The multiple roles of imidazolium ionic liquids in transition-metal catalysis: The palladium-catalyzed telomerization of 1,3-butadiene with acetic acid

Article abstract of DOI:10.1002/cctc.201402943

The telomerization of 1,3-butadiene with acetic acid catalyzed by palladium(II) acetate associated with a series of phosphines in 3-(2-methoxyethyl)-1-methylimidazolium acetate was used to investigate the role of the ionic liquid. The ionic liquid plays multiple roles in this reaction as it acts as the solvent, stabilizer, ligand, and cocatalyst. The reaction performed in the presence of Dan2phos, a trifluoromethylated sulfonated triarylphosphine, at 100 °C for 24 h gave a turnover number of 14 600 with 89 % selectivity to telomers at 75 % 1,3-butadiene conversion and complete acetic acid conversion.

Full text of DOI:10.1002/cctc.201402943

DOI: 10.1002/cctc.201402943
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The Multiple Roles of Imidazolium Ionic Liquids in
Transition-Metal Catalysis: The Palladium-Catalyzed
Telomerization of 1,3-Butadiene with Acetic Acid
Jo¼o M. Balbino,[a, b] Daniel Peral,[b] J. Carles Bayꢀn,*[b] and Jairton Dupont*[a, c]
The telomerization of 1,3-butadiene with acetic acid catalyzed
by palladium(II) acetate associated with a series of phosphines
in 3-(2-methoxyethyl)-1-methylimidazolium acetate was used
to investigate the role of the ionic liquid. The ionic liquid plays
multiple roles in this reaction as it acts as the solvent, stabilizer,
ligand, and cocatalyst. The reaction performed in the presence
of Dan2phos, a trifluoromethylated sulfonated triarylphos-
phine, at 1008C for 24 h gave a turnover number of 14600
with 89% selectivity to telomers at 75% 1,3-butadiene conver-
sion and complete acetic acid conversion.
Introduction
Ionic liquids (ILs) provide one of the most effective and versa-
tile liquid platforms for transition-metal and enzymatic multi-
phase catalysis.[1–3] Indeed, ILs have been used as solvents and
immobilizing agents for homogeneous (homotopic) transition-
metal catalysts[1] and enzymes,[4–7] liquid supports for heteroge-
neous (heterotopic) catalysts,[8] and transition-metal nanoparti-
cle catalysts.[9] In various cases, not only could the role of the
ILs be the immobilization of the catalysts[10] but they can also
act as modifying and/or stabilizing agents through weak to
strong interactions of the cation and/or the anion of the ILs
with the catalysts, such as ligand-like effects.[11,12] This is clearly
the case, for example, in the selectivity control observed in the
partial hydrogenation of benzene[13,14] or 1,3-butadiene[15] by
classical heterogeneous Ru catalysts or Pd nanoparticles, re-
spectively, embedded in ILs. Another outstanding example is
the enantioselectivity induced by ILs that contain chiral
anions[16–18] in transition-metal catalysis.[19] In most of these
cases, ILs are used as entropic drivers in view of their high
degree of organization that results from their peculiar cation–
anion supramolecular structure.[20] Indeed, by taking advantage
of these ion-pair contacts it was possible to obtain a high
enantioselectivity in the hydrogenation of a ketone moiety
bound to the imidazolium cation by a Ru/C catalyst.[21] Recent-
ly, the multiple roles of an imidazolium-based IL that contained
a methyl hydrogenophosphonate anion that acted as nanopar-
ticle stabilizer, base, and hydrogen-transfer agent was demon-
strated for an efficient Pd-catalyzed tandem coupling/reduc-
tion process.[22] Therefore, it is possible to design catalytic sys-
tems in which the IL plays various roles and thus reduces the
number of components of a specific reaction. We envisaged
that this approach could be extended for the delivery of one
of the reagents using a reactive anion that could be regenerat-
ed easily by the addition of its neutral analogue. The acetate
anion can act as a base and/or nucleophile in the Pd-catalyzed
telomerization of 1,3-butadiene with acetic acid (AcOH).[23] The
reaction of 1,3-butadiene with AcOH yields branched (5) and
linear (6) acetoxyoctadienes (Scheme 1), which can be used as
starting materials for the synthesis of many artificial and natu-
ral products.[24] The reaction, usually mediated by Pd catalysts,
also leads to the production of 1:1 adducts of the diene and
nucleophile, the acetoxybutenes 3 and 4, and the butadiene
dimers 1 and 2.[25–27] The conventional telomerization of 1,3-bu-
tadiene with AcOH employs the catalyst system Pd(OAc)2/
PPh3/base, which leads to a very high catalytic activity.[28] The
addition of a base in this reaction can have a beneficial
[a] MSc. J. M. Balbino, Prof. J. Dupont
Institute of Chemistry
Federal University of Rio Grande do Sul
Avenida Bento GonÅalves, 9500
CEP-91501-970 Porto Alegre, RS (Brazil)
E-mail: jairton.dupont@ufrgs.br
[b] MSc. J. M. Balbino, Dr. D. Peral, Prof. J. C. Bayꢀn
Department de Quꢁmica
Universitat Autꢂnoma de Barcelona
Bellaterra, 08193 Barcelona (Spain)
E-mail: joancarles.bayon@uab.cat
[c] Prof. J. Dupont
School of Chemistry
University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402943.
Scheme 1. Telomerization of butadiene with AcOH.
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effect[29,30] because it leads to the formation of the acetate,
which increases the nucleophilicity of AcOH.[31] Therefore, this
system is ideal to test the possible multiple roles of ILs. We
report here the telomerization of 1,3-butadiene by Pd(OAc)2 in
an imidazolium IL associated with the acetate anion using a va-
riety of new trifluoromethylated and sulfonated triarylphos-
phines disclosed recently by us.[32]
Results and Discussion
First, butadiene was heated at 708C, without additional re-
agents, to allow the exclusive formation of the thermal cyclodi-
merization product 4-vinylcyclohexene (2). This product is not
included in the results for the Pd-catalyzed telomerization of
butadiene reported below.
The IL 3-(2-methoxyethyl)-1-methylimidazolium acetate
(MeOImAcO) was chosen for this study because its viscosity is
lower than that of its most common analogue, 1-butyl-3-meth-
ylimidazolium acetate.[33] MeOImAcO was synthesized in 92%
overall yield from stoichiometric amounts of 1-methylimidazole
and 2-methoxyethylmethanesulfonate, followed by mesylate/
hydroxide exchange through an anion exchange resin, and fur-
ther neutralization with AcOH (Scheme 2).
Scheme 2. Synthesis of MeOImAcO.
Figure 1. Structure of ligands used in the reactions reported in Table 1.
A series of neutral phosphines with different basicities was
employed as ligands for the Pd-catalyzed telomerization
(Figure 1). Also, related anionic phosphines that contain sulfo-
nate groups were assayed to improve their support in the
MeOImAcO phase.[34]
the catalytic species. The addition of classical phosphines such
as PPh3 and its sulfonated analogues sodium triphenylphos-
phinemonosulfonate (NaTPPMS) and sodium triphenylphos-
phinedisulfonate (Na2TPPDS) causes a decrease in the TON
(from 190 without ligand to 40–130 in the presence of these li-
gands) and in the telomers selectivity (cf. entry 3 with entries 4,
5, and 6, Table 1).
The telomerization was performed using Pd(OAc)2 with
three equivalents of phosphine in MeOImAcO (0.15 mmol)
with AcOH/1,3-butadiene in a 1:1.5 molar ratio (Table 1). In all
these reactions the major products were the octadienyl ace-
tates 5 and 6, variable amounts of butadiene dimer 1 and bu-
tenyl acetates 3 and 4, and other minor products that repre-
sented less than 1% in total.
Interestingly, the use of Dan2phos, a phosphine related to
NaTPPMS that comprises trifluoromethyl groups in the nonsul-
fonated phenyl rings, generates a highly active and selective
catalytic system with which a TON of 830 was attained with
a selectivity of up to 94% to telomers (entry 7, Table 1). This is
a clear indication of the beneficial electronic effect of the tri-
fluoromethyl groups of the ligand in the telomerization reac-
tion. It is also consistent with the significant decrease observed
in both telomers selectivity and TON in the reactions per-
formed in the presence of p-Dan2phos and o-Dan2phos com-
pared with that with the Dan2phos-derived catalyst (entries 7,
9, and 10, Table 1). Earlier results for this reaction suggested
similar electronic effects if Pd catalysts with aryl-substituted
phosphites are used.[35] However, results with PBmmCF3 and
The reaction of 1,3-butadiene with AcOH in only IL (without
Pd/phosphine catalyst) gave only 2, which indicates that the
acetate anion in this medium is not nucleophilic enough to
react with the diene or the diene dimer (entry 1, Table 1). How-
ever, telomers are formed in the presence of Pd(AcO)2 in the
absence of MeOImAcO (i.e., AcOH and butadiene are the sol-
vents at the beginning of this reaction). However, the turnover
number (TON) achieved is much lower than that obtained
using the IL (cf. entries 2 and 3, Table 1), which suggests that
the IL plays an important role in the stabilization/activation of
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selectivity to telomers (80.6%) decrease significantly in the re-
action performed in the absence of MeOImAcO (cf. entries 7
and 8, Table 1). However, an optimization of the amount of IL
shows that a maximal activity is achieved if 0.30 mmol of IL is
used with a MeOImAcO/AcOH/1,3-butadiene/Pd molar ratio of
1:270:400:4ꢂ10À2 (Figure 2). For lower or higher quantities the
conversion decreases, although the selectivity to telomers re-
mains approximately constant (ꢀ95%).
Table 1. Telomerization of butadiene with AcOH using different phos-
phines.[a]
Entry
Phosphine
Selectivity [%]
TON
1
3+4
5+6 (6/5)
1[b]
2[c]
3
4
5
6
7
8[c]
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
–
–
–
PPh3
0.0
0.0
0.0
0.0
15.0
23.5
1.8
11.6
4.3
1.4
16.2
22.5
14.9
0.0
0.7
0.0
0.0
0.0
1.2
2.2
12.7
9.1
15.9
0.0
9.3
4.7
55.0
14.4
24.2
4.0
7.8
8.5
5.7
14.2
21.1
11.8
30.6
2.7
4.8
4.3
36.7
6.7
3.7
0.0
–
65
190
130
130
40
90.7 (96/4)
95.3 (98/2)
45.0 (65/35)
70.6 (91/9)
52.3 (97/3)
94.2 (93/7)
80.6 (95/5)
87.2 (90/10)
92.9 (97/3)
69.6 (94/6)
56.3 (95/5)
73.3 (95/5)
69.4 (70/30)
96.6 (87/13)
95.2 (98/2)
95.7 (99/1)
63.3 (70/30)
92.1 (89/11)
94.2 (96/4)
71.1 (82/18)
66.8 (65/35)
54.7 (76/24)
NaTPPMS
Na2TPPDS
Dan2phos
Dan2phos
p-Dan2phos
o-Dan2phos
Danphos
p-Danphos
o-Danphos
PBpCF3
PTpCF3
PBoCF3
PToCF3
PMmmCF3
PBmmCF3
PTmmCF3
PTpMe
PTpF
PTpOMe
830
245
325
250
210
65
220
130
690
240
240
400
720
400
180
70
16.2
24.0
29.4
50
[a] Reaction Conditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); phosphine/
Pd=3; MeOImAcO=30 mg (0.15 mmol); AcOH=4.6 mL (80 mmol);
C4H6 =10.0 mL (120 mmol); 708C; 5 h, 700 rpm. n-Dodecane was added
as an internal standard; 1=dimer; 3+4=butenyl acetates; 5+6=telo-
mers; 6/5 is the ratio of linear and branched telomers; TON=(moles of
butadiene converted/moles of Pd after 5 h); [b] reaction without
Pd(OAc)2; [c] reaction without MeOImAcO.
PTmmCF3 phosphines [bis(m,m-di-trifluoromethylphenyl) phe-
nylphosphine and tris(m,m-di-trifluoromethylphenyl) phos-
phine, respectively] (entries 19 and 20, respectively, Table 1),
suggest that an excess of the electron-withdrawing capacity of
the substituents has a deleterious effect on the catalyst per-
formance. Furthermore, the phosphine that contains p-CH3
substituents shows a higher activity than those with fluoro,
methoxy, or hydrogen groups (cf. entries 4, 15, and 21–23,
Table 1), contrary to that expected from the electron-withdraw-
ing capacity of the substituents.[36] A similar result was ob-
tained by Rose and Lepper[35] who studied the influence of
substituted triarylphosphite ligands for this reaction under ho-
mogenous conditions.
Figure 2. Effect of the quantity of IL on the catalytic activity (top) and selec-
tivity (bottom) of the telomerization of butadiene with AcOH. (Reaction con-
ditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); phosphine=3 equiv./Pd;
AcOH=4.6 mL (80 mmol); C4H6 =10.0 mL (120 mmol); 708C; 5 h, 700 rpm.
n-Dodecane was added as an internal standard); (1)=dimer; (3)+(4)=bu-
tenyl acetates; (5)+(6)=telomers.
Interestingly, the presence of a sodium sulfonate group in
the phosphines increases the selectivity to telomers to above
90% (Table 1). This must be considered, at least in part, as an
effect of the IL as there is no doubt that the sulfonate groups
are responsible for the interaction and/or the dissolution of
the catalyst with the IL. Therefore, Dan2phos, which combines
two meta-substituted trifluoromethyl aryl rings with a sulfonat-
ed aryl ring, leads to the best-performing catalyst in the IL
media employed. In view of this result, an optimization of the
reaction conditions using this ligand was undertaken for this
catalytic system.
The acetate anions in the IL play a role as cocatalyst in the
process. Such a role is exerted typically by the addition of
sodium acetate to the reaction medium, which leads to much
higher conversions than those obtained in the absence of an
acetate source. This was confirmed by using an IL with another
anion, such as BF4À, which provides a much lower conversion
and worse selectivity (entries 3 and 4, Table 2). Notably, com-
pared to other acetate sources, MeOImAcO is the most effi-
cient in terms of activity but with a similar selectivity profile
(cf. entries 1–3, Table 2).
Importantly, regardless of the mechanism (mono- or bipalla-
dium bis-allyl mechanism),[15] the optimal Pd/phosphine ratio is
the same as that for reactions performed in classical organic
Notably, the presence of MeOImAcO is essential to achieve
better activity and selectivity. Indeed, both the TON (245) and
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D2O together with the catalyst and tBuOK, a H/D exchange at
the C2 carbon is observed, which suggests that metal-carbene
species could be involved in this basic medium, but they are
unlikely to be formed in the acidic conditions used for the te-
lomerization of butadiene.[39,40]
Table 2. Telomerization of butadiene with AcOH in the presence of differ-
ent ionic species.[a]
Entry
Ionic species
Selectivity [%]
TON
1
3+4
5+6 (6/5)
1
2
3
4
MeOImAcO
NaAcO
BMImAcO
BMImBF4
1.5
2.1
1.4
3.5
3.6
2.8
95.0 (93/7)
94.3 (94/6)
95.8 (94/6)
65.2 (96/4)
980
850
840
210
An increase in the molar fraction of AcOH in the mixture
leads to a reduction of the conversion and selectivity, as ob-
served in classical homogeneous telomerization reactions.[24]
Although the conversion decreases with the increase of AcOH
in the reaction, the selectivity to telomers only decreases by
5% if AcOH is increased by eight times (cf. entries 1 and 4,
23.7
11.1
[a] Reaction Conditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); phos-
phine=3 equiv/Pd; Ionic species=0.30 mmol; AcOH=4.6 mL (80 mmol);
C4H6 =10.0 mL (120 mmol); 708C; 5 h, 700 rpm. n-Dodecane was added
as an internal standard; 1=dimer; 3+4=butenyl acetates; 5+6=telo-
mers; 6/5 is the ratio of linear and branched telomers; NaAcO=sodium
acetate; BMImAcO=3-butyl-1-methylimidazolium acetate; BMImBF4 =3-
butyl-1-methylimidazolium tetrafluoroborate.
Table 4. Influence of the amount of AcOH on the reaction output.[a]
Entry
AcOH [mmol]
Selectivity [%]
TON
1
3+4
5+6 (6/5)
1
2
3
4
20
40
80
0.7
1.0
1.5
2.4
1.3
2.5
3.5
4.4
98.0 (92/8)
96.5 (93/7)
95.0 (93/7)
93.2 (94/6)
1320
1060
980
solvents. In the case of a ligand excess, a second Pd coordina-
tion site is occupied and thereby blocks the diene activation,
which is a necessary step before dimerization can occur. A re-
duced amount of stabilizing P donor leads to a poorer catalytic
performance[37] and eventually to the formation of Pd black,
which was observed in some of our reactions, in particular, in
those performed in the absence of IL. However, in our case,
a Dan2phos/Pd ratio of 3:1 renders the best catalyst activity
combined with a high selectivity to telomers (Table 3). For
160
610
[a] Reaction conditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); Dan2phos=
3 equiv./Pd; MeOImAcO=60 mg (0.30 mmol); C4H6 =10.0 mL (120 mmol);
708C; 5 h, 700 rpm. n-Dodecane was added as an internal standard; 1=
dimer; 3+4=butenyl acetates; 5+6=telomers; 6/5 is the ratio of linear
and branched telomers.
Table 4). The use of 20 mmol of AcOH gives the highest cata-
lytic activity, but this is accompanied by the formation of large
amounts of the thermal dimer 2 (Table S5). Therefore, to mini-
mize the formation of the thermal product, 80 mmol of AcOH
was used.
Table 3. Effect of the amount of Dan2phos on the catalyst perform-
ance.[a]
Entry
P/Pd
Selectivity [%]
TON
1
3+4
5+6 (6/5)
An increase in the reaction temperature leads to a three
times increase in the TON with only a moderate effect in the
selectivity to telomers (Table 5).
1
2
3
4
5
1
2
3
6
12
0.0
1.5
1.5
1.2
1.5
2.6
3.7
3.5
7.2
14.9
97.4 (97/3)
94.8 (93/7)
95.0 (93/7)
91.6 (88/12)
83.6 (79/21)
330
360
980
970
820
[a] Reaction Conditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); MeOIm-
AcO=60 mg (0.30 mmol); AcOH=4.6 mL (80 mmol); C4H6 =10.0 mL
(120 mmol); 708C; 5 h, 700 rpm. n-Dodecane was added as an internal
standard; 1=dimer; 3+4=butenyl acetates; 5+6=telomers; 6/5 is the
ratio of linear and branched telomers.
Table 5. Influence of the temperature on the reaction output.[a]
Entry
T [8C]
Selectivity [%]
TON
1
3+4
5+6 (6/5)
1
2
3
50
70
100
0.9
1.5
2.8
1.5
3.5
5.3
97.6 (96/4)
95.0 (93/7)
91.9 (85/15)
210
980
2760
lower or higher amounts of Dan2phos, a decrease in the con-
version is observed. In AcOH and at a Dan2phos/Pd ratio of 3,
the 31P NMR spectrum shows a single signal at d=16.4 ppm.
[a] Reaction Conditions: Pd(OAc)2 =2.7 mg (1.2ꢂ10À2 mmol); Dan2phos/
Pd=3; MeOImAcO=60 mg (0.30 mmol); AcOH=4.6 mL (80 mmol);
C4H6 =10.0 mL (120 mmol); 5 h, 700 rpm. n-Dodecane was added as an
internal standard; 1=dimer; 3+4=butenyl acetates; 5+6=telomers; 6/
5 is the ratio of linear and branched telomers.
Moreover, ESI-HRMS shows
a peak that corresponds to
[Pd(AcO)2(Dan2phos)2], which suggests that nearly all the Pd is
in this form. Unfortunately, all attempts to isolate this com-
pound in its crystalline form have failed so far.
It is known that in the presence of a metal the alkylimidazo-
lium cations in ionic liquids can deprotonate to form carbene-
type complexes.[38] We did not observe the presence of typical
carbene signals in the 13C NMR spectrum of the IL after the cat-
alytic reaction. Further experiments using the 13C-enriched-C2-
imidazolium cation under catalytic conditions confirm the ab-
sence of carbenes in the solution. If the IL was dissolved in
In an attempt to scale up the reaction and to study the sta-
bility of the catalytic system, the amount of diene was in-
creased to 300 mmol and the reaction was performed for 24 h
(Table 6). Under these conditions, a slight decrease of the se-
lectivity to telomers was observed together with a huge in-
crease in the TON (14600). This corresponds to an effective
TON of 13000 in telomers (11400 in the linear telomer 6). At
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type fluorinated phosphines (currently commercially available from
Strem),[32] PMQl,[43] PMoNH2,[44] PMoNMe2,[45] BMImAcO,[46,47]
BMImBF4,[48] and BMIm(13C(2)-enriched)AcO[49] were prepared ac-
cording to reported procedures.
Table 6. Scale-up of the reaction and stability of the catalyst.[a]
Entry
AcOH
IL
Selectivity
[%]
TON
[mmol]
[mmol]
1
3+4
5+6 (6/5)
1
2
3
4
80
200
200
80
0.30
0.30
0.75
–
9.5
5.0
3.6
9.7
1.9
9.3
44.2
5.8
88.6 (88/12)
85.7 (90/10)
52.2 (92/8)
84.5 (87/13)
14600
7270
10640
9200
Synthesis of 3-(2-methoxyethyl)-1-methylimidazolium
acetate (MeOImAcO)
1-Methylimidazole (40.1 g, 482 mmol) and 2-methoxyethylmethane
sulfonate (75.1 g, 487 mmol) were mixed in a flask and kept at
508C under stirring for 48 h (Scheme 2). The obtained methylimi-
dazolium mesylate was washed five times with ethyl acetate to
remove 2-methoxyethylmethane sulfonate. The remaining solvent
was removed under reduced pressure to afford the pure product
in 83% yield. This salt (6.75 g) was diluted in deionized water, and
the solution was passed through an anionic exchange column Am-
berlite IRA-400 (1.4 equiv. OHÀ/L). The resulting solution was neu-
tralized with AcOH to produce MeOImAcO quantitatively after
[a] Reaction Conditions: Pd(OAc)2 =2.7 mg (0.012 mmol); Dan2phos/Pd=
3; C4H6 =25.0 mL (300 mmol); 24 h, 1008C, 700 rpm. n-Dodecane was
added as an internal standard; 1=dimer; 3+4=butenyl acetates; 5+6=
telomers; 6/5 is the ratio of linear and branched telomers.
1008C the effective TOF at 5 h (550 hÀ1) is very similar to that
at 24 h (610 hÀ1), which indicates that after 24 h there is not
a significant degradation of the catalyst (cf. entry 3, Table 5
and entry 1, Table 6). Under these optimized conditions, the
AcOH is consumed completely to produce an increased
amount of dimer 1. Therefore, an increase in the amount of
AcOH used from 80 to 200 mmol was assayed, which led to an
approximate 50% decrease of the TON and an increase of the
amount of butenyl acetates (entry 2, Table 6). The use of
a larger amount of the IL further increased the production of
butenyl acetates (entry 3, Table 6).
1
water evaporation (7.2 g, 94% yield). H NMR (400 MHz, D2O): d=
1.74 (s, 3H, CH3COO), 3.24 (s, 3H, NCH3), 3.70 (t, JHÀH =4.9 Hz, 2H,
NCH2), 3.78 (s, 3H, OCH3), 4.27 (t, JHÀH =4.9 Hz, 2H, OCH2), 7.35 (d,
J
HÀH =22.6 Hz, 1H, arom. H), 7.41 (d, JHÀH =22.6 Hz, 1H, arom. H),
8.66 ppm (s, 1H, NCHN); 13C NMR (100 MHz, D2O): d=23.34
(CH3COO), 35.64 (d, J 13C =2.8 Hz, NCH3), 48.75 (d, J 13C =2.4 Hz,
13CÀ
13CÀ
NCH2), 58.07 (OCH3), 69.67 (OCH2), 122.40 (d, J 13C =105.4 Hz,
13CÀ
arom. C), 123.46 (d, J 13C =105.4 Hz, arom. C), 136.25 (NCN),
13CÀ
180.53 ppm (CH3COO); IR (pure IL): n˜max =621.52 (gNÀCH , ring-puck-
2
ering), 697.78, 833.89 (gC2ÀH), 921.50 (ns CÀOÀC), 1011.45 (nNÀCH ),
3
Under the optimized conditions, the TON decreased by
more than 5000 turnovers in the reaction performed without
MeOImAcO (cf. entries 1 and 4, Table 6).
1043.10 (dring), 1117.27 (nNÀCH ), 1171.73 (nas COC), 1391.33 (nas C N C ),
2
2 3 4
1560.83 cmÀ1 (CH3COOÀ); MS (ESI+, MeOH): m/z: 141.1025 [M]+; el-
emental analysis calcd (%) for C9H16N2O3 (200.11 gmolÀ1): C 53.98,
H 8.05, N 13.99; found: C 53.13, H 8.35, N 13.17.
Unfortunately, the catalyst system could not be recycled
under these conditions because of the formation of polybuta-
diene, which hindered the recovery and reuse of the catalytic
system.
Telomerization reactions
The telomerization reactions in a batch system were performed in
a 50 mL stainless-steel reactor that was stirred magnetically. The re-
action temperature was controlled by using a thermocouple
dipped inside the reaction and a heating unit. The desired quanti-
ties of phosphine, n-dodecane (internal standard), and IL were dis-
solved in AcOH (2.0 mL) that contained the appropriate amount of
Pd(OAc)2. This solution was transferred, along with the remaining
AcOH, to the reactor under a flow of N2 by syringe, and the reactor
was frozen in liquid N2. Butadiene was liquefied in a flask cooled in
a bath at À788C, and the desired amount of the diene was trans-
ferred to the reactor by syringe. The reactor was heated to RT by
using a heating gun, then it was connected to the heating unit,
and the stirring was turned on once the working temperature was
reached. The pressure of the reactor was checked carefully
throughout the reaction to ensure that enough liquid butadiene
remained in the reactor. After the reaction time, heating and stir-
ring were turned off, the reactor was immersed in an ice bath, and
the remaining butadiene was vented in a hood. The reaction mix-
ture was treated with a saturated solution of NaHCO3 to neutralize
unreacted AcOH and extracted three times with CH2Cl2. The prod-
ucts were analyzed by GC with flame ionization detection (FID) by
using a Hewlett Packard 5890 Series II system and by GC–MS by
using a Hewlett Packard G1800A GCD system both equipped with
HP5 columns. 4-Vinylcyclohexene, 1-acetoxy-2,7-octadiene, and
trans-2-butenyl acetate (Sigma Aldrich) were used to calculate the
response factors to dimers, telomers, and butenyl acetates, respec-
tively. n-Dodecane (Sigma Aldrich) was used as an internal stan-
dard. The catalyst efficiency was determined by calculating the
Conclusions
The telomerization of 1,3-butadiene with AcOH to octadienyl
acetates is achieved readily by using Pd(OAc)2 plus a remark-
able p-acid sulfonated phosphine Dan2phos in 3-(2-meth-
oxyethyl)-1-methylimidazolium acetate. Under the optimized
conditions, a turnover number of 14600 can be reached with
89.0% of selectivity to telomers. Although the reaction occurs
in the absence of the ionic liquid, lower turnover numbers and
selectivities were obtained compared to the reactions per-
formed if the catalysts were supported in this medium. It is
also clear that the ionic liquid acts as solvent, stabilizer, and co-
catalyst for the activation of the AcOH. It can be anticipated
that this approach can be extended for other transformations
in which the basicity/nucleophilicity has to be modulated.
Experimental Section
Materials
1,3-Butadiene (Linde 2.5), AcOH (Sigma Aldrich), Pd(OAc)2 (Aldrich),
PPh3 (Acros Organics), PTpF, PTpOMe, PTpMe, DPPE, DPPP, DPPB
(Aldrich), 1-methylimidazole (Sigma Aldrich), and 2-methoxyethyl-
methanesulphonate (Acros Organics) were used without further
purification. NaTPPMS,[41] Na2TPPDS,[42] Dan2phos, and Danphos-
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[20] J. Dupont, Acc. Chem. Res. 2011, 44, 1223–1231.
[21] P. S. Schulz, N. Muller, A. Bosmann, P. Wasserscheid, Angew. Chem. Int.
Ed. 2007, 46, 1293–1295; Angew. Chem. 2007, 119, 1315–1317.
[22] E. Raluy, I. Favier, A. M. Lopez-Vinasco, C. Pradel, E. Martin, D. Madec, E.
Teuma, M. Gomez, Phys. Chem. Chem. Phys. 2011, 13, 13579–13584.
[23] A. Behr, M. Becker, T. Beckmann, L. Johnen, J. Leschinski, S. Reyer,
Angew. Chem. Int. Ed. 2009, 48, 3598–3614; Angew. Chem. 2009, 121,
3652–3669.
[24] A. Behr, T. Beckmann, P. Schwach, J. Organomet. Chem. 2008, 693,
3097–3102.
[25] J. R. Briggs, H. Hagen, S. Julka, J. T. Patton, J. Organomet. Chem. 2011,
696, 1677–1686.
TON, which is the number of moles of butadiene converted per
moles of Pd at a fixed time.
Analysis of the catalyst solution
The catalyst solution with different Dan2phos/Pd ratios in AcOH
was analyzed by 31P{1H} NMR spectroscopy by using a Bruker
Avance II 400 MHz spectrometer. The solution with a 3:1 Dan2-
phos/Pd(AcO)2 molar ratio was analyzed by ESI-HRMS by using
a Bruker Apolo II instrument in positive mode. A peak at m/z
1518.88 was observed, calculated for C48H26F24S2O10P2Na3Pd (cation
[Pd(OAc)2(Dan2phos)2+Na]+, 1518.8787). The catalyst solution in
D2O was analyzed by 13C NMR spectroscopy by using a Bruker
Avance II 400 MHz spectrometer.
[26] B. Estrine, S. Bouquillon, F. Hꢄnin, J. Muzart, Eur. J. Org. Chem. 2004,
2914–2922.
[27] F. Benvenuti, C. Carlini, M. Lami, M. Marchionna, R. Patrini, G. Sbrana, J.
Mol. Catal. A 1999, 144, 27–40.
[28] L. Magna, Y. Chauvin, G. P. Nicolai, J.-M. Basset, Organometallics 2003,
22, 4418–4425.
Acknowledgements
[29] E. J. Smutny, J. Am. Chem. Soc. 1967, 89, 6793–6794.
[30] F. Benvenuti, C. Carlini, M. Marchionna, R. Patrini, A. M. Raspoli, G.
Sbrana, J. Mol. Catal. A 1999, 139, 177–187.
[31] C. Damez, B. Estrine, A. Bessmertnykh, S. Bouquillon, F. Hꢄnin, J. Muzart,
J. Mol. Catal. A 2006, 244, 93–98.
We would like to thank the CNPq for financial support.
[32] J. C. Bayꢀn, D. Peral, PCT Int. Appl. WO 2011045417, 2011.
[33] L. C. Branco, J. N. Rosa, J. J. M. Ramos, C. A. M. Afonso, Chem. Eur. J.
2002, 8, 3671–3677.
Keywords: ionic liquids
phosphane ligands · telomerization
· ligand effects · palladium ·
[34] C. S. Consorti, G. L. P. Aydos, G. Ebeling, J. Dupont, Org. Lett. 2008, 10,
237–240.
[1] J. P. Hallett, T. Welton, Chem. Rev. 2011, 111, 3508–3576.
[2] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 3772–3789;
Angew. Chem. 2000, 112, 3926–3945.
[3] R. Sheldon, Chem. Commun. 2001, 2399–2407.
[4] M. T. Reetz, W. Wiesenhofer, G. Francio, W. Leitner, Adv. Synth. Catal.
2003, 345, 1221–1228.
[35] D. Rose, H. Lepper, J. Organomet. Chem. 1973, 49, 473–478.
[36] D. J. Adams, J. A. Bennett, D. Duncan, E. G. Hope, J. Hopewell, A. M.
Stuart, A. J. West, Polyhedron 2007, 26, 1505–1513.
[37] W. E. Walker, R. M. Manyik, K. E. Atkins, M. L. Farmer, Tetrahedron Lett.
1970, 11, 3817–3820.
[5] G. Quijano, A. Couvert, A. Amrane, Bioresour. Technol. 2010, 101, 8923–
8930.
[38] N. D. Clement, K. J. Cavell, C. J. Elsevier, Angew. Chem. Int. Ed. 2004, 43,
1277–1279; Angew. Chem. 2004, 43, 3845–3847.
[6] P. Lozano, Green Chem. 2010, 12, 555–569.
[7] F. Fischer, J. Mutschler, D. Zufferey, J. Ind. Microbiol. Biotechnol. 2011, 38,
477–487.
[39] J. D. Scholten, G. Ebeling, J. Dupont, Dalton Trans. 2007, 5554–5560.
[40] S. Filipuzzi, P. S. Pregosin, A. Albinati, S. Rizzato, Organometallics 2008,
27, 437–444.
[8] Y. L. Gu, G. X. Li, Adv. Synth. Catal. 2009, 351, 817–847.
[9] J. D. Scholten, B. C. Leal, J. Dupont, ACS Catal. 2012, 2, 184–200.
[10] J. W. Lee, J. Y. Shin, Y. S. Chun, H. B. Jang, C. E. Song, S. G. Lee, Acc.
Chem. Res. 2010, 43, 985–994.
[11] E. ꢃchsner, K. Schneiders, K. Junge, M. Beller, P. Wasserscheid, Appl.
Catal. A 2009, 364, 8–14.
[12] A. Riisagera, R. Fehrmann, M. Haumann, P. Wasserscheid, Top. Catal.
2006, 40, 91–102.
[13] E. T. Silveira, A. P. Umpierre, L. M. Rossi, G. Machado, J. Morais, G. V.
Soares, I. L. R. Baumvol, S. R. Teixeira, P. F. P. Fichtner, J. Dupont, Chem.
Eur. J. 2004, 10, 3734–3740.
[14] F. Schwab, M. Lucas, P. Claus, Angew. Chem. Int. Ed. 2011, 50, 10453–
10456; Angew. Chem. 2011, 123, 10637–10640.
[15] A. P. Umpierre, G. Machado, G. H. Fecher, J. Morais, J. Dupont, Adv.
Synth. Catal. 2005, 347, 1404–1412.
[16] L. C. Branco, P. M. P. Gois, N. M. T. Lourenco, V. B. Kurteva, C. A. M.
Afonso, Chem. Commun. 2006, 2371–2372.
[41] F. Joo, J. Kovacs, Inorg. Synth. 1998, 32, 1–8.
[42] T. Thorpe, S. M. Brown, J. Crosby, S. Fitzjohn, J. P. Muxworthy, M. J. Wil-
liams, Tetrahedron Lett. 2000, 41, 4503–4505.
[43] P. A. Aguirre, C. C. Lagos, S. A. Moya, C. ZfflÇiga, E. Sola, G. Peris, J. C.
Bayꢀn, Dalton Trans. 2007, 5419–5426.
[44] M. K. Cooper, J. M. Downes, P. A. Duckworth, M. C. Kerby, R. J. Powell,
M. D. Soucek, Inorg. Synth. 1989, 25, 129–133.
[45] H. Gilman, I. Banner, J. Am. Chem. Soc. 1940, 62, 344–345.
[46] K. Fukumoto, M. Yoshizawa, H. Ohno, J. Am. Chem. Soc. 2005, 127,
2398–2399.
[47] Y. Wu, T. Sasaki, K. Kazushi, T. Seo, K. Sakurai, J. Phys. Chem. B 2008, 112,
7530–7536.
[48] C. C. Cassol, G. Ebeling, B. Ferrera, J. Dupont, Adv. Synth. Catal. 2006,
348, 243–248.
[49] M. Ali, A. Gual, G. Ebeling, J. Dupont, ChemCatChem 2014, 6, 2224–
2228.
[17] D. J. Chen, M. Schmitkamp, G. Francio, J. Klankermayer, W. Leitner,
Angew. Chem. Int. Ed. 2008, 47, 7339–7341; Angew. Chem. 2008, 120,
7449–7451.
Received: November 25, 2014
Revised: January 9, 2015
[18] S. V. Malhotra, Y. Wang, Tetrahedron: Asymmetry 2006, 17, 1032–1035.
[19] M. H. G. Prechtl, J. D. Scholten, B. A. D. Neto, J. Dupont, Curr. Org. Chem.
2009, 13, 1259–1277.
Published online on && &&, 0000
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FULL PAPERS
Completing the puzzle: A Pd catalyst
with the Dan2phos ligand, a new
trifluoromethylated and sulfonated
phosphine, and MeOImAcO, an ionic
liquid with an acetate anion, is the right
combination for the telomerization of
1,3-butadiene with acetic acid.
J. M. Balbino, D. Peral, J. C. Bayꢀn,*
J. Dupont*
&& – &&
The Multiple Roles of Imidazolium
Ionic Liquids in Transition-Metal
Catalysis: The Palladium-Catalyzed
Telomerization of 1,3-Butadiene with
Acetic Acid
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