title: 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.
abstract: 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.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal.
authors.forename: Luis G
authors.initials: LG
authors.lastname: Alves
authors.forename: Frédéric
authors.initials: F
authors.lastname: Hild
authors.forename: Rui F
authors.initials: RF
authors.lastname: Munhá
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
authors.forename: Samuel
authors.initials: S
authors.lastname: Dagorne
authors.forename: Ana M
authors.initials: AM
authors.lastname: Martins
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D011091:Polyesters / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization; D015040:Zirconium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D006571:Heterocyclic Compounds; D011091:Polyesters; C024560:cyclam; C033616:poly(lactide); D015040:Zirconium