diethyl
ether thoroughly and then the reaction solution was analyzed by
GC to determine the conversions (n-dodecane as internal standard)
and the selectivities (normalization method). The products were
further identified by GC-Mass to determine the reaction products.
[18] Y. Canac, N. Debono, C. Lepetit, C. Duhayon, R. Chauvin, Inorg. Chem.
2011, 50, 10810–10819.
[19] I. Abdellah, C. Lepetit, Y. Canac, C. Duhayon, R. Chauvin, Chem. Eur. J.
2010, 16, 13095–13108.
[20] Y. Canac, C. Maaliki, I. Abdellah, R. Chauvin, New J. Chem. 2012, 36, 17–
Procedures for the Catalyst Recycling Experiment in [Bmim]PF6
27.
[21] C. Barthes, C. Lepetit, Y. Canac, C. Duhayon, D. Zargarian, R. Chauvin,
Inorg. Chem. 2013, 52, 48–58.
[22] P. Wang, D. L. Wang, H. Liu, X. L. Zhao, Y. Lu, Y. Liu, Organometallics
2017, 36, 2404–2411.
In the recycling experiment, the RTIL of [Bmim]PF6 was selected as
the solvent. In the first run, [Bmim]PF6 (3 mL) was mixed with
RuCl3 ·3H2O (0.01 mmol), L4 (0.004 mmol), methanol (10 mmol),
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
171
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
[23] H. Liu, D. L. Wang, X. Chen, Y. Lu, X. L. Zhao Y. Liu, Green Chem. 2017,
19, 1109–1116.
[24] H. Zhang, Y. Q. Li, P. Wang, Y. Lu, X. L. Zhao, Y. Liu, J. Mol. Catal. A 2016,
[35] A. S. Rrez, M. A. M. Rojas, A. Pizzano, Organometallics, 2002, 21, 4611.
[36] S. Jeulin, S. D. de Paule, V. R. Vidal, J. P. Genêt, N. Champion, P. Dellis,
Angew. Chem. Int. Ed., 2004, 43, 320.
[37] H. Liu, D. Yang, D. L. Wang, P. Wang, Y. Lu, G. Vo-Thanh, Y. Liu, Chem.
Commun. 2018, 54, 7979–7982.
[38] C. L. Zhou, J. Zhang, M. Đaković, Z. Popović, X. L. Zhao, Y. Liu, Eur. J.
Inorg. Chem. 2012, 21, 3435–3440.
[39] https://www.ccdc.cam.ac.uk/services/structures?id=doi:10.1002/
open.201800266. CCDC. 1878304 (L5) and 1878305 (L6) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge from http://www.ccdc.cam.ac.uk/, The Cam-
bridge Crystallographic Data Centre.
1
2
3
4
5
6
7
8
9
411, 337–343.
[25] H. X. You, Y. Y. Wang, X. L. Zhao, S. J. Chen, Y. Liu, Organometallics 2013,
32, 2698–2704.
[26] I. Abdellah, M. Boggio-Pasqua, Y. Canac, C. Lepetit, C. Duhayon, R.
Chauvin, Chem. Eur. J. 2011, 17, 5110–5115.
[27] R. Gholami, M. Alyani, K. J. Smith, Catalysts 2015, 5, 561–594.
[28] Y. Shen, Y. Guo, L. Wang, Y. Wang, Y. Guo, X. Gong, G. Lu, Catal. Sci.
Technol. 2011, 1, 1202–1207.
[29] X. Yu, P. G. Pickup, Electrochem. Commun. 2009, 11, 2012–2014.
[30] B. Ni, A. D. Headley, Chem. Eur. J. 2010, 16, 4426–4436.
[31] C. Huo, T. H. Chan, Chem. Soc. Rev. 2010, 39, 2977–3006.
[32] R. Šebesta, I. Kmentová, Š. Toma, Green Chem. 2008, 10, 484–496.
[33] Y. Q. Li, P. Wang, H. Liu, Y. Lu, X. L. Zhao, Y. Liu, Green Chem. 2016, 18,
1798–1806.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Manuscript received: November 26, 2018
[34] D. W. Allen, B. F. Taylor, Dalton Trans. 1982, 1, 51.
Revised manuscript received: December 27, 2018
ChemistryOpen 2019, 8, 166–172
www.chemistryopen.org
172
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA