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

Reaction of a lithium boryl, (THF)₂Li{B(DAB)}] (DAB=(DipNCH)₂]^2?, Dip=2,6‐diisopropylphenyl), with a dinuclear magnesium(I) compound {(^MesNacnac)Mg}₂] (^MesNacnac=HC(MeCNMes)₂]^?, Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, (^MesNacnac)(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, (^DepNacnac)BeBr] (Dep=2,6‐diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, {(^DepNacnac)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.