Magnesium catalysts incorporated by sterically bulky benzotriazole- phenoxide ligands ( CMe2PhBTP -, t-BuBTP - and TMClBTP -) are synthesized and structurally characterized. The reaction of Mg nBu 2 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 Mg nBu 2 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.
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