Synthesis, Structure of Zinc Complexes Containing Sulfonylated Binaphtholate Ligands and Their Catalytic Activities towards Ring-Opening Polymerization of Lactide and e-Caprolactone

Reaction of sulfonylated binaphthol [2-hydroxy-2'-tosyloxy-1,1-binaphthyl (1a, Ts-Binol) or 2-hydroxy-2'-(phenylsulfonyloxy)-1,1-binaphthyl (1b, Ps-Binol)] with 1 equiv. of ZnEt2 afforded zinc complexes [(Ts-Binol)ZnEt]2 (2a) and [(Ps-Binol)ZnEt]2 (2b). Further reaction of zinc complexes 2a and 2b with benzyl alcohol (BnOH) gave the zinc benzyloxide [(Ts-Binol)2Zn2(OBn)2]2 (3a) and [(Ps-Binol)2Zn2(OBn)2]2 (3b). Alternatively, the zinc benzyloxides 3a and 3b could also be obtained by reaction of compound 1a or 1b with Zn(OBn)2 (in situ reaction of ZnEt2 and BnOH). The complexes were fully characterized by elemental analyses and spectroscopic analyses, and complexes 2a, 2b and 3a were further characterized by single-crystal X-ray analyses. The catalytic activities of these zinc complexes towards ring-opening polymerization of e-caprolactone and D,L-lactide were studied.