Alkyl complexes of rare-earth metal centers supported by chelating 1,1′-diamidoferrocene ligands: Synthesis, structure, and application in methacrylate polymerization

Conversion of 1,1′-dianilinoferrocenes of the composition [3,4-R ₂C₅H₂(NHPh)]₂Fe (R = H, Ph) with 1 equiv of the rare-earth metal alkyl precursors Ln(THF)₂(CH ₂SiMe₃)₃ (Ln = Lu, Y) affords [R ₄Fc(NPh)₂]Ln(THF)₂CH₂SiMe ₃ (1a-2b) in yields of 73-83%. The steric bulk of the ferrocene moiety induces a pronounced stabilization of the complexes in comparison to alkyl-bridged analogues. Correspondingly, the complexes 1a-2b are stable in solution at room temperature and were characterized by multinuclear NMR spectroscopy and elemental analysis. A single-crystal X-ray diffraction study was performed for complex 2b. The synthesized rare-earth metal alkyls embedded into a 1,1′-diamidoferrocene framework effectively initiate the polymerization of methyl methacrylate (MMA) at room temperature, producing isotactic enriched poly(methyl methacrylate) (PMMA). The properties of the produced PMMAs are mainly governed by the substitution patterns of the ferrocenyl backbone.