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-tBu(2)-1-OC6H4)CH=N(trans-1,2-cyclo-C6H10)N=C(Me)CH2C(CF3)(2)O}(2-) ({(ONNOCF3)-O-Ar-N-Cy}(2-)) onto Al(III) and Y(III) centers has been studied. Pro-ligand {(ONNOCF3)-O-Ar-N-Cy}H-2 (1) reacts with AlMe2Cl, Al(OiPr)(3) and Y(N(SiHMe2)(2))(3)center dot(THF)(2) to give the corresponding complexes {(ONNOCF3)-O-Ar-N-Cy}AlX (X = Cl, 5; OiPr, 6) and {(ONNOCF3)-O-Ar-N-Cy}-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 H-1, C-13, and F-19 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).