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 [(mu-EDBP- RTs)(MgBu)-Bu-n](2) (2a-f) and magnesium alkoxides [(EDBP-RTs)Mg(mu-OBn)](2) (3a-f) were prepared and structurally characterized. In the presence of THF, coordination of [(EDBP-RTs)Mg(mu-OBn)](2) (3e) with THF gave the pentacoordinated magnesium complex [(EDBP-RTs)Mg(mu-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.