Aluminium complexes bearing functionalized trisamido ligands and their reactivity in the polymerization of ε-caprolactone and rac-lactide

Abstract

The addition of 1 and 2 equivalents of AlMe₃ to cis,cis-C₆H₉(NHCH₂C₆H₄-o-R)₃ (R = PPh₂ (3) and SPh (4)) gives complexes [cis,cis-C₆H₉(NCH₂C₆H₄-o-R-κN)₂(NHCH₂C₆H₄-o-R-κN)]AlMe (R = PPh₂ (7) and SPh (8)) and [cis,cis-C₆H₉(NCH₂C₆H₄-o-R)₃-κ⁵μ²N]Al₂Me₃ (R = PPh₂ (5) and SPh (6)), respectively. The bimetallic complexes are active in the polymerization of ε-caprolactone and rac-lactide whereas the monometallic complexes are not, although no cooperative behaviour is observed between the two aluminium atoms of 5 and 6. The polycaprolactone samples, which were characterized using ¹H NMR, MALDI-TOF, and SEC, show the presence of residual ligands 3 or 4 bound to the polymer and the in situ NMR studies confirm that the insertion occurs in an Al–N bond.