The metal role on the activity and stereoselectivity of ring opening polymerization of racemic lactide promoted by Salen catalysts

The stereoselective rac-lactide ring opening polymerization (ROP) promoted by enantiopure Salen catalysts has been studied by Density Functional Theory calculations with the aim of understanding the role of the metal atom in both the stereoselectivity and the activity of the process. The results obtained with M = Al, Sc, Y, La were compared to identify the steric and electronic effects deriving from the metal centre by combining a molecular descriptor based on the buried volume percentage (%VBur) and calculations of electronic parameters, including chemical hardness and electrophilicity. Our analysis gave insight into the parameters affecting the outcome of the ROP and we concluded that steric and electronic effects promoting stereoselective polymerization suppress catalyst activity and viceversa.