Tetrakis 4-methylpyridine boron III Cation Salts

A hexafluorophosphate salt is prepared from the crude product by dissolving 3.68 g. in 20 ml. of water acidified with a few drops of concentrated HC1 and mixing the filtered solution with 10 ml. of 4 M aqueous NH4PF6. The precipitate is washed with 20 ml. of water and recrystallized from a minimum amount of acidified boiling water (65 ml.) to yield dry hexafluorophosphate salt in 65% yield. This salt melts with decomposition at 220-225°C. Anal. C, 35.1 H, 3.6 N, 6.7%. Calcd. C, 35.2 H, 3.5 N, 6.8%. 

The boron cation is stable in acidic aqueous solution, somewhat less stable in water, but decomposes in alkaline solution. The proton magnetic resonance spectrum in D20 relative to external TMS shows three bands —8.60 (broad), - —8.19 (doublet, J = 7 Hz.), and —2.85 (singlet), with the expected intensities corresponding to the a- and /6-ring hydrogen atoms and the methyl group, respectively. The bromide is very soluble in cold water and hot ethanol but insoluble in acetone. The hexafluorophosphate is slightly soluble in cold water but very insoluble in acetone. 

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