Ring‐opening polymerization of β‐butyrolactone catalyzed by efficient magnesium and zinc complexes derived from tridentate anilido‐aldimine ligand

Magnesium (Mg) and zinc (Zn) complexes incorporating tridentate anilido‐aldimine ligand, (E)‐2, 6‐diisopropyl‐N‐(2‐((2‐(piperidin‐1‐yl)ethylimino)methyl)phenyl)aniline ( AA Pip ‐H, 1 ), were synthesized and structurally characterized. The reaction of AA Pip ‐H ( 1 ) with Mg n Bu 2 or ZnEt 2 in equivalent proportions afforded the monomeric complex [( AA Pip )Mg n Bu] ( 2 ) or [( AA Pip )ZnEt] ( 3 ), respectively. The coordination modes of these complexes differ in the solid state: Mg complex 2 shows a four‐coordinated and distorted tetrahedral geometry, whereas Zn complex 3 adopts a trigonal planar geometry with a three‐coordinated Zn center. Complexes 2 and 3 are efficient catalysts for the ring‐opening polymerization of β‐butyrolactone (β‐BL) in the presence of 9‐anthracenemethanol (9‐AnOH). The polymerization of β‐BL with the Zn catalyst system is demonstrated in a living fashion with a narrow polydispersity index, PDI = 1.01–1.10. The number‐averaged molecular weight ( M n ) of the produced poly(3‐hydroxybutyrate) (PHB) is quite close to the expected M n over diverse molar ratios of monomer to 9‐AnOH. A greater ratio of monomer to alcohol catalyzed by Zn complex 3 served to form PHB with a large molecular weight ( M n > 60000). An effective method to prepare PHB‐ b ‐PCL and PEG‐ b ‐PHB by the ring‐opening copolymerization of β‐BL catalyzed by zinc complex 3 is reported.