Notable effect of imino substituent for the efficient ring-opening polymerization of ε-caprolactone initiated by Al complexes containing phenoxy-imine ligand of type, Me2Al(L) [L: O-2-tBu-6-(RNCH)C6H3; R: 2,6-iPr2C6H3, tBu, adamantyl, C6F5]

Al complexes containing phenoxy-imine ligands of type, Me2Al[O-2-tBu-6-(RNCH)C6H3] [R = 2,6-iPr2C6H3 (1), tBu (2), adamantyl (3), C6F5 (4)] were prepared, identified, and their structures for 1–3 were determined by X-ray crystallography. The catalytic activity (turnover number, TON) in the ring-opening polymerization (ROP) of ε-caprolactone initiated by 1–4 upon the presence of nBuOH increased in the order: 4 ≫ 1 ≫ 2 > 3, suggesting that the imino substituent (R) plays an important role for the efficient ROP in a controlled manner; the highly efficient ROP has been achieved by the C6F5 analogue (4).