A Quantitative NMR Method for Silyllithium Analysis

Yingjian Bo; Scott McN. Sieburth

doi:10.1055/s-0036-1590902

Synlett, Inhaltsverzeichnis

Synlett 2017; 28(18): 2449-2452
DOI: 10.1055/s-0036-1590902

cluster

A Quantitative NMR Method for Silyllithium Analysis

Yingjian Bo

Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, Pennsylvania 19122, USA eMail: scott.sieburth@temple.edu

,

Scott McN. Sieburth*

Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, Pennsylvania 19122, USA eMail: scott.sieburth@temple.edu

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Abstract

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Published as part of the Cluster Silicon in Synthesis and Catalysis

Abstract

A rapid and extremely simple method for silyl anion analysis is presented. The progress of silyllithium reagent preparation can be determined by quenching an aliquot with neat chloro(trimethyl)silane, evaporation, dilution with CDCl₃, and direct proton NMR analysis. This procedure is fast, simple, and allows for identification and relative quantification of the starting reagent, intermediates, and the silyllithium product.

Key words

silicon - lithium - lithiation - organometallic reagents - halogens - hydrides

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Referenzen

References and Notes
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36 [Methyl(diphenyl)silyl]lithium from Chloro(methyl)diphenylsilane; Typical Analytical Procedure To a round-bottomed flask containing Li shot (41 mg, 5.9 mmol) under argon, cooled to 0 °C, was added TMSCl (0.1 mL, 0.79 mmol) in THF (2 mL), and the mixture was stirred for 30 min. The solution was removed by syringe, and the Li was washed with THF (3 × 1 mL). A solution of chloro(methyl)diphenylsilane (197 mg, 0.85 mmol) in THF (3.3 mL) was then added dropwise to the cleaned lithium shot. At intervals, aliquots (0.2 mL) of the solution were removed by syringe and added to a round-bottom flask containing chlorotrimethylsilane (0.1 mL, 0.79 mmol, ca. 16 equiv) at r.t. After mixing for 5 min, the mixture was concentrated in vacuo, taken up in CDCl₃ (1 mL), filtered through cotton and analyzed by ¹H NMR spectroscopy (see Ref. 44).
37 Reagents and solvents were purchased from Aldrich Chemical Company, Fisher Scientific, Alfa Aesar, or Acros Organics. Lithium (granular, 99% trace-metals basis) was purchased from Aldrich (catalogue number: 499811). Most silicon reagents were purchased from Gelest Inc. Reaction solvents were taken from a Grubbs-style Solvent Dispensing System purchased from Glass Contour or they were distilled as described in the literature.⁴⁵ Silica gel (60 Å, 170–400 mesh) or basic alumina (50–200 micron, activated) was used for flash column chromatography. Analytical TLC was performed on Analtech Uniplate Silica Gel GF (250 micron) precoated glass plates. Spots were detected by UV, iodine, or phosphomolybdic acid solution.
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42 1,1,1,2-Tetramethyl-2,2-diphenyldisilane (7) Granular Li shot [8 mg, 5.4 mmol, 6 equiv, in mineral oil (Aldrich)] was washed three times with hexane and transferred to a 25 mL round-bottomed flask fitted with a septum. The flask was evacuated and then filled with argon three times. THF (2 mL) was added, and the mixture was cooled to 0 °C. TMSCl (0.1 mL) was then added, the mixture was stirred for 30 min, and the solution was removed by syringe. The cleaned lithium shot was washed with THF (3 × 1 mL). A solution of methyl(diphenyl)silane (180 mg, 0.91 mmol) in THF (3 mL) was added, and the mixture was stirred at 0 °C for 8 h. To this mixture was added TMSCl (1.5 mL) and, after 5 min, the mixture was concentrated. Flash column chromatography (100:1 hexanes–EtOAc) gave a clear colorless oil; yield: 174 mg (71%).
43 1-[3-(Methoxymethoxy)propyl]-2,2,2-trimethyl-1,1-diphenyldisilane (11) Granular lithium shot [87 mg, 12.5 mmol, 14 equiv, in mineral oil (Aldrich)] was washed three times with hexane then transferred to a 25 mL round-bottomed flask fitted with a septum. The flask was evacuated and then filled with argon three times. THF (6 mL) was added, and the mixture cooled to 0 °C. TMSCl (0.3 mL) was then added, the mixture was stirred for 30 min, and the solution was removed by syringe. The cleaned lithium shot was washed with THF (3 × 3 mL). A solution of [3-(methoxymethoxy)propyl](diphenyl)silane (10; 259 mg, 0.90 mmol) in THF (3.0 mL) was added, and the mixture was stirred for 9 h. The solution was decanted and washed with H₂O. The aqueous phase was extracted with Et₂O (3 × 10 mL), and the combined organics were dried (Na₂SO₄, filtered, and concentrated. Purification by flash chromatography (gradient 100:1 to 10:1 hexanes–EtOAc) gave a clear, colorless oil; yield: 214 mg (60%); R_f = 0.53 (4:1 hexanes–EtOAc). IR (neat): 3067, 2947, 2086, 1954, 1428 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.45–7.50 (m, 4 H), 7.32–7.37 (m, 6 H), 4.60 (s, 2 H), 3.50 (t, J = 6.6 Hz, 2 H), 3.34 (s, 3 H), 1.64–1.73 (m, 2 H), 1.17–1.24 (m, 2 H), 0.17 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 136.3, 135.4, 128.9, 128.0, 96.5, 70.7, 55.3, 25.1, 9.1, –1.1. HRMS: m/z [M + NH₄]⁺ calcd for C₂₀H₃₄NO₂Si₂: 376.2123; found: 376.2123.
44 Okinoshima H. Weber WP. J. Organomet. Chem. 1978; 149: 279
45 Armarego WL. Chai CL. L. Purification of Laboratory Chemicals. 6th ed. Butterworth-Heinemann; Oxford: 2009

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