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Novel Bn2Cyclam-based zirconium complexes of the type (Bn2Cyclam)Zr(X)(X′) (3, X = X′ = OPh; 4, X = X′ = SPh; 5, X = Cl, X′ = OiPr) were synthesized in good yields via metathesis routes involving the reaction of the dichloro precursor (Bn2Cyclam)Zr(Cl)2 and the appropriate lithium salts. The molecular structures of compounds 3, 4 and 5, as determined by X-ray crystallographic studies, all confirmed the effective chelation of the Bn2Cyclam ligand in a κ4-N2N2′ fashion, with the hexa-coordinated Zr center adopting a trigonal prismatic geometry. Complexes 3–5 as well as the diisopropoxide derivative (Bn2Cyclam)Zr(OiPr)2 (2) were all found to initiate the ring-opening polymerization (ROP) of rac-lactide in a controlled manner, as deduced from SEC data and linear correlations between molecular weight numbers (Mn) and monomer conversion as the ROP proceeds. While initiator 2 polymerizes rac-lactide to afford, as expected, an OiPr-ester-end PLA, the ROP of rac-lactide by species 3 or 4 affords an unusual cyclam-end group PLA, as deduced from MALDI-TOF data. The bonding and the electronic structures of the dialkoxides 2 and 3 were assessed by DFT and their possible influence on the polymerization mechanism is discussed.
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