title: Aluminum complexes with bidentate amido ligands: synthesis, structure and performance on ligand-initiated ring-opening polymerization of rac-lactide.
abstract: A series of mononuclear aluminum dimethyl complexes bearing bidentate N-[2-(1-piperidinyl)benzyl]anilino or N-(2-morpholinobenzyl)anilino ligands were synthesized via reactions of the corresponding proligands with trimethylaluminum upon heating, while at ambient temperature two trimethylaluminum adducts with neutral N-[2-(1-piperidinyl)benzyl]aniline proligands were obtained. These complexes were well characterized by NMR spectroscopy, elemental analysis and occasionally by EI-HRMS. The molecular structures of the typical trimethylaluminum adduct 2b and aluminum dimethyl complex 3b were further confirmed by X-ray diffraction studies. All the aluminum dimethyl complexes could effectively initiate the ring-opening polymerization (ROP) of rac-lactide in a well-controlled manner to afford PLAs with narrow molecular weight distributions (PDI = 1.06-1.18). The polymer samples obtained are systematically end-capped with the bidentate ancillary ligands as characterized by (1)H NMR and ESI-TOF mass spectroscopy. Moreover, the introduction of substituent(s) at the ortho-position(s) of the anilino moiety in the ligand results in an obvious decrease in the catalytic activity of the corresponding aluminum complex, and complexes with meta-chloro substituted anilino units show higher activities likely due to the enhanced electrophilicity of the metal centers induced by the anilino groups.
authors.affiliation: Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, People's Republic of China. haiyanma@ecust.edu.cn.
authors.forename: Junpeng
authors.initials: J
authors.lastname: Liu
authors.forename: Haiyan
authors.initials: H
authors.lastname: Ma
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013053:Spectrophotometry; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D004146:Dioxanes; D008024:Ligands; D011108:Polymers; C091880:dilactide; D000535:Aluminum