Rare-Earth Metal Tris(trimethylsilylmethyl) Anionic Complexes Bearing One 1-Phenyl-2,3,4,5-tetrapropylcyclopentadienyl Ligand: Synthesis, Structural Characterization, and Application

Synthesis and structural characterization of half-sandwich rare-earth metal tris(trimethylsilylmethyl) anionic complexes bearing one 1-phenyl-2,3,4,5-tetrapropylc-yclopentadienyl ligand are achieved. These soluble anionic compounds show good reactivity in the stoichiometric reaction with dibenzoylmethane (DBM) to give the salt-free half-sandwich complex bearing two chelate DBM ligands. More importantly, they can serve as excellent and general catalyst precursors for the addition of different types of amines including primary aromatic amines (ArNH2), acyclic (RR'NH, ArRNH, and ArAr'NH; R, R' = Alkyl group, Ar, Ar' = Aromatic group), or cyclic secondary aliphatic amines to carbodiimides yielding efficiently guanidines. Acyclic secondary amines of the general formula ArAr'NH and ArRNH cannot be achieved efficiently by the previous rare-earth catalysts because of their weak nucleophilicity and steric hindrance. Our results show clearly the reactivities of anionic trialkyl precursors are comparable with the corresponding neutral alkyl complex in the stoichimetric reaction but exhibit better catalytic activity than the known catalysts.