Table 4 Results of iodobenzene carbonylation with 1, 2 and Pd
Synthesis of di-l-chlorobis(2-methoxycyclooct-5-enyl)-
dipalladium(II) (2)
colloid on PVPa
Et3N (0.1 g, 7.2 ꢂ 10ꢃ4 mol) was added to a suspension of 0.1 g
(3.5 ꢂ ꢄ10ꢃ4 mol) 1 in 2 ml of methanol and stirring continued
for 1 h. The color of the precipitate changed from yellow to
white, whereas the solution became colorless. The white preci-
pitate was filtered off and vacuum dried. Yield: 65%. Anal.
calcd for C9H15ClOPd (%): C 38.46, H 5.38; found: C 38.42,
H 5.60. 1H NMR (CDCl3 , d): 1.40 m (1H), 1.94 m (2H),
2.18 m (3H), 2.59 m (2H), 3.22 s (3H, OCH3), 3.55 m (2H),
Catalyst
1
2
Pd colloidb
X in [nBu4N]X % Yield TON % Yield TON % Yield TON
–
–
17
3
31
5
9
8
17
15
4
–
16
c
Brc
Br
93
98
87
83
95
77
171
180
160
152
174
141
93
91
89
95
88
74
171
167
163
174
162
136
–
5.46 m (1H, CH CH), 5.88 m (1H, CH CH). 13C NMR
=
=
73
39
72
70
60
292
156
288
280
240
(CDCl3 , d): 26.5 (CH2), 28.1 (CH2), 30.8 (CH2), 34.5 (CH2),
=
52.2 (C2), 56.6 (OCH3) 81.4 (C1), 101.9 (CH ), 106.4
I
Cl
=
(CH ). In the same way, using CD3OD instead of CH3OH,
BF4
PF6
the analogous complex 20, with an attached OCD3 group,
was obtained. 1H NMR (CDCl3 , d): 1.38 m (1H), 1.93 m
(2H), 2.18 m (3H), 2.60 m (2H), 3.58 m (2H), 5.46 m (1H,
[Pd] ¼ 4.9 ꢂ 10ꢃ5 mol, [NEt3] ¼ 2.2 ꢂ 10ꢃ2 mol, [CH3OH] ¼ 2.5 ꢂ
10ꢃ2 mol, [PhI] ¼ 9 ꢂ 10ꢃ3 mol [nBu4N]X ¼ 9 ꢂ 10ꢃ3 mol; 2 h, 5 atm
CO, 70 ꢀC. b [Pd] ¼ 2.25 ꢂ 10ꢃ5 mol. c Reaction mixture was stirred 1
h at 70 ꢀC and under 5 atm CO before PhI introduction.
a
CH ), 5.87 m (1H, CH ). 13C NMR (CDCl3 , d): 26.5
=
=
(CH2), 28.1 (CH2), 30.8 (CH2), 34.5 (CH2), 46.0 (OCD3),
=
51.9 (C2), 81.3 (C1), 101.8 (CH ), 106.3 (CH )
=
obtained for the catalytic system with addition of [nBu4N]Br
(Table 4). In the first reaction (98% yield of ester) all reaction
components were simultaneously introduced into the auto-
clave, whereas in the second reaction (ester yield 91%) iodo-
benzene was introduced into the autoclave after prior
heating of all other components for 1 h. Complex 2 used as
a catalyst precursor demonstrated behavior similar to complex
1. The addition of [nBu4N]Br increased the reaction yield from
9% to 93% or 91%. The heating of all reactants for 1 h before
iodobenzene introduction had very little influence on reaction
yield, which was 93%. Both systems (based on precursors 1 and
2) presented high catalytic activity in the carbonylation reac-
tion with all the ammonium salts used (Table 4). It may be
concluded that the [nBu4N]þ cation plays the most important
role in stabilizing in situ formed Pd colloids, whereas the effect
of the anion is insignificant.
Synthesis of Pd colloid/PVP
First 1 (0.078 g, 2.8 ꢂ 10ꢃ4 mol) and then 1 ml (7.2 ꢂ 10ꢃ3 mol)
of Et3N were added to 0.26 g PVP dissolved in 3 ml of benzene
in a Schlenk tube. The color of the solution changed from yel-
low to orange and subsequently became turbid. When the
Schlenk tube was filled up with CO, the solution immediately
turned black. After mixing and heating at 40 ꢀC for 3 h the sol-
vent (benzene) was evaporated and the obtained Pd colloid
was XRD analyzed and subsequently used as a catalyst in test
reactions. XRD and IR analyses showed that the colloid
contained Et3NꢄHCl and the Pd content was ca. 8%.
Another Pd colloid was obtained in the same way using
methanol instead of benzene.
Reduction of Pd(II) in the presence of Et3N and CO
The positive effect of ammonium salts was also evident in
reactions catalyzed by Pd colloid stabilized on PVP. The pre-
sence of PVP is not sufficient to stabilize a catalytically active
form of Pd colloid, as evidenced by the very low yield of ester
(ca. 4%). However, the addition of ammonium salt increased
the yield of ester to 73% for [nBu4N]Br and 39% for [nBu4N]I.
The data collected in Table 4 allow us to assume that Pd col-
loid stabilized on PVP is slightly less active than that obtained
in situ from precursors 1 or 2. This may be explained as an
effect of a decrease in the colloid active surface as a result of
Pd nanoparticle interaction with a large excess of the polymer
PVP ([PVP]:[Pd] > 10). A similar effect of PVP was also
observed in the Suzuki reaction.14
Reduction of complex 1. To a suspension of 0.05 g
(1.75 ꢂ 10ꢃ4 mol) of 1 in 1 ml of methanol or ethanol in a
Schlenk tube was added 0.1 ml (7.2 ꢂ 10ꢃ4 mol) of Et3N in a
CO atmosphere (1 atm) and stirring was continued for 0.5–3
h. A black precipitate was filtered off, vacuum dried and
XRD analyzed. 2-Alkoxy-5-cyclooctene carboxylic acid esters
were found in the filtrate by GC-MS. Some experiments were
done at higher Et3N concentrations—the reaction conditions
are given in Table 1.
Reduction of complex 2. To a suspension of 0.024 g
(9.1 ꢂ 10ꢃ5 mol) of 2 in 0.5 ml of CD3OD in a Schlenk tube
was added 0.05 ml (3.6 ꢂ 10ꢃ4 mol) of Et3N and stirring was
continued in a CO atmosphere (1 atm) for 3 h. A black preci-
pitate of Pd colloid was separated and vacuum dried and the
filtrate was GC-MS analyzed.
Experimental
General
Carbonylation reaction procedure
PdCl2(cod) was obtained according to the literature method.19
Methanol, Et3N and diethyl ether were purified using standard
procedures.20 Iodobenzene and mesitylene were used without
purification. Ammonium salts, [nBu4N]X (X ¼ Br, Cl, I,
BF4 , PF6 , were purchased from Merck and PVP was
purchased from Aldrich.
All syntheses were performed under an N2 atmosphere using
Schlenk techniques.
The following instruments were used: BRUKER 300 MHz,
GC-MS Hewlett Packard 8452A, DRON 3 powder diffracto-
meter with CuKa radiation, Hewlett Packard 8452 Diode
Array.
The carbonylation reactions were carried out in 50 cm3 glass
thermostatted vessel (reactions under 1 atm of CO) or in a
130 cm3 steel autoclave. Proper volumes of liquid reagents
were introduced under an N2 atmosphere. The palladium cat-
alyst was weighted in a small teflon vessel and placed in the
autoclave. After closing the appropriate CO pressure and tem-
perature were fixed. After the reaction, the autoclave was
cooled down, the CO excess was removed, the reaction
products extracted with diethyl ether (3 ꢂ 3 cm3) and analyzed
using the GC-MS method with mesitylene as internal
standard.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
862
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 8 5 9 – 8 6 3