Titanium complexes bearing amine bis(phenolate) ligands: Synthesis, structure and catalysis in ring-opening polymerization of lactide

Monomeric bis(isopropoxy) titanium complexes LTi((OPr)-Pr-i)(2) (L=OC6H2-4-R-1-6-R-2-2-CH2N[(CH2)(2)N(R-3)(2)]CH2-4-R-4-6-R-5-C6H2O, R-1=R-2=Bu-t, R-3=Et, R-4=R-5=Cl, (L-1)Ti((OPr)-Pr-i)(2); R-1=R-2=Me, R-3=Et, R-4=R-5=Me, (L-2)Ti((OPr)-Pr-i)(2); R-1=R-2=Bu-t, R-3=Et, R-4=OMe, R-5=Bu-t, (L-3)Ti((OPr)-Pr-i)(2); R-1=R-4=OMe, R-3=Et, R-2=R-5=Bu-t, (L-4)Ti((OPr)-Pr-i)(2); R-1=R-2=Bu-t, R-3=Me, R-4=OMe, R-5=Bu-t, (L-5)Ti((OPr)-Pr-i)(2)) supported by amine bis(phenolate) ligands were synthesized and characterized using NMR spectroscopy and elemental analysis. The solid-state structure of (L-3)Ti((OPr)-Pr-i)(2) was determined using single-crystal X-ray diffraction. (L1-5)Ti((OPr)-Pr-i)(2) were all found to initiate the ring-opening polymerization of l-lactide and rac-lactide in a controlled manner at 110-160 degrees C. As shown by kinetic studies, (L-1)Ti((OPr)-Pr-i)(2) polymerized l-lactide faster than did (L2-5)Ti((OPr)-Pr-i)(2). In addition, good number-average molecular weight and narrow polydispersity index (1.00-1.71) of polymers were also obtained. The microstructure of the polymers and a possible mechanism of coordination-insertion of polymerization were evidenced by MALDI-TOF and H-1 NMR spectra of the polylactides.