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

Abstract

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 insitu-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.

A Preference for Heterolepticity ‐ Schlenk Type Equilibria in Organometallic Beryllium Systems

“…However, in a different study on the behaviour of 9 BeBr 2 and 7 BeEt 2 rapid ligand exchange was reported and supported with NMR studies [18] . More recently, mixtures of [(Et 2 O) 2 BeI 2 ] and MeLi or n BuLi were shown to react like “BeR 2 ” (R=Me, n Bu) but are poorly defined in solution [19] . Additionally, there are only three X‐ray crystallographically authenticated beryllium Grignard compounds [20–22] .…”

“…[18] More recently, mixtures of [(Et 2 O) 2 BeI 2 ] and MeLi or n BuLi were shown to react like "BeR 2 " (R = Me, n Bu) but are poorly defined in solution. [19] Additionally, there are only three X-ray crystallographically authenticated beryllium Grignard compounds. [20][21][22] As organometallic beryllium chemistry is currently experiencing something of a resurgence, [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] knowledge of Schlenk type equilibria is important for further developments in the field.…”

Behavior of Lewis Bases toward Diphenylberyllium

“…In contrast to the ubiquity of organomagnesium reagents, organoberyllium chemistry is relatively unexplored due, at least in part, to the perceived toxicity of this element. − Indeed, although organoberyllium complexes were prepared as early as the 1920s, − the field has subsequently been relatively devoid of methodical, fundamental beryllium research. Recently, there has been renewed interest in the organometallic chemistry of beryllium, driven by a desire to understand the biotoxicity mechanisms of this element and exploit its unique electronic properties for chemical transformations. − Within the past five years, the first compounds containing formally zero- and monovalent beryllium centers, in addition to the first BeC and BeN bonds have all been reported. − …”

Dimethylsulfide Adducts of the Beryllium Halides

“…It was recently shown that the type of ether used has significant impact on the reaction outcome [7] . Hence, attempts have been made to synthesize beryllium alkyls in the presence of as few ether molecules as possible [21] or in the total absence of any O ‐donor [20] . However, even though the latter route yields beryllium alkyls, which are completely ether free, they contain trace amounts of phosphines, which are used as solubilizers for the beryllium halide.…”