The reaction of anhydrous CoCl2 with NaOAr （ArO=2,4,6-tri-tert-butylphenoxo） in THF at room temperature in 1 ： 3 molar ratio afforded anionic cobalt aryloxide [Na（THF）6][Co（OAr）3] （1）. The definite structure of this com- plex was characterized by X-ray single crystal diffraction. It was found that this anionic aryloxo cobalt（Ⅱ） complex could effectively initiate the ring-opening polymerization of L-lactide both in solution and in bulk, leading to high molecular weight poly（L-lactide）.
