Synthesis and structural characterization of alkaline-earth-metal bis(amido)silane and lithium oxobis(aminolato)silane complexes

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