Schlenk filtration

One drawback of this methodology was the sensitivity of the product silacyclopropane to the reaction conditions, which prevented isolation of the product. Woerpel and coworkers were able to overcome this debilitating limitation by changing the anion of silver catalyst to trifluoroacetate and reducing the catalyst load to <1 mol% (Scheme 7.11).74 The combination of these two modifications enabled the isolation of the silacyclopropane product after careful Schlenk filtration. Isolation of the silacyclopropane allowed for either zinc-64,75 or copper-mediated functionalization of the silacyclopropane to produce 1,2- or 1,3-disubstituted oxasilacyclopentanes.63... 

Technologies. A glove bag or Schlenk filtration is also suitable to effect filtration under an inert atmosphere when the humidity is high. 

A mixture of l,4-dibromo-2,5-bis(3-sulfonatopropoxy)benzene 61 (0.78 g, 1.39 mmol), 60 (0.23 g, 1.39 mmol), Na2C03 (0.99 g) in doubly distilled water (47 mL), and DMF (20 mL) was heated at 85°C until the solids were completely dissolved. The resulting solution was cannulated to a 200-mL Schlenk flask with tris[(sulfonatophenyl)phosphine]palladium(0) (0.045 g) and the mixture was stined at 85°C for 10 h. The reaction mixture was concentrated to 25 mL by boiling and filtered. The filtrate was added dropwise to cold acetone (250 mL) to precipitate out the polymer. The polymer was collected by filtration, redissolved in a minimum of hot water, and reprecipitated by cooling. After repeating this procedure twice, the polymer was redissolved in distilled water and dialyzed for 72 h in 3500 gmol 1 cutoff membrane. After drying under vacuum, polymer 63 was obtained in 64% (0.42 g). 

Ni(cod)2 (1.59g, 6.00mmol), 1,5-cyclooctadiene (531 mg, 5.00mmol), and 2,2 -bipyridyl (937 mg, 6.00 mmol) were dissolved in DMF (20 ml), in a Schlenk tube under argon. To the solution was added 2,5-dibromothiophene (1.21 g, 5.00 mmol) at room temperature. The reaction mixture was stirred at 60°C for 16 h to yield a reddish-brown precipitate. The reaction mixture was then poured into HCl-acidic methanol, and the precipitate of PT was separated by filtration. The precipitate was washed with HCl-acidic methanol, ethanol, hot toluene, a hot aqueous solution of EDTA (pH = 3.80), a hot aqueous solution of EDTA (pH = 9), and distilled water in this order and dried under vacuum to yield a reddish-brown powder of PT. 

Care must be taken to avoid loss of product that is easily taken up in the syringe. The checkers found it more convenient to perform the reaction in a tared, round-bottomed Schlenk flask. Solvent was then removed from the solid dicyclohexylborane by filtration using a positive nitrogen flow. 

The submitters found that the yield of 3 can be increased to 58% if crude 2, obtained in step B by rotary evaporation of the solvent (rather than filtration through a Schlenk tube followed by washing with ether), is taken directly into hot glacial acetic acid h step C. This procedure minimizes exposure of hygroscopic 2 to moisture. These changes were not checked. 

In a 100-mL Schlenk tube equipped with a magnetic stirrer, 10 equiv of 2-methylpropanethiol (3 mL, 33 mmol) are added at room temperature to the [NH2Me2] [Rh(CO)2Cl2] solution prepared as described in Section 27.A. After 30 min, the solution turns from light orange to brown, and an IR spectrum of the solution shows four vqo bands at 2062, 2050, 1999, and 1984 cm characteristic of Rh(p-S Bu)(CO)2 2- Then, a 1.5 molar equivalent of triphenylphos-phine per rhodium is added (1.5 g, 5.7 mmol). An immediate CO evolution is observed, and the reaction is completed within 5 min. The IR spectrum of the solution shows a single vqo band at 1977 cm Precipitation of the complex is achieved by adding slowly 50 mL of cold (20°C) distilled water. The product is collected by filtration on a Buchner funnel, washed with 150 mL of water, then dried under vacuum. Yield 1.51 g (82%). 

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