Acetylferrocenyloxime palladacycle-catalyzed Heck reactions

Article abstract of DOI:10.1016/S0040-4039(01)01604-5

Acetylferrocenyloxime palladacycle catalyzed the Heck reaction of aryl bromides and activated aryl chlorides.

Full text of DOI:10.1016/S0040-4039(01)01604-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7877–7878
Acetylferrocenyloxime palladacycle-catalyzed Heck reactions†
Suresh Iyer* and A. Jayanthi
Organic Chemistry Synthesis Division, National Chemical Laboratory, Pune 411 008, India
Received 16 July 2001; revised 13 August 2001; accepted 24 August 2001
Abstract—Acetylferrocenyloxime palladacycle catalyzed the Heck reaction of aryl bromides and activated aryl chlorides. © 2001
Elsevier Science Ltd. All rights reserved.
Several novel palladacycles have been reported in recent
times to catalyze the Heck reaction of aryl halides with
olefins, the advantages being the longer life time of the
catalysts and more efficient catalysis. Cyclopalladated
aromatic rings are the choice systems for such catalysts
as the starting materials offer a wide variety of sub-
stituents and are readily available and easily cyclopalla-
Cyclopalladation of substituted ferrocenes is facile and
these complexes could be excellent catalysts for the
Heck reaction. Acetylferrocenyl oxime was cyclopalla-
dated according to the reported literature procedure to
give the dimeric acetylferrocenyl oxime palladacycle 1,
which was then converted into the monomeric com-
7
plexes 2 and 3 by treatment with PPh3 and P(OEt)3
dated.
A
variety of palladacycles incorporating
(Scheme 1). These complexes are thermally stable and
are also not sensitive to oxygen and moisture because
of the stable five-membered ring palladacycle.
cyclometallated phosphine,1 phosphite,2 carbene,3
imine,4 thioether5 and oxime6 have been reported with
high turnover numbers upto 105–106.
The Heck reaction between 4-iodoanisole and ethyl
acrylate or styrene proceeded readily in NMP as sol-
vent and catalyzed by complex 1 under standard condi-
tions (catalyst 0.01 mmol, ArX 2 mmol, olefin 2–5
mmol, NaOAc 4 mmol, NMP 5 mL, reaction tempera-
These palladacycles are both thermally and oxidatively
stable and the catalytic cycle operates through Pd(II)–
Pd(IV) instead of the traditional Pd(0)–Pd(II)
mechanism.
Table 1. Acetylferrocenyloxime palladacycle catalyzed Heck reactions
Serial no.
Aryl halide (ArX)
Olefin
Yield (%)
Cat 1a
Cat 2a
Cat 3a
1
2
3
4
5
6
7
8
4-Iodoanisole
4-Iodoanisole
Bromobenzene
Bromobenzene
4-Bromophenol
1-Bromonaphthalene
1-Bromonaphthalene
4-Chloroacetophenone
Ethyl acrylate
Styrene
Ethyl acrylate
Styrene
Ethyl acrylate
Ethyl acrylate
Styrene
74
69
47
55
24
76
81
30
93
67
58
60
20
66
81
53
93
73
70
72
45
61
79
18
Styrene
a Catalyst 1, 2 or 3. See Scheme 1.
Reaction conditions: Catalyst concentration, 0.01 mmol; ArX, 2 mmol; olefin, 2–5 mmol; base, NaOAc (2 equiv.); temperature, 140–150°C;
solvent, NMP.
Keywords: acetylferrocenyloxime palladacycle; Heck reaction; aryl bromides.
* Corresponding author. E-mail: siyer@dalton.ncl.res.in
†
NCL Communication No. 6610.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01604-5

7878
S. Iyer, A. Jayanthi / Tetrahedron Letters 42 (2001) 7877–7878
Scheme 1.
Table 2. Acetylferrocenyloxime palladacycle catalyzed Heck reaction at low catalyst concentrations
Serial no.
Aryl halide (ArX)
Olefin
Yield (%)
Cat 1a (TON)
Cat 2a (TON)
Cat 3a (TON)
1
2
3
4
5
6
7
8
9
4-Iodoanisole
4-Iodoanisole
Bromobenzene
Bromobenzene
Ethyl acrylate
Styrene
Ethyl acrylate
Styrene
Ethyl acrylate
Ethyl acrylate
Styrene
65 (62500)
73
79 (15192)
84 (7000)
45
83 (31923)
94 (36153)
30 (38)b
22 (28)b
84 (14000)
67
78 (13000)
79 (5266)
92 (15333)
69
77 (10694)
83 (5533)
24
90 (25000)
97 (26944)
53 (81)b
37 (58)b
4-Bromophenol
20
1-Bromonaphthalene
1-Bromonaphthalene
4-Chloroacetophenone
4-Chlorobenzonitrile
86 (28666)
91 (30333)
–
–
Styrene
Styrene
a Catalyst 1, 2 or 3. Scheme 1.
b Bu4NBr, 1 mmol.
Reaction conditions: Catalyst concentration, 2.6×10−4 mmol to 1.3×10−3 mmol; ArX, 10–25 mmol; olefin, 10–50 mmol; base, NaOAc (2 equiv.);
temperature, 140–150°C; solvent, NMP.
ture 140–150°C) to give ethyl (E)-4-methoxycinnamate
and (E)-4-methoxystilbene in 74 and 69% yields, respec-
tively. The monomeric catalysts 2 and 3 gave a 93% yield
of ethyl (E)-4-methoxycinnamate and 73 and 67% yields
of (E)-4-methoxystilbene (Table 1). The reaction of 25
mmol of 4-iodoanisole with ethyl acrylate (50 mmol) in
the presence of 2.6×10−4 mmol of catalyst 1 gave the ethyl
(E)-4-methoxycinnamate in 65% yield with a turnover
number of 62500. Increasing the catalyst concentration
to 1.3×10−3 led to a shorter reaction time, but did not
improve the yield (76–84%). The catalysts 2 and 3 gave
84 and 92% yields of ethyl (E)-4-methoxycinnamate
(catalyst concentration 1.5×10−3 mmol) (Table 2).
substituted products. The acetylferrocenyloxime pallada-
cycles are thus excellent catalysts for the Heck reaction,
though not as active as the previously reported acetophe-
none and benzophenone oxime palladacycles.5
Acknowledgements
We thank the DST for research funds and CSIR for a
JRF to A.J.
References
Complexes 1, 2 and 3 showed appreciable catalytic
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NaOAc was a better base than K2CO3. 4-Bromophenol
reactedwithethylacrylatetogivetheethyl-4-(E)-hydroxy-
cinnamate in only 20–45% yields.
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