New aluminum complexes based on S,N,S-type Aminobisthiophenol Ligands for ring-opening polymerization of lactide and ε-caprolactone

In this work we report the synthesis of new aminobisthiophenol ligands BnN{CH₂[(6-R)(2-HS)C₆H₃]}₂, R = H (5a); R = Ph (5b), and also four-coordinated methyl aluminum complexes BnN{CH₂[(6-R)(2-S—)C₆H₃]}₂Al—Me, R = H (6a); R = Ph (6b). It was found that ligands of this type, according to ¹H and ¹³C NMR data, as well as X-ray diffraction (for complex 6a), successfully stabilize aluminum complexes in the monomeric form. The composition of the obtained complexes is confirmed by elemental analysis data. X-ray diffraction study of aluminum complex 6a showed that it is four-coordinate species with a distorted trigonal monopyramidal coordination core. Complexes 6a and 6b (in the presence of benzyl alcohol) were studied as initiators of ring opening polymerization (ROP) of ε-caprolactone (ε-CL), rac-lactide (rac-LA), and copolymerization of l-lactide (L-LA) and ε-CL. Complex 6b showed greater activity in ROP of rac-LA ([rac-LA]:[6b]:[BnOH]=100:1:1; full conversion of rac-LA polymerization in toluene solution at 80 °C was achieved after 48 h) and ε-CL ([ε-CL]:[6b]:[BnOH]=100:1:1; full conversion of ε-CL polymerization in toluene solution at 80 °C was achieved after 30 min and at room temperature after 6 h) compared to 6a.