Aluminum and Yttrium Complexes of an Unsymmetrical Mixed Fluorous Alkoxy/Phenoxy-Diimino Ligand: Synthesis, Structure, and Ring-Opening Polymerization Catalysis

Abstract

The coordination chemistry of the new unsymmetrical Schiff base ligand {(3,5-tBu2-1-OC6H4)CH═N(trans-1,2-cyclo-C6H10)N═C(Me)CH2C(CF3)2O}2− ({ArONCyNOCF3}2−) onto Al(III) and Y(III) centers has been studied. Pro-ligand {ArONCyNOCF3}H2 (1) reacts with AlMe2Cl, Al(OiPr)3 and Y(N(SiHMe2)2)3·(THF)2 to give the corresponding complexes {ArONCyNOCF3}AlX (X = Cl, 5; OiPr, 6) and {ArONCyNOCF3}Y(N(SiHMe2)2)(THF) (7) in high yields, with concomitant alkane, alcohol, and amine elimination, respectively. Single-crystal X-ray diffraction studies revealed that complexes 5 and 7 are mononuclear in the solid state with, respectively, five-coordinated distorted square-pyramidal and six-coordinated distorted octahedral geometries. Complexes 5−7 were also characterized in C6D6 solution by 1H, 13C, and 19F NMR spectroscopy, which indicated the existence of only one isomer at room temperature. Al-OiPr complex 5 is an effective, though sluggish, initiator for the ring-opening polymerization of racemic lactide, giving polymers with a highly isotactic-enriched microstructure (Pmeso = 0.87), molecular weights that match well the calculated values, and narrow polydispersities (Mw/Mn = 1.04−1.18).