Polyamine-Stabilized Sodium Aryloxides: Simple Initiators for the Ring-Opening Polymerization of rac-Lactide

Metalation of 2,4,6-tri(methyl)phenol (MeArOH) and 2,6-di(tert-butyl)-4-methylphenol (BuArOH) 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(μ-OArBu)(TMEDA)]2 (3), [Na(μ-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.