Mendeleev
Communications
Mendeleev Commun., 2014, 24, 229–230
Rhodium-catalyzed reductive carbonylation of iodobenzene
Oleg L. Eliseev,* Tatyana N. Bondarenko, Tatyana N. Myshenkova and Albert L. Lapidus
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 499 135 5303; e-mail: oleg@ioc.ac.ru
DOI: 10.1016/j.mencom.2014.06.014
Rhodium-phosphine complexes are efficient catalysts for the reductive carbonylation of iodobenzene to benzaldehyde.
Aromatic aldehydes belong to one of the most useful classes of
products as far as the formyl group can be easily involved in
C–C, C–N and C–S coupling reactions and other transforma-
tions. Generally, they are synthesized by the Gattermann–Koch,
Reimer–Tiemann, Vielsmeier–Haag, and Duff reactions. However,
these methods suffer from drawbacks like low yield, poor selec-
tivity and generating waste and by-products.1,2 Alternatively,
the catalytic formylation (reductive carbonylation) of aryl halides
with synthesis gas in the presence of palladium-phosphine com-
plexes was reported in 1974 by Schoenberg and Heck (Scheme 1).3
Table 1 Effect of catalyst on the reductive carbonylation of iodobenzene.
Reaction conditions: 4.5 mmol of PhI, 22 mmol of catalyst, 1.5 equiv. of
NEt3 and 5 ml of toluene. P = 1 MPa (CO/H2, 1:1), 4 h.
Yield (%)
Conver-
Catalyst
T/°C
sion (%)
PhCHO Benzene Biphenyl
PdCl2(PPh3)2
100
100
100
100
90
67.0
18.0
65.9
67.0
43.9
100
48.0
2.3
0.1
10.6
7.0
3.5
2.4
–
RhCl3·4H2O
HRh(CO)(PPh3)3
RhCl(CO)(PPh3)2
RhCl(CO)(PPh3)2
RhCl(CO)(PPh3)2
RhCl(CO)(PPh3)2
58.7
56.9
37.2
85.4
85.3
7.0
–
However, high pressure (8–10 MPa) and temperature (125–150°C
)
0.1
–
as well as high catalyst loading are obvious limitations of this
method. Lately, palladium/di-1-adamantyl-n-butylphosphine,4,5
palladium/di-tert-butylphosphinite,6 and Pd(acac)2/dppm7 systems
have been proposed. Despite high yields of aldehydes were
reached, serious disadvantages of these catalysts are low turn-
over frequency (10–25 h–1) and sophisticated ligands used in
catalyst formulations.
110
120
11.9
11.8
–
100
2.8
To find out the best reaction conditions, the effects of tem-
perature, synthesis gas pressure, bases and solvents on the reac-
tion have been studied. Decreasing temperature to 90°C in the
presence of RhCl(CO)(PPh3)2 led to a sharp decrease in both
iodobenzene conversion and benzaldehyde yield. On the contrary,
100% conversion and a high yield of benzaldehyde (85%) were
achieved at 110–120°C (Table 1).
Aromatic solvents such as toluene and o-xylene seem to be
the most suitable media, like previously mentioned for palla-
dium-catalyzed formylation.4–7 Other solvents such as heptane,
1,4-dioxane, methyl ethyl ketone, DMF and acetonitrile gave
a poor yield of benzaldehyde. Virtually no reaction occurred in a
tetrabutylammonium bromide (TBAB) melt. In a methanol solu-
tion, methyl benzoate was the main product (Table 2). Obviously,
Cat.
ArX + CO + H2
X = I, Br
Scheme 1
ArCHO
base
Rhodium complexes are well-known homogeneous catalysts
for olefin hydrogenation, hydroformylation and carbonylation
of methanol. Surprisingly, rhodium seems to be unexplored as
a catalyst for the reductive carbonylation of aryl halides. This
encouraged us to test rhodium salts and complexes in the reductive
carbonylation of iodobenzene as a model substrate.
The target reaction is accompanied by reductive dehalo-
genation leading to the formation of biphenyl, trace amounts of
benzene and some unidentified heavier products. Rhodium(iii)
chloride in the absence of stabilizing phosphine ligands gave
only a poor yield of aldehyde but greater amounts of benzene
and biphenyl. Good results were obtained with HRh(CO)(PPh3)3
and RhCl(CO)(PPh3)2.† These catalysts surpass the standard
palladium complex PdCl2(PPh3)2 in terms of selectivity to benz-
aldehyde (Table 1).
Table 2 Effect of solvent and base on the reductive carbonylation of iodo-
benzene. Reaction conditions: 4.5 mmol of PhI, 22 mmol of RhCl(CO)(PPh3)2,
1.5 equiv. of base and 5 ml of solvent. T = 110°C, P = 1 MPa (CO/H2, 1:1), 2 h.
Yield (%)
Conver-
Solvent
Base
sion (%)
PhCHO
Benzene
Toluene
o-Xylene
Heptane
1,4-Dioxane
MeC(=O)Et
DMF
MeCN
TBAB
MeOH
Toluene
Toluene
Toluene
Toluene
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
76.9
78.9
26.3
29.6
37.4
34.0
19.8
4.4
100.0
30.8
63.7
8.8
69.5
68.8
17.1
18.2
29.6
23.3
14.5
1.5
21.8
24.4
54.4
4.5
7.3
8.5
5.8
9.5
5.5
6.7
3.9
1.4
5.5a
4.6
7.9
1.0
0.5
†
Catalytic runs were carried out in a pressurized 50 ml glass-lined steel
reactor equipped with a magnetic stirrer and arrangements for automatic
temperature control. The reactor was charged with reagents and a catalyst,
flushed with CO/H2 (1:1) and filled with synthesis gas up to a desired
pressure. Then, the stirrer was switched on and the reactor was heated to
a desired temperature. After reaction complete the reactor was cooled
to ambient temperature and depressurized, the reaction mixture was
extracted with diethyl ether and analyzed by GC with nonane as an
NEt3
NBu3
NPr2iEt
K2CO3
Cs2CO3
7.6
5.5
1
internal standard. The product composition was confirmed by H NMR
a Methyl benzoate (65%) was found in the reaction mixture.
analysis.
© 2014 Mendeleev Communications. All rights reserved.
– 229 –