Zinc Complexes of Piperazinyl-Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

Abstract

A series of zinc complexes was prepared from 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenols ([ONNR′,R]H) [R′= Me, R = tBu, (L1H); R′ = R = tBu, (L2H); R′= R = tAm,{tert-Amyl} (L3H)] and characterized through elemental analysis, 1H and 13C{1H} NMR spectroscopy, and X-ray crystallography. Reaction of ZnEt2 with L1H-L3H gave Zn[ONNtBu,tBu]2 (1) as a monometallic complex and {[μ-ONNR′,R]ZnEt}2 (2-4) as bimetallic species with distorted tetrahedral environments about the Zn centres. Reaction of 3 and 4 with alcohols gave {[ONNtAm,tAm]Zn(μ-OR′′)}2 (5) and (6) bimetallic species with Zn centres bridged by benzyl alkoxide and ethoxide groups, respectively. A morpholinyl derived ligand was also synthesized and characterized (L4H) and its 1:1 stoichiometric reaction with ZnEt2 resulted in complex 7, {[μ-ONOtBu,tBu]ZnEt}2. The reactivity of complexes 2-7 in the ring opening polymerization of rac-lactide and ε-caprolactone was studied. Reactions of carbon dioxide with cyclohexene oxide in the presence of 6 or 7/ROH afforded cyclohexene carbonate.