resumo
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' = (OPr)-Pr-i) 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 kappa(4)-N2N2' 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((OPr)-Pr-i)(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 (OPr)-Pr-i-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.
palavras-chave
RING-OPENING POLYMERIZATION; MOLECULAR-ORBITAL METHODS; EXTENDED BASIS-SETS; VALENCE BASIS-SETS; CONTINUUM SOLVATION MODELS; EFFECTIVE CORE POTENTIALS; TRANSITION-METAL ATOMS; GAUSSIAN-BASIS SETS; MAIN-GROUP ELEMENTS; ORGANOMETALLIC COMPOUNDS
categoria
Chemistry
autores
Alves, LG; Hild, F; Munha, RF; Veiros, LF; Dagorne, S; Martins, AM
nossos autores
Grupos
agradecimentos
Fundacao para a Ciencia e Tecnologia is acknowledged for partial funding of this work (PEst-OE/QUI/UI0100/2011, PTDC/QUI-QUI/099389/2008, SFRH/BD/44295/2008 and SFRH/BD/29986/2006) and the Portuguese NMR Network (IST-UTL Centre) is acknowledged for providing access to the NMR facility. The CNRS and the University of Strasbourg are acknowledged for partial financial support. FH is grateful to the ADEME and the Region Alsace for a PhD fellowship.