FORMATION OF BETA-CH AGOSTIC ALKENYLZIRCONOCENE COMPLEXES

Reaction of phenyl(trimethylsilyl)acetylene with hydridozirconocene chloride yields the β-CH agostic alkenylzirconocene chloride formula-omitted (2a). Halogen exchange with lithium bromide or iodide produces the analogous alkenylzirconocene bromide 2b and iodide 2c, respectively. In contrast, hydrozirconation of (trimethylsilyl)acetylene gives Cp2ZrCl(—CH=CHSiMe3) (4), exhibiting the bulky SiMe3 substituent at the β-position of the α-alkenyl ligand, which lacks the β-agostic metal-C-H interaction that is characteristic of 2. The molecular structures of 2b and 4 were determined by X-ray diffraction. Complex 2b crystallizes in space group P21/n with cell constants a = 9.746 (1) Å, β = 17.968 (3) Å, c = 11.887 (1) Å, β = 90.46 (1)°, Z = 4, R = 0.051, and Rw = 0.049. The alkenylmetallocene 4 crystallizes in space group P21/c with cell parameters o = 10.866 (1) Å, b = 12.457 (1) Å, c = 13.373 (2) Å, β = 110.80 (1)°, Z = 4, R = 0.046, and Rw = 0.048. Model calculations have confirmed that steric in addition to electronic factors are mainly responsible for the formation of the β-CH agostic interaction in the alkenylzirconocene complexes 2. © 1990, American Chemical Society. All rights reserved.