A highly effective supported ionic liquid phase (SILP) catalysts

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A highly effective supported ionic liquid phase (SILP) catalysts – characterization and application to the hydrosilylation reaction Rafal Kukawka, Anna Pawlowska-Zygarowicz, Joanna Dzialkowska, Mariusz Pietrowski, Hieronim Maciejewski, Katharina Bica, and Marcin Smiglak ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04357 • Publication Date (Web): 22 Jan 2019 Downloaded from http://pubs.acs.org on January 26, 2019

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ACS Sustainable Chemistry & Engineering

A highly effective supported ionic liquid phase (SILP) catalysts – characterization and application to the hydrosilylation reaction Rafal Kukawka,*,†, ‡ Anna Pawlowska-Zygarowicz,†, ‡ Joanna Dzialkowska,‡ Mariusz Pietrowski,‡ Hieronim Maciejewski,†, ‡ Katharina Bica,§ and Marcin Smiglak,*, ‡ † MSc R. Kukawka, MSc A. Pawlowska-Zygarowicz, Prof. H. Maciejewski, Prof. M. Smiglak Poznan Science and Technology Park Adam Mickiewicz University Foundation ul. Rubież 46, 61-612 Poznań, Poland ‡ MSc R. Kukawka, MSc A. Pawlowska-Zygarowicz, J. Dzialkowska, Prof. M. Pietrowski, Prof. H. Maciejewski, Prof. M. Smiglak Faculty of Chemistry Adam Mickiewicz University ul. Umultowska 89b, 61-614 Poznań, Poland § Katharina Bica Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163, A-1060 Vienna, Austria *Corresponding authors E-mail: [email protected] Tel.: +48 618 279 789; [email protected] Tel.: +48 782 707 596.

KEYWORDS: Ionic liquids, supported ionic liquid phase, SILP, hydrosilylation, heterogeneous catalysis

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ABSTRACT

Organosilicon compounds, due to their unique properties, are widely used in a variety of organic processes, thus the constant improvement of current methods is still needed. Herein we present slurry-phase hydrosilylation reactions using novel supported ionic liquid-phase (SILP) catalysts containing rhodium complexes immobilized in four phosphonium ionic liquids (ILs) on silica support. The obtained new SILP catalysts were analyzed by IR technique, low-temperature nitrogen physisorption at 77K and scanning electronic microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) to provide structural information of these materials. Moreover, catalytic activity in hydrosilylation reactions was evaluated and compared to catalytic activity of rhodium catalysts dissolved in the same ILs when using a biphasic reaction system (IL/catalyst as one phase and mixture of substrates as a second phase). The rhodium-based SILP catalysts proved to be much more efficient than when used in biphasic system composed of similar catalyst and reactants. Furthermore, as a result of the presented study we have identified highly active SILP catalyst ([{Rh(cod)(µ-OSiMe3)}2]/[P66614][NTf2] supported on silica) which allowed to decrease the amount of catalyst used in the reaction by 1000 times in comparison to the amount of catalyst required while performing reaction using biphasic catalytic system. Proposed method of utilization of SILP materials, can become a significant step in reducing expensive organometallic catalyst consumption in organic chemistry, and when applied more broadly lead to significant cost savings and eventually making the production of many organic molecules more sustainable.

Introduction Organosilicon compounds generate a lot of attention in variety of organic processes, due to their unique properties. Given the industrial importance of these compounds organosilicon chemistry is


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still continuing to grow.1 The synthesis of most of mentioned substances is based on hydrosilylation reactions.2 Although these reactions are widely investigated and performed in homogenous single-phase systems,3 problem exists with the successive separation of the catalyst from the product after the reaction.4 In order to overcome this problem, efforts are being made to develop novel methods for hydrosilylation reaction performed in heterogeneous systems, for example with solid-supported catalysts that can be recovered after the reaction.5,6 Another approach investigated in recent years relies on the formation of biphasic reaction systems with substrates in one phase and ionic liquids (ILs) as second phase in which the catalyst is dissolved.7,8 This concept has been successfully applied to a number of hydrosilylation reactions with different metal catalysts.9-13 In such liquid-liquid biphasic set-up, the catalyst-containing IL phase can be easily separated from the products and reused in subsequent reaction cycles. As described in his study, Hofmann et al.14 used such biphasic system in platinum-catalyzed hydrosilylation reaction where IL phase was used in a continuous loop reactor, allowing for continuous operation for 48 h at constant activity and selectivity of platinum leaching. Later studies15 by the same group also addressed the immobilization of the catalyst on solid support, relying on supported ionic liquids phases based on silica for the facile separation of silanes formed with high selectivity. In a different approach Li et al16. prepared ionic liquid–modified silica in a “one-pot” reaction of activated silica, 3-chloropropyltriethoxysilane, and alkylimidazole or pyridine. It was found that the catalytic activity and β-adduct selectivity of the supported catalyst Rh(PPh3)3Cl/ionic-liquid–modified-SiO2 for the hydrosilylation reaction of alkenes with triethoxysilane was significantly improved. Until now, our group focused on investigating significant number of ILs with various anions and cations as an effective platinum and rhodium catalysts immobilizing phase in biphasic liquid/liquid systems.17-20 Our best results were obtained when using the phosphonium-based ILs [P66614][NTf2]


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and [P4441][MeSO4], allowing to carry out up to 10 reaction cycles with just using catalyst at concentration of 10-4 mol per mole of Si-H bond. The obtained results clearly proved that the application of ILs as catalyst-immobilizing phase allowed to decrease the amount of catalyst needed to carry out the reaction and to reduce overall process cost. These results obtained by our group and by other researchers confirmed that ILs could be considered as a good media for the immobilization of catalysts and be very useful in the biphasic hydrosilylation reactions. However, taking into account mass transport limitations between phases in liquid/liquid reactions, we decided to investigate new possibilities for catalyst immobilization using ILs. One of possible solutions of the problem of limited mass transfer seems to be the adsorption of the catalyst on highly porous solid support. This approach would also facilitate the catalyst separation after the reaction. In this case, SILP (supported ionic liquid phases) materials could be used, where transition metal complexes can be immobilized within a thin layer of IL deposited on solid support such as silica, active carbon or other mesoporous materials.21,22 The solid structure of these materials allows for simple recycling of the immobilized catalyst from the reaction mixture, leading to substantial cost savings and yields improvement.23 It can be noticed that the SILP concept has a great potential for (transition metal)-catalyzed processes, and recent examples which describe hydrogenation,24,25 hydrodeoxygenation,26 hydrosilylation,16,27,28 oxidation of alcohols,29 reforming of cellulose30 and many other organic reactions,31 confirm that assumption. Due to unique properties of SILP materials, such as high surface area supplied by the porous structure of support, high thermal stability of ILs and support, adjustable solubility of ILs and the improvement of mass transport, SILP materials could be also considered as efficient and reusable catalysts for hydrosilylation reactions.


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The main goal of this paper was to investigate novel SILP materials based on the previously optimized ionic liquids in hydrosilylation processes. Thus, we described the synthesis and characteristics of new SILP materials and later investigated their catalytic activity in a hydrosilylation reaction using 1-octene (1-oct) and 1,1,1,3,5,5,5-heptamethyltrisiloxane (HMTS) (Figure 1) as model substrates with three different rhodium catalysts: Wilkinson's catalyst [Rh(PPh3)3Cl],

[di-µ-trimethylsiloxy)bis{(1,5-cyclooctadiene)rhodium(I)}

[{Rh(cod)(µ-

OSiMe3)}2] and chloro(1,5-cyclooctadiene)rhodium(I) dimer [{RhCl(cod)}2] (see Supported Information, Section: Catalysts used in experiments). Results and Discussion Obtained ionic liquids Based on our previous experience from working with ILs as solvents in hydrosilylation reactions the following ILs were synthesized and characterized: tributylmethylphosphonium methyl sulfate [P4441][MeSO4], tributylmethylphosphonium bis(trifluoromethane)sulfonimide [P 4441][NTf2], tetraoctylphosphonium

bis(trifluoromethane)sulfonimide

[P8888][NTf2]

and

Figure 1. Model reaction of 1,1,1,3,5,5,5-heptamethyltrisiloxane and 1-octene (top) and structures of ILs used in experiments (bottom).


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trihexyltetradecylphosphonium bis(trifluoromethane)sulfonimide [P66614][NTf2] (Figure 1). Method of synthesis and analysis of obtained ionic liquids, including 1H NMR and ion chromatography are described in ESI (Figure S1 and in the section dedicated to synthesis and analysis of ionic liquids (ILs)). Before using ILs for the preparation of SILP materials, their thermal stability was analyzed using thermogravimetric analysis (TGA). Obtained data is summarized in Table S1 and Figure S2 in ESI. In each case, decomposition was not observed at the temperature at which the planned reactions should be carried out (100oC) (Table S1). Moreover, each of tested ILs proved to be stable till at least 275oC which allowed for further study of the properties of SILP materials in adsorption–desorption nitrogen experiments (tests required temperature equal ~120oC).


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Preparation of SILP materials Table 1. Prepared SILP materials loaded at 10% of IL (w/w) and at 4x10-3 % of rhodium (w/w). Name of SILP IL Complex material (A)

[P4441][MeSO4]

[Rh(PPh3)3Cl]

(B)

[P4441][MeSO4]

[{Rh(cod)(µ-SiMe3)}2]

(C)

[P4441][MeSO4]

[{RhCl(cod)}2]

(D)

[P4441][NTf2]

[Rh(PPh3)3Cl]

(E)

[P4441][NTf2]


(F)

[P4441][NTf2]

[{RhCl(cod)}2]

(G)

[P8888][NTf2]

[Rh(PPh3)3Cl]

(H)

[P8888][NTf2]


(I)

[P8888][NTf2]

[{RhCl(cod)}2]

(J)

[P66614][NTf2]

[Rh(PPh3)3Cl]

(K)

[P66614][NTf2]


(L)

[P66614][NTf2]

[{RhCl(cod)}2]

Obtained SILP materials (Table 1) were prepared by physical impregnation of calcined silica surface at 500oC (High-purity grade Davisil Grade 62) loaded with 10% of ionic liquid (w/w) and 4x10-3 % of rhodium (w/w) as it is described in details in the supported information (see ESI, Section Preparation of SILP material). Silica support, prior ionic liquid and rhodium catalyst impregnation, was calcined due to the fact that ligand-support interactions are crucial for effective stability of rhodium catalyst. Many sensitive catalysts impregnated on Brönsted-acidic silica support deactivate relatively fast, thus acidic sites on the silica support must be reduced by prior


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heating (500oC, 24h) to obtain dehydroxylate silica. Moreover, silica after calcination is characterized by higher active surface area (Table 2). Textural properties of SILP materials To characterize the obtained SILP materials and prove the successful adsorption of IL and catalyst, additional IR spectroscopy tests, SEM images, EDS analysis and low-temperature absorption of nitrogen on the surface experiments were performed. In order to prove the adsorption of IL on support surface, IR spectra after SILP preparation were recorded. IR spectra of silica support before and after calcination, presented in Figure S3 (see ESI), show the disappearance of the band at 3100-3500 cm-1 which indicates reduction in the amount of hydroxyl groups on the silica surface. In case of hydrosilylation reaction, catalyzed by rhodium organometallic complexes, lowering of the number of available hydroxyl groups on surface of silica leads to the enhancement in catalytic activity of the SILP material, due to the elimination of possible side reactions between catalyst and hydroxyl groups. Figure S4 presents IR spectrum of (J) SILP material, where the characteristic bands referred to IL (2900 cm-1 for P-alkyl bands) are clearly visible, thus proving the adsorption of IL on silica support. Unfortunately, due to the low sensitivity of the IR spectrometer and low Rh-catalyst loading (4x10-3 % in SILP material (w/w)), a direct observation of characteristic bands, related to the catalyst in SILP materials, was not possible. All other IR spectra of SILP materials are shown in ESI (Figures S5-S14).


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Analysis of low-temperature nitrogen adsorption/desorption measurements at temperature 77 K allowed to determine the average pore diameter, BET surface area and total pore volume values. These tests are important to show changes in surfaces area after calcination of support and after IL Table 2. BET characterization of silica, calcined silica, silica/IL and SILP materials, pore filling degree (α) and layer thickness. BET Total Layer thicknessb

Surface

Pore

Area

Volume

[m2/g]

[cm3/g]

SiO2

290.6

1.12

–

SiO2 calcined

326.5

1.10

–

SiO2/[P4441][MeSO4]

252.3

0.91

0.19

0.58

SILP (B)

234.8

0.89

0.21

0.64

SiO2/[P4441][NTf2]

229.6

0.89

0.21

0.64

SILP (E)

231.4

0.89

0.21

0.64

SiO2/[P8888][NTf2]

237.2

0.91

0.19

0.58

SILP (H)

230.0

0.87

0.23

0.70

SiO2/[P66614][NTf2]

227.5

0.89

0.21

0.64

SILP (K)

236.2

0.77

0.33

1.01

Sample

αa

[nm]

a - pore filling degree of support as the ratio IL volume/support pore volume. b – the ratio of the IL volume used for coating and the initial surface area

impregnation. As expected, the calcination process of silica increased the BET surface area of the silica, indicating that more surface is available for impregnation with IL (Table 2). Moreover, results from nitrogen adsorption/desorption tests (Table 2, Figure S16) showed a decrease of BET surface area and total pore volume after impregnation with IL in comparison to the pristine or calcined silica. The reduction in total pore volume is the result of the formation of a layer of IL


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within the pores with a thickness of 0.58 to 1.01 nm (Table 2). Moreover, the calculated α degree (pore filling degree of silica for IL volume to silica pore volume) is within the range of 0.17-0.33, which means that mesopores are not completely filled or blocked.23 In addition, the dependence of pore volume distribution curves from their size (ESI, Figure S16) indicates the formation of a thin layer of IL. Any significant changes in comparison to calcined silica was not observed which means that the pore structure is retained. SEM and EDX studies

Figure 2. SEM analysis of silica surface (left) and SILP (A) surface (right) at magnification 585, Acc. Voltage; 15.0 kV). Table 3. Average percentages content of Si, C, O, P and Rh from EDX of silica and SILP (A). Element silica SILP (A) content [wt.%] Si

44.5

39.3

O

47.8

54.2

C

7.5

4.1

Al

0.2

0.2

P

0.0

1.1

S

0.0

0.9

Rh

0.0

0.2

In another experiment scanning electron microscopy (SEM) combined with energy dispersive Xray (EDS) analysis was used to assess the SILP surface and obtain information about its chemical composition prior and after impregnation with IL on the example of SILP (A). Figure 2 shows


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differences between the surface of silica and a smoother surface of SILP material, as pores of silica are filled with IL. Table 3 provides results on the average chemical composition of the silica support and SILP materials surface. The observed signals from P, S and Rh, increasing amounts of O while decreasing content of Si, indicate the presence of [P4441][MeSO4] on silica surface. Catalytic activity Figure 3. Conversion of Si-H monitored in situ on example on SILP (A) between 1-octene and HMTS in different molar ratio of rhodium (blue dot 1:1:10-4, green dot 1:1:10-5 and red dot 1:1:10-6) at 100oC. 100

conversion of Si-H bond [%]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


90 80

1x10-4 1x10-5 1x10-6

70 60 50 40 30 20 10 0 0

5

10

15

20

25

30

time [min]

Initially, in order to determine reaction time and amount of SILP necessary to achieve high conversion, the test reaction with SILP (A) ([P4441][MeSO4]/[[Rh(PPh3)3Cl], using real time in situ IR (React15 by Mettler Toledo) was performed. The conversion of Si-H bond was calculated from the decreasing area of band (calculated from the band area related to the vibration of Si-H bond around 915 cm-1). After the reaction completion, the product, octylheptamethyltrisiloxane, was characterized by GC and GC/MS/MS to confirm the reaction selectivity (Figure S18-S21). As it is shown in chromatograms, only one peak of product was present (tr = 11.7 min, Figure S18 and S19). Moreover, fragmentation of product peak at retention time (11.4 min) confirmed the structure of octylheptamethyltrisiloxane (Figure S20 and S21). Results presented in Figure 3 and Table S2 indicate that the optimum reaction conditions are present at a reaction time of 30 minutes


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and at a molar ratio of 1-oct:HMTS:[Rh] 1:1:10-5. A higher molar ratio 1-oct:HMTS:[Rh]1:1:10-4 was unnecessary, whereas a lower molar ratio 1-oct:HMTS:[Rh] 1:1:10 -6 required long reaction time (> 60 minutes) and led to only 24% conversion of Si-H bond. In the following reactions the hydrosilylation of 1-octene to HMTS was carried out with SILP materials listed in Table 1 (molar ratio 1-oct:HMTS:[Rh] 1:1:10-5) (see procedure reported in the ESI (Section Reactions with using SILP materials). The use of SILP materials was intended to limit the leaching of the catalyst to the product phase and at the same time to allow for the preservation of the catalyst in the ionic liquid and its possible reuse. Thus, after 30 minutes (1st reaction cycle), the reaction mixture was cooled and the SILP material was separated from the remaining substrates and product. The recovered SILP material was reused in the next reaction cycle without addition of a new portion of catalyst. Table 4 reports the yields of reactions using various SILP materials as catalysts. For every SILP material yields were >99% after the 1st cycle. Lower activity was only observed when using SILP (A)-(C) with [P4441][MeSO4] due to possible reaction of the anion [MeSO4]-. The lower activity might be also attributed to the presence of hydroxyl group of SiO2, which existence was proved by means of 1H NMR of [P4441][MeSO4] after the last reaction cycle that showed a disappearance of CH3- peaks from [MeSO4]- (ESI, Synthesis and analysis of Ionic Liquids). As a result of hydrolysis, formed methanol and the [HSO4]- anion could poison the catalyst, which is evident in the yield dropping to below 70% after 7th reaction cycle in case of SILP (B) ([P4441][MeSO4]/[{Rh(cod)(μ-OSiMe3)}2]), (Table 4). In contrast, SILP materials based on ILs with the chemically stable and unreactive anion such as [NTf2]- were considerably more active. In addition, it was observed that the chain length in cation affected the yield of the reaction. It is clearly visible that more carbon atoms in the cation structure resulted in more cycles that can be carried out with high yield. The most active SILP material, (L) based on


12

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[P66614][NTf2] and [{RhCl(cod)}2] allowed for carrying out 20 cycles with high yield, most likely due to increased hydrophobic character of the cation core. In summary, the activity of SILP materials can be placed in the following order of supported ILs [P4441][MeSO4]< [P4441][NTf2]99

>99

>99

>99

>99

>99

99

>99

>99

>99

>99

>99

2

98

>99

99

98

>99

>99

98

>99

98

>99

>99

>99

3

96

94

73

97

>99

>99

98

>99

98

98

>99

>99

4

92

94

57

95

>99

97

97

99

97

98

97

>99

5

85

94

59

83

97

95

99

98

95

92

97

97

6

74

93

28

80

92

83

99

97

89

85

97

95

7

54

79

21

75

88

72

98

96

85

78

97

95

8

36

66

23

63

82

59

98

94

78

74

97

94

9

26

64

18

59

76

40

98

92

67

72

97

94

10

18

64

16

43

72

36

99

79

59

68

97

94

11

60

33

70

32

93

76

28

61

97

94

12

58

26

65

29

76

71

26

60

95

92

13

47

57

21

58

72

54

84

90

14

39

41

32

69

50

80

86

15

24

26

15

62

46

67

85

62

43

63

81

17

59

40

46

79

18

55

37

25

77

19

46

32

13

75

20

34

31

16

TOF

[h-1]

12

1 355 800

2 150 000

984 200

1 704 400

2 361 400

1 721 400

2 519 200

3 120 000

1 842 800

2 639 200

71 3 098 880


14

3 592 000

Page 15 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Leaching studies Apart from a possible decomposition of ILs the decrease in the catalytic activity of SILP materials can be caused by leaching of catalyst and ionic liquid from solid support. This phenomena is known for liquid phase reactions with SILP materials and particularly problematic in continuousflow processes, since even slight solubility of IL in substrate, product or solvent phase may cause removal of the thin IL film, accompanied by leaching of the catalyst. 23 To examine the leaching of IL from SILP material we performed studies using

31P

NMR (see ESI,

31P

NMR). Qualitative

analysis was implemented to prove the presence of IL leaching from SILP material. Experimental conditions were set to detect an amount of IL corresponding to > 5% of mass IL in SILP (0.025 mg of IL in 0.5ml of CDCl3). A lower amount of IL < 5% (0.025 mg) was below detection threshold in the used NMR setup. Characteristic IL peaks were observed in 31P NMR spectra of products phase from reactions performed with SILP (A)-(F) and (J)-(L), thus these ILs were leaching to the liquid product phase in amount higher than 5% of IL mass in SILP material. As the only exception, for reactions performed with using SILP (G)-(I) were ionic liquid used was [P8888][NTf2], ionic liquid was not observed in product phase in amounts >5%. These result showed that leaching of ionic liquid in small amount might be indeed responsible for falling catalytic activity over consecutive cycles. However, this phenomena is not a limiting process due to possibility of reusing SILP material up to 20 times. Moreover, after reaction completion (after maximum cycles performed with each SILP material), the presence of remaining IL in SILP was confirmed by IR (Figures S3-S15). In all cases characteristic band from IL were observed which proves that IL, despite the inactivity of SILP material after that many cycles, was still adsorbed to some extent on the support.


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In order to further determine the content of rhodium catalyst dissolved after several reaction cycles in the products phase, inductively coupled plasma (ICP) analysis was used. The experiments showed no leaching of rhodium to product phase in amount higher than limit of detection (1 ppm).19 Because of inconclusive results of ICP analysis, additional experiment was performed to investigate whether rhodium catalyst leaches to product phase and if it is still catalytically active. The experiment was performed only for SILP (C), as for this reaction system the yield of the reaction decreases the most significantly with every following reaction cycle. In order to investigate this, product phase was separated from reaction mixture, new portion of substrates was added to the product phase, and the experiment was performed as described in ESI in section: Three-phase test. Table 5 present the yields of products obtained after each reaction cycle with using SILP (C), and conversion of new portion of substrates added to product phase separated after each reaction cycle. Table 5. Yields obtained with reaction system containing SILP (C): I: yields of hydrosilylation reaction using SILP (C) materials and II: yields of hydrosilylation reaction after adding new portion of substrate to product phase (after separation from SILP (C))

Cycle numer

I SILP (C)

1

>99

II Product phase after adding new portion of catalyst (conversion of new portion) >99

2

99

70

3

73

61

4

57

50

5

59

45

6

28

31

7

21

26

8

23

24

9

18

15

As it can be observed, product phase separated after first reaction cycle must contain rhodium catalyst, due to the fact that after adding new portion of substrates, conversion of Si-H bond is still observed (>99%). In the following cycles, product phase progressively contain less rhodium


16

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catalyst as can be seen from decreasing conversion of new portion of substrates added to product phase. Presented results are indicative of slow washing out of the catalyst from SILP into the product phase. Comparison of TOF [h-1] for investigated and standard reaction systems Our experiments with use of SILP materials present significant improvements when compared to reactions carried out with conventional biphasic systems.19 Table 6 presents TOF values of using ILs as solvent for various catalysts in (i) liquid-liquid biphasic system and (iii) as supported SILP catalyst. Table 6. Comparison of TOF [h-1] in homogenous system and using ILs as solvent for catalyst in biphasic system and supported on silica (SILP materials). IL

[Rh(PPh3)3Cl]

[{Rh(cod)(µ-OSiMe3)}2]

[{RhCl(cod)}2]

19600

19800

19800

No IL present(homogenous system)[a]

Biphasic[b]

SILP[c]

Biphasic[b]

SILP[c]

Biphasic[b]

SILP[c]

[P8888][NTf2]

55.700[r]

2.519.200

87.100[r]

3.120.000

70.200[r]

1.842.800

[P66614][NTf2]

84.700

2.639.200

89.000

3.098.880

91.000

3.592.000

[P4441][MeSO4]

62.600[r]

1.355.800

87.100[r]

2.150.000

88.900[r]

984.200

[P4441][NTf2]

65.300[r]

1.704.400

49.200[r]

2.361.400

31.500[r]

1.721.400

[a] – r.t 60 minutes, molar ratio 1-oct:HMTS:[Rh] 1:1:10-4 [b] – r.t 60 minutes, molar ratio 1-oct:HMTS:[Rh] 1:1:10-4 [c]- r.t 30 minutes, molar ratio 1-oct:HMTS:[Rh] 1:1:10-5 [r] – results published before19

TOF values calculated for reactions carried out using ILs are in range from 31000 h-1 to 91000 h1

, thus significantly higher in comparison to reactions performed in homogenous system (19800 h-

1)

without addition of ionic liquid. When comparing TOF values calculated from reactions with

use of SILP materials, all SILP materials (D)-(L) showed significantly higher catalytic activity than biphasic systems with ILs. When, in turn, comparing TOF values calculated from reactions using SILP materials, all SILP materials (D)-(L) showed significantly higher catalytic activity than


17


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the corresponding biphasic systems. The TOF value for reactions with the most active SILP (L) is 40 times higher than when using biphasic system. Moreover, it is worth highlighting that the catalyst concentration can be decreased 10 times and that the reaction time is decreased by half when using SILP materials. Overall, the application of SILP materials as catalysts for hydrosilylation process lead to improved yields, decreased reaction times and catalyst concentrations, thus the cost of production and energy consumption can be significantly reduced. Catalytic activity of SILP (L) Due to the fact that SILP (L) indicated much higher catalytic activity than others SILPs, additional tests with lower catalyst concentration were performed, using for monitoring the reaction progress a real time in situ IR spectroscopy. Tests performed at molar ratio 1-oct:HMTS:[Rh] 1:1:10-6 and 1:1:10-7 showed outstanding catalytic activity. Even when a molar ratio of 1-oct:HMTS:[Rh] 1:1:10-7 was used, Si-H conversion reached 99% in15 minutes after adding SILP (L) to mixture of substrates (Figure S22).


18

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Moreover, the possibility to reuse SILP (L) by separating the supported catalysts from the post reaction mixture was also attempted. Due to the very small amount of used SILP catalyst in the Table 7. Yields of hydrosilylation reaction using SILP material (L) in different concentration of catalyst. Cycle number

1-oct:HMTS:[Rh]= 1:1:10-5

1-oct:HMTS:[Rh]= 1:1:10-7

1

>99

>99

2

>99

99

3

>99

95

4

>99

93

5

97

90

6

95

82

7

95

74

8

94

62

9

94

32

10

94

15

TOF [h-1]

3.592 000

297 080 000

reaction, the loss of mass of SILP after decantation was high, thus it was possible to reuse SILP catalyst only up to 5 times without the loss in yield. However, 12 cycles with yields above 90% was possible when using a molar ratio 1-oct:HMTS:[Rh] 1:1:10-5, Table 7). To sum up, applying SILP (L) catalyst allowed for: (i) shortening of the reaction time from 60 to 15 minutes, (ii) lowering amount of catalyst by 1000 times and (iii) simplifying the process of catalyst separation from the reaction mixture. Moreover, these results show significant improvement in relation to our previous studies using ILs as solvent for catalyst in hydrosilylation reaction, allowing for increasing TOF values from: (i) 19 800- h-1 in case of reaction performed in homogenous system, (ii) 91 000 h-1 in case of reaction performed with using ILs as solvent in biphasic system, (iii) 3 592 000 h-1 in case of reaction with SILP (L) (when using 1-


19


Page 20 of 30

oct:HMTS:[Rh]= 1:1:10 -5 concentration) to 297 080 000 h-1 when using SILP (L) in 1oct:HMTS:[Rh]= 1:1:10 -7 concentration. Nature of catalyst As suggested in literature, the specific reaction environment, presence of the ionic liquids and the reducing conditions ensured by the hydrosilane may result in the formation of metal colloids 32 that might be the active species. Trying to investigate the nature of the catalytically active species in hydrosilylation reaction using SILP catalyst, three additional tests were performed: Hot filtration tests, Transmission electron microscopy (TEM) measurements and Mercury poisoning test on example of reaction using SILP (L) (see ESI file, page S19 and S20). Results from hot filtration tests indicated that neither metal particles nor other precipitates were observed. Moreover, TEM images did not show any metal particles neither in SILP (L) catalyst (recovered after filtration) nor in evaporated product. Additionally, the mercury poisoning test has shown lack of inhibition of conversion Si-H bond which is the evidence for catalysis via Chalk and Harrod mechanism. Overall, these findings indicated that the organometallic rhodium complex rather than metal particles are the catalytically active species in this process. Conclusion In the present study, we have extended our previous work on liquid-liquid biphasic catalysis towards the application of supported ionic liquid phase (SILP) catalysts for the hydrosilylation reaction. The SILP materials were used due to their unique properties such as high surface area offered by the porous structure of support, resulting in the solution of the mass transport problem due to the thin film of ILs, and a facile recycling of the immobilized catalyst from the reaction mixture. In this work, 12 new SILP catalysts was obtained. The immobilization of IL on the silica


20

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surface was confirmed from the IR spectra and SEM-EDX analysis. Additionally, adsorption/desorption isotherms of nitrogen analysis confirmed the increase of BET surface area after calcination of silica and thus increasing surface available for impregnation with IL. On the other hand, after impregnation of silica with IL, BET surface area and total pore volume decreased which indicates that IL filled pores of silica. The catalytic activity of the obtained SILP catalysts was further evaluated in the hydrosilylation reaction of 1-octene. The rhodium based SILP catalysts proved to be much more efficient than any biphasic reaction system previously tested by us. In comparison to biphasic reactions, we were able to: (i) decrease the required amount of catalyst by 10 times, (ii) shorten reaction time from 1 hour to 30 minutes, (iii) extend number of cycles which could be carried out with using the same portion of SILP material without adding a new catalyst, and (iv) make the separation and reuse of the rhodium catalyst easy via a simple decantation of solid catalyst. In case of the most active SILP catalyst ([{Rh(cod)(µOSiMe3)}2]/[P66614][NTf2] supported on silica) a TOF value of 297.000.000 h-1 was reached, allowing to decrease amount of catalyst by 1000 times in comparison to the catalyst amount required in biphasic reactions. This is a significant step in reducing expensive organometallic catalyst consumption, resulting in substantial cost savings and eventually making the production of organosilicon compounds more sustainable. ASSOCIATED CONTENT Supporting Information. Additional information including synthesis and analysis of ILs, catalysts used in experiments, preparation of SILP materials, TGA analysis, determination of surface area, pore volume and pore diameter,

31P

NMR, leaching studies, IR spectra, reaction

progress monitored in situ, catalysis in biphasic system, reactions with using SILP materials, GC


21


Page 22 of 30

chromatograms, GC/MS/MS chromatogram, catalytic activity are available in Supporting Information file. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]; [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources This work was supported by the National Science Centre (Poland), project SONATA BIS (No. UMO-2017/26/E/ST8/01059). Moreover, Rafal Kukawka is Adam Mickiewicz University Foundation scholarship holder in the academic year 2017/2018. ABBREVIATIONS IL, ionic liquid; SILP, supported ionic liquid phase; 1-oct, 1-octene; HMTS, 1,1,1,3,5,5,5heptamethyltrisiloxane. REFERENCES (1) Organosilicon Compounds. Theory and Experiment (Synthesis), Lee, V. Y., Ed.; Elsevier: London, 2017, DOI 10.1016/C2014-0-01865-5. (2) Applied Homogenous Catalysis with Organometallic Compounds; Cornils, B., Hermann, W. A., Beller, M., Paciello R., Eds.; Wiley-VCH: Weinheim, 2017, DOI 10.1002/9783527619351.


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(30) Kudo, S.; Goto, N.; Sperry, J.; Norinaga, K.; Hayashi, Production of Levoglucosenone and Dihydrolevoglucosenone by Catalytic Reforming of Volatiles from Cellulose Pyrolysis Using Supported Ionic Liquid Phase. ACS Sustain. Chem. Eng. 2017, 5 (1), 1132-1140, DOI 10.1021/acssuschemeng.6b02463. (31) Riisager, A.; Fehrmann, R.; Haumann, M. Supported ionic liquids: versatile reaction and separation media. Top. Catal. 2006, 40 (1-4), 91-102, DOI 10.1007/s11244-006-0111-9. (32) Lewis, L.; Uriarte, R. Hydrosilylation catalyzed by metal colloids: a relative activity study. Organometallics 1990, 9 (3), 621–625, DOI 10.1021/om00117a015. SYNOPSIS The use of highly effective Supported Ionic Liquid Phase (SILP) Catalysts as a new method for sustainable hydrosilylation process. TABLE OF CONTENTS GRAPHIC

IONIC LIQUIDS

SOLID SUPPORT

HYDROSILYLATION

METALORGANIC COMPLEXES


27


Figure 1. Model reaction of 1,1,1,3,5,5,5-heptamethyltrisiloxane and 1-octene (top) and structures of ILs used in experiments (bottom). 115x64mm (150 x 150 DPI)


Page 28 of 30

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Figure 2. SEM analysis of silica surface (left) and SILP (A) surface (right) at magnification 585, Acc. Voltage; 15.0 kV). 78x28mm (150 x 150 DPI)



Figure 3. Conversion of Si-H monitored in situ on example on SILP (A) between 1-octene and HMTS in different molar ratio of rhodium (blue dot 1:1:10-4, green dot 1:1:10-5 and red dot 1:1:10-6) at 100oC 152x121mm (96 x 96 DPI)


Page 30 of 30

A highly effective supported ionic liquid phase (SILP) catalysts

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