Mixed ligands supported yttrium alkyl complexes:: Synthesis, characterization and catalysis toward lactide polymerization

Treatment of yttrium tris(alkyl)s, Y(CH2SiMe3)3(THF)2, by equimolar H(C5Me4)SiMe3(HCp′) and indene (Ind-H) afforded (η5-Cp′)Y(CH2SiMe3)2(THF) (1) and (η5-Ind)Y(CH2SiMe3)2(THF) (2) via alkane elimination, respectively. Complex 1 reacted with methoxyamino phenols, 4,6-(CH3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-OH (HL1) and 4,6-(CMe3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-OH (HL2) gave mixed ligands supported alkyl complexes [(η5-Cp′)(L)]Y(CH2SiMe3) (3: L = L1; 4: L = L2). Whilst, complex 2 was treated with HL2 to yield [(η5-Ind)(L2)]Y(CH2SiMe3) (5). The molecular structures of 3 and 5 were confirmed by X-ray diffraction to be mono(alkyl)s of THF-free, adopting pyramidal and tetragonal-bipyramidal geometry, respectively. Complexes 3 and 5 were high active initiators for the ring-opening polymerization of l-lactide to give isotactic polylactide with high molecular weight and narrow to moderate polydispersity.

Yttrium alkyl complexes bearing mixed Cp′(or indene)/O,N,O,O-multidentate ligands have been synthesized via sequential alkane elimination reactions among Y(CH2SiMe3)3(THF)2 and cyclopentadiene (or indene) and methoxyamino phenols. The molecular structure and catalytic performance for the polymerization of lactide of the resulting complexes depend strongly on the electronic and steric nature of the ligands.Figure optionsDownload as PowerPoint slide