RÉSUMÉ
Tetranuclear cubane-type rare-earth methylidene complexes consisting of four "Cp'LnCH(2)" units, [Cp'Ln(µ(3)-CH(2))](4) (4-Ln; Ln = Tm, Lu; Cp' = C(5)Me(4)SiMe(3)), have been obtained for the first time through CH(4) elimination from the well-defined polymethyl complexes [Cp'Ln(µ(2)-CH(3))(2)](3) (2-Ln) or mixed methyl/methylidene precursors such as [Cp'(3)Ln(3)(µ(2)-Me)(3)(µ(3)-Me)(µ(3)-CH(2))] (3-Ln). The reaction of the methylidene complex 4-Lu with benzophenone leads to CâO bond cleavage and CâC bond formation to give the cubane-type oxo complex [Cp'Lu(µ(3)-O)](4) and CH(2)âCPh(2), while the methyl/methylidene complex 3-Tm undergoes sequential methylidene addition to the CâO group and ortho C-H activation of the two phenyl groups of benzophenone to afford the bis(benzo-1,2-diyl)ethoxy-chelated trinuclear complex [Cp'(3)Tm(3)(µ(2)-Me)(3){(C(6)H(4))(2)C(O)Me}] (6-Tm).