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(t)MgDBA ( 5) (DBA = dibenzylamide), Bu-t MgDA ( 6) (DA = diisopropylamide), Bu-t MgHMDS ( 7) ( HMDS = 1,1,1,3,3,3-hexamethyldisilazide), (BuMgTMP)-Mg-t ( 8) (TMP = 2,2,6,6-tetramethylpiperidide) and Bu-t MgNCy2 ( 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 [Bu-n MgN(H) Dipp](12) ( 10a) and its monomeric solvate Bu-n MgN( H) Dipp center dot TMEDA ( 10b) ( Dipp = 2,6-diisopropylphenyl; TMEDA = N, N, N, N - tetramethylethylenediamine). The crystal structures of the oxo-insertion products Bu-t MgOBut center dot THF (11), Bu-t Mg(mu-OBut) (mu-TMP) MgTMP (12) and Mg(OBun) HMDS center dot solv [solv = THF (13a) or Et2O(13b)], made fortuitously during the course of this work, are also presented