METAL-BRIDING VS CHELATING ME2SI(C5H4)2 LIGANDS IN DINUCLEAR COMPLEXES .3. MASS-SPECTROMETRY OF ORGANO-RARE EARTH (M=Y,YB) HYDRIDES CONTAINING THE ME2SI(C5H4)2 LIGAND, AND CRYSTAL-STRUCTURE OF THE NEW COMPLEX [(ME2SI(ETA-5-C5H4)2YBIII(THF))2(MU-H)(MU-CL]

Reactions of [Me2Si(C5H4)2MCl]2 (Me = CH3; M = Y, Yb) with NaH in THF have given several new hydride species which have been investigated ma inly by high-resolution mass spectrometry (MS). For M = Y, the MS resu lts suggest, as expected, that the reaction gives the dimeric hydride with the ligands Me2Si(C5H4)2 in a chelating mode, while for M = Yb th e dimeric species isolated (4) contains only one chlorine and one hydr ogen bridging the two Yb atoms. An X-ray crystallographic study of the extremely labile Yb-chloro-hydride crystallized from THF-solution has confirmed the formulation [(Me2Si(C5H4)2Yb(THF))2(mu-H)(mu-Cl)] (4) with metal-bridging Me2Si(C5H4)2 ligands and one THF ligand on each Yb atom. The unit cell contains two different dimers each of which is ac companied by one additional THF molecule. The starting complex with M = Yb undergoes reversible addition of MeCN, and all its Cl- ligands ma y readily be replaced by NCS- or [Me2S(C5H4)2]2-.