Synthesis and structural characterization of magnesium complexes bearing benzotriazole phenoxide ligands: Photoluminescent properties and catalytic studies for ring-opening polymerization of l-lactide

Magnesium catalysts incorporated by sterically bulky benzotriazole-phenoxide ligands (CMe2PhBTP−, t-BuBTP− and TMClBTP−) are synthesized and structurally characterized. The reaction of MgnBu2 with CMe2PhBTP-H (2.0 mol Eq) in THF produces penta-coordinated monomeric magnesium complex [(CMe2PhBTP)2Mg(THF)] (1). However, six-coordinated bis-adduct magnesium complexes [(t-BuBTP)2Mg(THF)2] (2) and [(TMClBTP)2 Mg(THF)2] (3) result from treatments of MgnBu2 with t-BuBTP-H and TMClBTP-H in THF under the same stoichiometric proportion, in which each Mg center is coordinated by two THF molecules. Optical properties and catalytic studies for l-lactide polymerizations of magnesium complexes 1–3 are investigated. Magnesium complex 3 catalyzes the ring-opening polymerization effectively not only in a “controlled” fashion but also in an “immortal” manner, giving polymers with the expected molecular weights and narrow molecular weight distributions.