Lewis-Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium

Discrete organoimide complexes of the divalent rare-earth metals samarium, europium, and ytterbium are reported. Tandem salt metathesis-protonolysis reactions using Ln^II bis(tetramethylaluminate) precursors [Ln(AlMe₄ )₂ ]_n and monopotassium salts of 2,6-diisopropylaniline (H₂ NDipp) and triphenylsilylamine prove viable and efficient protocols. Depending on the ionic radius of the Ln^II metal centers and the steric demand of the imido carbon backbone, mono- and dilanthanide arrangements of general composition [(thf)_x Ln(NR)(AlMe₃ )]_y (Ln=Sm, Eu, Yb; R=Dipp, SiPh₃ ) are found in the solid state. Complex formation and stabilization is achieved by coordination of the Lewis acid AlMe₃ , which also prevents formation of higher aggregated species. The feasibility of redox chemistry is shown with the plumbocene derivative Cp*₂ Pb, providing access to the corresponding monomeric Ln^III half-sandwich complexes [Cp*Ln(NR)(AlMe₃ )(thf)₂ ] (Ln=Sm, Yb).