LEWIS-BASE-FREE CATIONIC ZIRCONOCENE COMPLEXES CONTAINING AN ALKENYL LIGAND

Electrophilic cations [Cp'2ZrMe(NMe2Ph)n][B(4-C6H4F)4] (1) (n = 1, Cp'2 = (C5H5)2 (a), {(Me3Si)C5H4}2 (b), {(Me3C)C5H4}2 (c), rac-C2H4(indenyl)2 (d); n = 0, Cp' = C5Me5 (e)), generated in situ by protonolysis, react with internal alkynes to give Lewis-base-free alkenyl complexes [Cp'2ZrC(R1) = C(R2)Me][B(4-C6H4F)4] (R1 = SiMe3, R2 = Me, 2a-d; R1 = R2 = Ph, 3a-e). H-1, C-13, and Si-29 NMR spectroscopy suggests that agostic coordination of a Si-Me group to the zirconium center occurs for complexes 2 in solution. The structure of 2d.CH2Cl2 has been determined by X-ray crystallography. Crystal data: C52H49BCl2F4SiZr, M = 950.99, monoclinic, P2(1)/n, a = 15.402 (3) angstrom, b = 17.606 (3) angstrom, c = 16.960 (3) angstrom, Z = 4, and R = 0.050 for 5392 "observed" reflections. The alkenyl ligand in 2d interacts with electron-poor zirconium via agostic coordination of a Si-C and a C-H bond of the alpha-SiMe3 group (Zr-Si = 2.935 (2) angstrom; Zr-C = 2.578 (5) angstrom; Zr-H = 2.26 (7) angstrom). F-19 NMR spectroscopy shows that the anion is noncoordinating in complexes 2, 3c, and 3e; labile fluorine coordination to zirconium in complexes 1, 3a, 3b, and 3d results in upfield-shifted F-19 NMR resonances for the anion.