Polyamine-stabilized sodium aryloxides: simple initiators for the ring-opening polymerization of rac-lactide

Metalation of 2,4,6-tri(methyl)phenol ((ArOH)-Ar-Me) and 2,6-di(tert-butyl)-4-methylphenol ((ArOH)-Ar-Bu) with NaN(SiMe3)(2) in toluene and in the presence of stoichiometric amounts of the polydentate amines N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N '',N ''-pentamethyldiethylenetriamine (PMDETA) affords three new sodium aryloxide complexes [Na(mu-OArBu)(TMEDA)](2) (3), [Na(mu-OArMe)(PMDETA)](2) (4), and [Na(OArBu)(PMDETA)] (5). Complexes 3 to 5 have been isolated as crystalline materials in reasonable yields and characterized in the solid state by X-ray crystallography and in solution by NMR spectroscopy. Complexes 3 to 5 and the related [tris(2-dimethylaminoethyl)amine] (Me6TREN) derivatives [Na(OArMe)(HOArMe)(Me6TREN)] (1) and [Na(OArBu)(Me6TREN)] (2), recently prepared in our group, are shown to be active as initiators for the ring-opening polymerization (ROP) of rac-lactide with benzyl alcohol as a co-initiator. However, during the course of the polymerization reactions intrachain and stereorandom transesterification side-reactions were observed under some of the experimental conditions tested.