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

Abstract

The syntheses of the homoleptic compounds Ae[N(SiMe 2 H) 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 2 H) 2 . These precursors constitute convenient starting materials for the subsequent preparation of {L n O}AeN(SiMe 2 H) 2 heteroleptic complexes of the large alkaline-earth metals, as exemplified by the syntheses of {LO 3 }AeN(SiMe 2 H) 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 2 H) 2 ( 7 ) and those of its potassium synthetic precursors 1 and {LO 3 }K·KN(SiMe 2 H) 2 ( 8 ) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented.