Synthesis, crystal structure of Co(II)(6-methoxybenzothiazole-2-carboxylate)2(DMF)2 and its application to carbonylation of benzyl chloride

Article abstract of DOI:10.1002/cjoc.201090023

A new complex, Co(MBTC)₂(DMF)₂ (MBTC(6-methoxybenzothiazole-2-carboxylate, DMF=N,N-dimethylformamide), was synthesized in DMF solution and characterized by single crystal X-ray diffraction analysis. Using the cobalt complex as catalyst, phenylacetic acid was prepared by the carbonylation of benzyl chloride with carbon monoxide (0.1 MPa). The effects of solvents, phase transfer catalysts and temperature on the reactions were investigated. The yield of phenylacetic acid was higher than 90% in optimized condition.

Full text of DOI:10.1002/cjoc.201090023

FULL PAPER
Synthesis, Crystal Structure of Co(II)(6-methoxybenzothiazole-
2-carboxylate)2(DMF)2 and Its Application to Carbonylation
of Benzyl Chloride
Zhang, Bin(张斌)
Li, Jianli*(李剑利)
Chen, Wei(陈伟)
Wang, Yunxia(王云侠)
Shi, Zhen(史真)
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of
Chemistry and Materials Science, Northwest Univesity, Xi'an, Shaanxi 710069, China
A new complex, Co(MBTC)2(DMF)2 (MBTC＝6-methoxybenzothiazole-2-carboxylate, DMF＝N,N-dime-
thylformamide), was synthesized in DMF solution and characterized by single crystal X-ray diffraction analysis.
Using the cobalt complex as catalyst, phenylacetic acid was prepared by the carbonylation of benzyl chloride with
carbon monoxide (0.1 MPa). The effects of solvents, phase transfer catalysts and temperature on the reactions were
investigated. The yield of phenylacetic acid was higher than 90% in optimized condition.
Keywords sodium 6-methoxybenzothiazole-2-carboxylate, cobalt catalyst, carbonylation, phenylacetic acid,
synthesis
Introduction
of studying the carbonylation of benzyl chloride, we
found that Co(MBTC)2(DMF)2 was an effective catalyst
for the synthesis of phenylacetic acid by the carbonyla-
tion reaction of benzyl chloride with CO (0.1 MPa), and
there were no double carbonylation products. The addi-
tional phase transfer catalyst could increase reaction
effectivity.
In this paper, we report the synthesis of phenylacetic
acid using Co(MBTC)2(DMF)2/CO/Bu4NBr/NaOH/to-
luene system in a good yield. The effects of solvents,
phase transfer catalysts and temperature on the reactions
have been investigated.
Transition-metal catalyzed carbonylation of organic
halides with carbon monoxide is one of the most useful
methods for the direct introduction of a carbonyl group
into organic molecules.1-3 Rhodium,4-6 palladium,7-12
and cobalt13-19 complexes are commonly used in this
field and most of them are efficient transition-metal
catalysts in carbonylation reactions.
Phenylacetic acid and its esters are important indus-
trial chemical intermediates.20 “Classical” syntheses of
arylacetic acid include the industrially important
stoichiometric reaction of arylmethyl halides with metal
cyanides to form analogous nitriles which are subse-
quently hydrolysed.21 This two-step process has many
drawbacks such as formation of a stoichiometric amount
of salt, for example, sodium chloride and ammonium
sulfate. Additionally, the introduction of a carbon atom
by a cyanide molecule is fairly expensive compared to
the cheaper monoxide.22 Compared with the classical
synthesis,13,14,16,18 synthesis of phenylacetic acid via the
carbonylation reaction has been investigated as a less
expensive and simple method.
Experimental
Reagents and characterization techniques
2-Amino-6-methoxybenzothiazole was purchased
from Suzhou Dongwu Dyestuff Co. Ltd., and used
without further purification. Benzyl chloride, CoCl2•
6H2O, and all the other solid and liquid materials were
commercial products of analytical purity. Carbon mon-
oxide with 99.9% purity was used directly from the
cylinders.
It was reported that cobalt complexes [cobalt
bis(2-pyridinecarboxylate)-tetrahydrate] showed very
good catalytic activity in the double carbonylation of
benzyl chloride for the synthesis of phenylpyruvic acid,
and the catalyst had also some advantages such as ease
of preparation and handling, while phenylacetic acid
was present in low yield as a by-product.19 In the course
－ 1
IR spectra in cm
were recorded on a Bruker
1
Equiox-55 spectrometer. H NMR spectra were ob-
tained at 400 MHz on a Varian Inova-400 spectrometer
and chemical shifts were reported relative to internal
Me4Si. X-ray single crystal diffraction was conducted
on a Bruker Smart APEX II CCD diffractometer.
*
E-mail: orgbin@hotmail.com; Tel./Fax: 0086-029-88303606
Received March 2, 2009; revised May 25, 2009; accepted October 9, 2009.
Project supported by the National Natural Science Foundation of China (No. 20872117), the China Postdoctoral Science Foundation (No.
20080431245) and the Science and Technology Program Foundation of Xi'an City (No. YF07070).
Chin. J. Chem. 2010, 28, 111— 114
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
111

Zhang et al.
FULL PAPER
GC-MS analysis was carried out with an Agilent
GC-6890 system linked to an Agilent MS-5973 instru-
ment.
2943, 2888, 2226, 1599, 1548, 1482, 1448, 1268, 1233,
1119, 1047, 1018, 827, 576, 489, 434 cm .
－1
Synthesis of sodium 6-methoxybenzothiazole-2-car-
boxylate (2)
Catalyst preparation
2-Cyano-6-methoxybenzo－thiazole (1.98 g) was sus-
The catalyst was prepared by reaction of CoCl2•
6H2O with sodium 6-methoxy-benzothiazole-2-car-
boxylate. The ligand was synthesized using the
Sandmeyer reaction and hydrolysis reaction of the ni-
trile (Scheme 1).
1
pended in 25 mL of 6 mol•L NaOH with stirring and
the suspension was kept in a boiling water bath for 1 h.
The crude product was filtered. White pale crystals
(1.71 g) were obtained by recrystallization from
CH3OH-H2O (V∶V＝1∶3, 20 mL), m.p. 257—261 ℃
(lit.24 257—262 ℃); 1H NMR (DMSO-d6, 400 MHz) δ:
3.87 (s, 3H), 7.10 (d, J＝9.2 Hz, 1H), 7.49 (s, 1H), 7.92
Scheme 1 Preparation of the catalyst Co(MBTC)2(DMF)2 (3)
(d, J＝9.2 Hz, 1H); IR (KBr)

ν: 3073, 3011, 2953, 2831,
1606, 1501, 1376, 1255, 1225, 1107, 1052, 1025, 841,
－1
825, 682, 557, 524, 440 cm .
Synthesis of Co(MBTC)2(DMF)2 (3)
Sodium 6-methoxybenzothiazole-2-carboxylate (0.460
g, 2 mmol) was added to DMF (40.0 mL) with stirring,
and CoCl2•6H2O (0.238 g, 1 mmol) was added to the
solution. The solution was continuously stirred for 30
min, then filtered in five test tubes. The test tubes were
put in a bottle in which there was ether (100.0 mL).
Brown crystals were obtained after 7 d. The crystals
were filtered, washed with methanol and dried in vacuo
(0.605 g, yield 97.4%), m.p.＞300 ℃. IR (KBr) ν: 3335,
2938, 2834, 1628, 1561, 1504, 1435, 1374, 1319, 1268,
1220, 1179, 1144, 1123, 1054, 1023, 905, 831, 779, 658,
－1
Synthesis of 2-cyano-6-methoxybenzothiazole (1)
574, 428 cm . Anal. calcd for C24H26CoN4O8S2: C
46.38, H 4.22, N 9.01; found C 46.27, H 4.06, N 9.23.
Commercial CuCN (11.5 g, 130 mmol) was sus-
pended in water (40.0 mL) with stirring in a 1000 mL
beaker and the mixture was cooled in an ice bath. To the
resulting suspension, a solution of commercial NaCN
(19.0 g, 390 mmol) in water (20.0 mL) was added
slowly to keep the temperature of the reaction below
room temperature. The mixture was stirred while the
CuCN was dissolved. The solution was held at about 0
℃ before use.
Carbonylation procedure
The carbonylation experiments were carried out in a
50 mL autoclave, equipped with an electric heating
jacket, a thermocouple and a sealed mechanical stirrer
driven by an electromagnet. The complex Co(MBTC)2-
(DMF)2 (132 mg, 0.2 mmol), Bu4NBr (65 mg, 0.2
mmol), toluene (20 mL) and 15% NaOH (15 mL) were
placed in the autoclave, which was sealed and flushed
with CO three times, pressurized to 0.1 MPa. The mix-
ture was stirred for 2 h at room temperature. Then ben-
zyl chloride (1.27 g, 10 mmol) was placed into the auto-
clave, which was again sealed and flushed with CO
three times, pressurized to 0.1 MPa. Then the reaction
mixture was heated for 18 h at 80 ℃, cooled to room
temperature and filtered. The aqueous layer was sepa-
rated, the organic layer was washed with H2O, and the
combined aqueous layer was acidified with 20% aq.
HCl, extracted with diethyl ether (40 mL×3). The
combined ether solution was dried over anhydrous
MgSO4, filtered and evaporated. Phenylacetic acid (1.23
g, yield 90.4%) was obtained (Scheme 2). The purity
was 98%, which was analyzed using＋a GC-MS method,
m.p. 76—77 ℃. MS m/z (%): 136 (M , 32), 91 ( PhCH＋2 ,
100), 65 (18), 39 (10).
A diazonium solution was prepared from 2-amino-
6-methoxybenzothiazole (9.0 g, 50 mmol), AcOH (30－.0
－1
1
mL), 6 mol•L H2SO4 (50.0 mL) and 2 mol•L
NaNO2 (50.0 mL) in a 250 mL flask. In the cyano com-
plex solution described above NaHCO3 (150.0 g) was
suspended with vigorous stirring, and AcOH (50.0 mL)
was added into the suspension slowly, then the dia-
zonium solution was added to the mixture in 1 h with
cooling in an ice bath. The mixture was continuously
stirred with cooling for 1 h, and then filtered, the solu-
tion was extracted with diethyl ether (100 mL×5), and
the ether was evaporated under vacuum after dried. The
solid was combined and purified by silica-gel column
chromatography with 50% petroleum ether-CH2Cl2 to
give the 2-cyano-6-methoxybenzothiazole (1.98 g), m.p.
1
129—130 ℃ (lit.23 129 ℃); H NMR (CDCl3, 400
MHz) δ: 3.93 (s, 3H), 7.25 (d, J＝9.2 Hz, 1H), 7.36 (s,
1H), 8.08 (d, J＝9.2 Hz, 1H); IR (KBr) ν: 3033, 2984,
112
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 111— 114

Synthesis, Crystal Structure of Co(II)(6-methoxybenzothiazole-2-carboxylate)2(DMF)2
Scheme 2 Procedure for the formation of phenylacetic acid by
Table 1 Crystal data and structural refinement parameters for
carbonylation of benzyl chloride
Co(MBTC)2(DMF)2
Complex
Empirical formula
Formula weight
Crystal system
Space group
a/Å
Co(MBTC)2(DMF)2
C24H26CoN4O8S2
621.54
Triclinic
P-1
8.4848(18)
9.379(2)
9.999(2)
83.605(3)
69.114(3)
66.086(3)
679.1(3)
1
b/Å
Results and discussion
c/Å
Structural analysis of the catalyst
α/(°)
Intensity data were collected on a Bruker Smart
APEX II CCD diffractometer with graphite-mono-
chromated Mo Kα radiation (λ＝0.71073 Å) at room
temperature. Empirical absorption corrections were ap-
plied by using the SADABS program. The structures
were solved by direct methods and refined by the
full-matrix least-squares based on F2 using SHELXTL-
97 program.25 All non-hydrogen atoms were refined
anisotropically and the hydrogen atoms of organic
ligands were generated geometrically. Crystal data and
structural refinement parameters for 3 are summarized
in Table 1. Crystallographic data for the structural
analyses have been deposited with the Cambridge Crys-
tallographic Data Centre, CCDC no. 706351. The sin-
gle-crystal X-ray structural analysis displays that 3 is a
mononuclear complex (Figure 1). The cobalt(II) atom is
hexa-coordinated by two oxygen atoms from two N,N-
dimethylformamide molecules and two nitrogen atoms
and two oxygen atoms from the ligand (the anion of
compound 2), which furnished a 4＋1＋1 distorted oc-
tahedron conformation, and cobalt(II) is approximately
coplanar with the equatorial plane of N(1), N(1A) O(1),
O(1A) [Co(1)—N(1), 2.1401(16) Å, Co(1)—N(1A),
2.1402(16) Å, Co(1)—O(2), 2.0849(13) Å, Co(1)—
O(2A), 2.0849(13) Å], and the bond angles of N(1)-
Co(1)-O(2) [78.91(6)°], O(2)-Co(1)-N(1A) [101.09(6)°]
and N(1A)-Co(1)-O(2A) [78.91(6)°], O(2A)-Co(1)-N(1)
β/(°)
γ/(°)
V/Å3
Z
3
D
µ/mm－
calc/(Mg•m－
)
1.520
1
0.840
F(000)
321
λ(Mo Kα)/Å
0.71073
Reflections collected
Unique reflections
Parameters
3386
2366
176
S on F2
1.053
R1, wR2 [I＞2σ(I0)]
R1, wR2 (all data)
∆ρmin and ∆ρmax/(e•Å－
0.0289, 0.0738
0.0343, 0.0765
0.212 and －0.299
3
)
[101.09(6)°] summed up to 360°. The apical sites are
occupied by O(1) and O(1A) atoms of the DMF
[Co(1)—O(1), 2.0945(13) Å, Co(1)—O(1A), 2.0945(13)
Å].
Influence of solvents on the carbonylation
The effects of the solvents on the carbonylation were
also studied. The results are summarized in Table 2.
Table 2 Effects of solvents on the carbonylationa
Solvent
Methanol
1,4-Dioxane
THF
Yield of phenylacetic acid/%
0
44.6
58.5
89.0
90.4
Benzene
Toluene
a Reaction conditions: Co(MBTC)2(DMF)2 (0.2 mmol), Bu4NBr
(0.2 mmol), 15% NaOH (15 mL), benzyl chloride (10 mmol),
T＝80 ℃, pCO＝0.1 MPa.
In liquid reaction system, the solvent molecule tends
to complex the central ion with the ligand. The stronger
capability of donating an electron pair of the solvent, the
stronger capability of complexing the central ion from
Figure 1 Perspective view of the coordination environment of
the cobalt atom in Co(MBTC)2(DMF)2 (3). Thermal ellipsoids are
drawn at the 30% probability level.
Chin. J. Chem. 2010, 28, 111— 114
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
113

Zhang et al.
FULL PAPER
the original complex.19,26 The capabilities of donating an
electron pair of the solvents are in the following se-
quence.
Conclusion
In this paper, the crystal structure of Co(MBTC)2-
(DMF)2 has been reported. The carbonylation of benzyl
chloride with this catalyst generated phenylacetic acid
in good to excellent yields. In the catalyst system the
yield of phenylacetic acid could be increased by the
phase transfer catalyst and the solvent, which do not
complex cobalt ion from the catalyst. The preferable
temperature of the carbonylation reaction is 80 ℃.
Methanol 1,4-dioxane THF benzene, toluene
＞
＞
＞
Compared with other solvents, the ability of benzene
and toluene to donate an electron pair is lower. So their
capability of competing for the central ion is lower,
which results in the better stability of cobalt complex in
benzene and toluene. The experiments also reveal that
the yield is higher in benzene and toluene.
References
Influence of phase transfer catalysts on the carbon-
ylation
1
Liégault, B.; Renaud, J. L.; Bruneau, C. Chem. Soc. Rev.
2008, 37, 290.
The effects of phase transfer catalysts on the yield
are presented in Table 3. Experiments show that the
phase transfer catalysts greatly affect the reaction. The
catalytic effectiveness of different phase transfer cata-
lysts is compared. Bu4NBr is the best one in the carbon-
ylation reaction of benzyl chloride－. Ion-pair compound,
like Bu4N＋•[BrCo(CO)2(MBTC)2] ,18 is easily formed,
so that the concentration of Co(CO)2(MBTC)2 in the
organic phase can be kept at a high level.
2
3
Heck, R. F. Synlett 2006, 2855.
Rita, S. F. In Modern Carbonylation Methods, Ed.: Kollár,
L., Wiley-VCH, Weinheim, 2008, pp. 311—316.
Mizuno,T.; Alper, H. J. Mol. Catal. A: Chem. 1997, 123, 21.
Giroux, A.; Nadeau, C.; Han, Y. X. Tetrahedron Lett. 2000,
41, 7601.
Morimoto, T.; Fujioka, M.; Fuji, K.; Tsutsumi, K.; Kakiuchi,
K. J. Organomet. Chem. 2007, 692, 625.
Cassar, L.; Foa, M.; Gardano, A. J. Organomet. Chem. 1976,
121, C55.
4
5
6
7
8
9
Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890.
Schull, T. L.; Fettinger, J. C.; Knight, D. A. Inorg. Chem.
1996, 35, 6717.
Table 3 Effects of phase transfer catalysts on the carbonylationa
Phase transfer catalyst
Bu4NBr
Yield of phenylacetic acid/%
10 Trzeciak, A. M.; Ziόłkowski, J. J. Coord. Chem. Rev. 2005,
249, 2308.
11 Sergeev, A.; Spannenberg, A.; Beller, M. J. Am. Chem. Soc.
2008, 130, 15549.
90.4
15.4
PEG400
12 Martinelli, J. R.; Watson, D. A.; Freckmann, D. M. M.;
Barder, T. E.; Buchwald, S. L. J. Org. Chem. 2008, 73,
7102.
13 Casser, L.; Foa, M. J. Organomet. Chem. 1977, 134, C15.
14 Gambarotta, S.; Alper, H. J. Organomet. Chem. 1981, 212,
C23.
15 Satyanarayana, N.; Periasamy, M. Tetrahedron Lett. 1987,
28, 2633.
16 Li, G. X.; Liu, Y. Chin. J. Appl. Chem. 1998, 15, 116 (in
Chinese).
36.9
a
Reaction conditions: Co(MBTC)2(DMF)2 (0.2 mmol), 15%
NaOH (15 mL), benzyl chloride (10 mmol), toluene (20 mL), T＝
80 ℃, pCO＝0.1 MPa.
Influence of reaction temperature on the carbonyla-
tion
The effects of the reaction temperature on the car-
bonylation were investigated in the temperature range
from room temperature to 100 ℃. The results are pre-
sented in Table 4, which show that the yield of
phenylacetic acid increases with the rising of reaction
temperature, but decreases above 80 ℃. When the tem-
perature is above 80 ℃, the catalyst may be destroyed.
17 Amer, I. Inorg. Chim. Acta 1994, 216, 97.
18 Hu, Y. L.; Wang, J. X.; Cui, W. F. Synth. Commun. 1994,
24, 1743.
19 Li, G. X.; Li, L.; Huang, H. M.; Cai, H. Q. J. Mol. Catal. A:
Chem. 2003, 193, 97.
20 Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W.
J. Mol. Catal. A: Chem. 1995, 104, 17.
21 Jones, R. V. H.; Lindsell, W. E.; Palmer, D. D.; Preston, P.
N.; Whitton, A. J. Tetrahedron Lett. 2005, 46, 8695.
22 Kohlpainter, C. W.; Beller, M. J. Mol. Catal. A: Chem. 1997,
116, 259.
23 Yoshiaki, T.; Masaharu, T.; Hisao, N.; Nobutaka, S. Bull.
Chem. Soc. Jpn. 1992, 65, 392.
24 White, E. H.; McCapra, F.; Field, G. F. J. Am. Chem. Soc.
1963, 85, 337.
25 Sheldrick, G. M. SHELXS-97 and SHELXL-97, Program for
X-ray Crystal Structure Solution and Refinement, Göttingen
University, Germany, 1997.
26 Huheey, J. E. Inorganic Chemistry, 3rd ed., Harper and
Row, New York, 1983, p. 340.
Table 4 Effects of reaction temperature on the carbonylationa
Temp./℃
22 (r.t.)
40
Yield of phenylacetic acid/%
8.1
15.4
78.8
90.4
36.9
60
80
100
a Reaction conditions: Co(MBTC)2(DMF)2 (0.2 mmol), Bu4NBr
(0.2 mmol), 15% NaOH (15 mL), benzyl chloride (10 mmol),
toluene (20 mL), pCO＝0.1 MPa.
(E0903021 Li, L.; Dong, H.)
114
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 111— 114