Highly selective and efficient catalyst for carbonylation of aryl iodides: Dimeric palladium complex containing carbon-palladium covalent bond

Article abstract of DOI:10.1055/s-2002-34836

Dimeric cyclometallated oxime palladium complex containing palladium-carbon covalent bond was found to efficiently catalyze the carbonylation reactions of aryl iodides with various alcohols to give esters in excellent yields with high selectivity. These complexes were also stable under a carbon monoxide atmosphere at high temperatures.

Full text of DOI:10.1055/s-2002-34836

SHORT PAPER
2171
Highly Selective and Efficient Catalyst for Carbonylation of Aryl Iodides:
Dimeric Palladium Complex Containing Carbon-Palladium Covalent Bond
Highly Selective
h
and
E
fficie
n
i
t
Cataly
n
st for Carbo
n
nylation of
A
a
ryl Iodidessamy Ramesh, Yoshihiro Kubota, Minoru Miwa, Yoshihiro Sugi*
Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan
E-mail: sugi@apchem.gifu-u.ac.jp
Received 26 April 2002; revised 30 July 2002
and to overcome the above-mentioned disadvantages, we
Abstract: Dimeric cyclometallated oxime palladium complex con-
taining palladium-carbon covalent bond was found to efficiently
catalyze the carbonylation reactions of aryl iodides with various al-
cohols to give esters in excellent yields with high selectivity. These
focused our study on finding efficient palladium catalysts
that are structurally important and stable under carbon
monoxide atmosphere. Very few research groups have re-
complexes were also stable under a carbon monoxide atmosphere at ported that Pd(II) complexes rather than traditional Pd(0)
high temperatures.
catalysts with PPh3 ligands were highly active in C–C
bond forming reactions such as Heck reaction, Suzuki and
Stille coupling and in which the high catalytic activity was
explained by the oxidative addition mechanism.10 The
study of the mechanism of oxidative addition involving
Pd(II) to Pd(IV) is an interesting aspect of palladium cat-
alyzed reactions and is attributed to higher activity of the
catalyst.
Key words: palladacycle, carbonylation, aryl iodides, turnover
numbers, aromatic esters
Carbonylation of aromatic halides catalyzed by Pd(0)
complexes is one of the versatile and convenient process-
es towards the synthesis of various aromatic carbonyl
compounds, especially key intermediates in organic syn-
thesis.1–3 The combination of aryl and vinyl halides with
nucleophiles such as alcohols and amines leads to an in-
teresting application in syntheses of natural products2,4
and polymers.5–8 Palladium-catalyzed carbonylation-
polycondensation reactions are also well recognized by
the polymer chemist in the synthesis of soluble organic
polymers namely polyesters and polyamides.6–8 Even
though many carbonylation catalysts have emerged in the
past few decades, the search for new catalysts continues
because of economical and environmental demands.9 In
most of the above reactions, Pd(0) complexes with phos-
phine ligand were employed as catalysts. The major draw-
backs of the use of phosphine ligands in such catalytic
reactions are (i) the oxidation of phosphine to phosphine
oxide causing degradation of the catalyst, (ii) reduction of
the complex catalyst to metal, (iii) termination of the cat-
alytic cycle, and (iv) separation of products from the com-
plex reaction mixture containing phosphine and
phosphine oxide. By considering the importance of palla-
dium-catalyzed carbonylation reactions in various fields
In our present study, we investigated the synthesis of nov-
el, covalently bonded, structurally stable cyclometallated
dimeric oxime palladium(II) catalysts and their stability
under carbon monoxide pressure. We also dealt with the
mechanism of oxidative addition reactions of Pd(II) to
aryl halides to give Pd(IV) complexes in carbonylation re-
actions. The Pd complex 1 has been synthesized from
readily available benzophenoneoxime and lithium tetra-
chloropalladate (Scheme 1).11 Such metal complexes with
a covalently bonded palladium to the aromatic ring could
be more stable and can perform as efficient catalysts un-
der carbon monoxide atmosphere.
Table 1 shows the results of carbonylation of aryl iodides
2 that have electron donating as well as electron with-
drawing groups at para-position with various alcohols 3
catalyzed by the complex 1. The complex 1 efficiently
catalyzed the reaction to give the corresponding esters 4
(Scheme 2), and was highly stable under carbon monox-
ide pressure of up to 1.0 MPa at high temperature
(120 °C). In all cases, clean reaction proceeded to give
single product with high selectivity. No deposition of pal-
OH
N
Cl
Cl
Ph
LiCl
Pd
Pd
OH
+
PdCl2
Ph
N
MeOH, r.t.
N
OH
1
Scheme 1
Synthesis 2002, No. 15, Print: 29 10 2002.
Art Id.1437-210X,E;2002,0,15,2171,2173,ftx,en;F03302SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

2172
C. Ramesh et al.
SHORT PAPER
ladium metal and no decomposition of the complexes The phenoxycarbonylation of 1-bromo-4-iodobenzene
were observed during the reaction. As shown in Table 1, leads to 4-bromobenzoic acid phenyl ester in high yield.
most of the reactions gave the target esters in high yields. Reactivities for aryl bromides and chlorides were low un-
The reaction proceeded smoothly under carbon monoxide der the conditions. These results prove that the complex 1
pressure of 0.1 to 1 MPa.
is highly selective to aryl iodides. We also examined the
carbonylation reactions of various aryl iodides (5.0 mmol)
with aliphatic alcohols as well as less reactive phenol us-
ing minimum amount of catalyst (0.0014 mmol, 1 mg) in
order to investigate its catalytic activity. It leads to suc-
cessful turnover number of 3915 and turnover frequency
of 978. However, -bromostyrene with phenol gave esters
in lower yield.
COOR1
I
1
R1OH
+
CO, DBU
120ºC
3
R
R
2
4
We emphasize that the complex 1 contains no phosphine
ligand and has carbon–palladium covalent bonds. This is
the first report of using 1 and such Pd(II) complexes as
catalysts for carbonylation. It is noteworthy that oxidative
addition [probably involving Pd(II) to Pd (IV)] with aryl
halides takes place without affecting the Pd–C covalent
R: H, CH3, OCH3, Ph
R1: Et, PhCH2, Ph
Scheme 2
Table 1 Alkoxy and Phenoxycarbonylations of Aryl Iodides Catalyzed by Dimeric Oximepalladacycle 1
Entry
1
Aryl halide
R1–OH
EtOH
Product
Yield (%) (isolated)
95
I
COOEt
2
3
PhCH2OH
PhOH
91
91
90
85
87
83
90
92
86
83
76
I
COOCH2Ph
COOPh
I
4
EtOH
Ph
Ph
Ph
COOEt
Ph
I
I
I
5
PhCH2OH
PhOH
COOCH2Ph
Ph
6
COOPh
Ph
7
PhCH2OH
EtOH
H3C
H3CO
H3CO
Br
I
H3C
H3CO
H3CO
Br
COOCH2Ph
COOEt
8
I
I
9
PhOH
COOPh
10
11
12
PhOH
I
COOPh
PhCH2OH
EtOH
EtOOC
COOCH2Ph
EtOOC
I
I
I
COOEt
13
14
EtOH
PhOH
80
81
I
I
EtOOC
PhOOC
COOEt
COOPh
I
Synthesis 2002, No. 15, 2171–2173 ISSN 0039-7881 © Thieme Stuttgart · New York

SHORT PAPER
Highly Selective and Efficient Catalyst for Carbonylation of Aryl Iodides
2173
bond. The large turnover number indicates that complex 1
is very stable even at high temperatures and has a longer
lifetime.
References
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In conclusion, the complex 1 proved to be an efficient cat-
alyst for the carbonylation of various aryl iodides with dif-
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give corresponding esters in excellent yields with high se-
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mmol), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU, 3.0 mmol) and
catalyst (0.01 mmol) in benzene (5 mL) were taken in autoclave (50
mL), flushed with nitrogen 3 times and pressurized with carbon
monoxide (0.5 MPa). The autoclave was placed in oil bath heated at
120 °C and the whole mixture was stirred for 3 h. After the reaction,
the autoclave was cooled, excess carbon monoxide was purged, and
benzene was evaporated in vacuo. The product was isolated by sil-
ica gel column chromatography (hexane benzene). All the prod-
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Acknowlegement
We are grateful to grant aid for the development of Innovative
Technology, Ministry of Education, Culture, Sports, Science and
Technology, Japan. C. Ramesh thanks Mr. T. Yamashita for NMR
and IR spectroscopy and STA for the fellowship.
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43, 326.
Synthesis 2002, No. 15, 2171–2173 ISSN 0039-7881 © Thieme Stuttgart · New York