Question

Why is NH4BF4 and not NaBF4 a preferred reagent for anion exchange with a transitionmetal chloride? Please Explain.

Answer 1

We perform reactions under aprotic polar solvents like THF, acetone, dioxane,CHCl₃, CH₂Cl₂ etc. If your complex is soluble in relatively nonpolar solvents such as acetone or dichloromethane, you can often use sodium tetrafluoborate for a metathesis reaction, as sodium chloride (from NaBF₄ + Transition metal chloride) isn't very soluble in such solvents.

Anion exchange resins are used for replacing anions of some transition metal salts or complexes. However, in case of such sensitive complexes, decomposition is expected by the required strong acids. In some cases portion of the transition metal (complex) can stick on the resin.

NH₄BF₄ is known to be a PTC (Phase Transfer Catalyst), in general quaternary ammonium salts are used as PTC reagents as NaBF₄ will not. PTC will shuttle between aqueous and organic phases thereby increase and enhances the reactions.

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