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.