Synthesis, characterization, and biphasic ionic liquid media 1-hexene hydrogenation reaction of RuCl2(DMSO)2(NC 5H4CO2Na-3)2

Article abstract of DOI:10.1007/s11243-011-9510-2

RuCl₂(DMSO)₂(NC₅H₄CO ₂Na-3)₂ is very soluble in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium tetrafluoroborate, [(BMIM)BF₄]. The complex was prepared by reacting RuCl₂(DMSO)₄ with NC ₅H₄CO₂Na-3, sodium nicotinate, in toluene, and was characterized by spectroscopic methods. The complex catalyzes the hydrogenation of 1-hexene (600 psi H₂, 100 °C) in a two-phase system consisting of cyclohexane/[(BMIM)BF₄] with 75% conversion in 24 h and modest substrate isomerization. The complex shows good stability and can be reused several times with little loss in activity.

Full text of DOI:10.1007/s11243-011-9510-2

Transition Met Chem (2011) 36:617–620
DOI 10.1007/s11243-011-9510-2
Synthesis, characterization, and biphasic ionic liquid media
1-hexene hydrogenation reaction
of RuCl (DMSO) (NC H CO Na-3)
2
2
5 4
2
2
Trino Su a´ rez
•
Bernardo Fontal
•
•
Joel E. Vielma
•
Marisela Reyes
Pedro Cancines
Fernando Bellandi
Juan C. D ´ı az
Yuraima Fonseca
•
•
•
Received: 7 April 2011 / Accepted: 3 June 2011 / Published online: 17 June 2011
Ó Springer Science+Business Media B.V. 2011
Abstract RuCl (DMSO) (NC H CO Na-3) is very soluble
2
De Souza [11] and Chauvin [12] in 1995. De Souza et al.
2
5
4
2
2
in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium tetra-
investigated the Rh-catalyzed hydrogenation of cyclohexene
fluoroborate, [(BMIM)BF ]. The complex was prepared by
4
in 1-n-butyl-3-methylimidazolium [(BMI)BF ] with 40%
4
reacting RuCl (DMSO) with NC H CO Na-3, sodium nico-
2
conversion in 120 h and turnover number (TON) = 6,000
4
5
4
2
-1
tinate, in toluene, and was characterized by spectroscopic
methods. The complex catalyzes the hydrogenation of 1-hex-
and turnover frequency (TOF) = 50 h . Chauvin et al.
dissolved the cationic ‘‘Osborn complex’’ [Rh(nbd)(PPh ) ]-
2
3
ene (600 psi H , 100 °C) in a two-phase system consisting of
[PF ] (nbd = norbornadiene, PPh = triphenylphosphine) in
6 3
2
-
cyclohexane/[(BMIM)BF ] with 75% conversion in 24 h and
ionic liquids with weakly coordinating anions (e.g., [PF ] ,
6
4
-
-
modest substrate isomerization. The complex shows good sta-
bility and can be reused several times with little loss in activity.
[BF ] , and [SbF ] ) and used the obtained ionic catalyst
4 6
solutions for the biphasic hydrogenation of 1-pentene. In our
laboratory, we have performed a detailed study on the cata-
lytic hydrogenation of 1-hexene using the RuCl (TPPMS)
2
3
Introduction
(DMSO), (TPPMS = triphenilphosphine monosulfonate)
complex in the ionic liquid (BMI)PF and have found that
6
Recently, ionic liquids (ILs) have received worldwide aca-
demic and industrial attention as replacements for organic
solvents in catalysis [1]. Some of the attractive features of ILs
in catalysis include the versatility to act both as catalyst and
solvent, the profound effect that may have on solvation, sol-
volysis, reaction rate, selectivity minimizing side reactions,
and the opportunity of an easy recovery of the catalyst. Ionic
liquids possess useful physical characteristics as solvents in
biphasic catalytic reactions with organometallic complexes
the system catalyzes 1-hexene hydrogenation (500 psi H2,
100 °C) with 80% conversion in 24 h with TON = 480 and
TOF = 20 h [13]. Campbell et al. [14] studied the hydro-
-1
genation of 1,3-cyclohexadiene with ruthenium nanoparticles
(30 °C, 1.2 bar H , 90 min) in ionic liquid media with high
2
selectivity toward cyclohexene and showed TON = 70 and
-1
TOF = 46 h . Lee et al. [15] studied asymmetric catalytic
hydrogenation reactions using a Rh complex stabilized in
ionic liquid and found low catalytic activity loss during cat-
alyst reuse. In this work, we report the synthesis, character-
ization, and catalytic hydrogenation reaction in ionic liquid
media [(BMIM)BF ] of the novel RuCl (DMSO) (NC H
[2–9]. In general, transition metal-catalyzed hydrogenation
reactions in ionic liquids are particularly promising owing in
part to the large number of known ionic hydrogenation cata-
lyststhatareavailable [10]. The first successfulhydrogenation
reactions in ionic liquids were studied by the groups of
4
2
2
5 4-
CO Na-3) complex.
2
2
Experimental
T. Su a´ rez (&) ꢀ B. Fontal ꢀ J. E. Vielma ꢀ M. Reyes ꢀ
F. Bellandi ꢀ P. Cancines ꢀ J. C. D ´ı az ꢀ Y. Fonseca
Departamento de Qu ´ı mica, Facultad de Ciencias,
Laboratorio de Organomet a´ licos, Universidad de Los Andes,
M e´ rida 5101, Venezuela
Materials and methods
All manipulations were carried out under argon atmo-
e-mail: suarez@ula.ve
sphere, using standard Schlenk techniques. RuCl ꢀ3H O
3
2
123

6
18
Transition Met Chem (2011) 36:617–620
Fig. 1 Proposed structure
for complex,
(
a)
H´
RuCl
according to a (a) H NMR and
2 2 6 4 2 2
(DMSO) (C H O Na)
1
H2
H2 '
1
3
Cl
Ru
S
(
b) C NMR
S
H3
H4
H3 '
N
O
Cl
N
A
B
N
H1
N
H1 '
H4 '
A
B
O
O
O
O
H´´
O
Na
Na
O
O
O
O
Na
Na
(
b)
2
2 'C
3
C
A
3 '
C
C
N
N
B
C
C
C
C
4
1
1 '
4 '
5C
5 'C
C
C
6
6 '
O
O
O
O
Na
Na
(
Strem) and NaBF (Aldrich) were used without further
4
(see Fig. 1a) d(ppm): H1
H , H , H = 8.78 (d,3H, J = 6.0 Hz); H = 8,29 (d, 1H,
0
4
0
= 9.24(s,1H); H = 9.07(s,1H);
1
purification. DMSO (Analar), 1-methylimidazol, n-butyl
chloride, 1-hexene, and cyclohexane (Aldrich) were purified
0
2
2
4
J = 6.0 Hz); H = 7.98 (t,1H, J = 6.5 Hz); H = 7.41
3
3‘
00
0
by distillation prior to use. H and Ar (Gases Industriales
2
(t,1H, J = 6.5 Hz); DMSO: H = 3.3 (s,6H), H = 2.68
1
(s,6H). C NMR data and assignments (see Fig. 1b) d(ppm):
C = 156.3; C = 145.4; C = 127.2; C = 144.8; C =
3
de Venezuela) were obtained commercially and used as
received. [(BMIM)BF ] and RuCl (DMSO) were synthe-
4
2
4
1
2
3
4
5
sized and characterized according to the literature [16–18].
136.2; C = 171.8; C
6
0
= 155.4; C2
0
= 143.8; C3
0
= 125.6;
1
C4 = 139.6; C5 = 133.8; C6 = 171.8. Mass spectrum:
0 0 0
?
[M ], m/e = 621; m/e = 540 (DMSO loss); m/e = 462 (two
Physical measurements
?
DMSO loss); [Ru(NC H CO Na)] m/e = 246.
5
4
2
-
Vibrational spectra (5,000–400 cm , KBr pellets) were
1
taken with a Fourier Transform Perkin-Elmer 1725X spec-
Catalytic runs
1
13
1
trophotometer. Room temperature H and C{ H} nuclear
magnetic resonance NMR spectra were recorded as DMSO-
d6 solutions using a Bruker Avance DRX 400-MHz spec-
trometer. Chemical shifts are expressed in ppm downfield
from external TMS. Mass spectra (EI) were obtained on a
Hewlett-Packard 5988 GC/MS spectrometer.
Catalytic trials were performed in a 10 mL Parr reactor with
internal glass liner, heating unit, temperature and stirring
control, and sampling valve. Conditions for a typical trial
were as follows: cyclohexane (3.0 mL), [(BMIM)BF4]
(
(
3.0 mL), 1-hexene (0.22 g, 2.6 mmol), RuCl (DMSO) -
2 2
-
NC H CO Na-3) (4.0 mg, 6.5 9 10 mmol), substrate/
3
5
4
2
2
Synthesis of RuCl (DMSO) (NC H CO Na-3)
2
2
2
5
4
2
catalyst = ca. 400:1, H pressure (200–1,000 psi), temper-
2
ature (25–125 °C), 1,600 rpm, 24 h reaction time. Reaction
products were analyzed on a Perkin-Elmer Autosystem 900
GC, using 50 m column (0.52 lm diameter) quadrex of
A solution of RuCl (DMSO) (1.00 g, 2.07 mmol) in toluene
4
2
(
10 mL) was mixed with a solution of sodium nicotinate
0.60 g, 4.13 mmol) in toluene (10 mL). The resultant solu-
(
methyl silicone with H carrying gas and a TC detector.
2
tion was refluxed for 3 h, yielding an air-stable dark orange
solid. This solid was recrystallized from methanol, and dried
under vacuum. Yield 1,02 g (80%), decomposes [300 °C,
-1
soluble in water, methanol. FTIR v(cm )(s = strong, m =
medium, w = weak), DMSO: vC-H 3008w, 2921w; vS-O
Results and discussion
1
,088 m, 922 m; NC H CO Na-3: vC=N 1,615 s, 1,564
5
Comparing the FTIR spectra of the complex and the free
ligand NC H CO Na, it was observed that the assigned
4
2
1
-
v C=C and v COO 1,384 s. H NMR data and assignments
5
4
2
1
23

Transition Met Chem (2011) 36:617–620
619
-
COO group vibrations remain unaltered upon coordina-
1
-Hexene
9
8
0
0
n-Hexane
cis-2-Hexene
trans-2-Hexene
tion, therefore suggesting that bonding does not occur
through the carboxylate groups, but instead through the
1
13
pyridyl nitrogen [19]. The H, C NMR spectra show two
series of signals that corresponds to a pair of nicotinate
sodium rings and two molecules of DMSO in different
chemical environments. The mass spectrum shows, in the
range m/z 625–612, a series of peaks that are consistent
with the isotopic pattern of Ru calculated with the Sheffield
Chemputer program [20]. Exploration of the area up to m/z
70
6
5
4
0
0
0
30
2
0
0
0
2
,000 shows no evidence of the presence of metal clusters.
1
Finally, the analysis of the spectroscopic evidence and the
proposed structure are both consistent with the minimum
energy structure for this complex obtained by calculations
performed with PC Spartan Plus software [21].
20
40
60
80
100
120
140
Temperature °C
Fig. 3 Temperature effect on 1-hexene hydrogenation. 600 psi H
2
pressure, S/C: 400:1, cyclohexane (3.0 mL), 3.0 mL (BMIM)BF
24 h
4
,
Hydrogenation reactions
The results of varying hydrogen pressure on the 1-hexene
hydrogenation reaction are given in Fig. 2. Hydrogenation
of 1-hexene increases when hydrogen pressure increases to
90
80
70
60
50
40
30
20
10
0
6
00 psi (64% conversion); however, at pressures greater
than 600 psi, there is a significant decrease in the pro-
duction of hexane, this is probably due to a hydrogen dif-
fusion problem or the formation of catalytically inactive
species. The isomerization reaction at 1,000 psi has high
activity (35% total isomerization conversion) while at low
pressures the rate of isomerization is lower.
1
-Hexene
n-Hexane
cis-2-Hexene
trans-2-Hexene
The effects of temperature are shown in Fig. 3. There is
a gradual increase in n-hexane hydrogenation product with
a temperature increase from 25 to 125 °C. An increase in
temperature decreases the ionic liquid viscosity, probably
allowing better contact between the substrate and the
400
500
600
700
800
900
1000
Substrate/Catalyst
1
00
Fig. 4 Substrate/catalyst (S/C) effect on 1-hexene hydrogenation.
00 psi H
pressure, 100 °C, cyclohexane (3.0 mL), (BMIM)BF
3.0 mL), 24 h
1
-Hexene
6
(
2
4
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
n-Hexane
cis-2-Hexene
trans-2-Hexeno
catalytic precursor improving total conversion, this
behavior has also been observed in similar systems [13].
Isomerization products remain below 5%, but at 100 °C we
observed an increase of isomers production (35%).
The results of varying the substrate/catalyst ratio (S/C)
are shown in Fig. 4. For lower S/C values (greater relative
amount of catalyst), there are higher rates of conversion,
this is presumably due to a saturation of active sites in
the catalytic precursor with the excess of substrate. The
optimum condition for the catalytic tests studied was
S/C = 400/1 because the highest substrate conversion was
obtained under this condition; however, this also gave high
isomerization products formation (35%).
200
400
600
800
1000
Pressure (psi)
Fig. 2 H
4
2
pressure effect on 1-hexene hydrogenation. 100 °C, S/C:
, 24 h
00:1, cyclohexane (3.0 mL), 3.0 mL (BMIM)BF
4
123

6
20
Transition Met Chem (2011) 36:617–620
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6
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2
2
5
4
2
2
1
-
1
a TON = 296 and TOF = 12 h , which was lower than
another study done in our laboratory (TON = 480, TOF =
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