SYNTHESIS AND REACTIVITY OF NEW MONO(CYCLOPENTADIENYL)ZIRCONIUM AND MONO(CYCLOPENTADIENYL)HAFNIUM ALKYL COMPLEXES - CRYSTAL-STRUCTURE AND MOLECULAR-STRUCTURE OF 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, H f; 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 accessib le in good yields. The ethyl complex is stable at room temperature. Th e 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 determi ned by X-ray diffraction. The cation [Cp '' HfMe(2)(toluene)](+) posse sses a bent-sandwich structure with an eta(6)-coordinated toluene liga nd. There is no close contact between the metal and the anion. The Hf- CH3 bonds are significantly shorter than the corresponding distances i n the isoelectronic neutral complex Cp(2)HfMe(2), while the Hf-Cp dist ances are comparable. The ethyl compound [Cp '' HfEt(2)(toluene)]+ eli minates ethane on warming to give an ethene-bridged species, [{Cp '' H fEt(toluene)}(mu-C2H4)](2+), a process indicative of a possible deacti vation pathway in olefin polymerization reactions.