Synthesis, characterization and catalytic activity of Salen–(sodium) 2 and (Salen) 2–lanthanum–sodium complexes

Abstract

Salen–Na 2( 1) and (Salen) 2–La–Na( 2) complexes have been prepared and structurally characterized [Salen = N, N′-bis (3,5-di- tert-butylsalicylidene)-1,3-propanediamine]. Experimental results show that the two complexes are efficient catalysts for the ring-opening polymerization (ROP) of l-lactide. According to the data of 1H NMR and electrospray-ionization (+ESI) mass spectrum, it is suggested that the obtained polymer is mainly cyclic polylactide (PLA) for a short PLA chain, but a mixture of cyclic and linear PLA for a long PLA chain. Structure–activity analysis of the two complexes is also done. We investigated why Salen–Na 2 complex is more active (Salen) 2–La–Na complex as the catalyst in the ROP of l-lactide and why the PLA catalyzed by complex 2 has lower PDIs than that catalyzed by complex 1.