Synthesis and Structure of Homo- and Heterometallic Lithium–Magnesium Complexes and Their Reactivity in the ROP of <i>rac</i>-Lactide

Abstract

The homometallic azo complexes of lithium [Li 2 {(η 2 -O(C 10 H 6 )N═N(C 6 H 5 )} 2 ] n and magnesium [Mg{(η 2 -O(C 10 H 6 )N═N(C 6 H 5 )} 2 ] n and the heterometallic lithium–magnesium derivative [Li 2 Mg 2 {(η 2 -O(C 10 H 6 )N═N(C 6 H 5 )} 6 ] have been synthesized. The heterometallic complex exhibits a novel structure described as two truncated cubes that share a Mg 2 O 2 ring as one of the cube sides. These complexes have been studied in the polymerization of rac -lactide. In order to gain insight into the behavior of these compounds as catalysts, 1 H NMR experiments, diffusion-ordered spectroscopy, and X-ray studies have been used. DOSY NMR experiments support the notion that the structure of the mixed-metal complex 3 persists in benzene solution, and 1 H NMR studies show that it follows an activated monomer mechanism.