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High catalytic and recyclable systems for heck reactions in biosourced ionic liquids
Molecular Catalysis 437 (2017) 121–129
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High catalytic and recyclable systems for heck reactions in biosourced ionic liquids Safa Hayouni, Nadège Ferlin ∗ , Sandrine Bouquillon ∗ Institut de Chimie Moléculaire de Reims, UMR CNRS 7312, Université de Reims Champagne-Ardenne, Boîte no 44, B.P. 1039, F-51687 Reims, France
a r t i c l e
i n f o
Article history: Received 23 February 2017 Received in revised form 8 May 2017 Accepted 8 May 2017 Keywords: Ionic liquids Heck reaction Pallado-catalyzed reaction Catalyst recyclability Biosourced acids Ammonium Phosphonium
a b s t r a c t Tetrabutylammoniums (TBA) and tetrabutylphosphoniums (TBP) ionic liquids (ILs) comporting a biosourced anion were easily synthesized by an acido-basic method. These ILS were then used as solvent for Heck reaction between iodoarene or halogenoaromatics with tert-butylacrylate in presence of PdCl2 as catalyst and a base. With NaHCO3 , good conversion and selectivity were obtained; however the catalytic system could not be recycled. Use of triethylamine as base permitted good efficiency of the reaction, with the advantage to have the possibility to recycle the catalytic system without loss of reactivity, especially with TBA l-lactate 1a, TBP l-lactate 2a and TBP i-malate 2b. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Ionic liquids (ILs) are ionic, salt-like materials which are liquid below 100 ◦ C. Their numerous properties (high solubility power, high stability, non volatility, . . .) make them an attractive choice of solvent in many important chemical processes [1]. Many examples are reported in (bio)catalysis [2], in organic synthesis [3], in electrochemistry [4] or in extraction [5]. Recently, appropriate reviews detailed the advantages of using ILs as new solvents in various fields [6]. Considering the use of ILs in metallo-catalyzed reactions, the most significant developments in palladium-catalyzed crosscoupling (Heck, Suzuki-Miyaura, Stille, Sonogashira, Ullman, and Negishi) have been recently reviewed by Mastrorilli et al. [7]. Beneficials effects of the used of ILs were described in terms of activity, of selectivity through the formation of metallic nanoparticles leading to a ligand free system and being most of the time more active on aryle bromide or chloride; furthermore the use of ILs can allow the possibility to recyclable catalytic systems. This work was in the continuity of previously reported works of Bellina and Chiappe [8a], Wu and al. [8b], Welton and Smith [8c] and Beller and Bölm [8d]. S-arylation coupling was also performed using ionic liq-
∗ Corresponding authors. E-mail addresses: [email protected] (N. Ferlin), [email protected] (S. Bouquillon). http://dx.doi.org/10.1016/j.mcat.2017.05.007 2468-8231/© 2017 Elsevier B.V. All rights reserved.
uid framework (Pd@IL-PMO) as an efficient green catalyst [8e] and efficient tandem aqueous room temperature oxidative amidations were realized in the presence of supported Pd nanoparticles on graphene oxide and ammonium salts as surfactant [8f]. For the Heck reaction, ILs as solvents play in general an important role for the formation on Pd nanoparticles, and as stabilizers or promoters of ligand-assisted or phosphine-free reactions [9]. This role was well described by Trzeciak et al. with imidazolium halides [10a] and Calo et al. with imidazolium or pyridinium derivatives [10b]. Supported ionic liquid layer catalysts (SILCs) or supported ionic liquid phase catalyst (SILPC) have been also largely described in the recent literature and proved the increasing interest of this kind of catalyst for many metal-induced processes, among them the Heck reactions [11]; homogeneous catalysts are by this way immobilized and can be recovered by simple filtration to be reused. Heck reaction employing simple ILs as tetrabutylammonium bromide (TBA Br), was reported by Böhm and Herrmann in 2000 [12a]. A wide range of phosphonium based room temperature ionic liquids (RTILs) have been used for the Heck reaction and allowed a ligand free approach for this reaction leading to a very attractive interest for purification, costs, and reaction scale up [12b]. However, it is clear today that ILs are nor green solvent considering thermodynamic and physical behaviours as mentioned in different publications of Marlair’s group [13]. Furthermore, their low biodegradability (or the toxicity of their degradation products) and their high (eco)toxicity led the scientific community to reduce their use or to find other greener alternatives [13]. Due to their
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biodegradability and non-toxicity, the use of renewable resources such as amino acids, amino alcohols, or sugars, could improve the green character of ILs [14]. Chiappe et al. [15a] developed Heck reactions in ILs derived from natural sugars folllowing previously work of Handy et al. [15b] on fructose-based ionic liquids. These works revealed the possibility to use this kind of ionic liquids as solvents for free ligand Heck reactions. Indeed, coupling between methyl cinnamate and electron-rich and electron-deficient compounds aryle iodide and bromide worked well and the catalyst/RTIL layer could be recycled three or four times with no detectable loss in activity. Our group developed a few years ago various ILs based on ammonium or phosphonium with anions from natural acids (llactic, l-tartaric, pyruvic, malic, malonic, succinic and osidic acids), but also l-proline and its derivatives. Even if they were not readily biodegradable, these compounds showed in general lower toxicity towards various organisms than usual chlorinated and commercial ILs [16a,b,c]. These ILs were used as solvents and showed good performance and recyclability (until 10 runs without loss of activity) in catalytic selective hydrogenation of 1,5-cyclooctadiene and linoleic acid at room temperature under atmospheric H2 pressure [16a,b]. The proline-based ILs were also used as co-solvent with iso propanol for the enantioselective hydrogenation of double carbon–carbon bonds of ␣,-unsaturated ketones still under mild conditions with PdCl2 [16c]. Previously described works in the literature proved the real improvement of ILs as solvent for Heck reaction. With our expertise in the use of biosourced ILs as solvents in hydrogenation processes, we wanted to explore the potentialities of these biosourced ILs in Heck reaction. The present paper describes the development of a new methodology for Heck coupling using bioderived ILs with PdCl2 in presence of a base.
2. Experimental 2.1. Materials All materials were analytical grade and used as received from Strem Chemicals (Palladium (II) chloride) and Alfa-Aesar (trimethylamine, tert-Butyl acrylate and all substrates). Ionic liquids were all known and prepared by previously described methods [16a,b].
2.2. Characterization NMR spectroscopy was performed at 500 MHz with Bruker Avance III spectrometer equipped with a BBFO+ probe and at 600 MHz with Bruker Avance III spectrometer equipped with a CPTCI cryoprobe. The sample was dissolved in MeOD-d4 and the resulting solution was placed in a 5 mm diameter NMR tube. 1H NMR spectra were taken with 30◦ pulse angle, 10 s relaxation delay and 16 scans. GC analyses were recorded on a Hewlett–Packard HP-6890 gas chromatograph, fitted with DB-1 capillary column (25 m, 0.32 mm), a flame ionization detector and HP-3395 integrator under the following conditions: helium as vector gas (5.104 Pa), temperature of injector: 250 ◦ C, temperature of the oven: isotherm 150 ◦ C, 5 min, then 150–300 ◦ C (10 ◦ C/min) and isotherm 300 ◦ C, 5 min. GC/MS analyses were recorded on a THERMOQUEST Draw GC on 2000 Series by using the techniques of chemical ionization under the following conditions: capillary column DB1 (length: 25 m, diameter: 0.32 mm), vector gas: helium (0.5 bar), temperature injector: 250 ◦ C.
2.3. General procedure for the Heck reaction with NaHCO3 as base PdCl2 (4.3 mg, 0.024 mmol, 0.02 eq) and NaHCO3 (121 mg, 1.44 mmol, 1.2 eq) were introduced in a Schlenk tube containing 600 mg of ionic liquid. The resulting mixture was dried for 2 h at 100 ◦ C under vacuum. The halogenoarene (1.2 mmol) and the tertbutylacrylate (210 L, 1.45 mmol, 1.2 eq) were introduced under inert atmosphere. The system was closed and heating for 24 h at 100 ◦ C. After cooling, the reacting mixture was extracted four times with 5 mL of diethylether. The reacting phase was kept and dried. The different organic phases were assembled, filtered through cotton. 1 L was injected in GC to determine conversion and selectivity. The organic phase was then concentrated and dried for NMR analysis if necessary. 2.4. Recycling/reuse of catalytic system After extraction with diethylether, the ionic liquid phase was kept in the Schlenk tube and dried at reduced pressure. NaHCO3 (121 mg, 1.44 mmol, 1.2 eq.) was added, then halogenoarene (1.2 mmol) and tert-butylacrylate (210 L, 1.45 mmol, 1.2 eq.) were introduced under inert atmosphere. Reaction was then performed again at 100 ◦ C for 24 h. Same work-up as for the first cycle was then realized and the liquid ionic phase re-used as necessary. 2.5. General procedures for the Heck reaction with NEt3 as base Under argon atmosphere, the substrate (bromobenzene, chlorobenzene or iodoarenes, 1.2 mmol), tert-butyl acrylate (210 L, 1.45 mmol, 1.2 eq.) and triethylamine (200 L, 1.44 mmol, 1.2 eq.) were mixed in a Schlenk tube containing 600 mg of ionic liquid and PdCl2 (4.3 mg, 0.024 mmol, 0.02 eq.). The resulting mixture was stirred for 24 h at the desired temperature (60 or 100 ◦ C). Once the reaction was completed, the crude product was extracted four times with 5 mL of diethyl ether, combined, filtered through cotton and then concentrated under reduced pressure. 1 L of the organic phase was injected in a gas chromatography (GC end GC/MS) to determine the conversion. The ratio E/Z was determined with 1 H NMR. 2.6. Recycling After the diethylether extraction, drying and a short vacuum/argon sequence, the respective substrates in similar ratios as before were added into the precedent ionic liquid phase in the Schlenk tube. The mixture was stirred vigorously for 24 h at the desired temperature under argon atmosphere. Same treatment as previously described was then employed for the separation and the analysis of the coupling product. 3. Results and discussion 3.1. Synthesis of bio-derived ionic liquids The ionic liquids (ILs) were easily synthesized using an acidbase method [16]. Tetrabutylammonium hydroxide (TBA OH) was reacted in water at reflux with an excess of a biobased acids (Table 1) [16a]. The acids (l-lactic, l-malic acid, pyruvic acid, malonic acid and succinic acid) were chosen for their low cost, their non–toxicity and high availability. ILs 1a-1f were obtained with quantitative yields. Same method was used to prepare phosphonium ILs with Llactic acid (2a) and L-malic acid (2b) (Table 2) [16b], this time using tetrabutylphosphonium hydroxide (TBP OH). Again, ILs were easily
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129 Table 1 Synthesis of ammonium ionic liquids with biocarboxylates.
R-COOH
Obtained IL
Number
Yield
L-lactic acid
1a
97%
L-malic acid
1b
97%
Pyruvic acid
1c
95%
L-tartaric acid
1d
98%
Malonic acid
1e
99%
Succinic acid
1f
98%
Table 2 Synthesis of phosphonium ionic liquids with biocarboxylates.
R-COOH
Obtained IL
Number
Yield
l-lactic acid
2a
87%
l-malic acid
2b
92%
Pyruvic acid
2c
87%
made with quantitative yields. With pyruvic acid, reflux in ethanol was processed as no IL was formed in water at 100 ◦ C. 3.2. Heck Reaction using NaHCO3 as base As the synthesized ILs have been successfully used as (co)solvent for hydrogenation of dienes in mild conditions in presence of palladium (II) salt as catalyst [16a,b], they are ideal greener medium for metal and pallado-catalyzed reaction compared to usual organic solvents. In addition, the catalytic system could be re-used 10 times without loss of reactivity [16a]. Like more common ILs, the synthesized compounds showed high thermal stability. Consequently, they were considered as solvent for C C coupling reaction, such as Heck reaction [7,8,17]. Coupling of iodobenzene with tert-butylacrylate, in presence of NaHCO3 as base and PdCl2 as catalyst, was studied as model reaction to determine the efficiency of the ILs. Used reaction conditions were already worked out by the laboratory [18]. At first, reaction was performed in usual organic solvents (Table 3). Conver-
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sion of iodobenzene, but also selectivity for the coupling product was determined by GC and/or GC/MS. The study was completed with 1 H NMR study to define the proportion of isomer E in the formed Heck coupling product. In water, low conversion was obtained. The lack of reactivity was certainly due to low miscibility of the reactants and/or low dispersity of the catalyst. Only the E isomer coupling product was obtained. It was proved by 1 H NMR performed after purification of the reaction product. Spectrum showed that only just one product was present and calculation of the coupling constant 3 J of alcenic hydrogens, which value was around 16 Hz, confirmed the E isomeric position. This result could be expected as the E isomer is generally the only or major compound obtained. It is more stable than the Z isomer [19], particularly when moieties present a steric hindrance, like with benzyl and tert-butyl groups. Low conversion was also observed in DMF and several not-identified by-products formed. Reaction almost did not occurred in toluene, which might be caused by the low polarity of the solvent. When DMSO was employed, good conversion and selectivity were observed. And as previously observed with water, NMR demonstrated that only the E isomer was synthesized. However, recycling attempt failed as conversion and selectivity both drastically decreased to around 10%. Study was then performed using commercials ILs, which are known to be able to recycle/recover metallic catalytic system [18,20]. Moreover, ILs being highly polar solvent [21], they might favour Heck coupling. Recycling of the catalytic system was also performed. After reaction and extraction of obtained products with diethylether, the ionic liquid phase was kept in the Schlenk tube and dried under vacuum. Reactants were introduced and reaction launched again in the same conditions. In tetrabutylammonium bromide (TBA Br), low conversion occurred and was even reduced during the second cycle. On the contrary, almost total conversion of the iodobenzene with 100% of selectivity for the E coupling product was observed with tetrabutylammonium chloride (TBA Cl). Unfortunately, reactivity decreased after recycling as conversion dropped to 57%. Finally, synthesized ammonium ILs 1a to 1f were tested (Table 3, entries 7–12). At the exception of TBA L-malate 1b and TBA Ltartrate 1d (Table 3, entries 8 and 10), total conversion with only formation of the E coupling product was observed. The low conversion in 1b and 1d was the consequence of the high viscosity of the ILs, which were respectively 260 cP and 3689 cP at 80 ◦ C. The high viscosity of 1d had also an effect on the selectivity as it was the only synthesized ILs in which by-products formed, certainly due to dimerisation or degradation of reactants. As it was the case with the commercial ILs, reactivity decreased severely during the second cycle with 1c, 1e and 1f (Table 3, entries 9b, 11b and 12b). With TBA l-lactate 1a, the reduction of reactivity was less drastic at the second run, as still 87% of iodobenzene were completely converted into the E coupling product. A third cycle was performed, but this time reactivity was not conserved and conversion fell down to 26%. 1a being the more efficient tested synthesized solvent, study with varying reactant, but still with NaHCO3 as base was continued. At first, reaction was performed with ethylacrylate (Table 4). For the 2 first cycles, excellent conversion and selectivity were obtained. Like it was the case with tert-butylacrylate, just the E isomer was obtained, even if the steric hindrance of the ethyl group was less important. Having just one of the isomer formed, whatever the acrylate used for the Heck coupling, was quite interesting. As isomers are in general quite difficult to separate [22], the fact that just one of them was obtained will permit to avoid purification steps. Unfortunately, at the third cycle, conversion decreased drastically to 6%.
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Table 3 Heck reaction with organic solvent or ionic liquids.
Entry
Solvent or ILs
Cycle
Conversion*
Selectivity*
isomer E¤
1 2 3 4a 4b 5a 5b 6a 6b 7a 7b 7c 8 9a 9b 10 11a 11b 12a 12b
Water DMF Toluene DMSO
1 1 1 1 2 1 2 1 2 1 2 3 1 1 2 1 1 2 1 2
32% 29% 1% 81% 11% 47% 32% 99% 57% 99% 87% 26% 50% 100% 68% 41% 100% 45% 99% 47%
100% 58% 100% 87% 8% 100% 64% 100% 99% 100% 100% 100% 100% 100% 100% 76% 100% 100% 100% 100%
100% 100% nd 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
TBA Br TBA Cl 1a
1b 1c 1d 1e 1f
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; ¤ determined by 1 H NMR; nd: not determined. Table 4 Heck reaction with ethylacrylate in TBA L-lactate 1a.
Cycle
Conversion*
Selectivity*
isomer E¤
1 2 3
99% 90% 6%
96% 99% 100%
100% 100% nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; ¤ determined by 1 H NMR; nd: not determined.
Heck reaction between tert-butylacrylate and various iodobenzene wearing chemical groups or halogenobenzene was performed and are listed in Table 5. At first, iodoarene with electro-donors group were tested. With iodophenols, the position of the substitution mattered. Conversion was very low for the ortho-derivatives, whereas it was excellent for meta- and para-positions. For 2iodophenol, the alcohol function being closed to the iodo group, it might destabilized the adduct during oxidative addition or insertion steps [23]. On the contrary, for amino and oxymethyl groups, complete or almost complete conversion occurred, whatever the position of the group. Selectivity with iodoanilines was lower, due to the higher reactivity of the function. Electro-acceptors group were also studied. Degradation occurred with 2-iodobenzoic acid and consequently no coupling product formed. For the other reactants, no effect of the position of the group was observed on the conversion with nitro and carboxylic acid functions. But it had an effect on the selectivity. Better selectivity was obtained with the meta-component, as electro-acceptor groups in this position provide better stability of the aromatic compounds [24]. The multiplication of group, causing steric hindrance and desactivation of the aromatic core, reduced the reactivity. Indeed, with trimethyliodobenzene, only 64% of the reaction was converted. As previously observed with iodobenzene, 1 H NMR spectra proved that only the coupling product in the E conformation was formed with all tested reactants.
Other iodoaromatic compounds were reacted, and total conversion of iodopyridine and iodonaphtalene was observed with total selectivity for the E coupling product. Unfortunately, with iodovanilline, reaction did not occurred. Indeed, GC and GC/MS analyses confirmed that vanilline was obtained. No insertion of the acrylate happened, which might be due to steric hindrance, but also de-iodation occurred. No reaction happened with bromobenzene, due to the lower reactivity of the compound as previously described in the literature [25]. In all case, recycling of the catalytic system contained in the ionic liquid phase failed as conversion of the iodoarenes fell down or did not even occurred. Into have the possibility to reuse the catalyst, reaction conditions were changed.
3.3. Heck reaction using the triethylamine as base NaHCO3 was replaced by triethylamine NEt3 , which is a relative strong homogeneous base which could be removed by evaporation under reduced pressure. With usual organic solvent, results were quite the same as the one obtained with NaHCO3 (Table 6). Reaction did not occur in toluene and conversion was very low in water. Use of DMSO improved the iodobenzene conversion, but it was not total, by-products formed and recycling was not possible. Commercial ILs were also tested. In tetrabutylphosphonium bromide (TBP Br), conversion of iodobenzene was estimated at 47%, so not sufficient to consider this IL as solvent for Heck reaction. On the contrary, in TBA Cl, complete conversion of the iodoarene was achieved with the formation of only the Heck coupling product in its E conformation. Moreover, recycling was possible as same results were obtained during the second cycle. Unfortunately, reactivity decreased during the third cycle as conversion fell down to 61%. Coupling reaction between iodobenzene and tert-butylacrylate with NEt3 as base was performed in synthesized ILs 1a, as it showed good efficiency with NaHCO3 . Reaction was also performed with ILs 2a, 2b and 2c. These phosphonium ILs were chosen for their low viscosity at 80 ◦ C, which values were 21, 105 and 16 cP respectively, but also for their high thermal stability above 200 ◦ C, or even 300 ◦ c for TBP L-lactate 2a and TBP pyruvate 2c. With TBA L-lactate
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129 Table 5 − Heck reaction with various halogenobenzene with t-butylacrylate in TBA L-lactate 1a.
125
Table 5 (Continued)
R-X R-X
Conversion*
Selectivity*
39%
100%
93%
90%
Conversion*
Selectivity*
Vanilline formation
0
nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; nd: not determined. 100%
100% Table 6 Heck reaction with organic solvent and ionic liquids with NEt3 as base.
100%
99%
100%
95%
100%
89%
Solvent or ILs
Cycle
Conversion*
Selectivity*
96%
100%
Toluene water DMSO TBP Br TBA Cl
1 1 1 1 1 2 3
1% 30% 76% 47% 99% 100% 61%
100% 100% 80% 100% 100% 100% 100%
100%
100%
100%
100%
degradation
100%
90%
100%
80%
100%
100%
100%
98%
100%
91%
64%
100%
100%
100%
100%
100%
Condition: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; nd: not determined.
1a, total conversion and selectivity for the E isomer was obtained. Moreover, recycling of the catalyst was achieved as it can be re-used for 6 more cycles without loss of neither reactivity nor selectivity (Fig. 1a). Quite the same results were obtained with TBP L-lactate 2a and TBP L-malate 2b (Fig. 1b and c). For TBP pyruvate 2c, conversion and selectivity were not as good as the previous ILs, even if catalytic system could be recycled. Our synthesized ILs, comporting an anion derived from bioresources, were more efficient than commercials ILs. At first, iodobenzene was completely converted with 1a, 2a and 2b and high selectivity for the E-coupling product obtained. Synthesized ILs also permitted to recycle the catalytic system. Heck coupling with iodoarenes is quite common and a well described reaction [26]. With the developed methodology, the possibility to recycle so many times the catalytic system without loss of reactivity and the use of greener reaction medium are real improvements. Moreover, this developed method is quite conformed to green chemistry principles [27], which goals are to develop environment-friendly synthesis, to limit pollution and use or volatile and/or toxic solvent, etc. . . Indeed, the use of biobased ILs, the small amount of catalyst added (only 0.02 eq.), the no requirement of ligand or phosphine, the efficiency of the system and the absence of by-products permit to consider the transformation as green, or at least greener than usual methods [26]. It is also important to note that the cost price of these biobased ionic liquid is lower than the price of the commercial ILs commonly used in chemical processes [28]. As previously, study was completed by screening halogenoarenes reactants with NEt3 as base and 1a as solvent (Table 7). With electro-donor groups, such as alcohol or amino,
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Conversion
Table 7 Heck reaction with various halogenobenzene with t-butylacrylate with NEt3 as catalyst with TBA L-lactate 1a.
Selectivity
Proportion in E isomer
100 80 60 R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5 6 7
93 98 96 94 98 93 94
96 98 98 98 92 98 98
1 2 3 4
100 100 100 100
100 91 100 100
1 2 3 4 5
100 100 100 100 100
100 97 98 100 97
1 2 3 4 5 6
100 100 100 100 100 100
100 100 100 100 100 100 100
1 2 3 4 5 6
100 100 100 100 100 100
100 100 100 100 100 100
1a
40 20 0
1
2
3
4
5
6
7
100 80 60
2a
40 20 0
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
100 80 60
2b
40 20 0
100 80 60
1 2 3 4 5 6
100 99 100 98 100 83
100 100 100 100 100 100
1 2 34 5
100 100 100 98 100
93 97 96 97 100
1 2 3 4
100 100 100 100
90 84 78 74
1 2
100 35
100 75
3
8
nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent;* determined by GC; nd: not determined.
2c
40 20 0
Fig. 1. Heck reaction between iodobenzene and t-butylacrylate with NEt3 as base in synthesized ILs.
almost total conversion and excellent selectivity were observed. Recyclability of catalyst occurred especially with 1-iodophenol as 6 cycles were performed without loss of reactivity. Electro-acceptor moities were also evaluated. With ortho- and para-iodobenzoic acid, total conversion and selectivity happened and was conserved during 5 more cycles. As it was the case with NaHCO3 , degradation occurred with 1-iodobenzoic acid. Whatever the position of the nitro groups, good conversion and selectivity were obtained. In all cases and as previously observed, only the isomer E was synthesized. With NEt3 , coupling occurred when iodovanilline was used as substrate and catalyst was able to be recycled two more times. Selectivity was lower than with mono-substituted iodoarenes, as the multiplication of groups favoured by-products formation. With iodopyridine, results were the same as with NaHCO3 . Total con-
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129
version and selectivity was observed during the first cycle, then reduced with the second one. Attempts to form the coupled product from bromobenzene failed, as just only 7% of the reactant was converted. The screening of iodoarenes was pursued with TBP L-lactate 2a as solvent (Table 8). Prior tests done in the laboratory proved that temperature could be reduced to 60 ◦ C. With methoxy and alcohols groups, total conversion and selectivity were observed during 5 cycles; at the exception with 1-iodophenol, where almost total conversion occurred during recycling. With 3-iodoaniline, conversion for both cycles was evaluated at around 60%. The reduction of reactivity compared was certainly due to the decrease of the temperature of reaction. However, reducing the temperature permitted to avoid the degradation of 1-iodobenzoic acid and resulted to the formation of the coupled product with excellent conversion and selectivity. Also two more cycles were performed with very slight diminution of reactivity. As observed with 1a, very good conversion, selectivity and possibility to recycle were obtained with metaand para- iodobenzoic acid and iodonitrobenzenes in 2a. Other halogenobenzenes were tested in the same condition in 2a. This time with NEt3 , reaction occurred with bromobenzene and total conversion and selectivity was observed. Performing Heck reaction on bromobenzene as not only the advantage to enhance applications of our methodology, but also to use less expensible bromoarenes compounds [29]. Unfortunately, conversion dropped when the catalyst was reused. On the contrary, no reaction happened with chlorobenzene. It could be forecast as chloroarene are few reactive and not generally used for C C coupling [25]. Again, with TBP L-lactate 2a in presence of NEt3 , recycling of the catalytic system was possible until five times without loss of reactivity for various iodoarenes derivatives. Phosphonium ILs were even more efficient than the ammoniums. At first, reaction could be performed at lower temperature, which avoided degradation of sensible substrate like 1-iodobenzoic acid and limited formation of by-products. Indeed, in general selectivities were higher in 2a than in 1a. Secondly, Heck reaction was also performed with bromobenzene, which was not possible with TBA L-lactate 1a. Such cation-based influence on performances of the ILs could be due to the physical differences between phosphonium and ammonium cations. The phosphonium ILs being generally more viscous than ammonium ones; this observation might be attributed to a larger radius of the phosphorus atom compared to the nitrogen atom, which decreases the lattice energy and gives more flexibility to the cation structure [16b,30].
4. Conclusion Ammonium and phosphonium carboxylates ionic liquids (ILs), obtained from biosourced acids like l-lactic acid or l-malic acid, were easily prepared and used as solvent for Heck reaction between halogenoarenes and tert-butylacrylate with PdCl2 as catalyst. When NaHCO3 was used as base, synthesized tetrabutylammonium (TBA) ILs showed better efficiency than typical Heck coupling media, such as usual organic solvents or commercial ILs. Indeed, total conversion and selectivity was achieved with TBA l-lactate 1a, TBA pyruvate 1c, TBA malonate 1e and TBA l-lactate 1f. In addition, Heck coupling with different iodoarenes wearing electro-donnor or electro-acceptor groups were realized with excellent conversion and selectivity in 1a. Whatever the conditions used, just only the E isomer of the coupling product was formed. Unfortunately, recycling of catalyst attempts failed as conversion fell down at the second cycle. Changing the base by triethylamine NEt3 finally permitted to recycle the catalyst, as the system was re-used at least 5 times without loss of reactivity for reaction of iodobenzene with tert-
127
Table 8 Heck reaction with various halogenobenzene with t-butylacrylate with NEt3 as catalyst with TBP L-lactate 2a.
R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5
100 98 96 95 95
96 98 98 98 96
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2
62 61
54 38
1 2 3
95 90 93
68 54 65
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 97 94 91 74
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
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Table 8 (Continued)
R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5
100 100 100 95 96
100 96 93 90 85
1 2 3
100 73 68
100 100 100
1
0
–
Conditions: 1.2 mmol of halogenoarene, 600 mg of solvent; * determined by GC; nd: not determined.
butylacrylate with 1a, but also tetrabutylphosphoniums (TBP) l-lactate 2a, TBP l-malate 2b and TBP pyruvate 2c to furnish only the E isomer products. Reaction and recyclability also occurred with the presence of groups on the iodobenzene ring in 1a, and even happened when iodovanilline was used as substrate. Performance was improved when 2a was used, as reaction was performed at lower temperature, better selectivities were observed and reaction happened with bromobenzene. To conclude, we have developed a new sustainable methodology for Heck reaction. At first, greener and non-volatile solvents and quite common catalyst, in low amount and without addition of ligands, were used. Reaction was performed with high efficiency and excellent selectivity for the E-coupling product and was transposable on various iodoarenes derivatives, and even on bromobenzene. The more important progress was the possibility to re-use the catalytic system. Further investigations are in progress concerning the possibility to reduce the quantity of catalyst and to extend to chloride derivatives. Acknowledgements This work was supported by the Fondation du Site Paris Reims (post-doctoral fellowship for Nadège Ferlin) and the FEDER for material funds. We thank also the Tunisian Ministry of Education and Research for financial support for the cotutoring PhD of Safa Hayouni. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.mcat.2017.05. 007. References [1] (a) J.D. Holbrey, K.R. Seddon, Clean Prod. Process. 1 (1999) 223–236; (b) P. Wassercheid, T. Welton, Ionic liquids in synthesis, 2nd edition, Wiley, VCH Weinheim, 2008. [2] (a) V.I. Parvulescu, C. Hardacre, Chem. Rev. 107 (2007) 2615–2665; (b) F.V. Rantwijk, R.A. Sheldon, Chem. Rev. 107 (2007) 2757–2785. [3] (a) L. Lafuente, G. Diaz, R. Bravo, A. Ponzinibbio, Lett. Org. Chem. 13 (2016) 195–199; (b) A.R. Hajipour, F. Rafiee, Org. Prep. Proced. Int. 47 (4) (2015) 249–308. [4] J.C. Plaquevent, Y. Genisson, F. Frédéric, Techniques de l’Ingénieur, Constantes Physico-Chimiques 51 (K 55) (2008) (K1230/1-K1230/17). [5] D. Wei, A. Ivaska, Anal. Chim. Acta 607 (2008) 126–135.
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Editor’s choice paper
High catalytic and recyclable systems for heck reactions in biosourced ionic liquids Safa Hayouni, Nadège Ferlin ∗ , Sandrine Bouquillon ∗ Institut de Chimie Moléculaire de Reims, UMR CNRS 7312, Université de Reims Champagne-Ardenne, Boîte no 44, B.P. 1039, F-51687 Reims, France
a r t i c l e
i n f o
Article history: Received 23 February 2017 Received in revised form 8 May 2017 Accepted 8 May 2017 Keywords: Ionic liquids Heck reaction Pallado-catalyzed reaction Catalyst recyclability Biosourced acids Ammonium Phosphonium
a b s t r a c t Tetrabutylammoniums (TBA) and tetrabutylphosphoniums (TBP) ionic liquids (ILs) comporting a biosourced anion were easily synthesized by an acido-basic method. These ILS were then used as solvent for Heck reaction between iodoarene or halogenoaromatics with tert-butylacrylate in presence of PdCl2 as catalyst and a base. With NaHCO3 , good conversion and selectivity were obtained; however the catalytic system could not be recycled. Use of triethylamine as base permitted good efficiency of the reaction, with the advantage to have the possibility to recycle the catalytic system without loss of reactivity, especially with TBA l-lactate 1a, TBP l-lactate 2a and TBP i-malate 2b. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Ionic liquids (ILs) are ionic, salt-like materials which are liquid below 100 ◦ C. Their numerous properties (high solubility power, high stability, non volatility, . . .) make them an attractive choice of solvent in many important chemical processes [1]. Many examples are reported in (bio)catalysis [2], in organic synthesis [3], in electrochemistry [4] or in extraction [5]. Recently, appropriate reviews detailed the advantages of using ILs as new solvents in various fields [6]. Considering the use of ILs in metallo-catalyzed reactions, the most significant developments in palladium-catalyzed crosscoupling (Heck, Suzuki-Miyaura, Stille, Sonogashira, Ullman, and Negishi) have been recently reviewed by Mastrorilli et al. [7]. Beneficials effects of the used of ILs were described in terms of activity, of selectivity through the formation of metallic nanoparticles leading to a ligand free system and being most of the time more active on aryle bromide or chloride; furthermore the use of ILs can allow the possibility to recyclable catalytic systems. This work was in the continuity of previously reported works of Bellina and Chiappe [8a], Wu and al. [8b], Welton and Smith [8c] and Beller and Bölm [8d]. S-arylation coupling was also performed using ionic liq-
∗ Corresponding authors. E-mail addresses: [email protected] (N. Ferlin), [email protected] (S. Bouquillon). http://dx.doi.org/10.1016/j.mcat.2017.05.007 2468-8231/© 2017 Elsevier B.V. All rights reserved.
uid framework (Pd@IL-PMO) as an efficient green catalyst [8e] and efficient tandem aqueous room temperature oxidative amidations were realized in the presence of supported Pd nanoparticles on graphene oxide and ammonium salts as surfactant [8f]. For the Heck reaction, ILs as solvents play in general an important role for the formation on Pd nanoparticles, and as stabilizers or promoters of ligand-assisted or phosphine-free reactions [9]. This role was well described by Trzeciak et al. with imidazolium halides [10a] and Calo et al. with imidazolium or pyridinium derivatives [10b]. Supported ionic liquid layer catalysts (SILCs) or supported ionic liquid phase catalyst (SILPC) have been also largely described in the recent literature and proved the increasing interest of this kind of catalyst for many metal-induced processes, among them the Heck reactions [11]; homogeneous catalysts are by this way immobilized and can be recovered by simple filtration to be reused. Heck reaction employing simple ILs as tetrabutylammonium bromide (TBA Br), was reported by Böhm and Herrmann in 2000 [12a]. A wide range of phosphonium based room temperature ionic liquids (RTILs) have been used for the Heck reaction and allowed a ligand free approach for this reaction leading to a very attractive interest for purification, costs, and reaction scale up [12b]. However, it is clear today that ILs are nor green solvent considering thermodynamic and physical behaviours as mentioned in different publications of Marlair’s group [13]. Furthermore, their low biodegradability (or the toxicity of their degradation products) and their high (eco)toxicity led the scientific community to reduce their use or to find other greener alternatives [13]. Due to their
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biodegradability and non-toxicity, the use of renewable resources such as amino acids, amino alcohols, or sugars, could improve the green character of ILs [14]. Chiappe et al. [15a] developed Heck reactions in ILs derived from natural sugars folllowing previously work of Handy et al. [15b] on fructose-based ionic liquids. These works revealed the possibility to use this kind of ionic liquids as solvents for free ligand Heck reactions. Indeed, coupling between methyl cinnamate and electron-rich and electron-deficient compounds aryle iodide and bromide worked well and the catalyst/RTIL layer could be recycled three or four times with no detectable loss in activity. Our group developed a few years ago various ILs based on ammonium or phosphonium with anions from natural acids (llactic, l-tartaric, pyruvic, malic, malonic, succinic and osidic acids), but also l-proline and its derivatives. Even if they were not readily biodegradable, these compounds showed in general lower toxicity towards various organisms than usual chlorinated and commercial ILs [16a,b,c]. These ILs were used as solvents and showed good performance and recyclability (until 10 runs without loss of activity) in catalytic selective hydrogenation of 1,5-cyclooctadiene and linoleic acid at room temperature under atmospheric H2 pressure [16a,b]. The proline-based ILs were also used as co-solvent with iso propanol for the enantioselective hydrogenation of double carbon–carbon bonds of ␣,-unsaturated ketones still under mild conditions with PdCl2 [16c]. Previously described works in the literature proved the real improvement of ILs as solvent for Heck reaction. With our expertise in the use of biosourced ILs as solvents in hydrogenation processes, we wanted to explore the potentialities of these biosourced ILs in Heck reaction. The present paper describes the development of a new methodology for Heck coupling using bioderived ILs with PdCl2 in presence of a base.
2. Experimental 2.1. Materials All materials were analytical grade and used as received from Strem Chemicals (Palladium (II) chloride) and Alfa-Aesar (trimethylamine, tert-Butyl acrylate and all substrates). Ionic liquids were all known and prepared by previously described methods [16a,b].
2.2. Characterization NMR spectroscopy was performed at 500 MHz with Bruker Avance III spectrometer equipped with a BBFO+ probe and at 600 MHz with Bruker Avance III spectrometer equipped with a CPTCI cryoprobe. The sample was dissolved in MeOD-d4 and the resulting solution was placed in a 5 mm diameter NMR tube. 1H NMR spectra were taken with 30◦ pulse angle, 10 s relaxation delay and 16 scans. GC analyses were recorded on a Hewlett–Packard HP-6890 gas chromatograph, fitted with DB-1 capillary column (25 m, 0.32 mm), a flame ionization detector and HP-3395 integrator under the following conditions: helium as vector gas (5.104 Pa), temperature of injector: 250 ◦ C, temperature of the oven: isotherm 150 ◦ C, 5 min, then 150–300 ◦ C (10 ◦ C/min) and isotherm 300 ◦ C, 5 min. GC/MS analyses were recorded on a THERMOQUEST Draw GC on 2000 Series by using the techniques of chemical ionization under the following conditions: capillary column DB1 (length: 25 m, diameter: 0.32 mm), vector gas: helium (0.5 bar), temperature injector: 250 ◦ C.
2.3. General procedure for the Heck reaction with NaHCO3 as base PdCl2 (4.3 mg, 0.024 mmol, 0.02 eq) and NaHCO3 (121 mg, 1.44 mmol, 1.2 eq) were introduced in a Schlenk tube containing 600 mg of ionic liquid. The resulting mixture was dried for 2 h at 100 ◦ C under vacuum. The halogenoarene (1.2 mmol) and the tertbutylacrylate (210 L, 1.45 mmol, 1.2 eq) were introduced under inert atmosphere. The system was closed and heating for 24 h at 100 ◦ C. After cooling, the reacting mixture was extracted four times with 5 mL of diethylether. The reacting phase was kept and dried. The different organic phases were assembled, filtered through cotton. 1 L was injected in GC to determine conversion and selectivity. The organic phase was then concentrated and dried for NMR analysis if necessary. 2.4. Recycling/reuse of catalytic system After extraction with diethylether, the ionic liquid phase was kept in the Schlenk tube and dried at reduced pressure. NaHCO3 (121 mg, 1.44 mmol, 1.2 eq.) was added, then halogenoarene (1.2 mmol) and tert-butylacrylate (210 L, 1.45 mmol, 1.2 eq.) were introduced under inert atmosphere. Reaction was then performed again at 100 ◦ C for 24 h. Same work-up as for the first cycle was then realized and the liquid ionic phase re-used as necessary. 2.5. General procedures for the Heck reaction with NEt3 as base Under argon atmosphere, the substrate (bromobenzene, chlorobenzene or iodoarenes, 1.2 mmol), tert-butyl acrylate (210 L, 1.45 mmol, 1.2 eq.) and triethylamine (200 L, 1.44 mmol, 1.2 eq.) were mixed in a Schlenk tube containing 600 mg of ionic liquid and PdCl2 (4.3 mg, 0.024 mmol, 0.02 eq.). The resulting mixture was stirred for 24 h at the desired temperature (60 or 100 ◦ C). Once the reaction was completed, the crude product was extracted four times with 5 mL of diethyl ether, combined, filtered through cotton and then concentrated under reduced pressure. 1 L of the organic phase was injected in a gas chromatography (GC end GC/MS) to determine the conversion. The ratio E/Z was determined with 1 H NMR. 2.6. Recycling After the diethylether extraction, drying and a short vacuum/argon sequence, the respective substrates in similar ratios as before were added into the precedent ionic liquid phase in the Schlenk tube. The mixture was stirred vigorously for 24 h at the desired temperature under argon atmosphere. Same treatment as previously described was then employed for the separation and the analysis of the coupling product. 3. Results and discussion 3.1. Synthesis of bio-derived ionic liquids The ionic liquids (ILs) were easily synthesized using an acidbase method [16]. Tetrabutylammonium hydroxide (TBA OH) was reacted in water at reflux with an excess of a biobased acids (Table 1) [16a]. The acids (l-lactic, l-malic acid, pyruvic acid, malonic acid and succinic acid) were chosen for their low cost, their non–toxicity and high availability. ILs 1a-1f were obtained with quantitative yields. Same method was used to prepare phosphonium ILs with Llactic acid (2a) and L-malic acid (2b) (Table 2) [16b], this time using tetrabutylphosphonium hydroxide (TBP OH). Again, ILs were easily
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129 Table 1 Synthesis of ammonium ionic liquids with biocarboxylates.
R-COOH
Obtained IL
Number
Yield
L-lactic acid
1a
97%
L-malic acid
1b
97%
Pyruvic acid
1c
95%
L-tartaric acid
1d
98%
Malonic acid
1e
99%
Succinic acid
1f
98%
Table 2 Synthesis of phosphonium ionic liquids with biocarboxylates.
R-COOH
Obtained IL
Number
Yield
l-lactic acid
2a
87%
l-malic acid
2b
92%
Pyruvic acid
2c
87%
made with quantitative yields. With pyruvic acid, reflux in ethanol was processed as no IL was formed in water at 100 ◦ C. 3.2. Heck Reaction using NaHCO3 as base As the synthesized ILs have been successfully used as (co)solvent for hydrogenation of dienes in mild conditions in presence of palladium (II) salt as catalyst [16a,b], they are ideal greener medium for metal and pallado-catalyzed reaction compared to usual organic solvents. In addition, the catalytic system could be re-used 10 times without loss of reactivity [16a]. Like more common ILs, the synthesized compounds showed high thermal stability. Consequently, they were considered as solvent for C C coupling reaction, such as Heck reaction [7,8,17]. Coupling of iodobenzene with tert-butylacrylate, in presence of NaHCO3 as base and PdCl2 as catalyst, was studied as model reaction to determine the efficiency of the ILs. Used reaction conditions were already worked out by the laboratory [18]. At first, reaction was performed in usual organic solvents (Table 3). Conver-
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sion of iodobenzene, but also selectivity for the coupling product was determined by GC and/or GC/MS. The study was completed with 1 H NMR study to define the proportion of isomer E in the formed Heck coupling product. In water, low conversion was obtained. The lack of reactivity was certainly due to low miscibility of the reactants and/or low dispersity of the catalyst. Only the E isomer coupling product was obtained. It was proved by 1 H NMR performed after purification of the reaction product. Spectrum showed that only just one product was present and calculation of the coupling constant 3 J of alcenic hydrogens, which value was around 16 Hz, confirmed the E isomeric position. This result could be expected as the E isomer is generally the only or major compound obtained. It is more stable than the Z isomer [19], particularly when moieties present a steric hindrance, like with benzyl and tert-butyl groups. Low conversion was also observed in DMF and several not-identified by-products formed. Reaction almost did not occurred in toluene, which might be caused by the low polarity of the solvent. When DMSO was employed, good conversion and selectivity were observed. And as previously observed with water, NMR demonstrated that only the E isomer was synthesized. However, recycling attempt failed as conversion and selectivity both drastically decreased to around 10%. Study was then performed using commercials ILs, which are known to be able to recycle/recover metallic catalytic system [18,20]. Moreover, ILs being highly polar solvent [21], they might favour Heck coupling. Recycling of the catalytic system was also performed. After reaction and extraction of obtained products with diethylether, the ionic liquid phase was kept in the Schlenk tube and dried under vacuum. Reactants were introduced and reaction launched again in the same conditions. In tetrabutylammonium bromide (TBA Br), low conversion occurred and was even reduced during the second cycle. On the contrary, almost total conversion of the iodobenzene with 100% of selectivity for the E coupling product was observed with tetrabutylammonium chloride (TBA Cl). Unfortunately, reactivity decreased after recycling as conversion dropped to 57%. Finally, synthesized ammonium ILs 1a to 1f were tested (Table 3, entries 7–12). At the exception of TBA L-malate 1b and TBA Ltartrate 1d (Table 3, entries 8 and 10), total conversion with only formation of the E coupling product was observed. The low conversion in 1b and 1d was the consequence of the high viscosity of the ILs, which were respectively 260 cP and 3689 cP at 80 ◦ C. The high viscosity of 1d had also an effect on the selectivity as it was the only synthesized ILs in which by-products formed, certainly due to dimerisation or degradation of reactants. As it was the case with the commercial ILs, reactivity decreased severely during the second cycle with 1c, 1e and 1f (Table 3, entries 9b, 11b and 12b). With TBA l-lactate 1a, the reduction of reactivity was less drastic at the second run, as still 87% of iodobenzene were completely converted into the E coupling product. A third cycle was performed, but this time reactivity was not conserved and conversion fell down to 26%. 1a being the more efficient tested synthesized solvent, study with varying reactant, but still with NaHCO3 as base was continued. At first, reaction was performed with ethylacrylate (Table 4). For the 2 first cycles, excellent conversion and selectivity were obtained. Like it was the case with tert-butylacrylate, just the E isomer was obtained, even if the steric hindrance of the ethyl group was less important. Having just one of the isomer formed, whatever the acrylate used for the Heck coupling, was quite interesting. As isomers are in general quite difficult to separate [22], the fact that just one of them was obtained will permit to avoid purification steps. Unfortunately, at the third cycle, conversion decreased drastically to 6%.
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Table 3 Heck reaction with organic solvent or ionic liquids.
Entry
Solvent or ILs
Cycle
Conversion*
Selectivity*
isomer E¤
1 2 3 4a 4b 5a 5b 6a 6b 7a 7b 7c 8 9a 9b 10 11a 11b 12a 12b
Water DMF Toluene DMSO
1 1 1 1 2 1 2 1 2 1 2 3 1 1 2 1 1 2 1 2
32% 29% 1% 81% 11% 47% 32% 99% 57% 99% 87% 26% 50% 100% 68% 41% 100% 45% 99% 47%
100% 58% 100% 87% 8% 100% 64% 100% 99% 100% 100% 100% 100% 100% 100% 76% 100% 100% 100% 100%
100% 100% nd 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
TBA Br TBA Cl 1a
1b 1c 1d 1e 1f
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; ¤ determined by 1 H NMR; nd: not determined. Table 4 Heck reaction with ethylacrylate in TBA L-lactate 1a.
Cycle
Conversion*
Selectivity*
isomer E¤
1 2 3
99% 90% 6%
96% 99% 100%
100% 100% nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; ¤ determined by 1 H NMR; nd: not determined.
Heck reaction between tert-butylacrylate and various iodobenzene wearing chemical groups or halogenobenzene was performed and are listed in Table 5. At first, iodoarene with electro-donors group were tested. With iodophenols, the position of the substitution mattered. Conversion was very low for the ortho-derivatives, whereas it was excellent for meta- and para-positions. For 2iodophenol, the alcohol function being closed to the iodo group, it might destabilized the adduct during oxidative addition or insertion steps [23]. On the contrary, for amino and oxymethyl groups, complete or almost complete conversion occurred, whatever the position of the group. Selectivity with iodoanilines was lower, due to the higher reactivity of the function. Electro-acceptors group were also studied. Degradation occurred with 2-iodobenzoic acid and consequently no coupling product formed. For the other reactants, no effect of the position of the group was observed on the conversion with nitro and carboxylic acid functions. But it had an effect on the selectivity. Better selectivity was obtained with the meta-component, as electro-acceptor groups in this position provide better stability of the aromatic compounds [24]. The multiplication of group, causing steric hindrance and desactivation of the aromatic core, reduced the reactivity. Indeed, with trimethyliodobenzene, only 64% of the reaction was converted. As previously observed with iodobenzene, 1 H NMR spectra proved that only the coupling product in the E conformation was formed with all tested reactants.
Other iodoaromatic compounds were reacted, and total conversion of iodopyridine and iodonaphtalene was observed with total selectivity for the E coupling product. Unfortunately, with iodovanilline, reaction did not occurred. Indeed, GC and GC/MS analyses confirmed that vanilline was obtained. No insertion of the acrylate happened, which might be due to steric hindrance, but also de-iodation occurred. No reaction happened with bromobenzene, due to the lower reactivity of the compound as previously described in the literature [25]. In all case, recycling of the catalytic system contained in the ionic liquid phase failed as conversion of the iodoarenes fell down or did not even occurred. Into have the possibility to reuse the catalyst, reaction conditions were changed.
3.3. Heck reaction using the triethylamine as base NaHCO3 was replaced by triethylamine NEt3 , which is a relative strong homogeneous base which could be removed by evaporation under reduced pressure. With usual organic solvent, results were quite the same as the one obtained with NaHCO3 (Table 6). Reaction did not occur in toluene and conversion was very low in water. Use of DMSO improved the iodobenzene conversion, but it was not total, by-products formed and recycling was not possible. Commercial ILs were also tested. In tetrabutylphosphonium bromide (TBP Br), conversion of iodobenzene was estimated at 47%, so not sufficient to consider this IL as solvent for Heck reaction. On the contrary, in TBA Cl, complete conversion of the iodoarene was achieved with the formation of only the Heck coupling product in its E conformation. Moreover, recycling was possible as same results were obtained during the second cycle. Unfortunately, reactivity decreased during the third cycle as conversion fell down to 61%. Coupling reaction between iodobenzene and tert-butylacrylate with NEt3 as base was performed in synthesized ILs 1a, as it showed good efficiency with NaHCO3 . Reaction was also performed with ILs 2a, 2b and 2c. These phosphonium ILs were chosen for their low viscosity at 80 ◦ C, which values were 21, 105 and 16 cP respectively, but also for their high thermal stability above 200 ◦ C, or even 300 ◦ c for TBP L-lactate 2a and TBP pyruvate 2c. With TBA L-lactate
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129 Table 5 − Heck reaction with various halogenobenzene with t-butylacrylate in TBA L-lactate 1a.
125
Table 5 (Continued)
R-X R-X
Conversion*
Selectivity*
39%
100%
93%
90%
Conversion*
Selectivity*
Vanilline formation
0
nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; nd: not determined. 100%
100% Table 6 Heck reaction with organic solvent and ionic liquids with NEt3 as base.
100%
99%
100%
95%
100%
89%
Solvent or ILs
Cycle
Conversion*
Selectivity*
96%
100%
Toluene water DMSO TBP Br TBA Cl
1 1 1 1 1 2 3
1% 30% 76% 47% 99% 100% 61%
100% 100% 80% 100% 100% 100% 100%
100%
100%
100%
100%
degradation
100%
90%
100%
80%
100%
100%
100%
98%
100%
91%
64%
100%
100%
100%
100%
100%
Condition: 1.2 mmol of iodobenzene, 600 mg of solvent; * determined by GC; nd: not determined.
1a, total conversion and selectivity for the E isomer was obtained. Moreover, recycling of the catalyst was achieved as it can be re-used for 6 more cycles without loss of neither reactivity nor selectivity (Fig. 1a). Quite the same results were obtained with TBP L-lactate 2a and TBP L-malate 2b (Fig. 1b and c). For TBP pyruvate 2c, conversion and selectivity were not as good as the previous ILs, even if catalytic system could be recycled. Our synthesized ILs, comporting an anion derived from bioresources, were more efficient than commercials ILs. At first, iodobenzene was completely converted with 1a, 2a and 2b and high selectivity for the E-coupling product obtained. Synthesized ILs also permitted to recycle the catalytic system. Heck coupling with iodoarenes is quite common and a well described reaction [26]. With the developed methodology, the possibility to recycle so many times the catalytic system without loss of reactivity and the use of greener reaction medium are real improvements. Moreover, this developed method is quite conformed to green chemistry principles [27], which goals are to develop environment-friendly synthesis, to limit pollution and use or volatile and/or toxic solvent, etc. . . Indeed, the use of biobased ILs, the small amount of catalyst added (only 0.02 eq.), the no requirement of ligand or phosphine, the efficiency of the system and the absence of by-products permit to consider the transformation as green, or at least greener than usual methods [26]. It is also important to note that the cost price of these biobased ionic liquid is lower than the price of the commercial ILs commonly used in chemical processes [28]. As previously, study was completed by screening halogenoarenes reactants with NEt3 as base and 1a as solvent (Table 7). With electro-donor groups, such as alcohol or amino,
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S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129
Conversion
Table 7 Heck reaction with various halogenobenzene with t-butylacrylate with NEt3 as catalyst with TBA L-lactate 1a.
Selectivity
Proportion in E isomer
100 80 60 R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5 6 7
93 98 96 94 98 93 94
96 98 98 98 92 98 98
1 2 3 4
100 100 100 100
100 91 100 100
1 2 3 4 5
100 100 100 100 100
100 97 98 100 97
1 2 3 4 5 6
100 100 100 100 100 100
100 100 100 100 100 100 100
1 2 3 4 5 6
100 100 100 100 100 100
100 100 100 100 100 100
1a
40 20 0
1
2
3
4
5
6
7
100 80 60
2a
40 20 0
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
100 80 60
2b
40 20 0
100 80 60
1 2 3 4 5 6
100 99 100 98 100 83
100 100 100 100 100 100
1 2 34 5
100 100 100 98 100
93 97 96 97 100
1 2 3 4
100 100 100 100
90 84 78 74
1 2
100 35
100 75
3
8
nd
Conditions: 1.2 mmol of iodobenzene, 600 mg of solvent;* determined by GC; nd: not determined.
2c
40 20 0
Fig. 1. Heck reaction between iodobenzene and t-butylacrylate with NEt3 as base in synthesized ILs.
almost total conversion and excellent selectivity were observed. Recyclability of catalyst occurred especially with 1-iodophenol as 6 cycles were performed without loss of reactivity. Electro-acceptor moities were also evaluated. With ortho- and para-iodobenzoic acid, total conversion and selectivity happened and was conserved during 5 more cycles. As it was the case with NaHCO3 , degradation occurred with 1-iodobenzoic acid. Whatever the position of the nitro groups, good conversion and selectivity were obtained. In all cases and as previously observed, only the isomer E was synthesized. With NEt3 , coupling occurred when iodovanilline was used as substrate and catalyst was able to be recycled two more times. Selectivity was lower than with mono-substituted iodoarenes, as the multiplication of groups favoured by-products formation. With iodopyridine, results were the same as with NaHCO3 . Total con-
S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129
version and selectivity was observed during the first cycle, then reduced with the second one. Attempts to form the coupled product from bromobenzene failed, as just only 7% of the reactant was converted. The screening of iodoarenes was pursued with TBP L-lactate 2a as solvent (Table 8). Prior tests done in the laboratory proved that temperature could be reduced to 60 ◦ C. With methoxy and alcohols groups, total conversion and selectivity were observed during 5 cycles; at the exception with 1-iodophenol, where almost total conversion occurred during recycling. With 3-iodoaniline, conversion for both cycles was evaluated at around 60%. The reduction of reactivity compared was certainly due to the decrease of the temperature of reaction. However, reducing the temperature permitted to avoid the degradation of 1-iodobenzoic acid and resulted to the formation of the coupled product with excellent conversion and selectivity. Also two more cycles were performed with very slight diminution of reactivity. As observed with 1a, very good conversion, selectivity and possibility to recycle were obtained with metaand para- iodobenzoic acid and iodonitrobenzenes in 2a. Other halogenobenzenes were tested in the same condition in 2a. This time with NEt3 , reaction occurred with bromobenzene and total conversion and selectivity was observed. Performing Heck reaction on bromobenzene as not only the advantage to enhance applications of our methodology, but also to use less expensible bromoarenes compounds [29]. Unfortunately, conversion dropped when the catalyst was reused. On the contrary, no reaction happened with chlorobenzene. It could be forecast as chloroarene are few reactive and not generally used for C C coupling [25]. Again, with TBP L-lactate 2a in presence of NEt3 , recycling of the catalytic system was possible until five times without loss of reactivity for various iodoarenes derivatives. Phosphonium ILs were even more efficient than the ammoniums. At first, reaction could be performed at lower temperature, which avoided degradation of sensible substrate like 1-iodobenzoic acid and limited formation of by-products. Indeed, in general selectivities were higher in 2a than in 1a. Secondly, Heck reaction was also performed with bromobenzene, which was not possible with TBA L-lactate 1a. Such cation-based influence on performances of the ILs could be due to the physical differences between phosphonium and ammonium cations. The phosphonium ILs being generally more viscous than ammonium ones; this observation might be attributed to a larger radius of the phosphorus atom compared to the nitrogen atom, which decreases the lattice energy and gives more flexibility to the cation structure [16b,30].
4. Conclusion Ammonium and phosphonium carboxylates ionic liquids (ILs), obtained from biosourced acids like l-lactic acid or l-malic acid, were easily prepared and used as solvent for Heck reaction between halogenoarenes and tert-butylacrylate with PdCl2 as catalyst. When NaHCO3 was used as base, synthesized tetrabutylammonium (TBA) ILs showed better efficiency than typical Heck coupling media, such as usual organic solvents or commercial ILs. Indeed, total conversion and selectivity was achieved with TBA l-lactate 1a, TBA pyruvate 1c, TBA malonate 1e and TBA l-lactate 1f. In addition, Heck coupling with different iodoarenes wearing electro-donnor or electro-acceptor groups were realized with excellent conversion and selectivity in 1a. Whatever the conditions used, just only the E isomer of the coupling product was formed. Unfortunately, recycling of catalyst attempts failed as conversion fell down at the second cycle. Changing the base by triethylamine NEt3 finally permitted to recycle the catalyst, as the system was re-used at least 5 times without loss of reactivity for reaction of iodobenzene with tert-
127
Table 8 Heck reaction with various halogenobenzene with t-butylacrylate with NEt3 as catalyst with TBP L-lactate 2a.
R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5
100 98 96 95 95
96 98 98 98 96
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2
62 61
54 38
1 2 3
95 90 93
68 54 65
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
1 2 3 4 5
100 97 94 91 74
100 100 100 100 100
1 2 3 4 5
100 100 100 100 100
100 100 100 100 100
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S. Hayouni et al. / Molecular Catalysis 437 (2017) 121–129
Table 8 (Continued)
R-X
Cycle
Conversion (%)*
Selectivity (%)*
1 2 3 4 5
100 100 100 95 96
100 96 93 90 85
1 2 3
100 73 68
100 100 100
1
0
–
Conditions: 1.2 mmol of halogenoarene, 600 mg of solvent; * determined by GC; nd: not determined.
butylacrylate with 1a, but also tetrabutylphosphoniums (TBP) l-lactate 2a, TBP l-malate 2b and TBP pyruvate 2c to furnish only the E isomer products. Reaction and recyclability also occurred with the presence of groups on the iodobenzene ring in 1a, and even happened when iodovanilline was used as substrate. Performance was improved when 2a was used, as reaction was performed at lower temperature, better selectivities were observed and reaction happened with bromobenzene. To conclude, we have developed a new sustainable methodology for Heck reaction. At first, greener and non-volatile solvents and quite common catalyst, in low amount and without addition of ligands, were used. Reaction was performed with high efficiency and excellent selectivity for the E-coupling product and was transposable on various iodoarenes derivatives, and even on bromobenzene. The more important progress was the possibility to re-use the catalytic system. Further investigations are in progress concerning the possibility to reduce the quantity of catalyst and to extend to chloride derivatives. Acknowledgements This work was supported by the Fondation du Site Paris Reims (post-doctoral fellowship for Nadège Ferlin) and the FEDER for material funds. We thank also the Tunisian Ministry of Education and Research for financial support for the cotutoring PhD of Safa Hayouni. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.mcat.2017.05. 007. References [1] (a) J.D. Holbrey, K.R. Seddon, Clean Prod. Process. 1 (1999) 223–236; (b) P. Wassercheid, T. Welton, Ionic liquids in synthesis, 2nd edition, Wiley, VCH Weinheim, 2008. [2] (a) V.I. Parvulescu, C. Hardacre, Chem. Rev. 107 (2007) 2615–2665; (b) F.V. Rantwijk, R.A. Sheldon, Chem. Rev. 107 (2007) 2757–2785. [3] (a) L. Lafuente, G. Diaz, R. Bravo, A. Ponzinibbio, Lett. Org. Chem. 13 (2016) 195–199; (b) A.R. Hajipour, F. Rafiee, Org. Prep. Proced. Int. 47 (4) (2015) 249–308. [4] J.C. Plaquevent, Y. Genisson, F. Frédéric, Techniques de l’Ingénieur, Constantes Physico-Chimiques 51 (K 55) (2008) (K1230/1-K1230/17). [5] D. Wei, A. Ivaska, Anal. Chim. Acta 607 (2008) 126–135.
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