Synthesis of cyclic polyesters: Effects of alkoxy side chains in salicylaldiminato tin(ii) complexes

Abstract

© The Royal Society of Chemistry 2015. A new class of salicylaldiminato tin(ii) catalysts having different alkoxy side chains has been developed. The ligands were modified to have different lengths and flexibilities such as -(CH2)2- (2a), -(CH2)3- (2b), -(ortho-C6H4)CH2- (2c) and -(CH2)2-O-(CH2)2- (2d). Complexes 2a, b were characterized crystallographically revealing a more constrained environment around the metal in complex 2a. These catalysts are active for the solvent-free polymerization of l-lactide and ε-caprolactone. Complex 2a having a shorter side chain was shown to better promote intramolecular transesterification affording cyclic polylactides and cyclic poly(ε-caprolactone). Complexes 2b and 2d having longer side chains produced cyclic poly(ε-caprolactone) as a major product but failed to give cyclic polylactides.