Preparation, Characterization, and Catalytic Studies of Magnesium Phenoxides: Highly Active Initiators for Ring-Opening Polymerization of l-Lactide

A series of sterically bulky phenols (1a−f; EDBP-RTs-H = 2,4-di-tert-butyl-6-(1-(3,5-di-tert-butyl-2-hydroxyphenyl)ethyl)phenyl benzenesulfonate) were synthesized. Their related n-butylmagnesium complexes [(μ-EDBP-RTs)MgnBu]2 (2a−f) and magnesium alkoxides [(EDBP-RTs)Mg(μ-OBn)]2 (3a−f) were prepared and structurally characterized. In the presence of THF, coordination of [(EDBP-RTs)Mg(μ-OBn)]2 (3e) with THF gave the pentacoordinated magnesium complex [(EDBP-RTs)Mg(μ-OBn)(THF)]2 (4). Crystal structures of 2a−c,e, 3a−c,f, and 4 have been determined. Experimental results show that magnesium alkoxides (3a−f) are very reactive initiators toward ROP of l-lactide, with a quantitative yield of polymer (1000 equiv) in less than 4 min.