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(CF 3 ) 2 CH 2 C(Me)═NCH 2 CH 2 N═C(Me)CH 2 C(CF 3 ) 2 O} 2− ({ON Et NO} 2− ) onto Y(III) and La(III) centers has been studied. The diimino−diol {ON Et NO}H 2 reacts with 1 equiv of Y(N(SiHMe 2 ) 2 ) 3 ·2THF to afford {ON Et NO}Y(N(SiHMe 2 ) 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 [{ON Et NO}Y(( R )- t Bu-lactate)] 2 ( 2 ) in 78% yield. A single-crystal diffraction study revealed that 2 is dinuclear in the solid state, with bridging μ, κ 2 O, O,O -lactate units and tetracoordinated {ON Et NO} units. The same geometry is retained in THF- d 8 solution, as indicated by 1 H, 13 C, and 19 F NMR spectroscopy. Reaction of {ON Et NO}H 2 with 1 equiv of La(N(SiHMe 2 ) 2 ) 3 ·2THF or La(N(SiMe 3 ) 2 ) 3 systematically yielded {ON Et NO}La{ON Et NOH} ( 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 -β-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.