Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring-opening polymerization of ε-caprolactone and trimethylene carbonate

Two novel sulfonate phenol ligands-3, 3′-di-tert-butyl2′- hydroxy-5, 5′,6, 6′-tetramethyl-biphenyl-2-yl 4-X-benzenesulfonate (X=CF₃, L^CF3 - H, and X=OCH₃, L ^OMe -H)-were prepared through the sulfonylation of 3, 3′-di-tert-butyl-5, 5′, 6, 6′-tetramethylbiphenyl-2, 2′-diol with the corresponding 4-substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgⁿBu₂ with L-H (2 equiv.) produces the four-coordinated monomeric complexes (L^CF3)₂Mg (1) and (L^OMe)₂Mg (2). Complexes 1 and 2 are efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) and trimethylene carbonate (TMC) in the presence of 9-anthracenemethanol; complex 1 catalyzes the polymerization of ε-CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε-CL polymerization, the activity of complex 1 is greater than that of complex 2, likely because of the greater Lewis acidity of Mg²⁺ metal caused by the electron-withdrawing substitute trifluoromethyl (-CF₃) at the 4-position of the benzenesulfonate group.