Selective catalytic hydrodimerization of 1,3-butadiene by palladium compounds dissolved in ionic liquids

Article abstract of DOI:10.1021/om970982p

Palladium(II) compounds dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI·BF₄) ionic liquid are shown to be able to catalyze the hydrodimerization of 1,3-butadiene. In most of the cases, only the 1,3-butadiene dimer 1,3,6-octatriene and the telomer octa-2,7-dien-1-ol have been obtained. The products' selectivity and catalytic activity depend on the reaction conditions. 1,3-Butadiene conversion up to 28%, a turnover frequency (TOF) of 118 h^-1, and a selectivity of 94% on telomer were achieved with (BMI)₂PdCl₄ dissolved in BMI·BF₄. The 1,3-butadiene conversion and TOF were significantly increased to 49% and 204 h^-1, respectively, by a 5-atm pressure of carbon dioxide. The reactions were performed under homogeneous conditions at 70 °C. However at temperatures below 5 °C, a two-phase system is formed and the products are easily removed from the reaction mixture by simple decanting. The recovered ionic catalyst solution can be reused several times without any significant changes in the catalytic performance. The structure of the new catalyst precursor (BMI)₂PdCl₄ has been determined by X-ray diffraction analysis.

Full text of DOI:10.1021/om970982p

Organometallics 1998, 17, 815-819
815
Selective Ca ta lytic Hyd r od im er iza tion of 1,3-Bu ta d ien e
by P a lla d iu m Com p ou n d s Dissolved in Ion ic Liqu id s
J eane E. L. Dullius, Paulo A. Z. Suarez, Sandra Einloft,
Roberto F. de Souza, and J airton Dupont*
Grupo de Cata´lise, Instituto de Quı´mica, UFRGS, Avenue Bento Gonc¸alves, 9500,
91501-970 Porto Alegre, RS, Brazil
J ean Fischer and Andre´ De Cian
Laboratoire de Cristallochimie, Universite´ Louis Pasteur, 4, rue Blaise Pascal,
67000 Strasbourg, France
Received November 7, 1997
Palladium(II) compounds dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate
(BMI‚BF4) ionic liquid are shown to be able to catalyze the hydrodimerization of 1,3-
butadiene. In most of the cases, only the 1,3-butadiene dimer 1,3,6-octatriene and the telomer
octa-2,7-dien-1-ol have been obtained. The products’ selectivity and catalytic activity depend
on the reaction conditions. 1,3-Butadiene conversion up to 28%, a turnover frequency (TOF)
of 118 h-1, and a selectivity of 94% on telomer were achieved with (BMI)2PdCl4 dissolved in
BMI‚BF4. The 1,3-butadiene conversion and TOF were significantly increased to 49% and
204 h-1, respectively, by a 5-atm pressure of carbon dioxide. The reactions were performed
under homogeneous conditions at 70 °C. However, at temperatures below 5 °C, a two-phase
system is formed and the products are easily removed from the reaction mixture by simple
decanting. The recovered ionic catalyst solution can be reused several times without any
significant changes in the catalytic performance. The structure of the new catalyst precursor
(BMI)2PdCl4 has been determined by X-ray diffraction analysis.
In tr od u ction
both catalytic systems (homogeneous and two-phase),
the use of carbon dioxide is essential for the production
of octa-2,7-dien-1-ol from 1,3-butadiene.1-4 Despite the
relatively vast number of studies over the past 20 years
on the use of water as solvent for two-phase catalysis,
limitations such as lower reaction rates due to poor
solvent properties of water for organic substrates or the
necessity to use special water-soluble ligands associated
with the transition metal catalyst precursors remain the
basic problem of these liquid-liquid catalytic systems.5
We6 and others7 have recently demonstrated that ionic
liquids based on the 1-n-butyl-3-methylimidazolium
cation are an important alternative to water as solvents
for the two-phase catalytic oligomerization, hydroform-
It is well-known that the homogeneous catalytic
hydrodimerization of 1,3-butadiene with soluble pal-
ladium complexes in the presence of carbon dioxide
affords in most of the cases octa-2,7-dien-1-ol.1 It has
also been demonstrated that palladium-water-soluble
phosphine compounds are also able to hydrodimerize
1,3-butadiene in typical two-phase (liquid-liquid) cata-
lytic reactions.2 In this respect, various patents3 have
recently appeared and a pilot plant based on two-phase
catalytic systems is operated by the Kuraray Co.4 In
(1) (a) Atkins, K. E.; Walker, W. E.; Manyik, R. M. J . Chem. Soc.,
Chem. Commun. 1971, 330. (b) Bianchini, J . P.; Waegell, B.; Gaydou,
E. M.; Rzehak, H.; Keim, W. J . Mol. Catal. 1981, 10, 247. (c) Dzhemilev,
U. M.; Sidorova, V. V.; Kunakova, R. V. Izv. Akad. Nauk SSSR, Ser.
Khim. 1983, 3, 584.
(2) (a) Monflier, E.; Bourdauducq, P.; Couturier, J .; Kervennal, J .;
Mortreux, A. J . Mol. Catal. 1995, 97, 29. (b) Monflier, E.; Bourdauducq,
P.; Couturier, J .; Kervennal, J .; Mortreux A. Appl. Catal. 1995, 131,
167.
(3) (a) Mori, T.; Kameo, H.; Isagai, S.; Saita, S. patent D. E. 19, 547,
498; Chem. Abstr. 1996, 125, 142108q. (b) Livingston, J . R. patent U.
S. 5,302,750; Chem. Abstr. 1994, 121, 86253m. (c) Miyazawa, C.; Mori,
T.; Kameo, H.; Isogai, S. patent W. O. 9400,410; Chem. Abstr. 1994,
120, 133838x. (d) Koga, K.; Noda, T.; Oguri, M. patent J . P. 5,155,795;
Chem. Abstr. 1993, 119, 249575t. (e) Thome, A.; Roeper, M.; Steeg-
mueller, F. J . patent D. E. 4,223,363; Chem. Abstr. 1993, 118, 254385q.
(f) Sato, K.; Nakajima, I.; Misu, Y. patent G. B. 2,260,136, 1993, 119,
138722u. (g) Drent, E. patent E. P. 542,366; Chem. Abstr. 1994, 120,
31538 g. (h) Packett, D. L. patent U.S. 5,169,981; Chem. Abstr. 1993,
118, 191171u. (i) Atkins, K. E.; Manyik, R. M.; O’Connor, G. L. patent
D. E. 2,018,054; Chem. Abstr. 1971, 74, 41892p. (j) Drent, W. T. patent
D. E. 2,148,156; Chem. Abstr. 1972, 77, 100777s. (k) Romanelli, M.
G.; Kelly, R. J . patent D. E. 2,011,163; Chem. Abstr. 1971, 74, 53040x.
(l) Roeper, M.; Bertleff, W.; Koeffer, D. patent D. E. 3,806,305; Chem.
Abstr. 1990, 112, 98016p.
(4) (a) Yasuo, T.; Tamio, H.; Kenichi, H.; Masami, M.; Noriaki, Y.
patent E. P. 436,226; Chem. Abstr. 1991, 115, 158508z. (b) Toshihiko,
M.; Yasuo, T.; Noriaki, Y. patent E. P. 296,550; Chem. Abstr. 1989,
110, 173469c. (c) Yasuo, T.; Noriaki, Y. patent E. P. 287,066; Chem.
Abstr. 1989, 110, 78070 g. (d) Maeda, T.; Tokito, Y.; Yoshimura, N.
patent J . P. 2,172,924; Chem. Abstr. 1991, 114, 5796w. (e) Yoshimura,
N.; Tamura, M. patent D. E. 3,034,098; Chem. Abstr. 1981, 95, 61442d.
(5) Herrmann, W. A.; Kohlpaintner, C. W. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1524.
(6) (a) Einloft, S. M. O.; Dietrich, F. K.; Souza, R. F.; Dupont, J .
Polyhedron 1996, 15, 3257. (b) Suarez, P. A. Z.; Dullius, J . E. L.; Einloft,
S. M. O.; Souza, R. F.; Dupont, J . Polyhedron 1996, 15, 1217. (c) Suarez,
P. A. Z.; Dullius, J . E. L.; Einloft, S. M. O.; Souza, R. F.; Dupont, J .
Inorg. Chim. Acta 1997, 255, 207. (d) Monteiro, A. L.; Zinn, F. K.;
Souza, R. F.; Dupont, J . Tetrahedron: Asymmetry. 1997, 8, 177.
(7) (a) Chauvin, Y.; Gilbert, B.; Olivier, H. J . Chem. Soc., Chem.
Commun. 1990, 1715. (b) Chauvin, Y.; Einloft, S. M. O.; Olivier, H.
Ind. Eng. Chem. Res. 1995, 34, 1149. (c) Chauvin, Y.; Olivier, H.;
Wyrvalski, C. N.; Simon, L. C.; Souza, R. F. J . Catal. 1997, 165, 275.
(d) Chauvin, Y.; Mussmann, L.; Olivier, H. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2698.
S0276-7333(97)00982-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/31/1998

816 Organometallics, Vol. 17, No. 5, 1998
Dullius et al.
Ta ble 2. Selectivity, Con ver sion , a n d Tu r n over
F r equ en cy (TOF ) of th e Hyd r od im er iza tion of
1,3-Bu ta d ien e by P a lla d iu m (II) Com p ou n d s
Dissolved in Ion ic Liqu id s u n d er Va r iou s Rea ction
Con d ition sa
Ch a r t 1
selectivity (%)
conversn TOF
catalyst
T
PCO
t
2
entry precursor (°C) (atm) (h)
4
5
(%)
(h-1
)
Ta ble 1. P h ysica l-Ch em ica l P r op er ties of Ion ic
Liqu id s BMI‚BF 4 a n d BMI‚P F 6 a t 30 °C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
1
2
3
1
2
3
6
6
70
70
70
70
70
70
40
70
100
70 10
70
70
70
70
70
70
70
24
24
24
3
3
3
3
3
3
3
3
3
3
3
24
3
24
89
88
90
85
88
90
88
84
88
89
94
60f
92
95
92
90
46f
11
12
10
15
12
10
12
16
12
11
6
10
8
5
8
10
12
28
23
27
36
38
19
29
49
19
40
28
17
22
29
31
26
22
15
12
14
152
161
82
118
204
81
169
118
73
93
122
16
solubilitye
ionic
liquid
ηa
db
κc
Td
(P) (g mL-1) (S cm-1) (°C) water hydrocarbons alcoholsf
5
5
5
5
5
5
BMI‚BF4 2.33
BMI‚PF6 3.12
1.17
1.37
0.0023 -81 yes
0.0019 -61 no
no
no
yes
yes
a
b
d
Viscosity. Density. c Specific conductivity. Glass transition.
e 50% weight solutions. f For methanol and ethanol.
6
6
6
6b
6b,c
6b,d
6
7
110
11
6e
a
Reaction conditions: 1,3-butadiene (125 mmol); water (125
mmol); catalyst precursor (0.1 mmol). Molten salt: BMI‚BF4 (15
b
mmol), [Pd] ) 0.035 mol/L. Molten salt: BMI‚PF6. c [Pd] ) 0.015
d
mol/L. [Pd] ) 0.050 mol/L. e Reaction in absence of molten salt.
f Formation of oligomers containing three to eight butadiene units.
Sch em e 1
F igu r e 1. Partial miscibility of MBI‚BF4 in water (w/w).
ylation, and hydrogenation of olefins by transition metal
complexes. In this work, we show that palladium(II)
compounds immobilized in 1-n-butyl-3-methylimidazo-
lium tetrafluoroborate are able to hydrodimerize selec-
tively 1,3-butadiene in the absence of carbon dioxide.
of 1,3-butadiene under different reaction conditions are
summarized in Table 2. In most of the cases, only the
telomer octa-2,7-dien-1-ol (4) and the 1,3-butadiene
dimer 1,3,6-octatriene (5) have been obtained (Scheme
1).
Resu lts a n d Discu ssion
It is noteworthy that both the alcohol and the 1,3-
butadiene dimer formed are soluble in this medium at
room temperature, but they are insoluble at tempera-
tures below 5 °C. The products can be easily separated
by simply decanting the reaction mixture at tempera-
tures below 5 °C. In the performed reactions using the
catalyst precursors 1-3, metallic palladium was de-
tected at the end of the reaction, thus limiting the
reutilization of this catalytic system. This can be
attributed to the instability of these palladium catalyst
precursors toward water. Nevertheless, it is important
to note that the hydrodimerization is effective even in
the absence of carbon dioxide (entries 1-3), but with
lower turnover frequency (TOF) as compared to the
reactions performed under carbon dioxide pressure
(entries 4-6).
The formation of metallic palladium could be sup-
pressed almost completely by the use of the new catalyst
precursor (BMI)2PdCl4 (6) (see later for its synthesis and
characterization). Atomic absorption analysis of metal
contents in the ionic and organic phases, after the
reaction, indicated that more then 97% of the palladium
is retained in the ionic phase. The recovered ionic
catalyst phase could be reused several times (at least
four) without any significant losses in catalytic ef-
ficiency. The increase of the reaction temperature from
40 to 70 °C (entries 7 and 8, respectively) causes an
Ion ic Liqu id s. The ionic liquids 1-n-butyl-3-meth-
ylimidazolium tetrafluoroborate (BMI‚BF4) and hexaflu-
orophosphate (BMI‚PF6) (Chart 1) have been chosen for
this study due to their distinct physical-chemical prop-
erties (Table 1).
The BMI‚BF4 is particularly interesting because of its
partial miscibility with water. Indeed, the miscibility
of this ionic liquid depends on the composition ratio
(molten salt/water) and on the temperature (Figure 1).
For example, a homogeneous mixture of 1/1 (w/w,
molten salt/water) is formed at temperatures above 5
°C and a two-phase mixture at temperatures below 5
°C. This allows one to perform the catalytic reaction
under homogeneous conditions in a relative large range
of temperatures and also to separate the products from
the catalytic solution at temperatures below 5 °C.
Moreover, classic palladium compounds such as [(η3-
C4H7)Pd-µ-Cl]2 (1) [(η3-C4H7Pd(1,5-cyclooctadiene)][BF4]
(2), and palladium acetate (3), which are known to
catalyze 1,3-butadiene telomerization reactions, are
completely soluble and stable, at room temperature, in
this ionic liquid.
Ca ta lytic Exp er im en ts. The catalytic systems were
prepared by mixing the palladium compound and the
ionic liquid at room temperature. The results obtained
with these catalytic systems in the hydrodimerization

Pd-Catalyzed Hydrodimerization of 1,3-Butadiene
Organometallics, Vol. 17, No. 5, 1998 817
Ta ble 3. X-r a y Exp er im en ta l Da ta
Sch em e 2
formula
mol w
cryst syst
C16H30N4Cl4Pd
526.66 g/mol
monoclinic
space group
P 1 21/n 1
a (Å)
8.833(2)
b (Å)
10.689(3)
c (Å)
11.766(3)
â (deg)
91.26(2)
1110.6(9)
V (Å3)
Z
color
2
enhancement of the 1,3-butadiene conversion without
any significant change in selectivity. However, at 100
°C, there is a dramatic decrease in the 1,3-butadiene
conversion. This is probably related to the instability
of the catalytic palladium-active species at higher
temperatures (100 °C). Indeed, metallic palladium was
observed at the end of the reactions performed at
temperatures above 100 °C (entry 9).
orange
crystal dimens (mm)
0.30 × 0.30 × 0.25
d
calc (g cm-3
)
1.57
F000
536
1.318
0.9062/1.0000
294
0.710 73
Mo KR graphite monochromated
Nonius CAD4-MACH3
θ/2θ
µ (mm-1
)
trans min/max
temp (K)
wavelength (Å)
radiation
diffractometer
scan mode
hkl limits
θ limits(deg)
no. of data meas
no. of data with I > 3σ(I)
weighting scheme
no. variables
R
The use of carbon dioxide on the catalytic systemsa
classical procedure in 1,3-butadiene hydrodimeriza-
tion1-4sincreases the 1,3-butadiene conversion (entries
8, 10, and 11), however, accompanied by a relative
decrease in octa-2,7-dien-1-ol selectivity from 94 to 84%.
The role of carbon dioxide in the hydrodimerization of
1,3-butadiene is not well understood: it is generally
accepted that CO2 facilitates the nucleophilic attack of
water on the η3-allylpalladium intermediates through
HCO3- species.2 The 1,3-butadiene hydrodimerization
catalyzed by palladium compounds dissolved in ionic
liquids occurs in the absence of carbon dioxide. In this
case, it is reasonable to assume that the ionic liquid
facilitates the ionization of water. This may also explain
the lower 1,3-butadiene conversion, catalytic activity,
and selectivity observed in the 1,3-butadiene hydrodimer-
ization reaction with 6 dissolved in BMI‚PF6, which is
insoluble in water and much less ionic then its tet-
rafluoroborate analogue (see entry 12 of Table 2 and
also Table 1).
There is no significant change in the catalytic selec-
tivity with increasing palladium concentration in the
ionic liquid (entries 11, 13, and 14). However, the TOF
increases with increase of the catalyst precursor con-
centrations to 0.035 mol/L. In concentrations higher
than 0.050 mol/L, metallic palladium was observed at
the end of the reaction. This behavior is probably
related to the saturation of the ionic phase by the
palladium species. This result suggests that the ionic
liquid also supports the stabilization of the catalytic
palladium active species.
-12, 12/0, 15/0, 16
2.5/30.40
3679
2598
4Fo2/(σ2(Fo2) + 0.0016 Fo
)
4
115
0.022
0.033
1.189
0.625
Rw
GOF
largest peak in final diff (e Å-3
)
Ta ble 4. Bon d Len gth s a n d An gles of 6
bond lengths (Å) bond angles (deg)
Pd-Cl1
2.2974(4)
2.3096(5)
1.325(2)
1.328(2)
1.367(2)
1.465(2)
1.340(3)
1.376(2)
1.472(2)
1.510(3)
1.512(3)
1.508(3)
Cl1-Pd-Cl2
90.05(2)
89.95(2)
108.4(2)
108.8(1)
125.8(2)
125.4(2)
107.3(2)
107.2(1)
108.3(1)
125.7(1)
126.0(1)
112.1(1)
112.9(2)
114.8(2)
Pd-Cl2
C1-N1
C1-N2
N1-C2
N1-C4
C2-C3
C3-N2
N2-C5
C5-C6
C6-C7
C7-C8
Cl1-Pd-Cl2
N1-C1-N2
C1-N1-C2
C1-N1-C4
C2-N1-C4
N1-C2-C3
C2-C3-N2
C1-N2-C3
C1-N2-C5
C3-N2-C5
N2-C5-C6
C5-C6-C7
C6-C7-C8
of the structure determination of 6 are presented in
Table 3. Selected bond lengths and angles of 6 are given
in Table 4. The ORTEP drawing of 6 is shown in Figure
2.
Compound 6 is constituted by a tetrachloropalladate
anion in which the coordination sphere of Pd including
the four chlorine atoms can be considered as essentially
planar. The two imidazolium cations adopted an eclipsed
conformation (with respect to the 1-butyl group). It is
interesting to note the relatively short distance between
the Cl2 atoms and the C1 carbon of the imidazolium
ring and that the Cl2-Pd bond length is ∼0.1 Å shorter
than Cl1-Pd. This can be attributed to the relative
strong hydrogen bonds existing between the ionic pair
through the chlorine atom and the hydrogen at C1 of
the imidazolium cation. These hydrogen bonds were
also corroborated by the presence of characteristic peaks
in the IR spectrum.
P r epar ation , Ch ar acter ization an d Cr ystal Str u c-
tu r e of 6. Compound 6 has been prepared in almost
quantitative yield by the reaction of palladium chloride
with 2 molar excesses of 1-n-butyl-3-methylimidazolium
chloride in acetonitrile at reflux temperature (Scheme
2). The palladium adduct 6 has been fully characterized
by means of C, H, N combustion analysis and IR, UV-
1
visible, H and 13C NMR spectroscopies. The IR spec-
trum of 6 shows the bands between 3100 and 3200 cm-1
(see Experimental Section) characteristic of hydrogen
bonding (C-H‚‚‚Cl interactions), already observed in
analogous compounds8 of Ni(II) and Co(II) containing
the 1-ethyl-3-methylimidazolium cation. The crystal
structure of the adduct 6 has been determined by X-ray
diffraction analysis. Crystallographic data and details
Ch em ica l Beh a vior of 6 Dissolved in BMI‚BF 4.
When water was added to an orange solution of 6 in
BMI‚BF4, the color slowly turned to light yellow with
evolution of a volatile product (Scheme 3). Compound
(8) Hitchcock, P. B.; Seddon, K. R.; Welton, T. J . Chem. Soc., Dalton
Trans. 1993, 2639.

818 Organometallics, Vol. 17, No. 5, 1998
Dullius et al.
16, Table 2) under the same reaction conditions. These
results clearly indicate that the true catalyst precursor
on the hydrodimerization of 1,3-butadiene is in fact 7.
Con clu sion s. The palladium compounds immobi-
lized in BMI‚BF4 ionic liquid catalyze the selective
transformation of 1,3-butadiene into octa-2,7-dien-1-ol.
This reaction was performed in homogeneous media at
70 °C, and the reaction products could be easily sepa-
rated from the reaction mixture by simply cooling the
system to temperatures below 5 °C followed by decanta-
tion. The recovered ionic catalyst solution could be
reused several times without any significant loss of the
catalytic performance. The complex BMI2PdCl4 under-
goes dealkylation in the presence of the ionic liquid and
water to produce the catalyst precursor trans-[PdCl2-
(MI)2]. Moreover, the hydrodimerization of 1,3-butadi-
ene could be performed even in the absence of carbon
dioxide. The selective hydrodimerization of 1,3-buta-
diene described in this work, associated with the
simplicity of the system, catalyst recovery, and separa-
tion of the products from the reaction mixture is an
outstanding example of technical applicability of molten
salts as immobilizing agents for transition metal cata-
lysts.10
F igu r e 2. ORTEP plot with atom labling scheme of the
structure of 6. H atoms are omitted for clarity.
Sch em e 3
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed under dry, oxygen-free argon using standard tech-
niques. All solvents were dried and distilled under argon prior
to use. Infrared (Nujol mulls or KBr pellets) spectra were
recorded in the region 4000-400 cm-1 using a Mattson 3020
FT-IR spectrophotometer. The 1H and 13C-{1H} NMR spectra
were recorded at 200.13 and 50.32 MHz, respectively, using a
Varian VXR-200 instrument. Proton and carbon shifts (δ/ppm,
J /Hz), are positive downfield relative to external SiMe4.
Elemental analyses were carried out by the Central Anal´ıtica
IQ/UFRGS (Porto Alegre, Brazil). Mass spectra were obtained
with GC/MS HP5988A (EI, 70 eV). The palladium contents
in both ionic and organic phases were determined by atomic
absorption analysis using a Perkin-Elmer 2380, HGA 400,
atomic absorption spectrometer with graphite tube atomizer
and autosampler. The reaction products were analyzed by gas
chromatography on a Varian 3400 chromatograph equipped
with an OV1 column, 30 m × 0.25 mm × 0.2 µm, and FID
detector; N2 was the carrier (1 mL/min); the temperature
program ranged from 50 (5 min) to 180 °C (5 min) at a heating
rate of 10 °C/min.
Ch a r t 2
7, whose crystal structure has already been reported,9
was isolated from the ionic solution and characterized
by C, H, N combustion analysis and IR, UV-visible and
1H and 13C NMR spectroscopy (see Experimental Sec-
tion). The formation of 7 is concomitant with the
evolution of but-1-ene (identified by CG/MS spectrom-
etry) and followed by the increase of the medium acidity
(pH changes from 7 to 3). It is important to note that
the transformation of 6 into 7 only occurs in the
presence of both BMI‚BF4 and water.
The (η3-allyl)palladium(II) derivatives11 1 and 2 and the
ionic liquids6b were prepared according to procedures described
in the literature. All other reagents were obtained from
commercial sources and were used as received without further
purification.
Syn th eses. Bis(1-bu tyl-3-m eth ylim id a zoliu m ) tetr a -
ch lor op a lla d a te (6). A mixture of 1-butyl-3-methylimida-
zolium chloride (1000 mg, 5.7 mmol) and palladium chloride
(507 mg, 2.8 mmol) in acetonitrile (75 mL) was heated at reflux
temperature for 24 h. The formed orange solution was
concentrated to ∼3 mL under reduced pressure. Addition of
toluene (25 mL) affords an yellow-orange solid that was
recovered by filtration, washed with toluene (2 × 10 mL), and
dried in vacuo (1.4 g, 93% based on Pd). Crystals suitable for
X-ray diffraction study were obtained by slow diffusion of
These results can be explained in terms of two
successive processes of oxidative addition reaction of the
imidazolium nitrogen-butyl bond to afford Pd(IV)-n-
butyl species (Chart 2), which undergo â-elimination
affording but-1-ene, followed by reductive elimination
of HCl. The ionic liquid should act as an ionizing agent
and is probably responsible for the stabilization of the
palladium species involved in this process.
Compound 7 was also isolated from the ionic catalyst
solution after the catalytic reaction. This compound has
a catalytic performance very similar (1,3-butadiene
conversion, activity, and selectivity) to 6 (entries 15 and
(10) (a) Dupont, J .; Souza, R. F.; Einloft, S. M. O.; Dullius, J . E. L.;
Suarez, P. A. Z. patent PI BR 9605670-3, 1996. (b) Dupont, J .; Souza,
R. F.; Einloft, S. M. O.; Dullius, J . E. L.; Suarez, P. A. Z. patent PI BR
9605493-0, 1996.
(9) Ranninger, M. C. N.; Carrera, S. M.; Blanco, S. G. Acta
Crystallogr., C 1983, 39, 186.
(11) Ito, T. S.; Hasegawa, S.; Takahashi, Y.; Ishii, Y. J . Organomet.
Chem., 1974, 73, 401.

Pd-Catalyzed Hydrodimerization of 1,3-Butadiene
Organometallics, Vol. 17, No. 5, 1998 819
toluene into an acetonitrile solution of the compound, at room
temperature. Anal. Calcd for C16H30Cl4N4Pd: C, 36.49; H,
5.74; N,10.64. Found: C, 36.31; H, 5.65; N, 10.57. IR (KBr):
3133, 3097, 3064 (νC-H aromatic); 2992, 2952, 2933, and 2871
(νC-H aliphatic); 1728 cm-1 (νCdN). 1H NMR (CDCl3): δ 8.95
(s, 1H, imidazolium ring); 7.39 (s, 1H, imidazolium ring); 7.36
chromatography using 2,4-pentanedione as internal standard.
The remaining light yellow catalytic ionic solution could be
reused several times.
Cr ysta llogr a p h ic Da ta Collection a n d Str u ctu r e De-
ter m in a tion of 6. Single crystals of 6 (C16H30N4Cl4Pd, MW
) 526.7), were obtained as described above. Data were
collected at room temperature using Mo KR graphite-mono-
chromated radiation, λ ) 0.7107 Å, on a Nonius CAD4-MACH3
diffractometer. The orange compound crystallizes in the
monoclinic system, space group P21/n, with a ) 8.833(2), b )
10.689(3), and c ) 11.766(3) Å, â ) 91.26(2), V ) 1110.6 Å,3
3
(s, 1H, imidazolium ring); 4.19 (t, 2H, J HH ) 5.9 Hz, CH2N);
3.88 (s, 3H, NCH3); 1.86 and 1.34 (2m, 4H, 2CH2); 0.93 (t, 3H,
3J HH ) 7.2 Hz, CH3). 13C-{1H} NMR (CDCl3): δ 137.5, 124.4,
and 123.1 (C-imidazolium ring); 50.2 (CH2N); 36.9 (NCH3); 32.7
and 20.0 (2CH2) and 13.7 (CH3).
Isola tion of Bis(m eth ylim id a zole) Dich lor op a lla d a te
(7). To an orange solution of 6 (53 mg, 0.1 mmol) in BMI‚BF4
(3 mL, 15 mmol) water (2.3 mL, 125 mmol) was added at room
temperature, immediately producing a light yellow solution.
After 24 h standing at room temperature, yellow-orange
crystals were formed which were recovered by filtration
washed with hexanes (10 mL) and dried in vacuo (15 mg, 44%).
Anal. Cald for C8H12Cl2N4Pd: C, 28.13; H, 3.55; N, 16.41.
Found: C, 29.05; H, 3.66; N, 17.12. IR (KBr): 3140, 3110,
3053 (νC-H aromatic); 2952, 2917 (νC-H aliphatic); 1698 cm-1
(νCdN). 1H NMR (CDCl3): δ 7.98 (s, 1H, imidazolium ring);
dcalcd ) 1.575 g cm-3, Z ) 2, and µ ) 13 177 cm-1
. A total
number of 3679 reflections were collected in the range 2° < θ
< 30°. Three standard reflections measured every hour during
the data collection period showed no significant trend. The
data were corrected for Lorentz, polarization, and absorption
factors (ψ scan of four reflections). A total of 2598 reflections
with I > 3 σ(I) were used. The structure was solved using the
heavy atom method. Hydrogen atoms were introduced as fixed
contributors (C-H ) 0.95 Å, B(H) ) 1.3 Beqv(C) Å2). For all
computations the Nonius MolEN package was used.12 Crystal
data and details on intensity collection parameters are indi-
cated in Table 3. Full-matrix least squares led to the final
values of R(F) ) 0.022, and Rw(F) ) 0.33.
3
7.41 (d, 1H, J HH ) 1.3 Hz, imidazolium ring); 6.78 (d, 1H,
imidazolium ring); 4.19 (s, 3H, NCH3); 1.86 and 1.34 (2m, 4H,
3
2CH2); 0.93 (t, 3H, J HH ) 7.2 Hz, CH3). 13C-{1H} NMR
Ack n ow led gm en t. This work was generously sup-
ported by the FINEP-PADCT and FAPERGS. J .E.L.D.
and P.A.S.Z. are indebted to CENPES-PETROBRAS for
fellowships.
(CDCl3): δ 139.2, 130.2, 119.4 (C-imidazolium ring); 34.4
(NCH3).
Ca ta lytic Exp er im en ts. In a typical experiment, 6 (53
mg, 0.1 mmol) was dissolved in the ionic liquid (3 mL) with
water (2.3 mL, 125 mmol), affording a light yellow solution.
To this solution, 1,3-butadiene (10 mL, 125 mmol) was
introduced, under an argon atmosphere, in a 100-mL stainless
steel autoclave equipped with a magnetic stirring bar. The
autoclave was pressurized with 10 bar of carbon dioxide and
heated at 70 °C for 3 h. The autoclave was then cooled and
degassed. The crude reaction mixture contained a single phase
that upon cooling to ∼5 °C produced two phases. The upper
phase was analyzed by gas chromatography. The 1,3-butadi-
ene conversion and butene selectivity were determined by gas
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters for non-hydrogen and for hydrogen atoms, thermal
parameters for anisotropic atoms, bond distances, and bond
angles (5 pages). Ordering information is given on any current
masthead page.
OM970982P
(12) Fair, C. K. MolEN, An Interactive Intelligent System for Crystal
Structure Analysis; Enraf-Nonius: Delft, The Netherlands, 1990.