Synthesis, structure and catalytic activity comparison of tris- and tetracoordinated lanthanide amides

Tetracoordinated lanthanide amides [(Me3Si)(2)N](3)Ln (mu-Cl)Li(THF)(3) (Ln=La (1), Pr (2)) were synthesized by the reaction of anhydrous lanthanide(III) chlorides LnCl(3) (Ln=La, Pr) with 3 equiv. of lithium bis(trimethylsilyl)amide (Me3Si)(2)NLi in THF, followed by recrystallization from toluene. Sublimation of 1 and 2 afforded the triscoordinate lanthanide amides [(Me3Si)(2)N](3)Ln (Ln=La, Pr). The crystal structure of 2 was determined by X-ray diffraction analysis. The catalytic activity studies show that the tetracoordinate amides can be used as single-component MMA (methyl methacrylate) polymerization catalysts, while the triscoordinate amides showed poor activity on MMA polymerization under the same conditions.