title: Comparative Study of Aluminum Complexes Bearing N,O- and N,S-Schiff Base in Ring-Opening Polymerization of ε-Caprolactone and L-Lactide.
abstract: A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.|Department of Chemistry, National Sun Yat-sen University , Kaohsiung, Taiwan 80424, R.O.C.
authors.forename: Meng-Chih
authors.initials: MC
authors.lastname: Chang
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
authors.forename: Wei-Yi
authors.initials: WY
authors.lastname: Lu
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
authors.forename: Heng-Yi
authors.initials: HY
authors.lastname: Chang
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Lai
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.|Department of Chemistry, National Sun Yat-sen University , Kaohsiung, Taiwan 80424, R.O.C.
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Chiang
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
authors.forename: Hsing-Yin
authors.initials: HY
authors.lastname: Chen
authors.affiliation: Department of Medicinal and Applied Chemistry, Kaohsiung Medical University , Kaohsiung, Taiwan 80708, R.O.C.
authors.forename: Hsuan-Ying
authors.initials: HY
authors.lastname: Chen