Synthesis and Characterisation of Two Lithium Tetramethylberyllate Salts and a Series of β-Diketiminato Beryllium Alkyl Complexes

A safer route than that previously published for the synthesis of [BeI2(OEt2)2] has been developed. Reactions of beryllium dihalide complexes [BeX2(OEt2)2] (X = Br or I) with either LiMe or LiBun lead to mixtures of products, which have been shown to act as sources of 'BeR2' (R = Me or Bun) in previous synthetic studies. Here, a titration method has been developed to determine the quantity of metal alkyl residues in these 'BeR2' mixtures that are available for subsequent alkane elimination reactions. Treating 'BeMe2' mixtures with N,N,N′,N′-tetramethylethylenediamine (tmeda) gave two lithium tetramethylberyllate compounds, [{(tmeda)Li}2(μ-BeMe4)] and [{[(tmeda)Li](BeMe4)(μ-Li)}∞], which were crystallographically characterised. Treatment of in situ-generated 'BeR2' solutions with several β-diketimines (HC{C(Me)=NR}{=C(Me)N(H)R}, NacnacH, R = aryl or alkyl) yielded a series of β-diketiminato beryllium alkyl complexes, [(Nacnac)BeR], including the first chiral example of such a compound. Crystallographic studies of these reveal them to be monomeric, with planar three-coordinate beryllium centres.