Neutral, Three-Coordinate, Chelating Diamide Aluminum Complexes: Catalysts/Initiators for Synthesis of Telechelic Oligomers and High Polymers

Reaction of the bulky chelating diamine ligand ArNH(CH2)3NHAr (Ar = 2,6-iPr2C6H3) with AlMe3 cleanly affords the monomeric, three-coordinate, chelating diamide aluminum complex [N∩N]AlMe (1). The isobutyl derivative [N∩N]AliBu (2) is prepared in the same manner using triisobutylaluminum. The Al/B alkyl/aryl ligand exchange between 1 and B(C6F5)3 in refluxing toluene cleanly produces the pentafluorophenyl-substituted derivative [N∩N]AlC6F5 (3). Studies of model reactions between 1 and e-caprolactone as well as analyses of low-molecular-weight oligomers demonstrate the ability of 1 to produce telechelic oligomers. At high monomer/initiator ratios, all three complexes are active for ring-opening polymerization of e-caprolactone and cyclohexene oxide, producing high-molecular-weight polymers. The isobutyl derivative 2 exhibits the highest activity for both polymerizations in this catalyst series and produces poly(e-caprolactone) having a number-average molecular weight over 1,000,000 Da.