Regio- and stereochemical aspects of the substitution reaction between themolybdenocene and tungstenocene dichlorides (eta(5)-C5H4-R)(2)MCl2 (R = CMe3, SiMe3; M = Mo, W) and metallophosphide anions [(CO)(5)M ' PPh2]Li (M ' = Mo, W)

The reaction of metallophosphide anions [(CO)(5)M'PPh2]Li (M' = Mo, W) with the metallocene dichlorides (eta (5)-Cp')(2)MCl2 (M = Mo, W; Cp' = C5H4-CM e3 (noted-CM) or C5H4- SiMe3 (noted -SiM)) leads to complexes (eta (5)-Cp " )(eta (5)-Cp')MHCl (Cp " = C5H3-1-R-3-PPh2M'-(CO)(5)), which arise from a n ucleophilic substitution on the cyclopentadienyl ligand. The reaction is pa rtially (molybdenocene series) or completely (tungstenocene series) diaster eogenic. In solution, a slow transformation of kinetic to thermodynamic pro ducts is detected in the molybdenum derivatives, while their tungsten homol ogues show a total stereostability. On the basis of X-ray structures and of NMR data the relative configurations of the stereoisomers are established.