Aluminum complexes of enantiomerically pure aminomethylpyrrolidine-based salalen ligands and their application in the stereoselective polymerization of lactide are described. Poly(lactic acid) featuring the new gradient isotactic multiblock microstructure was synthesized by isoselective catalysts, which operate by a combination of enantiomorphic-site and chain-end control mechanisms.

All lined up: C1‐symmetric octahedral titanium complexes (see structure, Ti dark gray, N blue, O red, I purple) whose labile positions reside in different electronic environments were designed using the readily available salalen ligands. With methylalumoxane as co‐catalyst, highly active catalysts were obtained, which yielded high‐molecular‐weight polypropylene with ultra‐high isotacticities (see 13C NMR spectrum) and melting transitions.

Three dinuclear aluminum alkyl complexes of the general formula LAlMe, where L are salen ligands with an alkyl backbone of different lengths between the nitrogen atoms (1,3-propylene (1), 1,5-pentylene (2) and 1,12-dodecaylene (3)), have been prepared through alkane elimination reactions between each ligand and two equivalents of AlMe. The related hemi-salen aluminum complex 4 was prepared by an analogous reaction between a phenoxy-imine ligand and a single equivalent of AlMe. The activities of these aluminum complexes in the ring-opening polymerization (ROP) of rac-lactide and of several epoxides have been investigated and compared. The dinuclear complex 1, bearing the salen ligand with the shortest alkyl bridge, was the most active in the ROP of LA producing isotactic enriched PLA. Otherwise, the other complexes (2 and 3), in which the metal centers are remote, produced atactic PLA with inferior activity. Analogous differences in terms of activity emerged in the ROP of epoxides. The comparison of the catalytic behavior of the dinuclear complexes as well as their mononuclear counterparts suggests the cooperation between the two aluminum metal centers of the dinuclear species in which these are close enough.

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A salen ligand and its derivatives salan and salalen, bearing the same substituents on the phenolate rings, have been synthesized and then used for the preparation of the corresponding Fe(iii) complexes. All complexes were characterized by MALDI ToF mass spectroscopy, Evans method, and UV-Vis and IR spectroscopy. Moreover, for the salalen-based iron complex, the X-ray structure was studied. A comparison of their behaviour in the catalysis of CO with benchmark epoxide substrates allowed us to individuate an order of reactivity of the different classes of complexes. A salen Fe(iii) complex was prepared with a longer bridge between the two nitrogen atoms of the ligand skeleton in order to evaluate the influence of the flexibility on the activity of the catalyst. Finally, the same complexes were tested as catalysts in the ring-opening polymerization of l-lactide and ε-caprolactone.