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B. Boualy et al. / Catalysis Communications 12 (2011) 1295–1297
Table 1
Table 3
Addition of CCl4 to styrene catalyzed by various metal acetylacetonates.
Temperature and styrene/CCl4 ratio on the addition of CCl4 to styrene catalyzed by
Fe(acac)3.
Entry
M(acac)n
Time (h)
Conversion (%)a
Yield (%)a
Entry
Styrene/CCl4
Temperature (°C)
Conversion (%)a
Yield (%)a
1
2
3
4
5
6
7
8
–
48
24
24
48
24
24
48
24
24
48
0
58
72
23
83
79
15
100
66
0
0
41
65
15
76
67
8
87
52
0
Zn(acac)2
Co(acac)2
V(acac)4
1
2
3
4
5
6
7
8
9
0.125
0.20
0.25
0.5
0.75
1
0.25
0.25
0.25
80
80
80
80
80
80
40
60
100
100
100
100
77
68
51
46
72
100
74
78
87
64
58
42
42
58
61
Ni(acac)2
MoO2(acac)2
Mn(acac)2
Fe(acac)3
Cr(acac)3
9
10b
Fe(acac)3
Reaction conditions: styrene/CCl4 (0.25), catalyst (0.01equiv), triethylamine (0.05 equiv),
temperature (80 °C), solvent (toluene), dodecane (150 mg).
Reaction conditions: Fe(acac)3 (0.01 equiv), solvent (toluene), triethylamine (0.05 equiv),
dodecane (150 mg), for 24 h.
a
a
Conversion and yields based on GC using dodecane as internal standard.
Conversion and yield are determined by GC using dodecane as internal standard.
b
Without triethylamine.
(entries 1, 2 and 4). In dioxane or ethanol almost 50% yield was
obtained (entries 6 and 7).
catalyzed by different metal acetylacetonates did not proceed with
similar activity (Scheme 1).
We have also investigated the combined effects of temperature
and styrene/CCl4 ratio. The reactions were performed under our
optimized conditions (Table 3). On the basis of these results, we found
some telomerization reaction at higher temperatures (entry 9). When
the temperature was decreased to 60 °C or 40 °C, the reaction was
incomplete with significant amount of styrene remaining but afforded
the monoadduct product (entries 7 and 8). The conversion and the
yield of the reaction were lower when increasing the molar ratio
under optimized reaction conditions. We can assume that the use of a
lower styrene/CCl4 molar ratio promoted also the telomerization
reactions (entry 1).
With the encouraging results obtained, we have extended this
protocol to a variety of alkenes (Table 4). The Fe(acac)3 which gives
the best results with styrene was then used under optimized reaction
conditions.
As expected in Table 4, α-methylstyrene and β-methylstyrene,
lead respectively to the corresponding adducts in 86% and 83% yields
(entries1 and 2). The Kharasch addition was less efficient in the
presence of simple alkenes but provided selectively the monoadduct
compounds. After 24 h at 80 °C, the CCl4 adducts of 1-hexene,
cyclohexene and 1-octene were obtained respectively in 72%, 65%
and 73% yields (entries 3, 4 and 5).
Among the transition metal acetylacetonates used, Mn(acac)2 and
V(acac)4, were found to be the less reactive (8–15%) even after
prolonged reaction time (entries 4 and 7). Zn(acac)2 and Cr(acac)3
catalysts, gave respectively the adduct in a moderate yields (41% and
52%, respectively). In contrast, Co(acac)2, Ni(acac)2 and Fe(acac)3
were the most reactive in catalyzing the addition of tetrachloro-
methane to styrene (entries 3, 5 and 8). Excellent yield was obtained
with Fe(acac)3 as catalyst (entry 8). On the other hand, several control
experiments were conducted to assess the role of the catalyst and/or
co-catalyst. As expected in Table 1, no reaction occurred in the
absence of a catalyst (entry 1) and triethylamine as co-catalyst (entry
10) even under long reaction time. It is known that the catalytic
activity of metal complexes in the reaction followed by homolysis of
C–X (X=Cl, Br, I) bond could be increased by using nucleophilic
additives (alcohols, amines, etc.) [19].
To optimize the reaction conditions, we next studied the effect
of the solvents in the addition of carbon tetrachloride to styrene using
Fe(acac)3 as catalyst in the presence of triethylamine as co-catalyst
at 80 °C. As can be seen in Table 2, the highest efficient protocol for
the Kharasch addition was achieved in toluene, CCl4 and CH3CN
4. Conclusions
CCl3
Cl
In conclusion, we have developed an efficient catalytic method for
the Kharasch addition of tetrachloromethane to olefins under mild
reaction conditions. Using various transition metal acetylacetonates
M(acac)n (M=Zn, Co, V, Ni, Mo, Mn, Fe and Cr) and triethylamine
as co-catalyst, Fe(acac)3 was found the highly active catalyst. A
systematic investigation on the effects of solvent, temperature, olefin/
CCl4 ratio and the presence of nucleophilic co-catalyst has been
performed. The extension of this methodology to a variety of alkenes
has been carried out. The reactions offer the halogen derivatives in
M(acac)n
CCl4
NEt3 , Solvent
Scheme 1. Addition of tetrachloromethane to styrene using M(acac)n as catalyst.
Table 2
Solvent effect on the addition of tetrachloromethane to styrene using Fe(acac)3 as
catalyst.
Table 4
Kharasch addition of carbon tetrachloride to representative olefins.
Entry
Solvent
Conversion (%)a
Yield (%)a
Entry
Olefins
Conversion (%)a
Yield (%)b
1
2
3
4
5
6
7
Toluene
CCl4
THF
CH3CN
DMF
Ethanol
Dioxane
100
100
93
100
81
87
72
67
82
73
52
45
1
2
3
4
5
α-methylstyrene
β-methylstyrene
1-hexene
cyclohexene
1-octene
96
94
83
71
79
86
83
72
65
73
72
63
Reaction conditions: Olefin/CCl4 (0.25), Fe(acac)3 (0.01 equiv), solvent (toluene),
Reaction conditions: styrene/CCl4 (0.25), Fe(acac)3 (0.01 equiv), triethylamine (0.05
equiv), temperature (80 °C), dodecane (150 mg), for 24 h.
triethylamine (0.05 equiv), temperature (80 °C), dodecane (150 mg), for 24 h.
a
Conversion based on GC using dodecane as internal standard.
a
b
Conversion and yield are based on GC using dodecane as internal standard.
Isolated yield.