title: Synthesis of cyclic polylactide catalysed by bis(salicylaldiminato)tin(II) complexes.
abstract: Eight bis(salicylaldiminato)tin(II) complexes have been synthesized from the reaction of Sn[N(SiMe(3))(2)](2) and 2 equiv of the corresponding ligands at room temperature. The ligands, synthesized from salicylaldehyde and amines, were designed to have different electronic and steric properties using different amines to synthesize the tin(II) complexes as aniline (2a), 2,6-dimethylaniline (2b), 2,6-diisopropylaniline (2c), 4-methoxyaniline (2d), 4-trifluoromethylaniline (2e), methylamine (2g), and tert-butylamine (2h). Ligand variation at the salicyl group synthesized from 4-bromosalicylaldehyde and 2,6-diisopropylaniline was used to form complex 2f. Complex 2c was characterized crystallographically. All catalysts were active for the neat polymerization of L-lactide at 115 °C. At a lactide : Sn molar ratio of 10 : 1, cyclic polylactide (PLA) was obtained as demonstrated by (1)H NMR and mass spectrometry. Addition of 1 equiv of benzyl alcohol in the polymerization produced linear PLA. At a higher lactide : Sn molar ratio of 200 : 1, high molecular weight PLAs with M(n) up to 132,200 Daltons were obtained. Results from GPC coupled with light scattering detector and viscometer suggested that they are cyclic PLA. The order of reactivity based on conversion was determined to be 2c < 2b < 2a in accordance with lower steric hindrance. For electronic contribution, the order of 2e < 2a < 2d was observed in agreement with the increasing electron donation of the ligands. Complex 2g having the smallest substituents was found to be the most active catalyst.
authors.affiliation: Center for Catalysis, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand.
authors.forename: Parichat
authors.initials: P
authors.lastname: Piromjitpong
authors.forename: Passachon
authors.initials: P
authors.lastname: Ratanapanee
authors.forename: Wipavee
authors.initials: W
authors.lastname: Thumrongpatanaraks
authors.forename: Palangpon
authors.initials: P
authors.lastname: Kongsaeree
authors.forename: Khamphee
authors.initials: K
authors.lastname: Phomphrai
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry*; D014001:Tin / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D009942:Organometallic Compounds; D011091:Polyesters; C033616:poly(lactide); D014001:Tin