Chiral Amido Aluminum and Zinc Alkyls: A Synthetic, Structural, and Polymerization Study

Reactions of racemic (±)-trans-1,2-(NHSiMe3)2-cyclohexane ((±)-trans-1,2-Cy(NHSiMe3)2) with 2 equiv of AlMe3, 2 equiv of ZnEt2, and 1 equiv of ZnEt2 produce the dinuclear aluminum complex {(±)-trans-Cy(NSiMe3)2}Al2Me4 (1) in 88% yield, the tetranuclear zinc complex {(±)-trans-Cy(NSiMe3)2}2Zn4Et4 (2) in 87% yield, and the dinuclear zinc complex {(±)-trans-Cy(NHSiMe3)(NSiMe3)}2Zn2Et2 (3) in 77% yield, respectively. Complex 1 features a puckered four-membered Al2N2 ring exhibiting a smaller N−Al−N angle (77.6(1)°) than any other dimeric alkyl aluminum amide reported. Complex 2 consists of four three-coordinate, planar zinc centers, two of which are symmetrically bonded to two amide groups via intramolecular Zn−N coordination, whereas the other two are nearly symmetrically bonded to two amide groups through intermolecular Zn−N coordination. In complex 3, there are a center of symmetry and a planar four-membered Zn2N2 core. The zinc alkyls 2 and 3 are effective initiators for polymerization of e-caprolactone a...