Synthesis and Characterization of Multi-Alkali-Metal Tetraphenolates and Application in Ring-Opening Polymerization of Lactide

A series of alkali metal complexes supported by two bulky tetraphenols were synthesized and characterized. The reactions of alpha,alpha,alpha',alpha'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene(para-tetraphenol) with (BuLi)-Bu-n, sodium, and KSi(NMe2)(3) gave bimetallic complexes 1, 2, and 3, respectively. Treatments of the alpha,alpha,alpha',alpha'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene(meta-tetraphenol) with 2 or 4 equiv of (BuLi)-Bu-n afforded complexes 4 or 5, while the reactions of meta-tetraphenol with sodium and KSi(NMe2)(3) gave only trimetallic complexes 6 and 7 for the additional p-pi interaction. Complexes 1-7 were all characterized by single-crystal X-ray diffraction techniques. In the presence of benzyl alcohol, all complexes are active catalysts for the ring-opening polymerization of L-lactide. Comparatively, bimetallic complexes 1, 2, and 3 are more efficient catalysts because of their symmetric structures, in which complex 3 presents as a rare highly active potassium catalyst for the ring-opening polymerization of lactide, leading to polymers with good molecular weight control and narrow molecular weight distributions.