Synthesis and characterisation of a series of alkylmagnesium amide and related oxygen-contaminated “alkoxy” compounds

Synthesised either by an unusual tert-butyl metathesis between tert-butyllithium and a n,s-butylmagnesium amide or by reaction of an alkyl Grignard reagent and a sodium amide, five tert-butylmagnesium amides, Bu^tMgDBA (5) (DBA = dibenzylamide), Bu^tMgDA (6) (DA = diisopropylamide), Bu^tMgHMDS (7) (HMDS = 1,1,1,3,3,3-hexamethyldisilazide), Bu^tMgTMP (8) (TMP = 2,2,6,6-tetramethylpiperidide) and Bu^tMgNCy₂ (9) (cy = cyclohexyl) have been isolated as crystalline solids. All five amides have been characterised by X-ray crystallography and solution NMR spectroscopic studies. The former studies reveal a common dimeric molecular structure with amido bridges in a planar (MgN)₂ ring and terminal Bu^t ligands on the Mg atoms. Also described is the dodecameric primary amide [BuⁿMgN(H)Dipp]₁₂ (10a) and its monomeric solvate BuⁿMgN(H)Dipp·TMEDA (10b) (Dipp = 2,6-diisopropylphenyl; TMEDA = N,N,N′,N′-tetramethylethylenediamine). The crystal structures of the oxo-insertion products Bu^tMgOBu^t·THF (11), Bu^tMg(μ-OBu^t)(μ-TMP)MgTMP (12) and Mg(OBuⁿ)HMDS·solv [solv = THF (13a) or Et₂O (13b)], made fortuitously during the course of this work, are also presented.