Bis(dimethylsilyl)amide complexes of the alkaline-earth metals stabilized by β-Si-H agostic interactions: synthesis, characterization, and catalytic activity
Résumé
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)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 {LO3}BaN(SiMe2H)2 (7) and those of its potassium synthetic precursors 1 and {LO3}K*KN(SiMe2H)2 (8) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented.