"Ionic carbenes": synthesis, structural characterization, and reactivity of rare-Earth metal methylidene complexes.

Treatment of mixed chloride tetramethylaluminate polynuclear clusters {Cp*Y[(mu-Me)2AlMe2](mu-Cl)}2 and {Cp*6La6[(mu-Me)3AlMe]4(mu3-Cl)2(mu2-Cl)6} with toluene/THF solutions produces "aluminum-free" methylidene complexes [Cp*3Ln3(mu-Cl)3(mu3-Cl)(mu3-CH2)(THF)3] (Ln = Y, La). The trinuclear methylidene complexes are isostructural in the solid state and feature a sterically well-shielded Schrock-type nucleophilic CH22- unit, which is prone to Tebbe-like methylenation reactions with ketones and aldehydes. The rapid polymerization of gamma-valerolactone reveals intrinsic rare-earth metal reactivity.