Synthesis and characterization of anionic lanthanide complexes {[o-(Me3SiN)2C6H4]Ln(MeC5H4)2}{Li(DME)3} (Ln = Yb, Sm, Nd) and their catalytic activity for the polymerization of methyl methacrylate

The syntheses and structures of a series of new lanthanide complexes supported by a chelating diamide ligand N,N′-bis(trimethylsilyl)-o-phenylenediamine are described. Anhydrous LnCl3 reacts with Li2[o-(Me3SiN)2C6H4], followed by treatment of NaC5H4Me in 1:1:2 molar ratio to afford the corresponding anionic complexes: {[o-(Me3SiN)2C6H4]Ln(MeC5H4)2}{Li(DME)3} [Ln = Yb (1), Sm (2), Nd(3)] in high yield. These complexes were characterized by elemental analysis, IR and 1H NMR. The molecular structures of 1 and 2 were further determined by X-ray diffraction techniques to be an ion-pair complex composed by an anion [o-(Me3SiN)2C6H4]Ln(MeC5H4)2] and a cation [Li(DME)3]. Complexes 1–3 showed high catalytic activity for the polymerization of methyl methacrylate (MMA) at r.t., giving the syndiotactic-rich polymers with relatively narrow molecular weight distributions (Mw/Mn = 1.64–1.82).