Synthesis and Characterization of a Magnesium Boryl and a Beryllium-Substituted Diazaborole

Reaction of a lithium boryl, [(THF)₂ Li{B(DAB)}] (DAB=[(DipNCH)₂ ]^2- , Dip=2,6-diisopropylphenyl), with a dinuclear magnesium(I) compound [{(^Mes Nacnac)Mg}₂ ] (^Mes Nacnac=[HC(MeCNMes)₂ ]^- , Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, [(^Mes Nacnac)(THF)Mg{B(DAB)}]. Attempts to prepare the magnesium boryl via a salt metathesis reaction between the lithium boryl and a β-diketiminato magnesium iodide compound, instead led to an intractable mixture of products. Similarly, reaction of the lithium boryl with a β-diketiminato beryllium bromide precursor, [(^Dep Nacnac)BeBr] (Dep=2,6-diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, [{(^Dep Nacnac)Be(4-DAB^-H )}BBr]. For sake of comparison, the same group 2 halide precursor compounds were treated with a potassium gallyl analogue of the lithium boryl, viz. [(tmeda)K{:Ga(DAB)}] (tmeda=N,N,N',N'-tetramethylethylenediamine), but no reactions were observed.