Ring opening polymerization of lactide promoted by alcoholyzed heteroscorpionate aluminum complexes

The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe2 (1) (bpzmp = 2,4‐di‐tert‐butyl‐6‐(bis‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo), promoted both by phenol and isopropanol, has been investigated. The reaction of 1 with phenol afforded the dimeric mono(phenoxo) derivative 2, whereas the alcoholysis of 1 with the less acidic isopropanol involved the coordinated heteroscorpionate ligand and led to the tetrahedral complex 3 in which the aluminum atom is surrounded by one κ2‐N,O− coordinated bpzmp ligand and one η1‐O− coordinated ppzmp ligand (ppzmp = 2,4‐di‐tert‐butyl‐6‐(i‐propoxy‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo). Complexes 1–3 have been tested in the ring opening polymerization (ROP) of L‐lactide. The dimeric mono(phenoxo) derivative 2 was inactive in the ROP of L‐lactide. Quite surprisingly, complex 3 was found to be active in ROP of L‐ and rac‐lactide, showing a good molar‐mass control.