Synthesis and characterization of samarium bis(phenolate) complexes and their catalytic activity for the polymerization of l-lactide

The synthesis, structure and catalytic activity for the polymerization of l-lactide of samarium complexes supported by the carbon-bridged bis(phenolate) ligand 2,2′-methylene-bis(6-tert-butyl-4-methyl-phenoxo) (MBMP2−) are described. The reaction of (C5H5)3Sm(THF) with MBMPH2 in a 1:1 M ratio in THF at 50 °C produced the bis(phenolato) samarium complex (C5H5)Sm(MBMP)(THF)2 (1) in a nearly quantitative yield. Complex 1 is a useful precursor for synthesizing bis(phenolato) samarium aryloxides. Complex 1 reacted with MBMPH2 in toluene at 80 °C to give the complex (MBMP)Sm(MBMPH)(THF)2 (2). The reactions of complex 1 with some mono-phenols, including 2,6-di-tert-butyl-4-methylphenol, 2,6-diisopropylphenol, 2,6-dimethylphenol and 4-methoxyphenol, in toluene produce the complexes (MBMP)Sm(OC6H2-But2-2,6-Me-4)(THF)2 (3), (MBMP)Sm(OC6H3-Pri2-2,6)(THF)3 (4), (MBMP)Sm(OC6H3-Me2-2,6)(DME)2 (5) and [(MBMP)Sm(OC6H4-OMe-4)(THF)2]2 (6). All of these complexes were well characterized by elemental analyses, IR spectra and single-crystal X-ray structure determination, except for complex 2. It was found that complexes 3–6 are efficient initiators for l-lactide polymerization.

Graphical abstractA series of samarium aryloxo complexes supported by a carbon-bridged bis(phenolate) ligand was synthesized by the proton exchange reaction using (C5H5)3Sm(THF) as the starting material. It was found that the bulkiness of the aryloxo groups has a profound influence on the solid state structure and the catalytic property of these complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide