Group 3 Metal Complexes of Salen-like Fluorous Dialkoxy-Diimino Ligands: Synthesis, Structure, and Application in Ring-Opening Polymerization of rac-Lactide and rac-β-Butyrolactone

The coordination chemistry of the dianionic fluorous dialkoxy-diimino ligand {OC(CF3)(2)-CH2C(Me)=NCH2CH2N=C(Me)CH2C(CF3)(2)O}(2-) ({(ONNO)-N-Et}(2-)) onto Y(III) and La(III) centers has been studied. The diimino-diol {(ONNO)-N-Et}H-2 reacts with 1 equiv of Y(N(SiHMe2)(2))(3)center dot 2THF to afford {(ONNO)-N-Et}Y(N(SiHMe2)(2))(THF) (1). Complex 1 slowly decomposes in solution, forming as yet undefined products, but could be stabilized by further reaction with 1 equiv of (R)-(+)-tert-butyl lactate, to give selectively [{(ONNO)-N-Et}Y((R)-tBu-lactate)](2) (2) in 78% yield. A single-crystal diffraction study revealed that 2 is dinuclear in the solid state, with bridging mu,kappa O-2,O,O-lactate units and tetracoordinated {(ONNO)-N-Et} units. The same geometry is retained in THF-d(8) solution, as indicated by H-1, C-13, and F-19 NMR spectroscopy. Reaction of {(ONNO)-N-Et}H-2 with 1 equiv of La(N(SiHMe2)(2))(3)center dot 2THF or La(N(SiMe3)(2))(3) systematically yielded {(ONNO)-N-Et}La((ONNOH)-N-Et} (3), which was characterized by single-crystal X-ray diffraction and NMR studies. Complex 2 is an effective initiator for the controlled-"living" ring-opening polymerization of rac-lactide and rac-beta-butyrolactone, giving atactic polymers with high molecular weights (M-n up to 55 000 g mol(-1)) that match well the calculated values and relatively narrow polydispersities (M-w/M-n = 1.06-1.60). The immortal ROP of rac-lactide appears feasible by combining complex 2 with 5 equiv of 2-propanol.