“Ionic Carbenes”:  Synthesis, Structural Characterization, and Reactivity of Rare-Earth Metal Methylidene Complexes

Treatment of mixed chloride tetramethylaluminate polynuclear clusters {Cp*Y[(μ-Me)2AlMe2](μ-Cl)}2 and {Cp*6La6[(μ-Me)3AlMe]4(μ3-Cl)2(μ2-Cl)6} with toluene/THF solutions produces “aluminum-free” methylidene complexes [Cp*3Ln3(μ-Cl)3(μ3-Cl)(μ3-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 CH2 2- unit, which is prone to Tebbe-like methylenation reactions with ketones and aldehydes. The rapid polymerization of γ-valerolactone reveals intrinsic rare-earth metal reactivity.