Bis(dimethylsilyl)amide Complexes of the Alkaline-Earth Metals Stabilized by β-Si-H Agostic Interactions: Synthesis, Characterization, and Catalytic Activity

The syntheses of the homoleptic compounds Ae[N(SiMe2H)(2)](2)(THF)(x)(Ae = Ca,x = 1,2; Sr, x =2/3, 3; Ba, x = 0, 4) are reported. They can be prepared by salt metathesis involving the alkaline-earth metal iodides and KN(SiMe3)(2) (1) or by transamination between Ae[N(SiMe3)(2)](2)(THF)(2) and HN(SiMe2H)(2). These precursors constitute convenient starting materials for the subsequent preparation of {LnO}AeN(SiMe2H)(2) heteroleptic complexes of the large alkaline-earth metals, as exemplified by the syntheses of {LO3}AeN(SiMe2H)(2) ({LO3} = 2-{(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methy1}-4,6-di-tert-butylphenolate; Ae = Ca, 5; Sr, 6; Ba, 7). Both homo- and heteroleptic complexes are stabilized in the solid state by secondary beta-Si-H agostic interactions. The structures of the kinetically stable {LO3}BaN(SiMe2H)(2) (7) and those of its potassium synthetic precursors 1 and {LO3}K center dot KN(SiMe2H)(2) (8) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented.