Neopentylmagnesium halides:

There is no -hydrogen atom present in methyl- and neopentylmagnesium halide therefore, no reduction reaction products are observed in their reactions. The highest yield of reduction reaction product was obtained with 2-methyl-1-propylmagnesium bromide, which has one tertiary hydrogen atom on the )9-position. In a footnote, the authors made mention of an unpublished result in which the reaction of diisopropyl ketone with fert-butylmagnesium halide, which has nine primary hydrogens in the )ff-position, yielded 65% of the reduction reaction product. 

Apart from differences in polarity of the carbon-magnesium bond, there may be other reasons why organomagnesium chlorides react faster than the other organomagnesium halides. This, then, may also cause a change in the composition of the reaction products, since slower reactions have no chance to develop, as in the reaction of neopentylmagnesium chloride with benzophenone in Scheme 4. 

---