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Pd-catalyzed alkoxycarbonylation of alkenes promoted by H2O free of auxiliary acid additive
Molecular Catalysis xxx (xxxx) xxx–xxx
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Molecular Catalysis journal homepage: www.elsevier.com/locate/mcat
Pd-catalyzed alkoxycarbonylation of alkenes promoted by H2O free of auxiliary acid additive Wen-Yu Liang, Lei Liu, Qing Zhou, Da Yang, Yong Lu, Ye Liu
⁎
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, PR China
ARTICLE INFO
ABSTRACT
Keywords: Alkoxycarbonylation Palladium hydride In situ FT-IR analysis
The Pd-catalyzed alkoxycarbonylation of alkenes using water as a promoter has been scarcely reported before. Herein, water instead of Brønsted/Lewis acid was found to effectively improve the catalytic performance of Pd (MeCN)2Cl2-Xantphos system for alkoxycarbonylation of alkenes. Under the optimal conditions, the best yield of 97% was obtained for the target products (methyl 3-phenylpropanoate and methyl 2-phenylpropanoate) with L/ B of 4.3 and TON of 192. With the involvement of water, Pd(MeCN)2Cl2-Xantphos system also exhibited the moderate to good generality to alkoxycarbonylation of different kinds of alkenes with alcohols. The in situ high pressure FT-IR analysis verified that water played an important role in promoting formation and stability of PdeH active species which was responsible for the efficient alkoxycarbonylation of alkenes. In addition, the ligand effect of Xantphos on this reaction was discussed.
1. Introduction
the acid as it is consumed in the reaction [21]. The non-protic Lewis acid of Al(OTf)3 was also applied as a co-catalyst in Pd-catalyzed methoxycarbonylation which was demonstrated benefit over the traditional Brønsted acids due to the depressed ligand alkylation [11,22,23]. Besides of Brønsted/Lewis acids, water serving as a hydride source for formation of [PdIIeH]+ active species has been universally observed in many carbonylative reactions [24] such as aminocarbonylation of alkenes [25] and hydroxycarbonylation of pentenoic acids (functional alkene) [26,27]. In fact, water can serve as hydride source like Brønsted acid as schematized by reaction (1) and (2) (Scheme 1), which are believed to play the key role in Pd-catalyzed carbonylations [21,25–27]. As schematized, water can restore cationic [PdIIeH]+ species from PdII-salts (1) while acids can add to the reduced palladium (0) with formation of hydrides for the reactivation of the Pd-catalyst and may also increase the concentration of [PdIIeH]+ species through the equilibrium (2). If the loss of proton is faster than the insertion of alkene into a PdeH bond, carbonylation of alkenes will be terminated. On the other hand, if [PdIIeH]+ species is consumed by high concentrated proton (Brønsted acid) alone with the release of H2 (protonolysis), carbonylation of alkenes will be also terminated. It is suggested that acid be like a double-edged sword for the formation of active [PdIIeH]+ species, depending on the concentration of acid and the applied ligands how to stabilize [PdIIeH]+ species against
Carbonylation with CO as carbonyl source in the presence of nucleophile (ROH, R1R2NH, H2O ect.) has emerged as a powerful tool for the production of value-added bulk and fine chemicals [1,2]. Recently, the use of (hetero) arenes in place of these typical nucleophile has also attracted much attention as an alternative protocol to insert CO into CeH bond [3–5]. Among various carbonylations, alkoxycarbonylation of alkenes in the presence of CO and MeOH to form branched or linear methyl esters has been broadly studied in the past decades [6–9]. It is a valuable process with 100% atom economy to functionalize alkenes towards a series of esters which are useful as a wide range of industrial and domestic products such as surfactants, cosmetic, and pharmaceuticals [10–12]. Typically, this protocol requires a Pd-catalyst modified by P- or N-containing ligand and a Brønsted/Lewis acid promoter (cocatalyst) [11–13]. A Brønsted protic acid (such as p-TsOH, MeSO3H, or aqueous HCl) can serve as a hydride source for the formation of catalytic active species through reactivating reductive Pd (0) to afford [PdIIeH]+ hydride species [14–18]. However, the high concentration of Brønsted acid may consume [PdIIeH]+ species with evolution of hydrogen gas [19,20]. On the other hand, the phosphine such as PPh3 can be deactivated upon alkylation over protic acids (catalysts) to form methyl triphenyl phosphonium cations, necessitating the use of a large excess of ligand to warrantee Pd-catalyst stable as well as an excess of
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Corresponding author. E-mail address: [email protected] (Y. Liu).
https://doi.org/10.1016/j.mcat.2018.10.016 Received 30 August 2018; Received in revised form 16 October 2018; Accepted 23 October 2018 2468-8231/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Liang, W.-Y., Molecular Catalysis, https://doi.org/10.1016/j.mcat.2018.10.016
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Scheme 1. The formation of [PdIIeH]+ species with the presence of water or acid in carbonylations. Table 1 Pd-catalyzed methoxycarbonylation of styrene with MeOH under different conditionsa.
Entry
Catalyst precursor
Ligand
H2O (μL)
Acid
Conv. (%)b
Yield (L + B. (%)c
L/Bd
TON
1 2e 3 4f 5g 6 7 8 9 10 11 12 13 14h
PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 Pd (OAc)2 Pd (OAc)2
Xantphos Xantphos Xantphos Xantphos Xantphos L1 L1 L2 PPh3 Nixantphos Binap dppf Xantphos Xantphos
– – 75 75 75 – 75 75 75 75 75 75 75 –
– CH3SO3H – – – – – – – – – – – CH3SO3H
62 100 97 77 84 63 92 – 40 19 24 80 – 96
62 95 97 77 84 63 92 – 40 19 24 80 – 91
4.3 4.0 4.3 4.0 2.8 2.7 2.7 – 2.7 3.5 3.5 3.8 – 3.3
124 190 192 154 168 126 184 – 80 38 48 160 – 182
a
PdCl2(MeCN)2 0.025 mmol (0.5 mol%), bidentate ligand 0.025 mmol (PPh3 or L2 0.05 mmol), styrene 5 mmol, MeOH 5 mL, CO 2.0 MPa, reaction temperature 120 °C, reaction time 4 h. b,c,d Determined by GC with n-dodecane as the internal standard. e 10% mmol acid (1 mmol). The by-product of (1-methoxyethyl) benzene was detected in the yield of 5%. f Reaction temperature 100 °C. g 1.0 MPa CO. h 10% mmol acid (1 mmol), The by-product of (1-methoxyethyl) benzene was detected in the yield of 5%.
decomposition. Compared to Brønsted/Lewis acid promoters, the use of water as the hydride source is advantageous not only with safety, low-cost, and environmental friendliness, but also with less possibility of protonolysis of PdeH species due to the low concentration of H+ released in situ in reaction (1) (Scheme 1). Actually, the catalytic amount of H+ released in reaction (1) is also capable to reactivate Pd (0) to Pd (II) to afford [PdIIeH]+ species (reaction (2) in Scheme 1). Rationally, we believe that the solely use of water as the promoter for alkoxycarbonylation of alkenes is feasible if the suitable phosphine is selected which can render the resultant [PdeH]+ species the necessitated stabilization. In this paper, it was found that with the presence of the bidentate rigid phosphine of Xantphos, water indeed served as a highly efficient promoter for alkoxycarbonylation of alkenes free of any auxiliary acid. In addition, the technique of in situ high pressure spectroscopy was applied to study the derivation and stability of PdeH hydride species (ν 1944 cm−1), which was significantly facilitated by the both presence of water and Xantphos.
received. The solvents were distilled and dried before they were used. Gas chromatography (GC) was performed on a SHIMADZU-2014 equipped with a DM-Wax capillary column (30 m × 0.25 mm × 0.25 μm). GC–mass spectrometry (GC–MS) was recorded on an Agilent 6890 instrument equipped with an Agilent 5973 mass selective detector. FT-IR spectra were recorded on a Nicolet NEXUS 670 spectrometer. 2.2. Synthesis of L1 and L2 L1 [28] and L2 [29] were synthesized respectively according to the procedures reported by our research group before. 2.3. General procedures for methoxycarbonylation of alkene In a typical experiment, styrene (5 mmol, or the other alkene), 5 ml MeOH, deionized water (75 u L), PdCl2(MeCN)2 (0.025 mmol) and Xantphos (0.025 mmol) were sequentially added in a high-pressure steel reactor (equipped with the pressure relief valve), which was then charged with 2 MPa CO (Cautious: CO is a very toxic gas without colour and odour. It should be handled carefully in fume hood). The reactor was heated in oil bath at 120 ℃ for 4 h. Upon completion, the reaction mixture was cooled to room temperature. The combined filtrate after washing the residue with ethyl acetate (3 × 3 mL) was analysed by GC to determine the conversions (n-dodecane as internal standard) and the
2. Experimental 2.1. Reagents and analysis The chemical reagents were purchased from Shanghai Aladdin Chemical Reagent Co. Ltd. and Alfa Aesar China, which were used as 2
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Table 2 The effect of water amount on Pd-catalyzed methoxycarbonylation of styrenea.
a
Entry
Catalyst precursor
Ligand
H2O (μL)
Conv. (%)b
Yield (L + B).(%)c
L/Bd
TON
1 2 3e 4e
PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2
Xantphos Xantphos Xantphos Xantphos
50 75 100 150
88 97 99 99
88 97 94 89
4.0 4.3 4.0 4.0
176 192 190 178
PdCl2(MeCN)2 0.025 mmol (0.5 mol%), Xantphos 0.025 mmol, styrene 5 mmol, MeOH 5 mL, CO 2.0 MPa, reaction temperature 120 °C, reaction time 4 h. Determined by GC with n-dodecane as the internal standard. The by-products of 3-phenylpropanoic acid and 2-phenylpropanoic acid were identified by GC-Mass.
b,c,d e
selectivities (normalization method), and the products were further identified by GC–MS spectrometry.
with H2O and styrene to coordinate to Pd-center. In addition, when Pd (OAc)2 in place of PdCl2(MeCN)2 was applied as the catalyst precursor to repeat the reaction with H2O as the additive, the conversion of styrene to the methyl esters didn’t occur at all (Entries 13 vs 3). As for Pd(OAc)2 precursor, the released H+ from H2O (as schematized in reaction (1)) was trapped by OAc− to form the weak acid of HOAc. Then the subsequent reactivation of Pd(0) back to [PdIIeH]+ active species (reaction (2) in Scheme 1) was forbidden. Hence, when CH3SO3H was added additionally instead of water which served as a more active hydride source, the high yield of the esters (91%) was still obtained (Entry 14), which further confirmed the indispensable role of free proton to form [PdIIeH]+ active species responsible for the catalytic cycle of methoxycarbonylation. Evidently, with water (75 μL) as a promoter, PdCl2(MeCN)2Xantphos system corresponded to the best yield of the target products with L/B ratio of 4.3 (Entry 3 of Table 1). Then the effect of the water amount on this model reaction was investigated in Table 2. It was found that the decreased amount of water (50 μL) decelerated the reaction rate along with the reduced product yield to 88% (Entry 1). However, the presence of too much water (more than 100 μL) obviously led to the decreased yields of the target products along with the formation of the by-products of 3-phenylpropanoic acid and 2-phenylpropanoic acid (Entries 3 and 4), derived from the hydrolysis of the corresponding esters or the competitive hydrocarboxylation of styrene with water. Evidently, comparing to other reported systems using Brønsted acids (p-TsOH, MeSO3H, HCl etc.) [14–18] or Lewis acids [11,22,23] as the additives, the use of water was advantageous with safety, low-cost, and environmental friendliness but with potential possibility for the competitive side-reactions of hydrolysis and hydrocarboxylation. When H2O was used as the hydride source, the exclusive ligand effect of Xantphos on this reaction implied that its unique nature facilitates the formation and stability of [PdeH]+ active species. As for a diphosphine ligand, the chelation ability and natural biting angle (PeMeP, βn) have enormous impact on the stability and catalytic performance of a transition metal complex. As listed in Table 3, Xantphos with the bite angle of 111° has a marked preference for the formation of a cis-positioned active mono-nuclear Pd-intermediate in square-planar configuration [30]. In contrast, Binap with the less natural bite angle of 92° is inclined to form a stable bi-nuclear Pd-complex [31], which has been proved to be the inactive catalyst for carbonylation of alkenes [19]. Additionally, the relatively stronger σ-donor ability of Binap in comparison to that of Xantphos (Table 2, Binap, 1 31 77 J P- Se = 739 Hz; Xantphos, 1J31P-77Se = 757 Hz. See S. Fig. 1 and 2 in ESI) didn’t favour CO insertion and migration, which might be
2.4. In situ high-pressure FT-IR spectral characterization The in situ high pressure FT-IR spectra were recorded on a Nicolet NEXUS 670 spectrometer. The spectral resolution was about 3 cm−1. A mixture containing 0.025 mmol of Xantphos with 0.025 mmol of PdCl2(MeCN)2 pre-solved in 0.05 ml CH2Cl2 and 0.1 ml of styrene in methanol (or methanol with 0.01 ml water) was fixed in the specially designed high-pressure IR cell, in which cylindric CaF2 was used as the sealing sheets. Then 2.0 MPa CO was inflated into the sealed call. Real time monitoring was performed under the different reaction temperatures. The mixture compositions including PdCl2(MeCN)2, Xantphos, styrene, CO and water (if required) were completely the same as those for the real reaction in Table 1, except for the much high concentration of PdCl2(MeCN)2 and the ligand required for FT-IR spectral detection. 3. Results and discussion The initial experiments were carried out in a high-pressure stainlesssteel autoclave with styrene as the substrate (Table 1). Under the selected conditions (120 °C, CO 2.0 MPa, P/Pd molar ratio of 2, and 4 h), without the presence of any additive, only 62% yield of the target methyl esters was obtained over Xantphos-PdCl2(MeCN)2 system (Entry 1). Under the same conditions, the use of Brønsted acid of CH3SO3H as the additive led to the improved yield up to 95%. However, the side product of (1-methoxyethyl) benzene was formed concurrently due to the competitive addition reaction of styrene with MeOH over a Brønsted acid catalyst (Entry 2). Interestingly, the use of H2O (75 μL) instead of CH3SO3H led to 97% conversion of styrene with 100% selectivity to methyl esters with L/B ratio of 4.3 (Entry 3). The decreased reaction temperature down to 100 °C and the reduced pressure of CO to 1.0 MPa decreased the yields of the products obviously (Entries 4 and 5). Then under the optimized conditions as applied in Entry 3, the ligand effect on the catalytic performance of Pd-catalyst with H2O as promoter was studied, where the typical diphosphines and monophosphines were selected. The modification of Xantphos afforded the diphosphine of L1 and the mono-phosphine of L2, respectively [28,29]. Compare to Xantphos, the SO3Na-incorporated diphosphine of L1 exhibited the similar promoting effect on the catalytic performance of PdCl2(MeCN)2 (Entries 7 vs 3; Entries 6 vs 1). However, L/B ratio in the methyl esters decreased from 4.3 down to 2.7 (Entry 7 vs 3). The electron-withdrawing effect of –SO3− group on the phenyl rings around P-atoms in L1 might account for the decreased selectivity to the linear ester to adapt the more capacious coordinating environment around Pdcenter. In comparison, the Lewis acidic phosphonium-incorporated mono-phosphine of L2 completely inhibited the reaction (Entry 8). And PPh3 didn’t show any benefit to the activity of Pd-catalyst either, resulting in 40% yield of the products (Entry 9). As for the other diphosphines such as Nixantphos, Binap and dppf, only dppf corresponded to acceptable yield of 80% (Entries 12 vs 10 and 11). As for Nixantphos, the fused NH-amino group might serve as a σ-donor ligand competing
Table 3 Comparison of the natural bite angle and 31P-77Se coupling constant (1J 31P-77Se) of Xantphos and Binap. Ligand Xantphos Binap a
3
Natural bite angle (βn, o) 111 92a
a
1
Yield (%)
757 739
97 (Entry 3 in Table 1) 24 (Entry 11 in Table 1)
J31P-77Se (Hz)
Natural biting angle (βn) of which was cited from Ref. [32].
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Scheme 2. The proposed catalytic mechanism over Xantphos-PdCl2(MeCN)2 for methoxycarbonylation of terminal alkenes with water as promoter.
another reason for the observed inefficient methoxycarbonylation (Entry 11 in Table 1). As indicated in the proposed mechanism for methoxycarbonylation over Pd-catalyst (Scheme 2), Xantphos as a more intensive π-acceptor with 1J31P-77Se of 757 Hz can develop a more consolidated PdeP bond and then a weakened PdeCO bond in the corresponding Pd-intermediates (A, B and B’), due to the increased πbackdonation in PdeP linkage. The weakness of PdeCO bonds helps CO migration and insertion to form Pd-acyl intermediate (C and C’) and the subsequent release of eaters upon the attack by MeOH. Hence, only Xantphos with the relatively intensive π-acceptor character (1J31P-77Se = 757 Hz) and the wide natural bite angle of 111° corresponded to the best efficiency for Pd-catalyzed methoxycarbonylation. In addition, the robustness of Xantphos against water further warranted the catalytic cycle. To further elucidate the role of water in formation and stability of the active PdeH ([PdIIeH]+) species of A ligated by Xantphos, the in situ high pressure FT-IR analysis was carried out over XantphosPdCl2(MeCN)2 and Xantphos-PdCl2(MeCN)2-H2O systems in comparison. As shown in Fig. 1, the intensive peaks at 2175 and 2116 cm−1 universally observed were attributed to the characteristic vibrations of gaseous CO. As for Xantphos-PdCl2(MeCN)2-H2O system (Fig. 1-A), when the temperature increasing from 30 to 120 °C, a weak absorption peak at 1944 cm−1 appeared at temperature of 90 °C immediately and then reached the maximum intensity at 120 °C, which was assigned to the vibration of the active PdeH (palladium-hydride) species [28,33]. After holding 60 min at 120 °C, the absorption peak at 1944 cm−1 decayed nearly to void. The always observed peak at 1821 cm−1 was attributed to PdeCO intermediate which was the result of the complexation of PdCl2(MeCN)2 with CO. Concurrently, the vibration at 1739 cm−1 attributed to the product of methyl 3-phenylpropanoate (its standard FT-IR spectrum was given as S. Fig. 4 in ESI) grew stronger and stronger due to the accumulation of the formed product in the course of monitoring. Simultaneously, the vibration at 1629 cm−1
coming from styrene (its standard FT-IR spectrum was given as S. Fig. 3 in ESI) decayed gradually due to the continuous consumption. In contrast, over Xantphos-PdCl2(MeCN)2 system (Fig. 1-B), the vibration of PdeH species at 1944 cm−1 was unobservable in the overall monitoring process. Correspondingly, the characteristic peak at 1739 cm−1 attributed to methyl 3-phenylpropanoate was not found either, which implied that the reaction was dramatically depressed without the presence of water. The in situ high pressure FT-IR analysis verified that the formation and stability of PdeH species (ν 1944 cm−1) was greatly facilitated by the presence of water, which guaranteed PdeH characteristic peak to reach the maximum intensity for detection and then inherently corresponded to the efficient methoxycarbonylation to afford methyl 3-phenylpropanoate. The generality of Xantphos-PdCl2(MeCN)2-H2O system for alkoxycarbonylation of the alkenes with different alcohols was summarized in Table 4. Under the selected reaction conditions, the uses of the EtOH and iPrOH instead of MeOH gave the corresponding esters in the excellent yields (90–95%) with high L/B ratio of 6.3 (Entries 2 and 3). 1Methyl-2-vinylbenzene with CH3-subsitutent at ortho-position converted to the target eaters in the yield of 64% but with very high L/B ratio of 20 due to the increased steric hindrance (Entry 4). The styrene derivatives with para-substituents corresponded to the excellent product yields (92–100%) without discrimination on the electronic effect of the substituted groups (entries 5–8). As for the linear aliphatic alkenes like 1-hexene and 1-heptene, the moderate yields (56–77%) were obtained (Entries 9 and 10). Cyclohexene could afford the corresponding esters in the moderate yield of 56% under the applied conditions (Entry 11), whereas norbornene with high reactivity converted to the corresponding esters in 100% yield (Entry 12). 4. Conclusions With the aid of H2O instead of Brønsted/Lewis acid, Xantphos-based 4
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Fig. 1. In situ high-pressure FT-IR spectra recorded after mixing PdCl2(MeCN)2, Xantphos, styrene, and H2O (if required) with MeOH in 2.0 MPa CO (the successive profiles recorded as the temperature increasing from 30 °C to 120 °C). Table 4 Alkoxcarbonylation of different alkenes with alcohols catalyzed by Xantphos-PdCl2(MeCN)2 with the presence of H2Oa.
Alcohol
Yield (%)b
L/Bc
1
MeOH
97
4.3
2
EtOH
95
6.3
3
iPrOH
90
6.3
4
MeOH
64
20
5
MeOH
92
4.2
6
MeOH
92
4.8
7
MeOH
99
3.7
8
MeOH
100
4.0
9 10 11
MeOH MeOH MeOH
77 56 56
4.4 6.9 –
12
MeOH
100
–
Entry
a
Alkene
PdCl2(MeCN)2 0.025 mmol, Xantphos 0.025 mmol, alkene 5 mmol, alcohol 5 mL, H2O 75 μL, CO 2.0 MPa, temperature 120 °C, time 4 h. Determined by GC and GC-MS with n-dodecane as the internal standard.
b, c
5
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PdCl2(MeCN)2 system proved to be efficient for alkoxycarbonylation of alkenes. The combination of water and Xantphos was verified by in situ FT-IR analysis to facilitate the formation and stability of the active PdeH species responsible for this reaction. The developed PdCl2(MeCN)2-Xantphos-H2O system also exhibited the generality to the alkoxycarbonylation of different alkenes including aryl ones and aliphatic ones. The use of water as the hydride source is advantageous with safety, low-cost, and environmental friendliness, but with potential possibility for the competitive side-reactions of hydrolysis and hydrocarboxylation. In addition, the required phosphines like Xantphos should be robust against water (hydrolysis). Based the results obtained in this work, we are highlighted to investigate methoxycarbonylation without the presence of any other additives upon the careful selection of the involved phosphines. Since MeOH itself also can serve as a hydride source for formation of [PdIIeH]+ active species to promote methoxycarbonylation. In this way, MeOH triply acts as reactant, additive and solvent without the possibility of competitive side-reactions (hydrolysis and hydrocarboxylation). The related work is in progress.
(2004) 4433–4440. [6] G. Kiss, Chem. Rev. 101 (2001) 3435–3456. [7] A. Seayad, S. Jayasree, K. Damodaran, L. Toniolo, R.V. Chaudhari, J. Org. Chem. 601 (2000) 100–107. [8] H. Ooka, T. Inoue, S. Itsuno, M. Tanaka, Chem. Commun. (2005) 1173–1175. [9] P. Kalck, M. Urrutigoïty, Inorg. Chim. Acta 431 (2015) 110–121. [10] Z. He, Z. Hou, Y. Luo, Y. Dilixiati, W. Eli, Catal. Sci. Technol. 4 (2014) 1092–1103. [11] M. Amézquita-Valencia, G. Achonduh, H. Alper, J. Org. Chem. 80 (2015) 6419–6424. [12] T.A. Tshabalala, S.O. Ojwach, M.A. Akerman, J. Mol. Catal. A: Chem. 406 (2015) 178–184. [13] G. Abarca, K. Brown, S.A. Moya, J.C. Bayon, P.A. Aguirre, J.C. Bayon, P.A. Aguirre, Catal. Lett. 145 (2015) 1396–1402. [14] E. Guiu, M. Caporali, B. Mun˜oz, C. Mu¨ller, M. Lutz, Anthony L. Spek, C. Claver, P.W.N.M. van Leeuwe, Organometallics 25 (2006) 3102–3104. [15] C.J. Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem. Commun. (2004) 1720–1721. [16] J.D. Nobbs, C.H. Low, L.P. Stubbs, C. Wang, E. Drent, M. van Meurs, Organometallics 36 (2017) 391–398. [17] K. Dong, X. Fang, S. Gulak, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell, M. Beller, Nat. Commun. 8 (2017) 14117–14124. [18] R. Sang, P. Kucmierczyk, K. Dong, R. Franke, H. Neumann, R. Jackstell, M. Beller, J. Am. Chem. Soc. 140 (2018) 5217–5223. [19] A. Vavasori, L. Toniolo, J. Mol. Catal. A: Chem. 110 (1996) 13–23. [20] G. Cavinato, L. Toniolo, A. Vavasori, J. Mol. Catal. A: Chem. 219 (2004) 233–240. [21] G.M. Roberts, P.J. Pierce, L.K. Woo, Organometallics 32 (2013) 2033–2036. [22] D.B.G. Williams, M.L. Shaw, M.J. Green, C.W. Holzapfel, Angew. Chem. Int. Ed. 47 (2008) 560–563. [23] D.B.G. Williams, T. Bredenkamp, ChemCatChem 4 (2012) 206–208. [24] H. Li, K. Dong, H. Jiao, H. Neumann, R. Jackstell, M. Beller, Nat. Chem. 8 (2016) 1159–1166. [25] H. Liu, N. Yan, P.J. Dyson, Chem. Commun 50 (2014) 7848–7851. [26] C.H. Low, J.D. Nobbs, M. van Meurs, L.P. Stubbs, E. Drent, S. Aitipamula, M.H.L. Pung, Organometallics 34 (2015) 4281–4292. [27] L.-L. Zhao, B. Pudasaini, A. Genest, J.D. Nobbs, C.H. Low, L.P. Stubbs, M. van Meurs, N. Rösch, ACS Catal. 7 (2017) 7070–7080. [28] D. Yang, H. Liu, D.-L. Wang, Z.-J. Luo, Y. Lu, F. Xia, Y. Liu, Green Chem. 20 (2018) 2588–2595. [29] X. Chen, X. Ye, W.-Y. Liang, Q. Zhou, G. Vo-Thanh, Y. Liu, Mol. Catal. 448 (2018) 171–176. [30] P.C.J. KAMER, P.W.N.M. van Leeuwen, J.N.H. Reek, Acc. Chem. Res. 34 (2001) 895–904. [31] K. Pignat, J. Vallotto, F. Pinna, G. Strukul, Organometallics 19 (2000) 5160–5167. [32] P.W.N.M. van Leeuwen, P.C.L. Kamer, J.N.H. Reek, P. Dierkes, Chem. Rev. 100 (2000) 2741–2769. [33] A.B. Goel, S. Goel, Inorg. Chim. Acta 45 (1980) 85–86.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 21673077 and 21473058), and the Science and Technology Commission of Shanghai Municipality (18JC1412100). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.mcat.2018.10.016. References [1] X.-F. Wu, X. Fang, L. Wu, R. Jackstell, H. Neumann, M. Beller, Acc. Chem. Res. 47 (2014) 1041–1053. [2] R. Chinchilla, C. Najera, Chem. Rev. 114 (2014) 1783–1826. [3] R. Lang, L. Shi, D. Li, C. Xia, F. Li, Org. Lett. 14 (2012) 4130–4133. [4] J. Liu, Z. Wei, H. Jiao, R. Jackstell, M. Beller, ACS Cent. Sci. 4 (2018) 30–38. [5] T. Asaumi, T. Matsuo, T. Fukuyama, Y. Ie, F. Kakiuchi, N. Chatani, J. Org. Chem. 69
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Pd-catalyzed alkoxycarbonylation of alkenes promoted by H2O free of auxiliary acid additive Wen-Yu Liang, Lei Liu, Qing Zhou, Da Yang, Yong Lu, Ye Liu
⁎
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, PR China
ARTICLE INFO
ABSTRACT
Keywords: Alkoxycarbonylation Palladium hydride In situ FT-IR analysis
The Pd-catalyzed alkoxycarbonylation of alkenes using water as a promoter has been scarcely reported before. Herein, water instead of Brønsted/Lewis acid was found to effectively improve the catalytic performance of Pd (MeCN)2Cl2-Xantphos system for alkoxycarbonylation of alkenes. Under the optimal conditions, the best yield of 97% was obtained for the target products (methyl 3-phenylpropanoate and methyl 2-phenylpropanoate) with L/ B of 4.3 and TON of 192. With the involvement of water, Pd(MeCN)2Cl2-Xantphos system also exhibited the moderate to good generality to alkoxycarbonylation of different kinds of alkenes with alcohols. The in situ high pressure FT-IR analysis verified that water played an important role in promoting formation and stability of PdeH active species which was responsible for the efficient alkoxycarbonylation of alkenes. In addition, the ligand effect of Xantphos on this reaction was discussed.
1. Introduction
the acid as it is consumed in the reaction [21]. The non-protic Lewis acid of Al(OTf)3 was also applied as a co-catalyst in Pd-catalyzed methoxycarbonylation which was demonstrated benefit over the traditional Brønsted acids due to the depressed ligand alkylation [11,22,23]. Besides of Brønsted/Lewis acids, water serving as a hydride source for formation of [PdIIeH]+ active species has been universally observed in many carbonylative reactions [24] such as aminocarbonylation of alkenes [25] and hydroxycarbonylation of pentenoic acids (functional alkene) [26,27]. In fact, water can serve as hydride source like Brønsted acid as schematized by reaction (1) and (2) (Scheme 1), which are believed to play the key role in Pd-catalyzed carbonylations [21,25–27]. As schematized, water can restore cationic [PdIIeH]+ species from PdII-salts (1) while acids can add to the reduced palladium (0) with formation of hydrides for the reactivation of the Pd-catalyst and may also increase the concentration of [PdIIeH]+ species through the equilibrium (2). If the loss of proton is faster than the insertion of alkene into a PdeH bond, carbonylation of alkenes will be terminated. On the other hand, if [PdIIeH]+ species is consumed by high concentrated proton (Brønsted acid) alone with the release of H2 (protonolysis), carbonylation of alkenes will be also terminated. It is suggested that acid be like a double-edged sword for the formation of active [PdIIeH]+ species, depending on the concentration of acid and the applied ligands how to stabilize [PdIIeH]+ species against
Carbonylation with CO as carbonyl source in the presence of nucleophile (ROH, R1R2NH, H2O ect.) has emerged as a powerful tool for the production of value-added bulk and fine chemicals [1,2]. Recently, the use of (hetero) arenes in place of these typical nucleophile has also attracted much attention as an alternative protocol to insert CO into CeH bond [3–5]. Among various carbonylations, alkoxycarbonylation of alkenes in the presence of CO and MeOH to form branched or linear methyl esters has been broadly studied in the past decades [6–9]. It is a valuable process with 100% atom economy to functionalize alkenes towards a series of esters which are useful as a wide range of industrial and domestic products such as surfactants, cosmetic, and pharmaceuticals [10–12]. Typically, this protocol requires a Pd-catalyst modified by P- or N-containing ligand and a Brønsted/Lewis acid promoter (cocatalyst) [11–13]. A Brønsted protic acid (such as p-TsOH, MeSO3H, or aqueous HCl) can serve as a hydride source for the formation of catalytic active species through reactivating reductive Pd (0) to afford [PdIIeH]+ hydride species [14–18]. However, the high concentration of Brønsted acid may consume [PdIIeH]+ species with evolution of hydrogen gas [19,20]. On the other hand, the phosphine such as PPh3 can be deactivated upon alkylation over protic acids (catalysts) to form methyl triphenyl phosphonium cations, necessitating the use of a large excess of ligand to warrantee Pd-catalyst stable as well as an excess of
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Corresponding author. E-mail address: [email protected] (Y. Liu).
https://doi.org/10.1016/j.mcat.2018.10.016 Received 30 August 2018; Received in revised form 16 October 2018; Accepted 23 October 2018 2468-8231/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Liang, W.-Y., Molecular Catalysis, https://doi.org/10.1016/j.mcat.2018.10.016
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Scheme 1. The formation of [PdIIeH]+ species with the presence of water or acid in carbonylations. Table 1 Pd-catalyzed methoxycarbonylation of styrene with MeOH under different conditionsa.
Entry
Catalyst precursor
Ligand
H2O (μL)
Acid
Conv. (%)b
Yield (L + B. (%)c
L/Bd
TON
1 2e 3 4f 5g 6 7 8 9 10 11 12 13 14h
PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 Pd (OAc)2 Pd (OAc)2
Xantphos Xantphos Xantphos Xantphos Xantphos L1 L1 L2 PPh3 Nixantphos Binap dppf Xantphos Xantphos
– – 75 75 75 – 75 75 75 75 75 75 75 –
– CH3SO3H – – – – – – – – – – – CH3SO3H
62 100 97 77 84 63 92 – 40 19 24 80 – 96
62 95 97 77 84 63 92 – 40 19 24 80 – 91
4.3 4.0 4.3 4.0 2.8 2.7 2.7 – 2.7 3.5 3.5 3.8 – 3.3
124 190 192 154 168 126 184 – 80 38 48 160 – 182
a
PdCl2(MeCN)2 0.025 mmol (0.5 mol%), bidentate ligand 0.025 mmol (PPh3 or L2 0.05 mmol), styrene 5 mmol, MeOH 5 mL, CO 2.0 MPa, reaction temperature 120 °C, reaction time 4 h. b,c,d Determined by GC with n-dodecane as the internal standard. e 10% mmol acid (1 mmol). The by-product of (1-methoxyethyl) benzene was detected in the yield of 5%. f Reaction temperature 100 °C. g 1.0 MPa CO. h 10% mmol acid (1 mmol), The by-product of (1-methoxyethyl) benzene was detected in the yield of 5%.
decomposition. Compared to Brønsted/Lewis acid promoters, the use of water as the hydride source is advantageous not only with safety, low-cost, and environmental friendliness, but also with less possibility of protonolysis of PdeH species due to the low concentration of H+ released in situ in reaction (1) (Scheme 1). Actually, the catalytic amount of H+ released in reaction (1) is also capable to reactivate Pd (0) to Pd (II) to afford [PdIIeH]+ species (reaction (2) in Scheme 1). Rationally, we believe that the solely use of water as the promoter for alkoxycarbonylation of alkenes is feasible if the suitable phosphine is selected which can render the resultant [PdeH]+ species the necessitated stabilization. In this paper, it was found that with the presence of the bidentate rigid phosphine of Xantphos, water indeed served as a highly efficient promoter for alkoxycarbonylation of alkenes free of any auxiliary acid. In addition, the technique of in situ high pressure spectroscopy was applied to study the derivation and stability of PdeH hydride species (ν 1944 cm−1), which was significantly facilitated by the both presence of water and Xantphos.
received. The solvents were distilled and dried before they were used. Gas chromatography (GC) was performed on a SHIMADZU-2014 equipped with a DM-Wax capillary column (30 m × 0.25 mm × 0.25 μm). GC–mass spectrometry (GC–MS) was recorded on an Agilent 6890 instrument equipped with an Agilent 5973 mass selective detector. FT-IR spectra were recorded on a Nicolet NEXUS 670 spectrometer. 2.2. Synthesis of L1 and L2 L1 [28] and L2 [29] were synthesized respectively according to the procedures reported by our research group before. 2.3. General procedures for methoxycarbonylation of alkene In a typical experiment, styrene (5 mmol, or the other alkene), 5 ml MeOH, deionized water (75 u L), PdCl2(MeCN)2 (0.025 mmol) and Xantphos (0.025 mmol) were sequentially added in a high-pressure steel reactor (equipped with the pressure relief valve), which was then charged with 2 MPa CO (Cautious: CO is a very toxic gas without colour and odour. It should be handled carefully in fume hood). The reactor was heated in oil bath at 120 ℃ for 4 h. Upon completion, the reaction mixture was cooled to room temperature. The combined filtrate after washing the residue with ethyl acetate (3 × 3 mL) was analysed by GC to determine the conversions (n-dodecane as internal standard) and the
2. Experimental 2.1. Reagents and analysis The chemical reagents were purchased from Shanghai Aladdin Chemical Reagent Co. Ltd. and Alfa Aesar China, which were used as 2
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Table 2 The effect of water amount on Pd-catalyzed methoxycarbonylation of styrenea.
a
Entry
Catalyst precursor
Ligand
H2O (μL)
Conv. (%)b
Yield (L + B).(%)c
L/Bd
TON
1 2 3e 4e
PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2 PdCl2(MeCN)2
Xantphos Xantphos Xantphos Xantphos
50 75 100 150
88 97 99 99
88 97 94 89
4.0 4.3 4.0 4.0
176 192 190 178
PdCl2(MeCN)2 0.025 mmol (0.5 mol%), Xantphos 0.025 mmol, styrene 5 mmol, MeOH 5 mL, CO 2.0 MPa, reaction temperature 120 °C, reaction time 4 h. Determined by GC with n-dodecane as the internal standard. The by-products of 3-phenylpropanoic acid and 2-phenylpropanoic acid were identified by GC-Mass.
b,c,d e
selectivities (normalization method), and the products were further identified by GC–MS spectrometry.
with H2O and styrene to coordinate to Pd-center. In addition, when Pd (OAc)2 in place of PdCl2(MeCN)2 was applied as the catalyst precursor to repeat the reaction with H2O as the additive, the conversion of styrene to the methyl esters didn’t occur at all (Entries 13 vs 3). As for Pd(OAc)2 precursor, the released H+ from H2O (as schematized in reaction (1)) was trapped by OAc− to form the weak acid of HOAc. Then the subsequent reactivation of Pd(0) back to [PdIIeH]+ active species (reaction (2) in Scheme 1) was forbidden. Hence, when CH3SO3H was added additionally instead of water which served as a more active hydride source, the high yield of the esters (91%) was still obtained (Entry 14), which further confirmed the indispensable role of free proton to form [PdIIeH]+ active species responsible for the catalytic cycle of methoxycarbonylation. Evidently, with water (75 μL) as a promoter, PdCl2(MeCN)2Xantphos system corresponded to the best yield of the target products with L/B ratio of 4.3 (Entry 3 of Table 1). Then the effect of the water amount on this model reaction was investigated in Table 2. It was found that the decreased amount of water (50 μL) decelerated the reaction rate along with the reduced product yield to 88% (Entry 1). However, the presence of too much water (more than 100 μL) obviously led to the decreased yields of the target products along with the formation of the by-products of 3-phenylpropanoic acid and 2-phenylpropanoic acid (Entries 3 and 4), derived from the hydrolysis of the corresponding esters or the competitive hydrocarboxylation of styrene with water. Evidently, comparing to other reported systems using Brønsted acids (p-TsOH, MeSO3H, HCl etc.) [14–18] or Lewis acids [11,22,23] as the additives, the use of water was advantageous with safety, low-cost, and environmental friendliness but with potential possibility for the competitive side-reactions of hydrolysis and hydrocarboxylation. When H2O was used as the hydride source, the exclusive ligand effect of Xantphos on this reaction implied that its unique nature facilitates the formation and stability of [PdeH]+ active species. As for a diphosphine ligand, the chelation ability and natural biting angle (PeMeP, βn) have enormous impact on the stability and catalytic performance of a transition metal complex. As listed in Table 3, Xantphos with the bite angle of 111° has a marked preference for the formation of a cis-positioned active mono-nuclear Pd-intermediate in square-planar configuration [30]. In contrast, Binap with the less natural bite angle of 92° is inclined to form a stable bi-nuclear Pd-complex [31], which has been proved to be the inactive catalyst for carbonylation of alkenes [19]. Additionally, the relatively stronger σ-donor ability of Binap in comparison to that of Xantphos (Table 2, Binap, 1 31 77 J P- Se = 739 Hz; Xantphos, 1J31P-77Se = 757 Hz. See S. Fig. 1 and 2 in ESI) didn’t favour CO insertion and migration, which might be
2.4. In situ high-pressure FT-IR spectral characterization The in situ high pressure FT-IR spectra were recorded on a Nicolet NEXUS 670 spectrometer. The spectral resolution was about 3 cm−1. A mixture containing 0.025 mmol of Xantphos with 0.025 mmol of PdCl2(MeCN)2 pre-solved in 0.05 ml CH2Cl2 and 0.1 ml of styrene in methanol (or methanol with 0.01 ml water) was fixed in the specially designed high-pressure IR cell, in which cylindric CaF2 was used as the sealing sheets. Then 2.0 MPa CO was inflated into the sealed call. Real time monitoring was performed under the different reaction temperatures. The mixture compositions including PdCl2(MeCN)2, Xantphos, styrene, CO and water (if required) were completely the same as those for the real reaction in Table 1, except for the much high concentration of PdCl2(MeCN)2 and the ligand required for FT-IR spectral detection. 3. Results and discussion The initial experiments were carried out in a high-pressure stainlesssteel autoclave with styrene as the substrate (Table 1). Under the selected conditions (120 °C, CO 2.0 MPa, P/Pd molar ratio of 2, and 4 h), without the presence of any additive, only 62% yield of the target methyl esters was obtained over Xantphos-PdCl2(MeCN)2 system (Entry 1). Under the same conditions, the use of Brønsted acid of CH3SO3H as the additive led to the improved yield up to 95%. However, the side product of (1-methoxyethyl) benzene was formed concurrently due to the competitive addition reaction of styrene with MeOH over a Brønsted acid catalyst (Entry 2). Interestingly, the use of H2O (75 μL) instead of CH3SO3H led to 97% conversion of styrene with 100% selectivity to methyl esters with L/B ratio of 4.3 (Entry 3). The decreased reaction temperature down to 100 °C and the reduced pressure of CO to 1.0 MPa decreased the yields of the products obviously (Entries 4 and 5). Then under the optimized conditions as applied in Entry 3, the ligand effect on the catalytic performance of Pd-catalyst with H2O as promoter was studied, where the typical diphosphines and monophosphines were selected. The modification of Xantphos afforded the diphosphine of L1 and the mono-phosphine of L2, respectively [28,29]. Compare to Xantphos, the SO3Na-incorporated diphosphine of L1 exhibited the similar promoting effect on the catalytic performance of PdCl2(MeCN)2 (Entries 7 vs 3; Entries 6 vs 1). However, L/B ratio in the methyl esters decreased from 4.3 down to 2.7 (Entry 7 vs 3). The electron-withdrawing effect of –SO3− group on the phenyl rings around P-atoms in L1 might account for the decreased selectivity to the linear ester to adapt the more capacious coordinating environment around Pdcenter. In comparison, the Lewis acidic phosphonium-incorporated mono-phosphine of L2 completely inhibited the reaction (Entry 8). And PPh3 didn’t show any benefit to the activity of Pd-catalyst either, resulting in 40% yield of the products (Entry 9). As for the other diphosphines such as Nixantphos, Binap and dppf, only dppf corresponded to acceptable yield of 80% (Entries 12 vs 10 and 11). As for Nixantphos, the fused NH-amino group might serve as a σ-donor ligand competing
Table 3 Comparison of the natural bite angle and 31P-77Se coupling constant (1J 31P-77Se) of Xantphos and Binap. Ligand Xantphos Binap a
3
Natural bite angle (βn, o) 111 92a
a
1
Yield (%)
757 739
97 (Entry 3 in Table 1) 24 (Entry 11 in Table 1)
J31P-77Se (Hz)
Natural biting angle (βn) of which was cited from Ref. [32].
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Scheme 2. The proposed catalytic mechanism over Xantphos-PdCl2(MeCN)2 for methoxycarbonylation of terminal alkenes with water as promoter.
another reason for the observed inefficient methoxycarbonylation (Entry 11 in Table 1). As indicated in the proposed mechanism for methoxycarbonylation over Pd-catalyst (Scheme 2), Xantphos as a more intensive π-acceptor with 1J31P-77Se of 757 Hz can develop a more consolidated PdeP bond and then a weakened PdeCO bond in the corresponding Pd-intermediates (A, B and B’), due to the increased πbackdonation in PdeP linkage. The weakness of PdeCO bonds helps CO migration and insertion to form Pd-acyl intermediate (C and C’) and the subsequent release of eaters upon the attack by MeOH. Hence, only Xantphos with the relatively intensive π-acceptor character (1J31P-77Se = 757 Hz) and the wide natural bite angle of 111° corresponded to the best efficiency for Pd-catalyzed methoxycarbonylation. In addition, the robustness of Xantphos against water further warranted the catalytic cycle. To further elucidate the role of water in formation and stability of the active PdeH ([PdIIeH]+) species of A ligated by Xantphos, the in situ high pressure FT-IR analysis was carried out over XantphosPdCl2(MeCN)2 and Xantphos-PdCl2(MeCN)2-H2O systems in comparison. As shown in Fig. 1, the intensive peaks at 2175 and 2116 cm−1 universally observed were attributed to the characteristic vibrations of gaseous CO. As for Xantphos-PdCl2(MeCN)2-H2O system (Fig. 1-A), when the temperature increasing from 30 to 120 °C, a weak absorption peak at 1944 cm−1 appeared at temperature of 90 °C immediately and then reached the maximum intensity at 120 °C, which was assigned to the vibration of the active PdeH (palladium-hydride) species [28,33]. After holding 60 min at 120 °C, the absorption peak at 1944 cm−1 decayed nearly to void. The always observed peak at 1821 cm−1 was attributed to PdeCO intermediate which was the result of the complexation of PdCl2(MeCN)2 with CO. Concurrently, the vibration at 1739 cm−1 attributed to the product of methyl 3-phenylpropanoate (its standard FT-IR spectrum was given as S. Fig. 4 in ESI) grew stronger and stronger due to the accumulation of the formed product in the course of monitoring. Simultaneously, the vibration at 1629 cm−1
coming from styrene (its standard FT-IR spectrum was given as S. Fig. 3 in ESI) decayed gradually due to the continuous consumption. In contrast, over Xantphos-PdCl2(MeCN)2 system (Fig. 1-B), the vibration of PdeH species at 1944 cm−1 was unobservable in the overall monitoring process. Correspondingly, the characteristic peak at 1739 cm−1 attributed to methyl 3-phenylpropanoate was not found either, which implied that the reaction was dramatically depressed without the presence of water. The in situ high pressure FT-IR analysis verified that the formation and stability of PdeH species (ν 1944 cm−1) was greatly facilitated by the presence of water, which guaranteed PdeH characteristic peak to reach the maximum intensity for detection and then inherently corresponded to the efficient methoxycarbonylation to afford methyl 3-phenylpropanoate. The generality of Xantphos-PdCl2(MeCN)2-H2O system for alkoxycarbonylation of the alkenes with different alcohols was summarized in Table 4. Under the selected reaction conditions, the uses of the EtOH and iPrOH instead of MeOH gave the corresponding esters in the excellent yields (90–95%) with high L/B ratio of 6.3 (Entries 2 and 3). 1Methyl-2-vinylbenzene with CH3-subsitutent at ortho-position converted to the target eaters in the yield of 64% but with very high L/B ratio of 20 due to the increased steric hindrance (Entry 4). The styrene derivatives with para-substituents corresponded to the excellent product yields (92–100%) without discrimination on the electronic effect of the substituted groups (entries 5–8). As for the linear aliphatic alkenes like 1-hexene and 1-heptene, the moderate yields (56–77%) were obtained (Entries 9 and 10). Cyclohexene could afford the corresponding esters in the moderate yield of 56% under the applied conditions (Entry 11), whereas norbornene with high reactivity converted to the corresponding esters in 100% yield (Entry 12). 4. Conclusions With the aid of H2O instead of Brønsted/Lewis acid, Xantphos-based 4
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Fig. 1. In situ high-pressure FT-IR spectra recorded after mixing PdCl2(MeCN)2, Xantphos, styrene, and H2O (if required) with MeOH in 2.0 MPa CO (the successive profiles recorded as the temperature increasing from 30 °C to 120 °C). Table 4 Alkoxcarbonylation of different alkenes with alcohols catalyzed by Xantphos-PdCl2(MeCN)2 with the presence of H2Oa.
Alcohol
Yield (%)b
L/Bc
1
MeOH
97
4.3
2
EtOH
95
6.3
3
iPrOH
90
6.3
4
MeOH
64
20
5
MeOH
92
4.2
6
MeOH
92
4.8
7
MeOH
99
3.7
8
MeOH
100
4.0
9 10 11
MeOH MeOH MeOH
77 56 56
4.4 6.9 –
12
MeOH
100
–
Entry
a
Alkene
PdCl2(MeCN)2 0.025 mmol, Xantphos 0.025 mmol, alkene 5 mmol, alcohol 5 mL, H2O 75 μL, CO 2.0 MPa, temperature 120 °C, time 4 h. Determined by GC and GC-MS with n-dodecane as the internal standard.
b, c
5
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PdCl2(MeCN)2 system proved to be efficient for alkoxycarbonylation of alkenes. The combination of water and Xantphos was verified by in situ FT-IR analysis to facilitate the formation and stability of the active PdeH species responsible for this reaction. The developed PdCl2(MeCN)2-Xantphos-H2O system also exhibited the generality to the alkoxycarbonylation of different alkenes including aryl ones and aliphatic ones. The use of water as the hydride source is advantageous with safety, low-cost, and environmental friendliness, but with potential possibility for the competitive side-reactions of hydrolysis and hydrocarboxylation. In addition, the required phosphines like Xantphos should be robust against water (hydrolysis). Based the results obtained in this work, we are highlighted to investigate methoxycarbonylation without the presence of any other additives upon the careful selection of the involved phosphines. Since MeOH itself also can serve as a hydride source for formation of [PdIIeH]+ active species to promote methoxycarbonylation. In this way, MeOH triply acts as reactant, additive and solvent without the possibility of competitive side-reactions (hydrolysis and hydrocarboxylation). The related work is in progress.
(2004) 4433–4440. [6] G. Kiss, Chem. Rev. 101 (2001) 3435–3456. [7] A. Seayad, S. Jayasree, K. Damodaran, L. Toniolo, R.V. Chaudhari, J. Org. Chem. 601 (2000) 100–107. [8] H. Ooka, T. Inoue, S. Itsuno, M. Tanaka, Chem. Commun. (2005) 1173–1175. [9] P. Kalck, M. Urrutigoïty, Inorg. Chim. Acta 431 (2015) 110–121. [10] Z. He, Z. Hou, Y. Luo, Y. Dilixiati, W. Eli, Catal. Sci. Technol. 4 (2014) 1092–1103. [11] M. Amézquita-Valencia, G. Achonduh, H. Alper, J. Org. Chem. 80 (2015) 6419–6424. [12] T.A. Tshabalala, S.O. Ojwach, M.A. Akerman, J. Mol. Catal. A: Chem. 406 (2015) 178–184. [13] G. Abarca, K. Brown, S.A. Moya, J.C. Bayon, P.A. Aguirre, J.C. Bayon, P.A. Aguirre, Catal. Lett. 145 (2015) 1396–1402. [14] E. Guiu, M. Caporali, B. Mun˜oz, C. Mu¨ller, M. Lutz, Anthony L. Spek, C. Claver, P.W.N.M. van Leeuwe, Organometallics 25 (2006) 3102–3104. [15] C.J. Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem. Commun. (2004) 1720–1721. [16] J.D. Nobbs, C.H. Low, L.P. Stubbs, C. Wang, E. Drent, M. van Meurs, Organometallics 36 (2017) 391–398. [17] K. Dong, X. Fang, S. Gulak, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell, M. Beller, Nat. Commun. 8 (2017) 14117–14124. [18] R. Sang, P. Kucmierczyk, K. Dong, R. Franke, H. Neumann, R. Jackstell, M. Beller, J. Am. Chem. Soc. 140 (2018) 5217–5223. [19] A. Vavasori, L. Toniolo, J. Mol. Catal. A: Chem. 110 (1996) 13–23. [20] G. Cavinato, L. Toniolo, A. Vavasori, J. Mol. Catal. A: Chem. 219 (2004) 233–240. [21] G.M. Roberts, P.J. Pierce, L.K. Woo, Organometallics 32 (2013) 2033–2036. [22] D.B.G. Williams, M.L. Shaw, M.J. Green, C.W. Holzapfel, Angew. Chem. Int. Ed. 47 (2008) 560–563. [23] D.B.G. Williams, T. Bredenkamp, ChemCatChem 4 (2012) 206–208. [24] H. Li, K. Dong, H. Jiao, H. Neumann, R. Jackstell, M. Beller, Nat. Chem. 8 (2016) 1159–1166. [25] H. Liu, N. Yan, P.J. Dyson, Chem. Commun 50 (2014) 7848–7851. [26] C.H. Low, J.D. Nobbs, M. van Meurs, L.P. Stubbs, E. Drent, S. Aitipamula, M.H.L. Pung, Organometallics 34 (2015) 4281–4292. [27] L.-L. Zhao, B. Pudasaini, A. Genest, J.D. Nobbs, C.H. Low, L.P. Stubbs, M. van Meurs, N. Rösch, ACS Catal. 7 (2017) 7070–7080. [28] D. Yang, H. Liu, D.-L. Wang, Z.-J. Luo, Y. Lu, F. Xia, Y. Liu, Green Chem. 20 (2018) 2588–2595. [29] X. Chen, X. Ye, W.-Y. Liang, Q. Zhou, G. Vo-Thanh, Y. Liu, Mol. Catal. 448 (2018) 171–176. [30] P.C.J. KAMER, P.W.N.M. van Leeuwen, J.N.H. Reek, Acc. Chem. Res. 34 (2001) 895–904. [31] K. Pignat, J. Vallotto, F. Pinna, G. Strukul, Organometallics 19 (2000) 5160–5167. [32] P.W.N.M. van Leeuwen, P.C.L. Kamer, J.N.H. Reek, P. Dierkes, Chem. Rev. 100 (2000) 2741–2769. [33] A.B. Goel, S. Goel, Inorg. Chim. Acta 45 (1980) 85–86.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 21673077 and 21473058), and the Science and Technology Commission of Shanghai Municipality (18JC1412100). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.mcat.2018.10.016. References [1] X.-F. Wu, X. Fang, L. Wu, R. Jackstell, H. Neumann, M. Beller, Acc. Chem. Res. 47 (2014) 1041–1053. [2] R. Chinchilla, C. Najera, Chem. Rev. 114 (2014) 1783–1826. [3] R. Lang, L. Shi, D. Li, C. Xia, F. Li, Org. Lett. 14 (2012) 4130–4133. [4] J. Liu, Z. Wei, H. Jiao, R. Jackstell, M. Beller, ACS Cent. Sci. 4 (2018) 30–38. [5] T. Asaumi, T. Matsuo, T. Fukuyama, Y. Ie, F. Kakiuchi, N. Chatani, J. Org. Chem. 69
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