Metal-Free Synthesis of 1,3-Disiloxanediols and Aryl Siloxanols

Abstract

The first example of metal-free oxidative hydrolysis of hydrido-siloxanes is reported. Both base-catalyzed and organocatalytic hydrolysis methods are demonstrated to transform 1,3-dihydrido-disiloxanes into 1,3-disiloxanediols. The first example of a chemoselective silane hydrolysis is demonstrated.

Introduction

Siloxanes are an important class of compounds found in a vast number of products that enable our modern lifestyles.¹ Silanols and siloxanols have broad utility as reagents,^2,3 coupling partners,⁴⁻⁶ ligands,⁷⁻¹¹ directing groups,¹² and hydrogen-bonding and anion-binding catalysts.¹³⁻¹⁵ Various methods have been reported for the direct synthesis of silanols from hydrosilanes using a variety of transition-metal compounds including Ru, Ir, Cr, and Rh and various nanoparticles;¹⁶⁻¹⁸ however, these metal reagents can be expensive and/or difficult to access. These methods represent the hydrolysis of the Si–H bond to a Si–O bond but are still often referred to as oxidation in analogy to organometallic chemistry and/or the oxidative reagents employed (Figure 1). Several methods for silane hydrolysis have also been reported using stoichiometric oxidants such as dioxiranes.¹⁹ Recently, an organocatalytic hydrolysis of non-oxygenated silanes with 2,2,2-trifluoroacetophenone (BzCF₃) was reported by Kokotos and co-workers, which relies on the in situ formation of a highly active oxidizing species under basic and biphasic conditions.^17,20−22 Arzumanyan et al. has investigated the hydrolysis of primarily alkyl siloxanes; however, a larger investigation of aryl siloxanes has not been demonstrated.¹⁷ Herein, we present the first examples of organocatalytic and base-catalyzed methods for conversion of hydrido-siloxanes to the corresponding 1,3-disiloxanediols.

Figure 1.

Hydrolysis methods converting hydrido-siloxanes to siloxanols.

The ability to produce silanols from hydrido-silanes under “metal-free” oxidative hydrolysis conditions is of particular interest because hydrosilanes are easy to handle and pose higher stability toward moisture compared to silyl chlorides; hydrosilanes produce hydrogen gas upon hydrolysis as opposed to chlorosilanes, which produce stoichiometric quantities of hydrochloric acid in their conversion to silanols. Notably, the production of hydrogen gas as a consequence of silane hydrolysis has been described to have application as a potential method of hydrogen storage.²³

Our investigation of the hydrolysis of hydrido-siloxanes began with a screen of hydrolysis methods for 1,3-dihydro-disiloxanes (Table 1). 1,1-Diisopropyl-3,3-di(naphthalene-1-yl)disiloxane (1a) was selected as a model compound because 1a contains both aryl and alkyl hydrido-silanes on the siloxane backbone. First, we evaluated the dichloro(p-cymene)ruthenium(II) dimer and 1,5-cycloocatadiene-iridium(I) chloride dimer catalysts (in the presence of water) because they are both known to be highly active catalysts for the hydrolysis of non-oxygenated hydrosilanes.^24,25 Neither transition-metal complex afforded the desired disiloxanediol 2a (Table 1, entries 1 and 2): the ruthenium catalyst resulted in a complex mixture, and the iridium catalyst resulted in the recovery of the starting material. In comparison, Pd/C is effective as a catalyst for the hydrolysis of 1,3-dihydro-disiloxane 1a, affording disiloxanediol 2a in 82% (Table 1, entry 3).¹³

Table 1. Screening of Metal Catalysts and Organocatalysts for Hydrolysis of 1,3-Dihydrido-disiloxane 1a.

entry	solvent	catalyst	mol (%)	time (h)	yield of 2a (%)a
1b	MeCN	[Ru(Cymene)Cl2]2	3	4	<5
2b	MeCN	[Ir(COD)Cl]2	3	4	<5
3b	THF	Pd/C	10	4	82
4c	THF	BzCF3; pH 11.0	10	2	quant.
5c	THF	BzCF3; pH 11.0	1	2	quant.
6c	THF	BzCF3; pH 11.0	0.1	3	quant.
7c	THF	BzCF3; pH 11.0	0.01	4	quant.
8c	THF	none; pH 11.0	0	4	<5d

^aIsolated yield.

^bReaction conditions include 5 equiv of H₂O.

^cReaction conditions include 4 equiv of H₂O₂ and MeCN.

^dChemoselective hydrolysis of the Np₂SiH side occurs; partially hydrolyzed siloxanol 3a was observed as the major product.

We then evaluated BzCF₃ as an organocatalyst for the oxidative hydrolysis of disiloxane 1a.²⁰ Using BzCF₃ under basic conditions (pH 11.0) in the presence of hydrogen peroxide afforded a quantitative yield of 2a with 10 mol % catalyst loading in 2 h (Table 1, entry 4). With these results, we lowered the catalyst loadings resulting in a final catalyst loading of 0.01 mol %, with a reaction time of 4 h (Table 1, entries 5–7). The BzCF₃ conditions yielded disiloxanediol 2a as a pure product that did not require any further purification after workup. When BzCF₃ was omitted from the reaction (Table 1, entry 8), disiloxanediol 2a was not observed. Using basic conditions with peroxide afforded only the selective hydrolysis of the naphthyl-bearing hydrido-silane with limited conversion of the alkyl hydrido-silane bond (i.e., affording siloxanol 3a as the major product).

With an optimized organocatalytic hydrolysis method, we then explored the substrate scope using a series of dihydrosiloxanes (Figure 2). Disiloxanediols 2a–2e are obtained in high yield, typically without further purification required. Notably, 2e was produced in high yield using the organocatalytic hydrolysis but was not produced using the other hydrolysis methods in Table 1. For some substrates (e.g., 1d and 1e), formation of ∼5% silanediol is also observed, corresponding to the cleavage of the disiloxane bond during activation of the silane. As a control experiment, resubjecting isolated disiloxanediol 2d to reaction conditions did not yield any silanediol, suggesting that the formation of the silanediol does not occur as a result of the hydrolysis of the siloxane bond under basic conditions. Exposure of phenyl-containing 1f and 1g did not afford any desired disiloxanediol, and a complex mixture was observed using ¹H NMR analysis of the crude reaction mixture. These data highlight a striking difference in the ability to access siloxanols bearing phenyl rings versus naphthyl rings using this organocatalytic method. While it is unsurprising that the silane bearing the phenyl ring is highly susceptible to Tamao–Fleming oxidation, the difference in reactivity between phenyl and naphthyl was more than anticipated. Being able to tame this “overoxidation” would allow us to access a larger variety of disiloxanediols using greener methods.

Figure 2.

Scope of an organocatalytic method for the synthesis of 1,3-disiloxanediols.

Because a control experiment had indicated that basic conditions excluding the BzCF₃ catalyst still afforded the selective hydrolysis of the naphthyl hydrido-silane portion of 1a (Table1, entry 8), we evaluated a base-catalyzed hydrolysis for the conversion of tetra-aryl 1,3-dihydrido-disiloxanes such as 1d to 1,3-disiloxanediol 2d (Table 2).²⁶ We hypothesized that the optimal selection of base could impart control and limit the Tamao–Fleming oxidation of C–Si bonds in 1,3-dihydrido-disiloxanes tetra-aryl disiloxanes.

Table 2. Screening of Hydrolysis Conditions for Disiloxane 1d.

entry	base	mol (%)	yield of 2d (%)a
1	none	0	recovered SM
2	KOH	100	complex mixture
3	NaOH	100	complex mixture
4	Et3N	100	75 (+ 25% silanediol)
5	Na2CO3	100	0b
6	K2CO3	100	70 (+ 30% silanediol)
7	Cs2CO3	100	87
8	Cs2CO3	50	95
9	Cs2CO3	10	95
10	Cs2CO3	5	>95

^aAll yields determined using ¹H NMR spectroscopy with PhTMS as an internal standard.

^b1,1,3,3-tetra(naphthalene-1-yl)disiloxane-1-ol) is the major product; di(naphthalene-1-yl)silanediol was also observed.

First, the necessity of base was confirmed. When 1d was subjected to three equivalents of hydrogen peroxide in the absence of base, only the starting material was recovered (Table 2, entry 1). Metal hydroxides generated a complex mixture based on ¹H NMR analysis (Table 2, entries 2 and 3), which is surprising, considering that the ability of these metal hydroxides to produce silyl ethers and silyl alkynes has been recently reported.^27,28 Using an organic base such as triethylamine (TEA) not only afforded promising results but also afforded silanediol resulting in a lower yield of 2d (Table 2, entry 4). When sodium carbonate was employed, the product 2d was not observed. Potassium carbonate generated the desired 1,3-disiloxanediol 2d, but the corresponding silanediol was also observed (Table 2, entry 6). Finally, cesium carbonate was investigated, which afforded the highest selectivity for the synthesis of 1,3-disiloxanediol 2d, with 5 mol % affording the highest yield and cleanest reaction (Table 2, entries 7–10).²⁹

Cesium carbonate was compared as a catalyst for the hydrolysis of three tetra-aryl 1,3-dihydro-disiloxanes (Figure 3). Catalytic cesium carbonate conditions generate disiloxanediols 2d and 2e with high efficiency. The cesium conditions were still not viable for phenyl-containing substrates; the reaction of 1f in these conditions led to the traditional Tamao–Fleming oxidation products (i.e., phenol).³⁰

Figure 3.

Base-mediated hydrolysis of tetra-aryl 1,3-dihydrido-disiloxanes.

These results led us to posit that a chemoselective hydrolysis of aryl silanes could be performed in the presence of alkyl silanes (Figure 4). The cesium-catalyzed hydrolysis of 1a and 1b afforded a mixture of products with low selectivity; however, using one equivalent of triethylamine promoted a chemoselective hydrolysis for the hydrosilane bearing the naphthyl rings to afford siloxanol 3a and 3b. This represents the first report of a chemoselective silane hydrolysis.

Figure 4.

Chemoselective hydrolysis of 1,3-dihydrido-disiloxanes.

Because the Tamao–Fleming oxidation was observed as a persistent issue in the synthesis of phenyl-containing siloxanols, we also synthesized a series of tertiary and secondary silanes to determine what electronic and steric differences between the phenyl and naphthyl rings would suppress this oxidation event (see Supporting Information, Figure S1). We determined that the presence of ortho substitution on at least one aryl ring can suppress the Tamao–Fleming oxidation pathway; however, this suppressive effect can be diminished by the presence of electron-withdrawing groups. These data provide additional mechanistic insight into the “fluoride-free” Tamao–Fleming oxidation (see the Supporting Information).

Conclusions

In conclusion, we have demonstrated the first organocatalytic hydrolysis of 1,3-dihydrido-disiloxanes to 1,3-disiloxanediols utilizing low catalyst loadings (0.01 mol %). We also optimized a base-catalyzed method for the hydrolysis of tetra-aryl disiloxanes using cesium carbonate. Observations and mechanistic insight into the competing oxidation and hydrolysis pathways led to the development of the first chemoselective hydrolysis of unsymmetrical disiloxanes. These results show that the differential reactivity of aryl and alkyl silanes within 1,3-dihydro-disiloxanes can be utilized for selective synthesis.

Experimental Section

General Information

All nuclear magnetic resonance (NMR) spectra were obtained on Varian Inova 400 (400 MHz for ¹H; 100 MHz for ¹³C) and/or Varian VNMRS 600 (600 MHz for ¹H; 150 MHz for ¹³C; 119 MHz for ²⁹Si) at room temperature unless noted otherwise. Chemical shifts were reported in parts per million (δ scale) and referenced according to the following standards: tetramethylsilane internal standard for ¹H signals in chloroform, chloroform residual solvent (δ 7.26) for ¹H signals in deuterated chloroform, chloroform (middle peak is δ 77.1) for ¹³C signals, and tetramethylsilane external standard in CDCl₃ for ²⁹Si signals. Coupling constants were reported in hertz (Hz), and multiplicities were reported as follows: singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m), and broadened (b). Compounds were analyzed by HRMS using electrospray in the negative ion mode at >60,000 resolution and using a 5 kV spray voltage, with a curtain plate temperature of 275 °C and a sheath gas setting of 15. These settings result in mass accuracies of <5 ppm. HRMS samples were analyzed via flow injection analysis by injecting 5 μL of samples into a stream of 50% acetonitrile and 50% aqueous solution of 0.1% formic acid, flowing at 200 μL/min.

Commercially available reagents were purchased and used without further purification unless otherwise indicated. Dichloromethane (DCM), hexane, ethyl acetate (EtOAc), and diethyl ether (Et₂O) were obtained from EMD Chemicals. Anhydrous magnesium sulfate and Pd/C (10 wt %) were obtained from Sigma-Aldrich. 1-Bromo-4-fluoronaphthalene and 2-bromotoluene were purchased from Oakwood Chemical. Phenyldichlorosilane, diphenylsilane, triphenylsilane, and triisopropylsilane were obtained from Gelest. [Ru(p-Cymene)Cl₂]₂ and [Ir(COD)Cl]₂ were purchased from Strem. Dimethylchlorosilane, magnesium turnings, 1-bromonaphthalene, trichloroisocyanuric acid (TCCA), and lithium aluminum hydride (4.0 M in Et₂O) were purchased from Acros. Diphenylmethylsilane was purchased from Alfa Aesar. 1,3-Dihydrodisiloxanes (1a–-1f) were synthesized according to literature procedures starting from the addition of the corresponding aryl Grignard reagent to trichlorosilane.¹³

Reactions were analyzed by thin-layer chromatography (TLC) on EMD glass plates that were precoated with silica gel 60 F254, and the reactions were purified by column chromatography using Acros silica gel 60 Å (0.035–0.070 mm). The following abbreviations are used throughout: lithium aluminum hydride (LAH), ethyl acetate (EtOAc), dichloromethane (DCM), acetonitrile (MeCN), and 2,2,2-trifluoroacetophenone (BzCF₃).

Synthesis of 1,1,3,3-Tetrakis(4-fluoronaphthalen-1-yl)disiloxane (1e)

Bis(4-fluoronaphthalen-1-yl)silanol and chlorobis(4-fluoronaphthalen-1-yl)silane were synthesized according to the literature.¹³ Bis(4-fluoronaphthalen-1-yl)silanol (0.367 g, 1.09 mmol, 1.0 equiv) was dissolved in DCM (10 mL) in a 100 mL flask and purged with reaction. TEA (0.23 mL, 1.65 mmol, 1.5 equiv) was then added, followed by a solution of chlorobis(4-fluoronaphthalen-1-yl)silane (0.387 g, 1.09 mmol, 1.0 equiv) in DCM (10 mL). The reaction was allowed to stir for 1 h and was then quenched with saturated aqueous NaHCO₃ (5 mL). The organic layer was separated, the aqueous layer was washed with DCM (3 × 5 mL), and the organic layers were combined and washed with brine (10 mL), dried over anhydrous MgSO₄, filtered, and then concentrated in vacuo. The crude product was purified via column chromatography (10:1 hexanes/EtOAc) to yield 1e as a white solid. Yield: 0.39 g (54%); ¹H NMR (CDCl₃, 600 MHz, δ): 8.08 (d, J = 8.4 Hz, 2H), 7.93 (d, J = 8.5 Hz, 2H), 7.64 (dd, J = 7.6, 6.0 Hz, 2H), 7.44 (t, J = 7.6 Hz, 2H), 7.18 (t, J = 7.6 Hz, 2H), 6.98 (dd, J = 10.5, 7.6 Hz, 2H), 6.25 (s, 1H); ¹³C NMR (CDCl₃, 150 MHz, δ): 160.9 (d, J¹_CF = 256.6 Hz), 138.2 (d, J⁴_CF = 4.6 Hz), 135.6 (d, J³_CF = 8.7 Hz), 128.1 (d, J³_CF = 4.7 Hz), 127.2 (d, J⁴_CF = 2.9 Hz), 127.1, 126.0 (d, J⁴_CF = 1.4 Hz), 123.6 (d, J²_CF = 15.2 Hz), 121.1 (d, J³_CF = 6.1 Hz), 108.9 (d, J²_CF = 18.8 Hz); ¹⁹F NMR (CDCl₃, 282 MHz, δ): −119.5 (m); ²⁹Si NMR (CDCl₃, 119 MHz, δ): −19.8.

Synthesis of 1,1,3,3-Tetraphenyldisiloxane (1f)

An oven-dried 50 mL flask was charged with TCCA (210 mg, 0.90 mmol, 0.33 equiv) and placed under Ar. A solution of diphenylsilane (0.5 mL, 2.7 mmol, 1.0 equiv) in THF (10 mL) was added in one portion, and the reaction was stirred for 1 h. A solution of THF (1 mL), TEA (0.19 mL, 1.35 mmol, 0.5 equiv), and H₂O (25 μL, 1.35 mmol, 0.5 equiv) was added dropwise. The solution was stirred for 1 h. The reaction was then quenched with saturated aqueous NaHCO₃ (5 mL). The organic layer was separated, the aqueous layer was washed with THF (3 × 5 mL), and the organic layers were combined and washed with brine (10 mL), dried over anhydrous MgSO₄, filtered, and then concentrated in vacuo. The crude product was then dissolved in hexanes and passed through a silica plug to yield 1f as a clear oil. Yield: 0.32 g (62%); ¹H NMR (CDCl₃, 600 MHz, δ): 7.60–7.54 (m, 8H), 7.45–7.39 (m, 4H), 7.35 (t, J = 7.3 Hz, 8H), 5.61 (s, 2H). Matched literature spectra.³¹

General Procedure for the Hydrolysis of 1,3-Dihydrido-disiloxanes (Method A)

1,3-Dihydrido-disiloxane (0.25 mmol) was dissolved in THF (0.25 mL) in a 4 mL vial and stirred at room temperature for 5 min. BzCF₃ (3.5 μL), buffer (0.25 mL, 0.6 M K₂CO₃, 4 × 10^–5 M EDTA tetrasodium salt), MeCN (0.11 mL), and 30% aqueous H₂O₂ (0.2 mL) were added consecutively. The reaction was allowed to stir for 4 h. The reaction was then poured into a 30 mL separatory funnel and diluted with DCM (5 mL). The layers were separated, and the organic layer was dried over anhydrous Na₂SO₄, filtered, and then concentrated in vacuo. The product was then purified using flash column chromatography (15% EtOAc in hexanes) to afford the desired product.

General Procedure for the Hydrolysis of 1,3-Dihydrido-disiloxanes (Method B)

1,3-Dihydrido-disiloxane (0.25 mmol) was dissolved in THF (1 mL) in a 4 mL vial and stirred at room temperature for 5 min. CsCO₃ and 30% aqueous H₂O₂ (0.15 mL) were added consecutively. The reaction was allowed to stir for 2 h. The reaction was then poured into a 30 mL separatory funnel and diluted with DCM (5 mL) and H₂O (5 mL). The layers were separated, and the organic layer was dried over anhydrous Na₂SO₄, filtered, and then concentrated in vacuo. The product was then purified using flash column chromatography (15% EtOAc in hexanes) to afford the desired product.

1,1-Diisopropyl-3,3-di(naphthalen-1-yl)disiloxane-1,3-diol (2a)

Synthesized using Method A. Yield: 0.11 g (quant.); ¹H NMR (CDCl₃, 600 MHz, δ): 8.29 (d, J = 8.4 Hz, 2H), 8.04 (dd, J = 6.8, 1.2 Hz, 2H), 7.91 (d, J = 8.2 Hz, 2H), 7.82 (d, J = 8.0 Hz, 2H), 7.46 (dd, J = 8.2, 6.9 Hz, 2H), 7.43–7.39 (m, 3H), 7.35 (ddd, J = 8.3, 6.9, 1.3 Hz, 3H), 3.58 (s, 1H), 2.46 (s, 1H), 0.90 (s, 14H). Matched literature spectra.¹⁴

1,1-Bis(4-fluoronaphthalen-1-yl)-3,3-diisopropyldisiloxane-1,3-diol (2b)

Synthesized using Method A. Yield: 0.112 g (93%); ¹H NMR (CDCl₃, 600 MHz, δ): 8.26 (d, J = 8.5 Hz, 2H), 8.12 (d, J = 8.0 Hz, 2H), 7.96 (dd, J = 7.6, 6.2 Hz, 2H), 7.47 (ddd, J = 8.2, 6.9, 1.0 Hz, 2H), 7.40 (ddd, J = 8.3, 6.9, 1.3 Hz, 2H), 7.13 (dd, J = 10.5, 7.7 Hz, 2H), 3.76 (s, 1H), 2.52 (s, 1H), 0.89 (s, 14H). Matched literature spectra.¹³

1,1,3,3-Tetraisopropyldisiloxane-1,3-diol (2c)

Synthesized using Method A. Yield: 0.066 g (95%); ¹H NMR (CDCl₃, 600 MHz, δ): 2.78 (s, 2H), 1.03 (d, J = 7.2 Hz, 24H), 0.94 (dq, J = 14.9, 7.5, 7.1 Hz, 4H). Matched literature spectra.³²

1,1,3,3-Tetra(naphthalen-1-yl)disiloxane-1,3-diol (2d)

Synthesized using Method A. Yield: 0.15 g (71%); ¹H NMR (CDCl₃, 600 MHz, δ): 8.19 (d, J = 8.4 Hz, 4H), 7.91 (dd, J = 6.8, 1.2 Hz, 4H), 7.86 (d, J = 8.2 Hz, 4H), 7.79 (d, J = 8.1 Hz, 4H), 7.35 (ddd, J = 8.0, 6.9, 1.0 Hz, 4H), 7.32 (dd, J = 8.2, 6.9 Hz, 4H), 7.11 (ddd, J = 8.2, 6.9, 1.2 Hz, 4H), 3.16 (s, 2H). Matched literature spectra.¹³

1,1,3,3-Tetra(4-fluoronaphthalen-1-yl)disiloxane-1,3-diol (2e)

Synthesized using Method A. Yield: 0.15 g (89%); ¹H NMR (CDCl₃, 600 MHz, δ): 8.08 (d, J = 8.5 Hz, 4H), 8.05 (d, J = 8.3 Hz, 4H), 7.79 (dd, J = 7.6, 6.1 Hz, 4H), 7.40 (dd, J = 7.6 Hz, 4H), 7.14 (ddd, J = 8.3, 6.9, 1.2 Hz, 4H), 6.95 (dd, J = 10.5, 7.7 Hz, 4H), 3.20 (s, 2H); ¹³C NMR (CDCl₃, 150 MHz, δ): 161.1 (d, J¹_CF = 256.6 Hz), 138.3 (d, J³_CF = 4.5 Hz), 135.9 (d, J³_CF = 8.7 Hz), 128.5 (d, J³_CF = 4.7 Hz), 128.1 (d, J⁴_CF = 2.8 Hz), 127.2, 126.1 (d, J⁴_CF = 1.6 Hz), 123.8 (d, J²_CF = 15.2 Hz), 121.2 (d, J⁴_CF = 6.3 Hz), 108.91 (d, J²_CF = 18.8 Hz); HRMS-ESI (m/z): [M – H]⁻ calcd for C₄₀H₂₅Si2O₃F₄, 685.1284; found, 685.1284.

General Procedure for Chemoselective Hydrolysis of Unsymmetrical 1,3-Dihydrido-disiloxanes (Method C)

1,3-Dihydrido-disiloxane (0.25 mmol) was added to a 4 mL vial and dissolved in THF (1 mL). Triethylamine (35 μL) was then added to the vial followed by H₂O₂ (38 μL). The vial was vented to the atmosphere with a needle as a large amount of gas is quickly generated. The reaction is then allowed to stir at room temperature for 30 min. The contents of the vial are then diluted with DCM (3 mL) and poured over Na₂SO₄. The product is then isolated using flash column chromatography (19:1 hexanes/EtOAc) over silica gel.

3,3-Diisopropyl-1,1-di(naphthalen-1-yl)disiloxane-1-ol (3a)

Prepared from 1a using Method C. Yield: 0.09 g (89%); ¹H NMR (toluene-d₈, 600 MHz, δ): 8.26 (d, J = 8.5 Hz, 2H), 8.14 (d, J = 8.3 Hz, 2H), 7.96–7.90 (m, 2H), 7.50 (t, J = 7.5 Hz, 2H), 7.47–7.41 (m, 2H), 7.15 (dd, J = 10.5, 7.7 Hz, 2H), 4.36 (s, 1H), 3.01 (s, 1H), 0.92 (s, 14H); ¹³C NMR (toluene-d₈, 150 MHz, δ): 138.4, 138.4, 136.5, 135.5, 134.9, 132.2, 130.3, 130.0, 127.2, 126.7, 18.3 (d, J = 5.3 Hz), 14.4; HRMS-ESI (m/z): [M – H]⁻ calcd for C₂₆H₃₀Si₂O₂, 429.1712; found, 429.1706.

1,1-Bis(4-fluoronaphthalen-1-yl)-3,3-diisopropyldisiloxan-1-ol (3b)

Prepared from 1a using Method C. Yield: 0.11 g (91%); ¹H NMR (CDCl₃, 600 MHz, δ): 8.26 (d, J = 8.5 Hz, 2H), 8.14 (d, J = 8.3 Hz, 2H), 7.96–7.90 (m, 2H), 7.50 (t, J = 7.5 Hz, 2H), 7.47–7.41 (m, 2H), 7.15 (dd, J = 10.5, 7.7 Hz, 2H), 4.36 (s, 1H), 3.01 (s, 1H), 0.92 (s, 14H); ¹³C NMR (CDCl₃, 150 MHz, δ): 160.9 (d, J¹_CF = 256.0 Hz), 138.4 (d, J⁴_CF = 4.4 Hz), 135.5 (d, J³_CF = 8.5 Hz), 129.3 (d, J³_CF = 4.8 Hz), 128.3 (d, J⁴_CF = 3.0 Hz), 127.1, 126.0 (d, J⁴_CF = 1.9 Hz), 123.8 (d, J²_CF = 15.0 Hz), 121.1 (d, J³_CF = 6.3 Hz), 108.9 (d, J²_CF = 18.6 Hz), 17.0 (d, J = 4.3 Hz), 13.0; HRMS-ESI (m/z): [M – H]⁻ calcd for C₂₆H₂₈Si₂O₂F₂, 465.1523; found, 465.1525.

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b00121.

• Synthesis of silanes for mechanistic investigation, structural investigation of silane hydrolysis mechanism, proposed mechanism for base-catalyzed silane hydrolysis, and NMR spectra (PDF)

The authors declare no competing financial interest.