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Synlett 2024; 35(20): 2417-2422
DOI: 10.1055/a-2379-9191
letter
Special Issue to Celebrate the 75th Birthday of Prof. B. C. Ranu

Dehydrosilylation of Alcohols Using Gold Nanoparticles Deposited on Citric Acid Modified Fibrillated Cellulose

Butsaratip Suwattananuruk
a   Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
,
Yuta Uetake
a   Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
b   Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
,
Hidehiro Sakurai  ∗
a   Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
b   Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
› Author Affiliations

This research was supported by the JST-Mirai Program (JPMJMI18E3) and by JSPS KAKENHI grants JP19K22187 (H.S.), JP20K15279 (Y.U.), and JP22K05095 (Y.U.).
› Further Information
 
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Dedicated to Professor B. C. Ranu on the occasion of his 75th birthday.

Abstract

The development of an effective catalytic system for the dehydrogenative coupling of hydrosilanes with alcohols remains an ongoing challenge, particularly for alcohol protection applications. In this study, we report the development and optimization of a highly efficient gold catalyst supported on fibrillated cellulose modified with citric acid. The catalyst exhibited remarkable catalytic activity under mild conditions with 0.01–0.05 mol% of Au loading, facilitating the formation of silyl ethers with excellent yield. Notably, our catalytic system overcomes the need for excess alcohol, typically required in such reactions, making it highly practical for alcohol protection applications. This work represents a significant advancement in the field of dehydrosilylation catalysis, offering a sustainable, efficient, and environmentally friendly approach for the synthesis of functional silanol-based materials and alcohol protection applications. The scope of substrates and the utility of the catalyst have been thoroughly studied.


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Key words

gold catalysis - nanoparticles - cellulose - dehydrogenative coupling - hydrosilanes - silylation

The etherification of silanes has emerged as a powerful strategy for preparing functional organosilicon compounds and for organic synthesis in general.[1] In particular, the protection of alcohols through silylation is well-known and frequently employed in preparing synthetic compounds.[2] For a long while, silyl ethers have commonly been synthesized by using chlorosilanes with alcohols in the presence of a stoichiometric base.[3] However, this method requires the use of corrosive reagents and inevitably produces stoichiometric amounts of organic salts as byproducts. As an alternative for synthesizing silyl ethers, the dehydrogenative coupling of hydrosilanes has been studied. This method produces H2 as a sole byproduct, presenting a substantial environmental advantage.[4] [5]

Extensive research has been conducted on metal-catalyzed dehydrosilylation. Whereas the initial studies focused on homogeneous metal catalysts,[4] heterogeneous catalysts have emerged as compelling alternatives due to their reusability.[5] [6] In most cases, the catalytic dehydrosilylation reactions have been investigated by using a solvent or an excess amount of alcohol, limiting their applicability in alcohol protection methodologies in organic synthesis. As the ideal catalyst hitherto developed, the single-atom cobalt catalyst reported by Cao and co-workers can overcome this limitation; one equivalent of various alcohols was successfully protected by using two to three equivalents of a hydrosilane.[7] Despite this progress, significant interest remains in developing novel heterogeneous catalysts for efficient hydroxy group protection.

Since the first report on dehydrosilylation using Al2O3-supported Au nanoparticles (AuNPs),[5c] AuNPs have been recognized as effective catalysts for this reaction and have been actively studied. Subsequent research has focused on developing various AuNP catalysts that demonstrate a high efficiency under mild reaction conditions together with a broad substrate scope.[8] These catalysts include self-assembled-monolayer-capped AuNPs,[8a] hydroxyapatite-supported AuNPs,[8b] silica-supported AuNPs,[8c] and graphene-supported single-atom Au(I) catalyst.[8d] However, these catalysts still face the issue of requiring excess amounts of the alcohol. Over the last few years, we have developed several reactions using a AuNP catalyst supported on citric acid-modified fibrillated cellulose (Au:F-CAC).[9] The nanofiber-like structure of F-CAC increases its surface area, allowing efficient deposition of metal nanoparticles and a high stability during catalytic reactions.[9] [10] More recently, we reported dehydrogenative oxidation of hydrosilanes under aerobic conditions using Au:F-CAC, revealing that the reaction takes place at the cationic Au sites generated by the adsorption of oxygen.[9c] Given our previous report, we conceived that the Au:F-CAC might also be applicable for the dehydrosilylation of alcohols. Herein, we describe the dehydrosilylation of alcohols using Au:F-CAC. Our investigation showed that Au:F-CAC is an efficient catalyst for dehydrosilylation using one equivalent of alcohol, and offers a clean silyl protection. This highlights the versatility and efficacy of our designed catalyst, emphasizing its potential significance for applications in environmentally friendly synthetic processes.

Our investigation commenced with optimizing the reaction conditions using one equivalent of dimethyl(phenyl)silane (1a) and an excess of ethanol. Au:F-CAC with a particle size of 1.7 ± 0.2 nm (1.7 × 10–3 wt%) was prepared according to our previous report and used without further modification.[9b] The dehydrogenative coupling of 1a was initially attempted using a solvent amount of ethanol in the presence of 0.01 atom% Au:F-CAC at room temperature under aerobic conditions. As a result, 1a was converted into ethoxy(dimethyl)phenylsilane (2b) in 99% yield, demonstrating that Au:F-CAC catalyzes not only dehydrogenative oxidation but also dehydrogenative coupling of the hydrosilane (Table [1], entry 1). Subsequently, the amount of ethanol was reduced to two equivalents, and the reaction was carried out in various organic solvents. Screening these solvents revealed that toluene provided the best result, affording 2a in 71% yield (entries 2–5). Although the reaction temperature showed a negligible effect, a slight extension of the reaction time increased the yield to 95% (entries 6 and 7). Notably, using one equivalent of ethanol reduced the yield to 63% (entry 8).

Table 1 Optimization of the Reaction Conditions

Entry

Solvent

Time (h)

Temp (°C)

Yield (%) of 1a

Yield (%) of 2b

1a

EtOH

3

27

–

>99

2

n-hexane

3

27

65

 30

3

EtOAc

3

27

70

 25

4

THF

3

27

60

 34

5

toluene

3

27

25

 71

6

toluene

3

50

24

 73

7

toluene

4

27

–

 95

8b

toluene

4

27

35

 63

a EtOH (1 mL) was used as the solvent.

b 100 mol% of EtOH was used.

With the optimized conditions in hand, we investigated the synthesis of silyl ethers using various combinations of silanes and alcohols (Scheme [1]). The dehydrogenative coupling of 1a with the primary alcohols methanol, ethanol, propan-1-ol, and butan-1-ol afforded the corresponding silyl ethers 2a–d in quantitative yield. Meanwhile, the coupling of 1a with i-PrOH delivered the desired silyl ether 2e in only 50% yield, even on prolonging the reaction time. Coupling of alcohols with methyl(diphenyl)silane (1b) or triphenylsilane (1c) showed a similar trend, although the reactivity of 1c with BuOH or i-PrOH was even lower (2p and 2q). Moreover, no reaction was observed when sterically demanding t-BuOH was used as a reactant, even on extending the reaction time or increasing the temperature.

Zoom Image
Scheme 1 Synthesis of silyl ethers from various silanes and alcohols catalyzed by Au:F-CAC. Reaction conditions: hydrosilane 1 (0.5 mmol), ROH (1 mmol), toluene (3.0 mL). The yields were determined by 1H NMR analysis. a At 50 °C for 24 h.

A reusability test was conducted to evaluate the durability of the Au:F-CAC catalyst. The spent catalyst was recovered and employed in subsequent recycle runs without additional treatment. During the first three recycle runs, the dehydrogenative coupling of 1a proceeded quantitatively (Scheme [2a]). Although a slight decrease in the catalytic activity was observed after the third cycle, 2a was still obtained in 80–86% yield, demonstrating the excellent durability of Au:F-CAC in this reaction. Transmission electron microscopy (TEM) observation of the fresh and reused catalysts showed slight aggregation of the AuNP (2.9 ± 0.5 nm) after the 6th cycle, which accounts for the slight reduction in the yield of 2a (Scheme [2b]). In addition, a hot-filtration experiment was performed.[11] The Au:F-CAC was filtered to separate the catalyst from the reaction mixture when the yield of 2b reached 70% (after about 3 h; Scheme [2c]). The filtrate was then subjected to the same reaction conditions without the catalyst, and no further increase in the yield of 2a was observed. Furthermore, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis confirmed the absence of gold species in the filtrate, indicating that the reaction occurred on the gold surface. The sustained catalytic activity signifies the high stability of this catalyst, probably attributable to the presence of carboxylic acid attached to cellulose. This study demonstrated that Au:F-CAC is a highly efficient, stable, and reusable catalyst for the dehydrosilylation of alcohols, offering a clean and mild process for industrial and functional silanol-based material applications.

Zoom Image
Scheme 2 Catalytic performance of Au-F-CAC catalyst for dehydrogenative coupling of dimethyl(phenyl)silane with ethanol. (a) Recycling run experiment. (b) TEM images of the fresh and spent catalyst after the sixth run. The mean diameter and standard deviation are based on the average for 300 particles. (c) Hot-filtration experiment.

Next, in order to apply this reaction to the protection of hydroxy groups, the reaction conditions were reoptimized using one equivalent of i-PrOH as a substrate. In the presence of 0.01 atom% of Au:F-CAC and 200 mol% of 1a, dehydrogenative coupling of i-PrOH with 1a gave silyl ether 4a in 46% yield (Table [2], entry 1). The yield increased to 71% when 400 mol% of 1a was used (entry 2). However, further increasing the amount of 1a to 600 mol% did not improve the yield of the silyl ether (entry 3). By using 400 mol% of 1a, the Au loading was then optimized. The best result was achieved when 0.1 atom% of Au:F-CAC was used, affording 4a in 89% yield (entries 4–6). To the best of our knowledge, this is the first example of a AuNP-catalyzed dehydrogenative silylation of an alcohol using a limited amount of a hydrosilane.[8]

Table 2 Optimization of the Reaction Conditions

Entry

x

y

Yield (%)

1

200

0.01

46

2

400

0.01

71

3

600

0.01

66

4

400

0.05

86

5

400

0.1

89

6

400

0.2

85

The scope of the dehydrogenative silylation was then examined using various primary and secondary alcohols (Scheme [3]). The dehydrogenative coupling of benzyl alcohol (3a) was completed after six hours to give the corresponding silyl ether 4a in 82% isolated yield. Benzyl alcohols bearing methoxy (3b), fluoro (3c), or bromo (3d) groups participated in the reaction to give the corresponding silyl ethers 4b–d in yields of 78, 83, and 93%, respectively. A benzyl alcohol containing an electron-withdrawing ester group (3e) was tolerated under the reaction conditions to afford the silyl ether 4e in 90% yield. Although the yield was moderate, the aldehyde 3f and nonprotected amine 3g were compatible, giving 4f and 4g in yields of 48 and 42%, respectively, with 42% and 46% recovery of the starting materials. The presence of a furan heteroaromatic ring did not interfere with the reaction and the silyl ether 3h was formed from 4h in 73% yield. An aliphatic alcohol containing an alkene moiety (3i) participated in this reaction to give 4i in 76% yield without a concomitant 1,5-cyclization reaction.

Zoom Image
Scheme 3 Substrate scope. The reactions were conducted on a 0.5 mmol scale in toluene (3 mL). The yields were determined by 1H NMR analysis. a Isolated yield. b Recovered yield of the starting material.

Dehydrogenative coupling with secondary alcohols was also investigated. Cyclopentanol (3j) and cyclohexanol (3k) were silylated under the reaction conditions to give 4j and 4k in yields of 75 and 83%, respectively. Butan-2-ol (3n) was converted into the corresponding silyl ether 4n in 76% yield. The dehydrogenative silylation of the secondary benzyl alcohols indan-1-ol (3l) and diphenylmethanol (3m) gave 4l and 4m in yields of 76 and 66%, respectively. Dehydrogenative silylation with the alcohol-containing natural product (–)-menthol (3o) provided 4o in 65% yields with 27% recovery of 3o, showcasing the synthetic utility of the Au:F-CAC catalyst.

Zoom Image
Scheme 4 Possible reaction mechanism

The high efficiency of Au:F-CAC in the dehydrosilylation could be attributed to the cationic Au sites generated by the adsorption of oxygen.[12] In fact, Zborǐl et al. showed that cationic Au(I) was the catalytically active species in their work on dehydrogenative silylation using a single-atom Au catalyst.[8d] In addition, our group has also experimentally revealed the formation of cationic Au sites through the adsorption of oxygen using near-ambient-pressure X-ray photoelectron spectroscopy.[9c] The reaction atmosphere was found to be important for this reaction as well as for dehydrogenative oxidation. The effect of the atmosphere was evaluated from the yield of 2b after one hour. The yields of 2b under oxygen, air, and argon atmospheres were 55, 17, and 3%, respectively, indicating a key role of oxygen on the reaction rate [Supporting Information (SI); Table S1]. A plausible reaction mechanism is shown in Scheme [4]. We consider that the resulting cationic Au sites facilitate O–H and/or Si–H bond cleavage, leading to the formation of intermediates B and C.[13] The silyl intermediate is then attacked through an SN2-type mechanism by a nucleophile derived from alcohol, generating a silyl ether and intermediate D. Finally, reductive elimination from D occurs on the Au surface to regenerate A or B with expulsion of H2, thus completing the catalytic cycle. The possibility of a transesterification mechanism was investigated by using triphenylsilanol as a substrate, and no reaction was observed, indicating that this reaction does not proceed from a silanol generated by residual water in the solvent (SI; Scheme S1).

In conclusion, the Au:F-CAC catalyst exhibited a high catalytic activity for dehydrogenative coupling of silanes with alcohols.[14] [15] [16] [17] Through comprehensive optimization and evaluation, we have demonstrated the effectiveness of our catalytic system in facilitating the direct introduction of silicon functionalities into organic molecules under mild reaction conditions. It should be noted that Au:F-CAC overcomes the limitations of existing Au-based catalysts by eliminating the need for excess alcohol, making it practical and cost-effective for alcohol protection applications. The robustness and stability of the Au catalyst were confirmed through reusability tests, highlighting its potential for industrial-scale applications. Furthermore, the broad substrate scope, including various primary and secondary alcohols, underscores our catalytic system’s versatility and synthetic utility.


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Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

We thank H. Uyama (Osaka Univ.) for preparing the F-CAC, and B.S. thanks JSPS for a scholarship.

Supporting Information

    Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/a-2379-9191.
  • Supporting Information

  • References and Notes

  • 2 Greene TW, Wuts PG. M. Protective Groups in Organic Synthesis, 3rd ed. Wiley-Interscience; New York: 1991
    Search in Google Scholar
  • 6 White RJ, Luque R, Budarin VL, Clark JH, Macquarrie D. J. Chem. Soc. Rev. 2009; 38: 481
    CrossrefPubMedSearch in Google Scholar
  • 7 Zhang Q, Peng M, Gao Z, Guo W, Sun Z, Zhao Y, Zhou W, Wang M, Mei B, Du X.-L, Jiang Z, Sun W, Liu C, Zhu Y, Liu Y.-M, He H.-Y, Li ZH, Ma D, Cao Y. J. Am. Chem. Soc. 2023; 145: 4166
    CrossrefPubMedSearch in Google Scholar
  • 11 Gupta R, Paul S, Gupta R. J. Mol. Catal. 2007; 266: 50.0
    CrossrefSearch in Google Scholar
  • 13 da Silva AG. M, Kisukuri CM, Rodrigues TS, Candido EG, de Freitas IC, da Silva AH. M, Assaf JM, Oliveira DC, Andrade LH, Camargo PH. C. Appl. Catal., B 2016; 184: 35
    CrossrefSearch in Google Scholar
  • 14 Dehydrosilylation of Alcohols; General Procedure A reaction tube equipped with a magnetic stirrer bar was charged with Au:F-CAC (0.05 atom%), PhSiHMe2 (2.0 mmol), the appropriate alcohol 3 (0.5 mmol), and toluene (3 mL), and the mixture was stirred for the appropriate time under an ambient atmosphere. The catalyst was then removed by filtration and washed with Et2O (3 × 5 mL). The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography (silica gel) or preparative TLC to give the silyl ether 4.
  • 15 (Benzyloxy)(dimethyl)phenylsilane (4a) Purified by preparative TLC (hexane–EtOAc, 20:1) to give a colorless oil; yield: 82%. 1H NMR (CDCl3): δ = 7.62–7.60 (m, 2 H), 7.42–7.37 (m, 4 H), 7.32–7.29 (m, 3 H), 7.26–7.24 (m, 1 H), 4.70 (s, 2 H), 0.41 (s, 6 H). 13C NMR (CDCl3): δ = 140.7, 137.6, 133.5, 129.7, 128.3, 127.9, 127.1, 126.5, 65.0, –1.7.
  • 16 4-({[Dimethyl(phenyl)silyl]oxy}methyl)benzaldehyde (4f) Purified by column chromatography [silica gel, hexanes–EtOAc (9:1)] to give a colorless oil; yield: 48%. IR (diamond): 3069, 2957, 2846, 2733, 1696, 1607, 1578, 1427, 1303, 1251, 1206, 1164, 1116, 1082, 1015, 845, 826, 784, 728, 698, 648, 618, 470 cm–1. 1H NMR (CDCl3): δ = 9.99 (s, 1 H), 7.86–7.81 (AA′BB′, 2 H), 7.60 (dd, J = 7.9, 1.8 Hz, 2 H), 7.49–7.43 (AA′BB′, 2 H), 7.42–7.37 (m, 3 H), 4.77 (s, 2 H), 0.44 (s, 6 H). 13C NMR (CDCl3): δ = 192.1, 147.9, 137.1, 135.4, 133.5, 129.9, 129.8, 128.0, 126.6, 64.4, –1.8. HRMS (EI+): m/z [M+•] calcd for C16H18O2Si: 270.1076; found: 270.1082.
  • 17 4-({[Dimethyl(phenyl)silyl]oxy}methyl)aniline (4g) Purified by gel column chromatography [silica gel, hexanes–EtOAc (3:7)] to give a brownish oil; yield: 42%. IR (diamond): 3450, 3359, 3225, 3019, 2954, 2862, 1623, 1517, 1427, 1375, 1252, 1214, 1173, 1116, 1046, 844, 823, 782, 727, 697, 642, 536, 493, 470 cm–1. 1H NMR (CDCl3): δ = 7.59 (dd, J = 7.1, 2.1 Hz, 2 H), 7.43–7.34 (m, 3 H), 7.11–7.05 (AA′BB′, 2 H), 6.67–6.61 (AA′BB′, 2 H), 4.57 (s, 2 H), 3.63 (s, NH2), 0.38 (s, 6 H). 13C NMR (CDCl3): δ = 145.6, 137.8, 133.6, 130.8, 129.6, 128.4, 127.8, 115.0, 65.0, –1.6. HRMS (EI+) m/z [M+•] calcd for C15H19NOSi: 257.1230; found: 257.1236.

Corresponding Author

Hidehiro Sakurai
Division of Applied Chemistry, Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, Osaka 565-0871
Japan   

Publication History

Received: 20 June 2024

Accepted after revision: 05 August 2024

Accepted Manuscript online:
05 August 2024

Article published online:
02 September 2024

© 2024. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

  • References and Notes

  • 2 Greene TW, Wuts PG. M. Protective Groups in Organic Synthesis, 3rd ed. Wiley-Interscience; New York: 1991
    Search in Google Scholar
  • 6 White RJ, Luque R, Budarin VL, Clark JH, Macquarrie D. J. Chem. Soc. Rev. 2009; 38: 481
    CrossrefPubMedSearch in Google Scholar
  • 7 Zhang Q, Peng M, Gao Z, Guo W, Sun Z, Zhao Y, Zhou W, Wang M, Mei B, Du X.-L, Jiang Z, Sun W, Liu C, Zhu Y, Liu Y.-M, He H.-Y, Li ZH, Ma D, Cao Y. J. Am. Chem. Soc. 2023; 145: 4166
    CrossrefPubMedSearch in Google Scholar
  • 11 Gupta R, Paul S, Gupta R. J. Mol. Catal. 2007; 266: 50.0
    CrossrefSearch in Google Scholar
  • 13 da Silva AG. M, Kisukuri CM, Rodrigues TS, Candido EG, de Freitas IC, da Silva AH. M, Assaf JM, Oliveira DC, Andrade LH, Camargo PH. C. Appl. Catal., B 2016; 184: 35
    CrossrefSearch in Google Scholar
  • 14 Dehydrosilylation of Alcohols; General Procedure A reaction tube equipped with a magnetic stirrer bar was charged with Au:F-CAC (0.05 atom%), PhSiHMe2 (2.0 mmol), the appropriate alcohol 3 (0.5 mmol), and toluene (3 mL), and the mixture was stirred for the appropriate time under an ambient atmosphere. The catalyst was then removed by filtration and washed with Et2O (3 × 5 mL). The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography (silica gel) or preparative TLC to give the silyl ether 4.
  • 15 (Benzyloxy)(dimethyl)phenylsilane (4a) Purified by preparative TLC (hexane–EtOAc, 20:1) to give a colorless oil; yield: 82%. 1H NMR (CDCl3): δ = 7.62–7.60 (m, 2 H), 7.42–7.37 (m, 4 H), 7.32–7.29 (m, 3 H), 7.26–7.24 (m, 1 H), 4.70 (s, 2 H), 0.41 (s, 6 H). 13C NMR (CDCl3): δ = 140.7, 137.6, 133.5, 129.7, 128.3, 127.9, 127.1, 126.5, 65.0, –1.7.
  • 16 4-({[Dimethyl(phenyl)silyl]oxy}methyl)benzaldehyde (4f) Purified by column chromatography [silica gel, hexanes–EtOAc (9:1)] to give a colorless oil; yield: 48%. IR (diamond): 3069, 2957, 2846, 2733, 1696, 1607, 1578, 1427, 1303, 1251, 1206, 1164, 1116, 1082, 1015, 845, 826, 784, 728, 698, 648, 618, 470 cm–1. 1H NMR (CDCl3): δ = 9.99 (s, 1 H), 7.86–7.81 (AA′BB′, 2 H), 7.60 (dd, J = 7.9, 1.8 Hz, 2 H), 7.49–7.43 (AA′BB′, 2 H), 7.42–7.37 (m, 3 H), 4.77 (s, 2 H), 0.44 (s, 6 H). 13C NMR (CDCl3): δ = 192.1, 147.9, 137.1, 135.4, 133.5, 129.9, 129.8, 128.0, 126.6, 64.4, –1.8. HRMS (EI+): m/z [M+•] calcd for C16H18O2Si: 270.1076; found: 270.1082.
  • 17 4-({[Dimethyl(phenyl)silyl]oxy}methyl)aniline (4g) Purified by gel column chromatography [silica gel, hexanes–EtOAc (3:7)] to give a brownish oil; yield: 42%. IR (diamond): 3450, 3359, 3225, 3019, 2954, 2862, 1623, 1517, 1427, 1375, 1252, 1214, 1173, 1116, 1046, 844, 823, 782, 727, 697, 642, 536, 493, 470 cm–1. 1H NMR (CDCl3): δ = 7.59 (dd, J = 7.1, 2.1 Hz, 2 H), 7.43–7.34 (m, 3 H), 7.11–7.05 (AA′BB′, 2 H), 6.67–6.61 (AA′BB′, 2 H), 4.57 (s, 2 H), 3.63 (s, NH2), 0.38 (s, 6 H). 13C NMR (CDCl3): δ = 145.6, 137.8, 133.6, 130.8, 129.6, 128.4, 127.8, 115.0, 65.0, –1.6. HRMS (EI+) m/z [M+•] calcd for C15H19NOSi: 257.1230; found: 257.1236.

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Zoom Image
Scheme 1 Synthesis of silyl ethers from various silanes and alcohols catalyzed by Au:F-CAC. Reaction conditions: hydrosilane 1 (0.5 mmol), ROH (1 mmol), toluene (3.0 mL). The yields were determined by 1H NMR analysis. a At 50 °C for 24 h.
Zoom Image
Scheme 2 Catalytic performance of Au-F-CAC catalyst for dehydrogenative coupling of dimethyl(phenyl)silane with ethanol. (a) Recycling run experiment. (b) TEM images of the fresh and spent catalyst after the sixth run. The mean diameter and standard deviation are based on the average for 300 particles. (c) Hot-filtration experiment.
Zoom Image
Scheme 3 Substrate scope. The reactions were conducted on a 0.5 mmol scale in toluene (3 mL). The yields were determined by 1H NMR analysis. a Isolated yield. b Recovered yield of the starting material.
Zoom Image
Scheme 4 Possible reaction mechanism