Cobalt-catalyzed photopromoted carbonylation of chloroalkanes in the presence of KI

Article abstract of DOI:10.1016/j.cclet.2010.04.027

The photopromoted carbonylation of chloroalkanes with carbon monoxide catalyzed by cobalt compounds [Co(OAc)₂, CoCl₂] in the presence of KI was carried out under ambient conditions. The results revealed that the catalytic activity of Co(OAc)₂ was higher than that of CoCl₂. A basic additive NaOAc was beneficial to the reaction. Interestingly, with NaOAc as an additive, Co(OAc)₂ and CoCl₂ exhibited similar catalytic activity. Preliminary work showed that the role of iodide ion was initially to form active iodoalkanes via substituting chloride ion in chloroalkanes in situ, and then, the carbonylation of iodoalkanes proceeded under irradiation.

Full text of DOI:10.1016/j.cclet.2010.04.027

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 1033–1036
www.elsevier.com/locate/cclet
Cobalt-catalyzed photopromoted carbonylation of chloroalkanes in
the presence of KI
Ying Ping Jia a,b, Ying Na Cui b, Jing Mei Yin b, Guang Yun Zhou b, Shen Min Li b,
Da Bin Gao b, Xiang Sheng Wang a,
*
a State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China
b Liaoning Key Laboratory of Bio-organic Chemistry, Dalian University, Dalian 116622,China
Received 21 December 2009
Abstract
The photopromoted carbonylation of chloroalkanes with carbon monoxide catalyzed by cobalt compounds [Co(OAc)2, CoCl2]
in the presence of KI was carried out under ambient conditions. The results revealed that the catalytic activity of Co(OAc)2 was
higher than that of CoCl2. A basic additive NaOAc was beneficial to the reaction. Interestingly, with NaOAc as an additive,
Co(OAc)2 and CoCl2 exhibited similar catalytic activity. Preliminary work showed that the role of iodide ion was initially to form
active iodoalkanes via substituting chloride ion in chloroalkanes in situ, and then, the carbonylation of iodoalkanes proceeded under
irradiation.
# 2010 Xiang Sheng Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Photopromoted carbonylation; Chloroalkanes; Cobalt complexes; KI
Transition-metal-catalyzed carbonylation of haloalkanes is one of the common reactions to synthesize a series of
compounds, such as ester, carboxylic acid and amide. However, in conventional method, iodoalkanes or bromoalkanes
are often used as substrates, and high temperature and pressure or precious metal catalysts (such as Rh, Pd, Pt) are
required [1,2].
In recent years, it has been reported that photopromoted carbonylation of iodoalkanes or bromoalkanes could
proceed in the presence of inexpensive cobalt catalyst under ambient conditions [3–5]. Unfortunately, chloroalkanes
are unreactive under the above conditions. Nevertheless, the ready availability and cheap price of chloroalkanes make
it a desirable substrate. Besides, various carbonyl compounds can be obtained due to the variety of chloroalkanes. It is
well known that iodide ion is not only a good attacking group but also a good leaving group in nucleophilic
substitution. Therefore, it will be a promising method to perform the photopromoted carbonylation of relative inert
chloroalkanes by generating active iodoalkanes in situ. In this study, we report the photopromoted carbonylation of
chloroalkanes with CO in the presence of KI. Two inexpensive commercially available cobalt compounds, Co(OAc)2
and CoCl2, were selected as the catalyst, and the role of iodide ion in the reaction was discussed, and the possible
pathways of the reaction were investigated.
* Corresponding author.
1001-8417/$ – see front matter # 2010 Xiang Sheng Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.04.027

[(Scheme_1)TD$FIG]
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Y.P. Jia et al. / Chinese Chemical Letters 21 (2010) 1033–1036
Scheme 1.
1. Experimental
Carbon monoxide (99.9%, Dalian Guangming Institute); methanol, chlorocyclohexane, 1-chlorooctane, 1-octene,
n-decane, cobalt acetate, cobalt chloride, sodium acetate, potassium iodide, sodium iodide, CD3OD (v(D) > 99%)
(A.R., Beijing Chemical Engineering Co.).
A typical reaction procedure was as follows: First, a quartz reactor equipped with a 400 W high-pressure mercury
lamp was cooled with circulated water to maintain the reactor at room temperature. Then a quartz test tube, containing
a methanol solution of chloroalkanes (100 mmol/L), catalyst (10 mmol/L) and KI (10 mmol/L), was placed closely
against the outer wall of the quartz reactor. The reactions were carried out with irradiation for 24 h at room temperature
under 0.1 MPa of CO. The products were analysed by GC (Hitachi GC-3900) and GC-MS (HP 6890/5973) with n-
decane (10 mmol/L) as the internal standard.
2. Results and discussion
The photopromoted carbonylation of chlorocyclohexane with CO catalyzed by cobalt compounds [Co(OAc)2,
CoCl2] was carried out in the presence of KI. Cyclo-C6H11-COOCH3 was produced. The reaction is shown in Scheme
1 and the results are listed in Table 1. It was found that the reaction did not occur when KI, the catalyst or the light was
absent.
In the absence of NaOAc, the yield and selectivity of the ester with Co(OAc)2 as catalyst are higher than those with
CoCl2 (Table 1, entries 1 and 3). This implies that anions of cobalt compounds can affect the activities of the cobalt-
based catalysts. The reasons probably are that: (1) Co(OAc)2 is easier to coordinate with substrate and CO than CoCl2
due to its stable chelation [6]; (2) the UV–vis absorption of Co(OAc)2 is stronger than that of CoCl2 (Fig. 1; 756PC
UV–vis spectrophotometer). In order to test the dependence of the wavelength of light source on the absorption
capacity, commercially available 254 nm single-wavelength UV lamp (8 W) was served as the light source. The ester
was obtained with 8% yield and 89% selectivity under the catalysis of Co(OAc)2, while chlorocyclohexane was
unreactive with CoCl2. The results were significantly related to the absorptivities of Co(OAc)2 (e254 nm
0.335 Â 102 L molÀ1 cmÀ1) and CoCl2 (e254 nm = 0 L molÀ1 cmÀ1).
=
Generally, basic additives are beneficial to the carbonylation of halohydrocarbons [3–5,7]. When NaOAc was
added as a basic additive to the reaction, both the yield and conversion of the carbonylation increased (Table 1, entries
2 and 4). The role of NaOAc is probably as a base to neutralize HX formed in the reaction [4]. Furthermore, the
changes of yield and selectivity of the ester are more obvious when NaOAc is added to the CoCl2/KI catalytic system,
e.g. the yield and selectivity of the ester can be increased from 2% and 18% to 40% and 87%, respectively. Notably, the
results obtained in the CoCl2/KI/NaOAc system are the same to those in the Co(OAc)2/KI/NaOAc system. As a result,
we suggest that NaOAc plays an important role in the CoCl2/KI catalytic system not only to neutralize HX but also to
form Co(OAc)2 via acetate exchange between NaOAc and CoCl2.
Table 1
The photopromoted carbonylation of chlorocyclohexane catalyzed by cobalt compounds in the presence of KI.
Entry
Catalyst
NaOAc
Conversion (%)
Yield (%)
Selectivity (%)
1
2
3
4
Co(OAc)2
Co(OAc)2
CoCl2
À
+
23
45
11
46
20
40
2
87
89
18
87
À
+
CoCl2
40
Chlorocyclohexane 100 mmol/L, catalyst 10 mmol/L, n-decane 10 mmol/L, KI 10 mmol/L, NaOAc 50 mmol/L, CH3OH 4 mL, hn 24 h.

[(Fig._1)TD$FIG]
Y.P. Jia et al. / Chinese Chemical Letters 21 (2010) 1033–1036
1035
Fig. 1. The UV–vis absorption spectra of CoCl2, CoCl2 + NaOAc, Co(OAc)2 and NaOAc. Concentration: 1 mmol/L for CoCl2 and Co(OAc)2, and
2 mmol/L for NaOAc.
In order to verify that there are Co(OAc)2 formed in the presence of NaOAc and CoCl2, the UV–vis absorption
spectra of CoCl2, CoCl2 + NaOAc, Co(OAc)2 and NaOAc in methanol are recorded, as shown in Fig. 1. The maximum
absorption wavelength of Co(OAc)2 (lmax = 214 nm) is shorter than that of CoCl2 (lmax = 224 nm), however, its
absorption is stronger than that of CoCl2. When NaOAc was added to the solution of CoCl2, the maximum absorption
wavelength of CoCl2 was blue shifted from 224 nm to 214 nm and its absorbance increased, which are similar to those
of Co(OAc)2. The results revealed that Co(OAc)2 was obtained via acetate exchange between NaOAc and CoCl2.
In the presence of KI and NaOAc, linear 1-chlorooctane can also be carbonylated with Co(OAc)2 or CoCl2 as a
catalyst. The products mainly included normal ester CH3(CH2)6CH2COOCH3 (A) and branched ester
CH3(CH2)5CH(CH3)COOCH3 (B). The results are presented in Table 2.
With 1-chlorooctane as substrate, the similar results are obtained in both the Co(OAc)2/KI/NaOAc and the CoCl2/
KI/NaOAc system. The tendency is the same as that in those systems with chlorocyclohexane as substrate.
It is worth to note that the photopromoted carbonylation of chloroalkanes does not occur without KI when using
Co(OAc)2 or CoCl2 as catalyst, which implies that iodide ion plays an important role in the reaction. GC-MS analysis
of the methanol solution of 1-chlorooctane containing KI indicated that 1-iodooctane was formed after irradiation in
the solution. Thus it is proposed that the role of iodide ion is to form active iodoalkanes via substituting chloride ion in
chloroalkanes in situ, then, successive photopromoted carbonylation proceeds.
Inaddition, thecarbonylatedproductsofstraight-chainchloroalkanesarethecorrespondingnormal esterssuch asA in
general. Besides the expected normal ester A, however, branched ester B was obtained in the experiments with 1-
chlorooctane as substrate. Meanwhile, 1-octenewas detected in the reaction. It has been reported [8] that haloalkanes can
convert into olefins via b-hydride elimination under irradiation. But there was no 1-octene formed in the methanol
solution of 1-chlorooctane after irradiation. In contrast, 1-octenewas detected when KI was added. Therefore, the reason
of the formation of 1-octene is that 1-iodooctane, which formed from 1-chlorooctane and KI, undergoes b-hydride
elimination under irradiation. According to the literature [5], 1-octene reacted further with CO to give branched ester B.
Surprisingly, with 1-octene in the place of 1-chlorooctane as substrate in the Co(OAc)2/KI/NaOAc system, a
mixture of normal ester A and branched ester B in a ratio of 1:2.5 (mol:mol) were obtained, i.e. branched ester B was
dominant. This was against the carbonylation of 1-chlorooctane, where the major product was normal ester A (normal
Table 2
The photopromoted carbonylation of 1-chlorooctane catalyzed by cobalt compounds in the presence of KI and NaOAc.a.
Entry
Catalyst
Conversion (%)
Yieldsb (%)
Selectivity (%)
A:B
1
2
Co(OAc)2
CoCl2
59
56
40
38
68
68
5:1
5:1
a
1-Chlorooctane 100 mmol/L, the other conditions are the same as Table 1.
Total yields of A and B.
b

[(Scheme_2)TD$FIG]
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Y.P. Jia et al. / Chinese Chemical Letters 21 (2010) 1033–1036
Scheme 2.
[(Scheme_3)TD$FIG]
Scheme 3.
to branched ratio A:B = 5:1 (mol:mol), Table 2, entry 1). These results indicated that 1-iodooctane formed in the
reaction of 1-chlorooctane could be directly carbonylated. Therefore, the carbonylation of 1-chlorooctane in the
presence of KI may proceed through two ways: (1) 1-iodooctane yielded from 1-chlorooctane and KI was carbonylated
directly; (2) 1-iodooctane was converted into 1-octene firstly and the latter reacted with CO and methanol to produce
ester. This process is described in Scheme 2.
In order to further confirm that the photopromoted carbonylation of chloroalkanes in the presence of KI proceeds
through two ways, the carbonylation of chlorocyclohexane using CD3OD as solvent was investigated. MS analysis
showed that cyclo-C6H11-COOCD3 (m/z 145) and cyclo-C6H10-2-D-COOCD3 (m/z 146) in a ratio of 2.3:1 (mol: mol)
were obtained. It can be deduced that cyclohexene is formed in the reaction (Scheme 3).
In addition, similar results were obtained when NaI was used instead of KI in the reaction of chloroalkanes.
In conclusion, cobalt-catalyzed the photopromoted carbonylation of chloroalkanes with CO in the presence of
iodides may proceed through two ways. The role of iodide ion in the reaction is to form active iodoalkanes via
substituting chloride ion in chloroalkanes in situ. The activity of the carbonylation can be improved by addition of
NaOAc.
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