Methylation of (pentamethylcyclopentadienyl)trichloro(diphenyldimethylenephosphoranyl-C,C)tantalum(V). Crystal structures of [TaCp*Cl3((CH2)2PPh2)] and [TaCp*Me2((CH)(CH2)PPh2)]

The X-ray diffraction study of [TaCp★Cl3{(CH2)2PPh2}] confirms its monomeric structure, previously proposed on the basis of its NMR behaviour. Alkylation of this compound leads to the isolation of its trimethyl derivative, along with a residue which contains minor amounts of the monomethyl complex. The pyrolysis of the trimethyl complex affords [TaCp★Me2{(CH)(CH2)PPh2}] whose crystal structure has been determined by X-ray diffraction methods.We thank CICYT (Grant No PB89-0208), CEE (SCl*/0137-C AM), C.N.R. (Rome) and Italian Ministero dell'Università e della Ricerca Scientifica e Tecno­ logica (MURST) for financial support for this research