Telomerization of 1,3-Butadiene with Carbon Dioxide: A Highly Efficient Process for δ-Lactone Generation

Article abstract of DOI:10.1002/cctc.201701058

A very efficient and selective telomerization of 1,3-butadiene with CO₂ that leads to the δ-lactone (3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one) was obtained using palladium acetate and tris(p-methoxyphenyl)phosphine as a catalyst in the presence of p-hydroquinone, N,N-diisopropylethylamine, and acetonitrile. A high turnover number of 4500 with 96 % selectivity to the δ-lactone was obtained after 5 h reaction at 70 °C. The reaction was deactivated by the presence of different 1,3-dialkylimidazolium ionic liquids, possibly by the formation of stable and inactive palladium-imidazole-2-ylidene carbenes.

Full text of DOI:10.1002/cctc.201701058

Accepted Article
Title: Telomerization of 1,3-Butadiene with Carbon Dioxide: a highly
efficient process for δ-lactone generation
Authors: Joao Balbino, Jairton Dupont, and J. Carles Bayón
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Telomerization of 1,3-Butadiene with Carbon Dioxide: a highly
efficient process for δ-lactone generation
João M. Balbino,a,b Jairton Dupont*a,c and J. Carles Bayón*b
Abstract: A very efficient and selective telomerization of 1,3-
butadiene with carbon dioxide leading to the δ-lactone (3-ethylidene-
6-vinyltetrahydro-2H-pyran-2-one) was obtained using palladium
acetate and tris(p-methoxyphenyl)phosphine as catalyst, in the
presence of p-hydroquinone, N,N-diisopropylethylamine and
acetonitrile. A high TON of 4500 with 96% selectivity to the δ-lactone
was acquired after 5 h reaction at 70°C. The reaction was
deactivated by the presence of different 1,3-dialkylimidazolium ionic
liquids, possibly by the formation of stable and inactive Pd-
imidazole-2-ylidene carbenes.
selectivities to the valuable δ-lactone 3-ethylidene-6-
vinyltetrahydro-2H-pyran-2-one (1). This lactone presents a
number
of
synthetic
applications
in
reactions
as
hydroformylation, hydroamination, hydroaminomethylation and
hydrogenation (Scheme 2), leading to many different products
like saturated and unsaturated diols, as well as unsaturated
hydroxyacids, with possible use as monomers for the polymer
industry.[11,12]
Introduction
The telomerization reaction of 1,3-dienes is a very important
catalytic process due to its versatility and 100% atomic efficiency,
which provides economic and ecological benefits.[1] The added
value of the reaction is increased by using cheap and easily
available feedstocks, as 1,3-butadiene and carbon dioxide.[2,3]
The catalytic reaction of 1,3-butadiene with CO2 was first
investigated by Inoue et al.[4,5] and Musco et al.[6,7] in the 1970s.
They succeed in synthesize the lactones 1-3, carboxylic acids 4
and 5, esters 6 and 7, and the usual butadiene dimers 8 and 9 in
small quantities, as illustrated on Scheme 1.
Scheme 2. Synthetic applications of δ-lactone.[13]
A very selective scheme for the telomerization of 1,3-butadiene
with carbon dioxide also includes, besides the Pd/phosphine
catalyst, a tertiary amine with pKb from 0 to 4 that boosts the
δ-lactone selectivity, hydroquinone, which raises up reaction rate
and allows to work with shorter time reaction, and a solvent
containing nitrile groups, usually acetonitrile.[14]
The usually accepted mechanism for this reaction is illustrated
on Scheme 3, based on detailed investigations by Behr et
al..[15,16] Oxidative coupling of two butadienes coordinated to the
Pd(0) species (A) leads to the intermediate (1,8-η1,η1-2,7-
octadiene)Pd(PR3)2 (B). The double bonds of this complex are
Scheme 1. Telomerization of 1,3-butadiene with CO2.
In subsequent years,[8-10] an intensive investigation of catalysts
for this reaction demonstrated that systems constituted by
palladium associated to phosphines as ligands lead to the best
[a]
Institute of Chemistry, Federal University of Rio Grande do Sul,
Avenida Bento Gonçalves, 9500, CEP-91501-970 Porto Alegre, RS,
Brazil.
E-mail: jairton.dupont@ufrgs.br
[b]
[c]
Department de Química, Universitat Autònoma de Barcelona,
Bellaterra, 08193 Barcelona, Spain.
E-mail: joancarles.bayon@uab.cat
School of Chemistry, University of Nottingham, University Park,
Nottingham, UK, NG7 2RD
Supporting information for this article is given via a link at the end of
the document.
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Scheme 3. Mechanism for the telomerization of 1,3-butadiene with CO2.
rearranged, forming the bis-allyl complex (1,2,3,6,7,8-η3,η3-2,7-
We also have investigated the effect of imidazolium ionic liquids
in this reaction.
octadienyl)Pd (C). This complex is then displaced by
a
phosphine to form the
D
intermediate (1,2,3,6-η3,η1-2,7-
octadienyl)Pd(PR3), which can follow two different paths. First
and less important, allyl de-chelation can occur, leading to the
formation of dimer 8. Second, CO2 can be inserted into the η3,η1-
octadienyl chain, producing the key intermediate (1,2,3-η3-6-
CO2-2,7-octadienyl)Pd(PR3) (E). The η3-6-CO2-octadienyl chain
can then undergo an internal cyclization, which involves a Pd-O
bond breaking followed by a new C-O bond formation, from the
nucleophilic attack at 3- or 4- positions of the carbon chain,
producing the lactones 1 or 2-3, respectively. On the other hand,
the carboxylate can abstract a proton at 4- position, leading to
the formation of acids 4-5. Alternatively, the allyl and phosphine
ligands from species E can be displaced by two new butadiene
molecules (one of them via transallylation), giving the
Results and Discussion
First, a series of triarylphosphines with different basicities (see
Figure 1) were essayed as ligands for the Pd catalyst. All the
reactions were pressurized with 30 bar of CO2 and kept at 70°C
for 5 h. In all of them, the major products obtained were lactones
1-3 and dimers 8-9. Other minor products that added
represented less than 1%. Vinylcyclohexene 9 was despised on
TON and a selectivities calculation, since this is a thermal
product of the reaction and it consumes approximately 0.1% of
the total amount of butadiene.
intermediate
(1,2,3-η3-2-butenyl)(1,2-η2-1,3-butadiene)Pd(6-
CO2-1,3,6-octratriene) (F). Pd-O bond can then breaks up,
allowing the nucleophilic attack at 1- or 2- positions of the η2-
butadiene chain, followed by its dimerization with the η3-butenyl
chain, leading to the formation of esters 6-7.
For this catalytic cycle, the more basic is the phosphine, the
easiest will be the displacement of η3,η3 intermediates C to η3,η1
D, thus facilitating the insertion of CO2 and the consequent
production of lactones.[17-19]
We report here the telomerization of 1,3-butadiene with CO2
catalyzed by Pd/phosphine in the presence of p-hydroquinone,
N,N-diisopropylethylamine (DIPEA) and acetonitrile as solvent.
Figure 1. Structure of ligands used in the reactions reported in Table 1.
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Table 1. Telomerization of butadiene with carbon dioxide using different
phosphines.[a]
Selectivity (%)
Entry Phosphine
TON
8
1+2+3 (1/2+3)
0.0
0.0
-
1
2
-
17.2
67.4
37.4
63.3
35.5
51.6
15.9
53.3
56.0
55.0
60.2
3.3
82.8 (93/7)
32.6 (100/0)
62.6 (100/0)
36.7 (100/0)
64.5 (100/0)
48.4 (97/3)
84.1 (94/6)
46.7 (91/9)
44.0 (79/21)
45.0 (91/9)
39.8 (79/21)
96.7 (99/1)
2200
60
PPh3
3
NaTPPMS
Na2TPPDS
Dan2phos
PTmmCF3
PToMe
90
4
25
5
360
930
2850
930
820
700
220
4500
6
7
8
PTpMe
9[b]
10[c]
11[b].[c]
12[d]
13
PTpMe
PTpMe
PTpMe
PTpMe
PTpOMe
[a]Reaction Conditions: Pd(OAc)2 = 2.7 mg (1.2 10-2 mmol); phosphine/Pd = 3;
p-hydroquinone = 33 mg (0.30 mmol); DIPEA = 77.4 mg (0.60 mmol); 4 mL of
acetonitrile; C4H6 = 10.0 mL (120 mmol); 30 bar of CO2; 70 °C; 5 h; 700 rpm.
n-dodecane was added as an internal standard; 8 = octatriene; 1+2+3 =
lactones; 1/2+3 is the ratio between δ-lactone and γ-lactone; TON = turnover
number (mol of butadiene converted/mol of Pd after 5 h reaction); [b]reaction
without hydroquinone; [c]reaction without DIPEA; [d]reaction without acetonitrile.
The reaction of 1,3-butadiene with CO2 does not occur in the
absence of a phosphine ligand (entry 1, Table 1). It shows very
low activity in the presence of ionic phosphines such as
NaTPPMS, Na2TPPDS or Dan2phos (entries 3-5, Table 1). In
the presence of the neutral triarylphosphines, catalytic activity
and selectivity to δ-lactone increase with increasing ligand
basicity (compare entries 2, 6, 8 and 13 of Table 1). Furthermore,
the phosphine containing ortho-substituted methyl groups on the
phenyl rings of the triphenylphosphine (PToMe) leads to a
reduction of both factors when compared to its analogue PTpMe
(compare entries 7 and 8 of Table 1). This is due to the steric
hindrance caused by the methyl groups in the arylphosphine that
hampers the CO2 insertion in the intermediate D.
A remarkable TON of 4500 with 96% selectivity toward the
valuable δ-lactone is obtained with the most basic phosphine
essayed here, the tris-(p-methoxyphenyl)-phosphine (PTpOMe).
To the best of our knowledge, this result is the best for the
telomerization of 1,3-butadiene with carbon dioxide (Scheme 4)
reported to date.[20-24]
Scheme 4. Comparison of different reactions for the production of lactone 1.
We have recently reported that the addition of an ionic liquid
containing the
1,3-dialkylimidazolium
cations
to the
telomerization reaction of butadiene and acetic acid has a
remarkable effect in the Pd/phosphine catalyst performance.[26]
On the other hand, it is known that the addition of these type of
ionic liquids to the telomerization reaction of 1,3- butadiene with
methanol leads to the complete deactivation of the catalyst,[27]
likely by the formation of a catalytically inactive Pd-carbene
species. The formation of this species requires a basic media to
deprotonate C2-H position of the imidazolium cation (Scheme
5),[28-30] as the one provided by the methoxide used as co-
catalyst in the telomerization with methanol.
In presence of Pd/PTpMe catalyst, but in the absence of any of
the
additional
reagents
(p-hydroquinone
or
N,N-
Scheme 5. Carbene formation from 1,3-dialkylimidazolium ionic liquids and Pd
diisopropylethylamine), there is a significant reduction in both
the TON and the selectivity to δ-lactone (compare entry 8 with 9-
11 of Table 1). These factors are also affected by the absence of
the acetonitrile solvent (entry 12, Table 1), corroborating the
importance of nitrile groups for this reaction.[16,25]
catalyst in the presence of base.
This deactivation also takes place in the telomerization of 1,3-
butadiene with carbon dioxide that requires the presence of N,N-
diisopropylethylamine. Thus, the Pd/PTpOMe catalyst is
deactivated by the presence of different 1,3-dialkylimidazolium
ionic liquids (Table 2). Although no evidence of carbene species
have been found in the NMR analysis of the reaction mixtures,
the fact that the deactivation is significantly less important in the
presence of the ionic liquid containing the 1,2,3-
trialkylimidazolium cation BMMImBF4 (compare entries 13 and
18 of Table 2), which blocks the formation of carbenes at the
active C2 position, supports the hypothesis of the formation of
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ionic liquid and n-dodecane (internal standard) were added to the glass
vessel and the reactor was closed and purged with nitrogen. 4 mL of
acetonitrile was transferred to the reactor under a flow of nitrogen gas
with the aid of a syringe. The reactor was frozen in liquid nitrogen and
then butadiene was liquefied in a flask cooled in a bath at 78°C and the
desired amount of the diene was transferred to the reactor via syringe.
The reactor was heated to room temperature with the aid of a heating
gun, then it was connected to the heating unit. Finally, the reactor was
connected to the gas line for carbon dioxide loading up to a pressure of
30 bar, held constant by a backpressure valve. Once the working
temperature was reached, the stirring was turned on. The pressure
reactor was carefully checked along the reaction to warrant that enough
liquid butadiene remains in the reactor. After the reaction time, heating
and stirring were turn off, the reactor was immersed in an ice bath and
the remaining butadiene/CO2 was vented in a hood. The obtained
mixture was diluted in CH2Cl2 and analyzed using (GC-FID) Hewlett
Packard 5890 Series II and GC-MS Hewlett Packard G1800A GCD
System, both equipped with HP5 columns. 4-vinylcyclohexene and δ-
lactone (3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one) were used to
calculate the response factors to dimers and lactones, respectively. n-
dodecane (Sigma Aldrich) was used as an internal standard. The TON
was calculated from the mols of butadiene converted, excluding the
amount of vinylcyclohexene formed, and the mols of Pd catalyst used.
these carbene species in the case of ionic liquids non-
substituted at the C2 position.[31,32]
Table 2. Telomerization of butadiene with carbon dioxide in the presence of
different imidazolium ionic liquids.[a]
Selectivity (%)
1+2+3 (1/2+3)
Ionic
Liquid
Entry
TON
8
3.3
20.1
0.0
0.0
0.0
3.1
96.7 (99/1)
79.9 (100/0)
100.0 (100/0)
0.0
4500
80
13
14
15
16
17
18
-
BMImBF4
BMImPF6
BMImCl
30
0
100.0 (100/0)
96.9 (99/1)
25
MeOImAcO
BMMImBF4
1630
[a]Reaction Conditions: Pd(OAc)2 = 2.7 mg (1.2 10-2 mmol); PTpOMe/Pd = 3;
p-hydroquinone = 33 mg (0.30 mmol); DIPEA = 77.4 mg (0.60 mmol); 4 mL of
acetonitrile; C4H6 = 10.0 mL (120 mmol); 30 bar of CO2; 70 °C; 5 h; 700 rpm.
n-dodecane was added as an internal standard; 8 = octatriene; 1+2+3 =
lactones; 1/2+3 is the ratio between δ-lactone and γ-lactone; TON = turnover
number after 5 h reaction.
Acknowledgements
We would like to thank the CNPq for the scholarship to Mr.
Balbino.
Conclusions
Keywords: butadiene, telomerization, carbon dioxide, δ-lactone,
3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one, ionic liquid.
The telomerization of 1,3-butadiene with carbon dioxide to δ-
lactone is readily achieved by using Pd(OAc)2 plus tris-(p-
methoxyphenyl)-phosphine in the presence of p-hydroquinone,
N,N-diisopropylethylamine and acetonitrile. A remarkably high
TON of 4500 with 96% selectivity to the valuable δ-lactone was
obtained after 5 h reaction at 70°C. This is the highest catalytic
activity reported so far for this reaction. The telomerization was
deactivated by the presence of different 1,3-dialkylimidazolium
ionic liquids, likely by the formation of inactive Pd-carbene
species.
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The telomerization reactions in a batch system were carried out in a 50
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dipped inside the reaction and a heating unit. 1 mL of 12 mM solution of
Pd(AcO)2 in dichloromethane was added to the reactor glass and the
solvent was evaporated under reduced pressure. Then the desired
quantities of phosphine, p-hydroquinone, N,N-diisopropylethylamine,
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CH3CN
Fine chemicals
Effective TON = 4300
A Pd catalyst plus tris-(p-methoxyphenyl)-phosphine in the presence of p-
hydroquinone, N,N-diisopropylethylamine and acetonitrile is the best system for the
telomerization of butadiene with carbon dioxide reported till now.
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