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)(3)NHAr (Ar = 2,6-(Pr2C6H3)-Pr-i) with AlMe3 cleanly affords the monomeric, three-coordinate, chelating diamide aluminum complex [(NN)-N-boolean AND]AlMe (1). The isobutyl derivative [(NN)-N-boolean AND](AlBu)-Bu-i (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 [(NN)-N-boolean AND]AlC6F5 (3). Studies of model reactions between 1 and epsilon-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 epsilon-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(epsilon-caprolactone) having a number-average molecular weight over 1,000,000 Da.