Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening polymerization of epsilon-caprolactone.

Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands (o-C6H4(NHAr)-CH=N)2CH2CH2 (Ar = 2,6-Me2C6H3,L1H2; Ar = 2,6-iPr2C6H3, L2H2) have been synthesized and characterized. Treatment of L1H2 or L2H2 with two equiv. of AlMe3 gives bimetallic complex L1(AlMe2)2 1 or L2 (AlMe2)2 2, respectively. Reaction of L1H2 or L2H2 with two equiv. of ZnEt2 leads to bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively. All of the complexes 1-4 are efficient catalysts for ring-opening polymerization of epsilon-caprolactone (CL) in the presence of benzyl alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al complexes 1 and 2.