Selective crystallization of di-sec-butylmagnesium. N,N,N′,N′-tetramethylethylenediamine from solutions containing mixtures of normal-butyl and secondary-butyl isomers

Found to crystallise selectively from treatment of commercial ^sBu(ⁿBu)Mg solutions with N,N,N′,N′-tetramethylethylenediamine (TMEDA), the complex (^sBu₂Mg·TMEDA) is mononuclear in the crystal state and undergoes a solvation-desolvation equilibrium in arene solution. The crystal structure is noteworthy for the large C---Mg---C bond angle of 133.6(2)°, attributable to the branched nature of the alkyl substituents. This angular distortion is thought to encourage the partial loss of TMEDA from Mg centres in solution.