SYNTHESIS AND REACTIVITY OF NEW MONO(CYCLOPENTADIENYL)ZIRCONIUM AND MONO(CYCLOPENTADIENYL)HAFNIUM ALKYL COMPLEXES - CRYSTAL-STRUCTURE AND MOLECULAR-STRUCTURE OF [(C5H3(SIME(3))(2))HFME(2)(ETA(6)-TOLUENE)][BME(C6F5)(3)]

The reaction of Cp '' MCl(3) with LiMe affords Cp '' MMe(3) [M = Zr, Hf; Cp '' = 1,3-C5H3(SiMe(3))(2)]. In the case of M = Hf the ethyl and n-butyl complexes Cp '' HfR(3) (R = C2H5, C4H9) are similarly accessible in good yields. The ethyl complex is stable at room temperature. The reaction of Cp '' MR(3) (M = Zr, R = Me; M = Hf, R = Me, Et) with B(C6F5)(3) in toluene affords the ionic compounds [Cp '' MR(2)(toluene)][BR(C6F5)(3)]. The structure of the hafnium methyl complex was determined by X-ray diffraction. The cation [Cp '' HfMe(2)(toluene)](+) possesses a bent-sandwich structure with an eta(6)-coordinated toluene ligand. There is no close contact between the metal and the anion. The Hf-CH3 bonds are significantly shorter than the corresponding distances in the isoelectronic neutral complex Cp(2)HfMe(2), while the Hf-Cp distances are comparable. The ethyl compound [Cp '' HfEt(2)(toluene)]+ eliminates ethane on warming to give an ethene-bridged species, [{Cp '' HfEt(toluene)}(mu-C2H4)](2+), a process indicative of a possible deactivation pathway in olefin polymerization reactions.