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-tetrapropylcyclopentadienyl
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.