Heterolepic β -Ketoiminate Zinc Phenoxide Complexes as Efficient Catalysts for the Ring Opening Polymerization of Lactide.

Zinc phenoxide complexes L ¹ ZnOAr 1 - 4 (L ¹ =Me ₂ NC ₂ H ₄ NC(Me)CHC(Me)O) and L ² ZnOAr 5 - 8 (L ² =Me ₂ NC ₃ H ₆ NC(Me)CHC(Me)O) with donor-functionalized β -ketoiminate ligands (L ^1/2 ) and OAr substituents (Ar=Ph 1 , 5 ; 2,6-Me ₂ -C ₆ H ₃ 2 , 6 ; 3,5-Me ₂ -C ₆ H ₃ 3 , 7 ; 4-Bu-C ₆ H ₄ 4 , 8 ) with tuneable electronic and steric properties were synthesized and characterized. 1 - 8 adopt binuclear structures in the solid state except for 5 , while they are monomeric in CDCl ₃ solution. 1 - 8 are active catalysts for the ring opening polymerization (ROP) of lactide (LA) in CH ₂ Cl ₂ at ambient temperature and the catalytic activity is controlled by the electronic and steric properties of the OAr substituent, yielding polymers with high average molecular weight ( M _n ) and moderately controlled molecular weight distribution (MWDs). 1 and 5 showed a living polymerization character and kinetic studies on the ROP of L -LA with 1 and 5 proved first order dependencies on the monomer concentration. Homonuclear decoupled ¹ H-NMR analyses of polylactic acid (PLA) formed with rac -LA proved isotactic enrichment of the PLA microstructure.
Competing Interests: The authors declare no conflict of interest.