A series of aluminum dimethyl complexes 1-6 bearing N-[2-(pyrrolidinyl) benzyl] anilido ligands were synthesized and well characterized. The molecular structure of complex 1 determined by an X-ray diffraction study indicates the bidentate chelating mode of the pyrrolidinyl-anilido ligand. In the absence of a coinitiator, these complexes exhibited excellent control toward the polymerizations of epsilon-caprolactone and raclactide, affording polyesters with quite narrow molecular weight distributions (M-w/M-n = 1.04-1.26). The end group analysis of epsilon-CL oligomer via H-1 NMR and ESI-TOF MS methods gave strong support to the hypothesis that the polymerization catalyzed by these aluminum complexes proceeds via a coordination-insertion mechanism involving a unique Al-N (amido) bond initiation. Via H-1 NMR scale oligomerization studies, it is suggested that the insertion of the first lactide monomer into Al-N bond of the complex is much easier than the insertion of lactide monomer into the newly formed Al-O (lactate) bond and might also be easier than the insertion of the first epsilon-CL monomer into Al-N bond. (c) 2014 Wiley Periodicals, Inc.