Controlled synthesis of mononuclear or binuclear aryloxo ytterbium complexes supported by β-diketiminate ligand and their activity for polymerization of ε-caprolactone and L-lactide

Abstract

The reaction of monomeric [(DIPPh)₂nacnac]YbCl₂(THF)₂ ((DIPPh)₂nacnac = N,N-diisopropylphenyl-2,4-pentanediimineanion) with NaOAr (OAr = 2,6-diisopropylphenoxide) in THF afforded the mononuclear complexes [(DIPPh)₂nacnac]Yb(OAr)Cl(THF) 1 and [(DIPPh)₂nacnac]Yb(OAr)₂2 depending on the molar ratio of dichloride to sodium salt, while the same reaction with NaOAr′ (OAr′ = 2,6-dimethylphenoxide) in toluene yielded the binuclear complex [{(DIPPh)₂nacnac}Yb(OAr′)]₂(μ-Cl)₂3. Treatment of [(DIPPh)₂nacnac]Yb(THF)(μ-Cl)₃Yb(Cl)[(DIPPh)₂nacnac] with NaOAr and NaOAr′, respectively, in toluene yielded selectively the corresponding binuclear complexes {[(DIPPh)₂nacnac]Yb(OAr)(μ-Cl)₃Yb[(DIPPh)₂nacnac](THF)} 4 and {[(DIPPh)₂nacnac]Yb(OAr′)(μ-Cl)₃Yb[(DIPPh)₂nacnac](THF)} 5 in high yields. All complexes were structurally characterized. Complex 2 was found to be a highly active initiator for both polymerizations of ε-caprolactone (ε-CL) and L-lactide. All monoaryloxide complexes can initiate the polymerization of ε-CL in a controlled manner giving polymers with narrow molecular weight distributions (M_w/M_n around 1.06) with relatively low activity relative to complex 2.