Synthesis and Structural Characterization of Alkaline-Earth-Metal Bis(amido)silane and Lithium Oxobis(aminolato)silane Complexes

Several of alkaline-earth-metal complexes [(η2:η2:μ(N):μ(N)-Li)+]2[{η2-Me2Si(DippN)2}2Mg]2– (4), [η2(N,N)-Me2Si(DippN)2Ca·3THF] (5), [η2(N,N)-Me2Si(DippN)2Sr·THF] (6), and [η2(N,N)-Me2Si(DippN)2Ba·4THF] (7) of a bulky bis(amido)silane ligand were readily prepared by the metathesis reaction of alkali-metal bis(amido)silane [Me2Si(DippNLi)2] (Dipp = 2,6-i-Pr2C6H3) and alkaline-earth-metal halides MX2 (M = Mg, X = Br; M = Ca, Sr, Ba, X = I). Alternatively, compounds 5–7 were synthesized either by transamination of M[N(SiMe3)2]2·2THF (M = Ca, Sr, Ba) and [Me2Si(DippNH)2] or by transmetalation of Sn[N(SiMe3)2]2, [Me2Si(DippNH)2], and metallic calcium, strontium, and barium in situ. The metathesis reaction of dilithium bis(amido)silane [Me2Si(DippNLi)2] and magnesium bromide in the presence of oxygen afforded, however, an unusual lithium oxo polyhedral complex {[(DippN(Me2Si)2)(μ-O)(Me2Si)]2(μ-Br)2[(μ3-Li)·THF]4(μ4-O)4(μ3-Li)2} (8) with a square-basket-shaped core Li6Br2O4 bearing a bis(aminolato)silane ligand. All complexes were characterized using 1H, 13C, and 7Li NMR and IR spectroscopy, in addition to X-ray crystallography.