ACTIVATION OF THE (TRIMETHYLSILYL)TETRAMETHYLCYCLOPENTADIENYL LIGAND IN THE [C5ME4(SIME3)](2)TICL2 MG SYSTEM, YIELDING INTRAMOLECULAR SI-CH2-MG AND SI-CH2-TI BONDS - MOLECULAR-STRUCTURES OF ))][ETA(5)-C5ME4(SIME3)]TI-III(MU-H)(2)MG(THF))(2) AND )ETA(1)-C5ME4SIME2CH2][ETA(5)-C5ME4(SIME3)]TI-III/

The reduction of [C5Me4(SiMe3)](2)TiCl2 by excess Mg in THF yields the paramagnetic compound })][eta(5)-C5Me4(SiMe3)]Ti-III(mu-H)(2)Mg(THF)} (2) (3). In the presence of Me3SiC=CSiMe3 the same system affords the paramagnetic compound ):eta(1)-C5Me4SiMe2CH2][eta(5)-C5Me4(SiMe3)]Ti-I II (4) in 75% yield. The crystal structures of 3 and 4 reveal that one SiMe3 group in each of the compounds has been activated by hydrogen a bstraction. In centrosymmetric dimer 3, two titanocene-magnesium hydri de-bridged units are held together by two methylene groups which link the two Mg atoms via a two-electron-three-center Mg-C-Mg bond. In the mononuclear 4, a regular Ti-CH2 sigma-bond (2.204(5) Angstrom) binds t he central Ti atom to the eta(5):eta(1)-C5Me4SiMe2CH2 ligand.