NH4PF6 salt additive

N-Methyl-4,4 -bipyridme. We dissolved 1.5 g (10 mmol) of 4,4 -bipyridine in 150 mL of dichloromethane to which 5.0 g (35 mmol) of iodometh-ane (Fisher Scientific) was added. The solution was stirred for 2 h, after which a yellow precipitate was evident. Stirring for an additional 8 h at room temperature completed the precipitation, and the resulting yellow sohd was collected, washed with CH2CI2 and diethyl ether, and dried in air. H-NMR in de-DMSO resulted in four sets of doublets in the aromatic region. AT-Methyl-4,4 -bipyri-dine iodide was converted to the PFg salt by dissolving it in water and adding an aqueous solution of NH4PF6. The white sohd was filtered, washed with water and ether, and dried in vacuum. 

A solution of the macrocyclic polyether 37 (0.18 mmol), the salt 41 (0.07 mmol), and the dibromide 42 (0.07 mmol) in dry MeCN (3 mL) was stirred for 14 days at ambient temperature. The solvent was removed under reduced pressure and the resulting solid residue was purified by column chromatography [Si02, MeOH-2M NH4Cl-MeN02 (7 2 1)] to afford a red solid which was dissolved in H2O (60 mL). After the addition of a saturated aqueous solution of NH4PF6, the [2]catenane 43 (70%) precipitated out of solution. 

Pyridyl ureas obtained by this protocol were used in the next synthetic step, formation of pyridinium salts, a tripodal anion receptors 149 by Af-alkylation (Scheme 3.41). In aU cases the solid reactants consisting of a pyridine derivative 148 and bromomethylaled triethylbenzene derivative 147 were milled for 1 h. LAG technique was used in aU cases (acetonitrile), except for compound R=H (Br ) where a liquid was used as a reagent. The solid-state synthesis appears to be significantly cleaner than the solntion-state method with significantly less impurity. Addition of methanol, filtration, and precipitation of product with NH4PF6 were employed for purification. In most cases, the mechanochemical technique is able to... 

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