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

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⁻ ({^ArON^CyNO^CF3}²⁻) onto Al(III) and Y(III) centers has been studied. Pro-ligand {^ArON^CyNO^CF3}H₂ (1) reacts with AlMe₂Cl, Al(OiPr)₃ and Y(N(SiHMe₂)₂)₃·(THF)₂ to give the corresponding complexes {^ArON^CyNO^CF3}AlX (X = Cl, 5; OiPr, 6) and {^ArON^CyNO^CF3}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 (P_meso = 0.87), molecular weights that match well the calculated values, and narrow polydispersities (M_w/M_n = 1.04−1.18).