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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
Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
E-mail: ana.martins@ist.utl.pt
b
Laboratoire DECOMET, Institut de Chimie de Strasbourg (CNRS-Université de Strasbourg), 1 rue Blaise Pascal, 67000 Strasbourg, France
E-mail: dagorne@unistra.fr
Dalton Trans., 2012,41, 14288-14298
DOI:
10.1039/C2DT31133J
Received
25 May 2012,
Accepted
10 Sep 2012
First published online
11 Sep 2012
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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