title: Magnesium complexes containing biphenyl-based tridentate imino-phenolate ligands for ring-opening polymerization of rac-lactide and α-methyltrimethylene carbonate.
abstract: A series of racemic 2-[(2'-(dimethylamino)biphenyl-2-ylimino)methyl]-4-R(2)-6-R(1)-phenols (L¹H-L⁴H) were reacted with {Mg[N(SiMe3)2]2}2 to provide four heteroleptic magnesium complexes (L¹⁻⁴)MgN(SiMe3)2·(THF)n (1, R(1) = (t)Bu, R(2) = Me, n = 1; 2, R(1) = R(2) = CMe2Ph, n = 0; 3, R(1) = CPh3, R(2) = (t)Bu, n = 1; 4, R(1) = Br, R(2) = (t)Bu, n = 0), which have been fully characterized. X-ray structural determination shows that complex 1 possesses a monomeric structure, but complex 4 is dimeric with C2-symmetry where the two metal centers are bridged by two phenolate oxygen atoms of the ligands. The coordination geometry around the magnesium center in these complexes can be best described as a distorted tetrahedral geometry. The heteroleptic complexes 1-4 efficiently initiate the ring-opening polymerization of rac-lactide and α-methyltrimethylene carbonate (α-MeTMC) and the polymerizations are better controlled in the presence of 2-propanol. In general, the introduction of a bulky ortho-substituent on the phenoxy unit results in increases of both the catalytic activity and the stereo- or regioselectivity of the corresponding magnesium complex. Microstructure analyses of the resulting PLAs revealed that P(r) values range from 0.46 to 0.81, depending on the catalyst and the polymerization conditions. For racemic α-MeTMC, detailed analyses using (1)H and (13)C NMR spectroscopy indicated the preferential ring-opening of α-MeTMC at the most hindered oxygen-acyl bond (X(reg) = 0.65-0.86).
authors: 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: Wei
authors: W
authors: Yi
authors: Haiyan
authors: H
authors: Ma
mesh_terms: D002254:Carbonates / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry; D008024:Ligands; D008274:Magnesium / Q000737:chemistry*; D008968:Molecular Conformation; D010636:Phenols / Q000737:chemistry*; D058105:Polymerization
chemical_list: D002254:Carbonates; D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; D010636:Phenols; C091880:dilactide; D008274:Magnesium