Zirconium complexes of an aminophenolate-etherphenolate ONO'O ligand: Synthesis, characterization and catalytic properties

A synthetic protocol to access new aminophenolate-etherphenolate ONO'O ligands is presented. Zirconium isopropoxide and benzyl complexes of a prototypical tert-butyl substituted ONO'O ligand can be synthesized in high yields as single conformational isomers. Combined NMR spectroscopy and single-crystal X-ray diffraction studies on (ONO'O)Zr(OiPr)2 show that the ligand binds to the metal center in a fac-fac coordination mode, like the well-known bis(aminophenolate) ONNO analogue. The iso-propoxide complex (ONO'O)Zr(OiPr)2 proved to be a competent catalyst for L- and rac-lactide polymerization, exhibiting a productivity similar to that of the benchmark (ONNO)Zr(OiPr)2 in solution and in neat monomer. The benzyl complex (ONO'O)ZrBn2 is inactive in ethylene polymerization under the reaction conditions explored, unlike the benchmark (ONNO)ZrBn2. DFT studies suggest that a larger range of geometries is accessible for cationic active species with ONO'O ligands compared to ONNO or OO'O'O ligands.