SYNTHESIS, CHARACTERIZATION, AND CHEMICAL-REACTIVITY OF ZIRCONIUM DIHYDRIDE [(C5H4R)2ZR(MU-H)H]2 (R = SIME3, CME3) - H/D EXCHANGE-REACTIONS OF ANIONIC SPECIES [(C5H4R)2ZRH2]- - X-RAY CRYSTAL-STRUCTURE OF [(C5H4SIME3)2ZR(MU-H)H]2

The reaction of (C5H4R)2ZrCl2 with LiAlH(OCMe3) (or NaAlH2(OCH2CH2OCH3)) gives the dihydride complex [(C5H4R)2Zr(mu-H)H]2 (R = SiMe3 (1); R = CMe3 (2)). The X-ray crystal structure of [(C5H4SiMe3)2Zr(mu-H)H]2, 1, is described. The structure of the complex was resolved in the space group Pn2(1)a with a = 22.099(4) angstrom, b = 21.816(4) angstrom, c = 16.177(5) angstrom, and Z = 8. The structure was refined to R = 6.06 and R(w) = 6.29. ESR studies were conducted to identify the paramagnetic Zr(III) species generated during the electrochemical or chemical reduction with various reductants (LiBu, LiMe, M(np) (M = Li, Na, K; np = naphthalenide)). The reduction process of 1 affords only one anionic paramagnetic species, [(C5H4SiMe3)2ZrH2]-, whereas two electrons are necessary to reduce the homodimetallic zirconium complex. H/D exchange is observed from [(C5H4CMe3)2ZrD2]- via a C-H cyclopentadienyl activation process whereas, in the presence of H-2, [(C5H4CMe3)2ZrH2]- is observed by EPR. Catalytic selective hydrogenation of 1,5- or 1,3-cyclooctadiene to cyclooctene is presented.