Organomagnesium fluorides

The order of reactivity of halides with magnesium is RI > RBr > RC1 (very few organomagnesium fluorides have been prepared), i) Aryl Grignard reagents are more easily prepared from aryl bromides and aryl iodides than from aryl chlorides, which react very sluggishly. 

Chlorides often react sluggishly and, in addition, may give an unwelcome precipitate of magnesium chloride, which, unlike magnesium bromide and iodide, is only very slightly soluble in ether. Organomagnesium fluorides eluded preparation until quite recently. 

Fluorobenzene reacts only with highly reactive Mg metal . Although other methods for organomagnesium fluorides are available (see 5.4.2.5), they are of limited practical value. 

It has been observed that organomagnesium fluorides (88) react faster with benzophenone and give a higher ratio of addition to reduction products than the corresponding bromo reagents. Both aspects attest to a harder nature of RMgF as would be expected. 

Carbanions in the form of organomagnesium, -sodium, or -lithium salts have been fluorinated with various reagents, including perchloryl [ F]fluoride, 1-[ F]fluoro-2-pyridone, A/-[ F]fluoropyridinium triflate and A/-[ F]fluoro-A/-alkylsulphonamides. 

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