Reactivity of a quasi-four-coordinate butylmagnesium cation.

We present the reactivity of the Mg-C and the β-CH bonds in the trigonal pyramidal [(pmdta)Mg( n Bu)] + exhibiting a weak Mg⋯F interaction with counter anion, [B(C 6 F 5 ) 4 ] - . Instantaneous β-hydride reactivity with benzophenone, reductive alkylation of phenyl benzoate, and straightforward synthesis of [(pmdta)MgH] + via metathesis with pinacolborane/phenylsilane are discussed.