beta-Keto Amino Enolates Binding to Transition Metals: Synthesis and Structure of the Ion-Pair Form and Its Mono- and Bidentate Coordination to Zirconium and Nickel

The 2-piperidinoacetophenone, 1, was deprotonated in THF by KH, and the resulting beta-keto amino enolate-potassium ion pair, 2, complexed with 18-crown-6 to give 3, in which the enolate group chelates the [K(18-crown-6)]+ moiety. The reaction of 2 with cp2-ZrCl2 [cp = eta5-C5H5] afforded complex 4 in which the beta-keto amino enolate exhibits an eta1-O bonding mode to zirconium(IV). The enolate 2 acts as a N-O bidentate ligand complexing Ni(II) in the form of a square planar, diamagnetic complex. Crystallographic details: 3 is monoclinic, space group P2(1)/n, with a = 11.836(2) angstrom, b = 16.757(3) angstrom, c = 13.899(2) angstrom, beta = 95-55(1)degrees, Z = 4, and R = 0.081; 5 is triclinic, space group P1BAR, with a = 9.415(1) angstrom, b = 11.533(1) angstrom, c = 17.892(3) angstrom, alpha = 102.81(2)degrees, beta = 92.00(2)degrees, gamma = 67.28(2)degrees, Z = 3, and R = 0.057.