Mixed pyrazolylborate/cyclopentadienyl derivatives of divalent lanthanides: synthesis and structure of (Tp(tBu,Me))Yb(C5H4R) (R = H, SiMe3)

Reaction of [(Tp(tBu,Me))YbH](2), with cyclopentadiene (C5H6) and trimethyl silyl cyclopentadiene (C5H5SiMe3) resulted in the formation of the correspo nding mixed-ligand complexes, (Tp(tBu,Me))Yb(C5H4R) (R=H, 1a; SiMe3, 1b), i n an essentially quantitative yield. The complexes were characterized by mu ltinuclear NMR spectroscopy and, Ib, by single-crystal X-ray diffraction. T he solid-state structure of 1b consists of well-separated monomeric units w ith a eta(5)-C5H4SiMe3 ring, but the Tp(tBu,Me) ligand exhibits an unusual distortion; one of the pyrazolyl rings is rotated in such a way as to bring both pyrazolyl nitrogens in bonding contact with ytterbium. The simple H-1 - and C-13-NMR spectra of one set of Tp(tBu,Me) resonances indicate fluxion al solution behavior. The barrier to pyrazolyl ring exchange is very small since no line broadening was observed down to - 100 degrees C. (C) 2000 Els evier Science S.A. All rights reserved.