Synthesis and structural characterization of novel cyclam-based zirconium complexes and their use in the controlled ROP of rac-lactide: access to cyclam-functionalized polylactide materials

• Published in: Dalton transactions : an international journal of inorganic chemistry 2012-12, Vol.41 (47), p.14288-14298
• Main Authors: Alves, Luis G, Hild, Frédéric, Munhá, Rui F, Veiros, Luis F, Dagorne, Samuel, Martins, Ana M
• Format: Article
• Language: English
• Subjects: Chelation; Coordination Complexes - chemical synthesis; Coordination Complexes - chemistry; Crystallography, X-Ray; Derivatives; Electronic structure; Heterocyclic Compounds - chemical synthesis; Heterocyclic Compounds - chemistry; Lithium; Models, Molecular; Molecular structure; Polyesters - chemical synthesis; Polyesters - chemistry; Polylactides; Polymerization; Zirconium; Zirconium - chemistry
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt31133j

Novel Bn(2)Cyclam-based zirconium complexes of the type (Bn(2)Cyclam)Zr(X)(X') (3, X = X' = OPh; 4, X = X' = SPh; 5, X = Cl, X' = O(i)Pr) were synthesized in good yields via metathesis routes involving the reaction of the dichloro precursor (Bn(2)Cyclam)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 Bn(2)Cyclam ligand in a κ(4)-N(2)N(2)' fashion, with the hexa-coordinated Zr center adopting a trigonal prismatic geometry. Complexes 3-5 as well as the diisopropoxide derivative (Bn(2)Cyclam)Zr(O(i)Pr)(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 (M(n)) and monomer conversion as the ROP proceeds. While initiator 2 polymerizes rac-lactide to afford, as expected, an O(i)Pr-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.