Bis(dimethylsilyl)amide complexes of the alkaline-earth metals stabilized by β-Si-H agostic interactions: Synthesis, characterization, and catalytic activity

摘要

The syntheses of the homoleptic compounds Ae[N(SiMe_2H) _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(SiMe _3)_2 (1) or by transamination between Ae[N(SiMe _3)_2]_2(THF)_2 and HN(SiMe _2H)_2. These precursors constitute convenient starting materials for the subsequent preparation of {L_nO}AeN(SiMe _2H)_2 heteroleptic complexes of the large alkaline-earth metals, as exemplified by the syntheses of {LO~3}AeN(SiMe _2H)_2 ({LO~3}~- = 2-{(1,4,7,10- tetraoxa-13-azacyclopentadecan-13-yl)methyl}-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 β-Si-H agostic interactions. The structures of the kinetically stable {LO~3}BaN(SiMe_2H)_2 (7) and those of its potassium synthetic precursors 1 and {LO~3} K·KN(SiMe_2H)_2 (8) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented.