Regio- and Stereochemical Aspects of the Substitution Reaction between the Molybdenocene and Tungstenocene Dichlorides (η⁵-C₅H₄-R)₂MCl₂ (R = CMe₃, SiMe₃; M = Mo, W) and Metallophosphide Anions [(CO)₅M‘PPh₂]Li (M‘ = Mo, W)

The reaction of metallophosphide anions [(CO)₅M‘PPh₂]Li (M‘ = Mo, W) with the metallocene dichlorides (η⁵-Cp‘)₂MCl₂ (M = Mo, W; Cp‘ = C₅H₄−CMe₃ (noted -CM) or C₅H₄−SiMe₃ (noted -SiM)) leads to complexes (η⁵-Cp‘ ‘)(η⁵-Cp‘)MHCl (Cp‘ ‘ = C₅H₃-1-R-3-PPh₂M‘(CO)₅), which arise from a nucleophilic substitution on the cyclopentadienyl ligand. The reaction is partially (molybdenocene series) or completely (tungstenocene series) diastereogenic. In solution, a slow transformation of kinetic to thermodynamic products is detected in the molybdenum derivatives, while their tungsten homologues show a total stereostability. On the basis of X-ray structures and of NMR data the relative configurations of the stereoisomers are established.